Modified Smith predictor for extruded diameter control

An overview is given of an adaptive strategy for controlling output dimensions from a plastic-on-wire extrusion process, using gain-scheduled PI control in a Smith predictor control scheme. Process behaviour is most easily understood and predicted by developing a process model, and hence the article details the problem of modelling the extrusion process, with the objective of developing a standardised routine for tuning dimensional control systems. The article describes the model of diameter measurement on a cable extrusion process which was used to provide the basis for further analysis and simulation. Next, three alternative control strategies for the diameter control problem are reviewed and compared, illustrating that a combination of well-proven strategies can give significant performance improvements.