運用自混干涉訊號之滑動模式基礎模糊控制於光學讀寫頭定位

Abstract

近場光碟機以近場光學原理突破了光學繞射極限，縮小了讀寫雷射光點，使得光儲存密度得以大幅提升。近場光碟機需藉由滑動片承載物鏡與固態浸潤透鏡，於碟片上方約50 nm處維持穩定飛行。由於滑動片飛行高度極為貼近碟片，附著於碟片上的粉塵粒子，對讀寫頭讀寫時的影響值得重視。為了運用於近場光碟機，且不需外加機構下，故本研究提議採用碟片旋轉時產生之氣流，以達到除塵或防塵的目的。本研究利用流場模擬軟體做分析研究，可協助解決動態讀寫時粉塵的干擾，使讀寫訊號更穩定。本研究設計有乳頭形與階梯形兩種不同形式的固態浸潤透鏡，藉由直接模擬蒙地卡羅法(DSMC)來模擬此奈米流場，分析讀寫頭在50 nm飛行高度下進行讀寫時，粉塵的動態分布情況，從而決定最佳的幾何設計。 此外，本論文改裝多功能數位碟片(DVD)讀寫頭作為致動器包含雷射頭用於感測。微調讀寫頭致動器中傾斜線圈致使雷射頭的傾斜用來補償待測物表面與雷射面之間的失焦；實驗結果表示傾斜線圈補償待測物表面與雷射面之間的失焦用來獲得有效的自混訊號。利用雷射頭之自混訊號效應呈現電壓與待測表面位移的一致性；自混訊號線性區之解析度為100 mV/nm。本研究另提出以滑動模式為基礎的模糊控制用於驅動讀寫頭中對焦線圈來達到快速的響應；模擬與實驗兩者結果皆表示本研究提出的方法相較於滑動模式控制佳。

Making use of near-field optics, optical disk drives can overcome the limit of diffraction and reduce laser light spot sizes. The data storage density of the optical disk can be thus increased. A slider on the pickup head of a near-field optical disk drive has to carry both objective lens and solid immersion lens (SIL). The slider maintains flying height about 50 nm above the disk surface. This height is smaller than the mean free path of molecules. Hence, the gas rarefied effect should be taken into account during data reading and writing. In addition, dust particles in disk drives may influence flying stability when pickup heads are reading/writing data. This study presents approaches to cleaning dust that sticks on the SIL of the pickup head. Dealing with the near-field optical disk drive, this study proposes to employ airflow for dust removal at the head-disk interface. Moreover, this study designs two kinds of SILs, i.e. a navel type and a stairway type, and analyzes the pressure distribution on the pickup head. A direct simulation Monte Carlo method is adopted to compute the nano-flow field. As a consequence, the pressure in simulation results by using the proposed stairway SIL design demonstrates dust removal capability. Furthermore, this study has modified a digital versatile disk (DVD) pickup head as an optical pickup head actuator with a laser diode package for sensing. Tuning a tilting coil in the optical pickup head actuator causes the tilt of a laser diode to compensate misalignment between a target surface and the laser diode facet. Experimental results show that tuning the tilting coil compensates misalignment between both surfaces to achieve effective self-mixing signal. In addition, this study presents the conformity between the output voltage and the target surface displacement from a laser diode package using the self-mixing effect. The resolution in linear region of self-mixing signal is 100 mV/nm. This study presents a sliding mode based fuzzy control method to achieve fast response of an optical pickup head actuator, which is driven in focusing direction. Both simulation and experimental results show the proposed method performs better than sliding mode control.