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-infinity controller. The proposed controller is validated by experimental results.