System Considerations for a Fullsheet Imaging System, 1998 Process Control, Electrical & Info. Conference Proceedings

In order to optimize the manufacturing processes and the quality of the sheet they produce, papermakers state their need for “100%” (full) measurement of the sheet. Since a further need of papermakers is to characterize ever finer sections of the sheet, a dilemma arises: how to measure more of the sheet, and do so at a fine resolution. Current measurement systems sacrifice the amount of the sheet measured to attain fine resolution. For example, a scanning system with a cross-direction (CD) measurement resolution of 1 cm on a sheet approaching 10 meters in width provides measurement as little as 0.1% of the sheet. A further dilemma arises as the measurements are scanned ever faster to improve the machine-direction (MD) and CD separation of data inherent in all scanned systems, but at the cost of increased measurement noise and wear on scanning mechanisms.

A camera-based Fullsheet Imaging System solves these dilemmas. Such a system provides measurement of 100% of the sheet at fine resolution, as fine as 1 mm in the CD. System design considerations relating to line speed, camera configuration, camera sweep rate, and overall data rates are described. In order to reduce data rates to manageable and meaningful sizes, various methods of data compression are utilized. At the heart of the data compression techniques is a unique, patented approach that tailors discrimination levels to camera pixel position, and provides data compression to optimize overall real-time, memory, and data transmission requirements. Such a measurement approach further provides an inherent separation of MD and CD components of paper variability, opening avenues for more effective control.