| Abstract: | A control system was developed using a two-degree of freedom control structure with four input variables in the feedforward, and two inputs, the screw rotation speed and the gap of the forming roller, in the feedback loop. The feedforward signals were predetermined from first principles and the operators' heuristic rules for each changeover operation and prepared in a database. At the end of each changeover operation, the values in the database were rewritten by evaluating control performance. The magnitude of the true dead time changed as the production rate was changed. The rate of sampling and control action in the feedback control was adapted in each changeover operation so that the changing time delay was always expressed by a one-sampling-step time delay in the discrete models and dealt with by the controller robustness against parameter uncertainty. The developed control system was applied to an actual industrial plastic sheet production line and allowed one to easily perform the changeover operation and reduce material consumption. |
