Creep Effect Analysis at the Friction Interface of a Rotary Ultrasonic Motor

Theoretical and experimental studies for the creep mechanism at the friction interface between rotor and stator of traveling wave type rotary ultrasonic motors (TRUM) are performed in this work. A modeling method is developed to investigate the creep and the distributed contact pressure in the friction interface for the piezoelectric composite stator with complex geometries. The annular laminated structure of the stator is discretized into a semi-analytical plate element in the radial direction, and the teeth on top of the stator are modeled by the finite element (FE) method. Then a coupled approach for the continuous plate and FE discretized teeth is proposed to investigate the interface contact mechanism. Finally, the accelerated aging tests for TRUM are conducted to study the creep effect in the friction layer during the long-term storage, the startup state is investigated experimentally by the transient characteristics measurement system. It is shown that transient characteristics of TRUM are strongly affected by the creep effect at the friction interface. The vibration response of the stator is weakened by the creep of the contact layer, and the amplitude of the piezoelectric composite plate decreases with increasing creep percentage. It is theoretically and experimentally proved that the creep percentage of over 20% can lead to the startup failure of TRUM.