DVD探頭自動聚焦位移回饋系統之研製

Abstract

在本研究中，主要是以DVD光學讀取頭為基礎，並利用到光碟機聚焦控制的原理。因而，當待測物其反射面不在讀取頭前端聚焦透鏡之聚焦平面時，經由光感測器得到之失焦訊號(FES)，經過DSP處理之後，將帶動透鏡回到聚焦平面，完成了自動聚焦控制。 同時，也應用了一個新的量測概念，即是將音圈馬達視為一位移之感測器。在相同的驅動條件之下，並聯另外一個自DVD讀取頭取出之音圈馬達（本文稱之為第二組音圈馬達），並以麥克生干涉儀來進行其位移之量測。經由後續之電子電路處理，並以程式完成干涉條紋之計數及細分割的動作，最終將可得到第二組音圈馬達的實際位移。由於兩組近似相同之音圈馬達，受到同樣的驅動條件。因此經由一對一轉換關係，將可得到實際待測物之位移或其表面輪廓。利用此種間接量測的方式，主要可避免因電壓與位移之間換算的過程，磁滯現象所可能導致的誤差，進而完成一套高精度之DVD自動聚焦探頭位移回饋系統。

In this research, a DVD probe system by means of auto-focusing control principle was developed. In this system, the distance between objective lens and workpiece is not exactly at the focal distance;therefore the focus error signal(FES) from photodiode will actuate the voice coil motor(VCM) to keep the lens to be within the focal distance. Furthermore, in order to avoid the hysteresis error of VCM in the DVD-pickup head, the second VCM was applied and connected in parallel with the first VCM. The second VCM was regarded as a displacement sensor observed by the Michelson interferometer. According to Ohm’s law, these two VCMs are driven by the equivalent current which ensures the VCMs to move synchronously. Thus, the displacement of the second VCM can be obtained by counting the fringes of interference. Finally, the displacement or surface profile of the workpiece can be obtained and also achieve a higher resolution of contour measurement.