Thickness Control for a Plate Mill

Abstract

The purpose of the paper is to describe the design of a multivariable control law for a hot plate mill. The design is performed on models adapted to the plate mill at The Danish Steel Works Ltd.The model for the rolling mill is divided into nonlinear models for the hydraulic systems performing the thickness control and a multivariable linear model for the rolling stand. The parameters of these models are found using measurements from the rolling mill at The Danish Steel Works Ltd. Most of the measurements are collected during rolling, but the plate thickness measurements are performed after rolling using special equipment. In general, good agreement is obtained between measurements and model outputs.The multivariable nonlinear model is used for designing a multivariable thickness control law which can be seen as an unified approach to control of mean thickness and plate wedge. The result is a second order nonlinear controller with rolling forces and roll positions as inputs and control signals to the servo valves as outputs.Since is it is not possible to implement the multivariable control law for the time being, the multivariable control law is simplified with the purpose of using it as a basis for an optimization of the existing thickness control equipment at The Danish Steel Works Ltd. This optimization can be seen as the first step in the practical verification of the mulitivariable control law.