Hair drying and / or styling apparatus

Abstract

A hair drying and / or styling apparatus is provided, comprising: a heater for heating a tress of hair; drive circuitry for providing power to heat the heater; sensor circuitry for providing sensor data indicative of at least one selected from the group consisting of: power delivered to the heater; the temperature of the tress of hair being dried and / or styled; and the temperature of the heater; and the temperature of the heater; and a controller for controlling the drive circuitry to deliver power to the heater in dependence upon sensor data provided by said sensor circuitry; means for determining at least one hair health metric in dependence upon sensor data provided by the sensor circuitry; and means for performing a control action in dependence on the determined at least one hair health metric.

Description

[0001] APPARATUS AND SYSTEM

[0002] Field of the Invention

[0003] The present invention relates to a hair drying and / or styling apparatus and system for determining hair health metrics from data gathered during a styling session, and performing control actions in dependence on the hair health metrics. In particular, the instructions may comprise altering a heating profile and / or outputting an alert and / or feedback to a user regarding how to improve their technique.

[0004] Background to the Invention

[0005] Heated hair styling tools use heat to increase the temperature of hair to a desired styling temperature. For example, a hair straightener having a heated plate applies heat directly via conduction to heat the hair, which may be either wet or dry, to achieve the desired temperature for styling. The hair may be heated to a temperature that is particularly suitable for styling hair (for example, to or beyond a hair glass transition phase temperature). At lower temperatures, the user may have to make many passes with the hair straightener over the hairto achieve a desired styling effect, whereas at highertemperatures, there is a risk of causing permanent damage to the hair.

[0006] Similarly, a heated brush or hair dryer can also be used to style hair by heating air which in turn heats the hair to a temperature suitable for styling. The hair is typically styled from wet, for example afterthe user has washed their hair, although the hair could also be styled from dry.

[0007] Existing hair styling appliances typically use relatively thick heating plates or heating tubes that provide a certain amount of thermal mass to the hair styling appliance. These heating plates or tubes are heated by a heater that is mounted on an inner surface of the heating plate / tube. As a result of the thermal mass, the heating plates / tubes take time to heat up and, once heated, they can take quite a long time to cool down. This thermal mass makes it quite difficult to control the heating of the hair and over heating or under heating of the hair can result. There has been recent development by the applicant and other companies in developing hair styling appliances that use heaters having a lower thermal mass that can therefore heat up and cool down much more quickly. Such low thermal mass heaters are therefore more responsive and are easier to dynamically vary the temperature with time.

[0008] Additionally, it is important to users to ensure that styling causes minimum damage to their hair. The sensitivity of the heaters of the hair styling appliance can facilitate data being gathered during a styling session, which can then be analyzed. The present invention seeks to provide ways in which this analysis can improve hair health and styling technique.

[0009] Summary of the Invention

[0010] The present invention is set out in the appended independent claims. Optional features are set out in the appended dependent claims. In the following, any examples and embodiments not falling within the scope of the claims do not form part of the invention and are provided for illustrative purposes only. According to a first aspect, there is provided a hair drying and / or styling apparatus comprising: a heater for heating a tress of hair; drive circuitry for providing powerto heat the heater; sensor circuitry for providing sensor data indicative of at least one selected from the group consisting of: power delivered to the heater; the temperature of the tress of hair being dried and / or styled; and the temperature of the heater; and a controller for controlling the drive circuitry to deliver power to the heater in dependence upon sensor data provided by said sensor circuitry; means for determining at least one hair health metric in dependence upon sensor data provided by the sensor circuitry; and means for performing a control action in dependence on the determined at least one hair health metric.

[0011] This advantageously provides an apparatus adaptable to the hair to be styled or being styled, in particular the ‘health’ of the hair. This can help to minimize any further potential damage to the hair and / or effectiveness of the styling.

[0012] In some preferable implementations, the control action may comprise controlling power and / or temperature settings of the heater, preferably controlling the setpoint temperature of the heater. This can adapt to the anticipated heating profile of the hair and can help to prevent overheating and damage.

[0013] In some preferable implementations, the control action may comprise outputting an alert, preferably wherein the alert comprises at least one selected from a group consisting of: a visual output; an audio output; a haptic output; verbal instructions; and a combination thereof. This can alert a user to adapt their technique, typically in order to help to improve styling and / or to reduce damage.

[0014] In some implementations, the apparatus may further comprise means for: i) determining a heat transfer coefficient between the heater and the tress of hair in dependence upon sensor data provided by the sensor circuitry; ii) determining at least one hair health metric from the determined heat transfer coefficient; and iii) performing a control action in dependence on the determined at least one hair health metric. Heat transfer coefficient can indicate hair health and can indicate how hair will respond to heating; the control of the styler can therefore be controlled in a manner tailored to the hair.

[0015] Preferably, the means for determining at least one hair health metric from the determined heat transfer coefficient is configured to retrieve prestored calibration data relating heat transfer coefficient to hair health metric, and to use the retrieved calibration data to determine the at least one hair health metric from the determined heat transfer coefficient.

[0016] In some implementations, the apparatus may further comprise means for: i) determining a heat capacity of the tress of hair in dependence upon sensor data provided by the sensor circuitry; ii) determining at least one hair health metric from the determined heat capacity; and iii) performing a control action in dependence on the determined at least one hair health metric. Heat capacity can indicate hair health and can indicate how hair will respond to heating; the control of the styler can therefore be controlled in a manner tailored to the hair. Preferably, the means for determining at least one hair health metric from the determined heat capacity is configured to retrieve prestored calibration data relating heat capacity to hair health metric, and to use the retrieved calibration data to determine the at least one hair health metric from the determined heat capacity.

[0017] In some implementations, the controller may be configured initially to control the drive circuitry to deliver power to the heater in dependence on at least one of: data input by a user; and a predetermined initial value.

[0018] The apparatus may comprise means for estimating a hair health metric in dependence on the data input by a user. This can be used to determine initial control commands, such as power and / or temperature.

[0019] The apparatus may comprise means for estimating a heating response of the tress of hair in dependence on the estimated hair health metric, and means for comparing the estimated heating response to a detected heating response detected from sensor data, and preferably wherein the controller is configured to control the drive circuitry to deliver power to the heater in dependence on the comparison of estimated heating response and detected heating response. This can allow the styler to adjust the power according to the detected heating response of the hair.

[0020] In some implementations, the apparatus may comprise means for comparing the estimated hair health metric and the determined hair health metric, and wherein the performing a control action comprises controlling the drive circuitry to deliver power to the heater in dependence on a difference between the estimated hair health metric and the determined hair health metric.

[0021] In some preferable implementations, the heater may comprise a plurality of heating zones and the sensor circuitry may be configured to provide sensor data for the plurality of heating zones; and the apparatus may further comprise means for determining which heating zones are in contact with the tress of hair in dependence upon the sensor data.

[0022] In some implementations, the apparatus may further comprise means for determining at least one score based on the at least one hair health metric, wherein the at least one score relates to use of the appliance and / or hair health, and preferably further comprises means for determining an overall score using a weighted combination of scores. Such a score can provide an overall indication of hair health, based on more than one metric.

[0023] Preferably, the apparatus further comprises a user interface configured for outputting an alert, and preferably configured for facilitating input of information.

[0024] In some implementations, the apparatus may comprise means for storing to a user profile the at least one hair health metric and / or the at least one score for each styling session of a user, preferably wherein the means for performing a control action in dependence on the determined at least one hair health metric is further configured to perform a control action in dependence on the at least one hair health metric over time. This can facilitate more information being gathered over time, which can provide a more holistic and tailored review of a user’s hair and / or styling technique. In preferable implementations, the apparatus comprises means for processing the sensor data to identify heating of a tress of hair in dependence on power delivered to the heater. This can assist with determining heating / styling patterns.

[0025] The means for processing the sensor data may be further configured to determine maximum hair temperature for each tress of hair by determining a difference between a maximum and minimum power delivered to the heater, and preferably further using a mean value of power delivered to the heater. Determination of maximum hair temperature can be used to determine / define the effect of heating on hair (e.g. damage).

[0026] In some implementations, the apparatus may comprise means for determining a maximum hair temperature for each tress of hair from sensor data indicative of the temperature of the tress of hair being dried and / or styled.

[0027] The apparatus may further comprise means for determining an average maximum hair temperature in dependence on a mean value of determined maximum hair temperatures for each tress.

[0028] In some preferable implementations, the apparatus may comprise means for defining new hair damage as a function of maximum hair temperature, preferably average maximum hair temperature.

[0029] In some implementations, the controller may be configured to determine new damage with reference to the hair metric determined from the heat transfer coefficient.

[0030] In some implementations, the apparatus may comprise means for processing the sensor data to identify repeated heating of a same tress of hair in dependence on the power delivered to the heater having a damped sinusoidal profile.

[0031] The apparatus may comprise means for determining number and frequency of repeated heating of a same tress of hair by identifying and processing peaks of the damped sinusoidal power profile.

[0032] In some implementations, the apparatus may comprise means for determining heat on hair time by summing intervals over which the damped sinusoidal power profile has a negative gradient.

[0033] In some preferable implementations, the apparatus may comprise sensor circuitry for providing sensor data indicative of motion of the apparatus. This may, for example, comprise: an inertial measurement unit (IMU), a speedometer, a distance meter and / or a proximity sensor.

[0034] The apparatus may comprise at least two arms moveable relative to one another, wherein at least one of the arms comprises the heater, and may further comprise means for determining configuration of the arms in dependence on the sensor data indicative of motion. The possible configurations of the arms may comprise at least an open configuration and a closed configuration (for example, the arms are in a closed configuration when they are clamped around a tress of hair - i.e. hair is loaded on the heaters). In some implementations, the apparatus may comprise means for determining hair on heat time by summing time intervals over which the arms are determined to be in a configuration indicative of the tress of hair being loaded on the heater, preferably in a closed configuration.

[0035] In some implementations, the apparatus may comprise means for correlating the time intervals over which the arms are determined to be in a configuration indicative of the tress of hair being loaded on the heater and the intervals over which the damped sinusoidal power profile has a negative gradient. This can be used to corroborate that the hair was being heated while the stylerwas closed.

[0036] In some implementations, the apparatus may comprise means for determining recurrent heating of a tress of hair in dependence on determining, from the sensor data indicative of motion, motion above a threshold speed value coincident with time intervals over which the arms are determined to be in a configuration indicative of the tress of hair being loaded on the heater, preferably in a closed configuration.

[0037] The apparatus may comprise means for comparing heat on hair time with one or more user metrics, preferably wherein the one or more user metrics comprises at least one of: hair length, hair health metric, hair damage metric.

[0038] In some preferable implementations, the heater may be a multilayer heater comprising a plurality of functional layers that are bonded together, wherein the multilayer heater is mounted within the appliance such that during use of the appliance by a user, hair contacts a hair contacting surface of the multilayer heater and is heated by conductive heating, wherein the multilayer heater includes: a heater electrode layer comprising one or more heater electrodes formed of a conductive material that generates heat when a current is passed through the one or more heater electrodes; and at least one upper dielectric layer over the heater electrode layer to electrically isolate the heater electrode layer; wherein the multilayer heater has a thickness, as measured across all of the plurality of layers of the multilayer heater, which is between 30pm and 2mm; and wherein a combined thermal conductivity of the multilayer heater in a plane perpendicular to the thickness that is less than 15 W / m.K and greater than 0.1 W / m.K.

[0039] The apparatus may comprise means for scheduling styling sessions to a calendar, preferably configured to output reminder alerts in dependence on the calendar.

[0040] The apparatus may preferably comprise a database for storing at least one hair health metric to a user profile.

[0041] The database may further comprise a database of a plurality of user profiles, wherein the apparatus comprises means for performing a clustering algorithm to cluster user profiles in dependence on at least one metric, preferably in dependence on at least one metric from: age, hair length, hair type, average styling time, favourite styles, hair colour, phone model, favourite products, location, styling frequency, and usage behaviour.

[0042] In some implementations, the apparatus may comprise means for performing control actions in dependence on analysis of user profiles in a same cluster, preferably wherein the performing control actions comprises outputting suggestions. This can provide feedback, advice and / or recommendations to a user, typically based on the analysis and preferably tailored to the user.

[0043] In some implementations, the apparatus may comprise at least one hair drying and / or styling device and a smart processing device in communication, preferably further comprising a cloud-based processing unit in communication with the at least one hair drying and / or styling device and / or the smart processing device. This can improve the user experience by providing interconnected components. For example, the smart processing device may run an application, preferably wherein the application can provide suggestions and / or alerts. This is preferably based on data from the hair drying and / or styling device. In some implementations, data may be processed by the smart processing device and / or the cloud-based processing unit.

[0044] The hair drying and / or styling device may be configured to send instructions to the smart processing device, preferably wherein the instructions comprise instructions to output an alert and / or preferably wherein the instructions comprise instructions to open and / or run an application on the smart processing device.

[0045] In some implementations, the hair drying and / or styling device may be configured to turn off in dependence on the smart processing device moving out of a defined range of the hair drying and / or styling device. Typically, the range may refer to a distance range.

[0046] According to a further aspect, there is provided a computer program product comprising computer implementable instructions for causing a programmable device to configure one or more processors to implement the features as described.

[0047] According to a first aspect, there is provided a hair drying and / or styling apparatus comprising: one or more sensors for providing sensor data indicative of at least one selected from the group consisting of: oil / sebum level of hair and / or scalp; pH level of hair and / or scalp; and scalp temperature; and means for analysing the sensor data to perform an assessment of scalp health.

[0048] Such sensor data can provide insight into the health of a user’s scalp. This in turn can have an effect on the health of the user’s hair. Outputs, control commands and / or instructions can be determined and instructed in dependence on this assessment.

[0049] The apparatus preferably further comprises means for outputting scalp health information in dependent on the assessment of scalp health, and preferably for outputting information comprising suggestions for improving scalp health. The means for outputting may comprise a user interface. This may be located on a styling and / or drying device and / or on a smart processing device in communication with a styling and / or drying device.

[0050] The apparatus may comprise at least one sensor selected from the group consisting of: sebum sensor; pH sensor; and scalp temperature measurement sensor. These may be located on a hair styling and / or drying device and / or on a smart processing device in communication with a hair styling and / or drying device and / or may be external to the hair styling and / or drying device and smart processing device and in communication with the one or both. The scalp temperature sensor may be a direct contact sensor or a non-contact temperature sensor. One or more sensors may be located adjacent to heaters of the apparatus.

[0051] In some implementations, the apparatus may further comprise one or more sensors for providing sensor data indicative of at least one characteristic selected from the group consisting of: blood circulation, scalp colour, hair density, and dandruff.

[0052] In some implementations, the apparatus may further comprise imaging sensor apparatus for recording one or more images of the scalp.

[0053] The apparatus may comprise means for analysing the one or more images of the scalp, preferably using computer vision techniques. The means for analysing is preferably a processor. It may be a processor located on a hair styling and / or drying device, a smart processing device and / or a cloud-based processing unit, or it may be comprised of a combination of these.

[0054] The apparatus may further comprise means for analysing one or more images of the scalp to determine a colour profile of the scalp. This may be the same means for analyising the one or more images, and may be a processor located on a hair styling and / or drying device, a smart processing device and / or a cloud-based processing unit, or it may be comprised of a combination of these.

[0055] In some implementations, the apparatus may comprise means for performing Eulerian video magnification techniques on one or more images of the scalp to analyse blood circulation to the scalp. In some implementations, the apparatus may comprise means for analysing one or more images of the scalp to detect hair follicles, and means for determining a hair follicle density of the scalp. In some implementations, the apparatus may comprise means for analysing one or more images of the scalp to detect dandruff. These means may be the same means, and may be a processor located on a hair styling and / or drying device, a smart processing device and / or a cloud-based processing unit, or it may be comprised of a combination of these.

[0056] In some preferable implementation, the means for analysing the sensor data may be configured to compare sensor data to predefined value ranges, and preferably further configured to define a scalp health metric.

[0057] The apparatus may preferably further comprise a database for storing scalp health information to a user profile. The database and / or user profile may be located on a hair styling and / or drying device, a smart processing device and / or a cloud-based processing unit, or of a combination of these.

[0058] The apparatus may comprise at least one hair drying and / or styling device and a smart processing device in communication, preferably further comprising a cloud-based processing unit in communication with the at least one hair drying and / or styling device and / or the smart processing device.

[0059] In some preferable implementations, the apparatus further comprises: a heater for heating a tress of hair; drive circuitry for providing power to heat the heater; a controller for controlling the drive circuitry to deliver power; and means for performing a control action in dependence on the scalp health, preferably wherein the control action comprises controlling power and / or temperature settings of the heater. According to a further aspect, there is provided a computer program product comprising computer implementable instructions for causing a programmable device to configure one or more processors to implement the features described above.

[0060] According to a further aspect, there is provided a hair drying and / or styling apparatus comprising: a heater for heating a tress of hair; drive circuitry for providing power to heat the heater; means for detecting movement of hair relative to the apparatus; and means for analysing the movement of hair to determine relative speed of the hair and the apparatus.

[0061] The means or detecting movement of hair relative to the apparatus is preferably configured to detect hair near or on the apparatus, for example near or on a heater of the apparatus (such as a heater on a hair styling and / or drying device). This may be in dependence on physical or thermal properties or in dependence on optical detection of hair, for example in dependence on changes in readings indicative of physical or thermal properties, and / or in dependence on features and / or changes in one or more recorded images.

[0062] In preferable implementations, the means for analysing is configured to determine a distance travelled during the movement over a time interval. The means for analysing is preferably a processor. It may be a processor located on a hairstyling and / or drying device, a smart processing device and / or a cloud-based processing unit, or it may be comprised of a combination of these.

[0063] The apparatus may preferably further comprise means for determining a distance by integrating the speed over a time interval. The means for determining is preferably a processor. It may be a processor located on a hair styling and / or drying device, a smart processing device and / or a cloud-based processing unit, or it may be comprised of a combination of these. The means for determining may be the same as the means for processing.

[0064] In preferable embodiments, the apparatus may further comprise means for determining hair length in dependence on a determined distance travelled by the tress of hair relative to the apparatus during a pass. The means for determining hair length is preferably a processor. It may be a processor located on a hair styling and / or drying device, a smart processing device and / or a cloud-based processing unit, or it may be comprised of a combination of these. The means for determining hair length may be the same as the means for processing and / or the means for determining a distance.

[0065] In some implementations, the apparatus may further comprise sensor circuitry for providing sensor data indicative of motion of the apparatus, and means for correlating the motion of the apparatus to the movement in order to define the pass. Such sensor circuitry may comprise an accelerometer and / or an inertial measurement unit (IMU). It may comprise a proximity sensor, wherein the proximity sensor is configured to determine whether arms of a hair styling and / or drying device are in an open or closed configuration. The means for correlating is preferably a processor. It may be a processor located on a hair styling and / or drying device, a smart processing device and / or a cloud-based processing unit, or it may be comprised of a combination of these. The means for correlating may be the same as the means for processing and / or the means for determining a distance and / or the means for determining hair length.

[0066] In some implementations, the apparatus may comprise at least two arms moveable relative to one another, preferably wherein at least one of the arms comprises the heater, and the apparatus may further comprise means for determining configuration of the arms in dependence on the sensor data indicative of motion. The means for determining configuration of the arms is preferably a processor. It may be a processor located on a hair styling and / or drying device, a smart processing device and / or a cloud-based processing unit, or it may be comprised of a combination of these. The means for determining configuration of the arms may be the same as the means for processing and / or the means for determining a distance and / or the means for determining hair length and / or the means for correlating.

[0067] In some implementations, the apparatus further comprises means for performing a control action in dependence on the determined speed and / or distance, preferably wherein the control parameter comprises controlling power and / or temperature settings of the heater, preferably controlling the setpoint temperature of the heater. The means for performing a control action may be a processor and / or controller. It may be a processor (and / or controller) located on a hair styling and / or drying device, a smart processing device and / or a cloud-based processing unit, or it may be comprised of a combination of these.

[0068] The apparatus may further comprise means for outputting alerts and / or suggestions in dependence on the determined speed, distance and / or hair length. This may comprise a processor (and / or controller) located on a hair styling and / or drying device, a smart processing device and / or a cloud-based processing unit, or it may be comprised of a combination of these. The means for outputting may further comprise a user interface, haptic unit, light display and / or speaker, or any combination of these, which may be located a hairstyling and / or drying device and / or on a smart processing device.

[0069] In some preferable implementations, the means for detecting movement of hair relative to the apparatus may be located on and / or within a heater. This can help to ensure that the movement can be detected during styling.

[0070] In some implementations, the apparatus may further comprise an imaging sensor apparatus configured to record a first image at a first time and a second image at a second time. Preferably, the image comprises hair being styled.

[0071] The apparatus preferably further comprises: means configured to detect a feature common to the first image and the second image, and to determine the vector between the location of the feature in the first image and the location of the vector in the second image, preferably wherein a real dimension is determined by multiplying a pixel dimension by a known constant; and wherein the means for analysing is configured to determine speed in dependence on the vector and the time interval between the first time and the second time.

[0072] In some preferable implementations, the imaging sensor apparatus is configured to perform darkfield imaging. This can be beneficial if hair is shiny, as this enables features to be detected above the light reflected from a shiny surface. In some implementations, the imaging sensor apparatus may comprise a CMOS sensor.

[0073] The apparatus may further comprise an odometer.

[0074] The apparatus may comprise a roller configured to contact hair during styling and rotate as the hair and apparatus move past one another, and further comprising means for measuring rotation of the roller, wherein the means for analysing is configured to determine speed in dependence on the rotation of the roller over a time interval.

[0075] In preferable implementations, the means for measuring rotation of the roller comprises a detector, and preferably comprises one or more optical encoders.

[0076] The roller may be cylindrical (e.g. ‘barrel-shaped’) and configured to rotate around an axis (or pivot line). The axis (or pivot) may comprise a heating element.

[0077] In preferable implementations, the roller is spherical and is configured to rotate (preferably about more than one axis) within a socket. In other words, the movement of the roller is multi-axis (within the plane of a surface of the apparatus and / or heater). Preferably, the socket comprises at least two cylindrical rollers configured to make contact with the spherical roller and be rotatable due to a component of the motion of the spherical roller, and more preferably further comprises means for measuring the rotation of the cylindrical rollers to measure the components of motion.

[0078] In some implementations, the roller may be in thermal connection with a heating element, preferably wherein the roller is configured to be heated via convention, radiation and / or conduction.

[0079] In some preferable implementations, the heater comprises at least one independently controllable heater zone of known width, and the apparatus further comprises: sensor circuitry for providing sensor data indicative of at least one selected from the group consisting of: power delivered to the heater zone; the temperature of the tress of hair being dried and / or styled; and the temperature of the heater zone; means for determining the temperature difference of the tress of hair as it enters the heater zone and as it leaves the heater zone; and means for determining the speed of the hair in dependence on the temperature difference, the power delivered to the heater zone and the known width of the heater zone.

[0080] Assuming that all the heat energy is used to raise the temperature of the hair, the temperature difference, the power delivered to the heater zone and the known width of the heater zone can be used to determine the time interval over which the hair is located on / within the heater zone. Using the known width of the heater zone, this can be used to determine the speed.

[0081] The apparatus may comprise: a first heater zone and a second heater zone immediately adjacent to the first heater zone, wherein the heater zones are arranged such that the tress of hair enters the first heater zone before the second heater zone; and means for determining the temperature of a tress of hair as it enters each heater zone in dependence on the sensor data of the same heater zone; and wherein the means for determining speed is configured to compare the temperature of the hair as it enters a first heater zone and the temperature of hair as it enters a second heater zone, and is further configured to determine speed in dependence on the temperature difference, the power delivered to the first heater zone and the known width of the first heater zone.

[0082] The apparatus may further comprise means for determining a heat capacity of the hair in dependence on the sensor data provided by the sensor circuitry. The apparatus may further comprise means for receiving any of: capacity and / or specific heat capacity of the tress, average tress size and / or further comprise means for determining gap between heaters, and inferring tress size.

[0083] In some preferable implementations, the apparatus may comprise at least one hair drying and / or styling device and a smart processing device in communication, preferably further comprising a cloud-based processing unit in communication with the at least one hair drying and / or styling device and / or the smart processing device. Any of the ‘means’ described above may be the processor and / or controller of the at least one hair drying and / or styling device, smart processing device and / or cloud-based processing unit, or any combination of these.

[0084] According to a further aspect, there is provided a method of determining relative speed of a tress of hair and a hair drying and / or styling apparatus, comprising: detecting movement of the tress of hair relative to the apparatus during styling; tracking a characteristic of the tress of hair over a time interval; and determining speed of the tress of hair relative to the apparatus in dependence on measured changes to the characteristic over the time interval.

[0085] The method may further comprise determining a distance by integrating the determined speed over a time interval.

[0086] The method may preferably further comprise determining a hair length in dependence on a determined distance travelled by the tress of hair relative to the apparatus during a pass.

[0087] In some implementations, the method may further comprise detecting a pass of the apparatus by determining the motion ofthe apparatus in dependence on sensor data indicative of motion ofthe apparatus, and correlating the motion of the apparatus and the detected movement of the tress of hair relative to the apparatus.

[0088] Preferably, the correlating comprises determining the configuration of two arms ofthe apparatus in dependence on the sensor data indicative of motion of the apparatus.

[0089] In some implementations, the method may performing a control action in dependence on the determined speed and / or distance, preferably wherein the control parameter comprises controlling power and / or temperature settings of the heater, preferably controlling the setpoint temperature of the heater.

[0090] The method may preferably further comprise outputting alerts and / or suggestions in dependence on the determined speed, distance and / or hair length. This can be useful in tailoring the use of a device / apparatus to a particular user, and for providing feedback to the user regarding how to improve their use of the device / apparatus. In some implementations, the determining speed comprises: recording a first image of the tress of hair at a first time and a second image of a tress of hair at a second time; detecting a feature common to the first image and the second image; determining the vector between the location of the feature in the first image and the location of the vector in the second image; preferably, multiplying the vector by a known constant to convert a pixel dimension vector to a real dimension vector; and determining speed in dependence on the vector and the time interval between the first time and the second time.

[0091] In some implementations, the recording the first image and the second image utilises darkfield imaging.

[0092] The method may comprise detecting movement of an odometer. The method may comprise detecting rotation of a roller configured to make contact with the tress of hair and rotate in dependence on the relative movement of the tress of hair and the apparatus, and wherein the determining speed comprises determining speed in dependence on rotation of the roller over a time interval.

[0093] In some implementations, the method may comprise: receiving sensor data indicative of at least one selected from the group consisting of: power delivered to the heater zone; the temperature of the tress of hair being dried and / or styled; and the temperature of the heater zone; processing the sensor data to determine the power delivered to a heater zone of known width as the tress of hair passes over the heater zone; processing the sensor data to determine the temperature difference of the tress of hair as it enters the heater zone and as it leaves the heater zone; and wherein the determining speed comprises determining speed in dependence on the temperature difference, the power delivered to the heater zone and the known width of the heater zone.

[0094] In some preferable implementations, the method may further comprise: receiving sensor data for a first zone and a second zone, wherein the tress of hair passes the first zone before the second zone (and preferably wherein the first heater zone is immediately adjacent to the second heater zone); determining the temperature of the hair as it enters the first heater zone and the temperature of the hair as it enters the second heater zone, and determining the temperature difference.

[0095] In some implementations, the method may further comprise: determining a heat capacity of the hair in dependence on the sensor data provided by the sensor circuitry. In some implementations, the method may comprise: receiving a heat capacity of the hair and / or a specific heat capacity of the hair (in some implementations it may further comprise determining a thickness and / or mass of a tress of the hair). In some implementations, the method may comprise utilizing an average or estimated heat capacity or specific heat capacity. The method may comprise determining a gap between heaters, and inferring tress size.

[0096] According to a further aspect, there is provided a computer program product comprising computer implementable instructions for causing a programmable device to configure one or more processors to implement any of the features described.

[0097] According to a further aspect, there is provided a hair drying and / or styling apparatus comprising: a heater for heating a tress of hair; drive circuitry for providing power to heat the heater; a controller for controlling the drive circuitry to deliver power; means for receiving ambient condition data relating to at least one selected from the group consisting of: temperature, humidity, and / or air pressure; means for receiving user preferences and / or inputs; and means for performing a control action in dependence on the ambient condition data in combination with the user preferences and / or inputs.

[0098] This can facilitate the control of the apparatus in dependence on complex factors. This can enable the performance to be adjusted in dependence on both the conditions and circumstances.

[0099] The control action may comprise controlling power and / or temperature settings of the heater, preferably controlling the setpoint temperature of the heater.

[0100] In some preferable implementations, a set of rules correlating the ambient condition data and the control actions is elected in dependence on the user preferences and / or inputs. The apparatus may store a series of different sets of rules correlating the ambient condition data and the control actions. In some implementations, the sets of rules infer priorities in dependence on the user preferences. The priorities may comprise one or more of: hair health, speed of styling, and longevity of style.

[0101] In some preferable implementations, the apparatus may comprise a means for implementing fuzzy logic architecture to process the ambient condition data and user preferences and to determine the control action. The fuzzy logic architecture may comprise a rule base, and preferably the rule base comprises the sets of rules.

[0102] In some preferable implementations, the user preferences comprise priorities, preferably wherein the priorities comprise one or more of: hair health, speed of styling, and longevity of style.

[0103] The apparatus may further comprise means for receiving relevant location data, preferably wherein the relevant location data comprises geographic location data and / or interior or exterior data.

[0104] In some implementations, relevant ambient condition data is determined in dependence on the relevant location data. This may comprise, for example, determining whether interior conditions or exterior conditions are relevant.

[0105] The means for receiving ambient condition data may be configured to receive meteorological and / or weather data. This may be received from local meteorological and / or weather authorities or services.

[0106] The apparatus may, in some implementations, further comprise means for determining geographical location, preferably comprising location tracking and / or identification of a location address of an internet connection.

[0107] The apparatus preferably further comprises a user interface configured for facilitating input of user preferences.

[0108] The apparatus preferably comprises means facilitating input of information and / or user preferences by the user. This may be a user interface, for example located on at least one hair drying and / or styling device and / or a smart processing device (preferably in communication with the at least one hair drying and / or styling device). The apparatus may, in some implementations, be configured to retrieve user preferences from a user profile, which may be stored in a database on at least one hair drying and / or styling device, a smart processing device and / or on a central and / or cloud-based processing unit.

[0109] In some implementations, the apparatus may comprise one or more of: a hygrometer, a barometer, and a thermometer.

[0110] The apparatus may comprise at least one hair drying and / or styling device and a smart processing device in communication, preferably further comprising a cloud-based processing unit in communication with the at least one hair drying and / or styling device and / or the smart processing device. Any of the ‘means’ described above may be the processor and / or controller of the at least one hair drying and / or styling device, smart processing device and / or cloud-based processing unit, or any combination of these.

[0111] According to a further aspect, there is provided a method of controlling a hair drying and / or styling apparatus, the method comprising: receiving ambient condition data relating to at least one selected from the group consisting of: temperature, humidity, and / or air pressure; receiving user preferences and / or inputs; and processing the ambient condition data in combination with the user preferences and / or inputs to determine a control action.

[0112] The method may comprise electing a set of rules correlating the ambient condition data and the control actions in dependence on the user preferences and / or inputs. In some implementations, the sets of rules infer priorities in dependence on the user preferences. The priorities may comprise one or more of: hair health, speed of styling, and longevity of style. The method may comprise inferring priorities in dependence on user preferences and / or inputs.

[0113] In some preferable implementations, the processing comprises processing using fuzzy logic. Preferably, it comprises assessing the (fuzzy) inputs with reference to sets of rules (e.g. stored in a rule base).

[0114] The user preferences may comprise priorities, preferably wherein the priorities comprise one or more of: hair health, speed of styling, and longevity of style.

[0115] The method may further comprise: performing a control action in dependence on the ambient condition data in combination with the user preferences.

[0116] Preferably, the control action comprises controlling power and / or temperature settings of the heater, preferably controlling the setpoint temperature of the heater.

[0117] In some implementations, the method further comprises receiving relevant location data, preferably wherein the relevant location data comprises geographic location data and / or interior or exterior data.

[0118] The method may further comprise determining relevant ambient condition data in dependence on the relevant location data. This may comprise, for example, determining whether interior conditions or exterior conditions are relevant. In some implementations, the ambient condition data may preferably comprise meteorological and / or weather data. For example, if exterior conditions are relevant, weather conditions may be the most appropriate ambient condition data.

[0119] The method may further comprise determining the geographical location of the apparatus, preferably in dependence on a location tracker and / or internet connection.

[0120] The user preferences may comprise priorities. The user preferences and / or priorities may comprise one or more of: hair health, speed of styling, and longevity of style.

[0121] According to a further aspect, there is provided a computer program product comprising computer implementable instructions for causing a programmable device to configure one or more processors to implement any of the features described.

[0122] The invention extends to methods and / or apparatus substantially as herein described with reference to the accompanying drawings.

[0123] Any apparatus feature as described herein may also be provided as a method feature, and vice versa.

[0124] Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. In particular, method aspects may be applied to apparatus aspects, and vice versa. Furthermore, any, some and / or all features in one aspect can be applied to any, some and / or all features in any other aspect, in any appropriate combination.

[0125] It should also be appreciated that particular combinations of the various features described and defined in any aspects of the invention can be implemented and / or supplied and / or used independently.

[0126] Brief Description of the Drawings

[0127] Embodiments of the invention will now be described, by way of example only, and with reference to the drawings in which:

[0128] Figure 1 a shows an overview of an exemplary hair styling device;

[0129] Figure 1 b shows a hair styling device in use;

[0130] Figure 2 is a block diagram illustrating the main electronic components of the hair styling device shown in Figure 1 ;

[0131] Figure 3a is an exploded view of a heater forming part of the hair styling device shown in Figure 1 ;

[0132] Figure 3b is an assembled partially transparent view of the heater shown in Figure 3a;

[0133] Figure 4a schematically illustrates the heating zones on the heating surface of the heater shown in Figure 3;

[0134] Figure 4b schematically illustrates an alternative arrangement of heating zones; Figure 5 schematically illustrates a further alternative arrangement of heating zones that are of different sizes and shapes;

[0135] Figure 6a illustrates the way in which the heating zones may be formed on a tubular substrate for use in a curling tong or the like;

[0136] Figure 6b illustrates the way in which the heating zones may be arranged on a curved substrate which may be used on a heated brush;

[0137] Figure 7 illustrates a tress of hair that partly overlaps with zones Z2 and Z4 of a heater;

[0138] Figure 8 illustrates a cross-sectional view of a further example of a low thermal mass heater that has curved edges and a supporting substrate onto which the heater is attached with an adhesive or via a diffusion bonding process (e.g. by melting them together) or via an In Mould Labelling process;

[0139] Figure 9 is a partially exploded cross-sectional and perspective view of the different layers that form the heater shown in Figure 8;

[0140] Figure 10 is a plan view illustrating the form of a heat spreading layer forming part of the heater illustrated in Figure 8;

[0141] Figure 11 illustrates a main heating element layer forming part of the heater shown in Figure 8;

[0142] Figure 12 is a simplified block diagram illustrating the way in which the heater electrodes of the heater shown in Figure 8 are used to heat the heater and to sense the temperature of the heating zones;

[0143] Figure 13 is a block diagram illustrating the main electronic components of a further embodiment of the hair styling device;

[0144] Figure 14 is an illustrative plot of hair damage against hair heat transfer coefficient;

[0145] Figure 15 is a further illustrative plot of hair damage against hair heat transfer coefficient;

[0146] Figure 16 is an illustrative plot of hair temperature over time;

[0147] Figure 17 is an exemplary plot of a power demand profile over time;

[0148] Figure 18 is an exemplary plot of a motion metric over time;

[0149] Figure 19a is a further exemplary plot of a motion metric over time;

[0150] Figure 19b is a further exemplary plot of a power demand profile over time;

[0151] Figure 20 is a yet further exemplary plot of a power demand profile over time; Figure 21 is a block diagram illustrating the main electronic components of a further embodiment of the hair styling device;

[0152] Figure 22 is an exemplary schematic of a tress of hair on a styler comprising an optoelectronic sensor;

[0153] Figure 23 is a schematic view of a uniaxial row of pixels detected by the optoelectronic sensor;

[0154] Figure 24 is a schematic view of a matric of pixels detected by the optoelectronic sensor;

[0155] Figure 25 shows a side view of a tress of hair passing between a heater and a roller;

[0156] Figure 26 shows a side view of a tress of hair passing between a heater and a roller located within a further heater;

[0157] Figure 27 shows a roller with a central heating element;

[0158] Figure 28 shows a side view of a tress of hair passing over two heater zones;

[0159] Figure 29 shows a top view of a tress of hair passing over a heater comprising multiple zones;

[0160] Figure 30 shows an exemplary system comprising a smart processing device and cloud-based processing unit in communication with the hair styling device;

[0161] Figure 31 is a block diagram illustrating the main electronic components of the smart processing device;

[0162] Figure 32 is a block diagram illustrating connections between components of an exemplary system;

[0163] Figure 33 is a block diagram illustrating the main electronic components of a further embodiment of the hair styling device;

[0164] Figure 34 is an exemplary schematic diagram of a fuzzy logic processing architecture;

[0165] Figure 35 shows an exemplary user interface output;

[0166] Figure 36 shows an exemplary plot illustrating a clustering algorithm; and

[0167] Figure 37 shows an exemplary calendar output.

[0168] Detailed Description of Preferred Embodiments

[0169] Overview of Hair Styling Device

[0170] Figure 1 a illustrates a hand held (portable) hair styler 101. The hair styler 101 includes a first movable arm 104a and a second movable arm 104b, which are coupled at proximal ends thereof to a shoulder or hinge 102. The first arm 104a bears a first heater 106a at its distal end, and the second arm 104b bears a second heater 106b at its distal end. The first and second heaters 106a, 106b oppose one another and are brought together as the first and second arms 104a, 104b are moved from an open configuration to a closed configuration. As shown in Figure 1 b, during use, a tress of hair 140 is sandwiched between the two arms 104 so that the user’s hair is in contact with, and therefore heated by, outer heating surfaces of the heaters 106a, 106b. Therefore, as the user pulls the hair styler 1 along the tress of hair 140, the tress of hair 140 is heated by conductive heating to a suitable temperature to facilitate styling.

[0171] One or more user interfaces 111 are provided to allow the user to set user defined parameters and for the device to output information to the user. For example, a desired operating temperature may be set via the user interface 111. The user interface 111 may have a dial, button or touch display for allowing the user to input information to the device 101 and the user interface 111 may have an indicator light, display, sound generator or haptic feedback generator for outputting information to the user. In this embodiment, the user interface 11 1 also comprises a control button or switch 114 to enable the user to turn the device 101 on or off; and an indicator light 115 to show whether the power is on.

[0172] A printed circuit board assembly (not shown) may be provided at any suitable location within the housing of the device 101 and carries the control circuitry for controlling the operation of the device 101 and for controlling the interaction with the user via the user interface 11 1. In this example, electrical power is provided to the device 101 by means of a power supply located at an end of the device, via a power supply cord 103. The power source may be an AC mains or a DC power supply. However, in an alternative embodiment the power supply may comprise one or more DC batteries or cells (which may be rechargeable, e.g. from the mains or a DC supply via a charging lead), thereby enabling the device 101 to be a cordless product.

[0173] In use, the device 101 is turned on, enabling power to flow through the heaters 106 to cause them to heat up. The userthen opens the first and second arms 104a, 104b and, normally starting from the roots of the hair (i.e. near the scalp), a length or tress of hair 140 (which may be clumped) is introduced between the arms 104a, 104b, transversely across the heaters 106a, 106b. The user then closes the arms 104a, 104b so that the length of hair 140 is held between the first and second arms 104a, 104b and then the user pulls the hair through the closed arms (as illustrated in Figure 1 b). The outer (hair contacting) surface of the heaters 106 is flat in this embodiment and so the hair styler 101 can be used to straighten the user’s hair. The hair styling device 101 shown in Figure 1 can also be used to curl the hair by turning the device 101 through approximately 180 degrees or more after clamping the hair between the arms 104a, 104b and before moving the device 101 along the tress of hair 140.

[0174] Hair has a relatively high thermal mass and when in contact with the heating surface of the heater 106 the hair absorbs a significant amount of the heat energy. The heaters 106 must quickly supply the lost heat energy back to the heating surface otherwise the temperature of the heating surface will drop and potentially impact on the quality of the thermal styling. If the temperature of the heaters 106 fall below that required to raise the hair temperature above the glass transition temperature of the hair, the hair will not retain the styled shape. However, if the hair is heated to a temperature that is too high, the hair can undergo significant damage. As such, the device 101 must be able to control the temperature so that the heating surface of the heaters 106 remains within a particular temperature range. Furthermore, it must maintain the temperature range both when hair is frequently and quickly loaded and unloaded onto the heating surface, and when hair is held on the heating surface for a prolonged period of time.

[0175] Control Circuitry

[0176] Figure 2 is a simplified block diagram of control circuitry 215 that controls the operation of the hair styler device 101 shown in Figure 1 . As shown, the control circuitry 215 comprises a power supply 221 that, in this embodiment, derives power from a battery power source (not shown). A power supply input may be provided to charge the battery via an AC to DC converter (not shown), which may be external or internal to the device 101 . Alternatively, the power supply 221 may derive power from an AC mains input.

[0177] In this example, power is provided to the heaters 206 for heating the user’s hair. The power supplied to the heaters 206 is controlled by a controller 228 having a microprocessor 229. The power supplied to the heaters 206 is controlled by drive circuitry 223 (which may include one or more power semiconductor switching devices) which controls the application of an AC mains voltage, or a DC voltage derived from AC mains via a power supply or from a battery, to the heaters 206 in accordance with instructions from the microprocessor 229. The microprocessor 229 is coupled to a memory 230 (which is typically a non-volatile memory) that stores processor control code for implementing one or more control methods that control the heating of the heaters 206 in accordance with a desired operating temperature of the heaters 206 and sensed temperatures of the heaters obtained from temperature measurement circuitry 225. The temperature measurement circuitry 225 may be temperature sensors such as thermistors or they may use circuitry that senses the resistance of heater electrodes that are used to heat the heaters 206, which resistance depends on the temperature of the heater electrode.

[0178] Figure 2 also shows that the user interface 211 is coupled to the microprocessor 229, for example to provide one or more user controls and / or output indications such as a visual indication or an audible alert. The output(s) may be used to indicate to the user, for example, if they have inserted too much hair between the heaters 206 or if they are moving the device 101 too quickly along the hair tress 140.

[0179] Finally, the control circuitry includes communications circuitry 227 to allow the device to communicate with a remote sensor, a remote server, or a remote application (e.g. on a mobile telephone). The communications circuitry 227 may use, for example, Bluetooth, Wi-Fi and / or 3GPP communication protocols to communicate with the remote device.

[0180] Heaters

[0181] The heaters 106, 206 are low thermal mass heaters and can therefore heat up and cool down quickly. Figures 3a and 3b show an exemplary embodiment of such heaters 306a, 306b, which comprise a stack of thin layers. Referring in particular to Figure 3a, the heaters 306a, 306b include an upper dielectric (electrically insulating) layer 362, an electrode layer 363 that has a plurality of separate heater electrodes 364, and a lower dielectric layer 366 which electrically insulates the heater electrodes 364 from other components mounted behind the heater 306a, 306b. The three layers 362, 363 and 366 are bonded together either through an adhesive layer (pressure set orthermoset) orthrough diffusion bonding of the contacting materials (e.g. melting them together) and define a heater 306 that is very thin (the three layers have an overall thickness of between 30pm to 1000pm (preferably between 75 pm and 300 pm) in the case of Safe Extra Low Voltage (SELV) operation (less than 42.4 Volts) and 0.8mm to 2.0mm in the case of AC operation) and with very low thermal mass. The upper surface of the layer 362 provides the hair contacting surface of the heater 306, although a non-stick coating may be applied to the upper surface of the layer 362 to facilitate the passage of the user’s hair over the heating surface if the layer 362 does not itself have such non-stick properties. The bonded layers 362, 363 and 366 define a flexible heater 306 and rigidity of the heater is provided in the illustrated embodiment by mounting the heater layers 362, 363 and 366 into a rigid support 368 which forms a base. These layers may be mounted onto the rigid support after the layers themselves have been bonded together or they may be bonded one at a time (or multiple at a time) onto the rigid support 368. If a flexible heater is desired, then there is no need for the rigid support 368 or if a support is used, this may be a non-rigid support. Thus, in this embodiment, there is no heater plate or tube that is heated by the heaters 306, and instead, the heaters 306 directly heat the user’s hair. This provides a hair styler 301 having a very low thermal mass which can therefore heat up and cool down much more quickly than prior art stylers.

[0182] In the illustrated embodiment, there are ten heater electrodes 364 that each snake across and back across the width of the heater 306, folding twice such that they each cross the width three times. The ends of each of the heater electrodes 364 are electrically connected through the lower dielectric layer 366 to electrical connections within the rigid support 368, which connect to an electrical connector 370. Drive circuitry 223 that is mounted within one of the arms 104 connects to the heater electrodes 364 via the electrical connector 370 and applies electrical power to the individual heater electrodes 364 to control the heat generated by each heater electrode 364. The electrical connector 370 extends from a surface of the rigid support 368 facing away from the surface layer 362 (shown in Figures 3a and 3b as extending directly away from the upper layer 362, but it could also be provided as extending in a perpendicular direction).

[0183] Each of the heater electrodes 364 thus creates an individual heating zone 467 on the hair contacting surface of the heater 306, which spans the width (which we shall refer to as the x-direction) of the heater 306 and the heater electrodes 364 are arranged sequentially one after the other along the length (the y-direction) of the heater 306. Figures 4a and 4b show schematic views of different arrangements of such heating zones 467. Figure 4a shows an arrangement corresponding to that of Figures 3a and 3b, in which the heating zones 467- 1 to 467-10 are arranged along the y-direction only. Figure 4b shows an alternative arrangement, in which heating zones 467-1 to 467-16 are arranged in both the x- and y-directions. Such an arrangement of heating zones 467 can be provided by arranging two sets of heater electrodes 364 like those shown in Figure 3a side by side in the width (x-) direction. The heaters 406 may be separated in this way into any number of heating zones 467 and may comprise any number of heating zones along the x- and y-directions. In particular, whilst Figure 4b shows two zones along the x-direction, a greater number of zones in the x-direction could also be provided. The heating zones 467 of the heaters 406a, 406b can be operated (heated) independently, which can help to reduce hot / cold spots when using very low thermal mass heaters 306 such as those shown in Figure 3. The heating zones illustrated in Figure 4 are all the same size. Of course, different sized heating zones 467 may be provided, as illustrated in Figure 5, which shows a heater 506 having seven different sized heating zones (labelled 5Z1 to 5Z7). The way in which the heater electrodes 364 would be arranged to define these different sized zones would be understood by the skilled reader and will not be described in detail here.

[0184] The heating zones 467 described above form part of a heater having a flat hair contacting surface. The heater is not limited to flat hair contacting surfaces and can be configured for use in a tubular form, with heating zones labelled 6Z1 to 6Z4 (as illustrated in Figure 6a), for example for use in a hair curler device or in a curved form, with heating zones labelled 6Z1 to 6Z4 (as illustrated in Figure 6b), for example for use in a heated hair brush. The heater surface may have a corrugated or ribbed shape to provide a hair crimping device.

[0185] The temperature of each heating zone 467 is independently controllable. Each heating zone 467 can be set to a target temperature. The target temperature of each heating zone 467 may be different. A separate temperature sensor may be provided for sensing the temperature of each heating zone 467 which is fed back to the microprocessor 229 to allow the microprocessor 229 to control the delivery of power to the heater electrode 364 of the corresponding heating zone 467. Alternatively, if the heater electrodes 364 are formed of a material having a Positive Temperature Coefficient (PTC) or a Negative Temperature Coefficient (NTC) (such that its resistance varies with its temperature), then the temperature of each heating zone 467 can be determined by determining the resistance of the corresponding heater electrode 364. The microprocessor 228 controls the heating in order to reduce the difference between the actual temperature of the heating zone 467 and the target temperature for that heating zone 467.

[0186] Heating Zone Sizing

[0187] One issue with low thermal mass heaters 106, 206, 306, 406 is the regulation of hair contacting surface temperature in the locally hair loaded regions of the heater within desired temperature limits, without causing overheating of the unloaded regions at the same time. Specifically, when the user loads a tress of hair 140 onto the heaters 106, 206, 306, 406, some parts of the heaterwill be loaded with hairwhilst other parts will not be loaded with hair. Upon loading with hair, more power is supplied to the heater 106, 206, 306, 406 to ensure that all regions on the hair contacting surface can be retained within and / or recovered back to the desired operating temperature limits. The low thermal mass heaters 106, 206, 306, 406 described above are relatively thin and the dielectric layers are formed of materials with relatively low thermal diffusivities. If there was just a single heating zone, and hence a single continuous heater electrode 364 running across the whole length and whole width of the heater 106, 206, 306, 406, then when more power is supplied to the heater 106, 206, 306, 406 to recover the temperature drop in the locally hair loaded regions, the unloaded regions would undergo overheating, which could cause the heater materials to exceed their maximum operating temperatures, or cause the overheated regions to burn relatively small bundles / strands / tresses of hair that come into contact with them. This overheating can be prevented by using materials with higher thermal diffusivities in the layers that constitute the heater, and / or by increasing the thicknesses of the layers that constitute the heater and / or by dividing the heater 106, 206, 306, 406 into multiple separately powered and controlled heating zones 467 across its length or its length and width. Increasing the thickness of the layers increases the thermal mass of the heater 106, 206, 306, 406 which is undesired and there are limited materials that have the required dielectric strength and high thermal diffusivity (and which are available for use in mass produced consumer products). Therefore, the inventors have divided the heaters 106, 206, 306, 406 up into plural heating zones. These heating zones can be equally and / or unequally sized and can be arranged regularly and / or irregularly across the width and length of the heater.

[0188] However, overheating can still occur within a single heating zone. For example, if half of the heating zone is loaded with hair (which is assumed to be the realistic worst case scenario during operation) and the other half is not loaded with hair, then the half that is loaded with hairwill cause the temperature of that part of the heating zone to drop which will cause more power to be applied to that heating zone in its entirety. That applied power will bring the average temperature of the heating zone back up to the desired operating temperature, but the unloaded part of the heating zone will be above the average temperature of the heating zone. This temperature increase may be sufficient to cause the unloaded part to overheat. At the same time the loaded part of the heating zone will be below the average temperature causing a reduction in heat transfer and reduced styling performance. This situation is illustrated in Figure 7, which shows a tress of hair 740 overlying heating zones 7Z2, 7Z3 and 7Z4, with heating zone 7Z3 being fully loaded with hair and heating zones 7Z2 and 7Z4 being only partially loaded with hair. This problem can be reduced by making the heating zones very small - but that is costly due to all the connections needed to connect each heater electrode 364 for each heating zone back to the drive circuitry 223 as well as the number of control switches in the drive circuitry 223 needed to control the powering of each heater electrode 364. The inventors have found that for a given permitted maximum temperature within the heater, a maximum size of the heating zones can be defined which depends on the maximum power density to hair that can be extracted from the heating zone and the material characteristics and thicknesses of the layers forming the heating zone.

[0189] Specifically, if it is assumed that only one half of a heating zone 467 is loaded with hair, upon loading with hair, the maximum temperature that occurs in the unloaded half of a heating zone 467 can be defined with the equation below: where,

[0190] TMax=maximum temperature (°C) on the surface of the heater which would occur in the unloaded half (worst case) of an individual heating zone;

[0191] TTar= target operational temperature or average temperature (°C) of individual heating zones; q = power density (Wm-2) required to heat hair passing over the surface to the desired temperature for styling;

[0192] W = width of a heating zone measured perpendicular to the motion of hair over the surface; t = total thickness of the layers that constitute the heating zone; and k = the thickness averaged thermal conductivity of the thin layers that constitute the heating zone.

[0193] If it is assumed that the thickness averaged thermal conductivity of the constituent layers of a heating zone 467 and the total thickness of the layers that form the heating zone 467 are known and fixed (for any given device), then the above equation can be used to determine the required zone width (W) and hence a number of divisions along the length ofthe heater that will prevent overheating of the unloaded halves, when their other halves are loaded with hair, and more power is supplied to maintain and / or recover the hair contacting surface temperatures back to the desired operating limits. Consequently, for a given surface area that must be covered with the considered heater technology, the equation above can be used to determine the number of heating zones that should be positioned along the length of the given surface area, so that each heating zone 467 can be operated without exceeding the maximum operating temperature of the heater materials and without causing the temperature of the unloaded part of a heating zone 467 to exceed the maximum temperature (AT,n0;f) that could cause burning of relatively small bundles / strands of hair that come in contact with such overheated regions of the heating zone.

[0194] Specifically, the required divisions along the length can be determined from:

[0195] Where,

[0196] L = length of the heater plate (perpendicular to the direction that hair typically travels across the surface); nL= number of zonal divisions along the length of the heater plate;

[0197] TMar= maximum permitted temperature (°C) on the surface of the heater (which would occur in the unloaded half (worst case) of an individual heating zone) needed to avoid damage to hair or the heater;

[0198] TTar= target operational temperature or average temperature (°C) of individual heating zones; k = the thickness averaged thermal conductivity (Wm-1 oC'1) of the layers that constitute the heating zone; t = total thickness of the layers that constitute the heating zone; and q = maximum power density (Wnr2) required to heat hair passing over the surface to the desired temperature for styling.

[0199] For a hair styling device, the inventors have found the following suitable ranges for these parameters: Peak power density required for styling dry hair (<j) is typically greater than 40,000 W / m2and less than 100,000 W / m2.

[0200] The average thermal conductivity of the layers forming the heating zone ( / <) (averaged through the depth of the various layers) is between 80 and 200 W / m.K.

[0201] The maximum permitted temperature of a heating zone to manage (ideally avoid) hair damage is less than 250°C, more preferably less than 220°C and most preferably less than 200°C.

[0202] The total thickness of the layers (t) which make up the heater is less than 300pm but no less than 75pm due to manufacturing limitations.

[0203] The target operational temperature of the heater (TTar) is between 150°C and 230°C.

[0204] Operating within these ranges, the inventors have found that the required number of heating zones per unit length (cm) along the length of the heater is between 0.6 and 2.5 per cm which is equivalent to a zone width (in the lengthwise direction of the heater) of between 0.4 cm and 1 .7 cm.

[0205] Of course, this is for the case of there not being multiple zones in the width direction of the heater as well (e.g. this is for the single row case shown in Figure 4a). If multiple rows of heating zones 476 are provided along the length of the heater (such as is shown in Figure 4b), then each row of heating zones 467 should meet the limits defined above if the above-described overheating problem is to be avoided.

[0206] Alternative Heater Arrangements

[0207] A first alternative flexible heater 806 is illustrated in Figure 8, which shows on the left hand side an exploded cross-sectional view of the heater 806 and substrate 868 and on the right hand side a perspective view of the heater 806 and substrate 868. As shown in Figure 8, the heater 806 has curved edges 872-1 and 872-2 that are shaped to match the shape of an upper surface 874 of the rigid support substrate 868 so that the flexible heater 806 can be bonded securely using an adhesive, or diffusion bonding (thermoforming) of the underlying materials to the upper surface of the rigid substrate 868, or by over-moulding in which the carrier is injection moulded over the back of the flexible heater within the mould. The curved edges of the heater 806 can be formed, for example, using a heat forming process. Figure 8 also illustrates that one or more surface mounted electronic components 876 may be attached to an underside of the heater 806. These components may be, for example, thermistors for sensing the temperature of the heating zones 867 of the heater 806 or fuses that can cut power to the heater electrode of each zone or all the zones in the case of a zone overheating. Figure 8 also shows a control printed circuit board (PCB) 878 that carries the drive and control electronics 215 illustrated in Figure 3 that controls the heating of the different heating zones 867 of the heater 806.

[0208] As before, the heater 806 is formed from a number of discrete layers that are mechanically or chemically bonded together. Each layer has a thickness between about 1 pm and 150 pm and preferably between 1 pm and 100 pm, more preferably between 10 pm and 70 pm or between 2 pm and 10 pm. The different layers forming part of the heater 806 are shown in exploded cross-sectional and perspective views in Figure 9. A description of each layer is given below. Low Friction Coating 981 (optional)

[0209] This is an optional layer and can be added to create a smooth, low friction surface to enhance the user experience by making the heater 806 feel less grippy against the hair. This layer would be as thin as possible (for example, between 1 and 3 pm) to reduce the thermal resistance from the heater 806 to the hair, whilst still being sufficiently durable and scratch resistant.

[0210] This layer would typically be applied last, possibly as a spray coating (e.g. Cerasol), after the rest of the heater 806 has been produced and assembled around the rigidifying substrate 868. This is needed because the coating is prone to cracking when flexed, and once applied the coating will reduce the natural flexibility of the heater, and so it should be applied once the heater 806 has been formed into its final shape.

[0211] Alternatively, this coating may comprise multiple layers including, for example, a primer layer (of about 6pm), a base coat layer (of about 25pm) and a top coat layer (of about 10pm).

[0212] Heat Spreading Layer 982 (optional)

[0213] This is also an optional layer and, when provided, helps to spread the heat within each heating zone 467, 867 to ensure that the temperature of individual heating zones 467, 867 is able to maintain an acceptable degree of homogeneity during typical use. As discussed above, if a heating zone 467, 867 was to be partially loaded with hair and was sufficiently large, the unloaded portion of the heating zone 467, 867 could develop an unacceptably high temperature, whereas the loaded region would be too cold, as heat could not adequately flow from the hot region to the cold region. This problem is exacerbated by the anisotropic thermal characteristics of the serpentine like heater electrodes 364, and by the fact the control electronics 215 would typically work to maintain an “average” temperature within the heating zone 467, 867 based on the overall resistance of the heater electrode that forms the heating zone 467, 867 - from the perspective of the control electronics 215, the heating zone 467, 867 would be at the “correct” temperature despite having hot and cold regions.

[0214] Each heating zone 467, 867 would have its own heat spreader, which is thermally separated (there is a high thermal impedance / low thermal conductivity) from the heat spreaders for adjacent zones. This is desirable to prevent heating zones 467, 867 from heating neighbouring heating zones 467, 867 which might otherwise increase power consumption, reduce warm up time and complicate algorithms based on zonal power consumption by adding crosstalk. Figure 10 illustrates an example form of the heat spreader layer 1082. As shown, in this example there are 20 heat spreaders 1091-1 to 1091-20, each formed of a relatively high thermal conductivity material (such as copper). Each heat spreader 1091 is separated from its neighbouring heat spreaders 1091 and in effect forms an island of thermally conductive material over the corresponding heating zone. The heat spreaders 1091 may be separated from each other by a solid material having a thermal conductivity lower than 35 W / mK or they may be separated by air. The heat spreaders 1091 may be formed, for example, by taking a planar layer of metal (such as a layer of copper) that is bonded onto the layer below and then etching this layer of copper to physically separate the individual heat spreaders 1091 (so that they do not touch each other). Provided there is a break between neighbouring heat spreaders 1091 , it is difficult for heat from one heating zone 467, 867 to pass into neighbouring heating zones 467, 867. The solid material (dielectric and / or scratch resistant low friction materials)) that is provided in the gap between adjacent heat spreaders 1091 may be provided by a PVD DLC, bond film, coating or a wash that is applied to the heat spreading layer 1082 after the etching process has formed the gaps between adjacent heat spreaders 1091 and may be the coating layer 1081 described above. Alternatively other suitable methods may be used to provide solid material in the gap between adjacent heat spreaders, such as masking and vapour deposition etc.

[0215] This layer 1082 can provide mechanical integrity to the overall heater 806, providing some protection from damage to the hair contacting surface that might otherwise expose the underlying heater electrodes 364, which in turn could lead to short circuits or loss of functionality.

[0216] Polyimide Separator layer 983

[0217] The polyimide separator layer 983 provides electrical insulation between the hair contacting surface of the heater 806 (which may be the upper surface of this layer 983 if the optional layers 981 and 982 are not provided) and the main heater electrode layer. This layer 983 would have as low thermal impedance as possible whilst still achieving the dielectric requirements of the layer. As the name suggests, this layer is formed of polyimide, although other dielectric materials could be used. Because this layer is relatively thin, the in-plane thermal diffusivity or thermal conductivity of this layer (in a plane perpendicular to its thickness) is quite low (less than 35 W / mK). This helps to prevent heat spreading from one heating zone 467, 867 to an adjacent heating zone 467, 867.

[0218] Main Heater Electrode & Sensing Layer 984

[0219] This layer 984 is where heat is created by dissipating electric power from the power source (e.g. a power supply unit (PSU) or one or more batteries).

[0220] This layer 984 comprises a number of independently controllable heater electrodes 364 each defining a corresponding heating zone 467, 867. Independently controllable means that each heating zone can be heated to any desired target temperature (or switched on / off) independently of the other heating zones. So, the set point temperature of a heating zone may, if desired, be different from the set point temperature of other heating zones. Figure 11 illustrates in more detail the form that this layer 984 takes in this example heater 806. As shown, in this example, there are twenty independently controllable heater electrodes 1164-1 to 1164-20 that each defines a corresponding heating zone 467, 867. Each heater electrode 1164 is formed of a track of resistive material, whose geometry (track width, thickness, length) and material is specified in order to achieve the desired resistance and peak power requirements for the relevant power source.

[0221] Each heater electrode 1164 is formed into a serpentine pattern using, for example, chemical etching as a manufacturing process. In more detail, a solid layer of electrically conductive material is provided and then etched to form the different heater electrodes 1164. The straight lines shown in Figure 1 1 are the etched parts of the layer 984 and the white parts of the figure show the serpentine conductor paths that form the heater electrodes 1164. Other processes such as printing, thick film printing, physical vapour deposition and the like could be used to form the heater electrodes 1164. In this illustrated example, adjacent heater electrodes 1164 share a common positive terminal (although in other embodiments they may share a common ground terminal) to reduce the number of electrical connections needed to be made between the drive and control board 878 and the heater 806. This common positive terminal is connected to the different heater electrodes at suitable vias 1165-1 to 1165-5, which connect through to connection circuitry below (not shown) that connects to the drive and control board 878. The other end of each heater electrode connects through a respective switch (not shown) to the drive and control board 878 to allow independent control of current flow through each heater electrode 1 164. As those skilled in the art will appreciate, it is not essential to have such a common positive (or ground) terminal, each heater electrode 1 164 may be physically separate from all other heater electrodes 1164 in which case, each end of each heater electrode 1164 would be connected separately back to the drive and control board 878.

[0222] As schematically illustrated in Figure 11 , the end of each heater electrode 1164 that is connected to the switch is provided at the side of the heater and the direction of the serpentine tracks changes in this edge portion (which corresponds to the portion of the heater which is curved over the upper surface 874 of the rigid support substrate 868). The inventors have found that this arrangement helps heat generated in the heater electrodes 1164 in these edge portions to pass up to the top surface of the heaterwhich is more likely to come into contact with the user’s hair. However, if the device is twisted in use such that the user’s hair comes into contact with the curved edge portion, then the hair will still be heated as this curved edge portion is heated.

[0223] The conductive material used in the layer 984 is preferably a PTC or an NTC material (such as stainless steel or copper) so that the resistance of the heater electrode 1164 depends upon its temperature - and so the temperature of the heating zone 467, 867can be determined by measuring a parameter that varies with the resistance of the corresponding heater electrode 1164. This removes the need for separate temperature sensors for each heating zone as a single sensor can be used to measure the temperature of each heating zone (as discussed below with reference to Figure 12).

[0224] Figure 12 is a schematic view of the way in which the heater electrodes 1264 may be connected together and to the drive circuitry 1223 and the power supply 1221 . As shown in Figure 12, each heater electrode 1264 is connected at one end to the power supply 1221 and at the other end to a respective switch (in this case a MOSFET switch) 1295-1 to 1295-20. The switches 1295 are controlled by the microprocessor 1229. When a heater electrode 1264 is to provide heat, the corresponding switch 1295 is closed thereby connecting the heater electrode 1264 to ground through the resistor 12R. As a result, current flows from the power supply 1221 to ground causing the heater electrode 1264 to heat up. The microprocessor 1229 can control the position of each switch 1295 independently thereby allowing each heater electrode 1264 to be powered independently.

[0225] When the temperature of a selected heating zone 467, 867is to be determined, the switch 1295 of the corresponding heater electrode 1264 is closed and all other switches 1295 are opened. In this way, the selected heater electrode 1264 is provided in series with the resistor R. Since the heater electrodes 1264 are formed of a PTC or an NTC material whose resistance changes with the temperature of the heater electrode 1264, by measuring the voltage dropped across the resistor 12R (using the operational amplifier 1297), the microprocessor 1229 can determine the resistance of the selected heater electrode 1264 and hence can determine the temperature of the corresponding heating zone 467, 867. If the determined temperature is above the desired temperature for that heating zone 467, 867, then the microprocessor 1229 can reduce the power applied to that heater electrode 1264; or if the heating zone 467, 867is at a lower temperature than that desired, then the microprocessor 1229 can increase the power applied to the corresponding heater electrode 1264. Any suitable ON / OFF control or PWM (pulse width modulation) control can be used to vary the power applied to the different heater electrodes 1264. The microprocessor 1229 can select each heater electrode 1264 in turn in order to determine the temperature of each heater electrode 1264 / heating zone 467, 867.

[0226] Polyimide Separator (Optional) 985

[0227] When an auxiliary heater electrode layer is provided, this layer is required to provide the required electrical separation (insulation) between that auxiliary heater electrode layer and the main heater electrode layer 984 described above. This polyimide layer 985 would have a low thermal resistance in the thickness direction whilst still achieving the dielectric requirements. Due to this layer being relatively thin, it will have a low thermal conductivity in the plane perpendicular to its thickness of less than about 35 W / mK. Other dielectric materials could be used instead of polyimide.

[0228] Auxiliary Heater Electrode Layer (Optional) 986

[0229] Some embodiments of the heater 806 may benefit from the presence of an additional heating element layer 986. This additional layer 986 could be used to dissipate power (create heat) from a secondary power source that operates at a different voltage to the main power source 221 , for example the main power source could be a power supply and the power source for the auxiliary heater electrode layer 986 could be one or more batteries or supercapacitors. In other embodiments the primary source could be one or more batteries and the auxiliary one or more supercapacitors. Alternatively still, the conductors on this auxiliary layer 986 could become the primary heaters, and those on the main heater electrode layer 984 would just be used for temperature sensing or vice versa.

[0230] The heater electrodes on the auxiliary layer 986 will typically have the same form as the heater electrodes 1164 used in the main heater electrode layer 984 - so that they will define the same heating zones 467, 867as the heating zones 467, 867defined by the heater electrodes 1164 on the main heater electrode layer 984. The path taken by the heater electrodes on the auxiliary layer 986 do not need to follow the same path as the corresponding heater electrodes 1164 formed on the main heater electrode layer 984. For example, whilst the main part of each heater electrode 1164 on the main heater electrode layer 984 (ignoring the edge part of each heater electrode 1164) serpentines in the longitudinal direction of the heater 806 in Figure 11 , the corresponding heater electrodes of the auxiliary heater electrode layer 986 could be arranged to serpentine in the width direction of the heater 806. Such an arrangement would reduce the anisotropic thermal conductivity caused by tracks mostly facing one direction, and may help to spread the heat flow within the heating zone 467, 867particularly if the heating zone 467, 867is only partially loaded with hair.

[0231] Polyimide backing 987

[0232] This layer encapsulates and electrically insulates the bottom heating layer (either the main or the auxiliary heating layer) so as not to allow its accidental exposure and to prevent moisture ingress. This backing layer 987 electrically separates the bottom heating layer from any surface mounted components that are present on the surface mounting layer 988 (discussed below) on the bottom of the heater 806. If desired, this dielectric layer 987 can be made thicker than the upper dielectric layers to provide enhanced structural integrity of the flexible part of the multilayer heater. As with the other dielectric layers, this backing layer 987 does not need to be a polyimide layer and other dielectric materials could be used.

[0233] Rear Side Surface Mount Components (Optional) 988

[0234] This layer is used to mount components on to the rear of the flexible heater 106, 206, 306, 406, 506, 806. These components may be temperature sensors (e.g. thermistors) or other components involved in providing fusing functionality for the heater (e.g. solder links).

[0235] This layer may be produced using standard chemical etching methods from the PCB manufacturing process. Additional surface mount components would be added later.

[0236] This layer may be treated during manufacturing to provide a rough copper surface (e.g. “Brown Oxide” or “Black Oxide”). This enables better bonding of the flexible heater 106, 206, 306, 406, 506, 806 to the underlying support structure 868 when using an adhesive film 989.

[0237] High Temperature Adhesive / Bonding Layer 989 (Optional)

[0238] The function of this layer is to enable bonding of the flexible heater 806 to the rigid substrate 868 (shown in Figure 8) that forms the final shape of the overall heater. Various types of adhesive could be used such as a pressure activated adhesive (PAA), heat activated adhesive (HAA), thermosetting epoxy films (prepregs and B-stage films). It could also be a thermoplastic bonding film which sets after heat and pressure have been applied in a forming tool.

[0239] Another method of joining the flexible heater 806 to the support carrier 868 is to mount the heater in its final shape and overmould (a form of injection moulding) the carrier directly onto the back. In this case, layer 989 may be a material chosen for moulding compatibility, ensuring the plastic that the support carrier 868 is made from fuses to the adhesive / bonding layer 989 providing a strong bond between the heater and carrier.

[0240] Hair damage determination

[0241] It can be advantageous to alterthe styling methodology in such a manner as to preserve hair health. As a basis of this, the extent of damage to hair can be quantified using defined metrics. The very low thermal mass of the styler can aid in facilitating not only agile styling, to ensure hair health is maintained, but also agile sensing of hair condition.

[0242] Figure 13 illustrates an exemplary block diagram of the control circuitry 1315 of the hair styling device 101 ; this corresponds to Figure 2 but with additional optional components of an Inertial Measurement Unit (IMU) 1312, an LED display 1310, a haptics unit 1313, and power measurement circuitry 1324. The IMU 1312 typically comprises an accelerometer, a gyroscope, and in some instances also a magnetometer. This is configured to determine measurements indicative of movements (e.g. speed and orientation) of the styler 101 , and so is configured to determine information relating to the manner in which the user is moving - and therefore using - the styler 101. In some implementations, the styler 101 may comprise a speedometer and / or distance-meter to measure the speed at which the styler 101 is being moved. The LED display 1310 may be the same as or additional to the user interface 211 , and comprises a series of LEDs which can be illuminated in different colours. Typically, the LED display 1310 illuminates different colours and different patterns in order to convey information, but in some implementations at least some of the LED display 1310 may be illuminated for aesthetics. The haptics unit 1314 is configured to provide tactile, haptic feedback and typically comprises any kind of device capable of exerting forces on a user to create tactile sensations, thereby providing haptic feedback. The power measurement circuitry 1324 is configured to sense the power delivered to the heaters 206.

[0243] Methods of defining hair damage

[0244] As illustrated in Figure 14, the inventors have found that hair damage can be modelled as roughly proportional to the heat transfer coefficient and / or the heat capacity or specific heat capacity of the hair. Damage can be modelled as a rate at which the hair heats up, as the more damaged the hair fibres are, the faster the heat transfer. By way of example, and as illustrated graphically in Figure 14, the heat transfer coefficient, h, and the hair damage metric, d, may be related according to: h = m ■ d + c

[0245] Where m and c are defined constants. (This is a simple version of the relationship and in some implementations, the relationship is not linear.) The styler 101 has stored within it (typically in the memory 230) calibration data relating hair heat transfer coefficient, h, to hair damage, d. This may be in the form of one or more look up tables and / or stored equations.

[0246] Figure 14 shows that virgin hair (meaning hair that has never been styled or coloured, especially has never been bleached) has the lowest level of hair damage and so, correspondingly, has the lowest heat transfer coefficient. Hair which is regularly styled using heat has an intermediate level of damage, and so an intermediate heat transfer coefficient. Bleaching hair is widely known to cause damage, and so hair which is regularly bleached has a high level of damage, and therefore a high hair heat transfer coefficient. Knowing the extent of the damage to hair to be styled can be used to adjust the performance of the hair styling device accordingly, in order to mitigate further damage. This can be determined via a combination of user input and measurements made by the hair styling device. This is similarly the case for the heat capacity or specific heat capacity of the hair and so similar equations may be defined with respect to these parameters.

[0247] The user can typically input information indicating the level of their hair damage; this can either be input directly into the styler 101 , via the user interface 21 1 , or via an external program or app in communication with the styler 101 via the communications circuitry 227. In this manner, the controller 228 receives the user’s indication of how they describe their hair damage. This may typically comprise the user inputting information regarding whether their hair is coloured / bleached / dyed, how frequently they heat-style it (streq) and to what temperature they typically style it (stemp); but it may additionally or alternatively comprise the user directly inputting an assessment of the condition of their own hair. This information may typically be stored in the memory 230 of the styler (or to external storage).

[0248] Using the user input, the controller 228 can determine a damage metric, d, in dependence on the input data such as the frequency of styling, Sfreq, and temperature of styling, stemp, for example according to equations such as: d = rr ' freq T ' ^temp T or d — e • Sreq ■ S temp + f

[0249] Where a, b, c, e and f are constants which may be defined empirically and / or for different users. For example, different sets of constants and / or different equations may be chosen in dependence on whether the hair has been dyed or bleached etc. By way of a particular example, the second equation may typically be used when the user indicates that their hair is coloured / bleached / dyed. For example, the constant e may be 0.5 and the constant f may be 20: -dyed — 0.5 ■ Sreq • Stemp + 20

[0250] In other instances (i.e. the user indicates that their hair is not dyed), then the first equation may be used. Simply by way of example, the constant a may be 0.25, constant b may be 1.25 and the constant c may be 10. Of course, the constants may take other values, dependent on particular implementations.

[0251] Using the damage metric, d, as determined from the user input and the stored calibration data, the controller 228 then determines a hair heat transfer coefficient, h, for the user’s hair. The controller 228 may determine the heat transfer coefficient, h, using look-up tables relating the damage metric, d, to heat transfer coefficient, h, and / or may determine the heat transfer coefficient, h, using one or more stored calibration equations. (If the heat capacity or specific heat capacity of the hair are being used, alternatively or additionally, values for these parameters may be determined using stored calibration data relating them to the damage metric.)

[0252] Optionally, the determined heat transfer coefficient, h, may be used to vary a target operating temperature of the heaters 206. This is typically configured to be an overcorrection, to avoid injecting too much heat into the hair on the first pass. This can avoid accidentally damaging the hair, especially if the user has underestimated their hair damage. In order to try to ensure this, the controller 228 is configured to estimate the anticipated response assuming a higher level of hair damage, d, than determined from the input of the user, and therefore the controller 228 sets a lower target temperature for the heaters, as it would for more highly damaged hair. This means the styler’s performance is moderated before touching the user’s hair. In some implementations, however, a predefined or set temperature setpoint is used initially.

[0253] Based on the determined hair heat transfer coefficient, h, and the target operating temperature of the heaters, the controller 228 can predict a heating profile for how a hair tress will heat up overtime in response to coming into contact with the heaters 206 of the hair styler 101. This may be based on further stored calibration data. In order to compare the predicted temperature with the actual temperature, the controller 228 is typically configured to compare the predicted temperature (Test) of the hair at a given time point after coming into contact with the heater to the actual temperature of the hair (Tdet) at the given time point after coming into contact with the hair. This given time point, th, may be, for example, a predefined time after the arms of the hair styler close around the hair.

[0254] Figure 15 shows the estimated hair heat transfer coefficient as determined by the controller 228 based on the user’s input of their assessment of hair damage and Figure 16 shows in the dashed line the anticipated change in hair temperature over time when the user’s hair is heated by the heater 206 during styling based on the estimated hair heat transfer coefficient. The solid line in Figure 16 shows the actual heating profile for the hair as it is heated over time after coming into contact with the heater 206. As discussed above, in order to compare the predicted profile with the actual profile, the controller 228 determines the difference between the predicted profile and the actual profile at a given time point - shown in Figure 16 as time th. The determined temperature difference, ATcm, at time th, between the actual hair temperature, Tdet, and the estimated hair temperature, Test, is indicated as ATditt in Figure 16.

[0255] If the temperature difference, ATditt, is less than a threshold amount, then the controller 228 determines that the estimated heat transfer coefficient that it calculated from the input provided by the user is correct and the controller 228 may output a message to the user confirming to the user the current level of damage of the hair. If the temperature difference, ATdiff, is greater than the threshold amount, then the controller 228 uses the determined temperature difference or the actual temperature of the hair to work out a more accurate estimate of the hair heat transfer coefficient. This can be achieved by consulting the same calibration data linking the expected temperature profile for the hair and heat transfer coefficient, h, as was used to determine the estimated temperature, Test. This calibration data may be in the form of a look-up table and / or equations.

[0256] The styler 101 then uses the more accurate value of the heat transfer coefficient, h, and the stored calibration data relating the heat transfer coefficient, h, and the damage metric, d, to determine a more accurate value of the damage metric, d. This can be determined from, for example: The value of the determined hair damage metric, d, is typically lower than the ‘estimated’ hair damage metric, d (meaning that the actual hair damage metric indicates a lower level of damage to the hair than the estimated hair damage metric). This can be seen in Figure 15, which shows the exemplary linear relationship between hair damage, d, and hair heat transfer coefficient, h, with the hair damage based on user input (the estimated hair damage metric) plotted at a higher point than the point indicating the actual hair damage (the determined hair damage metric) on the line indicating this linear relationship. This is because the estimated hair damage metric is typically deliberately an overestimation, to ensure a safety margin of the initial heating profile of the tress of hair.

[0257] Finally, this more accurate determined value of the hair damage metric, d, is output to the user and / or used to control an operating parameter of the styler 101 (such as the operating temperature of the heaters 206). For example, this may comprise altering the setpoint temperature of the heaters 206 to a higher temperature if the hair damage metric, d, is lower than estimated, and vice versa. The controller 228 is typically further configured to send the hair damage information, based on the determined hair heat transfer coefficient, to storage; this may be the internal memory 230 and / or an external storage. In some implementations, the controller 228 is further configured to output to a user via the LED display 1310 hair damage information, such as the hair damage metric. In some implementations, this may be accompanied with advice on how to improve hair health (such advice will be described in further detail in a later section).

[0258] Methods of defining damaging behaviours

[0259] In addition to determination of a hair damage metric, as described above, in some implementations the processor 229 is configured to determine whether the manner in which the styler 101 is being used is potentially damaging, in other words to determine damaging behaviours. This comprises recording and analyzing parameters of a styling session to identify such behaviours and then typically further comprises defining a corresponding metric.

[0260] Recurrent heating of a single tress

[0261] One such potentially damaging behaviour is the recurrent heating of a single, same tress of hair. The high level of heat input into the tress during repeated heat-styling can cause damage.

[0262] A first method for determining recurrent heating comprises analyzing the ‘power demand’ required to maintain the setpoint temperature of the heaters 206. The controller 228 of the styler 101 controls the power to the heaters 206 in dependence on temperature measurements of the heaters 206, either from temperature sensors or from resistance measurements (as described above). Power is delivered to the heaters 206 by the drive circuitry 223 in dependence on a difference between the temperature of the heaters 206 and the setpoint temperature. The larger the difference in temperature between the heaters 206 and the desired setpoint temperature, the larger the power input by the drive circuitry 223. Accordingly, the load on the heaters 6 can be tracked by reviewing the ‘power demand’. The processor 229 is configured to track this ‘power demand’ by tracking the sensed temperature measurements and the setpoint temperature, and calculating the power delivered accordingly, and / or the power input to the heaters 206 can be sensed directly by the power measurement circuitry 1324. In either case, the processor 229 is configured to record the power input over time, which can be processed to indicate the loading of the heaters 206 over time. Typically, this information is stored in the memory 230 of the styler, and analysis performed by the microprocessor 229; however, in some instances the information may be transmitted to and stored and / or processed by one or more external devices.

[0263] Figure 17 shows an exemplary profile of ‘power demand’ (the calculated and / or measured power input to the heaters 206) overtime, which is indicative of the loading of the heaters 206 over time. When a user repeatedly heats the same tress, the power demand lowers for each successive stroke, as less power is required to heat an already-heated tress (because the difference between the measured temperature and the desired setpoint temperature is smaller). This is illustrated in Figure 17, which shows that the power supplied to the heaters varies over time in a pattern akin to a damped decaying sinusoidal wave. The dashed line of Figure 17 follows the maximum power delivery, and shows that this follows a decay curve. Each wave corresponds to a stroke of the heaters 206 over the hair, whereby the power demand increases when the heater touches the hair, and then drops when the user removes the heater from the hair; the power demand increases again for the next stroke when the user places the heater on the hair once more. For each successive stroke, the power demand is lower, hence the decay profile. This is due to the reduction in power demand to heat the tress as the tress heats up (as the temperature difference between the hair and the setpoint temperature decreases). As such, the processor 229 can identify recurrent heating of the same tress from this characteristic power profile over time, namely a damped decaying sinusoidal wave. The processor 229 is typically further configured to determine the decay rate and count the number of peaks and to use this information to determine the frequency and number of repetitions (np) of the recurrent heating. For example, a decay curve with four peaks indicates the user has passed the heaters 206 over the same tress of hair four times and the time interval between those peaks provides an indication of the time delay between the recurrent passes.

[0264] A further method for determining recurrent heating of a single tress of hair relates to analysis of user motion, based for example on measurements from an inertial measurement unit (IMU) 1312 within the styler 101 . The controller 228 receives and processes motion data from the IMU 1312. The controller is configured to define a motion metric based on user speed, acceleration, and impulse data received from the IMU 1312. The motion metric is typically defined for each particular hair styling device. By way of example, this may be defined in dependence on acceleration, a, speed, s, and ‘jerk’ (which can also be referred to as impulse), j. The absolute net acceleration, aabs_net, can be determined according to: abs_net ax2+ ay2+ az2— G

[0265] This determines the magnitude of the net acceleration of the styler using measurements of the acceleration in the x-direction, ax, of the styler 101 ; acceleration in the y-direction, ay, of the styler 101 ; and acceleration in the z-direction, az, of the styler 101. Unless the axis lies in a horizontal plane, the measured acceleration in each axis (ax, ayand az) will include a component due to gravity, and accordingly, the value for gravity (G) is subtracted from the determined magnitude to remove the influence of gravity from the calculations. The absolute net speed, Sabs_net, can be determined from integrating the absolute net acceleration, aabs_net, over the relevant period of time, t, according to:

[0266] Where D is a drift constant.

[0267] Additionally or alternatively, speed measurements may be determined by a speedometer or distance-meter. For example, this may be implemented using an optical system capturing images of the hair as the styler passes over it. Using known values of frame rates and dimensions of the styler, the distance travelled over a time interval can be determined and hence the speed determined. Example methods for measuring dimensions of the hair, and consequently the speed with which a styler is being moved over a tress of hair, are described in the section ‘Hair Distance Ruler’. Alternative methods could also be used. If speed measurements are determined by a speedometer or distance- meter and received by the controller, then the controller can determine the measured speed vector, Smes, directly, the vector in the three orthogonal axes being written as:

[0268] The measured absolute scalar value, smes, can be therefore be found by finding the scalar of this vector, according to: mes ~ 1 1 mes 1 1

[0269] A value for the average speed can be determined by finding a weighted average of the measured scalar value of the speed, Smes, and the absolute net speed, Sabs_net, (as determined from integrating the absolute net acceleration, aabs_net). As the measured speed is considered more accurate than the speed calculated from acceleration measurements, this is given a higherweighting.

[0270] Simply by way of example, the ratio of the weightings may be 5:2, i.e. the weighting of the measured scalar value of the speed, Smes, is 5 / 7 and the weighting of the absolute net speed, Sabs_net, is 2 / 7. The average speed is therefore calculated according to:

[0271] Of course, however, different weightings may alternatively be used. Then a value for the upper limit of the speed, Sup, can be determined, which defines a maximum value for the speed which a user is moving the styler 101 over the tress of hair. The upper speed, sup, can be determined in dependence on the average speed, measured absolute scalar speed, Smes, and the absolute net speed, saps_net; in particular, by summing the value for average speed and an error estimation based on a weighted combination of the measured absolute scalar speed , Smes, and the absolute net speed, Sabs_net according to:

[0272] Of course, again, different weightings may be used. Typically, the weightings will be the same as those used determining the average speed (i.e. k = m and I = n); for the example above, this would mean the equation becomes:

[0273] Alternatively, if no speed measurement data is available or received, then the value of upper limit speed, sup, can be approximated as equal to the absolute net speed, Sabs net, i.e.: up ~ abs_net

[0274] A value for jerk or impulse, J, can be determined from the derivative of the vector acceleration, according to:

[0275] J = ft

[0276] The motion metric can then be defined in dependence on the determined values of the upper limit of the speed, absolute net acceleration and the determined scalar value of impulse:

[0277] An exemplary profile of a motion metric over time is illustrated in Figure 18. Such a metric can be used to determine whether a user is moving the styler 101 in an effective manner; for example, if the user is running the plates 206 over a tress of hair too quickly, then the styling is unlikely to be effective, which can lead to a user needing to repeat the motion and thereby heat the hair more than necessary. An upper threshold value of the motion metric can be defined which corresponds to a user moving the styler too fast, meaning they will need to repeat the motion. In typical implementations, the threshold is defined as a function of the upper limit of the speed, absolute net acceleration and impulse:

[0278] T = [Ts,ra, 7}]

[0279] Where Tsis the threshold speed value, Tais the threshold acceleration, and Tj is the threshold impulse. In typical implementations, if any of the thresholds are exceeded, then the user is considered to be moving too fast (i.e. the motion metric is above an acceptable threshold). For example, if the speed, sup> Ts, or if the acceleration, aabs_net > Taor if the impulse, |(|J |)| > Tj, then the user is considered to be moving too fast. The threshold is indicated by a thick line at a value of 0.2 on Figure 18. In some implementations, there may be an upper threshold indicating an ‘infraction’ zone and a ‘grey zone’ is also defined, which is below the upper threshold and in which the styler 101 is still being moved too fast; this is labelled ‘G’ in Figure 18 and is located between a dotted line at 0.1 and the thick solid line at 0.2. In such an implementation, the upper threshold defines an upper or ‘hard’ threshold, Thard, which is a combination of ‘hard’ thresholds for the speed, acceleration and impulse:

[0280] Thard = [Ths, Tfta, Th / ]

[0281] And the grey zone occupies a zone below the upper threshold, Thard, but above a lower threshold, Tgrey, defined according to:

[0282] Tgrey=[Tgs, Tga, TgJ]

[0283] Where each ‘grey threshold’ for speed, acceleration and impulse may be equal to or less than the corresponding ‘hard’ threshold, i.e.:Tgs< Ths' Tga< Tha' and Tgj< Th].

[0284] The movement of the styler 101 by the user is determined to be in the ‘grey zone’ if any two of the metrics exceed the grey thresholds; while the user is considered to be moving the styler 101 too fast if any of the metrics exceed the relevant ‘hard threshold’ value. Written in another way, the motion metric of the styler 101 is in the grey zone if:

[0285] Where:

[0286] The motion metric of the styler is above the threshold or in the ‘infraction’ zone if:

[0287] (sup> Ths) OR (anet> Tha) OR (j > Thj)

[0288] The values illustrated in Figure 18 and described above are of course just exemplary values and the metric bounds can be defined for the particular situation. Similarly, in some implementations, slightly different protocols for the thresholds and grey zone may be implemented. If the processor 229 determines, upon analysing the profile of motion metric over time, that the motion metric is above a threshold value or within the ‘grey zone’, G, then recurrent heating of the same tress is likely.

[0289] In the case that the styler has two heaters 206 on two arms 104 and hair is styled by placing between the arms 104 and closing the arms 104 around it (as is the case for a hair straightening device, for example), the motion metrics are typically analysed in combination with a determination of whether the styler 101 is open or closed. The processor 229 is typically configured to perform this determination based on feedback from sensors in the arms 104 of the styler 101 (for example, proximity sensors) and / or the data received from IMU 1312. Looking again to Figure 18, the solid line illustrates when the styler 101 is closed, and therefore the heaters 206 are likely to be engaged on a tress of hair; and the dashed line illustrates when the styler is open and therefore not engaged with a tress of hair. As such, the motion metrics determined in those intervals in which the styler 101 is closed are of particular interest as they are indicative of how the styler 101 is being moved over the tress. The processor 229 is configured to analyse the IMU data in combination with the data from, for example, proximity sensors regarding whether the arms 104 are open or closed; in this manner, they are configured to determine the time intervals between those periods when the arms 104 are closed (and so when the hair is engaged by the heaters 206). Using these determined intervals, the processor 229 is further configured to determine the frequency of recurrent heating of a tress of hair.

[0290] In some implementations, the processor 229 is configured to detect recurrent heating of a single tress of hair in dependence on the received data relating to the power delivered overtime; or in dependence on the received data relating to the motion of the styler 101 from the IMU 1312 (in some cases, in combination with data from proximity sensors); or the processor(s) may be configured to perform both methodologies. The processor 229 is typically further configured to instruct a control action in dependence on this analysis; this may comprise outputting an alarm or alert to a user via the user interface 211 of the styler 101 (or to an external device) and / or outputting control instructions to alter the settings of the styler, for example the setpoint temperature of the heaters 206.

[0291] Heat on hair time

[0292] A further behaviour which can be assessed relates to the time over which heat is applied to hair, known as heat on hair time. This provides an estimate of how much time the styler is applying heat to the user’s hair, and thereby provides an estimate for total heat accumulation in the hair. Simply, the longer the user is applying heat to the hair, the more damage occurs to the hair. There are generally two modes of usage that result in heat being applied to hair for too long. The first is when a user moves the heater 206 too slowly over a tress of hair, and so applies heat to hair for a long time on each stroke. The second mode is when a user moves the heater 206 too quickly over a tress of hair and so they need to reapply heat to the same tress of hair to repeat the stroke in order to achieve the desired styling (this is sometimes known as ‘clap-clap’ styling). The heat on hair time can be described by a combination of metrics: single session heat on hair, tn, which is the amount of time heat is applied to hair during one styling session; total heat on hair time, TH, which is the total amount of time heat has been applied to hair; and mean heat on hair time, tHm, which is the mean amount of time heat is applied to hair during each styling session.

[0293] The single session heat on hair time, tH, can be determined from the sum of the time during which the styler is closed (which is indicative of the plates 206 of the styler 101 being closed around a tress of hair). The controller 228 receives data from the IMU 1312 regarding movement of the styler and from the IMU 1312 and / or a separate sensor (such as a proximity sensor) indicating whether the arms 104 of the styler 101 are open or closed. The processor 229 is configured to process this data to determine the heat on hair time. Figure 19a shows the motion metric over time (as described above), with the time intervals over which the styler 101 is closed indicated as tciosedi and tciosed2. The processor 229 is configured to determine the total of these intervals, tm, by summing the time intervals over which the IMU data and / or sensor (e.g. proximity sensor) data indicates the arms 104 are closed:

[0294] The single session heat on hair time, tn, can also be determined using the profile of power delivered overtime. As described previously, the controller 228 controls power input in dependence on the measured temperature of the heaters 206, in particular in dependence on the difference between the measured temperature and the desired setpoint temperature. The processor 229 can therefore track the power delivered to the heater over time, as determined from temperature measurement data received from the temperature measurement circuitry 225 and / or from direct measurements of the power delivered as sensed by the power measurement circuitry 1324. The processor 229 is then configured to analyse the profile of power delivered (i.e. power demand, indicating the load on the heaters 206) over time. The single session heat on hair time, tn, can be estimated from the amount of time the power demand has a positive gradient, as power demand drops and the gradient becomes negative when the load is removed (making the assumption that the user does not leave the hair on the heater 206 until it reaches the heater temperature). Figure 19b shows an exemplary power demand profile over time, which has the form of a damped decaying sinusoidal curve. Those time intervals over which the power has a negative gradient are indicated in Figure 19b as tngi, tng2, tng3, tng4 and tngs. The processor 229 is configured to determine the total of these intervals, tP, by summing the intervals over a relevant period (corresponding to the single session):

[0295] There are therefore two different methods for estimating the total heat on hair time: using data relating to the arms 104 of the styler 101 being closed, and using data relating to the power delivered over time. In some implementations, the processor 229 is configured to determine estimates using both methods and then determine an average estimated value for the single session heat on hair time, tn, by calculating the mean of the two estimates, according to:

[0296] Using both the power profile and the determination of whether the styler is open or closed in combination enables corroboration that the heat was indeed applied to the hair, rather than the styler simply being closed without the heater 206 being in contact with a tress of hair.

[0297] The total heat on hair time, TH, is the sum of the heat on hair times for all of the sessions. The processor 229 can therefore be configured to determine an estimation of the total heat on hair time, TH, by summing the determined value for single session heat on hair time, tn, (as described above) over all of the n sessions, according to: n x=l

[0298] The processor 229 can then be further configured to determine the mean heat on hair, tHm, by dividing the total heat on hair time, TH, by the number of sessions, n, according to:

[0299] It can be useful to determine these metrics relating to the time over which hair has been subjected to heat, as the heat on hair time can affect the extent of damage of the hair. It can also provide an insight into the user’s styling technique, typically in combination with other metrics. For example, the heat on hair data can be used in combination with user hair length (typically input by a user) and movement speed (typically determined by the IMU 1312) to determine the behaviour the user is exhibiting and how damaging it is. For example, for a user with long hair, the heat on hair time would be expected to be longer, in the region of a few minutes. For a user with shoulder-length or short hair, the heat on hair time would be expected to be shorter. The length of the user’s hair can be determined using the techniques as described in the section ‘Hair Distance Ruler’ and / or from the input of a user. Therefore, if a heat on hairtime of a few minutes is determined for a userwith shoulder- length hair, then it is likely that too much heat is entering the hair and damage is being done to the hair. By contrast if this same heat on hair time is determined for a user with long hair, the damage is likely to be less. The controller 228 is typically configured to perform control actions in dependence on the determined metrics; this may for example comprise outputting an alert to the user (e.g. via a user interface 211 or LED display 1310, or via haptics or audio) and / or altering parameters of the styler 101 to minimise damage and / or optimize styling outcomes, for example by altering the heating profile. An alert may comprise advice to a user on how to alter their technique. This data can also be used to determine a ‘persona’ for the user (this will be explained further in later sections).

[0300] Average maximum hair temperature

[0301] A further metric which can be defined to describe styling behaviour and potentially damaging techniques is the average maximum hair temperature, Hm. This refers to the average of the maximum temperature to which each tress of hair is raised. The controller 228 is typically configured to determine a value for the average maximum hair temperature, Hm, by analyzing the profile of power delivered (which is used as an indication of ‘power demand’ indicating load on the heaters 206) over time. Figure 20 shows an extended exemplary plot of power demand overtime, similarto Figure 17 but extending further across time so as to capture two damped decaying sinusoidal waves. These two damped sinusoidal waves correspond to the styling of two different tresses of hair, which shall be referred to as the first tress and second tress. The amplitude difference between the highest peak and lowest trough of the power demand for each tress corresponds to the largest power input into the tress. These are typically the first peak and first trough as the power demand decreases as the tress heats up. The processor 229 is therefore configured to determine the amplitude difference of power demand for each tress, as indicated in Figure 20 and labelled 6Pdi for the first tress and 6Pd2 for the second tress. In addition, the processor 229 is configured to determine the mean power demand for each tress; this is also indicated in Figure 20 and labelled Pmifor the first tress and Pm2 for the second tress.

[0302] Using these determined parameters, the processor 229 is further configured to determine maximum temperature of each tress as a function of the power demand amplitude difference, 6Pdx, and the mean power, Pmx: -mx f 8Pdx,Pmx)

[0303] Alternatively or additionally, in some implementations the processor 229 may be configured to determine the maximum temperature of each tress by analysis of the heat control algorithm. As the heat control algorithm directly measures the temperature of the hair (and then determines power input in dependence on the difference between this measured temperature and a desired setpoint temperature), the temperature measurements can be analyzed to determine for each particular tress the maximum temperature. As the heating of a single tress is indicated by a characteristic power demand profile and from a characteristic heat profile, the processor 229 is configured to use this data to determine the intervals over which the styler 101 is heating a single, same tress. For example, a first tress heats up when styled and then the next tress will be comparatively cold.

[0304] Having determined the maximum hair temperature of the tresses by either method described above or both, the processor 229 is configured to determine the average maximum hair temperature, Hm, by calculating the mean value across all the tresses of hair:

[0305] The average maximum hair temperature, Hm, is a useful metric as it can provide insight into the maximum temperature to which each tress is subjected; as, if this is very high, more damage is likely to have occurred to the hair. Conversely, if this is very low, it may indicate that styling has not been effective. The controller 228 is then configured to perform a control action in dependence on the determined value of average maximum hair temperature, Hm. This may comprise, for example, outputting an alert to the user (e.g. via a user interface 211 and / or LED display 1310) and / or altering parameters of the styler 101 , such as the heating profile of the heaters 206.

[0306] Fibres damaged

[0307] In some implementations, the controller 228 is further configured to determine a percentage value of fibres damaged. For example, this may comprise either the total percentage of fibres damaged or the percentage of new fibres damaged from a particular session.

[0308] The controller 228 is configured to determine a baseline damage percentage using the hair damage model described above with reference to Figures 14 and 15, in which hair damage is linearly proportional to the determined heat transfer coefficient of the hair. The controller 228 is configured to determine a metric for the baseline damage, Dbi, using the hair damage model:

[0309] Dbi=f(hair damage model)

[0310] The processor is further configured to determine a metric for new damage, Dn, which can be defined as a function of the average maximum temperature, Hm, applied to hair and of the baseline damage, defined according to the equation:

[0311] Where:

[0312] Accordingly, if the average maximum temperature, HM, applied to the hair is below a first threshold temperature, Ti, then the hair is considered to have undergone no new damage and Dnis defined by the controller 228 as equal to zero. If HM is between the first threshold temperature, Ti, and a second threshold temperature, T2 (where Ti < T2), then the percentage of new damage, Dn, is defined as proportional to the difference of HM and the first threshold temperature, Ti. If HM is above the second threshold temperature, T2, then the multiplication factor becomes 1 and the percentage new damage is defined as equal to 100 - the baseline damage, Dbi. The first threshold temperature is typically around normal hair styling temperature. By way of example, the first threshold temperature, Ti, may have a value of about 180 °C and the second threshold temperature, T2, may have a value of about 230 °C. Of course, other values may also be chosen.

[0313] The controller 228 is further configured to determine total percentage damage, Dtotai, by summing the baseline damage, Dbi, and the new damage, Dn: totain+ Dbl

[0314] This total percentage damage, Dtotai, can provide an insight into the condition of the hair. In particular, the determined values can be stored in the memory and so used to track how the damage and condition changes over time. The controller 228 is typically further configured to perform a control action in dependence on the determined damage parameter and, in some instances, on an assessment of how this changes over time. For example, this may comprise outputting an alert (which may comprise outputting one or more determined values and / or advice) and / or updating styler parameters, such as heater setpoint temperature. Typically, the percentage of new fibres damaged from a particular session will be most relevant, as it is dependent on a user’s most recent styling technique. The controller 228 is therefore typically configured to output a value for and / or advice relating to the percentage of new fibres damaged from a particular session. This may, for example, include tips on how to improve styling technique so as to reduce hair damage when styling. The controller 228 is typically further configured to alter parameters of the styler 101 in dependence on the defined baseline damage, Dbi, new damage, Dn, and / or total percentage damage, Dtotai.

[0315] ‘Scoring’ parameters

[0316] As described above, each of the parameters calculated can be used by the controller 228 to control the outputting of information to the user and / or control the operation of the heaters during the styling. In addition, the parameters thus calculated can be used to calculate ‘scores’ relating to hair parameters (such as hair damage) and a user’s styling technique, which itself can have a large effect on hair condition and damage. These scores can then be combined to determine an overall ‘hair score’. Once it has calculated the scores, the controller 228 is typically configured to output them to a user, via a user interface 21 1 , typically along with feedback (such as advice) on how to improve their technique so as to improve the scores. In some implementations, the controller 228 is configured to alter styler control parameters (such as heating profiles) in dependence on one or more of the scores. Examples of these scores will now be described.

[0317] Behaviour score

[0318] The behaviour score, SB, relates to how a user has used the styler, and so takes into account the amount of time heat has been applied to the hair, maximum hair temperature etc. In particular, it is a function of the hair on heat time, tn, parameter y (which is itself is a function of maximum hair temperature, HM) and first and second threshold temperatures, Ti and T2 as outlined above in relation to the new damage, and the number of repetitions, nP.

[0319] A and B are constants, which can be chosen for each particular implementation. Constant A defines the contribution of the hair on heat time, tH, to the behaviour score, SB. Constant B defines the maximum contribution of the behaviour score, SB, to the overall hair score. By way of example, A and B may both take the value 30.

[0320] If, for example, the maximum hair temperature, HM, is below the first threshold temperature, T1, then parameter y takes a value of 0, and so the equation simplifies to:

[0321] In such a case, the hair on heat time must be equal to or greater than a value of (A x B) in order for the behaviour score, SB, to take a maximum value (in the case of A and B both having the value 30, this would mean the hair on heat time would need to exceed 900 s).

[0322] Looking at the alternative extreme, if for example the maximum hair temperature, HM, is above the second threshold temperature, T2, then parameter y takes a value of (T2 - T1), and so the equation simplifies to: SB= min + np

[0323] In this situation, the number of repetitions also contributes strongly to the value of the behaviour score, SB. Of course, if the maximum hair temperature, HM, is between the first threshold temperature, Ti, and the second threshold temperature, T2, then the weighting of the number of repetitions, nP, will be proportional to the difference between the HM and T1.

[0324] Hair heat score

[0325] The hair heat score, SH, is a function of the extent to which hair has been heated, and so is a function of maximum hair temperature, HM, and the first threshold temperature, T1 (in particular, the extent to which the maximum hair temperature exceeds the first threshold temperature):

[0326] Constants C and D can be chosen for each particular implementation and / or use case. The value of C defines what range of heat values relative to the first threshold temperature are considered relevant. The value of D determines the extent of the weighting of the hair heat score, SH, to the overall hair score. Simply by way of example, C may be 5 and D may be 10. In such a case, if the difference between the maximum hair temperature, HM, and the first threshold temperature, T1, is 50 °C or larger (either above or below T1), the hair heat score, SH, will have its maximum value of 10. However, if the maximum temperature, HM, is within ± 50 °C of the first threshold temperature, T1, then hair heat score, H, will have a value of between 0 and 10. The hair heat score, SH, is therefore a score of the extent to which the maximum hair temperature, HM, is within a set range of the first threshold temperature, T1.

[0327] If, by way of a further example, the value of C were 4 (and D remains 10), then if the difference between the maximum hair temperature, HM, and the first threshold temperature, T1, is 40 °C or larger, the hair heat score, SH, will take its maximum value of 10; and if the maximum hair temperature, HM, is within ± 40 °C of the first threshold temperature, T1, then hair heat score, SH, will have a value of between 0 and 10. As such, the constant C contributes to defining the range around the first threshold temperature, T1. If the value of the maximum hair temperature, HM, is outside of this range, then the hair heat score, SH, will take its maximum value defined by the constant D.

[0328] The constant D defines the maximum value the hair heat score, SH, will take; and thus the weighting of the hair heat score, SH, to the overall score. It also contributes to defining the relevant range, in combination with the constant C. For example, if the value of D were instead 20 and the value of C is 5, then the hair heat score, SH, would take its maximum value of 20 if the difference between the maximum hair temperature, HM, and the first threshold temperature, T1, were 25 °C or larger. As such, the constants are chosen in combination. Total damage score

[0329] The total damage score, STD, is a function of the total damage, Diotai, which is the sum of the baseline damage, Dbi, and the new damage, Dn, as calculated in the manner outlined above. The total damage score, STD, is then defined by the equation:

[0330] The constant E defines the contribution of the total damage score, STD, to the overall score. It can be defined for each particular use and / or implementation. By way of example, E may take a value of 20.

[0331] New damage score

[0332] The new damage score, SND, is a function of the new damage, Dn, relative to the baseline damage, Dbi. In other words, it is a function of the effect of the new styling to the hair. It can be defined according to the equation:

[0333] F ■ DnSnd~ 100 - Dbl

[0334] F is a constant which can be defined for each particular implementation, as it defines the contribution of the new damage score, SND, to the overall score, Soveraii (i.e. the weighting). As an example, F may take the value 25.

[0335] Energy score

[0336] The energy score, SE, is a measure of how efficiently the user has used the styler 1 from an energy use perspective. This is a function of the time overwhich the styler 1 is turned on, ton, according to the equation: c _ tOn E ~ ~G

[0337] The constant G again can be defined for each use case. It defines both the contribution to the overall hair score, but also the time range overwhich the styler 101 is on that is considered normal use, extended use etc. As an example, the value of G may be 60. In such a case, the value of the energy score, SE, increases by 1 for each minute (i.e. 60 seconds) over which the styler 101 is turned on.

[0338] In some implementations, the energy score is defined such that it also takes into account in the calculation the percentage of the total time the styler 101 is turned on that it is being applied to the user’s hair, it is idle etc. This can be determined based on measurements of the IMU 1312 and the heat demand profiles of the heaters 206, as discussed above.

[0339] Style difficulty

[0340] In some implementations, it can be useful to include a metric relating to the difficulty of the style or styles a user has attempted. The style is typically defined based on particular known styling techniques and methodologies. The user can input which styling technique they are following, for example, via the user interface 21 1 or through an app in connection with the styler 101 via the communications circuitry 227 (as will be explained in further detail in later sections). Alternatively or additionally, the controller228 may be configured to determine the user’s movements to ‘detect’ a particular styling technique from the movement of the styler 101 (using measurements received from the inertial measurement unit, IMU 1312).

[0341] The difficulty of the style is defined by a style difficulty score, SSD, which is defined by the equation:

[0342] SSD= (1 to H)

[0343] Where H is an upper value for the style difficulty score, SSD. For example, the value of the SSD may range between 1 and 5.

[0344] Overall ‘hair score’

[0345] The controller 228 can be configured to determine an overall ‘hair score’, Soveraii, by combining the individual scores. The Soveraii can be defined using all of the scores defined above by the equation:

[0346] ^Overall = 100 - (SB+ SH+ STD+ SND+ SE+ SSD)

[0347] Typically, the lowest possible value of the overall score is a number larger than zero. This is to avoid users being disheartened by a very low score. By way of example, if the values of the constants are A = 30, B = 30, C = 5, D = 10, E = 20, F = 25, G = 60, and H = 5; then the lowest possible value of the overall score, Soveraii, is 16.

[0348] Of course, different combinations of scores can be used and / or weighted as is relevant and suitable for each particular implementation and use. Further and / or alternative scores may also be defined and included.

[0349] Methods of Determining Scalp Health

[0350] A key factor of hair health is scalp health. As such, it can further be beneficial to implement methods of assessing and measuring scalp health of a user of a styling device 101 . This can be used to provide information to the user regarding their scalp, to provide insights to the user, and to output recommendations for improving scalp health (which will typically lead to an improvement of hair health too).

[0351] Figure 21 shows an exemplary block diagram of the control circuitry 2115 of the hair styling device 101 ; this corresponds to Figure 2 but with additional optional components of a pH sensor 2101 , a sebum sensor 2104, moisture sensor 2106, camera 2108, IR LED scanner 2110, and scalp temperature measurement sensor 2112. Any combination or subset of these components may be part of the hair styling device 101. Indeed, any combination of these components may be provided with any combination of the components as illustrated in Figure 13 (which are not illustrated again in Figure 21 for clarity). Scalp health can be assessed by measuring one or more properties of the scalp, typically via a combination of methods. These methods may be direct (i.e. contact sensing), indirect (i.e. non-contact sensing), and via inference (i.e. using analysis of measurements and sensor data).

[0352] One property of the scalp to be measured is the pH balance. Scalp pH is vital for anti-microbial protection. The pH level of the scalp should be between pH 5.5 and pH 4.5 (i.e. slightly acidic). If the pH balance becomes too low (i.e. it becomes too acidic), the scalp can typically become irritated, which can lead to irritation and inflammation of the skin of the scalp. In turn, this can result in hair loss. Furthermore, if the pH level is too low, the skin on the scalp can become sensitive, leading to a "greasy" look or even acne breakouts. On the other end of the spectrum, if the scalp pH level becomes too high, the layer of protective sebum (i.e. the oily substance produced by sebaceous glands, and which passes through the hair follicle to the outer layers of the skin) may be significantly reduced or even removed. The sebum layer is protective and anti-microbial. As sebum is slightly acidic, it prevents pathogens from penetrating the scalp, and so a reduction in sebum can make the scalp vulnerable to pathogens such as microbes. In response, this can trigger the sebaceous glands to over-produce protective oils, resulting in oily hair and in some instances an extreme accumulation of dandruff.

[0353] The hair itself has a slightly higher acidity than the scalp, the hair having a pH around pH 3.7. Creating an environment that is too basic can cause the hair follicle to open, resulting in more brittle hair. This increases the likelihood of hair frizz and can result in increased hair damage. Mildly acidic products, known as hair conditioners, are typically used to close hair cuticles. However, products which are overly acidic can cause the hair cuticles to close in a mannerwhich can result in a permanent change of hair texture (which, in some cases, may be a desired and intended consequence). However, using acidic products too often can damage the scalp, as they can cause irritation.

[0354] A further relevant property is the extent of sebum (‘oil’) on the scalp. Sebum is produced by the sebaceous glands and travels through the hair follicles to the surface of the scalp. It is a natural moisturiser that prevents dryness and protects from microbes and other pollutants. However, overproduction of sebum, or a collection of other oils, can result in a few problems. Mainly, the hair becomes significantly harder to style and manage. Oily hair clumps and sticks. The weight of the oil leads to a reduction in volume and can create a "greasy" look. After styling, the hair will typically therefore not hold the style for as long. Furthermore, a buildup of oil can trap dirt, sweat, and styling products, which can lead to excessive dandruff. In rare circumstances, an oily scalp can have an unwanted smell. An overly oily scalp can also lead to clogged hair follicles, which can contribute to scalp irritation and hair thinning.

[0355] On the other hand, a scalp can sometimes be too dry. This occurs when there is an underproduction of sebum, or indeed an over-removal of sebum. A dry scalp lacks moisture due to its lack of sebum, as the lack of protective oils can lead to faster water loss. The protection against microbes, pathogens and other pollutants is also compromised by a lack of protective oils. This can lead to irritation, itchiness, and inflammation. Chronic dryness can damage hair follicles, which can result in brittle hair and hair loss. Chronic dryness can also impact hair growth. Dryness can also often result in flaky dandruff. Dry scalp and hair can also be more prone to frizzing, and may typically can have a dull appearance (i.e. it lacks a glossy appearance, which is often associated with healthy hair).

[0356] Blood circulation can also be an important property in the determination of the health of a user’s scalp. Poor blood circulation can mean that the hair follicles do not receive sufficient nutrients and oxygen for healthy hair growth. Chronically poor blood circulation can lead to poor hair growth, resulting in reduced density of hair (i.e. hair thinning or hair loss) and brittle, short hair.

[0357] Each property typically has an effect on the other properties, and hence on the overall scalp health and the appearance of the hair and scalp. For example, pH balance and sebum level are typically closely linked as the pH is often dependent on the sebum level of the scalp, and vice versa. The scalp forms, in effect, an ecosystem. One property does not preclude another; for example, a scalp can be both oily and dry. As such, it can be preferable to use a combination of sensing methods to determine the health of a user’s scalp. pH balance can be determined using a pH sensor 2102, which is brought into direct contact with the scalp and / or hair (preferably both) during styling. A pH sensor 2102 typically determines the pH of the user’s hair and / or scalp by measuring voltage generated due to an exchange of hydrogen ions between the surface and an electrode of the sensor 2102. Epoxy or polymer electrodes may be preferable for longevity of the pH sensor 2102. A pH sensor 2102 may be located at a position on the hair styler 101 such that it makes direct contact with the hair and / or scalp. As the heaters 106 of the hair styler should not directly touch the scalp (so that they do not burn the skin on the scalp), the pH sensor 2102 may be located near but not on the heaters 106. For example, the pH sensor 2102 may be located adjacent to the heater components of a styler 101 . In some implementations, the pH sensor 2102 may be provided on a protruding part (e.g. a protruding brush part) which makes contact with the scalp during styling. In some implementations, a pH sensor may alternatively or additionally be located on an external brush (e.g. a ‘smart brush’), which is in communication with the styler 101 , for example via Bluetooth™, or, in some implementations, via an internet connection such as WiFi. Such a brush is described in the Applicant’s earlier application PCT / GB2025 / 050044.

[0358] The sebum level of hair can also be measured directly, for example using a sebum sensor 2104. A sebum sensor can function by exposing a tape within the sensor 2104 to the scalp, and then performing photometry on that region of tape to determine the transparency of the tape. The greater the extent of sebum, the more transparent the tape. This is typically referred to as ‘grease spot photometry’. Alternatively, the mass of a sample of sebum collected from contact with the scalp and / or hair can determined via measuring changes in oscillation frequency of a quartz crystal sebum sensor. A sebum sensor 2104 such as these therefore also requires direct contact with a user’s scalp and / or hair. When implemented on a styler 101 , it can therefore be preferable for the sensor to be located near to (e.g. adjacent) the heaters 105 but not on the heaters 106 to avoid burning the scalp. Again, the sebum sensor 2104 may be located on a protruding part (such as a brush or bristle part) which runs through the hair and / or contacts the scalp during styling. It may additionally or alternatively be provided on an external ‘smart hairbrush’ which is in communication with the styler 101 , as described above.

[0359] A temperature sensor 2112 can measure the temperature of the scalp, either through direct contact or using remote sensing technology. For example, the temperature sensor 2112 may be implemented as a digital thermometer which is configured to measure the temperature of the scalp when placed in direct contact with the scalp. Therefore, again, the temperature sensor 2112 should be positioned such that it can make contact with the user’s scalp, preferably during styling. As such, the temperature sensor 2112 may preferably be located near but not adjacent to the heaters 106, perhaps on a protruding part. Preferably, the temperature sensor 21 12 is located ‘ahead’ of the heaters 106, so that it is positioned to measure the scalp temperature before the heater 106 has heated adjacent hair (as that could affect the reading). Alternatively, the temperature sensor 2112 may be located on a further component in communication with the styler 101 , for example a ‘smart hairbrush’, as described above. Such a hairbrush may be used before styling, and be configured to communicate information regarding the scalp and / or hair health to the styler 101 and, in some instances, to the user. In some implementations, the temperature sensor 2112 can be implemented as a non-contact infrared thermometer, which measures the infrared radiation emitted by a person’s scalp and converts the reading, via calibration tables, into a temperature measurement. This means that the temperature sensor 2112 would not need to touch the user’s scalp in order to measure temperature. However, the temperature sensor 2112 should still preferably be positioned such that it measures the temperature of the user’s scalp before the heaters 106 make contact with the adjacent hair, when implemented on a heated hair styler 101.

[0360] In some implementations, the styler 101 may further comprise imaging sensors such as a camera 2108 and / or and IR LED scanner 2110. These components can acquire images, from which scalp properties and / or scalp health can be inferred. As such, one or more cameras 2108 and / or IR LED scanners 2110 are located such that they will be pointed towards a user’s scalp during styling. This may be achieved by locating the imaging sensors on an inner surface of an arm 104 of a hair straightening device, such as that illustrated in Figures 1 a and 1 b. Images captured by an optical camera 2108 and / or IR LED scanner can be analyzed, for example, using computer vision techniques to determine symptoms indicative of suboptimal scalp health. By way of example, scalp colour can be assessed, from which it can be determined whether the scalp is irritated. The exact colour change will be dependent on skin colour, but, typically, a red scalp may be indicative of scalp irritation. Colour analysis of the images can be performed to determine the level of redness, which can be compared to known colour profiles of healthy and unhealthy scalps, to assess the scalp health of a user. By way of example, this method may comprise performing edge analysis, image segmentation and / or object recognition techniques to determine which areas of the image are scalp and which are hair, and then assessing an average colour (e.g. average RGB value) for the portions of the image which are determined to be representative of the scalp. The (e.g. RGB) colour values detected could then be compared to (e.g. RGB) colour value ranges for typical for similar skin and / or hair colours, which are indicative of a healthy scalp and an unhealthy scalp (e.g. an irritated scalp). Such typical ranges can be defined via analysis of example empirical data, for example images of scalps which are irritated and scalps which are healthy. Of course, other colour value notation systems and / or other image processing techniques could also be used.

[0361] A series of recorded images can form videos. Such videos or simply a series of images recorded over a time interval can be analyzed using Eulerian video magnification techniques to track blood flow in the scalp. This technique comprises spatial decomposition, followed by temporal filtering, and then the signal is amplified to exaggerate colour shifts in an image. By this analysis, the subtle changes to the colour of the skin with blood flow pulses can be detected. The pulse rate and / or extent of the changes in the region of the scalp can be recorded and compared to predefined healthy levels to ascertain whether the circulation to the scalp is a healthy level.

[0362] Analysis of recorded images can also be used to estimate hair density. Spots in the image darker than the surrounding skin are typically indicative of hair follicles. As such, again, these spots can be located using, for example, edge analysis in combination with shape determination to locate the hair follicles. The density of hair follicles can be estimated by dividing the detected number of hair follicles by the area. The area of the user’s scalp can be determined, for example, by using the ‘ruler’ techniques as described in the section which follows, entitled ‘Hair Distance Ruler’. Alternatively, the area can be defined with respect to a thickness of the hair and / or hair follicle. The real area portrayed by the pixels of the image may also be calibrated using data relating to a proximity sensor. A compromised scalp can lead to hair thinning and / or hair loss. Analysis of the density of hair follicle on the scalp can thus be used to assess the level of thinning and / or hair loss. In some preferable implementations, the follicle density is tracked over an extended period of time, such as weeks, months or even years, by the controller 228 and / or an external controller to which the images to be analyzed and / or the results of the analysis are sent. The results may be communicated and stored to an associated user profile, in order to facilitate tracking over an extended period of time. This can enable the determined hair density to be tracked over a period of weeks, months or years. As will be described in greater detail later, the controller 228 and / or an external processor with which the styler 101 is in communication may typically output advice to the user how to improve their scalp health, in dependence on the scalp health assessment. Typically, changes to hair follicle density may take place slowly, over a matter of weeks or months. Tracking the hair follicle density over an extended period of time facilitates analysis of whether the hair follicle density is changing over that time. Tracking over an extended period can also be beneficial as it can define normal values for a particular user, and therefore detect any deviations from the normal values for that particular user (even if such values in isolation may not be considered unusual or in a range indicating concern). The system may be configured to output to a user recommendations as to how to improve hair density and / or scalp health. Further outputs can be instructed providing outputs regarding whether the user’s actions are leading to improvements in the hair density.

[0363] An irritated or unhealthy scalp may also lead to dandruff. The analysis of images captured by the camera 2108 and / or IR LED sensor 2110 can further comprise detection of the level of dandruff. Dandruff may be detected using image processing techniques such as edge analysis, image segmentation and / or object recognition techniques. The presence and density of the dandruff can be ascertained and output to a user. Similarly, a compromised scalp may have a higher level of sebum. A highly elevated sebum level can cause the hair and / or scalp to appear shiny, which can also be detected using image analysis techniques.

[0364] The processor 229 is configured to receive the outputs of the combination of sensors of the styler 101 . In some implementations, the processor 229 processes these outputs ‘onboard’ the styler 101 to build an indication of the health of the user’s scalp. The readings may be input into an algorithm stored in the memory 230, which determines whether there is any indication of poor scalp health. By way of example, this could be used to ascertain if a property is determined to be within a range for concern. For example, if it is determined that the sebum level is lower than or higher than a predefined ‘healthy range’, then the processor 229 may be configured to cause an output. Such ranges of measured levels can be defined using data from analysis of images of healthy scalps and scalps indicating issues (for example, irritation, greasy hair etc.). In some implementations, a scalp health ‘score’ may be defined, and the user’s scalp assigned a score value in dependence on features such as any combination of metrics describing: sebum level, pH level, dryness, scalp skin irritation, dandruff, hair follicle density, etc.

[0365] As will be described in further detail later, the processor 229 may be configured to instruct an output to the user indicating a potential issue with the scalp health. For example, this may be output to the user interface 21 1 of the styler 101 . Alternatively or additionally, the processor 229 may output a message to a further device 3010 and / or cloud-based processing unit 3020 (for example as illustrated in Figure 30), via the communications circuitry 227. Typically, the output will comprise advice on how to remedy the identified scalp issue. In some implementations, the controller 228 is configured to communicate the sensor outputs, via the communications circuitry 227, directly to external smart devices and / or cloud-based processing units. The relevant processors and / or controllers may then process the sensor data to perform assessments of scalp health. Such assessments may be communicated and stored to a user profile, for example in a database of a cloud-based processing unit.

[0366] Determining Hair Length and / or Styler Speed- Hair Distance Ruler

[0367] As referenced in previous sections, it can be beneficial to measure a length directly from the styler 101 . For example, this can be used to determine a length of hair being styled. This is advantageous for personalization of the styler 101 and / or a profile associated with the styler and for adjustment of styling parameters due to the hair length and age (as longer hair is older hair, which will typically have different characteristics). Determining the distance travelled by the styler 101 over a time interval means that the speed with which a user is moving the styler 101 can be determined. The speed data can be combined with acceleration readings to facilitate a more accurate picture of movement of the styler 101 . As described in previous sections, this can provide insight into the user’s styling technique. This can be used to determine and define outputs to a user regarding how to improve their technique. Beneficially, furthermore, the controller 228 can be configured to adjust the heating profile of the heaters 106 in dependence on the speed at which the user is moving the styler 101 over the hair; preferably ensuring the heaters 106 are sufficiently hot that the styler 101 need only be passed over the tress of hair once for effective styling to be complete, but also not so hot that the hair may become damaged. Three exemplary methods of determining distance will be described.

[0368] Figures 22, 23 and 24 illustrate a first exemplary method of measuring a length directly from the styler. As shown in Figure 22, an optoelectronic sensor 2202 is located within a heater 106b on an arm 104b of a styler. The optoelectronic sensor 2202 may alternatively be located adjacent to a heater 106 but is preferably sufficiently close that a tress of hair 140 passes in front of it during styling. The optoelectronic sensor 2202 typically comprises a light source, such as an LED or laser, which is positioned such that the light is emitted out from the sensor 2202, typically through a window, onto the surface in front of it (i.e. the tress of hair 140). The light is reflected back from the tress of hair 140, and is received by a photosensor component within the sensor 2202, for example a complementary metal-oxide semiconductor (CMOS) image sensor or an optical camera. A series of images are recorded overtime. Figure 23 illustrates a first schematic image 2300 recorded at a first time, t1 , by sensor 2202 located on a heater 106b, and a second schematic image 2302 recorded at a second time t2. The exemplary schematic images 2300 and 2302 are illustrated as having 1x5 pixel dimensions; in other words, they are unidirectional. In the first image 2300, recorded at time t1 , a feature 2310 (e.g. a spot or mark) can be observed within one of the pixels, Pi. This may typically be identified using pattern detection technology. In the second image 2302, recorded at time t2, the feature 2310 is observed within a different pixel, P2. The feature 2310 has therefore moved across a pixel distance Pi,2 between time t1 and t2. This can be described using the equation:

[0369] Pn-i,n= | (tn) - P(tn-i)l

[0370] Where Pn,n-i is the pixel distance travelled between time n-1 and time n, and P(tn) is the pixel location at time n and P(tn-i) is the pixel location at time n-1 . The distance represented by each pixel is known, and so the pixel distance, Pn-i,n can be multiplied by a known constant, C, to calculate the real distance, Dn-i,n, travelled by the feature 2310 (in the reference frame of the sensor) in the relevant time interval between n-1 and n: ^ Dn-l,n —1P n-l,n ■ c

[0371] As, typically, it is the styler 101 which is actually moving in the reference frame of the user, this can be understood to be the distance moved by the styler 101 in this time. The distance can be divided by the relevant time interval to calculate the speed with which the styler 101 is being moved:

[0372] Speed = n-l,n tn tn-i

[0373] A typical stroke of a hair styling device 101 during styling will pass the styler from near the roots to the ends of a tress of hair 140. As such, summing the total distance travelled during a stroke of a hair styling device can provide an indication of the hair length: In some implementations, IMU data and / or sensor (e.g. proximity sensor) data can be analysed by the controller 228 to determine whether the arms 104 are closed. The controller 228 may perform analysis of the profile of power delivered over time. Both of these techniques are described above and can be used to determine and identify a single stroke or ‘pass’ during styling. The timing of such a single stroke can be correlated with the distance and speed measurements to determine movement along a single tress of hair and thereby define a single stroke or ‘pass’ of the styler. In some implementations, the determined speed of the stroke over time can be analysed to identify a single stroke or pass, as typically the speed remains relatively smooth during a single stroke. Abrupt changes in speed indicate that the pass has ended.

[0374] Figure 23 illustrates a uniaxial configuration, but a matrix of pixels can also be used to measure speed within the plane of the heater 106, as is illustrated in Figure 24. This allows speed to be measured in further directions and more complex paths within the plane of the heater 106. This can be beneficial as a user may not be holding and / or moving the styler precisely in a uniaxial orientation or direction. In the illustrated schematic example of Figure 24, the sensor communicates the detected light as a 5x5 matrix of pixels. In the first image 2400, recorded at time t1 , a feature 2410 is detected in a first pixel Pi. In the second image 2402, recorded at time t2, the feature 2410 is detected in a second pixel P2. The vector Pi,2 therefore describes the distance travelled by the feature 2410 (within the frame of reference of the sensor) in the time interval between t1 and t2 - and therefore, typically, the distance traveled by the styler 101 . Using the equations above, the speed of the styler 101 can also be determined by dividing this distance by the time interval. Similarly, the length of the tress of hair 140 can be estimated by summing the distance travelled during the stroke / pass of the styler 101 .

[0375] In some implementations, the sensor 2202 may be adapted to ensure reliable reading of glossy (low-contrast) surfaces, such as shiny hair. The sensor 2202 may be adapted to perform ‘darkfield’ imaging by positioning the light source and photosensor such that only scattered light is collected i.e. only light which has been scattered by surface objects or roughness is collected, and the light which is directly reflected from the shiny surface is not collected (i.e. it is excluded or filtered out, typically by means of a light-stop). This means that small features (e.g. surface marks or roughness) can be identified against a ‘dark’ background. This may be implemented using two or more light sources, so that scattered light from different orientations can be detected. The use of two or more light sources can also increase the amount of light collected by the photosensor. This can help with increasing contrast, as a majority of light is blocked from reaching the photosensor. In some implementations, the light sources may have different characteristics, such as polarization, phase, wavelength or colour, which can also improve the ease with reflection from real features is identified and distinguished from noise. In some implementations, two or more light sources emit light out of phase such that when reflected directly from a shiny surface in the direction of the photosensor, the waves destructively interfere. Therefore, only light which has been scattered from surface features is collected, and these surface features can thus be identified. In order to achieve this, the location and orientation of the light sources and the photosensor are carefully controlled, and the phase difference of those light sources carefully controlled. In some implementations, the one or more light sources may emit polarized light and the photosensor may comprise a polarized filter, such that directly reflected light is blocked from the photosensor, and so only light scattered from surface features is collected. Figures 25 to 27 illustrate a further exemplary method for determining the length of a tress of hair 140 using odometer technology, by using a rollable barrel or sphere to detect the relative distance travelled by a tress of hair 140 passing over a styler 101 (or, in reality, typically vice versa). Figure 25 shows a simple schematic diagram of a tress of hair 140 travelling across a heater 106 on an arm 104 of a styler 101 . As the tress of hair 140 travels across the arm 104, it causes a roller 2502 to rotate (i.e. roll). The roller 2502 may typically be cylindrical and so formed as a rolling barrel. The roller 2502 has a known radius, r, and circumference. A cylindrical roller 2502 will roll around its central axis and so can roll only in a uniaxial direction. As such, each rotation of the roller 2502 means that the hair 140 and styler 101 have traveled a relative distance equal to the circumference of the roller. The rotation of the roller 2502 can be tracked in any number of known ways. For example, the roller 2502 may comprise markers which register and engage with corresponding sensors within the housing holding the roller 2502 (or vice versa). By way of example, these may be RFID tags. In some implementations, the roller 2502 may be connected to an optical encoding disk, which rotates with the roller 2502 to break a light source into pulses. A sensor detects these pulses and an on-chip processor processes the number and speed of the pulses to detect the distance travelled by the roller and its speed. The on-chip processor may communicate the data to a further processor (for example, the processor 229 of the controller 228, but it may be an alternative processor either internal to or external to the styler 101). One or more of the processors determines the distance traveled using the rotation data and the known dimensions of the roller 2502. For example, for a roller 2502 having a radius r, the distance travelled when rolling through an angle A0 is:

[0376] The processor is typically further configured to track the rotation against time (i.e. determine the extent of rotation within a time interval). It can therefore be further configured to calculate the speed by dividing the distance by the recorded time:

[0377] In some implementations, the roller 2502 may be spherical, such that it can rotate in multiple axes, rather than just one axis. This would mean that the roller 2502 can be used to detect movements along more than one direction within the plane of the heater 106, and even track complex movements. In such an implementation, the roller 2502 fits within a socket so that the roller 2502 can rotate freely in multiple directions (within the plane of the surface of the styler 101 and its heaters 106). Again, the roller 2502 may comprise markers which register and engage with corresponding sensors within the housing holding the roller 2502 (or vice versa). These may be electronic, such as RFID tags or physical, and preferably are located at different angular positions within the roller 2502 and / or the socket. In some implementations, the socket may comprise cylindrical rollers rotatable around different (e.g. perpendicular) axes and arranged such that they contact the roller 2502 and are rotated by the movement of the roller 2502. One cylindrical roller is arranged and configured to roll due to the components of the movement in the x-direction, and the other configured to roll due to the component of the movement in the y-direction. These cylindrical rollers may be connected to optical encoders to create light pulses descriptive of the speed of the roller 2502 in the x- and y-directions. Sensors can detect the speed and number of pulses, and one or more processors use this information to determine the direction, speed and distance travelled by the roller, and therefore the tress of hair 140 relative to the heater 106.

[0378] The roller 2502, whether cylindrical or spherical, is preferably located at a position on the styler 101 such that it makes direct and sustained contact with the tress of hair 140 while the hair is being styled. In some implementations, the roller 2502 is located directly within a heater 106 of the styler 101 . Figure 34 illustrates an exemplary embodiment in which the roller 2502 is positioned within a heater 106b of one arm 104b of the styler 101. When the tress of hair 140 is placed between the two heaters 106a, 106b of the two arms 104a, 104b, then the relative movement of the tress 140 and the styler 101 causes the rotation of the roller 2502.

[0379] In those implementations in which the roller 2502 is located within a heater 106, the roller 2502 itself may be heatable. This can prevent the roller 2502 affecting the heating and styling of the hair 140. For example, as illustrated in Figure 27, a roller 2702 may comprise a central heating element 2704. The heating element 2704 may be connected to a pivot hinge, to enable 360° rotation. In some implementations, the heating element 2704 may instead be detached and forms the pivot around which the roller 2702 rotates. The heating element 2704 heats the roller 2702 via convection, radiation (infrared), or via conduction, for example via a lubricated- coupling medium for conduction (i.e. using a thermally conductive medium). Preferably, the power transmission to the heating element 2704 is coupled to the power control of the heating zone 467, 867 in which it is located, so that the zonal temperature is controlled as a whole, including heating of the roller 2702.

[0380] The rollers 2502, 2702 are preferably further configured to prevent hair becoming caught in the mechanism. This may, for example, take the form of surrounding brushes or protectors around the edge of the rollers 2502, 2702. The rollers 2502, 2702 may be slightly recessed within their socket to reduce the tendency for hair to become caught in the mechanism.

[0381] Figures 28 and 29 illustrate a further exemplary method for determining the speed with which a styler is being moved over a tress of hair 140, and therefore estimating the length of the hair. This method uses a determination of the temperature increase of a tress of hair 140 as it moves over separate sections / zones of a heater 106. In particular, as illustrated in Figure 28, a tress 140 moves across a heater 106 on an arm 104 in a direction (indicated by the arrow) such that the tress of hair 140 passes across a first section 2802, having a length L, and then moves to a second section 2804. As the tress of hair 140 passes over the first section 2802, its temperature increases. The initial temperature can be estimated to be the room temperature, which may be measured directly by a room temperature sensor located on the styler 101 itself, or the controller 228 may receive information relating to the room temperature from external devices such as a smart device 3010. This may comprise known conditions forthe geographic location of the user. In some implementations, temperature measurements of the heaters 106 of the first section may be used to estimate the initial temperature of the tress of hair 140. As outlined above, the controller 228 of the styler 101 controls the power to the heaters 206 in dependence on temperature measurements of the heaters 206, either from temperature sensors or from resistance measurements (via the process as described above). Power is delivered to the heaters 206 by the drive circuitry 223 in dependence on a difference between the temperature of the heaters 206 and the setpoint temperature. The larger the difference in temperature between the heaters 206 and the desired setpoint temperature, the larger the power input by the drive circuitry 223. The temperature measurements of the heaters 106 of the first section 2802 can therefore be used to estimate the initial temperature of the hair 140. Similarly, the temperature measurements of the heaters 106 of the second section 2802 can then be used to estimate the second temperature of the tress of hair 140, after it has travelled across the first section 2802 and then makes contact with the second section 2804. The initial temperature, Ti, and the second temperature, T2, provide an indication of the increase of temperature of the tress of hair 140 as it travelled across the first section 2802.

[0382] We can make the assumption that all the heat energy of the first section 2802 is used to heat the tress of hair 140 during the interval over which is it touching the first section 2802. As described above, power is delivered to the heaters 206 by the drive circuitry 223 in dependence on a difference between the temperature of the heaters 206 and the setpoint temperature. The processor 229 of the styler 101 can therefore track the power delivered to the heater 206 over time, as determined from temperature measurement data received from the temperature measurement circuitry 225 and / or from direct measurements of the power delivered as sensed by the power measurement circuitry 1324.

[0383] The specific heat coefficient and / or heat coefficient of the hair can be determined by the methodology as outlined above in the ‘Methods of defining hair damage’ section and / or as outlined in the ‘Modifications and alternatives’ section as follows. In some implementations, an estimated specific heat coefficient for the hair may be determined based on user inputs (typically hair inputs relating to the condition of their hair, whether it is dyed or bleached, its length etc.).

[0384] Assuming all of the heat energy of the first section 2802 is used to heat the hair 140, the temperature increase can be described in terms of the power input to the first section, Px, over a time interval Atx, and the specific heat capacity, c, and mass of the tress, mtress, according to:

[0385] When making these calculations, the controller 28 may use a predefined average value for the mass of the tress of hair, mtress. The chosen predefined value may be dependent on user input, for example, dependent on the type of hair a user has indicated that they have, or it may be a factory set value for a typical tress size. In some implementations, the processor 229 may be configured to determine the extent to which the styler arms are closed based on feedback from sensors in the arms 104 of the styler 101 (for example, proximity sensors) and / or the data received from IMU 1312, as this can provide an indication of the mass of the tress of hair 140. Alternatively, the heat capacity for the tress may be estimated and used, according to the equation: P2~ Pl=~ Prr’ t

[0386] S -tress -r Using the determined values for the temperature difference, power, and specific heat capacity and mass (or simply heat capacity) of the tress of hair 140, the time interval over which the tress of hair 140 was in contact with the first section 3602 can be determined according to the following equation:

[0387] The relative speed of the styler 101 and the tress of hair 140 can then be determined by dividing the length, L, of the first section 2802 by this time interval:

[0388] The controller 228 may be configured to determine the total length of time during which the tress of hair 140 is in contact with the heater 106 of the styler 101 via analysis of the power profile of the heater. This can be implemented by tracking the sensed temperature measurements and the setpoint temperature, and calculating the power delivered accordingly, and / or by sensing the power input to the heaters 106 directly using the power measurement circuitry 1324 (as, for example, explained above in the section 'Recurrent heating of a single tress’). Additionally or alternatively, this can be implemented by recording the time interval over which the arms 104 of the styler 101 are closed using data from a proximity sensor and / or the IMU 1312 (as, for example, explained above in the section ‘Heat on hair time’). The controller 228 is configured to increase the powerwhen the sensed temperature of the heater 106 is below a setpoint temperature. When hair is loaded on the heater 106, this causes the temperature to drop and so the power demand is higher. The controller 228 can therefore measure the time period over which there is increased power demand in order to estimate the time interval over which the tress of hair 140 is loaded on the styler 101. Additionally or alternatively, the controller can record the time interval over which the arms 104 of the styler 101 are closed, as this can be taken as indicative that the arms 104 are clamping the tress of hair 140.

[0389] The controller 228 (or indeed an external processor to which the relevant data and measurements are communicated) can estimate the length of the tress of hair 140 by integrating the determined speed over the time interval the tress 140 is in contact with the heater 106.

[0390] These methods may be implemented singly or in combination. If multiple methods are implemented simultaneously, then the distances and speeds determined can be correlated to review their accuracy. In some implementations, different determined values may be averaged. In some implementations, the speed data may be combined with data from an accelerometer (for example, as provided in the IMU 1312) to build an accurate description of the movement of the styler 101.

[0391] These methods assume that the styler 101 remains in contact with the tress of hair 140 over the entire length of the hair. It is likely that the user will actually start styling the hair 140 a small distance from the scalp in order to avoid burning the scalp. The controller 228 and / or external processor may be configured to add a typical ‘starting’ margin to the determined length in order to estimate a likely complete total length of the tress of hair 140. This may be determined empirically. In some cases, the user may only style a small portion of the tress of hair 140, for example, they may run the styler over one section again or they may curl only the ends of the tress 140. Different regions of the user’s hair may also have different lengths; for example, a hairstyle may comprise a fringe, which has a much shorter length than the rest of the user’s hair. In some implementations, the controller 228 and / or an external processor may be configured to record the range of tress lengths, and to estimate the overall and / or average length of the user’s hair based on the longer values obtained. The controller 228 and / or an external processor may, in some instances, be configured to analyze the range of length values to perform an estimation as to the user’s hairstyle (for example, inferring that the user has a fringe). This can typically be checked against user inputs, for example the user inputs relating to their hair length and / or style. Such information can be stored to a user profile in a database, for example within a central cloud-based processing unit. Such information can also be used in the control of the heaters 106, 206 and in the output of suggestions and recommendations to a user.

[0392] As hair gets longer, it gets older and thinner. If the bulk thickness of the tress is significantly smaller at the ends than near the roots, then less heat may be required to achieve style on the ‘ends’ of a user’s hair as there is a reduced mass of hair to raise to above the glass transition temperature. Typically, older hair is also more damaged and each strand itself may thin with age (towards the tip). This can also mean that less heat is required to achieve a style on the ‘ends’ of a user’s hair. If the heating profile remains constant during a pass of the styler 101 over a tress of hair 140, then there may be a risk of damage to one or more portions of the hair. As a styler 101 is passed over a tress of hair, the temperature of the heaters 206 can be modulated so that damage is minimized to older hair. Typically, this can take the form of a reduction in setpoint temperature of the heaters 206 for the lengths and ends of the tress of hair 140. It may be understood that such changes in setpoint temperature may be applied in a gradual manner along the tress or as one or more step changes along the tress. (However, in some implementations, the temperature setpoint of the heaters 206 may be configured to increase slightly towards the ends of the tress 140 in order to maintain a relatively constant real temperature. As the heaters can drop in temperature during a pass or stroke of the styler 101 , a slight increase in the temperature setpoint can counteract the temperature drop to facilitate maintaining a relatively stable constant temperature.)

[0393] Determined hair length can be saved to the memory 230 of the styler 101 and / or to a personalized user profile. Such a user profile may typically be stored in a central cloud-based processing unit 3020, as illustrated in Figures 30 and 32, and retrieved and / or accessed by a styler 101 and / or by a smart processing device 3010 (e.g. via an application run on the smart processing device 3010). This can be particularly beneficial if a user uses more than one styler 101 and / or if more than one user uses one particular styler 101. In some implementations, the user may be prompted to input answers relating to their perception of their hair. For example, this may take the form of a ‘user hair quiz’. The controller 228 of the styler 101 , or, more typically, one or both processors of the processor 3224 of the cloud-based processing unit 3020 and the processing unit 3114 of a smart processing device 3010, typically running the software of a dedicated application, analyze the comparison of the user’s perception answers and the measured hair length. Comparing the measured value to the self-evaluation can provide insights into the user perception and self-evaluation.

[0394] Gathering information relating to hair length can also be used to tailor the recommendations output to a user. For example, this may comprise recommendations such as (but not limited to): wet line products, possible hair styles to try, and how to prepare the hair before styling.

[0395] Ambient Conditions

[0396] The conditions in which hair is being styled can dramatically affect the efficacy of the styling, and how well the style lasts (the longevity of the style). The relevant conditions may comprise the conditions of the environment in which the styler is being used (e.g. the conditions of the room where the styler is being used) and the conditions of the environment in which the user will be located after styling (for example, the weather conditions in their geographical location and / or, in some cases, whether the user will be indoors, for example at an indoor event such as a conference or wedding). As illustrated in Figure 30, the styler 101 is preferably in communication with a smart processing device 3010, for example be via Bluetooth™ (the communication circuitry comprising antennae) and / or via an internet connection such as WiFi. The smart processing device 3010 may typically be a mobile phone, laptop or tablet device, and may be running a dedicated application or ‘app’. The smart processing device 3010 and / or the styler 101 may be further in communication with a cloudbased processing unit 3020, typically via an internet connection such as WiFi.

[0397] Figure 31 illustrates a schematic of components of the smart processing device 3010. As illustrated in Figure 31 , the smart processing device 3010 typically comprises communications circuitry 311 1 for communicating with further devices, a user interface 31 13, via which the user can input information and preferences, a processor 3114, and a memory 31 15, which may comprise an operating system 3116, control modules 31 17 and data storage 3118. Figure 32 illustrates the connections between the smart processing device 3010, the cloud-based processing unit 3020 and two exemplary stylers 101 and 3201. As illustrated in Figure 32, the cloud-based processing 3020 unit preferably comprises a processor 3224 and a database 3222, comprising user profile 3226 to which user data can be stored. Instructions can also typically be retrieved from the database 3222 and communicated to the smart processing device 3010 and / or to one or more stylers 101 , 3201.

[0398] Figure 33 illustrates an exemplary block diagram of the control circuitry 3315 of the hair styling device 101 ; this corresponds to Figure 2 but with additional optional components of a hygrometer 3304, a barometer 3306 and a thermometer 3308. Any combination or subset of these components may be part of the hair styling device 101 . Indeed, any combination of these components may be provided with any combination of the components as illustrated in Figures 13 and 21.

[0399] The hygrometer 3304 is configured to measure the humidity of the environment, i.e. the level of water content in the air. Such hygrometers 3304 may be capacitive, such that they determine humidity via measurement of the dielectric constant of a material due to humidity. Hygrometers 3304 may be resistive, such that they measure the change in resistance of a material due to humidity. They may also be thermal (measuring change of thermal conductivity), or optical (measuring the absorption of light by water in the air). The controller 228 is configured to receive the humidity measurements from the hygrometer 3304, and in some implementations may further communicate this, via the communications circuitry 227, to the smart processing device 3010 and / or the cloud-based processing unit 3020.

[0400] The barometer 3306 is configured to measure the air pressure of the environment. The barometer 3306 will typically be a microelectromechanical system (MEMS) barometer, due to their compact size. The controller 228 is configured to receive the air pressure measurements from the barometer 3306, and in some implementations may further communicate this, via the communications circuitry 227, to the smart processing device 3010 and / or the cloud-based processing unit 3020.

[0401] The thermometer 3308 is configured to sense the ambient temperature. It is typically formed as a digital thermometer, located at a position on the styler 101 away from the heaters 106 in order to limit the effect hot hair from the heaters 106 may have on the temperature measurement. Again, the controller 228 configured to receive the temperature measurements from the thermometer 3308, and in some implementations may further communicate this, via the communications circuitry 227, to the smart processing device 3010 and / or the cloudbased processing unit 3020.

[0402] In some implementations, the smart processing device 3010 may itself comprise sensors, such as temperature sensors or barometers. The controller 228 of the styler 101 may then be configured to communicate with the smart processing device 2010 to receive ambient condition measurements from the smart processing device 3010. In some implementations, the styler 101 may be further configured to receive data relating to the weather in its location from external databases (for example, from relevant local meteorological and / or weather authorities). This may be received via the smart processing device 3010 and / or the cloud-based processing unit 3020; in other words, the smart processing device 3010 and / or the cloud-based processing unit 3020 may receive information from one or more relevant meteorological and / or weather authorities, and then communicate this information to the styler 101. The styler 101 and / or the smart processing device 3010 may typically comprise location trackers, so that their geographical location can be known. This may be determined by use of, for example, a Global Positioning System (GPS) tracker and / or via the IP address or wireless network connection of the styler 101 and / or smart processing device 3010 when connected to the internet.

[0403] Hair responds differently to heat styling depending on the ambient conditions, such as room temperature, air pressure and humidity. The controller 228 of the styler 101 can therefore be configured to adjust styling parameters in dependence on the measurements received from the hygrometer 3304, barometer 3306, and / or thermometer 3308 and / or from measurements received from external sensors and / or weather and meteorological databases. The controller 228 is typically configured to use the received measurements to determine the conditions relevant to one or more relevant environments, which may typically include the environment (e.g. room) in which the hair is being styled, and / or the environment in which the user will be after styling (e.g. the outdoor weather conditions in that geographic location). In particular, the processor may be configured to determine the dew point of the one or more relevant environments. The dew point is the temperature at which air becomes saturated with water vapour, and so any furtherwater will condense (akin to forming dew). It can also be described as the temperature to which air must be cooled to reach a relative humidity of 100%. The dew point depends on the air pressure and humidity. A higher air pressure causes a higher dew point; in other words, at higher air pressure, the water condenses at a highertemperature. The higherthe humidity of the air, the higherthe dew point (i.e. the air becomes saturated and so water condenses at a highertemperature). The dew point is a useful metric, as it can be used to indicate the ‘stickiness’ ofwaterto hair; in otherwords, the ease with which water can be removed from the hair. Higher dew points mean that a higher temperature (i.e. higher styler temperature) is required to remove water from the hair by a styling device 101 such as a hair dryer. For example, a high humidity and low temperature environment mean a relatively high dew point. If the ambient temperature is low, more heat is required to be input in order to remove water from the hair. Increased heat on the hair can be more damaging to the health of the hair. By contrast, dry environments will have a lower dew point, and so will require less heat input from a styler 101 to remove water and / or to style hair effectively. If the environment is relatively warm, this also means a reduction in the heat required to remove the water from the hair. As such, cold air and high humidity are worse conditions for styling hair, while dry (low humidity) and warm environments are preferable for hair styling.

[0404] The controller 228 is configured to adjust styler settings and / or parameters in dependence on the measured and received ambient humidity, pressure and temperature conditions. For example, in warm and dry environments, setpoint temperatures of heaters 106 can be reduced. This can beneficially minimize heat damage to hair during styling. In some implementations, the controller 228 may be configured to control the styler settings such that hair is dried to a moisture level consistent with the humidity if the environment in which a user will be located (e.g. the indoor conditions or outdoor weather conditions). The styler parameters are preferably tailored according to the ambient conditions to ensure hair is dried safely while maintaining volume and preserving style. Such parameters may be determined empirically and / or in a lab setting.

[0405] The controller 228 is preferably configured such that it can further receive user input and preferences. Users may input information and / or preferences directly into the styler 101 via the user interface 21 1 , or they may provide such inputs to the user interface 3113 of a smart processing device 3010, which can communicate the information to the styler 101 via the respective communications circuitries 3113, 227. The user preferences typically either contain - or can be used to infer - the priorities for the styling session. The user input may comprise information relating to the purpose of the styling; for example, if the style is simply for everyday or for a special occasion, and / or if the user will predominantly be inside or outside. For example, if the style is for a special occasion, a higher temperature may be used. In this case, style efficacy and longevity may be the priorities for the styling session. A higher temperature can achieve effective styling but can cause damage when used consistently; therefore, higher temperatures can be used occasionally but may be advised against for everyday use. If the userwill predominantly be located outside, the environmental conditions will be different than if the user is planning to remain indoors. If the user is planning to spend time outdoors (for example, they may be attending an outdoor wedding), then the environmental conditions, as received from relevant meteorological and weather data, are likely to be the most relevant to consider to ensure style longevity. If the styling session is simply, for everyday styling, then it may be inferred that hair health is the main priority. In some implementations, such input may comprise direct information relating to user priorities; for example, a user can input if their priorities are speed of styling, hair health, style longevity etc. If a user prioritizes speed of styling, for example, then a higher temperature setpoint of the heater may be used so that the hair can be dried or styled quickly. However, if a user prioritizes hair health, a lower temperature setpoint may be used in order to minimize damage (even if this means styling may take longer).

[0406] The memory 230 of the styler 101 and / or the memory 3115 of the smart processing device 3010 typically comprise instructions / algorithms for determining and implementing styler parameters based on the humidity, air pressure and / or temperature values, and preferably also in dependence on the input user information and preferences. Such instructions / algorithms may be received from a database 3222 of the cloud-based processing unit 3020. The instructions / algorithms typically utilize fuzzy logic, in which statements can be partially true or false as represented by values between 0 and 1 . This is beneficial for navigating complex parameter spaces, in which boundaries are not well-defined. This advantageously facilitates nuanced and adaptable reasoning. This can be of particular use as the humidity, temperature and air pressure are interrelated and affect the dew point. Additionally, the ambient conditions in a room can change quickly. By way of example, a user may be styling their hair in a room with low humidity and in which a radiator has just been turned on. This will cause the dew point to become lower. Alternatively, the user may move from one room to another, or from one part of a room to another part, perhaps located adjacent to the radiator. If fuzzy logic were not implemented - for example, if a fixed model were to be implemented - then the performance of the instructions / algorithm would be suboptimal in a changing environment. Indeed, there is also a higher probability that adjusting the styler parameters could cause ‘overshoot’ or overcorrection. The precise instructions of the algorithms / instructions may be defined using regression models based on empirical data.

[0407] Figure 34 illustrates an exemplary fuzzy logic architecture, comprising a Rule Base 3402, a Fuzzifier 3404 (or Fuzzification Interface), and Inference Engine 3406, and Defuzzifier 3408 (or Defuzzification Interface). The Rule Base 3402 comprises the sets of rules for the decision-making system, typically relating the ambient conditions to styler parameters such as temperature setpoint of the heaters. Preferably, it further accommodates the user inputs, such as their preferences and priorities and inference of those preferences and priorities from other information input by the user. The Rule Base 3402 comprises IF / THEN rules based on the relevant variables. The measurements of ambient conditions received from the hygrometer 3304, barometer 3306, and / or thermometer 3308 and / or from measurements received from external sensors and / or weather and meteorological databases are input, and the Fuzzifier 3404 converts them into fuzzy sets comprising a series of states. The Inference Engine 3406 assesses the fuzzy inputs with respect to the defined rules from the Rule Base 3402, and determines which rules are to be executed. Those rules are integrated to form the control actions. The Defuzzifier 3408 then maps the fuzzy outputs to determine precise control values. For example, these values may comprise styler settings such as temperature setpoint of the heaters 106. In some implementations, the controller 228 may be further configured to output user feedback, such as advice, in dependence on measured ambient conditions and / or the user inputs. These may form part of the outputs of the fuzzy logic architecture, or may be output in dependence on a simpler algorithm run by one or more of the styler processor 229, smart processing device processor 3114, and cloud-based processing unit processor 3224. Such outputs may comprise advice on how to improve styling technique, such as: how to comb before styling; which products to use, for example water absorbing products; how to adjust the frequency of hair washing; advice not to style hair in a steamy bathroom. The outputs may further comprise advice on how to maintain a style in particular conditions. Associated algorithms may be as simple as outputting advice not to style hair in a steamy bathroom in dependence on detecting a humidity value above a threshold value. In some examples, more complex algorithms may be implemented. The outputs may be dependent on weather conditions forthe relevant geographical area. The outputs are typically provided to a user via the user interface 211 of the styler 101 and / or the user interface 3113 of the smart processing device 3010.

[0408] Outputs to a user

[0409] In dependence on the analysis of hair and styler data and resulting metrics and scores, as described above, the controller 228 is configured to perform control actions. This may typically comprise outputting an alert and / or updating the styler parameters in dependence on the determined metrics and / or scores, for example in dependence on the metrics and / or scores falling outside of predefined acceptable threshold ranges (and thus indicating an issue regarding hair health and / or styling). The alert may be a written warning (output to the user interface 211), a visual alert (such as flashing of the LED display 1310), an audio alert, a haptic alert (in particular, via the haptics unit 1314), or any combination of these. The alert may comprise instructions how to correct the issue, for example output to the user interface 211. The controller 228 may additionally or alternatively amend the settings of the styler 101 in dependence on the determined metrics and / or scores, for example changing the setpoint temperature of the heaters 206.

[0410] The alerts may be output to the user interface 211 or the LED display 1310 of the styler 101 itself, or the styler 101 may be in communication with further components, to which the alert can be output. In some implementations, the further components are configured to perform at least some of the processing. Figure 30 illustrates an exemplary system 3000 within which the styler 101 may be provided. The system 3000 comprises at least one styler 101 in communication with at least one smart processing device 3010, which is in turn in communication with cloud-based processing unit 3020 (such as a server). The at least one smart processing device 3010 is typically a mobile phone which runs a specific application (‘app’), but it may also be a computer, smart watch etc. More than one smart processing device 3010 may be used in combination; for example, a user may use both a smart watch and a mobile phone. In some optional implementations, the at least one styler 101 is directly in communication with the cloud-based processing unit 3020.

[0411] The one or more stylers 101 communicate with the at least one smart processing device 3010 and / or cloudbased processing unit 3020 via the communications circuitry 227. Figure 31 illustrates an exemplary architecture of some main components of the smart processing device 3010. Communications circuitry 3111 of the smart processing device 3010 is in communication with the communications circuitry 227 of the one or more stylers 101. The communication of information between the styler 101 and the at least one smart processing device 3010 may for example be via Bluetooth™, and the communication circuitry may comprise antennae. Alternatively, in some implementations the communication may be via an internet connection such as WiFi. The communication circuitry 3111 is in communication with and sends the received information to a processor 3114, which also receives information from a user interface 3113. The user interface 3113 typically comprises a screen for displaying (outputting) information and buttons, touchscreen capabilities and / or other components which facilitate a user inputting information. The processor 31 14 is further connected to a memory 3115. The memory 3115 typically stores an operating system 3116 and one or more control modules 3117. By way of examples, the control modules 3117 may be configured to control communications, and / or to control settings of the styler 101 . The memory 3115 further comprises data storage 3118, which is configured to store pre-saved data, settings, and data accumulated during use.

[0412] As shown in Figure 30, the at least one smart processing device 3010 is further in communication with a cloudbased processing unit 3020. The processor 3114 of the smart processing device 3010 is configured to receive information and instructions from and send information to the cloud-based processing unit 3020 via the communications circuitry 3111 , typically over an internet connection. The processor 3114 of the smart processing device 3010 and the processor 3224 of the cloud-based processing unit 3020 can both be configured to process the data collected by the one or more stylers 101 during use. This may be in addition to or alternatively to processing performed by the processor 229 of the styler 101 . That is to say, in the abovedescribed example processes and calculations, the processor 3114 of the smart processing device 3010 and / or the processor 3224 of the cloud-based processing unit 3020 may perform the processing of the styler data in addition to or instead of the processor 229 of the styler 101 , thereby to determine metrics, values and / or scores.

[0413] Figure 32 shows a further exemplary architecture of the connections between the smart processing device 3010, a first styler 101 and second styler 3201 , and the cloud-based processing unit 3020. The cloud-based processing unit 3020 comprises a database 3222 and a processor 3224. The database 3222 stores user profiles 3226 and corresponding information. Typically, the data is stored in a graph-database, linking stylers 101 , 3201 , behaviours, and personas to user profiles 3226. A user can access their own user profile 3226 from the database 3222 and load it to one or more smart processing devices 3010. Typically, data from the user profile 3226 will be downloaded and stored in the data storage 3118 of the memory 3115 of the smart processing device 3010. The user profile 3226 can be linked to the user’s particular stylers 101 , 3201. The user profile 3226 can be updated via accumulation of data from the usage of those stylers 101 , 3201 (the details of the information extracted from the user’s usage of the stylers 101 , 3201 will be explained in detail below). This data can be stored in the data storage 3118 of the memory 3115 of the smart processing device 3010, which then sends the information to the database 3222 of the cloud-based processing unit 3020. This allows information to be collected even if the smart processing device 3010 is currently offline. The database 3222 further typically comprises advice on hair styling techniques; this may comprise, for example, styling routines to achieve particular hairstyles. The processor 2224 of the cloud-based processing unit 3020 is typically configured to process the information stored in the user profiles 3226 in the database 3222 relating to how users use their stylers; this can be used to determine trends, etc. The processor 3114 of the smart processing device 3010 and the processor 3224 of the cloud-based processing unit 3020 can both be configured to process the data collected for a particular user. The output of the processing of the collected data typically comprises advice, for example on how to improve technique; this will be explained in further detail in the following sections. The processing instructions run by the processor 3114 of the smart processing device 3010 may be received and / or updated from the cloud-based processing unit 3020. Updates may be made in dependence on the results of the processor 3224 of the cloud-based processing unit 3020 analyzing data from different users sent to and stored in the database 3222.

[0414] It can be beneficial to provide a user with meaningful metrics on hair and scalp health, hair properties and / or styling performance. As illustrated in Figures 30 to 32 and as described above, the styler 101 is configured to communicate with an external smart processing device 3010 and cloud-based processing unit 3020. The external smart processing device 3010 is typically a smart watch, mobile phone, tablet and computer, and its processor 3114 is configured to run an application (‘app’) designed to complement use of one or more stylers 101 . The app is typically downloadable to the memory 3215 of the smart processing device 3010 from the database 3222 of the cloud-based processing unit 3020. The user can create a user profile 3226 individual to them, in which their data can be stored. This user profile 3226 and its data is typically stored in the cloud-based database 3222 so that a user can log into their account (and user profile) from different smart processing devices; for example, on their mobile phone and on their smart watch.

[0415] The styler 101 is in communication with the smart processing device 3010 via their respective communications circuitry 227, 3111. Via this connection, data relating to each styling session can be sent to the smart processing device 3010 running the app. This data is typically raw styler data, such as the heat demand profile over time (as illustrated in Figures 17, 19b and 20), etc.; in which case the processor 3114 of the device 3010 analyses the data according to instructions encoded in the app in order to determine parameters and scores, such as those outlined in previous sections. In some implementations, the controller 228 of the styler 101 may perform some analysis on the raw data before it is transmitted to the smart processing appliance 3010. In some implementations, the data may be processed by the cloud-based processor 3224. The relevant one or more processors stores the parameters and scores to the user profile 3226.

[0416] The user can link more than one styler to their user profile 3226, such that data relating to all of their stylers is collected and saved to their profile 3226. For example, a person may own and style their hair with both a hair straightening appliance and a curling tong; data from both of these appliances can be processed and saved to the same user profile 3226 (for example automatically saved to the same user profile 3226, once these devices have been linked to that profile). The user can also input which interchangeable styling ‘heads’ they have for those stylers. This can aid in building a general picture of the health of the user’s hair.

[0417] The application (or ‘app’) is configured to provide feedback to a user regarding hair damage, hair health, scalp health, potentially damaging behaviours and / or styling technique. This is typically based on metrics which are defined and determined by the methods described above. On a most basic level, the app can output a simple alert if any of the metrics or scores is out of range of what has been defined to be acceptable values. The alert may be a written warning (such as a push notification), a visual alert (such as flashing of the LED display), an audio alert, or a haptic alert. Alternatively or additionally, the app is configured to output more detailed information on the hair and / or scalp health and styling performance. For example, the individual scores (behaviour score, hair heat score, etc.) and / or other metrics (e.g. hair follicle density, sebum measurement, etc.) can be output to a user directly to provide feedback regarding the user’s styling technique and the hair health. Either in addition to or in combination with outputting the individual scores, the overall hair score may be output to a user directly. The scores may be output after each styling session and / or there may be output a weekly, monthly etc. ‘review’ of how the user has used the styler, their hair and / or scalp condition, and / or styling technique (and improvements thereto).

[0418] Figure 35 shows an exemplary graphical user interface 3500 of the app. As shown in Figure 35, the interface 3500 provides a weekly summary of the total amount of time a styler has been turned on and breaks this into the time over which heat has been on hair, the styler is moving, and the styler is idle. This is provided both graphically, as a pie chart 3502, and verbally in the key 3504. The app interface 3500 also displays the overall user score 3506, with a selectable link 3508 to tips regarding how the user can improve their score. The interface 3500 may further comprise a ‘persona’ 3510 related to their score for that week.

[0419] In some implementations, the app may output the individual determined scores, such as behaviour score, hair heat score, etc., typically in addition to the overall score. By way of example, the app interface may include a selectable link to a breakdown of the individual scores. In some implementations, the scores will be output with corresponding direct feedback and advice regarding how to improve their technique. By way of example, this may include a message being output regarding how to improve hair and / or scalp health, such as: “Move the styler more slowly for improved hair health” or recommendations to use types of hair product. It may also include a message being output regarding styling technique, for example: “Don’t fully dry your hair for a tighter curl” or “Don’t use styler in a steamy bathroom”. In some implementations, the advice is output while the user is styling their hair, in order to give real-time feedback so that the user can adjust their styling technique. Recommendations may further comprise advice on how to prepare the hair and / or maintain a style, for example in dependence on hair and / or scalp health and / or ambient conditions.

[0420] The app is typically configured to store information regarding a user’s previous hair and / or scalp condition and styling techniques, for example by storing a log of the metrics and scores for each use. This typically comprises metrics describing the user’s hair, including length, heat capacity, etc. This typically comprises the processor 3114 of the smart processing device 3010 sending the information to the cloud-based database 3222 to store the information to the user’s profile. In this manner, the app can ‘track’ the user’s hair health, scalp health, hair style / cut and / or styling technique over all the styling sessions, and update after each use. This can be used to output personalized recommendations to the user. It can also be used to determine and output to a user any improvement (or otherwise) in their hair health, scalp health and / or styling technique. The data detected and stored to the user profile 3226 during use of the styler(s) can further be processed to determine and track the user’s favourite styles. This may be in dependence on inputs by the user via a styler user interface 111 , 211 and / or the user interface 31 13 of the smart processing device 3010; alternatively, one or more processors may detect the users most frequently used styles based on data from the IMU 1312 and / or temperature profiles of the heaters 106, 206. Tailored recommendations can be output in dependence on this information, for example other hairstyles which may be of interest to the user. Furthermore, in some implementations the app is configured to output suggestions for further styles based on information about the user. This information may typically comprise a combination of data input by the user (for example age, described hair type, estimated hair damage, etc.) and metrics determined during use (for example, styling frequency, determined hair type, determined hair damage, determined hair length, determined follicle density, etc.). If multiple stylers are linked to the same profile or account, then one or more processors, implementing instructions encoded in the app, can analyze the cumulative effect of their use and create and output recommendations accordingly. This is typically based on a knowledge bank stored in the cloud-based database 3222, which comprises knowledge regarding particular styles and styling techniques in relation to different hair types and in relation to different tastes of users.

[0421] The database 3222 stores the user profiles as a graph-database, linking products, behaviours, and ‘personas’ to user profiles 3226. Using a clustering algorithm, users are grouped into ‘personas’. Figure 36 illustrates a relatively simple two-dimensional algorithm, which clusters users into three different personas in dependence on hair length and age. A clustering algorithm can also be implemented in a higher dimensional space using additional features such as hair type, average styling time, favourite styles, hair colour, phone model, favourite products, location, styling frequency, usage behaviour, etc. The clustering algorithms are used to offer tips, styles, and products that benefit similar users. In this manner, the app outputs recommendations based on what similar users are doing.

[0422] In some implementations, the app may have access to the user’s calendar or comprise a calendar itself to schedule practice sessions for a styling technique and / or to advise on frequency of heat styling. Figure 37 shows an example of such a calendar; in the illustrated scenario, a user wants to practice a particular style for a wedding in a couple of months. The calendar schedules fifteen practice runs (indicated by patterned dates) and a final dress rehearsal (indicated by the hatched date) before the wedding (indicated by the cross-hatched date). The app comprises instructions to output a push notification to the user interface 3113 of the smart processing device 3010 to remind a user to practice the style. The data (including the metrics) from the styling sessions is saved to the user profile 3226 to aid in tracking their progress. In some implementations, the user can upload photos of the finished style after each session to aid in visually tracking their progress over time. The photos can typically be uploaded from the photo storage of the smart processing device 3010 to the user profile 3226, which is saved on the cloud-based database 3222.

[0423] Additionally, the app may be configured to allow a user to control styler parameters directly; for example, setpoint temperature, idle switch off time, LED display colours, etc. The relevant instructions may be stored in the control modules 3117 of the smart processing device 3010. The processor 3114 of the smart processing device 3010 can then send these instructions relating to the settings to the controller 228 of the styler 101. In some implementations, the settings are determined in dependence on the analysis of data from the styler 101 , for example in dependence on the determined metrics and scores, and / or determined ambient conditions. The settings may be determined in dependence on preferences as input by the user, for example prioritizing hair health, speed of styling etc., as described above. By way of example, the processor 3114 of the smart processing device 3010, implementing the instructions encoded in the app, may instruct the controller 228 of the styler 101 to amend the temperature setpoint of the heaters 106, 206 in dependence on the determined scores and metrics, determined ambient conditions and / or user preferences. For example, if the analysis determines a high level of damage to hair, the temperature setpoint may be lowered correspondingly.

[0424] In some implementations, the outputs to a user may comprise recommendations of hair products to use. The one or more relevant processors 229, 3114, 3224 may determine an issue with user scalp and / or hair health and / or user technique, and identify that a ‘wet’ hair product would be beneficial. For example, a user’s scalp may be irritated, so an alternative shampoo is recommended. By way of a further example, a user’s hair may be damaged and / or their technique includes a large amount of hair on heat time, and a recommendation to use a heat protection product may consequently be output to the user. In some implementations, the styler 101 may comprise a reservoir for storing wet product and a distribution mechanism for applying the product to the hair, such as a spray or roller etc. The controller 228 of the styler may be configured to apply the product to the hair in dependence on instructions determined in dependence on the analysis of data from the styler 101 , for example in dependence on the determined metrics and scores, and / or determined ambient conditions. It may further be configured to apply the product to the hair in dependence on instructions and / or preferences input by the user to the styler 101 and / or the smart processing device 3010.

[0425] Furthermore, in some implementations, the app is configured to be connectable to social media and / or a community platform and / or webpage, to enable users to interact with one another remotely via their own individual smart processing devices, for example sharing tips and photos. This connection is typically implemented via an internet connection. The community platform and / or webpage may form a networking platform within the app itself. Social media and / or the community page typical comprise capability to enable a user to upload ‘style recipes’, which can then be saved by other users to their own profiles, so that they can then also follow them.

[0426] In some implementations, the styler 101 communicates with the smart processing device 3010 to open the app or output a prompt (such as a push notification) upon connection to the styler 101 . Some smart devices may have security measures that prevent external devices from opening apps automatically; in which case, a prompt can be output to open the app. Other smart devices may be configured such that the styler 101 can directly open the app (this may be in the ‘background’). The styler 101 is typically configured such that it can communicate the relevant instructions to a connected smart processing device 3010. The communication between the styler 101 and the app on the smart processing device 3010 is configured to enhance the ease of use. For example, the app can indicate whether the styler 101 is turned on or off. Additionally, when the smart processing device 3010 goes out of a predefined range of the styler 101 , the styler 101 can be configured to turn off automatically. The app can indicate when the styler 101 was last turned off, for example via a relevant tab within the app (for example, an “is my styler off?” tab). Typically, the smart processing device 3010 may be a user’s mobile phone and / or smart watch, and it can provide the user with peace of mind that the styler 101 automatically turns off when the smart processing device 3010 goes out of range (for example, the user has left their house with the smart processing device 3010) and that they can check when the styler 101 was last turned off. Typically, if the smart processing device 3010 is out of the predefined range of the styler 101 , the styler 101 can still be operated as normal; for example, it can be switched on, used, and switched off as normal (so that the phone does not have to be within the defined range of the styler 101 in order for the styler 101 to be used). Modifications and alternatives

[0427] Detailed embodiments and some possible alternatives have been described above. As those skilled in the art will appreciate, a number of modifications and further alternatives can be made to the above embodiments whilst still benefiting from the inventions embodied therein. It will therefore be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the scope of the claims appended hereto.

[0428] The invention has been described above by way of implementation in a hair styling device for straightening hair (‘hair straighteners’) which employ flat hair styling heaters 106, 206. However, it could alternatively be implemented in any form of hair styling device, such as (but not limited to) crimpers, curlers or heated brushes. The heaters 106, 206 may define a heating surface that is flat, curved, ridged or in the shape of a barrel. The hair styling device may have two arms like the device illustrated in Figure 1 or it may be a single armed device. The heaters described above may also be used in hair dryers or in combination devices (so-called wet to dry stylers and the like) that use conductive heating and air to dry and style the user’s hair (such as those described in the applicant’s earlier PCT application WO 2021 / 019239). In embodiments where air is used, the heaters 106, 206 may be perforated so that air passes through the heater and is warmed by the heater as the air passes through.

[0429] In the above embodiments, Metal Oxide Semiconductor Field Effect Transistor (MOSFET) switches were used to control powering and sensing of the heater electrodes. As those skilled in the art will appreciate, other switches could be used instead. For example, Field Effect Transistors (FETs) could be used, such as Gallium Nitride FETs or bipolar junction transistors (BJTs).

[0430] In the above embodiments, a DC power source was used to provide electrical power for heating the heater electrodes 364, 1164, 1264. This DC power source will typically be one or more batteries, although DC supplies that derive their power from a mains power AC signal may be used. Thicker or more dielectric layers are typically used between the heater electrodes 364, 1164, 1264 and the hair contacting surface of the hair styler when AC power is used to heat the heaters.

[0431] In the above-described examples the hair styling device 101 may comprise a single heater 106, 206, or may alternatively comprise two or more heaters 106, 206. Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example “comprising” and “containing”, means “including but not limited to”, and is not intended to (and does not) exclude other components, integers or steps.

[0432] The expressions “to dry hair”, “drying hair” or “decrease a moisture level of hair” and the like, as used in the present disclosure, can refer both to the removal of “unbound” water that exists on the outside of hair when wet, or the removal of “bound” water, which exists inside individual hairs, and which can be interacted with when heat styling hair. The “bound” water need not necessarily be removed when drying hair, although removal of some bound water may occur during a drying or styling process.

[0433] In addition to or alternatively to the above-described methodologies for determining a value for the hair heat transfer coefficient, h, and so the damage metric, d, based on user inputs, the styler 1 may be configured to use measurements during styling to calculate values for these parameters directly rather than relying on such user inputs. As a general methodology, this may comprise the steps of:

[0434] 1) At some time ti, the styler 101 determines the temperature of the hair tress;

[0435] 2) The styler determines which heating zones 467, 867 are providing heat to the hair at time ti by detecting which heating zones 467, 867 dropped in temperature when hair was loaded in the styler 101 ;

[0436] 3) The styler monitors the electrical power delivered to the heaters at time ti;

[0437] 4) Assuming that the electrical power delivered to the heaters 106, 206 approximately equals the thermal power delivered to the hair, the styler 101 determines a value for the hair heat transfer coefficient, h, by dividing the thermal power delivered at time ti by the area of the heating zones that are delivering heat to the hair and by the difference between the measured hair temperature and the temperature of the heater(s) 106, 206 at time ti;

[0438] 5) The styler then uses this determined value of the hair heat transfer coefficient, h, to determine a value for the hair damage, d, using the stored calibration data (for example, as shown graphically in Figure 14);

[0439] 6) The hair damage information is then output to the user and / or used to control an operating parameter of the styler (such as the operating temperature of the heaters 106, 206).

[0440] According to this example, the heat transfer coefficient, h, can be calculated by the processor 229 by dividing the heat flux, q, by the temperature difference between the heater 106, 206 and the tress of hair, ATnt, according to:

[0441] Based on the determined hair heat transfer coefficient, the processor 229 is then configured to determine a more accurate heat transfer coefficient, h, of the hair, which can be used to determine a more accurate value of the damage metric, d, using the stored calibration data (such as that displayed graphically in Figure 14). In some implementations, the styler 101 may be configured to define the damage parameter with respect to heat capacity and / or specific heat capacity of the hair. In such an implementation, the same methodology as previously described, using user input data, can be performed, but using calibration data relating the damage metric, d, to the heat capacity, C, and / or specific heat capacity, c. Again, this may be a linear or non-linear relationship, and the calibration data may comprise look-up reference tables and / or equations.

[0442] If the heaters 106, 206 are in contact with the hair, the expected change in hair temperature, AThair, from the power input can be determined from:

[0443] Where P is the power delivered over a time interval, At, and AThair is the temperature difference over this time interval of the tress of hair, which has a mass mhair. This equation can then be used by the controller 228 to determine an estimated change in temperature, AThair, of the hair tress within interval At. This is based on an estimated value of the specific heat capacity, c, determined from calibration data relating specific heat capacity to the value of damage metric, d, based on user input.

[0444] Once the heaters 106, 206 are applied to the hair, temperature measurements can be used to determine the actual temperature difference of the hair, ATdet, from two temperature measurements made by the temperature measurement circuitry 225 at the interval At. When making these calculations, the controller 228 may use a predefined average value for the mass of the tress of hair, n . The chosen predefined value may be dependent on user input, for example, dependent on the type of hair a user has indicated that they have or it may be a factory set value for a typical tress size.

[0445] The controller 228 then compares the estimated value of AThair to the actual determined temperature change, ATdet and if the difference is greater than a threshold, then the controller 228 can determine a more accurate value for the specific heat capacity, c, using the equation as above. This can then be used to determine a more accurate value of the damage metric, d, using calibration data relating the specific heat capacity, c, and the damage metric, d.

[0446] Alternatively, in some implementations, the styler 101 may skip the estimation steps and simply determine a value for the specific heat capacity using the equation above and measured values for the temperature difference of the hair, AThair, and power measurements, P, and estimated tress mass, mhair.

[0447] In some implementations, the controller 228 may be configured to determine the heat capacity, C, of the tress of hair (in addition to or alternatively to the specific heat capacity, c), according to:

[0448] P ■ At C=NF ha~ir

[0449] This avoids the need to use an estimate of the tress mass, mhair, but effectively makes the assumption that all tresses will have a similar mass. This may be used as a reasonable approximation for other tresses of the same user’s hair, based on an assumption that the tresses are likely to be of a similar size (and so similar mass).

[0450] As described for the specific heat capacity, c, the heat capacity, C, may be used in a methodology based on estimation and then altering of damage metric, d, in dependence on measured values and / or it may simply be used to determine a damage metric value, d, directly.

[0451] In general, the styler 101 is configured to determine (and / or determine a metric indicative of) the manner in which hair absorbs heat from a heater. It is then typically configured to define and / or determine an associated damage parameter or metric. This is based on the principal that more damaged hair absorbs more heat (reaches a higher temperature for a particular heating profile). Different methodologies can be used to provide an indication of how hair responds to heat applied to it, for example including determination and / or estimation of: heat transfer coefficient, heat capacity, and / or specific heat capacity.

[0452] In some implementations, the controller and / or processors may define the values of the constants used in determination of the ‘scores’ (i.e. constants A to H) in dependence on information input by the user and / or determined by components of the styler. For example, this may relate to hair type and / or original hair condition.

[0453] Various other modifications will be apparent to those skilled in the art and will not be described in further detail here. Each feature disclosed in the description, and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination.

[0454] Reference numerals appearing in the claims are by way of illustration only and shall have no limiting effect on the scope of the claims.

[0455] No doubt many other effective alternatives will occur to the skilled person. It will be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the scope of the claims appended hereto. Throughout the description and claims of this specification, the words “comprise” and "contain" and variations of the words, for example "comprising" and "containing", means "including but not limited to”, and is not intended to (and does not) exclude other components, integers or steps.

[0456] Various examples have been described above. The following numbered clauses summarise one or more aspects of some of those examples:

[0457] Aspect 1

[0458] 1 . A hair drying and / or styling apparatus comprising: one or more sensors for providing sensor data indicative of at least one selected from the group consisting of: oil / sebum level of hair and / or scalp; pH level of hair and / or scalp; and scalp temperature; and means for analysing the sensor data to perform an assessment of scalp health. 2. The apparatus of clause 1 , further comprising means for outputting scalp health information in dependent on the assessment of scalp health, and preferably for outputting information comprising suggestions for improving scalp health; preferably wherein the means for outputting comprises a user interface.

[0459] 3. The apparatus of clause 1 or 2, comprising at least one sensor selected from the group consisting of: sebum sensor; pH sensor; and scalp temperature measurement sensor.

[0460] 4. The apparatus according to any preceding claim, further comprising one or more sensors for providing sensor data indicative of at least one characteristic selected from the group consisting of: blood circulation, scalp colour, hair density, and dandruff.

[0461] 5. The apparatus of clause 4, comprising imaging sensor apparatus for recording one or more images of the scalp.

[0462] 6. The apparatus of clause 5, further comprising means for analysing the one or more images of the scalp, preferably using computer vision techniques.

[0463] 7. The apparatus of clause 5 or 6, further comprising means for analysing one or more images of the scalp to determine a colour profile of the scalp.

[0464] 8. The apparatus of any of clauses 5 to 7, further comprising means for performing Eulerian video magnification techniques on one or more images of the scalp to analyse blood circulation to the scalp.

[0465] 9. The apparatus of any of clauses 5 to 8, further comprising means for analysing one or more images of the scalp to detect hair follicles, and means for determining a hair follicle density of the scalp.

[0466] 10. The apparatus of any of clauses 5 to 9, further comprising means for analysing one or more images of the scalp to detect dandruff.

[0467] 11 . The apparatus of any preceding clause, wherein the means for analysing the sensor data is configured to compare sensor data to predefined value ranges, and preferably further configured to define a scalp health metric.

[0468] 12. The apparatus of any preceding clause, further comprising a database for storing scalp health information to a user profile.

[0469] 13. The apparatus of any preceding clause, comprising at least one hair drying and / or styling device and a smart processing device in communication, preferably further comprising a cloud-based processing unit in communication with the at least one hair drying and / or styling device and / or the smart processing device.

[0470] 14. The apparatus of any preceding clause, further comprising: a heater for heating a tress of hair; drive circuitry for providing power to heat the heater; a controller for controlling the drive circuitry to deliver power; and means for performing a control action in dependence on the scalp health, preferably wherein the control action comprises controlling power and / or temperature settings of the heater.

[0471] 15. A computer program product comprising computer implementable instructions for causing a programmable device to configure one or more processors to implement any of clauses 1 to 14.

[0472] Aspect 2

[0473] 1 . A hair drying and / or styling apparatus comprising: a heater for heating a tress of hair; drive circuitry for providing power to heat the heater; means for detecting movement of hair relative to the apparatus; and means for analysing the movement of hair to determine relative speed of the hair and the apparatus.

[0474] 2. The apparatus of clause 1 , wherein the means for analysing is configured to determine a distance travelled during the movement over a time interval.

[0475] 3. The apparatus of any preceding clause, further comprising means for determining a distance by integrating the speed over a time interval.

[0476] 4. The apparatus of any preceding clause, further comprising means for determining hair length in dependence on a determined distance travelled by the tress of hair relative to the apparatus during a pass.

[0477] 5. The apparatus of clause 4, further comprising sensor circuitry for providing sensor data indicative of motion of the apparatus, and means for correlating the motion of the apparatus to the movement in order to define the pass.

[0478] 6. The apparatus of clause 5, wherein the apparatus comprises at least two arms moveable relative to one another, preferably wherein at least one of the arms comprises the heater, and further comprising means for determining configuration of the arms in dependence on the sensor data indicative of motion.

[0479] 7. The apparatus of any preceding clause, further comprising means for performing a control action in dependence on the determined speed and / or distance, preferably wherein the control parameter comprises controlling power and / or temperature settings of the heater, preferably controlling the setpoint temperature of the heater.

[0480] 8. The apparatus of any preceding clause, further comprising means for outputting alerts and / or suggestions in dependence on the determined speed, distance and / or hair length.

[0481] 9. The apparatus of any preceding clause, wherein the means for detecting movement of hair relative to the apparatus is located on and / or within a heater. 10. The apparatus of any preceding clause, comprising an imaging sensor apparatus configured to record a first image at a first time and a second image at a second time.

[0482] 11. The apparatus of clause 10, further comprising: means configured to detect a feature common to the first image and the second image, and to determine the vector between the location of the feature in the first image and the location of the vector in the second image, preferably wherein a real dimension is determined by multiplying a pixel dimension by a known constant; and wherein the means for analysing is configured to determine speed in dependence on the vector and the time interval between the first time and the second time.

[0483] 12. The apparatus of clause 10 or 11 , wherein the imaging sensor apparatus is configured to perform darkfield imaging.

[0484] 13. The apparatus of any of clauses 10 to 12, wherein the imaging sensor apparatus comprises a CMOS sensor.

[0485] 14. The apparatus of any preceding clause, comprising an odometer.

[0486] 15. The apparatus of clause 14, comprising a roller configured to contact hair during styling and rotate as the hair and apparatus move past one another, and further comprising means for measuring rotation of the roller, wherein the means for analysing is configured to determine speed in dependence on the rotation of the roller over a time interval.

[0487] 16. The apparatus of clause 15, wherein the means for measuring rotation of the roller comprises a detector, and preferably comprises one or more optical encoders.

[0488] 17. The apparatus of clause 15 or 16, wherein the roller is cylindrical and configured to rotate around an axis.

[0489] 18. The apparatus of clause 17, wherein the axis comprises a heating element.

[0490] 19. The apparatus of clause 15 or 16, wherein the roller is spherical and is configured to rotate about more than one axis within a socket.

[0491] 20. The apparatus of any of clauses 15 to 19, wherein the roller is in thermal connection with a heating element, preferably wherein the roller is configured to be heated via convention, radiation and / or conduction.

[0492] 21. The apparatus of any preceding clause, wherein the heater comprises at least one independently controllable heater zone of known width, and the apparatus further comprises: sensor circuitry for providing sensor data indicative of at least one selected from the group consisting of: power delivered to the heater zone; the temperature of the tress of hair being dried and / or styled; and the temperature of the heater zone; means for determining the temperature difference of the tress of hair as it enters the heater zone and as it leaves the heater zone; and means for determining the speed of the hair in dependence on the temperature difference, the power delivered to the heater zone and the known width of the heater zone.

[0493] 22. The apparatus of clause 21 , comprising: a first heater zone and a second heater zone immediately adjacent to the first heater zone, wherein the heater zones are arranged such that the tress of hair enters the first heater zone before the second heater zone; and means for determining the temperature of a tress of hair as it enters each heater zone in dependence on the sensor data of the same heater zone; and wherein the means for determining speed is configured to compare the temperature of the hair as it enters a first heater zone and the temperature of hair as it enters a second heater zone, and is further configured to determine speed in dependence on the temperature difference, the power delivered to the first heater zone and the known width of the first heater zone.

[0494] 23. The apparatus of clause 21 or 22, further comprising means for determining a heat capacity of the hair in dependence on the sensor data provided by the sensor circuitry.

[0495] 24. The apparatus of any preceding clause, comprising at least one hair drying and / or styling device and a smart processing device in communication, preferably further comprising a cloud-based processing unit in communication with the at least one hair drying and / or styling device and / or the smart processing device.

[0496] 25. A method of determining relative speed of a tress of hair and a hair drying and / or styling apparatus, comprising: detecting movement of the tress of hair relative to the apparatus during styling; tracking a characteristic of the tress of hair over a time interval; and determining speed of the tress of hair relative to the apparatus in dependence on measured changes to the characteristic over the time interval.

[0497] 26. The method of clause 25, further comprising determining a distance by integrating the determined speed over a time interval.

[0498] 27. The method of clause 25 or 26, further comprising determining a hair length in dependence on a determined distance travelled by the tress of hair relative to the apparatus during a pass.

[0499] 28. The method of clause 27, further comprising detecting a pass of the apparatus by determining the motion of the apparatus in dependence on sensor data indicative of motion of the apparatus, and correlating the motion of the apparatus and the detected movement of the tress of hair relative to the apparatus.

[0500] 29. The method of clause 28, wherein the correlating comprises determining the configuration of two arms of the apparatus in dependence on the sensor data indicative of motion of the apparatus. 30. The method of any of clauses 25 to 29, further comprising performing a control action in dependence on the determined speed and / or distance, preferably wherein the control parameter comprises controlling power and / or temperature settings of the heater, preferably controlling the setpoint temperature of the heater.

[0501] 31. The method of any of clauses 25 to 30, further comprising outputting alerts and / or suggestions in dependence on the determined speed, distance and / or hair length.

[0502] 32. The method of any of clauses 25 to 31 , wherein the determining speed comprises: recording a first image of the tress of hair at a first time and a second image of a tress of hair at a second time; detecting a feature common to the first image and the second image; determining the vector between the location of the feature in the first image and the location of the vector in the second image; preferably, multiplying the vector by a known constant to convert a pixel dimension vector to a real dimension vector; and determining speed in dependence on the vector and the time interval between the first time and the second time.

[0503] 33. The method of clause 32, wherein the recording the first image and the second image utilises darkfield imaging.

[0504] 34. The method of any of clauses 25 to 33, further comprising detecting rotation of a roller configured to make contact with the tress of hair and rotate in dependence on the relative movement of the tress of hair and the apparatus, and wherein the determining speed comprises determining speed in dependence on rotation of the roller over a time interval.

[0505] 35. The method of any of clauses 25 to 34, further comprising: receiving sensor data indicative of at least one selected from the group consisting of: power delivered to the heater zone; the temperature of the tress of hair being dried and / or styled; and the temperature of the heater zone; processing the sensor data to determine the power delivered to a heater zone of known width as the tress of hair passes over the heater zone; processing the sensor data to determine the temperature difference of the tress of hair as it enters the heater zone and as it leaves the heater zone; and wherein the determining speed comprises determining speed in dependence on the temperature difference, the power delivered to the heater zone and the known width of the heater zone.

[0506] 36. The method of clause 35, further comprising: receiving sensor data for a first zone and a second zone, wherein the tress of hair passes the first zone before the second zone, and wherein the first heater zone is immediately adjacent to the second heater zone; determining the temperature of the hair as it enters the first heater zone and the temperature of hair as it enters the second heater zone, and determining the temperature difference.

[0507] 37. The method of clause 35 or 36, further comprising: determining a heat capacity of the hair in dependence on the sensor data provided by the sensor circuitry.

[0508] 38. A computer program product comprising computer implementable instructions for causing a programmable device to configure one or more processors to implement any of clauses 1 to 37.

[0509] Aspect 3

[0510] 1 . A hair drying and / or styling apparatus comprising: a heater for heating a tress of hair; drive circuitry for providing power to heat the heater; a controller for controlling the drive circuitry to deliver power; means for receiving ambient condition data relating to at least one selected from the group consisting of: temperature, humidity, and / or air pressure; means for receiving user preferences; and means for performing a control action in dependence on the ambient condition data in combination with the user preferences.

[0511] 2. The apparatus of clause 1 , wherein the control action comprises controlling power and / or temperature settings of the heater, preferably controlling the setpoint temperature of the heater.

[0512] 3. The apparatus of clause 1 or 2, wherein a set of rules correlating the ambient condition data and the control actions is elected in dependence on the user preferences.

[0513] 4. The apparatus of any preceding clause, comprising means for implementing fuzzy logic architecture to process the ambient condition data and user preferences and to determine the control action.

[0514] 5. The apparatus of any preceding clause, wherein the user preferences comprise priorities, preferably wherein the priorities comprise one or more of: hair health, speed of styling, and longevity of style.

[0515] 6. The apparatus of any preceding clause, further comprising means for receiving relevant location data, preferably wherein the relevant location data comprises geographic location data and / or interior or exterior data.

[0516] 7. The apparatus of clause 6, wherein relevant ambient condition data is determined in dependence on the relevant location data. 8. The apparatus of any preceding clause, wherein the means for receiving ambient condition data is configured to receive meteorological and / or weather data.

[0517] 9. The apparatus of clause 8, further comprising means for determining geographical location, preferably comprising location tracking and / or identification of a location address of an internet connection.

[0518] 10. The apparatus of any preceding clause, further comprising a user interface configured for facilitating input of user preferences.

[0519] 11 . The apparatus of any preceding clause, comprising one or more of: a hygrometer, a barometer, and a thermometer.

[0520] 12. The apparatus of any preceding clause, comprising at least one hair drying and / or styling device and a smart processing device in communication, preferably further comprising a cloud-based processing unit in communication with the at least one hair drying and / or styling device and / or the smart processing device.

[0521] 13. A method of controlling a hair drying and / or styling apparatus, the method comprising: receiving ambient condition data relating to at least one selected from the group consisting of: temperature, humidity, and / or air pressure; receiving user preferences; and processing the ambient condition data in combination with the user preferences to determine a control action.

[0522] 14. The method of clause 13, comprising electing a set of rules correlating the ambient condition data and the control actions in dependence on the user preferences.

[0523] 15. The method of clause 13 or 14, wherein the processing comprises processing using fuzzy logic.

[0524] 16. The method of any of clauses 13 to 15, wherein the user preferences comprise priorities, preferably wherein the priorities comprise one or more of: hair health, speed of styling, and longevity of style.

[0525] 17. The method of any of clauses 13 to 16, further comprising: performing a control action in dependence on the ambient condition data in combination with the user preferences.

[0526] 18. The method of any of clauses 13 to 17, wherein the control action comprises controlling power and / or temperature settings of the heater, preferably controlling the setpoint temperature of the heater.

[0527] 19. The method of any of clauses 13 to 18, further comprising receiving relevant location data, preferably wherein the relevant location data comprises geographic location data and / or interior or exterior data.

[0528] 20. The method of clause 19, further comprising: determining relevant ambient condition data in dependence on the relevant location data. 21. The method of any of clauses 13 to 20, wherein the ambient condition data comprises meteorological and / or weather data.

[0529] 22. The method of any of clauses 13 to 21 , further comprising determining the geographical location of the apparatus, preferably in dependence on a location tracker and / or internet connection. 23. The method of any of clauses 13 to 22, wherein the user preferences comprise one or more of: hair health, speed of styling, and longevity of style.

[0530] 24. A computer program product comprising computer implementable instructions for causing a programmable device to configure one or more processors to implement any of clauses 1 to 23.

Claims

Claims1 . A hair drying and / or styling apparatus comprising: a heater for heating a tress of hair; drive circuitry for providing power to heat the heater; sensor circuitry for providing sensor data indicative of at least one selected from the group consisting of: power delivered to the heater; the temperature of the tress of hair being dried and / or styled; and the temperature of the heater; and a controller for controlling the drive circuitry to deliver power to the heater in dependence upon sensor data provided by said sensor circuitry; means for determining at least one hair health metric in dependence upon sensor data provided by the sensor circuitry; and means for performing a control action in dependence on the determined at least one hair health metric.

2. The apparatus of claim 1 , wherein the control action comprises controlling power and / or temperature settings of the heater, preferably controlling the setpoint temperature of the heater.

3. The apparatus of claim 1 or 2, wherein the control action comprises outputting an alert, preferably wherein the alert comprises at least one selected from a group consisting of: a visual output; an audio output; a haptic output; verbal instructions; and a combination thereof.

4. The apparatus of any preceding claim, comprising means for: i) determining a heat transfer coefficient between the heater and the tress of hair in dependence upon sensor data provided by the sensor circuitry; ii) determining at least one hair health metric from the determined heat transfer coefficient; and iii) performing a control action in dependence on the determined at least one hair health metric.

5. The apparatus of claim 4, wherein the means for determining at least one hair health metric from the determined heat transfer coefficient is configured to retrieve prestored calibration data relating heat transfer coefficient to hair health metric, and to use the retrieved calibration data to determine the at least one hair health metric from the determined heat transfer coefficient.

6. The apparatus of any preceding claim, comprising means for: i) determining a heat capacity of the tress of hair in dependence upon sensor data provided by the sensor circuitry; ii) determining at least one hair health metric from the determined heat capacity; and iii) performing a control action in dependence on the determined at least one hair health metric.

7. The apparatus of claim 6, wherein the means for determining at least one hair health metric from the determined heat capacity is configured to retrieve prestored calibration data relating heat capacity to hair health metric, and to use the retrieved calibration data to determine the at least one hair health metric from the determined heat capacity.

8. The apparatus of any preceding claim, wherein the controller is configured initially to control the drive circuitry to deliver power to the heater in dependence on at least one of: data input by a user; and a predetermined initial value.

9. The apparatus of claim 8, comprising means for estimating a hair health metric in dependence on the data input by a user.

10. The apparatus of claim 9, comprising means for estimating a heating response of the tress of hair in dependence on the estimated hair health metric, and means for comparing the estimated heating response to a detected heating response detected from sensor data, and preferably wherein the controller is configured to control the drive circuitry to deliver power to the heater in dependence on the comparison of estimated heating response and detected heating response.11 . The apparatus of claim 9 or 10 when dependent on any of claims 4 to 7, comprising means for comparing the estimated hair health metric and the determined hair health metric, and wherein the performing a control action comprises controlling the drive circuitry to deliver power to the heater in dependence on a difference between the estimated hair health metric and the determined hair health metric.

12. The apparatus of any preceding claim, wherein the heater comprises a plurality of heating zones and the sensor circuitry is configured to provide sensor data for the plurality of heating zones, and further comprising means for determining which heating zones are in contact with the tress of hair in dependence upon the sensor data.

13. The apparatus of any preceding claim, further comprising means for determining at least one score based on the at least one hair health metric, wherein the at least one score relates to use of the appliance and / or hair health, and preferably further comprising means for determining an overall score using a weighted combination of scores.

14. The apparatus of any preceding claim, further comprising a user interface configured for outputting an alert, and preferably configured for facilitating input of information.

15. The apparatus of any preceding claim, comprising means for storing to a user profile the at least one hair health metric and / or the at least one score for each styling session of a user, preferably wherein the means for performing a control action in dependence on the determined at least one hair health metric is further configured to perform a control action in dependence on the at least one hair health metric over time.

16. The apparatus of any preceding claim, comprising means for processing the sensor data to identify heating of a tress of hair in dependence on power delivered to the heater.

17. The apparatus of claim 16, wherein the means for processing the sensor data is further configured to determine maximum hair temperature for each tress of hair by determining a difference between a maximum and minimum power delivered to the heater, and preferably further using a mean value of power delivered to the heater.

18. The apparatus of any preceding claim, comprising means for determining a maximum hair temperature for each tress of hair from sensor data indicative of the temperature of the tress of hair being dried and / or styled.

19. The apparatus of claim 17 or 18, comprising means for determining an average maximum hair temperature in dependence on a mean value of determined maximum hair temperatures for each tress.

20. The apparatus of any of claims 17 to 19, comprising means for defining new hair damage as a function of maximum hair temperature, preferably average maximum hair temperature.21 . The apparatus of claim 20 when dependent on claim 4, wherein the controller is configured to determine new damage with reference to the hair metric determined from the heat transfer coefficient.

22. The apparatus of any preceding claim, comprising means for processing the sensor data to identify repeated heating of a same tress of hair in dependence on the power delivered to the heater having a damped sinusoidal profile.

23. The apparatus of claim 22, comprising means for determining number and frequency of repeated heating of a same tress of hair by identifying and processing peaks of the damped sinusoidal power profile.

24. The apparatus of claim 22 or 23, comprising means for determining heat on hair time by summing intervals over which the damped sinusoidal power profile has a negative gradient.

25. The apparatus of any preceding claim, further comprising sensor circuitry for providing sensor data indicative of motion of the apparatus.

26. The apparatus of claim 25, comprising at least two arms moveable relative to one another, wherein at least one of the arms comprises the heater, and further comprising means for determining configuration of the arms in dependence on the sensor data indicative of motion.

27. The apparatus of claim 25 or 26, comprising means for determining hair on heat time by summing time intervals over which the arms are determined to be in a configuration indicative of the tress of hair being loaded on the heater, preferably in a closed configuration.

28. The apparatus of claim 27 when dependent on claim 24, comprising means for correlating the time intervals over which the arms are determined to be in a configuration indicative of the tress of hair being loaded on the heater and the intervals over which the damped sinusoidal power profile has a negative gradient.

29. The apparatus of any of claims 25 to 28, comprising means for determining recurrent heating of a tress of hair in dependence on determining, from the sensor data indicative of motion, motion above a threshold speed value coincident with time intervals over which the arms are determined to be in a configuration indicative of the tress of hair being loaded on the heater, preferably in a closed configuration.

30. The apparatus of any of claims 24 to 29, comprising means for comparing heat on hair time with one or more user metrics, preferably wherein the one or more user metrics comprises at least one of: hair length, hair health metric, hair damage metric.31 . The apparatus of any preceding claim, wherein the heater is a multilayer heater comprising a plurality of functional layers that are bonded together, wherein the multilayer heater is mounted within the appliance such that during use of the appliance by a user, hair contacts a hair contacting surface of the multilayer heater and is heated by conductive heating, wherein the multilayer heater includes: a heater electrode layer comprising one or more heater electrodes formed of a conductive material that generates heat when a current is passed through the one or more heater electrodes; and at least one upper dielectric layer over the heater electrode layer to electrically isolate the heater electrode layer; wherein the multilayer heater has a thickness, as measured across all of the plurality of layers of the multilayer heater, which is between 30pm and 2mm; and wherein a combined thermal conductivity of the multilayer heater in a plane perpendicular to the thickness that is less than 15 W / m.K and greater than 0.1 W / m.K.

32. The apparatus of any preceding claim, comprising means for scheduling styling sessions to a calendar, preferably configured to output reminder alerts in dependence on the calendar.

33. The apparatus of any preceding claim, further comprising a database for storing at least one hair health metric to a user profile.

34. The apparatus of claim 33, wherein the database further comprises a database of a plurality of user profiles, and wherein the apparatus comprises means for performing a clustering algorithm to cluster user profiles in dependence on at least one metric, preferably in dependence on at least one metric from: age, hair length, hair type, average styling time, favourite styles, hair colour, phone model, favourite products, location, styling frequency, and usage behaviour.

35. The apparatus of claim 34, comprising means for performing control actions in dependence on analysis of user profiles in a same cluster, preferably wherein the performing control actions comprises outputting suggestions.

36. The apparatus of any preceding claim, comprising at least one hair drying and / or styling device and a smart processing device in communication, preferably further comprising a cloud-based processing unit in communication with the at least one hair drying and / or styling device and / or the smart processing device.

37. The apparatus of claim 36, wherein the hair drying and / or styling device is configured to send instructions to the smart processing device, preferably wherein the instructions comprise instructions to output an alert and / or preferably wherein the instructions comprise instructions to open and / or run an application on the smart processing device.

38. The apparatus of claim 36 or 37, wherein the hair drying and / or styling device is configured to turn off in dependence on the smart processing device moving out of a defined range of the hair drying and / or styling device.

39. The apparatus of any preceding claim, further comprising: one or more sensors for providing scalp health sensor data indicative of at least one selected from the group consisting of: oil / sebum level of hair and / or scalp; pH level of hair and / or scalp; and scalp temperature; and means for analysing the scalp heath sensor data to perform an assessment of scalp health.

40. The apparatus of claim 39, further comprising one or more sensors for providing scalp health sensor data indicative of at least one characteristic selected from the group consisting of: blood circulation, scalp colour, hair density, and dandruff.

41. The apparatus of any preceding claim, further comprising: means for detecting and measuring movement of hair relative to the apparatus; and means for analysing the movement of hair to determine relative speed of the hair and the apparatus.

42. The apparatus of any preceding claim, further comprising: means for receiving ambient condition data relating to: temperature, humidity, and / or air pressure; means for receiving user preferences; and means for performing a control action in dependence on the ambient condition data in combination with the user preferences.

43. A computer program product comprising computer implementable instructions for causing a programmable device to configure one or more processors to implement any of claims 1 to 42.

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