Sandwich-Type Multi-Degree-of-Freedom Ultrasonic Motor with Hybrid Excitation

A sandwich-type multi-degree-of-freedom (MDOF) ultrasonic motor with hybrid excitation is proposed in this paper. The motor adopts pair combination of three resonance modes to drive the sphere rotations around three coordinate axes. When the sphere rotates around any axis, all piezoelectric ceramics of the proposed motor are excited for the vibration of the motor. The final structure parameters of the motor are confirmed by way of finite element method, and the elliptical motion trajectories of the driving areas are verified. At last, the prototype is fabricated and tested. The prototype achieves no-load speeds of 109.8 r/min, 107.9 r/min, and 290.8 r/min in the YOZ, XOZ, and XOY driving modes, respectively. The proposed motor employs only four pieces of lead zirconate titanate ceramics to achieve the MDOF rotations of a spherical rotor.