Device and method for controlling the primary drive of a fine blanking press

A hydraulically driven fine blanking press, comprising a base;

• a main cylinder chamber formed in the base;
• a main piston disposed in the main cylinder chamber so as to carry out a stroke movement of the main piston along a vertical stroke axis between a lower dead point and an upper dead point, the piston including a radially outwardly extending protrusion having upper and lower faces;
• an upper and a lower hydraulic pressure chamber formed in the base, each of the upper and lower hydraulic pressure chambers being comprised of interior faces of the main cylinder chamber and exterior faces of the main piston including the protrusion and wherein the upper hydraulic pressure chamber includes the upper face of the protrusion and the lower hydraulic pressure chamber includes the lower face of the protrusion whereby the upper hydraulic pressure chamber acts on the upper face of the protrusion to push the main piston toward the lower dead point and the lower hydraulic pressure chamber acts on the lower face of the protrusion to push the main piston toward the upper dead point;
• a table supported by the main piston;
• respective fast stroke cylinders formed in the base and respective double-acting fast stroke pistons each received in a respective one of the fast stroke cylinders and each fast stroke piston comprising partitioning structure having an upper surface and a lower surface, the partitioning structure partitioning the fast stroke cylinder in which the fast stroke piston is received into an upper hydraulic pressure chamber which acts on the upper surface of the partitioning structure of the fast stroke piston to push the fast stroke piston downwards and a lower hydraulic pressure chamber which acts on the lower surface of the partitioning structure of the fast stroke piston to push the fast stroke piston upwards to a target position;
• respective piston rods each connecting to the table;
• an internal hydraulic system formed in the base;
• a hydraulic system external of the base and connected to the internal hydraulic system and including a hydraulic pump, a hydraulic fluid collection tank provided with a tank valve, a high pressure accumulator and a central control unit that sets the hydraulic fluid to a predetermined working pressure;
• the internal hydraulic system comprising a hydraulic fluid upper channel connecting with the upper hydraulic pressure chamber for the main piston, a hydraulic fluid lower channel connecting with the lower hydraulic pressure chamber for the main piston, and a hydraulic fluid bypass channel connecting between the hydraulic fluid upper channel and the hydraulic fluid lower channel;
• a pressure-controlled proportional valve connecting with the external hydraulic system and with the hydraulic fluid lower channel and the hydraulic fluid bypass channel;
• a vent channel connecting with the upper hydraulic pressure chamber of the main piston and, via the tank valve, with the hydraulic fluid collection tank;
• a hydraulic fluid supply channel connecting the hydraulic fluid lower channel, via a hydraulic fluid branch channel branching from the hydraulic fluid supply channel, to the external hydraulic system;
• and a hydraulic fluid branch channel branching from the hydraulic fluid supply channel and connected to the external hydraulic system, whereby the fine blanking press is controlled by the internal hydraulic system as follows:
• the fast stroke piston is pushed upwards toward its target position by hydraulic pressure in the lower hydraulic pressure chamber for the fast stroke piston while the pressure-controlled proportional valve is open and the main piston carries out a stroke movement from the lower dead point toward but not reaching the upper dead point during which the hydraulic fluid is displaced from the upper hydraulic pressure chamber for the main piston to the lower hydraulic pressure chamber for the main piston through the hydraulic fluid upper channel, the hydraulic fluid lower channel and the hydraulic fluid bypass channel;
• and when the fast stroke piston reaches its target position, the pressure-controlled proportional valve closes and the main piston is caused to effect a power stroke to the upper dead point by the hydraulic fluid being supplied through the hydraulic fluid supply channel and the hydraulic fluid bypass channel to the lower hydraulic pressure chamber for the main piston and being discharged from the upper hydraulic pressure chamber for the main piston to the hydraulic fluid collection tank via the tank valve.