A significant advance in damping of torsional vibration by the application of an additional control loop is described. The control feeds measured spindle torque into the drive current regulator, typically increasing damping by 50% to 100%, comparable to other damping methods reviewed. A scale model and a large full-scale mill have been tested with the new control loop. The increased damping is required as a result of efforts to increase rolling mill production through higher speeds and bite angles, with a consequent increase in the incidence of resonant torsional vibration problems, such as shudder or chatter. Altered rolling practices can help reduce the initiation of such resonances but, since the cause is poorly understood, cannot eliminate it, which usually leads to reduced productivity. Tuning of the motor speed and current regulators can be of some help in improving the damping of the drive system, but the speed-sensor ripple and sampling delays of the digital regulator limit the scope for improvement.
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