Importance

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Abstract

A double action oil hydraulic press is provided having a main cylinder for actuating a slide and a lower part forming cylinder for actuating a lower part forming unit, wherein the operations of the cylinders are controlled through the combined control of the rotation of an oil hydraulic pump of a power unit and servo valves whereby the amount of operation oil that must be used is reduced. To this end, the press comprises a power unit comprising a variable displacement oil hydraulic pump adapted to be driven by an inverter motor; controllable servo valves provided in hydraulic circuits connecting the power unit to the main cylinder and to the lower part forming cylinder, respectively; servo controllers for controlling the servo valves, respectively; cylinder pressure detecting sensors provided in the hydraulic circuits, respectively; position detecting sensors for sensing positions of the slide and the lower part forming unit, respectively; a control unit for furnishing the inverter motor of the power unit and the servo controllers with control signals, respectively, and means whereby respective sensing signals of the cylinder pressure and position detecting sensors are fed back to the control unit.

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First Claim