JPH0663646A - Press brake - Google Patents

Abstract

PURPOSE:To provide a press brake by which the superior bending is attained by compensating the change of the lower limit position caused by temperature change and pressurizing force difference of hydraulic oil. CONSTITUTION:A work W is bent by relatively moving an upper die (one metallic die) 19 freely attachably/detachably provided on a ram 17 which is freely vertically moving by a hydraulic circuit and a lower die (another metallic die) 13 freely attachable/detachable provided on a frame (main body of the press brake) 3. A lower limit positioning valve (limitation positioning valve) 27 by which the hydraulic circuit is controlled is provided on the frame 3 to limit the amount of stroke of the ram 17 when the upper and lower dies 19 and 13 get near each other and an extention shaft (dog) 87 whose vertical position is freely adjusted by a compensating unit 55 is provided on the ram 17. Thus, since the minimum distance between the upper and lower dies 19 and 13 is fixed, the bending having a fixed angle is uniformly executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a press brake, and more particularly to a press brake for accurately controlling the stroke amount of a vertically moving ram.

[0002]

2. Description of the Related Art Conventionally, in a press brake of a type in which an upper die is lowered and bending is performed in cooperation with a lower die, the stroke of the upper die is controlled in order to perform uniform and accurate bending. ing. That is, when the upper die attached to the ram is lowered by lowering the ram during bending, the dog attached to the ram hits the lower limit positioning valve attached to the press brake main body. This allows
The lower limit positioning valve is opened, and the hydraulic oil of the hydraulic cylinder driving the ram flows into the tank, so that the ram maintains its position.

Therefore, the lower limit position of the upper die in such a press brake is adjusted by turning the lower limit handle to move the lower limit positioning valve in the vertical direction so that the work can be bent at a desired angle. The lower limit position has been determined.

[0004]

However, in such a conventional technique, the temperature of the hydraulic oil of the hydraulic device rises and the lower limit position changes upward during the bending process. There is a risk that That is, the set lower limit position is changed by the expansion of the lower limit positioning valve shaft due to the increase of the oil temperature of the operating oil and the change of the opening of the lower limit positioning valve due to the change of the oil viscosity due to the increase of the oil temperature. Therefore, in order to avoid this, the lower limit handle must be moved to adjust the vertical position of the lower limit positioning valve as the oil temperature rises during bending, which is troublesome. If the work is carried out without noticing this, there is a possibility that defects such as insufficient bending may occur and accurate and uniform processing may not be performed.

Further, the lower limit position may change even when the pressure applied during bending is changed. That is,
Since the escape amount of the pressure oil changes due to the difference in the pressing force, the lower limit position changes. Therefore, in order to avoid this, even for works having the same plate thickness and the same bending angle, when the work lengths are different, it is necessary to adjust the pressing force during bending to adjust the lower limit position, which is troublesome.

The object of the present invention has been made in view of such a conventional technique, and a complicated handle operation is performed by correcting a lower limit position change due to a temperature change of working oil or a difference in applied pressure. It is to provide a press brake that can perform a favorable bending process.

[0007]

In order to achieve the above object, a press brake according to the present invention is provided with one of upper and lower molds detachably attached to a press brake main body.
A press brake in which the other die is detachably attached to a vertically movable ram by a hydraulic circuit, and which bends a work by the cooperation of the upper and lower dies, when the upper and lower dies approach each other. The limit positioning valve for controlling the hydraulic circuit to limit the stroke amount of the ram is provided in the press brake body, and the ram is provided with a correction unit having a dog whose vertical position is adjustable.

Here, the correction unit has an oil chamber in which the hydraulic oil of the hydraulic circuit is temporarily stored, and one end portion of which is fixed to the correction unit and an intermediate portion is immersed in the hydraulic oil in the oil chamber. A dog whose end contacts the limit positioning valve.

Alternatively, the correction unit is partitioned from the pressure chamber into which the hydraulic oil of the hydraulic circuit is press-fitted and the pressure chamber by a minute bendable flexible bend plate and sets the bend amount of the bend plate. And a dog having one end supported by the bend plate and the other end abutting the limit positioning valve.

Further, the correction unit includes an oil chamber in which the hydraulic oil of the hydraulic circuit is temporarily stored, a pressure setting chamber provided adjacently to the oil chamber in an isolated state, and the pressure setting chamber. A small amount vertically divided by a flexible bend plate and a pressure chamber into which hydraulic oil of the hydraulic circuit is press-fitted, and one end of which is supported by the bend plate and an intermediate portion is immersed in the hydraulic oil in the oil chamber. And a dog whose other end abuts against the limit positioning valve.

[0011]

According to the press brake of the present invention, one mold detachably mounted on the press brake main body is detachably mounted on the ram vertically movable by the hydraulic circuit. The work is bent by relatively moving. Here, in order to limit the stroke amount of the ram when the upper and lower molds approach each other, a limit positioning valve for controlling the hydraulic circuit is provided in the press brake main body, and the ram is provided with a dog whose vertical position is adjustable. Since the correction unit is attached, the minimum distance between the upper and lower molds is kept constant. As a result, it is possible to perform uniform bending with a constant bending angle.

The correction unit has an oil chamber in which the hydraulic oil of the hydraulic circuit is temporarily stored. Since the dog is immersed in the hydraulic oil in the oil chamber, the dog's temperature increases as the oil temperature rises. The temperature also rises. Therefore, when the shaft of the limit positioning valve is thermally expanded and the limit position is displaced due to the increase in oil temperature due to bending, the temperature of the dog is also increased by the hydraulic oil that is temporarily stored in the oil chamber, causing thermal expansion. Therefore, even if the oil temperature changes, the position of the dog relative to the shaft of the limit positioning valve is always corrected. As a result, the limit position is kept constant even if the temperature of the hydraulic oil rises.

Further, the correction unit has a pressure chamber into which the hydraulic oil of the hydraulic circuit is press-fitted, and the pressure setting chamber is provided by being partitioned by a flexible bend plate.
Since one end is fixed to the bend plate and the other end abuts against the limit positioning valve, the bend plate is bent by the pressure of the hydraulic oil press-fitted, and the dog moves vertically. Therefore, even if the shaft position of the limit positioning valve moves up and down due to the difference in pressure of the hydraulic oil, the limit position is kept constant.

Further, when all of the above-mentioned oil chamber, pressure chamber, pressure setting chamber and bend plate are provided, the limit position is set as described above even if the temperature of the hydraulic oil and the pressure of the hydraulic oil change. Since it can be kept constant, the bending angle is constant and uniform bending is performed.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below with reference to the drawings.

1 and 2 show the entire press brake 1 according to the present invention. In this press brake 1, a base plate 5 provided at the lower ends of a pair of left and right side frames 3 is fixed to a base 9 with bolts 7. A lower table 11 is fixed on the lower front side of the frame 3, and a lower mold 13 is detachably provided on the upper end of the lower table 11.

A hydraulic cylinder 15 is provided on the upper front side of the frame 3, and a motor M and a pump P for driving the hydraulic cylinder 15 are provided on the rear side of the hydraulic cylinder 15. A ram 17 is provided on the lower side of the hydraulic cylinder 15 so as to be vertically movable, and an upper die 19 is provided at a lower end of the ram 17 so as to face the lower die 13.
Is provided. A manual handle 21 is rotatably provided on the right side (the right side in FIG. 1) of the ram 17.

Referring also to FIG. 3, the manual handle 2
1 is attached to the lower end of a rotary shaft 23 rotatably provided on the frame 3. A ball screw 25 is rotatably provided adjacent to the rotary shaft 23, and a lower limit positioning valve 27 as a limit positioning valve is vertically movable on the ball screw 25. Rotating shaft 23
And the upper ends of the ball screw 25 are pulleys 29, 31 respectively.
Is attached, and a belt 33 is wound around the pulleys 29 and 31.

Therefore, when the manual handle 21 is rotated, the ball screw 25 is rotated via the belt 33, and the lower limit positioning valve 27 can be vertically positioned.

Returning to FIGS. 1 and 2, the lower table 1
An operation panel 35 equipped with various kinds of switches is provided on the front surface of 1, and a foot switch F is provided on the operation panel 35.
S is connected. The foot switch FS is provided with a ram down command pedal DS and a ram up command pedal US.

With the above-described structure, the press brake 1 operates roughly as follows: When the ram down command pedal DS is depressed, the pump P driven by the motor M drives the hydraulic cylinder 15 to lower the ram 17, and the upper die 19 is moved. The work W arranged between the lower die 13 and the lower die 13 is bent. When the ram rise command pedal US is depressed, the hydraulic cylinder 15 raises the ram 17 to complete the machining.

FIG. 4 shows a hydraulic circuit for driving the ram 17. Two pumps P are connected to the motor M.
This pump P sucks up hydraulic oil from the tank TNK via the filter F, and one pump P is divided into two in the middle of the oil passage OL1 and is connected to the tank TNK via the relief valve 37 by the oil passage OL2. In addition, it is connected to the main valve 39 by an oil passage OL1. The other pump P is connected to the tank TNK via a relief valve 41 by an oil passage OL3.

The main valve 39 is a 4-port electromagnetic switching valve, and the A port is connected to the hydraulic cylinder 15 by an oil passage OL4.
Connected to the first cylinder chamber S1 of the
5 is connected to the second cylinder chamber S2 via a counter balance valve 43. The oil passage OL4 is divided into an intermediate oil passage OL6 and is connected to a regulator 45 for setting a pressure.

An oil passage OL7 separated from the oil passage OL4 is connected to the P port of the speed switching valve 47, and the oil passage OL4 is connected by an oil passage OL8 to a cutoff valve 51 connected to a pressure gauge 49. There is. The speed switching valve 47 is connected to the check valve 53 of the counter balance valve 43.

The oil passage OL4 is connected to the lower limit positioning valve 27 by an oil passage OL9, and the lower limit positioning valve 2
7 is connected to the tank TNK. The lower limit positioning valve 27 is interlocked with the manual handle 21 as described above, and is supported so as to be vertically movable. Also, oil passage O
The oil passage OL10 separated from L9 is connected to a correction unit 55 described later.

On the other hand, the first cylinder chamber S1 of the hydraulic cylinder 15 is connected to the tank TNK through the check valve 57 by the oil passage OL11. This check valve 5
7 is connected to the oil passage OL5 described above. Oil passage O
The oil passage OL12, which is separated from L11, has a check valve 5
It is connected to the P port of the unload valve 61 via 9 and the pressure switch 63.
The oil passage OL12 is also connected to the oil passage OL3 described above.

The operation of the hydraulic circuit constructed as above during bending will be described.

First, when the power is turned on and the start push button switch (not shown) is pressed, the motor M rotates to drive the pump P and suck up the hydraulic oil from the tank TNK.

When performing the bending process, the ram down command pedal DS is depressed. As a result, the SO of the main valve 39
L2, SOL of the speed switching valve 47, and SOL4 of the unload valve 61 are simultaneously turned on. The hydraulic oil sucked up by the pump P passes through the oil passage OL1, the P port and the A port of the main valve 39, and passes through the oil passage OL4 into the first cylinder chamber S1 of the hydraulic cylinder 15.

When the ram 17 approaches the work W, a dog (not shown) touches a limit switch (not shown) at the speed switching position, so that the speed switching valve 47 returns and the check valve of the counter balance valve 43. 53
Close. As a result, the return hydraulic oil from the second cylinder chamber S2 of the hydraulic cylinder 15 will not be transferred to the counter balance valve 4
Drain the tank TNK through the relief valve 65 against the predetermined back pressure set by 3. Further, SOL4 of the unload valve 61 is cut off, and the oil of one pump P returns to the tank TNK. This is why the ram 17 has a slow speed.

The ram 17 whose speed has been switched is the upper die 19
When the workpiece W reaches the work W, the pressure in the hydraulic cylinder 15 rises and descends while performing the bending work. However, the correction unit 55 attached to the ram 17 moves the lower limit positioning valve 2
When the valve shaft 67 of No. 7 is tapped, the hydraulic oil is oil passage OL4.
To the oil passage OL9. Therefore, the hydraulic oil does not flow toward the hydraulic cylinder 15 but flows through the lower limit positioning valve 27 into the tank TNK, so that the ram 17 maintains its position and does not descend further.

When the ram rise command pedal US is depressed after the bending work is completed, the main valve SOL1 is turned on and the hydraulic oil is changed to P.
The ram 17 is raised by entering the second cylinder chamber S2 of the hydraulic cylinder 15 through the port, the B port and the check valve 53 of the counter balance valve 43. At this time, the check valve 57 opens and a part of the hydraulic oil in the first cylinder chamber S1 returns to the tank TNK through the oil passage OL11, and a part of the hydraulic oil returns to the tank TNK through the main valve 39.

The pressure switch 63 is turned on when a predetermined set pressure or more is applied during pressurization, the SOL 4 is turned off, the oil of one pump P is returned to the tank TNK, and the motor M is turned on.
Has the role of lightening the burden.

When the ram 17 rises, a dog (not shown)
Touches a limit switch (not shown), and SOL1 of the main valve 39 is cut off to be in the neutral position. Then, the oil discharged from the pump P returns to the tank TNK through the P port and the T port. The ram 17 remains in that position. The bending process is completed as described above.

Next, the lower limit positioning valve 27 will be described with reference to FIGS. 5 and 6. As described above, the lower limit positioning valve 27 is attached to the ball screw 25 which is rotationally driven by the manual handle 21,
It can be vertically positioned by rotating. The lower limit positioning valve 27 includes a lower limit positioning valve body 69 and a valve shaft 67.

On the right side of the lower limit positioning valve main body 69 in FIG. 5, there is provided a pressure oil inlet 71 to which the oil passage OL9 of the hydraulic circuit is connected and the working oil is press-fitted.
Is connected to a passage 73 provided in the vertical direction at the center of the lower limit positioning valve body 69. Also, the bottom wall 7
An outlet 77 for returning the hydraulic oil to the tank TNK is formed in the center of the tank 5. A vacant chamber 79 is provided between the passage 73 and the outlet 77.

The vacant chamber 79 and the passage 73 have a valve portion 67A at the lower end and an upper end 67B protruding upward from the lower limit positioning valve body 69.
7 is provided in a state of being always urged upward by a spring spring 81.

With the above-mentioned structure, the correction unit 55 attached to the ram 17 is provided with the valve shaft 6
When the valve shaft 67 is pressed down by contacting the upper end of the valve shaft 67, the valve portion 67A of the valve shaft 67 blocking the lower end of the passage 73 lowers to form the gap D. The hydraulic fluid flows out from this gap D into the empty chamber 79, and then from the outlet 77 to the tank TN.
Return to K. Therefore, the hydraulic oil sent by the oil passage OL4 is returned to the tank TNK via the oil passage OL9.
The hydraulic oil is not sent to the hydraulic cylinder 15, and the ram 17 remains at that position.

Next, the correction unit 55 will be described with reference to FIGS.

First, FIGS. 7 and 8 show an embodiment of the correction unit 55 which operates in response to the temperature change of the hydraulic oil. The correction unit 55 has a box-shaped correction unit main body 85 having an oil chamber 83 therein, and an extension shaft 87 as a dog. The oil chamber 83 is a place where the hydraulic oil that drives the hydraulic cylinder 15 by the oil passage OL10 or the hydraulic oil that returns from the hydraulic cylinder 15 is temporarily stored.

An inflow port 89, which is connected to the oil passage OL10 and into which the working oil of the hydraulic circuit flows, is provided at an intermediate height position of the right wall (right side in FIG. 7) of the correction unit main body 85. The left wall is provided with an outflow port 91 through which hydraulic oil flows. Since this outflow port 91 is located at a position higher than the inflow port 89, the hydraulic oil that has flowed in through the inflow port 89 is temporarily stored in the oil chamber 83 and flows out through the outflow port 91.

The extension shaft 87 is L-shaped as a whole, and the lower end thereof is vertically fixed to a plate 97 attached to the lower side of the correction unit main body 85 by bolts 95, 95 by a bolt 93. Then, the extension shaft 87 penetrates the upper wall of the correction unit main body 85 and extends upward, and is bent at a right angle to form a horizontal portion 87.
Forming A. The horizontal portion 87A is a member that transmits the position to the lower limit positioning valve 27.

O-rings 99 and 99 are provided at the places where the extension shaft 87 penetrates the bottom wall and the upper wall, respectively, so that the hydraulic oil temporarily stored in the oil chamber 83 does not leak. Therefore, since the extension shaft 87 is constantly immersed in the working oil accumulated in the oil chamber 83, the extension shaft 8
The temperature of 7 changes according to the temperature of hydraulic fluid.

Here, the extension shaft 87 is made of the same material and has the same length as the valve shaft 67 of the lower limit positioning valve 27 so that the amount of expansion and contraction due to the change of the oil temperature becomes the same.

With the above-mentioned structure, the lower limit positioning in bending is performed as follows. First, trial bending is performed, and the lower limit position is determined so that a desired bending angle can be obtained by operating the manual handle 21. When the temperature of the hydraulic oil in the hydraulic circuit rises during the work, the valve shaft 67 of the lower limit positioning valve 27 extends due to this temperature rise, and the upper end of the valve shaft 67 is displaced upward.

On the other hand, in the correction unit 55, the extension shaft 87 of the correction unit 55 expands by the same amount as the valve shaft 67 due to the temperature rise of the hydraulic oil that flows in and is temporarily stored, and the horizontal portion 87A is displaced upward. To do. Therefore, the position of the ram 17 when the horizontal portion 87A hits the upper end of the valve shaft 67 is the same position as when the work is started (that is, the lower limit position).

Thus, even if the temperature of the hydraulic oil rises during bending, the lower limit of the ram 17 can always be kept constant without operating the manual handle 21, so that an accurate bending angle can always be obtained. To be

Next, with reference to FIGS. 9 and 10, an embodiment of the correction unit 55 that operates in response to changes in the pressing force during bending will be described. This correction unit 55
Has a pressure setting chamber 103 inside the box-shaped correction unit main body 101 and a pressure chamber 105 below the inside. The pressure setting chamber 103 and the pressure chamber 105 are
A minute amount is partitioned in the vertical direction by a flexible bend plate 107.

The bottom wall of the pressure chamber 105 is provided with a pressure inlet 109 into which hydraulic oil of a hydraulic circuit is press-fitted, and the pressure inlet 109 is connected to an oil passage OL10 of the hydraulic circuit. The left and right sidewalls are attached to the mounting bases 111, 1
11 is provided, by which it is attached to the ram 17.

The extension shaft 113 is entirely L
The lower end is vertically fixed to the bend plate 107 with a bolt 117 sandwiching the seal washer 115, penetrates the upper wall of the correction unit main body 101 and extends upward, and is bent at a right angle to form a horizontal portion 113A. Is formed. The horizontal portion 113A is a member that transmits the position to the lower limit positioning valve 27. An O-ring 119 is provided between the bend plate 107 and the correction unit main body 101 so that pressure does not leak even when the bend plate 107 bends.

With the above-mentioned structure, when the hydraulic oil is pressed from the pressure inlet 109, the bend plate 107 is pressed.
Bends upward, and the extension shaft 113 moves upward accordingly. On the other hand, the valve shaft 67 of the lower limit positioning valve 27 is displaced upward due to the applied pressure, and this displacement is caused by the bend plate 10
Since it can be corrected by the deflection of 7, the horizontal portion 11
The position of the ram 17 when the 3A hits the upper end of the valve shaft 67 of the lower limit positioning valve 27 becomes the same position as before the pressure change.

As described above, even if the pressing force rises during bending, the ram 1 is always operated without operating the manual handle 21.
Since the lower limit of 7 can be kept constant, an accurate bending angle can always be obtained.

Next, with reference to FIGS. 11 and 12, an embodiment of the correction unit 55 that operates in response to changes in the oil temperature of the hydraulic oil and changes in the applied pressure due to bending will be described. Since the correction unit 55 is a combination of the above-mentioned two cases, common parts are denoted by common reference numerals, and description thereof will be omitted.

Inside the box-shaped correction unit main body 121, there is an oil chamber 83 in the first embodiment shown, and below the pressure setting chamber 103 and pressure chamber 105 in the latter embodiment. A bend plate 107 is provided between the pressure setting chamber 103 and the pressure chamber 105. And
The extension shaft 123 is vertically fixed to the bend plate 107. The extension shaft 123 penetrates the pressure setting chamber 103, and the oil chamber 8
In FIG. 3, the horizontal portion 123A is formed by being immersed in hydraulic oil and protruding above the correction unit main body 121.

The action and effect of this embodiment are the same as those of the first embodiment with respect to the change of the oil temperature, and the same action as the embodiment of the present invention with respect to the change of the pressurizing force. Since the effect is shown, the description is omitted.

As described above, since the position shift of the lower limit positioning valve 27 due to the change of the oil temperature of the hydraulic oil and the change of the pressurizing force can be corrected, if the bending angle and the plate thickness are the same, it is necessary to manually operate during working. The bending angle is kept constant without adjusting the lower limit position by the handle 21, and uniform bending can be continuously obtained.

In each of the above embodiments, the press brake for lowering the upper die 19 mounted on the lower end of the ram 17 and bending it in cooperation with the lower die 13 has been described, but the present invention is not limited to this. is not. The same applies to a press brake of a type in which the lower die 13 is lifted to perform bending in cooperation with the upper die 19. That is, by controlling the upper limit position of the lower mold 13 as in the above-described embodiment, the same operational effect can be obtained.

Further, as shown in FIG. 13, one end of the dog 125 is rotatably supported, and the correction unit 55 is arranged at an intermediate position of the dog 125 so as to expand the correction amount of the tip of the dog 125. Good.

[0059]

The press brake according to the present invention is configured as described above, and is a limit positioning valve provided in the press brake body to limit the stroke amount of the ram when the upper and lower molds approach each other. Since the dog whose vertical position has been corrected by the correction unit strikes, the limit position of the ram's slot talk is always kept constant, and the minimum distance of the upper and lower dies is kept constant. As a result, it is possible to perform uniform bending with a constant bending angle.

Even if the shaft of the limit positioning valve expands and contracts due to the increase in the oil temperature of the hydraulic oil, the dog is immersed in the hydraulic oil of the hydraulic circuit temporarily stored in the oil chamber of the correction unit. However, since the shaft expands and contracts similarly to the shaft, the limit position is always constant. For this reason,
Even if the oil temperature rises along with the bending process, it is possible to obtain a certain limit position.

Further, when the shaft position of the limit positioning valve moves up and down due to the difference in the pressure of the hydraulic oil, the dog is attached to the bend plate forming one surface of the pressure chamber. Bends in response to changes in the pressure of the pressure chamber, so that the dog moves in the vertical direction. Therefore, the limit position is kept constant even if the pressing force changes.

Further, when all of the above-mentioned oil chamber, pressure chamber, pressure setting chamber and bend plate are provided, the limit position is set as described above even if the temperature of the hydraulic oil changes and the pressure of the hydraulic oil changes. Since it can be kept constant, the bending angle is constant and uniform bending is performed.

[Brief description of drawings]

FIG. 1 is a front view showing an embodiment of a press brake according to the present invention.

FIG. 2 is a side view seen from the direction of the arrow II in FIG.

FIG. 3 is an enlarged structural diagram of a portion III in FIG.

FIG. 4 is a hydraulic circuit diagram.

FIG. 5 is a sectional structural view of a lower limit positioning valve.

FIG. 6 is a detailed view of the lower portion of the shaft of the lower limit positioning valve.

FIG. 7 is a sectional view of a temperature correction unit.

FIG. 8 is a side view seen from the direction of arrow VIII in FIG. 7.

FIG. 9 is a cross-sectional view of a pressing force correction unit.

FIG. 10 is a side view seen from the X direction of the arrow in FIG.

FIG. 11 is a cross-sectional view of a temperature and pressure correction unit.

FIG. 12 is a side view seen from the arrow XII direction in FIG.

FIG. 13 is a structural diagram showing a correction unit according to another embodiment.

[Explanation of symbols]

1 Press Brake 3 Frame (Press Brake Main Body) 13 Lower Die 17 Ram 19 Upper Die 27 Lower Positioning Valve (Limiting Positioning Valve) 55 Correction Unit 83 Oil Chamber 87, 113, 123 Extension Shaft (Dog) 103 Pressure Setting Chamber 105 Pressure Chamber 107 Bend plate W work

Claims (6)

[Claims] 1. One of the upper die and the lower die is detachably provided on the press brake body, and the other die is detachably attached to a vertically movable ram by a hydraulic circuit.
A press brake for bending a work by cooperation of a lower die, wherein a limit positioning valve for controlling the hydraulic circuit is provided in the press brake body so as to limit a stroke amount of a ram when the upper die and the lower die approach each other. A press brake, wherein the ram is provided with a correction unit having a dog whose vertical position is adjustable. 2. The correction unit includes an oil chamber in which hydraulic oil of the hydraulic circuit is temporarily stored, one end of which is fixed to the correction unit and an intermediate portion of which is immersed in the hydraulic oil in the oil chamber and the other end of which is located. The press brake according to claim 1, further comprising a dog whose portion abuts against the limit positioning valve. 3. The correction unit is partitioned from a pressure chamber into which hydraulic oil of the hydraulic circuit is press-fitted and a bend chamber which is flexible by a small amount in the vertical direction, and sets the bending amount of the bend plate. 2. The press brake according to claim 1, further comprising: a pressure setting chamber, and a dog having one end supported by the bend plate and the other end abutting the limit positioning valve. 4. The correction unit includes an oil chamber in which hydraulic oil of the hydraulic circuit is temporarily stored, a pressure setting chamber provided adjacently to the oil chamber in an isolated state, and the pressure setting chamber. A small amount vertically divided by a flexible bend plate and a pressure chamber into which hydraulic oil of the hydraulic circuit is press-fitted, and one end of which is supported by the bend plate and an intermediate portion is immersed in the hydraulic oil in the oil chamber. The press brake according to claim 1, further comprising a dog whose other end abuts against the limit positioning valve. 5. The press brake according to claim 2, wherein the dog of the correction unit and the valve shaft of the limit positioning valve are made of the same material and have the same length. 6. The press brake according to claim 3, wherein the displacement amount of the correction unit with respect to the pressure of the bend plate is matched with the displacement amount of the opening of the limit positioning valve.