Die cushion device

Abstract

To provide a die cushion device which can regenerate energy by a simple control system.SOLUTION: A die cushion device 2 includes: a hydraulic pump motor 51 which is driven as a hydraulic motor by hydraulic oil discharged from a cylinder unit 4 when a cushion pad 33 is descended; a proportional valve 7C through which hydraulic oil discharged from the cylinder unit 4 passes when the cushion pad 33 is descended; and a control device 9 for controlling an electric motor 52 for driving the hydraulic pump motor 51 and the proportional valve 7C. The control device 9 controls the number of rotation of the electric motor 52 so that a suction flow rate of the hydraulic pump motor 51 is smaller than a discharge flow rate of the cylinder unit 4, when the cushion pad 33 is descended, and controls the opening of the proportional valve 7C so that a cushion pressure detected by a pressure detector 93 is set at a set value.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a die cushion device for a press machine. [Background technology]

[0002] Conventionally, die cushion devices that act as a cushion for an upper die that descends along with the slide of a press machine have been known. For example, Patent Document 1 discloses a die cushion device that includes a hydraulic cylinder having a lower chamber that supports a cushion pad, a hydraulic pump motor connected to the lower chamber of the hydraulic cylinder, and a proportional valve connected to the lower chamber of the hydraulic cylinder in parallel with the hydraulic pump motor.

[0003] In the die cushion device of Patent Document 1, a hydraulic pump motor is driven by an electric motor to supply hydraulic oil to the lower chamber of a hydraulic cylinder, thereby raising the cushion pad. The cushion pad is connected to multiple blank holders arranged around the lower die with cushion pins. The blank holders, together with the lower die, support the blank, which is the material before forming.

[0004] When the upper die descends together with the slide and abuts against the blank holder plate via the blank, the cushion pad is pressed down by the upper die via the blank, blank holder plate, and cushion pin, and descends. At this time, the hydraulic pump motor is driven as a hydraulic motor by hydraulic oil discharged from the lower chamber of the hydraulic cylinder, and the electric motor functions as a generator, allowing energy to be regenerated.

[0005] In addition, the hydraulic oil discharged from the lower chamber of the hydraulic cylinder also passes through the proportional valve. In other words, not all of the hydraulic oil discharged from the lower chamber of the hydraulic cylinder is supplied to the hydraulic pump motor, so the capacity of the electric motor can be reduced.

[0006] The die cushion device of Patent Document 1 also includes a control device that controls the electric motor and the proportional valve, and a pressure detector that detects the cushion pressure, which is the pressure in the lower chamber of the hydraulic cylinder. When the cushion pad is lowered, the control device controls the aperture of the proportional valve and the torque of the electric motor so that the cushion pressure detected by the pressure detector becomes a set value. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 5296806 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the die cushion device of Patent Document 1, since the cushion pressure is controlled using both a proportional valve and an electric motor, it is necessary to establish control logic and adjust the gains for both the proportional valve and the electric motor. Furthermore, the proportional valve and the electric motor have significantly different responsiveness. Therefore, when an existing die cushion device is modified to resemble the die cushion device of Patent Document 1, the scope of modification to the control system becomes large.

[0009] Therefore, an object of the present disclosure is to provide a die cushion device that is capable of regenerating energy with a simple control system. [Means for solving the problem]

[0010] From one aspect, the present disclosure provides a die cushion device for a press machine, the die cushion device comprising: a cylinder unit including at least one hydraulic cylinder that supports a cushion pad; a hydraulic pump motor that operates as a hydraulic pump that supplies hydraulic oil to the cylinder unit when the cushion pad is raised and that is driven as a hydraulic motor by hydraulic oil discharged from the cylinder unit when the cushion pad is lowered; an electric motor that drives the hydraulic pump motor when the cushion pad is raised and that functions as a generator when the cushion pad is lowered; a proportional valve through which hydraulic oil discharged from the cylinder unit when the cushion pad is lowered; a control device that controls the electric motor and the proportional valve; and a pressure detector that detects a cushion pressure that is a pressure of hydraulic oil between the cylinder unit and the proportional valve, wherein the control device controls the rotation speed of the electric motor so that an intake flow rate of the hydraulic pump motor is smaller than a discharge flow rate of the cylinder unit when the cushion pad is lowered, and controls an aperture of the proportional valve so that the cushion pressure detected by the pressure detector becomes a set value.

[0011] From another aspect, the present disclosure provides a die cushion device for a press machine, the die cushion device including: an elevator cylinder that supports a cushion pad and has a head-side chamber and a rod-side chamber; a plurality of cushion cylinders that support the cushion pad and have pressure-receiving chambers; a hydraulic pump motor that connects the head-side chamber and the rod-side chamber of the elevator cylinder via a first selector valve and that connects the pressure-receiving chambers of the plurality of cushion cylinders via a second selector valve or a logic valve; an electric motor that drives the hydraulic pump motor to supply hydraulic oil to the head-side chamber of the elevator cylinder when the cushion pad is raised and that functions as a generator when the cushion pad is lowered; and proportional valves that are connected to the pressure-receiving chambers of the plurality of cushion cylinders. [Effects of the Invention]

[0012] According to the present disclosure, a die cushion device capable of regenerating energy with a simple control system is provided. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic configuration diagram of a press machine including a die cushion device according to a first embodiment. [Figure 2] FIG. 2 is a schematic configuration diagram of the die cushion device. [Figure 3] FIG. 3A is a graph showing the change in the position of the upper die and the position of the blank holder over time, FIG. 3B is a graph showing the change in the cushion pressure over time, and FIG. 3C is a graph showing the change in the discharge flow rate of the cylinder unit over time. [Figure 4] 4 is a flowchart of control by the control device. [Figure 5] 10 is a flowchart of a modified example. [Figure 6] FIG. 10 is a schematic configuration diagram of a die cushion device according to a modified example. [Figure 7] FIG. 10 is a schematic configuration diagram of a die cushion device according to a second embodiment. [Figure 8] FIG. 10 is a schematic configuration diagram of a die cushion device according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] 1 shows a press machine 1 including a die cushion device 2 according to a first embodiment. The press machine 1 performs press forming by sandwiching a blank between a lower die 17 and an upper die 16. The die cushion device 2 for the press machine 1 acts as a cushion for the upper die 16, which descends together with a slide 15, which will be described later.

[0015] Specifically, the press machine 1 includes a bed 11 having a lower die 17 attached to its upper surface, a crown 13 located above the bed 11, uprights 12 rising from the four corners of the bed 11 to support the crown 13, and a slide 15 arranged in the space surrounded by the bed 11, the crown 13, and the upright 12.

[0016] An upper mold 16 is attached to the underside of the slide 15. The crown 13 is provided with at least one pressure cylinder 14 that raises and lowers the slide 15. The number of pressure cylinders 14 may be one or more. In this embodiment, the pressure cylinder 14 is a hydraulic cylinder, but the pressure cylinder 14 may also be an electric cylinder.

[0017] In this embodiment, the lower die 17 has a convex shape, and the upper die 16 has a concave shape. Therefore, a plurality of blank holders 31 are arranged around the upward convex portion of the lower die 17 to support the blank together with the upward convex portion.

[0018] When the upper die 16 descends together with the slide 15, the upper die 16 abuts against the blank holder 31 via the blank. The blank holder 31 is a component of the die cushion device 2.

[0019] In addition to the blank holder 31, the die cushion device 2 includes a cushion pad 33 arranged in the bed 11, a plurality of cushion pins 32 that penetrate the lower die 17 and connect the cushion pad 33 and the blank holder 31, and a cylinder unit 4 arranged below the cushion pad 33.

[0020] In this embodiment, the cylinder unit 4 includes, as hydraulic cylinders supporting the cushion pad 33, a lift cylinder 4A arranged in the center of the cushion pad 33 and two cushion cylinders 4B arranged on both sides of the lift cylinder 4A. However, the number of cushion cylinders 4B may be three or more. Alternatively, the cylinder unit 4 may include only the lift cylinder 4A, and linear bushings may be used instead of the cushion cylinders 4B.

[0021] 2, the lift cylinder 4A is double-acting and has a lower head-side chamber 41 and an upper rod-side chamber 42. On the other hand, the cushion cylinder 4B is single-acting and has a pressure-receiving chamber 43. For example, the cushion cylinder 4B is a ram cylinder.

[0022] The die cushion device 2 further includes a hydraulic pump motor 51 that operates as a hydraulic pump that supplies hydraulic oil to the cylinder unit 4 when the cushion pad 33 is raised, a first switching valve 7A and a second switching valve 7B that are interposed between the hydraulic pump motor 51 and the cylinder unit 4, and a proportional valve 7C that is interposed between the cylinder unit 4 and the tank 21.

[0023] More specifically, the head-side chamber 41 and rod-side chamber 42 of the lift cylinder 4A are connected to the first selector valve 7A by supply and discharge lines 81 and 82, respectively. The pressure-receiving chambers 43 of both cushion cylinders 4B are connected to each other by a bridge line 83, which is connected to the second selector valve 7B by a first discharge line 84 and to the proportional valve 7C by a second discharge line 85. Furthermore, the bridge line 83 is connected to the tank 21 by a suction line 86 provided with a pilot check valve 87 or a pre-fill valve.

[0024] Alternatively, the tank 21 may be divided into an upper tank and a lower tank, with the suction line 86 connected to the upper tank and other lines (for example, tank lines 63, 65, 73, 22 and relief line 67) described later being connected to the lower tank.

[0025] The hydraulic pump motor 51 is connected to an electric motor 52 so as to be able to transmit torque. In this embodiment, the electric motor 52 is a servo motor, and is connected to a power source 54 via a servo amplifier 53. However, the electric motor 52 may be an induction motor, and may be connected to a power source 54 via an inverter. The electric motor 52 is controlled by the control device 9 via the servo amplifier 53.

[0026] In this embodiment, the hydraulic pump / motor 51 is a bidirectional pump that can switch the direction of hydraulic oil discharge depending on the direction of rotation. For example, a bidirectional pump is an axial piston pump. However, the hydraulic pump / motor 51 may also be an axial piston pump that rotates in one direction and switches the direction of hydraulic oil discharge depending on the tilt direction of a swash plate or bent axis from the center. Also, although the hydraulic pump / motor 51 is a variable displacement pump in the illustrated example, the hydraulic pump / motor 51 may also be a fixed displacement pump.

[0027] The hydraulic pump motor 51 is connected to the first switching valve 7A by pump lines 61 and 62. In other words, the head side chamber 41 and the rod side chamber 42 of the lift cylinder 4A are connected to the hydraulic pump motor 51 via supply / discharge lines 81 and 82, the first switching valve 7A, and the pump lines 61 and 62.

[0028] The pump line 61 is connected to the tank 21 by a tank line 63 equipped with a check valve 64, and the pump line 62 is connected to the tank 21 by a tank line 65 equipped with a check valve 66. The pump line 62 is also connected to the tank 21 by a relief line 67 equipped with a relief valve 68.

[0029] In this embodiment, the first switching valve 7A is a two-position valve. The first switching valve 7A is controlled by the control device 9 and is switched between a neutral position where the pump lines 61, 62 and the supply / discharge lines 81, 82 are blocked, and an actuated position where the pump line 61 communicates with the head-side supply / discharge line 81 and the pump line 62 communicates with the rod-side supply / discharge line 82. Note that in FIG. 1, some signal lines are omitted to simplify the drawing.

[0030] The pump line 61 is connected to the second switching valve 7B by the third discharge line 71. That is, the pressure receiving chambers 43 of both cushion cylinders 4B are connected to the hydraulic pump motor 51 via the bridge line 83, the first discharge line 84, the second switching valve 7B, the third discharge line 71, and the pump side portion of the pump line 61.

[0031] In this embodiment, the second switching valve 7B is a four-port valve. The second switching valve 7B is connected to the pump line 62 by a fourth discharge line 72, and is also connected to the tank 21 by a tank line 73.

[0032] The second switching valve 7B is controlled by the control device 9 and is switched between a neutral position in which the first discharge line 84, the third discharge line 71, the fourth discharge line 72 and the tank line 73 are blocked, and a communication position in which the first discharge line 84 is connected to the third discharge line 71 and the fourth discharge line 72 is connected to the tank line 73.

[0033] The proportional valve 7C is connected to the pressure-receiving chambers 43 of both cushion cylinders 4B via a bridge line 83 and a second discharge line 85, and is connected to the tank 21 via a tank line 22. In this embodiment, the proportional valve 7C is a direct proportional valve in which the command current and the opening exhibit a positive correlation. However, the proportional valve 7C may also be an inverse proportional valve in which the command current and the opening exhibit a negative correlation. The proportional valve 7C is also controlled by the control device 9.

[0034] The proportional valve 7C may be a spool type. In this case, the proportional valve 7C may be a servo valve with a built-in sensor for feedback control of the spool position, or it may not include such a sensor. Alternatively, the proportional valve 7C may be a poppet type electromagnetic proportional relief valve.

[0035] The control device 9 is electrically connected to a first position detector 91 that detects the position of the slide 15 and a second position detector 92 that detects the position of the cushion pad 33. The control device 9 is also electrically connected to a pressure detector 93 that detects the cushion pressure Pc, which is the pressure between the cylinder unit 4 and the proportional valve 7C. In this embodiment, the pressure detector 93 is provided in the bridge line 83 or the second discharge line 85.

[0036] With respect to the control device 9, the functions of the elements disclosed herein can be performed using circuits or processing circuits, including general-purpose processors, special-purpose processors, integrated circuits, application-specific integrated circuits (ASICs), conventional circuits, and / or combinations thereof, configured or programmed to perform the disclosed functions. A processor is considered a processing circuit or circuit because it includes transistors and other circuitry. In this disclosure, a circuit, unit, or means is hardware that performs the recited functions or hardware that is programmed to perform the recited functions. The hardware may be hardware disclosed herein or other known hardware that is programmed or configured to perform the recited functions. Where the hardware is a processor, which is considered a type of circuit, the circuit, means, or unit is a combination of hardware and software, and the software is used to configure the hardware and / or processor.

[0037] Before the start of press forming, the control device 9 switches the first switching valve 7A to the drive position while maintaining the second switching valve 7B in the neutral position, and causes the electric motor 52 to rotate in a direction in which the hydraulic pump motor 51 discharges hydraulic oil to the pump line 61. As a result, hydraulic oil is supplied from the hydraulic pump motor 51 via the pump line 61, the first switching valve 7A, and the supply / discharge line 81 to the head side chamber 41 of the lift-up cylinder 4A, causing the lift-up cylinder 4A to extend and the cushion pad 33 to rise.

[0038] The hydraulic oil discharged from the rod side chamber 42 of the lift cylinder 4A is sucked into the hydraulic pump motor 51 via the supply / discharge line 82, the first selector valve 7A, and the pump line 62. Because there is an area difference between the head side chamber 41 and the rod side chamber 42 of the lift cylinder 4A, the flow rate out of the rod side chamber 42 of the lift cylinder 4A is less than the flow rate into the head side chamber 41. For this reason, the shortage of the suction flow rate of the hydraulic pump motor 51 is made up for by replenishment from the tank 21 via the tank line 65.

[0039] When the cushion pad 33 rises, the cushion cylinder 4B also extends. Therefore, hydraulic oil is supplied from the tank 21 via the suction line 86 and the bridge line 83 to the pressure-receiving chambers 43 of both cushion cylinders 4B.

[0040] When the cushion pad 33 rises to the standby position, the control device 9 switches the second switching valve 7B to the communication position while maintaining the first switching valve 7A in the drive position. As a result, the head-side chamber 41 of the lift-down cylinder 4A and the pressure-receiving chambers 43 of both cushion cylinders 4B have the same cushion pressure Pc. In this state, the control device 9 controls the rotation speed of the electric motor 52 so that the position of the cushion pad 33 detected by the second position detector 92 is maintained at the standby position. As a result, the cushion pressure Pc is maintained at the standby pressure Pw, as shown in FIG. 3B.

[0041] 4 is a flowchart of the control performed by the control device 9 when the cushion pad 33 is lowered. The control device 9 independently controls the rotation speed N of the electric motor 52 and the opening of the proportional valve 7C. Specifically, the control device 9 outputs a rotation speed command to the servo amplifier 53 and an opening command to the proportional valve 7C.

[0042] As described above, when the cushion pad 33 is in the standby position, the first switching valve 7A is switched to the drive position, and the second switching valve 7B is switched to the communication position. When the slide 15 descends and reaches the cushion pad depression position (YES in step S5), the control device 9 rotates the electric motor 52 in a direction in which the hydraulic pump motor 51 discharges hydraulic oil to the pump line 62. In addition, the control device 9 controls the rotation speed N of the electric motor 52 so that the suction flow rate Qp of the hydraulic pump motor 51 is smaller than the discharge flow rate Qc of the cylinder unit 4 (step S6).

[0043] 3A, the cushion pad pressing position is a position where the upper die 16 abuts against the blank holder 31 via the blank. The control device 9 may determine whether the slide 15 has reached the cushion pad pressing position based on the position of the slide 15 detected by the first position detector 91 and the position of the cushion pad 33 detected by the second position detector 92. Alternatively, the control device 9 may determine that the slide 15 has reached the cushion pad pressing position when the cushion pressure Pc detected by the pressure detector 93 rises.

[0044] The discharge flow rate Qc of the cylinder unit 4 is the sum of the discharge flow rate Q1 from the head side chamber 41 of the lifting cylinder 4A and the discharge flow rate Q2 from the pressure receiving chambers 43 of both cushion cylinders 4B. For example, the suction flow rate Qp of the hydraulic pump motor 51 is 20% or more and 80% or less of the discharge flow rate Qc of the cylinder unit 4.

[0045] In step S6, the control device 9 determines a target rotation speed Nt of the electric motor 52. In this embodiment, the target rotation speed Nt is constant. Since the slide 15 is controlled to descend at a set speed, the control device 9 may calculate the discharge flow rate Qc of the cylinder unit 4 from the set speed of the slide 15 and determine the target rotation speed Nt of the electric motor 52 using the following equation. Nt=Qc / q×K q: Displacement volume per rotation of the hydraulic pump / motor 51 K: A coefficient greater than 0 and less than 1

[0046] Alternatively, when determining the target rotation speed Nt of the electric motor 52, the control device 9 may calculate the descent speed of the slide 15 by differentiating the position of the slide 15 detected by the first position detector 91, or may calculate the descent speed of the cushion pad 33 by differentiating the position of the cushion pad 33 detected by the second position detector 92, and then calculate the discharge flow rate Qc of the cylinder unit 4 from the calculated descent speed of the slide 15 or the cushion pad 33.

[0047] When the suction flow rate Qp of the hydraulic pump motor 51 is greater than the discharge flow rate Q1 from the head side chamber 41 of the lift cylinder 4A, that is, when the target rotation speed Nt is greater than Q1 / q, as the upper die 16 presses down on the cushion pad 33 via the blank, blank holder 31, and cushion pins 32, the hydraulic oil discharged from the head side chamber 41 of the lift cylinder 4A is supplied to the hydraulic pump motor 51, and part of the hydraulic oil discharged from the pressure receiving chambers 43 of both cushion cylinders 4B is supplied to the hydraulic pump motor 51. The remainder of the hydraulic oil discharged from the pressure receiving chambers 43 of both cushion cylinders 4B is supplied to the proportional valve 7C.

[0048] More specifically, the hydraulic oil discharged from the head-side chamber 41 of the lift-down cylinder 4A is supplied to the hydraulic pump motor 51 via the supply / discharge line 81, the first selector valve 7A, and the pump line 61. Also, a portion of the hydraulic oil discharged from the pressure-receiving chambers 43 of both cushion cylinders 4B is supplied to the hydraulic pump motor 51 via the bridge line 83, the first discharge line 84, the second selector valve 7B, the third discharge line 71, and the pump-side portion of the pump line 61, and the remainder is supplied to the proportional valve 7C via the bridge line 83 and the second discharge line 85.

[0049] Conversely, when the suction flow rate Qp of the hydraulic pump motor 51 is smaller than the discharge flow rate Q1 from the head side chamber 41 of the lift cylinder 4A, that is, when the target rotation speed Nt is smaller than Q1 / q, as the upper die 16 presses down on the cushion pad 33 via the blank, blank holder 31, and cushion pins 32, part of the hydraulic oil discharged from the head side chamber 41 of the lift cylinder 4A is supplied to the hydraulic pump motor 51. The remainder of the hydraulic oil discharged from the head side chamber 41 of the lift cylinder 4A and the hydraulic oil discharged from the pressure-receiving chambers 43 of both cushion cylinders 4B are supplied to the proportional valve 7C.

[0050] More specifically, a portion of the hydraulic oil discharged from the head-side chamber 41 of the lift-down cylinder 4A is supplied to the hydraulic pump motor 51 via the supply / discharge line 81, the first selector valve 7A, and the pump line 61, and the remainder is supplied to the proportional valve 7C via the supply / discharge line 81, the first selector valve 7A, the selector valve side portion of the pump line 61, the third discharge line 71, the second selector valve 7B, the first discharge line 84, the bridge line 83, and the second discharge line 85. In addition, the hydraulic oil discharged from the pressure-receiving chambers 43 of both cushion cylinders 4B is supplied to the proportional valve 7C via the bridge line 83 and the second discharge line 85.

[0051] When hydraulic oil is supplied to the hydraulic pump motor 51, the hydraulic pump motor 51 is driven as a hydraulic motor by the hydraulic oil, and the electric motor 52 functions as a generator. A portion of the hydraulic oil discharged from the hydraulic pump motor 51 is supplied to the rod side chamber 42 of the lift cylinder 4A, and the remainder, which is an excess amount, is discharged from the pump line 62 via the fourth discharge line 72, the second switching valve 7B, and the tank line 73 to the tank 21.

[0052] The control device 9 repeats step S6 until the slide 15 reaches a rotation speed command stop position slightly above the press bottom dead center (NO in step S7), and when the slide 15 reaches the rotation speed command stop position (YES in step S7), stops the electric motor 52 by setting the rotation speed command to zero (step S8). In other words, the control device 9 stops the electric motor 52 before the slide 15 reaches the press bottom dead center.

[0053] The control device 9 determines that the slide 15 has reached the rotation speed command stop position when the position of the slide 15 detected by the first position detector 91 coincides with the rotation speed command stop position. The press bottom dead center is a position above the mechanical lower limit position of the slide 15.

[0054] With regard to the proportional valve 7C, the control device 9 keeps the proportional valve 7C fully closed until the cushion pressure Pc detected by the pressure detector 93 becomes equal to or greater than the control start pressure P0, and when the cushion pressure Pc detected by the pressure detector 93 becomes equal to or greater than the control start pressure P0 (YES in step S1), as shown in Fig. 3B, the control device 9 controls the opening of the proportional valve 7C so that the cushion pressure Pc detected by the pressure detector 93 becomes equal to a set value Px (step S2). The set value Px is a value determined by the user.

[0055] When the proportional valve 7C is opened, the hydraulic oil supplied to the proportional valve 7C passes through the proportional valve 7C as described above. In other words, the sum of the intake flow rate Qp of the hydraulic pump / motor 51 and the flow rate Qv passing through the proportional valve 7C is the discharge flow rate Qc of the cylinder unit 4.

[0056] The control device 9 repeats step S2 until the slide 15 reaches the press bottom dead center (NO in step S3), and when the slide 15 reaches the press bottom dead center (YES in step S3), it fully closes the proportional valve 7C (step S4). The control device 9 determines that the slide 15 has reached the press bottom dead center when the position of the slide 15 detected by the first position detector 91 coincides with the press bottom dead center. Note that even after the slide 15 reaches the press bottom dead center, the control device 9 may not fully close the proportional valve 7C, but may instead control the aperture of the proportional valve 7C so that the cushion pressure Pc detected by the pressure detector 93 becomes the set value Px.

[0057] As described above, in the die cushion device 2 of this embodiment, the control system of the proportional valve 7C can be the same as that of a die cushion device without an energy regeneration function. Therefore, energy regeneration is possible with a simple control system without much modification to the control system of an existing die cushion device.

[0058] In this embodiment, the electric motor 52 is stopped before the slide 15 reaches the bottom dead center of the press. When the slide 15 reaches the bottom dead center of the press, the cushion pressure Pc decreases. Therefore, by stopping the electric motor 52 before that, the cushion pressure Pc can be well controlled.

[0059] <Modification> 5, in controlling the opening degree of the proportional valve 7C, step S5 may be adopted instead of step S1. This modification is also applicable to the second embodiment described later.

[0060] Instead of the second switching valve 7B, two logic valves 7D and 7E may be used as in a modified die cushion device 2A shown in Fig. 6. In this case, the pressure-receiving chambers 43 of both cushion cylinders 4B are connected to the hydraulic pump motor 51 via a bridge line 83, a first discharge line 84, the logic valve 7D, the third discharge line 71, and the pump-side portion of the pump line 61. The pump line 62 is connected to the logic valve 7E via a fourth discharge line 72, and the logic valve 7E is connected to the tank 21 via a tank line 73. The back pressure chambers of the logic valves 7D and 7E are connected to a switching valve 7F, which switches between introducing lock pressure into the back pressure chambers of the logic valves 7D and 7E and connecting the back pressure chambers of the logic valves 7D and 7E to the tank.

[0061] If a logic valve 7D is used instead of the second switching valve 7B as shown in FIG. 6, when the flow rate of hydraulic oil supplied from the pressure-receiving chambers 43 of both cushion cylinders 4B to the hydraulic pump motor 51 is high, the pressure loss can be reduced compared to when the second switching valve 7B is used.

[0062] Second Embodiment 7 shows a die cushion device 2B according to a second embodiment. In this embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and redundant explanations will be omitted.

[0063] In this embodiment, the hydraulic pump motor 51 is connected to the tank 21 by the tank line 23, and is also connected to the first selector valve 7A by the pump line 69. That is, the head side chamber 41 and the rod side chamber 42 of the lift cylinder 4A are connected to the hydraulic pump motor 51 via supply / discharge lines 81, 82, the first selector valve 7A, and the pump line 69. In addition, a relief line 67 is connected to the first selector valve 7A, and a tank line 88 provided with a check valve 89 is connected to the rod side supply / discharge line 82.

[0064] In this embodiment, the first switching valve 7A is a three-position valve that is controlled by the control device 9 and is switched between a neutral position, a first drive position, and a second drive position. In the neutral position, the first switching valve 7A blocks the pump line 69, the relief line 67, and the supply / discharge lines 81 and 82. In the first drive position, the first switching valve 7A connects the pump line 69 to the head-side supply / discharge line 81 and connects the relief line 67 to the rod-side supply / discharge line 82. In the second drive position, the first switching valve 7A connects the pump line 69 to the rod-side supply / discharge line 82 and connects the relief line 67 to the head-side supply / discharge line 81.

[0065] The pump line 69 is connected to the second switching valve 7B by the third discharge line 74. That is, the pressure receiving chambers 43 of both cushion cylinders 4B are connected to the hydraulic pump motor 51 via the bridge line 83, the first discharge line 84, the second switching valve 7B, the third discharge line 74, and the pump side portion of the pump line 69.

[0066] In this embodiment, the second switching valve 7B is a two-port valve. The second switching valve 7B is controlled by the control device 9 to be switched between a neutral position where the first discharge line 84 and the third discharge line 74 are blocked, and a communication position where the first discharge line 84 is connected to the third discharge line 74.

[0067] 7 , when the cushion pad 33 is raised, the control device 9 switches the first switching valve 7A to the first drive position while maintaining the second switching valve 7B in the neutral position, and rotates the electric motor 52 in a direction in which the hydraulic pump motor 51 discharges hydraulic oil to the pump line 69. Furthermore, when the cushion pad 33 is raised to the standby position, the control device 9 switches the second switching valve 7B to the communication position while maintaining the first switching valve 7A in the first drive position, and controls the rotation speed of the electric motor 52 so that the position of the cushion pad 33 detected by the second position detector 92 is maintained at the standby position.

[0068] In this embodiment, the relief valve 68 is a relief valve with an unloading function, and the control device 9 disables the function of the relief valve 68 when the cushion pad 33 is rising. Therefore, when the cushion pad 33 is rising, the pressure in the rod-side chamber 42 of the lift-down cylinder 4A is kept low.

[0069] In the die cushion device 2B, the control device 9 also controls the rotation speed N of the electric motor 52 and the aperture of the proportional valve 7C in the same manner as in the first embodiment when the cushion pad 33 is lowered. That is, when the suction flow rate Qp of the hydraulic pump motor 51 is greater than the discharge flow rate Q1 from the head-side chamber 41 of the lift-down cylinder 4A, the hydraulic pump motor 51 is supplied with the hydraulic oil discharged from the head-side chamber 41 of the lift-down cylinder 4A and with some of the hydraulic oil discharged from the pressure-receiving chambers 43 of both cushion cylinders 4B, and the remainder of the hydraulic oil discharged from the pressure-receiving chambers of both cushion cylinders 4B passes through the proportional valve 7C. Conversely, when the suction flow rate Qp of the hydraulic pump motor 51 is smaller than the discharge flow rate Q1 from the head side chamber 41 of the lift cylinder 4A, part of the hydraulic oil discharged from the head side chamber 41 of the lift cylinder 4A is supplied to the hydraulic pump motor 51, and the remainder of the hydraulic oil discharged from the head side chamber 41 of the lift cylinder 4A and the hydraulic oil discharged from the pressure-receiving chambers 43 of both cushion cylinders 4B pass through the proportional valve 7C.

[0070] This embodiment can also achieve the same effects as the first embodiment. In this embodiment, when it is desired to shorten only the lift cylinder 4A due to a changeover or the like, the control device 9 switches the first switching valve 7A to the second drive position and rotates the electric motor 52 in a direction in which the hydraulic pump motor 51 discharges hydraulic oil to the pump line 69. At this time, the relief valve 68 serves as a counterbalance valve.

[0071] <Other embodiments> The present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the gist of the present disclosure.

[0072] For example, as in a cushion device 2C shown in Fig. 8, the cylinder unit 4 may include only a lift cylinder 4A. In this case, the head-side chamber 41 of the lift cylinder 4A may be connected to a hydraulic pump motor 51 via a first selector valve 7A and may also be connected to a proportional valve 7C in parallel with the hydraulic pump motor 51. Note that, although the proportional valve 7C is connected to the pump line 61 via the discharge line 24 in Fig. 8, the proportional valve 7C may also be connected to a supply / discharge line 81 via the discharge line 24. Furthermore, the configuration in which the cylinder unit 4 includes only a lift cylinder 4A is applicable not only to the first embodiment in which the hydraulic pump motor 51 is connected to the first selector valve 7A via pump lines 61 and 62, but also to the second embodiment in which the hydraulic pump motor 51 is connected to the tank 21 via a tank line 23 and to the first selector valve 7A via a pump line 69.

[0073] The cylinder unit 4 may include only one or a plurality of cushion cylinders 4B. In this case, the pressure-receiving chamber 43 of the cushion cylinder 4B is connected to the hydraulic pump motor 51 via the second selector valve 7B, and is also connected to the proportional valve 7C in parallel with the hydraulic pump motor 51. However, if the cylinder unit 4 includes the lift cylinder 4A, the lift cylinder 4A can be used when lifting the cushion pad 33, thereby increasing the lifting speed of the cushion pad 33. This reduces the time it takes to lift the cushion pad 33, and improves the productivity of the press machine 1.

[0074] <Summary> As a first aspect, the present disclosure provides, from one aspect, a die cushion device for a press machine, the die cushion device including: a cylinder unit including at least one hydraulic cylinder that supports a cushion pad; a hydraulic pump motor that operates as a hydraulic pump that supplies hydraulic oil to the cylinder unit when the cushion pad is raised and that is driven as a hydraulic motor by hydraulic oil discharged from the cylinder unit when the cushion pad is lowered; an electric motor that drives the hydraulic pump motor when the cushion pad is raised and that functions as a generator when the cushion pad is lowered; a proportional valve through which hydraulic oil discharged from the cylinder unit when the cushion pad is lowered; a control device that controls the electric motor and the proportional valve; and a pressure detector that detects a cushion pressure that is a pressure of the hydraulic oil between the cylinder unit and the proportional valve, wherein the control device controls the rotation speed of the electric motor so that a suction flow rate of the hydraulic pump motor is smaller than a discharge flow rate of the cylinder unit when the cushion pad is lowered, and controls an aperture of the proportional valve so that the cushion pressure detected by the pressure detector becomes a set value.

[0075] According to the above configuration, the control system of the proportional valve can be the same as that of a die cushion device without an energy regeneration function. Therefore, energy regeneration is possible with a simple control system without requiring significant modification to the control system of an existing die cushion device.

[0076] As a second aspect, in the first aspect, for example, the die cushion device may further include a first position detector that detects a position of a slide of the press machine and a second position detector that detects a position of the cushion pad, and the control device may calculate a descending speed of the slide by differentiating the position of the slide detected by the first position detector, or calculate a descending speed of the cushion pad by differentiating the position of the cushion pad detected by the second position detector, and calculate the discharge flow rate of the cylinder unit from the calculated descending speed of the slide or cushion pad.

[0077] As a third aspect, in the second aspect, the control device may stop the electric motor before the slide of the press machine reaches the press bottom dead center. When the slide reaches the press bottom dead center, the cushion pressure decreases, so by stopping the electric motor before that point, the cushion pressure can be well controlled.

[0078] As a fourth aspect, in any of the first to third aspects, the cylinder unit may include a lift cylinder having a head-side chamber and a rod-side chamber, and multiple cushion cylinders having pressure-receiving chambers, the head-side chamber and the rod-side chamber of the lift cylinder being connected to the hydraulic pump motor via a first selector valve, and the pressure-receiving chambers of the multiple cushion cylinders being connected to the proportional valve and also to the hydraulic pump motor via a second selector valve or a logic valve. With this configuration, using the lift cylinder when lifting the cushion pad can increase the lifting speed of the cushion pad. This shortens the time it takes to lift the cushion pad, thereby improving the productivity of the press machine. In particular, using a logic valve can reduce pressure loss compared to using a second selector valve when the flow rate of hydraulic oil supplied from the pressure-receiving chambers of the multiple cushion cylinders to the hydraulic pump motor is high.

[0079] As a fifth aspect, in the fourth aspect, for example, when the cushion pad is raised, hydraulic oil may be supplied from the hydraulic pump motor to the head-side chamber of the lift-down cylinder, while hydraulic oil may be supplied from a tank to the pressure-receiving chamber of the cushion cylinder, and when the cushion pad is lowered, hydraulic oil discharged from the head-side chamber of the lift-down cylinder and some of the hydraulic oil discharged from the pressure-receiving chambers of the plurality of cushion cylinders may be supplied to the hydraulic pump motor, and the remainder of the hydraulic oil discharged from the pressure-receiving chambers of the plurality of cushion cylinders may pass through the proportional valve.

[0080] As a sixth aspect, in the fourth aspect, for example, when the cushion pad is raised, hydraulic oil may be supplied from the hydraulic pump motor to the head-side chamber of the lift-up cylinder, while hydraulic oil may be supplied from a tank to the pressure-receiving chamber of the cushion cylinder, and when the cushion pad is lowered, part of the hydraulic oil discharged from the head-side chamber of the lift-up cylinder may be supplied to the hydraulic pump motor, and the remainder of the hydraulic oil discharged from the head-side chamber of the lift-up cylinder and the hydraulic oil discharged from the pressure-receiving chambers of the plurality of cushion cylinders may pass through the proportional valve.

[0081] As a seventh aspect, the present disclosure provides, from another aspect, a die cushion device for a press machine, the die cushion device including: an elevator cylinder that supports a cushion pad and has a head-side chamber and a rod-side chamber; a plurality of cushion cylinders that support the cushion pad and have pressure-receiving chambers; a hydraulic pump motor that connects the head-side chamber and the rod-side chamber of the elevator cylinder via a first selector valve and that connects the pressure-receiving chambers of the plurality of cushion cylinders via a second selector valve or a logic valve; an electric motor that drives the hydraulic pump motor to supply hydraulic oil to the head-side chamber of the elevator cylinder when the cushion pad is raised and that functions as a generator when the cushion pad is lowered; and proportional valves that are connected to the pressure-receiving chambers of the plurality of cushion cylinders.

[0082] According to the above configuration, by using the lift cylinder when lifting the cushion pad, it is possible to increase the lifting speed of the cushion pad. This reduces the time it takes to lift the cushion pad, thereby improving the productivity of the press machine. In particular, if a logic valve is used, when the flow rate of hydraulic oil supplied from the pressure-receiving chambers of the multiple cushion cylinders to the hydraulic pump motor is high, it is possible to reduce pressure loss compared to when the second switching valve is used. [Explanation of symbols]

[0083] 1 Press machine 15 slides 16 Upper mold 17 Lower mold 2, 2A, 2B Die cushion device 31 Blank holder 32 cushion pins 33 Cushion Pad 4 Cylinder Unit 4A Lifting Cylinder 4B cushion cylinder 41 Head Concubine 42 Rod Concubine 43 Pressure Chamber 51 Hydraulic pump motor 52 Electric motor 7A First switching valve 7B Second switching valve 7C proportional valve 7D, 7E Logic Valve 9 Control Device 91 First position detector 92 Second position detector 93 Pressure detector

Claims

1. A die cushion device for a press machine, a cylinder unit including at least one hydraulic cylinder that supports a cushion pad; a hydraulic pump motor that is driven as a hydraulic pump that supplies hydraulic oil to the cylinder unit when the cushion pad is raised, and that is driven as a hydraulic motor by hydraulic oil discharged from the cylinder unit when the cushion pad is lowered; an electric motor that drives the hydraulic pump motor when the cushion pad is raised and that functions as a generator when the cushion pad is lowered; a proportional valve through which hydraulic oil discharged from the cylinder unit passes when the cushion pad is lowered; a control device for controlling the electric motor and the proportional valve; a pressure detector for detecting a cushion pressure, which is a pressure of hydraulic oil between the cylinder unit and the proportional valve; the control device controls the rotation speed of the electric motor so that an intake flow rate of the hydraulic pump motor is smaller than an exhaust flow rate of the cylinder unit when the cushion pad is lowered, and controls the aperture of the proportional valve so that the cushion pressure detected by the pressure detector becomes a set value.

2. a first position detector that detects a position of a slide of the press machine; a second position detector that detects a position of the cushion pad, 2. The die cushion device according to claim 1, wherein the control device calculates a descending velocity of the slide by differentiating the position of the slide detected by the first position detector, or calculates a descending velocity of the cushion pad by differentiating the position of the cushion pad detected by the second position detector, and calculates a discharge flow rate of the cylinder unit from the calculated descending velocity of the slide or the cushion pad.

3. 3. The die cushion device according to claim 1, wherein the control device stops the electric motor before a slide of the press machine reaches a press bottom dead center.

4. the cylinder unit includes a lifting cylinder having a head side chamber and a rod side chamber, and a plurality of cushion cylinders having pressure-receiving chambers; a head side chamber and a rod side chamber of the lift cylinder are connected to the hydraulic pump motor via a first switching valve; 3. The die cushion device according to claim 1, wherein the pressure-receiving chambers of the plurality of cushion cylinders are connected to the proportional valve and are connected to the hydraulic pump motor via a second switching valve or a logic valve.

5. When the cushion pad is raised, hydraulic oil is supplied from the hydraulic pump motor to a head side chamber of the lift cylinder, while hydraulic oil is supplied from a tank to a pressure receiving chamber of the cushion cylinder, 5. The die cushion device according to claim 4, wherein, when the cushion pad is lowered, the hydraulic pump motor is supplied with the hydraulic oil discharged from the head-side chamber of the elevating cylinder and with some of the hydraulic oil discharged from the pressure-receiving chambers of the plurality of cushion cylinders, and the remainder of the hydraulic oil discharged from the pressure-receiving chambers of the plurality of cushion cylinders passes through the proportional valve.

6. When the cushion pad is raised, hydraulic oil is supplied from the hydraulic pump motor to a head side chamber of the lift cylinder, while hydraulic oil is supplied from a tank to a pressure receiving chamber of the cushion cylinder, 5. The die cushion device according to claim 4, wherein when the cushion pad is lowered, a portion of the hydraulic oil discharged from the head-side chamber of the lift-up cylinder is supplied to the hydraulic pump motor, and the remainder of the hydraulic oil discharged from the head-side chamber of the lift-up cylinder and the hydraulic oil discharged from the pressure-receiving chambers of the plurality of cushion cylinders pass through the proportional valve.

7. A die cushion device for a press machine, an elevating cylinder having a head side chamber and a rod side chamber, the elevating cylinder supporting the cushion pad; a plurality of cushion cylinders each having a pressure-receiving chamber for supporting the cushion pad; a hydraulic pump motor to which a head side chamber and a rod side chamber of the lift cylinder are connected via a first selector valve, and to which pressure receiving chambers of the plurality of cushion cylinders are connected via a second selector valve or a logic valve; an electric motor that drives the hydraulic pump motor to supply hydraulic oil to a head side chamber of the lift cylinder when the cushion pad is raised, and that functions as a generator when the cushion pad is lowered; a proportional valve connected to the pressure-receiving chambers of the plurality of cushion cylinders; A die cushion device comprising:

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