JPH01252179A - Ultrasonic motor - Google Patents

Abstract

PURPOSE:To stabilize operation by using a spring, a spring constant of which in an applied-pressure allowable region is made smaller than that in regions lower than said region. CONSTITUTION:A section having the easy inclination of a characteristic curve is employed as a spring for pressure used for an ultrasonic motor in order to set a spring constant in an applied pressure allowable region at a value smaller than a spring constant in regions lower than the applied-pressure allowable region. Consequently, even when the set quantity of deflection is varied by the roughness, waviness and abrasion of the surface of a friction material 5, the change of. the applied pressure of a vibrator 3 and a moving body 7 is reduced. With said motor, the vibrator 3 is composed of an elastic body 1 and a piezoelectric body 2, and the moving body 7 consists of an elastic body 6 and the friction material 5. The vibrator 3 is fixed by a supporter 4, progressive waves are excited in the vibrator 3 when an AC field is applied to the piezoelectric body 2, and the moving body 7 is turned while using the excited progressive waves as the driving force. Accordingly, even when the set quantity of deflection is varied by the surface roughness, etc., of the friction material 5, the characteristic change of the motor is reduced.

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, which excite elastic vibrations in a vibrating body made of a piezoelectric material such as a piezoelectric ceramic, and rotate a moving body using this as a driving force.

Hereinafter, the conventional technology of an ultrasonic motor will be explained with reference to the drawings. FIG. 6 is a sectional view of the disc-shaped ultrasonic motor. The vibrating body 3 is constructed by laminating a disk expansion piezoelectric body 2 as a piezoelectric body to one of the disk surfaces of a disk-shaped elastic body 1 made of stainless steel or the like. Note that the vibrating body 3 is fixed to a support body 4. The movable body 7 is constructed by pasting together a friction material 6 made of a wear-resistant material and an elastic body 6 made of stainless steel or the like. The moving body is a coil spring 8
As a result, the vibrating body 3 is brought into pressure contact via the friction material 6. The coil spring 8 is fixed with a predetermined amount of deflection so as to obtain a predetermined pressing force on the retaining ring 1o. Note that a bearing 9 is provided in order to transmit rotational motion to the moving body 7 without loss. When an alternating current electric field is applied to the piezoelectric body 2, a traveling wave of bending vibration that advances in the circumferential direction of the vibrating body 3 is excited, and the movable body 7 It is driven and rotated by the frictional force determined by the pressure applied by 8. Therefore, the starting torque of the ultrasonic motor is determined by the frictional force.

Therefore, if the friction force determined by the friction coefficient and the pressing force is constant, the ultrasonic motor operates stably. However, as shown in Figure 7, in the past, a coil spring with a nearly constant spring constant was used as a pressurizing spring, and the amount of deflection and pressurizing force were in a proportional relationship. The amount of deflection is determined by the instability at the initial setting and the friction material 6 and vibrating body 3 during rotation.
The set deflection amount may deviate from the allowable range due to surface roughness or waviness on the contact surface with the vibrating body 3, and the relationship between the deflection amount and the pressurizing force described above may cause the set deflection amount to deviate from the allowable pressurizing force range, and the vibration body 3 The pressurizing force with body 7 was changed. Furthermore, it was not possible to apply pressure uniformly in the circumferential direction. As a result, it was difficult to obtain characteristics such as torque and efficiency. In addition, due to long-term operation of the ultrasonic motor, the friction material 6 wears out and the initial deflection of the coil spring becomes small, which causes the pressing force to change proportionally and the output of the ultrasonic motor to decrease. There were drawbacks.

Problems to be Solved by the Invention As explained above, conventional ultrasonic motors have used coil springs whose spring constant is approximately constant in the pressurizing force allowable range as springs for pressurizing the vibrating body and the movable body. There is a problem in that the surface roughness, waviness, and wear of the friction material cause the pressing force to change proportionally, resulting in unstable operation.

In view of this point, it is an object of the present invention to provide an ultrasonic motor that operates stably.

Means for Solving the Problem As a method of pressurizing the vibrating body and the movable body, a spring whose spring constant in the pressurizing force permissible region is smaller than the spring constant below the pressurizing force permissible region is used to press the vibrating body and the movable body. The ultrasonic motor is placed in pressure contact with the vibrating body to stabilize the operation of the ultrasonic motor.

By using a spring whose spring constant in the applied pressure permissible range is smaller than the spring constant below the applied pressure permissible range, the movable body is placed in pressurized contact with the vibrating body, thereby reducing the friction material. Even if the amount of deflection of the spring changes due to surface roughness, waviness, and wear, stable operation of the ultrasonic motor is realized by reducing the change in the pressing force.

EXAMPLES Hereinafter, examples of the present invention will be described in detail with reference to the drawings.

(Example 1) Fig. 1 is a characteristic diagram of the pressurizing spring used in the ultrasonic motor of the present invention.The spring constant is shown by the characteristic curve in the figure. In order to set the constant to be smaller than the spring constant below the allowable pressure range, the part with a gentle slope of the characteristic curve is used.Therefore, the set deflection amount depends on the roughness of the surface of the friction material. Even if the pressure changes due to waviness and wear, the change in the pressing force between the vibrating body and the moving body is small. Figure 2 (&) is a plan view of a platen spring for implementing this, and Figure 2 (b) is A cross-sectional view of the bellows spring is shown.Furthermore, since the bellows spring has a conical shape, pressure can be applied uniformly in the circumferential direction.

6th □□□ is a sectional view of an embodiment of the ultrasonic motor of the present invention. The vibrating body 3 is composed of an elastic body 1 and a piezoelectric body 2, and the movable body 7 is composed of an elastic body 6 and a friction material 6. The vibrating body 3 is fixed with a support body 4. When an alternating current electric field is applied to the piezoelectric body 2, a traveling wave of bending vibration traveling in the circumferential direction of the vibrating body 3 is excited, and this is used as a driving force to rotate the movable body 7. As shown in Fig. 1, the spring constant of the springs 11 and 11' is set to be smaller than the spring constant in the pressure permissible range below the pressure permissible range, so that the set amount of deflection of the friction material is Even if there are variations due to surface roughness, waviness, and wear, the changes in the pressing force between the vibrating body and the moving body are small, and therefore the characteristics of the ultrasonic motor do not change much.

In the figure, two springs with the same characteristics are stacked to increase the set deflection amount so that the pressing force can be easily set.

Note that it is also possible to stack one or more than two bellows springs.

In this way, by installing the movable body in pressure contact with the vibrating body using a bell spring whose spring constant in the pressurizing force permissible area is smaller than the spring constant below the pressurizing force permissible area, the friction material can be Even if the set deflection amount fluctuates due to surface roughness, waviness, and wear, stable operation of the ultrasonic motor is achieved by reducing the change in the 710 pressure.

(Example 2) The basic configuration is the same as in Example 1, but the pressure spring installed in Example 1 was replaced with a bell spring with multiple notches radially centered around the inner diameter. It is composed of

FIG. 3(&) shows a plan view of a pressure spring used in the ultrasonic motor of the present invention, and FIG. 3(Φ) shows a sectional view of the spring. The bell spring having a plurality of radial notches 11a has a conical shape and can be pressurized uniformly in the circumferential direction. Furthermore, the amount of deflection in the pressurizing force permissible region can be increased several times compared to conventional bell springs.

FIG. 4 is a characteristic diagram of the pressure spring. The spring constant is the characteristic curve shown in the same figure, and the spring constant in the pressurizing force permissible region is set to be smaller than the spring constant below the pressurizing force permissible region. Moreover, the amount of deflection of the pressurizing spring in the pressurizing force permissible region is increased due to the effect of the notch.

Therefore, even if the set deflection amount changes due to surface roughness, waviness, and wear of the friction material, the change in the pressing force between the vibrating body and the moving body is small.

In this way, by installing the movable body in pressure contact with the vibrating body using a bell spring whose spring constant in the pressurizing force permissible area is smaller than the spring constant below the pressurizing force permissible area, the friction material can be Even if the set deflection amount fluctuates due to roughness, waviness, or wear on the surface, stable operation of the ultrasonic motor is achieved by reducing the change in the pressing force.

Effect of the invention According to the present invention, the spring constant in the pressurizing force permissible region is as follows.

By using a bellows spring whose spring constant is smaller than the allowable pressure range, the set deflection amount of the spring may fluctuate due to surface roughness and waviness of the friction material or wear due to long-term operation of the ultrasonic motor. Also, since the change in the pressing force between the vibrating body and the movable body can be reduced, it is possible to realize an ultrasonic motor that operates stably.

[Brief explanation of the drawing]

Fig. 1 is a characteristic diagram of a bell spring used in an ultrasonic motor according to an embodiment of the present invention, Fig. 2 e) (b) is a plan view and a sectional view of the same bell spring, and Fig. 3 (IL) 4 is a characteristic diagram of a spring with a notch used in the ultrasonic motor of the present invention, and FIG. FIG. 6 is a sectional view of an ultrasonic motor using a bell spring with the spring characteristics shown, FIG. 6 is a sectional view of a conventional ultrasonic motor, and FIG. 7 is a characteristic diagram of a coil spring that is a conventional pressure spring. 1...Elastic body, 2...Piezoelectric body, 3...
... Vibrating body, 4... Support body, 6...
・Friction material, 6...Elastic body, 7...Moving body, 8...Coil spring, 9...R ring, 1o...・Retaining ring, 11.11'...
...Farewell. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Measurement amount Fig. 2 (α) tb) If, /f'---Sara 1; /, 6- Low body 11.11''- to 1 Yone Figure 6 Figure 7 r: 1F) Misato

Claims (3)

[Claims] (1) A moving body installed in pressurized contact with the vibrating body by driving the piezoelectric body with an alternating current voltage and exciting an elastic traveling wave in the vibrating body composed of a piezoelectric body and an elastic body. The movable body is brought into pressure contact with the vibrating body using a pressurizing spring whose spring constant in a pressurizing force permissible area is smaller than a spring constant below the pressurizing force permissible area. An ultrasonic motor characterized by having been installed. (2) The ultrasonic motor according to claim 1, characterized in that a bell spring is installed as the pressurizing spring. (3) The ultrasonic motor according to claim 2, wherein a conical spring having a plurality of notches or slits radially arranged around the inner diameter portion is installed as the pressurizing spring.