Transient wave motion analysis for modal suppression of a circular cylindrical wedge wave ultrasonic motor

This paper describes a modal suppression method for improving the transient wave motion responses of a wedge wave ultrasonic motor (WW-USM). Typically, an ultrasonic motor operates near the resonant frequency of a specific vibration mode that must be adequately separated from the resonant frequencies of other modes. In the developed prototype, longitudinal modes accompany a transient response to the designed flexural mode, because electrodes are placed at the half-wavelength around the piezoelectric lead zirconate titanate tube (PZT tube). An uncertain disturbance can be easily induced at the instant in which the motor is switched on or off, or when the direction of the motor is changed. This study proposes a modification of the electrode arrangement for suppressing these unexpected modes. The simulation and experimental results indicated that performance improved when the electrodes were placed over the entire-wavelength around the PZT tube. When the longitudinal mode produced by exciting the WW-USM was suppressed, the transient response of the revolution speed became quicker and smoother than that obtained using the previous design. The proposed modification increased the maximal output power and efficiency of the mechanical-electrical transformation by 21%.