JP2002101676A - Actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain the output and drive efficiency of an actuator by correcting errors such as the size, quality and mounting position of each member constituting the actuator and the change of a natural frequency caused by thermal expansion in the actuator elliptically moving the drive member as a displacement element such as a piezoelectric element is made a drive source and driving the driven member by pressurizing and bringing the drive member in contact on the driven member. SOLUTION: A chip member 20 is provided on the intersection part of the two piezoelectric elements 10A, 10B arranged to make a prescribed angle (for instance, 90 degrees), and the chip member 20 is pressurized in contact on a rotor 40 by a pressurization member 45 together with a base member 30 holding the piezoelectric elements 10A, 10B. In addition, a pressure adjusting mechanism 46 is provided on a pressurization member 45, and pressure is regulated so that the track of the chip member 20 is a desired shape while regulating the pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention utilizes a vibration of a displacement element such as a piezoelectric element to move a driving member so as to draw a desired trajectory, and to bring the driving member into pressure contact with a driven member so that the driving member is pressed. The present invention relates to a technique for optimizing a trajectory of a driving member in a vibration type actuator for driving a driving member.

[0002]

2. Description of the Related Art In recent years, two displacement elements such as piezoelectric elements are arranged so that their displacement directions form a predetermined angle (for example, 90 degrees), and a chip member provided at an intersection of each displacement element has an elliptical orbit. A truss-type actuator has been proposed in which each displacement element is driven by an AC voltage signal having a predetermined phase difference so as to draw a circular orbit, a tip member is brought into contact with a rotor, and the rotor is rotated in a predetermined direction.

When sinusoidal voltages having different phases are applied to two piezoelectric elements constituting a truss type actuator, the two piezoelectric elements are displaced in a sinusoidal manner having different phases. As a result, the tip member (drive member) coupled to the two piezoelectric elements performs an elliptical motion (a circular motion in the case of a phase difference of 90 degrees). When the tip member performs an elliptical motion or a circular motion, the tip member intermittently contacts the rotor (driven member), and the rotor moves due to frictional force acting between the tip member and the rotor during the contact period. And the rotor is intermittently rotated in a predetermined direction. By repeating this operation continuously, an output can be obtained via the rotor.

[0004]

In general, a driving unit is formed by fixing two piezoelectric elements to a base member and fixing a chip member at an intersection of the two piezoelectric elements. Adjustment of the voltage, phase difference, frequency, and the like of the drive signal is performed so as to draw a desired trajectory.

However, when the drive unit adjusted as described above is brought into pressure contact with the rotor as the driven member, the frequency of the piezoelectric element changes due to the influence of the rotor, and the desired trajectory of the chip member is obtained. Disappears. Further, when the trajectory of the tip member changes from a desired shape, the contact state between the tip member and the rotor changes, so that there is a problem that the output and the driving efficiency of the actuator itself decrease.

In particular, when the piezoelectric element is driven in a resonance state in order to increase the displacement of the piezoelectric element, errors in the dimensions, materials, mounting positions, etc. of the members constituting the actuator, thermal expansion, etc. Has a problem that the natural frequency of the actuator changes and the output and the driving efficiency of the actuator decrease.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and it is intended to maintain the trajectory of a chip member in a desired shape at the stage of assembling the actuator itself or an apparatus using the actuator. It is an object of the present invention to provide an actuator capable of performing the following.

[0008]

To achieve the above object, an actuator according to the present invention comprises a displacement element for generating a predetermined displacement, and a driving member coupled to the displacement element and driven by the displacement of the displacement element. A driven member driven by the contact of the driving member, a pressing member for pressing the driving member against the driven member, and a natural vibration by adjusting a pressing force by the pressing member. It is characterized by comprising a pressure adjustment mechanism for changing the frequency in the mode, and a drive circuit for applying a drive signal to each of the displacement elements.

In the above structure, it is preferable that the driving member is provided at an intersection of a plurality of displacement elements arranged so as to form a predetermined angle with each other.

Further, in the in-phase mode in which at least two displacement elements are displaced in the same phase and the anti-phase mode in which they are displaced in opposite phases, the natural frequency of the actuator in the in-phase mode and the natural vibration of the actuator in the anti-phase mode It is preferable to adjust the pressure so that the numbers have a fixed relationship.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described by taking a truss type actuator as an example. FIG. 1 is a diagram illustrating a configuration of a truss-type actuator according to the present embodiment.

The first drive unit 1 includes two stacked first and second piezoelectric elements 10A and 10B arranged at a predetermined angle (for example, 90 degrees) from each other.
A chip member (driving member) 20 joined to an intersecting end of the piezoelectric element 10A and the second piezoelectric element 10B by an adhesive or the like.
The base end of the first piezoelectric element 10A and the base end of the second piezoelectric element 10B are fixed with an adhesive or the like, and the base member 30 holding the first piezoelectric element 10A and the second piezoelectric element 10B, and the chip member 20 are connected to the rotor 40. A pressing member (elastic body such as a coil spring or a leaf spring) 45 for generating a pressing force for contacting the surface of the member, a pressing force adjusting mechanism 46 for adjusting the pressing force by the pressing member 45, and the like. Have been.

FIG. 2 shows details of the first and second piezoelectric elements 10A and 10B. Each of the piezoelectric elements 10A and 10B is formed by alternately laminating a plurality of ceramic thin plates 11 having piezoelectric characteristics such as PZT (lead zirconate titanate) and electrodes 12 and 13, respectively.
13 is fixed by an adhesive or the like. Each of the electrode groups 12 and 13 arranged alternately is connected to the signal line 1 respectively.
It is connected to a drive power supply 16 via 4 and 15. When a predetermined voltage is applied between the signal lines 14 and 15, the electrodes 12
An electric field is generated in the laminating direction on each of the ceramic thin plates 11 sandwiched between the ceramic thin plates 11 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 a protective layer 1 is provided at both ends of each of the piezoelectric elements 10A and 10B.
7 are provided.

When a DC drive voltage is applied between the electrodes 12 and 13 by a 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.

The material of the tip member 20 is preferably tungsten or the like, which can stably provide a high friction coefficient and is excellent in wear resistance. 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.

First piezoelectric element 10A and second piezoelectric element 10
By driving B with an AC signal having a phase difference, the chip member 20 can be driven so as to draw an elliptical orbit. When the tip member 20 is pressed against, for example, a cylindrical surface of the rotor 40 rotatable around a predetermined axis L, the elliptical motion or the circular motion of the tip member 20 can be converted 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 tip member 20 is pressed.
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, FIG. 3 shows a block configuration of a drive circuit according to the present embodiment. The oscillator 50 generates (oscillates) a first sine wave signal (basic signal) at a resonance frequency that matches in the in-phase mode and the anti-phase mode, as described later as an example. The phase control unit 51 controls the delay circuit 52 in accordance with the rotation speed, drive torque, rotation direction, and the like of the rotor 40, which is a driven member, and outputs a second sine wave having a phase shifted from the first sine wave signal. Generate a signal. The amplitude controller 53 controls the first amplifier 54 and the second amplifier 55 to amplify the amplitudes of the first sine wave signal and the second sine wave signal that are out of phase with each other. The first sine wave signal and the second sine wave signal (drive signal) amplified by the first amplifier 54 and the second amplifier 55 are applied to the first piezoelectric element 10A and the second piezoelectric element 10B constituting the drive unit 1, respectively. Is done.

First piezoelectric element 10A and second piezoelectric element 10
When drive signals having different phases are applied to B, the first piezoelectric element 10A and the second piezoelectric element 10B are displaced in a sinusoidal manner. When two independent movements orthogonal to each other by the first piezoelectric element 10A and the second piezoelectric element 10B are combined, the intersection point is represented by an elliptic vibration equation (Lissaj
draws an ellipse (including a circle) trajectory according to the ous equation).

First piezoelectric element 10A and second piezoelectric element 10
When the frequency of the drive signal applied to B is sufficiently small, the tip member 20 draws an elliptical locus according to the equation of elliptical vibration.
However, the first piezoelectric element 10A and the second piezoelectric element 10B
In order to increase the displacement of
When approaching the resonance frequency, the trajectory of the chip member 20 is shifted from a desired shape.

When a driving unit is actually manufactured and the first piezoelectric element 10A and the second piezoelectric element 10B are driven by driving signals having frequencies near their resonance frequencies so that the chip member 20 draws a circular locus, The trajectory of the tip member 20, which should be circular, is deformed into an elliptical shape that is greatly inclined from the center axis. In the course of the experiment, it became clear that this phenomenon occurs when the vibrations of the piezoelectric elements 10A and 10B influence each other via the chip member 20 and the base member 30. Since the vibration of one piezoelectric element (for example, 10A) is transmitted to the other piezoelectric element 10B with a phase delay of about 90 °, the piezoelectric element 10
The displacement of B is superimposed on the drive signal and enlarged, and the displacement of the piezoelectric element 10A that is displaced earlier is reduced. As a result, the trajectory of the tip member 20 becomes an elliptical shape extending in the displacement direction of the piezoelectric element 10B that is displaced later.

In order to solve this phenomenon, transmission of vibration of one piezoelectric element to the other piezoelectric element is suppressed as much as possible.
It is necessary to realize a system in which the two piezoelectric elements 10A and 10B can be independently displaced. By realizing such a system, the trajectory of the chip member 20 can be made to have a desired elliptical shape (including a circular shape) in all frequency bands including the resonance frequency. Further, by changing the amplitude and phase difference of the drive signal as necessary,
The shape of the zero trajectory can be arbitrarily changed, and speed control of the driven member such as the rotor 40 can be performed.

The present inventors have realized that "the natural frequencies of the elongational vibration in the in-phase mode and the elongational vibration in the opposite-phase mode match" realize a system in which the two piezoelectric elements 10A and 10B can be displaced independently. (For details, refer to Japanese Patent Application No.
-166919). In order to match the natural frequencies of the extension vibration in the in-phase mode and the extension vibration in the opposite phase mode, for example, the mass of the tip member 20 may be adjusted. Here, the in-phase mode is defined as a mode in which the phases of the displacements of the two piezoelectric elements 10A and 10B match, and the anti-phase mode is defined as a mode in which the phases of the displacements of the two piezoelectric elements 10A and 10B are reversed.

First piezoelectric element 10A and second piezoelectric element 10
FIG. 4 shows the eigenmode of the actuator when B undergoes elongation vibration. 4A shows the case of the in-phase mode, and FIG. 4B shows the case of the opposite-phase mode.

In the case of the in-phase mode, the tip member 20 vibrates in the direction of the axis of symmetry of the drive unit 1 (the direction of arrow X).
In the case of the reverse phase mode, the tip member 20 vibrates in a direction (arrow Y direction) orthogonal to the symmetric axis direction of the drive unit 1. In the in-phase mode and the anti-phase mode, when the frequency of the drive signal is close to the natural frequency, it approximates the vibration mode as shown in FIG. 4 regardless of the amplitude and phase of the drive signal.

On the other hand, it is also possible to make the trajectory of the chip member 20 a desired shape by positively utilizing the transmission of the vibration of the one piezoelectric element to the other piezoelectric element. For example,
By setting the ratio between the natural frequency in the in-phase mode and the natural frequency in the anti-phase mode to a predetermined value,
The trajectory of the chip member 20 can be made elliptical by simply driving one of the piezoelectric elements (for details, see the specification of Japanese Patent Application No. 2000-150180 filed by the present applicant). This is because a predetermined phase difference occurs between the vibrations of the in-phase mode and the anti-phase mode excited by the vibration of the piezoelectric element.
The ratio of the natural frequency in this case can also be adjusted by adjusting the mass of the tip member 20.

As described above, the trajectory of the chip member 20 is desired by matching the natural frequencies of the plurality of drive units constituting the actuator in the in-phase mode and the anti-phase mode or by setting them at a predetermined ratio. Can be shaped.

Next, FIG. 5 shows a model in which the actuator of this embodiment is replaced by a spring and weight vibration system. FIG.
As shown in FIG. 5, since the vibration direction of the in-phase mode and the vibration direction of the anti-phase mode are orthogonal to each other, these directions are defined as a coordinate system in FIG. In-phase mode vibration is replaced by a spring and weight vibration system extending in the X-axis direction, and anti-phase mode vibration is replaced by a spring and weight vibration system extending in the Y-axis direction.

In the in-phase mode, the spring system by the pressing member 45 is connected to the vibration system in the X-axis direction.
The natural frequency of the actuator changes with the spring constant of 5. On the other hand, in the vibration in the opposite phase mode, the spring system of the pressing member 45 does not deform, and the natural frequency of the actuator does not change.

In this model, the natural frequency does not change even if the pressing force is increased or decreased by changing the spring length, because the spring constant does not change. However, in practice, the piezoelectric elements 10A, 10B,
The tip member 20, the rotor 40, and the like are deformed, and the natural frequency of the actuator in the in-phase mode changes. According to the experiment, the natural frequency increases as the pressing force increases, and the natural frequency decreases as the pressing force decreases. Further, within a predetermined range, the change in the pressing force and the change in the natural frequency have a linear relationship. In contrast, no such change was observed in the anti-phase mode.

As described above, the natural frequency in the in-phase mode and the anti-phase mode can be adjusted by adjusting the mass of the tip member 20. If the spring constant and the mass of each member constituting the actuator are constant,
By using the tip member 20 having a predetermined mass, the natural frequencies in the in-phase mode and the anti-phase mode can be matched. However, in practice, the natural frequency of the actuator slightly changes due to errors in dimensions, materials, mounting positions, and the like of each member. The natural frequency of the actuator also changes due to the expansion of each member due to a rise in temperature. Therefore, it is impossible to adjust the mass of the tip member 20 one by one to correspond to the change of the natural frequency of these actuators.

In this embodiment, since the pressing member 45 is provided with the pressing force adjusting mechanism 46, it is possible to cope with a change in the natural frequency of the actuator irrespective of the adjustment of the mass of the tip member 20. As a specific configuration of the pressing force adjusting mechanism 46, for example, an eccentric cam, a screw, or the like can be used.

The natural frequency in the in-phase mode is detected by, for example, applying a drive signal having the same phase to each of the piezoelectric elements 10A and 10B, sweeping the drive frequency, and finding the peak position of the drive current. Can be. That is, when the vibration of the actuator approaches the resonance state, the impedance of the piezoelectric elements 10A and 10B rapidly changes, and accordingly, the current value of the drive signal also rapidly changes. Therefore, by monitoring the current value of the drive signal, the resonance state of the actuator, in other words, the natural frequency can be detected. The natural frequency in the opposite phase mode can be similarly detected by applying a drive signal having an opposite phase to each of the piezoelectric elements 10A and 10B.

Therefore, when the actuator itself or an apparatus using the actuator is shipped, or when the power is turned on, the natural frequencies in the in-phase mode and the anti-phase mode are detected while monitoring the current value of the drive signal. The pressurizing force adjusting mechanism 46 may be adjusted so that the natural frequencies of the two have a predetermined relationship, more specifically, a match or a fixed ratio. By doing so, it is possible to maintain the trajectory of the tip member 20 in a constant shape, and it is possible to maintain the output and drive efficiency of the actuator constant.

Next, the pressing force that can maximize the output of the actuator of the present embodiment will be discussed. When the rotor 40 is driven to rotate by the drive unit 1, according to an experiment by the present inventors, the contact ratio between the tip member 20 and the rotor 40 (the tip member 20 makes an elliptical motion by one The time during which the rotor 40 is in contact with the rotor 40 increases, and the state transitions from an intermittent contact (separation state) to a state of constant contact (normal contact state). The output of the actuator becomes maximum near the transition from the detached state to the normal state (the pressing force at this time is assumed to be N ₀ ). Assuming that the electric input to the actuator is constant, the condition for obtaining the maximum output of the actuator matches the condition for maximizing the driving efficiency.

In the above experiment, the output is larger in the normal state than in the separated state. The reason is that the increase in the frictional force due to the increase in the pressing force is larger than the decrease in the output due to the contact between the rotor 40 and the tip member 20 during the deceleration. Pressing force is N
_{If the value} is further increased from ₀ , the increase in the frictional force is offset between acceleration and deceleration, and the output of the actuator does not increase any more.

When the pressure applied by the pressing member 45 is increased or decreased in order to make the trajectory of the tip member 20 a desired shape, the contact state between the tip member 20 and the rotor 40 changes. However, in the normal state, the change in the output of the actuator is small even when the pressing force is changed. Therefore, the vibration state of the piezoelectric elements 10A and 10B may be controlled using the normal state.

In the above embodiment, the tip member 20
The two piezoelectric elements 10A and 10B for driving are arranged orthogonal to each other, but the present invention is not limited to this, and other angles such as 45 ° and 135 ° may be used. . Further, the number of displacement elements in the drive unit 1 is not limited to two, and three
It may be configured such that three or four degrees of freedom are driven by using one or more units. 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.

Further, the present invention is not limited to the truss-type actuator, and the contact portion is driven so as to draw an elliptical trajectory by using a displacement element such as a wedge-shaped actuator or an annular ultrasonic motor. Any structure may be used as long as the elliptical motion is frictionally transmitted to the driven member by pressurization.

[0040]

As described above, according to the actuator of the present invention, a displacement element for generating a predetermined displacement,
A driving member coupled to the displacement element and driven by the displacement of the displacement element, a driven member driven by the contact of the driving member, and a pressing member for pressing the driving member against the driven member. Since it includes a pressure member, a pressure adjustment mechanism for changing the frequency in the natural vibration mode by adjusting the pressure applied by the pressure member, and a drive circuit for applying a drive signal to each of the displacement elements, Even if the natural frequency changes due to errors in the dimensions, materials, mounting positions, etc. of the components that make up the actuator, thermal expansion, etc., the force applied by the pressure member using the force adjustment mechanism Is adjusted, the change in the natural frequency can be corrected. As a result, the trajectory of the driving member can be maintained in a desired shape, and the output and the driving efficiency of the actuator can be kept constant.

Further, a truss-type actuator can be formed by providing the driving members at the intersections of a plurality of displacement elements arranged at a predetermined angle to each other.

Further, in the in-phase mode in which at least two displacement elements are displaced in the same phase and the anti-phase mode in which they are displaced in opposite phases, the natural frequency of the actuator in the in-phase mode and the natural vibration of the actuator in the anti-phase mode By adjusting the pressure so that the numbers have a constant relationship, a large displacement amount in the displacement element can be obtained without increasing the voltage of the drive signal, and the drive efficiency of the actuator can be increased. it can.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a truss-type actuator according to an embodiment of the present invention.

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

FIG. 3 is a diagram showing a block configuration of a drive circuit in the embodiment.

FIG. 4A is a diagram showing a natural mode of an actuator when two piezoelectric elements constituting a drive unit are stretched and vibrated, and FIG.
(B) shows the case of the anti-phase mode.

FIG. 5 is a diagram showing a model in which the actuator in the embodiment is replaced by a vibration system of a spring and a weight.

[Explanation of symbols]

 1: drive unit 10A: first piezoelectric element (displacement element) 10B: second piezoelectric element (displacement element) 20: chip member (drive member) 30: base member 40: rotor (driven member) 45: pressing member 46 : Pressing force adjusting mechanism 50: Oscillator 51: Phase control unit 52: Delay circuit 53: Amplitude control unit 54: First amplifier 55: Second amplifier

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H680 AA00 AA06 AA08 BB01 BB13 BB15 BB20 CC02 CC10 DD01 DD02 DD23 DD27 DD30 DD37 DD53 DD55 DD67 DD73 DD95 EE10 EE21 EE24 FF08 FF17 FF21 FF26 FF27 FF33 FF20

Claims (3)

[Claims] 1. A displacement element for generating a predetermined displacement, a driving member coupled to the displacement element and driven by the displacement of the displacement element, and a driven member driven by contact of the driving member. A pressing member for pressing the driving member against the driven member, a pressing force adjusting mechanism for changing the frequency in the natural vibration mode by adjusting the pressing force of the pressing member, and each of the displacements; An actuator comprising a drive circuit for applying a drive signal to each of the elements. 2. The actuator according to claim 1, wherein the driving member is provided at an intersection of a plurality of displacement elements arranged so as to form a predetermined angle with each other. 3. The natural frequency of the actuator in the in-phase mode and the natural vibration of the actuator in the anti-phase mode in at least two in-phase modes in which at least two displacement elements are displaced in the same phase and anti-phase mode in which they are displaced in opposite phases. 3. The actuator according to claim 2, wherein the pressing force is adjusted such that the numbers have a constant relationship.