Friction compensation in the interstand looper of hot strip mills: A sliding-mode control approach

In the paper, the problem of designing an innovative control scheme for the interstand looper in hot strip finishing mills is considered. Specifically, the proposed scheme enhances the performances of the standard PI-based controllers in the presence of the unavoidable friction phenomena that strongly affect the mode of behavior of the looper mechanisms. Due to the highly nonlinear nature of the disturbances caused by friction, a control scheme is designed that is based on sliding-mode concepts. This solution has been considered thanks to the well-known robustness and simplicity characteristics of these nonlinear control schemes. Extensive simulation results on a model tuned in agreement with the measures obtained from a real hot strip finishing mill are provided showing the effectiveness of the proposed control architecture in comparison with the standard one.