Performance enhancement of multi-rate controller for hard disk drives

This paper describes a new multi-rate controller for hard disk drives, which has a modified state estimator to correct the estimated states not only at measurement instances of the position error signal but also at every control instance when updating the control input. This modification makes the control input smoother compared to the conventional multi-rate scheme. This estimator is obtained as a stochastic optimal estimator for a linear dynamic system with a 'random walk' input noise process. The effectiveness of the modified scheme is demonstrated by experiments.