NDLI: Automatic optical path alignment for a vertical scanning interference profiler

Content Provider	IEEE Xplore Digital Library
Author	Chwan-Hsen Chen
Copyright Year	2005
Description	Author affiliation: Dept. of Mech. Eng., Yuan-Ze Inst. of Technol., Chung-li, Taiwan (Chwan-Hsen Chen)
Abstract	The white-light vertical scanning interferometry (WLVSI) profiler can measure the three-dimensional profile of a minute object with great accuracy. The working principle of the WLVSI is to use the interference patterns measured with a CCD sensor at different objective distance to derive the specimen profile. However, due to the short coherence length nature of the WLVSl profiler, the focusing and leveling operations to bring the specimen surface within the coherence range are very time-consuming. Furthermore, these operations are coupled, for the adjustment of the surface orientation could change the focus condition. An operator has to iterate between focusing and leveling in order to generate a clear image with broad interference stripes. This paper describes an automatic optical path alignment method to focus the image and align the orientation of a specimen surface to perpendicular to the optical axis. Our method first finds the focus point for a specimen by a global search algorithm to establish a starting point. Then, based on a subsequent scanning at several different heights, a rough surface profile is obtained by the depth from focus approach. From this profile, we can fit a plane model to find the major orientation of the specimen. From the surface normal vector, we derive the necessary equations to calculate the rotation angles to restore an oblique surface to perpendicular to the optical axis. After the adjustment, the specimen is refocused again. This implemented automatic alignment system can complete the operations in a few runs.
Sponsorship	IEEE Ind. Electron. Soc. (IES) Chinese Inst. of Autom. Eng. (CIAE) Nat. Sci. Council, Taiwan, R.O.C. Minist. of Educ., Taiwan, R.O.C
Starting Page	602
Ending Page	605
File Size	618553
Page Count	4
File Format	PDF
ISBN	0780389980
DOI	10.1109/ICMECH.2005.1529327
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2005-07-10
Publisher Place	Taiwan
Access Restriction	Subscribed
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Interference Focusing Optical interferometry Optical sensors Rough surfaces Surface roughness Surface fitting Coherence Charge coupled devices Image generation
Content Type	Text
Resource Type	Article

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