ABSTRACT
U =control signal U +=control signal when cylinder pressure e-
quals Ps U-=control signal when cylinder pressure e-
quals 0 Xp =displacement of cylinder Y =height of electrode end
INTRODUCTION
The electrode control of modern electric-arc furnaces is mostly done by a hydraulic servo control[l]. Because disturbances in the electric-arc furnace are largely different in form and magnitude from each other, the electrode control system should have high positional accuracy for small disturbance as well as fast response for large disturbance. One method for this purpose is to use the servo valve with varying gain [ 2 ]. However, it then exhibits significant overshoot, its nominal flow should be large enough to satisfy the
highest velocity of cylinder. We suggest a new control scheme which uses a small servo valve along with two large onoff valves to control the electrode hydraulic cylinder. The servo valve is used for small disturbances and the on-off valves for the large disturbances. The optimal opening and closing time of the on-off control valves are determined by the method of optimality to produce the least overshoot under the prerequisite of fast response. Past studies on the electrode servo control system mostly were carried out for open loop case, the electric-arc is not included in the loop because of the difficulty of measuring the arc length[3][4]. In order to study the performance of the electrode control system in more detail, we established an experimental electric-arc furnace and measured the characteristics of the whold system including the electric arc. The management of control style (servo valve control or on-off control), the PI regulation and digital filtration of the sampling data are realized by a microprocessor.
