A Ball-type Multi-DOF Ultrasonic Motor with Three Embedded Traveling Wave Stators

Abstract A novel spherical ultrasonic motor, composed of three built-in stators and a hollow spherical rotor, is developed and tested for the design of a compact multi-degree-of-freedom (multi-DOF) piezoelectric driven actuator. The novel pre-pressure regulating mechanism is used to adjust pre-pressure along the axial direction of the stators simultaneously and homogeneously, so as to ensure the stability of the motor output. By finite element method, the admittance circle is obtained by frequency domain analysis, which can estimate the resonance frequency and electrical parameters of the motor, and the coordinated driving trajectories of the three stators at different tilt angles are predicted by transient analysis. After the fabrication of a prototype, the admittance characteristics of piezoelectric stator are tested by LCR digital bridge measurement unit. Meanwhile, the mechanical output speed is measured. The rotational speeds of X-axis, Y-axis and Z-axis can reach 29 r/min, 17 r/min and 16 r/min respectively when the frequency matches, which verifies the feasibility and rationality of the multi-DOF movement of the motor.