An actuator concept for a new type of piezoelectric motor

A new actuator concept based on shear actuation for use in piezoelectric ultrasonic motors (USM) is presented. Examples of working principles for piezoelectric ultrasonic motors working in the d(33), d(31) and d(15) mode are shown and compared to the proposed concept. The restriction to the plane electromechanical coupled problem is motivated from a consideration of the electrical field. The optimal geometries for the planar models with different mechanical boundary conditions are found using an optimization method based of a finite element analysis. It is shown that the free mechanical boundary condition is advantageous regarding the coupling coefficient. The modes dominated by plane shear waves are approximated by introducing appropiate kinematic relations for the promising actuator. The solution of the coupled equations of motion shows that elliptical surface motion can be excited, which is a crucial issue in USM.