Ultrasonic motor based on coupled longitudinal‐bending vibrations of a diagonally symmetric piezoelectric ceramic plate

This paper discusses the operating principle and performance characteristics of an ultrasonic motor based on the coupled longitudinal‐bending vibrations of a diagonally symmetric piezoelectric ceramic plate. It is well known that longitudinal and bending vibrations couple with each other in a diagonally symmetric piezoelectric ceramic plate. The objective of this investigation is to design a simple and thin ultrasonic motor based on these coupled mode vibrations. The design of a stator for an ultrasonic motor was optimized with respect to vibration mode, capacitance ratio, and direction of vibratory displacement by employing the finite element method. A simple ultrasonic motor was built and its performance was tested. The results indicate that its load characteristics vary widely depending on the contact point of the rotor and the geometry of a piezoelectric plate. Furthermore, attempts were made to equalize load characteristics for bidirectional operations. The efforts revealed that it is possible to equalize the rotation rate, but it is difficult to equalize efficiencies for bidirectional operations. By incorporating a self‐oscillation circuit with an inverter, it is possible to run the motor bidirectionally in a single‐phase mode.