A Practical Approach for the Design of Thickness and Tension Controllers in Multi-Stand Cold Rolling Mills

Thickness and tension control in multi-stand cold rolling mills is a multivariable problem which in literature is typically solved with MIMO control approaches. Nevertheless due to the realization and commissioning effort SISO PI-control is often preferred for practical applications. In this article the coupling between strip thickness and interstand tension is analyzed in detail. Based on this analysis an assignment of controlled and manipulated variables is proposed for the design of SISO PI-control loops. A method for the controller design based on the Internal Model Control approach is presented and it will furthermore be shown how the SISO loops can be extended stepwise to a more complex MIMO controller. This results in a scalable control concept where performance and controller complexity are directly linked.