A Mathematical Model for a Rolling Mill Thickness Control System and Its Digital Simulation

A mathematical model for a rolling mill thickness control system is given in block diagram. The system includes a hydraulic servo-control sub-system and a mechanical sub-system as a connection of multiple mass-spring-friction systems. As it is difficult and complex to achieve a transfer function for the whole system, a block diagram oriented digital simulation program is coded. The mathematical model is described in a diagram composed of 23 connected typical blocks. The mathematical model in block diagram is transferred into an equation of state for the closed-loop control system, which is solved by the fourth-order Runge-Kutta method. An actually rolled thickness-varying strip compares closely with computer simulation results. From the simulation, the basic characteristics of the mill thickness control system and the causes of thickness-varying strip errors are analysed, then suggestions to improve the thickness accuracy are provided.