Pointwise linear quadratic optimal control of a tandem cold rolling mill

The tandem cold rolling of metal strip is a complex nonlinear multivariable process whose optimization presents significant challenges to the control design. Existing systems using the present technology are limited in their capability for improvement in performance and robustness and therefore the need arises for a better approach. It is considered that a pointwise linear quadratic optimal control might fulfill this need. This paper presents the results of work performed to investigate the theoretical and applied aspects of this technique for control of a tandem cold rolling mill. In this paper nonlinear state space equations are derived from a mathematical model of the mill, and a pointwise linear quadratic optimal controller is developed. The controller when coupled to the model is shown by simulation of typical operating conditions to be effective in reducing the effects of disturbances in entry strip thickness and hardness.