Publication: Stereo vision based close-up dimensional inspection

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Title Stereo vision based close-up dimensional inspection
Authors/Editors* J. Mitchell, A. Spence, D. Capson, H. Chan, M. Goldstein
Where published* San Jose, CA
How published* Proceedings
Year* 2005
Volume 5679
Number 0
Publisher SPIE
Keywords Coordinate Measurement Machine, Stereovision, Dimensional Inspection, Strain Analysis
Quality control of manufactured parts requires inspection systems of ever-increasing accuracy. A method of achieving this for vision systems is to view parts close-up, thereby increasing feature resolution. One application for close-up vision based inspection is sheet metal strain analysis. This technique involves electrochemically etching a dark grid pattern of known size onto the flat sheet metal surface and then deforming the sheet. The change in the grid pattern after deformation can be used to calculate surface strain. The computer vision problem is to accurately detect the intersections of the grid pattern. To investigate this problem, a stereo camera system was designed and attached to a bridge style coordinate measurement machine. The stereo head consists of two high resolution monochrome CCD cameras mounted on a Renishaw PH10 motorized probe head that can be articulated into numerous, repeatable, preset positions. Stereo head calibration was achieved using Zhang’s technique with a planar target. Each probe position was calibrated using a global point set registration method to link coordinate systems. A novel approach to segmenting the grid pattern into squares involving region merging and watersheds is described. Grid intersections are determined to sub pixel accuracy and matched between images using a correlation based scheme. The accuracy of the system and experimental results are provided.
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