APPARATUS AND METHODS FOR DRYING OR STYLING HAIR

Field of the Invention

The present invention relates to apparatus for drying and/or styling the hair of a person (or conceivably an animal), for example after washing the hair or as part of a styling process. That is to say, 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. Such drying and styling of the hair may be performed by a user in respect of their own hair, for example, or by a hair stylist.

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 straighter having a heated plate applies heat directly via conduction to heat the hair, which may be either wet or dry, to achieve the desired temperature for styling. The hair may be heated to a temperature that is particularly suitable for styling hair (for example, to or beyond a glass transition phase temperature). At lower temperatures, the user may have to make many passes with the hair straightener 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. The hair is typically styled from wet, for example after the user has washed their hair. After being heated by the hot air from a hairdryer, a so-called ‘cool-shot’ of cooler air can be used to set a style in place.

However, regardless of the type of hair styling device and the techniques used to style the hair, over time the hair style will begin to deteriorate. For example, curly hair that has been straightened using a hair straightener will gradually return to its initial curly state. There is therefore a need for improved hair styling devices that enable longer lasting hair styling effects.

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.

A method of the present disclosure enables the longevity of hairstyles and/or the styling capability of hair heat styling tools to be greatly increased by controlling the moisture level of hair based on a target moisture level. The present inventors have realised that improved longevity of hairstyles, and improved styling performance, can be achieved by controlling the moisture level of the styled hair based on an ambient moisture level (e.g. ambient humidity). More specifically, the present inventors have realised that longer lasting hair styles can be achieved when the moisture level of the hair is controlled to match (or be within a threshold range of) an ambient moisture level. Advantageously, the longevity of a hair style (and the overall styling capability of the device) is improved by controlling the moisture content of the hair to be in equilibrium with the ambient humidity.

In one aspect, the invention provides apparatus for drying or styling hair, the apparatus comprising: heating means for heating hair, to decrease a moisture level of the hair; and a controller configured to control the apparatus to take an action for controlling the moisture level of the hair based on a target moisture level.

The controller may be configured to control the moisture level of the hair to be within a threshold range of the target moisture level. The target moisture level may correspond to an ambient moisture level.

The controller may be configured to control an operating parameter of the heating means based on the target moisture level to control the moisture level of the hair.

The controller may be configured to control the heating means to reduce a difference between the moisture level of the hair and the target moisture level.

The controller may be configured to control the heating means to reduce a heat output or operating temperature of the heating means as the moisture level approaches the target moisture level.

The apparatus may comprise a memory that is configured to store a plurality of operating parameters of the apparatus; and the apparatus may be configured to identify, based on the moisture level of the hair or based on the target moisture level of the hair, an operating parameter to use from the stored plurality of operating parameters, to control the moisture level of the hair towards the target moisture level. The operating parameters may include at least one of an operating temperature or a heat output.

The apparatus may further comprise at least one sensor for outputting a sensor output that varies with the moisture level of the hair; and the apparatus may be configured to determine the moisture level of the hair based on the sensor output. The apparatus may comprise a temperature sensor for sensing a temperature of the hair; and the apparatus may be configured to determine the moisture level of the hair based on the sensed temperature of the hair. The apparatus may be configured to determine the moisture level of the hair based on a measured change in the temperature of the hair over time.

The heating means may comprise a heatable surface for transferring heat to the hair; wherein the apparatus comprises a temperature sensor for sensing a temperature of the heatable surface; and wherein the apparatus is configured to determine the moisture level of the hair based on the temperature of the heatable surface. The temperature sensor may comprise at least one of a thermistor, a thermocouple, or an infrared radiation sensor.

The apparatus may comprise a plurality of temperature sensors for measuring a temperature of the heatable surface at two or more regions of the heatable surface, and the apparatus may be configured to determine a moisture level of the hair based on the measured temperatures.

The apparatus may be configured to obtain thermal loads at two or more regions of the heatable surface, and the apparatus may be configured to determine a moisture level of the hair based on the obtained thermal loads.

The apparatus may further comprise means for obtaining the target moisture level.

The target moisture level may be the ambient moisture level; the apparatus may comprise a sensor for outputting a sensor output that varies with the ambient moisture level; and the apparatus may be configured to determine the ambient moisture level using the sensor output. The sensor for outputting the sensor output that varies with the ambient moisture level comprises a hygrometer.

The apparatus may comprise a capacitive sensor for outputting a sensor output that varies with a current moisture level of the hair; and the apparatus may be configured to determine the current moisture level of the hair using the sensor output from the capacitive sensor that varies with a current moisture level of the hair.

The apparatus may be configured to generate a flow of air across or through the hair, and the capacitive sensor may be configured to sense a moisture level of the air that has flowed across or through the hair.

The apparatus may comprise an optical sensor; and the apparatus may be configured to determine the moisture level of the hair based on a light intensity of light that passes through the hair, based on a light intensity of light that is reflected from the hair, or based on a light intensity of light that passes through air adjacent to the hair, measured by the optical sensor. The apparatus may further comprise a light source for emitting the light that passes through the hair, is reflected from the hair, and/or passes through air adjacent to the hair.

The optical sensor may be configured to sense an intensity of light that is characteristic of a fluid or wetline product, to determine an amount of the fluid or wetline product in the hair.

The apparatus may comprise a sensor for measuring a resistance that varies with a current moisture level of the hair; and the apparatus may be configured to determine the moisture level of the hair based on the measured resistance. The sensor for measuring the resistance may comprise a hygroscopic conductive layer.

The apparatus may be configured to apply an electric field across the hair; wherein the apparatus is configured to measure at least one dielectric property of the hair using the applied electric field; and wherein the apparatus is configured to determine the moisture level of the hair based on the measured dielectric property.

The apparatus may further comprise means for generating an indication to a user that the moisture level of the hair is within a threshold range of the target moisture level.

The controller may be configured to control the apparatus to control the moisture level of the hair by outputting an indication to a user of the current moisture level of the hair.

The controller may be configured to control the apparatus to control the moisture level of the hair by outputting an indication to a user of the current moisture level of the hair relative to the target moisture level.

The apparatus may be configured to output, to the user, an indication of an instruction for operating the apparatus, and the apparatus may be configured to determine the instruction to output based on the moisture level of the hair or based on the target moisture level.

The apparatus may comprise a user interface. The user interface may be operable by a user to input an indication of the target moisture level.

The apparatus may further comprise a fluid dispenser for increasing the moisture level of the hair by dispensing a fluid onto the hair. The controller may be configured to control the apparatus to increase the moisture level of the hair using the fluid dispenser before heating the hair using the heating means.

The apparatus may be configured to vibrate the hair to disperse the fluid in the hair. The apparatus may comprise a vibrating member for vibrating the hair. The apparatus may be configured to generate a flow of air to vibrate the hair.

The apparatus may be a hair straightener, a hair dryer, a hot paddle brush, a hot round brush, a heater roller, or a hair curler. The target moisture level may be preconfigured and stored in the apparatus.

The apparatus may be configured to receive the target moisture level from a separate device. The apparatus may be configured to receive a target moisture level that has been input into a smartphone application by a user.

In another aspect the invention provides apparatus for drying or styling hair, the apparatus comprising: heating means for heating hair, to decrease a moisture level of the hair; a sensor for outputting a sensor output that varies with a current moisture level of the hair; and a controller configured to: i) determine the current moisture level of the hair using the sensor output; and ii) output an indication to the user that depends upon the determined current moisture level of the hair.

The indication may be an indication of the current moisture level of the hair.

The apparatus may be configured to obtain a target moisture level for the hair; and the indication may be an indication of a difference between the target moisture level for the hair and the determined current moisture level of the hair.

The target moisture level may correspond to an ambient moisture level.

The indication may comprise at least one of a visual indication, an audible indication, or a haptic indication.

The apparatus may be configured to receive the target moisture level from a separate device. The apparatus may be configured to receive a target moisture level that has been input into a smartphone application by a user.

In another aspect the invention provides a method for drying or styling hair, the method comprising: heating hair, to decrease a moisture level of the hair; and controlling the moisture level of the hair based on a target moisture level.

In another aspect the invention provides a method for drying or styling hair, the method comprising: heating hair, to decrease a moisture level of the hair; and outputting an indication of a current moisture level of the hair to a user.

In another aspect the invention provides a method for drying or styling hair, the method comprising: heating hair, to decrease a moisture level of the hair; obtaining a target moisture level for the hair and a current moisture level of the hair; and outputting an indication of a difference between the target moisture level for the hair and the current moisture level of the hair to a user.

In another aspect, the invention provides apparatus for drying or styling hair, the apparatus comprising: heating means for heating hair, to decrease a moisture level of the hair to be in equilibrium with an ambient moisture level. In another aspect, the invention provides a hair drying and styling device comprising: first and second mutually-opposing arms adapted for movement between an open configuration for receiving a length of wet hair therebetween and a closed configuration adjacent the hair, such that, in use, when the arms are in the closed configuration they form an inter-arm chamber across which the hair passes in use, and wherein an airflow conduit is provided within and along at least one of the first and second arms; means for delivering a flow of air along the conduit in the at least one of the first and second arms, and subsequently into the inter-arm chamber; a sensor for sensing whether the arms are in the open configuration or the closed configuration; and mans for controlling the means for delivering to vary the flow of air depending on whether the arms are in the open configuration or the closed configuration.

The means for controlling (which may be, for example, a control circuit or a microprocessor) is configured to cause the means for delivering to provide a first air flow rate when the arms are in the open configuration and a second air flow rate, which is greater than the first air flow rate, when the arms are in the closed configuration. In some embodiments, the means for controlling is configured to cause the means for delivering to vary the air flow in a stepwise manner or in a smoothly varying manner between said first flow rate and said second flow rate.

According to another aspect, the invention provides a hair drying and styling device comprising: an airflow conduit within and along at least one first arm of the device; means for delivering a flow of air along the conduit; a sensor for sensing a modality of operation of the device; and means for controlling the means for delivering to vary the flow of air depending on the output of the sensor. The sensor may be selected from the group consisting of an accelerometer, a gyroscope and a switch; and wherein the sensed modality of operation is either whether the device is currently in motion or whether the device is currently in a specified orientation or whether the device is currently close to or positioned on a surface.

According to another aspect, the present invention provides a hair drying and styling device comprising: first and second mutually-opposing arms adapted for movement between an open configuration for receiving a length of wet hair therebetween and a closed configuration adjacent the hair, such that, in use, when the arms are in the closed configuration they form an inter-arm chamber across which the hair passes in use, and wherein an airflow conduit is provided within and along at least one of the first and second arms; means for delivering a flow of air along the conduit in the at least one of the first and second arms, and subsequently into the inter-arm chamber; at least one air vent through which air from the inter-arm chamber can exit the device; and an air diffuser mounted between the at least one air vent and the inter-arm chamber to diffuse the air that exits the device. The air diffuser may be comprised of a heat conductive material such as copper, aluminium or a ceramic material. The air diffuser may be provided adjacent an outlet where dried and styled hair exits the device, to provide conductive and convective cooling of the hair as it exits the device to set a hair style created by the device.

In one embodiment, the device further comprises mutually-opposing hair contacting members disposed on the first and second arms, the mutually-opposing hair contacting members being arranged to come together when the first and second arms are in the closed configuration and, preferably, wherein at least one of the hair contacting members comprises a conductive heater.

The device may comprise: first and second hair contacting members disposed on the first arm, and respective opposing first and second hair contacting members disposed on the second arm, wherein the opposing hair contacting members disposed on the first and second arms are arranged to come together when the first and second arms are in the closed configuration; wherein the inter-arm chamber is located between the first and second hair contacting members of the first and second arms when the arms are in the closed configuration; wherein at least one hair contacting member comprises means for applying heat to a length of hair sandwiched between the hair contacting members during use, when the first and second arms are in the closed configuration; and wherein one or both of the arms further comprises an airflow guide structure arranged to receive the flow of air from the respective conduit and to direct the flow of air from a first direction (D1) that is substantially parallel to the length of the respective arm, to a second direction (D2) that is from the respective arm towards the opposing arm, into the inter-arm chamber.

In another aspect, the invention provides a hair drying and styling device comprising first and second mutually-opposing arms adapted for movement between an open configuration for receiving a length of wet hair therebetween and a closed configuration adjacent the hair, such that, in use, when the arms are in the closed configuration they form an inter-arm chamber across which the hair passes in use, and wherein an airflow conduit is provided within and along at least one of the first and second arms; means for delivering a flow of air along the conduit in the at least one of the first and second arms, and subsequently into the inter-arm chamber; a heater adapted for heating the flow of air; at least one air vent through which air from the inter-arm chamber can exit the device; at least one heater plate configured for conductive heating of hair in use; control electronics for controlling the device; and a quench activator switching or sensing means for activation by a device user, whereby each of the means for delivering, the heater and the at least one heater plate is switched on in general use; and whereby, when the quench activator switching or sensing means is activated by the device user, both the means for delivering and the at least one heater plate are switched on and the heater is switched off. According to another aspect, the present invention provides a hair drying and styling device comprising: first and second mutually-opposing arms adapted for movement between an open configuration for receiving a length of wet hair therebetween and a closed configuration adjacent the hair, such that, in use, when the arms are in the closed configuration they form an inter-arm chamber across which the hair passes in use, and wherein an airflow conduit is provided within and along at least one of the first and second arms; means for delivering a flow of air along the conduit in the at least one of the first and second arms, and subsequently into the inter-arm chamber; an air heater adapted for heating the flow of air; at least one air vent through which air from the inter-arm chamber can exit the device; at least one conductive heater configured for conductive heating of hair in use; control electronics for controlling the device; and a quench activator switching or sensing means for activation by a device user, wherein each of the means for delivering, the air heater and the at least one conductive heater is switched on in general use; and wherein, when the quench activator switching or sensing means is activated by the device user, both the means for delivering and the at least one conductive heater are switched on and the air heater is switched off.

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 a hair styling device in use;

Figure 1c shows a simplified block diagram of a hair styling device;

Figure 2 shows a flow diagram illustrating a method of controlling a moisture level of hair;

Figure 3 shows a flow diagram illustrating a further method of controlling a moisture level of hair; Figure 4 shows a flow diagram illustrating a further method of controlling a moisture level of hair; Figure 5a shows a user input dial;

Figure 5b shows a simplified schematic diagram of apparatus for steam drying hair;

Figure 6 shows a table stored by the device;

Figure 7 shows an element of a user interface for indicating a moisture level of hair;

Figure 8 shows a graph of hair temperature against drying time;

Figure 9 shows a flow diagram illustrating a method of controlling a moisture level of hair during a drying/styling process;

Figure 10 shows a modified version of the flow diagram of Figure 9; Figure 11a is a perspective overview of a combined hair dryer/styler device comprising mutually-opposing drying/sty ling arms in an open configuration, with each arm incorporating a pair of conductive heaters and an airflow guide structure;

Figure 11b shows the device of Figure 11a with the arms in a closed configuration;

Figure 11c illustrates the device of Figure 11 in use;

Figure 12 is a perspective longitudinal cross-sectional view of the lower arm of the device shown in Figure 11 , illustrating the main internal components of the device and the air flow within the device during use;

Figure 13 is a side cross-sectional view of the distal end of the lower arm shown in Figure 12 and illustrating directions of airflow through the distal end of the lower arm;

Figure 14 is a transverse cross-sectional view through the arms of the device of Figure 11 in the closed configuration, and also illustrating directions of airflow;

Figure 15 is a transverse cross-sectional view through the arms of the device of Figure 11 having diffusers to diffuse the air exiting the vents of the device; and

Figure 16 shows a simplified block diagram of the electrical components of the hair styler shown in Figure 11.

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.

Throughout this disclosure the term ‘moisture level’ is used, when referring to a moisture level of hair, to refer to an amount of bound and/or unbound water on the hair, or to refer to a humidity of air adjacent to (or between strands of) the hair. The moisture level of air may be referred to as a ‘humidity level’. Similarly, the ambient moisture level may also be referred to as the ‘ambient humidity level’.

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

Figure 1a shows an overview of a hair styling device suitable for implementing one or more methods of the invention. However, the hair styling device need not necessarily be of the type illustrated in Figure 1a. Any other suitable type of hair styling or hair drying device may be used, such as a heated brush (e.g. a paddle brush) or a hair dryer. The device may use any one of conductive heating, convective heating, or radiative heating (or any combination thereof) to transfer heat to the hair 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 heated plates 15a, 15b for transferring heat by conduction to the hair of a user. Figure 1b shows the device 10 in use during a styling process. In use, the device 10 will typically receive a length (tress) of hair 16.

A user interface 11 is provided to allow the user to set user defined parameters and for the device to output information to the user. For example, a moisture level of the user’s hair may be indicated to the user via the user interface 11, and/or the user may be able to set a desired moisture level for their hair via the user interface 11 . The user interface 11 may have a dial, button or 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 and carries the control circuitry 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 17. The power supply may be an AC mains power supply. However, in an alternative embodiment the power supply may comprise one or more DC batteries or cells (which may be rechargeable, e.g. from the mains or a DC supply via a charging lead), thereby enabling the device 10 to be a cordless product.

As will be described in more detail later, the device may comprise one or more sensors for determining a moisture level and/or temperature of a user’s hair and/or for sensing an ambient moisture level. 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.

The present invention is not limited to the type of device illustrated in Figure 1 a. For example, a device that instead (or additionally) transfers heat to hair using heated air could be used - such as the kind of hair styling device described in the applicant’s earlier application WO 2021/019239, the contents of which are hereby incorporated herein by reference. When heated air is used to heat the user’s hair, the device may comprise a heater having an electrically-powered heating coil (or any other suitable type of heating element), operable to heat air drawn in by a fan assembly. More generally, any suitable device capable of transferring heat to the hair of a user could be used.

The device may comprise bristles for improving the styling performance of the device. The bristles guide the hair as it passes over the bristles, enabling the user to have greater control over the styling of the hair, and enabling a greater range of styling techniques to be used. For example, the device may be a heated brush having a plurality of heated bristles.

Illustrative Block Diagram

Figure 1c is a simplified block diagram of the device 10 illustrating its main components.

As shown, the device 10 comprises a power supply 38 that derives power from a mains power supply input. Alternatively, power may be derived (for example) from 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 device 10.

In this example, power is provided to one or more heaters 25 that heat the plates 15. In the case that the device 10 is a hair dryer, the heaters 25 heat an air stream generated by one or more fans 27 that are rotated by one or more fan motors 28. The power supplied to the heater(s) 25 is controlled by a controller 36 having a microprocessor 62. The power supplied to the heater(s) 25 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 heater 25. When the device 10 comprises a plurality of heaters 25, a pair of heaters 25 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 plates 15 drops below a desired operating temperature when wet hair contacts the plates 15, both heaters 25 may be powered to provide a boost of heat (in a so-called “boost mode”) to counter heat lost to the hair, and to increase the removal rate of the water. At other times, only one of the heaters 25 might be powered to maintain the desired operating temperature. The device 10 may also include a mode in which both heaters 25 are switched off (disabled), and a stream of cool air (air at ambient or nearambient temperature) is generated by the fan 27 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 device 10 if overheating of the device 10 is occurring. The cool-shot mode could be provided using any other suitable method. The cool-shot mode could be provided using an actively cooled hair-contacting surface. For example, the hair-contacting surface could be cooled using a flow of cool air generated by the device. A Peltier device could be used to rapidly cool a hair contacting surface to provide the cool-shot mode.

The microprocessor 62 is coupled to a memory 63 (which is typically a non-volatile memory) that stores processor control code for implementing one or more control methods to be described below.

Figure 1c also shows that the user interface 11 is coupled to the microprocessor 62, for example to provide one or more user controls and/or output indications such as a visual indication or an audible alert. The output(s) may be used to indicate to the user, for example, when a moisture level of the user’s hair is within a predetermined range of a target moisture level.

To help control the moisture level of the user’s hair, it is advantageous to have accurate measurements (either direct or indirect) of the current moisture level of the user’s hair. Therefore, as described in detail below, the device 10 may be provided with one or more moisture sensors 64. The device 10 may also comprise one or more temperature sensors 65. The temperature sensor(s) 65 may be a noncontact type of sensor (for example, an infrared sensor) for sensing the temperature of the user’s hair, and/or for sensing the temperature of a part of the device 10 (for example the temperature of the heater plates 15). The moisture sensor(s) 64 and/or temperature sensor(s) 65 could be provided inside a main body portion of the device 10, or could be provided on an exterior surface of the device 10. A temperature measurement of a part of the device 10 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.

The device 10 may also comprise one or more wetline product dispensers 29 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 29 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 communication circuitry 67 to allow the device to communicate with a remote sensor, a remote server, or a remote application (e.g. on a mobile telephone). The communication circuitry 67 may use, for example, Bluetooth, Wi-Fi and/or 3GPP communication protocols to communicate with the remote device.

The microprocessor 62 may be configured to communicate with the heater 25, fan 27, fan motor 28, wetline product dispenser 29, moisture sensor 64, temperature sensor 65, user interface 11, communications circuitry 67 and power supply 38 via one or more communication interfaces or transceivers in accordance with software stored in the memory 63. The memory 63 may store, for example, one or more operating profiles or parameters. Software stored in the memory 63 may include, for example, an operating system and a moisture level 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 1c. For example, if the device 10 is a hair straightener, then there is no need for the fan(s) 27 and the fan motor(s) 28. Similarly, in some embodiments there may be no sensors 64, 65, no wetline product dispenser(s) 29 and no communications circuitry 67.

Moisture Level Control ■ Overview

Figure 2 is a flow diagram illustrating a method of controlling a moisture level of a user’s hair during a styling or drying process. Advantageously, the moisture level of the user’s hair is controlled based on a target moisture level - which may be an ambient moisture level (e.g. a current or future ambient moisture level) or based on a user set (or desired) moisture level. The inventors have found that controlling the moisture level of the user’s hair based on a target moisture level can result in longer-lasting hair styling effects. For example, the moisture level of the user’s hair could be controlled to be within a predetermined threshold (range) of an ambient moisture level at the end of the styling process. Alternatively, the moisture level of the user’s hair could be controlled to be a predetermined amount higher than an ambient moisture level at the end of the styling process, to account for subsequent evaporation as the hair cools to the ambient temperature. In a further alternative, the moisture level of the user’s hair could be controlled to be a predetermined amount lower than an ambient moisture level at the end of the styling process, to account for a subsequent increase in the moisture level of the hair caused by subsequent addition of wetline product by the user.

Thus, referring to the method shown in Figure 2, in step S201, a target moisture level is obtained. The target moisture level may be obtained by reading a predetermined moisture level from the memory 63 of the device 10, by receiving a target moisture level from a remote server (via the communication circuitry 67), by receiving a target moisture level from the user via the user interface 11 or by a sensor that senses the ambient moisture level. The sensor may be mounted within the device 10 (such as sensor 64) or may be remote from the device 10. Where the ambient moisture level is to be sensed, the ambient moisture level preferably corresponds to the humidity of the air in which the user is expected to spend most of their time, rather than the ambient moisture level in the area the device 10 is located during the styling/drying process. For example, when the user is styling their hair in a bathroom in which the ambient moisture level (humidity) is relatively high, but expects to spend a majority of their day in a separate location in which the ambient humidity is much lower, it is advantageous to control the moisture level of the user’s hair based on the ambient humidity in the location where the user expects to spend a majority of their time rather than on the humidity level of the bathroom. For this reason, the sensor may be provided remotely from the device 10 or the user may set the target moisture level via the user interface or the local humidity level for the country or geographic region in which the user is located may be obtained from a remote server.

Where at least one sensor 64 is mounted within the device 10 for sensing the ambient moisture level, the at least one sensor 64 is desirably located away from the position at which the user grips the device 10 in normal use, to mitigate against the effects of moisture from the user’s hand on the measurement of the ambient humidity.

In step S202, the device 10 is controlled to control the moisture level of the user’s hair based on the target moisture level obtained in step S201. Step S202 may comprise determining a current moisture level of the user’s hair, comparing that moisture level to the target moisture level and then taking a control action to control the drying of the hair. The control action may be to vary the heating applied to the hair using the heater(s) 25 and/or outputting an indication (audible, visual or haptic) to the user to define the number of passes needed to reach the target moisture level and/or outputting an indication (audible or visual) when the sensed moisture level of the user’s hair is within a predefined threshold (range) of the target moisture level. Detailed methods of determining the current moisture level of the user’s hair are described below.

In alternative methods, instead of sensing the current moisture level of the user’s hair, the device 10 can make an assumption about the initial moisture content (for example by using a predefined starting moisture level based on the hair being “towel dry”) and then controlling the device 10 based on that assumed moisture level and the target moisture level. Alternatively still, if the hair starts dry and then the device 10 wets the hair using liquid from the wetline product dispenser 29, then the device 10 can determine a starting moisture level for the hair based on the amount of liquid applied to the hair. In a simpler embodiment, the device 10 may simply take different control actions based solely on the target moisture content without using any sensed or expected moisture level for the hair. For example, for a first target moisture level, the device 10 may be programmed to heat the plates 15 to a temperature of 160 degrees Celsius and to output an indication to the user via the user interface 11 that they should pass each tress of hair three times through the heated plates 15; and for a second (different) target moisture level, the device 10 may be programmed to heat the plates 15 to a temperature of 135 degrees Celsius and to output an indication to the user via the user interface 11 that they should pass each tress of hair four times through the heated plates 15. Detailed methods of controlling the moisture level of the user’s hair during a styling or drying process based on the target moisture level are also described below.

Figure 3 shows further flow diagram illustrating a method of controlling a moisture level of hair during a styling or drying process, in which the device 10 is also operable to increase the moisture level of the user’s hair.

Step S301 is the same as step S201 of Figure 2.

In step S302, the current moisture level of the user’s hair is determined. Detailed methods of determining the current moisture level of the user’s hair are described below. For example, the device 10 may comprise one or more sensors 64, 65 the outputs from which can be processed to determine the moisture level of the user’s hair.

In step S303, the device 10 increases the moisture level of the user’s hair. For example, the device 10 may determine that the user’s hair is dry, or that the moisture level of the user’s hair (determined in step S302) is lower than a desired target moisture level (obtained in step S301). As mentioned above, the device 10 may be configured to increase the moisture level of the user’s hair by dispensing a fluid (or ‘wetline’ product) from the wetline product dispenser 29 onto the user’s hair. For example, the fluid may be dispensed in response to an input by a user (e.g. a press of a button provided on the device), or may be dispensed under the control of a controller of the device 10 in response to a determination that the moisture level of the user’s hair is below the ambient moisture level.

Step S304 is the same as S202 of Figure 2.

Advantageously, when the device 10 is operable to increase the moisture level of the hair, greater flexibility in the use of the device 10 is achieved. For example, when the device 10 is configured to control the moisture level in step S304 by heating the hair to decrease the moisture level (e.g. to match the ambient moisture level), the hair must have a higher moisture level than the target moisture level before the heating begins. Advantageously, when the user’s hair has a moisture level that is initially lower than the target moisture level, the moisture level of the hair can be increased in step S303, using the device 10, to be greater than the target moisture level so that step S304 can be performed.

Figure 4 shows further flow diagram illustrating a method of controlling a moisture level of hair, in which an indication of a moisture level is output to a user.

Steps S401 and S402 are the same as steps S301 and S302 of Figure 3, respectively.

In step S403, after the moisture level of the hair has been determined in step S402, an indication of the moisture level of the hair is output to the user. The indication may indicate, for example, the current moisture level of the hair on an arbitrary scale. The indication may be, for example, a visual indication, an audible indication and/or may comprise haptic feedback. The user is able to use the information regarding the moisture level to achieve better control of the moisture level of the hair. For example, when the device 10 is a hairdryer, the user may dry the hair using the hairdryer until the hairdryer indicates that the hair is within the threshold range of the target moisture level, at which point the user may decide to stop the drying process (or begin drying another section or tress of hair). Advantageously, the indication of the moisture level of the hair also reduces the risk of the user causing damage to the hair by over-drying the hair. It will be appreciated that in the exemplary method illustrated in Figure 4, the device 10 need not necessarily comprise a controller that controls the moisture level of the user’s hair by controlling the heaters 25, but may instead output the indication of the current moisture level of the hair to the user, thereby continuously guiding the user to control the moisture level of the hair towards the target moisture level.

Obtaining a Target Moisture Level

Methods of obtaining a target (e.g. ambient) moisture level for the hair will now be described. Any of these methods may be used, for example, in any of steps S201, S301 or S401 of figures 2 to 4 described above.

As discussed above, the device 10 may be provided with a sensor 64 for sensing the ambient moisture level. For example, the device may be provided with a hygrometer (or any other suitable type of humidity sensor) for measuring the ambient humidity. In a particularly advantageous example, the sensor 64 is situated away from the active styling area (e.g. away from the heater plates 15a, 15b in the example illustrated in Figure 1a - away from the hair of the user) and away from the position of the user’s hand during normal use. Beneficially, this reduces the effect of heat and/or evaporated water from the styling area, and of moisture from the user’s hand, on sensor measurements of the ambient moisture level. The device 10 may be configured to sense an ambient moisture level repeatedly (e.g. periodically or intermittently). For example, the device 10 may be configured to repeatedly sense an ambient moisture level when the device is connected to mains electricity. After the device 10 has obtained the ambient humidity level using the sensor 64, the device 10 may store that measured ambient humidity level in the memory 63 as a target moisture level for the user’s hair.

The sensor 64 for sensing the ambient moisture level may be provided in addition to a separate sensor 64 for sensing a moisture level of the user’s hair. Alternatively, the sensor 64 that senses the ambient moisture level may be configured to additionally sense the moisture level of the user’s hair (e.g. a single sensor may be provided to sense both the moisture level of the user’s hair and the ambient moisture level). For example, the sensor 64 may be configured to repeatedly (e.g. periodically or intermittently) sense the ambient moisture level when the device 10 is not in use by a user, and may be configured to sense the moisture level of the user’s hair when the device is in use for drying/sty li ng hair. Advantageously, when the sensor 64 is configured to repeatedly sense the ambient moisture level when the device 10 is not in use, the effects of heat and/or evaporated water from the styling area (and/or of moisture from the user’s hand) on the measurements of the ambient moisture level are reduced (or mitigated entirely), even when the sensor is located in the styling area or near a position at which the user grips the device, thereby increasing the accuracy of the measurements of the ambient moisture level.

Alternatively, the device may be pre-configured with a target moisture level (e.g. preconfigured with a stored ambient humidity level which may vary from country to country or geographical region). The target moisture level may be configured (e.g. at time of manufacture, or via a subsequent software update) as the average ambient moisture level at the geographic location in which the end user is located. For example, when the device is for a user in the United Kingdom, the target moisture level may be set as the average humidity level in the United Kingdom. When the device is assigned a stock-keeping unit (SKU) code, the average ambient humidity level may be preconfigured based on the assigned SKU. The device 10 may use the communication circuitry 67 to vary the average ambient moisture level depending on the time of year and the geographic region in which the device is located.

The device 10 may be configured to communicate with an in-building sensor using the communication circuitry 67 to obtain a target moisture level. For example, the device 10 may be configured to communicate with a heating, ventilation and air conditioning (H AC) system to obtain the target moisture (humidity) level.

The device 10 may be configured to determine the current location of the device 10, for example using location data obtained using a GPS chip, or obtained via a connected mobile phone application. The device 10 may also be configured to estimate the location of the device 10 based on an input voltage and/or frequency of a mains power supply connected to the device. The device 10 could then obtain the current local weather conditions (e.g. the current local humidity) for that estimated location in order to obtain an accurate measure of the ambient humidity level for that day in that geographical region. For example, the device 10 could use the communication circuitry 67 to obtain the current local weather conditions by communicating with an external server via the internet (or any other suitable form of communication network). The device 10 may also or instead be configured to obtain a future local weather condition that is used to determine the target ambient moisture level. For example, the device may be configured to obtain an ambient humidity level for later in the day. The device may be configured to calculate or obtain an average ambient humidity level for a period of time based on a local weather forecast, and may be configured to set the average ambient humidity level as the target moisture level for the user’s hair. The device may be configured to store information that indicates a routine of a user, and the device may be configured to determine the target moisture level for the user’s hair based on the routine. For example, the stored information may include an indication of a period of the day in which the user is typically located inside (e.g. in a lower humidity environment), or a period of the day in which the user is typically located outside (e.g. in a higher humidity environment). For example, the device may be configured to obtain information indicating that the user typically remains indoors on days in which it is raining and, when it is raining (or a weather forecast indicates that it is likely to rain), set the target moisture level to be a typical ambient moisture level for the indoor environment. The device may be configured to determine a target moisture level for the user’s hair based on a calendar or schedule of the user (which could be obtained, for example, via a connected smartphone application).

In a further alternative, the target moisture level for the hair may be set manually by a user of the device 10. For example, Figure 5a shows a dial 70 of the user interface 11 that may be operated by a user to set a target moisture level for the hair. The dial 70 may be provided, for example, on the outer casing of the device 10 (or conceivably may be provided on a remote control). In this example, the dial 70 is operable to select a moisture level between arbitrary values of 1 and 5, where 1 corresponds to a relatively low moisture level and 5 corresponds to a relatively high moisture level. Any other suitable element of a user interface 11 that allows the user to input a target moisture level could be used. For example, the device 10 could be configured to receive, via the communications circuitry 67, a target moisture level from a user using a connected smartphone application.

Advantageously, in this example, when the user expects that they will spend a large portion of their day in a high moisture environment, the user can manually increase the target moisture level for the hair, enabling improved matching between the moisture level of the hair and the expected ambient moisture level, which results in longer-lasting hair styling effects. For example, when the user expects to spend a period of time outside after it has rained (which results in higher ambient humidity levels), the user may increase the target moisture level for the hair.

Determining and Controlling the Moisture Level of Hair

Detailed methods of controlling a moisture level of hair during a styling or drying process (for example using the device illustrated in Figure 1a, or any other suitable device) will now be described. The moisture level of the hair may be controlled based on the ambient moisture level (or target moisture level) obtained according to any of the above described methods.

The device 10 may control the moisture level of the hair by heating the hair to decrease the moisture level, or by adding one or more fluids to the hair, using the wetline product dispenser 29, to increase the moisture level. The device 10 may also control the moisture level of the hair by blowing air across the hair at ambient temperature using the fan 27 and fan motor 28, to control the rate of evaporation.

The device 10 may alternatively (or additionally) be configured to control the moisture level of the hair by using superheated steam drying to decrease the moisture level of the hair. Superheated steam drying (SSD) utilises steam that is heated beyond its boiling point as a drying medium, to remove moisture from the hair. In comparison to drying using heated air, steam drying is a more energy efficient technique that reduces degradation of the hair structure, provides more uniform drying of the hair, and reduces the risk of over-drying the hair. Exhaust steam that has been used to reduce the moisture level of the hair can be recycled for further use, further increasing the energy efficiency of the method. Moreover, oxidation and denaturation of the hair that can occur when heated air is used to dry hair can be avoided or reduced. Further benefits of steam drying include sterilisation and deodorisation of the hair. Additional methods of transferring heat to the hair (e.g. using conductive plates) and/or controlling the moisture level of the hair could be used in addition to steam drying (e.g. simultaneously).

Figure 5b shows a simplified schematic diagram of apparatus for steam drying hair. The device 10 illustrated in Figure 1a (and illustrated schematically in Figure 1c) could be configured for steam drying the hair of a user using the apparatus illustrated in Figure 5b. As shown in the figure, the device includes a heater 50, a fan/blower 51, and a closed steam drying system 52. Steam is generated by a boiler (not shown in the figure), but could alternatively be generated using any other suitable means for generating steam. The heater 50 is configured to heat steam from the boiler to generate superheated steam. The fan/blower 51 is configured to drive a flow of steam through the device 10. The superheated steam is used to decrease the moisture level of the hair in the closed steam drying system 52. The closed steam drying system 52 may comprise, for example, a chamber (e.g. a plenum chamber) for receiving a flow of the superheated steam. The superheated steam decreases the moisture level of the user’s hair inside the chamber. Steam that has been used to decrease the moisture level of the user’s hair in the closed steam drying system 52 exits the chamber and is purged from the device, and/or is recycled back to the heater 50 using the fan/blower 51, for subsequent reheating and re-use in the closed steam drying system 52. In this example, energy from the purged steam is recovered using a heat exchanger, increasing the energy efficiency of the device. The heat recovered at the heat exchanger can be used by the heater 50 to heat steam, and/or can be used by the boiler to generate steam. The device 10 may also comprise means for removing condensate at the heat exchanger.

Conceivably, the styling process and the moisture level control could be performed using separate devices. For example, the hair could be styled using a brush, and control of the moisture level of the hair could be performed using a separate device (e.g. a hairdryer).

Any suitable sensor or arrangement of sensors, the outputs from which can be processed to determine the moisture level of the user’s hair, could be used. However, it will be appreciated that the device 10 need not necessarily comprise the sensor 64 for measuring the moisture level. For example, the device could heat the hair according to a predetermined operating profile based on the target moisture level and a typical moisture level of wet hair before styling. The predetermined operating profile (which may comprise, for example, a heater temperature, a duration for heating the hair, or any other suitable operating parameter) for achieving a particular target moisture level could be determined experimentally in advance, and stored in the memory 63 of the device 10. For example, a mapping of target moisture levels to operating profiles could be stored in the memory 63 of the device 10 (e.g. as a stored table such as the table shown in Figure 6, described below). Nevertheless, providing the device 10 with one or more sensors 64 for measuring the moisture level of the user’s hair allows for more precise control of the moisture level.

The controller 36 of the device 10 may control the moisture level of the hair based on the target moisture level and the current moisture level of the user’s hair, using any suitable control method. For example, the device 10 may be configured to operate according to a preconfigured stored operating profile (which may comprise, for example, a heater temperature, duration for heating the hair, or any other suitable operating parameter) based on the target moisture level and the current moisture level, to control the moisture content of the hair to move towards the target moisture level. Control of an amount of heat transferred to the hair, and therefore control of the moisture level of the hair (by controlling the amount of evaporation) can be achieved, for example, by controlling a flow of heated air that is heated by the heater 25, by controlling the temperature of a hair-contacting heated plate that is heated by the heater 25, and/or by controlling the power output of a radiative heater 25. In a particularly advantageous example, the device 10 comprises a thick film printed heater for heating the hair - such as the heater described in the applicant’s earlier application, application number GB2115266, the contents of which are hereby incorporated herein by reference. Beneficially, the thick film printed heater has a relatively low thermal mass, allowing more responsive control of the temperature of the hair, and therefore more responsive and precise control of the moisture level. Figure 6 shows an example of a table that maps a target moisture level and a current moisture level to a corresponding operating temperature of the device 10. The table is stored in the memory 63 of the device 10. The controller 36 is configured to determine, using the stored table, an operating temperature to use based on an obtained target moisture level and based on an obtained current moisture level. The table need not necessarily include the target moisture level; alternatively, the table may simply include the current moisture level and the corresponding operating temperatures. In other words, the device could store a mapping between a current moisture level of the user’s hair and the operating temperature to use to adjust the moisture level of the user’s hair (e.g. an operating temperature, that is determined experimentally in advance, for adjusting the moisture level of the hair to match a typical ambient moisture level). In a further alternative, the table may simply map the difference between the target moisture level and the current moisture level to the corresponding operating temperature.

Whilst the table shown in Figure 6 includes an operating temperature (e.g. a temperature of a heater plate 15, or a temperature of heated air heated by the heater 25), the table could also include any other suitable operating parameter for controlling a moisture level of the user’s hair (e.g. a power output value of the heater 25) instead of, or in addition to, the operating temperature. The table could alternatively map the target moisture level and/or current moisture level to an index that corresponds to a set of operating parameters stored separately in the memory 63.

In the first row of the table the current moisture level is higher than the target moisture level. However, as the current moisture level is relatively high, the device 10 is set to operate at a reduced temperature of 120 °C in order to avoid water cavitation (‘sizzle’). In the second to fourth rows of the table, the current moisture level is still higher than the target moisture level, and the corresponding operating temperature is set to 185 °C to provide effective styling capabilities and to drive the current moisture level towards the target moisture level. In the final row of the table, the current moisture level is the same as the target moisture level, and so the operating temperature is set as the ambient temperature (i.e. the heater 25 is switched off and allowed to cool).

The device 10 may output an indication to the user that the hair has reached the target moisture level (or is within a threshold range of the target moisture level) via the user interface 11 . For example, the device 10 may output an audible tone or visual indication (or any other suitable type of indication, such as haptic feedback) that the current section or tress of hair that is being dried is within a threshold range of the target moisture level, and therefore that the user should stop the styling/drying process for that section of hair. Instead of the controller 36 directly controlling the moisture level of the user’s hair, the controller 36 may instead output information to the user via the user interface to allow the user to control the way in which they use the device 10 and thereby indirectly control the moisture level of the user’s hair. Figure 7 shows an arrangement of indicating lights 71 that could form part of the user interface 11 to provide an indication of the current moisture level of the hair. In this example, two of the indicating lights 72 are illuminated, and three of the indicating lights 73 are not illuminated, indicating that the current moisture level of the section of hair being styled/dried is 2 out of 5 on an arbitrary scale (with 5 representing wet hair). The user can then continue heating the same section or tress of hair until the indicated moisture level is at a desired level on the arbitrary scale. The arrangement 71 could also provide an indication of the target moisture level, or an indication that the hair has reached (or is within a threshold range of) the target moisture level. For example, one or more of the indicating lights could illuminate in a red colour when the moisture level of the hair is below the target moisture level, illuminate in a green colour when the moisture level of the hair is at the target moisture level, and illuminate in a blue colour when the moisture level of the hair is above the target moisture level. By observing the indication of the current moisture level and the indication of the target moisture level, the user is able to control the moisture level of the hair towards the target moisture level, resulting in longer-lasting styling effects. However, the target moisture level need not necessarily be indicated to the user. For example, the user may have obtained the current ambient humidity level independently from a weather report, in which case only the indication of the current moisture level of the hair is needed for guiding the user to control the moisture level of the hair towards the ambient humidity level, to achieve the improved styling performance. For example, if the weather report indicates that today’s weather is going to be dry and sunny then the user may aim to dry/style each tress of hair until the indicated moisture level is at level 1 of the arbitrary scale; whereas if the weather report indicates that today’s weather is going to be wet then they may aim to dry/style each tress of hair until the indicated moisture level is at level 3 of the arbitrary scale.

The indication to the user of the current moisture level of the hair (and optionally the target moisture level) need not necessarily be a visual indication. For example, sound or haptic feedback, or any other suitable type of feedback, could be provided via the user interface 11 .

The device 10 may be configured to obtain the current moisture level of the user’s hair using one or more of the methods described below. When a plurality of the described methods for obtaining the moisture level of the user’s hair are used and the results combined, a more accurate and reliable determination of the moisture level of the hair can be achieved (for example, by calculating an average of the moisture levels obtained using the different methods). Methods of determining the moisture level of the user’s hair are described below and may be used, for example, as part of step S302 of Figure 3, or as part of step S402 of Figure 4. When the sensor(s) used to determine the moisture level of the user’s hair are also used to measure the ambient moisture level, it will be appreciated that the methods described below can also be used to measure the ambient moisture level (e.g. using the capacitive sensor method).

Thermal Load

The moisture level of the hair may be determined by measuring a thermal load on one or more components of the device 10. The amount of energy required to heat hair is dependant on the moisture content remaining within the hair. For a given tress of hair that is heated by the device 10, the thermal load is correlated with the temperature and water content of that tress of hair. Therefore, by measuring the thermal load, the moisture level of the hair can be determined (estimated) via a suitable look up table or calculation that is determined in advance and that relates measured thermal loads to moisture levels of the hair. For example, for a hair straightener of the type illustrated in Figure 1a, the moisture level of the hair can be determined based on a thermal load on the heater plates 15a, 15b.

The thermal load, and therefore the determination of the moisture level of the hair, depends on the amount of hair being heated. The moisture level of the hair can be determined (estimated) via a suitable look up table or calculation based on an estimate of the typical amount of hair received by the device in normal use. Alternatively, a pair of sequential heated plates can be used to increase the accuracy of the determination of the moisture level. As the user pulls the device across the hair, the hair passes over a first plate of the sequential heated plates and then passes over a second plate of the sequential heated plates. The hair is therefore first heated by the first heater plate and is then heated by the second heater plate. The thermal load on the first heater plate is greater than the thermal load on the second heater plate, due to the removal of some of the water from the hair at the first heater plate before the hair passes over the second heater plate (i.e. the moisture level of the hair at the first heater plate is greater than the moisture level of the hair at the second heater plate). Advantageously, since the first and second plates both receive the same amount of hair, this differential thermal load can be used to determine the moisture level of the hair in a way that is independent of the amount of hair being heated.

More generally, the device (10) may comprise a plurality of temperature sensors for measuring a temperature (or sensors for measuring a thermal load) at two or more regions of a heatable surface (or heatable surfaces) over which the hair passes sequentially (i.e. a tress of the hair first passes over a first region of the two or more regions, and then passes over a second region of the two or more regions). The device may be configured to determine a moisture level of the hair based on the measured temperatures (or measured thermal loads), for example based on a differential temperature or thermal load between the regions. The determination of the moisture level using the measured temperatures or measured thermal loads could be combined with measurements of the moisture level of the user’s hair obtained using other methods, to increase the accuracy of the determination of the moisture level.

The thermal load can be determined by monitoring the change in temperature of each of the heater plates 15 (e.g. using one or more temperature sensors), and/or by monitoring the power delivered to each heater plate 15, as the device 10 is used to style the hair.

Instead of using sequential heating plates to remove the effects caused by the user using hair tresses of different volumes, the device 10 may comprise a sensor for sensing the amount of hair in the tress that is being heated by the device, to enable a more accurate determination of the moisture level of the hair based on the thermal load.

Hair Temperature

The moisture level of hair can be determined by monitoring a change in temperature of the hair over time as heat is applied to the hair. The temperature sensor(s) 65 may be configured for sensing the temperature of the hair. The temperature sensor 65 may be configured to measure the temperature of the hair 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.

Figure 8 shows a graph of hair temperature against drying time as heat is transferred to the hair. The hair goes through a warming-up period, and then first and second drying periods, as described below. The first drying period corresponds primarily to the removal of unbound water, and the second drying period corresponds primarily to the removal of bound water. By measuring the change in temperature of the hair over time as heat is transferred to the hair, using the temperature sensor 65, the amount of unbound water and bound water in the hair (which corresponds to a moisture level of the hair) can be determined by the controller 36.

The following phases are illustrated in Figure 8:

• “Warming-up period”: In this phase (points A-B) the device 10 transfers heat to the hair using the heater 25, raising the temperature of the hair to that of the drying period (where a phase change of the liquid occurs). In the warming-up period, when a hair straightener of the type illustrated in Figure 1a is used to transfer heat to the hair, the heater plates 15a, 15b typically operate below a temperature of approximately 100°C to 135°C (e.g. 120°C) in order to avoid water cavitation (so- called ‘sizzle’) occurring. The warming up period can be identified by the controller 36 using the output of the temperature sensor 65, which senses the increase in temperature of the hair after the device 10 initially starts to transfer heat to the hair.

• “Drying period 1”: In this phase (points B-C) the device 10 continues to transfer heat to the water on the hair, but the temperature of the hair remains relatively constant. This is due to evaporation of the unbound water which limits the rise in temperature. This first drying period can be identified by the controller 36 using the output of the temperature sensor 65, which senses the constant temperature of the hair after the initial warming-up period.

• “Drying period 2”: In this phase (points C-E) the unbound water has evaporated, and bound water on the hair starts to evaporate and be driven off from within the hair fibre. In this phase, the temperature of the hair increases from an initial temperature (corresponding to the equilibrium temperature during drying period 1) towards a final temperature (at point E). This phase can be identified by the controller 36 using the output of the temperature sensor 65, which senses the increase in temperature of the hair above the constant temperature that is maintained during drying period 1. In other words, the beginning of this phase can be identified by identifying the increase in temperature that begins at the ‘elbow ¹ at point C.

By monitoring the temperature of the hair over time, the moisture level of the hair can therefore be determined or estimated during the styling/heating process. When the amount of hair received by the device is known (or estimated), the moisture level of the hair at point B can be determined based on the heat output from the heater 25 and the time taken to heat the hair from the temperature at point A to the temperature at point B. The moisture level of the hair in drying period 1 (between points B and C) can be determined based on the heat transferred from device 10 to the hair (which can be used to calculate the amount of evaporation of the unbound water), the determined or estimated moisture level of the hair at point B, and the amount of time that has elapsed since the beginning of drying period 1 . Similarly, the moisture level of the hair in drying period 2 can be determined based on the heat transferred from device 10 to the hair, the determined or estimated moisture level of the hair at point C (which is known, since point C corresponds to the point at which all of the unbound water has been driver off from the hair and the removal of bound water begins), and the amount of time that has elapsed since the beginning of drying period 2. A particular moisture level can therefore be achieved by heating the hair for a corresponding amount of time after the ‘elbow ¹ at point C has been detected, at a particular rate of heat transfer. A table mapping the moisture level of the hair to a time elapsed after point C of the graph could be determined experimentally in advance, and stored in the memory of the device 36. Alternatively, an experimentally determined equation could be stored in the memory 36.

As described before, the determined moisture level can be output to the user to allow the user to control the use of the device 10 or can be used by the controller 36 to control the operation of the device 10 to achieve a target moisture level for the tress of hair.

Capacitive Sensor

The device may be configured to determine the moisture level of the hair by measuring a capacitance. The moisture sensor 64 may comprise a capacitive sensor.

When moisture from the hair contacts a suitable material, a change in the dielectric properties of the material (and therefore the capacitance) occurs that is proportional to the amount water in contact with the material. Any suitable material for which a change in capacitance occurs in response to a change in the moisture level could be used (for example, any suitable polymer or metal oxide between a pair of conductive electrodes could be used). By arranging the capacitive sensor at a position in which it will contact moisture from the hair, the moisture level of the hair can therefore be determined based on the measured change in capacitance via a suitable look up table or calculation that is determined in advance and that relates measured capacitance to moisture levels of the hair. The capacitance of the material may also depend on the temperature. The temperature sensor 65 could be used to measure the temperature of the capacitive sensor in order to account for this effect, to achieve a more accurate measurement of the moisture level. Preferably, the capacitance of the material increases linearly (or approximately linearly) with an increase in the moisture level - as this allows for an easy mapping between a sensed capacitance and a determined moisture level.

The capacitive sensor need not necessarily be arranged for contact with the hair of the user. For example, the device 10 may comprise a fan for generating a flow of air across and/or through the hair, and the capacitive sensor may be arranged for sensing the moisture level of the air that has been blown across and/or through the hair, which provides an indication of the moisture level of the hair.

Optical Sensor

The moisture sensor 64 may comprise an optical sensor. The device 10 may be configured for determining the moisture level of the hair by measuring an amount of light reflected from the hair, by measuring an atenuation of light that passes through the hair, and/or by measuring an atenuation of light that passes through air adjacent to the hair.

The moisture sensor 64 may comprise a light emiter and a light detector (i.e. a light/optical sensor). The light emiter is configured to illuminate the hair with light (comprising any suitable wavelength of light, and not restricted to visible light), and the light detector is configured to detect the light that is reflected from the hair. For example, the light emiter and light detector may be provided on a styling arm (e.g. recessed from plate 15a, 15b shown in Figure 1a), or could be provided on a hair contacting surface of a brush. By measuring the amount of light that is reflected from the hair, the moisture level of the hair can be determined via a suitable look up table or calculation that is determined in advance and that relates measured light to moisture levels of the hair.

The light emiter and light detector may alternatively (or additionally) be configured to measure the atenuation of light that passes through the air adjacent to the hair, to measure the local humidity adjacent to the hair. It will be appreciated that the amount of atenuation of the light is proportional to the moisture level (humidity) of the air according to the Beer-Lambert law.

The light emiter may be configured to illuminate the hair using specific wavelengths of light (or a specific distribution of wavelengths of light). The light detector may be configured to detect, for example, Lyman alpha light or other water (or hydrogen) absorption or emission peaks in order to determine the moisture level of the hair. For example, water absorption peaks at 1950 nm, 1450 nm, 1200 nm and/or 970 nm could be measured.

Advantageously, the optical sensor could also be configured to determine the hair section size, hair colour, hair texture, hair shine and/or hair alignment of the hair by measuring the amount of light that passes through the hair, or the amount of light that is reflected from the hair. The target moisture level for the user’s hair could be set using one or more of the section size, hair colour, hair shine and/or hair alignment determined using the optical sensor. For example, a corresponding target moisture level (or scaling factor to be applied a target moisture level obtained using another method) that results in longer lasting hair styles could be determined in advance experimentally for any (or any combination of) the determined section size, hair colour, hair shine and/or hair alignment. The optical sensor could also be used to measure the speed at which hair is passing through the device (i.e. the speed at which the user is moving the device through the hair), by measuring changes in the light that is reflected from the hair over time (in a manner that is analogous to the way in which an optical mouse for a computer senses the speed/position of the mouse). The determined speed could be used to determine an operating parameter to use to control the moisture level of the user’s hair. For example, if hair is moving through the device relatively slowly, then an operating temperature of the device 10 may be reduced, to reduce the risk of overheating the hair (or over-drying the hair).

The optical sensor could also be configured to determine a distance (e.g. proximity) between the device and the head of the user. For example, the optical sensor could be configured to sense an amount of ambient light, which decreases as the device 10 is moved closer to the head of the user. The device 10 may be configured to input the output from the sensor into a stored equation to determine the distance between the device 10 and the head of the user. Alternatively, the device 10 may use a stored lookup table that maps sensor measurements of the ambient light level to the corresponding distance between the device 10 and the head of the user.

The optical sensor may be configured to sense an amount of wetline product in the hair of the user. For example, the optical sensor may be configured to sense a chemical signature of the wetline product (e.g. sense an amount of light at one or more wavelengths that are characteristic of the wetline product), for determining the amount of wetline product in the hair (e.g. by a controller or processor of the device 10 that is configured to receive an output from the sensor). A fluorescent signature of the wetline product could be sensed using the optical sensor. The determination of the amount of wetline product can be used as a proxy measurement for the amount of moisture in the user’s hair. For example, by measuring the decrease in the amount of wetline product in the hair as moisture is removed from the hair, the overall moisture level of the user’s hair can be determined or estimated. The wetline product could be applied to the hair before and/or during the styling process. The wetline product could be dispensed onto the hair by the device 10 (e.g. according to any of the methods for dispensing a fluid or wetline product described below), or could be worked into the hair manually by the user (e.g. as part of a shampoo or conditioner that is applied to the hair before the device 10 is used to style the hair).

Resistance Measurements

The moisture sensor 64 may be configured to measure a change in resistance (or resistivity) to determine a moisture level of the hair. The moisture sensor 64 may comprise a DC resistive sensor for measuring the moisture level of the hair.

A change in resistivity measured between two electrodes can be used to establish a value of relative humidity. The moisture sensor 64 may comprise a material that exhibits a change in resistance when a change in moisture level occurs. The resistance of the material may vary inversely with the humidity level. By measuring the change in resistance of the material, the moisture level can be determined via a suitable look up table or calculation that is determined in advance and that relates measured resistance values to moisture levels of the hair. The moisture sensor 64 may comprise, for example, a hygroscopic conductive layer in the form of a polymer humidity sensing film that is mounted on a substrate. However, any other suitable material could be used. For example, the material may comprise electro-ceramic materials, perovskite type ceramic materials, thick film ceramic materials, catalyst-added ceramic materials, doped/undoped semiconducting thin films, or organic/inorganic hybrid composites.

Time, Frequency or Amplitude Domain Reflectometer

The moisture sensor 64 may comprise a plurality of electrodes for passing an electromagnetic wave through the hair to determine the moisture level of the hair. Any suitable frequency of electromagnetic wave could be used. The speed and strength of the wave as it travels between the electrodes, and the change in frequency of the wave, is directly related to the dielectric properties of the hair which in turn depends on the moisture level of the hair, and can therefore be used to determine the moisture level of the hair via a suitable look up table or calculation that is determined in advance and that relates speeds and strengths of the wave to moisture levels of the hair .

For example, the moisture level of the hair may be determined by measuring a dielectric loss across the hair. The relationship between the dielectric loss and the moisture level could be measured experimentally in advance for a specific device configuration and used to populate a look up table that relates the measured dielectric loss to moisture level.

The electrodes may be provided, for example, as part of the plates 15a, 15b of the styler illustrated in Figure 1a. However, any other suitable arrangement of electrodes could be used. For example, the electrodes could be provided as bristles of a brush, or as printed tracks on a surface of the device 10.

Air Temperature Sensing

For devices that are configured to transfer heat to the hair using a flow of heated air (e.g. the device described in the applicant’s earlier application WO 2021/019239), the temperature of the airflow after it has transferred heat to the hair (referred to as the ‘outflow air temperature’) is proportional to the heat transferred to the air via the heater 25, is inversely proportional to the flow rate of the air through the device, and is inversely proportional to the amount of heat transferred to the hair. When a quantity of wet hair is placed in the stream of heated air, the latent heat of evaporation results in a reduced outflow air temperature compared to when dry hair is placed in the heated airflow. Therefore, by measuring the outflow air temperature the moisture level of the hair can be determined or estimated via a suitable look up table or calculation that is determined in advance and that relates measured outflow air temperature to moisture levels of the hair.

A hair sensor for sensing an amount of hair heated by the airflow could also be provided, to improve the accuracy and reliability of the determination of the moisture level of the hair obtained using this method (since the heat transferred to the hair also depends on the amount of hair received by the device 10).

The measurements of the moisture level of the hair obtained using any of the above-described sensors and methods may be combined with additional temperature and power data obtained by the device, to improve the accuracy of the determination of the moisture level of the hair.

Increasing the Moisture Level of the Hair

Methods and apparatus for increasing the moisture level of hair (which may, for example, form part of step S303 of Figure 3) to wet or re-wet the hair using the wetline product dispenser(s) 29 will now be described in detail. When the control of the moisture level of the hair to match the target moisture level is achieved by heating the hair to reduce the moisture level, the hair must have a higher moisture level than the target moisture level at the beginning of the heating process. Advantageously, when the device 10 is configured for increasing the moisture level of the hair by dispensing a fluid using the wetline product dispenser 29, the device 10 can increase the moisture level of the hair to be above the target moisture level, so that a subsequent heating process using the heater 25 will not cause the hair to become overly dry.

Whilst the above described methods of controlling the moisture level of hair can be used when the hair is already wet before the device is used (for example, when the user has washed their hair prior to using the device), the wetline product dispenser 29 could instead be used to wet the hair (either before, or as part of, a styling process). Advantageously, when the wetline product dispenser 29 is used to wet the hair, more precise control of the initial moisture level of the hair can be achieved. Moreover, finer control of the moisture level during and after the styling process can be achieved. For example, if the heat transferred to the hair using the heater 25 has caused to the hair to become dryer than the target moisture level, this could be corrected by dispensing a fluid onto the hair using the wetline product dispenser 29 (e.g. to restore the moisture level of the hair to the target moisture level).

The wetline product dispenser 29 may comprise a fluid reservoir within the device 10. Water, or any other suitable fluid, may be dispensed from the fluid reservoir onto the hair. The reservoir may by removable from the device 10 and/or may be refillable. Fluids dispensed from the wetline product dispenser 29 may also result in other benefits in addition to enabling more precise control of the moisture level of the hair. For example, chemical ingredients for enhanced styling performance could be used, such as fluids suitable for cleaning, colouring, enhanced style holding, moisturisation/lubrication, repair and/or protection of the hair. Lower viscosity wetline products may be preferred, as this enables a more consistent distribution of fluid throughout the hair to be achieved. Advantageously, the examples of fluid distribution described below enable the device 10 to distribute a fluid evenly amongst strands of the user’s hair, whilst minimising potential inhalation or ingestion of ingredients by the user.

Dispersion by Vibration

The wetline product dispenser 29 may comprise a mechanical vibrational element (for example, a string, cable, or vibrating rod) operating at a frequency and amplitude for separation of individual fibers of the hair. Alternatively, a flow of air generated by the fan 27 could be used to vibrate the hair. Advantageously, vibration of the hair results in a more even dispersion of liquid throughout the hair. The vibration of the hair may be beneficial even when additional fluid is not added to the hair by the wetline product dispenser 29, for example to achieve a more uniform distribution of unbound water that was present on the hair before the device 10 is used.

The vibrational element may be placed within a cavity of the device 10 such that the hair is gripped at either end of the cavity, whilst remaining unbound in a central region of the cavity to be vibrated by the vibrational element. Alternatively, a flow of air could be used to vibrate the hair within the cavity. The cavity may be at least partially sealed to reduce the risk of inhalation or ingestion of wetline products by the user.

The wetline product dispenser 29 may be configured to cause the hair to vibrate at any frequency and amplitude suitable for dispersing fluid amongst the hair. For example, a frequency of between 10 Hz and 1 kHz could be used, and an amplitude of between 0.5 mm and 10 mm could be used.

Atomisation by Piezo Transducer

The wetline product dispenser 29 may be configured to disperse a wetline product (or any other suitable fluid) into an airstream using a piezo transducer. Once atomised, the wetline product is delivered to the hair via the flow of air generated by the fan 27, and settles onto the surface of the hair, thereby increasing the moisture level of the hair. The piezo transducer may be placed directly against an internal wetline reservoir within the device 10, or may be configured to operate indirectly via an intermediary wick between the transducer and the reservoir. Mechanical Dispersion

The wetline product dispenser 29 may be configured to dispense a fluid onto the hair using a mechanical force driven by the user. For example, when the device 10 comprises a pair of arms (for example, the arms 12a, 12b of the device 10 illustrated in Figure 1a), the opening and closing action of the arms can be used to leverage a mechanical force on an internal reservoir of fluid within the device 10, causing the fluid to flow through a nozzle to wet the hair of the user. Some of the energy from the movement of the device 10 by the user may be stored in a compression spring or bellows, for pumping fluid from the reservoir. When the spring is compressed, a build up of pressure occurs that can be used to cause the fluid to escape through one or more apertures to wet the hair. Alternatively, an electrically powered pump could be used to pump the fluid through the apertures. The pump could be operated, for example, in response to an input from the user (e.g. a press of a button), or could be operated by the controller 36 of the device 10 (e.g. based on a determination of the current moisture level of the user’s hair, and a determination that the moisture level should be increased).

Sacrificial block

The wetline product dispenser 29 may comprise a sacrificial block of material for controlling the moisture level of the hair. For example, the device 10 may generate a flow of air over the sacrificial block using the fan 27, which results in transfer of material from the sacrificial block to the air stream (for example, by sublimation). The material can then be transferred to the user’s hair via the flow of air, to help control the moisture level of the hair. The sacrificial block may comprise any suitable material that aids in the control the moisture level of the user’s hair. For example, the sacrificial block may comprise a chemical that helps to regulate the amount of evaporation of bound or unbound water that occurs as the hair is heated using the heater 25.

Alternatively, a block of material that directly contacts the hair of the user could be provided. For example, a sacrificial block of material could be provided on or adjacent to the heater plates 15a, 15b of the device illustrated in Figure 1a.

Direct contact wick

A fluid may be transported from a reservoir to a hair contacting surface, where it can then be used to increase the moisture level of the hair. For example, the wetline product dispenser 29 may comprise an internal reservoir of fluid that is transported to a hair engaging surface via a wick that at one end is submerged within the internal reservoir, and at the other end is coupled to the hair contacting surface for transfer of the fluid. The hair contacting surface may be, for example, the heater plates 15a, 15b of the device illustrated in Figure 1a. However, it will be appreciated that the hair contacting surface could be any suitable surface of the device 10.

Vaporisation

The wetline product dispenser 29 may be configured to vaporise a fluid (for example by heating fluid in a fluid reservoir) for subsequent transfer to the user’s hair. The fluid may be vaporised into a flow of air generated by the fan 27. The flow of air comprising the vaporised fluid could then flow directly over the hair of the user to increase the moisture level of the hair. The air comprising the vaporised fluid may flow into a pressurised cavity (which can also be referred to as a plenum chamber) of the device 10, for subsequent transfer to hair inside the cavity.

Illustrative Example ■ Control Method

Figure 9 shows a method of controlling a moisture level of hair of a user based on a target moisture level. The method may be implemented using the controller 36 of the device 10.

In step S801 a section of hair is received by the device 10. For example, when the device 10 is of the type illustrated in Figure 1a, a section of hair is received between the heater plates 15a, 15b.

In step S802, a target moisture level for the hair is obtained. The target moisture level may be an ambient moisture level. The target moisture level may be obtained according to any of methods for obtaining the target moisture level described above.

In step S803, the current moisture level of the hair is obtained. The current moisture level may be obtained (e.g. measured) according to any of methods for obtaining the current moisture level of the hair described above.

In step S804, the device 10 transfers heat to the section of hair using the heater 25. For example, heat may be transferred to the hair via conduction using a heated plate 15, and/or may be transferred using a flow of heated air generated by the heater 25 and the fan 27, and/or using any other suitable method (including any of the methods described above).

An operating temperature used to heat the hair in step S804 (e.g. a temperature of a heater plate 15, or a temperature of heated air generated by the device 10) may be determined by the controller 36 based on the current moisture level obtained in step S803 and the target moisture level obtained in step S802. For example, the controller 36 may be configured to control the operating temperature based on a difference between the current moisture level and the target moisture level. The controller 36 may be configured to control the operating temperature based on a difference between the current moisture level and the target moisture level using an equation stored in the memory 63, or using a look up table stored in the memory 63, such as the table described above with reference to Figure 6. Advantageously, this allows the amount of heat transfer to the hair be reduced as the hair approaches the target moisture level, reducing the risk of ‘overshooting’ and over-drying the hair.

For example, when the device 10 comprises a heated plate 15 for transferring heat to the hair, the controller 36 may be configured to control the temperature of the heated plate 15 based on the amount of moisture detected (using the moisture sensor 64) above the target moisture level. When the hair has a large amount of excess water (e.g. the hair is visibly wet and has a large amount of unbound water) an operating temperature of less than or equal to 120°C could be used to prevent ‘sizzle’ (as described in detail above). When the hair has a moderate amount of excess water, a temperature between 120°C and 200°C could be used for more efficient drying and styling performance. When a small amount of excess water is present, the operating temperature may be controlled directly as a function of the amount of excess water. In other words, the amount of heat transferred to the hair may be controlled as a function of (M _c - Mt), where M _c is the current moisture level of the hair, and Mt is the target moisture level of the hair. As (M _c - Mt) approaches zero, the amount of heat transferred to the hair by the device 10 may also approach zero. When there is no excess water present (i.e. when M _c - Mt = 0), or when the difference between the target moisture level and the current moisture level is within a threshold range, the operating temperature may be controlled to be the minimum possible operating temperature. The minimum temperature may be the ambient room temperature. However, the minimum temperature may be higher than the ambient temperature if required for the device to respond sufficiently rapidly to the user starting to dry and/or style the next section of hair. Advantageously, when a thick film printed heater or radiative heater is used to transfer heat to the hair, the minimum heat transfer is reduced due to the fast temperature response of these types of heaters, and the risk of over-drying the hair is correspondingly reduced.

Step S804 may also comprise applying a controlled tension to the hair using the device 10 as the hair is heated and/or styled. For example, the hair may be held fixed at two points either side of a cavity, and heat could be transferred to the hair in the cavity (e.g. by using a flow of heated air generated by the device 10). Advantageously, by applying tension to the hair (e.g. by holding the hair fixed between the two points) as the hair is heated and/or styled, undesirable crossing and tangling of hair fibers is reduced, enabling increased fiber alignment, and providing improved shine and improved smoothness. In step S805, the current moisture level of the hair section is re-obtained. The current moisture level may be obtained (e.g. measured) according to any of methods for obtaining the current moisture level of the hair described in detail above.

In step S806, a determination of whether the current moisture level of the hair section is lower than or equal to the target moisture level is made by the controller 36. If the result of the determination in step S806 is ‘NO’, then the method returns to step S804 where the hair is further heated to reduce further the moisture level of the hair.

If the result of the determination in step S806 is ‘YES’, then the controller 36 may be configured to rapidly prevent any further heat transfer to the hair. For example, the power supply to an air heater could be disabled, a radiant heater could be immediately switched off, and conductive heaters (e.g. thick film printed heaters, which have a particularly low thermal mass) could be switched off and allowed to rapidly cool. Advantageously, this prevents excessive drying of the hair caused by heat transfer after it has been determined that the hair is already at or below the target moisture level.

The device 10 may also be configured to rapidly cool the hair to ambient temperature using a flow of ambient air (for example, generated using the fan 27), to prevent over-drying of the hair. Moreover, reducing the temperature of the hair once the style has been imparted beneficially causes the hair to transition to a more glassy and less plasticised state, which enables the hair section to better resist any adverse stresses applied to the hair.

If the result of the determination in step S806 is ‘YES’, the method may proceed to optional step S807. Alternatively, the method may simply proceed to step S808 in which the method is complete. Optionally, the method may return from step S808 to S801 if the user begins to dry/style the next tress of the hair.

In optional step S807, the device 10 increases the moisture level of the hair using the wetline product dispenser 29. Step S807 may be used, for example, when the current moisture level of the hair is significantly below the target moisture level, and should be re-wetted. The current moisture level may be increased according to any of methods for increasing the current moisture level of the hair described in detail above. The method then proceeds back to step S803.

Figure 10 shows a modification of the flow diagram of Figure 9 in which an additional step S806b is included. In step S806b, the user indicates, via the user interface 11 , whether or not the user is satisfied with the hair sty ling/drying result. The user may input the indication via any suitable element of the user interface 11, or via the communications circuitry 67 (e.g. using a smartphone app connected to the device 10 via the communications circuitry 67). If the user is not satisfied with the drying/styling result, then the method proceeds to step S807 in which the hair is re-wetted using the wetline product dispenser 29, and the heating/sty ling process restarts. If the user is satisfied with the styling/drying result then the method proceeds to step S808.

The device 10 may be configured to update one or more operating profiles stored in the memory 63 based on the feedback received from the user in step S806b. Advantageously, this enables the device 10 to modify the styling process for different types of hair (since the optimal operating parameters for styling/drying may depend on, for example, the thickness of the user’s hair) or based on the specific styling technique used by the user, to achieve longer lasting hair styles and to increase the overall effectiveness of the device 10. For example, the device 10 may be configured to alter an operating temperature or heating duration based on the feedback received from the user. The target moisture level may also be adjusted based on the feedback received in step S806b. The feedback received from the user need not necessarily be a simple yes/no response. For example, the feedback may comprise a rating on a numerical scale, or may comprise additional information such as feedback on the texture or feel of the styled hair. The device 10 may be configured to output a time-delayed query to the user. For example, at a predetermined amount of time after the styling process has been completed, the device 10 may be configured to output a query to the user regarding the longevity of the hair style (e.g. a query as to what extent the hair style is still in place). User feedback that is input in response to the time-delayed query could be used to train the device 10 (e.g. update stored operating parameters) to generate longer lasting hair styles, or could be used to output personalised product recommendations (e.g. wetline product recommendations) or styling tips to the user.

Further Embodiments

Figure 11a is a perspective overview of a combined hair dryer/styler device 110 according to another embodiment (which may or may not employ the moisture sensing techniques described above), with arms 114, 116 in an open configuration, and Figure 11 b shows the same device 110 with the arms 114, 116 closed (as in use, e.g. as shown in Figure 11c). Figures 12 to 14 show further views of parts of the device 110, with Figures 13 and 14 showing air flow through the device 110 in use.

Referring initially to Figures 11 a and 11 b, the device 110 is an all-in-one handheld device that can be used to dry hair in a quick and easy manner, whilst also enabling styling of the hair (e.g. to straighten the hair, or to add “body and volume” to it).

The device 110 comprises first and second mutually-opposing arms 114, 116 arranged in a broadly similar manner to the arms of a handheld hair styler. The first arm 114 has a main body portion 112 at a proximal end 192 of the arm 114 and a hair treating distal end 193. The second arm 116 is coupled at its proximal end 194 to the first arm 114 and has a hair treating distal end 195. The first and second arms 114, 116 are adapted for movement between an open configuration (as shown in Figure 11a) for receiving a length of wet hair therebetween, and a closed configuration (as shown in Figure 11b) adjacent the hair, to create tension in the hair, such that, in use, when the arms 114, 116 are in the closed configuration they form an inter-arm plenum chamber (113, Figure 14) across which the hair passes.

Figure 12 is a perspective view of the body part 112 of the lower arm 14 with half of the housing removed to expose the main components mounted within the body part 112. As can be seen in Figure 12, the body part 112 houses a fan assembly 138 at the proximal end 92 of the body part 112, for drawing air (represented by the arrows 173) into the body part 112 through an air inlet 160 and for forcing the air along the body 112 towards the distal hair treating end of the lower arm 114. The air inlet 160 is formed as an annular opening around a spigot 163 (shown in Figure 11) which extends out beyond the proximal end 192 of the body part 112. The spigot 163 therefore makes it difficult for items to close off the entire air inlet 160. Additionally, the proximal end 192 of the body part 112 is also preferably sloped relative to the longitudinal axis of the body part 112, as this also helps to reduce the likelihood of the entire air inlet 160 being blocked. The fan assembly 138 has an impeller and is typically also provided with a filter 165 for preventing dust and debris from reaching the fan assembly 138.

The air from the fan assembly 138 is heated by a heater 130 before being directed into the distal end 193 of the lower arm 114 where an air-flow guide structure 124 (that is shown in more detail in the cross-sectional view of Figure 13) guides the air towards the user’s hair. More specifically, and as shown in Figure 13, the heated air from the heater 130 passes along the distal end 193 of the lower arm 114 in a direction D1 that is substantially parallel to the length of the arm 114 and the air-flow guide structure 124 causes the air to change direction to a second direction D2, that is from the arm 114 towards the opposing arm 116, i.e. inwards into an inter-arm plenum chamber 113 formed by the arms 114, 116 in the closed position (which is shown in Figure 14). The heater 130 typically takes the form of an electrically-powered heating coil (or other electrical heating elements), that is operable to heat the air drawn in by the fan assembly 138.

As illustrated by the circuit board 136 shown in Figure 12, control electronics 137 are mounted within the body part 112 between the fan assembly 138 and the heater 130. This allows the incoming air to keep the control electronics 137 cool during use. Electrical power is provided to the device 110 via a power cord 164 which typically connects to an AC mains power supply. However, in an alternative embodiment the device 110 may be powered by 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 110 to be a cordless product. The control electronics 137 control the operation of the device 110. As shown in Figure 11 a, a control button or switch 123 may be provided on the device 110, to enable it to be turned on or off, and the control electronics 137 can control the switching on and off of an indicator light to show whether the power is on. The control electronics 137 can also cause a sound generator (not illustrated) to play out a sound when the device 110 is switched on and ready to use.

As illustrated for example in Figure 11a, the second arm 116 is coupled to the body part 112 of the first arm 114 by means of a hinge 118, by virtue of which the first and second arms 114, 116 are movable relative to one other (in the illustrated embodiment, by moving the second arm 116 towards and away from the first arm 114). Thus, the first and second arms 114, 116 can be brought together, into the closed configuration (as shown in Figure 11b), or moved apart, into the open configuration (as shown in Figure 11a), by a user in use. In the illustrated embodiment, each of the arms 114, 116 widens relative to the body part 112 to form a “head” of the device 110, distal from the body part 112, although other embodiments are possible in which the head does not widen in the illustrated manner.

The hinge 118 can incorporate any suitable means for allowing the first and second arms 114, 116 to be moved relative to one other. Preferably the hinge 118 also incorporates spring means configured to bias the first and second arms 114, 116 into the open configuration, such that the user is required to apply pressure to the arms 114, 116 to close them together (overcoming the effect of the spring means), and such that the arms 114, 116 automatically open, under the effect of the spring means, once the pressure is removed. For example, the hinge 118 may incorporate a leaf spring or a coiled spring.

The hinge 118 and the spring means can be one and the same. For example, the spring means itself can be used to couple the second arm 116 to the body part 112, thereby avoiding the need to provide a separate mechanical hinge and simplifying the overall construction of the device 110.

As shown in Figure 11a in the illustrated embodiment the inner surface of the first arm 114 incorporates first and second elongate heater plates 120a, 120b, extending along the length of the arm 114 either side of the airflow guide structure 124. The second arm 116 also incorporates first and second elongate heater plates 122a, 122b (not visible in Figure 11a, but shown for example in Figure 14) in corresponding positions to heater plates 120a and 120b. Each of the heater plates 120a, 120b, 122a, 122b is provided with a respective electrical heating element, operable to cause the respective heater plate to heat up. In the illustrated embodiment the operating temperature of the heater plates 120a, 120b, 122a, 122b is typically around 120-130°C. The first and second arms 114, 116 and the first and second heater plates on each arm 120a, 120b, 122a, 122b are arranged such that, when the arms 114, 116 are in the closed configuration, the first and second heater plates 120a, 120b of the first arm 114 come into contact with the first and second heater plates 122a, 122b of the second arm 116. Preferably the heater plates 120a, 120b, 122a, 122b are made of a material having relatively high thermal conductivity, and are preferably provided with one or more temperature sensors (e.g. a temperature sensor for each plate, or one or more temperature sensors that each serves a plurality of heater plates) for sensing the temperature of the heater plate. The sensed temperatures are then fed back to the control electronics 137 so that the control electronics 37 can control the power delivered to the heater plates 120a, 120b, 122a, 122b to maintain them at a desired operating temperature.

The heater plates 120a, 120b, 122a, 122b serve a number of purposes during use of the device 110. Firstly, with the user having sandwiched a length of wet hair between opposing plates 120a and 122a, and between opposing plates 120b and 122b (i.e. transversely across the plenum chamber 113 formed by the first and second arms 114, 116 in the closed configuration), and by drawing the device 110 along the length of wet hair, the heater plates 120a, 120b, 122a, 122b subject the wet hair to a squeegeeing effect, removing excess unbound water, and also heat the hair to promote subsequent evaporation of the water. Secondly, the heating provided by the heater plates 120a, 120b, 122a, 122b causes the walls of the plenum chamber 113 to be heated (via thermal conduction), and also helps maintain the temperature of the airflow delivered through the plenum chamber 113 by the fan assembly 138. Thirdly, the heater plates 120a, 120b, 122a, 122b can be used to style the hair, as an integral part of the drying process. The heater plates 120a, 120b, 122a, 122b are preferably configured as ceramic float plates with springs having a low spring rate or stiffness, thereby giving good control of hair tension.

Allowing for the airflow heating coil (or other heater elements) and the heater plates 120a, 120b, 122a, 122b, as well as the fan assembly 138, the overall power consumption of the device 110 is around 600-800 W, which is significantly less than a 2000 W conventional hairdryer. Of course, higher powered motors could be used in the device 10 which would increase the power consumption but would allow the device 110 to dry the user’s hair more quickly.

Turning now to Figure 14, this illustrates further directions of airflow though the arms 114, 116 of the device 110 when viewed in transverse cross-section, facing towards the body part 112 of the device 110.

Starting in the centre of Figure 14, the air flowing from the lower arm 114 in direction D2 can be seen entering the inter-arm plenum chamber 113 from an airflow conduit 115 via the cells of the airflow guide structures 124. Some of the air will bounce off the user s hair whilst some will pass into the other arm 116. Upon leaving the inter-arm chamber 113, the air spreads sideways and enters the airflow redirecting channels 128, from which the air then passes along airflow conduits 119a, 119b, 121a and 121b to leave the device 110 via vents 126 in directions D3 (via conduits 119a and 121a) and D4 (via conduits 119b and 121b). As shown in Figure 14, airflow conduits 119a, 119b, 121a and 121b respectively extend behind the heater plates 120a, 120b, 122a and 122b that are mounted on the first and second arms 114, 116. Advantageously, the vents 126 direct the outgoing air towards the roots of the hair, to dry the roots and create root lift.

The device 110 described above has been found to provide efficient drying and styling of the user’s hair. The combination of conductive heating of the hair by the heater plates 120a, 120b, 122a and 122b and the convective heating of the hair in the enclosed chamber 113 by the heated airflow significantly increases the drying efficiency of the device 110 over conventional hot air devices.

The inventors have made a number of improvements to the device 10 described above and these will now be described below.

One improvement relates to the use of diffusers at the air outlet vents 126 of the arms 114, 116. These diffusers can help to reduce flying away problems that can be created by having a concentrated airflow coming from the air vents 126 and can also help to cool the user’s hair as it leaves the device 110 which helps to set the hair style.

Figure 15 is a transverse cross-sectional view of the device 110 having four diffusers 140a, 140b, 142a, 142b mounted within the airflow conduits 119a, 119b, 121a and 121b (shown in Figure 14) that respectively extend behind the heater plates 120a, 120b, 122a and 122b that are mounted on the first and second arms 114, 116. As shown schematically, the air leaving the device is diffused in various different directions (illustrated by the arrows leaving the diffusers 140, 142 in the different directions) and not just in the directions D3 and D4 as before. This helps to prevent the exhaust exiting the device 110 from causing hair to fly away from the device when styling a section of hair and, ultimately, thereby reduces the likelihood of ‘flyaways’ in the resultant styled hair. ‘Flyaways’ or ‘frizz’ are terms in the art of hair styling that refer to undesirable fuzzy or irregular texture. Additionally, if the diffusers 140, 142 are made of a heat conducting material (such as copper or aluminium or ceramic), then hair that touches the outer casing of the devicel 10 as the hair leaves the device 110, will be cooled by conductive and convective cooling, which helps to set the style that the user has achieved. In particular, by the time that the heated air exits through the diffusers 140, 142, it will have lost much of its heat to the hair and to evaporation of water from the hair. Therefore, the air leaving the diffusers will be cool enough to set the style that the user has created using the device 110 - whether that style is the straightening of the hair or the curling of the hair (which is typically achieved by turning the device during use, so that the hair is forced to change directions as it leaves the device 110, which creates a curl).

Of course, the device illustrated in Figures 11 to 15 is designed to be symmetric so that it can be used in a left handed or a right handed manner. In a case where the device is intended for single direction of use, then only two diffusers 140, 142 may be provided at the hair outlet side of the device 110. In the device illustrated in Figures 11 to 15, air was supplied down one of the two arms 114, 116. As those skilled in the art will appreciate, if desired, air may be supplied down both arms 114, 116 and fed together in opposite directions into the central plenum chamber 113 formed between the two arms 114, 116.

Another improvement relates to the provision of a ‘quench’ activator switching or sensing means 129 on the combined hair dryer/styler device 110 (as shown in Figure 16). It is known in the art that to reshape hair (quickly) heat is needed to help plasticise the hair and mechanical stress is needed in the direction that the hair is to be deformed/reshaped/styled. Once heated, the hair exists in a more plastic state and is capable of being reshaped easily, therefore it is counterproductive to apply disruptive mechanical force in any direction other than the desired styling direction while the hair remains hot and pliable. This includes, for instance, the force of gravity working to lengthen a curl as it is removed from any styling device or tensioning the hair straight after curling with a styling device. If the hair can be cooled before any disruptive force (force in an undesired direction) is applied, then the bonds within the hair can be set and are less likely to be repositioned by the disruptive force. This action may be referred to as ‘quenching’ and can result in improved hair styling performance by a hair styling device - for instance, tighter curls or straighter straightened hair and reduced flyaways/frizz.

In the prior art, quenching has not been provided within a single, combined hair drying/styling device. The inventors have realised that within any such devices, as set out in this application, a simple switch (not shown) or a sensor which relays its sensed activity to a control system may be used to switch off heating of airflow while leaving conductive hair heating turned on and that this provides a novel ability to a user to simply ‘push a button’ (or equivalent action) in order to have the ability to quench the style they have created, thereby achieving superior styling results over prior art devices. In some embodiments, the ‘quench’ activator switching or sensing means 129 may be combined with a ‘cool-shot’ switch or sensing means (not shown) which is used for activating a separate ‘cool-shot’ mode as described previously.

Another improvement that the inventors have made is to control the speed of the fan of the fan assembly 138. In particular, the inventors have found that when the user of a two-armed device opens the arms 114, 116 to place a section of wet hair to be dried between the arms, the air flow coming from the fan assembly 138 makes it more difficult for the user to insert a section of hair between the two arms without hair flying away from the device. The inventors have found that this problem can be reduced by varying the speed of the fan assembly 138 depending on the open/close state of the arms 114, 116. More specifically, the inventors have found that varying the air flow speed between a first air flow speed when the arms 114, 116 are in the open configuration and a second airflow speed (which is higher than the first air flow speed) when the arms 114, 116 are in the closed configuration, helps to alleviate the above problem. The variation in air flow speed may be a step change (for example between on and off or between two set airflow rates) or it may be a step-wise variation or a smooth variation between the first and second airflow rates. Figure 16 is a block diagram illustrating the main control components of the hair drying and styling device 110 that can implement this improvement. As shown, the control circuitry is very similar to the circuitry shown above in Figure 1c, except that it has an open / close sensor 127 for sensing the state of the arms 114, 116. This may be a simple binary sensor (such as a microswitch or optical sensor) that senses if the arms 114, 116 are open or closed, with the microprocessor 62 using that information to control the speed of the fan assembly 138 in the manner discussed above. In a more complex device, the open / close sensor 127 may sense different degrees of openness of the arms 114, 116. This could be achieved, for example, using a potentiometer whose resistance changes gradually as the arms open and close or a position sensor that senses the position of the hinge 118 between the open and closed states. In this case, the microprocessor 62 can perform a more complex variation of the airflow speed rather than a simple switch between two air flow rates. In addition to reducing the airflow rate of the fan assembly 138, the microprocessor 62 also preferably reduces the heat generated by the air heater 130 so that the air heater 130 does not overheat and/or the temperature of the air flow at the lower airflow rate does not get too hot for the user. In other embodiments (not shown) - in particular in a combined drying/sty ling device having only a single arm, for instance in the general format of a hair curler but with an air conduit therein, for example as disclosed in US 6,363,215 - controlling the speed of a fan (not shown) in reaction to at least one other trigger mechanism (such as an accelerometer, a gyroscope, a microswitch etc (not shown)) which sense a modality of operation of the device offers a further important device safety advantage in terms of being able to avoid surface damage by the device to any surface (e.g. tabletop or scalp) it may be sufficiently close to so as to potentially cause such surface damage or to provide varying fan speeds for different scenarios (e.g. faster fan speed when hair is sensed as having been wrapped around such an airblown hair curler or faster fan speed when hair is sensed as being present in between the arms of a twoarmed combined dryer/styler). 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 25, or may alternatively comprise two or more heaters 25. More generally, the device 10 may comprise any suitable means for transferring heat to the hair of the user, such as any suitable conductive heater, thick film printed heater, steam heater, or radiative heater.

In some of the above-described examples, the device 10 need not necessarily comprise the moisture sensor 64 for sensing the moisture of the hair. Alternatively, for example, the device 10 could be configured for heating the hair using a predetermined set of operating parameters based on the target moisture level. For example, a table of target moisture levels and corresponding operating temperatures needed to achieve that target moisture level could be determined in advance and stored in the memory 63. In this configuration, the device 10 need only identify the operating temperature (and any other relevant operating parameters) to be used from the table, and it is not necessary to sense the moisture of the hair. However, providing a moisture sensor 64 for sensing the moisture of the hair is nevertheless beneficial for verifying that the hair has reached the intended moisture level, and enables more precise control of the moisture level.

In some of the above-described examples, the device 10 has been described as increasing the moisture level of the user’s hair (e.g. by dispensing a fluid onto the hair), before the hair is heated by the device to decrease the moisture level. However, the device 10 may also (or instead) be configured to dispense fluid onto the hair during and/or after the heating of the hair. For example, fluids that do not require dispersion into the hair (e.g. surfactants) could be dispensed onto the hair during the heating process. The wetline product could also be used to increase the rate of drying of the hair (i.e. the rate at which the moisture level of the hair is decreased). The wetline product may comprise a surfactant (wetting agent) that increases the drying rate of the hair by reducing the surface tension of the water on the hair. The wetline product may comprise a desiccant that reduces the moisture level of the hair by absorbing water from the hair. The wetline product may comprise one or more azeotropes that increase the drying rate of the hair by reducing the boiling point of the water on the hair. The wetline product may comprise one or more impurities that increase the drying rate of the hair by increasing the number of sites available for boiling of the water on the hair to occur.

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 that are typically used for straightening the user’s hair. In other embodiments, the device may use other types of heaters. For example, instead of having heating plates, ribbed heaters may be used to crimp the 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.