Control of Roll-to-Roll Web Systems via Differential Flatness and Dynamic Feedback Linearization

A novel method based on the techniques of differential flatness and dynamic feedback linearization is proposed to simultaneously control web tension, web transport velocity, and web displacement in the longitudinal direction in roll-to-roll web systems. Literature has mostly focused on the control of web tension and velocity, but has paid little attention to the control of web displacement. However, the control of the longitudinal displacement of web is important for register error reduction in multicolor image printing or multilayer flexible electronics printing. Hence, our result adds a new dimension to the control of roll-to-roll web systems. First, the dynamics of a class of roll-to-roll systems are reviewed and transformed into a form in which the longitudinal displacement of web can be observed directly. Second, the roll-to-roll systems are constructively shown to be differentially flat and thus dynamically feedback linearizable to chains of integrators. Third, a procedure for tracking control synthesis is provided for reference signals that are parameterized by flat output. The closed-loop system is shown to asymptotically track the reference inputs even in the presence of initial tracking errors and disturbances over finite time intervals. Last, a simulation study is carried out to illustrate the excellent tracking performance of the closed-loop system.