JPS6252666B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a welding current detection circuit necessary for operation of a control circuit of a semi-automatic arc welding machine or the like.

In a semi-automatic arc welding machine, a slowdown control method that slows down the welding wire feed speed at the start of welding is a control method that uses a signal that detects the presence or absence of welding current to control the welding wire feed speed. Regarding control, there is a hot start control method that applies a high voltage at the start of welding. In any case, these control methods require a signal from a part that generates a voltage in accordance with the welding current by some method. for example,
In the rectification method using the double star connection shown in Fig. 1, the voltage across the DC reactor 5 and the interphase transformer 4, which are considered as signal sources, has a different potential from the control circuit of the rectifier thyristors 2a and 2b, and is directly Not available. For this reason, conventionally, as shown in FIG. The voltage waveform was extracted and detected as a current detection signal. In the figure, 3 indicates a welding transformer with a star-shaped connection, and 7 indicates a current detection circuit consisting of a diode bridge 8, resistors 9, 10, 11, an electrolytic capacitor 12, and a transistor 13, and its output is input to a control circuit 1 that performs gate control of the output voltage control thyristors 2a and 2b.

However, according to the configuration shown in FIG. 1, since the current detection winding 6 is magnetically coupled to the interphase transformer 4, the welding machine with a built-in high frequency generator outputs the noise generated in the interphase transformer as it is. When used with the same power source and the same ground as a welding machine with a built-in high-frequency generator, noise was also induced on the output side, which could result in malfunction or damage to circuit elements. Further, since another current detection winding is added to the interphase transformer 4, the interphase transformer 4 becomes expensive. Furthermore, the voltage waveform of the interphase transformer 4 and the voltage waveform of the DC reactor 5 are as shown in FIGS. 2 and 3, respectively. When rectifying the voltage waveform of such an interphase transformer to generate a current detection signal, Due to the integral circuit formed in the current detection circuit 7 to smooth the pulsating current wave, the detection circuit itself has a delay time, and good arc welding cannot be expected.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art described above and to provide an inexpensive current detection circuit with an extremely short delay time that does not require a current detection winding in an interphase transformer.

In order to achieve the above object, the present invention electrically and magnetically separates a DC reactor and an interphase transformer from the output side of a current detection circuit, and uses a light-operated element as a means for detecting the welding current. It was constructed using Hereinafter, a specific example will be described in detail with reference to FIG.

FIG. 4 shows one embodiment of the present invention, and the figure shows an interphase transformer 4 for ease of explanation.
Only the DC reactor 5 and current detection circuit are shown. As shown in the figure, DC reactor 5
The voltage across the is rectified by diode bridge 8, and resistors 9, 10, 11 and electrolytic capacitor 1
2. This rectified output circuit is provided with a photo-operated element (photocoupler) 20. That is, a rectified output voltage is applied to the light emitting diode D of the optically active element 20, and the phototransistor Tr of the optically active element 20 is turned on. The collector and emitter terminals a and b of this phototransistor Tr are connected to the control circuit 1 described above. Therefore, a signal electrically and magnetically separated from the DC reactor 5 can be taken out between the terminals a and b, and can be used as a welding current detection signal.

Further, in the present invention, the optically operated element 21 is similarly connected to the interphase transformer 4. Its connection configuration consists of diodes 22 and 23 that rectify the voltage across the interphase transformer 4, and a resistor 2 that constitutes an integrating circuit.
4, 25, 26, an electrolytic capacitor 27, and a light emitting diode _D1 are connected to the rectified output terminal, and the collector and emitter terminals of the light receiving transistor _Tr1 are connected to terminals a and b connected to a control circuit (not shown). There is.

According to the circuit of the present invention described above, the DC reactor 5, the interphase transformer 4, the control circuit 1, and the photocoupler 2
0 and 21, so that the noise generated in the DC reactor 5 and interphase transformer 4 is not generated on the output side of the current detection circuit. Therefore, it can be applied to a welding machine with a built-in high-frequency generator, and even if it is used with the same power source and the same ground as a welding machine with a built-in high-frequency generator, there will be no malfunction or damage to the control element. Furthermore, it is less expensive than the conventional method shown in FIG. 1, which uses additional insulated windings. Further, according to the circuit of the present invention, the signal detected from the voltage waveform generated in the DC reactor 5 and the interphase transformer 4
The time constant of the detection circuit can be reduced by combining the voltage waveform generated in the detection circuit with the detected signal, and as a result, it is possible to detect the welding current with a shorter delay time.

It goes without saying that the present invention is not limited to the above-described embodiments, and can be applied to, for example, an AC arc welding machine that uses a rectangular wave output converted by an inverter.

As is clear from the above embodiments, the present invention
The voltage generated in the DC reactor and phase-to-phase transformer inserted in the power supply circuit of the arc welding machine is directly rectified and detected to operate the light-operated element, which electrically and magnetically disconnects the potential of the DC reactor and phase-to-phase transformer. By extracting the separated signal and inputting it to a welding current control circuit, the presence or absence of welding current in the welding machine is detected. Therefore, according to the present invention, it is possible to realize a welding current detection circuit with an inexpensive circuit configuration that does not cause malfunction or damage to control elements due to high frequency noise, etc., and also eliminates problems caused by time delays. It has the following advantages and effects.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a conventional DC arc welding machine with a rectifier circuit using double star connections, and Figure 2 is the voltage waveform that occurs at both ends of the interphase transformer when welding current is flowing in the circuit shown in Figure 1. Similarly, FIG. 3 is a voltage waveform diagram generated at both ends of the DC reactor when welding current is flowing, and FIG. 4 is a welding current detection circuit diagram of a DC arc welding machine showing an embodiment of the present invention. . 4... Phase-to-phase transformer, 5... DC reactor, 8
...Diode bridge, 9-11, 24-26
...Resistance, 12,27...Electrolytic capacitor, 2
0, 21... Optical operation element, 22, 23... Diode, D, D ₁ ... Light emitting diode, Tr, Tr ₁ ...
Light receiving transistor.

Claims (1)

[Claims] 1. Optical operating elements are provided that operate according to the voltages generated in the DC reactor and interphase transformer inserted into the welding current output circuit of the arc welding machine, and the welding current is detected by the output signals of these optical operating elements. A current detection circuit for an arc welding machine.