Optimal sliding mode control and PLPF based disturbance rejection for high pointing servo system

An optimal sliding mode control (OSMC) scheme with application to track-following control in hard disk drives (HDDs) is developed that explicitly takes into account unmatched nonrepeatable disturbance in this study. To reconstruct estimates of the system states for use in a full information sliding mode control law, the well-known Kalman filter is employed and the fulfillment of sliding condition is verified in the estimated state space. By converting the tracking problem into a regulator problem, the OSMC minimizes the expected value of the quadratic objective function composed of desired error states which always remain in the intersection of sliding hypersurfaces. Furthermore, the concept of varying width of boundary layer is also employed instead of fixed one to eliminate the chattering and improve the tracking performance as well. In addition, the proposed control scheme integrated with a phase leak peak filter (PLPF) is also investigated for further suppression of the narrow-band type non-repeatable disturbance at mid-frequency range. Simulation studies on the design of a track-following controller in HDDs are conducted to illustrate its feasibility and effectiveness. The simulation results also demonstrate that the proposed scheme provides better performance than the conventional PID control method.