Sliding mode control of a disk drive actuator for positioning a

Abstract

A sliding mode controller is disclosed for controlling the motion of a read/write head actuated by a voice coil motor over a rotating magnetic disk storage medium. The magnetic disk comprises a plurality of concentric data tracks recorded thereon wherein each data track comprises user data and servo data. The sliding mode controller operates by multiplying a head position error phase state and a head position error velocity phase state by respective switching gains to force the phase states to follow a predetermined phase state trajectory. The phase state trajectory can be defined by a single linear segment, a variable linear segment, multiple linear segments over the entire region of excursion, or optimum parabolic acceleration and deceleration segments. Switching logic, responsive to the phase states and a trajectory segment value .sigma., switches between positive and negative feedback gains to drive the phase states toward a current trajectory segment. A .sigma. processing block monitors the phase states to determine when to switch from a current trajectory segment to the next trajectory segment. The resulting servo control system is relatively inexpensive to implement in either software or hardware, and it is substantially insensitive to parametric changes and external load disturbances. Further, it does not require notch filters commonly used in conventional linear controllers to compensate for mechanical resonances.