Online quality monitoring of perforated steel strips using an automated visual inspection (AVI) system

This study presents an automated visual inspection (AVI) system to monitor dimensional quality during a steel strip perforation process. In the considered process (razor blade perforation) several dimensional quality parameters (e.g. pitch, strip width, centrality, slot width, ...) are estimated on line with strip speeds up to 30m/min. The dimensions are estimated accurately by applying sub-pixel edge detection techniques on gray intensity images. Telecentric lens and high shutter speed monochrome camera are used. Effect of strip speed and shutter speed on both measurement accuracy and repeatability has been investigated. A maximum error in the order of 2μm was recorded after eliminating zero shifts. Repeatability better than ±1.5μm (at 99% confidence level) is readily achievable on all estimated dimensions at a speed of 30m/min.