An optimal controller design using different methods for web guide control of cold rolling mill

Abstract

Many intermediate web guides are there in the cold rolling mill. Web handling involves unwinding material; feeding it to a processing plant and winding it back into a roll after processing. Accurate method of controlling the position of the web is one of the ways to improve the quality and production. In this work, web guide has been modelled using the geometrical relations of the guide ignoring the mass and stiffness of the web and the mathematical model of the web guide has been approximated to First Order Plus Time Delay with Integrator (FOPTDI) system. This transfer function model of the web guide system has been controlled by the PID controller differently tuned by Equating Coefficient method(EQ), Direct Synthesis method(DS), Model Reference Control(MRC), Dual Loop control (Dual loop) method and Fuzzy Logic Control(FLC) method. In the direct synthesis method, the desired output behavior of the closed loop can be specified as a trajectory model based on the process to design the required form of the controller. A PID controller in series with a lead/lag compensator has been designed for control of closed loop FOPTDI processes. Model reference control and dual loop control have been designed for FOPTDI system and performance evaluation is made. Fuzzy Logic (FL) based Proportional Integral Derivative (PID) self-tuning scheme has been used to control the transfer function of the web guide process of the cold rolling mill. Different tuning methods have been applied to control the FOPTDI system and the simulation work shows better response in terms of performance evaluation criteria. The performance of the system has also been compared with Internal Model Control (IMC) and Ziegler Nichols (ZN) methods. Model uncertainties exist in the web, and the robustness of the controller has been verified using Kharitonov s theorem for uncertainty in process gain, time constant and time delay separately.