1Institute of Dynamics and Vibration Research (IDS), Leibniz University Hannover, Hannover, Germany
Ultrasonic motors are characterized by high force or torque at low velocities or rotational speed, respectively. Most of these motors are based on a two-stage energy conversion. In a first step, electrical energy is transformed into high frequency mechanical vibrations by piezoelectric elements. In the second step friction processes in the interface between the vibrating element and a second body generate the driving force of the motor. A huge number of different designs of ultrasonic motors has been developed over the past decades, but there still is a huge potential for future developments. It is the aim of the present contribution to give a survey on the field of piezoelectric ultrasonic motors, including a brief desription of their historical development and an outline of current research trends and future perspectives of this interesting drive technology.
The different types of ultrasonic motors are classified according to their geometry and vibration modes. For each class the most important advantages and disadvantages will be discussed, and finally a comparison of typical motor characteristics of the different designs will be given. Mechanical models for the different motor types will be presented and the identification of motor parameters based on theoretical and experimental methods will be discussed. Practical considerations, like e.g. the proper choice of materials, control topologies and degradation of motor performance over service life will also be adressed.
Theoretical performance limits of piezoelectric ultrasonic motors will be presented and compared to practically achieved motor performances. The most important motor types are presented and compared based on the demands in various practical applications.
Piezoelectric ultrasonic motors have achieved exceptional performances. Many prototypes have been presented and characterized experimentally. Despite this very advanced state of the art, practical applications of piezoelectric ultrasonic motors are still limited to some niche applications. Further research is requred to exploit their full potential.