| 摘要 |
PROBLEM TO BE SOLVED: To eliminate the shock generated in changing over a speed changeover valve when a ram is stopped. SOLUTION: When a work W is pressed by the cooperation of a punch P and a die D mounted on a ram 5U, and the ram 5U is stopped at a predetermined position, in order to reduce the shock in changing over a speed changeover valve 47 by reducing the difference between the pressure in a rod side cylinder chamber side pipe 43 of the speed changeover valve 47 provided between a rod side cylinder chamber 19 of a hydraulic cylinder 13 and a two-way pump side pipe 49 of the speed changeover valve 47, a rod pressure keeping command unit 67 controls a servo motor 37 to rotate the two-way pump 29 in the reverse direction, and the working fluid having the pressure not exceeding the pressure caused by the gravity of the ram 5U is fed to the two-way pump side pipe 49 to boost the pressure. The pressure of the two-way pump side pipe 49 is detected by a hydraulic pressure detecting means 21 and fed back.
|
