Machine vision system for precision dimensional measurements and online SPC

A two-camera ROM-based machine vision system has been engineered for use on industrial processes and manufacturing lines where precision length measurements are required on the fly. A Mnemonics Inc. system has been employed successfully for continuous web processes where pattern length is critical, but it also can be used for dimensional measurements of moving discrete parts. Applications to date have been on patterned webs that are tension-sensitive. System accuracy is +or-0.002 in with repeatability of +or-0.0005 in. The authors discuss: measurement considerations relating to elastic webs in tension; system hardware, including the solid-state array camera scanner; and PC-AT-compatible system software that provides both real-time and offline statistical process control (SPC) analysis capabilities. Charts include X-bar, range or sigma, and data distribution histograms.<>