Many kinds of electro-hydraulic servo systems are applied to rolling mills such as a hot strip mill, a cold strip mill and a seamless tube mill because their quick response, high power and high positioning accuracy. However when applying such a system to a hot strip downcoiler, it was found that the controlled object has low natural frequency and is lightly damped so that stable control is very difficult. In the first report, Optimal control theory was applied, however, the derived control system was shown to be poor in robustness. Especially, the control effectiveness was highly influenced by the response of the servo valve and the length of piping between the servo valve and the cylinder. In the second report, in order to overcome this difficulty, a novel and practical control method was proposed and developed based on the Posicast Control proposed by O.J.M. Smith in 1957, which can make the system stable and give a high response. In this report, the practical design method of the proposed control system named new Posicast control is described, and it will be shown that this new Posicast control system realizes a kind of dead-beat control and gives high response and robust stable control by using the internal information of the controlled object. The effectiveness of the proposed control system is also shown by using the data of a downcoiler operated in a production line.
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