Micropositioning device for disk head testing system

Abstract

A micropositioner has a coarse positioner and a fine positioner, with a separate closed loop control circuit for the fine positioner. A disk head being positioned over a disk is attached to the stage of the fine positioner. The fine positioner includes a parallelogram flexure having first and second opposite sides attached respectively to the coarse positioning stage and the fine positioning stage. A piezoelectric translator translates the second side of the flexure relative to the coarse positioning stage. In order to sense displacement of the fine positioning stage relative to the coarse positioning stage, a differential electric field sensor is employed. The sensor includes a pair of side plates both mounted fixedly relative to one of the stages and opposing each other to create an electrical field between them, and a probe plate mounted fixedly relative to the other of the two stages and between the two side plates. As the second stage moves relative to the first, the voltage sensed by the probe plate is fed back to control the piezoelectric translator until the probe voltage indicates that the fine displacement amount matches a desired fine displacement amount indicated by a command signal. In an embodiment, the fine positioner feedback loop controls the voltages applied to the side plates such that the voltage sensed by the probe plate is zero whenever the fine positioner is at equilibrium.