Southwest Research Institute® (SwRI®) News

SwRI optical system yields precise 3-D scans of very large, small surfaces

San Antonio, Texas --  July 9, 2002 -- Engineers at Southwest Research Institute® (SwRI®) have developed an innovative optical technique for generating three-dimensional (3-D) images and for precisely measuring the surface features of objects as small as a coin or as large as an aircraft wing.

The patent-pending technique, called Dynamic Structured Light (DSL), was developed with internal funding. It offers many advantages over previous 3-D measurement techniques, said Dr. Ernest A. Franke, an Institute engineer in the Manufacturing Systems Department of SwRI’s Automation and Data Systems Division.

"Compared to previous methods, DSL 3-D imaging provides lower cost, higher accuracy, greater depth of field and greater stand-off distance," Franke said.

A rotating grid pattern is projected onto the object being measured, and the changing patterns of light and dark across the object’s surface are recorded with a machine vision camera. Video images of the changing patterns are then analyzed using SwRI-developed software to determine surface elevation at any location on the object without touching it.

The DSL system uses relatively low-cost, off-the-shelf cameras and computer hardware. The proprietary image processing software and computational algorithms compensate for optical distortion and provide high-accuracy measurements. Using DSL, objects of approximately 2 inches square have been measured with an accuracy of 0.004 inch. The method can be used for dimensional inspection of manufactured parts, for assessment of surface damage, or for reverse engineering applications.

The DSL system is scalable, producing accurate surface measurement over a wide range of sizes by changing camera and projector lenses and varying the stand-off distance.

When used at a distance, similar to that of a movie projector, the DSL system can produce surface measurements of large panels measuring five to 10 feet. In this configuration, DSL has been used to precisely map the depth of dents in aircraft control surfaces.

SwRI researchers plan to use DSL for future applications involving 3-D measurement of microscopic structures, such as micro-electromechanical systems (MEMS).

For more information on DSL applications, contact Dr. Ernest Franke at (210) 522-3678 or by e-mail, efranke@swri.org

Editors: A downloadable image of the process at work is available at http://www.swri.org/press/ship.htm and can be used to illustrate this release.

 For more information contact, Joe Fohn, Communications, (210) 522-4630, Fax: (210) 522-3547, PO Drawer 28510, San Antonio, Texas 78228-0510.

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