Automatisk reglering av färgnyans på pappret i en pappersmaskin

This paper deals with design and implementation of a regulator to control the tint of the paper on Stora Enso Nymolla AB’s paper machines. The paper industry is a major industrial area in Sweden with continuous processes running around the clock with as short downtime as possible, which places special demands on the running and testing of controllers. The paper machine is in many cases the bottleneck of production so small improvements often have great effect. To improve the overall efficiency of the paper machine a regulator has been made to reduce the downtime at grade changes. The controller is designed for programmable logic controllers in Metso DNA system’s fbCAD and a GUI has been designed for the machine operators. Tests on the paper machines show that an Otto-Smith predictor and associated controller can make grade changes significantly shorter with the result that less paper must be discarded than with the previous manual control strategy. A sufficient number of tests to ensure statistically how much the downtime decreases have not been made but the few that have been made show a decrease of downtime by 50 % at color grade changes compared to when they are done manually.