A multi-rate nonlinear state estimation for hard disk drives

In this paper, we propose a new multi-rate state estimator for seeking control of hard disk drives, which has a proportional, integral, and discontinuous error feedback structure to improve robustness. Conventional state estimators do not have enough accuracy under the existence of external disturbances and model uncertainty. With the proposed estimator, the seeking control system of hard disk drives can have better robustness. Our main focus is on the discontinuous action, which alleviates the estimation error caused by, for example, actuator gain variations. Integral action is secondarily introduced not only to cancel out a quasi-constant disturbance and uncertainty, but also to reduce the chattering motion caused by the discontinuous feedback. Simulations and experiments have been carried out to validate our proposed multi-rate state estimator. Finally, an experimental example of seeking control for a single stage actuated hard disk drive is demonstrated.