JP2551541Y2 - Press brake hydraulic circuit - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic circuit of a press brake for bending a plate-like work.

[0002]

2. Description of the Related Art Conventionally, as a hydraulic circuit of a bending machine for bending a plate-shaped work, for example, Japanese Utility Model Application Laid-Open No. Sho 62-18982.
No. 3 is known. In the conventional hydraulic circuit, a bypass circuit is provided in the middle of the circuit of the counterbalance valve and the servo valve that constitutes the return circuit of the hydraulic cylinder that moves up and down and up and down, from the electromagnetic switching valve to the safety valve through the orifice. Features.

[0003]

However, in the case where a relief valve is provided in the return circuit as in the above-mentioned conventional hydraulic circuit, the relief valve always operates when the ram descends.
There was a problem that the ram could only be lowered at a slow speed, resulting in poor work efficiency. The present invention has been made for the purpose of improving the above-mentioned problem, and an object of the invention is to provide a hydraulic circuit for a press brake in which a descending speed of a ram can be changed between a fast-forward and a slow-feed when descending.

In order to achieve the above object, the present invention provides a press brake for bending a plate-like work between an upper side attached to a ram moved up and down by a hydraulic cylinder and a lower side fixed to a table side. In the above, a plurality of extension chambers having different cross-sectional areas and at least one reduction chamber are provided in the hydraulic cylinder, and pressure oil is supplied to the extension chamber and the reduction chamber via a servo valve. A counterbalance circuit consisting of a pilot check valve and a relief valve is provided between the reduction chambers of the hydraulic cylinder,
When lowering the ram quickly with the above hydraulic cylinder , the solenoid valve
The pilot pressure is supplied by the pilot pressure supplied from
Open the shut-off valve and pressurize the oil in the reduction chamber with the servo valve
Drain the tank while controlling, and lower the ram slowly.
The pilot check valve, close the relief
While maintaining the pressure reduction chamber 1 ₃ side by the valve is obtained so as to lower the ram.

With the above structure, the ram can be quickly lowered until the upper side contacts the work, so that the productivity is improved and the servo is lowered.
The hydraulic oil supplied to the hydraulic cylinder by the valve and the hydraulic cylinder
Pressure oil is simultaneously controlled
Therefore, the ram can stably descend at a high speed. In addition, during machining by slow descent, the pressure is held on the contraction side of the hydraulic cylinder by the relief valve, so that no negative pressure is generated on the extension chamber side, and it is possible to prevent chatter vibration of the ram due to the negative pressure. .

[0005]

[Embodiment] An embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a hydraulic circuit of a press brake. In FIG. 1, reference numeral 1 denotes a pair of hydraulic cylinders for vertically driving a ram (both not shown) attached to an upper die. oil, adapted to be supplied to the proportional first said hydraulic cylinder 1 via the servo valve 4 after being pressure set by the solenoid relief valve 3, the second elongated chamber 1 _1, 1 ₂ or reduction chamber 1 ₃ And the servo valve 4 and the first
Between the extension chamber 1 ₁ solenoid valve 5, and a counter balance circuit 8 constituted by the pilot check valve 6 and the relief valve 7 between the servo valve 4 and the reduction chamber 1 ₃ is received. With the pilot check valve 6 of the counter balance circuit 8 is opened and closed by the pilot pressure supplied through the pilot circuit 10 from the solenoid valve 9, the return being connected to the first elongated chamber 1 ₁ of the hydraulic cylinder 1 circuit 12
The feeling valve 13 is provided to the pilot circuit 1 by an electromagnetic valve 14.
5 is opened and closed by a pilot pressure supplied via the control valve 5.

Next, the operation will be described. Now set to fast downward pressure by the proportional electromagnetic relief valve 3 so as to quickly lower the ram, hydraulic fluid is set to flow in the pressure flow is controlled by a servo valve 4 to the second elongated chamber 1 ₂ of the hydraulic cylinder 1, The piston 1a is pushed downward. At the same time the pilot check valve 6 is opened by the pilot pressure supplied from the solenoid valve 9, the oil of the reduction chamber 1 ₃ is drained by a pressure-flow rate controlled by a servo valve 4 to the tank 16. This together with the ram is fast lowered by the hydraulic cylinder 1, the oil tank 16 through a filling valve 13 which is opened by pilot pressure from the solenoid valve 14 is sucked to the first elongated chamber 1 ₁ of the hydraulic cylinder 1 You.

Next, when the ram is lowered by a certain distance, a slow descending operation is started. Pressure oil is set to slow down the pressure by the proportional electromagnetic relief valve 3 is controlled pressure flow by the servo valve 4, first to the extended chamber 1 ₁ through the second elongated chamber 1 ₂ and the solenoid valve 5 is switched Inflow. At this time, the filling valve 13 is closed. Thus, the hydraulic cylinder 1 lowers the ram at a slow descending speed, and starts working the workpiece between the upper die attached to the ram and the lower die (neither is shown) fixed to the table side, oil reduction chamber 1 ₃ of the hydraulic cylinder 1, the pilot check valve 6 is closed, is drained to the tank 16 while maintaining a constant pressure from the relief valve 7. The set pressure of the relief valve 7 is set to a pressure + α required for raising the ram.

When the forming of the workpiece is completed as described above, an ascending step is performed. Proportional pressure oil is set above boosted by electromagnetic relief valve 3 is flowed is a pressure flow control by the servo valve 4 to reduce chamber 1 ₃ of the hydraulic cylinder 1, thereby the piston 1a is pushed upwardly rising ram Start.
The first oil extension chamber 1 ₁ of the hydraulic cylinder 1 is drained via the filling valve 12 which is opened to the tank 16,
Oil of the second elongated chamber 1 ₂ is to be drained are pressure-flow controlled by a servo valve 4 to the tank 16. In the case where the slow down halfway stopped, the pilot check valve 6 and a relief valve 7 is closed, the oil of the reduction chamber 1 ₃ is cut off here. FIG. 2 is a time chart showing the operation of raising and lowering the ram and the operation of each part in the above operation.

On the other hand, in the conventional hydraulic circuit, if the descending speed of the ram at the time of slow descending becomes fast or the pressure is low, the first extension chamber 11 ₁
A negative pressure is generated in the ram, and chatter vibration is generated in the ram. This chatter vibration is generated by resonance of the system, and the resonance frequency of the system will be described below. FIG. 3 shows a conventional hydraulic circuit. The resonance frequency of the hydraulic circuit at the time of slowdown is

[0010]

(Equation 1)

## EQU1 ## FIG. 4 shows the hydraulic circuit according to the present invention.

[0012]

(Equation 2)

## EQU1 ## Generally, it is said that the larger the resonance frequency of the system and the larger the ratio of the resonance frequency loop gain, the more stable the system. As is clear from the above equation, A ₁
+ A ₃ and A ₂ , but the difference is usually (A
_{1 + A 3): A 2} = 6~10: since it is 1, only the amount more of this invention of the system becomes stable. The description of the symbols used in the above equation is as follows. Wn: System resonance frequency g: Gravity acceleration β: Oil compression ratio L: Cylinder stroke w / 2: Cylinder suspension weight Klp: Loop gain k: Lever ratio Q: Servo valve rated flow δ: Servo valve spool stroke A _1: cylinder pressure area (first decompression chamber area) A _2: 〃 pulling area (reduction chamber area) A _3: 〃 fast descent area (second decompression chamber area)

[0014]

[Effects of the Invention] As described in detail above, this invention has a pilot check valve of a counter balance circuit at the start of machining.
And drain the oil from the reduction chamber to the tank via the servo valve.
The conventional relief valve
The ram is higher than the one that was drained to the tank.
Fast descent becomes possible. This reduces cycle time
The productivity can be greatly improved because of the reduction. Also sir
The hydraulic oil supplied to the hydraulic cylinder by the valve and the hydraulic cylinder
In order to control both the pressure oil discharged from the
The ram can be moved down stably at a high speed, and at the time of molding, the ram is processed while the hydraulic pressure in the reduction chamber side of the hydraulic cylinder is kept constant by the relief valve to perform molding. , Regardless of the setting pressure level and the ram descent speed, the counter action works in the slow descent range, so there is no negative pressure on the extension chamber side and no chatter vibration on the ram,
High-precision processing becomes possible, and noise can be reduced. Further, even if the ram is stopped during the slow descending due to the low set pressure, the pressure on the reduction chamber side of the hydraulic cylinder is cut off by the counter balance circuit, so that the ram can be prevented from dropping naturally by its own weight.

[0015]

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram showing an embodiment of the present invention.

FIG. 2 is a timing chart showing the same operation.

FIG. 3 is an explanatory diagram illustrating a resonance frequency of a conventional hydraulic circuit.

FIG. 4 is an explanatory diagram illustrating a resonance frequency of the hydraulic circuit of the present invention.

[Explanation of symbols]

1 hydraulic cylinder, 1 ₁ extension room, 1 ₂ extension room, 1 ₃
Reduction chamber, 4 servo valves, 6 pilot check valves,
7 Relief valve, 8 Counter balance circuit.

Claims (1)

(57) [Scope of request for utility model registration] 1. A press brake for bending a plate-like work between an upper die attached to a ram moved up and down by a hydraulic cylinder 1 and a lower side fixed to a table side. and a plurality of elongated chambers 1 ₁ is a cross-sectional area _different, 1 ₂ and at least one reduction chamber 1 _3, supply pressure oil through the servo valve 4 to these extension chamber 1 _1, 1 ₂ and reduction chamber 1 ₃ None as, also with between reduction chamber 1 ₃ of the servo valve 4 and the hydraulic cylinder 1 provided counterbalance circuit 8 consisting of the pilot check valve 6 and a relief valve 7, fast lowering the ram by the hydraulic cylinder 1
At the time of pilot pressure supplied from the solenoid valve 9
Open the serial pilot check valve 6, the oil of the reduction chamber 1 ₃
The tank 16 is controlled while controlling the pressure and flow rate by the servo valve 4.
When draining and slowing down the ram,
Closed to preparative check valve 6, the hydraulic circuit of the press brake comprising as to lower the ram while maintaining the pressure reduction chamber 1 ₃ side by the relief valve 7.