Indirect position control of a piezoelectric motor

Piezoelectric motors are particular motors converting electrical energy into mechanical movement, based on the inverse piezoelectric effect. Piezoelectric material, when electrical field applied, produces acoustic or ultrasonic vibrations. These vibrations can be used to create a linear or rotary motion. The piezoelectric material has to be excited at its resonance frequency to actuate the rotor. In a first step of this master project, a new rotor for a standing wave ultrasonic motor with cylindrical actuators has been designed. The geometry of the rotor is modified so that the motional admittance, seen by the stator, depends on the actual position of the rotor. Figure 1 shows the CAD drawings. Three slots are distributed periodically with an angle of 30 degrees on the circumference. This will change the local stiffness of the rotor in front of the holes and causes a periodical variation of the admittance.