Two-Period Repetitive and Adaptive Control for Repeatable and Nonrepeatable Runout Compensation in Disk Drive Track Following

This paper presents the design and implementation of an integrated two-period repetitive and adaptive control scheme to reject both repeatable and nonrepeatable disturbances in the track-following servo control of a hard disk drive read-write head. A baseline linear quadratic Gaussian controller is augmented by a plug-in repetitive controller to reject periodic disturbances with two periods, one that is synchronized with the disk rotation and the other that is not, and an additional adaptive-Q control scheme to reject the remaining aperiodic and random disturbances. The adaptive-Q control algorithm uses the well-known result that all stabilizing controllers for a plant can be synthesized by conveniently parameterized augmentation to a nominal controller. The Q-filter is restricted to a finite impulse response filter, which minimizes the root-mean-square value of the track-following error. Experimental results show substantial performance improvement for the two-stage augmented controller over the single-stage repetitive or adaptive-Q control acting alone.