Delay-Dependent H Infinity Control For Steering Of Lateral Moving Strip In A Hot Rolling Mill

Abstract:

The lateral movement of the strip is defined by the distance between the centers of the strip and the roll. It caused by off-center rolling, entry side wedge, temperature difference along the strip width direction and an initial off-center. When asymmetric conditions such as temperature, roll gap, the friction coefficient occur, speed difference is generated. It causes lateral movement. It is also called snake motion because its motion appears to zigzag. Strip steering is important problem because it leads to strip tearing in extreme case and it reduces productivity.Control methods for lateral movement have been studied to reduce this problem. State feedback control, PID control, sliding mode control and fuzzy control have been studied. Recently, Choi et al. proposed mathematical model for lateral movement of strip and used the PID sliding mode control to reduce lateral movement and to improve performance. However, this solution did not consider time delay when the output is measured. In various systems, time-delays frequently make system unstable. The lateral movement of strip is also measured with time-delay in strip rolling process. In this paper, time-delay is considered to make the steering system stable. Mathematical model for the lateral movement of strip is solved as linear system with input delay. State derivative feedback is applied to the input time-delay system. Based on Lyapunov-Krasovskii theory, bilinear matrix inequalities are constructed to guarantee the asymptotic stability. State and state derivative feedback gain are solved iteratively not only depending on constant delay information but also satisfying H infinity performance. The results demonstrate that the proposed approach is suitable to control strip steering when the output measure has time-delay.

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