An approach to dual-stage servo design in computer disk drives

A novel design strategy is presented for a dual-stage actuator servo system in magnetic disk drives. Based on the existing decoupled-design strategy, we adopt the idea of the well-known zero-phase error tracking controller to minimize destructive effect resulting when two control loops are combined. Since the zero-phase tracking control requires previews of signals in a feedback loop, a kind of estimation scheme is suggested based on the actuators' dynamic model. The best practical advantage is that we achieve systematically a low-order DSA controller capable of high-accuracy track following as well as of high-speed short-span track seek; besides, the existing single-stage controller is fully utilized. The performance of the proposed method is analyzed and demonstrated through simulation and experiment.