Modelling and testing of a piezoelectric ultrasonic micro-motor suitable for in vivo micro-robotic applications

A piezoelectric ultrasonic resonant micro-motor is developed with a stator diameter of 241 mu m and an overall diameter of 400 mu m. The motor is shown to produce a start-up torque of 1.2 nN m and a peak output power of 0.25 mu W as designed, with a preload of 46.6 mu N. An increase in preload to 2264 mu N improved the performance to a start-up torque of 29 nN m and a peak output power of 9.1 mu W. The motor is five times smaller than the current smallest piezoelectric ultrasonic resonant motor produced by Kanda et al. The motor is designed to operate at approximately 771 kHz, matching the fundamental axial, second harmonic torsional and electro-mechanical resonant frequencies. This is achieved through the use of a novel design process that uses scaling theories to greatly reduce the computational time to design the device. The resultant size and performance of the motor make it the first motor design capable of meeting the requirements of a drive system in a tetherless swimming in vivo micro-robot.