Two-degree-of-freedom robust speed controller for high performance rolling mill drives

A scheme for the speed control of rolling mill drives is presented. The proposed speed controller is based on a two degree of freedom (TDF) structure and uses an observer-based state feedback compensator for the major control loop. The control method yields a robust system with respect to system uncertainties and modeling errors and is very effective for vibration suppression. Experimental verification is carried out on a prototype rolling mill mini-model system. The experimental drive system has a three-mass-model structure (motor-gear-load) connected by low stiffness shafts. The mechanical resonances and the inertia ratios between the motor, gear, and load are comparable to those of an actual rolling mill system (resonant frequencies are at 17.4 Hz and 51.32 Hz). The proposed scheme is compared to the conventional proportional plus integral controller, and the performance of each scheme is presented. A high closed loop speed bandwidth was obtained with the proposed TDF speed controller