Dynamic Control of Flatness and Elongation of the Strip in a Skin Pass Mill

Abstract

This paper proposes a dynamic control method for strip flatness and elongation in a skin pass mill. In conventional feedback control, the target values of flatness and elongation are fixed. However, elongation control to a fixed target value is often insufficient to achieve strip flatness when rolling force manipulation for elongation control causes work roll deflection. To improve flatness control performance, we propose an elongation control method which considers flatness. In the proposed method, an optimization problem is solved periodically. The objective function, including flatness control error, is minimized subject to constraints such as the range of elongation and strip thickness and the control outputs. A feedforward control method which suppresses elongation deviations during mill speed changes is also proposed. Accurate online prediction of rolling force using a physical model is difficult due to the heavy computational load. The proposed method utilizes the relationship between the strip strain rate and deformation resistance, which is measured offline, and the designated rolling force change from low to top rolling speed, and does not require a physical model or heavy computation load. An evaluation by simulation and experiments showed that the proposed method improves flatness and elongation control performance.