Study on Nonlinear Phenomenon of Traveling Wave Ultrasonic Motor Based on the Mechanism of Vibration and Electrical Properties

Greater growing demand for ultrasonic motor in aeronautics and astronautics engineering, especially the traveling wave type ultrasonic motor (ultrasonic motor), highlights its nonlinear problems. It is time to provide an appropriate explanation for the ultrasonic motor's sudden stoppage while working with load torque less than the locked torque. This paper analyzed this sudden stoppage phenomenon from vibration characteristics view and electrical properties view respectively, and found that the load torque change would increase or decrease the stator damping and stiffness simultaneously. These two important influences boost or diminish the ultrasonic motor stator's current vibration damping ratio. At the same time, bigger load distinctly decrease the impedance of the ultrasonic motor system, and further amplifying the actual resonance frequency. According to the unchanged driving frequency, sudden stoppage phenomena occurred when the practical motor resonance frequency became from low to high, until it equaled to the driving frequency. All experimental results clearly verify that the real influence factors for ultrasonic motor sudden stoppage are the increasing or decreasing of damping ratio and motor system impedance, led by the load torque changes. © 2017 Chin. Soc. for Elec. Eng.