Servohydraulic press with a closed loop control circuit and method of

Abstract

A fluid pressure operated press has a drive piston which is movable in a cylinder and has a drive surface side and an opposite return surface side which is connected with a ram which operates on a workpiece. An accumulator is connected to the respective cylinder spaces disposed on the respective drive and return surface sides through a control so as to effect the movement of the piston in a drive direction by admission of a fluid pressure source and pressure from an accumulator in a selected amount to the cylinder space on the drive surface side. The return of the drive piston is effected by applying a fluid pressure to the return surface side. A difference in the areas of the return surface side of the drive piston and the combination of the drive surface side with a central area surface associated with the drive surface side, defines an effective piston area. The accumulation is selectively connectable to the cylinder to effect a fluid pressure over the effective piston are which is in order to permit the fluid pressure on the central piston area side to direct flow to the accumulator so that the piston will be displaced against the accumulator pressure. A part of the force acts on the return side overcoming friction to lift the drive piston from the workpiece. Fluid pressure is removed from the accumulator as needed during the return movement in an amount equal to the product of the stroke times the return side area, and fluid pressure is delivered to the accumulator in an amount of the stroke times the drive side piston area so that the product of the fluid spent during the return movement equals the stroke times the difference between the effective surface areas of the drive side and the return side.