Decentralized control of web processing lines

The focus of this research is on modeling and design of a decentralized controller for web processing lines. First, an accurate dynamic model is developed for the unwind (rewind) roll in a web processing line by explicitly taking into account the time-varying nature of the roll inertia and radius. The unwind roll in a web processing line releases unfinished web to the process section; the rewind roll accumulates the finished web. Second, a strategy for computing the equilibrium inputs and reference velocities for each driven roll/roller is given; this strategy is based on dividing the web processing line into tension zones and using the reference web tension of each zone and the reference velocity of the master speed roller, which sets the desired web transport speed for the process line. Based on the new model developed, a decentralized controller is proposed. Variations in web tension and transport velocity in each tension zone are shown to exponentially converge to zero. A large experimental web platform, which mimics most of the features of an industrial process line, is used for experimentation. Extensive comparative experiments were conducted with the proposed decentralized controller and an often used decentralized industrial proportional-integral (PI) controller. A representative sample of the experimental results is shown and discussed.