Improved Coordinated Response and Disturbance Rejection in the Critical Sections of Paper Machines

Critical sections of a paper machine such as the wet end presses, size press, on-machine coater, and reel may be required to undergo large and fast load changes in normal operation. These changes must result in minimum disturbance to the ingoing sheet tension or nip roll speed in order to avoid sheet breaks or wrinkling. This paper evaluates two disturbance-rejection control techniques, one using disturbance feedforward (or disturbance input decoupling) based on a nip-pressure disturbance observer and the other using a two-degrees-of-freedom controller. Evaluations were done in both a press section and a size press section of a lightweight paper machine, and the results showed that both methods are very effective in reducing the maximum speed deviation to about 10% of the values without compensation and can operate combined with torsional oscillation compensation without interference between them