Optimal multivariable looper control for hot strip finishing mill

An optimal multivariable looper control system based on optimal-regulator theory was developed for hot strip finishing mills. Loopers of a hot strip finishing mill are installed between stands and are, in many cases, driven by motors. The goal of looper control is to maintain product quality at a high level by stabilizing the rolling operation. Stability is achieved by keeping the looper angle and tension applied to the strip at given reference values. The most difficult problem is mutual interaction in the simultaneous control of looper angle and strip tension. In particular, increasing use of low-temperature heating of slabs, high-carbon steels, and high-speed rolling places additional demands on the looper control system. Moreover, high quality of thickness, width, and crown are strongly requested. Controlling the rotational speed of the looper motor in addition to the existing looper motor current control has allowed a robust looper control system that can cope with changes in rolling conditions. Based on the current rolling conditions, the system selects the control gain calculated from different weight matrices for the linear quadratic criterion. The developed control system can maintain relatively constant strip tension without operator intervention in the presence of rapid changes of hydraulic screwdown, such as automatic gage control (AGC) operation