JPH0341895Y2 - - Google Patents

Description

[Detailed Description of the Invention] "Industrial Application Field" The present invention relates to a non-contact type DC arc welding machine that uses semiconductor main switching elements such as GTO, transistors, and thyristors to switch and close arc current.

"Prior Art" First, to explain the background, a conventional general DC arc welding machine was, for example, as shown in FIG. 4.

That is, a DC power supply 1 which receives a commercial power supply (not shown) as an input and generates a DC voltage of about 100V, and welding gun heads A and B and a switch S, which is an electromagnetic switch, are connected between the positive and negative poles of this DC power supply 1. death,
An arc generating circuit 2 is placed in parallel with the switch S.

In this configuration, if welding gun head B is a workpiece to be welded, and welding gun head A is a welding rod that melts during welding and welds to the welding member, then after welding gun heads A and B are brought into contact, the arc generating circuit is turned on. Substantially, a closed circuit is formed from the positive electrode of the DC power source 1 to the welding gun heads A and B to the arc generating circuit to the negative electrode of the DC power source 1.

Next, when welding gun head A is slightly separated from welding gun head B, which is the workpiece, welding gun head A,
An arc occurs between B. Immediately after this arc is generated, switch S, which is an electromagnetic switch, is closed and the main current is passed between the welding gun heads A and B, generating a powerful arc to weld the members.

To complete the welding, the arc is extinguished by opening the switch S.

However, in the DC arc welding machine shown in Fig. 4, the switch S is an electromagnetic switch and is mechanical, so
Because of the disadvantages of large size and limited life of the contacts, a switch element using a thyristor TH instead of an electromagnetic switch was realized, as shown in Fig. 5.

The DC arc welding machine shown in FIG. 5 is provided with a snubber circuit 3, which consists of a diode D, a resistor R, and a capacitor C, and protects the thyristor TH, which is a switch element, from overvoltage.

The operation is basically the same as the DC arc welding machine shown in FIG. Main current for welding is thyristor TH
An on signal is applied to the gate of the thyristor TH to turn it on and flow.

In the circuit of the DC arc welding machine shown in FIG. 5, the switch is composed of a thyristor TH and is non-contact, so it has a long life and high reliability.

``Problem to be solved by the invention'' However, in the improved DC arc welding machine shown in Fig. 5, after turning on the DC power source 1 when starting welding work, the welding gun head A, which is a welding rod, Welding gun head B, which is a welding workpiece
A spark is generated at the same time as the two come into contact.

This is because a large charging current flows through the capacitor C of the snubber circuit 3 through a closed circuit from the positive electrode of the DC power source 1 to the welding gun heads A and B to the resistor R to the capacitor C to the negative electrode of the DC power source 1.

This spark is undesirable for arc welding operations. In addition, if some abnormality occurs and a short circuit failure occurs in the thyristor TH, the next time you start welding,
A large current flows between welding gun heads A and B before an arc occurs, and the welding rod that makes up welding gun head A and the welding work that makes up welding gun head B may weld together, causing the thyristor TH to
There were problems in that it was not possible to determine from the external appearance whether a short circuit had occurred, making it time-consuming to discover the cause of the failure, and making maintenance inconvenient.

The present invention has been made by focusing on such conventional problems, and an object of the present invention is to provide a DC arc welding machine equipped with a semiconductor main switching element that can detect a failure of a switch element using a semiconductor. It is an object.

"Means for Solving the Problems" The gist of the present invention to achieve the above objectives is as follows: 1. Connecting a welding gun head and a semiconductor main switching element in series between the positive and negative electrodes of a DC welding power source. In a DC arc welding machine in which a snubber circuit and an arc generating circuit are connected in parallel to the semiconductor main switching element, a fault detection resistor is connected in parallel between both terminals of the welding gun head, and both ends of the fault detection resistor are connected in parallel. A DC arc welding machine characterized by being provided with a failure detection circuit comprising an abnormal voltage detection section that detects a voltage and detects a short circuit failure of the semiconductor main switching element.

2. The abnormal voltage detection section is included in the DC arc welding machine according to item 1, which comprises a zener diode set to a zener voltage higher than the arc welding voltage and a current limiting resistor connected in series.

``Operation'' Under normal conditions, the arc generating circuit is activated while the welding rod of the welding gun head and the welding workpiece are in contact with each other, and an arc is generated when the welding rod and the welding workpiece are slightly separated. Next, the semiconductor main switching element is turned on and arc welding is performed using a strong current from the welding DC power source.

When the semiconductor main switching element is turned off, the arc stops and welding ends.

As long as the DC arc welding machine is operating normally, a normal arc voltage is detected by the fault detection resistor, and the fault detection circuit will not detect a fault. In addition, the charging current of the snubber circuit is consumed by the fault detection resistor, and does not adversely affect the next welding operation.

The fault detection circuit operates when an abnormally high voltage is detected in the welding gun head.

If the semiconductor main switching element is short-circuited for some reason during welding work, it will remain on, so welding will continue, and when the welding rod and welding workpiece are separated sufficiently, the arc will stop and the work will end. .

However, when the welding DC power supply is turned on, a voltage is still applied to the failure detection resistor, and this voltage is the power supply voltage itself and has an abnormally higher value than the arc voltage.

The abnormal voltage generated across the failure detection resistor at the time of this failure is detected by the abnormal voltage detection section, thereby detecting a short circuit failure of the semiconductor main switching element.
The detection results are transmitted to the outside by the alarm unit, and a warning light or alarm buzzer is used to notify the failure.

Some abnormal voltage detection units use Zener diodes, and since the arc voltage is lower than the Zener voltage, the Zener diodes do not conduct during normal operation. However, in the event of a failure, the Zener diode becomes conductive due to the abnormal voltage generated across the failure detection resistor.

By outputting this conduction state, an abnormality can be detected from the outside.

If the semiconductor main switching element is short-circuited while the DC arc welding machine is not operating, an abnormal voltage will be generated across the fault detection resistor when it starts operating, and this will be detected by the abnormal voltage detection section of the fault detection circuit. A malfunction is discovered.

“Embodiment” An embodiment of the present invention will be described below based on the drawings.

1 and 2 show an embodiment of the present invention.

The DC arc welding machine 10 includes a welding DC power source 11.
The welding gun heads A, B and the semiconductor main switching element GTO are connected in series between the positive electrode 11a and the negative electrode 11b, and the snubber circuit 12 and the arc generating circuit 13 are connected in parallel to the semiconductor main switching element GTO,
Furthermore, a failure detection circuit 20 is provided.

The power supply voltage of the welding DC power supply 11 is set to about 100V. The snubber circuit 12 is a diode
Consists of DN, resistor RN, and capacitor CN. The welding DC power source 11 and the arc generating circuit 13 are well known, so their explanation will be omitted. In addition, welding gun head A,
The former is connected to the welding rod, and the latter is connected to the welding workpiece.

The welding voltage applied between welding gun heads A and B is applied to the semiconductor main switching element as shown in Figure 3.
In section a, where the GTO is turned on and arc welding is performed normally, a constant voltage of approximately 30V is maintained.

The failure detection circuit 20 includes a failure detection resistor 21 connected in parallel between both terminals of welding gun heads A and B.
and an abnormal voltage detection section 25 that detects the voltage across the failure detection resistor 21 to detect a short circuit failure of the semiconductor main switching element GTO.

The abnormal voltage detection section 25 is a Zener diode ZD
1 to ZD4 and current limiting resistor R1 are connected in series,
The sum of the zener voltages of the zener diodes ZD1 to ZD4 is set to about 40V, which is higher than the arc welding voltage. A photocoupler OC consisting of a photodiode DP and a phototransistor TR is connected to the Zener diode ZD4.

Next, the action will be explained.

When performing welding work under normal conditions, first
The arc generating circuit 13 is activated while the welding rod connected to the welding gun heads A and B is brought into contact with the welding workpiece.

After activating the arc generating circuit 13, when the welding rod and the welding workpiece are slightly separated, an arc is generated between the welding rod and the welding workpiece. Therefore, the semiconductor main switching element GTO is turned on and arc welding is performed using a strong current from the welding DC power source 11.

When the semiconductor main switching element GTO is turned on, the arc stops and welding ends.

As long as the DC arc welding machine 10 is operating normally, the fault detection resistor 21 will have a normal arc voltage of about
30V is detected, and the abnormal voltage detection section 25
Since it detects a voltage of 40V or more, the failure detection circuit 20 will not detect a failure.

The charging current of the snubber circuit 12 is determined by the failure detection resistor 21.
During the next welding operation, sparks will not suddenly fly between the welding rod connected to the welding gun heads A and B and the welding workpiece, and the welding operation will not be adversely affected.

The failure detection circuit 20 operates when an abnormally high voltage is detected in the welding gun heads A and B.

If the semiconductor main switching element GTOB is short-circuited for some reason during welding work, it will remain on, so welding will continue, and when the welding rod and welding workpiece are separated sufficiently, the arc will stop and the work will end. do.

However, when the welding DC power supply 11 is turned on, the fault detection resistor 21 and the semiconductor main switching element GTO
Since current flows from the DC power supply to the , a voltage is still applied to the failure detection resistor 21, and the voltage is approximately 100V, which is the power supply voltage of the welding DC power supply 11.
This is an abnormally higher value than the arc voltage of about 30V.

In the abnormal voltage detection section 25, a Zener diode
The voltage applied to ZD1 to ZD4 becomes higher than the sum of their Zener voltages, about 40 V, and the Zener diodes ZD1 to ZD4 become conductive.

When the Zener diode ZD4 becomes conductive, a voltage is applied to the photodiode DP while the current is limited by the current limiting resistor R1, and its optical output turns on the phototransistor TR, and the on/off state of the phototransistor TR can be externally checked. By doing so, you can know the failure.

When a short-circuit failure occurs in the semiconductor main switching element GTO in this way, an abnormal voltage is generated across the failure detection resistor 21, and the abnormal voltage is detected by the abnormal voltage detection section 25.
A short circuit failure is detected.

A failure can be easily detected by activating an appropriate warning means such as a lamp or a buzzer based on the conduction state of the phototransistor TR of the photocoupler OC of the abnormal voltage detection section 25.

Even if the semiconductor main switching element GTO is short-circuited while the DC arc welding machine 10 is not in operation, even if the welding gun head is not in contact when starting operation, the positive electrode 11a of the DC power supply 11 → resistor 21 → semiconductor main switching element Since current flows through the closed circuit of GTO → negative electrode 11b, an abnormal voltage is generated across the fault detection resistor 21, which is transmitted to the abnormal voltage detection section 2 of the fault detection circuit 20.
5, so the failure is discovered.

Note that it goes without saying that a transistor, a thyristor, etc. can be used as the semiconductor main switching element.

"Effect of the invention" According to the DC arc welding machine according to the invention, in a device that uses a semiconductor main switching element as a switch for turning on and off a DC power source for welding, the charging current of the snubber circuit that protects the semiconductor main switching element A fault detection resistor that detects the operating voltage as well as detects the operating voltage.
Since a failure detection circuit having an abnormal voltage detection section for verifying the voltage is provided, a short-circuit failure of the semiconductor main switching element can be easily detected, resulting in a DC arc welding machine with excellent maintainability.

Furthermore, the charging current of the snubber circuit prevents sparks from suddenly flying between the welding rod connected to the welding gun heads A and B and the welding workpiece, making it possible to perform welding work smoothly.

[Brief explanation of the drawing]

Figures 1 to 3 show an embodiment of the present invention. Figure 1 is a circuit diagram of a DC arc welding machine, Figure 2 is a circuit diagram of a failure detection circuit, and Figure 3 is a diagram showing normal operation. FIG. 4 is a circuit diagram of a conventional DC arc welding machine, and FIG. 5 is a circuit diagram of an improved conventional DC arc welding machine. A, B...Welding gun head, GTO...Semiconductor main switching element, OC...Photo coupler, R1...
Current limiting resistor, ZD1 to ZD4... Zener diode, 10... DC arc welding machine, 11... DC power source for welding, 12... Snubber circuit, 13... Arc generation circuit, 20... Failure detection circuit, 21... ...failure detection resistor, 25...abnormal voltage detection section.

Claims (1)

[Claims for Utility Model Registration] 1. A welding gun head and a semiconductor main switching element are connected in series between the positive and negative electrodes of a DC power supply for welding, and a snubber circuit and an arc generating circuit are connected in parallel to the semiconductor main switching element. A fault detection resistor connected in parallel between both terminals of a welding gun head and a voltage across the fault detection resistor are detected to detect a short-circuit failure of the semiconductor main switching element. A DC arc welding machine characterized by being provided with a failure detection circuit comprising a voltage detection section. 2. The DC arc welding machine according to claim 1, wherein the abnormal voltage detection section comprises a Zener diode set with a Zener voltage higher than the arc welding voltage and a current limiting resistor connected in series.