Coordinated profile control of base sheet and coated product properties

The quality of coated paper is strongly affected by the base sheet. Normally, cross direction (CD) controls of the paper machine minimize dry weight, moisture and caliper variations of the base sheet. This strategy does not, however, guarantee optimal CD properties of the final coated product. To optimize the properties of coated paper, the demands of the coating process should be taken into account when planning the controls for the base sheet. The variations in the base paper and final product properties cannot be minimized at the same time. Therefore it is necessary to have a coordinated control that takes into account the effects of the base paper properties on the coated product. The coordination is based on finding a trade-off between the different control criteria. This can be realized by a higher level supervisory system that computes set profiles for the individual control stations according to priorities given by the operator, The potential benefits of coordinated control were examined by simulation. A mill trial was completed to identify the response models needed in simulation. The results show clearly that considerable improvement can be achieved by utilizing coordinated control