MODELING AND IDENTIFICATION OF A STRIP GUIDANCE PROCESS WITH INTERNALFEEDBACK

A physically interpretable model of an experimental strip guidance ins tallation, operated at Hoogovens Research and Development in the Nethe rlands, is derived by means of system identification. This process con sists of an offset pivot guide steering roll with five degrees of free dom, four cylindrical guide rolls, and one driving roll. In this exper imental installation, an endless steel strip is created by welding the ends of the strip to allow for continuous experimentation. As this en dless strip introduces an internal mechanical feedback in the process, a closed-loop identification problem arises. Five identification stra tegies are applied and compared for a single operating condition, dete rmined by the strip speed and tension, using experimental data. One of these strategies is called the controller compensation in closed-loop strategy. This new technique is proposed to reduce the closed-loop id entification problem into an open-loop one by using a regulator to com pensate the internal feedback due to the endless strip. From the preli minary experiments for one operating condition, this strategy is selec ted for further analysis as it yields the smallest prediction error. T he physically interpretable model is obtained by identifying a Linear time-invariant system for different operation conditions, and by expre ssing the model parameters in terms of geometric and kinematic paramet ers that characterize the strip guidance installation. The model yield s improved prediction capabilities compared to other models proposed i n the literature. The results presented in this paper are achieved in cooperation between Hoogovens Research and Development and the Control Laboratory at the Delft University of Technology.