Design philosophy for ultrasonic motors using the bending hybrid modes

Abstract

Due to the merits of simple structure, large output force and high speed, a lot of ultrasonic motors based on the hybrid of bending modes have been presented in recent years, but the principle of selecting different bending modes has not been studied. A design philosophy for bending hybrid ultrasonic motors is proposed and studied in this work. The length-height ratio is introduced to evaluate the geometrical sizes of ultrasonic stator based on the resonance frequency, while the width-height ratio is used for the hybrid of different bending modes. Based on the mode shapes of different bending modes under the free-free and free-fixed boundary conditions, the practicable combination modes of bending modes are finally discussed and summarized including the layouts of piezoceramics and driving feet, the positions of clamping points, and the motion types of motors. The first three order bending modes are selected as test objects, some prototypes are designed and fabricated to validate the mode shapes of bending modes. With the proposed design philosophy, the combination modes of bending modes can be determined and the geometrical sizes of ultrasonic stator can be evaluated according to the practical application requirements.