JPH0815668B2 - Plasma cutting device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a plasma cutting device, and more particularly to prevention of electric shock due to no-load voltage.

[Conventional technology]

The no-load voltage of the power source of the plasma cutting device is generally a high voltage of 200 V or more, and when the electrode of the cutting torch and the nozzle are in contact with each other and are in a short circuit state, when the worker swings to the nozzle,
Risk of electric shock from unloaded voltage.

In order to prevent electric shock due to this no-load voltage, the following means have been devised.

(1) When there is a short circuit between the electrode of the cutting torch and the nozzle, it is detected and the output of the cutting power supply is stopped.

(2) It has a function of detecting the pilot arc current flowing from the power source to the nozzle of the cutting torch and controlling the constant current,
When the electrode-nozzle is short-circuited, this constant current control function reduces the no-load voltage of the power source for cutting to a low voltage without danger of electric shock (Japanese Patent Application No. 61-122129).

[Problems to be Solved by the Invention] However, both of the means (1) and (2) are based on the premise that the nozzle of the cutting torch and the power supply are normally connected, and between the power supply and the nozzle. If the pilot arc current cable connection of No. 1 is not properly made, there is a drawback that the electric shock protection function is lost.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a plasma cutting apparatus that avoids the loss of the electric shock protection function due to the leakage of the connection of the pilot arc current cable, which is a drawback of the above-mentioned prior art, and further improves safety.

[Means for solving problems]

The present invention for achieving the above object detects the short circuit between the electrode and nozzle of the cutting torch and stops the output of the power supply for cutting, or reduces the no-load voltage to the extent that there is no danger of electric shock. In the plasma cutting device having means for connecting, a means for detecting whether or not the power supply side connector of the pilot arc current cable for connecting the nozzle of the cutting torch to the power supply is normally connected, and the connector is normally connected. If not, the output of the disconnecting power supply is stopped by the signal from the detecting means.

[Action]

The plasma arc cutting device's pilot arc current cable is typically connected to the power source with a pluggable connector.
Conventionally, if the connection of this connector is forgotten, there is a possibility that a short circuit state between the electrode of the cutting torch and the nozzle cannot be detected, and a high no-load voltage may be applied to the nozzle. If the power supply side connector of the current cable is not connected properly, the output from the disconnecting power supply will be stopped by the connection leak detection signal, so there is no risk of electric shock even if the operator touches the nozzle, and safety is ensured. Is further improved.

〔Example〕

 FIG. 1 shows an embodiment of the present invention.

1 is a power source for cutting, 2 is a high frequency generator, 3 is a coupling coil for applying high frequency, 4 is a capacitor for high frequency bypass, 5 is a resistor for limiting pilot arc current, 6 is a contact for opening and closing the pilot arc circuit, 7 is a A current detector for opening the contact 6 when a main arc current flows, and 8 for generation of cutting power, generation of high frequency, supply of differential gas and cooling water in response to a start signal S from a torch switch (not shown). Sequence control circuit that performs a series of control such as
9 is a power supply box. 10 is a cutting torch, the electrode 11 of which is connected to the main current cable 15 and the nozzle 12 of which is connected to the pilot arc current cable 16. Reference numeral 17 is a ground side cable connected to the base material 14, and 18, 19 and 20 are power source side cable connection connectors.

In this embodiment, as a means for detecting a contact short circuit between the electrode 11 and the nozzle 12, the voltage applied between the electrode and the nozzle via the main current cable 15 and the pilot arc current cable 16 is used as a reference voltage in the short circuit detection circuit 21. In comparison, if the applied voltage is equal to or lower than the reference voltage, the short circuit detection signal is sent to the sequence control circuit 8. Further, in order to detect the connection failure of the pilot arc current cable 16, a three-core connector is used for the power supply side connector 19 of the pilot arc current cable 16, and the one connector 22 of the connector 22 connects the pilot arc current cable 16 to the power supply side. Connect the male side of the other two connectors 23, 24 to each other by the conductor 25, connect the female side to the connection leak detection circuit 26, and connect the connectors 23, 24 to the closed or open state. By this, whether the connector 19 is normally connected or not is electrically detected, and the detection signal is sent to the sequence control circuit 8.

When the control power supply is turned on at the start of disconnection, power is also supplied to the short circuit detection circuit 21 and the connection failure detection circuit 26, and respective detection signals are sent to the sequence control circuit 8. If there is no abnormality such as a short circuit between the power source of the cutting torch 10 and the nozzle or a cable connection failure, the sequence control circuit 8 operates normally, and the power source for cutting 1 connects between the electrode 11 and the base material 14 and the electrode. At the same time that no-load voltage is applied between the nozzle 11 and the nozzle 12, a high-frequency voltage is superimposed on the pilot arc circuit from the high-frequency generator 2 through the coupling coil 3, and the pilot arc is generated between the electrode 11 and the nozzle 12. An arc is generated, and then the main arc (plasma arc) 13 is turned on between the electrode 11 and the base material 14 by being guided to the plasma flow by the pilot arc, and the cutting is started. According to the present embodiment, if the electrode-nozzle of the cutting torch 10 is short-circuited due to the carelessness of the user, the voltage between the electrode-nozzle is almost zero, A short circuit detection signal is output from the short circuit detection circuit 21.
The sequence control circuit 8 does not operate even when receiving the activation signal S, and does not cause the disconnecting power supply 1 to output. Further, when the power supply side connector 19 of the pilot arc current cable 16 is not normally connected, the connection leakage detection circuit 26 outputs the connection leakage detection signal because the connection between the connectors 23 and 24 is in the open state. Even in this case, the sequence control circuit 8 is not operated and the output of the power source 1 for cutting is not generated. Therefore, even if the short-circuit detecting circuit 21 does not detect the short-circuit state between the electrode and the nozzle due to the leakage of the pilot arc current cable 16, there is no risk of the user touching the nozzle 12 and receiving an electric shock.

 FIG. 2 shows another embodiment of the present invention.

In this embodiment, a current setting device 27 is provided in the pilot arc circuit in place of the pilot arc current limiting resistor 5 shown in FIG. 1, and between the electrode 11 and the nozzle 12 of the cutting torch 10 at the start of cutting. When the pilot arc is turned on,
The detection signal of the current detector 27 corresponding to the pilot arc current and the setting signal of the pilot arc current setting device 28 are compared by the adder 29, and the difference signal is input to the cutting power supply 1 via the signal selection circuit 30. As a result, constant current control is performed so that the pilot arc current becomes the set value. When the main arc 13 is ignited between the electrode 11 and the base material 14, the relay drive circuit 31 is operated by the detection signal of the current detector 7 corresponding to the main arc current, and the relay 32 is energized to contact 6 Opens and shuts off the pilot arc circuit. Regarding the degree of transition to the main arc, the detection signal of the current detector 7 and the setting signal of the arc current setting device 33 are compared by the adder 34, and the difference signal is input to the cutting power supply 1 via the signal selection circuit 30. By doing
Constant current control is performed so that the main arc current becomes a set value.

In the case of such a configuration, even if the electrode of the cutting torch 10 and the nozzle are in a short-circuited state, it is usually a current detector.
Since the detection signal of 27 is negatively fed back to the adder 29, the constant current control function of suppressing the current flowing in the pilot arc circuit to a small current of about 5 to 10 A works, so that the output voltage of the power supply for cutting 1 is a shock. Although it does not generate dangerously high voltage, this electric shock protection function is
It is assumed that 16 is normally connected, and if the pilot arc current cable 16 is forgotten to be connected, there is no negative feedback of the detection signal from the current detector 27, so a high no-load voltage from the disconnecting power supply 1 It occurs and the electric shock prevention function is lost.

This embodiment is an example in which the leak detection switch 35 is incorporated in the power supply side connector 19 of the pilot arc current cable 16 in order to ensure safety even when the pilot arc current cable 16 is not normally connected. . As shown in FIG. 3, the connection leakage detection switch 35 has a structure in which the contact spring 36 is pushed by the connector 21 to open the contact 37 only when the connector 19 is normally connected. Is not normally connected, the contact 37 is closed and a connection leakage detection signal is sent to the sequence control circuit 8.
In this case, even if the activation signal S is input, the sequence control circuit 8 does not operate and the output of the power supply 1 for disconnection is not generated. Therefore, as in the embodiment of FIG. 1, even if the short circuit condition between the electrode and the nozzle is not detected by the current detector 27 due to the connection failure of the pilot arc current cable 16, the user touches the nozzle 12. There is no fear of electric shock.

〔The invention's effect〕

According to the present invention, it is possible to detect whether or not the power supply side connector of the pilot arc current cable is properly connected, and to stop the output of the power supply for disconnection when it is not normally connected. Even if the short circuit condition between the electrode of the disconnecting torch and the nozzle cannot be detected due to the connection failure of the cable, the electric shock protection function will not be lost, and the electric shock accident due to the no-load voltage when the user touches the nozzle will occur. Can be prevented.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing another embodiment of the present invention, and FIG. 3 is a detailed view of the connection failure detection switch in FIG. . 1 …… Disconnecting power supply, 10 …… Disconnecting torch 11 …… Electrode, 12 …… Nozzle 16 …… Pilot arc current cable 19 …… Power supply side connector, 21,27 …… Short circuit detection means 23,24,25, 26, 35 …… Means for detecting connection leakage

Claims (1)

[Claims] 1. A means for detecting a short circuit between the power source of the cutting torch and the nozzle to stop the output of the power source for cutting, or reducing the no-load voltage to the extent that there is no danger of electric shock. In the plasma cutting device, means for detecting whether or not the power supply side connector of the pilot arc current cable for connecting the nozzle of the cutting torch to the power supply is provided normally, and when the connector is not normally connected, A plasma cutting device characterized in that the output of the cutting power supply is stopped by a signal from the detecting means.