Copyright 2002 IFAC 15th Triennial World Congress, Barcelona, Spain ROBUST BOUNDARY CONTRO.pdf

1. INTRODUCTION Fig. 1 shows a continuous hot-dip zinc galvanizing process. The steel strips, of order of 1m wide by 1mm thick, are preheated and passed at a constant speed through a pot of molten zinc at a temperature in the region of about 450 C° . A zinc film is entrained onto the strip as it emerges from the pot. In order to achieve the target deposited mass and maintain it over a range of process conditions, a pair of air knives, which direct a long thin wedge-shaped jet of high- velocity air at the strip, are generally used to control the deposited mass by stripping excess zinc back into the pot. The deposited film solidifies while the strip runs vertically upward, cooling as it goes, for a distance of the order of about 110 m, to a gauge that measures the mass of zinc deposited on the strip surfaces. The control aims of the galvanizing line are to improve the uniformity of the zinc deposit on the strip surfaces and reduce the zinc consumption. The problem of regulating the hot-dip galvanizing process by adjusting the air knives has been studied by several researchers: McKerrow (1983) and Chen (1995). Fig. 1. The traveling steel strip in a zinc galvanizing line. However, an immediate problem to adjust the air knives is that there is a lack of the strip positional information. Shifting strip position and vibration are the main causes of differences between the average deposited masses of the top and bottom strip surfaces and the non-uniformity of the deposited mass across the strip. Many galvanized steel producers such as POSCO (Korea) and U.S. Steel have attempted to measure the strip position directly by installing laser ROBUST BOUNDARY CONTROL OF AN AXIALLY MOVING STEEL STRIP Kyung-Jinn Yanga and Keum-Shik Hongb a Department of Mechanical and Intelligent Systems Engineering, Pusan National University; 30 Changjeon-dong Kumjeong-ku, Pusan, 609-735, Korea. Tel: +82-51-510- 1481, Fax: +82-51-514