On model predictive control of the lateral strip motion in tandem hot rolling mills

Abstract

Almost all flat steel production involves processing in a tandem hot strip finishing mill. The mass flow in the hot strip finishing mill influences final product’s quality and the stability of the process. The mass flow can be categorized into longitudinal and lateral depending on its main direction. Uncontrolled lateral strip movement may lead to plant damage; therefore, the lateral strip motion must be controlled. An existing model for the lateral strip motion is extended to serve as a basis for a model predictive controller. The controller systematically respects the limits of the manipulated variable, its time derivative, and the lateral position of the strip and shows good convergence behavior. The proposed control strategy works on top of the control structure currently applied at the plant. A state observer is proposed for the angle and position of the strip in the roll gap, which are not directly measurable but are required by the model predictive controller. The observer also estimates the camber of the strip in the finishing mill, which is valuable information for the operators. The efficacy of the proposed control structure is evaluated by simulation studies utilizing a mathematical plant model validated by measurements.