JPH0235417Y2 - - Google Patents

Description

[Detailed Description of the Invention] "Industrial Application Field" The present invention relates to a device for detecting welding between a spot welding gun of a spot welding machine used in an industrial robot or an automatic machine, and a workpiece.

``Prior art'' Currently, welding conditions such as voltage in spot welding processes for automobiles, etc. are set somewhat high in consideration of wear of the welding electrode in spot welding machines and poor workpiece alignment. Immediately after polishing, for some reason, the flow of current locally concentrates, causing the welding electrode to melt at the point of contact with the workpiece and fuse with the workpiece (welding). If a robot or automatic machine is operated to open the spot welding gun with the welding electrode and workpiece still welded without detecting this welding, the welding electrode of the spot welding gun may come off, causing water leakage, or the robot There have been problems such as overload of the motor, deformation of the workpiece, and deformation of the welding gun bracket.

The conventional welding detection method for preventing these defects uses a welding detection device with a circuit configuration as shown in Fig. 3, which detects the welding in the spot welding gun 1 from the end of holding pressure in the spot welding process. A relay 3 connected in series between the spot welding gun 1 and the workpiece 2 determines whether or not the spot welding gun 1 and the workpiece 2 are in contact with each other at a determination timing after a certain delay time when a voltage is applied.
Alternatively, it is determined whether welding has occurred by detecting the on/off state of the transistor. However, in this method, as shown in Fig. 4, the detection time is only a moment at the judgment timing, so the relay 3
Even if conduction occurs, as shown in Figures 4g and 4h, spot welding gun 1 and workpiece 2 are simply in contact with each other due to burrs or the like at the judgment timing, and even in the case of cohesive welding, it will be judged as welding. , causing the robot or automatic machine to stop due to false welding.

In addition, the patent application filed in 1984 before the filing date of the present invention
-177380 (see Japanese Patent Application Laid-Open No. 62-38780),
The first one starts operating after the spot welding operation is completed.
and a second timer, the time-up time of the second timer is set longer than the time-up time of the first timer, and when the first timer times up and when the second timer times up, In the welding detection method in which the contact between the welding tip and the workpiece is detected by a detection means, the detection time is only at the moment when the first and second timers time up, so there is no possibility that the robot or automatic machine will stop due to false welding. The disadvantage is that it does not decrease in any way.

``Problems to be solved by the invention'' The invention was made to solve the above problems, and includes pseudo welding caused by mere contact between the spot welding gun and the workpiece due to burrs, etc.
It is an object of the present invention to provide a welding detection device capable of distinguishing true welding in which a spot welding gun and a workpiece are actually welded together.

"Means for Solving Problems" According to the present invention, as shown in FIG. Signal voltage applying means 5, 4 for applying voltage, signal voltage applied to the spot welding gun 1 by the signal voltage applying means 5, 4, and signal voltage generated on the workpiece 2 side via the spot welding gun 1. and a comparison means 6 which outputs a pulse signal in the case of no welding or pseudo welding based on the difference between both signal voltages, and a comparison means 6 which starts operating from the end of the pressurization holding and generates an output signal at the judgment timing. and the timer means 9, 10, 11 after the pulse signal is output from the comparison means 6.
A signal output continuation means 8 continues the signal output until the determination timing when the output signals of 0 and 11 are generated, and a signal from the signal output continuation means 8 at the determination timing when the output signals of the timer means 9, 10, and 11 are generated. The present invention is characterized by comprising a determining means 12 that outputs a welding detection signal only when there is no output, assuming that there is a true welding in which the spot welding gun 1 and the workpiece 2 are not in contact with each other even once during the determination period. A weld detection device for a spot welder is provided.

"Operation" According to the above configuration, the signal voltage applying means 4 and 5 apply a signal voltage to the workpiece 2 via the spot welding gun 1 within the welding judgment period from the end of pressurization holding to the end of the judgment timing. Therefore, if the spot welding gun 1 separates from the workpiece 2 even once during the welding determination period, no signal voltage is generated on the workpiece 2 side during that separation, and the spot welding gun 1 separates from the workpiece 2 within the welding determination period. If it is not separated, a signal voltage will continue to be generated on the workpiece 2 side. Since the comparison means 6 outputs a difference signal based on the difference between the two signal voltages, this difference signal becomes a pulse signal in the case of no welding or pseudo welding, and becomes zero (=0) in the case of welding. Since the signal output continuation means 8 continues to output the signal until the welding determination timing after the comparison means 6 outputs the pulse signal, the determination means 12 determines if there is a signal output from the signal output continuation means 8 at the welding determination timing. Determined as no welding or pseudo welding. Further, the determining means 12 determines that there is welding only when there is no signal output from the signal output continuation means 8, thereby ensuring that the spot welding gun 1 and the workpiece 2 do not come out of contact even once within the determination period. Welding is determined.

"Embodiment" Next, one embodiment of the present invention shown in the drawings will be described.

FIG. 1 is a circuit diagram showing the welding detection device of this embodiment, and FIG. 2 is a timing chart showing the detection mechanism.

The welding detection mechanism in this embodiment is such that after the holding end signal shown in FIG. 2c is generated, a voltage signal of waveform A that continues until after the determination timing as shown in FIG. 2d is sent to the spot welding gun 1 through a flip-flop circuit. 5 and transistor 4. on the other hand,
The waveforms B1 to B4 generated on the workpiece 2 side are examined, and the comparison circuit 6 detects the difference between waveform A and waveform B1 to B4, and the difference waveforms A-B1, A-B2, A-B are detected.
3 and A-B4 distinguish between cases where there is welding and cases where there is no welding. Here, the waveform B1 on the workpiece 2 side corresponds to the pressing force of 0 in Fig. 2b.
This is a waveform when the voltage signal detected on the workpiece 2 side becomes zero at the same time, and there is no welding between the spot welding gun 1 and the workpiece 2. Difference waveform A-B1
has a pulse waveform that rises when the pressing force is 0, as shown in FIG. 2i. Waveform B2 shows that in the case of using a robot or an automatic machine where the electrodes of the spot welding gun 1 are slightly opened when removing the pressurizing force, there is no interruption even after the pressurizing force is 0 until the judgment timing. This is a waveform when a voltage signal is continuously detected on the workpiece 2 side, and welding between the spot welding gun 1 and the workpiece 2 has occurred. The difference waveform A-B2 has no pulse signal as shown in FIG. 2j. Waveform B3 is a case where the voltage signal on the workpiece 2 side becomes zero once when the pressing force is 0, but the voltage signal is generated midway, and the voltage appears on the workpiece 2 side at the determination timing. Therefore, the spot welding gun 1 and the workpiece 2 are not welded together, and the difference waveform A-B
3 includes pulse signals that rise at multiple points in time as shown in FIG. 2k. In addition, waveform B4 is
At the time when the pressing force is 0, the voltage signal on the workpiece 2 side becomes zero once, and the voltage signal on the workpiece 2 side is detected again at the determination timing, so there is no welding. The difference waveform A-B4 is shown in Figure 2.
As shown in FIG. 2, a pulse signal that rises when the pressing force is 0 is included.

Therefore, in order to detect welding between the spot welding gun 1 and the workpiece 2, it is not necessary to determine whether or not a voltage appears on the workpiece 2 at the determination timing, but rather to check the voltage waveforms B1, B3, and B3 on the workpiece 2 side. and B4
and waveform B2 must be distinguished. Among the difference waveforms A-B1, A-B2, A-B3, and A-B4, waveform A-B2 in which no pulse signal occurs is true welding, and waveform A in which pulse signal occurs
-B1, A-B3 and A-B4 have no welding (including pseudo welding).

As shown in FIG. 1, a spot welding gun 1
A voltage signal is applied to the transistor 4 from a DC power source through a transistor 4, and a start signal is applied to the base of the transistor 4 through a flip-flop 5. A hold end signal is applied to the input of a flip-flop (hereinafter simply referred to as FF) 5 from a timer contact (not shown). and,
FF5 applies to the base of transistor 4 a start signal having the same waveform as waveform A that continues after the holding end signal is applied until after the determination timing. The transistor 4 and the FF 5 constitute a signal voltage applying means. Resistors 14A, 14B from work 2
The voltage signals of waveforms B1, B2, B3, B4, etc. derived from the above and the voltage signal of waveform A applied to the spot welding gun 1 are introduced into a comparison circuit 6. The difference waveforms A-B1, A-B of this comparison circuit 6
2, A-B3, A-B4, etc. output is filter 7
FF consisting of D-flip-flop etc.
8 input terminals. This FF8 constitutes a signal output continuation means. On the other hand, the start signal from FF5 is introduced to oscillator 10 via FF9, and is also introduced to FF8 and timer 11 via single shot multivibrator 14 as a reset signal. The output of an oscillator 10 is connected to the input side of this timer 11, and the time-up output side of the timer 11 is connected to one input terminal of an FF 12 consisting of a JK flip-flop or the like. The output terminal of FF8 is connected to the other input terminal of FF12, and the output terminal of FF8 is connected to the other input terminal of FF12.
The output terminal 12 is connected to a welding abnormality circuit 13 of the robot, and after welding is detected, the welding abnormality circuit 13 is activated to stop the robot or automatic machine.

According to the above configuration, when the hold end signal is applied to the input terminal of the FF5, a continuous start signal is generated at the output terminal of the FF5 until after the determination timing ends. The start signal is applied to the base of the transistor 4, and the conduction of the transistor 4 causes the DC power source to supply the spot welding gun 1 and the comparison circuit 6 with a pull signal from the time when the holding end signal is generated until after the determination timing as shown in FIG. 2d. A subsequent voltage signal of waveform A is applied. The voltage signals generated on the workpiece 2 are compared via the resistors 14A and 14B as waveforms B1, B2, B3, and B4 indicating the contact state between the spot welding gun 1 and the workpiece 2 as shown in FIG. 2 e to h. It is introduced into the circuit 6. Therefore, the output side of the comparison circuit 6 has difference waveforms A-B1, A-B2, A-B3, A-B as shown in FIG.
4 voltage signals are generated. This voltage signal is shaped by removing noise etc. through a filter 7.
It is introduced into one input terminal of FF8. In this embodiment, the start signal from FF5 is made into a pulse through the single shot multivibrator 14, and a reset signal is introduced by the pulse into the other input terminal of FF8.
is in the initial state when the start signal is generated. Difference voltage signal A to FF8 via filter 7
When -B1, A-B2, and A-B4 are introduced, an output signal that continues until after the determination timing is generated on the output side of FF8 at the time of introduction of the rising waveform. On the other hand, a reset signal for the single shot multivibrator 14 is applied to the timer 11. In addition, since the clock pulse from the oscillator 10 operated via FF9 is applied to the timer 11 from the time when the start signal of FF5 is generated, it counts up at the judgment timing and generates an output signal, and the rising waveform of the output signal is input to one input terminal of FF12. Therefore, the FF 12 is activated by the rising waveform of the output signal of the timer 11 at the determination timing. In the case of "no welding" (including the case of pseudo welding) as shown in Figure 2 i, k and l,
Since the continuous output signal from FF8 is applied to the other input terminal of FF12 until after the judgment timing, FF1 consisting of JK flip-flop etc.
2 does not generate an output signal. Therefore, the welding abnormality circuit 13 of the robot is not activated and the robot or automatic machine is not stopped. On the contrary, in the case of true "welding" as shown in FIG. 2j, the FF 12 generates an output signal because the subsequent output signal from the FF 8 is not applied to the other input terminal of the FF 12 until the determination timing. Therefore, the welding abnormality circuit 13 of the robot is activated and the robot or automatic machine is stopped.

"Other Embodiments" In the above embodiments, the signal voltage application means, the comparison means, the timer means, the signal output continuation means, and the determination means are the transistor 4 and the FF 5, the comparison circuit 6, the FF 9, the oscillator 10, the timer 11, Although configured with FF8 and FF12, the present invention is not limited to these components, and can be configured using various circuit elements.

"Effects" As stated above, the welding detection device of the present invention has the following effects:
a signal voltage applying means for applying a signal voltage to the spot welding gun during a welding determination period from the end of pressurization holding to the end of the determination timing; a signal voltage applied to the spot welding gun by the signal voltage applying means; a comparison means for comparing a signal voltage generated on the workpiece side through the spot welding gun and outputting a pulse signal in the case of no welding or pseudo welding based on the difference between the two signal voltages; a timer means that starts operation and generates an output signal at a determination timing; and a signal output continuation means that continues to output a signal after the pulse signal is output from the comparison means until a determination timing at which an output signal of the timer means is generated. , Only when there is no signal output from the signal output continuation means at the judgment timing when the output signal of the timer means is generated, true welding has occurred in which the contact between the spot welding gun and the workpiece does not separate even once during the judgment period. When detecting the welding state between the spot welding gun and the workpiece, the device is equipped with a determination means for outputting a welding detection signal as a welding detection signal, and when detecting the welding state between the spot welding gun and the workpiece, not only the determination timing but also the welding determination period from the end of pressurization holding to the determination timing The state of welding between the spot welding gun and the workpiece can be continuously detected, and the robot or automatic machine is stopped only in the case of true welding, and the robot or automatic machine is stopped in the case of no welding or pseudo welding. This has the excellent effect of dramatically reducing stoppage troubles due to false welding.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the welding detection device of the present invention, Fig. 2 is a timing chart showing its detection mechanism, Fig. 3 is a circuit diagram showing an example of a conventional welding detection device, and Fig. 4 is a timing chart showing a conventional weld detection method. 1... spot welding gun, 2... workpiece, 4...
...Transistor, 5, 8, 9, 12...Flip-flop, 6...Comparison circuit, 11...Timer.

Claims (1)

[Scope of Claim for Utility Model Registration] In a spot welding machine that performs spot welding of workpieces by holding the workpiece under pressure with a spot welding gun and applying electricity, within the welding judgment period from the end of the pressure holding to the end of the judgment timing. a signal voltage applying means for applying a signal voltage to the spot welding gun; a signal voltage applied to the spot welding gun by the signal voltage applying means; and a signal voltage generated on the workpiece side via the spot welding gun. and a comparison means that outputs a pulse signal in the case of no welding or pseudo welding based on the difference between the two signal voltages, and a timer means that starts operating from the end of the pressurization holding and generates an output signal at the judgment timing. , signal output continuation means for continuing to output the signal after the pulse signal is output from the comparison means until a determination timing when the output signal of the timer means is generated; A determination means that outputs a welding detection signal only when there is no signal output from the continuation means, assuming that true welding has occurred in which the spot welding gun and the workpiece are not in contact with each other even once during the determination period. Welding detection device for spot welding machines.