PIEZOELECTRIC ULTRASONIC MOTOR USING LONGITUDINAL TORSIONAL COMPOSITE RESONANCE VIBRATION

A piezoelectric ultrasonic motor, which uses longitudinal and torsional composite vibration, was investigated in order to obtain high torque characteristics with small diameter. Piezoelectric ceramic elements, oscillating in both longitudinal and torsional modes, respectively, are used as piezoelectric stiffened modes having high electromechanical coupling factors k33 and k15, respectively. It was found that the resonant frequencies for longitudinal mode and torsional mode could coincide with each other in the ultrasonic motor, according to finite element method analysis and experimental measurement. The motor operating in both resonant vibrations indicated good performance. As an obtained result, the 20-mm diameter motor exhibited 4 kgf.cm maximum torque, 450 r/min maximum rotational speed, 40% maximum efficiency, and quick responsiveness, within 2.5 ms.