JPS5847277B2 - Method for determining secondary cable deterioration of welding equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for determining deterioration of a secondary cable of a welding device.

The secondary cable that connects the secondary terminal of the 7-valley transformer and the terminal of the welding tip, especially the secondary cable used in welding robots, etc., is shaken a lot every time the welding location is changed and deteriorates quickly.

If welding work is continued using a secondary cable that has entered a deteriorated state, poor quality welding will be performed until the welding defects are detected, which is not desirable for the product.

However, in the past, the timing for replacing a degraded secondary cable was determined based on the welding results or cracks in the secondary cable (7), but if the replacement timing was missed, the worst possible situation would suddenly occur where welding was impossible. This is a serious hindrance to assembly line operations such as automobile assembly lines.

The present invention was developed in view of the drawback of sloping.The purpose of the present invention is to detect when the secondary cable deteriorates just before welding occurs, by detecting this deterioration state from changes in voltage and current values. It is an object of the present invention to provide a method for determining secondary cable deterioration of a device.

In addition to the deterioration of the secondary cable, there is a resistance change that occurs in the welding device due to wear and tear on the welding tip, but this is very small compared to the resistance change of the secondary cable.

In other words, when the secondary side terminal of a welding transformer with a capacity of 90KVA and the terminal of the welding tip are connected with a kickless cable of 300m long and 2.5m in size, the kickless cable has a kick resistance value of 200μΩ under normal conditions. There is data that the resistance value when the cable is deteriorated is 750μΩ, but the resistance value change due to wear and tear of the welding tip is the normal value of 50μΩ.
It is only a slight variation with respect to Ω.

This is thought to be because when the tip wears out, the increase in resistance due to the alloy formed in the tip and the decrease in resistance due to the enlarged contact area cancel each other out.

Therefore, monitoring the voltage and current near the terminals of the power transformer is an effective method for determining deterioration of the secondary cable.

Hereinafter, an embodiment of the present invention will be described with reference to FIG. 1. 1 is a welding transformer, 2 is a welding gun having a welding tip 3.3,
4, 4 are two secondary cables whose both ends are connected to the secondary side terminals 1a, 1a of the welding transformer 10 and the terminals 2a, 2a of the welding gun 2, and are connected to the chips 3, 3 by operation of a power input system (not shown). voltage is applied to the welding object sandwiched between them by passing a predetermined current through the welding device.

Reference numeral 5 denotes a voltage comparison circuit which compares the terminal voltage of the welding transformer 1 with the voltage from the reference voltage generator 6 and outputs the result to the comprehensive judgment circuit 8 through the delay circuit 7.

9 is a toroidal coil that detects the current near the terminal 1a of the welding transformer 1; 10 is a current comparison circuit that compares this detected current with the current from the reference current generator 11; the output of the current comparison circuit 10 is determined by the overall judgment It is input to circuit 8.

The delay circuit 7 is used to adjust the delay between when a welding voltage is generated on the secondary side of the welding transformer 1 and when a detection current is generated in the toroidal coil 9.

That is, the current flowing through the secondary cable 4.4 due to the welding voltage on the secondary side of the welding transformer 1 is
The inductance component of the welding gun 2 causes a maximum delay of 4 cycles.

When this current is detected by the toroidal coil 9, there is an additional delay of approximately one cycle.

Therefore, since the voltage is generated between the terminals 1a and 1a of the welding transformer and the current is detected by the toroidal coil 9, there is a delay of the maximum IA cycle - 3/4 t cycle, that is, about 1 cycle, so the voltage side This signal is delayed by approximately one cycle and synchronized with the signal on the detection current side.

Secondary cable 4 of a welding device equipped with a diagonal determination device 7
A method for determining deterioration will be explained.

1. First, conduct a test and measure the voltage generated between terminals 1a and Ia in a deteriorated state of the secondary cable that is determined to be a welding defect (NG), and set this voltage in the generator 6 as the reference voltage (i). In addition, in the same state, the current near the terminal 1a is measured by the toroidal coil 9, and this current is set in the generator 11 as a reference current.

As a result, a limit that allows proper welding is set in the determination device.

During welding work, by observing changes over time in the terminal voltage and current near the terminal as described above, plot changes in welding voltage and welding current as the resistance increases (secondary cable and chip). Then, a graph like the one shown in FIG. 2 is obtained.

If we take the reference voltage V a and the reference current A set from the test results conducted earlier in Figure 2, we can see that the secondary resistance value R i, which is an extension of the broken line A connecting these, will perform good welding. It turns out that this is a real limit.

Therefore, when the voltage detected from the secondary cables 4, 4 in use becomes higher than the set values of the voltage circuit 5 and the current comparison circuit 10, and the current becomes lower (the graph in Fig. 2). When the area on the right side of the broken line A is reached), the comprehensive judgment circuit 8 (determines that it is abnormal).

This result is obtained by connecting the warning means 12 to the comprehensive judgment circuit 8,
This can be activated by the output at the time of abnormality determination to issue a warning.

As described above, according to the method for determining the deterioration of a secondary cable of a welding device according to the present invention, it is possible to prevent sudden work failure during bumping during welding, and also to ensure stable high-quality welding. There are advantages to doing so.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a device used in the determination method of the present invention;
FIG. 2 is a graph showing changes in welding voltage and welding current as secondary resistance increases. 1...Welding transformer, 2...Welding gun, 3...Welding tip, 4...Secondary cable, 5...Voltage comparison Circuit, 6... Reference voltage generator, 7... Delay circuit, 8...
・Comprehensive judgment circuit, 9... Toroidal coil, 1
0...Current comparison circuit, 11...Reference current generator.

Claims (1)

[Claims] 1. When detecting deterioration of the secondary cable of a welding device that connects the terminal of a welding transformer and the terminal of a welding gun via a secondary cable, detect the deterioration of the secondary cable in advance by using a secondary cable that has deteriorated to the extent that it begins to cause problems in welding. Perform a welding test, measure the voltage near the terminal of the welding transformer, and set that value as the reference voltage.Measure the current and set that value as the reference current, and set the voltage near the terminal during welding. and current are detected and compared with the reference voltage forward rotation and reference current, respectively, and if the detected voltage is greater than the reference voltage and the detected current is smaller than the reference current, it is determined that the secondary cable has deteriorated. A method for determining the deterioration of secondary cables in welding equipment.