Chatter reduction in sliding mode control of a disk drive actuator

Abstract

A sliding mode controller is disclosed for controlling a read/write head actuator in a magnetic disk drive storage system wherein a voice coil motor connected to the actuator operates to adjust the position of the read/write head over a selected data track recorded on a magnetic medium. The sliding mode controller comprises an improved technique for reducing chatter associated with the inherent operation of such a controller--rapid switching between gains to force the observable phase states to follow a predetermined phase state trajectory. The sliding mode controller generates a motor control command by multiplying an actuator position error and an actuator position error velocity by respective switching gains. The gains are switched according to a predetermined relationship .sigma. between the phase states and a phase state trajectory. In order to reduce the switching frequency (i.e., chatter), a boundary layer around the phase state trajectory results in hysteresis, causing the gain blocks to switch only after the phase states cross over the boundary line. Further chatter reduction is achieved by generating the motor control signal proportional to an integral of sgn(.sigma.). The cost of the sliding mode controller is reduced by implementing the phase state trajectory .sigma. as a lookup table indexed by a single phase state.