NOVEL ULTRASONIC MOTORS WITH MONOMODAL AND BIMODAL DRIVES

Piezomotors use the piezoelectrically excited natural mechanical oscillations of resonators to drive a rotor. The monomodal motors presented here are based on a purely longitudinally oscillating rod which is positioned asymmetrically on a roller-shaped rotor. Lateral displacement of the resonator tip resulting from the hard impact drives the rotor. With a newly optimized longitudinal resonator, these unidirectional motors have efficiencies of greater than 35% at rotational speeds of around 150 rpm. These monomodal motors form the basis for a new bimodal motor which operates simultaneously with a longitudinal and a flexural mode. The rotational motion of the resonator tip, resulting from the superposition of these modes, is used to drive the rotor directly. With this concept, it has been possible for the first time to realize a reversible piezomotor requiring only one electrical power amplifier. © 1990.