Ultrasonic piezoceramic motor: The computation of traveling-wave velocity on the stator surface and excitation by PWM modulation with higher harmonic suppression

The article describes operating principle of traveling-wave piezoelectric ultrasonic motor. This motor makes use of the fact that when a surface traveling wave propagates along finite elastic body of the stator, the rotor is driven due to the friction between the stator and the rotor. The main part of this paper is focused on the computation of traveling-wave speed on the surface of piezoceramic transducer. Furthermore, the methods of the ultrasonic piezoceramic motors driving are presented. In detail there are described the possibilities of feeding by the nonharmonic signals, particularly by the pulse width modulation (PWM). The proportion of pulse width to the turn-off interval is selected with the stress on higher harmonic suppression. This way of ultrasonic piezoceramic drive controlling reduces reactive input power and increases efficiency. The realization of the control system by means of field programmable gate array (FPGA) and digital signal processing is introduced too.