Abstract
Requirements for the high accuracy in thickness of cold rolled strip are becoming ever more stringent and automatic gauge control systems (AGC) with high performance are also required for reversing cold mills. Moreover, reversing cold mills are turning to produce thin strip under high rolling speed in recent years. Therefore, it is necessary to design AGC systems also in terms of the dynamics in strip thickness change.
In this paper, the dynamics in strip tension response with conventional reel motor current control were examined by computer simulation. The simulation result indicates that the strip tension response to the reel motor current change is delayed especially under the conditions of high rolling speed and thin strip thickness. Therefore, the improvement of strip tension response based on the measurement of the actual strip tension is indispensable for high performance AGC systems. However, it is not practical to directly measure the actual strip tension because the maintenance of measurement accuracy is difficult under the rolling environment.
In order to solve the above problem, a new technique for estimating the actual strip tension using observer method was investigated. Based on the estimation of strip tension, a new type of strip tension control system (Active Tension Control) has been developed. In the Active Tension Control, the reel motor current reference from AGC is corrected by the accelerating or decelerating current so that the estimated value of strip tension corresponds to the strip tension reference. This system has been incorporated into the AGC system for No. 2 reversing cold mill at Wakayama Steel Works and operates effectively to provide high accuracy in thickness.
