| Hot strip finishing mills (HSFMs) are important processes of the iron and steel industry. The specifications which should be satisfied in HSFMs are surface and dimensional quality, mechanical properties and so on. The process is rather complicated and challenging, and modern HSFMs are equipped with expensive equipments with high accuracy. The dimension quality is guaranteed by dedicated control systems such as AGC (Automatic Gauge Control), AWC (Automatic Width Control), ASC (Automatic Shape Control) and so on. On the other hand, the strip speed leaving the upstream mill usually doesn't equal the the strip speed entering the downstream mill due to various disturbances, which will cause the deviations of the strip length and tension between the mills. Looper is equipped between each pair of mills to guarantee stable operation of the process with constant strip tension. Gauge, looper and tension are controlled independly in the conventional control strategies, which are not able to deal with the interactions between subsystems and are not suitable for the demanding market. In this paper, gauge, looper and tension control systems are studied from the SMC (Sliding Mode Control), nonlinear control and MPC (Model Predictive Control) aspect, including:(1) Looper-tension control strategy based on linearized model and SMC method is proposed to improve the robustness and performances of the system, and the looper-tension system is decoupled on the sliding manifold by interaction item canceling. And H∞control strategy based on ISMC (Integral SMC) is proposed to deal with both matching and mismatching disturbances, which achieves better performances than adopting H∞control strategy alone. (2) Nonlinear control strategies are proposed to deal with the nonlinear nature of the looper-tension system. SMC strategy is considered for its well-known robustness withstand matching disturbances and uncertainties, and with the help of nonlinear interaction canceling, the looper and tension interaction could be greatly reduced. A more systematic method: looper-tension almost disturbance decoupling control based on feedback linearization, is proposed and results in parameterized controllers which are easy to tune. Nonlinear controllers are global stable and can work within a wide range, whereas the linear controllers only can work within a limited range and usually needs to change according to the work point.(3) Most of the modern HSFMs are controlled based on PLC (Programmbale Logic Controller) which means discrete control strategies will be more adequate for application. For the strong interaction between the gauge system and looper-tension system, state space model of gauge-looper integrated system is propsed. Based on the integrated model, CDMPC (Constraint Discrete-time MPC) strategy is suggest to control the integrated system coordinately and systematicly, which is easy to deal with constraints on inputs and outputs of the intergral system, and convenient to adjust weight matrices to improve the performances of the overall system.(4) The reliability of the simulation program, which is built based on the state space model of the gauge-looper integrated system, is verified through simulations of disturbances of the integrated system with real plant data. And the effectiveness of the proposed CDMPC is thereby proved through numerical simulations based on the verified program.
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