Hair styling apparatus

Abstract

A hair styling apparatus comprises a body 102 having an inlet, an outlet and an airflow generator 104. A drive mechanism 114 is provided to control an orientation of the air outlet of the nozzle 110 relative to the body. A control unit may receive information from sensors 118, 119 which provide position information indicative of the orientation of the outlet relative to a user’s scalp. The sensors may comprise a distance sensor such as a time-of-flight sensor. The drive mechanism may control the orientation of an entire head portion (220, fig. 2A) of the device. The drive mechanism (330, fig. 3B) may be provided in an attachment (300, fig 3B) rather than the body of the device and the outlet (329, fig. 3B) may be repositioned relative to the air inlet. A computer-implemented method of controlling a hair styling apparatus is also described which comprises calculating an offset between the actual orientation of the air outlet relative to a user’s scalp and a predetermined orientation and controlling the drive mechanism 114 to reduce the offset.

Description

B ACKGROUND Various types of hair styling apparatuses for styling hair are known. One example is a hair dryer which typically includes a handle for holding by a user, and an outlet capable of discharging air, which may be heated, onto a user’s hair. The most basic use of a hair dryer involves directing the discharged air onto hair to dry the hair. Hair dryers (and other similar devices) can, however, be used to apply style to a hair through the application of heat. The heat in the discharged air breaks chemical bonds in the hair, which allows the hair to be reshaped (i.e. into a shape / style other than its natural shape / style). To aid in the application of a style using a hair dryer (or similar device), such devices can be modified to alter the airflow discharged therefrom and / or to interact physically with a user’s hair. For example, attachments are known that mount to an outlet of a hair dryer such that hot air discharged by the hair dryer passes through the attachment and onto a user’s hair in a modified manner. SUMMARY In a first aspect of the present invention there is provided a computer-implemented method of controlling a hair styling apparatus, wherein the hair styling apparatus comprises an air outlet and a drive mechanism arranged to control an orientation of the air outlet relative to a main body of the hair styling apparatus; the method comprising receiving position information indicative of an actual orientation of the air outlet relative to a user’s scalp, calculating an offset between the actual orientation of the air outlet and a predetermined orientation, and controlling the drive mechanism to reduce the offset. For example, the drive mechanism may be controlled to minimise or eliminate the offset between the actual orientation of the air outlet relative to the user’s scalp and a predetermined orientation. The extent to which the offset can be reduced or minimised may be limited according to the specific configuration of the drive mechanism and the hair styling apparatus (e.g., the number and position / orientation of the controllable axes of movement of the air outlet). The predetermined orientation may be a desired orientation, for example to achieve a particular hair style or drying effect, or according to an orientation desired by a user. Although the orientation is described as relative to a user’s scalp, it will be appreciated that in some examples (e.g., according to a sensing mechanism or sensing mode) the orientation may be determined relative to a user’s hair. For example, the sensing mechanism may detect any surface (or may not be able to differentiate or discriminate between surfaces), such that substantially any obstacle detected by the sensor would be understood by the system as a user’s scalp. The effectiveness of a hair styling apparatus may be sensitive to the orientation of the air outlet relative to the hair (or a user’s scalp) at which it is being aimed. Some users may struggle to orient the air outlet appropriately, or it may be uncomfortable for a user to do so. Furthermore, the most comfortable orientation to hold the hair styling apparatus relative to the user’s scalp may change frequently throughout a drying or styling routine or even during a single pass of the air outlet over a tress of hair. By controlling a hair styling apparatus according to this method, the drive mechanism may be controlled in order to reduce the offset between the actual orientation of the air outlet and a predetermined orientation, thereby ensuring that the air outlet is maintained at a most effective or desired orientation relative to a user’s scalp. This may make the hair styling apparatus more comfortable to use, and make the hair styling apparatus more effective. For example, the method reduces the required skill and dexterity for the user to get better results using the hair styling apparatus, and enables the user to both hold more comfortable positions during use of the hair dying apparatus and allow them to adjust position whilst maintaining airflow direction, thereby reducing user fatigue, allowing for longer styling routines and an overall improvement in comfort. The method may also reduce the drying time for areas of hair that are hard for a user to reach manually by better directing airflow from the air outlet. The drive mechanism may include a motor (e.g., a stepper motor, a DC motor, a servo motor or the like). In some examples, the drive mechanism may include position feedback, which may be integrated positional feedback from a motor or may be feedback from a separate sensor. For example, the drive mechanism may comprise a stepper motor and an encoder. In another example, a distance sensor of the hair styling apparatus may be used to derive position feedback for the drive mechanism. For example, a DC motor may be provided and a voltage provided to the motor may be a function of angular offset. This may provide a form of open-loop control. In another example, the drive mechanism may be a servo mechanism, and the driving signal is an angle (e.g., as a pulse width modulation signal). This may provide a form of closed-loop control. Optionally, receiving position information may include receiving distance data from a sensor of the hair styling apparatus, the distance data indicating a distance between the sensor and the user’s scalp. For example, the sensor may include a time of flight (ToF) sensor, inductive sensor, ultrasonic sensor etc. A ToF sensor may include a light emitter (e.g. a laser or a LED) and a receiver (e.g. a photodetector). The ToF sensor may be configured to emit a light signal with the light emitter, and to detect a reflected light signal that is reflected back from the user’s scalp. The light (i.e. electromagnetic radiation) emitted by the light emitter may be visible, infrared, ultraviolet, radiofrequency, microwave, or any other suitable type of electromagnetic radiation. The sensor may be part of a sensor arrangement which comprises a plurality of sensors (e.g., two or more sensors, such as three sensors). For example, the plurality of sensors may each comprise a single sensor type (sensing modality) or a mixture of different sensor types or sensing modalities. For example, the plurality of distance sensors may be spaced equidistantly from one another. In this way, position data may be obtained by the hair styling apparatus itself such that the method does not require additional apparatus. By providing a plurality of sensors, the position data obtained by each sensor can be combined in order to calculate a plane in which the sensors lie, and a plane in which the respective locations of the user’s scalp lie. These planes can be used to calculate the actual orientation of the air outlet for comparison with the predetermined orientation. In some examples, receiving position information may further include receiving orientation information of the main body of the hair styling apparatus. For example, this may include receiving inertial measurements, accelerometer data or the like from sensors within the hair styling apparatus, which may be used to derive the orientation of the main body. Such information may be used, for example, to help identify anomalous data in the position information which indicates the orientation of the air outlet relative to the user’s scalp (e.g., identifying anomalies in distance data). The information may also be used to indicate the position of the air outlet, for example in combination with known information regarding the position of the air outlet relative to the main body. Such an orientation sensor may be implemented using one or more of an accelerometer, a gyroscope, a magnetometer, and / or a tilt switch, for example. Optionally, the predetermined orientation may be a time-varying function. That is, the predetermined orientation may change over time. For example, the time-varying function may be configured such that controlling the drive mechanism comprises oscillating the air outlet. For example, oscillating the air outlet may comprise oscillating the air outlet about a fixed orientation (that is, a given, or preset orientation) or a fixed axis (that is, a given, or preset, axis). It will be appreciated that in other examples, the predetermined orientation may be static or fixed with time. For example, the predetermined orientation may be defined relative to a normal vector of the user’s scalp, such as a fixed offset or zero offset. Optionally, calculating an offset between the orientation of the air outlet and the predetermined orientation may comprise calculating an angle between a surface normal vector of the user’s scalp and a device normal vector, the angle lying in a plane corresponding to a plane in which the drive mechanism may move the air outlet (that is, a plane of motion provided by the drive mechanism). The drive mechanism may provide control in at least one such plane, for example two or three planes. Calculating the offset in this way may therefore include calculating multiple angles, with each angle corresponding to a respective plane in which the air outlet may be moved. Optionally, calculating an offset between the actual orientation and the predetermined orientation may comprise applying a filter, such as a noise filter, to the position information. The position information may be received as a stream of data (for example, as the data is acquired in real time as the hair styling apparatus is in use). Performing filtering on this data may smooth out the data, reducing the load on the drive mechanism. In examples, a filter may be applied to the position information, or to a signal sent to a drive mechanism in order to change how the device behaves - in particular providing smoother and less ‘jerky’ movement. In another example, similar control may be achieved using PID control that takes position information and outputs a control signal for the drive mechanism that takes into account the position information, and the rate of change of the position or orientation information etc. In a second aspect of the present invention there is provided a hair styling apparatus comprising a main body having a gripping portion to be held by a user; an air inlet; an air outlet; an airflow generator configured to generate a flow of air between the air inlet and the air outlet; and a drive mechanism arranged to control an orientation of the air outlet relative to the main body. The hair styling apparatus may further include a control unit configured to perform a method according to the first aspect of the present invention, as described above. Optionally, the hair styling apparatus may further comprise a sensor configured to output position information indicative of the orientation of the air outlet relative to a user’s scalp. In this way, position data may be obtained by the hair-drying apparatus itself, such that no additional apparatus is required. For example, the sensor may be a distance sensor configured to determine the distance between the sensor and the user’s scalp, such as a time of flight (ToF) sensor. The distance between the sensor and the user’s scalp may then be used to infer the orientation of the air outlet relative to a user’s scalp as described herein. In particular, the distance sensor may measure the distance between the distance sensor and a respective location on the user’s scalp. In some examples, the distance sensor may be one of a plurality of distance sensors (e.g., two or more sensors, such as three sensors), wherein the sensing axes of the plurality of distance sensors are not parallel to one another. For example, the sensing axes of the plurality of distance sensors may be divergent from one another, or may be convergent with one another. For example, the sensing axis of each distance sensor may be the axis (e.g., the main axis or the principal axis) along which the distance sensor measures or detects the distance between the sensor and the user’s scalp. For example, the plurality of distance sensors may be spaced equidistantly from one another. The line of sight of a TOF sensor may be considered as the sensing axis of the TOF sensor, for example. Arranging the sensing axes of the sensors to diverge may improve the accuracy of the plurality of distance sensors by reducing the error sensitivity of the sensor arrangement to distance from the scalp. That is, even for large distances the sensor arrangement configured in this way may accurately determine the distances between the sensors and the scalp. In other examples, the sensing axes of the plurality of distance sensors may converge slightly, which may improve detection of the local gradient of the scalp, particularly as the distances between the sensors and the scalp increases. By providing a plurality of sensors, the position data obtained by each sensor can be combined in order to calculate a plane in which the sensors lie, and a plane in which the respective locations of the user’s scalp lie. These planes can be used to calculate the actual orientation of the air outlet for comparison with the predetermined orientation. Optionally, the main body may comprise a handle portion which comprises the gripping portion to be held by a user; and a head portion which comprises the air outlet, wherein the drive mechanism is arranged to control an orientation of the head portion relative to the handle portion. The mechanism for adjusting the orientation of the air outlet may thereby be incorporated into the main body of the hair styling apparatus. The main body may comprise a connecting portion for removably connecting an attachment for the hair styling apparatus, such that the benefits of the present invention may be achieved with any attachment (as the attachment does not require any additional mechanism for suitability with the drive mechanism). Each attachment may have an associated predetermined orientation which is suitable for that attachment, for example. Optionally, the hair styling apparatus may further comprise an attachment which is removably connectable to the main body, the attachment comprising the air outlet and the drive mechanism. For example, the attachment may be an attachment which is configured to receive and modify airflow from the hair styling apparatus. Such an attachment may include, but may not be limited to, a comb, a diffuser, an airflow concentrator or the like. The mechanism for adjusting the orientation of the air outlet may thereby be incorporated into an attachment for the hair styling apparatus. The attachment may have a connecting portion for removably connecting to the main body of the hair styling apparatus (wherein the main body may have a corresponding connecting portion for receiving the attachment). The connecting portion may comprise electrical connectors for supplying power and / or a communications link between the main body to the attachment (e.g., to deliver power to the drive mechanism). The drive mechanism may be arranged to control the orientation of the air outlet relative to the connecting portion. Optionally, the drive mechanism may form part of a first attachment, wherein the first attachment may have a first connector for removably connecting to the main body and a second connector for removably connecting to a second attachment comprising the air outlet, and wherein the drive mechanism is configured to control the orientation of the second connector relative to the first connector. The first attachment may thus serve as an intermediate portion between the main body and the second attachment. The mechanism for adjusting the orientation of the air outlet may thereby be separate from both the main body and the second attachment, such that the benefits of the present invention may be achieved with any second attachment (as the second attachment does not require any additional mechanism for suitability with the drive mechanism). Each second attachment may have an associated predetermined orientation which is suitable for that attachment, for example. The or each connector may further comprise electrical connectors for supplying power and / or a communications link between the first attachment (intermediate portion) and the second attachment (e.g., to deliver power to the drive mechanism). Optionally, the drive mechanism may comprise a two-axis gimbal configuration, each axis being controlled by a respective servo motor. That is, the drive mechanism may have two controllable axes. For example, the two axes may be perpendicular to one another. In other embodiments, the drive mechanism may have any other suitable number of controllable axes, such as one, three or four. However, two controllable axes may provide substantial benefits of the invention without unduly increasing the weight, or increasing the power consumption, of the hair styling apparatus. The drive mechanism may include a motor (e.g., a stepper motor, a DC motor, a servo motor or the like). In some examples, the drive mechanism may include position feedback, which may be integrated positional feedback from a motor or may be feedback from a separate sensor. For example, the drive mechanism may comprise a stepper motor and an encoder. In another example, a distance sensor of the hair styling apparatus may be used to derive position feedback for the drive mechanism. For example, a DC motor may be provided and a voltage provided to the motor may be a function of angular offset. This may provide a form of open-loop control. In another example, the drive mechanism may be a servo mechanism, and the driving signal is an angle (e.g., as a pulse width modulation signal). This may provide a form of closed-loop control. According to a third aspect of the present invention, there is provided an attachment for a hair styling apparatus. The attachment comprises a first connector for removably connecting to a main body of the hair styling apparatus; an air inlet for receiving an airflow from the hair styling apparatus; an air outlet; and a drive mechanism arranged to control an orientation of the air outlet relative to the air inlet. For example, the attachment may be an intermediate portion generally as described herein, or may be another attachment, such as an attachment which is configured to receive and to modify airflow (for example including, but not limited to, a comb, a diffuser, an airflow concentrator or the like). The mechanism for adjusting the orientation of the air outlet may thereby be incorporated into an attachment for the hair styling apparatus. The connector may further comprise electrical connectors for supplying power and / or a communications link between the main body of the hair styling apparatus and the attachment (e.g., to deliver power to the drive mechanism). Optionally, the attachment may further comprise a control unit configured to perform the method of the first aspect of the present invention. In other examples, the main body of the hair styling apparatus may comprise such a control unit, and may be configured to send control instructions to the drive mechanism of the attachment. Optionally, the attachment may further comprise a second connector for removably connecting to a second attachment, wherein the second attachment is configured to receive and to modify airflow from the attachment. For example, the attachment may be an intermediate portion as described herein, and the second attachment may comprise a comb, a diffuser, an airflow concentrator or the like for directing airflow towards a user’s scalp in use. Optionally, a hair styling device may comprise the attachment of the third aspect of the present invention and the hair styling apparatus of the second aspect of the present invention, wherein the first connector of the attachment may be removably connectable with the main body of the hair styling apparatus, and wherein the orientation of the air outlet of the attachment may be controlled by one or both of the drive mechanisms of the attachment and the hair styling apparatus. The drive mechanism of the attachment may control this orientation at a finer degree than the drive mechanism of the hair styling apparatus. Optionally, the attachment may further comprise a sensor configured to output position information indicative of the orientation of the air outlet relative to a user’s scalp. In this way, position data may be obtained by the attachment itself, such that no additional apparatus is required. For example, the sensor may be a distance sensor configured to determine the distance between the sensor and the user’s scalp, such as a time of flight (ToF) sensor. The distance between the sensor and the user’s scalp may then be used to infer the orientation of the air outlet relative to a user’s scalp as described herein. In particular, the distance sensor may measure the distance between the distance sensor and a respective location on the user’s scalp. In some examples, the distance sensor may be one of a plurality of distance sensors (e g., two or more sensors, such as three sensors), wherein the sensing axes of the plurality of distance sensors are not parallel to one another. For example, the sensing axes of the plurality of distance sensors may be divergent from one another, or may be convergent with one another. For example, the sensing axis of each distance sensor may be the axis (e.g., the main axis or the principal axis) along which the distance sensor measures or detects the distance between the sensor and the user’s scalp. For example, the plurality of distance sensors may be spaced equidistantly from one another. The line of sight of a TOF sensor may be considered as the sensing axis of the TOF sensor, for example. Arranging the sensing axes of the sensors to diverge in this way may improve the accuracy of the plurality of distance sensors by reducing the error sensitivity of the sensor arrangement to distance from the scalp. That is, even for large distances the sensor arrangement configured in this way may accurately determine the distances between the sensors and the scalp. In other examples, the sensing axes of the plurality of distance sensors may converge slightly, which may improve detection of the local gradient of the scalp, particularly as the distances between the sensors and the scalp increases. By providing a plurality of sensors, the position data obtained by each sensor can be combined in order to calculate a plane in which the sensors lie, and a plane in which the respective locations of the user’s scalp lie. These planes can be used to calculate the actual orientation of the air outlet for comparison with the predetermined orientation. According to a fourth aspect of the present invention, there is provided a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of the first aspect of the present invention. According to a fifth aspect of the present invention, there is provided a computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to carry out the method of the first aspect of the present invention. The preceding summary is provided for purposes of summarising some examples to provide a basic understanding of aspects of the subject matter described herein. Accordingly, the above-described features should not be construed to narrow the scope or spirit of the subject matter described herein in any way. Moreover, the above and / or preceding examples may be combined in any suitable combination to provide further examples, except where such a combination is clearly impermissible or expressly avoided. Other features, aspects, and advantages of the subject matter described herein will become apparent from the following text and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram of a hair styling apparatus that is an example of the invention; Figures 2A and 2B show views of a hair styling apparatus that is another example of the invention; Figures 3A and 3B show views of an attachment for a hair styling apparatus that may be used in examples of the invention; Figures 4A and 4B show views of an intermediate portion for a hair styling apparatus that may be used in examples of the invention; Figure 5 is a flowchart of a method according to an example of the present invention; Figures 6A-6C show graphs of a target angle with respect to time, displaying examples of a predetermined orientation; and Figure 7 is a flowchart showing a method of determining an orientation of an air outlet relative to a user’s scalp which may be used in examples of the present invention. DETAILED DESCRIPTION Fig. 1 is a schematic diagram of a hair styling apparatus 100 that is an example of the present invention. The hair styling apparatus 100 may be, for example, a hair dryer, a hair curler, or some other type of hair styling apparatus. The hair styling apparatus 100 includes a body 102 in which an airflow generator 104 is housed. The airflow generator 104 is configured to generate an airflow which is directed towards an outlet of the body 102, so that the airflow can be directed at a user’s hair 106. The airflow generator 104 may include any suitable device for generating an airflow, such as a fan, turbine or blower. The body 102 may also house a heater (not shown) for heating the airflow generated by the airflow generator 104. The body 102 includes an attachment region 108 located on an end of the body 102, to which an attachment 110 is removably attachable. When the attachment 110 is attached to the body 102 at the attachment region 108, it is arranged to receive the airflow generated by the airflow generator 104 and discharge the airflow towards the user’s hair 106. In particular, the attachment region 108 may be located so that when the attachment 110 is attached at the attachment region 108, the airflow passes from the outlet of the body 102 into the attachment 110, which then discharges the airflow towards the user’s scalp 106 located in front of the attachment 110. For example, the attachment 110 may include a hollow body which defines a passageway or channel for directing and / or shaping the airflow. The attachment 110 itself also has an air inlet (for receiving airflow from the body) and an air outlet (for direction airflow towards the user’s scalp), such that when the attachment 110 is attached to the main body 102 the air outlet of the attachment 110 forms an air outlet of the hair styling apparatus 100. In Fig. 1, the attachment 110 is shown spaced apart from the attachment region 108, i.e. the attachment 110 is not attached to the body 102 in Fig. 1. The attachment region 108 and the attachment 110 may include any suitable means for removably attaching the attachment 110 at the attachment region 108. For instance, the attachment region 108 and the attachment 110 may include mutually engageable features which are configured to releasably engage one another, to hold the attachment 110 at the attachment region 108. The body 102 also includes a handle portion 121 which comprises a gripping portion to be held by a user. The body 102 further includes a control unit 112, which may be implemented for example by a microcontroller. The control unit 112 is communicatively coupled (via a wired or wireless connection) to the airflow generator 104, so that the control unit 112 can control operation of the airflow generator 104, e.g. by transmitting control signals to the airflow generator 104. The control unit 112 is also communicatively coupled (via a wired or wireless connection) to a first sensor 118 and a second sensor 119. The first sensor 118 is configured to detect position information of the hair styling apparatus 100 which is indicative of an actual orientation of an air outlet relative to the user’s scalp, whilst the second sensor 119 is configured to detect orientation information of the main body 102 of the hair styling apparatus 100. The first sensor 118 is arranged to provide an output signal indicative (representative) of the actual orientation of an air outlet relative to the user’s scalp to the control unit 112, whilst the second sensor 119 is arranged to provide an output signal representative of the orientation information of the main body 102 to the control unit 112. It will be appreciated that a second sensor 119 may not be present in all examples of the present invention. The control unit 112 is also communicatively coupled to a drive mechanism 114 which is arranged to control an orientation of the air outlet relative to the main body 102. For example, the drive mechanism 114 may comprise at least one servo motor (which may be any suitable type of motor, such as a stepper motor etc.) which is configured to adjust the orientation of the air outlet in at least one plane of motion. The first sensor 118 may include a variety of different sensor types, depending on the position information to be detected. For example, the position information may include distance data, and so the first sensor 118 can include a distance sensor which is configured to detect a distance between the distance sensor 118 and the user’s scalp 106 located in front of the hair styling apparatus 100. Various known types of distance sensors may be used. As an example, the distance sensor 118 may include a time of flight (ToF) sensor. Such a ToF sensor may include a light emitter (e.g. a laser or a LED) and a receiver (e.g. a photodetector). The ToF sensor may be configured to emit a light signal with the light emitter, and to detect a reflected light signal that is reflected back from the user’s scalp 106. The light (i.e. electromagnetic radiation) emitted by the light emitter may be visible, infrared, ultraviolet, radiofrequency, microwave, or any other suitable type of electromagnetic radiation. The distance to the user’s scalp 106 can then be calculated using any suitable technique. For example, the distance to the user’s scalp 106 can be calculated from an amount of time between the emission of the light signal by the emitter and detection of the reflected light signal at the receiver. As another example, the distance to the user’s scalp 106 can be calculated based on an intensity of the reflected light signal detected by the receiver. Of course, any other suitable distance sensor may be used, including (but not limited to) an ultrasonic sensor, inductive sensor, structured light sensor, and / or capacitive sensor. It will be appreciated that in certain examples, the first sensor 118 may be one of a plurality of distance sensors, wherein each sensor may be the same type or the plurality of sensors may be a variety of sensor types. The second sensor 119 may comprise an orientation sensor, for detecting an orientation of the hair styling apparatus, e.g. for detecting when it is in an upright position. Such an orientation sensor may be implemented using one or more of an accelerometer, a gyroscope, a magnetometer, and / or a tilt switch, for example. The control unit 112 is configured to use the output from the first sensor 118 and the second sensor 119 to determine an actual orientation of the air outlet relative to the user’s scalp 106, calculate an offset between the actual orientation and a predetermined orientation, and control a drive mechanism to reduce the offset, according to a method described herein. The hair styling apparatus 100 may include a memory 120 which is accessible by the control unit 112. In some cases, the memory 120 may be included as part of the control unit 112 itself. The memory 120 is configured to store instructions which, when executed by the control unit 112, cause the control unit 112 to carry out the method. The memory 120 may also store data indicative of the predetermined orientation. In this manner, the control unit 112 can compare the orientation information derived from an output signal received from the first sensor 118 and the second sensor 119 to the data stored in the memory 120, to determine how to reduce the offset between the actual orientation and the predetermined orientation. In some embodiments, the body 102 may be formed of a main body portion 122 in which the airflow generator 104 is located, and an intermediate portion (first attachment) 124 in which the control unit 112, drive mechanism 114, first sensor 118, second sensor 119 and memory 120 are located. The intermediate portion 124 may be removably attachable to the main body portion 122, e.g. the intermediate portion 124 may be engageable with the main body portion 122 to attach the intermediate portion 124 to the main body portion 122 by a first connector, and is removably attachable to the attachment (second attachment) 110 by a second connector. The drive mechanism 114 may operate by controlling the orientation of the first connector relative to the second connector, as described herein. The main body portion 122 and the intermediate portion 124 may have connectors (e.g. pogo pins or similar) which are configured to engage with one another when the intermediate portion 124 is attached to the main body portion 122, in order to connect the control unit 112 to the airflow generator 104. Alternatively, the control unit 112 may be configured to communicate wirelessly with the airflow generator 104. The attachment region 108 may be located on an end of the intermediate portion 124, such that in use the intermediate portion 124 may be connected between the main body portion 122 and the attachment 110. The intermediate portion 124 may be configured to convey the airflow from the airflow generator 104 to the attachment 110, which then discharges (i.e. expels) the airflow towards the user’s hair 106. Housing electronics such as the control unit 112, drive mechanism 114, first sensor 118, second sensor 119 and memory 120 in the intermediate portion 124 may enable a hair styling apparatus having the main body portion 122 to be retrofitted with the intermediate portion 124, in order to enable control of the airflow generator 104 by the control unit 112. In other examples, the control unit 112 may not control the airflow generator 104, and the main body portion 122 may comprise an additional control unit which controls the airflow generator. Although the control unit 112, drive mechanism 114, first sensor 118 and second sensor 119 are shown within the intermediate portion 124 in Fig. 1, it will be appreciated that one or more of the components may be provided in any suitable part of the hair styling apparatus 100, such as within the attachment 110 or within the main body portion 122. Fig. 2A shows a perspective view, and Fig. 2B shows a cross-section view, of a hair styling apparatus 200 that is an example of the present invention. The hair styling apparatus 200 comprises a main body having a handle portion 210 which comprises a gripping portion to be held by a user, and a head portion 220. An air inlet 215 is formed in the handle portion 210 and an air outlet 225 is formed in the head portion 220, and the main body houses an airflow generator (not shown) which generates a flow of air between the air inlet 215 and the air outlet 225 to be directed at a user’s scalp in use. The air inlet 215 is provided as a plurality of apertures in the handle portion 210, and the air outlet 225 is an opening in the head portion 220. The handle portion 210 and the head portion 220 are generally arranged in an inverted L-shape and, in use, the user grips the handle portion 210 and holds the apparatus 200 such that the air outlet 225 is directed at their scalp and a flow of air from the air outlet 225 dries their hair. However, some users may struggle to hold the apparatus 200 such that the air outlet 225 is optimally directed at their scalp during the entire hair styling process. In order to help address this, the hair styling apparatus 200 comprises a drive mechanism 230 between the handle portion 210 and the head portion 220, wherein the drive mechanism 230 is arranged so as to control an orientation of the head portion 220 relative to the handle portion 210. By controlling the drive mechanism 230 by a method described herein, the air outlet 225 may be directed towards a user’s scalp at a suitable orientation, aiding the user during the hair styling process. Specifically, the drive mechanism 230 is configured to move the head portion 220 about two axes, giving two degrees of freedom to the head portion 220. In particular, the drive mechanism 230 provides rotation about a longitudinal axis 232 of the handle portion 210 (yaw), and rotation about a transverse axis 234 (roll). Of course, it will be appreciated that, in other examples, the drive mechanism 230 may be configured to provide a further degree of freedom (e.g., about a pitch axis). To move the head portion 220 about each axis, the drive mechanism comprises two servo motors. A first servo motor 236 is arranged to rotate the head portion 220 about the longitudinal axis 232 of the handle portion 210, and a second servo motor 238 is arranged to rotate the head portion 220 about the transverse axis 234. For example, each motor 236, 238 may drive a corresponding drive wheel which is in contact with a curved bearing surface, where rotation of the wheel moves the bearing surface to effect rotation of the head portion 220 about the corresponding axis 232, 234. In another example, each motor 236, 238 may drive a circular gear which is engaged with a curved gear to provide motion of the head portion 220. The drive mechanism 230 is controlled by a control unit to reduce an offset between an actual orientation of the air outlet 225 relative to the user’s scalp and a predetermined orientation, according to a method as described herein. In order to derive position information which indicates the orientation of the air outlet 225 relative to the user’s scalp, the apparatus comprises a plurality of distance sensors 240a, 240b which are spaced about the air outlet 225, and which determine the distance between each sensor 240a, 240b and the user’s scalp. Although two sensors 240a, 240b are shown, it will be appreciated that more sensors may be present on the apparatus 200. For example, each sensor 240a, 240b may be a time of flight sensor. The actual orientation of the air outlet 225 relative to a user’s scalp may be calculated from the distance sensors 240a, 240b by a method as described herein. The head portion 220 may comprise a connector at or about the air outlet 225 for removably attaching an attachment to the apparatus 200. This may allow any suitable attachment to be used with the apparatus 200, such that the benefits of adjusting the orientation of the air outlet 225 may be achieved with a variety of attachments. Fig. 3A shows a perspective view, and Fig. 3B shows a cross-section view, of an attachment 300 that may be used in a hair styling apparatus in examples of the present invention. For example, the attachment 300 may be used in a hair styling apparatus in which the main body of the hair styling apparatus does not comprise a drive mechanism, but as the attachment 300 comprises a drive mechanism 330 the benefits of the present invention may be achieved. The attachment 300 is a diffuser attachment, but it will be appreciated that the concept described herein of controlling the orientation of an air outlet may be applied to any suitable attachment for a hair styling apparatus. The attachment 300 comprises a connecting portion 310 for removably connecting the attachment 300 to the main body of a hair styling apparatus. The connecting portion 310 comprises an air inlet for receiving an airflow from the main body. The attachment 300 also comprises an attachment body portion 320 which is configured to achieve a particular hair styling effect. In particular, the body portion 320 provides a diffuser, with a generally conical outer wall 322 defining a plenum space 324 therein, through which airflow from the main body of the hair styling apparatus passes. A top side of the plenum space 324 is enclosed by an upper wall 326, an outer surface of which comprises a plurality of hollow projections 328 which receive the airflow from the plenum space 324. Each of the plurality of projections 328 comprises an air outlet 329 which direct airflow out of the body portion 320 and generally towards a user’s scalp. Between the connecting portion 310 and the body portion 320, the attachment comprises a drive mechanism 330. The drive mechanism 330 is configured to move the body portion 320 relative to the connecting portion 310 about two axes, giving two degrees of freedom to the body portion 320. In particular, the drive mechanism 330 provides rotation about a longitudinal axis 332 of the attachment 300 (yaw), and rotation about a transverse axis 334 (roll). Of course, it will be appreciated that, in other examples, the drive mechanism 330 may be configured to provide a further degree of freedom (e.g., about a pitch axis). To move the body portion 320 about each axis, the drive mechanism 330 comprises two servo motors. A first servo motor 336 is arranged to rotate the head portion 330 about the longitudinal axis 332 of the attachment 300, and a second servo motor 337 is arranged to rotate the body portion 320 about the transverse axis 334. The servo motor 337 is arranged to operate a drive wheel 338 which is in contact with a curved bearing surface 339 connected to the body portion 320, such that rotation of the drive wheel 338 moves the bearing surface 339 and so rotates the body portion 320 about the transverse axis 334. The first servo motor 336 operates a second drive wheel in contact with a second bearing surface in a corresponding manner. The drive mechanism 330 is controlled by a control unit to reduce an offset between an actual orientation of the air outlet 329 relative to the user’s scalp and a predetermined orientation, according to a method as described herein. It will be appreciated that the attachment 300 may be used with the hair styling apparatus 200 described above, such that the orientation of the air outlet 329 may be adjusted using one or both of the attachment’s 300 drive mechanism 330 and the hair styling apparatus’ 200 drive mechanism 230. In one example, the drive mechanism 330 may be configured to make finer adjustments to the orientation of the air outlet 329 as compared to the drive mechanism 230. In order to derive position information which indicates the orientation of the air outlet 329 relative to the user’s scalp, the attachment 300 comprises a plurality of distance sensors 340a, 340b which are spaced about the top edge of the body portion 320, and which determine the distance between each sensor 340a, 340b and the user’s scalp. Although two sensors 340a, 340b are shown, it will be appreciated that more sensors may be present on the attachment 300 (e.g., three sensors may be equidistantly spaced about the body portion 320). For example, each distance sensor 340a, 340b may be a time of flight sensor. The actual orientation of the air outlet 329 relative to a user’s scalp may be calculated from the distance sensors 340a, 340b by a method as described herein. Fig. 4A shows a perspective view, and Fig. 4B shows a cross-section view, of an intermediate portion 400 that may be used in hair styling apparatus in examples of the present invention. For example, the intermediate portion 400 may be used in a hair styling apparatus in which neither the main body nor an attachment comprises a drive mechanism, but as the intermediate portion 400 provides a drive mechanism 430 the benefits of the present invention may be achieved. The intermediate portion 400 (first attachment) comprises a first connecting portion 410 having a first connector for removably connecting the intermediate portion 400 to the main body of a hair styling apparatus. The first connecting portion 410 defines an air inlet 415 for receiving an airflow from the main body. The intermediate portion 400 also comprises a second connecting portion 420 having a second connector for removably connecting an attachment (second attachment) to the intermediate portion 400. The second connecting portion 420 defines an air outlet 425 for providing an airflow to the second attachment from the main body of the hair styling apparatus. Of course, the air outlet 425 may be used without an attachment to direct an airflow towards a user’s scalp. Between the first connecting portion 410 and the second connecting portion 420, the intermediate portion 400 comprises a drive mechanism 430 configured to control the orientation of the second connecting portion 420 relative to the first connecting portion 410. In particular, the drive mechanism 430 provides rotation about a longitudinal axis 432 of the intermediate portion 400 (yaw), and rotation about a transverse axis 434 (roll). Of course, it will be appreciated that, in other examples, the drive mechanism 430 may be configured to provide a further degree of freedom (e.g., rotation about a pitch axis). To move the second connecting portion 420 about each axis, the drive mechanism 430 comprises two servo motors. A first servo motor 436 is arranged to rotate the second connecting portion 420 about the longitudinal axis 432 of the intermediate portion 400, and a second servo motor 437 is arranged to rotate the second connecting portion 420 about the transverse axis 434. The servo motor 437 is arranged to operate a drive wheel 438 which is in contact with a curved bearing surface 439 connected to the second connecting portion 420, such that rotation of the drive wheel 438 moves the bearing surface 439 and so rotates the second connecting portion 420 about the transverse axis 434. The first servo motor 436 operates a second drive wheel in contact with a second bearing surface in a corresponding manner. The drive mechanism 430 is controlled by a control unit to reduce an offset between an actual orientation of the air outlet 425 relative to the user’s scalp and a predetermined orientation, according to a method as described herein. It will be appreciated that the intermediate portion 400 may be used with the hair styling apparatus 200 and / or the attachment 300 as described above, such that the orientation of the air outlet of the hair styling apparatus can be adjusted using one or more of the drive mechanisms 230, 330, 430. In one example, each of the drive mechanisms 230, 330, 430 may be configured to provide different degrees of adjustment (e.g., fmer / coarser adjustments). In order to derive position information which indicates the orientation of the air outlet 425 relative to the user’s scalp, the intermediate portion 400 comprises a plurality of distance sensors 441a, 441b, 441c. Each sensor 441a, 441b, 44c is located at the distal end of a sensor arm 442a, 442b, 442c which extends laterally outwards from the connecting portion 420. The sensor arms 442a, 442b, 442c are equidistantly spaced from one another about the circumference of the connecting portion 420. Each distance sensor 441a, 441b, 441c is configured to determine the distance between each sensor 441a, 441b, 441c and the user’s scalp. For example, each distance sensor 441a, 441b, 441c may be a time of flight sensor. The actual orientation of the air outlet 425 relative to a user’s scalp may be calculated from the distance sensors 441a, 441b, 441c by a method as described herein. Fig. 5 is a flow diagram showing a method 500 that is an example of the present invention. In particular, the method 500 is a computer-implemented method of controlling a hair styling apparatus, such as a hair styling apparatus as described above with respect to Figs. 1-4. In a first step 502, the method 500 comprises receiving position information indicative of an actual orientation of the air outlet relative to a user’s scalp. For example, the position information may be derived from distance data obtained by one or more sensors of the hair styling apparatus. A method of deriving an actual orientation of the air outlet from position data is described below with respect to Fig. 7. When the position information has been received, the method 500 moves to a step 504 of calculating an offset between the actual orientation of the air outlet and a predetermined orientation. The predetermined orientation may be provided as an angle between a surface normal vector of the user’s scalp and a device normal vector, which is calculated based on the position information as described below with respect to Fig. 7. The predetermined orientation may be a fixed value, or may be a time-varying function, as described in more detail below with respect to Figs. 6A-6C. The predetermined orientation may be provided with reference to one or more planes of motion which are provided by the drive mechanism (e.g., in a yaw plane and a roll plane as described above), such that the determined offset corresponds with motion control which can be provided by the drive mechanism. When the offset has been calculated, the method 500 moves to a step 506 of controlling a drive mechanism to reduce the offset between the actual orientation of the air outlet relative to the user’s scalp and the predetermined orientation. For example, this may include operating one or more of the servo motors as described above with respect to Figs. 1-4. Examples of predetermined orientations of an air outlet relative to a user’s scalp will now be described with respect to Figs. 6A-6C, which show graphs of a target angle (Otarget) with respect to time. The target angle is an angle between a surface normal vector of the user’s scalp and a device normal vector, such that the target angle defines a predetermined orientation of the air outlet relative to the user’s scalp. In particular, the predetermined orientation may be given as an angle in the one or more planes of motion which are provided by the drive mechanism. Fig. 6A shows an example where the target angle is fixed at 0°, and does not vary over time. That is, the target angle between the surface normal vector of the user’s scalp and the device normal vector is 0°, such that a plane of the air outlet is substantially parallel to the user’s scalp. The hair styling apparatus is operated according to the method of Fig. 5 to reduce the offset between an actual orientation and this predetermined orientation. Fig. 6B shows an example where the target angle is fixed at an arbitrary non-zero angle, and does not vary over time. That is, the target angle between the surface normal vector of the user’s scalp and the device normal vector is greater than 0°, such that a plane of the air outlet is angled relative to the user’s scalp. The hair styling apparatus is operated according to the method of Fig. 5 to reduce the offset between an actual orientation and this predetermined orientation. Fig. 6C shows an example where the target angle varies over time. That is, the target angle between the surface normal vector of the user’s scalp and the device normal vector is a function of time. In particular, the function is a repeating function (e.g., a sine curve). The hair styling apparatus is operated according to the method of Fig. 5 to reduce the offset between an actual orientation and this predetermined orientation such that the air outlet oscillates about a fixed offset. Fig. 7 is a flowchart showing a method 700 of determining an orientation of an air outlet relative to a user’s scalp based on position information from one or more distance sensors of a hair styling appliance. For example, the method 700 may form part of a step 502 of receiving position information as described above with respect to Fig. 5. In a first step 702, the method 700 includes receiving distance data indicating a distance between a plurality of sensors and the user’s scalp. For example, the distance data may be received from one or more distance sensors as described above with respect to Figs. 1-4. The distance may be obtained using a time of flight sensor, or example, or any other suitable distance sensor. In particular, each distance sensor measures the distance between the distance sensor and a respective location on the user’s scalp (e.g., for a time of flight sensor this may be a location which is along the line of sight of the sensor). In some embodiments, the method 700 may also include a step 704 of receiving main body orientation information. For example, this may be from a second sensor as described above with respect to Fig. 1, wherein the sensor may be a gyroscopic sensor, an inertial sensor, an accelerometer or the like, which is able to provide information relating to the orientation of the main body of the hair styling apparatus itself. This orientation information may be used to help identify anomalous readings in the distance data which is received at step 702, for example. After the data has been received, there is a step 706 of applying a noise filter to the data. For example, this may be a low pass filter, a Kalman filter, a moving average or the like. This may help ‘smooth out’ the distance data received from the sensors, reducing the load of the drive mechanism. From the noise-filtered distance data an orientation of the air outlet relative to the user’s scalp may be calculated. To do so, at step 708 the distance data is plotted in 3D space to find the relative positions of the distance sensors and the location on the user’s scalp which is sensed by each sensor. Plotting these points may be performed with the aid of known information regarding the distance sensors, such as their position relative to one another, to the air outlet, and / or to the main body of the hair styling apparatus. Once the points have been plotted in 3D space, two planes can be fitted to the points. A first plane contains the locations of the distance sensors (from which may be derived a plane of the air outlet, for example, using known information relating the position of the air outlet relative to the distance sensors) such that the first plane describes the orientation of the distance sensors (and, therefore, the air outlet), and a second plane contains the locations on the user’s scalp which are sensed by each sensor, such that the second plane describes the orientation of the user’s scalp. A corresponding surface normal for each plane is calculated at step 712, giving a first surface normal relating to the distance sensors, and a second surface normal relating to the user’s scalp. The first surface normal coincides with the device normal vector and the second surface normal coincides with the surface normal vector of the user’s scalp. Finally, at step 714, one or more angles between the first surface normal and the second surface normal may be calculated. In particular, the one or more angles may be calculated in the one or more planes of motion provided by the drive mechanism, such that the angles which are calculated can be easily converted into motor signals for operating the drive mechanism after a difference between these angles and the target angles relating to the predetermined orientation of the air outlet relative to the user’s scalp (e.g., a target angle as described above with respect to Fig. 5). Whilst particular examples and embodiments have thus far been described, it should be understood that these are illustrative only and that various modifications may be made without departing from the scope of the invention as defined by the claims.

Claims

1. A computer-implemented method of controlling a hair styling apparatus, wherein the hair styling apparatus comprises an air outlet and a drive mechanism arranged to control an orientation of the air outlet relative to a main body of the hair styling apparatus; the method comprising:receiving position information indicative of an actual orientation of the air outlet relative to a user’s scalp,calculating an offset between the actual orientation of the air outlet and a predetermined orientation, andcontrolling the drive mechanism to reduce the offset.

2. The computer-implemented method of claim 1, wherein receiving position information includes receiving distance data from a sensor of the hair styling apparatus, the distance data indicating a distance between the sensor and the user’s scalp.

3. The computer-implemented method of claim 2, wherein receiving position information further includes receiving orientation information of the main body of the hair styling apparatus.

4. The computer-implemented method of any preceding claim, wherein the predetermined orientation is a time-varying function.

5. The computer-implemented method of claim 4, wherein controlling the drive mechanism further comprises oscillating the air outlet.

6. The computer-implemented method of any preceding claim, wherein calculating an offset between the orientation of the air outlet and the predetermined orientation comprises calculating an angle between a surface normal vector of the user’s scalp and a device normal vector, the angle lying in a plane corresponding to a plane in which the drive mechanism may move the air outlet.

7. The computer-implemented method of any preceding claim, wherein calculating an offset between the actual orientation and the predetermined orientation comprises applying a filter to the position information.

8. A hair styling apparatus comprising:a main body having a gripping portion to be held by a user;an air inlet;an air outlet;an airflow generator configured to generate a flow of air between the air inlet and the air outlet; anda drive mechanism arranged to control an orientation of the air outlet relative to the main body.

9. The hair styling apparatus of claim 8, further comprising a control unit configured to perform a method according to any one of claims 1 to 7.

10. The hair styling apparatus of claim 8 or claim 9, further comprising a sensor configured to output position information indicative of the orientation of the air outlet relative to a user’s scalp.

11. The hair styling apparatus of claim 10, wherein the sensor comprises a distance sensor configured to determine the distance between the sensor and the user’s scalp.

12. The hair styling apparatus of claim 11, wherein the distance sensor comprises a time of flight sensor.

13. The hair styling apparatus of claim 11 or claim 12, wherein the distance sensor is one of a plurality of distance sensors, wherein the sensing axes of the plurality of distance sensors are not parallel to one another.

14. The hair styling apparatus of any one of claims 8 to 13, wherein the main body comprises:a handle portion which comprises the gripping portion to be held by a user; and a head portion which comprises the air outlet,wherein the drive mechanism is arranged to control an orientation of the head portion relative to the handle portion.

15. The hair styling apparatus of any one of claims 8 to 13, further comprising an attachment which is removably connectable to the main body, the attachment comprising: the air outlet, and the drive mechanism.

16. The hair styling apparatus of any one of claims 8 to 13, wherein the drive mechanism is part of a first attachment, wherein the first attachment has a first connector for removably connecting to the main body and a second connector for removably connecting to a second attachment comprising the air outlet, and wherein the drive mechanism is configured to control the orientation of the second connector relative to the first connector.

17. The hair styling apparatus of any one of claims 8 to 16, wherein the drive mechanism comprises a two-axis gimbal configuration, each axis being controlled by a respective servo motor.

18. An attachment for a hair styling apparatus, the attachment comprising:a first connector for removably connecting to a main body of the hair styling apparatus;an air inlet for receiving an airflow from the hair styling apparatus;an air outlet; anda drive mechanism arranged to control an orientation of the air outlet relative to the air inlet.

19. The attachment of claim 18, further comprising a control unit configured to perform a method according to any one of claims 1 to 7.

20. The attachment of claim 18 or claim 19, wherein the attachment further comprises a second connector for removably connecting to a second attachment, wherein the second attachment is configured to receive and to modify airflow from the attachment.5 21. A computer program comprising instructions which, when the program is executed bya computer, cause the computer to carry out the method of any one of claims 1 to 7.

22. A computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to carry out the method of any one of claims 1 to 7.

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