US 5,631,517 AGranted

Ultrasonic motor and driving for the ultrasonic motor

AssigneesHitachi, Ltd., Hitachi Media Electronics Co., Ltd.

InventorsKazuo Kato, Takashi Sase, Kikuo Tomita, Shuzo Oshima, Muneo Chiba, Tomohiko Douken, Kazuyoshi Takizawa

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Abstract

An electrostrictive revolution type ultrasonic motor includes a piezoelectric ceramic disk shaped stator and a rotor. The piezoelectric ceramic disk shaped stator has an eccentric movement via excitation by two phase pulse like voltage. The rotor is fitted around the circumference of the stator and is transmitted by a rotating torque due to the eccentric movement via frictional contact therebetween. The rotor is formed of a plastic material by injection molding to achieve a reduction of a size variation of the rotor and a stable contact with the stator. A high and stable rotating torque is thereby obtained with a reduced production cost. Further, a driving device for the ultrasonic motor which varies the frequency of a voltage applied to the ultrasonic motor in a stepped manner discriminates the magnitude of the corresponding motor currents and drives the ultrasonic motor with the frequency which causes the maximum motor current. In this manner, a simple structured and low cost driving device which operates at a high speed and at a high resolution with a high efficiency is achieved.

Claims7

Dependent claims

An ultrasonic motor comprising:

a disk shaped piezoelectric stator having a center of gravity which revolves eccentrically through excitation by an ultrasonic resonant frequency signal;
and
a cap shaped plastic rotor fitted to said disk shaped piezoelectric stator through the outer circumference of said disk shaped piezoelectric stator, said cap shaped plastic rotor includes a side plate facing one of the major faces of said disk shaped piezoelectric stator and for transmitting a rotating torque for an external load and more than two and less than seven flat contacting members extending in the tangential direction of the outer circumference and in the axial direction of said disk shaped piezoelectric stator and disposed along the outer circumference of said disk shaped piezoelectric stator with an equal angular spacing, and is formed integrally through an injection molding with a plastic material having a high Young's modulus and a lower hardness than that of said disk shaped piezoelectric stator, thereby the elasticity of the cap shaped plastic rotor as a whole exerts substantially equal predetermined contacting pressures on the other circumference of said disk shaped piezoelectric stator through said respective flat contacting members.

Dependencies are inferred from the claim text.