Abstract: Single-phase driven ultrasonic motors have attracted more and more attention due to their advantages of simple driving circuit, flexible design, and compact structure. However, the existing single-phase driven ultrasonic motors are mainly linear motors, and their operating mode is generally a degenerate mode, holding the disadvantages of low energy utilization ratio and easy frequency drift. The rotating ultrasonic motors with single-phase excitation present some problems, such as poor output performance and difficult clamping, restricting their applications. In order to solve the aforementioned problems, a novel rotating ultrasonic motor with single-phase excitation is proposed, and its rotor is driven by friction. The stator of the proposed ultrasonic motor is mainly composed of a piezoelectric composite beam and a ring with driving tooth, and the two operating modes are generated under the alternating excitation of two groups PZT plates, respectively. Therefore, the two-directional rotating motions of the motor are realized by switching the two operating modes. At first, the finite element method is used to calculate the geometric dimensions of the ultrasonic motor stator and two operating modes (including resonance frequency and vibration shapes). Additionally, the vibration characteristics of the stator prototype are tested by the vibration measurement experiments, and the amplitude frequency characteristics, the vibration shapes, and the motion trajectory of the driving teeth of the stator are obtained and compared with the simulation results, verifying the correctness of the simulation analysis. Finally, the prototype of the rotating ultrasonic motor is assembled, and its output performance evaluation are carried out. The experimental results show that the maximum speeds of the motor prototype in the two operating modes are 123.9 r/min (clockwise rotation) and 450.9 r/min (anticlockwise rotation), respectively, and the maximum torques are 1.058 mN·m and 2.534 mN·m, respectively, under the excitation conditions of the voltage of 300 V voltage and the pre-pressure of 1 N. The results of finite element analysis and experimental studies have verified the feasibility of the structure design of the proposed motor and the correctness of its operating principle, and the studies provide a new idea for the subsequent design of the same type of ultrasonic motors.

Key words: ultrasonic motor, single phase excitation, standing wave, simulation analysis, dynamic characteristics