Loop-shaping controller design with the RBode plot for hard disk drives

The controller for the head positioning system of a hard disk drive must have both high performance and high robustness. This paper presents a user-friendly loop-shaping design method employing the Robust Bode (RBode) plot for the head positioning system. By using the RBode plot, control engineers can easily design controllers that can suppress disturbances and account for perturbations of the controlled object with frequency response data alone. A transfer function-based nominal model is not required. As a result, the engineer can avoid the excessively conservative designs while accommodating perturbations in the plant and improve the controller performance. The design results for a benchmark hard disk drive problem show the usefulness of proposed method.