A Novel Discrete-Time Sliding Mode Technique and its Application to a HDD Dual-Stage Track-Seek and Track-Following Servo System

A novel approach for the design of a discrete-time sliding mode controller is presented showing that the dynamics of a sliding-mode state-feedback controller can be designed using a singular LQR approach. The weighting of the control signal is set to zero and dead-beat behaviour for the sliding mode reaching dynamics is achieved. The reaching dynamics are modified when the states are a significant distance away from the sliding surface to avoid any high magnitude control action due to the partial dead-beat approach. The control law also takes into account the constraints on the actuator amplitudes and a stability analysis is presented using a discrete-time version of the Popov criterion.

The control approach is demonstrated in conjunction with a recently developed large-span track-seeking and track-following method for dual-stage actuator systems in a hard disk drive (HDD). It is shown how the discrete-time sliding mode control scheme can be incorporated into the observer-based control system for the secondary actuator. Superior performance for the track-seeking and track-settling process is demonstrated using an existing practical set-up of a dual-stage HDD servo system. Copyright (C) 2007 John Wiley & Sons, Ltd