A Gap Capacitance Method for Head Flying Height Control in Near-Field Optical Disk Drives

• Main Authors: Jian-Wei Chen, 陳建偉
• Other Authors: Tzong-Shi Liu
• Format: Others
• Language: en_US
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/00074562205505898986

博士 === 國立交通大學 === 機械工程系所 === 93 === Conventional optical disk drives are faced with diffraction limit. To substantially increase data storage capacity and density, near-field optical disk drives remain to be realized. The slider of a flying pickup head in a near-field optical disk drive has to fly at a very low and stable height above the disk surface. To sense the slider flying height, a gap capacitance method is developed in this study to measure capacitance variation between the pickup head and disk surface. The capacitance varying with the flying height is modulated by a Colpitts oscillator. Subsequent demodulation accounts for height variation of the flying pickup head. Measurement results of this method are verified by using a laser Doppler interferometer. The interface between the slider and optical disk constitutes an air bearing. The air bearing force is affected by disk rotation speed and deformation, which represent low-frequency periodic disturbance to the slider. A repetitive control method is adopted to eliminate the periodic disturbance. H∞ control inherited with robust properties and sliding control can deal with model uncertainty and disturbances. Therefore, this study designs two controllers. One is a repetitive controller cascaded by an H∞ controller, while the other error-feedback sliding mode control. The proposed controllers are validated by simulation and experimental results.