2-DEGREE-OF-FREEDOM ROBUST SPEED CONTROLLER FOR HIGH-PERFORMANCE ROLLING-MILL DRIVES

This paper presents a scheme for the speed control of rolling mill drives. 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 features of the control method is that it yields a robust system with respect to system uncertainties and modeling errors and is very effective for the 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 51.3 Hz). The proposed scheme is compared to the conventional PI-controller and the performance of each scheme is presented. A high closed loop speed bandwidth was obtained with the proposed TDF speed controller.