JPH11356068A - Device and method for driving vibrating actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a slippage between a vibrator and a relative motion member when intermittently driven and thereby suppress the abrasion on a contact face between these members, by changing the frequency of AC voltage for at least a part of the period during which AC voltage is applied to an electromechanical transducing element. SOLUTION: A pulse setting device 30 sets the applying time and the frequency of a driving signal to prescribed values, based on a target speed. A pulse generator 31 generates a pulse signal S1 having the pulse width and the pulse frequency accomodating the set values. A control signal generating section 32 generates a frequency control signal S2. An oscillator circuit 16 outputs a frequency signal S3 controlled by the frequency control signal S2 when the pulse signal S1 is ON. Then the frequency signal S3 is inputted to input regions 13a and 13c through an amplifier 17a while also being inputted to input regions 13b and 13d through a phase shifter 18 and an amplifier 17b. A speed control circuit 19 controls the pulse setting device 30 according to the output voltages from detection regions 13p, 13p'.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vibration actuator having a vibrator for generating vibration, and for generating a relative motion between a relative motion member in pressure contact with the vibrator and the vibrator.

[0002]

2. Description of the Related Art A vibrating body is constituted by an electromechanical transducer such as a piezoelectric element, and an alternating voltage, which is a drive signal, is applied to the electromechanical transducer to generate an elliptical motion in the vibrator. 2. Description of the Related Art A vibration actuator that generates relative motion between a vibrator and a relative motion member that is in pressure contact is known.

As a method of driving such a vibration actuator at a low speed or moving it by a very small amount, there is known an intermittent drive in which a drive signal is applied to a vibrator in the form of a burst wave. FIG. 7 is a waveform diagram illustrating an example of a drive signal applied to the electromechanical transducer. In this case, the frequency of the drive signal is kept constant at time t1 when the drive signal is applied to the electromechanical transducer.
Then, the relative speed between the vibrator and the relative motion member is controlled by changing the ratio of the application time t1 to the application period t2.

Further, Japanese Patent Publication No. Hei 7-89748 discloses that
A method is disclosed in which a burst signal in which at least one of the width and the interval of the burst signal is changed is applied as a drive signal in order to prevent generation of noise when driven by a burst wave.

[0005]

The vibration actuator has a problem that the contact surface is easily worn due to friction between the vibrator and the relative motion member during driving. In the intermittent driving as described above, the amplitude of the vibration generated in the vibrator changes abruptly at the beginning and end of the application time t1, that is, at the start and stop of the application of the drive signal. Sliding occurs between the moving member and the moving member, so that the member is more easily worn.

Further, during intermittent driving, the vibration actuator repeatedly stops and starts suddenly. Therefore, when an output (relative motion) obtained by the vibration actuator is taken out to an external device via a gear or the like, A phenomenon occurs in which an external device cannot follow this movement and the behavior becomes unstable. An object of the present invention is to solve such a problem.

[0007]

To achieve the above object, according to the first aspect of the present invention, an electromechanical transducer and a driving force for extracting a driving force obtained by vibration generated by the electromechanical transducer are provided. A vibrating actuator having a driving force take-out part, and generating a relative motion between the driving force take-out part and a relative motion member in contact with the driving force take-out part; and applying an AC voltage intermittently to the electromechanical transducer. A driving circuit for changing the frequency of the AC voltage during at least a part of the time during which the AC voltage is applied to the electromechanical transducer. provide.

[0008] According to the invention described in claim 2, according to claim 1 of the present invention.
In the driving device of the vibration actuator according to the above, the drive circuit, at least one of when the application of the AC voltage to the electromechanical transducer is started and when the application is stopped,
The frequency of the AC voltage is changed so as to reduce the change in the amplitude of the vibration. According to a third aspect of the present invention, in the vibration actuator driving device according to the first or second aspect, the driving circuit includes: an oscillating unit that generates the AC voltage; A driving means for driving and a frequency control means for generating a control signal for controlling the frequency of the AC voltage and outputting the control signal to the oscillation means.

According to a fourth aspect of the present invention, there is provided an electromechanical transducer, and a driving force extracting portion for extracting a driving force obtained by exciting the electromechanical transducer. In a driving method of a vibration actuator for generating a relative motion between a relative motion member in contact with a driving force extracting portion, an AC voltage is intermittently applied to the electromechanical conversion element, and the AC voltage is applied to the electromechanical conversion element. The frequency of the AC voltage is changed within at least a part of the time during which the voltage is applied to the element.

According to the invention described in claim 5, according to claim 4,
In the invention described in (1), the frequency of the AC voltage is changed such that a change in the amplitude of the vibration is reduced at least at the time of starting application and the time of stopping application of the AC voltage to the electromechanical transducer. I did it.

[0011]

Embodiments of the present invention will be described below in more detail with reference to the drawings. In the present embodiment, an example of an ultrasonic actuator using an ultrasonic vibration region will be described as the vibration actuator.
FIG. 1 is a schematic perspective view showing a configuration of a vibrator in the ultrasonic actuator used in the present embodiment. FIG.
FIG. 4 is an explanatory diagram showing a vibrator used in the present embodiment and waveforms of vibration generated in the vibrator.

The ultrasonic actuator 10 generates an elliptical motion by the first-order longitudinal vibration and the fourth-order bending vibration, and generates a driving force by the elliptical motion and a vibrator 11 by the driving force. And a relative movement member 21 for performing relative movement between them. The vibrator 11 includes an elastic body 12 formed in a rectangular flat plate shape of stainless steel or the like, and a piezoelectric element 13 which is an electromechanical transducer and is joined to the elastic body 12. The dimensions of each part of the elastic body 12 are as follows:
The natural frequency of each of the first-order longitudinal vibration and the fourth-order bending vibration generated in the vibrator 11 is set to be substantially the same. A piezoelectric element 13 is adhered to one plane of the elastic body 12, and on the other plane of the elastic body 12, as shown in FIG.
Two grooves are provided in the width direction of the elastic body 12. These two grooves are provided at a predetermined distance from a relative movement direction (a direction indicated by an arrow D in FIG. 1) generated between the vibrator 11 and the relative movement member 21. These two grooves are located on the end side of the elastic body 12 among four antinodes 11 to 14 (see FIG. 2) in the fourth bending vibration generated in the elastic body 12. It is provided so as to substantially coincide with the positions l1 and l4 of the two antinodes. A sliding member having a rectangular cross section is fitted into each groove, and is bonded with an epoxy adhesive in a state of protruding in a protruding shape. The sliding member to be fitted in each groove is arranged in a divided state on the end portion side in the width direction of the elastic body 12. Therefore, four sliding members are arranged on the vibrator 11. These four sliding members are arranged at positions substantially coincident with two antinode positions 11 and 14 located on the end side in the longitudinal direction of the elastic body 12.
Function as the driving force extracting portions 12a, 12b, 12c, and 12d. Therefore, the elastic body 12 comes into contact with the relative motion member 21 via the driving force extracting portions 12a to 12d made of these sliding members.

The piezoelectric element 13 converts electric energy into mechanical displacement, and is made of, for example, PZT (lead titanium zirconate: registered trademark) and is formed in a single plate. In this piezoelectric element, input areas 13a and 13c to which a first drive signal is input and an input area to which a second drive signal having a phase different from the first drive signal by about (π / 2) are input. 13b and 13d are provided. Each input area 1
3a to 13d are formed in four regions divided by five nodal positions n1 to n5 of the fourth-order bending vibration generated in the elastic body 12. At this time, each input area 13 deformed by the input of the first drive signal and the second drive signal
a to 13d are nodal positions n1 to n5 of the bending vibration.
Do not straddle. Therefore, the deformation of the input areas 13a to 13d is not suppressed by the node positions n1 to n5.

Among the five nodes of the bending vibration, two node positions n2, which are located second from the both ends, respectively.
In n3, detection regions 13p and 13p 'for outputting electric energy in accordance with the longitudinal vibration generated in the vibrator 11 are formed in a semicircular shape. Thereby, the vibration state of the longitudinal vibration generated in the vibrator 11 can be detected. Each of the input areas 13a to 13d and each of the detection areas 13p and 13p '
Each surface has silver electrodes 15a to 15d, 15p, 15
It is covered by p '. Thereby, each input area 13
The first drive signal or the second drive signal can be input independently to a to 13d. In addition, each detection area 13p, 13p '
The detection signal can be taken out independently of the above.

Silver electrodes 15a to 15d, 15p, 15p '
Are respectively soldered, and the transfer of electric energy such as the first and second drive signals is performed through the lead wires. In the present embodiment, as shown in FIG. 2, the vibrator 11 is formed so as to be point-symmetric about the center of the plane. Further, a common node n3 of the bending vibration and the longitudinal vibration of the vibrator 11
The U-shaped cutouts 11 are provided on both sides 11a and 11b at the positions
c and 11d are formed. And the vibrator 11
A fixing pin or the like (not shown) is fitted into these notches 11c and 11d to be fixed to a base member or the like. By fixing at a position that serves as a common node between the bending vibration and the longitudinal vibration, it is possible to minimize the influence on the vibration generated in the vibrator 11 when supporting and fixing the vibrator 11.

Further, the vibrator 11 is pressed against the relative motion member 21 with a suitable pressing force P by a pressing means (not shown), whereby the vibrator 11 and the relative motion member 21 are pressurized. Contact. FIG. 3 is a block diagram illustrating the configuration of the drive circuit according to the present embodiment. FIG. 4 is similar to FIG.
FIG. 4 is an explanatory diagram showing a relationship between output signals in each unit of the block diagram of FIG.

The driving circuit shown in FIG. 3 includes a pulse setting unit 30 and
A pulse generator 31, a control signal generator 32, an oscillation circuit 16, a phase shifter 18, and two amplifiers 17a and 17b
And a speed control circuit 19. Pulse setting device 3
0 sets the application time t1 and the application cycle t2 of the drive signal (burst signal) applied to the ultrasonic motor to predetermined values based on the target speed of the ultrasonic motor. And
The information is output to the pulse generator 31.

The pulse generator 31 generates a pulse signal S1 having a predetermined pulse width (corresponding to the application time t1) and a pulse cycle (corresponding to the application cycle t2) based on information from the pulse setting unit 30. I do. And this pulse signal
S1 is output to both the oscillation circuit 16 and the control signal generator 32. The pulse signal S1 directly input to the oscillation circuit 16
Acts as a signal for driving the oscillation circuit 16. When the pulse signal S1 is ON, the oscillation circuit 16 outputs a frequency signal S3 described later. Therefore, the pulse generator 31 functions as a driving unit that drives the oscillation circuit 16 intermittently.

The control signal generator 32 functions as frequency control means for controlling the frequency of the frequency signal S3.
The control signal generator 32 generates a pulse-shaped frequency control signal S2 based on the input pulse signal S1, and outputs the frequency control signal S2 to the oscillation circuit 16 in synchronization with the pulse signal S1. As shown in FIG. 4, the frequency control signal S2 has a pulse width equal to that of the pulse signal S1, but has a trapezoidal waveform in which a rising portion and a falling portion are inclined. The degree of the inclination is adjusted by the control signal generator 32.

As described above, the oscillation circuit 16 is driven by the pulse signal S1, and outputs the frequency signal S3 when the pulse signal S1 is ON. The oscillation circuit 16 is a voltage controlled oscillator (VCO), and the frequency of the frequency signal S3 is controlled by the voltage of the frequency control signal S2. Note that the voltage of the frequency signal S3 is substantially constant regardless of the voltage of the frequency control signal S2, and only the frequency is changed. In the case of the present embodiment, the frequency decreases as the voltage of the frequency control signal S2 increases, and the control signal S2
Is set so that the frequency becomes higher as the voltage becomes lower (approaches 0 volt). However, the control signal S
2 becomes 0 volts, the pulse signal S1 also becomes 0 volts (O
In this case, the oscillation circuit 16 does not output the frequency signal S3. As shown in FIG. 4, while the monotonically increasing waveform portion of the pulse signal S2 is being input,
The oscillation circuit 16 outputs a frequency signal S3 whose frequency decreases substantially monotonously (part of FIG. 4). Next, when a waveform portion having a constant value of the frequency control signal S2 is input, the oscillation circuit 16 outputs a frequency signal S3 having a substantially constant frequency (part of FIG. 4). Further, when a monotonically decreasing waveform portion of the frequency control signal S2 is input, the oscillation circuit 16 outputs a frequency signal S3 whose frequency increases substantially monotonously (part of FIG. 4). Thus, the oscillation circuit 16 responds to the waveform of the frequency control signal S2,
One waveform is a frequency signal S formed at the
3 is output.

The frequency signal S3 output from the transmission circuit 16
Is divided into two, one is input to the phase shifter 18, and the other is input to the amplifier 17a. The phase shifter 18 shifts the phase of the input frequency signal by (π / 2) and outputs the shifted signal to the amplifier 17b. The amplifier 17a amplifies the frequency signal S3 output from the oscillation circuit 16 to generate a first drive signal. This first drive signal is branched into two, one of which is a silver electrode 15.
The input is made to the input area 13a of the piezoelectric element via a, and the other is input to the input area 13c of the piezoelectric element via the silver electrode 15c. The amplifier 17b amplifies the frequency signal S3 output from the phase shifter 18 to generate a second drive signal. The second drive signal is branched into two, one of which is input to the input area 13b of the piezoelectric element via the silver electrode 15b, and the other is input to the input area 13d of the piezoelectric element via the silver electrode 15d.

The speed control circuit 19 includes silver electrodes 15p, 1
Output voltages from the detection regions 13p and 13p 'are input via 5p'. The speed control circuit 19 compares a preset reference voltage with the output voltage, and detects
When the output from 3p 'is smaller, the frequency signal S3
By changing the ratio between the application time t1 and the application cycle t2 in
The pulse setting unit 30 is controlled so that the ratio of the application time t1 increases. Then, the pulse setting device 30 outputs the converted information to the pulse generator 31. On the other hand, the detection area 13
When the output from p and 13p 'is larger than the reference voltage, the pulse setting unit 30 changes the ratio between the application time t1 and the application cycle t2 in the frequency signal S3 so that the ratio of the application time t1 decreases. Control. Pulse setting device 30
Outputs the converted information to the pulse generator 31. As a result, the amplitude of the vibration generated in the vibrator 11 of the ultrasonic motor 10 can be maintained at a predetermined value, and the target speed can be maintained.

As described above, the first drive signal is input to the input areas 13a and 13c of the piezoelectric element 13, and the input drive areas 13b and 13d of the piezoelectric element 13 are in phase with the first drive signal. A second drive signal that is different by about (π / 2) is input. As a result, as shown in FIG.
A first vibration (first-order longitudinal vibration) vibrating in the direction of relative movement (the direction of the double arrow in FIG. 2), and a second vibration (fourth-order bending vibration) substantially orthogonal to the vibration direction of the first vibration Occur simultaneously. These vibrations are combined, and an elliptical motion is generated in each of the driving force output portions 12a to 12d. Then, due to this elliptical motion, each driving force extracting portion 12a of the vibrator 11
The relative motion member 21 and the vibrator 11 in contact with
In between, relative motion occurs in the direction indicated by the arrow in FIG. That is, if the vibrator 11 is fixed and the relative motion member 21 is supported by a linear guide or the like, the relative motion member 21 linearly moves in one direction. If the relative motion member 21 is fixed and the vibrator 11 is supported by a linear guide or the like, the vibrator 11 linearly moves in one direction. To reverse the relative movement direction (moving direction), the phase shifter 18 reverses the sign of the phase difference between the first AC voltage and the second AC voltage (for example, + (π / 2) ) To-(π / 2)).

In the ultrasonic motor 10 of the present embodiment, the speed during the intermittent drive (the vibrator 11 and the relative motion member 21
Speed of the relative motion between the two) is the application cycle t2 of the frequency signal S3.
In a longer time, the application time t1 of the frequency signal S3
It is obtained as an average speed obtained by averaging the respective speeds of the relative motion occurring therein. On the other hand, looking at the application time t1 in one application cycle t2, the frequency signal S during the application time t1.
3 (that is, the first and second drive signals) change, so that the speed of the ultrasonic motor 10 also changes.

This state will be described with reference to FIG. FIG.
Shows the relationship between the frequency of the frequency signal S3 (first and second drive signals) and the amplitude of vibration (here, longitudinal vibration) generated in the vibrator 11 when the frequency signal is applied. It is a graph. In FIG. 5, the amplitude on the vertical axis corresponds to the speed of the ultrasonic motor 10. Further, fo on the horizontal axis represents the resonance frequency of the ultrasonic motor 10.

During the application time t1 of the frequency signal S3,
While the portion of the frequency signal S3 (see FIG. 4) is being input to the piezoelectric element 13, the amplitude of the vibration generated in the vibrator 11 in FIG. 5 gradually increases (see FIG. 5), and the ultrasonic motor 1
The speed of 0 also increases gradually. During the subsequent input of the frequency signal S3 (see FIG. 4), the amplitude of the vibration generated in the vibrator 11 in FIG. 5 is constant (see FIG. 5), and the speed of the ultrasonic motor 10 is also reduced. Be constant. The frequency fd of the frequency signal S3 at this time is set in advance to be higher than the resonance frequency fo of the ultrasonic motor. While the subsequent frequency signal S3 is being input (see FIG. 4), the amplitude of the vibration generated in the vibrator 11 in FIG. 5 gradually decreases (see FIG. 5). Therefore, the speed of the ultrasonic motor 10 also gradually decreases. As described above, in the ultrasonic motor 10 according to the present embodiment, during the intermittent driving, the amplitude of the vibration generated in the vibrator 11 within the application period t2 gradually changes.

Therefore, slippage between the vibrator and the relative motion member can be reduced, and wear of the contact surface between the vibrator and the relative motion member can be suppressed. Further, it is possible to suppress a sound generation phenomenon in which abnormal noise is generated from a contact portion between the vibrator and the relative motion member. In the present embodiment, the frequency signal S3 output from the oscillation circuit 16 is a rectangular wave, but may be a sine wave as shown by S3 'in FIG.

Further, the frequency control signal S2 is not limited to the waveform as shown in FIG. 4, but may be a waveform as shown in FIG. FIG. 6A shows the frequency control signal S
An example in which 2 is set in a triangular wave shape is shown. The frequency signal S3 at this time does not become constant after the frequency gradually increases, and thereafter the frequency gradually decreases. Therefore, the speed of the ultrasonic motor within the application period t2 gradually increases and then gradually decreases. In this case, since the speed is not constant, finer driving is possible.

FIG. 6B shows an example in which the triangular wave of FIG. 6A is set in a curved shape. In this case, as compared with the waveform of FIG. 6A, the transition from the increase in the speed of the ultrasonic motor to the decrease is performed more gently. Therefore, wear of the contact surface between the vibrator and the relative motion member can be more effectively suppressed.
FIG. 6C shows an example in which the rising portion and the falling portion of the waveform in the frequency control signal S2 of FIG. 4 are set in a curved shape.

FIG. 6D shows the frequency control signal S2 of FIG.
5 shows an example in which the change rate is set such that the slope of the rising part of the waveform is steeper than the slope of the falling part. In this case, the change in the speed (change in the amplitude of the vibration) is more gradual when the speed of the ultrasonic motor is decreased than when it is increased. Therefore, a stable stop operation can be realized.

FIG. 6E shows an example in which the value of the frequency control signal S2 is changed stepwise. At this time, the frequency signal S3 becomes constant after the frequency increases stepwise, and thereafter, the frequency decreases stepwise. Therefore, the speed of the ultrasonic motor within the application period t2 also increases stepwise, becomes constant, and then decreases stepwise. In the present embodiment, an ultrasonic actuator using an ultrasonic vibration region has been described as an example. However, the present invention can be applied to a vibration actuator using vibration in another region.

The type in which the driving force is generated by using the longitudinal vibration and the bending vibration is taken as an example, but the invention is not limited to such a type. For example, the present invention is similarly applied to a vibration actuator that generates rotational waves by generating a traveling wave in an annular or disk-shaped vibrator or a vibration actuator that extracts rotational motion using torsional vibration and longitudinal vibration. Can be.

[0033]

As described above, according to the invention described in each of the claims, the slip generated between the vibrator and the relative motion member during the intermittent driving is reduced, and the vibrator and the relative motion member are reduced. Abrasion of the contact surface with the substrate can be suppressed. In addition, since the sudden stop and start of the vibration actuator during intermittent driving are mitigated compared to the conventional method, the behavior of the external device is stabilized when the output obtained by the vibration actuator is taken out to the external device. Can be changed.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing a configuration of a vibrator of an ultrasonic actuator used in an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a vibrator used in the embodiment and a waveform of vibration generated in the vibrator.

FIG. 3 is a block diagram illustrating a configuration of a drive circuit of the ultrasonic actuator according to the embodiment.

FIG. 4 is an explanatory diagram showing a relationship between output signals in each unit of the block diagram of FIG. 3;

FIG. 5 is an explanatory diagram showing a relationship between a driving frequency of a vibration actuator and an amplitude of vibration generated in a vibrator.

FIG. 6 is a waveform diagram showing a modification of the frequency control signal S2.

FIG. 7 is a waveform diagram showing an example of a conventional drive signal in a vibration actuator.

[Description of Signs of Main Parts]

 Reference Signs List 10 ultrasonic actuator (vibration actuator) 11 vibrator 12 elastic body 13 piezoelectric element (electromechanical conversion element) 16 oscillation circuit 17 amplifier 18 phase shifter 19 speed control circuit 21 relative motion member 30 pulse setting device 31 pulse generator (drive) Means) 32 control signal generator (frequency control means)

Claims (5)

[Claims] An electromechanical transducer, and a driving force extracting portion for extracting a driving force obtained by vibration generated by the electromechanical converting device, wherein the driving force contacts the driving force extracting portion by the driving force. A vibration actuator that generates a relative motion between the electromechanical conversion element and a driving circuit that intermittently applies an AC voltage to the electromechanical conversion element. Within at least some of the time while being applied to the element,
A driving device for a vibration actuator, wherein a frequency of the AC voltage is changed. 2. The method according to claim 1, wherein the driving circuit is configured to reduce a change in the amplitude of the vibration during at least one of starting and stopping application of the AC voltage to the electromechanical transducer. The driving device for a vibration actuator according to claim 1, wherein 3. The driving circuit includes: an oscillating means for generating the AC voltage; a driving means for intermittently driving the oscillating means; and a oscillating means for generating a control signal for controlling a frequency of the AC voltage. 3. A vibration actuator according to claim 1, further comprising: frequency control means for outputting the vibration signal to the vibration actuator. 4. An electromechanical transducer, and a driving force extracting portion for extracting a driving force obtained by exciting the electromechanical converting element, wherein the driving force is in contact with the driving force extracting portion by the driving force. In a method of driving a vibration actuator that generates a relative motion between a moving member and an AC voltage intermittently applied to the electromechanical transducer, while the AC voltage is applied to the electromechanical transducer. A method of driving a vibration actuator, wherein the frequency of the AC voltage is changed within at least a part of the time. 5. The method according to claim 1, further comprising: changing a frequency of the AC voltage so that a change in an amplitude of the vibration is reduced at least when the application of the AC voltage to the electromechanical transducer is started or stopped. The method of driving a vibration actuator according to claim 4.