Stabilization of Tension Control in Reverse Rolling Mills Using State Feedback

In reverse cold rolling, tension control between the rolling stand and reels plays an important role in assuring stable rolling of strips. While in tandem mills tension control is performed by manipulating the roll velocity, the reel motor torque is manipulated to control tension in reversing mills, which characterizes the tension dynamics as a second-order system. As a result, when the dumping ratio of the second-order system is small, the tension dynamics becomes oscillatory and hard to control. To this end, a new control scheme is proposed to stabilize tension between the rolling stand and reels in reversing mills. In the proposed control scheme, a feedback loop of the derivative of the tension to the reel motor torque is newly introduced to the existing feedforward control. Since this feedback is equivalent to a state feedback of the strip velocity to the reel motor torque and increases the dumping ratio, it is effective to alleviate the oscillatory nature of the tension dynamics and to stabilize the tension. Simulation and experimental results are shown to demonstrate the efficient performance of the control scheme.