Tension control in a steel slitting line

Abstract

The problem presented in this chapter is tension control in a steel slitting line. This was addressed in the framework of the modernisation of the control system in a steel producing plant. Due to economic reasons and mechanical constraints, the established mechanical solutions, such as using a disburdening loop or the application of online measurements of the tension, were not acceptable for the customer. Therefore alternative solutions were sought. We proposed an original solution based on feedforward and feedback elements of the control structure. The key idea lies in online calculation of the required armature current of the uncoiler drive, which can be decomposed into the “tension current” and the “acceleration current”. The tension current is calculated by means of the required tension, determined by the operator on the basis of visual inspection of the sag of the steel strip. The acceleration current is calculated from the acceleration of the slitter, estimated by an open loop estimator, and a nonlinear function which incorporates characteristics of the drive and the gear and depends on the changing radius of the uncoiler. The approach has proven to be successful and the designed system has now been in service for several years. In the chapter the steel strip tension control problem is first analysed and then the solution is presented, including all design details that turned out to be relevant for the success of the project. Several interesting implementation issues related to HW, SW, signal interfacing, etc., are presented as well. The end of the chapter is devoted to the discussion of some practical difficulties encountered during the development of the control system.