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

Using piezoelectric actuators can reduce the bulk size of servomechanisms; they are thus very useful in avionics applications. However, mechanical overload on the shaft of a traveling-wave ultrasonic motor often results in the motor suddenly stalling. 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 combines the advantages of classical controls and controls in a rotating frame: Both stability and dynamic performances are obtained at low supply-voltage levels. Experimental runs are presented.