Optimization of Head-Positioning Control in a Hard Disk Drive Using the RBode Plot

We have developed a user-friendly loop-shaping method employing the Robust Bode (RBode) plot for optimizing the head-positioning system in a hard disk drive (HDD). The RBode plot represents the robust performance criterion as allowable and forbidden regions on the open-loop Bode plot. Using the RBode plot, control engineers can easily design controllers that suppress disturbances and account for perturbations of the controlled object with frequency response data alone. There is no need to construct the transfer function models of the controlled object and of the disturbance. Experimental results for a track-following control in an HDD show the utility of the method.