EP3845324A1

EP3845324A1 - Die cushion device

Info

Publication number: EP3845324A1
Application number: EP19854535.2A
Authority: EP
Inventors: Atsuhiro KANBAYASHI; Hirokazu Nakamura
Original assignee: Daikin Industries Ltd
Current assignee: Daikin Industries Ltd
Priority date: 2018-08-31
Filing date: 2019-08-23
Publication date: 2021-07-07
Anticipated expiration: 2039-08-23
Also published as: JP6702491B1; WO2020045300A1; EP3845324A4; JP2020171959A; EP3845324B1

Abstract

A die cushion device includes: a hydraulic cylinder (10) that vertically moves a cushion pad (14); a hydraulic pump (P) that supplies hydraulic oil from an oil tank (T) to the hydraulic cylinder (10); a relief valve (20) that returns hydraulic oil discharged from the hydraulic cylinder (10), to the oil tank (T); a pressure sensor (PS) that detects a hydraulic oil pressure, which is a die cushion pressure of the hydraulic cylinder (10); and a control device (40) that controls a flow rate and a pressure of hydraulic oil supplied from the hydraulic pump (P) to the hydraulic cylinder (10). The control device controls the number of rotations of the hydraulic pump (P) such that the hydraulic oil pressure detected by the pressure sensor (PS) reaches a die cushion pressure command value, and when a hydraulic oil pressure detected by the pressure sensor is equal to or higher than a set pressure of the relief valve (20), the control device (40) reversely rotates the hydraulic pump (P).

Description

TECHNICAL FIELD

The present disclosure relates to a die cushion device of a press machine.

BACKGROUND ART

Conventionally, as a die cushion device of a press machine, there is an air-type die cushion device that controls a die cushion pressure with air pressure.
However, in the air-type die cushion device described above, there is a problem that a cylinder diameter becomes large to increase a size of the device, and a problem that pressure adjustment and precise position control are difficult since pressure of air having compressibility is used.
Therefore, in order to solve such a problem, a die cushion device using a hydraulic cylinder is used in a press machine (see, for example, JP 2006-142312 A (Patent Literature 1)).

CITATION LIST

PATENT LITERATURE

Patent Literature 1: JP 2006-142312 A

SUMMARY OF INVENTION

TECHNICAL PROBLEMS

In the die cushion device using the hydraulic cylinder described above, since hydraulic oil having less compressibility than air is used, there is a problem that a large surge pressure is generated in a hydraulic circuit when an external force is generated during press molding, which adversely affects molding.
The present disclosure proposes a die cushion device that suppresses a surge pressure generated from a hydraulic cylinder, in die cushion pressure control of a press machine.

SOLUTIONS TO PROBLEMS

A die cushion device of the present disclosure includes:

a hydraulic cylinder that vertically moves a cushion pad;
a first hydraulic pump that supplies hydraulic oil from an oil tank to the hydraulic cylinder;
a relief valve that returns hydraulic oil discharged from the hydraulic cylinder, to the oil tank;
a pressure sensor that detects a hydraulic oil pressure in a flow path between the hydraulic cylinder and the first hydraulic pump; and
a control device that controls a number of rotations, or rotational speed, of the first hydraulic pump in accordance with the hydraulic oil pressure detected by the pressure sensor, in which
the control device reversely rotates the first hydraulic pump when a hydraulic oil pressure detected by the pressure sensor is equal to or higher than a predetermined pressure value.

According to the present disclosure, during press molding of a press machine, the control device controls the number of rotations of the hydraulic pump in accordance with a hydraulic oil pressure, detected by the pressure sensor, in a flow path between the hydraulic cylinder and the first hydraulic pump. In such die cushion pressure control of a press machine, when a surge pressure is generated in the hydraulic cylinder during press molding, and a hydraulic oil pressure detected by the pressure sensor is equal to or higher than a predetermined pressure value, the control device reversely rotates the hydraulic pump. Controlling a pressure with the hydraulic pump with high accuracy and high speed makes it possible to suppress a surge pressure generated from the hydraulic cylinder in the die cushion pressure control.
In a die cushion device according to one aspect of the present disclosure,
the pressure sensor detects a hydraulic oil pressure, which is a die cushion pressure of the hydraulic cylinder, and
the control device

controls a flow rate and a pressure of hydraulic oil supplied from the first hydraulic pump to the hydraulic cylinder, by controlling the number of rotations of the first hydraulic pump in accordance with the hydraulic oil pressure detected by the pressure sensor,
controls the number of rotations of the first hydraulic pump such that the hydraulic oil pressure detected by the pressure sensor reaches a die cushion pressure command value, and
reversely rotates the first hydraulic pump when a hydraulic oil pressure detected by the pressure sensor is equal to or higher than a set pressure of the relief valve, which is the predetermined pressure value.

According to the present disclosure, during press molding of a press machine, by the control device controlling the number of rotations of the hydraulic pump in accordance with the hydraulic oil pressure (corresponding to a die cushion pressure) detected by the pressure sensor, a flow rate and a pressure of hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder are controlled. In such die cushion pressure control of a press machine, when a surge pressure is generated in the hydraulic cylinder during press molding, the relief valve operates to cause hydraulic oil discharged from the hydraulic cylinder to be returned to the oil tank when the hydraulic oil pressure, which is a die cushion pressure of the hydraulic cylinder, is equal to or higher than the set pressure of the relief valve, which is the predetermined pressure value, while the control device reversely rotates the hydraulic pump when the hydraulic oil pressure detected by the pressure sensor is equal to or higher than the set pressure of the relief valve. Controlling a pressure with the hydraulic pump with high accuracy and high speed makes it possible to suppress a surge pressure generated from the hydraulic cylinder in the die cushion pressure control.
Further, a die cushion device according to an embodiment of the present disclosure includes
a check valve that is arranged, on a flow path between the hydraulic cylinder and the first hydraulic pump, on the first hydraulic pump side from a connection point at which the relief valve is connected to the flow path, and that regulates a flow of hydraulic oil from the hydraulic cylinder to the first hydraulic pump, in which
the set pressure of the relief valve is controlled with a pressure of hydraulic oil discharged from the first hydraulic pump, and
the control device reversely rotates the first hydraulic pump to open the relief valve when a hydraulic oil pressure detected by the pressure sensor is equal to or higher than the set pressure of the relief valve.
According to the present disclosure, when a hydraulic oil pressure detected by the pressure sensor is equal to or higher than the set pressure of the relief valve, the control device reversely rotates the hydraulic pump. At this time, the relief valve operates to cause hydraulic oil discharged from the hydraulic cylinder to be returned to the oil tank.
Further, a die cushion device according to one aspect of the present disclosure includes
a second hydraulic pump that controls the set pressure of the relief valve, in which
when the hydraulic oil pressure detected by the pressure sensor (PS) is equal to or higher than the set pressure of the relief valve (20), the control device reversely rotates the first hydraulic pump, and controls the number of rotations of the hydraulic first pump such that the hydraulic oil pressure detected by the pressure sensor reaches the die cushion pressure command value, and
when the hydraulic oil pressure detected by the pressure sensor (PS) reaches the die cushion pressure command value after a start of reverse rotation of the first hydraulic pump (P1), the control device (140) controls the number of rotations of the second hydraulic pump so as to increase the set pressure of the relief valve to close the relief valve.
According to the present disclosure, when a hydraulic oil pressure detected by the pressure sensor is equal to or higher than a set pressure of the relief valve, the control device reversely rotates the hydraulic pump, and controls the number of rotations of the hydraulic pump such that a hydraulic oil pressure detected by the pressure sensor reaches the die cushion pressure command value. Then, when the hydraulic oil pressure detected by the pressure sensor reaches the die cushion pressure command value after a start of reverse rotation of the hydraulic pump, the control device controls the number of rotations of a relief valve hydraulic pump so as to increase a set pressure of the relief valve to close the relief valve.
In a die cushion device according to one aspect of the present disclosure,
the first hydraulic pump has a discharge side connected to a vent port of the relief valve,
the pressure sensor detects a vent pressure of the relief valve,
the control device

controls the number of rotations of the first hydraulic pump in accordance with the vent pressure of the relief valve detected by the pressure sensor, and
reversely rotates the first hydraulic pump when the vent pressure of the relief valve detected by the pressure sensor is equal to or higher than the predetermined pressure value.

Here, reversely rotating the first hydraulic pump means rotating the first hydraulic pump in a rotation direction opposite to a rotation direction for discharging the hydraulic oil.
According to the present disclosure, in die cushion pressure control during press molding of a press machine, when a pressure of hydraulic oil discharged from the hydraulic cylinder is equal to or higher than the set pressure of the relief valve, the relief valve operates to cause hydraulic oil discharged from the hydraulic cylinder to be returned to the oil tank. When an external force is applied to the cushion pad during this press molding to cause a surge pressure in the hydraulic cylinder, a valve body of the relief valve is pushed and moved by the surge pressure to compress a vent chamber, and the vent pressure of the relief valve rises. Then, when the vent pressure of the relief valve detected by the pressure sensor is equal to or higher than the predetermined pressure value, the control device reversely rotates the first hydraulic pump. Controlling a pressure with the first hydraulic pump with high accuracy and high speed makes it possible to suppress a surge pressure generated from the hydraulic cylinder in the die cushion pressure control.
Further, a die cushion device according to one aspect of the present disclosure includes
a second hydraulic pump having a discharge side connected to a vent port of the relief valve, in which
the pressure sensor detects a vent pressure of the relief valve, and
the control device

controls the number of rotations of the first hydraulic pump in accordance with the vent pressure of the relief valve detected by the pressure sensor,
controls a set pressure of the relief valve by controlling the vent pressure of the relief valve with a pressure of hydraulic oil discharged from the second hydraulic pump, and
reversely rotates the first hydraulic pump and the second hydraulic pump when the vent pressure of the relief valve detected by the pressure sensor is equal to or higher than the predetermined pressure value.

According to the present disclosure, since hydraulic oil discharged from the hydraulic cylinder during die cushioning action is returned to the oil tank via the second hydraulic pump that is reversely rotated, it is possible to avoid heat generation (oil temperature rise) in the relief valve.
Further, in a die cushion device according to one aspect of the present disclosure,
when the vent pressure of the relief valve detected by the pressure sensor is equal to or higher than the predetermined pressure value, the first hydraulic pump and the second hydraulic pump are reversely rotated to cause hydraulic oil discharged from the hydraulic cylinder to be returned to the oil tank via the second hydraulic pump that is reversely rotated, while the number of rotations of the second hydraulic pump is controlled such that a die cushion pressure of the hydraulic cylinder reaches the die cushion pressure command value, and
when a die cushion pressure of the hydraulic cylinder reaches the die cushion pressure command value after a start of reverse rotation of the first hydraulic pump, the number of rotations of the first hydraulic pump is controlled to increase a set pressure of the relief valve from that before a start of the reverse rotation, to close the relief valve.
According to the present disclosure, when the vent pressure of the relief valve detected by the pressure sensor is equal to or higher than a predetermined pressure value, the control device reversely rotates the first hydraulic pump and the second hydraulic pump, and controls the number of rotations of the second hydraulic pump such that a die cushion pressure of the hydraulic cylinder reaches the die cushion pressure command value. This allows hydraulic oil discharged from the hydraulic cylinder to be returned to the oil tank via the second hydraulic pump. Further, when the die cushion pressure of the hydraulic cylinder reaches the die cushion pressure command value after a start of reverse rotation of the first hydraulic pump, the set pressure of the relief valve is increased from that before the start of the reverse rotation to close the relief valve, by controlling the number of rotations of the first hydraulic pump.
Further, in a die cushion device according to one aspect of the present disclosure,
the control device controls a set pressure of the relief valve by controlling the vent pressure of the relief valve with a pressure of hydraulic oil discharged from the first hydraulic pump.
Further, in a die cushion device according to one aspect of the present disclosure,
when the vent pressure of the relief valve detected by the pressure sensor is equal to or higher than the predetermined pressure value, the first hydraulic pump is reversely rotated to cause hydraulic oil discharged from the hydraulic cylinder to be returned to the oil tank via the relief valve, while the number of rotations of the first hydraulic pump is controlled such that a die cushion pressure of the hydraulic cylinder reaches the die cushion pressure command value.
According to the present disclosure, when the vent pressure of the relief valve detected by the pressure sensor is equal to or higher than the predetermined pressure value, the control device can reversely rotate the first hydraulic pump to cause hydraulic oil discharged from the hydraulic cylinder to be returned to the oil tank via the relief valve, and control the number of rotations of the first hydraulic pump such that a die cushion pressure of the hydraulic cylinder reaches the die cushion pressure command value.
Further, a die cushion device according to one aspect of the present disclosure includes
a check valve that is arranged on the oil path between the hydraulic cylinder and the first hydraulic pump and on the first hydraulic pump side from a connection point at which the relief valve is connected to the oil path, and that regulates a flow of hydraulic oil from the hydraulic cylinder to the first hydraulic pump.
According to the present disclosure, when the vent pressure of the relief valve detected by the pressure sensor is equal to or higher than the predetermined pressure value, and the first hydraulic pump is reversely rotated, all of hydraulic oil discharged from the hydraulic cylinder can be returned to the oil tank via the relief valve, by the check valve regulating a flow of hydraulic oil from the hydraulic cylinder to the first hydraulic pump.
Further, a die cushion device according to one aspect of the present disclosure includes
an electromagnetic valve that is arranged, on the oil path between the hydraulic cylinder and the first hydraulic pump, on the first hydraulic pump side from a connection point at which the relief valve is connected to the oil path.
According to the present disclosure, when the vent pressure of the relief valve detected by the pressure sensor is equal to or higher than a predetermined pressure value, and the first hydraulic pump is reversely rotated, the electromagnetic valve can be closed to reliably stop a flow of hydraulic oil from the hydraulic cylinder to the first hydraulic pump, and the vent pressure of the relief valve detected by the pressure sensor becomes stable, which enables stable control.
Further, a die cushion device according to one aspect of the present disclosure includes
a throttle that connects the connection point side and the pressure sensor, in which
in the die cushion device, the pressure sensor detects a hydraulic oil pressure, which is a die cushion pressure of the hydraulic cylinder.
According to the present disclosure, in a transitional period when a surge pressure is generated in the hydraulic cylinder in die cushion pressure control, the throttle connected to both ends of the check valve enables avoiding an influence of a sudden pressure change on the die cushion pressure control, which can ensure stable control.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic block diagram of a die cushion device according to a first embodiment of the present disclosure.
FIG. 2 is a graph showing an operation of the die cushion device.
FIG. 3 is a schematic block diagram of a die cushion device according to a second embodiment of the present disclosure.
FIG. 4 is a graph showing an operation of the die cushion device.
FIG. 5 is a schematic block diagram of a die cushion device according to a third embodiment of the present disclosure.
FIG. 6 is a graph showing an operation of the die cushion device of the third embodiment.
FIG. 7 is a schematic block diagram of a die cushion device according to a fourth embodiment of the present disclosure.
FIG. 8 is a graph showing an operation of the die cushion device of the fourth embodiment.
FIG. 9 is a schematic block diagram of a die cushion device according to a fifth embodiment of the present disclosure.
FIG. 10 is a graph showing an operation of the die cushion device of the fifth embodiment.
FIG. 11 is a schematic block diagram of a die cushion device according to a sixth embodiment of the present disclosure.
FIG. 12 is a graph showing an operation of the die cushion device of the sixth embodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments will be described. Note that, in the drawings, identical reference signs represent identical or corresponding parts.

[First embodiment]

FIG. 1 is a schematic block diagram of a die cushion device according to a first embodiment of the present disclosure.
As shown in FIG. 1, the die cushion device of the first embodiment includes: a hydraulic cylinder 10 that vertically moves a cushion pad 14; a hydraulic pump P that supplies hydraulic oil from an oil tank T to the hydraulic cylinder 10; a motor M that drives the hydraulic pump P; a relief valve 20 that returns hydraulic oil discharged from the hydraulic cylinder 10, to the oil tank T; a pressure sensor PS that detects a hydraulic oil pressure, which is a die cushion pressure of the hydraulic cylinder 10; a check valve 30 that regulates a flow of hydraulic oil from the hydraulic cylinder 10 to the hydraulic pump P; and a control device 40 that controls a flow rate and a pressure of hydraulic oil supplied from the hydraulic pump P to the hydraulic cylinder 10. The hydraulic pump P is an example of a first hydraulic pump.
The hydraulic cylinder 10 has a cylinder tube 11, a piston 12 that reciprocates in the cylinder tube 11, and a piston rod 13 having one end connected to the piston 12. The cushion pad 14 is connected to another end of the piston rod 13 of the hydraulic cylinder 10. The cushion pad 14 is supported by the hydraulic cylinder 10. The cushion pad 14 is provided with a position sensor (not shown) that detects a position of the cushion pad 14. A position signal indicating a position of the cushion pad 14 is outputted from the position sensor to the control device 40.
The check valve 30 is arranged on a flow path between the hydraulic cylinder 10 and the hydraulic pump P and on the hydraulic pump P side from a connection point at which the relief valve 20 is connected to the flow path,, i.e., the check valve 30 being arranged between the hydraulic pump P and the connection point on the flow path. The hydraulic cylinder 10 has a port 10a connected to a discharge side of the hydraulic pump P via the check valve 30.
Further, the pressure sensor PS is connected to the port 10a of the hydraulic cylinder 10. From the pressure sensor PS, a pressure signal is outputted to the control device 40.
Further, the port 10a of the hydraulic cylinder 10 is connected to an inlet port 21 of the relief valve 20, and an outlet port 22 of the relief valve 20 is connected to the oil tank T. The relief valve 20 is a pilot-operated relief valve, and the discharge side of the hydraulic pump P is connected to a vent port 23 (pilot port) of the relief valve 20. This allows a discharge pressure (a pilot pressure) of the hydraulic pump P to be supplied to the vent port 23 of the relief valve 20, to control a set pressure Pp of the relief valve 20.
The control device 40 receives a die cushion pressure command signal indicating a die cushion pressure command value, a position signal indicating a position of the cushion pad 14, and a pressure signal from the pressure sensor PS, and outputs a drive signal for driving the motor M, to control the number of rotations, or rotational speed, of the hydraulic pump P. The die cushion pressure command signal is inputted from a main machine controller (not shown) or the like of a press machine.
FIG. 2 shows an operation of the die cushion device.
As shown in FIG. 2, in press molding of a press machine, immediately before an external force is generated during die cushioning action, the control device 40 controls the number of rotations of the hydraulic pump P such that a hydraulic oil pressure detected by the pressure sensor PS reaches a die cushion pressure command value, and keeps a flow rate of the hydraulic pump P constant to set a pressure of the vent port 23 to a pressure corresponding to the die cushion pressure command value.
Then, when an external force is generated during die cushioning action, a surge pressure is superimposed on a die cushion pressure. When a die cushion pressure at the port 10a of the hydraulic cylinder 10 becomes equal to or higher than the set pressure Pp of the relief valve 20, the relief valve 20 operates to cause hydraulic oil discharged from the hydraulic cylinder 10 to be returned to the oil tank T via the relief valve 20. At this time, a hydraulic oil pressure detected by the pressure sensor PS is equal to or higher than the set pressure Pp of the relief valve 20, and the control device 40 reversely rotates the hydraulic pump P.
After that, the control device 40 controls the number of rotations of the hydraulic pump P such that the hydraulic oil pressure detected by the pressure sensor PS returns to the die cushion pressure command value.
As described above, according to the die cushion device having the above configuration, during press molding of a press machine, by the control device 40 controlling the number of rotations of the hydraulic pump P in accordance with a hydraulic oil pressure (corresponding to a die cushion pressure) detected by the pressure sensor PS, the flow rate and the pressure of hydraulic oil supplied from the hydraulic pump P to the hydraulic cylinder 10 are controlled. In die cushion pressure control of the press machine, when a surge pressure is generated in the hydraulic cylinder 10 during press molding, the relief valve 20 operates to cause hydraulic oil discharged from the hydraulic cylinder 10 to be returned to the oil tank T when a die cushion pressure at the port 10a of the hydraulic cylinder 10 becomes equal to or higher than the set pressure Pp of the relief valve 20, while the control device 40 reversely rotates the hydraulic pump P when a hydraulic oil pressure detected by the pressure sensor PS is equal to or higher than the set pressure Pp of the relief valve 20. Controlling a die cushion pressure with the hydraulic pump P with high accuracy and high speed makes it possible to suppress a surge pressure generated from the hydraulic cylinder 10.
In addition, in the die cushion device, since the set pressure Pp of the vent port 23 of the pilot-operated type relief valve 20 is directly controlled by the hydraulic pump P, operation delay of the relief valve 20 does not occur, and a surge pressure can be reliably suppressed, as compared to a balance piston type relief valve with a slow response.

[Second embodiment]

FIG. 3 is a schematic block diagram of a die cushion device according to a second embodiment of the present disclosure. In FIG. 3, components identical to those in FIG. 1 are denoted by identical reference signs.
As shown in FIG. 3, the die cushion device of the second embodiment includes: a hydraulic cylinder 10 that vertically moves a cushion pad 14; a hydraulic pump P1 that supplies hydraulic oil from an oil tank to the hydraulic cylinder 10; a motor M1 that drives the hydraulic pump P1; a relief valve 20 that returns hydraulic oil discharged from the hydraulic cylinder 10, to the oil tank T; a pressure sensor PS that detects a hydraulic oil pressure, which is a die cushion pressure of the hydraulic cylinder 10; and a control device 140 that controls a flow rate and a pressure of hydraulic oil supplied from the hydraulic pump P1 to the hydraulic cylinder 10. The hydraulic pump P1 is an example of a first hydraulic pump.
Further, the die cushion device includes a hydraulic pump P2 that controls a set pressure Pp of the relief valve 20, and a motor M2 that drives the hydraulic pump P2. The hydraulic pump P2 is an example of a second hydraulic pump, and has a smaller capacity than that of the hydraulic pump P1.
The hydraulic pump P1 has a discharge side connected to a port 10a of the hydraulic cylinder 10.
Further, the pressure sensor PS is connected to the port 10a of the hydraulic cylinder 10. From the pressure sensor PS, a pressure signal is outputted to the control device 140. In addition, a position sensor (not shown) is provided on the cushion pad 14 supported by the hydraulic cylinder 10, and a position signal indicating a position of the cushion pad 14 is outputted to the control device 40 from the position sensor.
Further, the port 10a of the hydraulic cylinder 10 is connected to an inlet port 21 of the relief valve 20, and an outlet port 22 of the relief valve 20 is connected to the oil tank T. The relief valve 20 is a pilot-operated relief valve, and a discharge side of the hydraulic pump P2 is connected to a vent port 23 of the relief valve 20. This allows a discharge pressure (a pilot pressure) of the hydraulic pump P2 to be supplied to the vent port 23 of the relief valve 20, to control the set pressure Pp of the relief valve 20.
The control device 140 receives a die cushion pressure command signal indicating a die cushion pressure command value, a position signal indicating a position of the cushion pad 14, and a pressure signal from the pressure sensor PS, and outputs a drive signal for driving the motors M1 and M2, to individually control the number of rotations of the hydraulic pumps P1 and P2. The die cushion pressure command signal is inputted from a main machine controller (not shown) or the like of a press machine.
FIG. 4 shows an operation of the die cushion device.
As shown in FIG. 4, in press molding of a press machine, immediately before an external force is generated during die cushioning action, the control device 140 controls the number of rotations of the hydraulic pump P1 such that a hydraulic oil pressure detected by the pressure sensor PS reaches a die cushion pressure command value, to keep the flow rate of the hydraulic pump P1 constant. At this time, the control device 40 controls the number of rotations of the hydraulic pump P2 such that the set pressure Pp of the vent port 23 of the relief valve 20 becomes a pressure corresponding to the die cushion pressure command value.
Then, when an external force is generated during die cushioning action, a surge pressure is superimposed on a die cushion pressure. When a die cushion pressure at the port 10a of the hydraulic cylinder 10 becomes equal to or higher than the set pressure Pp of the relief valve 20, the relief valve 20 operates to cause hydraulic oil discharged from the hydraulic cylinder 10 to be returned to the oil tank T via the relief valve 20. At this time, a hydraulic oil pressure detected by the pressure sensor PS is equal to or higher than the die cushion pressure command value, and the control device 140 reversely rotates the hydraulic pump P1.
After that, the control device 140 controls the hydraulic pump P1 to have an appropriate number of rotations such that the hydraulic oil pressure detected by the pressure sensor PS returns to the die cushion pressure command value. Further, the control device 140 closes the relief valve 20 by controlling the number of rotations of the hydraulic pump P2, to change a discharge pressure of the hydraulic pump P2 such that the set pressure Pp of the relief valve 20 becomes higher than a pressure immediately before the external force is generated during die cushioning action.
According to the die cushion device having the above configuration, during press molding of a press machine, by the control device 140 controlling the number of rotations of the hydraulic pump P1 in accordance with a hydraulic oil pressure (corresponding to a die cushion pressure) detected by the pressure sensor PS, the flow rate and the pressure of hydraulic oil supplied from the hydraulic pump P1 to the hydraulic cylinder 10 are controlled. In die cushion pressure control of the press machine, when a surge pressure is generated in the hydraulic cylinder 10 during press molding, the relief valve 20 operates to cause hydraulic oil discharged from the hydraulic cylinder 10 to be returned to the oil tank T when a die cushion pressure at the port 10a of the hydraulic cylinder 10 becomes equal to or higher than the set pressure Pp of the relief valve 20, while the control device 140 reversely rotates the hydraulic pump P1 when a hydraulic oil pressure detected by the pressure sensor PS is equal to or higher than the set pressure Pp of the relief valve 20. Controlling a die cushion pressure with the hydraulic pump P1 with high accuracy and high speed makes it possible to suppress a surge pressure generated from the hydraulic cylinder 10.
In addition, in the die cushion device, since the set pressure Pp of the vent port 23 of the pilot-operated type relief valve 20 is directly controlled by the hydraulic pump P2, operation delay of the relief valve 20 does not occur, and a surge pressure can be reliably suppressed, as compared to a balance piston type relief valve with a slow response.
In addition, in the die cushion device, since hydraulic oil discharged from the hydraulic cylinder 10 during die cushioning action is returned to the oil tank T via the hydraulic pump P1 that is reversely rotated, it is possible to avoid heat generation (oil temperature rise) in the relief valve 20.
Note that electric energy generated by the motor M1 when the motor M1 is reversely rotated by the hydraulic pump P1 that is reversely rotated is consumed by a regenerative resistor.
A conventional air-type die cushion device has a problem that a cylinder diameter becomes large to increase a size of the device, and a problem that pressure adjustment and precise position control are difficult since pressure of air having compressibility is used, but the first and second embodiments described above can solve these problems.

[Third embodiment]

FIG. 5 is a schematic block diagram of a die cushion device according to a third embodiment of the present disclosure.
As shown in FIG. 5, the die cushion device of the third embodiment includes: a hydraulic cylinder 10 that vertically moves a cushion pad 14 of a press machine (not shown); a hydraulic pump P that supplies hydraulic oil from an oil tank T to the hydraulic cylinder 10; a motor M that drives the hydraulic pump P; a relief valve 20 that returns hydraulic oil discharged from the hydraulic cylinder 10, to the oil tank T; a check valve 30 that regulates a flow of hydraulic oil from the hydraulic cylinder 10 to the hydraulic pump P; and a pressure sensor PS that detects a vent pressure of the relief valve 20; and a control device 240 that controls a flow rate and a pressure of hydraulic oil supplied from the hydraulic pump P to the hydraulic cylinder 10. The hydraulic pump P is an example of a first hydraulic pump.
The hydraulic cylinder 10 has a cylinder tube 11, a piston 12 that reciprocates in the cylinder tube 11, and a piston rod 13 having one end connected to the piston 12. Another end of the piston rod 13 of the hydraulic cylinder 10 is connected to the cushion pad 14. The cushion pad 14 is supported by the hydraulic cylinder 10. The cushion pad 14 is provided with a position sensor (not shown) that detects a position of the cushion pad 14. A position signal indicating a position of the cushion pad 14 is outputted from the position sensor to the control device 240.
The check valve 30 is arranged on an oil path between the hydraulic cylinder 10 and the hydraulic pump P and on the hydraulic pump P side from a connection point at which the relief valve 20 is connected to the oil path. The hydraulic cylinder 10 has a port 10a connected to a discharge side of the hydraulic pump P via the check valve 30.
Further, the pressure sensor PS is connected between the discharge side of the hydraulic pump P and the check valve 30. A pressure signal indicating a vent pressure of the relief valve 20 is outputted from the pressure sensor PS to the control device 240.
Further, the port 10a of the hydraulic cylinder 10 is connected to an inlet port 21 of the relief valve 20, and an outlet port 22 of the relief valve 20 is connected to the oil tank T. The relief valve 20 is a pilot-operated relief valve, and the discharge side of the hydraulic pump P is connected to a vent port 23 of the relief valve 20. This allows a discharge pressure of the hydraulic pump P to be supplied to the vent port 23 of the relief valve 20, to control a set pressure Pset of the relief valve 20.
The control device 240 receives a die cushion pressure command signal indicating a die cushion pressure command value, a position signal indicating a position of the cushion pad 14, and a pressure signal from the pressure sensor PS, and outputs a drive signal for driving the motor M, to control the number of rotations of the hydraulic pump P. The die cushion pressure command signal is inputted from a main machine controller (not shown) or the like of the press machine.
FIG. 6 shows an operation of the die cushion device. In FIG. 6, a horizontal axis indicates time [any scale], and a vertical axis indicates a pressure [any scale] and a flow rate [any scale].
As shown in FIG. 6, in press molding of the press machine, immediately before a slide (not shown) collides with the cushion pad 14 to generate an external force, the control device 240 controls the number of rotations of the hydraulic pump P such that a die cushion pressure of the hydraulic cylinder 10 reaches a die cushion pressure command value, on the basis of a vent pressure of the relief valve 20 detected by the pressure sensor PS. At this time, the control device 240 controls the number of rotations of the hydraulic pump P such that a pressure of the vent port 23 of the relief valve 20 becomes a set vent pressure Pv.
Then, when the slide (not shown) collides with the cushion pad 14 to generate an external force, a surge pressure is superimposed on a die cushion pressure. When a die cushion pressure at the port 10a of the hydraulic cylinder 10 becomes equal to or higher than the set pressure Pset of the relief valve 20, the relief valve 20 operates to cause hydraulic oil discharged from the hydraulic cylinder 10 to be returned to the oil tank T via the relief valve 20.
Here, when a set vent pressure is Pv and a differential pressure spring surface pressure of the relief valve 20 is Pd, the set pressure Pset of the relief valve 20 is expressed as follows. $Pset = Pv + Pd$
When a surge pressure is superimposed on a die cushion pressure, and a vent pressure of the relief valve 20 detected by the pressure sensor PS is equal to or higher than a predetermined pressure value Pv, the control device 240 reversely rotates the hydraulic pump P. In the present embodiment, the predetermined pressure value Pv is the same as the set vent pressure Pv, but the predetermined pressure value Pv may be larger than the set vent pressure.
After that, the cushion pad 14 is pushed down by the slide at a predetermined speed, and the control device 240 controls the number of rotations of the hydraulic pump P such that a vent pressure detected by the pressure sensor PS returns to the set vent pressure Pv.
As described above, in the die cushion device having the above configuration, by the control device 240 controlling the number of rotations of the hydraulic pump P in accordance with a vent pressure detected by the pressure sensor PS during press molding of the press machine, the flow rate and the pressure of hydraulic oil supplied from the hydraulic pump P to the hydraulic cylinder 10 are controlled. In addition, in die cushion pressure control of the press machine, when a surge pressure is generated in the hydraulic cylinder 10 during press molding, the relief valve 20 operates to cause hydraulic oil discharged from the hydraulic cylinder 10 to be returned to the oil tank T when a die cushion pressure at the port 10a of the hydraulic cylinder 10 becomes equal to or higher than the set pressure Pset of the relief valve 20, while the control device 240 reversely rotates the hydraulic pump P when a vent pressure of the relief valve 20 detected by the pressure sensor PS is equal to or higher than the predetermined pressure value Pv.
In the die cushion device, controlling the die cushion pressure with the hydraulic pump P with high accuracy and high speed makes it possible to suppress a surge pressure generated from the hydraulic cylinder 10.
In addition, in the die cushion device, since a vent pressure of the pilot-operated type relief valve 20 is directly controlled by the hydraulic pump P, operation delay of the relief valve 20 does not occur, and a surge pressure can be reliably suppressed, as compared to a balance piston type relief valve with a slow response.
Further, when a vent pressure of the relief valve 20 detected by the pressure sensor PS is equal to or higher than the predetermined pressure value Pv, the control device 240 reversely rotates the hydraulic pump P, and controls the number of rotations of the hydraulic pump P such that a die cushion pressure of the hydraulic cylinder 10 reaches the die cushion pressure command value. This allows hydraulic oil discharged from the hydraulic cylinder 10 to be returned to the oil tank T via the relief valve 20.
Further, when a vent pressure of the relief valve 20 detected by the pressure sensor PS is equal to or higher than the predetermined pressure value Pv, and the hydraulic pump P is reversely rotated, the check valve 30 regulates a flow of hydraulic oil from the hydraulic cylinder 10 to the hydraulic pump P. This allows all of hydraulic oil discharged from the hydraulic cylinder 10 to be returned to the oil tank T via the relief valve 20.
Further, in the die cushion device, stable control with good responsiveness is possible such that a discharge side of the hydraulic pump P does not have a negative pressure when the hydraulic pump P is reversely rotated, even when a pump capacity of the hydraulic pump P is large. Therefore, there is no need to devise ways such as adding a vacuum check valve that supplies hydraulic oil from the oil tank T to between the discharge side of the hydraulic pump P and the check valve 30, or limiting the reverse rotation.

[Fourth embodiment]

FIG. 7 is a schematic block diagram of a die cushion device according to a fourth embodiment of the present disclosure. The die cushion device of the fourth embodiment has the same configuration as the die cushion device of the third embodiment, except for an electromagnetic valve 50 and a control device 340.
As shown in FIG. 7, the die cushion device of the fourth embodiment has the electromagnetic valve 50 arranged, on an oil path between the hydraulic cylinder 10 and the hydraulic pump P, on a hydraulic pump P side from a connection point at which the relief valve 20 is connected to the oil path.
When a solenoid 53 is excited, this electromagnetic valve 50 is at a switching position on a left side, and a first port 51 and a second port 52 communicate with each other. On the other hand, when the solenoid 53 is not excited, the electromagnetic valve 50 is at a switching position on a right side, and the first port 51 and the second port 52 are individually closed.
FIG. 8 shows an operation of the die cushion device. In FIG. 8, a horizontal axis indicates time [any scale], and a vertical axis indicates a pressure [any scale] and a flow rate [any scale].
As shown in FIG. 8, in press molding of a press machine, immediately before an external force is generated during die cushioning action, the control device 340 controls the number of rotations of the hydraulic pump P such that a die cushion pressure of the hydraulic cylinder 10 reaches a die cushion pressure command value, on the basis of a vent pressure of the relief valve 20 detected by a pressure sensor PS. At this time, the control device 340 controls the number of rotations of the hydraulic pump P such that a pressure of a vent port 23 of the relief valve 20 becomes a set vent pressure Pv.
Then, when an external force is generated during die cushioning action, a surge pressure is superimposed on a die cushion pressure. When a die cushion pressure at a port 10a of the hydraulic cylinder 10 becomes equal to or higher than a set pressure Pset of the relief valve 20, the relief valve 20 operates to cause hydraulic oil discharged from the hydraulic cylinder 10 to be returned to the oil tank T via the relief valve 20. At this time, when a vent pressure of the relief valve 20 detected by the pressure sensor PS is equal to or higher than the predetermined pressure value Pv, the hydraulic pump P is reversely rotated.
After that, a cushion pad 14 is pushed down by a slide at a predetermined speed, and the control device 340 controls the number of rotations of the hydraulic pump P such that a vent pressure detected by the pressure sensor PS returns to the set vent pressure Pv.
The die cushion device of the fourth embodiment has effects similar to those of the die cushion device of the third embodiment.
Further, since the electromagnetic valve 50 is closed when a vent pressure of the relief valve 20 detected by the pressure sensor PS is equal to or higher than the predetermined pressure value Pv and the hydraulic pump P is reversely rotated, all of hydraulic oil discharged from the hydraulic cylinder 10 can be returned to the oil tank T via the relief valve 20.
As compared with the die cushion device provided with the check valve 30 of the third embodiment, the die cushion device of the fourth embodiment enables stable control by reliably blocking the oil path between the hydraulic pump P and the hydraulic cylinder 10 even if a pressure overshoot or undershoot occurs.

[Fifth embodiment]

FIG. 9 is a schematic block diagram of a die cushion device according to a fifth embodiment of the present disclosure. In FIG. 9, components identical to those in FIG. 5 are denoted by identical reference signs.
As shown in FIG. 9, the die cushion device of the fifth embodiment includes: a hydraulic cylinder 10 that vertically moves a cushion pad 14; a hydraulic pump P2 that controls a set pressure Pset of a relief valve 20; a motor M2 that drives the hydraulic pump P2; a hydraulic pump P1 that supplies hydraulic oil from an oil tank T to the hydraulic cylinder 10; a motor M1 that drives the hydraulic pump P1; the relief valve 20 that returns hydraulic oil discharged from the hydraulic cylinder 10, to the oil tank T; a pressure sensor PS2 that detects a vent pressure of the relief valve 20; a pressure sensor PS1 that detects a hydraulic oil pressure, which is a die cushion pressure of the hydraulic cylinder 10; and a control device 440 that controls the number of rotations of the hydraulic pumps P1 and P2 by controlling the motors M1 and M2.
The control device 440 controls the number of rotations of the hydraulic pump P2, to control a flow rate and a pressure of hydraulic oil supplied to a vent port 23 of the relief valve 20. The control device 440 controls the number of rotations of the hydraulic pump P1, to control a flow rate and a pressure of hydraulic oil supplied from the hydraulic pump P1 to the hydraulic cylinder 10.
The hydraulic pump P2 is an example of a second hydraulic pump. The hydraulic pump P1 is an example of a first hydraulic pump. The hydraulic pump P2 has a smaller capacity than that of the hydraulic pump P1.
The pressure sensor PS2 is connected to the vent port 23 of the relief valve 20. A second pressure signal indicating a vent pressure of the relief valve 20 is outputted from the pressure sensor PS2 to the control device 440.
The hydraulic pump P1 has a discharge side connected to a port 10a of the hydraulic cylinder 10. The pressure sensor PS1 is connected to the port 10a of the hydraulic cylinder 10. A first pressure signal indicating a die cushion pressure is outputted from the pressure sensor PS1 to the control device 440.
In addition, a position sensor (not shown) is provided on the cushion pad 14 supported by the hydraulic cylinder 10, and a position signal indicating a position of the cushion pad 14 is outputted to the control device 440 from the position sensor.
Further, the port 10a of the hydraulic cylinder 10 is connected to an inlet port 21 of the relief valve 20, and an outlet port 22 of the relief valve 20 is connected to the oil tank T. The relief valve 20 is a pilot-operated relief valve, and a discharge side of the hydraulic pump P2 is connected to the vent port 23 of the relief valve 20. This allows a discharge pressure of the hydraulic pump P2 to be supplied to the vent port 23 of the relief valve 20, to control the set pressure Pset of the relief valve 20.
The control device 440 receives a die cushion pressure command signal indicating a die cushion pressure command value, the position signal indicating a position of the cushion pad 14, and the first and second pressure signals from the pressure sensors PS1 and PS2, and outputs first and second drive signals for driving the motors M1 and M2, to individually control the number of rotations of the hydraulic pumps P1 and P2. The die cushion pressure command signal is inputted from a main machine controller (not shown) or the like of a press machine.
FIG. 10 shows an operation of the die cushion device. In FIG. 10, a horizontal axis indicates time [any scale], and a vertical axis indicates a pressure [any scale] and a flow rate [any scale].
As shown in FIG. 10, in press molding of the press machine, immediately before an external force is generated during die cushioning action, the control device 440 controls the number of rotations of the hydraulic pump P1 such that a hydraulic oil pressure detected by the pressure sensor PS1 reaches a die cushion pressure command value. At this time, the control device 440 controls the number of rotations of the hydraulic pump P2 such that a pressure of the vent port 23 of the relief valve 20 becomes a set vent pressure Pv1.
Here, when a differential pressure spring surface pressure of the relief valve 20 is Pd, the die cushion pressure command value is $die cushion pressure command value \leq Pset (= Pv 1 + Pd)$
and
the relief valve stands by without a flow from the hydraulic pump P1 to the relief valve 20.
Then, when an external force is generated during die cushioning action, a surge pressure is superimposed on a die cushion pressure. When a die cushion pressure at the port 10a of the hydraulic cylinder 10 becomes equal to or higher than the set pressure Pset of the relief valve 20, the relief valve 20 operates to cause hydraulic oil discharged from the hydraulic cylinder 10 to be returned to the oil tank T via the relief valve 20. At this time, when a vent pressure of the relief valve 20 detected by the pressure sensor PS2 is equal to or higher than the predetermined pressure value Pv1, the control device 440 reversely rotates the hydraulic pump P1. Alternatively, the hydraulic pump P1 is reversely rotated to cause hydraulic oil discharged from the hydraulic cylinder 10 to be returned to the oil tank T via the hydraulic pump P1 since a hydraulic oil pressure detected by the pressure sensor PS1 exceeds the die cushion pressure command value. In the present embodiment, the predetermined pressure value Pv1 is the same as the set vent pressure Pv1, but the predetermined pressure value Pv1 may be larger than the set vent pressure.
After that, the cushion pad 14 is pushed down by a slide at a predetermined speed, and the control device 440 controls the hydraulic pump P1 to have an appropriate number of rotations such that the hydraulic oil pressure detected by the pressure sensor PS1 returns to the die cushion pressure command value.
In addition, the control device 440 closes the relief valve 20 by controlling the number of rotations of the hydraulic pump P2, to change a discharge pressure of the hydraulic pump P2 such that a pressure at the vent port 23 of the relief valve 20 becomes a set vent pressure Pv2 that is higher than the set vent pressure Pv1 immediately before the external force is generated during die cushioning action.
According to the die cushion device having the above configuration, during press molding of the press machine, the flow rate and the pressure of hydraulic oil supplied from the hydraulic pump P1 to the hydraulic cylinder 10 are controlled, by the control device 440 controlling a number of rotations of the hydraulic pump P1 in accordance with a vent pressure (corresponding to a die cushion pressure) of the relief valve 20 detected by the pressure sensor PS2. In die cushion pressure control of the press machine, when a surge pressure is generated in the hydraulic cylinder 10 during press molding, the relief valve 20 operates to cause hydraulic oil discharged from the hydraulic cylinder 10 to be returned to the oil tank T when a die cushion pressure at the port 10a of the hydraulic cylinder 10 becomes equal to or higher than the set pressure Pset of the relief valve 20, while the control device 440 reversely rotates the hydraulic pump P1 when a vent pressure of the relief valve 20 detected by the pressure sensor PS2 is equal to or higher than the predetermined pressure value Pv1, or a hydraulic oil pressure detected by the pressure sensor PS1 exceeds the die cushion pressure command value.
In the die cushion device, controlling the die cushion pressure with the hydraulic pump P1 with high accuracy and high speed makes it possible to suppress a surge pressure generated from the hydraulic cylinder 10.
In addition, in the die cushion device, since a pressure of the pilot-operated type relief valve 20 is directly controlled by the hydraulic pump P2, operation delay of the relief valve 20 does not occur, and a surge pressure can be reliably suppressed, as compared to a balance piston type relief valve with a slow response.
In addition, in the die cushion device, since hydraulic oil discharged from the hydraulic cylinder 10 during die cushioning action is returned to the oil tank T via the hydraulic pump P1 that is reversely rotated, it is possible to avoid heat generation (oil temperature rise) in the relief valve 20.
Note that electric energy generated by the motor M1 when the motor M1 is reversely rotated by the hydraulic pump P1 that is reversely rotated is consumed by a regenerative resistor.
A conventional air-type die cushion device has a problem that a cylinder diameter becomes large to increase a size of the device, and a problem that pressure adjustment and precise position control are difficult since pressure of air having compressibility is used, but the third to fifth embodiments described above can solve these problems.
Further, when a vent pressure of the relief valve 20 detected by the pressure sensor PS2 is equal to or higher than the predetermined pressure value Pv1, the control device 440 reversely rotates the hydraulic pump P1 and the hydraulic pump P2, and controls the number of rotations of the first hydraulic pump P1 such that a die cushion pressure of the hydraulic cylinder 10 reaches a die cushion pressure command value. This allows hydraulic oil discharged from the hydraulic cylinder 10 to be returned to the oil tank T via the hydraulic pump P1.
Further, when the die cushion pressure of the hydraulic cylinder 10 reaches the die cushion pressure command value after a start of the reverse rotation of the hydraulic pump P2, the relief valve 20 is closed by controlling the number of rotations of the hydraulic pump P2 to increase a set pressure of the relief valve 20 from the set vent pressure Pv1 before a start of reverse rotation, to reach the set vent pressure Pv2.
Further, in the die cushion device, since large surge generation in response delay due to inertia can be covered by a response of the relief valve 20 even when a pump capacity of the hydraulic pump P1 is large, the surge generation can be minimized.

[Sixth embodiment]

FIG. 11 is a schematic block diagram of a die cushion device according to a sixth embodiment of the present disclosure. The die cushion device of the sixth embodiment has the same configuration as the die cushion device of the third embodiment, except for a throttle 60 and an operation of a control device 540.
In the die cushion device of the sixth embodiment, as shown in FIG. 11, the throttle 60 is connected to both ends of a check valve 30.
FIG. 12 shows an operation of the die cushion device. In FIG. 12, a horizontal axis indicated time [any scale], and a vertical axis indicates a pressure [any scale] and a flow rate [any scale].
As shown in FIG. 12, in press molding of a press machine, immediately before a slide (not shown) collides with a cushion pad 14 to generate an external force, the control device 540 controls the number of rotations of a hydraulic pump P such that a die cushion pressure of a hydraulic cylinder 10 reaches a die cushion pressure command value, on the basis of a hydraulic oil pressure detected by a pressure sensor PS. At this time, the control device 540 controls the number of rotations of the hydraulic pump P such that a pressure of a vent port 23 of a relief valve 20 becomes a set vent pressure Pv.
Then, when a slide (not shown) collides with the cushion pad 14 to generate an external force, a surge pressure is superimposed on a die cushion pressure. When a die cushion pressure at a port 10a of the hydraulic cylinder 10 becomes equal to or higher than a set pressure Pset of the relief valve 20, the relief valve 20 operates to cause hydraulic oil discharged from the hydraulic cylinder 10 to be returned to an oil tank T via the relief valve 20.
When a surge pressure is superimposed on a die cushion pressure, and a surge pressure detected by the pressure sensor PS via the throttle 60 is equal to or higher than the predetermined pressure value Pv, the control device 540 reversely rotates the hydraulic pump P.
After that, the cushion pad 14 is pushed down by the slide at a predetermined speed, and the control device 540 controls the number of rotations of the hydraulic pump P such that the pressure detected by the pressure sensor PS returns to the set vent pressure Pv. At this time, the die cushion pressure of the hydraulic cylinder 10 becomes slightly higher than that immediately before the surge pressure is generated due to an influence of a passage pressure loss and a flow rate-pressure characteristic of the relief valve 20, and the die cushion pressure of the hydraulic cylinder 10 gradually approaches the die cushion pressure command value, as compared with the case of the third embodiment.
As described above, in the die cushion device having the above configuration, in die cushion pressure control of a press machine, when a surge pressure is generated in the hydraulic cylinder 10 during press molding, the relief valve 20 operates to cause hydraulic oil discharged from the hydraulic cylinder 10 to be returned to the oil tank T when a die cushion pressure at the port 10a of the hydraulic cylinder 10 becomes equal to or higher than the set pressure Pset of the relief valve 20, while the control device 540 reversely rotates the hydraulic pump P when a surge pressure detected by the pressure sensor PS via the throttle 60 is equal to or higher than the predetermined pressure value Pv.
As compared with the die cushion device of the third embodiment, in the die cushion device of the sixth embodiment, the throttle 60 connected to both ends of the check valve 30 enables avoiding an influence of a sudden pressure change on the die cushion pressure control in a transitional period when a surge pressure is generated in the hydraulic cylinder 10 in the die cushion pressure control, which can ensure stable control.
Although the check valve 30 is used in the sixth embodiment, an electromagnetic valve may be used instead of the check valve as in the fourth embodiment.
In the first to sixth embodiments described above, the die cushion devices including one hydraulic cylinder 10 that vertically moves the cushion pad 14 have been described, but the present invention may be applied to a die cushion device provided with a plurality of hydraulic cylinders that vertically move a cushion pad.
Although specific embodiments of the present disclosure have been described, the present disclosure is not limited to the first to sixth embodiments, and various modifications can be made within the scope of the present disclosure.
A die cushion device of the present disclosure includes:

a hydraulic cylinder that vertically moves a cushion pad;
a hydraulic pump that supplies hydraulic oil from an oil tank to the hydraulic cylinder;
a relief valve that returns hydraulic oil discharged from the hydraulic cylinder, to the oil tank;
a pressure sensor that detects a hydraulic oil pressure, which is a die cushion pressure of the hydraulic cylinder; and
a control device that controls a flow rate and a pressure of hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder, by controlling a number of rotations, or rotational speed, of the hydraulic pump in accordance with a hydraulic oil pressure detected by the pressure sensor, in which
the control device
- controls the number of rotations of the hydraulic pump such that the hydraulic oil pressure detected by the pressure sensor reaches a die cushion pressure command value, and
- reversely rotates the hydraulic pump when a hydraulic oil pressure detected by the pressure sensor is equal to or higher than a set pressure of the relief valve.

According to the present disclosure, during press molding of a press machine, by the control device controlling the number of rotations of the hydraulic pump in accordance with a hydraulic oil pressure (corresponding to a die cushion pressure) detected by the pressure sensor, a flow rate and a pressure of hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder are controlled. In such die cushion pressure control of the press machine, when a surge pressure is generated in the hydraulic cylinder during press molding, the relief valve operates to cause hydraulic oil discharged from the hydraulic cylinder to be returned to the oil tank when a hydraulic oil pressure, which is a die cushion pressure of the hydraulic cylinder, becomes equal to or higher than the set pressure of the relief valve, while the control device reversely rotates the hydraulic pump when the hydraulic oil pressure detected by the pressure sensor exceeds the set pressure of the relief valve. Controlling a pressure with the hydraulic pump with high accuracy and high speed makes it possible to suppress the surge pressure generated from the hydraulic cylinder in the die cushion pressure control.
Further, a die cushion device according to one aspect of the present disclosure includes
a check valve that is arranged, on a flow path between the hydraulic cylinder and the hydraulic pump, on the hydraulic pump side from a connection point at which the relief valve is connected to the flow path, , and that regulates a flow of hydraulic oil from the hydraulic cylinder to the hydraulic pump, in which
the set pressure of the relief valve is controlled with a pressure of hydraulic oil discharged from the hydraulic pump, and
the control device reversely rotates the hydraulic pump to open the relief valve when a hydraulic oil pressure detected by the pressure sensor is equal to or higher than the set pressure of the relief valve.
According to the present disclosure, when a hydraulic oil pressure detected by the pressure sensor is equal to or higher than the set pressure of the relief valve, the control device reversely rotates the hydraulic pump. At this time, the relief valve operates to cause hydraulic oil discharged from the hydraulic cylinder to be returned to the oil tank.
Further, a die cushion device according to one aspect of the present disclosure includes
a relief valve hydraulic pump that controls the set pressure of the relief valve, in which
the control device

reversely rotates the hydraulic pump, and controls the number of rotations of the hydraulic pump such that a hydraulic oil pressure detected by the pressure sensor reaches the die cushion pressure command value, when the hydraulic oil pressure detected by the pressure sensor is equal to or higher than the set pressure of the relief valve, and
controls the number of rotations of the relief valve hydraulic pump so as to increase the set pressure of the relief valve to close the relief valve when the hydraulic oil pressure detected by the pressure sensor reaches the die cushion pressure command value after a start of reverse rotation of the hydraulic pump.

According to the present disclosure, when the hydraulic oil pressure detected by the pressure sensor is equal to or higher than the set pressure of the relief valve, the control device reversely rotates the hydraulic pump, and controls the number of rotations of the hydraulic pump such that the hydraulic oil pressure detected by the pressure sensor reaches the die cushion pressure command value. Then, when the hydraulic oil pressure detected by the pressure sensor reaches the die cushion pressure command value after a start of reverse rotation of the hydraulic pump, the control device controls the number of rotations of the relief valve hydraulic pump so as to increase the set pressure of the relief valve to close the relief valve.
A die cushion device of the present disclosure includes:

a hydraulic cylinder that vertically moves a cushion pad;
a relief valve that returns hydraulic oil discharged from the hydraulic cylinder, to an oil tank;
a first hydraulic pump having a discharge side connected to a vent port of the relief valve;
a pressure sensor that detects a vent pressure of the relief valve; and
a control device that controls a number of rotations of the first hydraulic pump in accordance with the vent pressure of the relief valve detected by the pressure sensor, in which
the control device reversely rotates the first hydraulic pump when the vent pressure of the relief valve detected by the pressure sensor is equal to or higher than a predetermined pressure value.

Here, reversely rotating the first hydraulic pump means rotating the first hydraulic pump in a rotation direction opposite to a rotation direction for discharging the hydraulic oil.
According to the present disclosure, in die cushion pressure control during press molding of a press machine, when a pressure of hydraulic oil discharged from the hydraulic cylinder becomes equal to or higher than the set pressure of the relief valve, the relief valve operates to cause hydraulic oil discharged from the hydraulic cylinder to be returned to the oil tank. When an external force is applied to the cushion pad during this press molding to cause a surge pressure in the hydraulic cylinder, a valve body of the relief valve is pushed and moved by the surge pressure to compress a vent chamber, and the vent pressure of the relief valve rises. Then, when the vent pressure of the relief valve detected by the pressure sensor is equal to or higher than a predetermined pressure value, the control device reversely rotates the first hydraulic pump. Controlling a pressure with the first hydraulic pump with high accuracy and high speed makes it possible to suppress a surge pressure generated from the hydraulic cylinder in the die cushion pressure control.
Further, a die cushion device according to one aspect of the present disclosure includes
a second hydraulic pump that supplies hydraulic oil from the oil tank to the hydraulic cylinder, in which
the control device

controls the set pressure of the relief valve by controlling the vent pressure of the relief valve with a pressure of hydraulic oil discharged from the first hydraulic pump, and
reversely rotates the second hydraulic pump when the vent pressure of the relief valve detected by the pressure sensor is equal to or higher than the predetermined pressure value.

According to the present disclosure, since hydraulic oil discharged from the hydraulic cylinder during die cushioning action is returned to the oil tank via the second hydraulic pump that is reversely rotated, it is possible to avoid heat generation (oil temperature rise) in the relief valve.
Further, in a die cushion device according to one aspect of the present disclosure,
when the vent pressure of the relief valve detected by the pressure sensor is equal to or higher than the predetermined pressure value, the first hydraulic pump and the second hydraulic pump are reversely rotated to cause hydraulic oil discharged from the hydraulic cylinder to be returned to the oil tank via the second hydraulic pump that is reversely rotated, while the number of rotations of the second hydraulic pump is controlled such that the die cushion pressure of the hydraulic cylinder reaches the die cushion pressure command value, and
when the die cushion pressure of the hydraulic cylinder reaches the die cushion pressure command value after a start of reverse rotation of the first hydraulic pump, the number of rotations of the first hydraulic pump is controlled to increase the set pressure of the relief valve from that before a start of the reverse rotation, to close the relief valve.
According to the present disclosure, when the vent pressure of the relief valve detected by the pressure sensor is equal to or higher than a predetermined pressure value, the control device reversely rotates the first hydraulic pump and the second hydraulic pump, and controls the number of rotations of the second hydraulic pump such that the die cushion pressure of the hydraulic cylinder reaches the die cushion pressure command value. This allows hydraulic oil discharged from the hydraulic cylinder to be returned to the oil tank via the second hydraulic pump. Further, when the die cushion pressure of the hydraulic cylinder reaches the die cushion pressure command value after a start of reverse rotation of the first hydraulic pump, the set pressure of the relief valve is increased from that before the start of reverse rotation to close the relief valve, by controlling the number of rotations of the first hydraulic pump.
Further, in a die cushion device according to one aspect of the present disclosure,
the control device controls the set pressure of the relief valve by controlling the vent pressure of the relief valve with a pressure of hydraulic oil discharged from the first hydraulic pump.
Further, in a die cushion device according to one aspect of the present disclosure,
when the vent pressure of the relief valve detected by the pressure sensor is equal to or higher than the predetermined pressure value, the first hydraulic pump is reversely rotated to cause hydraulic oil discharged from the hydraulic cylinder to be returned to the oil tank via the relief valve, while the number of rotations of the first hydraulic pump is controlled such that the die cushion pressure of the hydraulic cylinder reaches the die cushion pressure command value.
According to the present disclosure, when the vent pressure of the relief valve detected by the pressure sensor is equal to or higher than the predetermined pressure value, the control device can reversely rotate the first hydraulic pump to cause hydraulic oil discharged from the hydraulic cylinder to be returned to the oil tank via the relief valve, and control the number of rotations of the first hydraulic pump such that a die cushion pressure of the hydraulic cylinder reaches the die cushion pressure command value.
Further, a die cushion device according to one aspect of the present disclosure includes
a check valve that is arranged, on an oil path between the hydraulic cylinder and the first hydraulic pump, on the first hydraulic pump side from a connection point at which the relief valve is connected to the oil path, and that regulates a flow of hydraulic oil from the hydraulic cylinder to the first hydraulic pump.
According to the present disclosure, when the vent pressure of the relief valve detected by the pressure sensor is equal to or higher than a predetermined pressure value, and the first hydraulic pump is reversely rotated, all of hydraulic oil discharged from the hydraulic cylinder can be returned to the oil tank via the relief valve, by the check valve regulating a flow of hydraulic oil from the hydraulic cylinder to the first hydraulic pump.
Further, a die cushion device according to one aspect of the present disclosure includes
an electromagnetic valve that is arranged, on an oil path between the hydraulic cylinder and the first hydraulic pump, on the first hydraulic pump side from a connection point at which the relief valve is connected to the oil path.
According to the present disclosure, when a vent pressure of the relief valve detected by the pressure sensor is equal to or higher than a predetermined pressure value, and the first hydraulic pump is reversely rotated, the electromagnetic valve can be closed to reliably stop a flow of hydraulic oil from the hydraulic cylinder to the first hydraulic pump, and a vent pressure of the relief valve detected by the pressure sensor becomes stable, which enables stable control.

REFERENCE SIGNS LIST

10: Hydraulic cylinder
10a: Port
11: Cylinder tube
12: Piston
13: Piston rod
14: Cushion pad
20: Relief valve
21: Inlet port
22: Outlet port
23: Vent port
30: Check valve
40, 140, 240, 340, 440, 540: Control device
50: Electromagnetic valve
51: First port
52: Second port
60: Throttle
M, M1,: M2 Motor
P, P1: Hydraulic pump (first hydraulic pump)
P2: Hydraulic pump (second hydraulic pump)
PS, PS1, PS2: Pressure sensor
T: Oil tank

Claims

A die cushion device comprising:
a hydraulic cylinder (10) that vertically moves a cushion pad (14);

a first hydraulic pump (P, P1) that supplies hydraulic oil from an oil tank (T) to the hydraulic cylinder (10);

a relief valve (20) that returns hydraulic oil discharged from the hydraulic cylinder (10), to the oil tank;

a pressure sensor (PS, PS2) that detects a hydraulic oil pressure in a flow path between the hydraulic cylinder (10) and the first hydraulic pump (P, P1); and

a control device (40, 140, 240, 340, 440, 540) that controls a number of rotations of the first hydraulic pump (P, P1) in accordance with the hydraulic oil pressure detected by the pressure sensor (PS, PS2), wherein

the control device (40, 140, 240, 340, 440, 540) reversely rotates the first hydraulic pump (P, P1) when the hydraulic oil pressure detected by the pressure sensor (PS, PS2) is equal to or higher than a predetermined pressure value.
The die cushion device according to claim 1, wherein
the pressure sensor (PS) detects a hydraulic oil pressure, the hydraulic oil pressure being a die cushion pressure of the hydraulic cylinder (10), and
the control device (40,140)
controls a flow rate and a pressure of hydraulic oil supplied from the first hydraulic pump (P, P1) to the hydraulic cylinder (10), by controlling the number of rotations of the first hydraulic pump (P, P1) in accordance with the hydraulic oil pressure detected by the pressure sensor (PS),

controls the number of rotations of the first hydraulic pump (P, P1) to cause the hydraulic oil pressure detected by the pressure sensor (PS) to reach a die cushion pressure command value, and

reversely rotates the first hydraulic pump (P, P1) when a hydraulic oil pressure detected by the pressure sensor (PS) is equal to or higher than a set pressure of the relief valve (20), the set pressure being the predetermined pressure value.
The die cushion device according to claim 2, comprising
a check valve (30) that is arranged, on the flow path between the hydraulic cylinder (10) and the first hydraulic pump (P), on the first hydraulic pump (P) side from a connection point at which the relief valve (20) is connected to the flow path, the check valve (30) being adapted to regulate a flow of hydraulic oil from the hydraulic cylinder (10) to the first hydraulic pump (P), wherein
the set pressure of the relief valve (20) is controlled with a pressure of hydraulic oil discharged from the first hydraulic pump (P), and
the control device (40) reversely rotates the first hydraulic pump (P) to open the relief valve (20) when a hydraulic oil pressure detected by the pressure sensor (PS) is equal to or higher than the set pressure of the relief valve (20).
The die cushion device according to claim 3, comprising
a second hydraulic pump (P2) that controls the set pressure of the relief valve (20), wherein
when the hydraulic oil pressure detected by the pressure sensor (PS) is equal to or higher than the set pressure of the relief valve (20), the control device (140) reversely rotates the first hydraulic pump (P1) and controls the number of rotations of the first hydraulic pump (P1) to cause the hydraulic oil pressure detected by the pressure sensor (PS) to reach the die cushion pressure command value, and
when the hydraulic oil pressure detected by the pressure sensor (PS) reaches the die cushion pressure command value after a start of reverse rotation of the first hydraulic pump (P1), the control device (140) controls the number of rotations of the second hydraulic pump (P2) to increase the set pressure of the relief valve (20) to close the relief valve (20)..
The die cushion device according to claim 1, wherein
the first hydraulic pump (P) has a discharge side connected to a vent port (23) of the relief valve (20),
the pressure sensor (PS) detects a vent pressure of the relief valve (20), and
the control device (240, 340, 540)
controls the number of rotations of the first hydraulic pump (P) in accordance with the vent pressure of the relief valve (20) detected by the pressure sensor (PS), and

reversely rotates the first hydraulic pump (P) when the vent pressure of the relief valve (20) detected by the pressure sensor (PS) is equal to or higher than the predetermined pressure value.
The die cushion device according to claim 1, comprising
a second hydraulic pump (P2) having a discharge side connected to a vent port (23) of the relief valve (20), wherein
the pressure sensor (PS2) detects a vent pressure of the relief valve (20), and
the control device (440)
controls the number of rotations of the first hydraulic pump (P1) in accordance with the vent pressure of the relief valve (20) detected by the pressure sensor (PS2),

controls a set pressure of the relief valve (20) by controlling the vent pressure of the relief valve (20) with a pressure of hydraulic oil discharged from the second hydraulic pump (P2), and

reversely rotates the first hydraulic pump (P1) and the second hydraulic pump (P2) when the vent pressure of the relief valve (20) detected by the pressure sensor (PS2) is equal to or higher than the predetermined pressure value.
The die cushion device according to claim 6, wherein
when the vent pressure of the relief valve (20) detected by the pressure sensor (PS2) is equal to or higher than the predetermined pressure value, the first hydraulic pump (P1) and the second hydraulic pump (P2) are reversely rotated to cause hydraulic oil discharged from the hydraulic cylinder (10) to be returned to the oil tank (T) via the first hydraulic pump (P1) that is reversely rotated, while the number of rotations of the first hydraulic pump (P1) is controlled to cause a die cushion pressure of the hydraulic cylinder (10) to reach a die cushion pressure command value, and
after a start of reverse rotation of the second hydraulic pump (P2), when the die cushion pressure of the hydraulic cylinder (10) reaches the die cushion pressure command value, the number of rotations of the second hydraulic pump (P2) is controlled to increase a set pressure of the relief valve (20) from that before a start of the reverse rotation, to close the relief valve (20).
The die cushion device according to claim 5, wherein
the control device (240, 340, 540) controls a set pressure of the relief valve (20) by controlling the vent pressure of the relief valve (20) with a pressure of hydraulic oil discharged from the first hydraulic pump (P).
The die cushion device according to claim 8, wherein
when the vent pressure of the relief valve (20) detected by the pressure sensor (PS) is equal to or higher than the predetermined pressure value, the first hydraulic pump (P) is reversely rotated to cause hydraulic oil discharged from the hydraulic cylinder (10) to be returned to the oil tank (T) via the relief valve (20), while the number of rotations of the first hydraulic pump (P) is controlled to cause a die cushion pressure of the hydraulic cylinder (10) to reach a die cushion pressure command value.
The die cushion device according to claim 8 or 9, comprising
a check valve (30) that is arranged, on the oil path between the hydraulic cylinder (10) and the first hydraulic pump (P), on the first hydraulic pump (P) side from a connection point at which the relief valve (20) is connected to the oil path, the check valve (30) being adapted to regulate a flow of hydraulic oil from the hydraulic cylinder (10) to the first hydraulic pump (P).
The die cushion device according to claim 8 or 9, comprising
an electromagnetic valve (50) that is arranged, on the oil path between the hydraulic cylinder (10) and the first hydraulic pump (P), on the first hydraulic pump (P) side from a connection point at which the relief valve (20) is connected to the oil path.
The die cushion device according to claim 10 or 11, comprising
a throttle (60) that connects the connection point side and the pressure sensor (PS), wherein
the pressure sensor (PS) detects a hydraulic oil pressure, the hydraulic oil pressure being a die cushion pressure of the hydraulic cylinder (10).