This paper deals with the multivariable control for wire rod rolling. The control objective in wire rod rolling is to maintain the interstand tension and output height and width of wire rod product as prescribed. In a conventional method, only the interstand tension is controlled by updating the roll speed. But the interstand tension and the output height and width are strongly connected, so we must handle the wire rod rolling system as a multivariable system to improve the accuracy of product.
In this paper, we take a modern control theory approach to cope with a wire rod rolling system. First, we derive a linear statespace model for wire rod rolling system from nonlinear rolling model and mill driving dynamics. We modify it applicable to control system design stage using a relation of interstand transmission delay. Based on the optimal regulator theory, we design an optimal control system of wire rod rolling.
Then two types of control system, i.e. (i) a simultaneous control system of tension control and AGC (Automatic Gauge Control), and (ii) block mill AGC, are introduced as a result of a characteristic of a objective mill. The control law is implemented by the statevector feedback and the disturbance vector feedforward, where No.1 stand entry temperature, height and width of the material are used as a feedforward signal.
To evaluate the control performance, step responses due to entry diameter change are computed and measured on a 4-stand tandem model mill. From the computed and experimental results, the validity of the present control system is confirmed.
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