Application of a discrete sliding mode technique to a HDD dual-stage track-seek and track-following servo system

This paper describes the application of a discrete-time sliding mode controller to a dual-stage actuator system in a hard disk drive. It is shown how the sliding mode control scheme can be incorporated into the observer based control system for the secondary actuator. Improved performance for the track-seeking and track-settling process is demonstrated. The dynamics of the discrete-time sliding-mode state-feedback controller are designed using a singular LQR-approach so that dead-beat behaviour for the sliding mode reaching dynamics is achieved in close proximity to the ideal sliding surface. The reaching dynamics are modified when the states are a significant distance away from the sliding surface to avoid any high magnitude control action. The control law also takes into account constraints on the actuator amplitudes. The design approach for this controller is novel in its own right.