Cable monitoring system and monitoring method thereof

1. A cable monitoring system which monitors failure of a plurality of primary cables connecting a power supply and a welding transformer, a secondary side of which is connected to a welding gun, the cable monitoring system comprising:

two voltage detection lines for each of the primary cables connected to two arbitrary points of each of the primary cables;

an insulating transformer for each of the primary cables, a primary side of which is connected to the voltage detection lines of each primary cable; and

a failure detector connected to a secondary side of each insulating transformer and detecting failure of each primary cable based on voltage on the secondary side of the respective insulating transformer for each primary cable.

2. A cable monitoring system according to claim 1 ,

wherein the insulating transformer sets voltage on the secondary side to voltage lower than voltage on the primary side to isolate the failure detector from the power supply at high voltage.

3. A cable monitoring system according to claim 1 ,

wherein the failure detector comprises:

a current detection unit configured to detect a value of current flowing through each primary cable;

a voltage detection unit configured to detect a value of voltage on the secondary side of the respective insulating transformer;

a resistance calculation unit configured to calculate a resistance value between the arbitrary two points of each primary cable from the detected values of the current and voltage;

a reference resistance memory unit configured to store a normal value of the resistance between the arbitrary two points of each primary cable as a reference resistance value;

a comparison unit configured to compare the resistance value with the reference resistance value; and

a judgment unit configured to judge the primary cable to be normal when the resistance value between the arbitrary two points of each primary cable is within a predetermined range with respect to the reference resistance value and to judge the primary cable to be abnormal when the resistance value between the arbitrary two points of each primary cable is not within the predetermined range.

4. A cable monitoring system according to claim 1 ,

wherein a welding controller configured to control welding current is provided between the power supply and the welding gun,

wherein the welding gun incorporates a welding transformer,

wherein a plurality of the primary cables connect a secondary side of a switching element provided for the welding controller and a primary side of the welding transformer, and

wherein the failure detector is incorporated in the welding controller.

5. A cable monitoring system according to claim 1 ,

wherein the welding gun is attached to a working end of a robot, and

the insulating transformers are incorporated in a relay box which is placed on an arm of the robot and is connected to the primary cables.

6. A cable monitoring system according to claim 1 ,

wherein the welding gun includes a moving electrode driven by a motor actuator.

7. A cable monitoring method for monitoring failure of a plurality of cables connecting a power supply and a welding gun attached to a work end of an arm of a multi-axis robot, comprising:

detecting a value of voltage between two arbitrary points of each of the cables through an insulating transformer while the welding gun is being energized through the cables; and

judging presence of failure of each cable based on the detected value of the voltage.

8. A cable monitoring method according to claim 7 ,

wherein the value of the voltage is detected while the welding gun is being energized for welding after an arm shaft of the multi-axis robot rotates to move the arm to a predetermined position.

9. A cable monitoring method according to claim 7 ,

wherein the judging further comprises:

calculating a resistance value between the arbitrary two points of each cable from the detected value of the voltage and a value of current of each cable;

comparing the resistance value with a reference resistance value of each cable previously stored; and

judging the cable to be normal when the calculated resistance value is within a predetermined range with respect to the reference resistance value and judging the cable to be abnormal when the calculated resistance value is not within the predetermined range.

10. A cable monitoring method according to claim 7 ,

wherein the insulating transformer is incorporated in a relay box which is placed on an arm of the robot and is connected to the cables.

11. A cable monitoring system which monitors failure of a plurality of primary cables connecting a power supply and a welding transformer, a secondary side of which is connected to a welding gun, the cable monitoring system comprising:

two voltage detection lines for each of the primary cables connected to two arbitrary points of each of the primary cables;

an insulating transformer for each of the primary cables, a primary side of which is connected to the voltage detection lines of each primary cable; and

failure detecting means, connected to a secondary side of each insulating transformer, for detecting failure of each primary cable based on voltage on the secondary side of the respective insulating transformer for each primary cable.