A grey box bending stiffness model for paper board manufacturing

This paper presents a semi-physical grey box model for the bending stiffness of cardboard at the AssiDoman Frovi cardboard plant. The reason for using a semi-physical nonlinear model is that one wants the model to be valid under different production settings, with the intention to use it for both control and simulation. The latter is of great importance, since finding optimal production settings is a costly procedure to do directly on the plant. The modelling was done with the aid of the IdKit software tool with the data coming from 80 days of production, including all different types of products. The IdKit tool allows not only for the use of nonlinear deterministic models but also for the use of nonlinear stochastic models for unmeasurable disturbances. One deterministic and two stochastic models were identified and then validated on independent data. The result was that the stochastic models showed good performance, while it might be possible to improve the performance of the deterministic model.