JPS63277480A - Ultrasonic motor - Google Patents

Abstract

PURPOSE:To improve efficiency, by a method wherein bending oscillations of radial secondary and circumferential tertiary or higher are employed as the oscillating mode of a motor and the position of an oscillating body is fixed through a shaft, located at the center of the oscillating body. CONSTITUTION:An ultrasonic motor is provided with a shaft 14 at the center of an oscillating body 9 and the position of the same is fixed to a base table 15 below the shaft 14. A moving body 13 is attached to the upper part of the shaft 14 through a bearing 16 and is pressed against an oscillating body 9 to contact it through a leaf spring 17 and a pressure regulator 18. Piezoelectric ceramics 8 is bonded to one of the main surfaces of an elastic body 7 to constitute said oscillating body 9. The structure of the electrodes of the ceramics 8 is provided with the groups EF of equal electrodes having circumferential lengths equivalent to 1/2 of a wave length. According to this constitution, the oscillating body 9 is excited so as to generate the traveling wave of radial secondary and circumferential quartic bending oscillations.

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 perturbations are excited in a vibrating body using a piezoelectric material such as a piezoelectric ceramic, and this is used as a driving force.

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

FIG. 5 is a perspective view of a conventional toroidal ultrasonic motor, in which a vibrating body 3 is constructed by pasting a toroidal piezoelectric ceramic 2 as a piezoelectric body to one of the toric surfaces of a toroidal elastic body l. 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 vibrating body 3, thereby driving the movable body 6. Note that the arrow in the figure indicates the rotation direction of the moving body 6.

FIG. 6 shows an example of the electrode structure of the piezoelectric ceramic 2 used in the ultrasonic motor of FIG. In the figure, nine elastic waves are placed in the circumferential direction. In the same figure,
A and B are electrode groups each consisting of a small region 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 wavelength (=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. 6, and the electrode is a solid electrode. When in use, electrode groups A and B are short-circuited, as indicated by diagonal lines in FIG.

V 1 -V ox sin (ωt) --- (1) V 2 at electrodes A and B of the piezoelectric body 2 of the ultrasonic motor configured as above.
−V Oxcos(ωt) ---(2
) However, if we apply voltages v1 and v2, where vo: instantaneous value of voltage ω: angular frequency t: time, respectively,
The vibration body 3 has ξ−ξo x(cos(ωt)xcos(kx)+5i
n(ωt)xsin(kx), )−vo xcos(ω
t-kx) ---(2) where ξ: Amplitude value of bending vibration ξ0: Instantaneous value of bending vibration k: Wave number (2π/λ) λ: Wavelength A traveling wave of is excited.

FIG. 7 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 vibrating body 3 moves in an ellipse. This figure shows how the waves move at a speed of ωXU in the direction opposite to the direction of wave movement due to frictional force due to contact near the apex.

Problems to be Solved by the Invention In order to increase the output of an ultrasonic motor, the kinetic energy of the vibrating body should be increased. Kinetic energy is proportional to the square of the mass and speed of the vibrating body. Therefore, the output can be increased by increasing the mass or speed of the vibrating body.Once the external shape of the ultrasonic motor is determined, the size of the hole in the vibrating body must be made small to increase the mass, and the output can be increased by increasing the mass or speed of the vibrating body. However, there is a limit to the amplitude of vibration due to the allowable strain of the piezoelectric body.In addition, conventional ultrasonic motors can handle circular bending vibrations of first order in the radial direction, third order in the circumferential direction or higher. As shown in Figure 8, the amplitude value suddenly decreases near the inner periphery, and the kinetic energy does not increase much even if the hole in the vibrator is made smaller.
Conventional ultrasonic motors that use circular bending vibration of first order in the radial direction and third order in the circumferential direction have a problem in that the output cannot be increased.

Furthermore, since the entire vibrating body of the annular ultrasonic motor vibrates as shown in FIG. 8, it is difficult to fix the position of the vibrating body. Additionally, mechanical loss is unavoidable due to fixation.

The present invention has been made in view of these points, and an object of the present invention is to provide an ultrasonic motor that can increase output with the same volume and is highly efficient.

Means for solving the problem By using a disc-shaped vibrating body as the vibrating body and using bending vibration of 2nd order in the radial direction, 3rd order or more in the circumferential direction as the vibration mode, the output can be increased with the same volume, Moreover, a shaft is installed at the center of the vibrating body, and the position of the vibrating body is fixed via the shaft.

By using a disc-shaped vibrating body as the active vibrating body and using bending vibration of radial second order, circumferential direction third order or higher as the vibration mode, the inside of the vibrating body can also effectively contribute to the kinetic energy of the vibrating body. By doing so, it is possible to increase the output. Further, by installing the shaft at the center where the amplitude of the vibration of the vibrating body is extremely small and fixing the position of the vibrating body via the shaft, it is possible to reduce loss due to fixation and realize an 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 sectional view of one embodiment of the ultrasonic motor of the present invention. In the figure, a shaft 14 is installed at the center of the vibrating body 9, and is fixed to a base 15 at the bottom of the shaft 14. A moving body 13 is attached to the upper part of the shaft 14 via a bearing 16, and a leaf spring 17 and a pressure adjustment tool 1 are attached to the upper part of the shaft 14.
The movable body 13 is brought into pressure contact with the vibrating body 9 by the vibrator 8 .

FIG. 2 is a cutaway perspective view showing the configuration of the ultrasonic motor. A vibrating body 9 is constructed by pasting a disk-shaped piezoelectric ceramic 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 10 for extracting 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 pressurized contact with a protrusion 10 installed on the vibrating body 9 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 9, and the movable body 13 is driven by frictional force. The moving body 13 starts rotating around the axis 14.

FIG. 3 is a plan view showing the electrode structure of the disc-shaped piezoelectric ceramic 8. As shown in FIG. In the figure, E and F are electrode groups each having a length equivalent to a half wavelength in the circumferential direction, and consisting of small electrode portions in which the polarization directions of adjacent electrode portions are opposite in the thickness direction. The electrode groups E and F have a phase of 4 in the circumferential direction.
They are configured to be shifted by an amount equivalent to one-tenth of a wavelength (90 degrees).

Therefore, if electrode groups E and F are short-circuited and a voltage with a temporal phase difference of 90 degrees is applied between them and the solid electrode on the back surface, the vibrating body 9 will undergo bending vibration of second order in the radial direction and fourth order in the circumferential direction. traveling waves are excited.

FIG. 4 shows a vibration displacement state and a displacement distribution diagram of the vibrating body 9 when radial second order bending vibration and circumferential direction fourth order bending vibration are excited. Unlike when the first-order radial vibration mode is used, the displacement does not suddenly become smaller even at the inner circumference. Therefore, when the ultrasonic motor occupies the same volume, the kinetic energy of the vibrating body 9 is larger (
This makes it possible to realize an ultrasonic motor that can generate large output. In addition, the amplitude of vibration is extremely small at the center where the shaft 14 is taken out, and since the imaging object 9 is attached to the base 15 via this shaft 14, mechanical loss is almost eliminated by fixing the position of the vibrating body (efficiently The moving body 13 can be driven.

According to the present invention, it is possible to provide an ultrasonic motor that is efficient and has a large output.

Effects of the Invention According to the present invention, by using radial secondary, circumferential tertiary or higher bending vibration as the vibration mode, a large output can be achieved.
A highly efficient ultrasonic motor can be provided by installing a shaft at the center of the vibrating body where the amplitude of vibration is small and fixing the position of the vibrating body via this shaft.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of one embodiment of the disc-shaped ultrasonic motor of the present invention, FIG. 2 is a cutaway perspective view for explaining the operation of the disc-shaped ultrasonic motor, and FIG. 3 is the same as that of FIG. 1. Fig. 4 is a plan view of the piezoelectric ceramic used in the ultrasonic motor, and Fig. 4 is a diagram of the vibration state and radial displacement distribution of the moving body when radial secondary and circumferential tertiary bending vibrations are used as vibration modes. Figure 5 is a cutaway perspective view of an annular ultrasonic motor, Figure 6 is a plan view showing the shape and electrode structure of the piezoelectric body used in the ultrasonic motor of Figure 5, and Figure 7 is the operating principle of the ultrasonic motor. FIG. 8 is a diagram showing the vibration state of the vibrating body and the radial displacement distribution when bending vibration of first order in the radial direction and eighth order in the circumferential direction is used as the imaging mode. 7...Elastic body, 8...Piezoelectric body, 9...
... Vibrating body, 10... Protrusion, 11...
...Friction material, 12...Elastic body, 13...
... Moving body, 14 ... Axis, 15 ... Base, 16 ... Bearing, 17 ... Leaf spring, 18 ... Pressure adjustment tool. Name of agent: Patent attorney Toshio Nakao and one other person M1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 7

Claims (1)

[Claims] By driving the piezoelectric body with an alternating current voltage and exciting a traveling wave of bending vibration of second order in the radial direction, third order in the circumferential direction or higher in the disc-shaped vibrating body composed of the piezoelectric body and the elastic body, An ultrasonic motor for moving a movable body placed in contact with a vibrating body, characterized in that a shaft is installed in the center of the vibrating body, and the vibrating body is fixed via the shaft. motor.