Field of the Invention

The present invention relates to apparatus and method for styling hair, for example after washing the hair or as part of a styling process. Such styling of hair may be performed by a user in respect of their own hair, for example, or by a hair stylist. The invention has particular, although not exclusive relevance to hair styling apparatus having one or more sensors to measure hair temperature, hair position, tress size, and/or other characteristics relating to usage of the hair styling apparatus.

The invention may be used for styling dry hair. Alternatively, the hair may be wet (or “towel-dry”) prior to use of the invention, and may then be dried and/or styled using the invention. It should also be noted that the term “wet” as used herein should be interpreted broadly, to encompass not only hair wetted by water, but also hair wetted by liquids other than water. For example, hair may be wetted by a solvent-based colourant, which the invention may be used to dry and/or style.

Background to the Invention

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

Similarly, a heated brush or hair dryer can also be used to style hair by heating the hair to a temperature suitable for styling. After being heated by a heated brush or the hot air from a hairdryer, a so-called ‘cool-shot’ of cooler air can be used to set a style in place. A desired curl compression (e.g. tight curl, loose curl, straight hair) can be achieved depending on a number of factors, including but not limited to: the type of device being used, the moisture level of the hair (e.g. before/after styling); the temperature used for styling; ambient temperature, the amount of time the hair is exposed to heat; and the rate of cooling down the hair after styling.

However, regardless of the type of hair styling device and the techniques used to style the hair, users may have difficulty achieving the desired look. For example, it may be difficult to achieve an even curl compression or straightened hair, especially for inexperienced users. The risk of hair damage may also be increased when the user needs to make several attempts to get the desired hair style using the hair styling device. There is therefore a need for improved hair styling devices that can help to improve the user experience and allow achieving the desired hair styling effects with ease.

The present invention aims to address or at least partially ameliorate one or more of the above problems.

Summary of the Invention

The present invention provides apparatus for drying or styling hair, and methods for drying or styling hair, as set out in the appended claims.

The present invention provides an apparatus for styling hair, the apparatus comprising: a handle portion for holding the apparatus; a styling portion for styling the hair; heating means for heating hair that is being styled by the styling portion; at least one sensor on a casing of the apparatus for determining a temperature or a position associated with the hair whilst performing a styling process; and a controller configured to control the apparatus to take at least one action in relation to an output of the at least one sensor. The at least one action may be to store the output for subsequent processing for hair diagnostic purposes, for user educational information etc. That subsequent processing may be performed on the apparatus or on a remote device such as a remote server or the user’s mobile telephone or the like. Alternatively, the at least one action may be to process the output from the at least one sensor during the styling process to provide feedback to the user during the styling; or to control the heater(s) to increase the heating if the hair is not being heated enough to create a desired style or to decrease the heating if the hair is being overheated and damaged.

The at least one action may also or instead comprise one or more of actions selected from the group of: adjusting a power supplied to the heating means (for example to make sure that the hair is not damaged); determining a type of styling process (for example a straightening or curling process); determining an amount of hair to be heated (for example a size of a tress of hair being styled by the apparatus); determining the type of hair being heated; determining an angle or a curvature at which the hair is removed from the casing whilst performing the styling process (which is indicative of an amount of curl imparted to the hair); determining whether a specific style has been achieved by the styling process; predicting user satisfaction with the styling process; storing the output from the at least one sensor for subsequent processing; storing the output to adjust future performance; storing the output to calculate competence of the user; sending the output from the at least one sensor to a remote device; and/or outputting feedback relating to the styling process to a user of the apparatus (which may include instructions for how to use the device to achieve a desired hair style or instructions to use a different control setting of the apparatus or the like).

The controller may be configured to control the styling process, based on an output of the at least one sensor, to attain a curl compression level of the hair within a threshold range of a target curl compression level.

The at least one sensor may be located on an edge of a surface heated by the heating means. A plurality of sensors may be arranged over the handle portion and/or the styling portion. Where the at least one sensor is arranged on the handle portion of the apparatus, the at least one action may include determining a grip or an orientation of the apparatus.

According to another aspect, the present invention provides an apparatus for styling hair, the apparatus comprising: a handle portion for holding the apparatus; a styling portion for styling the hair; at least one sensor mounted on the handle portion for determining information on how the user is holding the apparatus during a hair styling operation; and a controller configured to control the apparatus to take at least one action based on the determined information.

The at least one action may be to store the determined information for subsequent processing for hair diagnostic purposes, for user educational information etc. That subsequent processing may be performed on the apparatus or on a remote device such as a remote server or the user’s mobile telephone or the like. Alternatively, the at least one action may be to process the determined information during the styling process to provide feedback to the user during the styling; or to control the heater(s) to increase the heating if the hair is not being heated enough to create a desired style or to decrease the heating if the hair is being overheated and damaged. The determined information may be used to predict the type of style the user is trying to achieve or the competence of the user using the device and the controller may control the operation of the device based on the predicted style or competence of the user.

The at least one sensor may comprise a continuous sensor arranged along a width or length of the handle portion and/or the styling portion or may comprise a plurality of sensors arrayed over the styling portion and/or over the handle portion.

The at least one sensor may comprise one or more selected from the group of: a thermistor, a negative temperature coefficient (NTC) sensor, a thermocouple, an infrared radiation sensor, a pressure sensor, a force sensor, a proximity sensor, an optical sensor, a light sensor, a humidity sensor, an integrated ohmmeter, an accelerometer, a gyroscope, a magnetometer, and an anemometer.

The apparatus may comprise a memory that is configured to store a plurality of operating parameters of the apparatus for controlling the styling process; and the apparatus may be configured to identify, based on an output of the sensor, an operating parameter to use from the stored plurality of operating parameters. The operating parameters may include at least one of an operating temperature or power, or a heat output. The apparatus may further comprise means for generating an indication to the user, based on the output of the at least one sensor, whether a desired hair styling result has been achieved. The indication comprises at least one of a visual indication, an audible indication, and a haptic indication.

The at least one sensor may be mounted on a circuit board inside the casing or may be embedded within the casing.

In some embodiments, the casing is deformable and the sensor is a force sensor that is configured to sense deformation of the casing.

According to a further aspect, the invention provides apparatus for styling hair, the apparatus comprising: a heating member for heating hair that comes into contact with the heating member, the heating member comprising a heating portion and a sensing portion; a heater for heating the heating portion of the heating member; at least one temperature sensor mounted on the sensing portion; and wherein the heating member comprises a thermal restriction portion positioned between the heating portion and the sensing portion that restricts propagation of heat from the heating means towards the sensing portion.

The thermal restriction portion may provide a thermal bottleneck to heat flow from the heater to the sensing portion.

The thermal restriction portion may comprise a gap, a slot, or a groove between the heater portion and the sensing portion. The gap, slot or groove may be at least partially filled with a thermally insulating material.

The heating member may comprise a heater plate having a heater surface that heats hair that contacts the heater surface.

The sensing portion is typically located along an edge or peripheral portion of the heating member, and the at least one temperature sensor is configured to measure a temperature of the hair as the hair passes from the heating portion to the sensing portion.

The apparatus may comprise a plurality of bristles and the heating member comprises at least one of the bristles. The sensing portion may be located on or at the base of one or more of the plurality of bristles. The at least one temperature sensor may be configured to measure a temperature of the hair as the hair passes from the heating portion to the sensing portion. The at least one temperature sensor may comprise at least one of a thermistor, a negative temperature coefficient (NTC) sensor, a thermocouple, a resistive track or wire, an infrared radiation sensor, and an optical sensor.

The apparatus may be a hair straightener, a hair curler, a hair dryer, a hot paddle brush, a hot round brush, a heater roller, or a combination thereof.

The at least one sensor may be a point sensor or a continuous sensor that extends along a length of the sensing portion.

The present invention also provides an apparatus for styling hair, the apparatus comprising: a handle portion for holding the apparatus; a styling portion for styling the hair, the styling portion comprising a heating member for heating hair that comes into contact with the heating member and a plurality of bristles for applying tension to the hair, wherein at least one of the bristles is a sensor bristle for sensing the temperature of the hair; and a controller configured to control the apparatus to take at least one action based on the sensed temperature of the hair.

The at least sensor bristle may comprise a temperature sensor mounted on the sensor bristle or mounted at a base of the sensor bristle.

One or more of the bristles may be heated bristles that are thermally coupled to the heating member. The at least one sensor bristle may be a heated bristle that is thermally coupled to the heating member. The controller may be configured to control a heat output of a heater that heats the heating member in dependence upon the sensed temperature of the hair. This can help to avoid damage of the hair.

The invention also provides corresponding methods.

Brief Description of the Drawings

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

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

Figure 1b shows the hair styling device in use;

Figure 2a shows an overview of a second exemplary hair styling device;

Figure 2b shows the second hair styling device in use;

Figure 3 shows a simplified block diagram of the main electrical and electronic components of the hair styling device shown in Figure 1a or 2a;

Figure 4a to 4g illustrate schematically exemplary ways in which sensors mounted around a casing of the styling device may be used;

Figures 5a and 5b illustrate the way in which a thermal bottleneck can be used to allow a temperature sensor to be mounted on a heater plate of a hair styling device;

Figures 6a and 6b illustrate how a filler material may be used to fill a gap in a heater plate that forms a temperature bottleneck;

Figures 7a and 7b illustrate different sensors that can be mounted on the heater plate;

Figures 8a, 8b and 8c illustrate a hair styling device having six point temperature sensors mounted on each heater plate of the device;

Figures 9a, 9b and 9c illustrate a hair styling device having two distributed temperature sensors mounted on each heater plate of the device;

Figure 10a and 10b illustrate the way in which a wire based temperature sensor can be mounted on the heater plate of the hair styling device;

Figure 11 a and 11 b illustrate the way in which a thick film or printed temperature sensor track can be formed on an inner surface of the heater plate;

Figure 12 illustrates the way in which thick film or printed temperature sensor tracks can be formed on an outer surface of the heater plate; Figure 13 illustrates the way in which tabs on a heater carrier can be received in slots of the heater plate to provide a smooth hair contacting surface on the upper (hair contacting) surface of the heater plate;

Figures 14a to 14c illustrate an exemplary way in which thermal bottlenecks are formed in the heater plate by shaped slots and fillers that are shaped to fill the slots in the heater plate;

Figures 15a to 15d illustrate schematically an exemplary way in which the present invention may be realised using a hair curler device;

Figures 16a to 16c illustrate schematically an exemplary way in which the present invention may be realised using a brush type of hair styling device;

Figure 17a and 17b illustrate the way in which a thermal bottleneck can be formed in a bristle of a hot brush hair styling device;

Figures 18, 19 and 20, illustrate how one or more sensor bristles can be provided in a hot brush type of hair styling device;

Figure 21 shows a user input dial;

Figures 22a and 22b show an overview of another exemplary hair styling device; and Figures 23 shows an overview of an exemplary hot brush type of hair styling device.

In the figures, like elements are indicated by like reference numerals throughout.

Detailed Description of Preferred Embodiments

The present embodiments represent the best ways known to the applicant of putting the invention into practice. However, they are not the only ways in which this can be achieved.

Device Overview

Figure 1a shows an overview of a hair styling device suitable for implementing one or more of the inventions described herein. However, the hair styling device need not necessarily be of the type illustrated in Figure 1 a. Any other suitable type of hair styling or hair drying device may be used, such as a heated brush (e.g. a paddle brush), a hair dryer, or a combined hair dryer I sty ler device (e.g. as shown in Figure 2a). The device may use any one of conductive heating, convective heating, or radiative heating (or any combination thereof) to transfer heat to the hair 16 of a user. The device 10 shown in Figure 1a is a hair straightener that comprises a pair of arms 12a, 12b, and a corresponding pair of heater plates 15a, 15b for transferring heat by conduction to the hair 16 of a user. The arms 12 are moveable between an open position in which a tress of hair 16 can be inserted between the heater plates 15 and a closed position in which the tress of hair 16 is sandwiched between and in contact with the heater plates 15. As a result, the hair 16 is heated through conduction of heat from when the tress of hair 16 touches the heater plates 15. Figures 1 b and 2b show the hair styling devices 10 in use during a styling process. During use, the user will insert a tress of hair 16 to be styled between the heater plates 15 and then they will pull the device 10 down along the tress of hair 16. If the device 10 is pulled straight down the tress of hair 16, then the device 10 can straighten the hair. If the device 10 is rotated so that the hair 16 that exits the device 10 is forced to go through a change in direction, then a curl can be imparted to the hair. The amount of curl depends on the speed with which the user pulls the device 10 along the tress of hair 16 and the amount that the device 10 is rotated. It has also been observed that the shape/path over which the hair is cooled has a strong influence on the curl shape. Thus, the device 10 can be used to both straighten and to curl the hair 16, or to provide “body and volume” to the hair 16 (if necessary, preceded or succeeded by the application of styling products such as mousse, gel, wax, hairspray, etc.).

A user interface 11 is provided to allow the user to set user defined parameters (if applicable) and for the device 10 to output information to the user. For example, optimum styling settings (such as an optimum styling temperature, power, direction, or speed) may be indicated or confirmed to the user via the user interface 11. In some devices, the user may be able to set a desired curl level for their hair 16 via the user interface 11. The user interface 11 may have a dial, button, or a touch display for allowing the user to input information to the device 10 and the user interface 11 may have an indicator light, display, sound generator or haptic feedback generator for outputting information to the user. In this embodiment, the user interface 11 also comprises a control button or switch 14 to enable the user to turn the device on or off; and an indicator light 13 to show whether the power is on. A printed circuit board assembly may be provided at any suitable location within the housing of the device 10 for controlling the operation of the device 10 and for controlling the interaction with the user via the user interface 11. In this example, electrical power is provided to the device 10 by means of a power supply located at an end of the device, via a power supply cord 7. The power supply may be an AC mains power supply. However, in an alternative embodiment the power supply may comprise instead or in addition one or more DC batteries or cells (which may be rechargeable, e.g. from the mains or a DC supply via a charging lead), thereby enabling the device 10 to be a cordless product.

As will be described in more detail later, the hair styling device 10 may comprise one or more sensors for determining a temperature of a user’s hair, for sensing an ambient temperature, sensing hair presence and/or thermal load (a combination of section size, speed, packing density, moisture content, and/or the like). It will be appreciated that the user interface 11 may be provided at any suitable location on the device, for example adjacent to the indicator light 13 and control switch 14 illustrated in Figure 1a. A separate user interface may be provided, for example, as a smartphone application and/or the like.

As shown in Figure 2a, the hair styling device 10 is not restricted to devices having two arms 12 and instead may be a single arm device that has bristles 20 for imparting tension on the hair as the device 10 is moved through the hair. In the device 10 shown in Figure 2a, the bristles 20 extend out from a heated surface 5 that heats hair that comes into contact with the heated surface 5. One or more of the bristles 20 may also be heated to increase the heating surface area available for heating the hair. Heated air may also be delivered to heat the hair via holes in the heated surface 5 or via holes in the bristles. This allows the hair to be heated by both heated air and by conduction when the hair touches the heated surface 5 or the heated bristles 20.

The present invention is not limited to the types of hair styling devices 10 illustrated in Figures 1a and 2a. For example, a hair styling device 10 that instead (or additionally) transfers heat to hair using radiative heating can also be used. More generally, any suitable hair styling device capable of transferring heat to the hair of a user could be used.

Illustrative Block Diagram

Figure 3 is a simplified block diagram of the main electrical components of the hair styling device 10. As shown, the hair styling device 10 comprises a power supply 31 that may derive power from a mains power supply input. Additionally or alternatively, power may be derived from a DC power supply and/or a battery, in which case the mains power supply input can be used to charge the battery via an AC to DC converter, which may be external or internal to the hair styling device 10.

In this example, power is provided to one or more heaters 32 that heat the heater plates 15 or the heated surface 5. In the case that the device 10 delivers a heated air stream that heats the hair 16, the heaters 32 heat the air stream generated by one or more fans 33 that are rotated by one or more fan motors 34. The power supplied to the heater(s) 32 is controlled by a controller 35 having a microprocessor 36. The power supplied to the heater(s) 32 may be controlled using one or more power semiconductor switching devices (triacs) to control application of an AC mains voltage (or a DC voltage derived from the AC mains or from the battery) to the heaters 32. When the hair styling device 10 comprises a plurality of heaters 32, a pair of heaters 32 may be powered during a heat-up phase to reduce the time taken to reach a desired operating temperature. Similarly, if the temperature of a hair contacting surface of the device 10 drops below a desired operating temperature when wet hair comes into contact with the heater plates 15 or the heater surface 5, both heaters 32 may be powered to provide a boost of heat (in a so-called “boost mode”) to counter heat lost to the wet hair, and to increase the removal rate of water from the hair. At other times, only one of the heaters 32 might be powered to maintain a desired (set point) operating temperature. The device 10 may also include a mode in which both heaters 32 are switched off (disabled), and a stream of cool air (air at ambient or near-ambient temperature) is generated by the fan 34 for cooling the hair of the user. This mode is a so-called “cool-shot” mode, which may be used to set a style of the hair, or may be used to control the evaporation of moisture from the hair, to provide finer control of the moisture level. The cool-shot mode may also be used to cool a part of the hair styling device 10 if it is overheating.

The cool-shot mode could be provided using any other suitable method.

The microprocessor 36 is coupled to a memory 37 (which is typically a non-volatile memory) that stores processor control code for implementing one or more control methods to be described later.

Figure 3 also shows that the user interface 11 is coupled to the microprocessor 36, for example to provide one or more user inputs and/or output indications such as a visual indication, haptic indication (vibration), or an audible alert. The output(s) may be used to indicate to the user, for example, general styling efficacy.

To help control the styling process, it is advantageous to have accurate measurements (either direct or indirect) of the current temperature of the user’s hair 16 and/or the position of the hair 16 in relation to the styling device 10. Therefore, as described in detail below, the hair styling device 10 may be provided with one or more temperature sensors 18 and/or force/proximity sensors 19.

The temperature sensor(s) 18 may be configured for sensing the temperature of the hair 16 through direct contact measurements using (for example) a thermistor, negative temperature coefficient (NTC) sensor, or a thermocouple. Alternatively, or additionally, non-contact measurements (e.g. using an infrared sensor) could be used to measure the temperature of the hair. More generally, the device 10 may comprise any suitable sensor for measuring the temperature of the hair 16.

The temperature sensor(s) 18 are configured to measure or sense the temperature of a part of the device 10 that comes into contact with the user’s hair and which is thermally isolated (to a certain extent) from the heater 32 used to heat the hair. The temperature sensor(s) 18 and/or force/proximity sensor(s) 19 could be provided inside a main body portion of the device 10, on the heater plates 15 for example, or could be provided on an exterior/interior surface of the device 10. A temperature can be measured directly or indirectly. For example, a heat pipe could be used to transfer heat through conduction from the part whose temperature is to be measured to an internal sensor 18. Force sensors 19 may be provided internally, for example on the head (or styling portion) of the device 10, and they may be configured to measure the force exerted by the hair 16 on the casing 17, at various points. The casing 17 may be made of a soft or deformable material to allow sensing force internally.

The device 10 may also comprise one or more wetline product dispensers 38 for dispensing liquids such as water or styling products onto the user’s hair. The device 10 may be configured to dispense liquid from a dispenser 38 onto the user’s hair during the drying or styling process to provide improved control of the moisture level of the hair. Alternatively, a wetline product dispenser could be provided separately from the device, for example as a separate diffuser (e.g. a desktop-based diffuser).

Finally, the device 10 may have communications circuitry 39 to allow the device to communicate with a remote sensor, a remote server, or a remote application (e.g. on a mobile telephone or tablet computer). The communications circuitry 39 may use, for example, Bluetooth, Wi-Fi and/or 3GPP communication protocols to communicate with the remote device.

The microprocessor 36 may be configured to communicate with the heater 32, fan 33, fan motor 34, wetline product dispenser 38, temperature sensor(s) 18, force/proximity sensor(s) 19, user interface 11 , communications circuitry 39 and power supply 31 via one or more communication interfaces or transceivers in accordance with software stored in the memory 37. The memory 37 may store, for example, one or more operating profiles or parameters. Software stored in the memory 37 may include, for example, an operating system and a hair styling control module suitable for implementing one or more of the control methods described below.

As those skilled in the art will appreciate, the device 10 does not need to have all of the blocks illustrated in Figure 3. For example, if the device 10 is a hair straightener, then it may not have the fan(s) 33 and the fan motor(s) 34. Similarly, in some embodiments there may be no sensors 18/19, no wetline product dispenser(s) 38 and no communications circuitry 39. Case Sensing

Beneficially, the hair styling device 10 detects (or estimates) the amount of curl imparted to the user’s hair by using a plurality of temperature sensors 18 that are arrayed across the outer casing (or housing) 17 of the hair styling device 16 (as illustrated in Figure 1a). The styling performance is determined based on a combination of temperature and angle. Specifically, the heater plates 15 of the styling device 10 heat the hair to above the glass transition temperature of hair making it mouldable and the angle at which the hair 16 leaves the device 10 is detected from the outputs from the temperature sensors 18 located around the circumference of the device 10, and from this angle the microprocessor 36 can determine the amount of curl imparted to the user’s hair. More specifically, as mentioned above, if the user pulls the hair styling device 16 along the user’s hair without rotating the device 16, then the hair styling device 16 will straighten the user’s hair and the heated hair will not touch the casing 17 and so none of the temperature sensors 18 mounted around the circumference of the casing 17 will register an increase in temperature caused by the heated hair touching the casing 17 in the vicinity of each temperature sensor 18.

This scenario is illustrated in Figure 4a, which is a schematic transverse cross-sectional view of the hair styling device 10 shown in Figure 1a. If the user rotates the device 10 through 90 degrees relative to the direction of travel of the hair styling device 10 along the user’s hair 16, as shown in Figure 4b, then as the hair leaves the heater plates 15, it will turn sharply through 90 degrees and this will impart a certain amount of curl to the user’s hair 16. The heated hair 16 coming out of the device 10 will also come into contact with the casing 17 near the temperature sensor 18-1 which will mean that the temperature sensed by this temperature sensor will be higher than the temperatures sensed by the other temperature sensors 18-2 to 18-6 that are located further around the circumference of the casing 17. If the device 10 is rotated a further 90 degrees, then, as illustrated in Figure 4c, the heated hair 16 will be pulled into a tighter curl and will also come into close contact with the part of the casing 17 near temperature sensor 18-2. This means that the microprocessor 36 will receive elevated temperatures from temperature sensors 18-1 and 18-2 compared with the sensor measurements from temperature sensors 18-3 to 18-6. As the device 10 is rotated more and more, a tighter curl is imparted to the user’s hair when the device 10 is rotated through approximately 450 degrees (as shown in Figure 4d) or possibly more (the device 10 can be rotated many times around the hair 16 to leave a desirable shape). In this case, all of the temperature sensors 18-1 to 18-6 will register an elevated temperature. Therefore, by processing the temperature sensor signals from the temperature sensors 18 and looking at the temperature differentials between the measurements obtained from the temperature sensors arrayed around the circumference of the casing 17, the microprocessor 36 can work out how much the user has rotated the hair styling device 10 and therefore how much of a curl will be imparted to the user’s hair. This calculation can be further validated or performed instead using a gyroscope and accelerometer. The microprocessor can also look at the difference in temperature sensed from the sensors 18-1 and 18-6 to determine which direction the user has rotated the device 10 - if the measurement from sensor 18-1 is higher than the measurement from sensor 18-6 then the device has been rotated anticlockwise whereas if the measurement from sensor 18-6 is higher than the measurement from sensor 18-1 then the device has been rotated clockwise. A pressure or force sensor can be used in addition or instead to model the direction of hair tension. The information on the direction of the hair may be used to help achieve symmetry of hair style and/or a desired style. For example, the information on hair direction may be used for facilitating appropriate symmetry of hair style between left and right sides of the user’s head or to achieve alternating curl directions among adjacent tresses of hair. Different styles may require different directions of curls, e.g. some styles may alternate direction of curls between adjacent sections of hair and in case of other styles all curls twist towards (or aways from) the users face. Therefore, by gathering this information and comparing it to style information for a style the user is trying to replicate, the microprocessor can provide useful feedback to the user to teach them how to achieve the desired style.

Of course, the amount of curl imparted to the hair does not just depend on the amount that the hair styling device 10 is rotated during use. It also depends, among other things, on the speed with which the user pulls the device 10 along the tress of hair 16 and the size of the tress of hair 16 that is inserted between the heating plates 15. When considering the size of the tress and the speed with which the tress is pulled through the device 10, the microprocessor can again use the signals from the temperature sensors 18 to estimate these variables. Specifically, if the device 10 is pulled slowly along the tress, then the hair 16 will heat up more and the casing 17 will also heat up more because the hotter hair 16 is in contact with the casing 17 for longer than if the device 10 is pulled more quickly along the tress of hair 16. Therefore, the microprocessor 36 can estimate the speed with which the device 10 is pulled along the tress from the absolute temperature that the temperature sensors 18 register and using predetermined calibration data that relate the sensed temperatures to a speed of use (which calibration data may be determined in the factory or in a calibration routine performed with the user in which the user is asked to pull the device through their hair at different speeds).

The size of the tress can be estimated by looking at the relative temperatures from different temperature sensors arrayed along the length of the device. In particular, Figure 4e is a plan view showing the temperature sensors 18 arrayed over the casing 17a of the upper arm 12a. As shown, there are twelve temperature sensors that are arranged in 2-dimensional grid - with three sensors 18-1 to 18-3 in the width direction and 4 sensors 18-1 a to 18-1 d in the length direction. Of course, the sensors 18 do not have to be arrayed in such a regular 2-dimensional grid - such an arrangement is simply shown for illustration purposes. Depending on the size of the tress, different temperature sensors 18 will register a rise in temperature. Thus, for example as shown in Figure 4e a small tress of hair may come into contact with the casing 17 near just one column of the temperature sensors 18 (in this illustration sensors 18-1 b, 18-2b and 18-3b) and so all of these temperature sensors will register an increase in temperature compared to the temperatures registered by the other temperature sensors 18. However, as the tress of hair 16 gets larger, it will come into contact with the casing 17 nearer more of the temperature sensors 18 so more of the temperature sensors 18 in the length direction will register a temperature rise - as illustrated in Figures 4f and 4g. So, by looking at the difference in temperature measurements obtained from the temperature sensors arrayed along the length direction, the microprocessor 36 can determine an estimate for the size of the tress of hair 16. With knowledge of the size of the tress of hair, the speed with which the device 10 was moved along the tress of hair 16 and the amount that the device was rotated during the styling process, the microprocessor 36 can make a good prediction on whether a curl has been achieved and, if so, how much and how tight a curl has been achieved. If the user has entered (via the user interface 11) in to the microprocessor 36 what kind of curl they wish to achieve, then the microprocessor 36 can compare the predicted curl that has been achieved with the desired curl and then output feedback to the user to help them achieve the curl that they wish to achieve. For example, the feedback might be instructions output on a display to move the device 10 less quickly along the tress of hair 16 or it might be instructions to reduce the size of the tress of hair 16 that is put through the device 10 at any one time or it might be to rotate the device 10 more during use or any combination of these.

It will be appreciated that instead of or in addition to the array of temperature sensors 18 mounted in the casing 17, an array of force/proximity sensors 19 may be used in the same way to determine the size of the tress of hair 16 and the amount that the device 10 is rotated during use. Force/proximity sensors 19 may be provided on the external surface of the head of the device 10. Alternatively, they may be provided under the casing (which may be made of soft or deformable material to allow sensing of the presence of hair 16 and/or a force exerted by the hair 16 at specific parts of the head). Force/proximity sensors 19 cannot be used to sense the speed with which the device 10 is moved along the tress of hair 16, but some other sensor could be used for that - such as a single temperature sensor or a motion sensor or the like. Another factor when determining the efficacy of a curl is humidity. The longevity of a curl can be influenced by the saturation of the hair and the ambient humidity during styling. Sensing the temperature of the hair as it exits the device and comparing that to the plate temperature, the controller can determine the heat capacity of the hair and thus how wet it is. Then, a humidity sensor can be used to measure the ambient humidity, and the controller can then adjust the plate temperature to optimise performance for the styling environment. Additionally, or alternatively, a solvent applicator (this can be automatic from the device or manually by the user) can wet the hair further keeping the hair in optimal condition for the styling environment.

Energy delivered to hair (power over known period of time) can be used as a proxy for hair temperature (e.g. if direct measurements of hair temperature are not available). In conjunction with measurements of section (tress) size, speed, and an assumption of moisture content the power delivered to hair is proportional to temperature.

In summary, appropriate temperature sensors 18 and/or force/proximity sensors 19 may be mounted on the casing 17 or inside the casing 17 to determine the size or volume of hair 16 (when the sensors 18/19 are arranged along the circumference of the device 10) and they may be used to determine the amount that the device 10 is rotated during use and/or the angle at which the hair 16 leaves the device 10 (when the sensors 18/19 are arranged in a length direction of the casing 17).

Measuring hair temperature through heater contact

In prior art hair stylers, temperature sensors are used to detect the temperature of the heater and this information is fed back to a controller to control the heating of the heater in a closed control loop. The inventors have realised that better control can be achieved if the temperature sensors actually sense the temperature of the user’s hair that is being heated rather than an internal part of the heater - as it is the temperature of the user’s hair that should be controlled to avoid damage and to ensure it is heated to a sufficient temperature to allow a style to be applied to the hair. If hair temperature (or a proxy for the hair temperature) can be measured, then the control system can provide the following benefits:

• Improved styling performance (e.g. by changing/adapting the power supplied to the heater 32)

• Decrease hair damage (e.g. by changing/adapting the power supplied to the heater 32)

• Improved power efficiency (e.g. by changing/adapting the power supplied to the heater 32)

• Provide user feedback

• Provide diagnostic data The inventors have realised that the temperature sensors around the casing 17 can provide a good indication of the temperature of the hair that contacts the casing. For example, in the situation illustrated in Figure 4, the temperature sensor 18-1 next to the edge of the device 10 can be used to give a reasonable measurement of the temperature of the hair as it leaves the heater plates 15. Ideally the temperature sensor would be mounted as close as possible to the edge of the heater plate 15 where the hair has been heated to its hottest temperature. However, conventional wisdom suggests that placing temperature sensors on or near the heater plate 15 will not work because the temperature measurements will be affected by the heat from the heater 32 that heats the heater plate 15. In particular, the heater plate 15 is designed to be a good thermal conductor. So, mounting a temperature sensor 18 at the edge of the heater plate 15 will normally render the measurements too noisy to use as a measure of the hair temperature. However, the inventors have realised that by introducing a thermal bottleneck between the temperature sensor(s) 18 and the heater 32 used to heat the heater plate 15, more accurate measurements of the hair temperature can be made.

The aim of this design is to accurately measure a signal which represents hair temperature. As generally shown in Figure 5a, if a temperature sensor 18 is mounted in a sensing region 152 at the edge of a traditional heater plate 15, the temperature measurement obtained from this sensor 18 will be relatively noisy due to heat from the heat source 32 passing along the heater plate 15 and heating up the temperature sensor 18, leading to low sensitivity to hair temperature. However, the thermal bottleneck 40 shown in Figure 5b aims to improve the signal-to-noise ratio and allow measuring the hair temperature signal more accurately using the temperature sensor 18 mounted in the sensing region 152 at the edge of the heater plate 15. Although not shown in Figures 1a and 2a, such a thermal bottleneck 40 can be applied to various hair styling devices 10 such as stylers (aka straighteners), curlers, and hot brushes that are equipped with temperature sensors 18. In this context, the term ‘signal’ is the signal output of the temperature sensor representing the temperature of the hair or a proxy measurement, and the term ‘noise’ refers to any alternative source(s) of heat (notably the heater temperature) affecting the sensor output. In the example illustrated in Figure 5, the thermal bottleneck 40 is located between the sensing region 152 at the edge of the heater plate 15 (which comes into contact with hair during device use) and the main part 151 of the heater plate 15 that is heated directly by the heater 32. Effectively, the thermal bottleneck 40 restricts the flow of heat from the heater 32 along the heater plate 15 to the sensing region 152 at the edge of the heater plate 15 where the temperature sensor 18 is mounted. An optimal thermal bottleneck 40 maximises the temperature drop in the sensing region when one tress of hair 16 is removed from the device 10 and the next tress of hair 16 is placed onto the heater plate 15 and heated to the desired temperature (e.g. 185 °C) in the main part 151 of the heater plate 15 adjacent to the heater 32. This arrangement improves the signal-to-noise ratio of the hair temperature measurement, allowing the measured temperature values from the sensor 18 to be used as a proxy for hair temperature. The larger the temperature drop in the sensing region, the more sensitive (faster and more accurate) the hair temperature proxy measurement becomes.

Thermal bottleneck

The following is a detailed description of the thermal bottleneck 40 used in some embodiments. Beneficially, the thermal bottleneck 40 is used for improving/maximising sensitivity of the temperature sensors 18 by reducing the effect of the heater 32 on the temperature sensors 18.

In more detail, when using a heater plate 15 with a relatively high thermal mass (e.g. a ceramic heater sty ler plate or brush head) the sensitivity of the system to temperature changes during a hair pass is quite low. To improve the sensitivity of the system a thermal bottleneck 40 is created by reducing the area of conduction between two bodies, which reduces the possible heat flux (shown by Fourier’s Law of conduction). This allows a greater temperature change in the bottleneck area when a load (the hair) is applied, allowing better sensitivity for a sensor in this area. The thermal bottleneck area is also more heavily influenced by the hair temperature rather than the central heater temperature. This means that a sensor in this region can be relied on as a proxy for hair temperature. The thermal bottleneck 40 may be realised as a region with a relatively small cross- sectional area which restricts the transfer of heat from the heater 32 to the temperature sensor 18. In one configuration, the thermal bottleneck 40 is a provided in the form of a groove on or slot in at least one surface of the heater plate 15. In other words, the thermal bottleneck 40 may be realised either as a blind hole (or groove) or as a through hole (or slot) in the heater plate 15 that is located between the sensing region 152 and the main part 151 of the heater plate 15 that is coupled to or adjacent to the heater 32.

As shown in Figures 6a and 6b, the groove that forms the thermal bottleneck 40 may be provided with an appropriate insert 45, such as an l-profile insert 45-1 or a n-profi le insert 45-2. The insert 45 may be made from a thermally insulating material or a metal having a relatively low heat conduction coefficient (e.g. aluminium) compared to the material of the heater plate 15. The use of an insert 45 may be particularly beneficial when the thermal bottleneck 40 is provided on a surface of the heater plate 15 that comes into contact with the hair 16 as it helps to present a smoother surface to the user’s hair than if a groove or a slot is present.

Regardless of which type of thermal bottleneck 40 is used, the temperature sensors 18 are generally located on a side of the thermal bottleneck 40 that is opposite to the side on which the heater 32 is located to optimise the effect of the thermal bottleneck 40. Beneficially, providing a thermal bottleneck 40 on the side of the heater plate 15 that the hair contacts maximises the sensed temperature drop signal.

The addition of the thermal bottleneck 40 means that the sensor region 152 (the region where the temperature sensors 18 are located) has a larger temperature gradient when a tress of hair 16 is applied to the heater plate 15. Since the sensor 18 has a larger temperature change to read, the signal to noise ratio is improved.

Temperature sensor types

Figures 7a and 7b are schematic plan views of the heater 32 and heater plate 15 showing two exemplary sensor designs that can be used to sense the temperature of the hair as it exits the heated surface of the heater plate 15. Specifically, Figure 7a shows a number (in this example 6) of discrete point temperature sensors 18 located along the two elongate edges of the heater plate 15. Temperature sensors 18 are provided along both edges because the hair styling device 10 is typically designed to be able to be used in a left hand or a right hand of the user - so hair can pass through the device 10 in either direction. Figure 7b shows two continuous (or distributed) sensors 18 along the edges of the heater plate 15. Thus, temperature sensing may be realised using point sensors such as thermocouples, thermistors and RTDs or using distributed sensors such as resistive wires, resistive tracks, optical temperature sensors, or a combination thereof. Continuous sensors (distributed sensors) may only need two sensors for full coverage of the edge of the heater plate 15 and they may be more accurate than the same number of discrete sensors. On the other hand, discrete sensors (point sensors) may provide a more accurate reading of respective hair temperatures of different parts of the styling device although multiple sensors may be needed for full coverage along the edge of the heater plate 15. Multiple sensors can also be used to estimate hair section (tress) size or at least section width based on the number of sensors covered by hair and/or size of signal.

For the sake of completeness, Figures 7a and 7b also show the thermal bottlenecks 40 although they are optional in some embodiments. In this example, the point sensors 18 in Figure 7a are each surrounded by an associated thermal bottleneck 40 band (with or without a filler 45). The distributed sensors in Figure 7b are separated from the heat source I heater element 32 by thermal bottlenecks 40 in the form of grooves or linear slots or gaps 40 in the heater plate 15.

It will also be appreciated that any other suitable thermal bottleneck 40 may be used regardless of the sensor type or sensor technology. For example, the thermal bottleneck 40 design used for the point sensors shown in Figure 7a may be used for the distributed sensors shown in Figure 7b and the thermal bottleneck 40 design used for the distributed sensors shown in Figure 7b may be used for the point sensors shown in Figure 7a, if appropriate. It will also be appreciated that any other suitable thermal bottleneck 40 may be used.

Exemplary designs and concepts for some sensor types are shown in Figures 8a to 14c. Point sensors

Figures 8a to 8c illustrate schematically an exemplary way in which discrete sensors may be placed at various points on the heater plates 15 of the styling device 10. In this example, there are six sensors on each heater plate 15, in two rows of three sensors one row along each of the two opposite longitudinal edges. It should also be noted that the sensors 18 that are in view in Figure 8a would not be in view in the actual product as these would be hidden beneath the surface of the heater plate 15 and hidden by the surrounding casework/housing. Such discrete sensors may provide a very accurate measurement of a particular area and may allow an improved control of the overall styling process and/or the operation of the device 10. Figure 8b is a cross-sectional view of the heater plate assembly 22 comprising the heater plate 15 (that contacts the user’s hair) and a heater carrier 50 that holds the heater plate 15 in the caseworks/housing of the sty ler arm. Figure 8c illustrates the underside of the heater plate 15 and showing the arrangement of the temperature sensors 18 in a sensing region along the edge of the heater plate 15. Figure 8c also illustrates the heater 32 that provides the heat to the heater plate 15 and which is held in place against the inner surface of the heater plate 15 by the heater carrier 50.

Distributed sensors

Figures 9a to 9c illustrate schematically an exemplary way in which distributed sensors (temperature sensors 18) may be placed on the edges of the heater plates 15 of the styling device 10. In this example, there are two sensors on each heater plate 15, one on each edge. Figure 9b is a cross section of the exemplary heater plate assembly 22 showing the arrangement of the temperature sensors 18 in relation to the heater plate 15 and the heater 32 (which is located inside the assembled device). Figure 9c illustrates the underside of the heater plate 15 showing the location of the temperature sensors 18 and the heater 32.

Turning now to Figures 10a to 10c, the temperature of the hair may be measured using a nickel wire temperature sensor 18 that changes resistance with temperature. In this case, the nickel wire acts as a distributed temperature sensor 18. It will be appreciated that any other suitable material may be used for the wire. The wire resistance change can be measured by the microprocessor 36 and then converted into an accurate temperature measurement. This approach may be combined with the thermal bottleneck 40 to give more accurate hair temperature measurements. This represents a low-cost alternative to thermocouples and NTCs with the added benefit of being an average measurement, reducing the possibility of hot spots and heater cracking.

Figure 10a is a cross-sectional view of the heater assembly 22 illustrating the heater carrier 50 and the heater plate 15. Figure 10b is a close-up perspective view of part of the heater carrier 50 showing the temperature sensor wire 18. The temperature sensor wire 18 may be wrapped around the heater carrier 50 to give tension and keep it in place. The wire is pushed against the heater plate 15 by the heater carrier 50. The heater carrier 50 may be compressed by appropriate means, such as spring clip(s), screw(s), and/or compression spring(s). The wire may be a bare wire or may have an outer coating or insulative layer.

Figure 11a and 11 b illustrate schematically another type of distributed temperature sensor 18 deposited by a process such as thick-film printing, chemical etching and/or the like in the sensing region at the two longitudinal edges of the heater plate 15. Typically, the heater plate is made of an electrically conductive material. In order to prevent shorting between the sensor 18 and the heater plate 15, a dielectric layer 55 is provided between the conductive metal heater plate 15 and the sensor track 18. In this case, compression is not needed to hold the temperature sensor 18 against the heater plate 15 as the dielectric layer 55 and the sensor track 18 are thermally and mechanically bonded to each other and the heater plate 15. Benefits of this approach include reduced component count and reduced thermal resistance between the sense track 18 and heater plate surface.

Temperature sensing tracks 18 may also be deposited on the hair side of the heater plate 15, as illustrated in Figure 12. In this case, the hair is directly in contact with the sensing tracks 18 thus the track temperature may more closely represent the hair temperature. In this arrangement, the tracks 18 measure hair temperature as the hair is pulled directly across the tracks. It will be appreciated that conductive vias may be provided through the heater plate 15 to provide an electrical connection between the microprocessor 36 and the temperature sensing tracks 18. The temperature sensing tracks 18 may be formed as thick film tracks or as chemically etched tracks (formed over a suitable dielectric layer) like in the embodiments illustrated in Figures 11a and 11 b.

Figures 13a to 13c illustrate schematically an exemplary thermal bottleneck design on the hair side of the heater plate 15, in which raised tabs 51 on the heater carrier 50 are received into slots 40 formed along the two longitudinal edges of the heater plate 15 which create the above described thermal bottleneck. At least the raised tabs 51 of the heater carrier 50 are made of a plastics material that is thermally insulative so that it is harder for heat from the heater (not shown) to pass into the sensing region 152 of the heater plate 15 where the temperature sensor 18 is mounted.

Figures 14a to 14c illustrate an exemplary design in which fillers 45 made of a thermally insulative material (such as plastics) are provided in the gap between the main part 151 of the heater plate 15 that is adjacent the heater 32 and the sensing regions 152 of the heater plate 15 on which or adjacent to which the temperature sensors 18 are mounted. The fillers 45 again ensure that the hair side of the heater plate 15 presents a continuous smooth surface to the hair being styled. As shown in Figures14b and 14c, the fillers 45 extend between both the hair side and heater side of the heater plate 15.

In the various designs described above, various material and manufacturing options are available. For example, the heater carrier 50 may be made from polyphenylene sulfide (PPS) or a similar plastics material. The heater plate 15 may be made from metal by machining or die casting and in some cases by extrusion. The heater plate 15 may also be manufactured from a formed sheet. The filler 45 may be made of a thermally insulative material.

Optical Temperature Sensing

Another way of sensing the temperature of the hair in the sensing region 152 of the heater plate 15 is to use an optical temperature sensor 18. Using an optical temperature sensor reduces the complexity of having to isolate a resistive temperature sensor 18 from the heater power supply 31 (if AC mains power is used, to avoid the risk of electrocution to the user), and reduces EMC compatibility issues.

An example of a suitable optical temperature sensor is a high temperature Fiber Bragg Grating (FBG) sensor, which is stable under temperatures up to 300 °C. The FBG sensor reflects a wavelength of light, depending on external influences such as temperature, pressure, or expansion fluctuations on the FBG fiber. FBG sensors are manufactured using holographic interferences or a phase mask, which permanently change the refractive index of the fiber depending on the light intensity. This refractive index is referred to as the Fiber Bragg Grating. When a broadband light beam is sent into an FBG, induced reflections of certain wavelengths of the coupled light occur at the points with the manipulated refractive index and these reflections depend on the temperature of the fiber. Therefore, by processing the signal received back from the optical sensor the microprocessor 36 can determine the temperature of the fiber and hence the temperature of the user’s hair 16.

The FBG fiber may be installed in the styler device 10 for example by threading the fiber through a deep-drawn hole through the heater plate 15. The fibre is kept in good thermal contact with the heater plate 15 by a suitable mechanical fit, allowing for easy assembly. Once assembled, the fiber would be clamped in place mechanically to avoid excessive strain or sliding during use.

Thermal Bottleneck Examples - Hair Curler

The thermal bottleneck examples described above have focussed on bottleneck designs for hair stylers like the one illustrated in Figure 1 . In the case of a hair curler, such as the one shown in Figure 15a, the device 10 has a heated outer surface 5 that is heated by one or more heaters mounted within the device. Typically, a thermally conductive heater block 51 is mounted within the device and whose outer shape is matched to the shape of the heated surface 5 of the hair curler. A flat shelf 52 is provided on which a heater (not shown) can be mounted. Heat from the heater passes around the circumference of the heater block 51 and through to the heated surface 5. By placing a pair of slots or grooves 40 at the top of the heater block 51 and/or at the bottom of the heater block 51 , the region between the slots 40 will be thermally isolated (to a certain extent) from the heater and so a temperature sensor 18 placed in either of these regions will be able to determine an accurate measurement of the hair temperature. The slots/grooves 40 may be blind holes or through holes, and they may be filled with appropriate fillers 45 in order to further restrict heat conduction from the heater 32 towards the sensors 18. The sensors 18 may be point sensors or continuous (distributed) sensors, as described above, including resistive wires/tracks, etched or deposited on or below the heated surface 5.

Thermal Bottleneck Examples - Hot Brush

In addition to stylers and curlers, the bottleneck idea can be applied to a hot brush type of hair styling device 10, similar to the device shown in Figure 2a. The design of the hot brush ensures that the sensor region is (at least partially) thermally isolated from the heater. If the sensor is partially isolated, it will regulate at the hot-brush temperature and its temperature will drop as cooler hair comes into contact with the sensor. If the sensor is fully isolated, it will regulate at air temperature (because a fully isolated sensor is no longer part of the heater block) and its temperature will increase when heated hair comes into contact with the sensor. In either case, the microprocessor 36 can process the temperature sensor signal from the sensor to determine the hair temperature. The main concepts are further explained below, with reference to Figures 16 to 20.

Figures 16a to 16c illustrate an exemplary thermal bottleneck 40 on the heating plate 15 of the styler device 10. As shown, the hot brush 10 includes a handle portion 23 and a styling portion (or head) 24 having a plurality of bristles, including plastic bristles 20, heated bristles 25 which are thermally coupled to the heating plate 15 and plastic edge bristles 134. Figure 16b illustrates the heating plate 15 having the heated bristles 25 attached thereto. Figure 16b also illustrates the through holes 27 through which the plastic bristles 20 extend. Figure 16c schematically illustrates the heating plate 15 without the bristles 25 which shows that the heating plate has a generally convex main heating area 151 , with a thermal bottleneck 40 formed by a groove that runs around the edge of the heating plate 15 to define the sensing region 152 on which one or more temperature sensors (not shown) can be mounted. Of course, the groove does not need to run around the entire periphery of the heating plate 15 and could instead be located at one or more edge portions of the heating plate where the temperature sensors will be mounted. Similarly, instead of a groove, the thermal bottleneck can be realised by adding one or more slot(s) to the heating plate 15.

Alternatively still, and as shown in Figures 17a and 17b, some of the heated bristles 25- 1 and 25-2 on the heater plate 15 may be thinned (relative to the other heated bristles 20) to create the thermal bottleneck 40. The thinned bristles 25-1 and 25-2 are supported mechanically by less thermally conductive plastic overmoulds 56 - as shown in more detail in Figure 17b. A wire temperature sensor 18 may then be mounted to these thinned bristles 25-1 and 25-2, for example, in the overmoulds 56 or between the overmoulds 56 and the thinned bristles 25-1 and 25-2. Beneficially, the overmoulds 56 have a good contact with the user’s hair whereas the thinned bristles 20-2 take longer to reach the temperature of the heater plate 15 to which the bristles of the hot brush are connected due to the thermal bottleneck that they present to the heater plate 15. Thus, when cooler hair comes into contact with these thinned bristles, they will cool down towards the temperature of the hair (because of the thermal bottleneck created by the thinner cross-section of these bristles). Accordingly, the temperature sensed by the temperature sensor 18 will be a more accurate representation of the temperature of the user’s hair than if there was no thermal bottleneck.

It is not necessary for the bristles used for temperature sensing to be thermally connected to the heating plate 15. Figure 18 illustrates two co-moulded plastic bristles 136-1 and 136-2 that function as temperature sensors 18. These bristles 136 may be provided on the outer perimeter of the brush head 24 or may form part of the rows of plastic bristles 20 that are located between the heated bristles 25. In a preferred embodiment, four of the outer bristles 134 shown in Figure 16a are replaced with sensor bristles 136 (two on each side of the brush head 24). Additional sensor bristles 136 may of course be provided if desired. The temperature sensors 18 used in this example contain thermocouples mounted to aluminium elements. Plastic supports 43 are comoulded onto the aluminium elements. Wires (e.g. copper) run through the core of the plastic supports 43 to connect to the temperature sensors 18. The wires may be configured to mate to a conductive pad (e.g. on a printed circuit board in the head 24 of the hot brush) for ease of connection during assembly. Due to the small thermal mass of the temperature sensors 18 (in this case on the tip of the bristles 136) this design allows efficient and relatively fast cooling between each brush stroke through the hair being brushed. Although Figure 18 shows two adjacent sensor bristles 136, it will be appreciated that a single sensor bristle 136 may be used instead.

Figure 19 illustrates another way in which sensor bristles 136 may be realised. In this case, the sensor 18 is provided between the pair of bristles 136 as a temperature sensitive wire winding. For example, four of the outer bristles 134 may be replaced with such sensor bristles 136 (two on each side of the brush head 24). The bristle pairs 136 may be made of cast aluminium, and act as ‘thermal bridges’ that transmit the heat form the hair down to the temperature sensor 18. In this example, wire windings 18 are provided at the base of the bristle pairs 136 for sensing the temperature. This arrangement makes it easier to connect the temperature sensor 18 to the microprocessor 36 as wires that connect to the temperature sensor 18 can be routed from the underside of the bristles 136. During use, the efficiency of this design would depend on sufficiently fast cooling of the sensor bristle pairs 138 between each brush stroke of the hair.

Figure 20 illustrates a yet further alternative arrangement of sensor bristles 136, in which temperature sensing wire windings 18 are provided on the plastic bristles 136. For example, the sensor bristles 136 may be PPS mouldings, with sensor wires wrapped around them. The sensor wires 18 are heated by the hair, and then cool to air temperature. The sensor wires 18 may connect back to the board via grooves on the outside of the bristles 136, or through the core of the bristles 136 (as in Figure 18). This arrangement has the advantage of simplicity, and low thermal mass of the temperature sensor 18 (resulting in improved cooling of the sensor between brush strokes of the hair). Although Figure 20 shows two adjacent sensor bristles 136, it will be appreciated that a single sensor bristle may be used instead or where two or more sensor bristles 136 are used, they may be spaced apart rather than being immediately next to each other. When there are multiple temperature sensors 18, they may be located at different heights on the bristles 136, as shown in Figure 20. This may improve temperature readings regardless of the amount of hair passing between the bristles (e.g. by averaging the measurements from multiple sensors 18) and/or allow detecting the amount of hair 16 (e.g. based on temperatures I temperature difference measured at different heights).

Detection of hand position/gesture sensing

Temperature sensors 18 and/or force/proximity sensors 19 may also be used for detection of the hand position and/or for sensing gestures by the user, which may be indicative of a desired hair styling process. For example, the user’s hand position and grip of the handle portion 23 may be detected using force sensors 19 and/or temperature sensors 18 distributed along the handle 23 for one or more of the following potential benefits:

• Grip strength proportional to skill and stress;

• Hand temperature proportional to stress;

• Grip size as an indicator of different users;

• How the product is gripped indicates technique used I style created; and

• How the product is gripped also indicates which hand is used (left/right) .

It will be appreciated that any other suitable sensors may be used, such as light sensors, rotation sensors (e.g. gyroscopes), acceleration sensors, etc. For example, strain gauges positioned between the plates may be used to identify if the arms 12 are open or closed, and this information may be used to down-regulate or operate the device 10 at a lower plate temperature when the arms are open, thereby minimising energy usage and extending battery life.

Temperature or force sensors 18/19 may in addition or alternatively be mounted on the tip 26 of the device 10 - which is a common place for users to hold the device 10 when using two hands during a styling operation.

Force (pressure sensors, capacitive sensors, touch display) sensors may be arranged in a way within the handle 23 of the styling device 10 to generate gesture-related information about the user’s interaction with the device 10 and the resulting hair style.

A sensor may be arranged over a large enough surface area of the handle 23 so as to capture the touchpoints of the palm and fingers on the handle 23. The position of the palm and fingers can be translated into force and position which may be used by the microprocessor 36 to:

• Distinguish between straightening or curling behaviour.

• Distinguish between different methods of styling hair with the styling device 10.

• Identify changes in position during the use of the styling device 10.

• Monitor different usage cases for the same user by monitoring the frequency and duration of different baseline hand positions.

• Determine if the user is an experienced or inexperienced user of the hair styling device 10 and vary an operating parameter of the device accordingly (e.g. if the user is determined to be inexperienced then the microprocessor 36 may reduce the power supplied to the heater if the hair temperature is found to be greater than a threshold temperature - thereby avoiding damage to the hair by an inexperienced user).

This data can then be interpreted by the microprocessor 36 on the device or by a processor located off the device 10 that connects to the device 10 via Bluetooth or the like. The information about the user may then be presented to the user on the device or on a peripheral interface (e.g. on the display of a phone or laptop) during the styling session or after their styling session.

A visual, audible and/or haptic indicator may be provided on the styling device 10 to indicate the key events related to the user’s grip, such as the positioning of their hand(s), finger(s) or amount of force applied to the handle of the styling appliance.

Sensors may be arranged around the exposed surfaces of the hair styling device 10 in a large continuous sensing zone, or multiple sensing zones. Such a sensor or sensors may be connected to an internal printed circuit board (PCB) but form a ‘breakout’/separated PCB which may be rigid or flexible or printed onto the casing.

Modifications and alternatives

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

The device 10 may be partially or entirely formed of a unitary structure, e.g. by 3D printing.

In the above-described examples the device 10 may comprise a single heater 32 (e.g. in case of a hot brush, a hair curler device), or may alternatively comprise two or more heaters 32 (e.g. hair straightener or hair curler device, or a combined dryer and sty ler device). More generally, the device 10 may comprise any suitable means for transferring heat to the hair 16 of the user, such as any suitable conductive heater, thick film printed heater, steam heater, or radiative (e.g. infrared) heater.

Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example “comprising” and “containing”, means “including but not limited to”, and is not intended to (and does not) exclude other components, integers or steps.

The device illustrated in Figure 1a uses plates 15 that are typically used for straightening the user’s hair. In other embodiments, the device may use other types of heater plates 15. For example, instead the heating plates 15 may have a ribbed surface so that the device can be used to crimp the user’s hair during the styling process. Similarly, the heating surface may be defined by a cylindrical heater as typically used in a curling tong.

Various other modifications will be apparent to those skilled in the art and will not be described in further detail here.