Nonlinear Control of the Interstand Looper in Hot Strip Mills: a Backstepping Approach

A hot strip mill for the production of steel is a complex process where nonlinear dynamic phenomena occur and many control loops need to be tuned taking into account their interference. The control problem of the interstand tension and looper arm position is addressed in this paper. With respect to the conventional PID control approach, our investigation aims at exploiting nonlinear control techniques based on the backstepping methodology in order to improve the performance along with the requirements of the most modern rolling mills where short off-gauge lengths are desired even for thin products (0.7-1.2 mm) and for setup on the fly of the plant. The design of the controller is described in detail and several simulation trials are reported showing the effectiveness of the control scheme under the action of typical disturbance inputs.