Apparatus and method for controlling driving of a ram of a hydraulic cylinder of a hydraulic press equipment

In a method for controlling equipment of driving a ram of a hydraulic press, wherein

• four proportional sheet valves are connected with a hydraulic circuit so as to form a full-bridge hydraulic circuit, one pair of valves operating the down stroke of said ram, the other pair of valves operating the upstroke of said ram,
• said hydraulic circuit comprises a low-pressure-large-flow-rate hydraulic pump and a hydraulic cylinder to make said ram of said hydraulic press equipment to move upward and downward and each of said proportional sheet valves comprises a sheet-formed main valve and a pilot valve for controlling motions of said main valve,
• the improvement comprising:
• connecting in parallel one proportional sheet valve which operates a compression stroke in a case of a stamping process and a variable displacement hydraulic pump with high pressure and with small flow rate with the proportional sheet valve operating said down stroke in the oil supply side;
• operating said proportional sheet valves by a control means that, in a case of said ram being operated with high speed, selects the hydraulic pump with low pressure and large flow rate as the hydraulic power source, while in case of a machining process with a wide load fluctuation, selects the variable displacement hydraulic pump with high pressure and with small flow rate as the hydraulic power source;
• and
• calculating and controlling by said control means, timing of turn-on of said proportional sheet valve which operates a compression stroke from a plate thickness of machining work, so as to calculate a load force of the ram in stamping machining process and to control the optimal machining pressure of said work plate by said ram.