Importance of Overlapping Decomposition for a Web Tension Control System

Abstract: The increasing requirement on the control performance for systems handling web material led to investigation for sophisticated control strategies. Actually many industrial web-transport systems use decentralized PI-type controllers. But when decentralized control is applied to a web tension control system, the interactions among control stations are the major problem for the controller design. One of the authors has proposed a control methodology based on overlapping decomposition of the controlled object showing that it is possible to have good control performance. But since there exist many sources of disturbance for this kind of system e.g. roller non circularity, roller change, web sliding, change of web-elasticity etc., a robust control technique (e.g. H-infinity control) has been chosen and tested for the system model. Then an interesting comparison has been carried out in this paper, comparing the results of the overlapping decomposition technique with the conventional decentralized controller based on disjoint decomposition. Experimental data about the sensors behavior and noise are considered for evaluating the performances of the controllers.