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Proceedings of CAD'15, 2015, 402-407
Dot Grid Detection and Tracking for Sheet Metal Strain Analysis

Tyler Kenyon, Allan Spence, McMaster University
David Capson, University of Victoria

Abstract. A substantial fraction of the automotive assembly comprises formed sheet metal parts.  To reduce vehicle weight and improve fuel economy, total sheet metal mass should be minimized without compromising the structural integrity of the vehicle. Excessive deformation during manufacture contributes to tearing or wrinkling of the metal, and therefore a forming limit is investigated experimentally to determine the extent to which each particular material can be safely strained. To assess sheet metal formability, this paper investigates sheet metal surface strain measurement using a scalable dot grid pattern. Aluminum sheet metal samples are marked with a regular grid of dot features and imaged with a close-range monocular vision system. After forming, the samples are imaged once again to examine the deformation of the surface pattern, and thereby resolve the material strain. Grid features are localized with sub-pixel accuracy, and then topologically mapped using a novel algorithm for deformation invariant grid registration. Experimental results collected from a laboratory setup demonstrate consistent robustness under practical imaging conditions. Representative accuracy, repeatability, and timing statistics are reported for the SURF feature detector.

Keywords. Computer vision, Feature detection, Strain analysis, Fiducial tracking

DOI: 10.14733/cadconfP.2015.402-407