Hair cutting apparatus comprising a current detector

Abstract

The present invention is directed to a hair cutting apparatus (600), such as a shaver, which is enabled to detect whether hair is currently being cut in a robust way. Such apparatus has a motor (102) for driving a cutting element. The motor current (106) is evaluated by filtering and amplifying it in such a way that a time derivative of the motor current (106) is processed and other parts of the motor current (106), such as noise and DC-5 parts, are eliminated. An evaluator determines whether the time derivative of the motor current is above a predefined threshold value.

Claims

1. A hair cutting apparatus comprising: a cutting element configured to cut hair, a motor configured to drive the cutting element for cutting the hair when powered by a motor current, and a current detector configured to detect the motor current as a function of time, the current detector comprising: a current sensor configured to sense the motor current and to provide a current signal indicative of the sensed motor current, wherein the current detector further comprises a current manipulator configured to determine a time derivative signal of the current signal, wherein the current manipulator comprises an evaluator configured to detect whether the time derivative signal or an amplified signal of the time derivative signal is above a predetermined threshold value to detect a hair-cutting action of the cutting element.

2. The hair cutting apparatus according to claim 1, wherein the current manipulator comprises a first high-pass filter adapted to determine the time derivative signal of the current signal.

3. The hair cutting apparatus according to claim 2, wherein the current manipulator comprises a second high-pass filter configured to differentiate the amplified signal to eliminate a DC-offset of the amplified signal.

4. The hair cutting apparatus according to claim 1, wherein a first high-pass filter comprises a series capacitor.

5. The hair cutting apparatus according to claim 1, wherein the hair cutting apparatus comprises a drive system coupling the motor to the cutting element, and wherein the current manipulator comprises a first low-pass filter configured to eliminate high frequency components of the current signal caused by torque changes of the drive system.

6. The hair cutting apparatus according to claim 5, wherein the current manipulator comprises a second low-pass filter configured to eliminate residual high frequent noise of the amplified signal.

7. The hair cutting apparatus according to claim 1, wherein the current manipulator comprises an operational amplifier configured to amplify the time derivative signal into the amplified signal.

8. The hair cutting apparatus according to claim 1, wherein the evaluator is configured to associate an occurrence of a value of the time derivative signal or the amplified signal being above the predetermined threshold value with a hair-cutting action of the cutting element.

9. The hair cutting apparatus according to claim 1, wherein the current sensor is provided as an analog electric circuitry, the current manipulator is provided as an analog electrical circuitry comprising an operational amplifier, and the evaluator is provided as a digital processor.

10. The hair cutting apparatus according to claim 1, further comprising a cutting indicator configured to indicate a detected hair-cutting action of the cutting element, wherein the cutting indicator comprises a light indicator configured to be activated to instantaneously indicate whether a hair-cutting action of the cutting element is detected.

11. The hair cutting apparatus according to claim 10, wherein the light indicator is arranged in the proximity of the cutting element.

12. The hair cutting apparatus according to claim 10, comprising a progress determining unit for determining a status of progress of a hair-cutting process, based on the detected hair-cutting actions.

13. The hair cutting apparatus according to claim 12, wherein the light indicator comprises a plurality of light elements, and wherein the progress determining unit is adapted to individually control the light elements to indicate the status of progress of the hair-cutting process by a number of light elements being activated.

14. The hair cutting apparatus according to claim 10, wherein the light indicator is adapted to be activated in different colors, at least in mutually different first and second colors, and wherein the current detector is adapted to control the light indicator such that the first color is instantaneously generated when a hair-cutting action is detected and the second color is instantaneously generated when no hair-cutting action is detected.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following drawings:

(2) FIG. 1 is an electric circuitry of a hair cutting apparatus comprising a motor and a switch for switching,

(3) FIG. 2 is a current detector for detecting a motor current of the motor shown in

(4) FIG. 1,

(5) FIG. 3 is a diagram showing a processed current signal and a threshold value,

(6) FIG. 4 is a diagram showing a processed current signal of a motor current and the motor current,

(7) FIG. 5 is a Bode-Diagram of a current manipulator,

(8) FIG. 6 is a schematic view of a shaver as an example of a hair cutting apparatus,

(9) FIG. 7 is an evaluator configured to compare a time derivative signal with a predetermined threshold value, and

(10) FIG. 8 is a schematic view of a further shaver as an example of a hair cutting apparatus.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(11) FIG. 1 shows an electric circuitry 100 of a shaver as an example of a hair cutting apparatus. This circuitry 100 comprises a motor 102 and a switching device 104 for controlling the motor 102. A DC motor current 106, also indicated with the capital letter I, can flow through the motor 102 and the switching device 104 to an interface 108 having the connection points X2 and X3.

(12) The motor current 106 can be sensed and detected with the current detector 200 shown in FIG. 2, which will be connected to the connection points X2 and X3 of the interface 108 of FIG. 1.

(13) FIG. 2 shows the current detector 200 having an interface 208 for connection to the interface 108 of the electric circuitry according to FIG. 1. Accordingly, the connection points X2 and X3 are indicated with the same letter numbers. In fact this can also be understood as a possibility of dividing the technical drawing of the circuitry into two drawings. In the same manner, the connection point X1 is also present in FIGS. 1 and 2. The current detector 200 basically comprises a current sensor 210 and the current manipulator 212, which is basically the rest of the current detector. The current sensor 210 basically just comprises a sense resistor 211, so that there is a voltage drop U1 across this sense resistor 211 which is basically proportional to the motor current I shown as motor current 106 in FIG. 1.

(14) The current manipulator 212 basically comprises a first low-pass filter 214, a first high-pass filter 216, a second high-pass filter 218 and a second low-pass filter 220 as well as an operational amplifier 222. The purpose of the current manipulator 212 is to provide a processed current signal U5 at the output 224 of the current manipulator 212.

(15) The working principle of the current detector consists of a current sensing circuit, a filter circuit and an amplification circuit and can be explained using FIG. 2.

(16) The motor current 106 is sensed at the sense resistor 211, resulting in a voltage signal U1. The voltage signal U1 is an example of a current signal indicative of the motor current. The voltage signal U1 is fed to the first low-pass filter 214 having a −3 dB frequency of 2 Hz. This low-pass filter 214 eliminates all high frequency components due to commutation, but also high frequency components due to torque changes, which basically appear as noise produced by the drive train and shaving system.

(17) The output of the first low-pass filter 214 is fed into a series capacitor 226 of the first high-pass filter 216. The series capacitor 226 acts to time-differentiate the voltage signal U2 which is the output of the first low-pass filter 214. The filter cutoff frequency of the first high-pass filter 216 can be in a −3 dB range of 2 Hz to 20 Hz.

(18) The function of this series capacitor 226 is to pass only the time derivative signal dI/dt of the signal coming from the first low-pass filter 214. The output of the first high-pass filter will be zero when there are no current changes, due to the differentiating character of the first high-pass filter.

(19) It was found that for setting a detection threshold, this differentiated voltage U3, which is the output of the first high-pass filter 216, will be easier to use, because there is no DC bias between multiple circuits. So, the absolute motor current or an absolute current signal indicative of the motor current is not present anymore in this voltage.

(20) A discharge resistor 228 is connected between the output of this series capacitor 226 and ground, in order to discharge the capacitor 226.

(21) Because filtering will cause signal gain loss, the operational amplifier 222 is provided. It is used to boost the output signal of the first high-pass filter 216, namely the voltage U3. The output voltage U4 of the operational amplifier is connected to a further series capacitor 230, which is part of the second high-pass filter 218. This further series capacitor 230, and thus the second high-pass filter 218, works as a differentiator to eliminate a DC offset which is generated by the operational amplifier 222.

(22) This further series capacitor 230 has also a discharge resistor 232 connected between the output of the series capacitor 230 and ground 234 to discharge the further series capacitor 230, as it was found that otherwise the signal will be clipped.

(23) The signal coming out of the series capacitor 230 will be fed into the second low-pass filter 220 to eliminate residual high frequent noise. The cutoff frequency of the second low-pass filter 220 is in the range of 30 Hz to 50 Hz.

(24) The result of the current detector 200 and thus of the current manipulator 212 is the voltage U5 at the output 224.

(25) The total gain of the current manipulator 212 is 40 dB and therefore 100V/V. This is also illustrated in the Bode-Diagram according to FIG. 5. That Bode-Diagram shows the curve of the gain 500 in dB and the curve of the phase 520 in degrees over the logarithmic frequency. For the final evaluation purpose of the current manipulator, the curve of the phase is of less interest. The curve of the gain 500 shows the highest value of about 40 dB at 10 Hz and falls to 0 dB at about 60 Hz. From 0.4 Hz to 60 Hz the gain is above 0 dB.

(26) When contrary to the suggested principle an absolute value of the motor current is used for evaluation, the problem occurs that, when the load changes e.g. due to wear or by using a different interchangeable shaving or grooming unit, the absolute value of the motor current will change substantially. It was found that setting a threshold value for detecting peaks of such an absolute motor current will not be robust enough to handle torque changes over time, because the no-load current will change.

(27) In view of that, the advantage of the present working principle, in particular as explained using the example of FIG. 2, is that the enhancing of the changes in the current signal associated with hair-cutting actions of the cutting element is not very sensitive to slow changes of the system and thus is robust to changes of the system. In other words, the explained electronics automatically adapt to slow torque changes due to wear, pollution and so on.

(28) Results illustrating this are shown in FIGS. 3 and 4. FIG. 3 shows the processed current signal 300 that shows the output voltage U5 at the output 224 of FIG. 2 over time. The graph also shows a threshold value 310. FIG. 4 also shows the processed current signal 300 and in addition the current signal 400 which is the voltage U1 of FIG. 2 over time.

(29) FIG. 3 illustrates that peaks of the processed current signal 300 can easily be detected by comparing the processed current signal 300 with the threshold value 310. Even large changes of the processed current signal 300, which might occur due to changes of the shaver, will not change the result of the comparison.

(30) FIG. 4 shows the current signal 400 and that makes clear that any peaks are difficult to detect. However, besides the superimposed noise, the DC-portion of the current signal 400 is much bigger that the overlaid characteristics which are associated with hair-cutting actions of the cutting element. Accordingly, any changes of the amplitude of the current signal 400 affect the amplitude of the overlaid characteristics even more. The suggested solution prevents this problem, because the processed current, inter alia, eliminates the DC-portion.

(31) FIG. 6 shows a hair cutting apparatus 600 having a shaving head 610 comprising a plurality of cutting elements 612. The cutting elements 612 of this embodiment are basically arranged in three groups, each group being prepared to rotate in order to cut hair. The shaving head is attached to a main body 614 of the hair cutting apparatus 600. The main body is also designed to be hand-held by a user when used for shaving.

(32) The main body comprises a lower end 616 and an upper end 618 arranged towards the shaving head 610. At the upper end, in the proximity of the shaving head 610 and thus in the proximity of the cutting elements 612, there is provided a light indicator 620 which is part of a cutting indicator. During use, the light indicator 620 indicates whether hairs are actually being cut or not by the cutting elements 612. When using the hair cutting apparatus 600, the shaving head 610 contacts the skin with the cutting elements 612. While shaving, the user looks at the skin near the shaving head 610 and therefore also looks at the shaving head and, consequently, sees the light indicator 620 as well. In this way, the user can easily recognize whether hairs are actually being cut and can move the shaver accordingly.

(33) FIG. 7 shows an evaluator 250 having the output voltage U5 at the output 224 of FIG. 2 as an input voltage at the evaluator input 252. This inputted analog voltage U5 is converted in the AD-converter 254 into a digital derivative signal U5.sub.d that is inputted in the comparator 256. A predetermined threshold value TV is also inputted in the comparator 256. The comparator compares these values and provides a comparison result at the output 258. That result can be the value “1” if the digital derivative signal U5.sub.d is larger than the predefined threshold value TV, or the result can be the value “0” otherwise. Accordingly, the value “1” at the output 258 of the comparator 256 and thus at the evaluator 250 indicates an operating condition wherein a hair is actually being cut by any of the cutting elements 612.

(34) The output 258 can be used for different purposes. In a first example, the output 258 is used to directly control the light indicator 620 such that the light indicator 620 is activated to instantaneously indicate whether or not a hair-cutting action of the cutting elements 612 is actually detected by the hair-cutting detector. This can be realized by configuring the light indicator 620 such that, when the output 258 provides the value “1”, the light indicator 620 will be activated and, when the output 258 provides the value “0”, the light indicator 620 will not be activated. For this purpose, the light indicator 620 might be provided with suitable electronics having an input for receiving an output signal from the output 258. Alternatively, the light indicator 620 might be configured to be able to generate light of different colors. In such an embodiment, the light indicator 620 is activated in a first color when receiving the value “1” from the output 258 to indicate an actual hair-cutting action, and the light indicator 620 is activated in a second color, different from the first color, when receiving the value “0” from the output 258 to indicate that actually no hairs are being cut. Alternatively, the light indicator 620 might be configured to be able to generate light in a continuous mode as well as in a blinking mode. In such an embodiment, the light indicator 620 is activated to generate light in the continuous mode when receiving the value “1” from the output 258 to indicate an actual hair-cutting action, and the light indicator 620 is activated in the blinking mode when receiving the value “0” from the output 258 to indicate that actually no hairs are being cut.

(35) The output 258 can also be used to additionally detect a progress of a hair-cutting process. For this purpose, the signal of the output 258 is input into a progress determining unit 260 for further processing. The progress determining unit 260 can determine the progress of the hair-cutting process in a particular manner, for example by counting a number of detected hair-cutting actions during a predetermined time interval, or by identifying time intervals between consecutively detected hair-cutting actions. The result of this counting process may provide an indication of the progress of the hair-cutting process. For example, a relatively high number of detected hair-cutting actions during a predetermined time interval or a relatively short time interval between consecutively detected hair-cutting actions may indicate an early stage of the hair-cutting process, whereas a relatively low number of detected hair-cutting actions during a predetermined time interval or a relatively long time interval between consecutively detected hair-cutting actions may indicate a late stage of the hair-cutting process. The progress determining unit 260 might comprise suitable software to provide an output signal at its output 262 indicating the degree of progress of the hair-cutting process. This software might determine the output signal, depending on the signal received from the output 258 of the comparator 256.

(36) The output 262 of the progress determining unit 260, i.e. the degree of progress of the hair-cutting process, may be visualized by means of the light indicator 620, in different ways. The light indicator 620 may e.g. be provided with a plurality of individual light sources such as LEDs (not shown in the figures), wherein the number of activated individual light sources is dependent on the determined degree of progress of the hair-cutting process. For example, an early stage of the hair-cutting process is indicated by activating all light sources, a late stage of the hair-cutting process is indicated by activating only few light sources or a single light source, while no light source is activated when actually no hair-cutting actions are detected. Any intermediate stage of the hair-cutting process might be indicated by activation of a proportional number of light sources. In an alternative embodiment as described hereinbefore, wherein the light indicator 620 is configured to be activated in two different colors, the light indicator 620 might be configured to provide a fading function enabling the light generated by the light indicator 620 to gradually change from the first color to the second color, depending on the signal received from the output 262 of the progress determining unit 260. In this embodiment, an early stage of the hair-cutting process is indicated by activating the light indicator 620 in the first color. An end stage of the hair-cutting process, wherein no hair-cutting actions are actually being detected, is indicated by activating the light indicator 620 in the second color, while any intermediate stage of the hair-cutting process might be indicated by activating the light indicator 620 in an intermediate color between the first and the second colors. For this purpose, the light indicator 620 might comprise a number of LEDs of different colors.

(37) FIG. 8 shows a hair cutting apparatus 650 having a main body 664. The main body 664 is also designed in a way to be held by the hand of a user when the apparatus is used for shaving. The main body 664 comprises a lower end 666 and an upper end 668 arranged towards a shaving head which is not shown in this figure. At the upper end 668, in the proximity of the shaving head and thus in the proximity of cutting elements, there is provided a light indicator light 670 which is part of a cutting indicator. During use, the light indicator 670 indicates whether hairs are actually being cut or not by the cutting elements. The light indicator 670 has the shape of a partial ring, i.e. it is substantially C-shaped. The light indicator 670 partially surrounds the upper end 668 of the shaver 650. The shaving head and thus the cutting elements are basically right behind the light indicator 670.

(38) Accordingly, one idea is to use filters and an amplifier to make the conventional motor current measurement in shaving and grooming devices more robust. It was found that some functions in a shaver can be improved by a robust current measurement. Such robust current measurement is suggested and used to detect hair-cutting actions or to measure hair density. By using filters and an amplifier the current peaks in the motor current associated with hair-cutting actions can be derived from a noise-shaped motor current. This solution is robust enough to reliably detect the current peaks in the motor current associated with hair-cutting actions in case of pollution and in case of using different types of interchangeable shaving or grooming units, such as shaver-type, trimmer-type and brush-type attachments.

(39) It was found that at least one conventional sense resistor motor current measurement used in shaving and grooming devices works as follows. Simple motor current measurement measures the voltage drop across a sense resistor. Such a resistor might have a value of 0.05 Ohm. A microcontroller's AD converter measures the sense resistor voltage drop. The AD converter value, which is a 10-bit value most of the time, is input to measure the absolute motor current by using Ohm's law. The result looks similar to the current signal 400 shown in FIG. 4 and is evaluated by analyzing it.

(40) Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

(41) In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality.

(42) A single unit or device may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

(43) An improvement or replacement of such measurement is suggested and that can particularly be used for an appliance that has a light ring or divided light ring to show the cutting of the beard. Such an appliance is suggested. The suggested solution uses the motor current to detect the cutting torque. To make this function robust it is suggested to make the conventional motor current measurement more robust to slow torque changes caused by wear, unit replacement and pollution of the shaving system.

(44) Any reference signs in the claims should not be construed as limiting the scope.

(45) This solution particularly provides a suggestion to overcome the problem of setting a threshold level for motor current detection in appliances.

(46) The suggested solution is an improvement to solutions which are tailored to an exact system and which do not consider variations in motor current for each shaver or groomer. It was found that it is difficult to set a threshold level in the current because of variation in torque of shaving systems due to pollution, friction differences or wear.

(47) The suggested solution can particularly be used in male skin care products, shavers, grooming devices and hair clippers.