JPH0363461B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a power supply device for an arc welder that performs AC arc welding on aluminum or the like using a switching transistor.

(b) Prior Art As a conventional power supply device for an AC arc welding machine, a power supply device for an arc welding machine that once converts a commercial power source into a high frequency wave, then transforms it and shapes it into a rectangular wave has been put into practical use.

A circuit diagram of this power supply device for an arc welding machine is shown in FIG. As shown in FIG. 4, three-phase alternating current is rectified and smoothed by a rectifier circuit 41 and a smoothing capacitor 42, and then converted to a high frequency by high frequency switching by switching transistors 43, 44 and an output control circuit 45. Furthermore, the high frequency output is transformed into a transformer 50.
The voltage is transformed from several tens to a hundred and several tens of V, and the rectifier 46,4
7. The smoothing reactor 48 and smoothing capacitor 49 convert the current into direct current again. Thereafter, a reverse switching operation is performed by the switching transformers 51, 52, 53, and 54 and the low frequency control circuit 55 to obtain a highly accurate rectangular wave welding current. Incidentally, if one of the switching transformers 51, 54 or 52, 53 is kept on, a DC welding current can be supplied to the welding electrode 56 and the base material 57. In the figure, 58 is a high frequency oscillator for facilitating arc ignition at the start of operation when performing TIG welding or the like. Further, 59 is a current detector, and its detected value is fed back to the output control circuit 45 to perform constant current control of the output.

In the above power supply device for an arc welding machine, since voltage transformation and rectification can be performed at high frequencies, the transformer and reactor can be configured for high frequency use, making it possible to achieve miniaturization and low cost, as well as output based on the detected value of the current detector 59. Current control of the control circuit 45 can be performed accurately with a fast response speed. Also, the low frequency control circuit 55
Accordingly, AC arc welding can be performed by the reverse switching operation of the switching transistors, and DC arc welding can be performed by keeping either one of the switching transistors 51, 54 or 52, 53 on.

(c) Problems to be Solved by the Invention However, in the above power supply device for an arc welding machine, when the welding current during AC arc welding becomes 0 when the polarity changes, the arc becomes unstable. In particular, when the welding polarity is reversed from positive to reverse, there is a possibility that the base metal cannot sufficiently emit thermionic electrons and arc misfires occur frequently. Therefore, conventionally,
A high-frequency oscillator is constantly operated to stabilize the arc transition by applying a superimposed high-frequency voltage to the arc welding electrode even when changing polarity from positive to negative polarity, which may cause arc restriking failure. was. but,
Generating high frequencies generates noise in the welding machine power supply or other equipment, and if there is equipment using an IC or the like on the power supply side, there is a risk that the equipment will malfunction.

In view of the above drawbacks, an object of the present invention is to apply a restriking voltage to the arc voltage when the welding electrode changes polarity, especially when the arc voltage changes from positive polarity to reverse polarity. An object of the present invention is to provide a power supply device for an arc welding machine that facilitates stable AC arc welding without using a high-frequency oscillator.

(d) Means for Solving the Problems FIG. 1 is a block diagram showing the configuration of a power supply device for an arc welding machine according to the present invention.

As shown in FIG. 1, the power supply device for an arc welding machine of the present invention includes a first rectifier circuit 101 that rectifies an AC power source, a high frequency conversion circuit 102 that converts a DC voltage into a high frequency, and a high frequency converter circuit 102 that converts a DC voltage into a high frequency. A smoothing circuit 104 comprising a transformer 2 that transforms a voltage, a rectifier circuit 103 that rectifies the output of the transformer, a smoothing reactor and a smoothing capacitor that smooth the rectified output, and a smoothing output that alternately has a positive polarity and a reverse polarity. A switching circuit 105 for applying voltage to the base material and the welding electrode is provided, and a forward diode is connected between the smoothing reactor and the smoothing capacitor of the smoothing circuit 104, and a discharge circuit for discharging the charging voltage of the smoothing capacitor is connected in parallel to this diode. A DC power supply 33 whose output voltage is set higher than the smoothing output voltage and is connected in parallel to the smoothing capacitor.
, a pulse generating circuit 46 that generates a pulse of a constant width when the welding polarity is reversed from positive to reverse polarity by the switching circuit 105, and a pulse generating circuit 46 that generates a pulse of a constant width when the welding polarity is reversed from positive polarity to reverse polarity by the switching circuit 105; The present invention is characterized in that it is provided with a switch circuit 106 that applies voltage to the base material and the welding electrode via the welding electrode.

(e) Effect In the power supply device for an arc welding machine having the above configuration, the AC power source 1 is once rectified into DC by the rectifier circuit 101 of the diode 1, and then converted into a high frequency by the high frequency conversion circuit 102. Furthermore, after the high frequency voltage is transformed by the transformer 2, the rectifier circuit 103 and the smoothing circuit 104
Rectified and smoothed by . Further, when the current is applied alternately to the base material and the welding electrode in positive and reverse polarity in the switching circuit 105, AC arc welding is performed. During this AC arc welding, the pulse generating circuit 46 generates a pulse of a constant width when the welding polarity changes from positive to negative during alternation of the welding current. When this pulse is generated, the switch circuit 106 applies the DC power supply voltage to the load via the switching circuit. Since this applied voltage is sufficient for arc re-ignition, the arc between the arc welding electrodes flows continuously without breaking.

(f) Embodiment FIG. 2 is a circuit diagram of a power supply station for an arc welding machine which is an embodiment of the present invention.

The first rectifier circuit is composed of a full-wave rectifier circuit 9. The full-wave rectifier circuit 9 includes a smoothing capacitor 1
Series circuits 0a and 10b are connected in parallel.
The DC voltage smoothed by the smoothing capacitor is supplied to the high frequency conversion circuit.

The high frequency conversion circuit includes series-connected transistors 11 and 12 connected to the primary winding of the transformer 2, and a high frequency conversion circuit control section 13 that turns these transistors 11 and 12 on and off alternately. The primary winding of the transformer 2 is a transistor 11,
The transistors 11 and 12, the smoothing capacitors 10a and 10b, and the primary winding of the transformer constitute a half-bridge circuit.

The secondary winding of transformer 2 is provided with an intermediate tap. The intermediate tap is connected to the welding electrode 7 via a current detector 23 by a transistor 19 constituting a switching circuit, and is also connected to the base material 8 by a transistor 20.

A rectifier circuit composed of diodes 14 and 15 is connected to both terminals of the secondary winding. This rectified output is sent to a smoothing circuit.

The smoothing circuit is composed of a smoothing reactor 16 connected to a rectified output terminal, a diode 31, and a smoothing capacitor 17 in series, and the series circuit is as follows:
Output terminal of smoothing reactor 16 and current detector 23
Connected to the load side terminal of the

A switching circuit is connected to the output terminal of the smoothing circuit.

The opening/closing circuit includes a switching transistor 18,
19, 20, 21, and a switching transistor control section 22 that controls on/off of these transistors.

The switching transistor control unit 22 controls the positive output or the negative output of the smoothing circuit to the welding electrode 7 via the high frequency oscillator 24 by keeping either the transistors 18, 21 or the transistors 19, 20 in an on state during DC arc welding. and the base material 8. As a result, the welding electrode 7
A DC arc voltage is applied to the base metal 8 and the base metal 8. Further, during AC arc welding, the on state of transistors 18 and 21 and the on state of transistors 19 and 20 are switched alternately, and the positive output and negative output of the smoothing circuit are alternately supplied to the welding electrode 7 and the base material 8, respectively. . As a result, a low frequency AC arc voltage is applied to the welding electrode 7 and the base material 8. This frequency is determined by the volume 2 of the switching transistor control section 22.
Set in 2a.

Pulse generation circuit is monostable multivibrator 4
6, and when the smooth output is applied to the welding electrode 7 and the base metal 8 alternately with positive polarity and reverse polarity, respectively, by the above-mentioned switching circuit, the welding polarity is changed from positive polarity to negative polarity. Generates a pulse with a constant width when it reaches the peak. This pulse width is 0.5~1m
It is set to s.

A resistor 34 is connected in series to the DC power supply 33 and connected in parallel to a smoothing capacitor 32 of the smoothing circuit. The DC power supply 33 is a battery with a voltage higher than the smoothed output voltage.

The switch circuit consists of transistor 4 shown in Figure 1.
It is composed of a switching circuit consisting of 0, 42, and 44. Transistor 44 is connected in parallel to diode 31 of the smoothing circuit.

When the transistor 40 is in an off state, the transistor 44 is turned on by being supplied with a base current from the capacitor 32, and discharges the charge in the smoothing capacitor 32 to the load side. The transistor 42 is controlled by a monostable multivibrator 46, which is a pulse generation circuit, and is turned on when a pulse is generated, turning off the transistor 40.
That is, in normal times, the transistor 44 is
When a pulse is output from the monostable multivibrator 46, it turns on and discharges the charge in the smoothing capacitor 32 to the load side. The smoothing capacitor 32
is constantly charged by the battery 33, so when the transistor 44 is turned on, a charging voltage approximately equal to the battery voltage is immediately supplied to the load side. Moreover, since the charging voltage is higher than the smoothed output voltage, arc failure does not occur when the above-mentioned pulse is generated, that is, when the polarity is changed from the positive polarity output to the negative polarity output.

The charging potential of the smoothing capacitor 32 is determined by voltage dividing resistors 35 and 36 and a Zener diode 37.
and is constantly monitored by transistor 39. When the charging potential becomes too high, the Zener diode 37 becomes conductive and the transistor 39 is turned on. Since the transistor 39 is connected in parallel with the transistor 42, this transistor 3
When transistor 9 is turned on, transistor 40 is turned off and transistor 44 is turned on. That is, the electric charges accumulated in the smoothing capacitor 32 are discharged.
By providing such an overcharge protection circuit, it is possible to prevent overvoltage from being applied to the transistors 18 to 21 during polarity reversal from a positive output to a negative output.

Next, the operation of the switch circuit of the power supply device for an arc welding machine of this embodiment will be explained with reference to FIGS. 3A, B, C, D, and E.

Figure 3 A shows the welding load current during AC arc welding,
B in the figure shows the pulse voltage generated in the multivibrator, C in the figure shows the voltage across the smoothing capacitor 32, D in the figure shows the base signal of the transistor 39, and E in the figure shows the base signal of the transistor 34.

Transistors 18, 2 of the switching circuit shown in FIG.
When the on-state of the transistor 1 and the on-state of the transistors 19 and 20 are alternately switched, an arc voltage of positive polarity and reverse polarity is applied between the welding electrode 7 and the base material 8. This causes the welding current shown in FIG. 3A to flow. At time _t1 shown in FIG. 3A, transistors 19 and 20 are turned on and transistors 18 and 21 are turned off. At this time, the welding polarity changes from reverse polarity to positive polarity,
A welding current of positive polarity (base metal 8 is +, welding electrode 7 is -) begins to flow. As a result, a voltage is generated in the smoothing reactor in the direction of the arrow in FIG. Furthermore, Figure 3A
At time _t2 , transistors 19 and 20 are turned off, transistors 18 and 21 are turned on, and the welding polarity is reversed. During this polarity reversal, as mentioned above, the base material 8 cannot sufficiently emit thermionic electrons, so
The arc is likely to misfire. However, during a certain time period (about 100 μs) during polarity reversal, the welding electrode 7
Since the ionic state between the base material 8 and the base material 8 is maintained and the impedance is low, arc misfire can be prevented by applying a relatively high voltage.

On the other hand, at time _t2 in FIG. 3B, ie, when the welding electrode is switched from positive polarity to reverse polarity, the multivibrator 46 generates a pulse with a constant pulse width. When this pulse is generated, transistor 4
2 is turned on, and then the transistor 44 is turned on, and the charging voltage of the smoothing capacitor 32 is applied between the welding electrode 7 and the base material 8. Since the charging voltage of the smoothing capacitor 32 is higher than the smoothed output voltage appearing on the output side of the smoothing reactor 12, this high voltage is applied between the welding electrode 7 and the base metal 8, thereby re-igniting the arc. . That is, when the welding electrode is in a low impedance state when changing from positive polarity to negative polarity, the charging voltage of the smoothing capacitor is applied as the restriking voltage between the welding electrode 7 and the base material 8 via the switching circuit. The arc current can be maintained without arc failure.

By the way, when the welding current is a large current, the energy stored in the smoothing reactor 16 becomes correspondingly large, so that the charging potential of the smoothing capacitor 32 also becomes high. Due to this operation, when the voltage across the smoothing capacitor 32 exceeds the reference value (at time t ₃ ) as shown in FIG. 3C, the Zener diode 37 is energized, and the transistor A base voltage is applied to transistor 39, and transistor 39 is turned on. This reference value is based on the Zener voltage of the Zener diode 39 and the resistors 35 and 36.
is set by a voltage divider circuit. This turns off the transistor 40, turns on the transistor 44, and releases the charged voltage of the smoothing capacitor 32 to the load. That is, overcharging of the smoothing capacitor 32 is prevented.

As described above, according to this embodiment, when the welding polarity is reversed from positive polarity to reverse polarity by the multivibrator 46, which is a pulse generation circuit, during AC arc welding, a pulse of a constant width is applied to the switch circuit, and the pulse By applying the high voltage charged in the smoothing capacitor between the welding electrode and the base metal during the time when the arc is occurring, reliable restriking can be performed without causing the arc to misfire. Furthermore, since it is not necessary to constantly drive a high frequency oscillator as in the conventional case, it is possible to eliminate the influence of noise and the like.

(g) Effect of the invention As described above, the power supply device for an arc welding machine of the present invention is provided with a DC power supply having a voltage value higher than the smoothed output voltage, and furthermore, when the welding polarity is reversed from positive polarity to reverse polarity. In addition to providing a pulse generating means that generates a pulse with a constant pulse width, the charging voltage of the smoothing capacitor is applied to the base material and the welding electrode when the pulse is generated, so that when the welding polarity changes from positive to reverse polarity. However, the arc is re-ignited with certainty. Therefore, there is an effect that a stable welding current can be obtained without constantly driving a high frequency oscillator as in the conventional case.

Furthermore, since the high-frequency oscillator is not constantly driven, noise generation is prevented and there is an advantage that it does not adversely affect surrounding electronic equipment.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a power supply device for an arc welding machine according to the present invention. FIG. 2 is a circuit diagram of a power supply device for an arc welding machine which is an embodiment of the present invention. Figure 3 A, B, C, D, and E show the welding load current during AC arc welding of the power supply device for the arc welding machine, the pulse voltage generated in the multivibrator, the voltage across the smoothing capacitor 32, and the base of the transistor 39. FIG. 4 is a diagram showing a signal and a base signal of a transistor 44, respectively. FIG. 4 is a circuit diagram of a conventional power supply device for an arc welding machine. 1... Three-phase AC power supply, 2... Transformer, 7... Welding electrode, 8... Base material, 17... Diode, 33
...DC power supply, 46 ... Monostable multivibrator (pulse generation circuit), 101 ... First rectifier circuit, 102 ... High frequency conversion circuit, 104 ... Smoothing circuit, 105 ... Switching circuit, 106 ... Switch circuit.

Claims (1)

[Claims of Claims] 1. A first rectifier circuit that once converts an AC power supply into a DC voltage, a high frequency conversion circuit that converts the voltage converted into a DC voltage, a transformer that transforms the high frequency voltage, and a secondary winding of the transformer. A smoothing circuit consists of a smoothing reactor and a smoothing capacitor that smooth the rectified output of a rectifier circuit including diodes connected to each end of the wire, and the smoothed output is alternately connected to the base metal and welded with positive polarity and reverse polarity, respectively. In a power supply device for an arc welding machine having a switching circuit for applying voltage to an electrode, a forward diode is connected between the smoothing reactor and the smoothing capacitor, and a discharging resistor for discharging the charging voltage of the smoothing capacitor is connected in parallel to the diode. At the same time, the output voltage is set higher than the smoothed output voltage, and when the welding polarity is reversed from positive to reverse by the DC power supply connected in parallel to the smoothing capacitor and the switching circuit, For an arc welding machine, comprising: a pulse generating circuit that generates a pulse; and a switch circuit that applies the charging voltage of the smoothing capacitor to the base material and the welding electrode via the discharging resistor when the pulse is generated. power supply.