利用間隙電容量測於控制近場光碟機讀寫頭之飛行高度

Abstract

傳統光碟機已經面臨繞射極限的瓶頸，為了增加資料存儲容量和密度，近場光碟機的技術值得研發。在近場光碟機內，飛行讀寫頭的滑塊必須在碟片表面以極低而穩定的高度飛行。為了量測滑塊飛行高度，本研究發展出一種間隙電容的方法，以測量讀寫頭與碟片表面之間的電容變化。隨著飛行高度而變化的電容，利用振盪器作調變，解調出飛行讀寫頭的高度變化，本文使用雷射都卜勒干涉儀驗證這個方法的測量結果。在滑塊的飛行高度控制方面，本研究之滑塊設置了壓電彎片致動器，但具模型不確定性，所以發展具有強健性能的H∞ 控制以及滑動模式控制方法。空氣軸承介於滑塊與碟片之間，碟片的轉速與變形迫使空氣軸承對讀寫頭產生週期性擾動，所以採用能處理週期訊號的反覆控制方法，消除此擾動。因此，本研究設計了兩種控制器，其一為反覆控制器串接一個H∞ 控制器，其二為誤差回授的滑動模式控制，根據模擬和實驗結果，這兩種控制方法均展現了效果。

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.