Discrete sliding mode control for pickup head flying height

This study aims to stabilize the fly height of the pickup head in near-field optical disk drives. The bit density on a data track, and hence the storage capacity of a disk drive can be increased by reducing the head-to-disk spacing, i.e. flying height. The reduction in fly height has recently accelerated and is approaching near-contact conditions. Consequently, the design and control is directed to achieve a relatively constant fly height over the disk. In this study, a piezoelectric bender is used as a fine actuator of the pickup head. Due to hysteresis of the piezoelectric material, a discrete sliding mode controller inherited with robust properties is developed to deal with model uncertainty and external disturbances, so as to maintain a stable flying height. The proposed discrete sliding mode controller is insensitive to matched disturbances and parameter variation, so as to maintain a stable flying height for focusing.