Application of Electro-Hydraulic Servo Systems to Hot Strip Down Coilers

Many kinds of electro-hydraulic servo systems have been applied to rolling mills, such as hot strip mills, cold strip mills, and seamless tube mills, for their quick response, high power, and high positioning accuracy. However, when an electro-hydraulic servo system is applied to a hot strip down coiler, it is found that the controlled object has low natural frequency and is lightly damped, so stable control is very difficult to achieve. In order to overcome these issues, first, the optimal control theory is applied to eliminate these deficiencies [1, 2]. However, the derived control system is found to lack robustness. Control effectiveness is highly influenced by the response of servo valve and the length of the piping between the servo valve and the cylinder in particular. Finally, a novel, practical controlmethod is found and proposed in the process of adjusting the production machine. The novel control method proposed here, based on the “posicast” control proposed by O. J. M. Smith in 1957 [3], has realized a kind of dead-beat control and has been found to be robust because it uses the internal information of the controlled object.