JPS6323574A - Ultrosonic motor - Google Patents

Abstract

PURPOSE:To stabilize working against the variation of a load, by permitting a mover to come in pressure contact with the position of less influence to the amplitude of the oscillation of a driver due to the variation of resonance frequency, or only near the position. CONSTITUTION:On the rear surface of an elastic unit 7, a piezoelectric unit 8 is put together to compose a driver 9. At the position P of less influence due to the resonance frequency of the driver 9, a projection 13 for taking out mechanical output is set. A mover 12 consisting of an elastic unit 11 and a slider 10 is pressure-set to come in contact with the projection 13. When the piezoelectric unit 8 is driven by two AC electric-fields different in timing from each other in phase by 90 deg., then the progressive wave of bending vibration is passed onto the driver 9, and the mover 12 is rotated.

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 drive body using a piezoelectric body such as a piezoelectric ceramic, and the vibrations are used as a driving force.

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

FIG. 4 is a perspective view of a conventional ultrasonic motor, in which a piezoelectric driving body 3 is constructed by bonding a circular piezoelectric ceramic 2 as a piezoelectric body to one of the circular surfaces of a circular elastic body 1. 4 is a slider made of a wear-resistant material, and 5 is an elastic body, which are pasted together to form a moving body 6. The moving body 6 is in contact with the driving body 3 via the slider 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 driving 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. 5 shows an example of the electrode structure of the piezoelectric ceramic 2 used in the ultrasonic motor shown in FIG. In the figure, nine wavelengths of elastic waves are placed in the circumferential direction. In the figure, AlB is an electrode consisting of a small region each corresponding to a half wavelength, C is an electrode with a length of three-quarters of a wavelength, and D is an electrode with a length of a quarter of a wavelength.

Therefore, there is a phase shift between the electrode A and the electrode B by a quarter of a wavelength (-90 degrees). Adjacent small electrode portions in electrode A1B are polarized oppositely to each other in the thickness direction.

The bonding surface of the piezoelectric ceramic 2 with the elastic body 1 is the surface opposite to the surface shown in FIG. 5, and the electrodes are solid electrodes. When in use, electrode groups A and B are shown with diagonal lines in FIG.
They are used by shorting each other.

The operation of the ultrasonic motor configured as above will be described below. To the electrode A of the piezoelectric body 2? V1 xsin(ωt) −m−(
When the voltage represented by 1) is applied (where vl is the instantaneous value of the voltage, ω is the angular frequency, and t is the time), the driving body 3 bends and vibrates in the circumferential direction.

FIG. 6 is a perspective view of the driving body of the ultrasonic motor shown in FIG. 4 when approximated by MM. FIG. The state when a voltage is applied to the body 2 is shown.

FIG. 7 shows an enlarged view of the contact situation between the moving body 6 and the driving body 3. V1×5 inches (
ωt), and by applying voltages of Vl xcos(ωt) whose phases are temporally shifted by π/2 from each other to the other electrode B, a traveling wave of bending vibration can be created in the circumferential direction of the driving body 3. . Generally speaking, if the amplitude of a traveling wave is ξ, then ξ−ξ1 xcos(cc>t−kx)
---(2) However, it can be expressed as the instantaneous value of the magnitude of ξ18 wave k: wave number (2π/λ) λ: wavelength X: position. Equation (2) is ξ−ξ1x(cos(ωt)xcos(kx)+5in
(ωt)xsin(kx)) ---(3) can be rewritten. Equation (3) shows that the traveling wave is π/
Waves out of phase by 2, cos(ωt) and 5in(ωt
), and cos(
This shows that it can be obtained by the sum of the products of 5in(kx) and 5in(kx). From the above explanation, since the piezoelectric body 2 has the electrode groups A and B whose phase is shifted from each other by π/2 (-λ/4), it has a frequency output equal to the resonant frequency of the driving body 3. A traveling wave of bending vibration can be created in the driving body 3 by creating alternating current voltages temporally shifted by a phase of π/2 from the outputs of the oscillators and applying them to the electrode group.

Figure 7 shows that the mass point on the surface of the driving body is moving in an ellipse with the major axis 2 W and the minor axis 2 u due to the excitation of the traveling wave at point A of the driving body, which is placed on the driving body 3. The figure shows how the moving body 6 makes contact with the ellipse at the apex and moves at a speed of V-ω×u in the direction opposite to the direction of wave propagation. That is, the moving body 6 is pressed against the driving body 3 with an arbitrary static pressure,
It contacts the surface of the driving body 3 and is driven at a speed V in a direction opposite to the direction of wave propagation due to the frictional force between the moving body 6 and the driving body 3. When there is slippage between the two, the speed will be smaller than the above slip.

FIG. 8 shows the displacement distribution of the annular vibrator. Short axis U above
Since is proportional to the amplitude ξ of the traveling wave, the maximum speed can be obtained by taking the mechanical output from the position N (outer periphery) where the amplitude is maximum. Conventionally, the mechanical output is taken from the outer periphery of the driving body.

Problems to be Solved by the Invention As explained above, in order to increase the speed of the moving body, an ultrasonic motor conventionally extracts its output from near the outer periphery of the annular moving body. The amplitude of the outer periphery of the driving body changes greatly due to changes in the resonant frequency due to changes in load or changes in temperature. Therefore, there is a drawback that the rotational speed of the moving body is unstable.

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 operate stably against changes in load and temperature.

Means for Solving the Problems The movable body is installed in pressurized contact only at or near a position where the amplitude of vibration of the driving body is less affected by changes in resonance frequency.

At a position where the amplitude of the vibration of the driving body is less affected by changes in the working resonance frequency, the component U of the elliptical locus of the mass point on the surface
is also stable, and therefore the speed of the moving object is also stable.

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 an ultrasonic motor according to an embodiment of the present invention. In the figure, reference numeral 7 denotes an elastic body, and a piezoelectric body 8 is bonded to the back surface of the elastic body to constitute a driving body 9. Drive body 9
A protrusion 13 for extracting mechanical output is installed at a position P that is less affected by the resonance frequency. A moving body 12 consisting of an elastic body 11 and a slider 10 is placed under pressure so as to contact the protrusion 13 . When the piezoelectric body 8 is driven by two alternating current electric fields having temporally different phases by 90 degrees, a traveling wave of bending vibration is excited in the driving body 9, and the movable body 12 rotates.

FIG. 2 is a sectional view of an ultrasonic motor according to another embodiment of the present invention. In the figure, a slider 10 is attached to a portion of an elastic body 11 so as to correspond to a position that is less affected by the resonance frequency of the driving body 9. Therefore, in this embodiment as well, mechanical output is taken out from position P, similar to the embodiment shown in FIG.

FIG. 3 shows changes in the radial displacement distribution of the annular moving body depending on the resonance frequency. In the figure, the horizontal axis is the radius normalized by the outer diameter, and the vertical axis is the amplitude of bending vibration normalized by the maximum displacement of the outer circumference.

This figure shows changes in the displacement distribution when the driving frequency is constant and the resonance frequency changes due to changes in load and temperature. From the figure, even if the relationship between the driving frequency and the resonant frequency of the driving body changes, the influence is small at point Q shown in the figure. Therefore, by extracting the mechanical output from the vicinity of this Q point, it is possible to realize an ultrasonic motor that operates stably and is less affected by fluctuations in load and temperature. In the embodiment shown in FIG. 1, this is achieved by installing the protrusion 13 near the Q point, and in the embodiment shown in FIG. 2, this is achieved by installing the slider 10 near the Q point.

Effects of the Invention According to the present invention, it is possible to provide an ultrasonic motor that has a simple structure and operates stably against load fluctuations and temperature changes.

[Brief explanation of drawings]

Fig. 1 is a sectional view of an ultrasonic motor according to an embodiment of the present invention, Fig. 2 is a sectional view of an ultrasonic motor according to another embodiment of the invention, and Fig. 3 shows a displacement distribution according to the driving frequency of the driving body. The diagram shown,
Fig. 4 is a perspective view of a conventional ultrasonic motor, Fig. 5 is a plan view showing the shape and electrode structure of the piezoelectric body used in Fig. 4, and Fig. 6 is a vibration of the driving body of the ultrasonic motor. FIG. 7 is an explanatory diagram of the principle of the ultrasonic motor, and FIG. 8 is a perspective view and a radial displacement distribution diagram showing the vibration state of the driving body. 7...Elastic body, 8...Piezoelectric body, 9...
...Driver 10...Slider, 11...
...Elastic body, 12...Moving body, 13...
··protrusion. Name of agent: Patent attorney Toshio Nakao and one other person Figure 1 Bivi Figure 3 Chika Figure 6 (OJ) Figure 7 Figure 8

Claims (1)

[Claims] In an ultrasonic motor that moves a movable body placed in contact with the driving body by exciting an elastic traveling wave in a driving body made of an elastic body and a piezoelectric body, the amplitude of the vibration of the driving body is An ultrasonic motor characterized in that the movable body is installed in pressurized contact with a position that is less affected by changes in resonance frequency or in the vicinity thereof.