Subspace model identification and H/sup /spl infin// servo control of tandem cold mill

This paper studies the development of a mathematical model and the design of H/sup /spl infin// servo controller to produce precisely mill product of tandem cold mill (TCM). To improve the performance of the automatic gauge control system based on the Taylor linearized model of TCM, a new mathematical model which can complement Taylor linearized model is constructed by using the MIMO output-error state-space model identification algorithm based on the subspace method. The H/sup /spl infin// servo controller is designed for robust stability on the variation of system parameters, restrain disturbances and tracking the setup value of the strip thickness. The H/sup /spl infin// servo problem is modified as a usual H/sup /spl infin// control problem, and this modified problem can be solve by using linear matrix inequality techniques. Consequently, the effectiveness of the proposed H/sup /spl infin// servo controller is shown in comparison with the existing PD feedforward controller.