Modal Analysis and Output Characteristics of an Ultrasonic Motor With a Square Prismatic Shell Stator

A rotary traveling wave ultrasonic motor having a square prismatic shell stator is proposed. The stator contacts with the rotor through an interference fit, elastically deforms slightly, and then presses against the rotor. Then, the pre-pressure is created by the initial deformation of the stator with a simple structure. The in-plane modal problem of the stator is analyzed by a numerical method as a folded beam, and the results are compared with those from finite element method (FEM) and laser doppler measurement. The third and fifth degenerate modes with repeat natural frequencies are selected as working modes, and the influence of actuating frequency and voltage on the no-load speed and stall torque is studied by multi-physics simulation for the operation of these two modes. A prototype is fabricated and the output characteristics were tested and compared with the simulated results. The 3rd working mode is found to have better performance and can reach a no-load speed of 205 rpm and maximum torque of 3.9 mN<middle dot>m when the input is 28.0 kHz and 100 V. The effect of the pre-pressure for the third working mode is discussed further.