Adaptive-repetitive control of a hard disk drive

This paper presents a control scheme intended to target both the non-repeatable and repeatable runout disturbances affecting the dynamics of a hard disk drive (HDD). The design can be broken up into three stages. The first stage consists of a LTI feedback controller designed using classical techniques. The second stage consists of a RLS-based adaptively tuned controller. Finally, the last stage incorporates a new controller which integrates repetitive and adaptive elements. The repetitive part of this controller allows us to target specific periodic disturbances visible in the disturbance spectrum. The adaptive part is intended to cancel the inter-notch stochastic disturbances. The key element in this design is the formulation of an appropriate optimization problem, solvable recursively by the use of some of the available adaptive-filtering algorithms. Experimental results obtained from the implementation of this method in a commercial HDD demonstrates the effectiveness of this approach.