Closed-loop control of a microfabricated actuator for dual-stage hard disk drive servo systems

This paper examines a dual-stage actuation scheme for magnetic hard disk-drives. The secondary actuator in this dual-stage design is a microfabricated, electrostatic actuator which has been used to position a disk-drive slider over a 2.5 kHz closed-loop bandwidth. Actuation tests were performed using laser-Doppler vibrometer measurements of slider displacement, and both phase-lead and proportional-derivative controllers were implemented. The experimental results verify that the device has excellent linearity, suggesting that the dual-stage control system may use an observer to estimate the actuator displacement, resulting in significantly reduced implementation complexity. To this end, a SIMO dual-stage control system which uses only position error signal (PES) measurements is presented, and compared to a MIMO control system which utilizes both the PES and measurements of the micro-actuator displacement.