A Study on Non-interactive Looper and Strip Tension Control for Hot Finishing Mill using Disturbance Observer

Abstract

In this research, the non-interactive looper and strip tension control methods for a hot finishing mill has been studied.The looper-strip tension control system was modeled as mathematical state equations, which expresses the system as the interacted two SISO (single-input, single-output) subsystems. To decouple the interacted subsystems, disturbance observer technique was utilized.The disturbance observer has the advantages compared with the conventional non-interactive compensation technique. It compensates not only the interactions but also the external disturbances and the modeling uncertainties.In the first study, the conventional linear disturbance observer was considered to decouple the system. To apply the linear disturbance observer, the system model was linearized.And robust controllers were designed to control the looper angle and the strip tension.Some simulation results are given to verify the robustness of this control scheme against the external disturbances.In second study, using the NDOB (nonlinear disturbance observer), the looper-tension control system was decoupled into two independent subsystems. Adoption of NDOB allowed to use nonlinear looper-tension dynamic model, which is accurate in the entire domain.Moreover, the model uncertainties and the external disturbances generated from forward slip, strip thickness variation and outgoing strip speed were also compensated by NDOB. A modified TSM (terminal sliding mode) controller is utilized to control the looper angle while the output-feedback controller regulates the strip tension by adjusting the incoming roll speed.Hardware experiment with the 2-stand hardware looper simulator was performed to verify the effectiveness of the proposed approach.