Motor unit and personal care device having a motor unit

Abstract

The present application relates to a motor unit comprising a motor having a stator and an armature, the armature being configured for relative driving movement with respect to the stator, and a motor control unit having a supply circuit providing a supply voltage to the motor so as to provide the motor with a set power level for driving the armature into movement, and a measurement circuit for measuring a value of a physical variable indicative of a current through the motor, the motor control unit being configured to interrupt the provision of a supply voltage by the supply circuit and dynamically brake the motor during a braking time interval, and further to measure the value of the physical variable during the braking time interval, the motor control unit being further configured to compare the measured value of the physical variable with a target value, the target value depending on the supplied power level and the intended movement amplitude of the armature, to determine a new set power level depending on the comparison result, and thereafter to provide the new set power level to the motor.

Description

[Technical Field]

[0001] This application relates to a motor unit comprising a motor driven by supplying a set power level to the motor, wherein a motor control unit is configured to control the subsequent power supply to the motor based on measured values ​​of physical variables. This application also relates to a personal care device and a method for controlling a motor unit. [Background technology]

[0002] It is known that the power required by a vibration motor to achieve a constant vibration amplitude or velocity varies depending on the load applied to the motor. Without proper control of the power level supplied to the motor, the amplitude or velocity of the vibration motor will decrease as the load increases. One method of measuring the amplitude or velocity of a motor is to directly determine the so-called inverse electromagnetic force (inverse EMF) in the motor coil, i.e., the voltage induced in the motor coil by the relative motion between the motor coil (e.g., located in the stator of the motor) and the permanent magnet (e.g., located in the moving part of the motor). When the amplitude decreases, the motor velocity decreases, and therefore the inverse EMF decreases. To enable the direct measurement of the inverse EMF in the motor coil, the drive current flowing through the motor coil is typically reduced to zero to avoid other voltages that would interfere with the measurement of the inverse EMF. This means that when the supply voltage to the motor is cut off, the drive current flowing through the motor coil must first be dissipated before the inverse EMF can be measured. If a decrease in the inverse EMF is determined, more energy must then be applied to the motor in each subsequent cycle (i.e., a higher power level must be provided) in order to maintain a constant motor amplitude. The document, European Patent No. 1063760(B1), generally discusses such control methods. This solution requires a long interruption in the motor's operation, during which energy within the motor must be dissipated, thus causing a decrease in motor efficiency.

[0003] Instead of determining the back EMF in the motor coil itself, it has been proposed to use a secondary measurement coil to determine the speed of the moving permanent magnet of the vibrating motor, but such a solution requires additional components and thus increases the cost of the motor.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The object of the present disclosure is to provide a motor unit, preferably a brushless motor, configured to be controlled by a method that mainly enables maintaining a constant motor amplitude or speed and provides improved or at least different motor control compared to known motor units. Another object of the present disclosure is to provide a method for controlling a motor unit such that a constant motor amplitude can be mainly maintained, and this method represents an improved or at least different method compared to known methods. Preferably, the motor unit and the associated control method provide higher motor efficiency than known motor units / control methods.

Means for Solving the Problems

[0006] According to one aspect, there is provided a motor unit including a motor having a stator and an armature, the armature being configured to perform a relative driving movement with respect to the stator, and a motor control unit including a supply circuit configured to provide a supply voltage to the motor so as to provide a set power level for driving the armature to move, and a measurement circuit configured to measure a value of a physical variable indicating a current flowing through the motor. The motor control unit is configured to interrupt the provision of the supply voltage by the supply circuit, dynamically brake the motor during a braking time interval, and further measure the value of the physical variable during the braking time interval. The motor control unit is further configured to compare the measured value of the physical variable with a target value, the target value depending on the supplied power level and the intended movement amplitude of the armature, determine a new set power level depending on the comparison result, and then provide the new set power level to the motor.

[0007] According to one aspect, there is provided a personal care device including the above-described motor unit.

[0008] According to one aspect, there is provided a method for controlling a motor unit, preferably a motor unit of a personal care device, the method comprising: - providing a motor having a stator and an armature configured to perform a relative driving movement with respect to the stator; - supplying a set power level to the motor so as to drive the armature to move, preferably by supplying a preferably pulse-width-modulated supply voltage to the motor; - dynamically braking the motor during a braking time interval; - measuring a value of a physical variable indicating a current flowing through the motor during the braking time interval; - comparing the value of the physical variable with a target value, the target value depending on the set power level and the intended amplitude of the movement of the armature; - determining a new set power level depending on the comparison result; A method is provided which includes the step of then providing the motor with a new set power level. [Brief explanation of the drawing]

[0009] This disclosure will be further clarified by a detailed description of exemplary embodiments and reference to the drawings. [Figure 1] This figure shows the elements of an exemplary motor unit, which includes a motor, an H-bridge for applying a rectified DC voltage to the motor, and a motor control unit for controlling the H-bridge. [Figure 2A] This is a diagram of the relevant elements of the motor unit shown in Figure 1 during the first rectification phase. [Figure 2B] This is a diagram of the relevant elements of the motor unit shown in Figure 1 during the dynamic braking time interval. [Figure 2C] This is a diagram of the relevant elements of the motor unit shown in Figure 1 during the second rectification phase. [Figure 3] This diagram shows a voltage signal measured as a physical variable indicating the current flowing through the motor, depending on the power supply level, with three curves shown for three different constant inverse EMF values. [Figure 4] This figure shows the voltage and current signals against time for an example with a moderate braking time interval, where disturbances related to the intended sinusoidal current flow through the motor are observed in the time-current behavior. [Figure 5] This figure shows the voltage and current signals against time for an example with a small braking time interval, where disturbances related to the intended sinusoidal current flow through the motor are observed in the time-current behavior. [Figure 6A] This is a magnified view of the simulated voltage signals before, during, and after the dynamic damping time interval for the first level of inverse electromagnetic force. [Figure 6B] This is a magnified view of the simulated voltage signals before, during, and after the dynamic damping time interval for a second level of inverse electromagnetic force that is higher than the first level. [Figure 6C]This figure shows magnified simulated voltage signals before, during, and after the dynamic damping time interval for a third level of inverse electromagnetic force that is lower than the first level. [Figure 7A] These are schematic diagrams illustrating the relationship between the set power level supplied to the motor and the measurement signal, for several examples. [Figure 7B] These schematic diagrams illustrate, for several examples in a time sequence, the relationship between the set power level supplied to the motor and the measured signal, as well as the repeated application of the resulting set power level. [Figure 8] This is a schematic diagram of a motor comprising a stator and a rotor that may be used in a motor unit as described herein. [Figure 9] This is a diagram of a personal care device in which the disclosed motor unit is used. [Figure 10] This is a flowchart illustrating the method for controlling a motor unit according to this disclosure. [Modes for carrying out the invention]

[0010] In the context of this specification, “personal care” means the grooming (or care) of the skin and its appendages (i.e., hair and nails) and the teeth and oral cavity (including the tongue, gums, etc.), with the aim of preventing disease and maintaining and enhancing health, and on the other hand, the aim of cosmetic treatment and improvement of appearance of the skin and its appendages. This includes maintaining and enhancing well-being. This includes skin care, hair care, oral care, and nail care. This further includes grooming actions such as beard care, shaving, and hair removal. Accordingly, “personal care device” means any device for performing such grooming or grooming actions, such as (cosmetic) skin treatment devices such as skin massage devices or skin brushes; wet razors; electric shavers or trimmers; electric hair removal devices; and oral care devices such as manual or electric toothbrushes, (electric) flossers, (electric) scrubbers, (electric) tongue cleaners, or (electric) gum massagers. This does not preclude the possibility that the proposed personal care device may have a more significant advantage in one or more of these developmental or device areas than in any other of these areas. In this description, an electric toothbrush has been selected to illustrate the details of the proposed personal care device. Unless the details are specific to an electric toothbrush, the proposed technology can be used in any other personal care device.

[0011] As used herein, the term “dynamic braking” refers to a motor control state in which the motor terminals are connected to each other, for example, via two switches of an H-bridge, and the current within the motor recirculates through the motor and dissipates in any resistance present in the recirculation circuit (e.g., the resistance of the motor coils and the resistance of the H-bridge switches). During the dynamic braking interval, the motor is used as a generator and continues to drive the armature. In the embodiments described herein, since non-regenerative braking has higher energy efficiency than regenerative braking, the dynamic braking interval does not include a regenerative mode; that is, the energy stored in the motor is not supplied to an energy source. This does not preclude the possibility that the concepts discussed herein may be combined with regenerative braking.

[0012] The motors in this disclosure comprise a stator and a rotor or armature as the movable motor section, where the term rotor is typically used when the movable motor section performs oscillating rotation, and the term armature may be typically used when the movable motor section performs reciprocating linear motion. For simplicity, only the term "armature" will be used below. Thus, the motors in this disclosure are typically oscillating motors. An oscillating motor has a resonant frequency at which input energy (represented by the power supply level) is most efficiently converted into motor amplitude, and such a motor is therefore driven regularly at its resonant frequency or a typically fixed drive frequency close to its resonant frequency. When a load is applied to the motor, damping is added and the resonant frequency shifts, so that the motor amplitude decreases when a load is applied. Here, "motor amplitude" means either the peak amplitude provided by the linearly reciprocating armature or the peak angular deflection of the oscillating rotor (see a more detailed explanation below). Users may not be aware of the fluctuating amplitude of the motor that causes the fluctuating amplitude of the driven part (e.g., the movable head of a personal care device). For an improved consumer experience, it may be desirable to maintain, or at least nearly maintain, the motor amplitude despite fluctuations in the applied load. Therefore, it may be desirable to measure the instantaneous motor amplitude or determine the value of a physical variable indicating the motor amplitude and adjust, for example, the power supply level, so that the motor amplitude remains constant or at least closer to a constant amplitude level than without adjustment. This means that fluctuations in the applied load may be faster than the adjustment loop, or the adjustment process may intentionally respond to load changes with only incremental or partial adaptations of the set power level to avoid motor amplitude jitter or generally unstable behavior. Thus, motor amplitude steadyness can only be achieved approximately or with some delay.

[0013] Due to the structure of a vibration motor comprising at least one permanent magnet and a coil that move relative to each other at a fixed drive frequency during operation, a voltage induced in the coil by the permanent magnet, also known as the reverse electromagnetic force (or reverse EMF or BEMF), provides a signal indicating the motor amplitude (or motor linearity or rotational speed). Therefore, determining the signal indicating the reverse electromagnetic force provides a measurement of the current motor amplitude and, thus, a basis for controlling the motor amplitude, in order to infer the reverse electromagnetic force from the signal or to establish an indirect correlation with the BEMF from the signal. Accordingly, a motor control unit is equipped with a measurement circuit for determining such a signal, which is a value of a physical variable indicating the current flowing through the motor within a dynamic braking interval. How measuring the value of the physical variable indicating the current flowing through the motor makes it possible to derive insights about the reverse electromagnetic force will be explained in more detail below.

[0014] Motor amplitude is typically given by the peak-to-peak value of the linear reciprocating motion of the motor shaft, or by the peak-to-peak deflection angle of the oscillating rotation of the motor shaft. Instead of peak-to-peak amplitude, a half-amplitude, i.e., peak amplitude which is understood to be half of the peak-to-peak amplitude, may be referred to. Maintaining peak-to-peak amplitude means maintaining peak amplitude in this disclosure. When a oscillating motor is loaded, the motor amplitude decreases, as already stated. Since the frequency of the motor's oscillating motion is fixed by the drive frequency utilized by the motor control, a decrease in amplitude means a decrease in armature speed. As mentioned above, the armature speed can be directly determined by measuring the inverse EMF (i.e., the induced voltage in the motor's stator coil due to the movable permanent magnet(s) attached to the armature), but the inverse EMF is the voltage in the motor due to the motor resistance U R =R·I(t) is 0, and the self-induced voltage U in the motor due to the change in motor current LThe inverse EMF can only be directly measured if the current driven through the motor is reduced to zero over a period of time, so that =L·(dI(t) / dt) is also zero. If the motor control does not inherently provide a sufficiently long time interval during which the motor current becomes zero, the motor's power supply must be interrupted to create a situation where the inverse EMF can be directly measured, and the energy stored in the motor coils must be dissipated or supplied back to the battery. This makes it possible to determine the current motor amplitude and define whether the set power level supplied to the motor should be increased or decreased to maintain a constant motor amplitude. Since this is energetically inefficient, more energetically efficient motor control methods and motor units are proposed herein, i.e., methods or motor units that do not require the motor current to be reduced to zero in order to determine the inverse EMF / motor amplitude.

[0015] One motor control method for determining motor amplitude is discussed in U.S. Patent Application Publication 2005 / 0146296(A1), which allows for the determination of motor speed (and therefore motor amplitude) by measuring at least two current values ​​during a motor control phase in which a voltage is applied to the motor and a current is driven through the motor. In U.S. Patent Application Publication 2005 / 0146296(A1), a single long voltage pulse is applied for each half-cycle of the motor's periodic drive, and the current driven through the motor only loosely approximates a sinusoidal shape. In contrast, the motor control concept proposed herein includes embodiments in which the current driven through the motor is shaped, for example, the current may be shaped into an approximate sinusoidal shape by applying a set power level in the form of multiple voltage pulses for each half-cycle, and the length of each voltage pulse may be controlled by pulse width modulation (PWM).

[0016] According to some aspects of this disclosure, a motor unit comprises a motor and a motor control unit having a supply circuit and a measurement circuit. The motor is driven by applying an electrically rectified supply voltage (e.g., a DC voltage) to the motor by the supply circuit, which is part of the motor control unit. To apply the DC voltage to the motor, the supply circuit may comprise an H-bridge, as is commonly known in the art. The H-bridge may be a full H-bridge, but this does not preclude the use of, for example, a half-bridge circuit. The motor control unit is used to control the supply circuit to electronically rectify the DC voltage that may be supplied by a battery or rechargeable battery. The motor control may be periodic; that is, the motor control may be characterized by a drive frequency or a drive period length, for example, the drive frequency may be 100 Hz, in which case the drive period length is 0.01 seconds. A current that periodically changes direction is driven through the motor by applying a DC voltage that periodically changes its polarity to the motor.

[0017] A motor control unit can use pulse-width modulation (PWM) to control the supply circuit to provide the supply voltage in pulses, and the varying duty cycles of these voltage pulses allow for shaping the current driven through the motor. For example, PWM can be used to drive a nearly sinusoidal current through the motor. The PWM signal can have a PWM frequency that is higher than the drive frequency, preferably considerably higher, and multiple voltage pulses are applied to the motor with each half-drive cycle. As just one example, the drive frequency may be about 145 Hz and the PWM frequency may be about 37 kHz, i.e., 256 voltage pulses can then be applied with each drive cycle (or 128 pulses can then be applied with each half-drive cycle), and the duty cycle of each voltage pulse can be controlled to shape the current flow. As described in U.S. Patent Application Publication 2005 / 0146296(A1), in order to apply one PWM-controlled voltage pulse per half-drive cycle, the PWM frequency must be twice the drive frequency.

[0018] Generally, the drive frequency may be selected to have a value in the range of 10Hz to 1,000Hz, preferably in the range of 30Hz to 500Hz, and more preferably in the range of 50Hz to 300Hz, but is not limited to these ranges. The PWM frequency may be the same as the drive frequency, or it may be twice the drive frequency, but a PWM frequency much higher than the drive frequency may offer certain benefits, such as more detailed shaping of the current flow through the motor. Switching losses may need to be considered, but frequencies that are too high may not balance higher precision and efficiency. Therefore, the PWM frequency may be higher than the drive frequency by a coefficient in the range of 4 to 10,000, preferably in the range of 10 to 5,000, and more preferably in the range of 20 to 1,000, but is not limited to these ranges. A single PWM-controlled voltage pulse may have an on-length between 0% and 100% of the full length of each PWM period, and this relative on-length is typically called the duty cycle. The duty cycle may be controlled analogously or digitally, and the digital resolution may be selected to be in the range of 2 to 64 bits, preferably 4 to 16 bits, but not limited to this range. With an 8-bit resolution, the duty cycle of the voltage pulse can take one of 256 levels from 0% duty cycle to 100% duty cycle. The on and off lengths of each PWM controlled voltage pulse may then be controlled by an underlying clock signal having a higher frequency, each enabling 256 levels of duty cycle, and the individual on lengths of each PWM controlled voltage pulse for each drive cycle may be stored in a lookup table in the motor control unit's memory unit. Controlling the duty cycle of the voltage pulse applied to the motor makes it possible to shape the driven motor current into an approximate sinusoidal waveform, which of course means that the motor current can be shaped to approximately take any other intended shape, e.g., triangular, trapezoidal, etc. For this purpose, multiple lookup tables may be provided in the memory unit to enable different current shapes.

[0019] The motor control unit, specifically the measurement circuit of the motor control unit, is configured to determine the value of a physical variable indicating the current flowing through the motor. A signal representing this value is then generated and supplied to the processing unit of the motor control unit. The physical variable may be a voltage or a current, as will be described in more detail below. The value (the signal representing the value) is determined during at least the measurement portion of the braking time interval; that is, the value may be determined at a moment within the braking time interval that does not coincide with the start of the braking time interval, or the value may be determined during a period within the braking time interval that is shorter than the braking time interval, does not start at the start of the braking time interval, and / or does not end at the end of the braking time interval. In some embodiments, the value of the physical variable is determined by sampling the physical variable multiple times during the braking time interval and averaging or otherwise combining the sample values. In this disclosure, the phrase “during the braking time interval” means either the moment the braking time interval begins or ends, or any moment or period therein.

[0020] The fundamental insight described herein is the understanding that the value of a physical variable indicating the current flowing through the motor, measured during a braking time interval, is affected by the inverse EMF, and therefore it is possible to derive or estimate the inverse EMF from such measurements. However, the measurements are also affected by other parameters, specifically by non-zero currents resulting from the energy stored in the motor when dynamic braking begins, and therefore (as already stated) direct measurement of the inverse EMF is impossible. According to this disclosure, the measured value of the physical variable indicating the current flowing through the motor is compared to a predetermined target value that depends on the currently applied power level, i.e., a set power level, and the intended motor amplitude. This comparison makes it possible to determine, at least, whether the set power level currently supplied to the motor needs to be increased or decreased in order to maintain the intended motor amplitude, or at least to keep the resulting motor amplitude closer to the intended amplitude than would be without such control. The underlying insight and control steps are described in more detail below.

[0021] The motor current I, which may particularly be substantially sinusoidal (where a sinusoidal waveform is assumed here), M is at its peak as given by the following equation. I M,p = (V BATT - V BEMF ) / √(R 2 + R X 2 ) Here, I M,p is the peak motor current, V BATT is the supply voltage, i.e., the battery voltage, V BEMF is the back electromotive force, R is the sum of all ohmic resistances, and R X is the reactance of the motor coil. When the current flowing through the motor is sinusoidal and is driven by a relative PWM signal in the range from 0 to 1, the motor current can be approximated by the following equation. I M = PWMW · I M,p · sin(ω · t + φ L ) Here, PWMW may be a number between 0 and 1 representing the weight of PWM, and φ L is the phase shift between the supply voltage and the motor current. (Based on the X value and R value of the exemplary motor circuit used in the evaluation of the present disclosure, it was found that φ L is about 19.7 degrees.) Assuming that the dynamic braking time interval starts when the sin function is 1, the voltage V Measure measured in parallel with the motor circuit at exactly the start of the dynamic braking time interval is given as follows. V Measure = -R S · PWMW · (V BATT - V BEMF ) / √(R 2 + R X 2 ) Here, R Sis the ohm resistance of the resistor on which the voltage is measured. The PWM weighting coefficient PWMW reflects the set power level supplied to the motor. While the aforementioned PWM lookup table may provide duty cycle values ​​representing a sine function with a normalized peak of 1, the PWMW coefficient is a global weighting coefficient that determines the power level and is applied to all PWM values. When PWMW=1, the maximum power level is set and supplied to the motor, and when PWMW=0, the minimum power level is set and no energy is supplied to the motor. The PWMW coefficient can take any value from 0 to 1 to set the power level supplied to the motor. For illustrative purposes, PWMW may be 0.35 for one intended motor amplitude under no-load conditions and 0.6 for another intended motor amplitude under no-load conditions.

[0022] The equation derived in this way is a PWMW value representing the set power level supplied to the motor and a given inverse electromagnetic force V BEMF Measured voltage V Measure This shows a linear relationship between the two. In other words, the relationship between PWMW and the measured voltage is linear for any intended amplitude. The linear formula can be rewritten as follows: V Measure =-A·PWMW or V Measure =-A·PWMW+B Here, A is just a constant for a given motor amplitude that depends on the inverse EMF value, and a second variation having an additional constant value B is actually V Measure However, this only indicates that it may include absolute shifts due to the overall structure of the measurement circuit (for example, due to pull-up or pull-down resistors in the measurement circuit, which may be necessary because the measurement circuit cannot actually measure negative voltages). Figure 3, which will be further described below, shows the measured voltage as a function of PWMW for three different constant inverse EMF values.

[0023] This linear relationship is an approximation, for example, because here we assume that, at a constant motor amplitude, the inverse electromagnetic force does not experience a significant phase shift with respect to the motor current. In reality, some phase shift occurs, but for the purposes of this study, it can be ignored. It has been found that in most cases, assuming a linear relationship is sufficient. A linear relationship is easy to calibrate; for example, in the above equation, the voltage at PWMW=0 is a known constant, so only one additional point on the curve needs to be measured, and the PWMW setting required for the intended motor amplitude when there is no additional external load on the motor can be used to determine the linear relationship.

[0024] However, if the linear relationship approximation is insufficient, for example, if the relationship between PWMW and the measured voltage can be calibrated under various load conditions, such as two, three, or four different load conditions (e.g., a 0.5N load, a 1N load, a 1.5N load, a 2N load, and / or a 2.5N load), then it is certainly possible to apply a more complex calibration scheme.

[0025] When the external load changes, the inverse EMF changes, which is the measured voltage V Measure However, this means a deviation from the linear curve above for the set power level / PWMW, i.e., the measured voltage will be higher when the load decreases (inverse EMF increases as motor amplitude increases) or lower when the load increases (inverse EMF decreases as motor amplitude decreases). Therefore, if the measured voltage is above the linear curve for the intended amplitude, the set power level, i.e., the PWMW value in the above formula, needs to be decreased so that the measured voltage returns to the linear curve for the intended motor amplitude. Conversely, if the measured voltage is below the linear curve for the intended amplitude, the set power level, i.e., PWM in the above formula, needs to be increased so that the measured voltage returns to the linear curve for the intended motor amplitude.

[0026] This further indicates that, for a given PWMW value, a measured voltage that deviates from the linear curve for the intended motor amplitude is an indicator of a changed load condition, and that the set power level should be changed to a new set power level, i.e., a different PWMW value, that yields a motor amplitude that is essentially the same as, or at least close to, the intended motor amplitude. Incremental adaptation of the power level has been found to be sufficient, on the one hand, to achieve the intended motor amplitude in a short time, and on the other hand, to avoid jumps or significant jitter in the motor amplitude. Furthermore, it has been found that applying a threshold between the measured voltage and the calibrated linear curve is wise to avoid small deviations below the threshold failing to yield the new set power level. "Threshold" means the absolute difference between the measured value and the calibrated linear curve. In control systems, this is commonly known as hysteresis. This helps stabilize the motor amplitude and avoid significant jitter. This concept is further explained below with reference to Figures 7A and 7B. Essentially, calibration can be performed for multiple intended amplitude values ​​and a single PWMW value (i.e., under no-load conditions) for linear relationships, or for multiple PWMW values ​​per amplitude in the case of nonlinear relationships. As a result, for any subsequent measurement, it is possible to derive (e.g., by interpolation or extrapolation) which amplitude (and therefore load condition) the measurement relates to, and then calculate the change in PWMW required to shift the amplitude back to the intended amplitude (i.e., onto the target curve).

[0027] Regarding the phase shift of the motor current, it is also possible to measure or track the phase shift using a measurement circuit to compensate for any errors in the calculation. The measurement circuit can, for example, track the positions of voltage peaks (two relative to the sine wave) and their relative positions to the tabled PWM values. Then, it is possible to shift the dynamic damping interval by the amount by which the tracked voltage peaks have moved so that the measurement circuit always measures the recirculating current at approximately the same position relative to the BEMF sine wave.

[0028] As described above, the duty cycle of the PWM control voltage pulse applied during one drive cycle may be selected so as to generate a sinusoidal drive current through the coil. The duty cycle value during the drive cycle may be stored in the memory unit of the motor control unit; for example, if the PWM frequency is 256 times the drive frequency, 256 duty cycle values ​​will be stored. The duty cycle value may have values ​​between 0 and 1 or between 0% and 100%. For clarity, the duty cycle value may be stored digitally, as described in the following paragraphs.

[0029] In operation, the duty cycle applied to the voltage pulse is the stored duty cycle multiplied by the PMWM coefficient. As already mentioned, the duty cycle may be digitized and may have an 8-bit resolution so that duty cycle values ​​from 0 to 255 can be used, or a 7-bit resolution so that duty cycle values ​​from 0 to 127 can be used.

[0030] Furthermore, it was stated above that the PWMW value may be between 0 and 1. Below, for the sake of clarity, we will assume that PWMW is also mapped to a 7-bit digital scheme, where 0 is 0 and 1 is 127. Please understand that this is an unrestricted assumption.

[0031] As an example, the PWMW value may be set to 63 to achieve the intended peak-to-peak amplitude of the motor shaft, e.g., 0.8 mm. As will be explained in more detail, the value of the measured voltage, i.e., the value of the physical variable expected under no-load conditions for a peak-to-peak amplitude of 0.8 mm, is known from the linear formula described above by pre-calibration. During operation, the set power level may change under varying load conditions, i.e., the weighting coefficient PWMW is adapted and set so that the new power level maintains the motor amplitude. Assume that the motor unit starts with a weighting coefficient PWMW of 63, which yields a peak-to-peak amplitude of 0.8 mm under no-load conditions. Now, for example, when a personal care device is used and the movable head is pressed against the body part being treated, if the applied load changes, the load will result in a decrease in motor amplitude, which in turn results in a change in the value of the physical variable being determined, in this case the measured voltage. Next, since the decrease in motor amplitude leads to a decrease in inverse EMF, the measured voltage will fall below the target value under no-load conditions. During operation, the applied load may, at some point, become lower than the previously applied load, then the motor amplitude increases, resulting in an increase in the inverse EMF, and therefore the measured voltage may be higher than the expected value of the measured voltage. An illustrative description of the control scheme is further given below with particular reference to Figures 7A and 7B.

[0032] The calibration described above may ideally be a global calibration for the personal care device or even for all personal care devices of a given type from the manufacturer, but the personal care device may have different interchangeable movable heads, each of which may have its own calibrated target function, or the tolerances of the various parts of the personal care device may require each personal care device to have its own target curve.

[0033] To maintain the intended motor amplitude, the PWMW coefficient may be changed. For example, following the example above where PWMW is 63 under no-load conditions, PWMW needs to be higher when a load is applied. For example, PWMW may be increased to 85 to compensate for the additional load, where it should be noted that the given values ​​are for illustrative purposes only and are not limiting. The necessary changes can be made in a single step, but it is also intended to change PWMW incrementally. For example, PWMW can be increased from 63 to 64 to set a new power level until the value of a physical variable indicating the current flowing through the motor, such as the measured voltage, matches the expected value, i.e., the value of the calibrated linear relationship described above, and then PWMW can be increased from 64 to 65, etc., after the next measurement. If the applied load decreases, PWMW may also be decreased, preferably in an incremental step.

[0034] Such incremental adjustments avoid large adjustments occurring with each drive cycle and rapid jumps in the positive and negative directions. For example, a comparison of signals may indicate that an increase in the power level should be made from a weighting coefficient of 63 to 79 due to an increased load, but in the incremental control scheme described here, this is not the new set power level that will subsequently be applied (i.e., in the next drive cycle). In contrast, only an incremental increase to 64 is applied. For example, at a drive frequency of 145 Hz, by determining the value of a physical variable indicating the current flowing through the motor in each cycle, the adjustment from the highest duty cycle (127) to the lowest duty cycle (0) still takes less than 1 second (i.e., about 0.9 seconds), and from 63 to 79 takes 0.11 seconds. This, of course, does not preclude adjustments from being made non-incrementally, for example, that a new set power level to be applied is made in each period determined to immediately compensate for the difference in the applied load.

[0035] Furthermore, if the comparison between the determined signal and the target signal results in a difference less than the absolute threshold difference, subsequent power level adjustments may not be applied. This effectively avoids adjustment jitter and / or can lead to more stable behavior as already mentioned. This, in turn, means that nothing is changed, and the new set power level remains the set power level.

[0036] As previously mentioned, a one-step change in power level may be used instead of an incremental change. If the measured voltage is not on the target curve for the intended amplitude, the PWMW may be modified as described below. It is clear that the measured value lies on a linear curve having the same origin as the target curve, and therefore the slope with respect to the currently measured voltage for an unknown amplitude can be easily determined based on the known currently set power level / PWMW and the corresponding measured value, as well as the known value of the target curve at PWMW=0 (value B in the above equation). The slope of this curve may be denoted as A'. By vertical projection of the currently measured voltage value at the measured voltage on the PWMW graph onto the target curve along a line rotated 90 degrees, i.e., a line with a slope of A''=-1 / A', the intersection between the rotated line and the target curve defines the new set power level.

[0037] Although this disclosure focuses on linear vibration or oscillating motors (or resonant motors), the motor control proposed herein is independent of specific motor types and can operate with all types of motors that can be driven by applying an electrically rectified DC voltage to the motor, such as all types of brushless DC motors or permanent magnet synchronous motors.

[0038] Figure 1 is a schematic diagram showing some elements of an exemplary motor unit 100 according to the present disclosure. Some elements shown in Figure 1 are optional as described. The motor unit 100 comprises a motor 101, a motor control unit 110 having a supply circuit 120 including an H-bridge, and a measurement circuit 130. The motor 101 is shown here as being represented by resistance, inductance, and voltage source. As is commonly known in the art of electronic rectification, the motor 101 is here located in the bridge section of an H-bridge having four controllable switches 121, 122, 123, and 124. The H-bridge can be controlled to apply a DC voltage Vdd to the motor 101, and the polarity of the applied DC voltage depends on which of the controllable switches is closed. When switches 121 and 124 are closed, providing a current path, and switches 122 and 123 are open, a DC voltage is applied to the motor 101 in positive polarity. When switches 122 and 123 are closed and switches 121 and 124 are open, a DC voltage is applied in negative polarity. Switches 121, 122, 123, and 124 can be implemented by MOSFETs, as is common in the art. For this reason, a diode may be placed in parallel with each MOSFET, as shown in Figure 1. Switches 121, 122, 123, and 124 are controlled by the controller 140 as indicated by four control signals S1, S2, S3, and S4, which can be output by the controller 140. The four control signals S1, S2, S3, and S4 are used to control switches 121, 122, 123, and 124, respectively; that is, to control the point in time when the switches are closed, allowing current to flow through the resistors of each switch, and when the switches are opened, interrupting the current through the resistors of each switch.

[0039] The exemplary measurement circuit 130 shown in Figure 1 comprises an RC low-pass filter 131 having a capacitor 1311 and a resistor 1312, a pull-up resistor 132, and an analog-to-digital converter (ADC) 133, all of which are configured to determine the value of a physical parameter representing the reverse electromagnetic force of the motor 101, which in this case is voltage. The RC low-pass filter 131 is connected to the positive terminal of the motor 101. The pull-up resistor 132 has one end connected to a reference voltage, which in this case is a DC voltage Vdd that may be provided by a battery or accumulator, and functions to stabilize the voltage provided by the RC low-pass filter 131 and pull it up to a value optimized for supplying to the ADC 133. The ADC 133 is used here to convert the analog voltage signal to a digital signal and may be configured to sample the voltage value at least within the measurement portion during the braking time interval in which the motor 101 is dynamically braked, as will be described in more detail below. For completeness, it should be noted that the ADC 133 may be part of the hardware components that make up the processor 140, and for example, the ADC 133 and the processor 140 may be implemented together by a microprocessor. The RC low-pass filter 131 and the pull-up resistor 132 are optional components, and the voltage across the switch 123 may be supplied directly to the measurement circuit 130, for example, directly to the ADC 133 or any other component that can convert and / or compare the voltage signal.

[0040] Dynamic braking is achieved, for example, by closing switches 123 and 124 and leaving switches 121 and 122 open, thereby effectively short-circuiting the motor 101 through the resistances of switches 123 and 124. During such a dynamic braking phase, the kinetic energy of the motor 101 is converted into electrical energy. The current flowing through the motor 101 at the start of the braking time interval is recirculated through the motor 101 via the current path provided by switches 123 and 124, and the current is dissipated in the resistances of switches 123 and 124 as well as the motor resistance. In contrast to regenerative braking, where motor current is supplied to return to the battery, the current drop is slower in dynamic braking, making dynamic braking more energetically efficient than regenerative braking.

[0041] Figures 2A and 2C show the effective circuit configuration of the motor unit 100 shown in Figure 1, divided into the positive half-cycle of motor drive when a voltage pulse is applied (Figure 2A), the braking time interval (Figure 2B), and the negative half-cycle of motor drive when a voltage pulse is applied (Figure 2C). For simplification, the controller 140 is not shown in Figures 2A and 2C, but it should be understood that the controller 140 is, of course, there to control the H-bridge so that the effective circuit structure shown is generated.

[0042] In Figure 2A, switches 121 and 124 are closed and essentially function as resistors, while switches 122 and 123 are open and do not contribute to an effective circuit structure, and are therefore not shown. In this phase, a DC voltage Vdd is supplied to the positive terminal of the motor 101. As already described, the DC voltage Vdd may be applied to the motor at a PWM frequency higher than the drive frequency, and Figure 2A naturally applies only to the on-period of voltage pulse application. The supply of a DC voltage Vdd with positive polarity may be maintained over a first period which may be interrupted by a dynamic braking time interval. Figure 2C shows the circuit structure when the DC voltage is supplied to the motor with the opposite polarity (i.e., negative polarity), with switches 122 and 123 closed and switches 121 and 124 open. The supply of a DC voltage Vdd with negative polarity may be maintained over a second period (in this case as well, the DC voltage Vdd may be applied in pulses), and this second period is preferably the same length as the first period. The provision of positive and negative DC voltages may be repeated periodically (at the drive frequency). The period of this periodic function is given by the sum of the first and second periods. For example, the period may be 6.8966 ms, in other words, the motor is driven at a drive frequency of 145 Hz for this reason. This is merely an example, and it should be understood that in general, any other drive frequency such as 0.5 Hz, 2 Hz, 7 Hz, 13.4 Hz, 29 Hz, 52 Hz, 84 Hz, 112 Hz, 140 Hz, 141 Hz, 142 Hz, 143 Hz, 144 Hz, 146 Hz, 147 Hz, 148 Hz, 149 Hz, 150 Hz, 184 Hz, 250 Hz, 400 Hz may be used.

[0043] Figure 2B shows the circuit configuration during the dynamic braking time interval, with switches 123 and 124 closed and switches 121 and 122 open. The same circuit configuration is typically also effective during the "off" phase of PWM voltage pulse application, but only for a short time. The dynamic braking interval is typically longer than the period for applying a single voltage pulse, and may span, for example, the time interval for applying at least two or more DC voltage pulses. As will be described in more detail below, it is preferable to apply the shortest possible braking time interval so as to minimize the effect on the shape of the current flowing through the motor 101. The motor 101 is short-circuited via switches 123 and 124, and the motor current I M The current is recirculated through the motor 101 and the resistors of switches 123 and 124, and the kinetic energy of the motor 101 is converted into electrical energy. The measurement circuit 130 is configured to measure the value of a physical variable indicating the current flowing through the motor 101 only during a dynamic braking time interval, preferably only within a measurement portion of a braking time interval shorter than the braking time interval itself. That is, the measurement portion does not have to start at the moment the braking time interval begins, but may start later, and / or does not end when the braking time interval ends, but may end earlier. The measurement may be performed at a single moment, or several measurements may be performed within the measurement portion. The signal measured according to the setup shown in Figures 1 and 2B is the voltage drop V across the resistor of switch 123. M This is the same voltage that can be measured across the resistances of motor 101 and switch 124, and therefore, this voltage indicates the reverse electromagnetic force induced in the motor coil due to the motion of the permanent magnet. This example does not preclude the possibility that the signal indicating the reverse electromagnetic force is a voltage that can be measured between the positive and negative terminals of motor 101, or that the current actually flowing through motor 101 is measured as a physical variable.

[0044] The DC voltage Vdd may also be supplied to the motor 101 by pulse width modulation (PWM), as already shown, i.e., the H-bridge may be controlled to intermittently supply the DC voltage Vdd during first and second periods at a PWM frequency higher than the drive frequency. For example, if the drive frequency is about 145 Hz, the frequency at which the DC voltage Vdd is supplied by the PWM control pulse may be about 37.12 kHz, meaning that 256 DC voltage pulses are applied periodically and 128 voltage pulses are applied every half-period, i.e., during a positive or negative half-period (the terms period and cycle are used interchangeably herein). As a braking time interval is proposed according to this disclosure, the number of pulses applied every half-period may, of course, be less than 128 (in the given example). The voltage signal applied by PWM may have a pulse-varying length. For example, the voltage signal may have low on-times at the beginning and end of a half-cycle and a high on-time in the middle of the half-cycle, so that the shape of the current driven through the motor can be controlled (the sum of the on- and off-times for each applied pulse is typically constant and, of course, determined by the PWM frequency, e.g., 37.12 kHz in this embodiment). In some examples, the PWM can apply voltage pulses such that a sinusoidal current is nearly achieved. During the off-time following each on-time, the H-bridge can be controlled to switch to a circuit configuration such as that shown in Figure 2B for dynamic braking of the motor, as already shown. For clarity, any other current shape other than sinusoidal, e.g., trapezoidal, triangular, rectangular, etc., may be similarly intended, where it is understood that the current is a periodic function according to the drive frequency.

[0045] Figure 3 shows the measured voltage V as a physical variable value indicating the current flowing through the motor for different constant inverse EMF values ​​with respect to the PWM weight PWMW. Measure This is the figure. As derived in the previous paragraph, the measured voltage is V Measure =-R S ·PWMW·(V BATT -V BEMF ) / √(R 2 +RX 2 ) or, more generally, under the assumption discussed, V Measure It can be expressed as =-A·PWMW+B. In Figure 3, the offset value was assumed to be B=0, but please understand that the offset B may have a non-zero value due to the pull-up resistors that may be used or due to other circuit specifications. Curve 200 represents a moderate inverse EMF value (e.g., V BEMF Curve 201 shows the measured voltage for a lower inverse EMF value (e.g., V = 0.5 volts), and curve 201 shows the measured voltage for a lower inverse EMF value (e.g., V BEMF Curve 202 shows the measured voltage for <0.5 volts, and for higher inverse EMF values ​​(e.g., V BEMFThe measured voltage is shown for >0.5 volts. As already explained, a given inverse EMF value is related to a given amplitude. Thus, curve 200 can be related to the peak amplitude value of a given linear reciprocating motor of, for example, 0.8 mm and can represent the target curve. If the measured voltage is not on the target curve 200 (PWMW is known by the system and represents the set power level), the motor control unit takes measures to change PWMW so that, ideally, the measured voltage in the next measurement will be at least closer to the target curve. It is clear that the space between curves 201 and 202 is filled with curves, each related to one inverse EMF value, and therefore one motor amplitude. Thus, it can be understood that all points between these curves can be assigned to inverse EMF values, and therefore motor amplitudes. In order to produce the intended amplitude under no-load conditions, a specific power level needs to be provided in the motor, and this power level is shown as P1, such that the voltage V1 is measured and each point 203 on the target line 200 is shown. If the load increases here, the measured voltage decreases. For example, at a given load value, the measured voltage decreases to V2, and since PWMW is still P1, each point in the figure is 204. Here, the concept is to increase PWMW to another obviously higher value so that the measured voltage is again on the target line 200. A more detailed description of exemplary adaptive process steps is provided below in relation to Figures 7A and 7B. However, it can be said here that the P and V values ​​for various amplitude and load values ​​are determined so that, for example by two-dimensional interpolation, it is possible to determine which amplitude and load values ​​the currently determined P / V combination corresponds to, and what P value is required to reach the intended target line under the current load conditions.

[0046] Figure 4 shows the current signal 210 flowing through the motor and the voltage signal 211 that can be measured over a time interval of approximately 1.5 cycles by the measurement circuit 130 shown in Figure 1. These signals represent actual measured values, and the measurement circuit includes an RC filter circuit as shown in Figure 1, but note that, as already mentioned, the RC filter is an optional circuit element. The RC filter does not drop the voltage pulse to 0 and does not raise it to Vdd. The braking time interval T during which the motor is dynamically braked. B1 This is shown. Negative voltage cannot be measured by the measurement circuit 130, and therefore there is no negative voltage visible during the negative polarity phase. Since the voltage signal 211 essentially shows a pulse and the current signal 210 shows a ripple associated with the application of the voltage pulse, it can be seen that signals 210 and 211 reflect the application of DC voltage by PWM. The current signal 210 has a damping time interval T B1 During this period, there is a significant decrease, which can be seen as a notable deviation from the sinusoidal waveform of the current flowing through the motor. The reactivation phase occurs during the braking period T. B1 Following this, energy is supplied to the system until the current signal 210 returns to approximately a sinusoidal curve. Damping time interval T B1 The longer the damping time interval T, the more strongly the current signal 210 deviates from the sinusoidal curve. The voltage signal 211 also deviates from the damping time interval T. B1 It decreases after the start. The value of the physical parameter indicating the current flowing through the motor, i.e., the measured voltage in the example described here, is the braking time interval T. B1 Measurement part T M1 Measurements may be taken inside, measuring part T M1 The braking time interval T is B1 It may be smaller. The measured voltage is the braking time interval T. B1 The determination may be made at any given moment within, or the measured voltage may be measured in part T. M1 The determination may be made by averaging several sampled voltage values ​​or by combining them in other ways.

[0047] Figure 5, similar to Figure 4, shows the current signal 220 and voltage signal 221 for a time interval with a length of approximately 3 periods. Each positive half-period has a length T B2The braking time interval T is shown. B2 The braking time interval T shown in Figure 4 is shown here. B1 It is smaller than that. Due to the shorter braking interval, the distortion of the current signal 211 is less pronounced than the distortion of the current signal 201 shown in Figure 4. A shorter braking interval results in more energy-efficient motor control because less energy is dissipated during the braking interval. Furthermore, the intended current shape is not distorted as much. A sinusoidal current has less prominent harmonics, which can lead to a fairly quiet overall motor design. The greater the distortion, the stronger the harmonics, which can increase motor noise. Overall, shortening the braking interval is prudent, but this must be balanced with the accuracy of measuring the values ​​of the physical parameters that indicate the current flowing through the motor. The length of the braking interval shown in Figure 5 is about 5% of the length of the drive period. In general, the length of the braking interval should not be limited, but the braking interval may have a length of about 20% or less of the period, preferably about 15% or less, more preferably about 10% or less, even more preferably about 5% or less, for example, less than 3%. This does not preclude the possibility of varying the length of the braking time interval over time. The braking time interval may also be used to support other aspects of motor control. For example, a motor control unit may be configured to increase the braking time interval when the signal indicates a high load on the motor that exceeds a threshold. Such a high load will ultimately lead to a significant increase in the on-time of the PWM voltage pulse, applying more energy to the motor to overcome the high load and maintain a constant amplitude. However, the sudden release of the load may then lead to a sudden over-current of the motor when no load is applied, which can cause problems with the motor. Therefore, a motor control unit may be configured to increase the braking time interval at higher loads that exceed the threshold load in order to actually brake the motor. Another solution may be to not provide power levels that exceed a certain power level threshold.

[0048] Figures 6A–6C show magnified simulated voltage signals within and around the braking time interval for three different inverse EMF values. The simulation was performed without the RC filter shown in Figure 1. Without the RC filter, the voltage signal drops immediately at the start of the braking time interval. Figure 6A shows voltage curve 231 for a given inverse EMF value, e.g., 1.5 volts; Figure 6B shows voltage curve 241 for a higher inverse EMF value, e.g., 2.5 volts; and Figure 6C shows voltage curve 251 for a lower inverse EMF value, e.g., 0.5 volts. In all three Figures 6A–6C, three measurement points 232, 233, 234 and 232, 243, 244 and 252, 253, 254 are shown, and in each case these measurement points occur at three identical moments t0, t1, and t2 after the start of the braking time interval. The measurement time is assumed to be constant; that is, if t0 is selected as the measurement time, the voltage signal is always assumed to be measured at t0. Again, we assume that Figure 6A shows the voltage curve when the target amplitude is achieved. Then Figure 6B shows a lower load condition, and Figure 6C shows a higher load condition. Figures 6B and 6C show the respective voltage values ​​of the target voltage curve shown in Figure 6A. Figures 6A to 6C demonstrate that where in the damping time interval the voltage is measured is actually irrelevant, since the voltage values ​​behave similarly at regular intervals but have different offsets.

[0049] Figure 7A is a depiction of the target line 401 for a measured voltage signal S that depends on the currently delivered power level P. The target line 401 represents a line for one given inverse EMF value or motor amplitude that depends on PWMW, i.e., a line for different load conditions because increasing the load requires increasing the set power level to maintain the amplitude. For example, dot D01 represents the voltage signal S01 measured in a situation with no external load where power level P01 is supplied to the motor to achieve the motor amplitude. If the load increases, a higher power level needs to be supplied to the motor in order to still achieve the same motor amplitude. For example, in a first load situation associated with a first non-zero external load, power level P02 is supplied to the motor and signal S02 is measured, while at a second increased load level, power level P03 needs to be supplied to achieve the intended motor amplitude and signal S03 is measured. As described, the target curve can be assumed to be linear, and each curve can be made available simply by memorizing its absolute value and gradient.

[0050] As already explained with reference to Figure 3, the measured voltage signal changes when the load changes. When the current load is 0, a load change can only mean an increase in load, and since PWMW remains the same, the measured voltage signal decreases as the increased load reduces the amplitude and therefore the BEMF decreases. PWMW then needs to be increased to compensate for the decrease in amplitude so that the amplitude is maintained and the measured voltage value is again on the target line. During operation, when a load is applied, the applied load may decrease or increase, and therefore the measured voltage signal may also increase or decrease. As a result, if the load decreases, PWMW needs to be decreased, or if the load increases, PWMW needs to be increased. The motor control unit may be configured to set a new power level that fully compensates for the changed load, so that the next measurement is ideally on the target curve.

[0051] Instead of directly adjusting the set power level so that the intended motor amplitude is theoretically achieved in the next cycle (which may not be achievable in any way due to the inertia of the actual motor system), an incremental approach may be chosen, as already mentioned, which will be illustrated with reference to Figure 7B. In Figure 7B, the currently applied power level P is again plotted on the horizontal axis, and the measured voltage signal S is plotted on the vertical axis. The target curve 411 represents the target line for the intended motor amplitude. The dots Dn1 schematically represent the known P value (currently set power level Pn1) and the determined S value (measured voltage signal Sn1), respectively. As explained, the currently applied power level Pn1 may relate to the weighting coefficients of the 69 normalized voltage pulse duty cycle (this is, of course, merely an example used for illustrative purposes only). Any dot above the target line 411 is known to relate to a motor amplitude that is too high, i.e., the currently provided power level Pn1 is too high. Instead of significantly reducing the currently applied power level to hit the target line 411 in the next cycle, a new set power level is increased incrementally. For example, the new set power level may be associated with a weighting coefficient of 68 in a later cycle, which in turn may result in a dot Dn2 associated with power level Pn2 and signal Sn2 in the next cycle. Of course, the load conditions may change from cycle to cycle, but here we will assume that the load conditions are constant. As expected, dot Dn2 is closer to the target curve, but indicates that the new set power level Pn2 is still too high. In the next period, a subsequent power level Pn3 associated with a weighting coefficient of 67 is thus applied, resulting in a dot Dn3 associated with power level Pn3 and signal Sn3, which is still too high, so the new set power level is lowered again to Pn4 associated with a weighting coefficient of 66, which in turn leads to dot D04. The final incremental adjustment in this example then results in a dot D05 that is very close to the target line 411. In Figure 7B, the two tolerance or hysteresis lines 412 and 413 are shown as dashed lines.To avoid adjustment jitter, the adjustment procedure may be stopped if the P and S value dots are within the band indicated by these tolerance lines 412 and 413. In this example, the complete adjustment procedure from Dn1 to Dn5 required four adjustment steps. Of course, this is just a schematic example, but four adjustment steps at a drive frequency of 150 Hz require less than 3 ms.

[0052] As described above, the user can change the load conditions fairly quickly, and as a result of adjustments made after determining dot Dn1, dot Dn6 may be determined instead of the expected Dn2. However, this is not a problem for the adjustment procedure. Dot Dn6 is obviously related to a set power level Pn2 (weighting coefficient 68) that, under a given load condition, leads to a motor amplitude that is too low, as implied by the signal value Sn6; i.e., the motor amplitude currently achieved is below the intended motor amplitude, and the adjustment procedure subsequently increases the applied power level (again to weighting coefficient 69), and dot Dn7 (by determination of signal Sn7) may be determined in the next cycle, where dot Dn7 is therefore within the band defined by the tolerance or threshold or hysteresis lines 412 and 413 in the shown example, and no further adjustment is made until the next determination of the S value (at the current power level Pn1 related to weighting coefficient 69) is again outside the tolerance band given by lines 412 and 413.

[0053] The objective of the systems and methods proposed herein is to enable the maintenance of an intended motor amplitude, or at least remaining close to an intended motor amplitude, based on the measurement of the value of a physical variable indicating the current flowing through the motor. As previously described, the signal may be sampled at the very beginning of the braking time interval or within the measurement portion of the braking time interval. Whenever sampling is performed within the braking time interval, it has been found to include relevant motor amplitude information, i.e., relevant inverse electromagnetic force information that needs to be extracted.

[0054] Here, it should be noted that individual duty cycle values ​​for the intended current shape (i.e., sinusoidal shape) may be stored in the motor control unit's memory unit, and therefore any increase or decrease as described will similarly affect all duty cycle values ​​by adjusting the weighting coefficient PWMW. This means that an absolute increase / decrease of 0.5% at 50% duty cycle is converted to a relative increase / decrease of 1% across all tabled duty cycle values. In other words, the tabled duty cycle values ​​are scaled according to the currently defined increase or decrease values.

[0055] Figure 8 shows an exemplary motor 500 that may be used in a motor unit such as the one proposed in this application. The motor 500 comprises a stator 510 having a coil 511 and an armature 520 having at least one permanent magnet 521, although in the illustrated example two permanent magnets 521 are used, and the coil 511 is wound around an E-shaped stator core. A drive shaft 530 is fixed to the armature 520. The stator 510 is fixedly mounted to a motor carrier 540, and the armature 520 is attached to the motor carrier 540 by an armature mounting spring 528.

[0056] During operation, an electronically rectified DC current is applied to coil 511 so that current is driven through coil 511. In this disclosure, the current through coil 511 in the illustrated example is referred to as the motor current. The flow of current generates an electromagnetic field that interacts with the permanent magnet 521. When the current is driven through coil 511 in a first direction, the electromagnetic force acting on the permanent magnet 521 deflects the armature 520 in one direction, and when the direction of current flow is reversed, the armature 520 is deflected in the opposite direction, as indicated by the double arrow M. When a DC voltage is applied to coil 511 such that the polarity of the DC voltage changes periodically, the armature 520 is driven into a periodic linear reciprocating motion. Since the spring-mounted armatures 520, 528 form a spring-mass system, the excitation of the spring-mounted armatures 520, 528 can be characterized by the resonant frequency that yields the maximum deflection amplitude. A motor 500, as shown in Figure 7, can typically be driven at a drive frequency of a period DC voltage that is at or near the resonant frequency.

[0057] In the illustrated embodiment, a so-called dynamic vibration absorber 550 is attached to the motor carrier 540 to compensate for vibrations of the motor carrier 540 caused by the periodic driving of the armature 520. According to Newton's third law (an action is equal to the conservation of reaction or impulse in a closed system), the impulse of the driven armature 520 must be compensated for by the reverse impulse of the motor carrier / stator unit. The reverse impulse of the motor carrier / stator unit results in vibration of the handle of the device in which the motor is located, unless the motor is completely mechanically disconnected from the handle. Handle vibration is detrimental to the positive user experience during the operation of the device, and therefore, measures that may take the form of a dynamic vibration absorber are taken to at least reduce such vibrations. The dynamic vibration absorber 550 comprises a mass body 551 and a mounting spring 558. To optimally compensate for the vibration of the motor carrier 540, the resonant frequency of the dynamic vibration absorber is tuned to the driving frequency (or the driving frequency is set to be as close as possible to the resonant frequency of the dynamic vibration absorber). It is understood that the dynamic vibration absorber 550 is an optional feature.

[0058] The resonant vibration motor 500 shown is merely one example of a motor that may be used in the motor unit described herein; it should be noted that, for example, any brushless DC motor may be used in the same manner.

[0059] As described above, in the motor 500 described with reference to Figure 8, the drive frequency is governed by the resonant frequency of the dynamic vibration absorber and not by the resonant frequencies of the spring-mounted armatures 520 and 528. The resonant frequencies of the spring-mounted armatures 520 and 528 may mean that in a series of motors 500, there is a fluctuating spread of the drive frequency and resonant frequency of the spring-mounted armature, and it is known that such a difference affects the phase difference between the motion of the armature, and therefore the motion of the inverse electromagnetic force and the excitation force, i.e., the motion of the drive function. Under some conditions, it has been found that the linear calibration of the target curve between the currently applied power level and the determined signal as described herein may no longer adequately describe the system. In such cases, a nonlinear target curve (e.g., a quadratic target curve) may be applied, and / or the position of the damping time interval within each half-cycle may be adjusted to approach the maximum value of the inverse electromagnetic force. This position can be determined by simulation or experiment of the system. Similarly, when a motor is used to drive different interchangeable head parts of a personal care device, and the inertia of the driveable head parts changes, it was found that the calibration of the target curve may be effective for all such interchangeable head parts, and that individual target curves should be used for different driveable head parts.

[0060] Figure 9 shows an exemplary personal care device 600, which is implemented here as an electric toothbrush. The personal care device 600 comprises a handpiece 610 and a head 620 for applying care procedures such as brushing teeth. A motor unit housed within the handpiece 610 is configured to drive and move a movable head 621. During operation, the movable head 621 is pressed against a body part, and thus a load is applied to the motor of the motor unit. As already described, such a load may lead to a reduction in the deflection amplitude of the movable head 621, and as described, the motor unit can measure the applied load and apply a suitable amount of energy to the motor to essentially maintain a constant deflection amplitude. This does not preclude the idea that a complete head 620 realizes the movable head 621.

[0061] Figure 10 is a diagram illustrating a method for controlling a motor unit, such as a motor unit for a personal care device, which has multiple steps.

[0062] In step 700, a motor is provided having a stator and an armature configured to drive relative to the stator. In step 701, a set power level is supplied to the motor to drive the armature into motion. The supply voltage to the motor can be supplied using pulse width modulation. In step 702, the motor is dynamically braked during a braking time interval. In step 703, a value of a physical variable indicating the current flowing through the motor is measured during the braking time interval. In step 704, the value of the physical variable is compared to a target value, which depends on the set power level and the intended amplitude of the armature's motion. In step 705, a new set power level is determined according to the comparison result. Then, in step 706, after the end of the dynamic braking period, the new set power level is supplied to the motor. The method is then repeated starting from step 702 until the loop is interrupted, for example, until the device on which the method is used is switched off.

[0063] This method may include a step of calibrating the target value by assuming a linear relationship between the set power level at a constant amplitude of the armature and the measured value of the physical variable.

[0064] The dimensions and values ​​disclosed herein should not be understood as being strictly limited to the exact numerical values ​​listed. Instead, unless otherwise indicated, each such dimension is intended to mean both the listed value and the functionally equivalent range encompassing that value. For example, a dimension disclosed as "40 mm" is intended to mean "approximately 40 mm."

Claims

1. It is a personal care device, Personal care head and The personal care head is provided with a motor unit for driving the personal care head, The motor unit is A motor having a stator and an armature, wherein the armature is configured to perform relative driving motion with respect to the stator, A motor control unit, A supply circuit provides a supply voltage for driving and moving the armature by pulse-width modulating (PWM) a DC voltage according to a set power level, A measurement circuit for measuring the value of a physical variable indicating the current flowing through the motor, A motor control unit having, The motor control unit is configured to interrupt the supply of the supply voltage by the supply circuit, dynamically brake the motor during the braking time interval, and further measure the value of the physical variable indicating the current flowing through the motor during the braking time interval. The motor control unit is further configured to compare the measured value of the physical variable indicating the current flowing through the motor with a target value, the target value of which depends on the set power level and the intended amplitude of motion of the armature, determine a new set power level based on the comparison result, and then supply the motor with the DC voltage pulse-width modulated according to the new set power level. The motor control unit is configured to modify the target value depending on the newly set power level, The motor control unit is configured to periodically control the supply of the supply voltage, and the supply voltage is supplied with a periodically changing polarity. The motor control unit is configured such that it does not change to the new set power level if the measured value of the physical variable is within a predetermined tolerance band with respect to the target value, and changes to the new set power level if it is outside the tolerance band. Personal care device.

2. The personal care device according to claim 1, wherein the motor control unit is configured to set the new set power level higher than the previous set power level when the comparison result indicates that the load of the motor has increased, and to set the new set power level lower than the previous set power level when the comparison result indicates that the load of the motor has decreased.

3. The personal care device according to claim 1 or 2, wherein the motor control unit is configured to gradually increase or decrease the new set power level relative to the set power level.

4. The personal care device according to claim 1, wherein the motor control unit is configured to set the new set power level to the set power level when the comparison result indicates that the change in the motor load is below a threshold.

5. The personal care device according to claim 1, wherein the motor control unit is configured to measure the value of the physical variable in a fixed time instance within the braking time interval.

6. The personal care device according to claim 1, wherein the motor control unit is configured to repeatedly measure the value of the physical variable and determine a new set power level, and the previous new set power level becomes the set power level.

7. The personal care device according to claim 1, wherein the motor control unit is configured to set the new set power level such that changes in the load applied to the motor are at least partially compensated, and the amplitude of the armature resulting from the new set power level is closer to the intended amplitude of the armature than the set power level.

8. The personal care device according to claim 1, wherein the measurement circuit comprises at least one pull-up resistor or pull-down resistor.

9. The personal care device according to claim 1, wherein the motor control unit is configured to control the measurement circuit to sample the current or voltage signal of the motor at multiple points in time within the braking time interval, and to determine the value of the physical variable by averaging the multiple sampled signals or combining the multiple sampled signals.

10. The personal care device according to claim 1, wherein the motor control unit is configured to control the supply circuit such that the supply voltage is supplied to the motor by a pulse width modulated signal, and the frequency of the pulse width modulated signal is higher than the frequency of the periodic supply of the supply voltage.

11. A method for controlling a motor unit of a personal care device comprising a personal care head and a motor unit, The motor unit comprises a motor having a stator and an armature, wherein the armature is configured to perform relative driving motion with respect to the stator, and a motor control unit. The motor control unit, The steps include providing a supply voltage for driving and moving the armature by pulse-width modulating (PWM) a DC voltage according to a set power level, The steps include dynamically braking the motor during the braking time interval, The steps include measuring the value of a physical variable indicating the current flowing through the motor within the braking time interval, The step of comparing the value of the physical variable indicating the current flowing through the motor with a target value, the target value of which depends on the set power level and the intended amplitude of the motion of the armature, The steps include determining a new set power level according to the comparison results, Subsequently, the step of providing the motor with the supply voltage obtained by pulse width modulation of the DC voltage according to the newly set power level is performed. The motor control unit is configured to modify the target value depending on the newly set power level, The motor control unit is configured to periodically control the supply of the supply voltage, and the supply voltage is supplied with a periodically changing polarity. A method wherein the motor control unit is configured not to change to the new set power level if the measured value of the physical variable is within a predetermined tolerance band with respect to the target value, and to change to the new set power level if it is outside the tolerance band.

12. The method according to claim 11, further comprising the step of calibrating the target value by assuming a linear relationship between the set power level at a constant amplitude of the armature and the measured value of the physical variable.

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