GB2626020A

GB2626020A - Improvements in and relating to haircare appliances

Info

Publication number: GB2626020A
Application number: GB2300198.5A
Authority: GB
Inventors: Oliver Tate Mills Henry; Donal McGuckian Patrick
Original assignee: Dyson Technology Ltd
Current assignee: Dyson Technology Ltd
Priority date: 2023-01-06
Filing date: 2023-01-06
Publication date: 2024-07-10
Also published as: WO2024147050A1

Abstract

A haircare appliance 30 comprises a body 32 for engaging hair in use. A sensor arrangement 48 is configured to output a signal indicative of the presence of hair comprising an amount of water at a region of the body. A control unit 43 is configured to determine the measure indicative of the amount of water based on temporal changes in the signal. The body may comprise a number of non-contact sensors such as self-capacitance sensors or mutual capacitance sensors. A rate of change of signals output by the sensors may indicate the amount of coverage of the body by hair. The heater or air flow may be controlled in accordance with the moisture content indicated, the coverage indicated, or both. The heat or power may be terminated when a pre-set time has passed or when a threshold is met. The sensors are preferably arranged at different regions of the body and the amount of water is determined based on temporal changes in the first signal and the second signal. A control unit which determines the moisture content and a method of determining the moisture content are also disclosed.

Description

I

IMPROVEMENTS IN AND RELATING TO HAIRCARE APPLIANCES

Field of the Invention

The present invention relates to haircare appliances and particularly, though not exclusively, to haircare appliances configured for drying or styling hair by the application of heat to the hair.

Background

Many haircare appliances are configured for drying or styling hair by the application of heat to the hair. The ability to detect when a quantity of hair (e.g., a tress) is fully styled has numerous benefits. These include protecting hair health and reducing cognitive load on a user whilst styling or drying their hair.

The present invention has been devised in light of the above considerations.

Summary of the Invention

At its most general, the invention the invention exploits the discovery that a capacitive sensor(s) is able to accurately measure the moisture content of an amount of hair in proximity to the capacitive sensor(s), such as when engaged with a haircare product incorporating the capacitive sensor. When used in a haircare product in this way, the capacitive sensor response (i.e., output, signal etc.) is found to change differently according to the moisture content of the hair.

A haircare styling process typical involves the application of heat to style a tress of hair. This process will typically reduce the amount of water in the tress over time (i.e., dry it). If a drying hair tress is in contact with, or proximity to, a capacitive sensor, the inventors have observed that a capacitive sensor response consequentially changes (e.g., falls) over time. A small amount of relatively more moist hair will likely dry (i.e., to lose moisture, or to have a rate of moisture loss) more quickly than a larger amount of relatively less moist hair. The inventors have found that, when heat is applied to a tress of hair, the rate of change of the capacitive sensor response can serve as an indication as to how much material is covering the capacitive sensor. Therefore, a capacitive sensor positioned at the hair-engaging parts of a haircare appliance (e.g., styling device) may be used to predict moisture content of hair.

In a first aspect, the invention may provide a haircare appliance comprising: a body for engaging hair in use: a sensor arrangement configured to output one or more signal(s) being indicative of a presence of hair comprising an amount of water at a region of the body; and, a control unit configured to determine a measure indicative of the amount of water based on temporal changes in the signal(s).

In this way, the inventors exploit the realisation that a good proxy for predicting when hair is fully dried and/or styled is its moisture content. A hair styling process typically begins with damp hair and continues until the hair is dry.

The sensor arrangement preferably comprises one or more non-contact sensors each configured to output a said signal. The one or more non-contact sensors may comprise one or more self-capacitance sensors and/or one or more mutual capacitance sensors.

A capacitive sensor (sometimes known as a capacitance sensor) may comprise at last one electrode (e.g., a plate or wire) of conductive material positioned with or upon a nonconductive medium (e.g., dielectric such as: air, plastic, etc.). The electrode is configured to be capable of being electrically charged, and the time taken to fully charge the electrode in response to a pre-set applied voltage, may be returned as the sensor response value.

Two types of capacitive sensors exist, and each type exploits a different respective capacitance mechanism. A first type of capacitive sensor is known as a self-capacitive sensor (sometimes known as a self-capacitance sensor), and a second type of capacitive sensor is known as a mutual-capacitive sensor (sometimes known as a mutual-capacitance sensor).

A self-capacitive sensor measures a change in capacitance with respect to earth ground. Here, the electrode forms one electrode of a notional capacitor, with the other electrode being provided either by earth ground or by the user's quantity of hair when in proximity to (or contact with) the electrode.

Proximity to (or contact with) the electrode causes the electrode capacitance to increase, as the quantity of hair "adds" capacitance to that of the system. The greater the quantity of water (i.e., moisture content) in the hair in question then the greater is the capacitance "added" to that of the system. Self-capacitive measurement may employ a single electrode and may measure a capacitance, and/or a change in capacitance with respect to ground caused by the user's quantity of hair when in proximity to (or contact with) the electrode. A self-capacitive sensor's electrode, in use, projects salient electric field lines some of which change direction so as to terminate on charges present within the user's quantity of hair (as opposed to elsewhere beyond the sensor) when that hair is brought into proximity with (or contact with) the electrode. The hair may result in a higher capacitance as compared to the baseline measured value.

A mutual-capacitive sensor employs two electrodes that together represent a two-electrode capacitor.

The sensor measures a change in capacitance of the capacitor. The user's quantity of hair when in proximity to (or contact with) the two electrodes, changes the electric field between the two electrodes and reduces the capacitive coupling between the electrodes. Electrodes of a mutual-capacitive sensor project salient electric field lines from one of the two electrodes to the other electrode. Once more, some electric field lines may change direction so as to terminate not on an electrode of the sensor but, instead, on charges present within the user's quantity of hair when that hair is brought into proximity with (or contact with) either or both electrodes. Put in other words, the user's quantity of hair when in proximity to (or contact with) the electrode(s), in effect "steals" electric field lines from the two-electrode capacitor system. This may result in a lower capacitance as compared to a baseline measured value of the capacitance of the system.

If a medium having a moisture content is placed in proximity to (e.g., adjacent to or in contact with) the electrode, the capacitive sensor response changes in value. The sensor response may be a change in the capacitance (C) of the capacitive sensor. An equivalent circuit of a capacitive sensor may comprise an effective resistance (R) across which a pre-set voltage (potential difference) is provided, in which one terminal of the effective resistance may be connected to ground (e.g., earth ground) via a capacitance corresponding to the capacitance of the capacitive sensor. The product of the effective resistance and the capacitance of the capacitive sensor, R x C = 1-, defines a time constant, 1-, (known as the "RC time constant") corresponding to either the time required to charge the capacitor, of capacitance (C), through the effective resistance (R), from an initial charge voltage of zero to approximately 63.2% (1-e-I) of the value of an applied DC voltage, corresponding to 'Case #2' below, or to discharge the capacitor through the same resistor to approximately 36.8% (e-1) of its initial charge voltage, corresponding to 'Case #1' below: Case #1: Discharging toward zero from initial voltage, with an initial voltage of V0 across the capacitor, and a constant zero voltage across resistor and capacitor together: V (t) = Voe-tir Case #2: Charging toward an applied voltage, Vo, with an initial zero voltage across capacitor and a constant applied voltage V, across resistor and capacitor together: V (t) = V0(1 -e-t/r) In this way, with prior knowledge of the effective resistance (R), a measured value of the "RC time constant", T, may be measured by the capacitive sensor and used to determine a value of the capacitance of the capacitive sensor as: C = R-The haircare appliance may be arranged to calculate the capacitance, C, using a measured value of the "RC time constant", 1-, of a capacitive sensor of the sensor arrangement. The capacitive sensor(s) of the sensor arrangement may be arranged to have, in use, values of "RC time constant" in the range of: about 1 x 10-5s < y < 1 X 10-3S, such as e.g., T = 8 x 10-5s. The capacitive sensor(s) of the sensor arrangement may be arranged to have effective resistance (R) values of 1 x 10612 < P < 1 x 10011, such as, e.g., R = lx 10751. The capacitive sensor(s) of the sensor arrangement may be arranged to have capacitances, in use, in the range: 1 x 10-12F < C < 1 x 10-1°F such as, e.g., C = 8 x 10-12F. The value of the capacitance, C, has been found to vary according to the moisture content of hair in proximity (or contact) with the capacitive sensor(s) when in contact with the haircare appliance, in use.

The moisture content of a quantity of hair may be measured as a function of weight -i.e., what percentage of its weight is water. In other words, of the total weight (W70"1) of a quantity of moist hair can be partitioned into the weight (WH",..) of the hair alone, plus the weight (Ww"t") of water within that quantity of hair, then the moisture content (M) may be defined as: WWater WWater X 100 - x100 "Total WHair "Water The electrode(s) of the capacitive sensor may comprise a conductive material. In a mutual capacitive sensor, two electrodes of the sensor may be positioned next to each other with a nonconductive medium between them (e.g., dielectric: such as air, plastic, etc.). The electrode (or one or them if there are two) may be charged, in use. The sensor arrangement may comprise a capacitive sensor (or a plurality of them) and the control unit may be configured to determine an interval time required to charge (or discharge) the capacitive sensor(s) by a predetermined proportion (e.g., by the factor (1 -6,-1), or (e-1) in which case the interval time corresponds to the "RC time constant", r) and to output a signal accordingly. This interval of time may be returned as the capacitive sensor response value. The capacitive sensor response value may be used, by the control unit, to determine the measure indicative of the amount of water based on temporal changes in the signal returned as the capacitive sensor response value or output signal. The control unit may be arranged to calculate the capacitance, C, using interval of time (e.g., using: C = T/R).

The sensor arrangement is preferably configured to output a plurality of signals, each signal being indicative of a presence of an object at a respective region of the body, and wherein the control unit is preferably configured to determine whether the object is hair comprising an amount of water based on temporal differences between the signals.

For example, in a mutual-capacitive sensor, if a quantity of a user's hair is placed in-between the two electrodes of the sensor, then the sensor response value increases (i.e., the time interval to charge increases), the more so the greater the moisture content of the hair. The sensor arrangement may comprise a self-capacitive sensor. Contact or proximity of a tress of hair may cause the electrode capacitance of the capacitive sensor to change (e.g., increase is a self-capacitive sensor, or decrease if a mutual capacitive sensor) typically by a value in the range of about lpF to 10pF. The electrodes may comprise one or more plates, which may be flat or curved. When more than one plate electrode is employed, these plates may be positioned side-by-side. The electrodes may be positioned on a curved surface. Electrode(s) of the capacitive sensor(s) may comprise a metal paint (e.g., copper) forming electrode pads on the body for engaging hair. The body for engaging hair may comprise one or more Coander airflow veins upon, or within, which one or more electrodes of a one or more capacitive sensors are formed. The one or more electrodes may be formed on an underside of a respective Coanda airflow vein. The Coander airflow vein(s) are preferably formed from a dielectric material.

The heating arrangement may be arranged to generate heat at the body for engaging hair, for application to hair engaged therewith, in use, and the control unit may be arranged to determine a plurality of capacitance readings from the one or more capacitive sensors immediately. These readings may be taken before, during and immediately after generation of heat at the body for engaging hair. The control unit may be configured to receive absolute sensor values from the one or more capacitive sensors and to calculate a rate of change of the respective sensor values over time. The control unit may be arranged to input the sensor values and/or the calculated rate(s) of change of the respective sensor values to a machine learning model configured to predict the presence of hair and/or a value for the moisture content of the hair (e.g., as a °/0). Accordingly, the body may comprise a heating arrangement configured to apply heat to hair engaged to the body in use, wherein the control unit may be configured to determine a rate of change of a signal output by the sensor arrangement during the application of the heat and to determine therefrom a measure indicative of an amount coverage of the body by the hair.

Thus, the use of capacitive sensors has been found to be effective for guiding a haircare product's styling process according to measured moisture content of a tress of hair. By heating the tress and monitoring a rate of change of its moisture content, the inventors have realised that one may predict the amount of hair present.

The haircare appliance may be configured to continuously predict hair moisture as the tress is styled until the predicted hair moisture value falls below a certain value (e.g., for optimal style). The haircare appliance may be configured to then automatically end the styling process. This may help avoid over drying of the hair tress, leading to hair damage. The styling assistance provided to users improves user experience.

The haircare appliance may be configured to measure hair moisture at the start of a styling procedure. At this point the moisture content of hair is likely to be at its highest and it has been found that the signal-to-noise ratio (SNR) of the capacitive sensors is typically greater than occurs when hair moisture content reduces during the styling/drying process. This means that measurements of hair moisture content and/or predictions of subsequent moisture content of hair later during a hair styling process, are generally more accurate. The haircare appliance may be configured to use this measurement(s) of hair moisture content to predict how long it would take to correctly style the hair. The haircare appliance may be configured to then generate heat at the body for engaging hair, for application to hair engaged therewith, in use, for styling the hair for this amount of time before automatically ending the heat generation process and/or other aspects of the styling process performed by the body for engaging hair. This may avoid over-drying of hair and may guide users in the styling process.

The control unit may be configured to determine the measure indicative of the amount of water, to determine the measure indicative of an amount coverage, by the hair, of the body for engaging hair to calculate a duration of time for the application of heat by the heating arrangement based on the determined measure indicative of the amount of water and based on the determined measure indicative of an amount coverage of the body by the hair, and, to reduce or terminate the application of heat by the heating arrangement when the duration of time expires.

The control unit may be configured to comprise (and be configured to control the haircare appliance to implement) one or more pre-set heating profiles defining changes to an amount of heat to be applied by the heating arrangement during the duration of time, and the control unit is configured to select a pre-set heating profile based on the determined measure indicative of the amount of water and based on the determined measure indicative of an amount coverage of the body by the hair.

The haircare appliance is preferably configured to expel an airflow, in use, and the control unit is preferably operable to control one or more of a flow rate of said airflow and a temperature of the airflow based on the determined measure indicative of an amount of water.

The haircare appliance preferably comprises a heater. The control unit is preferably configured to operate the heater at a temperature determined based on the determined measure indicative of an amount of water. The control unit may be configured to operate the heater at a temperature determined based on the determined measure indicative of an amount coverage of the body by the hair.

The haircare appliance may be configured to expel an airflow, in use, and the control unit may be operable to control one or more of a flow rate of the airflow and a temperature of the airflow based on the determined measure indicative of an amount coverage of the body by the hair.

The body may comprise a heating arrangement configured to apply heat to hair engaged to the body in use, wherein the control unit may be configured to continually determine the measure indicative of an amount of water during the application of the heat and to reduce or terminate the application of heat by the heating arrangement when the measure indicative of an amount of water falls below a pre-set threshold value.

The body may comprise a heating arrangement configured to apply heat to hair engaged to the body in use, wherein the control unit is configured to: determine the measure indicative of the amount of water when commencing the application of heat by the heating arrangement; calculate a duration of time for the application of heat by the heating arrangement based on the determined measure indicative of the amount of water; and, reduce or terminate the application of heat by the heating arrangement when the duration of time expires.

The sensor arrangement may be configured to output a plurality of signals, each signal being indicative of a presence of hair comprising an amount of water at a respective region of the body, wherein a first signal of the plurality of signals changes in response to hair comprising an amount of water present at a first region of the body; a second signal of the plurality of signals changes in response to hair comprising an amount of water present at a second region of the body; and the control unit is configured to determine the measure indicative of the amount of water based on a difference between the temporal changes in the first signal and the second signal.

The body may comprise a curved portion and the regions are distributed so as to follow a curve of the curved portion.

The sensor arrangement may comprise a plurality of sensors, each sensor being located at a respective region of the body and being configured to output a respective one of a plurality of the signals.

In some examples, the control unit may be located in a main part, for example a handle, of a haircare appliance. In some examples, the signal(s) from the sensor arrangement may be received from an attachment, for example an attachment that includes the body, which attachment is attachable to and/or detachable from the main part. The signal(s) may be pre-processed by a processor, or other suitable circuitry, located in the attachment or simply transmitted as raw data sent to a processor located in the main part. This may allow for improved flexibility in the functioning of the haircare appliance. The signals may be received wirelessly or over wires or conductive tracks, for example.

In a second aspect, the invention may provide a control unit for a haircare appliance, the control unit configured to: receive a signal being indicative of a presence of hair comprising an amount of water at a region of a body of the haircare appliance; and determine a measure indicative of the amount of water based on temporal changes in the signal.

The control unit according to the second aspect may comprise any one or more of the features disclosed above in respect of the control unit forming a part of the invention in its first aspect. In other words, the control unit as disclosed in relation to the first aspect of the invention may be made and sold separately from both the body for engaging hair and the control unit.

In a third aspect, the invention may provide a method of determining a measure indicative of the amount of water in hair when present at a body of a haircare appliance, the method comprising: receiving a signal being indicative of a presence of hair comprising an amount of water at a region of the body; and determining a measure indicative of the amount of water based on temporal changes in the signal.

In a fourth aspect, the invention may provide a computer program adapted to perform the method according to the third aspect of the invention when run on a computer or computer processor, and/or a computer or computer processor programmed with said computer program, and/or a computer-readable storage medium/data carrier comprising said program.

Summary of the Figures

Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which: Figures 1A and 1B show a mutual-capacitive sensor in the absence (Fig. 1A) and in the presence (Fig. 1B) of a wet tress of hair.

Figures 2A and 2B show a self-capacitive sensor in the absence (Fig. 2A) and in the presence (Fig. 2B) of a wet tress of hair.

Figure 3 shows a circuit for a capacitive sensor according to Fig.1A, 1B, 2A or 2B.

Figure 4 shows a haircare appliance.

Figure 5 shows a body for engaging hair as a part of a haircare appliance.

Figures 6A and 6B show the outputs of six capacitive sensors upon a body of a haircare appliance for engaging hair when the hair is wet (Fig. 6A, 6B) and when the hair is dry (Fig. 6C).

Figures 7A to 7D show the positions, at four successive times, of a tress of hair as it is wrapped around a body for engaging hair as a part of a haircare appliance, the body carrying six capacitive sensors producing outputs as shown in Fig. 6A, 6B and 6C.

Figure 8 shows a graph of capacitive sensor output of a haircare appliance, in response to proximity to a tress of hair of different amounts of water moisture content.

Figure 9 shows a graph of capacitive sensor output of a haircare appliance, in response to proximity to a tress of hair, at different successive times corresponding to different temperatures of a heated body for engaging hair on a haircare appliance.

Figure 10 shows a graph of capacitive sensor output values, and their rates of change, of a haircare appliance.

Figures 11A, 11B and 11C show an exploded view, and selected component parts, of a body for engaging hair as a part of a haircare appliance.

Figure 12 shows a cross-sectional view of a Coander airflow vein of a body for engaging hair comprising an electrode of a capacitive sensor.

Figure 13 shows steps on a method of determining a measure indicative of the amount of water in hair when present at a body of a haircare appliance.

Detailed Description of the Invention

Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art All documents mentioned in this text are incorporated herein by reference.

Figures 1A and 1B show a schematic representation of a mutual-capacitive sensor 1 of a haircare appliance according to an example of the invention. The mutual-capacitive sensor 1 comprises two electrodes (4, 5) each in the form of a conductive strip or plate that together represent a two-electrode capacitor. The two electrode strips are positioned upon a surface of a dielectric substrate 3 in a spaced-apart arrangement within a dielectric inter-electrode material 6 within which the electrodes are embedded. The inter-electrode material 6 is disposed upon the dielectric substrate and fills the space between the electrodes and the space around the non-opposing sides of the electrodes but does not cover the upper or lower surfaces of the conductive electrode strips. A dielectric cover material 2 is disposed upon the inter-electrode material 6 and the upper surfaces of the two electrodes. A power supply unit 10 of the haircare appliance is responsive to control signals from the control unit (not shown) of the haircare appliance to apply a potential difference, V, between the two electrodes.

The mutual-capacitive sensor 1 is responsive to the proximity of a quantity of hair 8 to change the electric field 7 extending between the electrodes of the sensor when the potential difference, V, is applied between the two electrodes. The electrodes of the mutual-capacitive sensor project salient electric field lines 7 extending from one of the two electrodes 4 to the other electrode 5. Some electric field lines 9 (see Fig. 1B) change direction so as to terminate not on an electrode 5 of the sensor but, instead, on charges present within the user's quantity of hair 8 when that hair is brought into proximity with (or contact with) either or both electrodes. The hair reduces the capacitive coupling between the electrodes.

Figures 2A and 2B show a schematic representation of a self-capacitive sensor 11 of a haircare appliance according to an example of the invention. The self-capacitive sensor 11 comprises one single electrode 14 in the form of a conductive strip or plate that represents one half of a two-electrode capacitor. The other half of the capacitor is provided by ambient earth ground. The electrode strip is positioned upon a surface of a dielectric substrate 13 within a dielectric embedding material 16 within which the electrode is embedded. The embedding material 16 is disposed upon the dielectric substrate and fills the space around the sides of the electrode but does not cover the upper or lower surfaces of the conductive electrode strip. A dielectric cover material 12 is disposed upon the dielectric embedding material 16 and the upper surfaces of the electrode. A power supply unit 20 of the haircare appliance is responsive to control signals from the control unit (not shown) of the haircare appliance to apply a potential difference, V, to the single electrode.

The self-capacitive sensor 11 is responsive to the proximity of a quantity of hair 18 to change the electric field 17 extending from the electrode 14 of the sensor when the potential difference, V, is applied to the electrode. Salient electric field lines 17 project from the electrode 14. Some electric field lines 19 (see Fig. 2B) change direction so as to terminate on charges present within the user's quantity of hair 18 when that hair is brought into proximity with (or contact with) the electrode. The hair and increases the capacitive coupling between the electrode and its environment.

Whether a mutual-capacitive sensor or a self-capacitive sensor, the response of the sensor to proximity of the user's hair (8, 18) is a change in the capacitance (C) of the capacitive sensor. An equivalent circuit of either type of capacitive sensor arrangement is illustrated in Figure 3. The circuit comprises a resistance (R) at one terminal ("pin 4") a pre-set voltage (V) is provided. The other terminal of the resistance ("pin 2") is connected to ground (e.g., earth ground) via a capacitance (C) corresponding to the capacitance of the capacitive sensor. A monitoring unit 21 of the capacitive sensor arrangement is configured to continuously measure the potential at "pin 2". The monitoring unit 21 of the capacitive sensor arrangement is configured to set "pin 4" to a high state (V) and continuously measure the potential at "pin 2" until it reaches that of "pin 4".

The product of the resistance R and the capacitance C of the capacitive sensor arrangement, R x C = T, defines a "RC time constant", T, corresponding to either the time required to charge the capacitor, of capacitance (C), through the resistance (R), from an initial charge voltage of zero to approximately 63.2% (1-eil) of the value of an applied DC voltage (V), corresponding to 'Case #2' below, or to discharge the capacitor through the same resistor to approximately 36.8% (e-1) of its initial charge voltage (V), corresponding to 'Case #1' below: Case #1: Discharging toward zero volts (ground/earth) from an initial voltage of V, across the capacitor, and a constant zero voltage across the resistor and capacitor together (t) = Voe-tir Case #2: Charging toward an applied voltage, V0, with an initial zero voltage across capacitor and a constant applied voltage V, across resistor and capacitor together: V (t) =170(1-e-t/r) The monitoring unit 21 of the capacitive sensor arrangement is configured to calculate the capacitance, C, using a measured value of the "RC time constant", T. A pre-set value for the resistance (R) is stored within, or is accessible by, the monitoring unit 21 for use in calculating the capacitance via a measured value of the "RC time constant", T, as: C= -

R

The monitoring unit 21 of the capacitive sensor arrangement is configured to output the calculated value of the capacitance, C, as an output signal. A control unit of the haircare appliance (see Figure 4) is configured to determine a measure indicative of the amount of water based on temporal changes in the output signal of the monitoring unit 21.

The moisture content of a quantity of hair is, in an example, measured as a percentage of the weight of the hair corresponding to water. The total weight (VVTotat) of a quantity of moist hair can be partitioned into the weight (Wnaw) of the hair alone, plus the weight (Wwat".) of water within that quantity of hair. The moisture content (M) determined by the control unit is defined as: WWater WWater M(%) x 100 - x 100 "Total WHair WWater Referring to Figure 4, there is illustrated a haircare appliance 30 according to an example. The haircare appliance 30 comprises a body 32 for engaging hair in use (hair is not shown in Figure 4 but see e.g., the hair tress 100 in Figure 7A to 7D described below). The body 32 comprises a plurality of regions A, B, C. The haircare appliance 30 comprises a sensor arrangement 48. The sensor arrangement 48 is configured to output a plurality of signals, each signal being indicative of a presence of hair comprising an amount of water at a respective region A, B, C of the body 32 (an object is not shown in Figure 1, but see e.g. the hair tress 100 in Figure 7A to 7D described below). The haircare appliance 30 comprises a control unit 43. As described in more detail below, the control unit 43 is configured to determine a measure indicative of the amount of water based on temporal changes in the signals.

In this example, the haircare appliance 30 comprises a main part 34 and the body 32 is provided as an attachment 32 (see Fig. 5) that is attachable and/or detachable from the main part 34. In some examples, the control unit 43 is located in a main part, for example a handle, of the haircare appliance. In some examples, the signal(s) from the sensor arrangement are received from an attachment, for example an attachment that includes the body 32, which attachment is attachable to and/or detachable from the main part 34. This may allow for improved flexibility in the functioning of the haircare appliance. The signals may be received wirelessly or over wires or conductive tracks, for example. In some examples, the control unit may be located in a main part, for example a handle, of a haircare appliance. The signal(s) may be pre-processed by a processor (e.g., 210 of Fig. 11A), or other suitable circuitry, located in the attachment 32 or simply transmitted as raw data sent to a processor located in the control unit 43 of the main part 34. This may allow for improved flexibility in the functioning of the haircare appliance. The signals may be received wirelessly or over wires or conductive tracks, for example.

The main part 34 comprises an airflow generator 44 and a heater 45. It is to be understood that, in examples of the invention, either the body 32 or the main body 34 may comprise a heating arrangement (e.g., heater 45) configured to apply heat to hair engaged to the body in use.

The airflow generator 44 is configured to generate an airflow from an air inlet 42 to an air outlet 44. In this example, the air inlet 42 is in the main part 34, and the air outlet 44 is in the body 32. The heater 45 is located downstream of the airflow generator 44. The heater 45 may be configured to heat the airflow so as to provide a heated airflow at the air outlet 44. The body 32 of this example is shown in more detail in Figure 5. In this example, the body 32 is generally in the form of a cylinder or a cone. In this example, each region A, B, C corresponds to an elongate member. In this example these regions/members A, B, C are distributed around a circumference (see 50 in Figure 5) of the cylinder or cone forming the body 32. In this example, an air outlet 44 is provided by a gap in between each member A, B, C which directs airflow across the surface of an adjacent member A, B, C. As is known per se, in use, the airflow expelled from these air outlets 44 causes, via the Coanda effect, hair, or more specifically a hair tress 100, in the vicinity of the body 32 to wrap around the body 32, where it can be styled. In some examples, the control unit 43 may be configured to control an operating mode of the haircare appliance 30, for example control one or more of a flow rate and a temperature of the airflow, for example control a flow rate of the airflow generated by the airflow generator 44 and/or control a temperature at which the heater 45 is operated. In some examples, the control unit 43 may be configured to control the operating mode in response to the determination of the amount of moisture in the hair. As explained in more detail below, this may allow for improved styling experience and improved haircare.

As mentioned, the haircare appliance 30 comprises a sensor arrangement 48 configured to output a plurality of signals, each signal being indicative of a presence of hair comprising an amount of water at a respective region A, B, C of the body 32. In this example, the sensor arrangement 48 comprises a plurality of sensors 36, 38, 40, each sensor 36, 38,40 being located at a respective region A, B, C of the body 32 and being configured to output one of the plurality of signals. In this example, each sensor 36, 38,40 is positioned so as to sense radially outwardly from the body 32 (i.e., radially outwardly of the region A, B, C to which the sensor corresponds). In some examples, one or more of the sensors 36, 38, 40 may be non-contact sensors. For example, a non-contact sensor may be configured to output a signal indicative of a presence of hair comprising an amount of water at the sensor 36, 38, 40 without the hair necessarily coming into physical contact with the sensor 36, 38, 40 itself. Examples of non-contact sensors include a capacitive sensor (e.g., either a self-capacitive sensor or a mutual-capacitive sensor.

The sensor arrangement 48 may be connected to the control unit 43 by wired or wireless means, in order to provide the plurality of signals to the control unit 43. In examples where the body 32 is provided by an attachment and the control unit 43 is in the main part 34, the body 32 and the main part 34 may form a connection, which may be wired or wireless, over which the signals may be transmitted from the sensor arrangement 48 to the control unit 43. In some examples, the sensor arrangement 48 may comprise the sensors 36, 38, 40 and the signals output by each sensor may be provided directly to the control unit 43 as the plurality of signals. In other examples, the sensor arrangement 48 may comprise the sensors 36, 38,40 and a multichannel reader (not shown), and the plurality of signals may be provided to the control unit 43 by the multichannel reader (not shown). For example, the multichannel reader may sample each of the signals output by the sensors as a temporal series of values and provide these temporal series of values to the control unit 43 as the plurality of signals. In any case, the sensor arrangement 48 is configured to output a plurality of signals, each signal being indicative a presence of hair comprising an amount of water at a region A, B, C of the body 32.

Referring to figures 6A to 6B and figures 7A to 7D, figures 7A to 7D illustrate the way in which hair, or more specifically a hair tress 100, may wrap around the cylindrical body 32 of the haircare appliance 30 according to the example of Figure 4 at different successive times Ti, T2, T3, T4; and figures 6A to 6B illustrate graphs of the plurality of signals sA, sB, sC, sD, sE, sF output by the sensor arrangement 48 for a respective one of the plurality of regions A, B, C, D, E, F of the body 32, as a function of time, according to an example. It is noted that regions D, E, F (and their associated sensors) are present on the body 32 illustrated in Figures 4 and 5, but are not visible in Figures 4 and 5. As can be seen from figures 6A to 6B and figures 7A to 7D, the regions A to F are distributed around the circumference of the cylindrical body 32 in the order A, B, C, D, E, F. In this example, the larger the moisture content in the tress of hair present at a given one of the regions A-F, the larger the signal sA-sF that is output corresponding to that given region A-F. Figure 6A provides an example of signals output by the sensor arrangement of six self-capacitance sensors in respect of a tress of wet hair, and figure 6B provides a comparative example of signals output by the sensor arrangement of six self-capacitance sensors in respect of a tress of dry hair. The difference in signal magnitudes and signal patterns over time as the tress is wound around the body 32, is striking. Accordingly, the sensor arrangement is configured to output a plurality of signals being indicative of a presence of hair comprising an amount of water at a region of the body.

The control unit may be arranged, for example, to calculate an average of the maxima of each of the plurality of sensor output signal values: e.g., Average = [max(sA)+ max(sB)+ max(sC)+ max(sD)+ max(sE)+ max(sF)]/6 The control unit may be configured to then use that average value to determine the moisture content in the tress of hair. For example, the average value may be used to determine whether the hair is wet or dry. The average value may be compared to a suitable threshold value in order to make this determination (e.g., exceeding the threshold indicates wet hair). Alternatively, or in addition, control unit may be arranged, for example, to calculate a time rate of change of each of the plurality of sensor output signal values: e.g., Rate(sA) = d(sA)/dt; Rate(sB) = d(sB)/dt; Rate(sC) = d(sC)/dt; Rate(sD) = d(sD)/dt; Rate(sE) = d(sE)/dt; Rate(sF) = d(sF)/dt The control unit may be configured to then use these rate values to determine the moisture content in the tress of hair. For example, the rate values may be used to determine whether the hair is wet or dry.

The rate values may be compared to a suitable threshold value in order to make this determination (e.g., exceeding the threshold indicates wet hair). Alternatively, or in addition, machine learning algorithm may be used by the control unit to determine the moisture content in the tress of hair (e.g., to determine whether the hair is wet or dry).

At time Ti, the hair tress 100 is present at regions A and B, but not at regions C to F. Accordingly, at time T1, the values of the signals sA and sB have increased, but the those of the other signals sC to sF have not. At a later time 12, the hair tress 100 has wrapped further around the body 32, and is now present at regions A to C, but not at regions D to F. Accordingly, at time T2, the values of the signals sA to sC have increased, but those of the other signals sD to sF have not. At a still later time T3, the hair tress 100 has wrapped still further around the body, and is now present at regions A to D, but not at regions E and F. Accordingly, at time 13, the values of the signals sA to sD have increased, but those of the other signals sE to sF have not. At a yet still later time T4, the hair tress 100 has wrapped yet still further around the body 32, and is now present at regions A to F. Accordingly, at time T4, the values of the signals sA to sF have all increased.

As mentioned, the control unit 43 is configured to determine the amount of moisture in the tress of hair based on temporal differences between the signals sA-sF output by the sensor arrangement 48. For example, as illustrated above in figures 6A to 6B, each signal of the plurality of signals sA-sF may change (e.g. a value of the signal may increase) in response to an tress 100 being present at a respective region A, B, C of the body. The control unit 43 may be configured to determine the amount of moisture in the tress of hair based on the temporal differences between these changes in the plurality of signals sA-sF.

For example, the temporal difference between two signals may comprise a time at which a change in one signal (e.g. an increase in the value of one signal) occurs relative to a time at which a change in the other signal (e.g. an increase in the value of the other signal) occurs. Based on the sequence in which the changes in the signals occur, the time in between each change and/or other temporal differences between the signals, the control unit 43 may determine the amount of moisture in the tress of hair. For example, when the temporal differences between the signals output by the sensor arrangement 48 correspond to temporal differences known or expected to occur when hair is engaging the body 32 (e.g. as illustrated in Figure 7A-7D), the control unit 43 may determine the amount of moisture in the tress of hair. For example, when changes in the signals correspond to those which would occur when an object wraps around the circumference (item 50, Fig.5) of the body, the control unit 43 may determine that the object is wet hair.

Figure 8 illustrates a graph showing results of measurements, using the outputs of the sensor arrangement 48, of moisture content (M(%)) within tresses of hair each having a respective one of three different pre-set/known moisture contents. Here, each one of the three known moisture content values was applied to five tresses of hair, giving 15 tresses of hair in total (i.e., five separate tresses per moisture content value, and three different moisture content values). The sensor arrangement was used to measure each tress of hair, at each one of the three pre-set moisture content values, ten times (i.e., ten repeat measurements). A mean value and an error margin was calculated for each group of 10 repeated measurements. The results shown in Figure 8 demonstrate that the sensor arrangement is able demonstrate a strong and consistent correlation between the average values of the signals output by the sensor arrangement, and the moisture content of a tress of hair.

The inventors have discovered that the response/output of a capacitive sensor increases in value (for a given, constant moisture content value) as the sensor is heated when in the presence of a tress of hair.

This heating occurs, for example, when heat is applied to the tress of hair by the haircare product. If a relatively larger amount of hair is upon the body 32 of the haircare appliance then this has been found to reduce the rate at which the body 32 may increase in temperature (i.e., heat up). Thus, the moisture content of the tress will fall faster (as it is drying). Consequently, the sensor response of the sensor arrangement for relatively smaller (e.g., thinner) tresses will grow at a relatively faster rate. The invention may exploit this finding by determining a rate of change of the capacitive sensor output signal values and determining a measure of the quantity of hair in the tress covering the body 32. This may be illustrated, for a better understanding, by considering the following two hypothetical (but common) situations: Situation 1: A user of the haircare appliance wraps tress 100 around the body 32 of the haircare appliance. The tress comprises a relatively large quantity of relatively dry hair 100. The moisture present in this tress 100 dries relatively quickly. The larger quantity of hair conducts heat from the body 32 more effectively and this restricts rate of increase of the temperature of the body 32. Consequently, the rate of increase of the capacitive sensor output signal values is relatively lower, or negligible.

Situation 2: A user of the haircare appliance wraps tress 100 around the body 32 of the haircare appliance. The tress comprises a relatively small amount of relatively wet hair. Heating of the tress, by the body 32, results in a relatively smaller absolute change in moisture content in the tress 100. The smaller quantity of hair conducts heat from the body 32 less effectively and the rate of increase in the temperature of the body 32 therefore rises. Consequently, the rate of increase of the capacitive sensor output signal values is relatively higher. Two examples of this higher rate of increase of the capacitive sensor output signal values are shown in the graph of Figure 9.

By measuring the rate of change of capacitive sensor data, the haircare product may provide a proxy for a quantity of hair in a tress engaging with the body 32 of the haircare appliance.

The control unit 43, in an example, is configured to apply a trained machine learning algorithm arranged to predict a value for the moisture content of a quantity of hair present at the body 32 of the haircare appliance, based on capacitive sensor output signals from the sensor arrangement 48. The control unit 43 may be arranged to convert the capacitive sensor output signals into a time series of signal values from some or all of the capacitive sensors of the sensing arrangement 48.

The control unit may be arranged to determine rates of change of the values of the time series of signal values. The rates of change may comprise a plurality of separate values of rates of change determined using separate successive signal values form amongst the time series. The control unit may be arranged to determine a time series of sequential rate of change values.

The control unit 43, in an example, is configured to apply a trained machine learning algorithm arranged to predict a value for a quantity of hair in a tress engaging with the body 32 of the haircare appliance, according to the time series of signal values, or according to the time series of sequential rate of change values, or according to both.

Figure 10 shows an example of a time series of sensor data ("Absolute Data") and a corresponding time series of the rate of change values ("Gradient Data") for the time series of sensor data. A trained machine learning algorithm for this purpose may comprise, but is not limited to, one of: a Neural Network algorithm, a Support Vector Machine, Baysiean Ridge algorithm. These, at least, have been found to be effective.

As mentioned, the heater 45 is arranged to generate heat at the body for engaging hair, for application to hair engaged therewith, in use. In examples, the control unit is arranged to determine a plurality of capacitance readings from the one or more capacitive sensors. These readings may be taken before, during and immediately after generation of heat by the heater. The control unit is configured to receive absolute sensor values from the one or more capacitive sensors and to calculate a rate of change of the respective sensor values over time. The control unit is arranged to input the sensor values and/or the calculated rate(s) of change of the respective sensor values to a machine learning model, as mentioned above, which is configured to predict the presence of hair and/or a value for the moisture content of the hair (e.g., as a %).

In examples of the invention, the control unit 43 is configured to predict hair moisture, e.g., using the machine learning algorithm, as the tress is styled until the predicted hair moisture value falls below a certain value (e.g., for optimal style). The haircare appliance, in examples, is configured to then automatically end the styling process. This may help avoid over drying of the hair tress, leading to hair damage. The styling assistance provided to users improves user experience.

For example, the control unit 43 of the haircare appliance may be configured to measure hair moisture content (M) e.g., using the machine learning algorithm, at the start of a styling procedure such as when a user first activates the haircare appliance. The relatively higher moisture content of hair at this time allows the capacitive sensors of the sensor arrangement 48 to produce signals with a higher signal-to-noise ratio (SNR) than would be the case later when the tress of hair has lost moisture. Consequently, the measurements of hair moisture content are less noisy and predictions of subsequent moisture content of hair later during a hair styling process, are generally more accurate. In examples of the invention, the control unit 43 is configured to use this measurement of hair moisture content to predict how long it would take to correctly style the hair, and to activate the heater 45 to generate heat for styling the hair for this amount of time before automatically turning off or cooling down. This helps to avoid the user over-drying their hair.

In examples of the invention, the control unit is configured to determine the measure of moisture (M) when commencing the application of heat by the heater 45, and to calculate a duration of time for the application of heat by the heater based on the determined measure of moisture (M), and to reduce or terminate the application of heat by the heating arrangement when the duration of time expires.

In examples of the invention, the control unit 43 is configured to determine the measure (M) indicative of the amount of water in the tress of hair, to determine the aforementioned measure indicative of an amount coverage, by the hair, of the body 32, and to calculate a duration of time for the application of heat by the heater 45 based on both the measured amount of water (M) and the measure indicative of hair coverage of the body 32 by the hair. The control unit 43 is configured to reduce or terminate the application of heat by the heater 45 arrangement when that duration of time expires.

In examples of the invention, the control unit 43 is configured to contain information defining one or more pre-set heating profiles. These profiles define amounts of heat to be generated by the heater 45 and any changes to those amounts of heat to be applied by the heater 45 during the duration of time. The changes may comprise times at which the changes are to be implemented. In examples of the invention, the control unit 43 is configured to select a pre-set heating profile based on the determined measure of moisture (M) and based on the determined measure indicative of an amount coverage of the body by the hair.

In examples of the invention, the control unit 43 is configured to control one or more of a flow rate of airflow provided by the airflow generator 44 and an amount of heat to be applied by the heater 45 to heat the airflow to a desired temperature based on the measured moisture (M) and/or based on the determined measure indicative of an amount coverage of the body 32 by the hair.

In examples of the invention, as mentioned above, the sensor arrangement 48 may be configured to output a plurality of capacitive sensor signals (e.g., the plurality of signals sA, sB, sC, sD, sE, sF of Fig. 6A) with each such signal being indicative of a presence of hair comprising an amount of water at a respective region of the body 32. Amongst the plurality of signals may be a first signal (e.g., one of the plurality of signals sA, sB, sC, sD, sE, sF of Fig. 6A) which changes in response to hair comprising moisture when present at a first region (e.g., the location of one of the sensors 36, 38 or 40) of the body 32, and at least a second signal (e.g., another one of the plurality of signals sA, sB, sC, sD, sE, sF of Fig. 6A) which changes in response to hair comprising moisture when present at a second region of the body 32 (e.g., the location of another one of the sensors 36, 38 or 40). In these examples, the control unit 43 is configured to determine the measure of moisture based on a difference between the temporal changes in the first signal and the second signal, such as by application of a machine learning model as discussed above. The body 32 comprises a plurality of Coander veins each defining a respective curved portion, as well as collectively defining a curved portion. The regions (e.g., the locations of one of the sensors 36, 38 or 40) are distributed so as to follow a curve of the curved portion.

As shown in Figure 12, in examples of the invention, each of the sensors 36, 38,40 etc.) comprise copper electrode pads painted on the underside of a respective Coanda airflow vein. The respective Coander airflow veins are formed from a dielectric material thereby creating a self-capacitive sensor element.

Figures 11A to 11C show an exploded view of an example of the body 32 of the haircare appliance, comprising a tip part 200 configured to define the distal end of the body 32 located beyond the distal ends of the six Coander airflow veins (A, B, C,... etc.) of the body. Located between the tip part 200 and the distal ends of the six Coander airflow veins is a printed circuit board (PCB) piece 202 bearing circuitry components forming a part of the capacitive sensor arrangement 48 including resistors (R) (not shown) each forming a part of an RC circuit of a respective capacitive sensor such as is illustrated schematically in Figure 3 as discussed above, together with a processor 210 providing the function of the monitoring unit 21 of the capacitive sensor arrangement, configured to determine capacitance values (C) for each of the electrodes of the capacitive sensors (36, 38, 40 etc.) of the sensor arrangement 48. Shown in more detail in Figure 11B is the distal end of one of the six Coander airflow veins (A, B, C,... etc.) of the body. Pairs of electrical terminals 206 provide electrical contact points enabling electrical communication between an electrode of a given capacitive sensor upon a given Coander airflow vein, and the printed circuit board (PCB) piece 202. An intermediate annular adaptor part 204 (optional) presents a circumferentially ordered array of six pairs of electrical contact pins 208 which are spaced around the outer circumference of the spacings in register with the locations of respective pairs of electrical terminals 206 of capacitive sensors.

Figure 13 illustrates steps in a method of determining a measure (M) indicative of the amount of water in hair when present at the body 32 of the haircare appliance 30. The method is implemented by the control unit 43 and comprises: Step 300: Receiving a signal(s) (e.g., the plurality of signals sA, sB, sC, sD, sE, sF of Fig. 6A) being indicative of a presence of hair comprising an amount of water at a region of the body.

Step 302: Determining the measure (M) indicative of the amount of water (moisture) based on temporal changes in the signal(s).

The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

Throughout this specification, including the claims which follow, unless the context requires otherwise, the word "comprise" and "include", and variations such as "comprises", "comprising", and "including" will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

It must be noted that, as used in the specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from "about" one particular value, and/or to "about" another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent "about," it will be understood that the particular value forms another embodiment. The term "about" in relation to a numerical value is optional and means for example +/-10%.

Claims

Claims: 1. A haircare appliance comprising: a body for engaging hair in use; a sensor arrangement configured to output a signal being indicative of a presence of hair comprising an amount of water at a region of the body; and a control unit configured to determine a measure indicative of the amount of water based on temporal changes in the signal.
2. A haircare appliance according to any preceding claim, wherein the sensor arrangement comprises one or more non-contact sensors each configured to output a said signal.
3. A haircare appliance according to claim 2 wherein the one or more non-contact sensors comprise one or more self-capacitance sensors and/or one or more mutual capacitance sensors.
4. A haircare appliance according to any preceding claim, wherein the sensor arrangement is configured to output a plurality of signals, each signal being indicative of a presence of an object at a respective region of the body, and wherein the control unit is configured to determine whether the object is hair comprising an amount of water based on temporal differences between the signals.
5. A haircare appliance according to any preceding claim, wherein said body comprises a heating arrangement configured to apply heat to hair engaged to the body in use, wherein the control unit is configured to determine a rate of change of a said signal output by the sensor arrangement during the application of said heat and to determine therefrom a measure indicative of an amount coverage of said body by said hair.
6. A haircare appliance according to claims, wherein the control unit is configured to: determine said measure indicative of the amount of water; determine said measure indicative of an amount coverage of said body by said hair; calculate a duration of time for the application of heat by the heating arrangement based on said determined measure indicative of the amount of water and based on said determined measure indicative of an amount coverage of said body by said hair; and, reduce or terminate the application of heat by the heating arrangement when said duration of time expires.
7. A haircare appliance according to claim 6, wherein the control unit comprises one or more pre-set heating profiles defining changes to an amount of heat to be applied by the heating arrangement during said duration of time, and the control unit is configured to select a pre-set heating profile based on said determined measure indicative of the amount of water and based on said determined measure indicative of an amount coverage of said body by said hair.
8. A haircare appliance according to any preceding claim, wherein the haircare appliance is configured to expel an airflow, in use, and the control unit is operable to control one or more of a flow rate of said airflow and a temperature of the airflow based on said determined measure indicative of an amount of water.
9. A haircare appliance according to any preceding claim, wherein the haircare appliance comprises a heater, and the control unit is configured to operate the heater at a temperature determined based on said determined measure indicative of an amount of water.
10 A haircare appliance according to any preceding claim, when dependent on claim 5, wherein the haircare appliance is configured to expel an airflow, in use, and the control unit is operable to control one or more of a flow rate of said airflow and a temperature of the airflow based on said determined measure indicative of an amount coverage of said body by said hair.
11. A haircare appliance according to any preceding claim, when dependent on claims, wherein the haircare appliance comprises a heater, and the control unit is configured to operate the heater at a temperature determined based on said determined measure indicative of an amount coverage of said body by said hair.
12. A haircare appliance according to any preceding claim in which said body comprises a heating arrangement configured to apply heat to hair engaged to the body in use, wherein the control unit is configured to continually determine said measure indicative of an amount of water during the application of said heat and to reduce or terminate the application of heat by the heating arrangement when said measure indicative of an amount of water falls below a pre-set threshold value.
13. A haircare appliance according to any preceding claim in which said body comprises a heating arrangement configured to apply heat to hair engaged to the body in use, wherein the control unit is configured to: determine said measure indicative of the amount of water when commencing the application of heat by the heating arrangement; calculate a duration of time for the application of heat by the heating arrangement based on said determined measure indicative of the amount of water; and, reduce or terminate the application of heat by the heating arrangement when said duration of time expires.
14. A haircare appliance according to any preceding claim, wherein the sensor arrangement is configured to output a plurality of signals, each signal being indicative of a presence of hair comprising an amount of water at a respective region of the body, wherein a first signal of the plurality of signals changes in response to hair comprising an amount of water present at a first region of the body; a second signal of the plurality of signals changes in response to hair comprising an amount of water present at a second region of the body; and the control unit is configured to determine said measure indicative of the amount of water based on a difference between the temporal changes in the first signal and the second signal.
15. A haircare appliance according to any preceding claim, wherein the body comprises a curved portion and the regions are distributed so as to follow a curve of the curved portion.
16. A haircare appliance according to any preceding claim, wherein the sensor arrangement comprises a plurality of sensors, each sensor being located at a respective region of the body and being configured to output a respective one of a plurality of said signals.
17. A haircare appliance according to any preceding claim comprising an attachable attachment that includes the body.
18. A haircare appliance according to claim 17 wherein the control unit is located in a main part of the haircare appliance and the signal(s) from the sensor arrangement are received from the detachable attachment which is attachable to and/or detachable from the main part.
19. A control unit for a haircare appliance, the control unit configured to: receive a signal being indicative of a presence of hair comprising an amount of water at a region of a body of the haircare appliance; and determine a measure indicative of the amount of water based on temporal changes in the signal.A method of determining a measure indicative of the amount of water in hair when present at a body of a haircare appliance, the method comprising: receiving a signal being indicative of a presence of hair comprising an amount of water at a region of the body; and determining a measure indicative of the amount of water based on temporal changes in the signal.