A discrete-time composite nonlinear feedback control law is proposed in this paper for a hard disk drive (HDD) servo system. This control law is composed by combining a linear and nonlinear parts. The linear part is designed to yield a fast response, while the nonlinear part is to reduce overshoot of the closed-loop system as the system output approaches the step command input. This control law is more suitable for the track seeking mode of HDD servo though it call be used in the track following mode. In the face of actuator saturation, the designed control law improves the system specifications such as the rising time and the overshoot. Implementation results show that the proposed method out-performs the conventional proximate time-optimal servomechanism by 50% in seeking time.
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