Non-interactive robust tension control for the looper system via disturbance observer

In the rolling mill system of steel making process, the uniform strip tension and looper position are very important, because they affect the dimensional quality of product. However, the disturbances from several sources and the interaction between the looper angle and the strip tension make it difficult to control the system. Up to now, various kinds of control method are proposed, and non-interactive control (NIC) is one of them. General NIC uses the cross controller to cancel out the interaction terms, then the system is decoupled into two independent SISO(single-input single-output) subsystems. However, the looper system model is usually linearized around the operating state since the original model is highly non-linear. So there would be the system uncertainties as well as other unknown disturbances, which can not be removed by cross controller. In this paper, we propose the disturbance observer instead of cross-controller to decouple the looper system. Disturbance observer detects not only the interaction terms but also the uncertainties and disturbances from system input and states. So the bad effect of uncertainties can be reduced by proposed method. And a robust controller is designed to cover the estimation error of disturbance observer.