Modal separation of circular cylindrical ridge wave ultrasonic motors

This paper proposes a strategy to improve the performance of ridge wave ultrasonic motors (RW-USM) in their infancy. In general, USMs are operated in the vicinity of a resonant frequency of a specific vibration mode, which must be well separated from the resonant frequencies of other modes. In the current prototype, unexpected disturbance occurred at the instant of switching on/off or changing the direction of the motor, both in simulations and through actual experimental observation. The simulated results indicated that good modal separation could be achieved if the height of the upper base beneath the piezoelectric tube was selected correctly. The experimental results show that the transient response in the revolution speed is quicker and more stable in this new design. The maximum output torque was increased by 8% when the unexpected modes were separated from excitation of the RW-USM.