Linear quadratic optimal dual-stage servo control systems for hard disk drives

With the rapid increase in recording density in disk drives, it is predicted that a voice coil motor (VCM) actuator can not satisfy the tighter performance requirements of very high recording density disk drives of the future. A dual-stage servo-mechanism where the secondary stage is a high bandwidth micro-actuator is one promising solution. In this paper, a linear quadratic optimization based controller is designed for a dual-stage disk drive servo system. We first identify the model of the dual-stage actuator using experimental data. Then the controller is designed such that the VCM rejects the lower frequency disturbances and the micro-actuator compensates for the higher frequency ones. Simulation results for the closed loop system are presented.