JP2582176B2 - Ultrasonic motor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic motor that generates a driving force by exciting an elastic traveling wave using a piezoelectric material such as a piezoelectric ceramic.

2. Description of the Related Art Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 is a partially cutaway perspective view of a conventional ring-shaped ultrasonic motor, and a piezoelectric body is formed on the other ring-shaped surface of the ring-shaped elastic substrate 1 having the projections 3 formed on one ring-shaped surface. The ring-shaped vibrating body 4 is formed by laminating the ring-shaped piezoelectric ceramics 2. Reference numeral 6 denotes a moving body in which a friction material 5 of a wear-resistant material is formed on a contact surface side with the vibrating body 4. Since the friction material 5 is provided for stabilizing the output characteristics and improving the wear resistance, it can be omitted. Although not shown here, the movement resistance 6 is installed in pressure contact with the vibrating body 4 by pressure means such as a disc spring.

Two sets of drive electrodes (not shown) are formed on the piezoelectric body 2 shifted by a predetermined position, and when two AC voltages having a predetermined phase difference are applied to the drive electrodes, as shown in FIG. A standing wave of two bending vibrations having a large radial amplitude is excited, and the two standing waves are superposed to form a traveling wave. The moving body 6 is frictionally driven by the lateral component of the wave front of the traveling wave and rotates.

FIG. 5 is a partially cutaway perspective view of a disk-type ultrasonic motor, in which a disk-shaped elastic substrate 7 having a projection 9 on one disk surface is provided with a disk. The disk-shaped vibrating body 10 is formed by bonding the piezoelectric bodies 8 together. Reference numeral 13 denotes a moving body in which a wear material 12 of a wear-resistant material is formed on a contact surface side with the vibrating body 10. As in the case of the annular ultrasonic motor, the wear material 12 can be omitted. Although not shown here, the moving body 13 is placed in pressure contact with the tip of the projection 9 by a pressing means such as a disc spring.

Two sets of drive electrodes are formed on the piezoelectric body 8 so as to be shifted from each other by a predetermined position. When two AC voltages having a predetermined phase difference are applied to the drive electrodes, a radial direction as shown in FIG. A traveling wave of bending vibration having an amplitude is excited. Due to the transverse component of the wave front of the traveling wave, the moving body 13 is driven by friction and rotates around the rotating shaft 11.

FIG. 7 is a sectional view showing the principle that the moving body 15 is driven by the frictional force by the traveling wave of the bending vibration excited by the vibrating body 14. An arbitrary point on the surface of the vibrating body 14 is excited by the traveling wave of the flexural vibration, as shown in FIG.
Make an elliptical motion. The moving body 15 placed under pressure on the vibrating body 14 comes into contact only near the apex of the elliptical trajectory, and is driven by friction to move in the direction opposite to the traveling direction of the wave. The velocity v of the moving body 15 is the horizontal component u of the wave front of the traveling wave.
Is determined by the angular frequency ω of the vibration, and v = uω (1), and the output torque is determined by the frictional force, which is the product of the friction coefficient between the vibrating body and the moving body and the pressing force, and the driving radius.

FIG. 8 is a cross-sectional view of the vibrating body for explaining the role of the projection. The velocity v of the moving body 18 is proportional to the lateral component u of the surface of the vibrating body 16 due to the traveling wave of the bending vibration according to the equation (1). U = hAk (2) is given by the distance h from the active surface N to the contact surface and the wave number k. Therefore, in order to increase the speed v of the moving body 18, the amplitude A of the bending vibration may be increased. However, the material of the vibrating body 16 has a breaking limit, and there is a limit in increasing the amplitude of the bending vibration and increasing the speed v of the moving body 18. Therefore, by forming a projection 17 on the vibrating body 16 and expanding the distance h from the neutral surface N to the contact surface to h ', the lateral component is expanded, and the amplitude of the bending vibration is kept within the breaking limit. Therefore, the speed of the moving body 18 is increased.

Problems to be Solved by the Invention The ultrasonic motor drives the moving body stably by enlarging the lateral component u due to the traveling wave of the bending vibration having a small amplitude of about several microns by the projection. However, since the design guideline of the protrusion for increasing the speed was not clear, the distortion due to the bending vibration of the vibrator exceeded the breaking limit of the material constituting the vibrator due to the formation of the protrusion. There have been problems such as a remarkable decrease in reliability, and an inability to efficiently increase the speed of the moving body.

An object of the present invention is to provide an ultrasonic motor that solves the above-described problems of the conventional ultrasonic motor.

Means for Solving the Problems The present invention provides a distance h ₁ from the neutral surface in the elastic substrate to the surface of the elastic substrate, a height h _{2 of} the protrusion, a width w ₁ between the roots of the protrusion, The amplitude of the traveling wave to be excited on the vibrating body is limited to w ₁ / (w ₁ + w ₂ ) of the maximum allowable amplitude when there is no protrusion, and ((h ₁ + h ₂ ) / h ₁ ) (w ₁ / (W ₁ + w ₂ ))> 1 is an ultrasonic motor in which the shapes of the elastic substrate and the projection are determined so that the following condition is satisfied.

In effect the present invention, to excite h ₁ the distance from the neutral surface of the elastic substrate to the surface of the elastic substrate, h ₂ the height of the protrusions, the width between the base of the projections w _1, a vibrator The amplitude of the traveling wave should be within w ₁ / (w ₁ + w ₂ ) of the maximum allowable amplitude when there are no protrusions, and ((h ₁ + h ₂ ) / h ₁ ) (w ₁ / (w ₁ + w ₂₎ ))> By determining the shapes of the elastic substrate and the projection so that> 1 is satisfied, the speed is improved as compared with the case without the projection, while keeping the distortion of the flexural vibration of the vibrator within the breaking limit. Thus, an ultrasonic motor with improved reliability and high speed is realized.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.
This embodiment is an embodiment common to an annular ultrasonic motor and a disk ultrasonic motor.

FIG. 1 is a sectional view of a vibrating body of an ultrasonic motor according to one embodiment of the present invention. Reference numeral 101 denotes an elastic substrate having a protrusion 103 on one surface, and a vibrator 104 formed by bonding a piezoelectric body 102 to the other surface with an adhesive. In the figure, h ₀ is the distance from the neutral surface N in the elastic substrate 101 to the surface of the piezoelectric body 102,
h ₁ is the distance from the neutral plane N in the elastic substrate 101 to the surface of the elastic substrate 101, h ₂ is the height of the projection 103, w ₁ is the width between the roots of the projection 103 (the part without the projection 103). ), W ₂ is the width of the base of the projection 103.

FIG. 2 is a sectional view taken on a plane orthogonal to the sectional view of the vibrating body of FIG. In the figure, the vibrating body 104 has a rectangular cross section having a width w. Stiffness (flexural rigidity) D ₁ with respect to flexural vibration of the portion having no protrusion 103 of the vibrator 104, D ₁ = a ^{_{(h 0 + h 1) 3}} wE / 12 (3), the protrusions 103 of the vibrator 104 The bending stiffness D ₂ of a certain portion against flexural vibration is D ₂ = (h ₀ + h ₁ + h ₂ ) ³ wE / 12 (4). Therefore, the ratio of the bending stiffness to the place where there is no protrusion is D ₂ / D ₁ = [1+ {h ₂ / (h ₀ + h ₁ )}] ³ (5), and h ₂ / (h ₀ + h ₁₎ If) is large, the bending stiffness of the portion having the protrusion 103 is sufficiently larger than the bending stiffness of the portion without the protrusion 103, and therefore, the bending occurs almost in the portion without the protrusion 103.

From the expressions (1) and (2), the amplitude A of the vibration is usually increased to increase the speed v of the moving body.
Has a fracture limit with respect to strain, and the amplitude A must be increased within the fracture limit. Therefore, the maximum speed of the moving body is determined by the breaking limit strain. When the projection 103 is not provided, the entire vibrating body is uniformly distorted. However, when the projection 103 is provided, the vibrating body 104 bends and vibrates due to the distortion at the place where the projection 103 is not provided as described above. That vibrator 104 of FIG. 1 deflects only the portion of the width w _2. If the strain in this portion is set to a certain value within the same breaking limit as the strain without the protrusion 103, the amplitude A 'with the protrusion 103 is
A ′ = {w ₁ / (w ₁ + w ₂ )} A (6) That is, in order to improve the reliability,
The amplitude of the bending vibration to be excited is set so as to satisfy the expression (6) from the amplitude value within the breaking limit when the projection 103 is not provided. Therefore, in the normal case where the condition that the neutral plane position does not change significantly is satisfied, the speed v ₁ of the moving object with the protrusion 103 is equal to the speed v ₀ of the moving object without the protrusion 103, v ₀ = h ₁ kAω (7) v ₁ = (h ₁ + h ₂ ) (w ₁ / (w ₁ + w ₂ )) kAω = ((h ₁ + h ₂ ) / h ₁ ) (w ₁ / (w ₁ + w ₂ )) v ₀ (8). Therefore, if the shape of the projection 103 of the elastic substrate 101 is determined so as to satisfy ((h ₁ + h ₂ ) / h ₁ ) (w ₁ / (w ₁ + w ₂ ))> 1 (9), the vibration pair 104 By keeping the strain at a value within the breaking limit, the speed of the moving body can be increased more effectively than when there is no protrusion 103.

As described above, according to the present invention, by designing the shape of the elastic substrate and the projections constituting the vibrating body so as to satisfy the conditional expression (9), the distortion of the vibrating body is kept within the breaking limit, and the reliability is improved. It is possible to provide an ultrasonic motor in which the speed of the moving body is increased more efficiently than when there is no protrusion, while improving the performance.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a vibrating body of an ultrasonic motor according to one embodiment of the present invention, FIG. 2 is a cross-sectional view taken along a plane orthogonal to the cross section of FIG.
FIG. 3 is a partially cutaway perspective view of a conventional annular ultrasonic motor, FIG. 4 is a radial displacement distribution diagram of a vibrating body of the conventional annular ultrasonic motor, and FIG. FIG. 6 is a partially cutaway perspective view of the ultrasonic motor, FIG. 6 is a radial displacement distribution diagram of a vibrating body of the disk-type ultrasonic motor, FIG. 7 is a cross-sectional view for explaining the operation principle of the ultrasonic motor, FIG. 8 is a cross-sectional view for explaining the role of the projection. 101: elastic substrate, 102: piezoelectric body, 103: projection, 104
…… oscillator, h ₀ …… distance from the neutral surface in the elastic substrate to the surface of the piezoelectric body, h ₁ …… distance from the neutral surface in the elastic substrate to the surface of the elastic substrate, h ₂ …… protrusion Body height, w ₁ … width between bases of protrusions (width of part without protrusions), w ₂ … width of bases of protrusions.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsushi Takeda 1006 Kazuma Kadoma, Kadoma City, Osaka Inside Matsushita Electric Industrial Co., Ltd. (56) References JP-A-1-255484 (JP, A)

Claims (1)

(57) [Claims] 1. A vibrating body is formed by coupling a piezoelectric body to another surface of an elastic substrate having a plurality of protrusions formed on one surface, and two sets of driving electrodes formed on the piezoelectric body are provided. By applying two voltages each having a predetermined phase difference, an ultrasonic motor that excites the traveling wave of the bending vibration to the vibrating body and moves the moving body pressed and abutted on the tip of the protruding body. The distance from the neutral surface in the elastic substrate constituting the vibrating body to the surface of the elastic substrate is h ₁ , the height of the protrusion formed on one surface of the elastic substrate is h ₂ , The distance between the roots
w ₁ , assuming that the width of the base of the protrusion is w ₂ , the amplitude of the traveling wave to be excited in the vibrator is limited to within w ₁ / (w ₁ + w ₂ ) of the maximum allowable amplitude when there is no protrusion. And (vii) the elastic substrate and the vibrating body having the protrusions so that ((h ₁ + h ₂ ) / h ₁ ) (w ₁ / (w ₁ + w ₂ ))> 1 is satisfied. The ultrasonic motor characterized by the above.