P. Minotti et al., MICROMACHINED TRAVELING-WAVE MOTORS - 3-DIMENSIONAL MECHANICAL OPTIMIZATION AND MINIATURIZATION LIMITS EVALUATION, JPN J A P 1, 36(11), 1997, pp. 7009-7018
This paper concerns a physical limits evaluation with respect to the m
iniaturization of traveling wave type ultrasonic motors (TWUM) down to
the millimeter scale. According to present knowledge in research dedi
cated to centimeter scale TWUM, two different prototypes, whose extern
al diameters are phi 5 mm and phi 2 mm, have previously been designed
through numerical calculations, and fabricated using watch making tech
nologies. An experimental characterization has been carried out in ord
er to identify the main physical and technological limitations specifi
c 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 mechani
cal assumptions such as those related to the two-dimensional mechanica
l behavior of the stator/rotor interface and also to the rotor's rigid
ity are clearly shown by a three dimensional finite element calculatio
n. New design rules are thus given in order to allow the mechanical ar
chitecture of TWUM to be optimized. The corresponding results indicate
that powerful torque/speed characteristics can be expected, and there
fore show the adequacy of traveling wave ultrasonic motors for direct-
drive actuation down to the millimeter scale.