白光干涉儀高速低成本自動對焦系統

High Speed Low Cost Auto-focusing System for White Light Interferometer

陳培榮(PEI JUNG-CHEN)

指導教授 ： 章明

中原大學/工學院/機械工程研究所/碩士(2009年)

https://doi.org/10.6840/cycu200900241

摘要

白光干涉儀的量測精度可達奈米級，是目前國內半導體產業與平面顯示器產業在表面形貌顯微量測領域使用最為廣泛的設備之ㄧ，為了達到高速量測的目的，自動對焦系統的建立是相當重要的一環，但目前國內白光干涉儀生產廠商對於自動對焦領域發展進度卻無法符合快速對焦之需求，亦或國外已具有此一技術，但受其價格昂貴、對焦距離受限且設定繁雜等因素，並不符合經濟效益，因此國內目前在使用高放大倍率之物鏡時並無有效之對焦設計實際應用於白光干涉系統中，有鑑於此，本研究乃以白光干涉顯微儀快速低成本自動對焦系統之研製為導向，相較於一般顯微鏡而言，干涉顯微鏡擁有於對焦位置時更大影像亮度之特性，利用此一特性以光電二極體作為感測裝置，取其具備反應時間快、靈敏度高及容易使用之優勢，依據影像對焦時其強度為極值之現象，將影像之能量強度轉化成直覺可觀察之電壓數值，依序設計雜訊濾除、電壓放大、類比數位轉換以及8051運算控制電路，即時偵測光電二極體輸出電壓之變化，並利用本系統之焦點判斷演算及馬達控制電路模組判斷出對焦之準確位置，實驗結果顯示本系統目前之對焦速度可達2mm/sec，對焦重複度可達1μm。

關鍵字

自動對焦 ； 白光干涉

並列摘要

Autofocussing is an important part in high speed metrology. The development made in the autofocussing system till now has not met the exact requirements for industrial applications. Consequently there is no effective design for white light interferometer with high magnification.
This investigation describes about the development of a high speed low cost autofocussing system for white light interferometer. Interferometer has higher intensity in comparison to general microscope at focus position. This study uses one photodetector as a sensor for its high response time and high sensitivity to convert the light intensity to its characteristic voltage. A noise filter circuit, analog to digital converter circuit and 8051 operation circuits have been designed to detect the real time variation of photodetector output voltage. The focus position has been precisely determined by using focus determination circuit and stepper motor module. The experimental study shows the system can achieve the focus position at 2mm/sec speed with 1m repeatability.

並列關鍵字

Autofocus ； Mirau’s interferometer.

參考文獻

[1] Nayar, S. K., and Nakagawa, Y., “Shape from Focus,” Proceedings of the IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol.4, No.8, pp.824-831, 1994.

[4] Subbarao, M., and Tyan, J. K., “Selecting the Optimal Focus Measure for Autofocusing and Depth-from-Focus,” Proceedings of the IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol.20, No.8, pp.864-870, 1998.

[6] Ng Kuang Chern, N., Poo Aun Neow, and Ang, M.H., Jr., “Practical Issues in Pixel-Based Autofocusing for Machine Vision,” Proceedings of the IEEE International Conference on Robotics and Automation, Vol.3, pp.2791-2796, 2001.

[7] Horn, B. K. P., “Focusing,” Technical Report AIM-160, Massachusetts Institute of Technology, 1968.

[8] Davies, E. R., “Machine Vision: Theory, Algorithms, Practicalities,” Academic Press Limited, 1990.