Robust PI-LPV Tension Control with Elasticity Observer for Roll-to-Roll Systems

摘要

Flexible materials such as textiles, papers, polymers and metals are transported on rollers during their processing. Maintaining web tension in the entire processing line under an expected web speed is a key factor in achieving good final product quality. It is common practice in industrial web transport systems to use decentralized PI-type controllers. The performances of such control strategies highly depend on web speed and elasticity because of the strong coupling between these two variables. Moreover web speed and elasticity are subject to large variations during a same processing. The emphasis of this paper is on the design of linear parameter varying PI controllers with quadratic H_∞ performance to increase closed-loop system robustness regarding these parameters variations. First a polytopic model of the experimental plant is derived from web speed and tension dynamics. A design methodology of the PI-LPV controllers, that guarantees closed-loop quadratic stability and H_∞ performance, is then presented. The method uses an optimization software with genetic algorithms to determine the controllers parameters while minimizing the H_∞ norm. Moreover, as it is difficult to measure web elasticity online, an observer is synthesized to estimate the Young's modulus. The effectiveness of the proposed control strategy is illustrated with simulations.