Hair removal device

Abstract

To provide a hair removal device, such as an electric shaver or epilator, provided for determining wear of a hair cutting unit.SOLUTION: The hair removal device comprises a hair cutting unit 3, a motor 5 for driving the hair cutting unit, a measurement unit 16 for measuring motor current and / or induced voltage, and a cutting activity determiner 17 for determining cutting activity from half cycles of a signal of the measurement unit. A wear determination unit 18 determines wear of the hair cutting unit from a cutting activity signal of the cutting activity determiner.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a hair removal device, such as an electric shaver or epilator, comprising a hair-cutting unit, a motor for driving the hair-cutting unit, a measurement unit for measuring the motor current and / or induced voltage, and a cutting activity determiner for determining the cutting activity from a signal of the measurement unit. [Background technology]

[0002] The motor-driven hair-cutting unit of the hair removal device may include a perforated shear foil and a cooperating cutter block that may reciprocate linearly or pivotally under the shear foil or rotate continuously to cut hairs entering the perforations of the shear foil. Other types of cutters, such as trimmers, may include a comb-like cutter bar or disk, where the hair is cut between cutting fingers that slide over each other. Epilators may include a cutting tool for tearing the hair (performing an action that may be considered a cutting action in the context of this application).

[0003] When a cutting event occurs, i.e. when the cutting edge of the cutter block hits a hair trapped in the perforation or the hair is clamped by the hair removal tool, the operation of the motor typically slows down to a certain extent, which in turn affects the level of the motor current and / or the induced voltage. Essentially, such a slowdown of the motor operation may be accompanied by a reduction in the level of the induced voltage.

[0004] More specifically, the cutting activity changes the timing characteristics of the induced voltages: in the case of a rotating motor, a delay as a result of such a slowdown can be expected, whereas in a linear type motor operating at mechanical resonance, a delay and vice versa may occur.

[0005] Such timing characteristics of the induced voltage may include the so-called half-cycle duration, i.e. the time distance between a zero crossing from a negative value to a positive value and / or a next zero crossing from a positive value to a negative value of the induced voltage. The induced voltage typically oscillates around a base line that defines said zero crossing. The signals measured by a measurement unit monitoring the motor current and / or the induced voltage typically exhibit a cyclical or periodic pattern, roughly similar to a sinus wave. The shape of such a periodic pattern is affected by a cutting event, so that analyzing the timing characteristics and / or the time pattern of such signals makes it possible to determine the cutting activity.

[0006] For example, EP 3427910 B1 suggests determining the aforementioned half cycle of the voltage signal of a motor-driven hair-cutting unit and determining the cutting activity based on the determined half cycle variation. The determined cutting activity is then removed or, more generally, taken in association with the drive resistance determined from the motor current to determine the force with which the shaver head is pressed onto the skin and to provide a feedback signal to the user if the skin contact pressure exceeds a reasonable range. Since pressure on the skin is expected to cause a more uniform drive resistance, filtering the vibrations generated by the cutting event should reveal the true drive resistance caused by the skin pressure, which allows the determination of unreasonable skin pressure.

[0007] On the other hand, WO 2016 / 055509 A1 suggests using the measurement of the motor current for the determination of wear and tear of the cutter head. More specifically, the document suggests giving the cutting tool a specific structure and design to significantly change the friction of the cutting tool when wear and tear occurs, such that the change in friction of the cutting tool can be evaluated based on the motor current. To avoid the complex effect of the cutting activity on the friction, it is suggested that the motor current is determined immediately after the start of the shaver to determine the wear-based friction change while the shaver is idling.

[0008] It has also been proposed to count the number of shavings performed or to measure the overall operating time in order to indicate whether a shaver head replacement is necessary or reasonable. This is based on the assumption that a certain number of shavings and / or a certain overall operating time will result in a degree of wear and tear that will require a shaver head replacement. After the shaver head is replaced, the counter is reset to start counting the number of shavings or measuring the overall operating time again with the new shaver head. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] European Patent No. 3427910(B1) [Patent Document 2] International Publication No. 2016 / 055509(A1) Summary of the Invention [Means for solving the problem]

[0010] The object underlying the present invention is to provide an improved personal care device which avoids at least one of the drawbacks of the prior art and / or further develops existing solutions. A more specific object underlying the present invention is to provide an improved method for determining the sharpness of the hair-cutting unit and its wear and tear.

[0011] Another object underlying the present invention is to provide a reliable and accurate determination of the sharpness and wear and tear of the hair-cutting unit, without requiring complex modifications to the cutting components to relate friction and drive resistance to wear and tear, and without requiring manual resetting when changing shaver heads.

[0012] A still further object underlying the present invention is to make it possible to reliably determine wear and tear without the need for specific sensor units or other additional components specifically required for wear and tear determination.

[0013] To achieve at least one of the above-mentioned objects, it is suggested to further analyze the cutting activity of the motor-driven hair-cutting unit and determine the wear of the hair-cutting unit from a cutting activity signal representative of the cutting activity. More specifically, the wear determining unit is configured to determine the wear of the hair-cutting unit from a cutting activity signal issued by a cutting activity determiner that determines the cutting activity from a signal of a measurement unit measuring the motor current and / or the induced voltage. Said cutting activity signal is affected by hair-cutting events by the hair-cutting unit, which signal exhibits timing characteristics that vary with wear and tear of the cutting unit. Thus, by analyzing the cutting activity signal, it is possible to determine whether the hair-cutting unit is sharp or not, or more generally, the wear and tear state of the hair-cutting unit.

[0014] By determining the wear of the hair-cutting unit based on analyzing the cutting activity signal, it is possible to reset the hair removal device after replacing the hair-cutting unit and to omit any switch for this purpose, thus making the operation of the device simpler.

[0015] Furthermore, no complex modifications of the cutting parts are necessary to achieve significant changes in friction due to wear and tear.Addition of specific sensor equipment can be avoided, since measuring units for measuring the motor current and / or induced voltage are usually present and used to control the motor operation.

[0016] More specifically, the cutting activity signal may be indicative of and / or derived from the half-cycle duration and / or the variation in said half-cycle duration of the induced voltage signal provided by the measurement unit.

[0017] To determine wear and tear from such cutting activity signals, at least one of the following characteristics of the cutting activity signal may be determined:

[0018] A maximum value of cutting activity may be determined and compared to a threshold value, where the maximum value may be determined over multiple hair removal sessions and / or multiple predetermined time intervals. Furthermore, the number of times such a threshold is exceeded may be determined to improve the robustness of the determination to a single error.

[0019] Additionally or alternatively, a peak value of the oscillating cutting activity signal can be determined and compared to a threshold value, whereby the number of times the peak threshold is exceeded per shave or per defined time interval can be determined.

[0020] Additionally or alternatively, the area under the cutting activity signal can be determined, for example by integrating the cutting activity signal over a single shaving or hair removal session, and the derived area and / or integral can be compared to a threshold value.

[0021] The wear determination unit can issue a wear signal when at least one of the aforementioned characteristics is determined, i.e. when the maximum value exceeds a threshold value, and / or when the maximum threshold value is exceeded a predetermined number of times, and / or when the signal peak of the cutting activity signal is exceeded a predetermined number of times during one hair removal treatment and / or per predetermined time interval, and / or when the area / integral value of the cutting activity signal exceeds a predetermined threshold value.

[0022] Advantageously, said integral value of the cutting activity signal for one hair removal treatment can be compared with an integral value of the cutting activity signal measured in a previous initialization operation and / or a previous initialization shave and / or a previous initialization procedure, the latter integral value being derived from a signal from a first hair removal treatment using the respective cutting component or from a factory-measured cutting activity signal. If the determined integral value of the cutting activity signal for one treatment changes to a certain extent compared to the benchmark integral value, the respective hair-cutting unit can be considered dull and blunt.

[0023] Additionally or alternatively, a trend line may be determined from any one or more of the aforementioned characteristics, and a wear signal may be issued when the trend line reaches or exceeds a particular threshold value or exhibits a rate of increase that reaches or exceeds a threshold rate of increase. [Brief description of the drawings]

[0024] [Figure 1] FIG. 2 is a function diagram of the cutting activity signal over time, where sub-figure a shows the cutting activity signal of a sharp / fresh hair-cutting unit and sub-figure b shows the cutting activity signal of a dull hair-cutting unit. [Diagram 2] FIG. 1 is a side view of a hair removal device in the form of an electric shaver having a motor-driven hair-cutting unit. [Diagram 3] FIG. 3 is a cross-sectional view of the hair-cutting unit of the hair removal device of FIG. 2, including a perforated shear foil and a cooperating reciprocating cutter block, showing a hair trapped in one of the perforations immediately prior to cutting. [Figure 4] FIG. 4 is a close-up view of a hair in the hair-cutting unit of FIG. 3 immediately prior to a cutting event. [Diagram 5] 13 is a flow chart of the operational steps for determining wear and tear of a motor-driven hair-cutting unit of the hair removal device shown in the previous figures. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] As becomes clear from the figure, it is suggested to provide a further analysis of the cutting activity of the motor-driven hair-cutting unit in order to determine the wear of the hair-cutting unit from a cutting activity signal representative of the cutting activity. More specifically, the wear determining unit is configured to determine the wear of the hair-cutting unit from a cutting activity signal issued by a cutting activity determiner, which determines the cutting activity from a signal of a measurement unit measuring the motor current and / or the induced voltage. Said cutting activity signal is affected by hair-cutting events by the hair-cutting unit, which signal exhibits timing characteristics that vary with wear and tear of the cutting unit. Thus, by analyzing the cutting activity signal, it is possible to determine whether the hair-cutting unit is sharp or not, or more generally, the wear and tear state of the hair-cutting unit.

[0026] By determining the wear of the hair-cutting unit based on analyzing the cutting activity signal, it is possible to reset the hair removal device after replacing the hair-cutting unit and to omit any switch for this purpose, thus making the operation of the device simpler.

[0027] Furthermore, no complex modifications of the cutting components are required to achieve significant changes in friction due to wear and tear.

[0028] More specifically, the cutting activity signal may be indicative of the half-cycle duration and the variation in that half-cycle duration of the induced voltage signal provided by the measurement unit.

[0029] To determine wear and tear from such cutting activity signals, at least one of the following characteristics of the cutting activity signal may be determined:

[0030] A maximum value of the cutting activity can be determined and the maximum value can be compared to a threshold, whereupon the number of times such a threshold is exceeded can be determined to improve the robustness of the determination to a single error.

[0031] The wear determination unit includes a data storage unit for storing first data of the cutting activity signal during the hair removal treatment, and a data comparator for comparing the earlier first data with the more recent first data and issuing a wear signal when a threshold value is reached or exceeded.

[0032] Additionally or alternatively, a peak value of the cutting activity signal can be determined and compared to a threshold value, whereby the number of times the peak threshold is exceeded per shave or per defined time interval can be determined.

[0033] Additionally or alternatively, the area under the cutting activity signal can be determined, for example by integrating the cutting activity signal over a period of one shaving or hair removal treatment, and the area and / or integral thus derived can be compared to a threshold value.

[0034] The wear determination unit can issue a wear signal when at least one of the aforementioned characteristics is determined, i.e. when the maximum value exceeds a threshold value, and / or when the maximum threshold value is exceeded a predetermined number of times, and / or when the signal peak of the cutting activity signal is exceeded a predetermined number of times during one hair removal treatment and / or per predetermined time interval, and / or when the area / integral value of the cutting activity signal exceeds a predetermined threshold value.

[0035] Advantageously, said integral value of the cutting activity signal for one hair removal treatment can be compared with an integral value of the cutting activity signal measured in a previous initialization operation and / or a previous initialization shave and / or a previous initialization procedure, the latter integral value being derived from a signal from a first hair removal treatment using the respective cutting component or from a factory-measured cutting activity signal. If the determined integral value of the cutting activity signal for one treatment changes to a certain extent compared to the benchmark integral value, the respective hair-cutting unit can be considered dull and blunt.

[0036] To determine wear early or to make some predictions about wear, a trend and / or trend line can be determined from one or more of the above characteristics. For example, a trend can be determined from the determined maximum value of the cutting activity signal of multiple hair removal treatments, and / or a trend line can be determined from the number of signal peaks that exceed a peak threshold. Additionally or alternatively, a trend line can be determined for the area under the cutting activity signal and / or the integral value determined from the cutting activity signal during multiple hair removal treatments and / or multiple predetermined time units. The trend of the integral value and / or area value under the curve is an early indicator of wear and tear.

[0037] For example, wear on the hair-cutting system may be predicted or determined as soon as a trend line determined from any of the aforementioned characteristics reaches and / or exceeds a threshold value and / or reaches and / or exceeds a predetermined level of increase compared to previous measurements.

[0038] In addition to or as an alternative to the above-mentioned determination procedure, the difference between the changes in the overall power consumption and the cutting activity signal at one time or on average can also deliver further information on the use conditions and derive hints on maintenance parameters such as cleaning and / or lubrication of the cutting parts, independent of the sharpness of the blade. For example, if the integral of the cutting activity signal over one or more shaves becomes significantly lower than the integral over a previous shave or the average of the integrals over the previous shaves, it can be assumed and determined that a cleaning and / or lubrication process has been performed. The control unit can also issue a maintenance signal as described above, indicating an improvement in cleaning and / or lubrication, etc.

[0039] As can be seen in FIG. 2, the hair removal device 7 may include an elongated handle 9 for being grasped by a user's fingers or hand, with the working head 8 attached to the handle 9 for movement along the body surface.

[0040] The working head 8 comprises one or more hair-cutting units 3 which may for example comprise a perforated shear foil 10 cooperating with an undercutter or cutter block 13 which may reciprocate linearly or pivotally beneath the shear foil 10 or may rotate continuously.

[0041] Said hair-cutting unit 3 is motor-driven by a motor 5 connected to the hair-cutting unit 3 by a transmission or drive train 4, see FIG. 2. It should be noted that for example the motor 5 can be an electric motor having an output motor shaft, the rotation of which is transmitted by the drive train 4 to the undercutter / cutter block 13, and the rotary motion of the motor can be converted into a reciprocating motion of said undercutter. Alternatively, a linear type motor can be used as the motor 5 already generating an oscillating back and forth drive motion, which is transmitted to the undercutter / cutter block 13 by a drive train adapted thereto.

[0042] The motor 5 may be controlled by an electronic control unit 6, which may include a microprocessor and a memory device for storing operating programs and / or data, and may include power electronics for controlling the operation of the motor 5.

[0043] As can be seen in Figures 3 and 4, a hair 12 enters the hair-cutting unit 3 and extends through one of the perforations of the shear foil 10, where the hair 12 becomes trapped between the foil edge 15 of one of the perforations of the shear foil 10 and the blade edge 14 of one of the blades 11 of the cutter block 13. As the blade 11 moves further to the right, the hair 12 is cut off. Such a cutting event increases the movement resistance of the cutter block 13 and affects the mechanical operation of the motor 5, which in turn affects the motor currents and induced voltages, which are monitored by a measurement unit 16, which may be part of and / or attached to the electronic control unit 6.

[0044] The cutting activity determiner 17 may analyze the motor current signal and / or the induced voltage signal of said measuring unit 16, whereby the cutting activity determiner 17 may also be part of and / or attached to the electronic control unit 6. For example, the cutting activity determiner 17 may be a software application stored in a storage of the electronic control unit 6.

[0045] More specifically, the cutting activity determiner 17 can analyze the time characteristics of the induced voltage signal and / or the motor current signal to determine a half cycle of the oscillating voltage and / or current signal, said half cycle being the time distance between a zero crossing of the voltage signal from a negative value to a positive value and the next zero crossing from a positive value to a negative value, such time characteristic being evaluated by testing the induced voltage signal with a comparator or in any other suitable manner. With regard to the determination of the half cycle duration of the induced voltage signal provided by the measuring unit 16, reference may be made to EP 3427910 (B1).

[0046] The aforementioned timing characteristics of the signal of the measuring unit 16 in terms of the half cycle duration and its variation are indicative of the cutting activity and are influenced by hair-cutting parameters, such as the number of hairs 12 cut per unit time, the thickness of the hairs and the force required by the blade edge 14 and the shear foil edge 15 to cut the hairs 12. The cutting parameters affect the energy that the cutting event extracts and absorbs from the movement of the motor 5. The force required to cut a hair depends, among other things, on the sharpness of the cutting edges 14 and 15 of the cutting elements. In general, a dull cutting element requires more force, comparable to an old knife or old scissors, which require more force to cut a piece of material, compared to a new knife or new scissors. Thus, the measured cutting activity increases over time as the cutting parts become duller or less sharp. The cutting activity may be understood as the force exerted by the hair-cutting unit 3 to perform a cutting event as previously described.

[0047] The effect of dull and sharp cutting edges can be seen in Fig. 1, where sub-figure a) shows the cutting activity signal 1 of a sharp hair-cutting system over time and sub-figure b) shows the cutting activity signal 2 of a dull / soft hair-cutting system 3 over time. The cutting activity signal may be derived from the aforementioned half-cycle duration of the signal provided by the measurement unit 16 and may be indicative of variations in the half-cycle duration.

[0048] As can be seen from Fig. 1, the cutting activity signal 2 is generally at a higher level when the hair-cutting unit 3 is dull or exhibits wear and tear (see sub-view b) of Fig. 1 compared to sub-view a) of Fig. 1. When the cutting edges 14 and 15 are sharp and / or new, there is less slowing down of the movement of the motor 5 and less energy consumption compared to a hair-cutting system 3 exhibiting wear and tear and / or having dull cutting edges.

[0049] A wear determination unit 18 may be part of and / or connected to the electronic control unit 16 and may include a software application. Such a wear determination unit 18 may analyze characteristics of the cutting activity signals 1, 2 shown in Figure 1 to determine wear of the cutting unit 3.

[0050] More specifically, the wear determination unit 18 may determine a maximum value of the cutting activity signals 1, 2 and may further compare the determined maximum value with a threshold value. If the determined maximum value reaches or exceeds such threshold value, the wear determination unit 18 may issue a wear signal.

[0051] Additionally or alternatively, the number of times such a threshold is exceeded by a determined maximum value can be counted. Furthermore, as soon as a threshold or counter value is reached or exceeded, the hair-cutting unit 3 may be considered as dull and / or a wear signal may be issued by the wear determination unit 18. Considering multiple determined maximum values ​​can improve the robustness of the method against single errors.

[0052] In addition to or instead of determining the maximum value, a peak value of the oscillating signal may be determined and the peak value may be compared to a peak threshold. The number of times the determined peak reaches or exceeds the peak threshold per hair removal treatment or per predefined time interval may be counted. If the number of times the peak threshold is exceeded per shaving / hair removal treatment or per predefined time interval reaches a certain count or threshold, a dull hair-cutting unit 3 may be assumed and the wear determination unit 18 may issue a wear signal.

[0053] As can be seen from Fig. 5, the wear determination unit 18 can determine the area under the cutting activity signal 1, 2, i.e. the area between said cutting activity signal and a baseline, such as the time axis of the function diagram of Fig. 1. To determine the area under the cutting activity signal, the cutting activity signal can be integrated, for example, over one hair removal treatment and / or one shaving, and the determined integral value can be compared with a previously defined threshold value, see Fig. 5. When the predefined threshold value is exceeded by the determined area value and the determined integral value, respectively, the wear determination unit 18 can issue a wear signal.

[0054] For example, the determined area under the cutting activity signal and / or the calculated integral of the cutting activity signal per shave / hair removal treatment may be compared to the integral of the cutting activity signal (or the area under the cutting activity signal) measured in a previous initialization or benchmark shaving / hair removal treatment, or in a previous shave (e.g., the first hair removal treatment using the hair-cutting unit 3), or measured at a manufacturing facility. When the calculated integral and / or the determined area under the cutting activity signal has changed by a predetermined amount compared to the benchmark hair removal treatment, the hair-cutting unit 3 may be considered dull and a wear signal may be issued.

[0055] The area under the cut activity signal may also be determined by other methods, such as, for example, by fitting a column of a given width under the signal curve, or by other approximation methods.

[0056] To determine wear early or to make some predictions about wear, a trend and / or trend line can be determined from one or more of the above characteristics. For example, a trend can be determined from the determined maximum value of the cutting activity signal of multiple hair removal treatments, and / or a trend line can be determined from the number of signal peaks that exceed a peak threshold. Additionally or alternatively, a trend line can be determined for the area under the cutting activity signal and / or the integral value determined from the cutting activity signal during multiple hair removal treatments and / or multiple predetermined time units. The trend of the integral value and / or area value under the curve is an early indicator of wear and tear.

[0057] For example, wear of the hair-cutting system may be predicted or determined as soon as a trend line determined from any of the aforementioned characteristics reaches and / or exceeds a threshold value and / or reaches and / or exceeds a predetermined level of increase compared to previous measurements.

[0058] In addition to or as an alternative to the above-mentioned determination procedure, the difference between the changes in the overall power consumption and the cutting activity signal at one time or on average can also deliver further information on the use conditions and derive hints on maintenance parameters such as cleaning and / or lubrication of the cutting parts, independent of the sharpness of the blade. For example, if the integral of the cutting activity signal over one or more shaves becomes significantly lower than the integral over a previous shave or the average of the integrals over the previous shaves, it can be assumed and determined that a cleaning and / or lubrication process has been performed. The control unit can also issue a maintenance signal as described above, indicating an improvement in cleaning and / or lubrication, etc. Preferred embodiments of the present invention are described below. [1] A hair removal device, such as an electric shaver or epilator, comprising: a hair-cutting unit (3); a motor (5) for driving the hair-cutting unit (3); a measuring unit (16) for measuring the motor current and / or induced voltage; and a cutting activity determiner (17) for determining cutting activity from a signal of the measuring unit (16), characterized in that a wear determination unit (18) is provided for determining wear of the hair-cutting unit (3) from the cutting activity signal of the cutting activity determiner (17). [2] The hair removal device described in [1], wherein the wear determination unit comprises: a data storage unit for storing first data of the cutting activity signal during a hair removal process; and a data comparator for comparing earlier first data with more recent first data and issuing a wear signal when a threshold value is reached or exceeded. [3] The hair removal device described in [2], wherein the wear determination unit (18) is configured to determine an area under the cutting activity signal of at least one hair removal treatment, compare the determined area with a threshold, and issue a wear signal if the threshold is reached or exceeded by the determined area. [4] A hair removal device as described in any of [1] to [3], wherein an area under the cutting activity signal for multiple hair removal treatments is determined, a trend line indicating a trend of the determined area is determined and compared to a trend line threshold and / or a trend line increase threshold, and a wear signal is issued when the trend line reaches or exceeds the trend line threshold and / or the increase in the trend line reaches or exceeds the trend line increase threshold. [5] The hair removal device according to [3] or [4], wherein the wear determination unit (18) includes an integrator for calculating the area under the cutting activity signal by its integral. [6] A hair removal device described in any of [1] to [5], wherein the wear determination unit (18) is configured to determine a maximum value of the cutting activity signal for one or more hair removal treatments, compare the determined maximum value with a maximum threshold, and issue a wear signal if the maximum threshold is reached or exceeded. [7] The hair removal device described in any of [1] to [6], wherein the wear determination unit (18) is configured to determine a maximum value of the cutting activity signal for multiple hair removal sessions and a trend line indicating a trend of the maximum values, compare the trend line with a trend line threshold and / or a trend line increase threshold, and issue a wear signal when the trend line reaches or exceeds the trend line threshold and / or the increase in the trend line reaches or exceeds the trend line increase threshold. [8] A hair removal device as described in any of [1] to [7], wherein the wear determination unit (18) is configured to determine peaks of the vibration cutting activity signal of one or more hair removal treatments, compare the peak values ​​of the peaks with a peak threshold to determine the number of the peaks that exceed the peak threshold, and issue a wear signal if the number of times the peak threshold is reached or exceeded per shaving or per unit time exceeds a predetermined count or threshold. [9] The hair removal device described in any of [1] to [8], wherein the wear determination unit (18) is configured to determine peak values ​​of the cutting activity signal for multiple hair removal sessions and a trend line indicating a trend of the determined area, compare such trend line with a trend line threshold and / or a trend line increase threshold, and issue a wear signal when the trend line reaches or exceeds the trend line threshold and / or the increase in the trend line reaches or exceeds the trend line increase threshold.

[10] A hair removal device described in any of [1] to [9], wherein the cutting activity determiner (17) is configured to determine the cutting activity signal from a half-cycle duration of a vibration signal of the measuring unit (16), such that the cutting activity signal indicates a variation in the half-cycle duration of the signal of the measuring unit (16).

Claims

1. The hair-cutting device comprises a hair-cutting unit (3), a motor (5) for driving the hair-cutting unit (3), a measuring unit (16) for measuring an induced voltage, and a cutting activity determiner (17) for determining a cutting activity from a signal of the measuring unit (16), and a wear determination unit (18) is provided for determining wear of the hair-cutting unit (3) from a cutting activity signal of the cutting activity determiner (17), The wear determination unit comprises: a data storage unit for storing first data of the cutting activity signal during hair removal treatment; and a data comparator for observing the first data in a time series and issuing a wear signal when a threshold value is reached or exceeded; the wear determination unit (18) is configured to determine an integral of the cutting activity signal for at least one hair removal session, to compare the determined integral with a threshold value, and to issue a wear signal if the threshold value is reached or exceeded by the determined integral value, a trend line indicating a trend of the determined integral value and a trend line increase threshold which is a threshold for the integral value and / or a threshold for the rate of increase of the integral value, and a wear signal is issued when the trend line reaches or exceeds the trend line threshold and / or when the rate of increase of the trend line reaches or exceeds the trend line increase threshold.

2. 2. The hair removal device of claim 1, wherein the wear determination unit (18) comprises an integrator for calculating the integral value of the cutting activity signal by integrating the area of ​​the region between the cutting activity signal and a baseline in a function diagram of the cutting activity signal over time.

3. 2. The hair removal device according to claim 1, wherein the wear determination unit (18) is configured to determine a maximum value of the cutting activity signal for one or more hair removal treatments, compare the determined maximum value with a maximum threshold value, and issue a wear signal if the maximum threshold value is reached or exceeded.

4. 2. The hair removal device of claim 1, wherein the wear determination unit is configured to determine a maximum value of the cutting activity signal for multiple hair removal sessions and a trend line indicating a trend of the maximum values, compare the trend line with a trend line threshold and / or a trend line increase threshold, and issue a wear signal when the trend line reaches or exceeds the trend line threshold and / or when a rate of increase of the trend line reaches or exceeds the trend line increase threshold.

5. 2. The hair removal device according to claim 1, wherein the wear determination unit (18) is configured to determine peaks of the vibration cutting activity signal of one or more hair removal treatments, compare the peak values ​​of the peaks with a peak threshold to determine the number of the peaks exceeding the peak threshold, and issue a wear signal if the number of times the peak threshold is reached or exceeded per shave or per unit time exceeds a predetermined count or threshold.

6. 2. The hair removal device of claim 1, wherein the wear determination unit is configured to determine peak values ​​of the cutting activity signal for multiple hair removal sessions and a trend line indicative of a trend of the determined area, compare such trend line with a trend line threshold and / or a trend line increase threshold, and issue a wear signal when the trend line reaches or exceeds the trend line threshold and / or the increase rate of the trend line reaches or exceeds the trend line increase threshold.

7. 2. The hair removal device of claim 1, wherein the cutting activity determiner (17) is configured to determine the cutting activity signal from a half-cycle duration of an induced voltage signal provided by the measurement unit (16), such that the cutting activity signal is indicative of a variation in the half-cycle duration of the signal of the measurement unit (16).

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