JPH03174974A - Ac arc welding machine - Google Patents

Abstract

PURPOSE:To prevent danger to receive an electric shock by providing a keying circuit to supply output of an auxiliary power source circuit to the input side or output side of a switching element only when a starting detector outputs a signal during welding starting. CONSTITUTION:When an electrode 6 comes into contact with materials 7 to be welded, a short-circuit current flows and a contact part is fused and shifted to an arc. In addition, the short-circuit current is detected by a detector 10 and an output signal of an amplifier 11 is made to a high level and the keying circuit 12 is closed and an auxiliary DC power source 9a is connected in parallel with a capacitor 3 through a resistor 9b. By this method, the capacitor 3 is charged by the auxiliary DC power source 9a besides a DC power source 1. In this state, in order to reverse the polarity of the output current, the switching element in continuity is cut off by an output signal of a switching element control circuit 8 and when a signal S1 is turned OFF and then, a signal S2 is turned ON, for instance, since the output current is once diminished to zero, the arc disappears.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an AC arc welding machine, and in particular to a DC power source obtained by a method such as rectifying commercial AC, by using a switching element to convert it into a forward or reverse direction. The present invention relates to an improvement of an arc welding machine which is equipped with an auxiliary power supply circuit to facilitate the re-ignition of an arc that is once extinguished when polarity is switched in a machine that is switched to obtain an alternating current output.

<Conventional equipment> In an AC arc welding machine, when the polarity is switched, the arc disappears once and then the arc is re-ignited as the voltage increases in the opposite direction, but if the no-load output voltage of the welding machine is low. or,
Depending on the electrode material, the object to be welded, the components of the shielding gas, etc., re-ignition may be difficult even if the no-load voltage is high. In order to facilitate restriking in such cases, a method has been proposed in which a voltage is supplied from an auxiliary power source with a voltage higher than the no-load voltage of the welding power source when switching polarity to assist restriking. There is.

FIG. 5 shows an example of a conventional device using this method. In the figure, 1 is a DC power supply, which is usually obtained by rectifying a commercial AC power supply. 2 is an output smoothing reactor, 3 is a smoothing and surge absorption capacitor, 4a, 4b, 5a,
5b is a switching element connected in a bridge manner, and a transistor or a thyristor with a commutation circuit is used. 6
is an electrode, 7 is an object to be welded, and 8 is a switching element 4.
a.

This is a switching element control circuit for controlling 4b or 5a and 5b as one set to alternately turn ON and OFF in a predetermined time width. 9 is an auxiliary power supply circuit for restriking;
Consists of an auxiliary DC power supply 9a and a current limiting resistor 9b,
It is connected in parallel with capacitor 3 to charge it. This auxiliary DC power supply 9 is set to a high voltage necessary for restriking the arc.

In the apparatus shown in the figure, while an arc is generated between the electrode 6 and the workpiece 7, the auxiliary DC power supply 9a is superimposed on the output of the DC power supply 1, and the switching element 4a, 4b or 5
The welding current and voltage are supplied to the electrode 6 and the workpiece 7 through a and 5b, but the output current is suppressed by the resistor 9b, and this causes a voltage drop, so the welding current and voltage are approximately equal to that of the DC 7 source 1. It will be determined by the output. When switching the polarity, for example, the switching element 4a.

When 4b is disconnected from the conductive state, the arc is extinguished and current no longer flows, so that capacitor 3 is charged to the high voltage of auxiliary DC power supply 9a. Since this voltage is set higher than the output of the DC power supply 1, the switching elements of the next polarity, such as the switching elements 5a and 5b in the previous example.

When conductive, the terminal voltage of the capacitor 3 charged to this high voltage is applied to the electrode 6 and the workpiece 7 immediately after the arc is extinguished.
The arc is re-ignited by being supplied between the two and destroying the recovering ground edge.

<Problems to be Solved by the Invention> Since the conventional welding machine is configured as described above, the output voltage of the auxiliary power circuit 9 is equal to that of the electrode 6 and the welded object even when no arc is actually generated. is applied between the object 7 and the object 7. At this time, if no arc is occurring, and there is no short circuit between the electrode 6 and the workpiece 7, and no current is flowing at all, the current from the auxiliary DC power source 9a is approximately zero. Since no voltage drop occurs due to the resistor 9b, the high output voltage of the auxiliary DC power supply 9a appears as it is between the electrode 6 and the workpiece 7.

The output voltage of this auxiliary DC power supply 9 is normally set to about 200 to 300 V so that the arc can be easily re-ignited when changing the polarity.
(the workpiece 7 is normally at ground potential), it becomes extremely dangerous for the worker. Of course, the switching element 4a.

4b 5a and 5b are a start command circuit (not shown), and a switching element control circuit 8 is configured so that it will not conduct unless a start switch attached to the welding torch is pressed, but please do not touch the electrode 6 during inspection or repair. If you accidentally press the start switch while touching it, high voltage will be applied and an electric shock will occur.

Furthermore, when using an electrode holder for manual welding and a manual welding rod as the electrode 6, there is no start switch and the power output is constantly applied, so when replacing the welding rod or leaving the holder unattended. The power switch had to be turned off each time the device was used, and failure to do so was an extremely dangerous device that could immediately lead to an electric shock accident.

Means for Solving the Problems> In order to solve the problems of the conventional device described above, the present invention aims to solve the problems of the conventional device described above. A detector for detecting the welding current and a welding start detector are provided, and the auxiliary power source for arc re-ignition is connected to the main power circuit only when the welding current is flowing.

<Example> FIG. 1 shows an example of the present invention. In the figure, 10 is a welding current detector, and a current transformer, a Hall element, etc. are used. Reference numeral 11 denotes an amplifier that amplifies the output of the welding current detector 1°, and a smoothing amplifier that prevents sensing of a short current interruption period that occurs during polarity switching among the outputs of the welding current detector 10. The welding current detector 10 and the welding current detector 10 constitute a welding start detector.

Reference numeral 12 denotes a switching circuit, which uses a switching element such as a thyristor or a transistor to connect the output of the auxiliary power supply 9 to the capacitor 3 according to the output of the amplifier 11. Other parts in FIG. 1 have the same functions as those of the conventional device shown in FIG. 5, and are given the same reference numerals, and detailed explanations thereof will be omitted.

In FIG. 1, the output of the welding current detector 10 is zero and the output of the amplifier 11 is also zero until the electrode 6 comes into contact with the workpiece 7 or an arc is generated between the two and current begins to flow. Therefore, the switching circuit 12 remains open. Therefore, even if the switching element control circuit 8 outputs signals sl and s2 between the electrode 6 and the workpiece 7 in response to the welding start command, only the output voltage of the DC power supply 1 is applied to the switching element 4a.

It appears as a voltage of polarity according to the conduction of 4b or 5a and 5b. Therefore, in this state, only the relatively low output voltage of the DC power supply 1 is applied to the electrode 6, so that the risk of electric shock is significantly reduced. Next, when the electrode 6 and the object to be welded 7 come into contact, a short circuit current flows through them due to the output of the DC power supply 1, and the contact portion is fused and turned into an arc by this short circuit current. Further, the short circuit current is detected by the detector 10, the output signal of the amplifier 11 is set to a noise level, the switching circuit 12 is closed, and the auxiliary DC power supply 9a is connected in parallel to the capacitor 3 through the resistor 9b. The capacitor 3 is thereby charged not only by the DC power supply 1 but also by the auxiliary DC power supply 9a. In this state, in order to reverse the polarity of the output current, the output signal of the switching element control circuit 8 interrupts the conducting switching element, and then, for example, a signal sl is applied so as to cause the previously interrupted switching element to conduct. OFF, then the signal s
When 2 is turned ON, the output current becomes zero once, and the arc disappears. As a result, the voltage drop across the resistor 9b is eliminated, the capacitor 3 is rapidly charged by the high output voltage of the auxiliary DC power supply 9a, and this high voltage then sends a conduction drive signal to the switching elements (5a, 5b) of opposite polarity. When (s2) is supplied, it is supplied between the electrode 6 and the workpiece 7 to re-ignite the arc. At this time, since the amplifier 11 has a slight smoothing function as mentioned above,
Even if the arc is cut off, the welding starting signal will not disappear and the switching circuit 12 will not open.

Also, at this time, an arc is occurring or a short circuit is occurring, so the electrode 6
Even if a high voltage is applied to the device, there is no possibility that the worker will touch it, and therefore there is no risk of electric shock.

Another embodiment is shown in FIG. In FIG. 2, the output of the amplifier 11 and the signal s1 (a drive signal that makes the reverse polarity switching elements 4a and 4b conductive) are connected so that the switching circuit 12 is closed only when the polarity is reversed (the polarity in which the electrode 6 side is at a positive potential). An AND gate 13 is provided so that it closes when both are supplied, and the rest of the structure is exactly the same as the embodiment shown in FIG. In the embodiment shown in the figure, the switching circuit is closed only when the welding current is flowing and the polarity is reversed, so that the capacitor 3 is charged to a high voltage at the beginning of the reverse polarity period, and this is charged to the electrodes through the switching elements 4a and 4b. will be supplied to

Therefore, the embodiment shown in FIG. 2 is suitable for arc welding (TIG arc welding) using a non-consumable electrode, in which re-ignition is easy even with a normal welding voltage when the polarity is positive, but difficult when the welding voltage is reversed.

FIG. 3 is a connection diagram showing yet another embodiment.

In the figure, 1 is a DC power supply, and a commercial AC power supply 101
The rectifier circuit 102 rectifies the voltage to make it direct current, and the inverter circuit 103 converts it to high-frequency alternating current.The transformer 104, which connects the center tap to the secondary wire, converts it to a voltage suitable for arc welding. A double-wave rectifier circuit 105 converts the output voltage into positive and negative direct current using the center tap as a common terminal. Here, the inverter circuit 103 has a reference signal setter 106 which determines the output current. Comparator 107. The comparator 107 compares the output If of the amplifier 11, which is composed of a pulse width modulation circuit 108 and amplifies and smoothes the output of the output current detector 10, and the output 1r of the reference signal setter 106, and generates a difference signal ( A drive signal with a pulse width determined by Ir-1f) is supplied from the pulse width modulation circuit 108 to the switching element of the inverter circuit 103, and the DC/
AC conversion is performed.

2a and 2b are actuators connected to the positive output terminal and negative output terminal of the DC power supply 1, and both reactors share an iron core as shown in the figure, and the current flowing through each winding causes the shared iron core to flow in the same direction. are closely coupled to produce a magnetic flux of 4 and 5 are reactors 2a,
2b are respectively connected in series, and the other ends thereof are connected in common and serve as an output terminal together with the center tap of the transformer 104, a common output terminal C1 of the DC power supply 1, and are connected to the electrode 6 and the workpiece 7. Ru.

8 is a switching transistor 4°5 control circuit; 9
1 is an auxiliary power supply circuit consisting of a resistor 9a and an auxiliary DC power supply 9b; 10 is an output current detector; 11 is an amplifier; 12 is a switching element such as a thyristor that constitutes a switching circuit;
Reference numeral 3 designates an AND circuit, which substantially corresponds to the portions with the same reference numerals in FIGS. 1 and 2, respectively.

Further, a surge absorption circuit in which capacitors 3a and 3b and diodes 14a and 14b are connected in series is connected between the reactor 2a and the transistor 4, between the reactor 2b and the transistor 5, and between the common terminal C. A resistor 15 is connected in parallel to the capacitor 3b of the surge absorption circuit on the positive polarity side, and a resistor 16 is connected in parallel to the diode 14b to form a discharge circuit and a reverse current path. On the other hand, a switching circuit 12 is connected in antiparallel to the diode 14a in the surge absorption circuit on the reverse polarity side, and an auxiliary power source 9 is connected in parallel to the capacitor 3a. Further, this switching circuit 12 is made conductive by the output signal of the AND circuit 13.

In the embodiment shown in the figure, the output current of the DC power supply 1 is determined by an inverter circuit 103 whose pulse width is controlled by the difference between the output current detection signal If and the reference signal 1r, and the output current of the inverter circuit 103 is , the negative double-wave rectified DC output is alternately turned 0N-O by the switching elements 4 and 5 whose energization order and ratio are determined by the control circuit 8.
F-controlled, the alternating current has a substantially rectangular wave shape due to close coupling with each other, and the action of the axles 2a and 2b, and is supplied to the welding load consisting of the electrode 6 and the object to be welded 7. The surge voltage generated during this polarity switching is absorbed through the capacitors 3a, 3b and the diodes 14a, 14b so as to suppress it to below the maximum rated voltage of the switching elements 4, 5.

On the other hand, the capacitor 3a is charged by the auxiliary DC power supply 9a of the auxiliary power supply circuit 9 and has a voltage higher than the output voltage of the DC power supply 1. The charging voltage of this capacitor 3a is obtained by amplifying the output of the output current detector 10.

When the S1 signal If) τ and the reverse polarity period signal d of the control circuit 8 are supplied together, the output of the AND circuit 13 becomes a high level signal, the switching circuit 12 is closed, and the electrode 6 is connected to the workpiece 7. A reverse polarity voltage is applied in the opposite direction to re-ignite the reverse polarity arc.

Further, in the embodiment shown in FIG. 3, during the conduction period of one switching element, for example, the switching element 5, the change in current is suppressed by the beam handle 2b and remains almost constant, and the current flowing through the reactor 2b is The corresponding electromagnetic energy is stored. This electromagnetic energy is immediately transferred to the reactor 2a when the switching element 5 is cut off and at the same time the switching cable 4 of the opposite polarity is made conductive.
It moves to the side and induces a high voltage in order to cause the same current value to flow in the circuit passing through the reactor 2a and the switching element 4. Therefore, the arc that has been interrupted by the interruption of the switching element 5 is immediately regenerated by the current in the opposite direction, that is, the current flowing from the object to be welded 7 toward the electrode 6.

In this way, in the embodiment of FIG. 3, the beam axle 2a,
The effect of 2b causes the voltage to rise steeply during polarity reversal, making it easier to re-ignite the arc.In addition, in the case of reverse polarity, where re-ignition of the arc is relatively difficult, when the output current is flowing, Since the high voltage of the auxiliary power supply circuit is supplied to promote the restriking of the arc, a welding machine equipped with an auxiliary arc restriking circuit that is more reliable and free from the risk of electric shock can be obtained.

In addition, in FIG. 3, in order to fully utilize the functions of the beam axles 2a and 2b, a switching element control circuit 8 is required.
The output signal s1. The switching element 4 outputs s2 alternately without any gap or with some overlap time.
．． It is desirable to control the conduction periods of 5 with substantially no gaps or with some overlapping time. By doing this, when switching the polarity, if a conduction signal is supplied to the other switching element in the early hours of the conduction period of one switching element, the output of the rectifier circuit 105 will be short-circuited at the switching elements 4 and 5; Due to the presence of the axles 2a, 2b, the current value hardly changes from the previous current value, while the arc immediately ends because it is short-circuited by the switching element 4.5. In this state, when the switching element that was conducting first is cut off, the short circuit between the electrode 6 and the workpiece 7 is eliminated, and the reactors 2a and 2b are driven to a high voltage to maintain the currents flowing through them. This causes the arc to regenerate through the switching element that later became conductive. As a result, the welding current has a substantially rectangular waveform, and from above the auxiliary power source 9 to be applied between the electrode and the workpiece when switching the polarity.
It is more effective to supply the voltage when the short circuit caused by the switching elements 4 and 5 is removed, that is, at the moment when the bipolar switching elements are conducting and the element that was conducting first is cut off. I understand that.

FIG. 4 is a connection diagram showing an embodiment in this case. In the figure, an AND circuit 13 differs from the embodiment in FIG. The output of the voltage detector 17 that generates the voltage is manually input. In the embodiment shown in the figure, a current flows at the end of the positive polarity period, and the switching circuit 12 becomes closed only when the cutoff switching element 5 is cut off and its terminal voltage rises. For this reason, the switching circuit 12 is closed at the moment when the arc should really be re-ignited when changing from positive polarity to reverse polarity, and the output of the auxiliary power source 9 is supplied between the electrode 6 and the workpiece 7. As a result, more reliable arc re-ignition can be achieved.

In FIG. 4, the reverse polarity period signal sl may also be supplied to the other two signals as a manual input to the AND circuit 13. Furthermore, in FIGS. 3 and 4, the charging of the capacitor 3a Another switch that is closed by the signal s2 may be connected in series to the auxiliary power supply circuit 9 so that the period of the opposite polarity, that is, the positive polarity period.

In this case, no current is wasted from the auxiliary power supply 9a during the reverse polarity period.

In the embodiments shown in FIGS. 3 and 4, a resistor may be connected in parallel to the capacitor 3a and the diode 14a, respectively, in the same way as the capacitor 3b and the diode 14b, and the capacitor 3b and the diode on the positive polarity side may be connected in parallel. An auxiliary power supply circuit 9 and a switching circuit 12 similar to those on the reverse polarity side may be connected in parallel to 14b to assist in re-ignition of the arc at the time of positive polarity.

Furthermore, in FIGS. 1 to 4, an auxiliary power source for restriking may be provided on the output side of each switching element, that is, between the switching element and the welding load.

<Effects of the Invention> As described above, in the arc welding machine of the present invention, the arc welding occurs only when the electrode is in contact with the workpiece to be welded or when the arc is substantially in the welding starting state. Since the output of the auxiliary power source for restriking is superimposed on the output of the main power circuit and supplied to the welding load, there is no risk of electric shock to the operator.

[Brief explanation of drawings]

Fig. 1 is a connection diagram showing an embodiment of the present invention, Figs. 2 to 4 are connection diagrams showing another embodiment of the invention, and Fig. 5 is a connection diagram showing an example of a conventional welding machine. . 1... DC power supply, 2.2a, 2b... Reactor, 3.3a, 3b-capacitor, 4, 4a, 4b, 5
, 5a, 5b... switching element (transistor)
, 6... Electrode, 7... Welded object, 8... Switching element control circuit, 9... Auxiliary power supply, 9a...
Auxiliary DC power supply, 9b...Resistor, 10...Output current detector, 12...Switching circuit, 13-A N D circuit, 14a, 14b-...Diode, 17...Voltage detector

Claims (1)

[Claims] 1. In an arc welding power source that switches the output of a DC power source between positive and reverse polarities using a switching element and supplies it to a welding load, the output of the DC power source is connected to the input side or the output side of the switching element at the time of polarity switching. An auxiliary power supply circuit for supplying high voltage for arc restriking, a welding start detector for detecting that current is actually flowing through the welding load, and the start detector detects the output of the auxiliary power supply circuit for welding. An AC arc welding machine comprising an opening/closing circuit that supplies a signal to the input side or the output side of the switching element only when a starting signal is output. 2. The opening/closing circuit is a circuit that supplies the output of the auxiliary power source to the input side or the output side of the switching element based on the AND of the activation signal of the activation detector and the reverse polarity period signal of the switching element. The AC arc welding machine according to item 1. 3. The auxiliary power supply circuit is a circuit having a relatively high voltage auxiliary DC power supply that charges a capacitor provided on the input side of the switching element through a resistor.
or the AC arc welding machine described in 2. 4. The switching element includes a surge absorption circuit in which a capacitor and a diode connected in series with respect to the output of the DC power supply are connected on the input side, and the auxiliary power supply circuit charges the capacitor through a resistor. 4. The AC arc welding machine according to claim 3, wherein the AC arc welding machine comprises an auxiliary DC power source, and the switching circuit is a switching element connected in antiparallel to the diode. 5. A DC power source in which two sets of DC power supplies are connected in series and has positive, zero, and negative output terminals, and a unidirectional switching element that is connected to the positive output terminal and the negative output terminal of the DC power source, respectively, in the forward direction. and the other end is commonly connected to serve as one output terminal for welding, the common connection point of the DC power source is used as the other output terminal for welding, and the switching element is controlled to conduct on and off alternately with substantially no gaps. a switching element control circuit for detecting the voltage of at least one terminal of the switching element and outputting a signal when the terminal voltage exceeds a certain value; and a voltage detector that detects the terminal voltage of at least one of the switching elements and outputs a signal when the terminal voltage exceeds a certain value; an auxiliary power supply circuit for supplying a high voltage for arc re-ignition at the time of polarity switching to the input side or output side of the switching element facing the voltage detector; an opening/closing circuit that supplies the output of the circuit to the input side or the output side of the switching element when the activation detector receives both the welding activation signal and the output of the terminal voltage detector of the switching element of the opposite polarity; AC arc welding machine equipped with. 6. A DC reactor is connected in series between each of the switching elements and the DC power supply, and each of the DC reactors is wound around a common iron core and conducts the switching elements connected in series. 6. The AC arc welder according to claim 5, further comprising a coil whose winding direction is determined by a polarity that produces magnetic flux in the same direction in a shared iron core. 7. The voltage detector is a voltage detector that detects the terminal voltage of a switching element that supplies a current in the direction (positive polarity) from the object to be welded to the electrode with respect to the welding load, and the auxiliary power source When both the output signal of the welding device and the welding start signal of the welding start detector are supplied, the direction from the electrode of the two sets of DC power supplies to the workpiece (reverse polarity)
The AC arc welder according to claim 5 or 6, wherein the AC arc welder is a power source that supplies a high voltage of the same polarity superimposed on the output of a DC power source that supplies a current of the same polarity. 8. The DC power source is a commercial AC power source that is once rectified into DC power, which is then converted to high-frequency AC power by an inverter circuit.
6. The AC arc welding machine according to claim 1, which is a power source that converts the voltage to a voltage suitable for arc welding by a transformer and rectifies it again by a rectifier circuit to obtain direct current. 9. The transformer is a transformer having a center tap in the secondary winding, and the rectifier circuit converts the secondary winding output of the transformer into a direct current having positive and negative polarities and a neutral point. 9. The AC circuit according to claim 8, wherein the switching element is two sets of switching elements connected in series in the forward direction to the positive and negative DC output terminals and having the other ends commonly connected. arc welding machine.