Abstract
Ultrasonic motors for low electrical power applications are considered for portable devices such as an electronic wristwatch. For the study of a standing wave type motor, a modular approach was proposed, where stators and rotors are added in an assembly step. The mode conversion principle called the `elastic fin motor' and its extension to an `elastic force motor' suitable for a flat profile motor are discussed. Fabrication methods and the mechanical response of silicon diaphragms covered by PZT and ZnO (zinc oxide) piezoelectric thin films are compared. A closed loop position control using an integrated piezoelectric stress detection is proposed and demonstrated. The target torque of at a mechanical power of a few has been achieved. A long-term test during 2 months of continuous operation proved an acceptable reliability for the specified applications.
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