ULTRASONIC MOTOR BASED ON COUPLED LONGITUDINAL-BENDING VIBRATIONS OF A DIAGONALLY SYMMETRICAL PIEZOELECTRIC CERAMIC PLATE

This paper discusses the operating principle and performance character istics of an ultrasonic motor based on the coupled longitudinal-bendin g vibrations of a diagonally symmetric piezoelectric ceramic plate. It is well known that longitudinal and bending vibrations couple with ea ch other in a diagonally symmetric piezoelectric ceramic plate. The ob jective of this investigation is to design a simple and thin ultrasoni c 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 employi ng the finite element method. A simple ultrasonic motor was built and its performance was tested. The results indicate that its load charact eristics vary widely depending on the contact point of the rotor and t he geometry of a piezoelectric plate. Furthermore, attempts were made to equalize load characteristics for bidirectional operations. The eff orts revealed that it is possible to equalize the rotation rate, but i t is difficult to equalize efficiencies for bidirectional operations. By incorporating a self-oscillation circuit with an inverter, it is po ssible to nm the motor bidirectionally in a single-phase mode.