JP2001232481A - Abnormality detector for welding cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect breaking of a conductor and coating of a welding cable. SOLUTION: An abnormality detection circuit 48 that operates on a floating DC power source 92 is provided between a flexible conductive material 64 covering an insulated covered conductor 53 for the power supply and the ground, and the potential fluctuation of the DC power source 92 is made detectable by a comparator 90 constituting the abnormality detection circuit 48; hence, abnormality such as ground-defect of a welding cable 30 can be detected on the basis of a potential fluctuation due to the ground-defect or the like of the DC power source 92. Basically, the resistance of resistors 94, 96 is preliminarily set so that the reference voltage Ea of the comparator 90 in the absence of the ground-defect becomes higher than comparative voltage Eb. In the occurrence of the ground-defect, the reference voltage Ea becomes lower than the comparative voltage Eb, inverting the comparator 90. Thus, the ground-defect can be detected by the abnormality detection output Sout of a photo-coupler 106.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding cable abnormality detecting device for detecting an abnormality such as a ground fault in a welding cable connecting a welding power supply device and a welding transformer in a resistance welding robot or the like.

[0002]

2. Description of the Related Art Recently, a welding transformer has been arranged near a gun arm, and a primary coil of the welding transformer has a voltage of about several hundred volts from a welding power supply via a welding cable.
A resistance welding apparatus for supplying a secondary AC voltage is provided for use. In this resistance welding apparatus, the primary AC voltage is reduced by the welding transformer to a voltage of about several volts or less, and a large current of, for example, about tens of thousands of amperes can be supplied to the work.

[0003] The resistance welding apparatus having such a configuration allows the welding cable to be made relatively thin, so that it is excellent in mov- ability and moves the gun arm at high speed in the case of multi-point welding of a work or the like. Becomes possible.

However, in a resistance welding apparatus having a movable welding cable as described above, there is a possibility that the resin coating of the welding cable is peeled off due to abrasion or the like, and the core wire is grounded.

A device for detecting this ground fault is disclosed in
A technique disclosed in Japanese Patent Application Laid-Open No. 9-127977 (referred to as a first technique) and a technique disclosed in Japanese Utility Model Laid-Open Publication No. 7-15175 (referred to as a second technique) can be given.

In the first technique, an insulating transformer is provided between a welding power supply device and a primary side of a welding transformer, and a secondary welding cable (movable cable) of the insulating transformer is provided.
A current detector is provided between the core wire and the ground, and when a ground fault occurs in the welding cable, the occurrence of the ground fault is detected by the current flowing through the current detector.

[0007] In the second technique, a shield wire is arranged in a resin which is an insulating coating of a welding cable, and between the shield wire and an inner conductor (core wire) of the welding cable and between a shield wire and a work potential. Are provided with an insulation circuit, respectively, and a ground fault between the shield wire and the core wire and a ground fault between the shield wire and the work potential are detected by outputs of these two insulation circuits.

[0008]

However, in the first technique, an insulating transformer is provided between the welding power supply device and the primary side of the welding transformer, so that the current efficiency of welding by the insulating transformer is reduced. However, there is a problem that the cost of the resistance welding apparatus itself increases because the cost is low and the insulating transformer is expensive.

In the second technique, an abnormality detection circuit is required for both a ground fault between the shielded wire and the core of the welding cable and a ground fault between the shielded wire and the work potential. However, there is a problem that the cost is increased due to the complexity, and furthermore, since it is necessary to draw out the core wire which is usually at a high voltage with a conductor, this conductor also requires a high-voltage insulated wire, which also increases the cost. There is a problem.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to provide a welding cable abnormality detecting device which has a simple configuration and does not require the core wire of the welding cable to be drawn out. I do.

Another object of the present invention is to provide a welding cable abnormality detecting device which can be constructed at low cost.

[0012]

According to the present invention, there is provided an abnormality detecting apparatus for a welding cable for supplying power to a primary coil of a welding transformer, wherein the welding cable comprises an insulated conductor for supplying power and the insulated conductor. A flexible conductive material covering the conductive material, and a flexible insulating material covering the conductive material. A floating DC power supply operates between the conductive material and the ground, and a potential of the DC power supply. An abnormality detection circuit for detecting a change is connected (the invention according to claim 1).

According to the present invention, an abnormality detection circuit that operates with a floating DC power supply is provided between the flexible conductive material covering the insulated conductor for supplying power and the ground, and the abnormality detection circuit provides the abnormality detection circuit. Since the fluctuation of the potential of the DC power supply is detected, an abnormality such as a ground fault of the welding cable can be detected based on the fluctuation of the potential of the DC power supply.

In this case, when a DC potential change of the DC power supply is detected, an abnormality detection output for detecting a ground fault generated between the conductive material and the ground can be generated. 2) an abnormality detection output for detecting a ground fault generated between a core wire of the insulating coating conductor for supplying power and the conductive material when an AC potential fluctuation of the DC power supply is detected. As a result, an on / off abnormality detection output utilizing the dynamic potential fluctuation can be generated (the invention according to claim 3).

Further, an isolation means for insulating the abnormality detection circuit is connected to the output side of the abnormality detection circuit, and when a potential change of the DC power supply is detected, an abnormality detection output is generated via the isolation means. So that
An isolated output can be obtained as the abnormality detection output (the invention according to claim 4).

[0016]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic external configuration of a resistance welding apparatus 10 to which an embodiment of the present invention is applied, in which various mechanical drive mechanisms are omitted.

This resistance welding apparatus 10 is a welding robot 1
1, a welding power supply 32 for supplying welding power to the welding robot 11, and a robot controller (not shown) for controlling operations of the welding power supply 32 and the welding robot 11. I have.

The welding robot 11 has a base 14 arranged on the floor 12 and movable in the direction of the arrow, and a turntable 16 that rotates in the horizontal direction is provided on the base 14.
An arm 20a is mounted on the turntable 16 via a joint 18a that rotates in the direction of the arrow. The joint 18 that rotates in the direction of the arrow is provided at the tip of the arm 20a.
b, the joint 21 that rotates in the direction of the arrow via the arm 20b
, And a welding transformer 22 is integrally fixed to the joint 21.

The output side of the welding transformer 22 is connected to the root side of a conductive welding gun (gun arm) 26 that is opened and closed by a cylinder 24 in the direction of the arrow.

A pair of welding tips 28 for welding the work W therebetween is attached to the tip side of the welding gun 26.

In this case, the input side of the welding transformer 22 is
A welding power supply 32 is connected via a flexible welding cable 30.
It is connected to the. In this case, the welding cable 30 is connected to the welding power supply 32 using the internal space of the welding robot 11.
From the welding transformer 22.

FIG. 2 shows a schematic block configuration of an electric circuit from the welding power supply device 32 to the welding tip 28.

The welding power supply 32 is connected to an external AC power supply 41.
Circuit 42 for full-wave rectification of alternating current output from
And an inverter circuit 44 for repeatedly converting the DC output from the converter circuit 42 into a square-wave high-frequency AC.
And a welding controller 4 for controlling the inverter circuit 44.
0 and an abnormality detection circuit 48 which is a point of the present invention.

The high-frequency AC generated by the inverter circuit 44 is supplied via a welding cable 30 to the primary coil side of a welding transformer 22 in which a rectifying diode is integrally incorporated. The rectified output is supplied to the welding gun 26 by rectifying the side output.

FIG. 3 shows a detailed circuit of the abnormality detecting circuit 48, a schematic configuration of the welding cable 30, and a configuration of a circuit connected to the input and output sides of the flexible welding cable 30. .

The welding cable 30 includes two flexible insulated conductors 53 for power supply, each having a core 51 and an insulating coating 52, and a core 61 and an insulating coating 62. A flexible insulated conductive wire 63 for grounding, a flexible conductive material 64 such as conductive rubber embedded so as to cover the insulated conductive wires 53 and 63, and the entirety of the conductive material 64 is connected to an external ground. And an insulating material (also referred to as a coating) 66 that is a flexible coating such as butyl rubber that is covered to insulate from the like. In addition,
As the flexible conductive material 64, a braid that is a shield wire can be used instead of conductive rubber.

Referring to FIG. 3, converter circuit 42 includes two positive / negative DC power sources 42 for generating voltages + E1 and -E1.
a and 42b schematically. Here, the inverter circuit 44 basically includes four transistors 46
a, 46b, 46c, and 46d. The base terminals of these transistors 46a to 46d are on / off controlled through the welding controller 40 (see FIG. 2).

A DC power supply 42a is connected to the collector terminals of the transistors 46a and 46c.
A DC power supply 42b is connected to the emitter terminal of 46b.

The emitter terminal of the transistor 46a is connected to the collector terminal of the transistor 46d, and the common connection point is connected to the core wire 51 of one of the insulated conductors 53. Further, the emitter terminal of the transistor 46c is connected to the collector terminal of the transistor 46b, and the common connection point is connected to the core wire 51 of the other insulated conductor 53.
Further, the insulating-coated conductor 63 is grounded (also referred to as ground or earth) on the welding power supply device 32 side.

The core wire on the opposite side of the insulated conductor 63 is also grounded on the welding transformer 22 side. Further, the opposite sides of the two insulated conductors 53 are the primary coils 2 of the welding transformer 22.
2a. Secondary coil 22 of welding transformer 22
The output of b is connected to the anode terminals of rectifying diodes 70 and 72, respectively.
The cathode terminals 72 are connected in common and connected to one input side of the welding gun 26. The intermediate tap of the secondary coil 22b is connected to the other input side of the welding gun 26. As described above, the welding tips 28 are each detachably attached to the tip of the welding gun 26.

The conductor at one end of the insulated conductor 80 is connected to the conductive material 64 disposed inside the sheath 66 of the welding cable 30, and the conductor at the other end is connected to the abnormality detecting circuit 48.
One of the coils 8 constituting the in-phase transformer 82 constituting
2a is connected to the coil end. The other end of the coil 82a is connected via a resistor 84 to the cathode terminals of diodes 85 and 86 functioning as gate means.

The abnormality detecting circuit 48 further has a comparator 90 as a comparison circuit (comparing means) composed of an operational amplifier.
A low voltage (here, voltage value Ed = 24) as a floating power source different from the welding power source by welding power source device 32
[V]) DC power supply 92 is connected. Here, the positive terminal of the DC power supply 92 is also referred to as a reference point Q, and the negative terminal is also referred to as a reference point P. Note that the floating DC power supply 92 is a power supply in which the reference points P and Q simultaneously fluctuate by the same potential while the inter-terminal voltage Ed remains unchanged with respect to the infinity point reference (ground reference).

As will be described in detail later, when the abnormality detecting circuit 48 detects a ground fault or the like of the welding cable 30 through the insulated conductor 80, the potential fluctuation of the DC power supply 92, in other words, the reference point P , Q can be detected by the comparator 90 to output an abnormality detection output Sout corresponding to the type of ground fault.

To the negative input terminal of the comparator 90, resistors 94 and 96 are connected as voltage dividing means for dividing the inter-terminal voltage value Ed of the DC power supply 92. Here, the reference voltage Ea appearing at the negative input terminal is Ea = about 4
× Ed / 24 [V] = 4 [V] is set.

On the other hand, the positive input terminal of the comparator 90 has a cathode terminal connected to the diode 9 connected to the reference point Q.
8 is connected to the capacitor 100 and the resistor 102 connected in parallel to the reference point P, and to one coil end of the other coil 82 b of the common-mode transformer 82.
The other coil end of the coil 82b is grounded. This ground becomes a floating potential as described later. Here, the voltage appearing at the positive input terminal of the comparator 90 is referred to as a comparison voltage Eb.

The output terminal of the comparator 90 has a bias resistor 104 connected to the positive terminal of the DC power supply 92 and a light emitting diode 108 constituting a photocoupler 106 as an isolation means (isolation circuit). The cathode terminal is connected. The anode terminal of the light emitting diode 108 is connected to the positive terminal of the DC power supply 92 via the resistor 109.

An abnormality detection output So is provided between output terminals 112 and 114 to which the collector terminal and the emitter terminal of the phototransistor 110 constituting the photocoupler 106 are connected.
ut occurs. Note that the photocoupler 106 as an isolation unit can be replaced with an electromagnetic relay. As isolation means, the output is optical,
Any material that can be electromagnetically or electrostatically isolated (insulated) may be used.

The resistance welding apparatus 10 according to this embodiment
Is basically configured as described above, and its operation will be described below.

First, the overall operation of the resistance welding apparatus 10 will be described. When the workpiece W is positioned and arranged in a state where the power is supplied to the resistance welding apparatus 10, the welding robot 11 is controlled by a robot controller (not shown).
Is moved in the playback mode to the position where the welding gun 26 sandwiches the work W.

That is, based on the teaching data created in advance, the base 14, the turntable 16, the joint 18
The welding tips 28 of the welding gun 26 in the open state are moved to positions facing each other via the workpiece W by driving the a, 18b, 21 and the arms 20a, 20b by a predetermined movement amount.

Next, the welding gun 26 is closed by the cylinder 24, and a pressing force is applied to the work W via the welding tip 28. As described above, when the welding force is applied to the workpiece W by the welding gun 26 via the welding tip 28, the welding power supply device 32 is driven for a predetermined time by a command from the robot controller.

That is, the + E1 and -E1 positive and negative DC power supplies 42a and 42b generated by the converter circuit 42 based on the AC power supply from the external AC power supply 41 constitute the inverter circuit 44 under the control of the welding controller 40. The transistors 46a to 46d are supplied to the welding cable 30 by being turned on / off for a predetermined time.

In this case, when the transistors 46a and 46b are turned on and the transistors 46c and 46d are turned off, the current flowing from the positive terminal of the voltage E1 of one DC power supply 42a flows to the transistor 46a and one insulating Core wire 51 on one end side of insulated conductor 53, welding cable 3
0, the core wire 5 on the other end side of the one insulated wire 53
1. One end of the primary coil 22a of the welding transformer 22, the other end of the primary coil 22a, and the other insulation-coated conductor 53
Through the core wire 51 on the one end side, the inside of the welding cable 30, and the core wire 51 on the other end of the other insulated conductor 53, via the transistor 46b to the negative terminal of the voltage -E1 of the other DC power supply 42b.

Similarly, when the transistors 46a and 46b are on and the transistors 46c and 46d are off, the current flowing from the positive terminal of the voltage E1 of the one DC power supply 42a flows to the transistor 46c and the other One end of the insulated conductor 53, inside the welding cable 30, the other end of the one insulated conductor 53, one end of the primary coil 22a of the welding transformer 22, the other end of the primary coil 22a, and the other insulated sheath One end of the conducting wire 53, inside the welding cable 30,
The voltage returns to the negative terminal of the voltage −E1 of the other DC power supply 42b through the transistor 46d through the other end of the other insulating covered conductor 53.

By repeating such an operation for a predetermined period of time, the core 51 (the primary coil 22
In a), as shown in FIG. 3, a repetitive square wave voltage of amplitude + E1 to -E1 is applied.

The repetitive square wave voltage is applied to the secondary coil 2
2b, induced by the voltage drop, rectified by the diodes 70 and 72, and converted into a DC voltage by the welding gun 26 and the welding tip 2.
8 is applied to the work W. At this time, for example, the secondary current value flowing through the work W or the primary coil 2
The primary current value flowing through 2a is detected by a current detector (not shown) and supplied to the welding controller 40, thereby performing feedback control of the current value, and applying a desired pressing force to the workpiece W for a desired time. , A desired current is supplied, and the work W is suitably welded.

After the welding process on the workpiece W, the drive of the inverter circuit 44 by the welding controller 40 is stopped, the welding gun 26 is opened by the cylinder 24, and the welding gun 26 starts moving to the next hitting position.

In this manner, the welding operation on the work W by the resistance welding apparatus 10 is performed.

Next, the resistance welding apparatus 1 in the power-on state
0, the welding cable 30 by the abnormality detection circuit 48
Will be described below. The abnormality detection operation of the abnormality detection circuit 48 is performed by the reference voltage Ea generated at the positive and negative input terminals of the comparator 90.
Of the welding cable 30 (so-called internal damage (the core wire 51 of the insulated conductor 53 and the conductive material 6)
This is an operation of discriminating between an abnormal state such as a ground fault between the conductive material 64 and the ground (a ground fault between the conductive material 64 and the ground caused by the breakage of the coating 66) and a normal state.

A. Description of detection operation when welding cable 30 is normal When welding cable 30 is normal, resistor 94,
The reference voltage Ea set by the division ratio of 96 is about 4
[V]. At this time, the comparison voltage Eb generated at the positive input terminal of the comparator 90 is
Is grounded through the coil 82b of
b = 0 [V]. Therefore, the output of the comparator 90 is at a low level.

Therefore, a current flows from the DC power supply 92 to the light emitting diode 108 forming the photocoupler 106 through the resistor 110, and the output phototransistor 110 of the photocoupler 106 is turned on. One output terminal 114 is connected to the ground of a monitor circuit (not shown), and the other output terminal 112 has a pull-up configuration in which a current is supplied from a positive DC power supply through a resistor. It operates as an open collector circuit, and the abnormality detection output Sout supplied to the monitor circuit becomes a low-level stationary state (DC state) indicating normality. In the following description, the phototransistor 110 operates as such an open collector circuit.

B. Description of a detection operation when a damage is generated in the welding cable 30 As schematically shown in FIG. 4, when a damage occurs in a coating (skin) 66 of the welding cable 30, the conductivity inside the welding cable 30 is reduced. When the conductive material 64, which is a resin, comes into contact with the ground, a ground fault occurs.

At this time, the DC power supply 9 of the abnormality detection circuit 48
The current i flowing out of the positive terminal of the diode 85
The current flows to the ground G1 through the resistor 84, the coil 82a, the insulated conductor 80, and the conductive material 64. Further, the capacitor 100 is charged by the current i flowing from the ground G1 to the ground G2 and the other coil 82b of the common-mode transformer 82, and the resistor 10
2, the current i flows into the negative terminal of the DC power supply 92.
Since a forward bias is applied to the diode 85, the diode 85 is opened when the diode 85 is considered as a gate unit.

In this case, the grounds G1 and G2 are obtained by dividing the voltage Ed of the DC power supply 92 by the forward voltage (about 0.7 [V]) of the diode 85 and dividing the voltage by the resistor 84 and the resistor 102. Floating potential, and eventually
The comparison voltage Eb is set to the floating potential. By setting the resistance values of the resistor 84 and the resistor 102 such that the floating potential is higher than the reference voltage Ea, the comparator 90 is inverted when the conductive material 64 is grounded, The output voltage becomes high level. For this reason, the photocoupler 106 is turned off, and the abnormality detection output Sout is held at a DC high-level output indicating an external abnormality. In this state,
The DC power supply 92 generates a DC potential fluctuation, and as a result, the DC potential fluctuation is detected by the comparator 90.

C. Description of Detection Operation When Internal Damage Has Occurred in Welding Cable 30 As shown in the broken portion in FIG. 5, the coating 52 of the insulated conductor 53 serving as a power supply conductor inside the welding cable 30 is broken and the internal wound is damaged. Occurs, and a ground fault also occurs when the core wire 51 comes into contact with the conductive material 64.

In this case, a positive voltage + E1 (+300 [V] in this embodiment) which is a high-frequency alternating current is applied to the core wire 51.
And negative voltage −E1 (−300 [V] in this embodiment).
Occur alternately, so that a positive voltage + E1 and a negative voltage -E1 of the same potential are alternately generated in the conductive material 64 as well.

When a positive voltage + E1 is applied to the conductive material 64 due to a ground fault, the diode 8 serving as a gate means
Since the positive voltage + E1 is applied to the cathode terminals of the transistors 5 and 86, a reverse bias is applied and the transistor is turned off (closed as the gate means), so that the output of the comparator 90 becomes the same non-inverted low level as in the normal state. Become.

However, when the negative voltage -E1 is applied, as shown in FIG. 6, the diodes 85 and 86 conduct (the gate means are opened), and the potential of the DC power supply 92 fluctuates. The reference voltage Ea is equal to the comparison voltage Eb.
Lower voltage. In other words, the comparison voltage Eb becomes higher than the reference voltage Ea, and the output of the comparator 90 becomes the inverted high level.

Therefore, when a ground fault occurs in which the core wire 51 comes into contact with the conductive material 64, the comparator 9
0 indicates that an AC potential fluctuation of the DC power supply 92 is detected,
As a result, the abnormality detection output Sout is an abnormality detection output that repeats on and off.

As described above, according to the above-described embodiment, the abnormality detection that operates with the floating DC power supply 92 is provided between the ground and the flexible conductive material 64 that covers the insulating coating conductor 53 for supplying the welding power. The circuit 48 is provided, and the comparator 90 constituting the abnormality detection circuit 48 detects the potential change of the floating DC power supply 92. Therefore, the ground of the welding cable 30 is detected based on the potential change of the DC power supply 92 due to ground fault or the like. An abnormality such as a tangling can be detected.

Basically, the resistor 94 is set to a resistance value that sets the reference voltage Ea higher than the comparison voltage Eb so that the output of the comparator 90 is in a non-inverted state when no ground fault occurs. , 96 are set in advance. Then, when the DC power supply 92 floats when the ground 66 such as the coating 66 of the welding cable 30 is broken and comes into contact with the ground, the resistor / diode is set so that the reference voltage Ea becomes lower than the comparison voltage Eb.・ Capacitors (84, 8)
By determining the circuit configurations and values of 5, 86, 98, 100, and 102), the comparator 90 is inverted.

By providing the photocoupler 106 as an isolation means on the output side of the comparator 90, a ground fault can be detected by a monitor circuit or the like (not shown) based on the abnormality detection output Sout of the photocoupler 106. In the monitor circuit, a ground fault can be lit and displayed, or it can be known by an alarm. It can also be displayed in characters or the like on the display. Note that the polarity of the comparator 90 can be reversed.

It should be noted that the present invention is not limited to the above-described embodiment, but can adopt various configurations without departing from the gist of the present invention.

[0065]

As described above, according to the present invention, an abnormality detection circuit that operates with a floating DC power supply is provided between a ground and a flexible conductive material that covers an insulated conductor for supplying power. Since the potential change of the DC power supply is detected by the abnormality detection circuit, an abnormality such as a ground fault of the welding cable can be easily detected based on the potential change of the DC power supply.

Therefore, according to the present invention, unlike the first technique in the prior art, there is no need to provide an insulating transformer between the welding power source and the primary side of the welding transformer, so that the current efficiency of welding is reduced. Can be suppressed, and since it is not necessary to use an expensive insulating transformer, the cost can be reduced.

Further, unlike the second technique of the prior art, there is no need to use two systems of abnormality detection circuits, so that the circuit configuration is simple and the cost can be reduced.

That is, according to the present invention, it is possible to use a simple structure and not to draw out the core of the welding cable.
An abnormality detection device for the welding cable is obtained.

[Brief description of the drawings]

FIG. 1 is an external view of a resistance welding apparatus to which an embodiment of the present invention is applied.

FIG. 2 is an electric circuit block diagram of the resistance welding apparatus of FIG. 1;

FIG. 3 is a circuit diagram showing details of a main part of the resistance welding apparatus of FIG. 1;

FIG. 4 is a circuit diagram for explaining the operation of the abnormality detection circuit when a flaw or the like occurs in the coating of the welding cable;

FIG. 5 is a circuit diagram for explaining the operation of the abnormality detection circuit when a scratch or the like occurs in the core wire of the welding cable.

FIG. 6 is a circuit diagram for explaining the operation of the abnormality detection circuit when a scratch or the like occurs in the core wire of the welding cable.

[Explanation of symbols]

REFERENCE SIGNS LIST 10 resistance welding device 11 welding robot 22 welding transformer 22 a primary coil 22 b secondary coil 26 welding gun (gun arm) 28 welding tip 30 welding cable 32 welding power supply device 40 welding controller 41 external AC power supply 42 ... Converter circuit 42a, 42b ... Positive and negative DC power supply 44 ... Inverter circuit 48 ... Abnormality detection circuit 51, 61 ... Core wire 52, 62 ... Coating 53, 63, 80 ... Insulating coating conductor 64 ... Conductive material 66 ... Insulating material (Coating) 82 ... In-phase transformer 90 ... Comparator 92 ... DC power supply 106 ... Photocoupler (isolation means) Sout ... Abnormality detection output

Claims (4)

[Claims] 1. An abnormality detecting device for a welding cable for supplying power to a primary coil of a welding transformer, wherein the welding cable comprises an insulating covered conductor for supplying power, and a flexible conductive material covering the insulating covered conductor. And a flexible insulating material covering the conductive material. An abnormality detection circuit that operates with a floating DC power supply and detects a potential change of the DC power supply between the conductive material and ground. An abnormality detection device for a welding cable, which is provided. 2. The fault detection device according to claim 1, wherein a ground fault generated between the conductive material and the ground when the fault detection circuit detects a DC potential change of the DC power supply. An abnormality detection device for a welding cable, which generates an abnormality detection output for detecting an abnormality. 3. The abnormality detection device according to claim 1, wherein when the abnormality detection circuit detects an AC potential change of the DC power supply, the abnormality detection circuit detects a change between the core wire of the insulating coated conductor and the conductive material. An on-off abnormality detection output as an abnormality detection output for detecting a ground fault occurring in a welding cable. 4. The abnormality detection device according to claim 1, wherein an isolation unit that insulates the abnormality detection circuit is connected to an output side of the abnormality detection circuit. An abnormality detection device for a welding cable, wherein the circuit outputs the abnormality detection output via the isolation means when detecting a potential change of the DC power supply.