Ultrasonic motors for linear positioning tasks in automobiles

Piezoelectric ultrasonic motors are a new kind of actuators that produce high driving-forces related to their volume. Beside rotary drives like the travelling wave motor many linear drives have been developed and are already commercially available today. These motors can provide static holding-forces and driving-forces of up to 30 N at velocities of up to 220 mm/s. These operational characteristics, which are expected to be improved continuously, make these devices attractive as direct-drives for sliding roofs or windows in automobiles. In this contribution a short outline of the present state-of-the-art of linear ultrasonic motors is given. Different operating principles are compared with respect to the potential driving-force and power. Finally the working-principle of a newly developed motor, which uses the piezoelectric d33-effect, is explained in detail. Theoretical and experimental results show that this motor is capable of achieving high driving-force and rated output-power