JPH0434701B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is a resistance spot welding machine in which a reciprocating line connecting the secondary side of a welding transformer and an electrode of a welding gun is incorporated into one hose. The present invention relates to a method and apparatus for detecting short circuits in electrically mutually insulated cables, ie, cables of the Kinkless type.

(Prior art) In the case of cables of the KITSUKURES type, the condition of the content covered by the hose, that is, the reciprocating wires and the insulating material used to insulate the reciprocating wires from each other, cannot be seen from the outside, so the insulating material is damaged and the reciprocating wires are damaged. Even if a short circuit occurs, it is difficult to detect it, and it is also difficult to predict it through periodic checks. Therefore, in automatic welding processes using robots or the like, welding defects frequently occur, so welding quality inspections have to be carried out more frequently. However, even if this welding quality inspection is carried out, it is only possible to judge the results, that is, the quality of the product that has already been completed, so we have no choice but to manually correct the welding defective parts of the product.
The number of man-hours required for rework is enormous, which has become a problem.

(Object of the Invention) In view of the above-mentioned circumstances, the present invention is capable of detecting short circuits in cables extremely reliably, and detecting short circuits immediately before welding objects to be welded, thereby preventing welding defective products. It is an object of the present invention to provide a method and device for detecting short circuits in cables, which can reduce the number of man-hours required for repair.

(Structure of the Invention) The structure according to the present invention for achieving the above-mentioned object is to perform a dry firing operation on a welding gun before welding the workpiece every 1 takt operation, and during this dry firing operation, the electrode of the welding gun The current value detected during dry firing is compared with the set current that is set when the secondary cable of the welding gun is in a normal state. This method is characterized by a method for welding by detecting an abnormality in the secondary cable of the welding gun, and as a device for carrying out this method, there is a device for dry firing the welding gun, separate from the lower electrode of the welding gun. A detection electrode is provided, and the detection electrode detects the current value of the current flowing through the electrode of the welding gun when dry firing is performed,
A current detection means that outputs the detection signal, and a comparison means that compares the magnitude of the detected value with a reference current value set when the secondary cable of the welding gun is in a normal state, and outputs a comparison signal. and determining means for determining whether there is a short circuit in the cable connected to the electrode based on the comparison signal.

(Function) Since the present invention is configured as described above, the detection electrode is used to perform blank firing of the welding gun before welding the object to be welded. Then, the current value flowing through the electrode of the welding gun that is generated during this dry firing is detected by the current detection means, and the current value is output. This output current value is compared with a current reference value set when the secondary cable of the welding gun is in a normal state, and the determination is made by a determining means that determines whether or not there is a short circuit in the cable. Thereby, a short circuit in the secondary cable is determined every takt before welding the workpiece, and the occurrence of defective products due to poor welding is prevented.

(Example) Examples of the method and apparatus according to the present invention will be described below with reference to the drawings, but first the apparatus will be described.

In FIG. 1, welding equipment (not shown), that is, table electrodes 2 that serve as the lower electrodes of welding guns such as robot welders, multi welders, or manual portable welders, are arranged in parallel on a table 1 for the number of welding points. In addition, only one detection electrode 3 for blank firing operation, which will be described later, is provided in parallel with the table electrode 2 and protrudes from the table electrode 2. 4 is an upper electrode of a welding gun (not shown);
moves in the direction of arrow _Y1 in the figure to be resistance spot welded to the superposed welding objects _W1 and _W2 , and the portion indicated by the symbol X is the welding site.
Note that the welding gun (not shown)
It is possible to perform the blank firing operation twice, and here, the blank firing operation is performed at the position of the detection electrode 3. The one-tact operation mentioned here means the following. First, FIG. 3A is a time chart showing the operation of the welding equipment, FIG. 3B is a time chart showing the pressurizing operation of the welding gun, and FIG. 3C is a waveform chart of the welding current of the welding gun. Figure 3A
In, t ₁ is the operating time of the equipment, t ₂ is the down time, and one takt operation is the operating time t ₁ and the down time.
_t2 , that is, the operation in the time range shown by T in the figure. Welding guns are designed to produce objects to be welded by repeating this operation. Furthermore, as shown in Fig. 3B and Fig. 3C, if the number of times the equipment welds is n, welding is performed n times, and each weld is performed by applying a preload to apply pressure to the objects to be welded W ₁ and W ₂ . Welding is completed in the following order: time S, time W for applying welding current, and holding time H for maintaining pressure after welding. In addition, the part indicated by the broken line in FIG. 3A shows the operation of conventional welding equipment, and the one in the present application has a one-step blank striking operation, that is, the α dot is added. It is clear.

Reference numeral 5 denotes a toroidal coil constituting a part of a current detection circuit which will be described later as a current detection means, and this toroidal coil 5 is wound around the detection electrode 3, thereby _causing ,
This is a place where W ₂ is not welded and where the upper electrode 4, which constitutes a part of the welding gun, can move, and the welding current is applied to the upper and lower electrode parts (that is, the upper electrode 4 and the detection electrode 3 here). ) is fixed in a place where it can be measured. This toroidal coil 5
is for detecting a change in the welding current flowing through the detection electrode 3. That is, when the welding current is Iy and the current application time is ty, the output is a differential value expressed as dIy/dty.

Next, a circuit for processing the output signal of the toroidal coil 5 will be explained. In Figure 2,
6 is an integrator, and 7 is a waveform shaper. These integrator 6, waveform shaper 7, and toroidal coil 5 constitute a current detection circuit 8 as current detection means. In other words, this current detection circuit 8 integrates the differential output dIy/dty of the toroidal coil 5 using an integrator 6 to obtain Iy, and then uses a waveform shaper 7 to shape the waveform into a waveform that can be easily processed by a comparator (described later) in the next stage. The detection value signal is output as a detection value. 9 is a reference generator;
This reference generator 9 has a current value of 2~
This outputs a current value that is 30% lower, that is, a reference value. The reason why the reference value is set to a value 20 to 30% lower than the current value of the current flowing through the detection electrode 3 during normal operation is because the welding current fluctuates slightly even during normal operation. This was done to prevent this slight variation as much as possible since there is a risk that it may be mistakenly determined as a cable shot. Reference numeral 10 denotes a comparator as a comparison means, and this comparator 10 receives the detected value signal from the current detection circuit 8 and the reference value signal from the reference generator 9, and calculates the detected value (i.e., It compares the actual value measured by the toroidal coil 5 with a reference value and outputs a comparison signal. For example, when Iy≧Ib where the detected value is Iy and the reference value is Ib, L is output.
(low) level, and when Iy<Ib, an H (high) level signal is output. Reference numeral 11 denotes an abnormality determining device as a determining means, and this abnormality determining device 11
receives a comparison signal from the comparator 10, determines whether or not there is a short circuit in the cable based on this comparison signal, and outputs the determination signal. When the input signal is at H level, it is determined that there is a short circuit in the cable, that is, there is an abnormality, and when the input signal is at L level, it is determined that there is no short circuit in the cable, that is, there is no abnormality. The judgment signal of this abnormality judgment device 11 is inputted to an alarm (not shown), a sequence circuit for welding operation control, etc., and when a short circuit occurs in the cable, the alarm, lamp, etc. are notified by the alarm, and the welding sequence is temporarily stopped. It is becoming more and more common. An AND gate (hereinafter referred to as AND gate) 1 is provided in the signal path between the abnormality determiner 11 and the comparator 10.
2 is interposed, and the comparison signal from the comparator 10 is passed through the AND gate 12 to the abnormality determiner 11.
It is now entered into . AND gate 1
2, in addition to the comparison signal, an energization signal P which means that the detection electrode 3 is energized at the time of α dot is input. For example, if this energization signal P is an H level signal, the comparison signal is at an H level. and when the energization signal is generated, the abnormality determination device 11
An H level input is made from the AND gate 12, and an L level input is made at other times.

Note that a current transformer or a Hall element may be used instead of the toroidal coil 5, and if these are used, the current value is directly detected, unlike the toroidal coil 5 which detects changes in the current value, so the integration There is an advantage that the circuit 6 is unnecessary, the circuit is simplified, and costs can be reduced.

Having described the apparatus above, the method according to the present invention will now be described.

First, before welding the non-weld objects W ₁ and W ₂ , blank welding is performed using the detection electrode 3 and the upper electrode 4 . When welding is performed using a robot, this blank firing can be programmed in advance and is performed by energizing the detection electrode 3. The current flowing during this blank firing is detected by the current detection circuit 8 and output to the comparator 10. Detector 1
At 0, the current value detected by the current detection circuit 8 is compared with a reference value input from the reference generator 9. In comparison with this reference value, the reference value is set to a value 20 to 30% lower than the current value of the current flowing through the detection electrode 3 when the cable is not short-circuited, so that no erroneous judgment will occur. Therefore, if a short circuit occurs in the cable, the current value flowing to the detection electrode 3 will decrease, so the AND gate 12
An H level signal is output to the abnormality determination unit 11 via the cable, and it is determined that the cable is short-circuited. Thereby, a cable short circuit is detected in advance before welding the objects W ₁ and W ₂ to be welded, thereby preventing welding defects from occurring.

FIG. 4 shows another embodiment of the method and apparatus of the present invention, which is applied to welding equipment in which both the upper and lower electrodes 13, 14 of the welding gun move in the _Y2 direction in the figure. Note that the works W ₁ ' and W ₂ ' are fixedly held by a clamp device (not shown), and the toroidal coil 5' is set at a blank beating operation position.

In this case, during the blank firing operation, both the upper and lower electrodes 1
This is done by shooting the coils 3 and 14 within the loop of the toroidal coil 5'.

(Effects of the Invention) As detailed above, according to the present invention, a detection electrode is provided, dry firing is performed every takt, and a short circuit in the cable is detected by comparing the current flowing during this dry firing with a reference current value. This makes it possible to detect any abnormality in the cable before welding the object to be welded. This eliminates welding defects caused by short circuits in cables, greatly reduces the number of defective welded products, reduces the need to rework unnecessary welded products, and significantly improves productivity.

[Brief explanation of drawings]

FIG. 1 is a diagram of an embodiment of welding equipment to which the method and apparatus of the present invention are applied, FIG. 2 is a block diagram of the apparatus of the present invention, FIG. 3A is a time chart showing the operation of the welding equipment, and FIG. Figure 3B is a time chart showing the pressurizing operation of the welding gun, Figure 3C is a waveform diagram of the welding current of the welding gun, and Figure 4 is another embodiment of welding equipment to which the method and device of the present invention are applied. Figure. 3... Detection electrode, 4... Upper electrode, 5... Toroidal coil, 8... Current detection circuit, 9... Reference generator, 10... Comparator, 11... Abnormality determiner.

Claims (1)

[Scope of Claims] 1. Before welding the workpiece for each tact operation, the welding gun is operated in a blank firing operation, and during this blank firing operation, the current value of the current flowing through the electrode of the welding gun is detected, The current value detected during welding is compared with the set current that flows when the welding gun's secondary cable is in a normal state, and an abnormality in the welding gun's secondary cable is detected before welding the workpiece. A method for detecting short circuits in cables that are welded together. 2. A detection electrode for dry firing the welding gun is provided separately from the lower electrode of the welding gun, and the detection electrode detects the current value of the current flowing through the electrode of the welding gun when dry firing is performed, and outputs the detection signal. a current detection means for comparing the magnitude of the detected value with a current reference value set when the secondary cable of the welding gun is in a normal state, and outputting a comparison signal; and determining means for determining whether or not there is a short circuit in the cable connected to the electrode. 3. The short-circuit detection device for a cable with a knotless cable according to claim 2, wherein a part of the current detection means is constituted by a toroidal coil. 3. The short-circuit detection device for a cable cable according to claim 2, wherein a part of the current detection means is constituted by a current transformer. 4. The short-circuit detection device for a cable cable according to claim 2, wherein a part of the current detection means is constituted by a Hall element.