Study on micro ultrasonic motor using a preload mechanism

We propose a preload mechanism to be assembled in a micro ultrasonic motor. The micro ultrasonic motor consists of a metallic stator with a volume of approximately one cubic millimeter, but its small size makes the preload mechanism difficult to be miniaturized. In this report, we build a micro ultrasonic motor with the preload mechanism using a micro coil spring. The total motor size is miniaturized to approximately 3 mm. In the prototypes, two preload mechanisms are tested: the rotor is pressed to the stator by a micro coil in axial and radial directions. We evaluate the motor performance using both preload mechanisms experimentally.