Precision positioning with a rotary-linear motor driven by a pair of 2-D ultrasonic actuators

A new rotary-linear motor is proposed, the spindle of which is driven by a pair of two-dimensional ultrasonic actuators in the axial and rotational directions. A preliminary experiment applying a position feedback control system to a prototype of the motor revealed that a selfinduced voltage of a piezostack reduced the positioning accuracy. An improved control system with a PI controller and an additional RC circuit which compensates the self-induced voltage of a piezostack was proposed and built up. Consequently, step responses with a steady error of 0.007 mm in the axial direction and that of 0.05 degree in rotational direction were achieved.