Modal separation of circular cylindrical wedge wave ultrasonic motors

This paper presents an effort to improve the performance of wedge-wave ultrasonic motors (WW-USM) driven by circumferentially traveling flexural waves. In general, USM is operated in the vicinity of the resonant frequency of a specific vibration mode, which needs to be well separated from the resonant frequencies of other modes. In the current prototype, unexpected disturbance induced at the instant of switching on/off or changing direction of the motor were found through both simulation and measurement. The fluctuations are attributed to the vibration modes other than driving mode occurring around the operating frequency. The simulated results indicate the excellent modal separation has been achieved if the upper base height under the piezoelectric tube was appropriately selected. The experimental results show that the transient response of revolution speed is quicker and more stable in new design. The rotary torque becomes twice when the unexpected modes are suppressed from excitation of the WW-USM.