A piezoelectric motor and its control method

Abstract

For a piezoelectric actuator used to linearly drive a driven element by inducing elliptical motion in a vibrating element through vibration of the piezoelectric element, a drive device is provided that improves control at very low speeds and / or enables the use of a smaller boost circuit to provide the drive voltage for the piezoelectric actuator. According to one embodiment, a drive device for axially driving a driven element is provided. The driving device includes: a piezoelectric actuator, wherein the piezoelectric actuator includes a vibrating element in contact with a driven element and one or more sets of piezoelectric elements attached to the vibrating element; and a controller, wherein each set of piezoelectric elements includes one or more piezoelectric elements, and in each set of piezoelectric elements, a first electrode for expanding or contracting a first region of the piezoelectric element in the set of piezoelectric elements and a second electrode for expanding or contracting a second region of the piezoelectric element in the set of piezoelectric elements are arranged along the axial direction, wherein in each set of piezoelectric elements, a common third electrode or a separate third electrode paired with the first electrode and the second electrode is provided, such that the vibrating element of the piezoelectric actuator has: a bending mode, wherein the middle portion along the axial direction becomes convex or concave, thereby causing the ends of the vibrating element to move along the axial direction at both ends; and an expansion / contraction mode, wherein one end expands / contracts at both ends of the axial direction, while the other end expands / contracts with opposite phases over time, thereby causing the ends of the vibrating element to move in a direction perpendicular to the axial direction. The controller is used to cause the vibrating element to vibrate by applying oscillating voltage signals of the same frequency to the first and second electrodes, thereby driving the driven element in contact with the vibrating element along the axial direction. When the oscillating voltage signals applied to the first and second electrodes are in phase, a first mode of vibration based on the bending mode is generated in the vibrating element; when the oscillating voltage signals applied to the first and second electrodes are in opposite phase, a second mode of vibration based on the expansion / contraction mode is generated in the vibrating element, wherein the controller is used to control the speed of the driven element by controlling the phase difference between the voltage signals applied to the first electrode and the voltage signals applied to the second electrode. Another aspect of the invention provides a small boost circuit for providing a drive voltage for a piezoelectric actuator.

Description

Technical Field

[0001] This application relates to the field of piezoelectric actuator technology, and more particularly to a drive device (also known as a piezoelectric motor) that uses a piezoelectric actuator to drive a driven element, and a method for controlling such a drive device. Background Technology

[0002] Nowadays, most cameras are equipped with an autofocus mechanism. The autofocus mechanism is used to focus on the subject by adjusting the optical distance from the lens unit to the image sensor. The lens unit is typically driven by an actuator.

[0003] In recent years, there has been a growing demand for telephoto or motion imaging using cameras mounted on portable devices such as smartphones. Telephoto imaging requires longer focal lengths, while autofocus necessitates a lens unit actuator stroke greater than 1 mm. Since the moving parts are heavier than before, greater thrust is required to move them. For still imaging, high power is needed to move the moving parts quickly. On the other hand, for motion imaging, the actuator needs to be controlled at very low speeds to allow the lens unit to smoothly begin or stop moving from a stationary state.

[0004] Actuators commonly used in portable devices such as smartphones are linear VCMs (voice coil motors), while piezoelectric actuators used in larger single-lens reflex cameras, despite their smaller size, offer the advantages of high energy density and high power. Summary of the Invention

[0005] A piezoelectric actuator has been proposed for linearly driving a driven element (e.g., a shaft or some other body) by causing an elliptical motion of a vibrating element through the vibration of the piezoelectric element. However, for some of these piezoelectric actuators, it is difficult to control them at very low speeds. Furthermore, since piezoelectric actuators require high voltages (e.g., 40V to 100V), a boost converter (a device for increasing the voltage) is needed to integrate them into portable devices such as smartphones (which typically operate at around 3V), and it is desirable that such a boost converter be smaller in size.

[0006] This application addresses the aforementioned issues.

[0007] A first implementation of the first aspect of this application provides a driving device for axially driving a driven element, the driving device comprising: a piezoelectric actuator, wherein the piezoelectric actuator includes a vibrating element in contact with the driven element and one or more sets of piezoelectric elements attached to the vibrating element; a controller, wherein each set of piezoelectric elements includes one or more piezoelectric elements, and in each set of piezoelectric elements, a first electrode for expanding or contracting a first region of the piezoelectric element in the set of piezoelectric elements and a second electrode for expanding or contracting a second region of the piezoelectric element in the set of piezoelectric elements are disposed along the axial direction, wherein in each set of piezoelectric elements, a common third electrode or a separate third electrode paired with the first electrode and the second electrode is disposed, such that the vibrating element of the piezoelectric actuator has: a bending mode, wherein the middle portion along the axial direction becomes convex or concave, thereby allowing the ends of the vibrating element to move along the axial direction at both ends; and an expansion / contraction mode, wherein... The vibrating element expands / contracts at one end at both ends of the axial direction, while the other end expands / contracts with opposite phase over time, thereby causing the end of the vibrating element to move in a direction perpendicular to the axial direction. The controller is configured to vibrate the vibrating element by applying oscillating voltage signals of the same frequency to the first and second electrodes, thereby driving the driven element in contact with the vibrating element along the axial direction. When the oscillating voltage signals applied to the first and second electrodes are in phase, a first mode of vibration based on the bending mode is generated in the vibrating element; when the oscillating voltage signals applied to the first and second electrodes are in opposite phase, a second mode of vibration based on the expansion / contraction mode is generated in the vibrating element. The controller is configured to control the speed of the driven element by controlling the phase difference between the voltage signals applied to the first and second electrodes.

[0008] This implementation is characterized by driving the driven element using both bending-mode and expansion / contraction-mode vibrations, and controlling the speed of the driven element by controlling the phase difference between the voltage signals applied to the first and second electrodes. Even when the phase difference is essentially π and there is no thrust, the vibrating element vibrates in a direction perpendicular to the thrust. Therefore, the friction generated between the vibrating element and the driven element is kinetic friction. This avoids problematic behavior where the switch from static to kinetic friction causes the driven element to start moving abruptly, or where the driven element stops abruptly due to the switch from kinetic to static friction. Thus, the linearity of the movement relative to the control signal is improved.

[0009] According to a second implementation of the first aspect of this application, based on a first implementation of the first aspect of this application, the voltage signal is applied to the first electrode and the second electrode to cause the end of the vibrating element to perform elliptical motion, the elliptical motion being a combination of a vibration component along the axial direction and a vibration component perpendicular to the axial direction, and the controller is used to control the vibration amplitude of the vibration component along the axial direction and the vibration amplitude of the vibration component perpendicular to the axial direction by controlling the phase difference.

[0010] According to this implementation, the vibration of the vibrating element generates thrust on the driven element in a favorable manner.

[0011] According to a third implementation of the first aspect of this application based on a first or second implementation of the first aspect of this application, the vibrating element includes a hole, the driven element includes a cylindrical shape, and the driven element inserted into the hole is driven along the axial direction.

[0012] This implementation method can stabilize the axis of the driven element.

[0013] According to a fourth implementation of the first aspect of this application based on any of the first to third implementations of the first aspect of this application, the group or more piezoelectric elements attached to the vibrating element include two or more groups of piezoelectric elements attached at positions symmetrical about the vibrating element, the same voltage signal is applied to the first electrode of each piezoelectric element, and the same voltage signal is applied to the second electrode of each piezoelectric element.

[0014] According to this implementation, the driven element can be driven by a force balanced around the axis.

[0015] According to a fifth implementation of the first aspect of this application, which is based on any of the first to fourth implementations of the first aspect of this application, the controller is configured to make the phase difference substantially π so that the speed of the driven element is zero.

[0016] According to this implementation, since the vibrating element will vibrate in a direction perpendicular to the thrust even when the phase difference is π and there is no thrust, the friction between the vibrating element and the driven element is kinetic friction, while the driven element is basically stationary (without axial movement).

[0017] According to a sixth implementation of the first aspect of this application based on any of the first to fifth implementations of the first aspect of this application, the controller is configured to gradually decrease or increase the phase difference from substantially π when the driven element is started to be driven from zero speed, and / or the controller is configured to gradually bring the phase difference closer to approximately π when the speed of the driven element is set to zero.

[0018] According to this implementation method, the speed of the driven element can be adjusted by gradually changing the phase difference.

[0019] According to a seventh implementation of the first aspect of this application, based on a second implementation of the first aspect of this application, the controller is further configured to control the amplitude of the voltage signal applied to the first electrode and the second electrode to compensate for the amplitude change of the vibration component perpendicular to the axial direction caused by the control of the phase difference.

[0020] According to this implementation, when the phase difference between the voltage signals applied to the first electrode and the second electrode changes to control the speed of the driven element, the amplitude of the vibration component perpendicular to the axial direction can remain constant.

[0021] According to an eighth implementation of the first aspect of this application, which is based on any of the first to seventh implementations of the first aspect of this application, the controller is used to control the speed of the driven element by further controlling the frequency and / or amplitude of the voltage signals applied to the first electrode and the second electrode.

[0022] According to this implementation, a larger speed change of the driven element can be achieved compared to simply changing the phase difference between the voltage signals applied to the first and second electrodes.

[0023] According to a ninth implementation of the first aspect of this application, which is based on any of the first to seventh implementations of the first aspect of this application, the controller is configured to control the speed of the driven element by controlling the frequency and / or amplitude of the voltage signal applied to the first electrode and the second electrode, rather than the phase of the voltage signal, when the speed of the driven element is equal to or greater than a predetermined value.

[0024] According to this implementation, when speed control at low speeds is not required, the speed of the driven element can be efficiently adjusted by controlling the frequency and / or amplitude of the voltage signals applied to the first and second electrodes.

[0025] According to the tenth implementation of the first aspect of this application, which is based on any of the first to ninth implementations of the first aspect of this application, the voltage signal applied to the first electrode and the second electrode is a square wave, a triangular wave, a sawtooth wave, or a sine wave.

[0026] According to at least some of the choices of this implementation method, it is convenient to digitally control the voltage signals applied to the first electrode and the second electrode.

[0027] According to the eleventh implementation of the first aspect of this application, which is based on any one of the first to tenth implementations of the first aspect of this application, the driving device further includes a boost circuit, wherein the boost circuit is used to convert the voltage of the power supply into a voltage for driving the piezoelectric actuator.

[0028] According to this implementation, the piezoelectric actuator can be driven even when the power supply voltage (e.g., the power supply voltage of a portable device) is lower than the voltage required to drive the piezoelectric actuator.

[0029] According to a twelfth implementation of the first aspect of this application, which is based on an eleventh implementation of the first aspect of this application, the boost circuit includes a driver for providing voltage to the piezoelectric actuator via an external inductor.

[0030] According to the thirteenth implementation of the first aspect of this application, which is based on the twelfth implementation of the first aspect of this application, the piezoelectric actuator is represented by an equivalent circuit, which includes an internal RLC (resistor-inductor-capacitor) series resonant circuit and a capacitor component connected in parallel. The resonant frequency of the RLC series resonant circuit, which is composed of the output impedance of the driver, the external inductor, and the capacitor component of the piezoelectric actuator, is substantially matched with the resonant frequency of the internal RLC series resonant circuit of the piezoelectric actuator.

[0031] According to this implementation, the energy of the oscillating voltage signal is efficiently transferred to the vibration element of the piezoelectric actuator.

[0032] According to the fourteenth implementation of the first aspect of this application, which is based on any of the first to thirteenth implementations of the first aspect of this application, the parameters of the internal RLC series resonant circuit of the piezoelectric actuator are adjusted so that the inductance of the external inductor is 30μH or lower.

[0033] According to this implementation, the external inductor is relatively small in size, making it suitable for inclusion in portable devices. Furthermore, the small inductance can be achieved through circuit parameter design within the piezoelectric actuator without introducing additional components.

[0034] According to the fifteenth implementation of the first aspect of this application, which is based on any of the first to thirteenth implementations of the first aspect of this application, the boost circuit has an external capacitor connected in parallel with the capacitive component of the piezoelectric actuator, such that the inductance of the external inductor is 30 μH or lower.

[0035] According to this implementation, the external inductor is relatively small in size, making it suitable for inclusion in portable devices. Furthermore, the small inductance can be achieved by adding external components without altering the circuit parameters within the piezoelectric actuator.

[0036] According to a second aspect of this application, a driving device is provided, comprising: a piezoelectric actuator, the piezoelectric actuator including a vibrating element and one or more sets of piezoelectric elements attached to the vibrating element; and a controller. Each set of piezoelectric elements includes one or more piezoelectric elements, in each set of piezoelectric elements, a first electrode for expanding or contracting a first region of the piezoelectric element in the set of piezoelectric elements and a second electrode for expanding or contracting a second region of the piezoelectric element in the set of piezoelectric elements are arranged along the axial direction, wherein in each set of piezoelectric elements, a common third electrode or a separate third electrode paired with the first electrode and the second electrode is provided, such that the vibrating element of the piezoelectric actuator has: a bending mode, wherein the middle portion along the axial direction becomes convex or concave, thereby moving the ends of the vibrating element along the axial direction at both ends; and an expansion / contraction mode, wherein one end expands / contracts at both ends of the axial direction, while the other end expands / contracts with opposite phases over time, thereby moving the ends of the vibrating element in a direction perpendicular to the axial direction, wherein the controller uses... The vibrating element's end portion is elliptical in motion by applying oscillating voltage signals of the same frequency to the first and second electrodes. This elliptical motion is a combination of an axial vibration component and a vibration component perpendicular to the axial direction. The controller controls the vibration amplitude of the axial vibration component and the vibration amplitude of the perpendicular vibration component by controlling the phase difference between the voltage signals applied to the first and second electrodes. When the oscillating voltage signals applied to the first and second electrodes are in phase, a first mode of vibration based on the bending mode is generated in the vibrating element; when the oscillating voltage signals applied to the first and second electrodes are in opposite phase, a second mode of vibration based on the expansion / contraction mode is generated in the vibrating element.

[0037] This implementation is characterized by driving the driven element using both bending-mode and expansion / contraction-mode vibrations, and controlling the speed of the driven element by controlling the phase difference between the voltage signals applied to the first and second electrodes. Even when the phase difference is essentially π and there is no thrust, the vibrating element vibrates in a direction perpendicular to the thrust. Therefore, the friction generated between the vibrating element and the driven element is kinetic friction. This avoids problematic behavior where the switch from static to kinetic friction causes the driven element to start moving abruptly, or where the driven element stops abruptly due to the switch from kinetic to static friction. Thus, the linearity of the movement relative to the control signal is improved.

[0038] According to a first implementation of the third aspect of this application, a driving device for driving a driven element is provided. The driving device includes: a piezoelectric actuator, the piezoelectric actuator including a vibrating element in contact with the driven element and one or more sets of piezoelectric elements attached to the vibrating element; a controller for controlling a voltage signal applied to the piezoelectric elements to vibrate the vibrating element of the piezoelectric actuator, thereby driving the driven element; and a boost circuit for converting the voltage of a power supply into a voltage for driving the piezoelectric actuator, wherein the boost circuit includes a driver for providing voltage to the piezoelectric actuator via an external inductor, the piezoelectric actuator being represented by an equivalent circuit, the equivalent circuit including... The resonant frequency of the RLC series resonant circuit, consisting of the output impedance of the driver, the external inductor, and the capacitive component of the piezoelectric actuator, is substantially matched with the resonant frequency of the internal RLC series resonant circuit of the piezoelectric actuator, wherein (i) the parameters of the internal RLC series resonant circuit of the piezoelectric actuator are adjusted, and / or (ii) the boost circuit has an external capacitor connected in parallel with the capacitive component of the piezoelectric actuator, such that the inductance of the external inductor is 30 μH or lower.

[0039] According to this implementation, the piezoelectric actuator can be driven even when the power supply voltage (e.g., the power supply voltage of a portable device) is lower than the voltage required to drive the piezoelectric actuator. Furthermore, the external inductor is relatively small, making it suitable for inclusion in portable devices. Additionally, the small inductance can be achieved by modifying the circuit parameters within the piezoelectric actuator and / or by adding external components.

[0040] According to a second implementation of the third aspect of this application based on a first implementation of the third aspect, each group of piezoelectric elements includes one or more piezoelectric elements. In each group of piezoelectric elements, a first electrode for expanding or contracting a first region of the piezoelectric element in the group and a second electrode for expanding or contracting a second region of the piezoelectric element in the group are arranged along the axial direction. In each group of piezoelectric elements, a common third electrode or a separate third electrode paired with the first and second electrodes is provided, such that the vibrating element of the piezoelectric actuator has: a bending mode, wherein the middle portion along the axial direction becomes convex or concave, thereby causing the ends of the vibrating element to move along the axial direction at both ends; and an expansion / contraction mode, wherein one end expands / contracts at one end of the axial direction, while the other end expands / contracts with opposite phases over time. The expansion / contraction causes the end of the vibrating element to move in a direction perpendicular to the axial direction. The controller is configured to cause the vibrating element to vibrate by applying oscillating voltage signals of the same frequency to the first and second electrodes, thereby driving the driven element in contact with the vibrating element along the axial direction. When the oscillating voltage signals applied to the first and second electrodes are in phase, a first mode of vibration based on the bending mode is generated in the vibrating element; when the oscillating voltage signals applied to the first and second electrodes are in opposite phase, a second mode of vibration based on the expansion / contraction mode is generated in the vibrating element. The controller is configured to control the speed of the driven element by controlling the phase difference between the voltage signals applied to the first and second electrodes.

[0041] This implementation is characterized by driving the driven element using both bending-mode and expansion / contraction-mode vibrations, and controlling the speed of the driven element by controlling the phase difference between the voltage signals applied to the first and second electrodes. Even when the phase difference is essentially π and there is no thrust, the vibrating element vibrates in a direction perpendicular to the thrust. Therefore, the friction generated between the vibrating element and the driven element is kinetic friction. This avoids problematic behavior where the switch from static to kinetic friction causes the driven element to start moving abruptly, or where the driven element stops abruptly due to the switch from kinetic to static friction. Thus, the linearity of the movement relative to the control signal is improved.

[0042] According to a third implementation of the third aspect based on the second implementation of the third aspect of this application, the voltage signal is applied to the first electrode and the second electrode to cause the end of the vibrating element to perform elliptical motion, the elliptical motion being a combination of a vibration component along the axial direction and a vibration component perpendicular to the axial direction, and the controller is used to control the vibration amplitude of the vibration component along the axial direction and the vibration amplitude of the vibration component perpendicular to the axial direction by controlling the phase difference.

[0043] According to this implementation, the vibration of the vibrating element generates thrust on the driven element in a favorable manner.

[0044] According to a fourth aspect of this application, an electronic device is provided, including a driving device according to any implementation of the first to third aspects of this application.

[0045] According to a fifth aspect of this application, an electronic device is provided, the electronic device including a camera, wherein the camera includes a driving device according to any implementation of the first to third aspects of this application, wherein the driving device is used to drive a lens unit of the camera attached to the driven element for autofocus.

[0046] According to the sixth aspect of this application, an electronic device according to the fourth or fifth aspect is provided, said electronic device being a mobile phone or a smartphone.

[0047] According to a first implementation of the seventh aspect of this application, a method is provided for a piezoelectric actuator to drive a driven element axially by a driver. The piezoelectric actuator includes: a vibrating element in contact with the driven element and one or more sets of piezoelectric elements attached to the vibrating element; wherein each set of piezoelectric elements includes one or more piezoelectric elements, and in each set of piezoelectric elements, a first electrode for expanding or contracting a first region of the piezoelectric element in the set of piezoelectric elements and a second electrode for expanding or contracting a second region of the piezoelectric element in the set of piezoelectric elements are arranged axially; wherein in each set of piezoelectric elements, a common third electrode or a separate third electrode paired with the first and second electrodes is provided, such that the vibrating element of the piezoelectric actuator has: a bending mode, wherein the middle portion along the axial direction becomes convex or concave, thereby allowing the ends of the vibrating element to move along the axial direction at both ends; and an expansion / contraction mode, wherein one end expands / contracts at one end of the axial direction, while the other end... The portion expands / contracts with opposite phases over time, thereby causing the end of the vibrating element to move in a direction perpendicular to the axial direction. The method includes: causing the vibrating element to vibrate by applying oscillating voltage signals of the same frequency to the first and second electrodes, thereby driving the driven element in contact with the vibrating element along the axial direction; controlling the speed of the driven element by controlling the phase difference between the voltage signals applied to the first and second electrodes; wherein when the oscillating voltage signals applied to the first and second electrodes are in phase, a first mode of vibration based on the bending mode is generated in the vibrating element; and when the oscillating voltage signals applied to the first and second electrodes are in opposite phases, a second mode of vibration based on the expansion / contraction mode is generated in the vibrating element.

[0048] This implementation is characterized by driving the driven element using both bending-mode and expansion / contraction-mode vibrations, and controlling the speed of the driven element by controlling the phase difference between the voltage signals applied to the first and second electrodes. Even when the phase difference is essentially π and there is no thrust, the vibrating element vibrates in a direction perpendicular to the thrust. Therefore, the friction generated between the vibrating element and the driven element is kinetic friction. This avoids problematic behavior where the switch from static to kinetic friction causes the driven element to start moving abruptly, or where the driven element stops abruptly due to the switch from kinetic to static friction. Thus, the linearity of the movement relative to the control signal is improved.

[0049] According to a second implementation of the seventh aspect of this application, based on a first implementation of the seventh aspect, the voltage signal is applied to the first electrode and the second electrode to cause the end of the vibrating element to perform an elliptical motion, the elliptical motion being a combination of a vibration component along the axial direction and a vibration component perpendicular to the axial direction, wherein controlling the speed of the driven element by controlling the phase difference includes controlling the vibration amplitude of the vibration component along the axial direction and the vibration amplitude of the vibration component perpendicular to the axial direction by controlling the phase difference.

[0050] The beneficial effects that can be achieved by the various dependent implementations based on the first implementation of the seventh aspect are the same as or similar to the corresponding implementations of the first aspect, and will not be elaborated here.

[0051] According to a third implementation of the seventh aspect of this application, based on a first or second implementation of the seventh aspect, the method further includes making the phase difference substantially π so that the velocity of the driven element is zero.

[0052] According to a fourth implementation of the seventh aspect of this application based on the first or second implementation of the seventh aspect of this application, the method further includes: gradually decreasing or increasing the phase difference from substantially π when starting to drive the driven element from zero speed, and / or gradually approaching the phase difference to approximately π when the speed of the driven element is set to zero.

[0053] According to a fifth implementation of the seventh aspect of this application, which is based on any of the first to third implementations of the seventh aspect of this application, the method further includes controlling the amplitude of the voltage signal applied to the first electrode and the second electrode to compensate for the amplitude change of the vibration component perpendicular to the axis caused by the control of the phase difference.

[0054] According to a sixth implementation of the seventh aspect of this application, which is based on any of the first to fifth implementations of the seventh aspect of this application, the method further includes controlling the speed of the driven element by further controlling the frequency and / or amplitude of the voltage signals applied to the first electrode and the second electrode.

[0055] According to a seventh implementation of the seventh aspect of this application based on any one of the first to fifth implementations of the seventh aspect of this application, the method further includes controlling the speed of the driven element by controlling the frequency and / or amplitude of the voltage signal applied to the first electrode and the second electrode, rather than the phase of the voltage signal, when the speed of the driven element is equal to or greater than a predetermined value.

[0056] According to an eighth aspect of this application, a computer program is provided for causing a driver to perform the method described in any of the first to seventh implementations of the seventh aspect of this application.

[0057] According to a ninth aspect of this application, a computer-readable storage medium is provided on which a computer program according to an eighth aspect of this application is stored. Attached Figure Description

[0058] Figure 1 A schematic diagram is shown illustrating the axial driving of a driven element by a piezoelectric actuator controlled by a controller, according to an embodiment of this application.

[0059] Figure 2 A piezoelectric actuator according to an embodiment of this application is shown;

[0060] Figure 3 The principle of a piezoelectric actuator according to an embodiment of this application is shown;

[0061] Figure 4 Elliptical motion in a piezoelectric actuator according to an embodiment of this application is shown;

[0062] Figure 5 The two-phase signal applied to the piezoelectric actuator according to an embodiment of this application is shown;

[0063] Figure 6 The relationship between phase difference and thrust in elliptical motion in a piezoelectric actuator according to an embodiment of this application is shown.

[0064] Figure 7 This is a flowchart of a method for driving a piezoelectric actuator axially to control the movement of a driven element according to an embodiment of this application;

[0065] Figure 8 The parameters of the equivalent circuit of the piezoelectric actuator and boost circuit according to embodiments of this application are shown;

[0066] Figure 9 The parameters of the equivalent circuit of the piezoelectric actuator and boost circuit according to embodiments of this application are shown;

[0067] Figure 10 An electronic device including a drive device comprising a piezoelectric actuator is shown according to an embodiment of this application. Detailed Implementation

[0068] Although embodiments of this application are described below with reference to the accompanying drawings, the invention is not limited to the embodiments shown or described.

[0069] Piezo-actuators (also known as piezoelectric actuators), despite their small size, offer high energy density and high power, and have long been used in SLR cameras and other applications. Since devices that use piezo-actuators to drive driven elements can be called piezoelectric motors, the terms piezo-actuator and piezoelectric motor can be used synonymously. A piezoelectric motor that uses the vibration of a piezoelectric element in the ultrasonic range to linearly drive a driven element along its axis can be called a linear ultrasonic motor (USM).

[0070] Figure 1 A schematic diagram is shown illustrating the axial driving of a driven element 120 by a piezoelectric actuator 100 controlled by a controller 110 according to an embodiment of this application. The controller, as used herein, generally refers to one or more components, including circuitry for applying a voltage signal (also referred to as a drive signal) to operate the piezoelectric actuator and circuitry for controlling the voltage. Control of the voltage signal can be performed according to a computer program stored on a storage medium.

[0071] Figure 2 Image (a) shows a piezoelectric actuator 200 for axially driving a driven element according to an embodiment of this application. According to this embodiment, one or more sets of piezoelectric elements 220 are attached around a vibrating element (vibrator) 210. As described below, in the example shown, the vibrating element has a hole into which a cylindrical driven element is inserted. However, the shape of the vibrating element is not limited to the example shown. As described below, in the example shown, each set of piezoelectric elements includes a piezoelectric element 220 having electrodes 230 and 240. However, each set of piezoelectric elements may include a piezoelectric element with electrode 230 and a separate piezoelectric element with electrode 240. The piezoelectric element in each set of piezoelectric elements includes a first electrode 230 for expanding or contracting a first region of the piezoelectric element in the set and a second electrode 240 for expanding or contracting a second region of the piezoelectric element in the set. The first electrode 230 and the second electrode 240 are arranged axially. In the example shown, each group of piezoelectric elements includes one piezoelectric element 220, and the first region and the second region are two regions of the same piezoelectric element 220, but this application is not limited to this. For example, the piezoelectric element in each group of piezoelectric elements may include two piezoelectric elements, and the first region and the second region may belong to separate piezoelectric elements. The cylindrical follower element 250 inserted into the hole of the vibrating element is driven axially by the controlled vibration of the vibrating element 210. The first region and the second region of the piezoelectric element are arranged along the axial direction of the insertion hole. One or more electrodes mating with the first electrode and the second electrode are connected to ground (GND), as follows. Figure 2 As described in (b) of the document.

[0072] This invention is not limited to the embodiments shown. These piezoelectric elements can be attached symmetrically around the vibrating element. The shape of the vibrating element is not limited, particularly not limited to a shape with a hole for inserting a cylindrical driven element, as long as the vibrating element contacts the driven element and applies force to it. The piezoelectric element can be, but is not limited to, a PZT (lead zirconate titanate) element. Furthermore, although a piezoelectric element is used herein as an example, any suitable electromechanical transducer can be used. Furthermore, although the terminology used herein is "actuator" or similar to drive the driven element, it will be apparent to those skilled in the art that this is a description from the perspective of the actuator (or a component of the fixed actuator), typically causing relative motion between the actuator and the driven element. The vibrating element can be referred to as a stator. The driven element can be referred to as a slider, shaft, etc. The use of such terms does not limit which of the actuator or driven element is fixed. Furthermore, more than one piezoelectric actuator, as shown, can be provided along the axial direction of the driven element.

[0073] Figure 2 (b) shows the application to, for example Figure 2 The piezoelectric actuator shown in (a) has a drive voltage. A first voltage signal Ea is applied to the first electrode 230, and a second voltage signal Eb is applied to the second electrode 240. These voltage signals can be two-phase voltage signals, and in one embodiment, these voltage signals can be defined as:

[0074] Ea = a * sin ωt (1)

[0075] Eb = a * sin (ωt + ps) (2)

[0076] Where a is the signal amplitude, ps is the phase difference between Ea and Eb, ω is the angular frequency, and t is time. The first and second voltage signals have the same signal amplitude and angular frequency.

[0077] In one embodiment, the vibrating element is made of a conductor such as metal. Figure 2 In (b) of the diagram, GND represents ground. In one embodiment, a third electrode, paired with the first electrode, is located on the side of the piezoelectric element opposite to the first electrode, and a first voltage signal Ea is applied between the first and third electrodes. The third electrode may be placed between the piezoelectric element and the vibrating element made of conductor. Similarly, a fourth electrode, paired with the second electrode, is located on the side of the piezoelectric element opposite to the second electrode, and a second voltage signal Eb is applied between the second and fourth electrodes. The fourth electrode may be placed between the piezoelectric element and the vibrating element made of conductor. The third and fourth electrodes may be separate electrodes or a common electrode. The third and fourth electrodes are connected to ground (GND) to provide a reference for the voltage signal. Figure 2 In the embodiment shown in (b), the vibrating element is made of a conductor and the conductor is connected to ground (GND).

[0078] Figure 3 yes Figure 2 The schematic diagram of the cross-section of the piezoelectric actuator shown is used to illustrate the principle of the piezoelectric actuator of this application.

[0079] Figure 3 Figure (a) shows the vibration of the vibrating element when ps = 0 (i.e., when Ea and Eb are in phase) (this is called the bending mode). While the middle portion vibrates up and down, the ends (e.g., points represented by open circles) move laterally. Therefore, the bending mode generates axial vibration at the ends of the vibrating element. This produces axial thrust, as described below.

[0080] Figure 3 Figure (b) shows the vibration of the vibrating element when ps = π (i.e., when Ea and Eb are in opposite phases). This is a vibration mode in which one end expands / contracts while the other end expands / contracts in opposite phases, referred to as the expansion / contraction vibration mode or expansion / contraction mode. When the wall of the vibrating element is tilted, the end (e.g., the point indicated by the opening circle) moves up and down. Therefore, the expansion / contraction mode vibrates in a direction perpendicular to the axis (along the direction perpendicular to the plane of the piezoelectric element).

[0081] For a typical phase ps, the end of the vibrating element undergoes a motion consisting of axial vibration and vertical (perpendicular to the axis) vibration. The magnitude of the axial vibration can be considered proportional to Ea + Eb (this can be called the first mode, similar to the bending mode described above). The magnitude of the vibration in the direction perpendicular to the axis can be considered proportional to Ea – Eb (this can be called the second mode, similar to the expansion / contraction mode described above). It should be noted that this does not imply addition or subtraction of Ea and Eb applied to different electrodes as electrical signals. The vibrations caused by these voltages at the end of the vibrating element are combined.

[0082] The amplitudes of the axial vibration component and the vibration component perpendicular to the axis, caused by the piezoelectric actuator at the end of the vibrating element, can be estimated to be proportional to equations (3) and (4), respectively, as shown below:

[0083] (In phase) Ea + Eb = a * (sin (ωt + ps) + sin ωt) = 2 * a cos(ps / 2) *sin (ωt + ps / 2) (3)

[0084] (Opposite phase) Ea–Eb = a * (sin (ωt + ps) – sin ωt) = 2 * a sin(ps / 2) * cos (ωt + ps / 2) (4)

[0085] In this embodiment, the phase difference ps between the voltage signals Ea and Eb applied to the first and second electrodes of the piezoelectric actuator is set to be equal to π / 2. (It should be noted that the value of ps can be controlled by a controller, as described below.) In this case, as... Figure 3 As shown in (c), the end of the vibrating element (e.g., the point indicated by the opening circle) undergoes an elliptical motion. This elliptical motion translates (pushes, drives, or propels) the driven element inserted into the hole of the vibrating element along the axial direction.

[0086] Figure 4 Elliptical motion is shown, which is caused by the vibration of the vibrating element at its end. It is a combination of the amplitude of the vibration component along the axial direction (the direction of the thrust, the direction of translational motion of the driven element) and the amplitude of the vibration component in a direction perpendicular to the axis. The direction of motion of the driven element is also shown.

[0087] Figure 5 An example of a two-phase signal with ps = π / 2 is shown, which would cause... Figure 3 The elliptical motion is shown in (c). At time A, when the two curves of these voltage signals intersect, Ea and Eb have the same sign and the same magnitude, which corresponds to... Figure 3 The case of (i) in (c) of the above. Thereafter, when the two signals have the same magnitude but opposite signs, time B corresponds to... Figure 3 In (c) of (ii). At time C, when the two curves intersect again, Ea and Eb again have the same sign and the same magnitude, which corresponds to Figure 3 (c) of (iii). When two signals have the same magnitude but opposite signs, time D corresponds to Figure 3 (d) in (iv).

[0088] It should be noted that although the voltage signals Ea and Eb are represented as sine waves here for ease of understanding, it may be advantageous to use other waveforms such as square waves, triangle waves, or sawtooth waves. For example, waveforms that facilitate digital control of the voltage signals applied to the first and second electrodes can be used.

[0089] The vibrating element needs to press the driven element down with a relatively large force so that the driven element can be driven by the piezoelectric actuator. In a conventional piezoelectric motor, a relatively large force is required to overcome the static friction generated when the driven element is stationary relative to the vibrating element when it begins to move. At the instant the driven element begins to move, static friction turns into kinetic friction, causing a sudden decrease in frictional force. This is problematic because the driven element starts moving abruptly. On the other hand, when the speed of the driven element is reduced, the kinetic friction turns into static friction, causing a sudden increase in frictional force, which may lead to a sudden stop of the driven element. Low-speed control is difficult due to techniques that control the frequency or amplitude of the voltage signal used to drive the piezoelectric actuator, as it requires precise voltage control or feedforward control (e.g., applying a larger force only at the start of movement to overcome static friction).

[0090] The inventors recognize from equations (3) and (4) above that in the elliptical motion of the end of the vibrating element driving the driven element, the ratio of the amplitude of the axial component to the amplitude of the component perpendicular to the axial direction can be controlled by changing the value of ps, and the overall amplitude can be changed by changing the value of a.

[0091] Figure 6 The relationship between the amplitude of vibration along the axial (horizontal axis) and the amplitude of vibration perpendicular to the axial (vertical axis) is shown for phase differences ps = π / 2, (3 / 4)π, (11 / 12)π, and π. The efficiency of thrust generation is highest when ps = π / 2. With a phase difference p = (3 / 4)π, the force pressing on the driven element is large, while the thrust is small. With a phase difference ps = π, the thrust is zero.

[0092] Therefore, by changing the value of ps instead of controlling the frequency or amplitude of the voltage signal applied to the piezoelectric actuator, the controller of the drive device can control the thrust on the driven element without being affected by the switching between static and kinetic friction. At the start of movement, the thrust can be gradually increased from zero by gradually decreasing the value of ps starting from π. The efficiency of generating thrust is highest when ps = π / 2. Alternatively, the thrust can be gradually increased in the opposite direction from zero by gradually increasing the value of ps starting from π. The efficiency of generating the opposite thrust is highest when ps = (3 / 2)π. When stopping, the thrust can be gradually reduced to zero by gradually bringing the value of ps closer to π. Even when ps = π and there is no thrust, the vibrating element will vibrate in a direction perpendicular to the thrust. Therefore, the friction between the vibrating element and the driven element is kinetic friction. This avoids problematic behavior where the switch from static to kinetic friction causes the driven element to start moving abruptly when movement begins, or the driven element stops abruptly due to the switch from kinetic to static friction. Therefore, the movement improves the linearity of motion relative to the control signal.

[0093] Therefore, the method for controlling the piezoelectric actuator according to this application can improve low-speed control because changing the phase difference allows for free control of the thrust on the driven element without being affected by the switching between static and dynamic friction.

[0094] According to embodiments of this application, in addition to controlling the phase difference between the voltage signals applied to the first electrode and the second electrode, or as an alternative, the frequency and / or amplitude of the voltage signals applied to the first electrode and the second electrode can be controlled.

[0095] As can be seen from equations (3) and (4) above, when the amplitude a of the voltage signal remains constant, the thrust generated by the vibration component along the axial direction of the elliptical motion decreases because the phase difference ps is changed from π / 2 to π. Therefore, the vibration amplitude in the direction perpendicular to the axis increases. According to the embodiments of this application, when the phase difference ps changes, the signal amplitude a can also be changed to compensate for this increase in the vibration amplitude in the direction perpendicular to the axis.

[0096] Figure 7 This is a flowchart outlining a method for driving a piezoelectric actuator when a driven element in a stationary state moves axially and then comes to a standstill again. In one embodiment, the drive may be performed by... Figure 1 The controller 110 performs this action. In one embodiment, the desired speed of the driven element along the axial direction is provided by a higher-level controller or the user. In a non-limiting embodiment for driving a lens unit for autofocus in motion picture imaging, the desired speed is the speed at which the lens unit is moved to a desired position for focusing, and this desired speed can be dynamically determined by the higher-level controller. It should be noted that the terms "controller 110" and "higher-level controller" refer to a logical distinction. Controller 110 and the higher-level controller can be physically implemented by the same controller. Embodiments are not limited thereto.

[0097] In one embodiment, the higher-level controller determines a non-zero velocity indication value based on the current position and desired position of the driven element (e.g., a lens unit). The velocity indication value is set to zero when the driven element reaches the desired position. In one embodiment, the higher-level controller can gradually increase the velocity indication value from zero and then gradually decrease it back to zero, allowing the driven element to smoothly begin and then smoothly stop moving. In one embodiment, a position sensor is provided for detecting the position of the driven element, enabling the higher-level controller to know the position of the driven element. In one embodiment, the position of the driven element is detected periodically, and the velocity of the driven element can be determined based on the difference from previously detected values. Therefore, it can be determined whether the desired velocity has been reached.

[0098] refer to Figure 7In the flowchart, in step 710, the driven element is stationary, and the voltage signal applied to the first and second electrodes of the piezoelectric element of the piezoelectric actuator is disconnected.

[0099] In step 720, controller 110 receives a speed indication value (instead of zero) for the driven element from the higher-level controller.

[0100] In step 730, the controller 110 begins to apply oscillating voltage signals of the same frequency to the first and second electrodes of the piezoelectric actuator. Initially, the phase difference between the voltage signals applied to the first and second electrodes is essentially π. In this case, the end of the vibrating element of the piezoelectric actuator vibrates only in a direction perpendicular to the axis, without driving the driven element axially. Due to power loss when the driven element is not moving, it is desirable to begin applying voltage signals to the first and second electrodes after receiving a speed indication value of the driven element (instead of zero), although this application is not limited to this.

[0101] In step 740, the controller 110 sets the phase difference between the voltage signals applied to the first and second electrodes within the range of π to (3 / 2)π or π to π / 2, based on the received speed indication value. When the phase difference is within the range of π to (3 / 2)π, the direction of movement of the driven element (e.g., the positive direction) is opposite to the direction of movement of the driven element (e.g., the negative direction) when the phase difference is within the range of π to π / 2. In one embodiment, the controller 110 can set the phase difference according to a lookup table (LUT) indicating the correspondence between the desired speed indication value and the phase difference, although this application is not limited thereto.

[0102] The controller 110 dynamically adjusts the phase difference between the voltage signals applied to the first and second electrodes based on the speed indication received from the higher-level controller. A phase difference of π / 2 (or (3 / 2)π) corresponds to the most efficient drive of thrust control via phase difference. It should be noted that, in order to obtain greater speed, in addition to the phase difference between the voltage signals applied to the first and second electrodes, the controller 110 can also control the amplitude and frequency of the voltage signals applied to the first and second electrodes.

[0103] In step 750, controller 110 receives a zero speed indication value from the higher-level controller. This could occur, for example, when the driven element reaches the desired position. It should be noted that in some embodiments, the higher-level controller may take into account the inertia of the driven element and determine the speed indication value to be zero before the driven element reaches the desired position.

[0104] In step 760, the controller 110 sets the phase difference between the voltage signals applied to the first and second electrodes to be substantially equal to π. Similarly, the end of the vibrating element of the piezoelectric actuator vibrates only in a direction perpendicular to the axis, without axially moving the driven element.

[0105] In step 770, controller 110 disconnects the voltage signal applied to the first and second electrodes. This eliminates power loss when the driven element is not moving.

[0106] Step 780 is the final state, in which the driven element is stationary and the voltage signals applied to the first and second electrodes are disconnected.

[0107] It should be noted that when the speed of the driven element is equal to or greater than a predetermined value, the speed of the driven element can be controlled by controlling the frequency and / or amplitude of the voltage signals applied to the first and second electrodes, rather than by controlling the phase difference between the voltage signals applied to the first and second electrodes. At high speeds, control by frequency and / or amplitude may be effective because there are no issues arising from the switching between static and dynamic friction, which could lead to sudden initiation or sudden stop.

[0108] Another aspect of the invention relates to a boost device or boost circuit (a device or circuit for increasing voltage) for providing a drive voltage to a piezoelectric actuator.

[0109] Because piezoelectric actuators require high voltage (e.g., 40V to 100V), a boost converter (a device for increasing the voltage) is needed to integrate them into portable devices such as smartphones (which typically operate at around 3V). The piezoelectric actuator mentioned in this aspect of the invention can be, but is not limited to, those referenced above. Figures 2 to 7 The piezoelectric actuator described.

[0110] A piezoelectric actuator can be represented by an equivalent circuit consisting of an internal RLC (resistor-inductor-capacitor) series resonant circuit and a parallel-connected capacitive component Cd. Figure 8 In the diagram, the equivalent circuit corresponds to the portion enclosed by the dashed line.

[0111] In one embodiment, the boost circuit includes a driver for supplying voltage to the piezoelectric actuator via an external inductor. The output voltage Vout and resonant frequency f0out of the boost circuit can be expressed as follows:

[0112]

[0113] Where Vin is the input voltage from the power supply, Rout is the internal resistance of the driver, Lext is the inductance of the external inductor, and Cd is the capacitive component of the piezoelectric actuator.

[0114] The resonant frequency of the RLC (resistor-inductor-capacitor) series resonant circuit, determined by the driver's output impedance Rout, the inductance Lext of the external inductor, and the capacitive component Cd of the piezoelectric actuator (referred to herein as the driver-side resonant frequency), is substantially matched with the resonant frequency of the piezoelectric actuator's internal RLC series resonant circuit. This matching maximizes the drive amplitude. Strictly speaking, the driver-side resonant frequency also involves a contribution from the piezoelectric actuator's internal RLC series resonant circuit, but this contribution is negligible because the driver's output impedance Rout is much smaller than the resistance R of the piezoelectric actuator's internal RLC series resonant circuit (R >> Rout). As a non-limiting example, Rout is represented by a value of 1 ohm, while R is represented by a value of 5 kiloohms.

[0115] However, the components inside portable electronic devices such as smartphones are very small. When the inductance (Lext) of an external inductor is tens of μH, the component height will exceed 1 mm, making it unsuitable to include an external inductor in portable electronic devices. Therefore, the Lext should be as small as possible.

[0116] Generally, various types of inductors are known, including coil inductors with coiled wires, multilayer inductors with a stack of sheets (on which conductive traces are printed), and thin-film inductors formed by sputtering or vapor deposition using semiconductor manufacturing techniques known as sputtering or vapor deposition to create coil-shaped metal film patterns. Multilayer and thin-film inductors are typically smaller than coil inductors, making them suitable for installation in portable devices such as smartphones, but their inductance is generally smaller than that of coil inductors.

[0117] This application proposes two methods to reduce the inductance of an external inductor (Lext). Embodiments of this application based on these methods can use inductors with lower inductance, enabling the use of multilayer or thin-film inductors as external inductors.

[0118] According to the first approach, the desired or permissible value of Lext is first determined based on the component height requirements. Based on the determined Lext value, the resonant frequency of the piezoelectric actuator is designed to meet the aforementioned resonance conditions. For example, the parameters of the RLC series resonant circuit in the piezoelectric actuator are adjusted so that the inductance of the external inductor is less than 30 μH (or preferably less than 20 μH, or most preferably less than 10 μH). This contrasts with traditional design techniques, where the motor parameters are fixed and the Lext value is determined accordingly. However, it should be noted that current design methods often result in higher resonant frequencies, which tend to increase switching losses.

[0119] In the second method, such as Figure 9 As shown, by adding an external capacitor with a capacitance Cadd connected in parallel with the capacitive component Cd of the piezoelectric actuator, the two resonant frequencies are essentially matched. The output voltage Vout and resonant frequency f0out of this boost circuit can be expressed as...

[0120]

[0121] Where Cadd is the capacitance of the additional parallel capacitor. Other parameters are defined as above.

[0122] The addition of this parallel capacitor increases the driver's output current due to the additional current flowing through it, but it does not waste energy because the parallel capacitor is a reactive power source that does not consume energy. The larger output current necessitates an increase in the size of the driver components, but this increase is generally tolerable in typical implementations (e.g., smartphones).

[0123] This exemplary embodiment of this aspect of the invention can reduce the inductance of the external inductor of the driver in a boost device used to provide a drive voltage for a piezoelectric actuator. This facilitates the inclusion of boost circuitry in small portable electronic devices.

[0124] Figure 10 Portable electronic devices, such as smartphones, are illustrated, incorporating any embodiment of any aspect of this application. The embodiments of this application can be used for autofocus in portable electronic devices such as smartphones, but their use is not limited thereto.

[0125] Although various embodiments have been described above and shown in the accompanying drawings, the invention is not limited to the specific embodiments described or shown.

[0126] The unit division disclosed in the embodiments of this application is not limiting; other component divisions may also be configured in the embodiments.

[0127] Where appropriate, some functions can be implemented as computer programs to enable a processor or computing device to perform one or more functions. For example, various signal processing and control functions can be implemented as computer programs. Computer programs can be stored on non-transitory computer-readable storage media. The storage medium can be any medium capable of storing computer programs, and can be: solid-state storage, such as USB drives, flash drives, read-only memory (ROM), random-access memory (RAM); magnetic storage media, such as removable or non-removable hard disks; or optical storage media, such as optical discs.

[0128] The foregoing description merely illustrates various embodiments of this application and is not intended to limit the scope of the invention. Any variations readily conceived by those skilled in the art based on the invention will fall within the scope of this application. For example, separately disclosed measures may be suitably combined in a single embodiment, provided that these measures are not mutually exclusive.

Claims

1. A drive device for driving a driven element along an axial direction, characterized in that, The driving device includes: A piezoelectric actuator, wherein the piezoelectric actuator includes a vibrating element in contact with a driven element and one or more sets of piezoelectric elements attached to the vibrating element; Controller Each group of piezoelectric elements includes one or more piezoelectric elements. In each group of piezoelectric elements, a first electrode for expanding or contracting a first region of the piezoelectric element in the group and a second electrode for expanding or contracting a second region of the piezoelectric element in the group are arranged along the axial direction. In each group of piezoelectric elements, a common third electrode or a separate third electrode paired with the first and second electrodes is provided, such that the vibrating element of the piezoelectric actuator has: A bending pattern in which the middle portion along the axial direction becomes convex or concave, thereby allowing the ends of the vibrating element to move along the axial direction at both ends. An expansion / contraction mode is described, wherein one end of the vibrating element expands / contracts at both ends of the axial direction, while the other end expands / contracts with opposite phases over time, thereby causing the end of the vibrating element to move in a direction perpendicular to the axial direction. The controller is configured to cause the vibrating element to vibrate by applying an oscillating voltage signal of the same frequency to the first electrode and the second electrode, thereby driving the driven element in contact with the vibrating element along the axial direction. Specifically, when the oscillating voltage signals applied to the first electrode and the second electrode are in phase, a first mode of vibration based on the bending mode is generated in the vibrating element; when the oscillating voltage signals applied to the first electrode and the second electrode are in opposite phase, a second mode of vibration based on the expansion / contraction mode is generated in the vibrating element. The controller is used to control the speed of the driven element by controlling the phase difference between the voltage signal applied to the first electrode and the voltage signal applied to the second electrode.

2. The driving device according to claim 1, characterized in that, The voltage signal is applied to the first electrode and the second electrode, causing the end of the vibrating element to perform an elliptical motion, the elliptical motion being a combination of a vibration component along the axial direction and a vibration component perpendicular to the axial direction. The controller is used to control the vibration amplitude of the vibration component along the axial direction and the vibration amplitude of the vibration component perpendicular to the axial direction by controlling the phase difference.

3. The driving device according to claim 1 or 2, characterized in that, The vibrating element includes a hole, and the driven element includes a cylindrical shape, wherein the driven element inserted into the hole is driven along the axial direction.

4. The driving device according to claim 1 or 2, characterized in that, The group or more piezoelectric elements attached to the vibrating element include two or more groups of piezoelectric elements attached at positions symmetrical about the vibrating element, a first identical voltage signal being applied to the first electrode of each piezoelectric element, and a second identical voltage signal being applied to the second electrode of each piezoelectric element.

5. The driving device according to claim 1 or 2, characterized in that, The controller is used to make the phase difference substantially equal to This is to make the speed of the driven element zero.

6. The driving device according to claim 1 or 2, characterized in that, The controller is configured to, when starting to drive the driven element from zero speed, essentially be Gradually decrease or increase the phase difference, and / or The controller is configured to gradually approach the phase difference to approximately [value missing] when the speed of the driven element is set to zero. .

7. The driving device according to claim 2, characterized in that, The controller is also configured to control the amplitude of the voltage signal applied to the first electrode and the second electrode to compensate for the amplitude variation of the vibration component perpendicular to the axial direction caused by the control of the phase difference.

8. The driving device according to claim 1 or 2, characterized in that, The controller is used to control the speed of the driven element by further controlling the frequency and / or amplitude of the voltage signals applied to the first electrode and the second electrode.

9. The driving device according to claim 1 or 2, characterized in that, The controller is used to control the speed of the driven element by controlling the frequency and / or amplitude of the voltage signal applied to the first electrode and the second electrode, rather than the phase of the voltage signal, when the speed of the driven element is equal to or greater than a predetermined value.

10. The driving device according to claim 1 or 2, characterized in that, The voltage signal applied to the first electrode and the second electrode is a square wave, a triangular wave, a sawtooth wave, or a sine wave.

11. The driving device according to claim 1 or 2, characterized in that, The driving device further includes a boost circuit, wherein the boost circuit is used to convert the voltage of the power supply into a voltage for driving the piezoelectric actuator.

12. The driving device according to claim 11, characterized in that, The boost circuit includes a driver for supplying voltage to the piezoelectric actuator via an external inductor.

13. The driving device according to claim 12, characterized in that, The piezoelectric actuator is represented by an equivalent circuit, which includes an internal RLC (resistor-inductor-capacitor) series resonant circuit and a parallel-connected capacitive component. The resonant frequency of the RLC series resonant circuit, which consists of the output impedance of the driver, the external inductor, and the capacitive component of the piezoelectric actuator, is substantially matched with the resonant frequency of the internal RLC series resonant circuit of the piezoelectric actuator.

14. The driving device according to claim 13, characterized in that, Adjust the parameters of the internal RLC series resonant circuit of the piezoelectric actuator so that the inductance of the external inductor is 30 μH or lower.

15. The driving device according to claim 13, characterized in that, The boost circuit has an external capacitor connected in parallel with the capacitive component of the piezoelectric actuator, such that the inductance of the external inductor is 30 μH or lower.

16. A driving device, characterized in that, The driving device includes: A piezoelectric actuator, the piezoelectric actuator comprising a vibrating element and one or more sets of piezoelectric elements attached to the vibrating element; Controller Each group of piezoelectric elements includes one or more piezoelectric elements. In each group of piezoelectric elements, a first electrode for expanding or contracting a first region of the piezoelectric element in the group and a second electrode for expanding or contracting a second region of the piezoelectric element in the group are arranged axially. In each group of piezoelectric elements, a common third electrode or a separate third electrode paired with the first and second electrodes is provided, such that the vibrating element of the piezoelectric actuator has: A bending pattern in which the middle portion along the axial direction becomes convex or concave, thereby allowing the ends of the vibrating element to move along the axial direction at both ends. An expansion / contraction mode is described, wherein one end of the vibrating element expands / contracts at both ends of the axial direction, while the other end expands / contracts with opposite phases over time, thereby causing the end of the vibrating element to move in a direction perpendicular to the axial direction. The controller is configured to cause the end of the vibrating element to perform elliptical motion by applying oscillating voltage signals of the same frequency to the first and second electrodes. The elliptical motion is a combination of a vibration component along the axial direction and a vibration component perpendicular to the axial direction. The controller is used to control the vibration amplitude of the vibration component along the axial direction and the vibration amplitude of the vibration component perpendicular to the axial direction by controlling the phase difference between the voltage signal applied to the first electrode and the voltage signal applied to the second electrode. Specifically, when the oscillating voltage signals applied to the first electrode and the second electrode are in phase, a first mode of vibration based on the bending mode is generated in the vibrating element; when the oscillating voltage signals applied to the first electrode and the second electrode are in opposite phase, a second mode of vibration based on the expansion / contraction mode is generated in the vibrating element.

17. A drive device for driving a driven element, characterized in that, The driving device includes: A piezoelectric actuator, the piezoelectric actuator comprising a vibrating element in contact with a driven element and one or more sets of piezoelectric elements attached to the vibrating element; A controller is used to control the voltage signal applied to the piezoelectric element to vibrate the vibrating element of the piezoelectric actuator, thereby driving the driven element; A boost circuit is provided to convert the voltage of the power supply into a voltage for driving the piezoelectric actuator. The boost circuit includes a driver for supplying voltage to the piezoelectric actuator via an external inductor. The piezoelectric actuator is represented by an equivalent circuit, which includes an internal RLC (resistor-inductor-capacitor) series resonant circuit and a parallel-connected capacitive component. The resonant frequency of the RLC series resonant circuit, composed of the output impedance of the driver, the external inductor, and the capacitive component of the piezoelectric actuator, is substantially matched with the resonant frequency of the internal RLC series resonant circuit of the piezoelectric actuator. in, (i) Adjusting the parameters of the internal RLC series resonant circuit of the piezoelectric actuator, and / or (ii) The boost circuit has an external capacitor connected in parallel with the capacitive component of the piezoelectric actuator. This makes the inductance of the external inductor 30 μH or lower.

18. The driving device according to claim 17, characterized in that, in, Each group of piezoelectric elements includes one or more piezoelectric elements. In each group of piezoelectric elements, a first electrode for expanding or contracting a first region of the piezoelectric element in the group and a second electrode for expanding or contracting a second region of the piezoelectric element in the group are arranged axially. In each group of piezoelectric elements, a common third electrode or a separate third electrode paired with the first and second electrodes is provided, such that the vibrating element of the piezoelectric actuator has: A bending pattern in which the middle portion along the axial direction becomes convex or concave, thereby allowing the ends of the vibrating element to move along the axial direction at both ends. An expansion / contraction mode is described, wherein one end of the vibrating element expands / contracts at both ends of the axial direction, while the other end expands / contracts with opposite phases over time, thereby causing the end of the vibrating element to move in a direction perpendicular to the axial direction. The controller is configured to cause the vibrating element to vibrate by applying an oscillating voltage signal of the same frequency to the first electrode and the second electrode, thereby driving the driven element in contact with the vibrating element along the axial direction. Specifically, when the oscillating voltage signals applied to the first electrode and the second electrode are in phase, a first mode of vibration based on the bending mode is generated in the vibrating element; when the oscillating voltage signals applied to the first electrode and the second electrode are in opposite phase, a second mode of vibration based on the expansion / contraction mode is generated in the vibrating element. The controller is used to control the speed of the driven element by controlling the phase difference between the voltage signal applied to the first electrode and the voltage signal applied to the second electrode.

19. The driving device according to claim 18, characterized in that, The voltage signal is applied to the first electrode and the second electrode, causing the end of the vibrating element to perform an elliptical motion, the elliptical motion being a combination of a vibration component along the axial direction and a vibration component perpendicular to the axial direction. The controller is used to control the vibration amplitude of the vibration component along the axial direction and the vibration amplitude of the vibration component perpendicular to the axial direction by controlling the phase difference.

20. An electronic device, characterized in that, The electronic device includes a drive device according to any one of claims 1 to 19.

21. The electronic device according to claim 20, characterized in that, The electronic device is a smartphone.

22. An electronic device, characterized in that, The electronic device includes a camera. The camera includes a driving device according to any one of claims 1 to 19. The driving device is used to drive the lens unit of the camera attached to the driven element for automatic focusing.

23. The electronic device according to claim 22, characterized in that, The electronic device is a smartphone.

24. A method for controlling a piezoelectric actuator to drive a driven element axially by an actuator, characterized in that, The piezoelectric actuator includes: A vibrating element in contact with a driven element and one or more sets of piezoelectric elements attached to the vibrating element; Each group of piezoelectric elements includes one or more piezoelectric elements. In each group of piezoelectric elements, a first electrode for expanding or contracting a first region of the piezoelectric element in the group and a second electrode for expanding or contracting a second region of the piezoelectric element in the group are arranged along the axial direction. In each group of piezoelectric elements, a common third electrode or a separate third electrode paired with the first and second electrodes is provided, such that the vibrating element of the piezoelectric actuator has: A bending pattern in which the middle portion along the axial direction becomes convex or concave, thereby allowing the ends of the vibrating element to move along the axial direction at both ends. An expansion / contraction mode is described, wherein one end of the vibrating element expands / contracts at both ends of the axial direction, while the other end expands / contracts with opposite phases over time, thereby causing the end of the vibrating element to move in a direction perpendicular to the axial direction. The method includes: By applying an oscillating voltage signal of the same frequency to the first electrode and the second electrode, the vibrating element is made to vibrate, thereby driving the driven element in contact with the vibrating element along the axial direction. The speed of the driven element is controlled by controlling the phase difference between the voltage signal applied to the first electrode and the voltage signal applied to the second electrode. Specifically, when the oscillating voltage signals applied to the first electrode and the second electrode are in phase, a first mode of vibration based on the bending mode is generated in the vibrating element; when the oscillating voltage signals applied to the first electrode and the second electrode are in opposite phase, a second mode of vibration based on the expansion / contraction mode is generated in the vibrating element.

25. The method according to claim 24, characterized in that, Applying the voltage signal to the first and second electrodes causes the end of the vibrating element to perform an elliptical motion, the elliptical motion being a combination of a vibration component along the axial direction and a vibration component perpendicular to the axial direction. The control of the speed of the driven element by controlling the phase difference includes controlling the vibration amplitude of the vibration component along the axial direction and the vibration amplitude of the vibration component perpendicular to the axial direction by controlling the phase difference.

26. The method according to claim 24 or 25, characterized in that, The method further includes making the phase difference substantially equal to... This is to make the speed of the driven element zero.

27. The method according to claim 24 or 25, characterized in that, The method further includes: When starting to drive the driven element from zero speed, it is essentially... Gradually decrease or increase the phase difference, and / or When the velocity of the driven element is set to zero, the phase difference is gradually brought closer to approximately [value missing]. .

28. The method according to claim 25, characterized in that, The method further includes controlling the amplitude of the voltage signals applied to the first electrode and the second electrode to compensate for the amplitude variation of the vibration component perpendicular to the axial direction caused by the control of the phase difference.

29. The method according to claim 24 or 25, characterized in that, The method further includes controlling the speed of the driven element by further controlling the frequency and / or amplitude of the voltage signals applied to the first electrode and the second electrode.

30. The method according to claim 24 or 25, characterized in that, The method further includes controlling the speed of the driven element by controlling the frequency and / or amplitude of the voltage signal applied to the first electrode and the second electrode, rather than the phase of the voltage signal, when the speed of the driven element is equal to or greater than a predetermined value.

31. A computer program product, characterized in that, The computer program product includes a computer program for causing the driver to perform the method according to any one of claims 24 to 30.

32. A computer-readable storage medium, characterized in that, A computer program is stored on the computer-readable storage medium, the computer program being used to cause the driver to perform the method according to any one of claims 24 to 30.

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