| Web handling systems are widely used in industries such as pulp and paper, printing press, and steel milling. Tension variations in web materials are very common in operation and tension control is critical to the quality control of the related manufacturing facilities. Speed variations or changes will cause fluctuations in web tension; as a result, speed control is another important issue in web handling systems to prevent machinery performance degradation and to maintain desired productivity.; The web system control problem is investigated comprehensively in this research on both intermediate zone and unwinding-winding process. First, active tension control strategies are studied. Two MIMO control strategies, Hinfinity and LQR, are developed and compared with a PI-based decentralized control strategy in terms of control performance and robustness properties of the resultant closed-loop system. A gain scheduling scheme is suggested to deal with the time varying parameters in a winding process. Robust stability analysis is proposed to quantitatively determine the necessity of gain scheduling. Comprehensive test results show that the proposed Hinfinity control is superior to other strategies in the investigated web system application.; The second contribution of this work is the development of an inactive tension control strategy to effectively eliminate the 'tension transfer' phenomenon among web spans in a multi-stage web handling system. This strategy is implemented by a looper-like actuator which is controlled by a PID controller. It is the first inactive looper tension control technique in literature for thin web system applications. The developed active and inactive web control strategies are verified by both simulation and experimental tests. |
