A state observer for speed regulation in rolling mill drives

Rolling mill drive-trains, driven by AC or DC motors, have historically experienced premature component fatigue failures even when the perceived operating load is well below the design limit. This is often related to low damped torsional vibrations, especially to self-excited vibrations in rolling slippage (especially during threading and tailing out of a rolled piece), overloading the elements of the drive-train. Long transmission shafts make these vibrations become more critical. A regulator aimed at damping the torsional vibrations of the rolling mill drive-train and thus reducing the electric motor speed fluctuations is presented in this paper. The proposed regulator relies on a reduced order state observer able to estimate the shaft torque amplifications due to the working process. The capability of the regulator to damp out torsional vibrations has been verified through simulations on a lumped parameter torsional model of a single-stand rolling mill accounting for torsional deformability of the power-train shafts.