A ROTARY LINEAR MOTOR DRIVEN BY A PAIR OF 2-DIMENSIONAL ULTRASONIC ACTUATORS

There is a need to draw various patterns on the inner wall of a small pipe several millimeters in diameter to develop a precise linear scale . Since the authors have already developed a two-dimensional ultrasoni c actuator that can move an object is two orthogonal directions indepe ndently, they now offer a rotary linear motor, in which the motor shaf t is driven by a pair of two-dimensional ultrasonic actuators. Hence, the motor can rotate and move directly, simultaneously, or independent ly. Good positioning accuracy was obtained for simultaneous two direct ional drive by controlling the motor with a proportional control: the steady errors were: 1.41 degrees and 0.73 mm in the rotary and linear directions, respectively. However, the positioning accuracy greatly de creased for one-directional drive: the steady errors were 27.5 degrees for rotational motion and 20.3 mm for linear motion. To improve these poor positioning accuracies for the one-directional drive, RC series circuits were connected parallel to the piezoelectric devices of a two -dimensional ultrasonic actuator in order to reduce the interference d ue to the self-EMF induced by the ultrasonic vibration of one pair of piezoelectric devices on another pair. In addition, proportional contr ol was replaced with proportional and integral control. As the result, the positioning accuracy for one-directional drive has been greatly i mproved, to 0.05 degrees for rotational motion only and 0.006 mm for l inear motion only (C) 1998 Scripta Technica.