JPH073447B2 - Cable abnormality detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of application) The present invention relates to a cable abnormality detection device capable of detecting cable breakage and grounding of a resistance welding machine.

[Prior art]

When the resistance welding machine is made into a robot, there are many accidents of cable breakage of the welding machine transformer. Bending, pulling, and twisting torque are applied to the cable several hundred to several thousand times a day, and it is necessary to replace the cable once every two weeks to one month. If a cable break occurs during line work, the line will stop and the damage will be significant.
To avoid this, replacing the cable early leads to an increase in equipment repair costs, and it is ideal if the cable can be replaced only when there is a risk that the cable will deteriorate and a grounding accident will occur.

Fig. 3 shows a conventional cable accident detection device for a resistance welding machine.

In FIG. 3, the AC of the AC power supply 1 is converted into DC by the rectifier 2 and smoothed by the capacitor 3. This direct current is converted into high frequency alternating current by the inverter bridge 4. This AC voltage is stepped down by the transformer 5 and rectifier
It is converted into direct current again by 7a and 7b and supplied to the welding electrode 8 to flow welding current. Weld current is inverter bridge 4
By controlling the PWM (pulse width modulation), the DC voltage applied to the welding electrode is adjusted and smoothed by the inductance of the DC main circuit. Welding current is transformer 5
Welding control circuit detected by current transformer 6 provided on the primary side of
Controlled by 10.

The transformer 9 supplies control power from the AC power supply 1 to the welding control circuit 10. In addition, one end of the tertiary winding of the transformer 9 is grounded at a point c, and is connected to one end a of the shield portion of the shield wire 11 that supplies power to the transformer 5 via the exciting coil of the relay 12 so that the shield portion The other end b is connected via a resistor 14 to the other end of the tertiary winding of the transformer 9.

When the shielded cable 11 is healthy, the relay 12 is illustrated and the contact 13 is closed. When the shield part of the shield wire 11 is broken, the relay 12 is de-excited and the contact 13 is opened. Also, when the shield part of the shield wire 11 is grounded, the relay 12 is in the non-excited state. Relay in this way
By detecting the 12 non-excited state, it is possible to detect that the shield part of the shielded wire is grounded or disconnected, and display the shielded wire replacement time.

(Problems to be Solved by the Invention) However, the conventional methods have the following drawbacks. The first is
Since it is impossible to distinguish between the disconnection and grounding of the shield part, this distinction was desired in order to know the state of the shield part.

Second, the PWM control of the inverter bridge 4 causes 500Hz
When an alternating current of 5 KHz was output, a high surge voltage close to the main circuit voltage was applied to the exciting coil of the relay 12 due to the stray capacitance of the shield wire 11 and the stray capacitance of the shield portion, and there was a concern of insulation deterioration.

The present invention has been made in view of the above points, it is possible to distinguish between grounding and disconnection of the shield part of the shielded wire, and there is no fear of insulation deterioration due to surge voltage generated in the shield part, of a resistance welding machine. It is intended to provide a cable accident detection device.

[Structure of Invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention includes a DC power supply whose one end is grounded, and detects the presence or absence of a DC current flowing in one direction at the other end of the DC power supply. Of the DC power source through the second current detecting means that is connected to one end of the shield portion of the shielded cable via one current detecting means and detects the presence or absence of a DC current flowing in one direction at the other end of the shield portion. A cable abnormality detection device is configured by connecting to the intermediate potential or the ground side of the DC power supply.

(Operation) The first current detecting means detects a direct current flowing from the other end of the direct current power source to the intermediate potential of the direct current power source through the shield part, and the second and current detecting means are the shield currents. When the part is grounded, the DC current flowing from the intermediate potential of the DC power supply through the ground point of the shield part is detected, and when the first current detecting means does not detect the DC current, the shield part is disconnected. When the second current detecting means detects a direct current, it is determined that the shield part is grounded.

Further, the first and second current detecting means detect a direct current flowing from the other end of the direct current power source to the ground side of the direct current power source through the shield part, and the first and second current detecting means. When both do not detect a direct current, it is determined that the shield part is disconnected, and when the first current detecting means detects a direct current and the second current detecting means does not detect a direct current, the shield part Is determined to have been touched down.

(Embodiment) An embodiment of the main part according to the present invention is shown in FIG. The same parts as those in FIG. 3 are designated by the same reference numerals and the description thereof will be omitted. Although not shown, the main circuit portion and the control circuit portion, which are not shown, are the same as the conventional ones.

DC power supplies 20 and 21 are connected in series, one end of the DC power supply 20 is grounded, and one end of the DC power supply 21 is a resistor 22, a photocoupler 23, and a resistor.
It is connected to one end of the shield part of the shielded wire 11 through 25. The capacitor 24 is provided to absorb the surge current from the shield wire side.

On the other hand, the other end of the DC power supply 20 is a resistor 26, a photocoupler 27, a resistor
Connected to the shield wire 11 and the other end of the shield portion via 29. The capacitor 28 is for absorbing a surge current from the shield wire side, and the diode 30 is connected in parallel to the photocoupler 27 in the reverse direction.

The collector of the phototransistor 33 of the photocoupler 23 is
It is connected to the + V power supply via the resistor 34, and the collector of the phototransistor 37 of the photocoupler 27 is + V via the resistor 38.
Connect to the power supply. The capacitor 39 is the stray capacitance of the shield wire 11 and the core wire of the shield wire 11.

If the shielded wire 11 is normal, connect it to the resistor 22
→ Photocoupler 23 → Resistor 25 → Shield section → Resistor 29 → Diode 30 → Resistor 26 Since current is flowing in the circuit, the output voltages e and f of phototransistors 33 and 37 are "0" and "1", respectively.
Is the state of. Here, when the shield wire 11 and the shield portion are disconnected at point k, the current of the photocoupler 23 becomes zero and the output e changes from "0" to "1".

Next, when the point l of the shield part is installed, a current flows from the DC power source 20 to the photocoupler 27 through the resistors 26 and 29, so that the output f of the phototransistor 37 changes from "1" to "0". The status changes to ", and the details of the failure can be identified.

By the switching of the inverter bridge 4, a square wave voltage is equivalently applied between the earth and the ground, and a surge voltage approximately equal to the inverter main circuit voltage is induced in the shield through the stray capacitance 39. This surge voltage is transferred to capacitors 24, 2
Absorbed by 8.

Note that it is extremely easy to make the discrimination possible even if the polarities of the photocoupler 27 and the diode 30 are reversed.

According to the present embodiment, it is possible to judge whether the shield wire is broken or grounded with a simple circuit. Further, the ground detection detects the intermediate potential of the DC power supplies 20 and 21 and the potential between the grounds, so that it is possible to detect the stage of insulation deterioration at a ground current level of several mA at an early stage. Further, by providing filters such as C and R at the connecting portion to the shield portion, it is possible to eliminate the influence of the surge voltage due to the stray capacitance of the shield line.

(Other Embodiments) Further, as shown in FIG. 2, only the DC power source 20 can be used. In this case, when the shield line is normal, current flows through the photocouplers 23 and 27, and the output voltages e and f of the phototransistors 33 and 37 are both "0".

When the shield wire is broken, both output voltages e and f are "1".
When the shield wire is grounded, the output voltage e remains "0" and f changes from "0" to "1". This makes it possible to distinguish between disconnection and grounding.

Since a surge voltage is induced in the shield portion during energization, it is desirable that the output voltages e and f be checked during a non-energized period.

(Effects of the Invention) As described above, according to the present invention, it is possible to detect a break in a shield of a shield wire and a ground separately with a simple and economical circuit. ,
When a conveyor line is used, it is possible to obtain a cable abnormality detecting device for a resistance welding machine capable of detecting wear of the cable early and stopping the line for a minimum time.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the main part of a cable abnormality detecting device according to the present invention, FIG. 2 is another embodiment diagram showing a modification thereof, and FIG. 3 is a conventional cable abnormality detecting device. It is a block diagram. 1 ... AC power supply, 2 ... Rectifier, 3 ... Capacitor, 4
...... Inverter bridge, 5 …… Transformer, 6 …… Current transformer, 7a, 7b …… Rectifier, 8 …… Welding electrode, 9 …… Transformer, 10 …… Welding control circuit, 11 …… Shield wire, 12 …… relay, 13 …… contact, 41 …… current limiting resistance, 20,21 …… DC power supply, 22,25,26,29,34,38 …… resistor, 23,27 …… photocoupler (diode section ), 33, 37 ... Photo coupler (light receiving part), 24, 28 ... Capacitor.

Claims (3)

[Claims] 1. A one end of a shield part of a shielded cable is provided with a direct current power source having one end grounded, and a first current detecting means for detecting the presence or absence of a direct current flowing in one direction through the other end of the direct current power source. And connecting the other end of the shield part to the intermediate potential of the DC power supply or the ground side of the DC power supply through a second current detecting means for detecting the presence or absence of a DC current flowing in one direction. Cable abnormality detection device. 2. The first current detecting means detects a direct current flowing from the other end of the direct current power source to the intermediate potential of the direct current power source through the shield part, and the second current detecting means, When the shield part is grounded, the direct current flowing from the intermediate potential of the direct current power supply through the ground point of the shield part is detected, and when the first current detecting means does not detect the direct current, the shield part is It is judged that the wire is broken,
The cable abnormality detection device according to claim 1, wherein when the second current detection means detects a direct current, it is determined that the shield part is grounded. 3. The first and second current detecting means detect a direct current flowing from the other end of the direct current power source to the ground side of the direct current power source through the shield portion, and the first and second current detecting means are provided. When both the current detecting means do not detect a direct current, it is determined that the shield part is broken, the first current detecting means detects a direct current, and the second current detecting means does not detect a direct current, The cable abnormality detection device according to claim 1, wherein it is determined that the shield portion is grounded.