Tension control for winding systems with two-degrees-of-freedom H∞ controllers

In web transport systems, the main concern is to control independently speed and tension in spite of perturbations such as radius variations and changes of setting point. Multivariable controllers including gain scheduling have already given good results in that sense. Nevertheless, in these control techniques, tracking properties and perturbation rejection are interdependent and cannot be specified separately. In this paper, we present multivariable H_∞ robust control with two degrees of freedom (2DOF) and gain scheduling applied to winding systems. Three controller structures are considered: a global controller, a semidecentralized controller, and a semidecentralized controller with overlapping. Simulation results are given, based on a nonlinear model identified on an experimental bench. In each case, the 2DOF controller is compared to the classical 1DOF controller. The 2DOF approach allows improving significantly disturbance rejection while reducing coupling between tension and velocity.