Abstract: First the definition of flexible rotor of traveling wave type rotary ultrasonic motor (TRUM) is given. It is pointed out that the flexible rotor can be classified in the range of elastic annular plate with large overall motion. And the kinematical equation of flexible rotor is derived. Then the rigid-flexible coupling dynamic model of flexible rotor is obtained by Lagrange equation. So the complete model of TRUM is derived by the integration of the contact model based on flexible rotor, stator’s semi-analytical model and flexible rotor model. The analysis examples show that the complicated contact mechanism with asymmetry occurs at the interface between the stator and flexible rotor. The analyses explain how the appropriate damp of rotor can lead to the good performance of motor. Moreover the proper flexible rotor is proved to improve the motor’s output efficiency by decrease of the friction in the radial direction at the interface. Finally the results of simulation are found to be in good agreement with those of experiments, so the proposed model provides the theoretical foundation for the design of the flexible rotor.

Key words: Flexible rotor, Rigid-flexible coupling, Sliding in the radial direction, Traveling wave type rotary ultrasonic motor