A Combined Variable Displacement–Digital Cylinder Hydraulic Drive for Large Presses With High Operating Frequencies

In this technical brief, a novel hydraulic drive for large forces and power ratings at relatively high operating frequencies combining variable displacement control and hydraulic digital control is introduced. Basic analog motion control is achieved via variable displacement pumps driving a first cylinder stage. Digital control is realized by switching additional hydraulic cylinder stages on and off to support the analog stage if high forces are needed. The control strategy corresponds to this hydraulic concept. It consists of a feed forward control, a switching logic for the digital booster stages and a feed back proportional-integral (PI) control for stabilization. The validity of this concept and of the control strategy are shown by experiments on a highly downscaled test rig.