Unified gauge-tension control in cold rolling mills: A robust regulation technique

Abstract

In this paper, the unified gauge-tension control problem is formulated by defining the exit strip thickness of stands and interstand tensions as controlled outputs. It is shown that cold rolling process can be described by a nominal model perturbed by an additive uncertainty. This model is used to design a robust tracking controller, based on H∞ control theory, to ensure robust stability and performance despite the perturbations. The controller is first designed for a wide class of uncertain time-delay MIMO systems and then applied to a typical cold rolling mill. The main contributions of the proposed method are (i) overcoming the interaction between tension stabilization and thickness control, (ii) considering time-delay caused by measurements, (iii) guaranteeing robustness against model uncertainties and external disturbances. The performance of the method is also demonstrated and discussed by various simulations.