Triple degree-of-freedom piezoelectric ultrasonic micromotor via flexural-axial coupled vibration

Abstract

Actuators remain a limiting factor in robotics, especially in microrobotics where the power density of actuators is a problem. A 3 × 3 × 8.7 mm 3-axis piezoelectric ultrasonic micromotor system is described here in an effort to help solve this problem. Formed from 4 bulk lead zirconate titanate (PZT) thickness-polarized elements placed around the periphery of a rectangular rod, the stator is designed to combine axial and flexural vibrations in a way that permits rotation of a hardened steel ball as a rotor about an arbitrary axis. A simple prototype of the micromotor was found to produce at least a rotation speed of 10.4 rad/s with 4 μN-m torque about all 3 orthogonal directions at an excita..