JP2002233175A - Actuator and its drive method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize low-speed drive, the efficient utilization of a battery capacity, and a stable operation of an actuator which moves a driven element in the prescribed direction by applying an AC drive signal to a displacement device, such as a piezoelectric device, etc., to make the displacement device vibrate. SOLUTION: Information concerning the amplitude of the vibration of the displacement device, for instance a current applied to the piezoelectric device, is monitored. When the peak value of the current reaches a value which is not larger than a target value, the application of a drive signal is started, and when the peak value reaches a value larger than the target value, the application of the driving signal is discontinued.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an actuator using a displacement element such as a piezoelectric element and a method of driving the same.

[0002]

2. Description of the Related Art Conventionally, burst modulation drive (intermittent drive) has been used for the purpose of speed control and effective use of battery capacity in an actuator (ultrasonic motor) using a piezoelectric element.
Has been done.

For example, Japanese Patent Publication No. 7-89748 discloses that
There is disclosed a technique for controlling the speed by changing the frequency and duty ratio of a burst signal (AC voltage drive signal).
Also, in Japanese Patent No. 283116, a lower limit value of the continuous application time of the drive voltage is set, the application time is changed until the application time reaches the lower limit value, and a pause time is set after the application time reaches the lower limit value. Techniques for controlling speed by varying it are disclosed. In addition, Japanese Patent No.
There is disclosed a technique for improving the utilization rate of battery capacity by changing the duty ratio of a burst signal.

[0004]

However, all of the above prior arts relate to speed control of the actuator by burst modulation drive or effective use of battery capacity. Techniques for stabilizing the output of the actuator by burst modulation drive include: Unknown at present.

An object of the present invention is to solve the above-mentioned problems of the conventional example, and an object of the present invention is to provide an actuator whose output is stabilized by burst modulation driving and a driving method thereof.

[0006]

In order to achieve the above object, in the actuator of the present invention, a plurality of displacement elements are arranged so that displacements of the respective displacement elements are combined, and a displacement combining portion of the displacement element is covered. An actuator for driving a driven member by bringing a pressure contact with a driving member into contact with the driving member, wherein the displacement detecting unit detects information on displacement of at least one displacement element, and the information detected by the displacement detecting unit is at least one. It is characterized by comprising a comparison unit for comparing with a target value, and a control unit for controlling an application time and a pause time for applying a drive signal to the displacement element using a comparison result by the comparison unit.

In the above arrangement, the target value is one, and when the information becomes higher than the target value, the application of the drive signal is stopped, and when the information becomes lower than the target value, the driving is stopped. It is preferable to start applying the signal.

The target value is a first target value and a second target value lower than the first target value, and the information is the first target value.
It is preferable that the application of the drive signal is stopped when the value becomes higher than the target value, and the application of the drive signal is started when the information becomes equal to or less than the second target value.

Further, at least one target value is set for each of at least two displacement elements of a first displacement element and a second displacement element, and the displacement detecting section sets the first displacement element and the second displacement element having the set target values. Each of the displacement elements detects information relating to displacement, and the comparing section compares the information of the first displacement element and the information of the second displacement element with a target value. It is preferable that the application of the driving signal is stopped when the driving signal becomes higher than the target value, and the application of the driving signal is started when the information on the second displacement element becomes lower than the target value.

Further, it is preferable that at least one of the plurality of displacement elements is excited by vibration of another displacement element.

Further, it is preferable that the information on the displacement of the displacement element is information on the amplitude of the displacement element.

Further, the displacement element is a piezoelectric element,
It is preferable that a value of a current flowing through the displacement element is detected as the information on the amplitude of the displacement element.

Further, it is preferable that an application time and a pause time for applying a drive signal to the displacement element are synchronized with a cycle of the drive signal.

On the other hand, a method of driving an actuator according to the present invention is a method of driving an actuator that drives a driven member by synthesizing displacements of a plurality of displacement elements and bringing a displacement synthesis portion of the displacement element into press contact with the driven member. A driving method, comprising detecting information on displacement of at least one displacement element, comparing the detected information with at least one target value, and applying a drive signal to the displacement element using the comparison result, and The pause time is controlled.

In the above method, the target value is set to one, and when the information becomes higher than the target value, the application of the driving signal is stopped, and when the information becomes lower than the target value, the driving signal is stopped. Is preferably started.

Further, the target value is a first target value and a second target value lower than the first target value, and when the information becomes higher than the first target value, the application of the drive signal is stopped. It is preferable that the application of the drive signal is started when the information becomes equal to or less than the second target value.

Further, at least one target value is set for each of at least two displacement elements of the first displacement element and the second displacement element, and the target value is set for each of the first displacement element and the second displacement element for which the target value is set. Detecting information on the first displacement element and the second displacement element, comparing the information on the displacement elements with a target value, and applying the drive signal when the information on the first displacement element becomes higher than the target value. Is preferably stopped, and the application to the drive signal is started when the information on the second displacement element becomes equal to or less than a target value.

Further, a drive signal is applied to at least one of the plurality of displacement elements to cause vibration,
Preferably, at least one other displacement element is excited by the vibration of the displacement element.

Further, it is preferable that information relating to the amplitude of the displacement element is detected as the information relating to the displacement of the displacement element.

Further, it is preferable that a piezoelectric element is used as the displacement element, and a value of a current flowing through the displacement element is detected as information on the amplitude of the displacement element.

Further, it is preferable that an application time and a pause time for applying a drive signal to the displacement element are synchronized with a cycle of the drive signal.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An actuator according to an embodiment of the present invention will be described. FIG. 1 shows a configuration of a truss-type actuator which is an actuator according to the present embodiment.

As shown in FIG. 1, the drive units are arranged at a predetermined angle (for example, 90 degrees) from each other.
Two stacked first and second piezoelectric elements 10A and 10A
B, a chip member (driving member) 20 joined to an intersecting end of the first piezoelectric element 10A and the second piezoelectric element 10B with an adhesive or the like, and the first piezoelectric element 10A and the second piezoelectric element 1
OB is fixed with an adhesive or the like to generate a pressing force for bringing the base member 30 holding the first piezoelectric element 10A and the second piezoelectric element 10B and the chip member 20 into contact with the surface of the rotor 40. Pressure member (an elastic body such as a coil spring or a leaf spring) 45 or the like.

First piezoelectric element 10A and second piezoelectric element 10
Details of B are shown in FIG. Both have substantially the same configuration. Each of the piezoelectric elements 10A and 10B is a PZT
(Lead zirconate titanate) and a plurality of ceramic thin plates 11 exhibiting piezoelectric characteristics and electrodes 12, 13 are alternately laminated, and each ceramic thin plate 11 and electrodes 12, 13 are fixed by an adhesive or the like. I have. Each of the electrode groups 12 and 13 arranged alternately is connected to a signal line 14, 1 respectively.
5 is connected to a drive power supply 16. Signal line 14
When a predetermined voltage is applied between the electrodes 12 and 15, the electrodes 12 and 13
An electric field is generated in the laminating direction of each of the ceramic thin plates 11 sandwiched therebetween, and the electric field is in the same direction every other one.
Therefore, the ceramic thin plates 11 are stacked so that the polarization direction of every other ceramic thin plate 11 is the same (the polarization direction of two adjacent ceramic thin plates 11 is opposite). Note that protective layers 17 are provided at both ends of each of the piezoelectric elements 10A and 10B.

When a DC drive voltage is applied between the electrodes 12 and 13 by the drive power supply 16, all the ceramic thin plates 11 expand or contract in the same direction, and the piezoelectric elements 10A, 10A
B expands and contracts as a whole. In a region where the electric field is small and the displacement history is negligible, the electric field generated between the electrodes 12 and 13 and the displacement of each of the piezoelectric elements 10A and 10B can be regarded as a substantially linear relationship.

On the other hand, when an AC drive voltage (AC signal) is applied between the electrodes 12 and 13 by the drive power supply 16, the ceramic thin plates 11 repeatedly expand and contract in the same direction according to the electric field, and the piezoelectric elements 10A , 10B repeat expansion and contraction as a whole. Each of the piezoelectric elements 10A and 10B has a unique resonance frequency determined by its structure and electrical characteristics. When the frequency of the AC drive voltage is equal to each piezoelectric element 10A, 1
When the resonance frequency matches the resonance frequency of 0B, the impedance decreases and the displacement of each of the piezoelectric elements 10A and 10B increases. Since each of the piezoelectric elements 10A and 10B has a small displacement with respect to its external dimensions, it is desirable to utilize this resonance phenomenon in order to drive the piezoelectric elements at a low voltage.

As a material of the tip member 20, tungsten or the like, which can stably obtain a high friction coefficient and is excellent in wear resistance, is preferable. As a material of the base member 30,
Stainless steel or the like, which is easy to manufacture and has excellent strength, is preferred. Further, as the adhesive, an epoxy resin having excellent adhesive strength and strength is preferable.

First piezoelectric element 10A and second piezoelectric element 10
By driving B with an AC signal having a phase difference, or driving one of the piezoelectric elements 10A or 10B, the chip member 20 can be driven so as to draw an elliptical orbit. This tip member 20 is
For example, when pressed against a cylindrical surface of the rotor 40 that can rotate around a predetermined axis L, it becomes possible to convert the elliptical motion or the circular motion of the tip member 20 into the rotational motion of the rotor 40. Alternatively, it is possible to convert the elliptical motion or the circular motion of the tip member 20 into a linear motion of the bar member by pressing the tip member 20 against, for example, a flat portion of a bar member (not shown). The material of the rotor 40 is preferably a lightweight metal such as aluminum.
In order to prevent abrasion due to friction with the surface, it is preferable to apply a tuftride treatment or an alumite treatment to the surface.

As a driving method of the truss type actuator as shown in FIG. 1, a driving signal having a predetermined phase difference is applied to each of the two piezoelectric elements 10A and 10B, and the two piezoelectric elements 10A and 10B are simultaneously driven. Method and one of the piezoelectric elements (drive-side elements) 10A or 10B
And the other piezoelectric element (driven side element) 10B or 1
A driving method that transmits vibration with a phase delay or vibration with a phase advance to 0 A is conceivable. In the actuator of the present embodiment, the latter driving method is adopted.

Either one of the piezoelectric elements 10A or 10B
In the case of driving only the piezoelectric element 10A or 10B serving as a driving element and the vibration of the piezoelectric element 10B or 1B serving as a passive element.
The phase difference of the vibration of 0A changes according to the frequency of the drive signal,
In addition, the shape of the trajectory of the chip member 20 provided at the intersection of one piezoelectric element 10A and 10B is expressed by an elliptical vibration formula (Liss
ajous equation), these two piezoelectric elements 10A and 1A
It changes according to the phase difference of the vibration of 0B.

As is well known, when a voltage is applied to a piezoelectric element, it expands and contracts in the direction of an electric field, and when a tensile or compressive force is applied to a piezoelectric element in a predetermined direction, a voltage is generated in that direction. . Therefore, by monitoring the current flowing through the drive-side element and the current flowing through the voltage generated in the driven-side element, it is possible to know the vibration state of the drive-side element and the driven-side element.

Next, one piezoelectric element (driving element) 10
A or 10B is driven by inputting an AC voltage (sine wave) drive signal to the other piezoelectric element (driven side element) 10B or 10B.
A when each of the piezoelectric elements 10A and 10A is vibrated.
Changes in the value of the current flowing through B are shown in FIGS. FIG. 3 shows a current waveform immediately after the application of the drive signal to the driving element (at the time of starting), and FIG. 4 shows a current waveform immediately after the application of the driving signal to the driving element is stopped (at the time of stop). . These current waveforms are detected using resistors connected in series to the respective piezoelectric elements 10A and 10B.

As can be seen from FIG. 3, at the time of startup, it takes time for the drive-side element and the driven-side element to rise until reaching a predetermined amplitude. Further, the drive-side element starts to vibrate relatively soon after the start of application of the drive signal, but it takes a while before the driven-side element starts to vibrate. Also, as can be seen from FIG.
It takes time for the drive element and the driven element to fall to a predetermined amplitude. In addition, the driven-side element has a slower fall than the driving-side element, and still vibrates at a predetermined amplitude even when the driving-side element is almost attenuated. As described above, when only one of the piezoelectric elements is driven, the resonance phenomenon is used, so that it takes time for the vibration of each of the piezoelectric elements to rise, and the vibration of each of the piezoelectric elements lasts for a certain time even after the drive signal is stopped. I do.

Next, burst modulation driving in the actuator according to the present embodiment will be described with reference to FIGS. In each figure, (a) represents a current value flowing through the monitored piezoelectric element 10A or 10B, (b) represents a burst signal, and (c) represents a drive signal actually applied to the piezoelectric element. The monitored piezoelectric element may be either the driving element or the driven element.

The burst modulation drive utilizes a phenomenon in which the vibration of each piezoelectric element continues for a certain period of time even when the drive signal applied to the drive-side element is stopped. The driving example shown in FIG. 5 is a case where only one control target value is set. The driving signal is continuously applied until the current value flowing through the piezoelectric element 10A or 10B becomes higher than a predetermined value, and the predetermined value is set. The application of the drive signal is stopped when the current value exceeds the threshold, and the application of the drive signal is restarted when the current value becomes equal to or less than the predetermined value. In the driving example shown in FIG. 5, a burst signal is output while the peak value of the alternating current flowing through the monitored piezoelectric element is equal to or less than the target value.
The drive signal is applied to the drive element only while the burst signal is being output.

The driving example shown in FIG. 6 is a case where two control target values are set. The driving signal is continuously output until the current flowing through the piezoelectric element 10A or 10B becomes higher than the first predetermined value. When the current exceeds a first predetermined value, the application of the driving signal is stopped, and when the current value becomes equal to or less than a second predetermined value smaller than the first predetermined value, the application of the driving signal is restarted. In the driving example shown in FIG. 6, a burst signal is output from the time when the peak value of the alternating current value flowing through the monitored piezoelectric element falls below the second target value until the peak value exceeds the first target value, and the burst signal is output. The drive signal is applied to the drive-side element only during the output. By repeating these operations, the actuator is apparently vibrating continuously, but the drive signal is supplied only intermittently, so that the actuator can be driven at low speed and the battery capacity can be effectively used. Further, since the peak value of the current flowing through the monitored piezoelectric element is controlled to be within a certain range, the speed and torque of the driven member by the actuator can be stabilized.

Next, FIG. 7 shows an example of a block configuration of the drive circuit according to the present embodiment. In the example shown in FIG. 7, a sine wave voltage signal is used as a drive signal applied to the piezoelectric element 10A or 10B.

The first piezoelectric element 10A and the second piezoelectric element 10
B is connected in series with resistors 51A and 51B for detecting currents flowing through the respective piezoelectric elements 10A and 10B. The terminal voltages of the resistors 51A and 51B are input to the first current detector 52A and the second current detector 52B, respectively, and are detected as sine wave current waveforms as shown in FIGS. 3 and 4, for example. Each current detector 52A, 52B
Are each formed of an amplifier, a zero-cross comma, and the like. After shaping the sinusoidal current waveform into a square wave, the square wave signal is input to the phase difference detection unit 53. The phase difference detection unit 53 includes, for example, an exclusive OR circuit and a low-pass filter, and detects a phase difference between two input signals.

The analog phase difference signal obtained by the phase difference detection section 53 is input to an A / D conversion section 61 of an arithmetic processing section (MPU) 60, converted into a digital signal, and then converted to a phase difference comparison section (Comp). ) 62, the target phase difference (Ref)
Is compared to The comparison result (difference between the target phase difference and the actual phase difference) by the phase difference comparing section 62 is input to the D / A conversion section 63, converted into a digital signal, and then input to the voltage controlled oscillator (VCO) 54. . The arithmetic processing unit 60 is provided with an input / output control unit (I / O) 64, the function of which will be described later.

The oscillator 54 adjusts its oscillation frequency in accordance with the output from the processing unit 60. The sine wave signal whose frequency has been adjusted is output from the first to fourth switch elements 55A to 55A.
The signal is input to the first amplifier 56A and the second amplifier 56B via D, and is amplified to a predetermined amplitude. Each switch 55A ~
55D is composed of elements such as transistors, respectively.
For example, it is assumed that the circuit is configured to turn on when a signal corresponding to a high level or “1” is input, and to be turned off when a signal corresponding to a low level or “0” is input.
In the following description, a “high-level signal” and a “low-level signal” are used for convenience.

The drive signal amplified by the first amplifier 56A is applied to the first piezoelectric element 10A.
The drive signal amplified by 6B is applied to the second piezoelectric element 10B. As described above, the actual vibration state of the first piezoelectric element 10A and the second piezoelectric element 10B is detected using the current value or the like, and the frequency of the drive signal is adjusted so that the phase difference between the vibrations matches the target phase difference. By performing the feedback control, the trajectory of the tip member 20 can be approximated to a desired shape.

The switch elements 55A to 55D are used to switch between the first piezoelectric element 10A and the second piezoelectric element 10B as the driving element and the driven element, and to provide a driving signal for burst modulation control. Is used to control the start and stop of the application of. Further, in this embodiment, only one of the piezoelectric elements 10A or 10B is driven and the other is driven, so that the driving signal is applied to both the first piezoelectric element 10A and the second piezoelectric element 10B at the same time. The switch elements 55A to 55D are not controlled.

On the other hand, the output of the first current detector 52A is the first
The signal is input to the peak detector 57A, and the second current detector 5
The output of 2B is input to the second peak detection unit 57B. Each of the peak detectors 57A and 57B is connected to a corresponding one of the current detectors 52A.
5 (a) or 6 (a) detected by FIG.
These peaks are detected from a sine wave signal as shown in FIG. The peak value signals detected by the peak detection units 57A and 57B are input to the first current value comparison unit 58A and the second current value comparison unit 58B, respectively, and are compared with target values. As an example, each current value comparison unit 58A and 58B
The peak value of the detected current is the target value (in some cases, 2
If the value is higher than one of the two target values, a low-level signal is output, and if it is lower than the target value, a high-level signal is output. Each of the current value comparing sections 58A and 58B constantly compares the peak value of the current flowing through each of the piezoelectric elements 10A and 10B with a predetermined target value, and outputs the result to the monitor element switching section 70.

The monitor element switching unit 70 includes, for example, a first AN
An output signal from the first current value comparing section 58A is input to the first AND circuit 71, and the second current value comparing section 5 includes a D circuit 71, a second AND circuit 72, and an OR circuit 73.
The output signal from 8B is input to the second AND circuit 72. The first AND circuit 71 and the second AND circuit 72
Are connected to the input / output control unit 64 of the arithmetic processing unit 60, respectively. The input / output control unit 64 includes the first piezoelectric element 10A
And outputs a high-level signal to the AND circuit 71 or 72 connected to the side of the second piezoelectric element 10B to be used as a monitor element, and outputs a low-level signal to the other. For example, when the first piezoelectric element 10A is used as a monitor element, the input / output control unit 64 controls the first AND circuit 71
To the second piezoelectric element 10B.
Outputs a low level signal. Therefore, even if a high level signal is output from the second current value comparison unit 58B, the second AN
The D circuit 72 does not turn on, and the second AND circuit 72 outputs a low level signal. On the other hand, when the peak value of the current flowing through the first piezoelectric element 10A becomes equal to or less than the target value,
Since a high-level signal is output from the first current value comparison unit 58A, the first AND circuit 71 is turned on, and the first AND circuit 7
1 outputs a high level signal. Since a high-level signal is input from the first AND circuit 71 to the OR circuit 73 and a low-level signal is input from the second AND circuit 72, the high-level signal is output from the OR circuit 73 to the drive element switching unit 80. Is output.

The drive element switching section 80 is, for example, a third AND
Circuit 81 and a fourth AND circuit 82.
The output from the R circuit 73 is supplied to the third AND circuit 81 and the fourth
The signal is input to the ND circuit 82. Also, the third AND circuit 81
The fourth AND circuit 82 is connected to the input / output control unit 64 of the arithmetic processing unit 60. Input / output control unit 64
Outputs a high-level signal to the AND circuit 81 or 82 connected to the side used as the driving-side element of the first piezoelectric element 10A and the second piezoelectric element 10B, and outputs a low-level signal to the other. I do. For example, the first piezoelectric element 1
When 0A is used as the driving element, the input / output control unit 6
4 outputs a high level signal to the third AND circuit 81 and outputs a low level signal to the second piezoelectric element 10B. Therefore, even when the OR circuit 73 outputs a high-level signal, the fourth AND circuit 82 does not turn on, and the fourth AND circuit 82 outputs a low-level signal. On the other hand, when a high level signal is output from the OR circuit 73,
The third AND circuit 81 is turned on, and a high-level signal is output from the third AND circuit 81.

The third AND circuit 81 includes the oscillator 54 and the first
First switch element 55 provided between the first switch element 55 and the amplifier 56A
A, and the fourth AND circuit 82 is connected to the oscillator 5
4 and a third switch element 55C provided between the second amplifier 56B. Also, the input / output control unit 64
Are ground and the first and second amplifiers 56A and 56A.
B are connected to the second switch element 55B and the fourth switch element 55D provided between B.

When a high-level signal is output from the third AND circuit 81, the first switch element 55A is turned on, and the sine wave signal output from the oscillator 54 is input to the first amplifier 56A and amplified to a predetermined amplitude. As the drive signal
Applied to the piezoelectric element 10A. When the low-level signal is output from the third AND circuit 81, the first switch element 55
A is turned off, the sine wave signal output from the oscillator 54 is no longer input to the first amplifier 56A, and the first piezoelectric element 10A is turned off.
The application of the drive signal to A is stopped. Note that, from the configuration of the drive element switching unit 80 described above, the first switch element 55A and the third switch element 55C do not turn on at the same time.
The second switch element 55B and the fourth switch element 5
5D is used to discharge the electric charge stored in the driven element when the first piezoelectric element 10A or the second piezoelectric element 10B is used as the driven element.

With such a circuit configuration, the chip member 2 is driven while one of the first piezoelectric element 10A and the second piezoelectric element 10B is used as a driving element and the other is driven as a driven element.
The frequency of the drive signal can be feedback-controlled so that 0 draws a predetermined trajectory, and the burst modulation drive that controls the start and stop of application of the drive signal while monitoring the current flowing to any of the elements can be performed. it can.

In the above description, the positive peak value of the alternating current is used as the current value of the piezoelectric element 10A or 10B to be monitored, and this value is compared with the target value. However, the present invention is not limited to this. Any information may be used as long as the information is related to the amplitude of the displacement element (piezoelectric element), such as the effective value of the current or the negative peak value. Further, a target value is set to either the driving element or the driven element, and information on the amplitude of the element is monitored. However, the present invention is not limited to this, and the driving element and the driven element are not limited to this. One or two target values may be set for both of them, and both the driving-side element and the driven-side element may be monitored. In this case, for example, the burst signal may be raised using information on the amplitude of the driving element, and the burst signal may be lowered using information on the amplitude of the driven element. In this case, the input / output control unit 64 may switch the signals input to the first AND circuit 71 and the second AND circuit 72 of the monitor element switching unit 70 alternately. These applications are the same in the following modifications.

Next, FIG. 8 shows a block configuration of a modified example of the drive circuit according to the present embodiment. 9 shows details of the H-bridge driver control unit in FIG. 8, and FIG. 10 shows details of the H-bridge driver. 8 to 10, a square wave voltage signal is used as a drive signal applied to the piezoelectric element 10A or 10B. Note that components denoted by the same reference numerals as those in the circuit shown in FIG. 7 are substantially the same, and a description thereof will be omitted.

In FIG. 8, the voltage controlled oscillator 54X oscillates a square wave signal and is input to the H-bridge driver control unit 90. Further, the third AND circuit 81 of the drive element switching unit 80
The output from the fourth AND circuit 82 is also input to the H-bridge driver control unit 90. The H-bridge driver control unit 90 controls the first H-bridge driver 100A connected to the first piezoelectric element 10A and the second H-bridge driver 100B connected to the second piezoelectric element 10B, respectively.

As shown in FIG. 9, the H-bridge driver control section 90 includes first to fourth NAND circuits 91A to 91A.
D and an inverter 92. Oscillator 54X
From the first NAND circuit 91A and the 3N
The signal is directly input to the AND circuit 91C, and
After being inverted by the second NAND circuit 91B and the fourth NAND circuit 91B.
Input to NAND circuit 91D. On the other hand, the output of the third AND circuit 81 is the first NAND circuit 91A and the second NAN
The input to the D circuit 91B and the output of the fourth AND circuit 82 are input to the third NAND circuit 91C and the fourth NAND circuit 91D.

Therefore, for example, when the first piezoelectric element 10A is selected as the driving element, the square wave signal from the oscillator 54X is at a high level and the third AND circuit 81
When the output from the first NAND circuit 91 is at a high level, a low-level signal is output from the first NAND circuit 91 and a high-level signal is output from the second NAND circuit 92, respectively.
A is input to A. Conversely, when the square wave signal from the oscillator 54X is at a low level and the output from the third AND circuit 81 is at a high level, a high level signal from the first NAND circuit 91, a low level signal from the second NAND circuit 92,
Each is input to the first H-bridge driver 100A. On the other hand, since the signal from the fourth AND circuit 82 is at a low level, the third NAND circuit 91C and the fourth NAND circuit 91C
A high-level signal is output from each of the circuits 91D. The same applies to the case where the second piezoelectric element 10B is selected as the driving element.

Next, the H-bridge driver 100A, 1
FIG. 10 shows the configuration of 00B. A series circuit of the first piezoelectric element 10A and the resistor 51A or the second piezoelectric element 10B and the resistor 51A
A first NOR circuit 102A connected to the fifth to eighth switch elements 101A to 101D and a fifth switch element 101A that constitute a bridge circuit for controlling start and stop of application of the drive voltage Vcc to the series circuit of B , The second NOR circuit 102 connected to the seventh switch element 101C
B, sixth switch element 101B and eighth switch element 1
Buffers 103A and 103 connected to 01D, respectively.
3B, second and third inverters 104A and 104B connected to the respective NOR circuits 102A and 102B. The buffers 103A and 103B
Is a switching element 1 composed of a transistor or the like.
It is used to adjust the impedance of 01B and 101D.

First NAND circuit 91A or third NAND circuit
The output signal from the circuit 91C is the second inverter 104A
And input to the first NOR circuit 102A via
The signal is directly input to the second NOR circuit 102B. On the other hand, the second
An output signal from the NAND circuit 91B or the fourth NAND circuit 91D is directly input to the first NOR circuit 102A and the buffer 103A, and the third inverter 104B
NOR circuit 102B and buffer 103B
Is input to

First NAND circuit 91A or third NAND circuit
Whether the signal from the circuit 91C is at a high level or a low level, and whether the second NAND circuit 91B or the fourth NAND circuit 91D
Table 1 below shows ON / OFF of the fifth to eighth switch elements and operation states of the piezoelectric elements 10A or 10B according to the combination of the signal from the high level and the low level. In Table 1, the signal “X” indicates a signal from the first NAND circuit 91A or the third NAND circuit 91C, and the signal “Y”
Is the second NAND circuit 91B or the fourth NAND circuit 91D
Represents the signal from "H" and "L" indicate that the signal level is a high level and a low level, respectively, and SW5 to SW8 indicate the fifth to eighth switch elements, respectively. Further, the “drive mode” refers to the piezoelectric element 10A.
Or, it represents the state of 10B.

[0057]

[Table 1]

In the above-described modification, the signal oscillated by the oscillator 54X is amplified and used as a drive signal.
Instead of applying a voltage to 0A or 10B,
The signal from X is supplied to the H bridge driver 100A or 10
Since the driving voltage Vcc supplied to the driving circuit 0B is used as a timing signal for applying the driving voltage Vcc to the piezoelectric element 10A or 10B, the frequency signal generated by the oscillator 54X can be handled digitally, and an amplifier is not required. Can be simplified.

Although the driving signal applied to the piezoelectric elements 10A or 10B is a square wave, its frequency is near the resonance frequency of each of the piezoelectric elements 10A and 10B. It becomes sinusoidal. Therefore, the waveform of the current flowing through each of the piezoelectric elements 10A and 10B also becomes sinusoidal, but the noise flowing due to the rush current due to the drive signal is superimposed on the current flowing through the drive-side element. Therefore, it is preferable to subject the current waveforms detected by the current detection units 52A and 52B to low-pass filtering.

Next, the burst signal and the oscillator 54 or 54
Synchronous and asynchronous with the frequency signal output from X will be described. FIGS. 11A and 11B are timing charts in the case of synchronous and asynchronous cases. FIG. 11A shows an oscillator (VCO).
Frequency signal (square wave) from 54X, (b) is a burst signal when asynchronous, (c) is a drive signal when asynchronous, (d) is a burst signal when synchronous, (e) is a synchronous signal Represents the waveforms of the drive signals of FIG.

In each of the drive circuits shown in FIGS. 7 and 8, the burst signal and the frequency signal output from the oscillator 54 or 54X are not synchronized, that is, are driven asynchronously. In each of the above driving circuits, a sine wave signal or a square wave signal of a predetermined frequency is continuously output from the oscillator 54 or 54X, but the driving signal is applied to the piezoelectric element 10A or 10B only while the burst signal is being output. It is configured not to be applied. If reduced, the drive signal applied to the piezoelectric element 10A or 10B is, as shown in FIG. 11 (c), the AN of the frequency signal of (a) and the burst signal of (b).
The waveform becomes as if D was taken. Burst signal and oscillator 5
Since the frequency signal output from the oscillator 54 or 54X is not synchronized with the frequency signal output from the oscillator 54 or 54X, a driving signal having a waveform different from the frequency signal output from the oscillator 54 or 54X as shown in FIG. In this case, if a signal with a short cycle such as both ends shown in FIG.
The vibration of A or 10B may become slightly unstable.

On the other hand, when the burst signal is synchronized with the frequency signal output from the oscillator 54 or 54X as shown in (d), the frequency output from the oscillator 54 or 54X as shown in (e) is obtained. A drive signal having the same waveform as the signal is applied to the piezoelectric element. As a result, the piezoelectric element 10
The vibration of A or 10B can be further stabilized.

FIGS. 12 and 13 show a circuit configuration for synchronizing the burst signal with the frequency signal output from the oscillator 54 or 54X.

FIG. 12 shows a circuit configuration in the case where the output signal from the oscillator (VCO) 54 is a sine wave signal. In the drive circuit shown in FIG. This is schematically illustrated by adding a flip-flop (D.FF) 111 and omitting some components. In this case, the output signal of the oscillator (VCO) 54 is the zero-cross comparator 1
The output of the zero-cross comparator 110 (indicating the timing at which the voltage of the output signal of the oscillator (VCO) 54 becomes “0”) is input to the D flip-flop 111.
As a timing signal. The output of the current value comparison unit 58A or 58B is input to the D terminal of the D flip-flop 111, and the switch element 55 is output using the output from the Q terminal of the D flip-flop 111.
A or 55C is controlled. As a result, the switching element 55
The ON / OFF timing of A or 55C is synchronized with the rise or fall of the output signal from the oscillator 54.

FIG. 13 shows a circuit configuration in the case where the output signal from the oscillator (VCO) 54 is a square wave signal. A D flip-flop (D .FF) 111,
It is schematically shown with some components omitted.
In this case, the output signal of the oscillator (VCO) 54X is directly input to the clock terminal of the D flip-flop 111 as a timing signal. Further, the current value comparison unit 58A or 5
The output of 8B is input to the D terminal of the D flip-flop 111, and the output from the Q terminal of the D flip-flop 111 and the oscillator (VC
O) AND the output signal of 54X and use that signal to control the H-bridge driver 100A or 100B. As a result, the switch elements 101A to 101D are turned on /
The OFF timing is synchronized with the rise or fall of the output signal from the oscillator 54X.

Next, a brief description will be given of a method of low-speed driving using the actuator of the present embodiment. As described above, the vibration of the piezoelectric element requires time to rise and fall. By utilizing this characteristic, the target value of the current flowing through the piezoelectric element during the burst modulation drive is set to a value lower than the target value when the drive signal is continuously applied. Then, the amplitude of the vibration of the monitored piezoelectric element,
As a result, the amplitude of the vibration of the driving element is kept almost constant in a small range. As a result, apparently, the same driving speed as when the voltage of the driving signal applied to the piezoelectric element is reduced is obtained. In this case, since the voltage of the drive signal is constant, it is not necessary to change the amplification factor of the amplifier, and the circuit configuration can be simplified. Conversely, when the amplification factor of the amplifier is variable, the control accuracy of low-speed driving can be increased.

Although the truss type actuator has been described in the above embodiment, the present invention is not limited to this, and it goes without saying that the present invention can be applied to other actuators utilizing ultrasonic vibration. Further, in the description of the above embodiment, the tip member is provided at the intersection of the two piezoelectric elements, and the tip member is configured to contact the rotor that is the driven member. However, the present invention is not limited to this. The crossing portion of a displacement element such as a piezoelectric element may be configured to directly contact the driven member.

Further, in the above embodiment, a drive signal is applied to one of the piezoelectric elements to be a drive element, and a drive element is not applied to the other piezoelectric element to be a driven element. Instead, a burst modulation drive for controlling the timing of the application time for applying the drive signal and the pause time while simultaneously applying the drive signal to each piezoelectric element may be performed. Further, the number of piezoelectric elements (displacement elements) is not limited to two, and may be three or more. In that case, at least one piezoelectric element may be driven to be driven. Further, the displacement element is not limited to the stacked piezoelectric element shown in FIG. 2, but may be a magnetostrictive element or a combination of a piezoelectric element and an elastic member.

[0069]

As described above, according to the actuator of the present invention, a plurality of displacement elements are arranged so that the displacements of the respective displacement elements are combined, and the displacement combined portion of the displacement elements is used as the driven member. An actuator that drives a driven member by bringing it into pressure contact, a displacement detection unit that detects information relating to displacement of at least one displacement element, and at least one target value that is information detected by the displacement detection unit. A comparison unit that performs comparison, and a control unit that controls an application time and a pause time for applying a drive signal to the displacement element using the comparison result by the comparison unit.

Further, according to the actuator driving method of the present invention, the driven members are driven by synthesizing the displacements of the plurality of displacement elements and bringing the displacement-combined portion of the displacement elements into pressure contact with the driven members. A method for driving an actuator, comprising: detecting information regarding displacement of at least one displacement element, comparing the detected information with at least one target value, and applying a drive signal to the displacement element using the comparison result. Control time and pause time.

That is, according to the present invention, the application of the drive signal to the displacement element does not start immediately after the start of application of the drive signal, but requires a certain period of time to reach the predetermined displacement. Gradually increases, and the displacement amount does not become 0 immediately after the application of the drive signal is stopped, and the displacement amount gradually attenuates. For example, when the displacement amount of the displacement element exceeds the target value, the application of the drive signal is stopped, and when the displacement amount becomes equal to or less than the target value, the driving signal is restarted so that the drive signal application is restarted. The ratio of the drive signal application time to the time can be reduced, the power consumption of the actuator can be reduced, and the battery life can be extended. Also,
By setting the target value low, it is possible to obtain the same drive speed as when the actuator is apparently driven at a voltage lower than the voltage of the drive signal. In addition, batteries
It is more efficient to use the battery capacity effectively by taking out the output intermittently than by taking out the output continuously.Therefore, the drive capacity is used effectively by intermittently supplying the drive signal to the displacement element. can do.

Further, the target value is set to one, and when the information becomes higher than the target value, the application of the driving signal is stopped, and when the information becomes lower than the target value, the application of the driving signal is stopped. , The displacement amount of the displacement element, in other words, the driving speed or output of the actuator can be made substantially constant.

Alternatively, the target value is set to a first target value and a first target value.
A second target value lower than the target value, wherein the information is the first target value;
By controlling so that the application of the drive signal is stopped when the value becomes higher than the target value and the application of the drive signal is started when the information becomes equal to or less than the second target value, the displacement amount of the displacement element is controlled. Can be made substantially constant within an allowable range, and the drive signal application time can be further shortened.

Alternatively, at least one of the target values is set for each of at least two displacement elements of a first displacement element and a second displacement element, and the displacement detecting section sets the first displacement element and the second displacement element having the set target values. Each of the displacement elements detects information relating to displacement, and the comparing section compares the information of the first displacement element and the information of the second displacement element with a target value. By controlling the application of the drive signal to stop when the value becomes higher than the target value and to start applying the drive signal when the information on the second displacement element becomes equal to or less than the target value, the two displacements are controlled. Even when the displacement characteristics of the elements vary, the driving characteristics such as the driving speed of the actuator can be stabilized.

Further, by driving at least one of the plurality of displacement elements by the vibration of another displacement element, the drive circuit and control of the actuator can be simplified.

Further, by using the information relating to the displacement of the displacement element as the information relating to the amplitude of the displacement element, the information relating to the displacement of the displacement element can be easily detected and the detection accuracy can be improved.

In particular, the displacement element is a piezoelectric element, and by detecting the value of the current flowing through the displacement element as information on the amplitude of the displacement element, the voltage at both ends of the displacement element is monitored by utilizing the properties of the piezoelectric element. Thus, information on the displacement of the displacement element can be obtained very easily.

Further, by synchronizing the application time and the pause time for applying the drive signal to the displacement element with the cycle of the drive signal, a signal having a cycle different from that of the drive signal at the rise and fall of the drive signal can be obtained. Since no voltage is applied, the operation of the actuator can be further stabilized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a truss-type actuator which is an embodiment of the actuator of the present invention.

FIG. 2 is a diagram showing a detailed configuration of a piezoelectric element used in the embodiment.

FIG. 3 is a diagram showing a change in a current value flowing through each piezoelectric element when one piezoelectric element (drive-side element) is driven and the other piezoelectric element (driven-side element) is vibrated in the embodiment. 5 shows a current waveform immediately after the start of applying a drive signal to the drive-side element (at the time of startup).

FIG. 4 is a diagram illustrating a current waveform immediately after stopping the application of the drive signal to the drive-side element (when stopped) in the same manner as in FIG. 3;

FIG. 5 is a diagram for explaining an example of burst modulation driving in the actuator of the embodiment.

FIG. 6 is a diagram for explaining another example of burst modulation driving in the actuator of the embodiment.

FIG. 7 is a diagram illustrating an example of a block configuration of a drive circuit according to the embodiment.

FIG. 8 is a diagram showing another example of the block configuration of the drive circuit in the embodiment.

FIG. 9 is a diagram illustrating a detailed configuration of an H-bridge driver control unit in FIG. 8;

FIG. 10 is a diagram showing a detailed configuration of an H-bridge driver in FIG. 8;

FIG. 11 is a timing chart showing signal waveforms when a burst signal and a frequency signal output from an oscillator are synchronized and when the signal is asynchronous.

FIG. 12 is a diagram showing a circuit configuration for synchronizing a burst signal and a frequency signal output from the oscillator when the output signal from the oscillator is a sine wave signal.

FIG. 13 is a diagram showing a circuit configuration for synchronizing a burst signal and a frequency signal output from the oscillator when the output signal from the oscillator is a square wave signal.

[Explanation of symbols]

 10A: first piezoelectric element 10B: second piezoelectric element 20: chip member 30: base member 40: rotor 51A: resistor 51B: resistor 52A: first current detector 52B: second current detector 53: phase difference detector 54 : Oscillator 54X: Oscillator 55A: First switch element 55B: Second switch element 55C: Third switch element 55D: Fourth switch element 56A: First amplifier 56B: Second amplifier 57A: First peak detector 57B: Second Peak detector 58A: first current value comparator 58B: second current value comparator 60: arithmetic processing unit 61: A / D converter 62: phase difference comparator 63: D / A converter 64: input / output controller 70: monitor element switching section 80: drive element switching section 90: bridge driver control section 100A: first bridge driver 100B: second bridge Driver 110: Zero cross comparator 111: D flip-flop

Claims (16)

[Claims] An actuator that drives a driven member by arranging a plurality of displacement elements so that the displacements of the respective displacement elements are combined, and bringing a displacement combining portion of the displacement element into pressure contact with the driven member. A displacement detection unit that detects information relating to displacement of at least one displacement element, a comparison unit that compares information detected by the displacement detection unit with at least one target value, and a comparison result by the comparison unit. A control unit for controlling an application time and a pause time for applying a drive signal to the displacement element. 2. The method according to claim 1, wherein the target value is one, and when the information becomes higher than the target value, the application of the drive signal is stopped, and when the information becomes lower than the target value, the drive signal is deactivated. The actuator according to claim 1, wherein the application is started. 3. The target value is a first target value and a second target value lower than the first target value. When the information becomes higher than the first target value, the application of the drive signal is stopped. ,
2. The actuator according to claim 1, wherein the application of the drive signal is started when the information becomes equal to or less than the second target value. 4. The at least one target value is set for each of at least two displacement elements of a first displacement element and a second displacement element, and the displacement detection unit sets the first displacement element and the second displacement element each having a target value set. Each of the displacement elements detects information relating to displacement, and the comparing section compares the information of the first displacement element and the information of the second displacement element with a target value. 2. The method according to claim 1, wherein the application of the drive signal is stopped when the value becomes higher than the target value, and the application of the drive signal is started when the information on the second displacement element becomes equal to or less than the target value. Actuator. 5. The actuator according to claim 1, wherein at least one of the plurality of displacement elements is excited by vibration of another displacement element. 6. The actuator according to claim 1, wherein the information on the displacement of the displacement element is information on an amplitude of the displacement element. 7. The actuator according to claim 6, wherein the displacement element is a piezoelectric element, and detects a value of a current flowing through the displacement element as information on an amplitude of the displacement element. 8. The actuator according to claim 1, wherein an application time for applying a drive signal to the displacement element and a pause time are synchronized with a cycle of the drive signal. 9. A method of driving an actuator for driving a driven member by synthesizing displacements of a plurality of displacement elements and bringing a displacement synthesis portion of the displacement element into pressure contact with the driven member, comprising: Detecting information on displacement of the displacement element, comparing the detected information with at least one target value, and controlling an application time and a pause time for applying a drive signal to the displacement element using the comparison result. Method of driving the actuator. 10. The method according to claim 1, wherein the target value is set to one, and when the information becomes higher than the target value, the application of the drive signal is stopped, and when the information becomes lower than the target value, the drive signal is applied. 10. The method of driving an actuator according to claim 9, wherein: 11. The target value is a first target value and a second target value lower than the first target value, and when the information becomes higher than the first target value, the application of the drive signal is stopped.
The method according to claim 9, wherein the application of the drive signal is started when the information becomes equal to or less than the second target value. 12. The at least one target value is set for each of at least two displacement elements of a first displacement element and a second displacement element, and each of the first and second displacement elements for which a target value is set is displaced. Detecting information on the first displacement element and the second displacement element, comparing the information on the displacement elements with a target value, and applying the drive signal when the information on the first displacement element becomes higher than the target value. 10. The method of driving an actuator according to claim 9, wherein the operation of the actuator is stopped, and the application of the drive signal is started when the information on the second displacement element becomes equal to or less than a target value. 13. A method according to claim 1, wherein a driving signal is applied to at least one of the plurality of displacement elements to cause the displacement element to vibrate, and the other at least one displacement element is excited by the vibration of the displacement element. Item 13. The method for driving an actuator according to any one of Items 9 to 12. 14. The actuator driving method according to claim 9, wherein information relating to the amplitude of the displacement element is detected as the information relating to the displacement of the displacement element. 15. A piezoelectric element is used as the displacement element,
15. A value of a current flowing through the displacement element is detected as the information on the amplitude of the displacement element.
A driving method of the above-described actuator. 16. The actuator driving method according to claim 9, wherein an application time and a pause time for applying a drive signal to the displacement element are synchronized with a cycle of the drive signal.