Ultrasonic motors

Ultrasonic motors represent an alternative to the conventional electromagnetic motor principle. They comprise a stationary resonator, which is excited to produce mechanical oscillations in the ultrasonic frequency range, and a passive rotor. The oscillating end of the resonator drives the rotor via a friction contact. Two newly-developed operating principles for ultrasonic motors based on rod-shaped resonators will be discussed. A single-mode drive utilizes the longitudinal oscillation of a tapered rod-shaped resonator, resulting in an ultrasonic motor with a single direction of rotation. The bimodal motor uses superimposed longitudinal and flexural oscillations and can easily be electronically driven in both directions. Ultrasonic motors are distinguished by high torques at low speed, a large holding torque when switched off and the absence of a magnetic field.