Abstract: A ram driving method including the steps of fixing one end of a large-diameter piston rod integral with a large-diameter piston reciprocably included in a large-diameter cylinder attached integrally to a ram to a fixing unit, connecting one end of a small-diameter piston rod integral with a small-diameter piston reciprocably included in a small-diameter cylinder integral with the large-diameter cylinder to a moving member moved by a motor driving, integrally moving the small-diameter cylinder and the small-diameter piston and communicating a first compartment and a second compartment of the large-diameter cylinder divided by the large-diameter piston with each other, moving the ram integrally with the small-diameter piston rod moved by the moving member, and communicating the small-diameter cylinder with the large-diameter cylinder, thereby moving the large-diameter cylinder with a strong force by a working fluid supplied from the small-diameter cylinder.

Abstract: A ram driving method including the steps of fixing one end of a large-diameter piston rod (5R) integral with a large-diameter piston (5P) reciprocably included in a large-diameter cylinder (5) attached integrally to a ram (3) to a fixing unit (9), connecting one end of a small-diameter piston rod (7R) integral with a small-diameter piston (7P) reciprocably included in a small-diameter cylinder (7) integral with the large-diameter cylinder to a moving member (17) moved by a motor driving, integrally moving the small-diameter cylinder and the small-diameter piston and communicating a first compartment (5A) and a second compartment (5B) of the large-diameter cylinder divided by the large-diameter piston with each other, moving the ram integrally with the small-diameter piston rod moved by the moving member, and communicating the small-diameter cylinder with the large-diameter cylinder, thereby moving the large-diameter cylinder with a strong force by a working fluid supplied from the small-diameter cylinder.

Abstract: If an instruction to move a ram (5U) is issued, a ram instructed speed is instructed to be suppressed to a certain warming-up speed not higher than a target speed until a release speed determination section (75) determines that a moving speed of the ram (5U) calculated by a ram moving speed calculation section (51) reaches a predetermined warming-up release speed; if the release speed determination section determines that the moving speed of the ram (5U) reaches the predetermined warming-up release speed, the warming-up speed is released to accelerate the ram (5U) to the target speed.

Abstract: A rod pressure holding instruction section controls a servo motor to rotate a two-way pump in a counter direction, and to supply hydraulic oil, with pressure which does not exceed pressure from a weight of a ram, to a two-way pump-side piping, increasing pressure. A difference between pressure in a rod-side cylinder chamber-side piping of a speed switching valve and pressure in a two-way pump-side piping of the speed switching valve is decreased, thereby decreasing an impact generated when switching the speed switching valve and stopping the ram at a predetermined position.

Abstract: A controller for a press brake controls a servomotor to reverse the rotation of a bidirectional piston pump so as to reverse the vertical movement of a hydraulic cylinder and a ram. A command generator maintains a constant speed for a predetermined warmup time or distance after the ram movement is reversed, and afterwards changes the ram speed to a predetermined speed. A ram position, set according to a moving speed pattern, is compared to the actual position of the ram to conform the ram to the moving speed pattern. The moving speed may be limited based on at least one of a pressure and a detected by a pressure sensor.

Abstract: A rod pressure holding instruction section (67) controls a servo motor (37) to rotate a two-way pump (29) in a counter direction, and to supply hydraulic oil with pressure, which does not exceed pressure applied by an own weight of a ram (5U), to a two-way pump-side piping (49), increasing pressure. A difference between pressure in a rod-side cylinder chamber-side piping (43) of a speed switching valve (47) and pressure in a two-way pump-side piping (49) of the speed switching valve (47) is decreased, thereby decreasing an impact generated when switching the speed switching valve (47) and stopping the ram (5U) at a predetermined position.

Abstract: If an instruction to move a ram (5U) is issued, a ram instructed speed is instructed to be suppressed to a certain warming-up speed not higher than a target speed until a release speed determination section (75) determines that a moving speed of the ram (5U) calculated by a ram moving speed calculation section (51) reaches a predetermined warming-up release speed; if the release speed determination section determines that the moving speed of the ram (5U) reaches the predetermined warming-up release speed, the warming-up speed is released to accelerate the ram (5U) to the target speed.