A Nonlinear Control Scheme Applied to Track-Seeking in Hard Disk Drive Dual Stage Servo System

A nonlinear control scheme applied to track-seeking in hard disk dual stage servo system is presented. A reference input-shaping generator is designed to produce a smooth approximation of step signal so as to reduce the variation of tracking error. As the plant is a DISO (dual-input single-output) system, two seperate reference signals are used for the VCM controller and the MA controller. The VCM controller is designed as a nonlinear one to compensate for the usual tradeoff between reponse speed and overshoot in the step response of linear system and the MA control loop is a simple bandpass filter to attenuate the effect of the MA high frequency resonance and compensate for the small tracking error caused by the VCM loop. A switch is used in the MA loop to make it work only when error is in the range of ±1μm due to MA stroke limitation. Simulation is given in the end.