Modeling and unbalance force control of four-cylinders synchronization electro-hydraulic loading system in superplastic forming equipment

The four hydraulic cylinders pressing equipment is commonly used in superplastic forming equipment and other similar applications. But it hardly to arrange the reaction force in the geometry center of four cylinder which makes the depress equipment unbalance and very harmful for these equipment. In this paper the coupling between four cylinders is considered and the linear model of four-cylinders pressing system is built by the form of state-equation. Based on this model, the balanced force control strategy is studied. This paper propose a control strategy which is based on detecting the displacement of the four cylinders to amend the force commands of four cylinder. The simulation results shows that it can achieve load control precisely and the tilt angle of loading platform is small.