Position control of hydraulic cylinder using hydraulic transformer

In this paper the position control of a hydraulic cylinder using hydraulic transfomer is studied. In press machines or lifting equipments using hydraulic cylinder, a hydraulic transformer is used as a control component instead of control valve and a component for recovering potential energy of load. The transformer is a combination of a variable displacement pump/motor and a fixed one. Multiple closed loop controller with displacement feedback of variable pump/motor, speed feedback and position feedback of cylinder are designed and inplemented. With these controllers the friction torque and the leakage of the transformer can be compensated for and sufficient accuracy of positioning is achieved.