Piezoelectric stick-slip motor and control method thereof

Abstract

The invention relates to a piezoelectric stick-slip motor and a method for controlling the same. In order to enable a variation of the speed of a piezoelectric stick-slip motor with reduced noise generation, the invention provides a method for controlling a piezoelectric stick-slip motor according to claim 1, the method comprising the following steps: Step A: applying to the motor a periodic sawtooth waveform drive voltage signal with a constant frequency, wherein the drive voltage (V) is increasing towards a peak voltage (Vp) and decreasing from the peak voltage (Vp), for the motor to run at a constant speed; Step B: while keeping the frequency of the drive voltage signal constant, varying the speed of the motor by gradually increasing or decreasing the gradient (dV / dt) of the drive voltage (V) increasing towards the peak voltage (Vp) with each subsequent sawtooth waveform drive voltage signal cycle (C).

Description

Technical Field

[0001] This invention relates to a piezoelectric stick-slip motor and its control method. Background Technology

[0002] For example, piezoelectric stick-slip motors are known from US 2015 / 0076965, WO 2018 / 134637 A1 or EP 3 120 449 B1.

[0003] In the case of a piezoelectric stick-slip motor drive, the piezoelectric actuator element is charged with a periodic voltage, particularly a high-frequency sawtooth voltage. The high-frequency expansion and contraction of the voltage-affected actuator element is transmitted to the friction body via friction elements arranged on the actuator element, causing the friction body to move during the deflection of the actuator element in the stick phase (where there is static friction between the friction elements and the friction body), while in the sliding phase, there is sliding friction between the friction elements and the friction body, so that the friction body is not driven by the movement of the friction elements, or is driven only to a small extent.

[0004] During the bonding phase, the acceleration or velocity of the actuator element is configured such that, due to the forces acting in the frictional contact between the friction element and the friction body, no sliding friction or only negligible sliding friction occurs, thus the friction body is driven by the friction element under all circumstances. Conversely, during the sliding phase, the acceleration or velocity of the actuator element is so high that the forces in the frictional contact between the friction element and the friction body are insufficient to drive the friction body, and due to the inertia of the friction body, relative movement (i.e., sliding) occurs between the friction element and the friction body.

[0005] As attached to this article Figure 1 The voltage distribution over time illustrates two cycles of a typical periodic stick-slip drive signal according to the prior art, where stage 1 represents the movement or sticking phase, stage 2 represents the pause after movement, stage 3 represents the sliding phase, and stage 4 represents the pause after sliding. Vb is the base voltage, Vp is the peak voltage, and dV / dt is the gradient of the drive voltage from the base voltage Vb to the peak voltage Vp during stage 1 of period C.

[0006] Phase 3 (“sliding phase”) needs to be as short as possible (typically <2 μs), and phases 2 and 4 (“pause after movement” and “pause after sliding”) are typically between 3 and 10 μs. Pauses that are too short or too long will negatively impact motor efficiency, resulting in a slight decrease in speed.

[0007] The effective speed of the motor is mainly determined by the frequency and peak voltage of the signal. Since phase 2 ("pause after movement"), phase 3 ("sliding phase"), and phase 4 ("pause after sliding phase") are relatively stable, the frequency of the signal is mainly determined by the duration of the movement phase.

[0008] In a typical stick-slip controller, the peak voltage Vp remains stable and the motor speed is controlled by the frequency of the signal. Thus, during acceleration, deceleration, and low-speed periods, the piezoelectric motor must operate at a low and audible frequency. This results in a stick-slip motor and consequently, audible noise from the motion device. In a closed-loop circuit, this noise is particularly disturbing to the user because the servo circuit continuously changes its frequency to compensate for varying tracking errors.

[0009] Some controllers attempt to avoid noise generation by operating only at high frequencies (typically 20kHz). The main limitation of this approach is that acceleration, deceleration, or low speeds are not permitted. However, when operating in a closed-loop circuit, the frequency must still be changed, and this frequency modulation can still generate interfering noise. Summary of the Invention

[0010] The purpose of this invention is to reduce noise generation during speed changes in piezoelectric stick-slip motors.

[0011] The objective of this invention is achieved by the method of claim 1. The dependent claims are the preferred embodiments to be protected.

[0012] The method for controlling a piezoelectric stick-slip motor according to claim 1 includes the following steps:

[0013] Step A: Apply a periodic sawtooth waveform drive voltage signal with a stable frequency to the motor, wherein the drive voltage increases towards a peak voltage and decreases from the peak voltage, for operating the motor at a stable speed;

[0014] Step B: While keeping the frequency of the drive voltage signal stable, the speed of the motor is changed by gradually increasing or decreasing the gradient of the drive voltage towards the peak voltage with each subsequent sawtooth waveform drive voltage signal period.

[0015] Using this motor control, the speed variation of the piezoelectric stick-slip motor can be achieved without generating significant noise, since the frequency of the drive voltage signal remains stable and only the gradient of the drive signal voltage ramping up to the peak voltage changes.

[0016] It is advantageous if the period of each sawtooth waveform driving voltage signal in step A includes the following stages:

[0017] - The first stage represents the pasting (moving) stage, in which the driving voltage increases from the base voltage to the peak voltage.

[0018] - The second stage represents a pause after the first stage, wherein the drive voltage is maintained at the peak voltage.

[0019] - The third stage represents the sliding stage, wherein the driving voltage decreases from the peak voltage to the base voltage, wherein preferably the third stage lasts for less than 2 μs, and

[0020] - The fourth stage represents a pause after the third stage, wherein the driving voltage is maintained at the base voltage, and preferably the fourth stage lasts between 3 and 10 μs.

[0021] The period of this drive voltage signal is related to the operation of the piezoelectric stick-slip motor.

[0022] If step B includes gradually increasing or decreasing the peak voltage for each subsequent drive voltage signal cycle, preferably until the peak voltage exceeds the threshold voltage level for starting or stopping the motor respectively, the operating performance of the piezoelectric stick-slip motor can be improved. By gradually decreasing the gradient of the drive voltage increase towards the peak voltage with each subsequent sawtooth waveform drive voltage signal cycle, the motor can smoothly decelerate and stop. By gradually increasing the gradient of the drive voltage increase towards the peak voltage with each subsequent sawtooth waveform drive voltage signal cycle, the motor can smoothly start and accelerate.

[0023] If the method of protection includes maintaining a stable increasing and / or decreasing gradient of the driving voltage between the base voltage and the peak voltage during each driving voltage signal cycle in step A and / or step B, the operating performance of the piezoelectric stick-slip motor can also be enhanced.

[0024] If, in order to reduce the motor speed, step B includes at least one of the following sub-steps, compared to step A, to change the sawtooth waveform drive voltage signal, the operating performance of the piezoelectric stick-slip motor can be further improved:

[0025] Sub-step B1: While maintaining the peak voltage stable, gradually reduce the gradient of the driving voltage to the peak voltage with each subsequent sawtooth waveform driving voltage signal cycle, so as to prolong the first stage, while shortening the second stage by the same amount to compensate for the prolongation of the first stage.

[0026] Sub-step B2: With each subsequent sawtooth waveform drive voltage signal cycle, gradually reduce the peak voltage and the gradient of the drive voltage increasing towards the peak voltage, so as to prolong the first stage, while eliminating the second stage and shortening the third stage to compensate for the prolongation of the first stage.

[0027] In step B1, the gradient of the driving voltage to the peak voltage is reduced by extending stage 1 without decreasing the peak voltage, wherein the extension of stage 1 is compensated by shortening stage 2 by the same amount. In step B2, stage 1 is extended to be longer than the combination of stage 1 and stage 2 in step A, such that stage 2 is completely skipped, and stage 3 follows directly after stage 1.

[0028] If the method of protection includes maintaining a gradient stability of the drive voltage as it decreases from the peak voltage to the base voltage for each subsequent drive voltage signal cycle in step A and / or step B, the operating performance of the piezoelectric stick-slip motor can be further enhanced.

[0029] If the claimed method includes maintaining the stability of the fourth stage time period for each subsequent drive voltage signal cycle in step A and / or step B, the operating performance of the piezoelectric stick-slip motor can be further improved.

[0030] If a periodic sawtooth waveform drive voltage signal with a stable frequency of 20 kHz or higher is applied to the motor, noise generation in the piezoelectric stick-slip motor can be avoided.

[0031] If the method of protection includes maintaining a stable base voltage for each subsequent drive voltage signal cycle in step A and / or step B, the operating performance of the piezoelectric stick-slip motor can be further improved.

[0032] If the required method involves operating the motor in a closed-loop circuit and / or servo circuit, the speed control and position accuracy of the piezoelectric stick-slip motor can be improved.

[0033] If the method of protection required includes adjusting the peak voltage in real time at a servo clock frequency, it can advantageously affect the operating performance of the piezoelectric stick-slip motor.

[0034] Another aspect disclosed herein relates to a piezoelectric stick-slip motor comprising a driven element and a stator having a friction element, a controller, and at least one piezoelectric actuator configured to deform upon application of a drive voltage signal from the controller to apply movement to the friction element thereby driving the driven element through stick-slip contact, wherein the controller is configured to perform the method according to any one of the preceding claims.

[0035] Further preferred embodiments can be obtained by combining the features disclosed in the claims, drawings and specification. Attached Figure Description

[0036] Figure 1 The shape of a typical stick-slip sawtooth waveform drive voltage signal after two consecutive drive voltage signal cycles is shown.

[0037] Figure 2 This is a graph illustrating the relationship between peak voltage and speed. According to the graph, speed is not directly proportional to peak voltage. Below a certain peak voltage value, the motor will stop moving. The relationship between peak voltage and speed cannot be precisely defined.

[0038] Figure 3 The diagram illustrates the shape of a stick-slip sawtooth waveform drive voltage signal according to the claimed invention, wherein stages 3 ("slipping stage") and 4 ("slipping pause") remain relatively stable while stage 2 ("pause after movement") is absorbed by stage 1 ("movement stage"). The loss of stage 2 ("pause after movement") reduces the efficiency of the motor, which increases the reduction in desired speed. Detailed Implementation

[0039] The piezoelectric stick-slip motor according to this application includes a driven element and a stator, the stator having a friction element, a controller, and at least one piezoelectric actuator configured to deform upon application of a drive voltage signal from the controller, thereby applying movement to the friction element and driving the driven element through stick-slip contact. As described below, the controller is configured to perform the method according to any one of the appended claims.

[0040] The proposed protection method is essentially able to change the speed of the piezoelectric stick-slip motor by keeping the motor drive signal at a stable high frequency and changing the peak voltage of the signal, while simultaneously eliminating noise generation.

[0041] The method includes the following steps:

[0042] Step A: Apply a periodic sawtooth waveform drive voltage signal with a stable frequency to the motor, wherein the drive voltage V increases towards the peak voltage Vp and decreases from the peak voltage Vp, so that the motor can run at a stable speed;

[0043] Step B: While keeping the frequency of the drive voltage signal stable, the speed of the motor is changed by gradually increasing or decreasing the gradient dV / dt of the drive voltage V towards the peak voltage Vp according to the period C of each subsequent sawtooth waveform drive voltage signal.

[0044] Preferably, the motor is controlled in a closed-loop circuit, wherein the servo circuit changes the peak voltage in real time at a high resolution at the servo circuit clock frequency.

[0045] During the acceleration of the piezoelectric stick-slip motor, the gradient dV / dt of the driving voltage V increasing towards the peak voltage Vp gradually increases, making it larger in the second driving voltage signal period C than in the first driving voltage signal period C, and larger in the third driving voltage signal period C than in the second driving voltage signal period C.

[0046] During the deceleration of the piezoelectric stick-slip motor, the gradient dV / dt from the driving voltage V to the peak voltage Vp gradually decreases, making it smaller in the second driving voltage signal period C than in the first driving voltage signal period C, and smaller in the third driving voltage signal period C than in the second driving voltage signal period C.

[0047] The following combination Figure 3 Describe the deceleration of a piezoelectric stick-slip motor:

[0048] like Figure 3 The solid line indicates (in) Figure 3 The periodic sawtooth waveform drive voltage signals in steps A and B are superimposed. The period C of the sawtooth waveform drive voltage signal in step A includes:

[0049] - Phase 1 represents the pasting / moving phase, where the driving voltage V increases from the base voltage Vb to the peak voltage Vb.

[0050] - Phase 2 represents the pause following Phase 1, where the drive voltage V remains at the peak voltage Vp.

[0051] - The third stage, 3, represents the sliding stage, in which the driving voltage V decreases from the peak voltage Vp to the base voltage Vb, and

[0052] - Phase 4 indicates the pause after Phase 3, where the driving voltage V is maintained at the base voltage Vb.

[0053] The periodic sawtooth waveform drive voltage signal is typically applied to motor 1 at a stable frequency above 20Hz. In this example, the third phase 3 lasts for less than 2μs, while the fourth phase 4 lasts for between 3 and 10μs.

[0054] To reduce the motor speed, compared to step A, step B specifically includes the following sub-steps: modifying the sawtooth waveform drive voltage signal:

[0055] Sub-step B1: While maintaining the peak voltage Vp stable, gradually reduce the gradient dV / dt of the driving voltage V increasing towards the peak voltage Vp with each subsequent sawtooth waveform driving voltage signal period C, so as to extend the first stage 1, while shortening the second stage 2 by the same amount to compensate for the extension of the first stage 1. Figure 3 As shown by the dashed line, the gradient dV / dt in stage 1 of cycle B is less than the gradient dV / dt in stage 1 of cycle A. The peak voltage VpB1 in the first cycle of step B is the same as the peak voltage VpA in step A.

[0056] Sub-step B2: With each subsequent sawtooth waveform driving voltage signal period C, gradually decrease the peak voltage Vp and the gradient dV / dt from the driving voltage V to the peak voltage Vp, in order to extend the first stage 1, while eliminating the second stage 2 and shortening the third stage 3 to compensate for the extension of the first stage 1. Figure 3 As shown, in step B, the gradient dV / dt and peak voltage VpB2 of phase 1 in the second cycle are less than the gradient dV / dt and peak voltage VpB1 of phase 1 in the first cycle of step B, respectively. Furthermore, with each subsequent sawtooth waveform drive voltage signal cycle C, the gradient dV / dt of phase 1, as well as the peak voltages VpB3, VpB4, and VpB5, gradually decrease until the peak voltage VpB5 (below) the threshold voltage level Vt at which motor 1 stops operating.

[0057] In essence, the peak voltage Vp and the gradient dV / dt from the driving voltage V to the peak voltage Vp vary with the period C of the sawtooth waveform driving voltage signal. However, in each driving voltage signal period C of steps A and B, the gradient dV / dt of the driving voltage V from the base voltage Vb to the peak voltage Vp and the gradient dV / dt of the driving voltage V from the peak voltage Vp to the base voltage Vb are stable. Furthermore, for each subsequent driving voltage signal period of steps A and B, the base voltage Vb and the time period of the fourth stage 4 are stable.

[0058] like Figure 2 As shown, the motor speed is not directly proportional to the peak voltage. Below a certain peak voltage value, the motor will stop moving. The relationship between these two cannot be precisely defined.

[0059] This is not a problem in a closed-loop circuit because the servo circuit adjusts the peak voltage Vp to the required value to produce the desired speed. The slope or gradient dV / dt in Phase 1 (“Movement Phase”) is adjusted in real time at the servo clock frequency, from the ideal shape required for high speed to a low value where the motor stops moving.

[0060] In step B, stages 3 (“sliding stage”) and 4 (“pause after sliding”) remain relatively stable, while stage 2 (“pause after movement”) is absorbed by stage 1 (“movement stage”). The loss of stage 2 (“pause after movement”) leads to a decrease in motor efficiency, which increases the desired speed reduction.

[0061] Figure Labels

[0062] 1. (First stage of the driving voltage signal cycle)

[0063] 2 (Second stage of the driving voltage signal cycle)

[0064] 3 (Third stage of the driving voltage signal cycle)

[0065] 4 (Fourth stage of the driving voltage signal cycle)

[0066] C drive voltage signal period

[0067] dV voltage increment

[0068] dt time increment

[0069] t time

[0070] V drive voltage

[0071] Vb base voltage

[0072] Vp peak voltage

[0073] Vt threshold voltage

Claims

1. A method for controlling a piezoelectric stick-slip motor, the method comprising the following steps: a. Step A: Applying a periodic sawtooth waveform drive voltage signal with a stable frequency to the motor, wherein the drive voltage (V) increases towards and decreases from the peak voltage (Vp) to operate the motor at a stable speed; characterized in that: b. Step B: While maintaining the frequency of the drive voltage signal stable, the speed of the motor is changed by gradually increasing or decreasing the gradient (dV / dt) of the drive voltage (V) towards the peak voltage (Vp) with each subsequent sawtooth waveform drive voltage signal period (C). During the acceleration of the piezoelectric stick-slip motor, the gradient (dV / dt) of the increase in the driving voltage (V) towards the peak voltage (Vp) gradually increases, such that it is larger in the second driving voltage signal cycle (C) than in the first driving voltage signal cycle (C), and larger in the third driving voltage signal cycle (C) than in the second driving voltage signal cycle (C). During the deceleration of the piezoelectric stick-slip motor, the gradient (dV / dt) of the increase of the driving voltage (V) to the peak voltage (Vp) gradually decreases, such that it is smaller in the second driving voltage signal period (C) than in the first driving voltage signal period (C), and smaller in the third driving voltage signal period (C) than in the second driving voltage signal period (C).

2. The method according to claim 1, characterized in that, Each sawtooth waveform drive voltage signal cycle (C) in step A includes the following stages: a. The first stage (1) represents the pasting stage, wherein the driving voltage (V) is increased from the base voltage (Vb) to the peak voltage (Vp). b. The second stage (2) represents a pause after the first stage (1), wherein the driving voltage (V) is maintained at the peak voltage (Vp). c. The third stage (3) represents the sliding stage, wherein the driving voltage (V) decreases from the peak voltage (Vp) to the base voltage (Vb), and d. The fourth stage (4) represents the pause after the third stage (3), wherein the driving voltage (V) is maintained at the base voltage (Vb).

3. The method according to claim 1, characterized in that, Step B involves gradually increasing or decreasing the peak voltage (Vp) for each subsequent drive voltage signal cycle.

4. The method according to claim 2, characterized in that, During each driving voltage signal cycle (C) in step A and / or step B, the increasing gradient (dV / dt) and / or decreasing gradient (dV / dt) of the driving voltage (V) between the base voltage (Vb) and the peak voltage (Vp) are kept stable.

5. The method according to claim 2, characterized in that, To reduce the speed of the motor, compared to step A, step B includes at least one of the following sub-steps: changing the sawtooth waveform drive voltage signal: a. Sub-step B1: While maintaining the peak voltage (Vp) stable, gradually reduce the gradient (dV / dt) of the increase of the driving voltage (V) to the peak voltage (Vp) with each subsequent sawtooth waveform driving voltage signal period (C), so as to prolong the first stage (1) and shorten the second stage (2) by the same amount to compensate for the prolongation of the first stage (1). b. Sub-step B2: With each subsequent sawtooth waveform drive voltage signal period (C), gradually reduce the peak voltage (Vp) and the gradient (dV / dt) of the drive voltage (V) to the peak voltage (Vp) to extend the first stage (1), while eliminating the second stage (2) and shortening the third stage (3) to compensate for the extension of the first stage (1).

6. The method according to claim 2, characterized in that, For each subsequent drive voltage signal cycle (C) in step A and / or step B, the gradient (dV / dt) of the drive voltage (V) decreasing from the peak voltage (Vp) to the base voltage (Vb) is maintained stable.

7. The method according to claim 2, characterized in that, For each subsequent drive voltage signal cycle in step A and / or step B, the time period of the fourth stage (4) is kept stable.

8. The method according to claim 1, characterized in that, A periodic sawtooth waveform drive voltage signal with a stable frequency of 20 kHz or higher is applied to the motor.

9. The method according to claim 2, characterized in that, For each subsequent drive voltage signal cycle in step A and / or step B, the base voltage (Vb) is maintained stable.

10. The method according to any one of the preceding claims, characterized in that, The motor operates in a closed-loop circuit and / or a servo circuit.

11. The method according to claim 10, characterized in that, The peak voltage (Vp) is adjusted in real time according to the servo loop clock frequency.

12. A piezoelectric stick-slip motor comprising a driven element and a stator, the stator having a friction element, a controller, and at least one piezoelectric actuator configured to deform upon application of a drive voltage signal from the controller to apply movement to the friction element, thereby driving the driven element through stick-slip contact, wherein the controller is configured to perform the method according to any one of the preceding claims.

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