A life test of ultrasonic motors under different torque loads and the analysis of the characteristics of wearing surfaces

Without a coil and a gearbox, an ultrasonic motor has an important application in space engineering and so forth with advantages of light weight, small volume, less electromagnetic radiation, fast dynamic response, and high energy density. However, the obvious friction and wear between the stator and the friction material (as a part of the shaft assembly) restrict the reliability and life time of the ultrasonic motor. In this paper, a life test of ultrasonic motors is designed and carried out for 3041.7 h, and the eight motors are divided into four groups with torque loads of 0.03 Nm, 0.09 Nm, 0.16 Nm, and 0.21 Nm in the test. The evolution characteristics of the displacement frequency response and the wear on the stator contact surface under different torque loads during the wear process are analyzed. Some start-up problems occur during the early time in the life test are found and explained based on a meshing effect between the stator and the friction material, and some targeted suggestions are proposed to overcome the problems. The study can help to understand the wear failure mechanism and characteristics of ultrasonic motors.