Micromachined Traveling Wave Motors: Three Dimensional Mechanical Optimization and Miniaturization Limits Evaluation

Abstract

This paper concerns a physical limits evaluation with respect to the miniaturization of traveling wave type ultrasonic motors (TWUM) down to the millimeter scale. According to present knowledge in research dedicated to centimeter scale TWUM, two different prototypes, whose external diameters are φ 5 mm and φ 2 mm, have previously been designed through numerical calculations, and fabricated using watch making technologies. An experimental characterization has been carried out in order to identify the main physical and technological limitations specific to millimeter scale traveling wave motors. The very first numerical results presented in this paper show important outcomes related to the miniaturization of TWUM. In particular, the limits of current mechanical assumptions such as those related to the two-dimensional mechanical behavior of the stator/rotor interface and also to the rotor's rigidity are clearly shown by a three dimensional finite element calculation. New design rules are thus given in order to allow the mechanical architecture of TWUM to be optimized. The corresponding results indicate that powerful torque/speed characteristics can be expected, and therefore show the adequacy of traveling wave ultrasonic motors for direct-drive actuation down to the millimeter scale.