JPH0337839Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a hydraulic circuit in a bending machine.
More specifically, the present invention relates to a hydraulic circuit in a bending machine in which a bypass circuit incorporating a safety valve via an orifice from an electromagnetic switching valve is provided in a movable table lowering circuit.

[Technical background of the invention and its problems] Conventionally, for example, a hydraulic circuit for raising and lowering a movable table of a hydraulic press brake has been designed to supply pressure oil from a hydraulic pump to a cylinder for raising and lowering via an electromagnetic switching valve, and to raise and lower the movable table. It comprised a circuit that performs the lifting and lowering operations.

However, when the upper mold approaches the lower mold by an appropriate distance, and once the approach is stopped and the state is maintained, there is a lack of accuracy in maintaining the accuracy of the stopping position, and furthermore,
If an abnormal pressure is applied between the molds, there is a problem in that the single-configuration circuit lacks safety.

[Purpose of the invention] The purpose of the invention was proposed in order to solve the problem in view of the above-mentioned circumstances.The purpose of the invention is to provide a bypass that connects the lowering electromagnetic switching valve to the safety valve via an orifice in the movable table lowering circuit of the bending machine. By providing the circuit, the purpose is to improve the accuracy of the stop position of the movable table and to provide a hydraulic circuit in a bending machine that serves as a double safety circuit.

[Means for solving the problem] In order to achieve the above object, the present invention provides a system in which a pump is connected to one oil chamber of a hydraulic cylinder for vertically moving a movable table that supports a mold in a bending machine. A counterbalance valve and a safety valve are sequentially arranged and provided in a return line connected to the other oil chamber of the hydraulic cylinder, and the safety valve is connected to the B port of the servo valve. The electromagnetic switching valve that controls the opening and closing of the safety valve is connected to the safety valve via an orifice.

[Operation] By adopting the present invention, in order to bring the upper mold and the lower mold closer to each other and stop them at an appropriate distance, for example, when lowering the movable table to which the upper mold is fixed, the servo valve decelerates and stops the mold. At the same time, a delay time is set so that the safety valve opens after the orifice is narrowed to a predetermined amount. This makes it possible, for example, to stop the lowering stop position of the upper mold without deviation from the target value.

[Example] Hereinafter, an example of the present invention will be described in detail based on the drawings.

Referring to FIG. 1, the press brake 1 includes:
A fixed table 5 is provided at the bottom of the body 3, and a movable table 11 is provided at the top, which is moved up and down by a piston 9 of a hydraulic cylinder 7.

An upper mold 13 is attached to the lower part of the movable table 11, and works together with a lower mold 15 attached to the upper part of the fixed table 5 to bend the workpiece.

The hydraulic circuit that operates the piston 9 of the hydraulic cylinder 7 includes a pipe that leads to the oil chamber 23 of the hydraulic cylinder 7 where hydraulic pressure is sucked up from the oil tank 17 by a pump 19, passes through the A port of the servo valve 21, and lowers the movable table 11. There is a road.

It also includes a pipe line that returns oil in the oil chamber 25 of the hydraulic cylinder 7 to the oil tank 17.

The oil discharged from the oil chamber 25 of the hydraulic cylinder 7 passes through the counterbalance valve 27 and returns to the oil tank 17 via the B port of the servo valve 21 in the pipe line returning to the oil tank 17. A bypass circuit 29 is provided between the downstream side of the servo valve 21 and the servo valve 21 .

The structure of this bypass circuit 29 consists of an orifice 33 that passes through a lowering electromagnetic switching valve 31 and is narrowed to a predetermined amount.
The safety valve 35 is operated via the servo valve 21, and the oil is drained into the oil tank 17 via the servo valve 21.

Furthermore, a relief valve 3 is provided with a throttle in the middle of the pipe connecting the counterbalance valve 27 and the safety valve 35.
7 is provided to form a protection circuit.

The circuit around the pump is a general return circuit that returns to the oil tank 17 via the relief valve 39. Furthermore, when excessive load pressure occurs in the oil chamber 23 of the hydraulic cylinder 7, a return circuit is used to return the oil. A pilot check valve 41 is provided, which opens and closes according to oil pressure fluctuations downstream of the counterbalance valve 27.

With the above circuit configuration, when the upper mold is stopped at a predetermined position as shown in FIG. 2, the solenoid of the lowering electromagnetic switching valve 31 is turned off in response to a stop signal, thereby forming the bypass circuit 29.

In addition, a delay time X is set by the orifice 33 so that the safety valve 35 is turned off after the servo valve 21 decelerates and stops at a predetermined position in response to a stop signal.

Therefore, the upper mold 13 can be stopped without deviation Y from the target value.

Furthermore, the dotted line in Figure 2 shows the movement of the upper mold according to the conventional circuit, but since the safety valves are activated at the same time due to the stop signal, the deviation Y amount is large and the stopping accuracy is poor. There is.

Note that, without being limited to the above-mentioned embodiments,
Of course, various modifications may be made without departing from the gist of the present invention.

[Effects of the invention] As can be understood from the description of the embodiments above, the present invention has a bypass circuit using a safety valve via an orifice from the descending electromagnetic switching valve, so that a predetermined delay time can be achieved by throttling the orifice. can be set.

This eliminates the deviation in the stop position of the upper mold, significantly improving the accuracy of the stop position, and creates a double safety circuit as the upper mold will not descend unless both the servo valve and the lowering electromagnetic switching valve are damaged. Therefore, work safety can be ensured.

[Brief explanation of drawings]

1 and 2 show a hydraulic circuit according to the present invention, FIG. 1 is an explanatory diagram of the hydraulic circuit, and FIG. 2 is an explanatory diagram of its operation. Explanation of symbols representing main parts of the drawings, 13...
... Upper mold, 21 ... Servo valve, 27 ... Counter balance valve, 29 ... Bypass circuit, 31 ...
Lowering solenoid switching valve, 33... Orifice, 35...
...Safety valve, 37...Relief valve.

Claims (1)

[Scope of utility model registration request] A port of a servo valve 21 connected to a pump 19 is connected to one oil chamber 23 of a hydraulic cylinder 7 for vertically moving a movable table 11 that supports a mold in a bending machine. A counterbalance valve 27 and a safety valve 35 are sequentially arranged in a return line connected to the other oil chamber 25 of the servo valve 21, and the safety valve 35 is connected to the B port of the servo valve 21, so that the opening and closing of the safety valve 35 is controlled. A hydraulic circuit for a bending machine, characterized in that a controlled electromagnetic switching valve 31 and the safety valve 35 are connected via an orifice 33.