JPH04112687A - Excitation method for piezoelectric element and control method for actuator - Google Patents

Abstract

PURPOSE:To get excitation method for a piezoelectric element by which the control in vibrational direction of ultrasonic elliptic vibration is easy by changing the direction of the application of the voltage applied to an electrode thereby controlling the direction of the ultrasonic elliptic vibration of the piezoelectric element. CONSTITUTION:When voltage is applied to the piezoelectric element 14 of an electrostrictive revolver type ultrasonic motor, the part where voltage is applied in the same direction as the direction of polarization is deformed in the peripheral direction of the piezoelectric element 14, and the part where voltage is applied in the opposite direction to the direction of polarization is deformed in the direction of shrinkage. Accordingly, when AC voltage is applied to electrodes 121-124, the piezoelectric element 14 performs ultrasonic elliptic vibration. Moreover, for a rotor 4, the part against which the rotor 4 is pressed vibrates in the peripheral direction, besides it is dragged in the vibrational direction of the part contiguous to that part, so the rotor 4 rotates receiving the force by these vibration continuously.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention provides a method for exciting a piezoelectric element that generates ultrasonic elliptic vibration by converting electrical energy into mechanical energy, and an actuator using the piezoelectric element. This relates to a control method.

[Conventional technology]

In recent years, since piezoelectric elements were discovered to have a large electromechanical coupling coefficient, they have been developed by many researchers and are used in various technologies such as ultrasonic motors.

Ultrasonic motors have been attracting particular attention recently because the piezoelectric element itself constitutes a vibrator and utilizes the ultrasonic vibration of the vibrator rather than the interaction between current and magnetic field.

[Problem to be solved by the invention]

By the way, conventional piezoelectric elements used in electrostrictive rotor-type ultrasonic motors, for example, have electrodes formed on both surfaces of a donut-shaped piezoelectric thin plate divided radially into four equal sets, and then the piezoelectric thin plate Formed by polarization treatment. To excite such a piezoelectric element, alternating current voltages with a phase shift of π/4 are applied between the four sets of upper and lower electrodes in order. As a result, the piezoelectric element performs ultrasonic elliptical vibration, and the rotor part of the ultrasonic motor rotates by continuously receiving force due to vibration from the part against which it is pressed and the part adjacent thereto. However, in such conventional methods, the piezoelectric element vibrates only in a fixed direction at the same contact location, and therefore the rotor section can only rotate in a fixed direction. Furthermore, little research has been done on controlling the forward and reverse rotation of the ultrasonic motor.

For this reason, when controlling the forward and reverse rotations of the ultrasonic motor, the forward and reverse rotations must be controlled by, for example, changing the contact location of the rotor portion.

As described above, the conventional method has the problem that it is not easy to control the vibration direction of the piezoelectric element, and therefore it is not easy to control the rotation direction of the ultrasonic motor.

The present invention has been made based on the above-mentioned circumstances, and an object of the present invention is to provide a method for exciting a piezoelectric element in which the vibration direction of ultrasonic elliptical vibration can be easily controlled.

Further, the present invention has been made based on the above-mentioned circumstances, and an object of the present invention is to provide an actuator control method that allows easy control of the direction of movement.

[Means to solve the problem]

A method for exciting a piezoelectric element according to a first aspect of the invention for achieving the above object includes radially dividing electrodes formed on both surfaces of a circular or annular piezoelectric thin plate into at least three groups, and It is formed by polarizing a piezoelectric thin plate in the thickness direction.
In a method for exciting a piezoelectric element that generates ultrasonic elliptical vibrations due to radial strain, the direction of vibration of the ultrasonic elliptical vibrations of the piezoelectric element is controlled by changing the direction of a voltage applied to the electrodes. It is characterized by this.

In addition, a method for controlling an actuator according to a second aspect of the invention for achieving the above object includes dividing electrodes formed on both surfaces of a disk or annular piezoelectric thin plate radially into at least three groups, and In a method of controlling an actuator having a piezoelectric element formed by polarizing a body 'iR temporary in the thickness direction and generating ultrasonic elliptic vibration due to distortion in the radial direction, the direction of application of the voltage applied to the electrode is changed. Accordingly, the direction of movement of the actuator is controlled.

[Effect]

The method for exciting a piezoelectric element according to the first invention uses the above-described configuration to generate ultrasonic elliptic vibration by applying a voltage to each set of electrodes of a piezoelectric element in which the electrodes are divided radially into three equal sets. By reversing the direction of voltage applied to at least one set of the 3&ll electrodes (changing the phase of the AC voltage) when can be changed in the opposite direction.

A method for controlling an actuator according to a second aspect of the present invention has the above-described configuration, for example, applying a voltage to each set of electrodes of a piezoelectric element in which the electrodes are equally divided into three strings radially to generate ultrasonic elliptic vibration; As a result, when the actuator is rotating or reciprocating, for example, by reversing the direction of voltage applied to at least one of the three sets of electrodes (changing the phase of the AC voltage), the piezoelectric material By reversing the vibration direction of the ultrasonic elliptical vibration of the element, the movement direction of the actuator can be easily changed to the opposite direction.

〔Example〕

A first embodiment of the present invention will be described below with reference to FIG. FIG. 1(a) is a schematic enlarged plan view of an electrostrictive rotor type ultrasonic motor according to a first embodiment of the present invention. The figure (b) is a sectional view taken along the line A-A, and the figure (C) is a cross-sectional view taken along the line B-A.
It is a sectional view taken along arrow B.

The electrostrictive rotor-type ultrasonic motor shown in FIG. , and a rotor portion 4 crimped to the outer peripheral side surface of the piezoelectric element I4.

The piezoelectric element 14 is made of Pb (
It consists of a piezoelectric thin plate 10 made of ZrT 1)03 and four sets of excitation electrodes 12t to 4 formed on the upper and lower surfaces thereof. The electrode 12 is formed by hardening (=1) fine silver powder on the surface of the ceramic with glass powder, etc., and as shown in FIG.
It is divided equally.

The piezoelectric thin plate 10 is polarized in the thickness direction,
Electrode 12. ,．． The part corresponding to electrode 12. is polarized in the direction from the front to the back at V(a). ．． 1
2. The part corresponding to is polarized from the back to the front. The arrows in (b) and (c) of the figure indicate the state of this polarization.

When a voltage is applied to the piezoelectric element 14 of the electrostrictive rotator type ultrasonic morph configured as described above, the portion to which the voltage is applied in the same direction as the polarization direction is the outer periphery of the piezoelectric element 14. The part to which the polarization is applied in the direction opposite to the polarization direction is deformed in the contraction direction t. Therefore, electrode 12
When an alternating current voltage is applied to the piezoelectric element 14, the piezoelectric element 14 performs ultrasonic elliptical vibration.

In addition, the part of the rotor part 4 against which the rotor part 4 is pressed vibrates in the outer circumferential direction, and is dragged in the vibration direction of the part adjacent to that part, so the rotor part 4 continuously absorbs the force caused by the vibration of the debris. To receive; rotate. This type of ultrasonic motor does not require a separate metal vibrator unlike other types of ultrasonic motors (for example, torsion coupler type ultrasonic motors), and also utilizes rolling friction. Since torque is transmitted to the rotor, the structure is simple and energy efficient, and the torque and output are large.

The present inventors pressed the rotor part 4 against the outer circumferential side surface of the doughnut-shaped piezoelectric element 14 (the outer circumferential side surface of the electrode 12 □) with a constant pressure, and determined the direction of application of the voltage (6V) to be applied to each set of electrodes. The rotation direction of the rotor section 4 was investigated by changing the rotation direction. The measurement results are shown in Table 1.

Table 1 However, in Table 1, the voltage application direction is the direction at the moment the voltage is applied, and in Figure 1, the direction from front to back is indicated by 10, and the direction from back to front is indicated by -. . Regarding the rotation direction of the rotor part, electrode 1 in FIG.
2. ．． The direction in which 12z, 12a, and 12- rotate in this order is indicated as clockwise, and the opposite direction is indicated as counterclockwise. Note that measurement example 0 is a conventional example, and each electrode 12. -4 indicates that the rotor rotates clockwise when all voltage application directions are set to 10.

First, in Measurement Examples 1 to 4, experiments were conducted by changing the voltage application direction. However, in order to make it easier to compare the results, only the direction of application of the electrode 12° against which the rotor portion 4 was pressed was made the same in all measurement examples. When voltage is applied to all electrodes 12 of 4 & 11 as shown in Table 1, the rotor section 4 can be rotated forward or reverse, or stopped rotating by changing the direction of voltage application. .

Therefore, by providing a means for switching the direction of application of the drive voltage in the electrostrictive rotor type ultrasonic motor,
The rotor section 4 can be freely controlled to rotate forward, reverse, or stop.

Next, the inventors short-circuited the electrodes 124, applied voltages in the directions shown in Measurement Examples 5 to 7 in Table 1, and examined the rotational direction of the rotor section 4. As a result, by changing the direction of voltage application, it was possible to rotate the rotor section 4 in the normal or reverse direction, or it was possible to keep it from rotating. Therefore, since the short-circuited electrode 12 can be treated as a fixed end, it is possible to form the electrode into a disk shape, for example, and use the short-circuited electrode 124 as a holding part, instead of forming the electrode into a donut shape. can. Therefore, even if the piezoelectric element needs to be formed in a different expansion/softness depending on the application, it is easy to install the holding means 81 for the piezoelectric element.

Furthermore, the rotational direction of the rotor section 4 was investigated by short-circuiting both the electrodes 123 and 124 to change the voltage sum direction. In this case, the rotor portion 4 could be rotated forward or reverse.

In the above embodiment, only the case where the rotor part is pressed against the outer circumferential side of the donut-shaped piezoelectric element has been described, but the present invention is not limited to this. It may also be configured to be pressed against the inner circumferential side of the body element.

FIG. 2 is a schematic diagram of an electrostrictive rotor-type ultrasonic linear morph according to a second embodiment of the present invention. The second embodiment is the first
The difference from this embodiment is that the rotor section of the first embodiment rotates, whereas the rotor section of the second embodiment reciprocates. The ultrasonic linear motor shown in FIG. 2 includes a stator section 2, a slide table 24 that is a rotor section, a slide bearing 26 that slidably supports the slide table 24, and a pedestal 28 that supports the slide ring 26. It includes. Incidentally, in the second embodiment, those having the same functions as those in the first embodiment are given the same reference numerals, and detailed explanation thereof will be omitted.

The inventors prototyped an ultrasonic linear motor with the above configuration,
When an AC voltage is applied to the piezoelectric element 14, actually,
It was investigated whether this slide table 24 performs reciprocating motion. The voltage application direction was determined from measurement example 1 of the first embodiment above.
As a result of conducting an experiment in the same manner as in Example 4, it was found that the slide table 24 moved in the lateral direction in the figure, except for measurement example 3 of the first embodiment. In measurement example 1, the slide table 24 first moved to the left in FIG. 2, and in measurement example 2.4, the slide table 24 moved to the right. Other functions and effects are the same as in the first embodiment.

In the above embodiment, a case has been described in which the electrodes are divided into four equal parts, but the present invention is not limited to this, and the electrodes may be divided into three sets or 5 Mi or more.

However, as the number of divisions increases, the phase relationship becomes complicated and the AC voltage also becomes multiphase, so it is considered that up to 6 divisions is practical.

As can be seen from the above explanation, the piezoelectric element excitation method of the present invention is not only applicable to the electrostrictive rotor type ultrasonic motor in the above embodiment, but also to other types of ultrasonic motors. It can be applied to actuators that move reversibly.

〔Effect of the invention〕

As explained above, according to the present invention, the vibration direction of the ultrasonic elliptical vibration of the piezoelectric element can be easily electrically controlled by changing the direction of application of the AC voltage applied to each set of electrodes of the piezoelectric element. A method for exciting a piezoelectric element can be provided.

Further, according to the present invention, by changing the applied force of the AC voltage applied to each set of electrodes of the piezoelectric element, the vibration direction of the ultrasonic elliptical vibration of the piezoelectric element is changed, and the direction of movement of the actuator is changed. A method of controlling an actuator that can be easily electrically controlled can be provided.

[Brief explanation of drawings]

FIG. 1(a) is a schematic enlarged plan view of an electrostrictive rotor-type ultrasonic motor according to a first embodiment of the present invention, and FIG. 1(b) is an A
- A sectional view taken along arrow A, the same figure (C) is a sectional view taken along line B-B,
FIG. 2 is a schematic diagram of an ultrasonic linear motor according to a second embodiment of the present invention. 2... Stator section, 4... Rotor section, 10...
Piezoelectric thin plate, 12... electrode, 14... piezoelectric element,
16... Piezoelectric body holder, 24... Slide table.

Claims (2)

[Claims] (1) The electrodes formed on both surfaces of a disk or annular piezoelectric thin plate are radially divided into at least three groups, and the piezoelectric thin plate is polarized in the thickness direction. A method for exciting a piezoelectric element to generate ultrasonic elliptical vibrations, characterized in that the vibration direction of the ultrasonic elliptical vibrations of the piezoelectric element is controlled by changing the direction of application of a voltage applied to the electrodes. Excitation method of piezoelectric element. (2) The electrodes formed on both surfaces of a disc or annular piezoelectric thin plate are radially divided into at least three groups, and the piezoelectric thin plate is polarized in the thickness direction, and the piezoelectric thin plate is polarized in the thickness direction. A method for controlling an actuator having a piezoelectric element that generates ultrasonic elliptical vibration, the method comprising: controlling the direction of movement of the actuator by changing the direction of voltage applied to the electrodes.