| 主权项 |
1. A die cushion device for a press machine that clamps a workpiece between a blank holder and an upper die of the press machine and moves the blank holder up and down while applying an upward cushion force to the blank holder via a cushion pad, the die cushion device comprising:
a linear driving device that drives a piston stop member along a predetermined line and regenerates energy from the linear movement of the piston stop member by combination of a servo motor and a conversion mechanism that converts the rotational movement of the servo motor into the linear movement of the piston stop member; and a hydraulic speed change device that transfers the speed of the cushion pad to the piston stop member via the pressure of noncompressible first hydraulic fluid while increasing the speed at a constant speed ratio and transfers the speed of the piston stop member to the cushion pad via the pressure of the hydraulic fluid while decreasing the speed at the constant speed ration; and an air cushion that constantly applies an upward cushion force to the cushion pad due to the air pressure, wherein the hydraulic speed change device includes
a large diameter piston that is located below the cushion pad and is movable up and down along with the blank holder,a small diameter piston that is connected to the piston stop member to move linearly along with the piston stop member and has a diameter smaller than that of the large diameter piston, anda Pascal cylinder that guides the large diameter piston and the small diameter piston to be movable in an axial direction thereof and encloses the first hydraulic fluid between the large diameter piston and the small diameter piston, wherein the Pascal cylinder includes an upper chamber liquid-tightly sealing a rod side of the large diameter piston, a lower chamber liquid-tightly sealing a rod side of the small diameter piston, and a middle chamber liquid-tightly sealing a space between the large diameter piston and the small diameter piston that encloses the first hydraulic fluid therein, wherein the middle chamber is a communication channel where the large diameter piston cylinder and the small diameter piston cylinder are directly connected, and wherein the upper chamber and the lower chamber enclose a noncompressible second hydraulic fluid therein, and communicate with each other via a communication pipe. |
