Stability Analysis of an Ultrasonic Motor for a New Wave Amplitude Control

Using piezo electric actuators can reduce bulk size of servomechanisms; they are thus very interesting in avionics applications. But mechanical overload on shaft of a Traveling Wave Ultrasonic Motor often results in a sudden stop and stalling of the motor. To avoid this drawback, one can increase the supply voltage or add a control loop in the rotating reference frame of the traveling wave. The consequences are extra power losses or lower dynamic performances. The proposed method takes advantage of classical control and in a rotating frame one : stability and dynamic performances are obtained at low supply voltage level. Experimental runs are presented.