Modeling and identification of a strip guidance process with internal feedback

A physically interpretable model of an experimental strip guidance installation, operated at Hoogovens Research and Development in the Netherlands, is derived by means of system identification. This process consists of an offset pivot guide steering roll with five degrees of freedom, four cylindrical guide rolls, and one driving roll. In this experimental installation, an endless steel strip is created by welding the ends of the strip to allow for continuous experimentation. As this endless strip introduces an internal mechanical feedback in the process, a closed-loop identification problem arises. Five identification strategies are applied and compared for a single operating condition, determined 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 identification problem into an open-loop one by using a regulator to compensate the internal feedback due to the endless strip. From the preliminary experiments for one operating condition, this strategy is selected for further analysis as it yields the smallest prediction error. The physically interpretable model is obtained by identifying a linear time-invariant system for different operation conditions, and by expressing the model parameters in terms of geometric and kinematic parameters that characterize the strip guidance installation. The model yields improved prediction capabilities compared to other models proposed in 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.