Four-Dimensional Characterization of Paper Web at the Wet End

This report presents a detailed description of a vision system whose purpose is to detect and to localize the nonuniformities that appear on the paper slurry (wood fiber and water mixture) at the wet end of a paper machine. Specifically, the system is capable of monitoring the paper slurry upon its exit from the headbox and alerting the operators of any event (e.g., streaks) that disrupts the otherwise homogeneous background. Such events are thought to affect crucial product properties such as formation, which if poor, results in thick and thin spots on the sheet and impacts its strength and printability. This report describes the vision system in terms of its hardware modules, as well as the image processing algorithms that it utilizes to perform its function. Basically, the system acquires both intensity and topographic information from the scene and uses texture-based features for the detection, and facet-based descriptors for the localization of the nonuniformities. In addition to being tested in a laboratory environment, a prototype of this system was constructed and deployed to a paper mill, where its performance was evaluated under realistic conditions. Installed on a fourdrinier paper machine, running at 480 m/min and producing linerboard material, the vision system was able to monitor an approximately 1-meter-wide area and to successfully detect and localize slurry streaks