JPH0744854B2 - Ultrasonic motor - Google Patents

Description

TECHNICAL FIELD The present invention relates to an ultrasonic motor in which a surface wave generated in a stator is used to move a mover in pressure contact with the stator.

"Prior Art" Various ultrasonic motors have been invented in which a piezoelectric element is caused to vibrate a stator to generate a surface wave, and a mover in pressure contact with the stator is moved.

In order for the mover to move by receiving the surface wave of the stator, the mover must be pressed against the stator so that frictional force acts on the mover. For this reason, it is general that the mover is pressed against the stator side by various springs or magnetic forces, and a friction body is interposed between the stator and the mover (for example, JP-A-59-185180). Gazette).

“Problems to be Solved by the Invention” In the conventional surface wave motor, since the moving element receives a traveling force from the stator surface by friction, a friction body is interposed between the moving element and the stator surface, and the moving surface is suitable between the two. There is a lot of friction. However, the surface wave travels in a sin curve, and the elliptical motion at each position progresses in the peaks and recedes in the valleys.If the slider is pressed too strongly against the stator to increase the friction coefficient, There is a problem in that the mover receives not only the progressing force but also the retreating force, which hinders the progress as a whole.

Further, there has been a problem that the pressure contact surfaces of the stator and the friction body are worn, and sufficient progress cannot be obtained for a long time.

Therefore, it is an object of the present invention to prevent wear between the stator and the friction body, and also to enable the moving element that is in pressure contact with the stator to efficiently obtain a traveling force.

"Means for Solving Problems" The present invention is a surface wave motor in which a moving element is pressed against a stator that causes surface waves and a viscous fluid is interposed between the stator and the moving element.

The reason why the viscous fluid is interposed is to allow the surface waves of the stator to be sufficiently transmitted to the mover due to viscosity.

[Operation] When a stator is vibrated by applying a voltage with a 90 ° phase difference to multiple piezoelectric elements provided on the stator, a surface wave is generated on the stator and propagates on the stator surface. . In this case, one point on the surface of the stator is a vibration that describes an elliptical activation. Therefore, the mover brought into pressure contact with this stator receives a force in the traveling direction of the elliptical motion of the stator surface due to the viscosity and moves.

The viscous force when the mover moves on the stator is generated by the viscosity of the viscous fluid interposed between the two, and this viscous force F
Is the contact area A, viscosity coefficient η, fluid velocity gradient dU
/ dx; (where U is the relative velocity of the viscous fluid to the mover,
If x is the surface distance of the viscous fluid, then F = A · η · dU / dx.

The relationship between the viscous force F and the relative velocity U is as shown in FIG. 2 while the mover is moving. As can be seen from FIG. 2, the frictional force is not affected by the speed of the moving element when only the conventional friction body is used, whereas when a viscous fluid is interposed, the viscous force gradually increases as the relative speed increases. , If the relative velocity of the fluid is higher than a certain value, the viscous force becomes larger when the viscous fluid is interposed. Therefore, the viscous coefficient such that the viscous force exceeds a predetermined value,
A desired surface wave motor can be obtained by setting and using the relative speed and the like.

"Embodiment" An embodiment of the present invention will be described with reference to FIG.

The ultrasonic motor has a cushion part 2 in the casing part 1.
A ring-shaped stator 3 is provided via the
A large number of piezoelectric elements 4 are provided on the surface of the cushion material side. By applying a voltage having a phase difference of 90 ° to each piezoelectric element 4, the stator 3 is vibrated to generate a surface wave.

A ring-shaped mover 5 is provided on the surface of the stator 3 on which the piezoelectric element 4 is not provided, and the mover 5 is pressed against the stator 3 by a pressing member 6. The pressing member 6 has a central axis 6a.
Is penetrated from the mover 5 side to the casing 1 side, and the end of the central shaft is fixed with a nut via a spring 7. The viscous fluid 8 is interposed between the mover 5 and the stator 3, and the mover 5 moves the surface wave of the stator 3 via the viscous fluid 8 due to viscosity.

As the viscous fluid 8, for example, JIS No. 3 oil is used, and the oil film thickness is about 1 to 3 μm. Since the oil film thickness is thin, the viscous fluid will not leak to the outside due to surface tension, but even if a sealing material is arranged at the outer peripheral portion and the inner peripheral portion of the moving element 5 and the stator 3, even if leakage is prevented. Good. Also viscous fluid 8
Is easily held between the stator 3 and the mover 5,
An oil absorbing member may be interposed between the stator 3 and the mover 5, or a friction body may be interposed as in the conventional case and a viscous fluid may be interposed between the friction body and the stator.

In the above embodiment, the outer diameter of the moving element 5 and the stator 3 was 60 cm, the applied voltage to the piezoelectric element 4 was 80 V, and the ultrasonic motor was driven with a pressing force of the disc spring of 13 kg. The rotation speed was 100 rpm and the torque was 6 k.
It is g · cm, and it can be seen that the viscous force acts sufficiently by interposing a viscous fluid.

In the above embodiment, the moving element 5 is of a type that rotates, but the ring-shaped stator is formed to have a long linear portion so that the moving element reciprocates along the linear portion of the stator. The present invention can be similarly applied to the above-mentioned type.

[Advantages of the Invention] In the ultrasonic motor of the present invention, a viscous fluid is interposed between the mover and the stator, and the surface wave of the stator is moved by the viscous viscous force to move. Can be used efficiently. In addition, since there is no wear between the mover and the stator, the material of the mover etc. can be freely selected, and even when storing without using the ultrasonic motor, The joint surface of does not stick.

[Brief description of drawings]

FIG. 1 is a sectional view of an ultrasonic motor of the present invention, and FIG. 2 is a graph showing the relationship between viscous (friction) force and relative speed. 3; stator, 4; piezoelectric element 5; mover, 6; pressing member 7; spring, 8; viscous fluid

Claims (1)

[Claims] 1. An ultrasonic motor in which a surface wave is generated on a surface of a stator by vibrating the stator with a piezoelectric element, and the mover pressed against the stator is moved by the surface wave. An ultrasonic motor characterized in that a viscous fluid is interposed on the surface that is brought into pressure contact with the stator.