Servo control of micro-cylindrical ultrasonic motor using single/dual mode control

Cylindrical ultrasonic motor (CUSM), is a relatively new kind of piezoelectric actuator, having different type of characteristics from that of conventional electromagnetic motors. In order to choose the most suitable control variable for speed/position control applications, this paper evaluates the dynamic and steady state performance of the CUSM drive system by using three different control variables, namely, the amplitude, the frequency and the phase difference of the excitation signals. In the single mode control, only one control variable is used while the other two are maintained constant. Among the three variables, amplitude control is found to be superior as compared to other control variables. Furthermore, to achieve quick and precise position control, the dual mode control method is proposed in which two control variables are used simultaneously while maintaining the third variable constant. Experimental test results obtained by using a 10 mm diameter and 30 mm long CUSM verify that the dual mode control is superior to the single mode control. In dual mode control, the combination of amplitude and frequency control is the best choice for position control application.