Time Optimal Based DSMC with Time-varying Surface and Its Application to Hard Disk Drives

A time optimal based discrete-rime sliding mode control (DSMC) approach is developed in this paper. In this approach, a proximate time optimal switching curve is adopted for the time varying sliding mode design and a controller, consisting of an equivalent part and a discontinuous one, is designed such that the trajectory from any initial point is driven into a sliding region in the vicinity of the switching surface without chartering and thereafter remains inside it. By using the time-varying switching surface, one unified framework for both track seeking and track following control in hard disk drives (HDDs) is provided and the smooth transition from seeking control to track following control is achieved. In addition, a time-varying sliding region is also used instead of rime-invariant one to eliminate the chattering and overshoot and improve the tracking performance. Simulation studies in HDDs demonstrate that the proposed control scheme provides better performance during track seeking than the commonly used discrete-time proximate time-optimal servomechanism (PTOS) and sliding mode proximate time optimal servomechanism (SMPTOS). Moreover, the unified controller achieves better disturbance rejection in track-following than the SMPTOS control.