JP2001016878A - Actuator and drive method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate control by ensuring that a drive unit drives a first displacement element and a second displacement element by the drive signal of a single frequency contained in a region, where a first frequency region and a second frequency region overlap with each other. SOLUTION: When a first piezoelectric element and a second piezoelectric element are driven at a frequency f1, where the phase difference between the voltage and current of the first piezoelectric element and the phase difference between the voltage and current of the second piezoelectric element are equal to each other, a region where the phase difference between voltage and current is substantially constant with respect to the first piezoelectric element and a region, where the phase difference between voltage and current is substantially constant with respect to the second piezoelectric element overlap with each other. Therefore, by taking f1 to be the frequency of a drive signal and the phase difference to be 90 deg. and inputting them to the first piezoelectric element and the second piezoelectric element, respectively, the phase difference of the currents passed through the mechanical arms of the first piezoelectric element and the second piezoelectric element can be set to 90 deg., and the locus of a chip material is made almost circular. Thus the drive speed, drive direction, drive force, and the like of a member to be driven can be controlled readily.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an actuator using a displacement element such as a piezoelectric element, for example, a truss-type actuator which generates an elliptical motion by synthesizing displacements of a plurality of displacement elements. And a method of driving by enlarging.

[0002]

2. Description of the Related Art Conventionally, a displacement element such as a piezoelectric element is arranged so as to be orthogonal to each other via a chip member, and each displacement element is driven by a drive signal having a different phase so that the chip member is moved along an elliptical locus. A truss-type actuator that drives to draw is known. By the way, since the displacement of the piezoelectric element is small, in order to efficiently drive an actuator using the piezoelectric element, it is preferable to drive the actuator using a resonance phenomenon.

[0003] Since the piezoelectric element is electrically equivalent to a capacitor, when the frequency of the drive signal approaches the resonance frequency, the phase difference between the supplied voltage and the flowing current changes. Since the displacement of the piezoelectric element is equivalent to the current, if there is a deviation in the resonance frequency of the two piezoelectric elements, the phase difference given to the drive signal will not be accurately reflected on the trajectory shape. Since a difference occurs between the displacement amounts of the two piezoelectric elements, the shape of the trajectory of the chip member does not become as intended.

In order to solve such a problem, for example, a technique described in Japanese Patent Application Laid-Open No. 63-110970 (this prior art relates to a traveling wave type ultrasonic motor) is applied, and two piezoelectric elements are used. A mechanical arm current (see FIG. 11) flowing through the element is detected, the voltage amplitude is controlled so that the amplitude becomes a predetermined value, and the phase of the current becomes a predetermined value (for example, 90 degrees).
A method of controlling the phase difference of the input voltage so as to make the trajectory of the chip member a predetermined ellipse (circle) can be considered.

FIG. 11 shows an equivalent circuit of a piezoelectric element. Although the amount of displacement of the piezoelectric element is proportional to the current value on the mechanical arm side, the current value is actually detected from the voltage at both ends of the resistor Ra, so it is necessary to subtract the current flowing on the electric arm side. The capacitance C on the electric arm side can be obtained in advance by measurement, and its value hardly changes and can be regarded as substantially constant. The current value flowing to the electric arm side can be obtained from the voltage of the drive signal supplied to the piezoelectric element, so that the current value flowing to the electric arm side is subtracted from the current value flowing to the resistor Ra to flow to the mechanical arm side. The current value is known.

FIG. 12 shows a block configuration of a drive circuit of the above-mentioned application example (which does not exist as a conventional example). FIG.
In, the oscillator 50 is variable in oscillation frequency so as to be able to follow a change in resonance frequency due to a change in environment or the like, and generates (oscillates) a sine wave signal of a predetermined frequency. The phase control unit 51 controls the delay circuit 52 according to the rotation speed, drive torque, rotation direction, and the like of the rotor 40, which is a driven member, and generates a sine wave signal with a phase shift. The amplitude controller 53 controls the first amplifier 54 and the second amplifier 55 to amplify the amplitudes of the two sinusoidal signals that are out of phase with each other. The sine wave signals amplified by the first amplifier 54 and the second amplifier 55 are respectively connected to the first piezoelectric element 10 and the second piezoelectric element 1.
0 ′, the first piezoelectric element 10 and the second piezoelectric element 1
0 'is driven. The first current detector 56 and the second current detector 57 detect currents flowing through the mechanical arms of the first piezoelectric element 10 and the second piezoelectric element 10 ′, respectively, and convert the detected current signals into phase control units 51 and It is input to the amplitude controller 53. The phase control unit 51 includes a first current detector 56 and a second current detector 56.
The phase difference between the currents flowing through the mechanical arms of the first piezoelectric element 10 and the second piezoelectric element 10 'is detected from the current signal detected by the current detector 57, and the delay circuit 52 is set so that the phase difference between the currents becomes a predetermined value. Control. In addition, the amplitude control unit 53 converts the current signals detected by the first current detector 56 and the second current detector 57 into the first piezoelectric element 10 and the second piezoelectric element 1.
The amplitude of the current flowing through the mechanical arm of 0 'is detected, and the first amplifier 54 and the second amplifier 55 are controlled so that the amplitude of each current becomes a predetermined value.

[0007]

However, according to the above-described application, the first piezoelectric element 10 and the second piezoelectric element 1
The phase and the amplitude of the current flowing through the mechanical arm of 0 'must be detected and controlled so that the phase and the amplitude each become a predetermined value, and the control is complicated. In addition, a variable delay circuit and a variable amplifier are required, and the configuration of the control circuit becomes complicated, which causes an increase in cost.

The present invention has been made to solve the above problems, and has as its object to provide an actuator having a simple structure, easy control, and high driving efficiency, and a driving method thereof.

[0009]

In order to achieve the above object, an actuator according to the present invention is connected to at least a first displacement element and a second displacement element, and a tip of each of the first displacement element and the second displacement element. A displacement synthesizer for synthesizing the displacements of the respective displacement elements, and a driver for driving the respective displacement elements such that the displacement synthesizer performs an elliptical motion. The resonance frequency and the anti-resonance frequency of the first displacement element are included. Between the first
An area where the phase difference between the voltage of the drive signal supplied to the displacement element and the current flowing through the first displacement element is substantially constant is defined as the first frequency area, and is between the resonance frequency and the anti-resonance frequency of the second displacement element. The driving unit includes a region where the phase difference between the voltage of the drive signal supplied to the second displacement element and the current flowing through the second displacement element is substantially constant, as a second frequency region. The first displacement element and the second displacement element are driven by a drive signal of one frequency included in the region where the first displacement element and the second displacement element are overlapped.

In the above configuration, the one frequency is:
The median frequency of a first frequency having a low frequency among the resonance frequencies of the first displacement element and the second displacement element and a second frequency having a high frequency among the anti-resonance frequencies of the first displacement element and the second displacement element. Is preferred.

It is preferable that a predetermined phase difference is provided between a drive signal for driving the first displacement element and a drive signal for driving the second displacement element.

Further, another actuator of the present invention is coupled to at least the first displacement element and the second displacement element, and to the distal ends of the first displacement element and the second displacement element, respectively, and synthesizes displacements of the respective displacement elements. And a drive unit for driving each displacement element so that the displacement synthesis unit performs an elliptical motion, wherein the drive unit operates in a frequency region near the resonance frequency of the first displacement element and the second displacement element. Driving the first displacement element and the second displacement element at a frequency at which the displacement amounts of the first displacement element and the second displacement element are equal.

In the above configuration, the drive signal for driving the first displacement element and the drive signal for driving the second displacement element are set such that the phase difference between the current flowing through the first displacement element and the current flowing through the second displacement element becomes a predetermined value. It is preferable to provide a predetermined phase difference to the drive signal.

[0014] In each of the above-described configurations, it is preferable that a current detecting unit for detecting a current flowing through the first displacement element and the second displacement element is further provided.

On the other hand, the method of driving an actuator according to the present invention comprises at least a first displacement element and a second displacement element;
A displacement combining unit coupled to the distal ends of the displacement element and the second displacement element, respectively, for combining displacements of the respective displacement elements, wherein the displacement combining unit drives the respective displacement elements such that the displacement combining unit performs an elliptic motion. Wherein the phase difference between the voltage of the drive signal supplied to the first displacement element and the current flowing through the first displacement element is substantially constant between the resonance frequency and the antiresonance frequency of the first displacement element. Is defined as a first frequency region, and the phase difference between the voltage of the drive signal supplied to the second displacement element and the current flowing through the second displacement element is substantially between the resonance frequency and the antiresonance frequency of the second displacement element. The first displacement element and the second displacement element are driven by a drive signal of one frequency included in an area where the first frequency area and the second frequency area overlap each other, with a certain area as a second frequency area. I do.

In the above configuration, the one frequency is:
It is preferable that the center frequency is a median value of a first frequency having a low frequency among the resonance frequencies of the first displacement element and the second displacement element and a second frequency having a high frequency among the anti-resonance frequencies of the first displacement element and the second displacement element. .

It is preferable that a predetermined phase difference is provided between the drive signal for driving the first displacement element and the drive signal for driving the second displacement element.

Further, another driving method of the actuator according to the present invention comprises the steps of: at least a first displacement element and a second displacement element;
A displacement combining unit for combining the displacements of the respective displacement elements, the displacement combining unit driving the respective displacement elements such that the displacement combining unit performs an elliptical motion. In a driving method, in a frequency region near a resonance frequency of a first displacement element and a second displacement element, a first displacement element is driven at a frequency at which displacement amounts of the first displacement element and the second displacement element become equal.
Driving the displacement element and the second displacement element.

In the above configuration, the drive signal for driving the first displacement element and the second displacement element are driven such that the phase difference between the current flowing through the first displacement element and the current flowing through the second displacement element becomes a predetermined value. It is preferable to provide a predetermined phase difference to the drive signal.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A truss-type actuator according to one embodiment of the present invention will be described. First, the configuration of a laminated piezoelectric element used as a displacement element in the present embodiment is shown in FIG. As shown in FIG.
Are a plurality of ceramic thin plates 1 exhibiting piezoelectric characteristics such as PZT.
1 and electrodes 12 and 13 are alternately laminated, and each ceramic thin plate 11 and electrodes 12 and 13 are fixed by an adhesive or the like. The alternate electrode groups 12 and 13 arranged alternately are connected to a driving power supply 16 via signal lines 14 and 15, respectively. When a predetermined voltage is applied between the signal lines 14 and 15, an electric field is generated in the laminating direction on each ceramic thin plate 11 sandwiched between the electrodes 12 and 13, 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 the multilayer piezoelectric element 10
Are provided with protective layers 17 at both ends.

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 entire piezoelectric element 10 expands and contracts. In a region where the electric field is small and the displacement history can be neglected, the electric field generated between the electrodes 12 and 13 and the displacement of the piezoelectric element 10 can be regarded as a substantially linear relationship. This is shown in FIG. In the figure, the horizontal axis represents the electric field intensity, and the vertical axis represents the distortion rate.

Next, when an AC drive voltage (AC signal) is applied between the electrodes 12 and 13 by the drive power supply 16, each ceramic thin plate 11 repeatedly expands and contracts in the same direction in accordance with the electric field. Repeated expansion and contraction as a whole. The piezoelectric element 10 has a unique resonance frequency determined by its structure and electrical characteristics. When the frequency of the AC drive voltage matches the resonance frequency of the piezoelectric element 10, the impedance decreases and the displacement of the piezoelectric element 10 increases. Since the displacement of the piezoelectric element 10 is small with respect to its external dimensions,
In order to drive at a low voltage, it is desirable to use this resonance phenomenon.

Next, the structure of a truss-type actuator (hereinafter, simply referred to as an actuator) of the present embodiment is shown in FIG.
Shown in As shown in FIG. 3, two displacement elements (laminated first piezoelectric element and second piezoelectric element) 10, 10 'are arranged to intersect at a substantially right angle, and a tip member (displacement) is provided at an intersection side end thereof. (Synthesizing part) 20 is joined by an adhesive. On the other hand, the other ends of the first and second piezoelectric elements 10 and 10 ′ are joined to a base member (fixed portion) 30 by an adhesive. As a material of the tip member 20, tungsten or the like, which can stably obtain a high friction coefficient and has excellent wear resistance, is preferable. The material of the base member 30 is preferably stainless steel or the like, which is easy to manufacture and has excellent strength. Further, as the adhesive, an epoxy resin or the like having excellent adhesive strength and strength is preferable. The first piezoelectric element 10 and the second piezoelectric element 10 'are substantially the same as the piezoelectric element 10 shown in FIG. The base member 30 is biased by a spring 41,
The tip member 20 comes into contact with the rotor 40 at a predetermined pressure by the urging force of the spring 41.

When the piezoelectric elements 10 and 10 'are each driven by a drive signal having a predetermined phase difference, the chip member 20 is driven so as to draw an elliptical (including circular) locus.
When the tip member 20 is pressed against, for example, the cylindrical surface of the rotor 40 rotatable about a predetermined axis, the tip member 2
It is possible to convert the elliptical motion of 0 (including the circular motion) into the rotational motion of the rotor 40. Alternatively, the tip member 20
Is pressed against, for example, a flat portion of a rod-shaped member (not shown), so that the elliptical motion of the tip member 20 can be converted into a linear motion of the rod-shaped member. As a material of the rotor 40, a lightweight metal such as aluminum is preferable. In order to prevent abrasion due to friction with the tip member 20, it is preferable to apply a treatment such as alumite to the surface.

Next, the principle of rotation of the rotor 40 by the actuator will be described. First piezoelectric element 10 and second piezoelectric element 10
When the frequency of the sine wave voltage applied to the piezoelectric element 10 ′ (the driving frequency of the piezoelectric element) is small and the rotation speed of the tip member 20 is low, the actuator itself follows the displacement of the tip member 20 by the urging force of the spring 41. Therefore, the tip member 20 does not separate from the surface of the rotor 40 and is reciprocally driven in a state of being in contact with the surface of the rotor 40. Therefore, in this case, the rotor 40 cannot be rotated.

On the other hand, the first piezoelectric element 10 and the second
When the frequency of the sine wave voltage applied to the piezoelectric element 10 ′ is large and the rotation speed of the tip member 20 is high, the actuator itself may be driven by the biasing force of the spring 41.
, The tip member 20 is temporarily separated from the surface of the rotor 40. Accordingly, the tip member 20 is moved in a predetermined direction while the tip member 20 is in contact with the surface of the rotor 40, and is moved in a direction opposite to the predetermined direction while the tip member 20 is separated from the surface of the rotor 40. By doing so, the rotor 40 can be rotated in a predetermined direction. This state is shown in FIG.

FIGS. 4A and 4E show a state where the first piezoelectric element 10 and the second piezoelectric element 10 are both extended and the chip member 20 is in contact with the surface of the rotor 40, and FIG. A state in which the element 10 is contracted, the second piezoelectric element 10 ′ is extended, and the tip member 20 is separated from the surface of the rotor 40;
(C) is a state where the first piezoelectric element 10 and the second piezoelectric element 10 are both contracted and the chip member 20 is separated from the surface of the rotor 40, and (d) is a state where the first piezoelectric element 10 is extended and the second piezoelectric element 1
The state where the tip member 20 is in contact with the surface of the rotor 40 is shown in FIG. As can be seen from FIG. 4, the rotor 40 can be rotated by the tip member 20 moving away from the surface of the rotor 40. Note that the conditions for separating the tip member 20 from the surface of the rotor 40 have no direct relation to the essential part of the present invention, and thus the description thereof is omitted.

Next, drive signals for driving the first piezoelectric element 10 and the second piezoelectric element 10 'will be described. When two independent motions that are orthogonal to each other are synthesized, the intersection points draw a trajectory according to the equation of elliptical vibration (Lissajous equation). Also in the actuator of the present embodiment, various trajectories can be obtained by changing the amplitude and phase difference of the drive signal for driving the first piezoelectric element 10 and the second piezoelectric element 10 '. When the amplitude of each drive signal is equal, the phase difference between each drive signal is 0 °, 45 °,
Locuses at 90 °, 135 °, and 180 ° are shown in FIGS. 5A to 5E, respectively.

As described above, by controlling the trajectory of the tip member 20, the rotation direction, the rotation speed, the rotation force (torque) and the like of the rotor 40 can be controlled. Specifically, if the diameter of the trajectory of the tip member 20 in the tangential direction with respect to the rotor 40 is increased, the rotation speed increases.
Further, if the diameter of the trajectory of the tip member 20 in the direction normal to the rotor 40 is increased, the rotational force increases.
Further, if the phase is reversed, the rotation direction can be reversed.

Next, the resonance characteristics of the piezoelectric element will be described. 6A shows a change in impedance with respect to a change in the frequency (hereinafter, simply referred to as “frequency”) of the drive signal of the piezoelectric element, and FIG. 6B shows an input voltage and a mechanical arm of the piezoelectric element with respect to the change in frequency. The change in the phase difference of the flowing current
(C) represents a change in the displacement of the piezoelectric element with respect to a change in the frequency, and the horizontal axis represents the frequency.

Attention is paid in order from the left to the right in each figure.
When the frequency is gradually increased, the impedance decreases, and the displacement of the piezoelectric element increases accordingly. The phase difference between voltage and current is usually 90 degrees ahead of current,
Rapid phase difference becomes smaller when approaching the resonance frequency f _r.
When the frequency is the resonance frequency f _r, the impedance becomes minimum, the phase difference between the voltage and current is zero. Further, the displacement amount of the piezoelectric element becomes maximum.

[0032] When the frequency is greater than the resonance frequency f _r, the impedance rapidly increases, the phase of the drive current to lag behind the voltage phase. On the other hand, the amount of displacement of the piezoelectric element gradually decreases as a peak when the resonance frequency f _r. As the frequency further increases, the phase difference between the voltage and the current becomes substantially constant, and there is a stable frequency region.

As the frequency further increases, the phase difference between the voltage and the current decreases, and the phase difference between the two becomes zero at the anti-resonance frequency f _z . At this time, the impedance becomes maximum. When the frequency becomes higher than the anti-resonance frequency f _z , the impedance gradually decreases, and the phase of the current advances with respect to the phase of the voltage. As described above, in the vicinity of the resonance frequency _fr , the relationship (phase difference) between the phase of the input voltage and the phase of the current flowing through the mechanical arm of the piezoelectric element rapidly changes.

Next, as an example, consider a case where the actuator is driven so that the tip member 20 draws a circular locus. If the resonance frequencies of the first piezoelectric element 10 and the second piezoelectric element 10 ′ match and the impedances are uniform, even if the frequency of the drive signal is changed near the resonance frequency, the first piezoelectric element 10 and the second piezoelectric element 10 ′ are changed. The displacement amount of the element 10 'and the phases of the voltage and the current change similarly. Therefore, the frequency of the drive signal is made equal to the resonance frequency, and the amplitudes of the voltages of the drive signals input to the first piezoelectric element 10 and the second piezoelectric element 10 'are made equal.
Further, only by keeping the phase difference at 90 degrees, the trajectory of the tip member 20 can be made a circle having the maximum diameter as shown on the left side of FIG. The state of the drive signal at that time is as shown on the right side of FIG.

However, in practice, there are many cases where a difference occurs between the resonance frequency and the impedance of the first piezoelectric element 10 and the second piezoelectric element 10 'due to variations in the manufacture of the piezoelectric elements and variations during the assembly. FIG. 7 shows the resonance characteristics of two piezoelectric elements having different characteristics such as resonance frequency and impedance.
7, (a), (b) and (c) are the same as those in FIG. The solid line indicates the resonance characteristic of the first piezoelectric element 10, and the broken line indicates the resonance characteristic of the second piezoelectric element 10 '.

Paying attention to the resonance frequency f _a of the first piezoelectric element 10 shown by a solid line in FIG. 7, the phase difference between the voltage and current of the first piezoelectric element 10 is 0, while the frequency f _a is the second piezoelectric element 10. 'because it is below the resonance frequency f _b of the second piezoelectric element 10' element 10 phase of the current of is proceeding about 60 degrees with respect to the voltage phase.

With respect to the first piezoelectric element 10 and the second piezoelectric element 10 'having such a relationship, the phase of the voltage of the drive signal of the first piezoelectric element 10 is 90 degrees as shown on the right side of FIG. When the advanced drive signal is input, the first piezoelectric element 10 and the second
The phase difference of the current of the piezoelectric element 10 'is about 30 degrees, and the trajectory of the chip member 20 has an elliptical shape whose major axis is the symmetric axis direction of the actuator as shown on the left. Conversely, FIG.
As shown on the right side of (c), when a drive signal in which the phase of the voltage of the drive signal of the second piezoelectric element 10 'is advanced by 90 degrees is input,
The phase difference between the currents of the first piezoelectric element 10 and the second piezoelectric element 10 'is about 150 degrees, and as shown on the left side, the tip member 20
Has an elliptical shape whose minor axis is the axis of symmetry of the actuator. Therefore, the tip member 20 (or the rotor 40)
There is a speed difference depending on the direction of rotation.

As a first method for solving this problem, a frequency f at which the phase difference between the voltage and the current of the first piezoelectric element 10 and the phase difference between the voltage and the current of the second piezoelectric element 10 'are equal.
The first piezoelectric element 10 and the second piezoelectric element 10 'are driven by _i . As described above, there is a region where the phase difference between the voltage and the current is substantially constant between the resonance frequency and the antiresonance frequency of the piezoelectric element and is stable. Paying attention to FIG. 7B, the region where the phase difference between the voltage and the current for the first piezoelectric element 10 is almost constant and the region where the phase difference between the voltage and the current for the second piezoelectric element 10 ′ are almost constant are the frequencies. It can be seen that they overlap near f _i .

Accordingly, the frequency of the drive signal is set to f _i , and the phase difference is set to 90 degrees and input to the first piezoelectric element 10 and the second piezoelectric element 10 ′.
The phase difference between 0 and the current flowing through each mechanical arm of the second piezoelectric element 10 'can be set to 90 degrees. The first piezoelectric element 1
0 and the second piezoelectric element 10 'resonant frequency f _a of, since f _b are different, the frequencies f _i, the displacement amount and the second piezoelectric element 10 of the first piezoelectric element 10' displacement amount of which may vary slightly.
However, since one as compared to the case of driving at the resonance frequency f _a or f _b difference of the displacement amounts of the piezoelectric elements 10, 10 'it is small (see FIG. 7 (c)), the tip member 2
The locus of 0 can be made substantially circular, and there is no practical problem.

FIG. 9 shows a block diagram of a drive circuit according to the first method. The oscillator 50 is variable in frequency, and generates (oscillates) a sine wave signal at a predetermined frequency. The delay circuit 52 generates, for example, a sine wave signal whose phase is shifted by 90 degrees with respect to the sine wave signal from the oscillator 50. The first amplifier 54 and the second amplifier 55 amplify the amplitudes of the two sinusoidal signals having phases shifted from each other, respectively.
And the second piezoelectric element 10 '. First current detector 5
6 and the second current detector 57 are respectively connected to the first piezoelectric element 1
The current flowing through the zero and the mechanical arm of the second piezoelectric element 10 ′ is detected, and a current signal as a detection result is input to the oscillator 50.
The oscillator 50 detects a region where the phase difference between the voltage and the current of the first piezoelectric element 10 is substantially constant and the second piezoelectric element 10 ′ based on the current signals from the first current detector 56 and the second current detector 57.
Locate the area where the phase difference between the voltage and current are overlapped and the substantially constant region, determines the driving frequency f _i. Once the drive frequency f _i is determined, the oscillator 50 will continue to oscillate at that frequency.

As a method of determining the frequency f _i , while gradually changing the oscillation frequency of the oscillator 50, the first
The resonance frequency f _a of the first piezoelectric element 10 and the anti-resonance frequency f _b ′ of the second piezoelectric element are obtained from the currents detected by the current detector 56 and the second current detector 57 and the voltage of the drive signal, and the median value is obtained. You may decide. Alternatively, while gradually changing the oscillation frequency of the oscillator 50, the first piezoelectric element 10
Alternatively, the frequencies near the phase difference between the voltage and the current of the second piezoelectric element 10 ′ at which the respective phases are maximized may be compared to determine any of the frequencies included in common.

As compared with the driving circuit of the application example shown in FIG. 12, the phase control unit 51 and the amplitude control unit 53 are not required, and the circuit configuration is simplified. In addition, since the amplitude and phase of the voltage of the drive signal are not adjusted, the control is simplified. Further, since the phase is stable near the driving frequency fi, if the change in the resonance frequency due to the environmental change is small, even if the driving is always performed at the driving frequency fi obtained in advance, there is almost no change in the phase. Can be kept round. In that case, the frequency adjustment of the oscillator and the current detector are not required, and the circuit configuration is further simplified.

Next, a second method for solving the above problem will be described.
As a method, the resonance frequency f of the first piezoelectric element 10_aAnd the second
The resonance frequency f of the piezoelectric element 10 '_bBetween the first piezoelectric element
Frequency at which the displacement amount of the element 10 and the second piezoelectric element 10 'becomes equal.
Number f_eDrive the first piezoelectric element 10 and the second piezoelectric element 10 '.
Move. As described above, the amount of displacement of the piezoelectric element
When the number coincides with the resonance frequency, the maximum
Then, the amount of displacement decreases. Therefore, the first piezoelectric element 10
Vibration frequency f_aAnd the resonance frequency f of the second piezoelectric element_bBetween each
Frequency f at which displacement amounts of piezoelectric elements 10 and 10 'are equal_e
Exists. Each to the mechanical arm of each piezoelectric element 10, 10 '
The current f_e
And find its frequency f_eDrive. In addition,
Drive frequency f _eIs the resonance frequency of each piezoelectric element 10, 10 '
f_aAnd f_bTherefore, each of the piezoelectric elements 10 and 10 ′
The voltage level of the drive signal is adjusted so that the current phase difference is 90 degrees.
It is necessary to adjust the phase difference.

FIG. 10 shows a block diagram of a drive circuit according to the second method. The oscillator 50 is variable in frequency,
A sine wave signal is generated (oscillated) at a predetermined frequency. The phase control section 51 controls the delay circuit 52 to generate a sine wave signal having a phase shift. First amplifier 54 and second amplifier 55
Amplifies the amplitudes of two sinusoidal signals that are out of phase with each other, and the first piezoelectric element 10 and the second piezoelectric element 10 ′.
Is applied. First current detector 56 and second current detector 5
7 denotes a first piezoelectric element 10 and a second piezoelectric element 1
A current flowing through the mechanical arm of 0 ′ is detected, and a current signal as a detection result is input to the oscillator 50 and the phase control unit 51. The oscillator 50 includes a first current detector 56 and a second current detector 5
From the current signal from 7, in the vicinity of the resonance frequency f _b of the resonant frequency f _a and the second piezoelectric elements of the first piezoelectric element 10, find the frequency f _e of the displacement amount of the piezoelectric elements 10 and 10 'are equal, The drive frequency _fe is determined. Also, the phase control unit 51
The delay circuit 52 is configured such that the phase difference between the current signals from the first current detector 56 and the second current detector 57 becomes 90 degrees.
Adjust

As a method of determining the frequency f _{e at} which the displacement amounts of the piezoelectric elements 10 and 10 ′ are equal, the first current detector 56 and the second current detector 56 are gradually changed while the oscillation frequency of the oscillator 50 is gradually changed. The frequency at which the current values become equal may be found based on the amplitude of the current signal from 57.

As compared with the driving circuit of the application example shown in FIG. 12, the amplitude control section 53 becomes unnecessary and the circuit configuration becomes simple. Further, since the amplitude of the voltage of the drive signal is not adjusted, the control is simplified.

In the description of the above embodiment, the two displacement elements 10 and 10 'for driving the tip member 20 are arranged so as to be orthogonal to each other. However, the present invention is not limited to this. For example, 45 °, 135 °
Any angle may be used. Further, the number of displacement elements is not limited to two, and three or more displacement elements may be used to drive three or four degrees of freedom. Further, as the driving source of the displacement element, not only the piezoelectric element but also another electric or mechanical displacement element such as a magnetostrictive element may be used.

In the above embodiment, an example was described in which the tip member 20 is driven so that the trajectory is circular. However, the present invention is not limited to this.
It may be configured to be driven in an arbitrary elliptical shape according to the rotation speed, rotation direction, torque, and the like.

Further, in the above embodiment, the truss type actuator has been described as an example, but the present invention is not limited to this, and it is also possible to apply to a traveling wave type actuator.

[0050]

As described above, according to the first actuator of the present invention, at least the first displacement element and the second displacement element are connected to the distal ends of the first displacement element and the second displacement element, respectively. A displacement synthesizer for synthesizing the displacements of the respective displacement elements, and a driver for driving the respective displacement elements such that the displacement synthesizer performs an elliptical motion. The resonance frequency and the anti-resonance frequency of the first displacement element are included. And a region in which the phase difference between the voltage of the drive signal supplied to the first displacement element and the current flowing through the first displacement element is substantially constant is defined as the first frequency region, and the region opposite to the resonance frequency of the second displacement element. The drive unit includes a region between the resonance frequency and a phase difference between the voltage of the drive signal supplied to the second displacement element and the phase difference of the current flowing through the second displacement element as a second frequency region. One frequency domain and second
The first displacement element and the second displacement element are driven by a drive signal of one frequency included in an area where the frequency area overlaps.

That is, the phase difference between the voltage and the current of the first displacement element becomes equal to the phase difference between the voltage and the current of the second displacement element, and the phase difference between the drive signals input to the first displacement element and the second displacement element. Is directly reflected as the phase difference between the displacements of the first displacement element and the second displacement element. As a result, the shape of the trajectory of the displacement synthesizing unit is desired (for example, a circle when the phase difference is 90 degrees).
The driving speed, driving direction,
Control of driving force and the like becomes easy. Further, although none of the displacement elements is driven at the resonance frequency, the difference between the displacement amounts of the respective displacement elements becomes smaller than when driven at the resonance frequency of one of the displacement elements, and Can be made into a substantially desired shape. Further, there is no need to adjust the phase and amplitude of the drive signal, and the configuration and control method of the control circuit are simplified, leading to cost reduction.

Further, according to the second actuator of the present invention, at least the first displacement element and the second displacement element are coupled to the distal ends of the first displacement element and the second displacement element, respectively. A displacement combining unit for combining
The displacement synthesis unit includes a drive unit that drives each displacement element so as to perform an elliptical motion, and the drive unit includes a first displacement element and a second displacement element in a frequency region near a resonance frequency of the first displacement element and the second displacement element. The first displacement element and the second displacement element are driven at a frequency at which the displacement amounts of the two displacement elements become equal.

That is, since the driving is performed at a frequency at which the amount of displacement becomes equal in the vicinity of the resonance frequency of each displacement element, the trajectory of the displacement synthesizing section can be made into a substantially desired shape. Further, although none of the displacement elements is driven at the resonance frequency, a large amount of displacement close to that when driven at the resonance frequency can be obtained, so that the driving efficiency of the actuator can be increased. Further, there is no need to adjust the amplitude of the drive signal, which simplifies the configuration and control method of the control circuit, leading to cost reduction.

According to the first actuator driving method of the present invention, at least the first displacement element and the second displacement element are coupled to the distal ends of the first displacement element and the second displacement element, respectively. A displacement synthesizing unit for synthesizing the displacement of the element, wherein the displacement synthesizing unit drives each of the displacement elements such that the displacement synthesizing unit performs an elliptical motion, wherein A region where the phase difference between the voltage of the drive signal supplied to the first displacement element and the current flowing through the first displacement element is substantially constant is defined as a first frequency region;
A region between the resonance frequency and the anti-resonance frequency of the second displacement element, where the phase difference between the voltage of the drive signal supplied to the second displacement element and the current flowing through the second displacement element is substantially constant, is defined as the second frequency. As a region, the first frequency drive signal is included in a region where the first frequency region and the second frequency region overlap each other.
Driving the displacement element and the second displacement element.

That is, by using the first driving method for an existing actuator, the first actuator of the present invention can be easily realized, and its effect can be obtained.

According to the second actuator driving method of the present invention, at least the first displacement element and the second displacement element are coupled to the distal ends of the first displacement element and the second displacement element, respectively. A displacement synthesizing unit for synthesizing displacements of the elements, wherein the displacement synthesizing unit drives each of the displacement elements such that the displacement synthesizing unit performs an elliptical motion. In the frequency domain of
The first displacement element and the second displacement element are driven at a frequency at which the displacement amounts of the first displacement element and the second displacement element are equal.

That is, by using the second driving method for an existing actuator, the second actuator of the present invention can be easily realized, and its effect can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a laminated piezoelectric element used as a displacement element in a truss-type actuator according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between an electric field generated between electrodes of the multilayer piezoelectric element and displacement of the piezoelectric element.

FIG. 3 is a diagram showing a configuration of a truss-type actuator in the embodiment.

FIG. 4 is a view showing a principle of rotating a rotor by an actuator in the embodiment.

FIG. 5 is a diagram showing a trajectory when the amplitudes of drive signals applied to two piezoelectric elements are made equal and the phase difference between the drive signals is changed in the embodiment.

FIG. 6 is a diagram showing resonance characteristics of a piezoelectric element.

FIG. 7 is a diagram illustrating resonance characteristics of two piezoelectric elements having different characteristics such as a resonance frequency and an impedance.

FIG. 8 is a diagram illustrating a relationship between a phase difference between drive signals input to two piezoelectric elements and a trajectory of a chip member.

FIG. 9 is a block diagram illustrating a configuration example of a driving circuit suitable for a first driving method according to an embodiment of the present invention.

FIG. 10 is a block diagram illustrating a configuration example of a driving circuit suitable for a second driving method according to an embodiment of the present invention.

FIG. 11 is a diagram showing an equivalent circuit of a piezoelectric element.

FIG. 12 is a diagram illustrating a configuration example (unknown) of a drive circuit when a conventional drive method is applied to a truss-type actuator.

[Explanation of symbols]

 10: first piezoelectric element (first displacement element) 10 ': second piezoelectric element (second displacement element) 20: chip member (displacement synthesizing section) 30: base member 40: rotor (driven member) 50: oscillator 51 : Phase control unit 52: delay circuit 54: first amplifier 55: second amplifier 56: first current detector 57: second current detector

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H680 AA06 AA10 AA19 BB03 CC02 CC10 DD02 DD15 DD37 DD73 DD84 FF25 FF27 FF30 FF33 FF36 GG21

Claims (11)

[Claims] 1. A displacement combining unit coupled to at least a first displacement element and a second displacement element, and a tip of the first displacement element and the second displacement element for combining displacements of the displacement elements, A driving unit that drives each of the displacement elements so that the combining unit performs an elliptical motion. The driving unit supplies a driving signal between the resonance frequency and the anti-resonance frequency of the first displacement element and supplied to the first displacement element. The region where the phase difference between the voltage and the current flowing through the first displacement element is substantially constant is defined as the first frequency region, and is between the resonance frequency and the anti-resonance frequency of the second displacement element and is supplied to the second displacement element. The region where the phase difference between the voltage of the driving signal and the current flowing through the second displacement element is substantially constant is defined as the second frequency region, and the driving unit includes one region included in the region where the first frequency region and the second frequency region overlap. The first displacement element and the drive signal of two frequencies Actuator and drives the second displacement element. 2. The one frequency is a first frequency having a low frequency among the resonance frequencies of the first displacement element and the second displacement element and a high frequency among the anti-resonance frequencies of the first displacement element and the second displacement element. 2. The actuator according to claim 1, wherein the frequency is a median frequency of the second frequency. 3. A driving signal for driving a first displacement element and a second driving signal.
The actuator according to claim 1, wherein a predetermined phase difference is provided to a drive signal for driving the displacement element. 4. A displacement synthesizing unit coupled to at least the first displacement element and the second displacement element, the tip of each of the first displacement element and the second displacement element, and for synthesizing the displacement of each displacement element. The combining unit includes a driving unit that drives each displacement element so as to perform an elliptic motion. The driving unit includes a first displacement element and a second displacement element in a frequency region near a resonance frequency of the first displacement element and the second displacement element. An actuator for driving a first displacement element and a second displacement element at a frequency at which displacement amounts of the displacement elements become equal. 5. A drive signal for driving the first displacement element and a drive signal for driving the second displacement element such that a phase difference between a current flowing through the first displacement element and a current flowing through the second displacement element becomes a predetermined value. 5. The actuator according to claim 4, wherein a predetermined phase difference is provided to the actuator. 6. The actuator according to claim 1, further comprising a current detection unit that detects a current flowing through the first displacement element and the second displacement element. 7. At least a first displacement element and a second displacement element, and a displacement synthesizing unit coupled to distal ends of the first displacement element and the second displacement element, respectively, for synthesizing displacements of the respective displacement elements. A method of driving an actuator that drives each displacement element such that the displacement synthesis unit performs elliptical motion, wherein the actuator is between the resonance frequency and the anti-resonance frequency of the first displacement element and is supplied to the first displacement element. A region in which the phase difference between the voltage of the drive signal and the current flowing through the first displacement element is substantially constant is defined as the first frequency region, and is between the resonance frequency and the anti-resonance frequency of the second displacement element. The region in which the phase difference between the voltage of the drive signal supplied to the second displacement element and the current flowing through the second displacement element is substantially constant is defined as the second frequency region, and the first frequency region and the second frequency region
A method of driving an actuator, comprising: driving a first displacement element and a second displacement element with a drive signal of one frequency included in a region where a frequency region overlaps. 8. The one frequency includes a first frequency having a low frequency among resonance frequencies of the first displacement element and the second displacement element and a high frequency among anti-resonance frequencies of the first displacement element and the second displacement element. 8. The method of driving an actuator according to claim 7, wherein the frequency is a median frequency of the second frequency. 9. A driving signal for driving a first displacement element and a second driving signal
8. The method of driving an actuator according to claim 7, wherein a predetermined phase difference is provided to a drive signal for driving the displacement element. 10. A system comprising: at least a first displacement element and a second displacement element; and a displacement combining part coupled to respective distal ends of the first displacement element and the second displacement element for combining displacements of the respective displacement elements. A driving method of an actuator for driving each displacement element such that the displacement synthesis unit performs an elliptic motion, wherein the first displacement element and the second displacement element are arranged in a frequency region near a resonance frequency of the first displacement element and the second displacement element. A method for driving an actuator, comprising: driving a first displacement element and a second displacement element at a frequency at which displacement amounts of the displacement elements are equal. 11. The first displacement element such that a phase difference between a current flowing through the first displacement element and a current flowing through the second displacement element becomes a predetermined value.
11. The actuator driving method according to claim 10, wherein a predetermined phase difference is provided between the drive signal for driving the displacement element and the drive signal for driving the second displacement element.