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Proceedings Paper

The use of holographic and diffractive optics for optimized machine vision illumination for critical dimension inspection
Author(s): Todd E. Lizotte; Orest Ohar
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Paper Abstract

Illuminators used in machine vision applications typically produce non-uniform illumination onto the targeted surface being observed, causing a variety of problems with machine vision alignment or measurement. In most circumstances the light source is broad spectrum, leading to further problems with image quality when viewed through a CCD camera. Configured with a simple light bulb and a mirrored reflector and/or frosted glass plates, these general illuminators are appropriate for only macro applications. Over the last 5 years newer illuminators have hit the market including circular or rectangular arrays of high intensity light emitting diodes. These diode arrays are used to create monochromatic flood illumination of a surface that is to be inspected. The problem with these illumination techniques is that most of the light does not illuminate the desired areas, but broadly spreads across the surface, or when integrated with diffuser elements, tend to create similar shadowing effects to the broad spectrum light sources. In many cases a user will try to increase the performance of these illuminators by adding several of these assemblies together, increasing the intensity or by moving the illumination source closer or farther from the surface being inspected. In this case these non-uniform techniques can lead to machine vision errors, where the computer machine vision may read false information, such as interpreting non-uniform lighting or shadowing effects as defects. This paper will cover a technique involving the use of holographic / diffractive hybrid optical elements that are integrated into standard and customized light sources used in the machine vision industry. The bulk of the paper will describe the function and fabrication of the holographic/diffractive optics and how they can be tailored to improve illuminator design. Further information will be provided a specific design and examples of it in operation will be disclosed.

Paper Details

Date Published: 26 February 2004
PDF: 8 pages
Proc. SPIE 5265, Two- and Three-Dimensional Vision Systems for Inspection, Control, and Metrology, (26 February 2004); doi: 10.1117/12.512000
Show Author Affiliations
Todd E. Lizotte, NanoVia, LP (United States)
Orest Ohar, NanoVia, LP (United States)

Published in SPIE Proceedings Vol. 5265:
Two- and Three-Dimensional Vision Systems for Inspection, Control, and Metrology
Bruce G. Batchelor; Heinz Hugli, Editor(s)

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