JP2020089133A - Control method of piezoelectric drive device - Google Patents

Abstract

To provide a control method of a piezoelectric drive device capable of exhibiting excellent drive characteristics.SOLUTION: A control method of a piezoelectric drive device including a piezoelectric vibrator that includes a vibrating portion including first and second piezoelectric elements, and a convex portion connected to the vibrating portion, and in which the vibrating portion expands and contracts in the expansion and contraction direction due to expansion and contraction of the first piezoelectric element, and are bent and vibrated in a direction orthogonal to the expansion and contraction direction due to expansion and contraction of the second piezoelectric element, and a driven portion that comes into contact with the convex portion and transmits and moves the rotational movement of the convex portion, and in a case in which the driven portion is moved toward the target position by vibrating the piezoelectric vibrator, when the driven portion becomes in an abnormal condition which is a state where the driven portion moves in the direction opposite to the direction in which the target position is or a state where the movement of the driven portion is stopped, one of a phase difference between a first drive signal applied to the first piezoelectric element and a second drive signal applied to the second piezoelectric element, the amplitude of the first drive signal, and the frequencies of the first drive signal and the second drive signal is changed.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for controlling a piezoelectric drive device.

The ultrasonic motor described in Patent Document 1 is a rotor that is rotatable about a rotation axis, an elastic body that is provided in contact with the rotor, and an elastic body. It has a piezoelectric body for rotating the rotor around a rotation axis and a torque sensor for detecting a load applied to the rotor. Then, based on the load detected by the torque sensor, the operation is always performed at a frequency higher than the resonance frequency of the ultrasonic sensor to prevent the rotation of the rotor from stopping or reversing. If the rotation of the rotor is stopped or the rotor is rotated in the reverse direction, the drive is temporarily stopped and the drive start control is restarted from the beginning.

Japanese Patent Laid-Open No. 2-303379

The ultrasonic motor configured as described above has a problem that the rotation of the rotor is likely to stop or reverse again because the conditions for re-driving are the same as those of the previous time.

A control method for a piezoelectric drive device according to the present invention includes a vibrating portion including a first piezoelectric element and a second piezoelectric element, and a convex portion connected to the vibrating portion, wherein the vibrating portion is the first piezoelectric element. A piezoelectric vibrator in which the convex portion rotates by vibrating in the direction of expansion and contraction due to expansion and contraction of the element and bending and vibration in a direction orthogonal to the direction of expansion and contraction due to expansion and contraction of the second piezoelectric element,
A method for controlling a piezoelectric vibrating device, comprising: a driven portion that is in contact with the convex portion and is moved by transmitting the rotational movement of the convex portion,
When the piezoelectric vibrator is vibrated to move the driven part toward the target position, the driven part moves in a direction opposite to the direction in which the target position exists, or the movement of the driven part stops. If there is an abnormal condition that is
The phase difference between the first drive signal applied to the first piezoelectric element and the second drive signal applied to the second piezoelectric element, the amplitude of the first drive signal, and the first drive signal and the second drive. It is characterized in that any one of the frequencies of the signal is changed.

It is a top view showing the whole piezoelectric motor composition concerning a 1st embodiment of the present invention. It is a figure which shows the drive voltage applied to the piezoelectric vibrator shown in FIG. FIG. 3 is a plan view showing a state of the piezoelectric vibrator when the drive voltage shown in FIG. 2 is applied. It is a figure which shows the drive voltage applied to the piezoelectric vibrator shown in FIG. FIG. 5 is a plan view showing a state of the piezoelectric vibrator when the drive voltage shown in FIG. 4 is applied. 3 is a flowchart for explaining a method of controlling the piezoelectric motor shown in FIG. It is a graph which shows the relationship between the frequency of a drive signal, and the amplitude of a convex part. It is a figure which shows an example of the change order of a drive condition. It is a flow chart which shows the control method of the piezo-electric motor concerning a 2nd embodiment of the present invention.

Hereinafter, a method for controlling a piezoelectric driving device of the present invention will be described in detail based on an embodiment shown in the accompanying drawings.

<First Embodiment>
FIG. 1 is a plan view showing the overall configuration of the piezoelectric motor according to the first embodiment of the present invention. FIG. 2 is a diagram showing a drive voltage applied to the piezoelectric vibrator shown in FIG. FIG. 3 is a plan view showing a state of the piezoelectric vibrator when the drive voltage shown in FIG. 2 is applied. FIG. 4 is a diagram showing a drive voltage applied to the piezoelectric vibrator shown in FIG. FIG. 5 is a plan view showing a state of the piezoelectric vibrator when the drive voltage shown in FIG. 4 is applied. FIG. 6 is a flow chart for explaining the method of controlling the piezoelectric motor shown in FIG. FIG. 7 is a graph showing the relationship between the frequency of the drive signal and the amplitude of the convex portion. FIG. 8 is a diagram showing an example of the order of changing the driving conditions.

In the following description, for convenience of description, three axes orthogonal to each other are referred to as an X axis, a Y axis, and a Z axis, a direction along the X axis is an X axis direction, a direction along the Y axis is a Y axis direction (first direction), and The direction along the Z axis is also referred to as the Z axis direction (second direction). The arrow side of each axis is also referred to as a "plus side", and the opposite side of the arrow is also referred to as a "minus side". Further, the X-axis direction positive side is also referred to as "upper" or "upper side", and the X-axis direction negative side is also referred to as "lower" or "lower side".

A piezoelectric motor 1 shown in FIG. 1 is a piezoelectric drive device, and is a disk-shaped member that is in contact with an outer peripheral surface 21 of a rotor 2 and a rotor 2 that is a driven portion that is rotatable about its central axis O, and that drives the rotor 2. It has a piezoelectric vibrator 4 that rotates about a central axis O, and a control device 7 that controls driving of the piezoelectric vibrator 4. Further, the piezoelectric motor has a biasing member (not shown) that biases the piezoelectric vibrator 4 toward the rotor 2. In the piezoelectric motor 1 having such a configuration, when the piezoelectric vibrator 4 flexurally vibrates, the vibration is transmitted to the rotor 2, and the rotor 2 rotates around the central axis O in the arrow B1 direction or the arrow B2 direction. When the rotor 2 rotates, the outer peripheral surface 21 of the rotor 2 moves in the circumferential direction.

The configuration of the piezoelectric motor 1 is not limited to that shown in FIG. For example, a plurality of piezoelectric vibrators 4 may be arranged along the circumferential direction of the rotor 2 and the rotor 2 may be rotated by driving the plurality of piezoelectric vibrators 4. The piezoelectric vibrator 4 may be in contact with the main surface 29 of the rotor 2 instead of the outer peripheral surface 21 of the rotor 2. Further, the driven part is not limited to the rotating body such as the rotor 2, and may be, for example, a slider that moves linearly. Here, “moving” of the driven member is synonymous with displacement, and not only when the entire driven member moves in the X-axis, Y-axis, or Z-axis direction, but also a part of the driven member, for example, The case where the outer peripheral surface 21 moves in the circumferential direction is also included. Therefore, rotation of the rotor 2 can be said to be movement of the driven member.

An encoder 9 is provided on the rotor 2, and the encoder 9 can detect the behavior of the rotor 2, in particular, the rotation amount and the angular velocity. The encoder 9 is not particularly limited, and may be, for example, an incremental encoder that detects the amount of rotation of the rotor 2 when the rotor 2 is rotated, or regardless of whether the rotor 2 is rotated or not. It may be an absolute encoder that detects an absolute position. The encoder 9 functions as a detection unit that detects an abnormal state described later.

The piezoelectric vibrator 4 is connected to the vibrating portion 41, the supporting portion 42 that supports the vibrating portion 41, the connecting portion 43 that connects the vibrating portion 41 and the supporting portion 42, and the vibrating portion 41 vibrates. And a convex portion 44 that transmits to the rotor 2.

The vibrating portion 41 has a plate shape that extends in the YZ plane including the Y axis and the Z axis with the thickness direction in the X axis direction, and is S-shaped by bending in the Z axis direction while expanding and contracting in the Y axis direction. Flexing and vibrating. In addition, the vibrating portion 41 has a longitudinal shape with the Y-axis direction, which is the expansion/contraction direction, as the longitudinal direction in a plan view from the X-axis direction. However, the shape of the vibrating portion 41 is not particularly limited as long as it can exhibit its function.

Further, the vibrating portion 41 has piezoelectric elements 6A to 6E for causing the vibrating portion 41 to flexurally vibrate. The piezoelectric element 6C is arranged in the central portion of the vibrating portion 41 along the Y-axis direction that is the longitudinal direction of the vibrating portion 41. Piezoelectric elements 6A and 6B are arranged side by side in the longitudinal direction of the vibrating section 41 on the positive side of the vibrating section 41 with respect to the piezoelectric element 6C, and piezoelectric elements 6D and 6E vibrate on the negative side of the Z axis direction. The parts 41 are arranged side by side in the longitudinal direction. In addition, each of the piezoelectric elements 6A to 6E expands and contracts in the Y-axis direction, which is the longitudinal direction of the vibrating portion 41, by energization. The piezoelectric elements 6A and 6E are electrically connected to each other, and the piezoelectric elements 6B and 6D are electrically connected to each other.

In the present embodiment, the piezoelectric element 6C corresponds to the "first piezoelectric element", and the piezoelectric elements 6A and 6E or the piezoelectric elements 6B and 6D correspond to the "second piezoelectric element".

The convex portion 44 is provided at the tip of the vibrating portion 41 and projects from the vibrating portion 41 to the Y axis direction plus side. The tip surface of the convex portion 44 is in contact with the outer peripheral surface 21 of the rotor 2. Therefore, the vibration of the vibrating portion 41 is transmitted to the rotor 2 via the convex portion 44.

When the drive signal V1 shown in FIG. 2 is applied to the piezoelectric elements 6A and 6E, the drive signal V2 is applied to the piezoelectric element 6C, and the drive signal V3 is applied to the piezoelectric elements 6B and 6D, as shown in FIG. 6C expands and contracts to vibrate the vibrating part 41 in the Y-axis direction, and the vibrating part 41 flexurally vibrates in the Z-axis direction in the Z-axis due to the expansion and contraction of the piezoelectric elements 6A and 6E and the piezoelectric elements 6B and 6D at different timings. Then, the stretching vibration and the bending vibration are combined, and the tip of the convex portion 44 makes an elliptic motion that draws an elliptical orbit counterclockwise as shown by an arrow A1. The rotor 2 is sent out by such an elliptic movement of the convex portion 44, and the rotor 2 rotates clockwise as indicated by an arrow B1.

On the contrary, when the drive signal V1 shown in FIG. 4 is applied to the piezoelectric elements 6B and 6D, the drive signal V2 is applied to the piezoelectric element 6C, and the drive signal V3 is applied to the piezoelectric elements 6A and 6E, as shown in FIG. While the vibrating part 41 expands and contracts in the Y-axis direction due to the expansion and contraction of the piezoelectric element 6C, the vibrating part 41 is S-shaped in the Z-axis direction due to the expansion and contraction of the piezoelectric elements 6A and 6E and the piezoelectric elements 6B and 6D at different timings. The bending vibration is generated, and the stretching vibration and the bending vibration are combined, and the convex portion 44 makes an elliptic motion in the clockwise direction as shown by an arrow A2. Due to the elliptic movement of the convex portion 44, the rotor 2 is sent out, and the rotor 2 rotates counterclockwise as indicated by the arrow B2.

The drive signals V1, V2, and V3 have the same frequency f. Further, the phase difference between the drive signals V1 and V2 is maintained at 180°. This relationship is maintained even when the driving condition of the piezoelectric vibrator 4 is changed, as will be described later.

The control device 7 controls the drive of the piezoelectric vibrator 4 based on a command from a host computer (not shown) so that the position of the rotor 2 becomes a target position (target angle) at a predetermined time. That is, the control device 7 controls to apply desired drive signals to the piezoelectric element 6C that is the first piezoelectric element and the second piezoelectric elements 6A, 6B, 6D, and 6E, respectively. Further, the control device 7 has a function of determining whether or not it is in an “abnormal state” described later. Such a control device 7 is composed of, for example, a computer having at least one CPU that executes a predetermined program, a main memory that temporarily stores programs and data, and an auxiliary memory such as a flash memory. ing.

For example, as shown in FIG. 3, the convex portion 44 is caused to make an elliptical motion in the counterclockwise direction as indicated by an arrow A1, and the rotor 2 is rotated around the arrow B1 to apply the drive signal V1 to the piezoelectric elements 6A, 6E, Even if the drive signal V2 is applied to the piezoelectric element 6C and the drive signal V3 is applied to the piezoelectric elements 6B and 6D, the elliptical motion of the convex portion 44 does not become the elliptical orbit indicated by the arrow A1 for some reason, and the Thus, the rotor 2 may rotate around the arrow B2 opposite to the arrow B1, or the rotor 2 may rotate around the arrow B1, but the angular velocity thereof may be slower than the target angular velocity. The "some cause" is, for example, the posture of the piezoelectric vibrator 4 immediately before the vibration of the piezoelectric vibrator 4 is started, the contact state between the convex portion 44 and the outer peripheral surface 21 of the rotor 2, the tip of the convex portion 44. The surface state of the surface and the outer peripheral surface 21, the method of applying the drive signals V1, V2, V3, and the like are considered.

In this way, when the rotor 2 moves abnormally, the driving characteristics of the piezoelectric motor 1 deteriorate. Therefore, when an abnormal movement of the rotor 2 occurs, the control device 7 promptly returns to the normal movement of the rotor 2, that is, the piezoelectric vibration so as to return to the movement having the desired angular velocity around the arrow B1 in the above example. The drive of the child 4 is controlled. Hereinafter, a method of controlling the piezoelectric motor 1 by the control device 7 will be described with reference to the flowchart shown in FIG.

As shown in FIG. 6, first, in step S1, a drive command is input to the control device 7 via a host computer (not shown) or the like. The drive command includes the target position of the rotor 2 at each time. In the figure, “5000 in the direction of arrow B1” corresponds to the target position. Next, the control device 7 acquires the current position information of the rotor 2 from the encoder 9 in step S2.

Next, in step S3, the control device 7 generates drive signals V1, V2, V3 such that the position of the rotor 2 becomes the target position, applies the drive signal V1 to the piezoelectric elements 6A, 6E, and drives the drive signal V2. Is applied to the piezoelectric element 6C, and the drive signal V3 is applied to the piezoelectric elements 6B and 6D. As a result, when the piezoelectric vibrator 4 is normally driven, the convex portion 44 makes an elliptic motion as shown by an arrow A1, and accordingly the rotor 2 rotates at a predetermined angular velocity around the arrow B1 and the rotor 2 moves at a predetermined time. Becomes the target position.

Next, the control device 7 acquires the current position information of the rotor 2 from the encoder 9 in step S4. Then, in step S5, the control device 7 sets the “current position”, which is the position of the encoder 9 acquired in step S4, and the “previous position”, which is the position of the encoder 9 acquired in step S2 prior to that, To compare. If the current position-previous position>0, the rotor 2 is rotating normally around the arrow B1 toward the target position, and if the current position-previous position<0, the rotor 2 is the target position. It is an abnormal state of rotating around the arrow B2 toward the opposite side, and if the current position-previous position=0, it can be determined that the rotor 2 is in an abnormal state of being stopped.

If the determination in step S5 is Yes, that is, if the rotation of the rotor 2 is in a normal state, the control device 7 drives the "current position", which is the position of the encoder 9 acquired in step S4, in step S6. Compare with the "target position" included in the command. When the determination in step S6 is Yse, that is, when the current position is equal to the target position, the control device 7 stops applying the drive signals V1 to V3 to the piezoelectric elements 6A to 6E in step S7. The driving of the piezoelectric vibrator 4 is stopped. As a result, the rotor 2 stops at the target position. As described above, the piezoelectric vibrator 4 is biased toward the outer peripheral surface 21 of the rotor 2 by a biasing member (not shown). Therefore, when the driving of the piezoelectric vibrator 4 is stopped, the convex portion 44 is pressed against the outer peripheral surface 21, thereby braking the rotor 2 and maintaining the rotor 2 at the target position.

On the other hand, when the determination in step S6 is No, that is, when the current position is different from the target position, the control device 7 returns to step S4 and repeats steps S4 and S5 until the determination in step S6 becomes Yse. repeat.

Further, when the determination in step S5 described above is No, that is, when the rotation of the rotor 2 is in an abnormal state, the control device 7 can change the driving condition of the piezoelectric vibrator 4 in step S8. To judge. The "driving condition" will be described in detail later. Then, if the determination in step S8 is Yes, that is, if the drive condition of the piezoelectric vibrator 4 can be changed, the control device 7 changes the drive condition of the piezoelectric vibrator 4 and changes the new condition. The piezoelectric vibrator 4 is driven according to the driving conditions. In this way, by driving the piezoelectric vibrator 4 under different driving conditions, the elliptical movement of the convex portion 44 may be restored to the normal elliptical orbit indicated by the arrow A1, and the movement of the rotor 2 may return to the normal state.

Next, the control device 7 returns to step S4 and acquires the current position information of the rotor 2 from the encoder 9. Then, in step S5, the control device 7 sets the "current position", which is the position of the encoder 9 obtained in the immediately preceding step S4, and the "previous position", which is the position of the encoder 9 obtained in step S4 one time before that. Position". That is, the position of the rotor 2 is compared before and after changing the driving condition of the piezoelectric vibrator 4. If the determination in step S5 is Yes, the process proceeds to step S6, and if No, the process proceeds to step S8 to determine again whether the drive condition of the piezoelectric vibrator 4 can be changed. If the determination in step S8 is No, that is, if the driving conditions of the piezoelectric vibrator 4 have been completely changed and there is no driving condition to be changed, the control device 7 proceeds to step S7 and Stop driving. If the determination in step S8 is No, it means that the measure for returning the movement of the rotor 2 from the abnormal state to the normal state has been exhausted. Therefore, by stopping the driving of the piezoelectric vibrator 4 as described above, Further movement of the rotor 2 in an abnormal state can be suppressed, and deviation of the rotor 2 from the target position can be suppressed small.

The control method of the piezoelectric vibrator 4 by the control device 7 has been briefly described above. Next, step S9 described above, that is, the change of the driving condition of the piezoelectric vibrator 4 will be described in more detail. The control device 7 changes the driving condition in order to change the locus of the elliptical vibration of the convex portion 44. The control device 7 has, as drive conditions to be changed, a phase difference θ between the drive signals V1 and V2, an amplitude D of the drive signal V2, and a frequency f of the drive signals V1, V2, and V3. Each time S9 is repeated, at least one of these three conditions is changed.

In the present embodiment, the only condition to be changed in step S9 is any one of the phase difference θ, the amplitude D and the frequency f. As a result, it is possible to prevent the driving conditions from being changed excessively and complicatedly. Further, if the movement of the rotor 2 returns to the normal state due to the change of the driving condition, it is possible to more clearly determine the cause of the abnormal state and feed it back to the future driving. Become.

Further, in the present embodiment, the control device 7 changes the driving condition of the piezoelectric vibrator 4 in the order of the phase difference θ, the amplitude D, and the frequency f. That is, first, if the phase difference θ is changed and the movement of the rotor 2 still does not return from the abnormal state to the normal state, the amplitude D is changed and the movement of the rotor 2 still does not return from the abnormal state to the normal state. To change the frequency f.

The reason for changing in this order will be described. When the phase difference θ is changed, the inclination of the major axis of the elliptic motion of the convex portion 44 changes, and when the amplitude D is changed, the Y axis of the elliptic motion of the convex portion 44 mainly changes. When the amplitude in the axial direction changes and the frequency f is changed, the magnitude of the elliptic motion of the convex portion 44 (the overall amplitude) mainly changes. Therefore, changing the phase difference θ among the phase difference θ, the amplitude D, and the frequency f is most effective for changing the locus of the elliptic motion of the convex portion 44, and changing the amplitude D is as follows. Is effective, and changing the frequency f is effective next. Therefore, as described above, by changing the driving condition of the piezoelectric vibrator 4 in the order of the phase difference θ, the amplitude D, and the frequency f, the movement of the rotor 2 is returned from the abnormal state to the normal state in a shorter time. be able to.

As another reason, the phase difference θ and the amplitude D can be changed without stopping the application of the drive signals V1 to V3 to the piezoelectric elements 6A to 6E, respectively. That is, the phase difference θ and the amplitude D can be changed while continuing to drive the piezoelectric vibrator 4. Therefore, with the phase difference θ and the amplitude D, the driving condition can be changed quickly, and the movement of the rotor 2 can be returned from the abnormal state to the normal state in a shorter time. On the other hand, to change the frequency f, the driving of the piezoelectric vibrator 4 must be temporarily stopped. That is, it is necessary to stop applying the drive signals V1 to V3 to the piezoelectric vibrator 4 and apply the drive signals V1 to V3 having the changed frequency f to the piezoelectric vibrator 4 again. This is because “down sweep control” is performed to drive the piezoelectric vibrator 4, as described later. Therefore, when the frequency is f, the drive condition cannot be changed promptly. For this reason, it is preferable to change the phase difference θ and the amplitude D before changing the frequency f.

However, the order of changing the drive conditions is not limited to the order of the phase difference θ, the amplitude D, and the frequency f, and may be the order of the phase difference θ, the frequency f, and the amplitude D, or the amplitude D, the phase difference θ, and the frequency. The order may be f, the order may be the amplitude D, the frequency f, and the phase difference θ, the order may be the frequency f, the phase difference θ, and the amplitude D, or the frequency f and the amplitude D. , The phase difference θ may be in this order.

First, the change of the phase difference θ will be described. For example, even in the abnormal state, when the rotor 2 is rotating around the arrow B2 toward the side opposite to the target position, the convex portion 44 follows the locus indicated by the arrow A2 opposite to the locus indicated by the arrow A1. It is highly possible that it is moving in an elliptical fashion. Therefore, in order to reverse the locus of the elliptic movement, the control device 7 changes the driving condition of the piezoelectric vibrator 4 to one in which the phases of the driving signals V1 and V3 are reversed. That is, the phase shown in FIG. 2 is changed to the phase shown in FIG. As a result, the locus of the elliptic motion of the convex portion 44 is reversed, and the movement of the rotor 2 may return from the abnormal state to the normal state.

When the movement of the rotor 2 does not return from the abnormal state to the normal state even if the drive conditions are changed as described above, the control device 7 sets the phase difference θ to 30°, 60°, 90°, 120°, 250°. As described above, the locus of the elliptic movement of the convex portion 44 is gradually changed. Every time the controller 7 changes the phase difference θ, the controller 7 determines in step S5 whether the movement of the rotor 2 has returned from the abnormal state to the normal state. As described above, by gradually changing the phase difference θ, the locus of the elliptic movement of the convex portion 44 becomes a normal locus somewhere, and the movement of the rotor 2 may return from the abnormal state to the normal state.

The controller 7 changes the phase difference θ as described above while continuing to apply the drive signals V1 to V3 to the piezoelectric elements 6A to 6E. As a result, the phase difference θ can be changed more quickly, and the movement of the rotor 2 can be returned from the abnormal state to the normal state in a short time. Further, the control device 7 is in the process of changing the phase difference θ, that is, from the start of changing the phase difference θ to the start of driving the piezoelectric vibrator 4 with the changed phase difference θ. The amplitudes of the drive signals V1 and V3 may be temporarily reduced. As a result, during the process of changing the phase difference θ, the angular velocity of the rotor 2 becomes small, the movement of the rotor 2 in an abnormal state can be suppressed, and the expansion of the deviation from the target position can be effectively suppressed. be able to. However, the present invention is not limited to this, and the control device 7 may change the phase difference θ as described above by stopping the application of the drive signals V1 to V3 to the piezoelectric elements 6A to 6E.

When the movement of the rotor 2 does not return from the abnormal state to the normal state even by changing the phase difference θ as described above, the control device 7 resets the drive condition to the initial value and then sets the amplitude D of the drive signal V2. change. Specifically, the control device 7 gradually increases the initial value, such as 1.5 times, 2.0 times, 2.5 times, and 3.0 times, and the locus of the elliptic motion of the convex portion 44. Gradually change. Each time the control device 7 changes the amplitude, it determines in step S5 whether the movement of the rotor 2 has returned from the abnormal state to the normal state. In this way, by gradually changing the amplitude D, the locus of the elliptic movement of the convex portion 44 becomes a normal locus somewhere, and the movement of the rotor 2 may return from the abnormal state to the normal state.

As described above, by resetting the condition of the phase difference θ to the initial value when the amplitude D is changed, if the movement of the rotor 2 returns to the normal state due to the change of the amplitude D, an abnormal state occurs. It is possible to more clearly determine that the cause is the amplitude D, and it is possible to feed this back to future driving. Note that the change of the amplitude D does not gradually increase from the initial value, but gradually decreases from the initial value such as 0.8 times, 0.6 times, 0.4 times, and 0.2 times the initial value. You may let me.

The controller 7 changes the amplitude D as described above while continuing to apply the drive signals V1 to V3 to the piezoelectric elements 6A to 6E. As a result, the amplitude D can be changed more quickly, and the movement of the rotor 2 can be returned from the abnormal state to the normal state in a short time. Further, during the process of changing the amplitude D, that is, during the period from the start of the change of the amplitude D to the start of the driving of the piezoelectric vibrator 4 with the changed amplitude D, the controller 7 drives the drive signal. The amplitudes of V1 and V3 may be temporarily reduced. As a result, during the process of changing the amplitude D, the angular velocity of the rotor 2 becomes small, the movement of the rotor 2 in an abnormal state can be suppressed, and the expansion of the deviation from the target position can be effectively suppressed. You can However, the present invention is not limited to this, and the control device 7 may change the amplitude D as described above by stopping the application of the drive signals V1 to V3 to the piezoelectric elements 6A to 6E.

When the movement of the rotor 2 does not return from the abnormal state to the normal state even by the change of the amplitude D as described above, the control device 7 resets the drive condition to the initial value and then the frequencies of the drive signals V1 to V3. Change f.

Here, before explaining the change of the frequency f, the frequency characteristic of the piezoelectric vibrator 4 will be described with reference to FIG. 7. FIG. 7 is a graph showing the relationship between the frequency f of the drive signals V1 to V3 and the amplitude of the convex portion 44. As shown in the figure, in the region where the frequency is lower than the resonance frequency f0, the amplitude of the convex portion 44 sharply decreases as the frequency f is separated from the resonance frequency f0, but in the region where the frequency is higher than the resonance frequency f0. , The amplitude gradually decreases as the frequency f moves away from the resonance frequency f0. Therefore, the initial value fa of the frequency f is set in a region higher than the resonance frequency f0. As a result, the rate of change of the amplitude of the convex portion 44 with respect to the frequency f becomes small, so that the amplitude of the convex portion 44 can be controlled more finely and accurately.

Based on such a premise, the control device 7 gradually lowers the frequency f of the drive signals V1 to V3 from the initial value fa toward the resonance frequency f0, and gradually moves the locus of the elliptic movement of the convex portion 44. Change to. Every time the control device 7 changes the frequency f, it determines in step S5 whether the movement of the rotor 2 has returned from the abnormal state to the normal state. As described above, by gradually changing the frequency f, the locus of the elliptic movement of the convex portion 44 becomes a normal locus somewhere, and the movement of the rotor 2 may return from the abnormal state to the normal state.

As described above, by resetting the condition of the amplitude D to the initial value when changing the frequency f, if the movement of the rotor 2 returns to the normal state due to the change of the frequency f, an abnormal state occurs. It is possible to more clearly determine that the cause is the frequency f, and it is possible to feed this back to future driving. Note that the frequency f may be changed gradually from the initial value fa instead of gradually decreasing from the initial value fa.

Since the piezoelectric vibrator 4 is pressed against the rotor 2, the Q value of the piezoelectric vibrator 4 is low. Therefore, even if drive signals V1 to V3 having a frequency equal to the frequency f1 (frequency close to the resonance frequency f0) set in the drive condition are suddenly applied to the piezoelectric elements 6A to 6E, the piezoelectric vibrator 4 does not oscillate and the convex portion is formed. The elliptical motion of 44 may not occur. Therefore, the control device 7 applies drive signals V1 to V3 having a frequency fm higher than the frequency f1 to the piezoelectric elements 6A to 6E to cause elliptical movement of the convex portion 44 with a small amplitude, and then gradually drives from there. The "down sweep control", which is a control for bringing the frequencies of the signals V1 to V3 closer to f1 from the frequency fm, is performed. Therefore, when the frequency f is changed as described above, it is preferable to change the frequency fm for starting the down sweep control accordingly.

The controller 7 changes the frequency f as described above by stopping the application of the drive signals V1 to V3 to the piezoelectric elements 6A to 6E. Thereby, the piezoelectric vibrator 4 can be re-driven by the down sweep control, and the piezoelectric vibrator 4 can be driven more reliably at the changed frequency f. However, the present invention is not limited to this, and the control device 7 may change the frequency f as described above while continuing to apply the drive signals V1 to V3 to the piezoelectric elements 6A to 6E.

The change of the driving condition performed by the control device 7 has been described above. When the determination in step S5 results in No even though the phase difference θ, the amplitude D, and the frequency f have all been changed in order, the control device 7 proceeds from step S8 to step S8 as described above. Proceeding to S7, the piezoelectric vibrator 4 is stopped urgently.

Note that, in the present embodiment, the control device 7 sequentially changes only one of the phase difference θ, the amplitude D, and the frequency f, but the present invention is not limited to this, and the phase difference θ, the amplitude D, and the frequency f are not limited thereto. Two or all selected from may be changed at the same time. For example, as shown in FIG. 8, initially, only one element selected from the phase difference θ, the amplitude D and the frequency f is changed, and even if the movement of the rotor 2 does not return to the normal state, the phase difference θ , The amplitude D and the frequency f are changed, and if the movement of the rotor 2 still does not return to the normal state, the phase difference θ, the amplitude D and the frequency f may all be changed.

Further, for example, when the current position and the target position are close to each other and there is no time to change the driving condition, that is, when the current position passes the target position while changing the driving condition, the driving condition that can be changed However, even if there is left, the application of the drive signals V1 to V3 to the piezoelectric vibrator 4 may be stopped and the driving of the piezoelectric vibrator 4 may be stopped.

The control method of the piezoelectric motor 1 has been described above. As described above, the method of controlling the piezoelectric motor 1 includes the vibrating section 41 including the piezoelectric element 6C as the first piezoelectric element and the piezoelectric elements 6A, 6B, 6D, and 6E as the second piezoelectric element, and the vibrating section. The vibrating portion 41 expands and contracts in the Y-axis direction, which is the direction of expansion and contraction, by the expansion and contraction of the piezoelectric element 6C, and the expansion and contraction of the piezoelectric elements 6A, 6B, 6D, and 6E. By bending and vibrating in the Z-axis direction, which is a direction orthogonal to the expansion and contraction direction, the convex portion 44 makes a rotational movement, in particular, the piezoelectric vibrator 4 which makes an elliptical movement in the present embodiment, and the convex portion 44 comes into contact with the convex portion 44. A method of controlling a piezoelectric motor 1 as a piezoelectric vibrating device having a rotor 2 as a driven part that is moved by transmitting the rotational motion of the above. In such a control method, when the piezoelectric vibrator 4 is vibrated and the rotor 2 is moved toward the target position, the rotor 2 moves in the direction opposite to the direction in which the target position is present, or the movement of the rotor 2. In the case of an abnormal state in which is stopped, the drive signal V2 as the first drive signal applied to the piezoelectric element 6C and the drive signal V1 as the second drive signal applied to the piezoelectric elements 6A and 6E are compared with each other. Any one of the phase difference θ, the amplitude D of the drive signal V2, and the frequency f of the drive signals V1, V2, and V3 is changed. By changing the driving condition in this way, the movement of the rotor 2 can be more reliably returned from the abnormal state to the normal state in which the target position moves in a certain direction. Therefore, the piezoelectric motor 1 has excellent driving characteristics.

That is, the piezoelectric motor 1 has the control device 7 that controls the piezoelectric element 6C to apply the drive signal V2 and the piezoelectric elements 6A, 6B, 6D, and 6E to apply the drive signals V1 and V3. Then, when the piezoelectric vibrator 4 is vibrated to move the rotor 2 toward the target position, the rotor 2 moves to the opposite side of the target position or the abnormal state in which the movement of the rotor 2 is stopped. In such a case, the control device 7 controls to change at least one of the phase difference θ between the drive signals V2 and V1, the amplitude D of the drive signal V2, and the frequency f of the drive signals V1, V2, and V3. .. In this way, by changing the driving condition, the movement of the rotor 2 can be more reliably returned from the abnormal state to the normal state. Therefore, the piezoelectric motor 1 has excellent driving characteristics.

Further, as described above, when the movement of the rotor 2 is in an abnormal state, the phase difference θ between the drive signal V1 and the drive signal V2 is changed. Among the phase difference θ, the amplitude D, and the frequency f, changing the phase difference θ is most effective for changing the locus of the elliptic motion of the convex portion 44. Therefore, first, by changing the phase difference θ, the movement of the rotor 2 can be returned from the abnormal state to the normal state in a short time.

Further, as described above, if the movement of the rotor 2 continues to be in the abnormal state even if the phase difference θ is changed, the amplitude D of the drive signal V2 is changed. Among the phase difference θ, the amplitude D, and the frequency f, changing the amplitude D is effective for changing the phase difference θ and then changing the locus of the elliptical motion of the convex portion 44. Therefore, first, when the movement of the rotor 2 does not return to the normal state due to the change of the phase difference θ, next, by changing the amplitude D, the movement of the rotor 2 is changed from the abnormal state to the normal state in a short time. Can be returned to.

Further, as described above, when changing the amplitude D of the drive signal V2, the phase difference θ is returned to the initial value before the change. As a result, the parameter that is changed from the initial drive condition can be only the amplitude D, so that the drive condition can be easily changed. Further, if the movement of the rotor 2 returns to the normal state by changing the amplitude D, it is possible to more clearly determine that the cause of the abnormal state is the amplitude D.

Further, as described above, if the movement of the rotor 2 is in an abnormal state even if the amplitude D of the drive signal V2 is changed, the frequency f of the drive signals V1 to V3 is changed. Among the phase difference θ, the amplitude D, and the frequency f, changing the frequency f has the least effect on changing the locus of the elliptical motion of the convex portion 44. Therefore, the movement of the rotor 2 can be returned from the abnormal state to the normal state in a short time by changing the frequency f last and then performing the phase difference θ and the amplitude D which are more effective than the change. ..

Further, as described above, when the frequency f of the drive signals V1 to V3 is changed, the amplitude D is returned to the initial value before the change. As a result, the parameter that is changed from the initial drive condition can be only the frequency f, so that the drive condition can be easily changed. Further, if the movement of the rotor 2 returns to the normal state by changing the frequency f, it is possible to more clearly determine that the cause of the abnormal state was the frequency f.

<Second Embodiment>
FIG. 9 is a flowchart showing a method of controlling a piezoelectric motor according to the second embodiment of the present invention.

The present embodiment is the same as the above-described first embodiment except that the driving of the piezoelectric vibrator 4 is temporarily stopped when the driving condition of the piezoelectric vibrator 4 is changed. In the following description, the present embodiment will be described focusing on the differences from the above-described embodiment, and the description of the same matters will be omitted. Further, in FIG. 9, the same components as those in the above-described embodiment are designated by the same reference numerals.

As shown in FIG. 9, in the method for controlling the piezoelectric motor 1 of the present embodiment, if the determination in step S5 is No, that is, if the rotation of the rotor 2 is in an abnormal state, the control device 7 performs step S10 as follows. The application of the drive signals V1 to V3 to the piezoelectric elements 6A to 6E is stopped, and the drive of the piezoelectric vibrator 4 is stopped. Then, the control device 7 proceeds to step S8 and determines whether or not the driving condition of the piezoelectric vibrator 4 can be changed. As described above, by stopping the driving of the piezoelectric vibrator 4 before determining whether the driving condition of the piezoelectric vibrator 4 can be changed, the movement of the rotor 2 is prevented during the process of changing the driving condition. The expansion of the deviation from the target position can be effectively suppressed.

As described above, in the present embodiment, when any one of the phase difference θ, the amplitude D and the frequency f is changed, the driving of the piezoelectric vibrator 4 is stopped. As a result, movement of the rotor 2 is prevented during the process of changing the drive condition, and it is possible to effectively suppress the expansion of the deviation from the target position.

According to such a second embodiment, the same effect as that of the above-described first embodiment can be exhibited.

Although the method for controlling the piezoelectric drive device according to the present invention has been described above based on the illustrated embodiment, the present invention is not limited to this, and the configuration of each part may be any configuration having the same function. Can be replaced with one. Moreover, other arbitrary components may be added to the present invention. Moreover, you may combine each embodiment suitably.

DESCRIPTION OF SYMBOLS 1... Piezoelectric motor, 2... Rotor, 21... Outer peripheral surface, 29... Main surface, 4... Piezoelectric vibrator, 41... Vibration part, 42... Support part, 43... Connection part, 44... Convex part, 6A-6E... Piezoelectric Element, 7... Control device, 9... Encoder, A1, A2, B1, B2... Arrow, D... Amplitude, O... Central axis, S1 to S10... Step, V1 to V3... Drive signal, f, f1... Frequency, f0 … Resonance frequency, fa… Initial value, fm… Frequency, θ… Phase difference

Claims (7)

A vibrating section including a first piezoelectric element and a second piezoelectric element and a convex section connected to the vibrating section are provided, and the vibrating section expands and contracts in the expanding and contracting direction due to expansion and contraction of the first piezoelectric element. Along with the expansion and contraction of the second piezoelectric element, bending vibration in a direction orthogonal to the expansion and contraction direction causes the convex portion to rotate, and the piezoelectric vibrator.
A method for controlling a piezoelectric vibrating device, comprising: a driven portion that is in contact with the convex portion and is moved by transmitting the rotational movement of the convex portion,
When the piezoelectric vibrator is vibrated to move the driven part toward the target position, the driven part moves in a direction opposite to the direction in which the target position exists, or the movement of the driven part stops. If there is an abnormal condition that is
The phase difference between the first drive signal applied to the first piezoelectric element and the second drive signal applied to the second piezoelectric element, the amplitude of the first drive signal, and the first drive signal and the second drive. A method of controlling a piezoelectric driving device, characterized in that any one of the frequencies of signals is changed. The method of controlling a piezoelectric drive device according to claim 1, wherein the phase difference is changed in the abnormal state. The control method of the piezoelectric drive device according to claim 2, wherein the amplitude is changed when the abnormal state continues even if the phase difference is changed. The method of controlling the piezoelectric drive device according to claim 3, wherein when the amplitude is changed, the phase difference is returned to the initial value before the change. The control method of the piezoelectric drive device according to claim 3, wherein the frequency is changed when the abnormal state is caused even when the amplitude is changed. The method for controlling a piezoelectric drive device according to claim 5, wherein when the frequency is changed, the amplitude is returned to the initial value before the change. 7. The method for controlling a piezoelectric drive device according to claim 1, wherein the driving of the piezoelectric vibrator is stopped when any one of the phase difference, the amplitude, and the frequency is changed.

Images