Ultrasonic Motor Using Longitudinal-Torsional Hybrid Vibration

Abstract

The ultrasonic motor using a longitudinal-torsional (L-T) hybrid vibration (LTUM) is a significant type of ultrasonic motor. The longitudinal and torsional vibrations are combined to generate the elliptic motions of points on a driving surface. The rotor is driven by the friction force between the stator and rotor. The tangential and axial direction vibrations of the point on the driving surface of LTUM can be excited by longitudinal and torsional piezoelectric pieces, respectively. In this way, the load characteristics of the motor can be controlled independently by changing two input voltages. One controls the rotary speed of the rotor, and the other controls the friction which transmits the driving force. While the motor operates, the contact area between the stator and rotor covers the whole end surface of the stator, which allows the motor to yield greater output torque. In general review, LTUMs can be divided into two main types: the first is a multi-mode type, which has the longitudinal and torsional vibrators in the stator. The second one is a mode conversion type, in which only one longitudinal vibration mode is involved, and the torsional vibration can be induced by the longitudinal vibration. LTUM can be applied to robots, saloon cars, household appliances, pinpoint devices, spacecrafts, and especially, where large torque at low speed is needed. Based on the research on LTUM in PDLab, this section expounds the movement mechanism, structural design and dynamic analysis of several LTUMs.