Finite element analysis of a non-contact rotary ultrasonic motor

In this paper, levitation characteristics of a noncontact rotary ultrasonic motor are analyzed by the finite element method, with the COMSOL MULTIPHYSICS software. The motor consists of a bowel-shaped stator and semispherical rotor, and the rotor is levitated by acoustic field in the air gap between the stator and rotor, generated by a traveling wave vibration of the stator. It has no mechanical bearing and provides a full-noncontact rotary drive. After verifying the effectiveness of the calculation method by experimental results, dependence of the levitation force and stiffness on design parameters are theoretically investigated. The design parameters include the radius of the stator´s radiation surface, shape of the rotor. The acoustic radiation pressure on the rotor´s surface is uneven. The levitation force and stiffness are very sensitive to the radius of the stator´s radiation surface and the rotor´s shape.