H∞ repetitive control for pickup head flying height in near-field optical disk drives

The slider of a flying pickup head in a near-field optical disk drive has to fly at a stable height above the disk surface. An air bearing force between the slider and optical disk is affected by disk rotation speed and deformation, which represent low-frequency periodic disturbance to the slider. The repetitive control is adopted in this study to eliminate the periodic disturbance. H_∞ control inherited with robust properties can deal with model uncertainty and disturbances. Therefore, to solve model uncertainty and disturbance, this study designs a repetitive controller cascaded by an H_∞ controller. The proposed controller is validated by experimental results.