Dieter Dipl Phys Stein

New type of piezoelectric ultrasonic motor

The authors describe a newly developed motor concept which allows a bidirectional piezoelectric ultrasonic motor to be operated with only a single voltage feed and thus only one power amplifier. The motor concept is based on the superposition of a longitudinal and a flexural oscillation of a rod-shaped resonator. In a way analogous to the generation of a Lissajous figure, this superposition produces a rotary movement of the resonator end by means of which a rotor is directly driven. By selecting the relative phase of the electrical stimulations of both modes, the speed can be continuously varied in both directions. The motor can be driven in both right and left directions with speeds of 0 to 300 r/min, and a freewheeling state can be set up by means of a suitable phase between the oscillation modes. In the off state, the motor blocks the motion.<<ETX>>

Ultrasonic piezomotor with longitudinally oscillating amplitude-transforming resonator

An ultrasonic piezoelectric motor concept is presented that is based on the transformation of the longitudinal oscillations of a rod-shaped resonator into continuous motion by arranging the resonator diagonally to a drum. The efficiency of the motor was enhanced by increasing the amplitude of motion at the point of motion transfer by tapering the resonator. To optimize the resonator design, the validity of the predictions derived from the one-dimensional analytical theory for longitudinal ultrasonic resonators was tested with respect to this application by means of finite-element calculations. The one-dimensional calculation turned out to be hardly applicable at all to real resonators. The finite-element calculations showed that maximum final amplitude is attained when the resonator tapers as steeply as possible, no preference being shown for any special mathematical form of cross-sectional reduction. Efficiencies of 35% and torques of 25 N-cm were attained at 150 r/min.<<ETX>>

Novel utrasonic motors with mono- and bimodal drives

Abstract 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.