Hair styling device and method for controlling a hair styling device

Abstract

Hair styling device comprising a main body having a back end and a front end, the front end including an air exit, wherein the main body is configured to guide air from an air entrance to the air exit; the hair styling device further comprising a motor configured to force air from the air entrance through said main body and a sensor system configured to determine an airflow rate of said air through said main body.

Description

HAIR STYLING DEVICE AND METHOD FOR CONTROLLING A HAIR STYLING DEVICEField of the Invention

[0001] The present invention generally relates to a hair styling device, in particular to a professional hair styling device for use in a hairdressing salon, comprising an airflow rate control mechanism, as well as to a method for controlling a hair styling device.Background of the Invention

[0002] Hair styling devices are generally known electric devices and may be configured to blow heated air through a main body. The heated air can be directed to a person’s hair to dry and style the hair. Hair styling devices can be handheld devices, including a handle mounted substantially transversely to the main body. Other handheld hair styling devices may include a pair of movable jaws in between which hair can be clamped such that it can be styled. Alternatively, hair styling devices may be standalone devices and may for example include a headset, such as hood hair dryers. Hair styling devices may come in various types, such as a personal hair styling device, for example for occasional use at home generally by a person drying and / or styling its own hair, a travel hair styling device which may for example be relatively small, lightweight and / or foldable for easy transportation, or a professional hair styling device which may be used by a person styling someone else’s hair, for example in a professional setting, used by a hairdresser in a hairdressing salon. Each of these various types of hair styling devices can include specific technical requirements due to the different use made of said type of hair styling devices. As an example, some hair styling devices offer multiple heat and speed settings to accommodate different hair types and styling preferences.

[0003] In the field of professional hair styling devices, which are generally used by a hairdresser drying and / or styling a client’s hair in a professional context, such as in a hairdressing salon, in photo studios, before fashion shows, in education, or in any other professional context, power consumption of a hair styling device may be an issue due to the intensive use of the hair styling device, in particular when the hair styling device includes one or more heat generating elements. Moreover, different types of hair mayrequire different settings while prior art hair styling devices usually only include a relatively limited choice of settings, for example two or three settings or pre-set options, selectable for example by switches, resulting in a finite number of discrete airflow settings, the settings configured to adjust the motor speed and consequently the airflow rate. While simple and cost-effective, said settings have limited granularity in controlling airflow and often lack precision.

[0004] It is therefore an aim of the present invention to solve or at least alleviate one or more of the above-mentioned problems. In particular, the invention aims at providing an improved hair styling device, in particular for professional use, which is relatively easy and safe to use.Summary of the Invention

[0005] To this aim, according to a first aspect of the invention, there is provided a hair styling device having the features of claim 1. In particular, the hair styling device comprises a main body having a back end and a front end, the front end including an air exit. The main body is configured to guide air from an air entrance to the air exit, which can define a direction of airflow through the main body. The air entrance can preferably, but need not, be included in the main body, for example at the back end or laterally.

[0006] The hair styling device further comprises a motor configured to force air from the air entrance through said main body, thus generating an airflow. The motor may for example be configured to drive a fan, which is configured to draw in air through rotation. The motor may then be connected to the fan, which is typically made of plastic or metal. As the motor spins, it rotates the fan blades rapidly, which forces the air from the air entrance to the air exit of the main body. The motor may for example be an electric motor. Other ways to generate an airflow can be considered as well.

[0007] The hair styling device further comprises a sensor system configured to determine an airflow rate of said air through said main body. The airflow rate is the volume of air expelled per unit of time. The sensor system is configured to determine said volume of air expelled per unit of time. The sensor system comprises at least one sensor and electronics configured to provide a signal that corresponds to the measured airflow rate. The at least one sensor is preferably positioned in the airflow.

[0008] The hair styling device further comprises a main controller configured to control said motor such that said determined airflow rate corresponds to a predetermined setpoint. The predetermined setpoint may for example be provided by a user through a user interface. Said setpoint may for example be expressed as a desired air speed, or as a desired airflow rate, or as a fraction of a maximal airflow rate or in any other known way. The main controller is configured to transmit a signal to the motor including an initial target rotational speed based on said predetermined setpoint. To further control said motor, the main controller is then configured to compare the determined airflow rate to the predetermined setpoint. If there is a difference between the target airflow rate based on the predetermined setpoint and the airflow rate determined by the sensor system, the main controller is configured to amend the rotational speed of the motor. This control is being performed continuously. Since the sensor system is configured to determine the airflow rate independently of the actual rotational speed of the motor, the main controller can control the motor such that the target airflow rate based on the predetermined setpoint can nearly always be reached, in spite of variable operating conditions.

[0009] Usage circumstances or operating conditions may vary due to, for example, the use of nozzles, partial obstructions of the airflow entrance or exit, wear on the motor or of electronic components, weakening of magnets in the motor, or alike, and have an impact on the actual airflow rate produced by the hair styling device. When a user holds the hair styling device closer to one’s body, or when a filter at the air entrance is not clean, air intake may be hindered, which can be compensated for by a hair styling device according to the present invention. Since an optimal airflow rate is not only important for good hair styling results, but also for preventing potential overheating of the device, the present invention can allow to provide a hair styling device enhancing styling results as well as safety. Controlling the airflow rate can allow users to adapt to various hair types, styles, and personal preferences. The design and shape of a nozzle attached to an air exit of a hair styling device can significantly impact the airflow rate, which may thus be compensated for. Narrower nozzles increase the air velocity, resulting in higher pressure and focused airflow. Wider nozzles, on the other hand, provide a broader airflow pattern. Nozzle attachments, such as concentrators and diffusers, further enhance the versatility of hair styling devices by modifying the airflow pattern to suit specific styling requirements. Additionally, it can enable manufacturersto optimize energy consumption and improve user comfort. Moreover, controlling the airflow rate may be used to compensate for the wear to which a motor is subjected during its lifetime.

[0010] The hair styling device can further comprise a heat generating element configured to heat said air forced through said main body thereby producing a dissipated power (Q). The heat generating element can be positioned in the airflow path and is configured to heat the air by dissipating power Q such that the air exiting the main body has a desired temperature which is higher than an air temperature at the air entrance. The dissipated power Q may be measured based on a continuous measurement of the mains input voltage U delivered to the device. Knowledge of the fixed resistance R of the heat generating element can provide the dissipated power Q as follows:This mains input voltage U may for instance be measured at the motor, at the heat generating element or at any other component powered by the mains input.

[0011] Said sensor system preferably comprises a first temperature sensor positioned upstream of the heat generating element configured to measure an air temperature (T1 ) before heating said air and a second temperature sensor positioned downstream of the heat generating element configured to measure an air temperature (T2) after heating said air. The temperature sensors may for example be a thermistor, a digital temperature sensor, or any other known temperature sensor. Said sensor system may then be configured to determine said airflow rate based on a difference between said air temperatures measured respectively before and after heating the air, and on said dissipated power produced by said heat generating element.

[0012] This way of determining an airflow rate is based on Thermal Mass Flow Measurement: by measuring the change in temperature of a passing fluid such as air, the fluid having a certain heat capacity Cp, over a heated surface dissipating a power Q expressed in Watt or Joules of heat per second, the mass flow, expressed for example in grams per second, or in any other way such as a volume unit per second, can be calculated according to the following equation:V = - - -Cp(T2 — Tl) and wherein Cprepresents the heat specific capacity of air. This method of determining an airflow rate can be implemented relatively easily in a hairstyling device while providing a relatively reliable way to determine the actual airflow rate independently of any motor information. Given the positioning of the first temperature sensor and the second temperature sensor, for example near the air entrance and the air exit respectively, the mounting of the sensors into the hair styling device can be performed relatively easily. Moreover, said temperature sensors are relatively small, so they do not influence on the airflow itself nor on the total weight of the hair styling device. Said temperature sensors do not include any moving elements, which makes them relatively robust. Said sensors are also relatively insensitive to dust, which is important in a hair styling device. Finally, said temperature sensors can be relatively cost-efficient, more than other sensors configured to determine an airflow rate, such as for example pressure sensors.

[0013] Alternatively, other methods to determine said airflow rate may be used, such as Thermal Anemometry, Differential Pressure Sensors or Ultrasonic Flow Measurement. Thermal Anemometry relies on a heated element exposed to the airflow. As the air flows over the heated element, it cools down, and the change in temperature is used to calculate the flow rate. Miniaturized thermal anemometers can be designed using thin-film or MEMS (Micro-Electro-Mechanical Systems) technology. While this technique is very accurate in airflows with a constant temperature, the positioning of the sensor in the device may be delicate, as the accuracy of the measurements are influenced by variations in the air temperature and / or by accumulation of dust particles which are too small to be filtered.

[0014] Miniature differential pressure sensors can be used to measure the pressure difference across a constriction placed in the airflow path. The pressure difference is directly proportional to the air flow rate. MEMS-based pressure sensors are well-suited for miniaturization.

[0015] Finally, Ultrasonic Flow Measurement utilizing ultrasonic waves, is a technique measuring the time it takes for sound pulses to travel with and against the airflow. Bycomparing the time difference, the flow rate can be calculated. Miniature ultrasonic sensors can be integrated into the device's airflow path.

[0016] Said second temperature sensor may be advantageously positioned near the air exit. As an example, the second temperature sensor may be mounted on the heat generating element near the air exit or may be mounted on an inner side of a housing of the hair styling device enclosing for example the motor and the heat generating element, close to, near, adjacent to or at the air exit. Any position downstream of the heat generating element within the airflow may be chosen for the second temperature sensor.

[0017] The first temperature sensor may be positioned near the air entrance. The air entrance may be positioned at a backend of the main body or may be a lateral air entrance. The air entrance may even be positioned in a handle of the hair styling device. Depending on where the air entrance is, the first temperature sensor may also be positioned between the motor and the heat generating element to avoid any bias caused by preheating of the air by the motor. The first temperature sensor is preferably positioned at a distance of any additional heat producing element. The first temperature sensor may, but need not, be a digital temperature sensor. It may be advantageous to position the first temperature sensor on or near electronic circuitry, such as a printed circuit board. In case the backend of the hair styling device includes a screen, the first temperature sensor may be advantageously positioned on the printed circuit board controlling the screen, as long as the first temperature sensor can remain in the airflow.

[0018] The main controller can advantageously be a PID controller, which is a proportional-integral-derivative controller. The determined airflow rate can then be considered as a process variable and a rotational speed of said motor can be considered as a control variable for said PID controller. The PID controller can provide a control loop mechanism employing the airflow rate measured or determined by the sensor system as the measured process variable for controlling the rotational speed of the motor which may drive a fan. PID systems can automatically apply accurate and responsive correction to a control function. The controller's PID algorithm can restore the determined airflow rate to the target airflow rate based on the predetermined setpoint with minimal delay and overshoot by increasing or decreasing the rotational speed of the motor in a controlled manner. A PID controller has the advantage of beingable to react to a wide range of situations in a relatively reliable way. Other type of controllers known to the person skilled in the art, such as rapid ON-OFF switching control algorithms, may be used as well.

[0019] The motor can preferably include a motor controller which is bidirectionally connected to the main controller. In other words, the main controller is not only configured to send a signal to the motor controller but may also be configured to receive a signal from the motor controller. The motor controller may then preferably be configured to transmit a signal including an actual rotational speed to the main controller, or the control signal generated by the main controller to control the rotational speed of the motor may be passed onto the motor controller as a parameter setting which represents the setpoint. In this way, the main controller does not only control the motor via the motor controller, but the main controller can also receive operational information from the motor controller, which may then be used by the main controller. An actual rotational speed of the motor can for example be transmitted to the main controller. Other operational parameters may also be transmitted from the motor controller to the main controller, such as for example power usage, or potential errors detected by the motor controller. The motor controller can be further configured to power the motor to achieve the rotational speed corresponding to the setpoint.

[0020] The main controller may be configured to compare the actual rotational speed to a target rotational speed based on the predetermined setpoint. If the target rotational speed based on the predetermined setpoint is not reached by the motor in spite of the control of the motor by the main controller based on the determined airflow rate, then this may point to a problem with the motor, for example by a fan being hindered in its rotation.

[0021] The main controller can for example be configured to emit a warning when the difference between an expected rotational speed based on the determined airflow rate and the actual rotational speed is larger than a first predetermined threshold value. The relation between an expected rotational speed for a given airflow rate can for example have been determined in tests in ideal circumstances and may be stored by the main controller. Alternatively, the main controller may have access to said data, or may be configured to derive said expected rotational speed for an airflow rate. The actual rotational speed of the motor, or a motor’s power consumption, may be received by the main controller from the motor controller. A difference between the expectedrotational speed based on the determined airflow rate and the actual rotational speed may point to a problem in the air intake, for example due to clogging of a filter, or to a temporary and potentially inadvertent covering of the air entrance. A filter may be positioned at an air entrance of the device and can prevent particles exceeding a certain particle size from entering into the airflow and from damaging or clogging up internal parts of the device. Over time, the filter may become more and more clogged, causing greater resistance to the airflow entering the device, and thus requiring more effort from the motor to maintain a constant airflow rate. Clogging of the air entrance filter will therefore lead to an increased driving power of the motor to achieve a same intended airflow rate defined by the predetermined setpoint. If this difference exceeds a predetermined first threshold, the main controller may be configured to emit a warning to the user while continuing to function or operate. The warning for potential clogging may also be emitted based on a comparison between the actual rotational speed of the motor, or a motor’s consumption, and an expected rotational speed derived from testing at predetermined airflow rates. In this way, a relatively reliable and objective way to determine filter clogging is provided without the warning being based on time of use or on other estimations. As a result, the user can check air intake and, if needed, timely clean the filter, which can prevent further problems with the hair styling device.

[0022] Alternatively, the main controller may be configured to emit a warning when a temperature determined by the first temperature sensor near the air entrance and / or by the second temperature sensor near the air exit exceeds a predefined threshold value, which may be caused by clogging of the air entrance filter.

[0023] The main controller may further be configured to deactivate the motor when the difference between an expected rotational speed based on the determined airflow rate and the actual rotational speed is larger than a second predetermined threshold value. The second predetermined threshold may preferably be higher than the first predetermined threshold. In case said difference becomes relatively large, for example due to a closure of the air entrance or a serious clogging of the filter, further operation of the hair styling device may be harmful, for example for the motor. The main controller may then be configured to stop the motor, as well as further operational elements of the hair styling device, such as a heat generating element. A sudden drop of the airflow rate or an unusually low airflow rate may for example be caused by a blockage orobstruction of the air entrance or air exit, a clogging of a filter at the air entrance, or by motor obstruction or breakdown. When such an unusual drop of the airflow rate or an unusually low airflow rate is detected, the device may act upon it accordingly by shutting off certain functions, such as for instance the heating element and / or the motor. Alternatively, the main controller may be configured to control the motor by sending a signal including a sequence of different and varying motor speeds. By applying a sequence of variable rotational speeds, a filter clogging may be freed and / or a user may be warned that a clogging problem may be present. Alternatively, the hair styling device may be configured to provide haptic feedback to the user, for example by vibrating, to warn the user of a potential problem.

[0024] The motor controller can be configured to control a power input to the motor. In other words, the motor controller may include an internal control loop amending power input to arrive at the target rotational speed received from the main controller. The control loop may be configured to monitor the actual rotational speed, and to adjust it when necessary to maintain the targeted rotational speed. In this way, the motor controller may compensate for normal wear and tear on the motor. The aging and usage of the motor will require a gradually higher driving power over time to achieve the same rotational speed. As such, the hair styling device of the invention can provide a constant airflow rate over time, regardless of normal wear and tear, not only by controlling the rotational speed of the motor based on a comparison between the determined flow rate and the predetermined setpoint, but also by compensation of the driving power. Alternatively, the main controller may directly control the motor and include such an additional control loop.

[0025] Said predetermined setpoint may be selectable from a substantially continuous range of values through a user interface. Contrary to prior art devices, in which a user can generally choose between two or three predetermined airflow rates, the user of the present hair styling device may choose an airflow rate within a predetermined range in a substantially continuous way. User input, which may determine the setpoint, may for example be provided as an air speed, for example in a range between more or less 5 m / s and 20 m / s, more preferably between 8 m / s to 14 m / s, or as an airflow rate expressed in m3 / s. Speed or airflow rate may for example be incremented within said range. This is in contrast to prior art devices in which the user can only choose between a very limited number of settings with respect to the airflow, usually a high, mediumand low airflow. Alternatively, said predetermined setpoint may be selectable from a number of predefined settings, for example from at least four, preferably from at least five predefined settings for the airflow rate.

[0026] Additionally, and / or alternatively, the hair styling device may include other types of sensors or systems configured to detect a proximity and / or movement of the hair styling device relative to someone’s hair, for example a proximity sensor or a camera or a radar system. The controller may then further be configured to adjust the predetermined setpoint to a distance to the hair to be styled for optimal performance and safety.

[0027] The motor may advantageously be a variable speed motor of which the rotational speed is electronically adjustable over a continuous range of rotational speeds, allowing a precise and efficient control of the motor's speed, providing benefits such as energy savings, smoother operation, and the ability to tailor the motor's performance to the specific application requirements of the hair styling device. A variable speed motor can adjust the motor speed within a wide range, enabling fine- tuning of the airflow to meet specific needs. Variable speed motors can enhance user experience and facilitate more effective hair drying and styling. In particular, the motor can for example be a brushless DC motor.

[0028] According to a second aspect of the invention, there is provided a method for controlling a hair styling device having the features of claim 12 or 13. The method can provide one or more of the above-mentioned advantages.

[0029] Specific examples and preferred embodiments are set out in the dependent claims. Further advantages and embodiments of the present invention will become apparent from the following description and drawings.Brief Description of the Drawings

[0030] Fig. 1 shows a side view on a preferred embodiment of a hair styling device according to an aspect of the invention;

[0031] Fig. 2 shows a cross-sectional side view of the hair styling device shown in Figure 1 ;

[0032] Fig. 3 shows a process flow of a preferred embodiment of the method according to a second aspect of the invention.Detailed Description of Embodiment(s)

[0033] Figure 1 shows a side view of a preferred embodiment of a hair styling device 1 according to an aspect of the invention. The hair styling device 1 may be used for drying and / or styling someone’s hair, for example one’s own hair or, more preferably, a client’s hair, for example by a professional hairdresser in a hairdressing salon. The hair styling devices may also be known as a hairdryer, a blow dryer or hair blower, which is an electrical device used to blow hot air over damp hair to accelerate the evaporation of water and dry the hair. It is commonly used in hair styling routines to achieve various hairstyles, set hair in place, or simply dry the hair quickly after washing. Other hair styling devices may also be considered.

[0034] The hair styling device comprises a main body 2 having a back end 3 including an air entrance 4 and a front end 5 including an air exit 6. The main body 2 is configured to guide air from the air entrance 4 to the air exit 6. The main body 2 can include a housing 7 at least partially enclosing for example a fan, a motor block and / or heating elements. Said housing 7 may for example include a thickening or a protrusion 7a where a width of the housing is maximal. Said protrusion can provide additional strength and / or protection to the housing 7 on the portion which is in contact with a surface when the hair styling device is laid down sideways on said surface. The hair styling device further comprises a motor configured to generate said airflow. In particular, the motor can be configured to drive a fan, which is configured to draw in air through an air entrance 4. The hair styling device 10 further comprises a handle 12 attached to the main body 11 and configured to hold the hair styling device 10 by hand and / or to provide a grip of the hair styling device by a user, whereas the main body is not configured to be held by a user during normal use of the device. The handle 12 can for example be mounted substantially transversely to the main body 11. Alternatively, the handle 12 may be in line with the main body and / or may be incorporated into the main body 11. The handle 12, in particular an upper end of the handle, may preferably be fixedly attached to the main body. Alternatively, the handle12 may be tiltable or foldable with respect to the main body 11 , for example to allow compact storing of the hair styling device 10. Other embodiments of hair styling devices may not necessarily include a handle. The main body 1 , as well as the handle 8, can allow to define a longitudinal axis 2a of the main body 2 and a longitudinal axis 8a of the handle 8. Said two longitudinal directions 2a, 8a are included in a plane defining two lateral sides of the hair styling device 1. The hair styling device 1 may further include a power supply cable 9. Said power supply cable 9 can for example be connected to a lower end 8I of the handle at a distance of the main body 2. The power supply cable 9 may be fixedly attached to the handle 8, or in a rotatable or swivelling manner, and / or in a detachable way. The power supply cable 9 may preferably be attached using a strain relief device to prevent damaging an electric connection when the hair styling device 1 is hanging on the power supply cable 9, which might be dangerous for the user of the hair styling device 1 . Alternatively, the power supply cable may be connected or connectable to the hair styling device at any other suitable location. Alternatively, the hair styling device may be chargeable at a remote charging station, thus being operable without connected power cable.

[0035] Figure 2 shows a cross-sectional side view of the hair styling device shown in Figure 1. The housing 7 can for example enclose a fan 10 configured to cause air to be sucked in via the air entrance 4. The housing can further enclose a motor 11 configured to generate said airflow, for example to drive said fan, in particular to cause the fan 10 to rotate. The fan 10 may be positioned close to the air entrance 4. The dotted arrows indicate a direction of the airflow through the main body 2 of the device 1. The housing 7 can include a narrowing 12, for example a substantially conical narrowing, towards an air exit 6. The housing 7, in particular said narrowing portion 12, can enclose one or more heat generating elements 13 configured to heat air such that the air exiting the main body 2 has a desired temperature which is higher than an air temperature at the air entrance 4. The heat generating elements 13 may be coiled around an insulating structure supporting the heat generating elements 13. The hair styling device can further include a controller 14 or a main internal controller, for example one or more PCB's, configured to control an operation of the hair styling device 1. Said control element 14 may for example be located at least partially in the handle 8 of the hair styling device 1. The main controller 14 may be configured to determine an airflow rate based on the sensor system, compare said determinedairflow rate to a target airflow rate based on the predetermined setpoint received from user input and control the motor, in particular a rotational speed of the motor, such that said determined airflow rate corresponds to the predetermined setpoint. The device 1 may include an additional motor control element 15 configured to control operation of the motor, which motor control element may be positioned adjacent to said motor block 11 in the main body 2 of the hair styling device 1. The motor controller 15 may be configured to receive a control signal from the main controller 14 including the predetermined setpoint and / or the target rotational speed based on said predetermined setpoint, and to control the rotational speed of the motor based on said control signal. The sensor system can include a first temperature sensor positioned upstream of the heat generating element 13, for example near the air entrance 4, such as at location 21 and configured to measure an air temperature before heating said air. The sensor system can include a second temperature sensor positioned downstream of the heat generating element 13 configured to measure an air temperature after heating said air, for example near the air exit 6, such as at location 20, for example at a tip of the insulating structure of the heat generating element 13. Said sensor system is configured to determine said airflow rate based on said air temperatures measured respectively before and after heating the air, and on said dissipated power produced by said heat generating element, for example according to a thermal mass flow measurement method.

[0036] Figure 3 shows a process flow of a preferred embodiment of the method according to the invention. The method for controlling a hair styling device may be applied by the hair styling device shown in Figure 1 or 2, or by any other hair styling device including an airflow. In a first step 210, a user may provide a desired airflow, for example as a desired airflow rate or air speed, for example via a user interface, which may include a display. By utilizing electronic circuits and / or switches or control buttons, the hair styling device can offer relatively precise and incremental adjustments to the airflow rate. Electronic controls often include digital displays, touch-sensitive interfaces, and programmable settings, enabling users to select their preferred airflow rate with higher accuracy. The main controller receives the target airflow as a predetermined setpoint. In a next step 100, the main controller can initiate control of the motor by sending a control signal including for example the target rotational speed based on the predetermined setpoint.

[0037] In a next step 201 , the airflow rate of air forced through the main body of the hair styling device is determined by a sensor system. The air flow rate may be determined through a measurement of different parameters of the sensor system followed by a conversion to a value corresponding to the airflow rate. The parameters depend on the type of sensor system used, and may be for instance temperatures, pressures, rotation speeds, frequencies or alike. The air flow rate may for example be determined by measuring air temperatures before and after heating said air and by deriving the airflow rate via a thermal mass flow measurement method.

[0038] In step 202, the determined airflow rate V is subsequently compared to the predetermined setpoint corresponding to the airflow rate as chosen by the user. In case that both values are different, a further control step 203 may be performed, which may include three options. In a first scenario 203a, a difference between the determined airflow rate and predetermined setpoint is relatively small. In that case, the main controller can instruct the motor, for example via an additional motor controller, to adjust the rotational speed of the motor 204, in particular to increase or decrease said rotational speed. The method then iterates back to the determination step 201 of the airflow rate until the setpoint is reached in step 300. Even when the determined airflow rate corresponds to the predetermined setpoint, the iterative verification loop is continuously repeated since the airflow rate may change during operation of the hair styling device due to changing operation conditions. As an example, an air entrance may get obstructed, or a nozzle may be added to the hair styling device thus impacting on the actual airflow rate. In a second scenario 203b, the predetermined setpoint may not be reached in spite of slight adjustment of the rotational speed of the motor. The main controller may compare an expected rotational speed of the motor based on the predetermined setpoint with an actual rotational speed of the motor reported by the motor controller in step 205. If said difference is higher than a first threshold but lower than a second threshold, the main controller may emit a warning while continuing to control the motor in step 206. In case said difference is even higher than the second threshold, then the main controller may stop the motor and other operating elements of the hair styling device such as the heat generating elements in step 301 . Additional comparison of values, control loops, and emission of warnings may of course be added and / or may be performed in parallel, such as for example control loops on temperature of the air before and / or after heating by the heat generating element.

[0039] Although the present invention has been illustrated by reference to specific embodiments, it will be apparent to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied with various changes and modifications without departing from the scope thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. In other words, it is contemplated to cover any and all modifications, variations or equivalents that fall within the scope of the basic underlying principles and whose essential attributes are claimed in this patent application. It will furthermore be understood by the reader of this patent application that the words "comprising" or "comprise" do not exclude other elements or steps, that the words "a" or "an" do not exclude a plurality, and that a single element, such as a computer system, a processor, or another integrated unit may fulfil the functions of several means recited in the claims. Any reference signs in the claims shall not be construed as limiting the respective claims concerned. The terms "first", "second", third", "a", "b", "c", and the like, when used in the description or in the claims are introduced to distinguish between similar elements or steps and are not necessarily describing a sequential or chronological order. Similarly, the terms "top", "bottom", "over", "under", and the like are introduced for descriptive purposes and not necessarily to denote relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and embodiments of the invention are capable of operating according to the present invention in other sequences, or in orientations different from the one(s) described or illustrated above.

Claims

CLAIMS1 . Hair styling device comprising- a main body having a back end and a front end, the front end including an air exit, wherein the main body is configured to guide air from an air entrance to the air exit;- a motor configured to force air from the air entrance through said main body;- a sensor system configured to determine an airflow rate of said air through said main body;- a main controller (34) which is configured to control said motor (33) such that said determined airflow rate (V) corresponds to a predetermined setpoint (SP).

2. Hair styling device (10) according to claim 1 , further comprising a heat generating element (30) configured to heat said air forced through said main body (11 ) thereby producing a dissipated power (Q); and wherein said sensor system comprises;- a first temperature sensor positioned upstream of the heat generating element configured to measure an air temperature (T1 ) before heating said air;- a second temperature sensor positioned downstream of the heat generating element configured to measure an air temperature (T2) after heating said air; wherein said sensor system is configured to determine said airflow rate (V) based on said air temperatures measured respectively before and after heating the air, and on said dissipated power produced by said heat generating element.

3. Hair styling device according to claim 2, wherein said second temperature sensor is positioned near the air exit.

4. Hair styling device according to any of the preceding claims 2 - 3, wherein the first temperature sensor is positioned near the air entrance.

5. Hair styling device according to any of the preceding claims, wherein the main controller (34) is a PID controller, wherein said determined airflow rate (V) is considered as a process variable and a rotational speed (R) of said motor (33) is considered as a control variable for said PID controller.

6. Hair styling device according to any of the preceding claims, wherein the motor includes a motor controller which is bidirectionally connected to the main controller, wherein the motor controller is configured to transmit an actual rotational speed to the main controller.

7. Hair styling device according to claim 6, wherein the main controller is configured to compare the actual rotational speed to a target rotational speed based on the predetermined setpoint.

8. Hair styling device according to any of the preceding claims 6 - 7, wherein the main controller is configured to emit a warning when the difference between an expected rotational speed based on the determined airflow rate and the actual rotational speed is larger than a first predetermined threshold value.

9. Hair styling device according to any of the preceding claims 6 - 8, wherein the main controller is configured to deactivate the motor when the difference between an expected rotational speed based on the determined airflow rate and the actual rotational speed is larger than a second predetermined threshold value.

10. Hair styling device according to any of the preceding claims 6 - 9, wherein the motor controller is configured to control a power input to the motor.

11. Hair styling device according to any of the preceding claims, wherein said setpoint (SP) is selectable from a substantially continuous range of values through a user interface.

12. Method for controlling a hair styling device, the hair styling device comprising a main body having a back end and a front end, the front end including an air exit, wherein the main body is configured to guide air from an air entrance to the air exit, the device further comprising a motor configured to force air from the air entrance through said main body, the method comprising the steps of:- determining an airflow rate of the air forced through said main body of the hairstyling device by a sensor system;- controlling the motor such that said determined airflow rate corresponds to a predetermined setpoint.

13. Method according to claim 12, wherein the step of the sensor system determining an airflow rate of the air forced through said main body of the hairstyling device includes the steps of- a first temperature sensor determining a first temperature upstream of a heat generating element of the hair styling device;- a second temperature sensor determining a second temperature downstream of said heat generating element;- determining the airflow rate based on said first temperature and said second temperature and on a dissipated power produced by said heat generating element.

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