Real-time tension control in a multi-stand rolling system

Abstract

The problem of real-time tension control in a metal-strip processing line is addressed. The tension in a metal strip changes due to not only the speed difference but also thickness changes at the ends of a span. The mathematical dynamic model which describes relationship between the tension change and the roll-speed change is improved to include the effect of the strip thickness change on tension variation. Through the computer simulation of this model. the parameter sensitivity analysis and the static and dynamic characteristic study are carried out. The tension variation in a metal strip turned out to be very sensitive to the thickness variation as well as to the speed difference at the ends of the metal strip. In the rolling process, the master speed drive is usually located at the last stand. The speeds of rollers in upstream stands are adjusted with respect to the speed of the last stand to compensate the speed change for the tension regulation. A new tension control strategy in a multi-stand rolling process is suggested. The tension transfer phenomena is used in the design of the suggested controller. The developed mathematical model is used to design a controller for the real-time control system. A set of requirements for the real-time tension control is suggested. Based on the requirements, a real-time software for the tension control in a multi-stand system is designed and real-time simulation was carried out by using the Vx Works real-time scheduler and the Force Target board. The cancellation mechanism of the roll gap control due to the tension interaction is clearly defined by using the mathematical model derived in this study. It is confirmed that the suggested control strategy needs less control efforts and shows better performance than those of the existing control method in a rolling process.