Looper and tension control in hot strip finishing mills based on different control approaches

Abstract

Abstract The looper control of hot strip finishing mill is one of the most critical control items in hot strip rolling mill process. It is a highly complex nonlinear system, with strong states coupling and uncertainty that present a difficult control challenge. Loopers are placed between finishing mill stands not only to control the mass flow of the two stands but also to generate a constant specific strip tension during rolling, independent of the actual strip stock which influences the width of the strip. Some of the applicable control architectures for the finishing mill are reviewed. Two general approaches are considered: the first is based on a loop or SISO (single input single output) strategy, while the second is based on a MIMO strategy: In the loop approach, two different schemes are considered with distinct loop configuration. For both schemes, PID and fuzzy-PID are considered for comparison purposes. Since in the second scheme the most important loop is the looper control loop, it is investigated whether a nonlinear sliding mode control can significantly improve the response. In the multi-variable or MIMO approach, standard LQR (linear quadratic regulator) is investigated after linearization of the system.

Keywords

• Hot strip finishing mill
• Looper control
• Tension control
• Fuzzy-like PID control
• Sliding mode control
• LQR