JPH04236177A - Disposition of vibrating segment of piezoelectric element and shape of driving part - Google Patents

Abstract

PURPOSE:To increase a driving area and to obtain an ultrasonic motor having a stable driving state and a high efficiency by bringing the node position of a standing position to be driven in each phase into coincidence with a boundary of vibrating segments, and equalizing the widths. CONSTITUTION:A phase A of a piezoelectric element is formed linearly symmetrically in polarizing segments 5, 6, 9, 10 in good balance, and a phase B is formed linearly symmetrically in polarizing segments 7, 8, 11, 12 in good balance. When an AC voltage of a suitable frequency is applied between an electrode 1 and a common electrode, since the phase A is formed linearly symmetrically in good balance, a standing wave in which a boundary and both ends of the segments 5, 6 of the phase A become nodes, is generated in the entire stator. When the AC voltage is applied between an electrode 2 and the common electrode, since the phase B is formed linearly symmetrically in good balance, a second standing wave in which a boundary and both ends of the segments 7, 8 of the phase B become nodes, is generated in the entire stator. Thus, the node position of the vibrating wave is accurately formed at an expected position in the driving state.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vibrating section arrangement or drive part configuration of a piezoelectric element in an ultrasonic motor.

0002

BACKGROUND OF THE INVENTION A conventional ultrasonic motor has a vibrating section arrangement of piezoelectric elements, as shown in FIG. The area was different from that of B phase 2 formed in .

As another example, as shown in FIG.
Vibration sections 9, 10 and 11, 12 smaller than the sections 11 and 12 were formed.

0004

[Problems to be Solved by the Invention] However, in the conventional vibration section arrangement of a piezoelectric element as shown in FIG.
Since the area of the B phase formed by There were problems such as the location not matching.

In addition, in the other conventional piezoelectric element vibration section arrangement shown in FIG. Although the amplitude and resonance frequency of the standing waves are approximately equal, polarization sections 9, 10, 11, and 12 smaller than 1/2 of the wavelength of the standing wave excited in the elastic body are formed at both ends of each phase. Since vibration sections 9 and 10 and 11 and 12 have different areas, the vibration sections are not line symmetrical in each phase, and when each phase is driven independently, the position of the node of the standing wave in each phase is Inconveniences occurred such as not matching the boundary between polarization sections 5 and 6 in phase A and the boundary between polarization sections 7 and 8 in phase B.

Due to the above-mentioned differences and inconveniences, it goes without saying that when each phase is driven individually, an ultrasonic motor that uses the node positions of synthetic waves and vibration waves that are excited by driving the A and B phases simultaneously is not suitable. However, serious problems have arisen, such as the nodes of the composite wave not being at the predicted positions, the operation of the rotating body of the motor becoming unstable, and the efficiency decreasing.

The present invention is intended to solve these problems, and its purpose is to match the node position of the standing wave excited in the elastic body with the required position, and to further increase the driving area. The object of the present invention is to provide an ultrasonic motor with a stable driving state and high efficiency by making the driving area larger or by making the driving area smaller and driving the current consumption lower.

[0008]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides (1) an elastic body to which a piezoelectric element having a piezoelectric effect is joined by applying a voltage, and a frictional contact with the elastic body. The piezoelectric element includes a rotating body that is rotationally driven and a pressurizing means that brings the rotating body into pressure contact with the elastic body, and the piezoelectric element is composed of several vibrating sections, and the vibrating sections cause the elastic body to be pressed against the elastic body. In an ultrasonic motor in which vibration waves are excited, the piezoelectric element has drive portions A phase and B phase consisting of a plurality of vibration sections, and the shapes of the vibration sections in each drive section are approximately line symmetrical. It is characterized by (2) The shape of the vibration sections in the A-phase and B-phase of the drive portion described in claim 1 is characterized by being substantially equal to each other. (3) In the case where the piezoelectric element in the ultrasonic motor according to claim 1 is composed of a plurality of vibrating sections and a plurality of the vibrating sections are used to form a driving part, the driving portion formed by the vibrating sections It is characterized by the shape of the part being almost line symmetrical. (4) The shape of the driving portion described in claim 3 is approximately line symmetrical with respect to the antinode position of the vibration wave in the range of half the wavelength of the vibration wave excited in the elastic body. It is characterized by the presence of

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is an embodiment of a layout diagram of polarization sections of a piezoelectric element according to the present invention. The + and - symbols in the figure indicate the direction of polarization treatment of the piezoelectric element. FIG. 1(a) shows the front side of the piezoelectric element, and FIG. 1(b) shows the back side. 5 in the diagram
, 6, 7, and 8 are 1/1 of the wavelength of the vibration wave excited in the elastic body.
This is a polarization division corresponding to part 2. In the case of Figure 1, vibration waves of three wavelengths are excited on the circumference of the elastic body, so polarization sections 5, 6, 7, and 8 are each 1/6 of the circumference. This corresponds to 1/2 of the wavelength of the vibration wave. Polarization sections 9, 10, 11, and 12 are smaller than polarization sections 5, 6, 7, and 8, and are 1/1/2 of the wavelength of the vibration wave.
There are 8 categories. In addition, polarization sections 9 and 10 are located at both ends of the A phase, and 11 and 12 are located at both ends of the B phase. 7, 8, 11, and 12 are arranged line-symmetrically and in a well-balanced manner. The A phase and the B phase are configured to have a positional phase difference of 1/3 wavelength of the vibration wave on the circumference. The polarization section 3-b is a detection section for detecting the state of vibration waves excited on the elastic body, and 1 on the front side is an A electrode, 2 is a B electrode, and 3-a is a detection electrode.

[0011] Next, an embodiment of the operating state in which an ultrasonic motor is constructed by bonding the piezoelectric element in which the polarization sections described above are formed to an elastic body will be described.

If the back surface of the piezoelectric element described above is bonded to an elastic body to form the stator of an ultrasonic motor, voltages of the same potential can be applied to the back surface of the piezoelectric element. This is used as a common electrode.

First, when an AC voltage of an appropriate frequency is applied between the electrode 1 and the common electrode, since the A phase is formed line-symmetrically and well-balanced, the boundary between the polarization sections 5 and 6 of the A phase and both ends Standing waves such as nodes are generated throughout the stator. This is defined as a first standing wave, and this drive state is defined as a first drive state. Next, as a second driving state, the electrode 2
When an AC voltage of the above frequency is applied between the B phase and the common electrode, the B phase is also formed line symmetrically and well balanced.
A second standing wave is generated throughout the stator such that the boundaries and both ends of the phase polarization sections 7 and 8 serve as nodes. Further, as a third driving state, when AC voltages having the same phase and frequency are applied between the electrode 1 and the common electrode and between the electrode 2 and the common electrode, the first standing wave and the second standing wave are applied. A composite wave with the standing wave is generated throughout the stator, and the node of the composite wave is located midway between the first standing wave node and the second standing wave node.

On the other hand, FIG. 2 shows an embodiment of the rotor of the ultrasonic motor described above, which has six notches or six protrusions 13-a on the circumference. When the rotor formed in this manner is pressed into contact with the stator described above to excite standing waves in the stator, as described in Japanese Patent Application No. 2-70324, the protruding portions of the rotor will cause standing waves to be excited. Force is applied in the direction from the antinode toward the node, and it finally stabilizes and stops at the node. Therefore, the above-mentioned driving states are
, 3, or in the reverse order, the node position rotates on the circumference of the stator accordingly, so the rotor that is in pressure contact with the stator also rotates with the node. It turns out. Here, A phase and B phase are 1/3
Since the rotor is configured to have a phase difference equal to the wavelength, that is, a phase difference of 40 degrees, the rotor is driven intermittently at intervals of 20 degrees.

In the ultrasonic motor described above, not only the resonant frequency of the standing wave caused by driving each phase independently, but also the node position and the magnitude of the amplitude are important.

In this embodiment, the phase difference between phase A and phase B is set to 1.
/3 wavelength (=40°), but the present invention is not limited to this.

The embodiment described above is an intermittent drive ultrasonic motor that utilizes A-phase and B-phase standing waves and their composite standing waves.

Next, as another embodiment, an intermittent drive ultrasonic motor that uses only standing waves without using composite waves will be described.

Since the driving principle is the same as that described above, the explanation will be omitted, and the vibration section and the driving portion will be described here. FIG. 3 shows a piezoelectric element according to this embodiment, in which twelve vibration sections 21 to 32 are formed. In the piezoelectric element configured in this way, a standing wave of two wavelengths is generated on the elastic body, and the antinode of the standing wave is the vibration section 31, 22, 25,
If it is desired to cause vibration to occur at the position 28, for example, the vibration section shown by the shaded area in FIG. 3(a) may be driven. Here, the + and - signs in the figure indicate the polarity of the driving voltage at a certain time, and the driving portion is line-symmetrical as a whole. Also, in Fig. 3(b), Fig. 3(a)
), the vibrating sections 23, 27 are also driven, the drive parts being line-symmetrical as a whole. Furthermore, in Fig. 3(c), the vibration section shown by the hatched part in the figure is driven, and vibration section 2, which corresponds to half the wavelength of the vibration wave, is driven.
7, 28, and 29, 27 and 29 are being driven. Therefore, the driving portion is line symmetrical in this half-wavelength vibration section. In the driving state described above, the node position of the vibration wave can be accurately positioned at the expected position.

Furthermore, in the above two embodiments, only the intermittent driving of the ultrasonic motor by the standing waves has been explained, but the present invention is not limited to this. There is also a driving method in which different alternating current voltages are applied to excite a traveling wave, the output time of the drive voltage is made intermittently, the rotor is intermittently driven by the traveling wave, and the standing wave described above is excited at constant or arbitrary intervals. Conceivable. With this drive method, the rotation error that occurs during intermittent traveling wave drive is
When a standing wave is excited, it is canceled out, which has the effect of eliminating cumulative errors in rotation.

[0021]

[Effects of the Invention] The present invention has been described above, and the present invention has the following effects.

[0022] In the conventional vibrating arrangement of piezoelectric elements, the areas covered by the A and B phases are different, so when each phase is driven independently, differences occur in the amplitude and resonance frequency of the vibration waves of each phase. However, according to the present invention, since the A phase and B phase are line symmetrical and have the same area, Problems such as those mentioned above are eliminated.

[0023] In addition, as for the polarization arrangement of other conventional piezoelectric elements, in order to obtain a larger driving area, one of the wavelengths of the vibration waves is
Vibration sections larger or smaller than /2 were formed at both ends of each phase, but the areas of the polarization sections were different at both ends of each phase. Therefore, there were problems such as the balance of each phase being lost and the position of the vibration wave node of each phase not matching the boundary of the vibration section when each phase was driven independently.However, with the arrangement of the vibration section according to the present invention, For example, since the polarization sections larger or smaller than 1/2 of the vibration wavelength are arranged with equal area at both ends of each phase,
The balance of each phase is improved, the nodes of the vibration waves are located at the boundaries of the vibration sections, and the above problem is solved. Furthermore, in the present invention, the nodal positions of the standing waves driven by each phase coincide with the boundaries of the vibration sections, and the amplitudes of each are equal, so the nodal positions of the composite wave of these standing waves are also at the predicted positions. In addition, since the driving area becomes equally large, a highly efficient ultrasonic motor with stable driving conditions can be realized.

Furthermore, in the embodiment shown in FIG. 3, the driving area can be reduced without shifting the expected node positions of the vibration waves, so an ultrasonic motor with low power consumption can be realized.

In this embodiment, only a driving method using only standing waves has been described, but the present invention is not limited to this, and may include driving methods using traveling waves or a mixture of traveling waves and standing waves. But it goes without saying that the same effect can be obtained.

[Brief explanation of the drawing]

FIGS. 1 and 3 are diagrams showing the polarization division arrangement of a piezoelectric element in an embodiment of the present invention.

FIG. 2 is a plan view of a rotor in one embodiment.

FIGS. 4 and 5 are diagrams showing the vibration division layout of a conventional piezoelectric element.

[Explanation of symbols]

1 A electrode 2 B electrode 3-a Detection electrode 3-b Detection polarization section 4 A phase and B phase phase difference portions 5, 6, 7, 8, 9, 10, 11, 12, 21, 22,
23, 24, 25, 26, 27, 28, 29, 30, 3
1, 32 Vibration section 13 Rotor 13-a Projection 13-b Rotor pinion 13-c Rotor shaft

Claims (4)

[Claims] 1. An elastic body to which a piezoelectric element having a piezoelectric effect is bonded by applying a voltage; a rotating body that is rotationally driven by frictional contact with the elastic body; and a rotating body that is driven to rotate by frictionally contacting the elastic body. the piezoelectric element includes a plurality of vibration sections, and the vibration section excites vibration waves in the elastic body, the piezoelectric element includes a plurality of vibration sections; The shape of the vibration section in each drive part is as follows:
A vibration segmented arrangement of piezoelectric elements characterized by approximately line symmetry. 2. The vibration section arrangement of piezoelectric elements according to claim 1, wherein the shapes of the vibration sections in the A-phase and B-phase drive portions are substantially equal to each other. 3. In the ultrasonic motor according to claim 1, in the case where the piezoelectric element comprises a plurality of vibrating sections and a plurality of the vibrating sections are used to form a driving section, the driving section is formed by the vibrating sections. A shape of a driving portion of a piezoelectric element characterized in that the shape is almost line symmetrical. 4. The shape of the driving portion according to claim 3 is approximately line symmetrical with respect to the position of the antinode of the vibration wave within a half wavelength range of the vibration wave excited in the elastic body. The shape of the driving part of the piezoelectric element is characterized by: