Compliance control of circular traveling wave motor

Traveling wave ultrasonic motors (TWUSMs) were used as actuators for a prosthetic arm, because of their light weight, compact size, silent motion, high-speed response, and low-speed rotation. The prosthetic arm has to move in compliance with the environmental force around every joint, as in the human arm. In order to realize a compliant prosthetic arm, it is desired that the actuator have a compliant characteristic in itself, but TWUSMs have no such characteristic. The TWUSM is driven by two-phase sine-wave electric signals. Bending traveling waves which generate rotational torque on the rotor are propagated in its stator. Usually the phase difference of the driving signals is adjusted to 90 degrees to get the maximum output torque, but can be adjusted in range from 90 degrees to -90 degrees to regulate rotational torque. The authors were able to develop an adjustable compliant motion to the TWUSM using a phase difference control method of the driving signals. This controlled system acts much like a compliance adjustable spring with a minor damping characteristic.<>