近場光碟機之數位滑動模態控制與小波分析

Abstract

近場光碟機突破傳統光學儲存技術的繞射極限，大幅增加資料的儲存容量及密度；然而由於其軌距及飛行高度已達奈米等級範圍，故讀寫頭的控制效能要求也相對提高。本研究利用壓電材料PZT來驅動讀寫頭的微調定位，由於PZT具有遲滯效應，故採用強健性的滑動模態控制來克服系統的非線性與外界干擾，使讀寫頭保持穩定的飛行高度。在實驗中設計一電容式感測器，利用讀寫頭與碟片表面間的間隙電容，經由FM系統來偵測讀寫頭的飛行高度變化。此外為了研究碟片與讀寫頭間的暫態行為，利用小波轉換在低頻域的高解析度優點，來檢測當系統受到外力碰撞時，其振動訊號在時間-頻率平面上的局部變化資訊，進而有效辨識系統承受外力碰撞後的響應特徵。

Near-field optical disk drives can overcome the diffraction limit of conventional techniques, thereby substantially increasing storage capacity and density. Since the precision of track pitches and the flying height lie within range of nanometers, it is required to enhance control performance to improve focusing speed and accuracy. In this study, a PZT bender is used as a fine actuator of the pickup head. Due to hysteresis of the PZT 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. In the experiment, a gap capacitance sensor utilizes an FM system to extract capacitance change corresponding to flying height variation. Furthermore, to investigate the transient response at the head/disk interface, wavelet transform with flexible time-frequency resolution is applied to analyze transient behavior, and identify the dynamic characteristics as the system subject to impulsive shock loading.