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Track seek control for hard disk dual-stage servo systems

A new decoupled track-seeking controller for a dual-stage servo system of a magnetic disk drive has been developed. The controller is applied to the dual-stage system with a push-pull piezoelectric (PZT) micro-actuator and enables high-speed one-track seeking and short-span track seeking. A one-track seeking controller was designed in three steps: (1) a voice coil motor (VCM) feedforward controller was designed to prevent overshoot in response of VCM actuator; (2) a feedforward loop from the VCM reference signal to the PZT actuator was designed in order to decouple the dual-stage actuator system; (3) a feedforward controller for the PZT actuator was designed such that an output PES (position error signal) only follows a PES reference signal. In the design of the short-span seeking controller, the PZT actuator's stroke limit was considered. Simulations and experiments show that the proposed dual-stage track-seeking controller performs better than the conventional single VCM servo.