Optimal operation of a QCS scanner in a paper machine based on the information of QCS and WIS measurements

The scanner is a measuring device which travels over the running paper web in the paper machine. The device simply travels back and forth despite of the stability of the paper making process. However, the back and forth policy is not necessarily the optimal one when the best control performance is required. This paper introduces an optimal operation method for QCS scanner based on the information gathered from both QCS and WIS devices. The optimal operation is based on the optimal path finding algorithm which predicts web quality uncertainties several time steps ahead. The uncertainty estimation is based on the Kalman filter approach which combines the current measurements (QCS and WIS) and the previous estimates. It was noticed that the regular zig-zag scanning is an optimal solution in several cases however the irregular scanning provides more information especially in the highly unstable situations. The developed method could be utilized in scanner control and it would not require major modification to the current systems.