JPH0223076A - ultrasonic motor - Google Patents

Abstract

PURPOSE:To improve driving efficiency of an ultrasonic motor by employing secondary bending vibration in a radial direction and tertiary bending vibration in a circumferential direction as vibration modes, and mounting a plurality of concentric protrusions on a vibrator. CONSTITUTION:In an ultrasonic motor, a piezoelectric element 8 adheres to one main face of a disc-shaped elastic element 7 thereby to construct a vibrator 10. A mechanical output producing protrusion 9 is composed on the other main face of the element 7. Further, a frictional material 11 of a wear resistant material adheres to an elastic element 12 each other to construct a moving body 13 to be driven by pressure contact with the protrusion 9. Secondary bending vibration in a radial direction and tertiary bending vibrations in a circumferential direction are excited so that the vibration displacement state of the vibrator 10 is not abruptly reduced in displacement on the inner periphery. Accordingly, when ultrasonic motors occupy the same volume, kinetic energy of the vibrator 10 can be increased larger than that when the radial primary vibration mode is employed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an ultrasonic motor that generates driving force using a piezoelectric material.

2. Description of the Related Art In recent years, ultrasonic motors have attracted attention, in which elastic vibrations are excited in a vibrating body using a piezoelectric material such as a piezoelectric ceramic, and this vibration is used as a driving force.

Hereinafter, the conventional technology of an ultrasonic motor will be explained with reference to the drawings.

FIG. 3 is a perspective view of a conventional annular ultrasonic motor, in which a vibrating body 3 is constructed by laminating a toroidal piezoelectric body 2 as a piezoelectric body to one of the toric surfaces of a toroidal elastic body 1. There is. Reference numeral 4 indicates a friction material made of a wear-resistant material, and reference numeral 5 indicates an elastic body, which are pasted together to form a moving body 6. The moving body 6 is in contact with the vibrating body 3 via the friction material 4. When an electric field is applied to the piezoelectric body 2, a traveling wave of bending vibration is excited in the circumferential direction of the moving body 3,
The moving body 6 is driven. Note that the arrow in the figure indicates the rotation direction of the moving body 60.

FIG. 4 shows an example of the electrode structure of the piezoelectric body 2 used in the ultrasonic motor of FIG. In the figure, nine elastic waves are placed in the circumferential direction. In the figure, A and B are electrode groups each consisting of a small area corresponding to a half wavelength, C is an electrode group having a length of three-quarters of a wavelength, and D is an electrode having a length of a quarter of a wavelength. Electrodes C and D create a positional phase difference of 1/4 wave length (90 degrees) between electrode groups A and B. Adjacent small electrode portions in electrodes A and B are polarized oppositely to each other in the thickness direction. The adhesive surface of the piezoelectric body 2 with the elastic body 1 is the opposite surface to the surface shown in FIG. 4, and the electrodes are solid electrodes. During use, electrode groups A and B are short-circuited, as indicated by diagonal lines in FIG. 4.

V x −V ox sin(ωt ) at the electrodes A and B of the piezoelectric body 2 of the ultrasonic motor configured as above.
---(1) V2-V Oxcos(ωt)
---(2) However, if vo: instantaneous value of voltage ω: angular frequency t: voltages v1 and v2 expressed in time are applied,
The camera body 3 has ξ−ξox(cos(ωt)xcos(kx)+5in
(ωt)xsin(kx)) -vo xcos(ωt-kx) ---(
2) However, ξ: Amplitude value of bending imaging ξ0: Instantaneous value of bending vibration k: Wave number (2π/λ) λ: Wavelength .

FIG. 6 shows that point A on the surface of the vibrating body 3 moves in an ellipse with a long axis 2w and a short axis 2u due to the excitation of the traveling wave, and the movable body 6 placed under pressure on the photographing body 3 moves in an ellipse. The figure shows how the waves move at a speed of V-ωx (H) in the direction opposite to the direction of wave propagation due to frictional force due to contact near the apex.

Problems to be Solved by the Invention In order to drive the ultrasonic motor efficiently, it is sufficient to increase the kinetic energy of the imaging object. Kinetic energy is proportional to the square of the mass and velocity of the object being photographed, so
The output can be increased by increasing the mass or speed of the vibrating body.

Once the outer diameter of the ultrasonic motor is determined, the size of the hole in the vibrating body can be made smaller to increase the mass, and the amplitude of vibration can be increased to increase the speed. However, depending on the tolerance of the piezoelectric body There is a limit to the amplitude of vibration due to distortion.Also, since conventional ultrasonic motors use circular bending imaging with primary radial direction and tertiary or higher order circumferential direction, as shown in Figure 5, , the amplitude value suddenly becomes small near the inner circumference, and the hole in the vibrating body becomes small (
However, the kinetic energy does not increase much. Therefore,
Conventional ultrasonic motors that use annular bending imaging with a first order in the radial direction and a third order in the circumferential direction have a problem in that the output cannot be increased.

Furthermore, since the entire moving body of the annular ultrasonic motor is moving as shown in FIG. 5, it is difficult to fix the position of the vibrating body, and mechanical loss is unavoidable due to fixing. Furthermore, there is a problem in that the displacement distribution of the vibrating body is easily affected by external load fluctuations, making it difficult to obtain stable driving.

The present invention has been made in view of the above, and an object of the present invention is to provide an ultrasonic motor with high drive efficiency, which can increase output with the same volume, and provide stable drive even when the load fluctuates.

Means for Solving the Problem A disc-shaped vibrating body is used as the imaging body, a bending vibration of 2nd order in the radial direction, 3rd order or more in the circumferential direction is used as the vibration mode, and the vibrating body has a plurality of concentric vibrations. Equipped with a protrusion.

Effect According to the above configuration, the inside of the vibrating body also effectively contributes to the kinetic energy of the vibrating body, and ideal traveling waves can be easily excited without exciting unnecessary standing waves. E
In addition, since the protrusion always exists at the maximum point of displacement in response to changes in the radial displacement distribution during load fluctuations, circumferential displacement can be amplified without waste, resulting in stable performance even during load fluctuations. It is possible to obtain a highly efficient ultrasonic motor.

EXAMPLE Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a cutaway perspective view showing the configuration of the ultrasonic motor of the present invention. The vibrating body 10 is configured by pasting a disk-shaped piezoelectric body 8 as a piezoelectric body to one of the main surfaces of the disk-shaped elastic body 7. Further, on the other main surface of the elastic body 7, a protrusion 9 for taking out mechanical output is formed. 11 is a friction material made of a wear-resistant material, and 12 is an elastic body, which are pasted together to form a moving body 13. The moving body 13 includes the friction material 11
It is in pressure contact with the protrusion 9 installed on the vibrating body 10 via. When an electric field is applied to the piezoelectric body 8, a traveling wave of bending vibration is excited in the circumferential direction of the vibrating body 10, and the movable body 13 is driven by frictional force. The moving body 13 starts rotating around the rotating shaft 14 .

FIG. 2 is a photographic displacement state and a displacement distribution diagram of the vibrating body 10 when exciting secondary bending vibration in the radial direction and third order in the circumferential direction. Unlike when using the first-order radial vibration mode, the displacement suddenly becomes smaller even at the inner circumference. Therefore, when the ultrasonic motor occupies the same volume, the first-order radial imaging mode It is possible to increase the kinetic energy of the vibrating body 10 compared to when using an ultrasonic motor that can generate a large output.

Further, the protrusions 9 are arranged in two concentric rows. This is caused by the fluctuation of the load on the vibrating body 10 shown in FIG.
Since the maximum displacement point of changes, it is independent of changing loads.
The protrusion 9 is installed so that it always exists above the maximum displacement point. For example, when the load is low, the outer protrusion exists at the maximum displacement point of the vibrating body 9, and when the load is high, the inner protrusion exists at the maximum displacement point. In this way, even if the load fluctuates, since the protrusion 9 is always present at the maximum displacement point of the vibrating body 10, the vibration of the vibrating body 10 can be transmitted to the movable body 13 with minimal loss. Stable drive change is possible even when the load fluctuates.

According to the present invention, it is possible to provide an ultrasonic motor that provides stable drive even when the load fluctuates, has good drive efficiency, and has a large output.

Effects of the Invention According to the present invention, radial second-order and circumferential third-order bending vibrations are used as vibration modes, and a plurality of concentric protrusions are installed on the vibrating body to reduce the load. It is possible to provide an ultrasonic motor with high drive efficiency and large output that can provide stable drive even during fluctuations.

[Brief explanation of the drawing]

Fig. 1 is a cutaway perspective view of the disc-shaped ultrasonic motor of the present invention, and Fig. 2 shows the vibration state and diameter of the vibrating body when radial secondary and circumferential tertiary bending vibrations are used as vibration modes. Fig. 3 is a cutaway perspective view of the annular layer sound wave motor, Fig. 4 is a plan view showing the shape and electrode structure of the piezoelectric body used in the ultrasonic motor of Fig. 3, Fig. 5 6 is a diagram of the vibration state of the vibrating body and the radial displacement distribution when using bending imaging of the first order in the radial direction and the eighth order in the circumferential direction as the vibration mode, and FIG. 6 is an explanatory diagram of the operating principle of the ultrasonic motor. . l...Elastic body, 2...Piezoelectric body, 3...
... Vibrating body, 4 ... Friction material, 5 ...
- Elastic body, 6... Moving body, 7... Elastic body, 8... Piezoelectric body, 9... Protruding body, 1
0... Vibrating body, 11... Elastic body, 12
...Friction material, 13... Moving body, 14.
·····Axis of rotation.

Claims (1)

[Claims] A superstructure that moves a moving body placed in contact with the vibrating body by driving a piezoelectric body with an alternating current voltage and exciting an elastic traveling wave in a vibrating body composed of the piezoelectric body and an elastic body. In the sonic motor, a disk-shaped vibrating body is used as the vibrating body, a bending vibration of 2nd order in the radial direction, 3rd order or more in the circumferential direction is used as the vibration mode, and the vibrating body is provided with a plurality of concentrically arranged bending vibrations. An ultrasonic motor characterized by having a protrusion.