Discrete-time sliding mode with time delay for RRO compensation of hard disk drives

The paper presents a study on the problem of disturbance rejection, specifically the periodic disturbance, by applying discrete-time sliding mode control methods for hard disk drives. For perturbation such as modeling errors and external disturbances, their compensation is formulated using the designed sliding mode control. The convergence rate between the disturbance and its compensation has been shaped by an additional parameter. Computation time delay is presented to address the perturbation effects. The approach developed ensures the robustness of the sliding mode dynamics to parameter uncertainties and exogenous disturbances, and the rejection of the periodic disturbance component. Satisfactory simulation and experimental results have been achieved based on a servo system of a hard disk drive (HDD) to illustrate the validity of the controller for repeatable run-out (RRO) compensation.