Vibration Control in Rolling Mills

This paper is concerned with the active compensation of eccentricity induced periodic vibrations in hot and cold rolling mills. These vibrations appear as periodic distrurbances in the strip exit thickness and they may even define the limit of the achievable tickness tolerances. An important factor for the controller design is the derivation of a mathematical model that comprises the essentail dynamic properties of the hydraulic adjustment system, the mill stand and the strip deformation. Moreover, the mathematical model must include all effects like transducer and quantization noise, friction forces between the stand and the roll chocks as well as the fact that not all quantities are available through measurement. This is essential for obtaining a controller that can be implemented practically in the plant. The presented control strategy is based on the input-output linearization and for the disturbance rejection an algorithm derived from the projection theorem in a Hilbert space is used. The so obtained controller has the nice feature that the closed loop performance remains nearly the same all over the operating range and it contains only quantities that are measurable directly. Simulation results will demonstrate the feasibility of the proposed design.