Observer-based multivariable control of the aluminum cold tandem mill

Abstract

Innovation in thickness control of the aluminum cold tandem mill has emerged from an application of modern control theory. Any good control system must deal appropriately with two fundamentals of mill operation: (1) the mutual interaction between strip thickness and interstand tension, and (2) disturbances in the mill environment. In this paper, a synthesis of multivariable control systems for aluminum cold tandem mills is presented based on the theory of output regulation established basically by Wonham and his colleagues (Wonham, 1974, Linear Multivariable Control—A Geometric Approach. Springer, New York; Wonham and Pearson, 1974, SIAM J. Control, 12, 5–18; Francis and Wonham, 1976, Automatica, 12, 457–465). The synthesis procedure is composed of the three major steps. The first one is to improve the response characteristics by state feedback. The second one is to compute the feedforward control input to counterbalance the disturbance. The third one is to implement the feedforward control by feedback control based on the estimation of the disturbance by observer. The obtained system was actually implemented and has been in full commercial operation since 1986, making splendid accomplishments.