Optimal Control of Sendzimir Mill

Abstract

Nippon Steel Corporation has successfully developed and put into commercial use two computer-based optimum control techniques for Sendslmir mills. Both are based on a process control computer to optimize process parameters for the cold rolling of stainless steels on a Sendzimir mill by exploiting fully the structural and operational advantages of the mill. One of the control techniques is an optimum, automatic thickness control system designed to ensure high accuracy in thickness over a full range of rolling speeds and lengths of plate being rolled and having the following features:1)Eliminates delay in control by incorporating in the system a feed forward control function.2)Assures high accuracy by strictly setting the distribution of optimum control gain for each pass based on rolling theory.3)Enables corrcction of the control for the subsequent pass judged from the pattern of variation in thickness.4)Essentially eliminates any lag in response even at a rolling speed as high as 500 M/min with a high-speed reduction control technique NSC has developed un the basis uf Puntryagiii's maximum principle to get rid of the bottleneck to system response associated with the current screw-down device.An epoch-making commercial exploitation of the latest control theory, this thickness control system has proved most useful and effective through both digital simulation and actual rolling operation.The other control technique is a shape detection system. Since most stainless steels are non-magnetic and are rolled at high tension, there has been no practical means of detecting the shape of rolled strip and it has generally been thought that the realization of shape control in this product area was a long way off.Allowing a quantitative translation of operators' empirical control practices into clectrical control signals utilizing the most up-to-date signal processing technology, the Frequency Analyzing Shape Detection System provides a detection accuracy within 0.19% at steepnesses, a major factor for the improved operating performance of Scndzimir mills at NSC.