Magnetic-head positioning control of HDDs with improved H_∞ controller by Robust Controller Bode (RCBode) plot

Abstract

In this paper, we present a robust controller design method for a magnetic-head positioning system in a hard disk drive (HDD) based on the H_∞ control theory and the Robust Controller Bode (RCBode) plot. The RCBode plot represents robust performance criteria as allowable and forbidden areas on Bode diagrams for a controller. Using the RCBode plot, we can improve an existing H_∞ controller with visualized guidelines in order to compensate for disturbances against plant perturbations. We show utilities of the proposed method by applying it to a popular benchmark problem for the HDDs. Simulation results with the HDD benchmark problem showed that the proposed method enables us to improve positioning accuracy of the magnetic-head position by about 15% without losing stability margins from the original H_∞ controller.