Walking Beam Speed Feedforward And Robust Control Based On Load Observation

Heating furnace is the key equipment of billet rolling, it is used for heating the steel billet, in order to ensure the reheated billet temperature to satisfy the technological requirements of the rolling process. Since the walking beam furnace has plenty of advantages, it has replace the pusher reheating furnace and been widely used by lots of steel rolling enterprises domestic and overseas. Walking beam is composed of fixed beams and moving beams, it is the key equipment in reheating furnace. Driven by the hydraulic cylinder, moving beams lift hundreds of tons of steel billets step by step from the billet charging side to the out side, doing the rectangular movement in the order of rising, forward, down and backward.Considering the total weight of the system is very large, and there are movements like lift up and put down the billet in the contour line, the walking beam have the characteristics of nonlinearity, large inertance and step load disturbances, etc. In the meanwhile, some interference factors that exist in the actual production, such as oil leakage, the existence of the liquid viscous drag and nonlinear characteristics of the oil itself will also impact the walking beam system. The velocity of the walking beam should ensure the production rhythm and guarantee the gently handle of the billet to avoid the damage of moving beam and the fixed beam. Therefore, the accurate control of the velocity and displacement of walking beams is essential. In order to avoid the system overshoot and oscillation, open loop control method is widely used. But the accuracy of step distance and speed cannot be guaranteed, occasionally, the accumulation of the multi-step error in steel production may cause an accident.By analyzing the principle of the walking beam system and the working parameters, three mathematical models including step institutions, electro-hydraulic proportional directional valve and hydraulic cylinder are established in this paper. To solve the uncertainty of system and load, a feedforward and robust control strategy is designed, which can realize the accurate closed-loop control of the movement process of the walking beam; considering the billet weight is difficult to measure directly in engineering problems, a state observer is proposed based on signals including the pressure difference between the two cavities and velocity, the reconstruction of the load signal was realized in this way. Meanwhile, the system is simulated by Simulink Toolbox of Matlab, the simulation results show that the feedforward and robust control strategy based on load observation can realize accurate tracking of the speed and accurate control of the displacement of the walking beam.