Motion error correction for non-contact ultrasonic motor driven by multi-layered piezoelectric actuators

An active non-contact ultrasonic motor with the micro positioning abilities of a rotor was proposed and performances were tested. The stator had a simple cylindrical form, which enabled low manufacturing costs. A resonant frequency of 22.2 kHz at eighth flexural mode of vibration was observed. With appropriate assembly and operation of piezoelectric actuators, the flexure vibration of the stator travels in the circumferential direction. The component of the stator deformation in radial direction creates an air film pressure higher than ambient thereby suspending the rotor. Simultaneously, the component that propagates in the circumferential direction rotates the rotor based on acoustic viscous flow. It was experimentally confirmed by electrical conduction test that the rotor rotated with levitation from stator. In addition, piezoelectric actuators around the stator exciting the deflective vibration could make contact-free micro positioning abilities of the rotor with a minimum step width of 0.15 mu m.