THEORETICAL AND EXPERIMENTAL STUDIES OF A PIEZOELECTRIC ULTRASONIC LINEAR MOTOR WITH RESPECT TO DAMPING AND NONLINEAR MATERIAL BEHAVIOR

In piezoelectric ultrasonic motors, high-frequency mechanical oscillat ions are used to create frictional driving forces. The surface points of the cuboid-shaped ultrasonic oscillator presented perform an ellipt ical motion which is obtained by the superposition of longitudinal and bending vibrations. Both vibration modes can be obtained as solutions of the wave equation and the Timoshenko-Bresse beam equation, respect ively, if linear piezoelectric constitutive equations are assumed. Dam ping and nonlinear material behaviour, which can be observed experimen tally, must be taken into account. For this purpose, generalised const itutive equations for piezoceramics were investigated and identified e xperimentally for SONOX P88 ceramics. The effects of damping and nonli near material behaviour were introduced in the modelling of the oscill ator. The results of the analytical calculation allow an accurate defi nition of the geometry of the oscillator, so that the two vibration mo des have the same resonance frequency. Thus, good controllability of t he motor can be obtained. A prototype motor was designed and investiga ted experimentally. We discuss the material modelling as well as some other important design aspects of this type of motor (e.g. the design of the support, force flow at the stator/rotor interface, and toleranc es). (C) 1998 Elsevier Science B.V.