近場光碟機內空氣軸承動力學之研究

Abstract

利用近場光學，為了資料儲存的需求，碟片的溝槽深度與讀寫頭的飛行高度相當。為了使飛行讀寫頭在近場光碟機上穩定的飛行，在碟片溝槽部分對於氣壓的影響是不可忽略的。凡得瓦爾力和靜電力對於飛行動態的影響，也因為飛行高度的下降而變成顯著。本文旨在研究近場光碟機空氣軸承的動力學，比較當讀寫頭的滑動片飛行於近場光碟片與飛行於傳統碟片上方時，流場現象的差異。利用都卜勒雷射干涉儀量測各種近場光學讀寫頭設計的飛行結果，顯示不同的設計導致不同的飛行高度和飛行高度變化。本文利用由實驗量到的碟片振動做為動態模型的碟片變形訊號，探討在近場光學的飛行距離下，凡得瓦爾力和靜電力對於飛行動態的影響，並與實驗比較之。 計算結果顯示，當飛行在近場光碟片上方比傳統硬碟片上方，滑動片底面所受的壓力較小，因為碟片的溝槽可以調節氣體分子數目的密度與氣體壓力的大小。較高的飛行高度會使近場光碟片上與傳統碟片的滑動片負壓區壓力大小愈接近。接著探討近場光碟片的溝槽深度與記錄軌軌距變化，對於近場飛行讀寫頭之影響，由結果得知在±10奈米的溝槽深度或±10%的記錄軌距變化時，對於讀寫頭與碟片間的壓力變化影響不顯著，因此可以忽略。然後探討了近場光學飛行讀寫頭在不同流速與不同飛行高度下之升力變化情形。 最後量測在固定碟片轉速下時，不同徑向位置的飛行讀寫頭在碟片上之飛行高度變化；利用不同的讀寫頭底面設計，量測靜止起飛情形，得到有最低飛行高度之設計，並利用具有最低飛行高度之讀寫頭設計做變轉速度之靜止起飛實驗。

The groove depth is comparable to the flying height in near-field optical disk drives. To achieve stable flying of pickup heads in near-field optical disk drives, the influence of disk grooves on the airflow of an air bearing deserves investigation. The van der Waals force and electrostatic force affect the slider flying height when the flying height is close to the disk. This study aims to investigate air bearing dynamics in near-field disk drives. This study compares air bearing airflows between the near-field optical disk with grooved surface and optical disks without grooved surface. The flying heights of different near-field optical slider surface topology are measures by a laser Doppler vibrometer. Experimental results show that different slider designs lead to different flying heights and height variations. Disk vibrations are measured and employed in the slider dynamic analysis. The van der Waals force and electrostatic force are computed in the slider dynamic analysis. Computational results of the slider vibration amplitude are compared with experimental results. Computational results show that grooved disks generate smaller pressure than smooth disks since grooves can accommodate air molecules and hence tune air pressure. Further, in negative pressure regions on sliders flying higher makes pressure magnitudes closer between grooved disks and smooth disks. Effects of the groove depth change and track pitch variation are employed in air bearing analysis. Computational results show that the pressure change is inconspicuous when the groove depth change is within ±10nm or track pitch variation is within 10 percentage. Hence, the effects of groove depth change within ±10nm and the 10 percentage track pitch variation are negligible. Finally, the influence of the flow speed variation and slider flying height variation is investigated. In experiments, slider flying heights at different radial position on near-field disk are measured when the disk speed maintains constant. A contact-start procedure is used in the slider flying measurement.