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Rolling Mill Shape Control

System Description

Cold rolling mills are an abundant source of control problems. Typically, the stand consists of a small diameter work roll and a larger backup roll on each side of the steel strip. Significant amounts of energy are required to achieve the desired thickness reduction. Much of this energy appears as heat on the work roll, which is removed with cooling sprays. This leads to non-uniform thermal expansion across the work roll, referred to as thermal camber. The problem of keeping the roll edge flat is called shape control.

Numerous cooling sprays are located across the roll, and the flow through each spray is controlled by a valve. The cool water sprayed on the roll reduces the thermal expansion. The interesting thing is that each spray affects a large section of the roll, not just the section directly beneath it. This leads to an interactive MIMO system, rather than a series of decoupled SISO systems.

Overview of the Example

It is recommended that you follow the example in order, but you may skip ahead if you wish:

Part 1 Spray interaction and decoupling

Part 2

Actuator saturation

Diagram of the System

A typical flatness control system is shown in the figure below. A comprehensive strip shape control system which incorporates some of the ideas discussed here is available from Industrial Automation Services Pty Ltd.

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