Proposal of seeking control of hard disk drives based on perfect tracking control using multirate feedforward control

In this paper, novel multirate two-degree-of-freedom controllers are proposed for digital control systems, where it is restricted that the speed of the A/D converters are slower than that of the D/A converters. The proposed feedforward controller assures the perfect tracking at M inter-sampling points. Moreover, it is shown that the structure of the proposed perfect tracking controller is very simple and clear. Next, the proposed method is extended to systems with time delay. The proposed scheme is applied to the seeking control for hard disk drive, and advantages of this approach are demonstrated by simulations and experiments.