JPS635876A - Arc welding machine - Google Patents

Abstract

PURPOSE:To discriminate an arc state from a short-circuited state at the time of welding regardless of inductance of a wiring cable between a welding power source and a torch by discriminating whether or not a ratio of a peak value of the positive voltage induced at the time of accumulating the energy of a reactor for smoothing an output power source to an absolute value of a peak value of the negative voltage induced at the time of giving off the energy is more than a prescribed value. CONSTITUTION:The positive voltage induced at the time of accumulating the energy of the reactor 27 for smoothing an output electric current is inputted to a circuit 32 via a diode 31 and the peak value VP of the positive voltage outputted from the circuit 32 is added to a comparator 36 as it is. On the other hand, the negative voltage induced at the time of giving off the accumulated energy of the reactor 27 is inputted to a circuit 34 via a diode 33 and the peak value VN of the negative voltage outputted from the circuit 34 is inversed by an inversing amplifier 35 and amplified and added to the comparator 36. Then, when a ratio of VP/VN to be a discriminating reference of arc/short-circuit is more than the prescribed value, the output of a H level which is a detected signal of the short-circuited state is produced on the comparator 36 and when the ratio of VP/VN is less than the prescribed value, the output of a L level which is the detected signal of the arc state is produced on the comparator 36.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an arc welding machine, and more particularly to an arc/short circuit detection device in an arc welding machine using an inverter-controlled welding power source whose output is controlled by a high-frequency inverter.

[Conventional technology]

Arc welding machines are equipped with an arc/short-circuit detection device that can distinguish between arc conditions and short-circuit conditions during welding, in order to perform current control at touch start and current control during the arc period and short circuit period in short-circuit arc welding. It may be necessary.

Section 3 provides an overview of the arc/short circuit detection device in an arc welding machine using a conventional welding power source with thyristor phase control at commercial frequency (hereinafter referred to as thyristor-controlled welding power source).
The operation sequence is shown in FIG.

In FIG. 3, a thyristor-controlled welding power source 1 includes a DC rectifier power source 4 consisting of a transformer 2 and a thyristor rectifier circuit 3.
It has an output current smoothing reactor 5, an AC input terminal 6, and a DC output terminal 7, and its output is supplied to a welding torch 9 via a wiring cable 8, and a welding arc 11 is generated between it and the base metal 10. let

Reference numeral 12 denotes a control circuit that performs thyristor phase control to control the output of the welding power source 1. The arc/short end detection device 13 is
A reference voltage generator 14 that sets a threshold level for arc/short circuit detection, and a comparator 15 that compares the output voltage Eout of the welding power source 1 output from the DC rectifier power source 4 through the output current smoothing reactor 5 with a reference voltage. and the output voltage E. When ut is above the reference voltage, an arc state detection signal u Hn is output, and when it is below the reference voltage, a short circuit state detection signal II L IF is output.

[Problem that the invention seeks to solve]

- In general, in an arc welding machine using a thyristor-controlled welding power source, in order to remove ripples at the commercial frequency, the inductance L0 of the output current smoothing reactor 5 is set to 250 to 350 μH.
On the - side, welding power source 1 and welding torch 9
The inductance LQ of the wiring cable 8 connecting the
Since it is about 5 μH/m (50 μH if the cable length is 10 m), which is smaller than the inductance L0 of the output power smoothing reactor 5, the induced voltage due to the inductance L of the wiring cable 8 is ignored when detecting arcs/short circuits. I was able to do that. That is, the output voltage E of the welding power source 1. u
Since the difference between t and the welding arc voltage vayc was small, the arc/short circuit could be detected without any problem by comparing the output voltage Eout with the reference voltage as described above.

However, in recent arc welding machines that use inverter-controlled welding power sources, the inverter operates in a high frequency range (for example, 20kHz).
z), the transformer and the output current smoothing reactor are made smaller and lighter, and the inductance L0 of the output current smoothing reactor used therein is 1710 times smaller than that of the thyristor-controlled welding power source. below(
(approximately 10 μH). Along with this, the induced voltage due to the inductance L of the wiring cable becomes so large that it cannot be ignored compared to the induced voltage due to the inductance L0 of the output current smoothing reactor built into the welding power source, and as a result, the output voltage Eout of the welding power source The difference from the welding arc voltage V a r c increases.

And if the inductance L varies depending on the cable length and the state in which the cable is placed, the output voltage E. ut will also change significantly. Therefore, when the arc/short circuit detection device according to the prior art is used in an arc welder having an inverter-controlled welding power source, it often malfunctions.
There was a problem that stable arc/short circuit detection was not possible.

Therefore, an object of the present invention is to provide an arc welding machine equipped with a highly reliable arc/short circuit detection device that can distinguish between an arc state and a short circuit state during welding, regardless of the inductance of the wiring cable between the welding power source and the torch. Our goal is to provide the following.

[Means for solving problems]

In order to achieve the above object, the present invention provides a first means for maintaining the peak value of the positive voltage induced when energy is stored in an output current smoothing reactor provided in an inverter-controlled welding power source, and a first means for maintaining the peak value of the positive voltage induced when the reactor releases the stored energy. a second means for holding the peak value of the negative voltage; and a third means for determining whether the ratio of the absolute values of the outputs of the first means and the second means is equal to or greater than a predetermined value, The present invention is characterized by comprising an arc/short circuit detection device which uses the output of the third means as a detection signal for an arc state and a short circuit state during welding.

[Effect]

Next, the operating principle of the arc/short circuit detection device according to the present invention will be described.

Figure 2 is an explanatory diagram of its operation, showing the output voltage waveform of the inverter-controlled DC rectifier power supply (Fig. 1, 21) and the output current smoothing reactor that smoothes the output current of the DC rectifier power supply in an arc state and a short circuit state. The waveform of the induced voltage is shown.

The output voltage waveform of the DC rectification power supply obtained by full-wave rectification of the AC output of the high frequency inverter whose pulse width is controlled becomes an intermittent waveform as shown by vo in FIG. During the period when the output voltage v0 is generated, energy is accumulated in the output current smoothing reactor, and at this time, an induced voltage v in the opposite direction to the output voltage v0 is generated in the reactor. If the direction of this induced voltage is positive, a negative induced voltage Vi will be generated in the output current smoothing reactor during a period when the output voltage v0 is zero and the energy stored in the output current smoothing reactor is released.

Similarly, the inductance L of the wiring cable connecting the welding power source and welding torch also has an output voltage V.

An induced voltage in the same direction as the induced voltage due to the inductance L0 of the output current smoothing reactor is generated during the period when the output voltage v0 is zero, and during the period when the output voltage v0 is zero, and during the period when the output voltage vo is generated, the DC rectification Power supply output voltage v0
The value obtained by subtracting the induced voltage due to the inductance L0 and the voltage from the inductance L0 is approximately equal to the welding arc voltage V a r c , and during the period when the output voltage v0 is zero, the inductance L.

The sum of the induced voltages due to and is the welding arc voltage V a
It becomes almost equal to rc.

Therefore, the peak value Vp of the positive voltage induced during energy storage in the output current smoothing reactor and the peak value VN of the negative voltage induced during the release of stored energy are calculated by the following equation (1
), (2).

Vp-r(Vo Vayc) X Lo/(Lo+
Li) (1) VN#Varc X Lo/ (L
o+L i) (2) Here, Vo
is the no-load output voltage of the DC rectified power supply.

From the above formulas (1) and (2), the ratio of VP/VN is Vp
/ Vs”= (Vo-Vayc) / Varc
It is expressed as (3).

The ratio of VP/VN varies depending on whether the electrode and base material are in an arc state or a short circuit state. For example, if the value of vo is 60V
, if the value of VarC in the arc state is 20V and the value of Vare in the short circuit state is 8V, then in the arc state, Vp/VN"=2.0 - in the short circuit state, Vp/VN: 6.5 Therefore, in this case, the predetermined value of VP/VN, which is the criterion for arc/short circuit, is set to 4, and the absolute value of each of the output Vp of the first means and the output VN of the second means is When the value ratio is Vp/VN≧4, a short circuit state detection signal is output from the third means, and VP
When /VN<4, an arc/short circuit can be detected by outputting an arc state detection signal from the third means.

From equation (3), the ratio of VP/VN is related only to the welding arc voltage and the no-load output voltage of the DC rectifier power supply, and is unrelated to the output current smoothing reactor and the inductance LO + Lm of the wiring cable. The arc/short circuit detection device using this method does not malfunction due to the induced voltage of the inductance of the wiring cable.

〔Example〕

FIG. 1 is a circuit block diagram showing one embodiment of the present invention.

The inverter-controlled welding power source 20 includes an inverter-controlled DC rectifying power source 21 and an output current smoothing reactor 27 that smooths the output current. As is well known, the DC rectified power supply 21 controlled by an inverter has an AC input terminal 2.
2, and a diode rectifier circuit 23 that converts the commercial frequency AC input supplied to DC into DC.

It consists of a high-frequency inverter 24 that converts the DC output into high-frequency AC, a transformer 25 that steps down the inverter output, and a diode rectifier circuit 26 that rectifies the secondary output of the transformer. It passes through the smoothing reactor 27, is supplied to the welding torch 9 via the wiring cable 8 connected to the DC output terminal 28, and is supplied to the base material 10.
A welding arc 11 is generated between the two. DC rectifier power supply 2
1 output control is performed by pulse width control of the high frequency inverter 24 by the control circuit 29. Since the output voltage v0 of the DC rectifier power supply 21 has an intermittent waveform as shown in FIG. 2, the output current smoothing reactor 27 repeatedly stores energy and releases the stored energy. Positive induced voltage Vi toward the left
When the stored energy is released, a negative induced voltage Vu is generated from the left to the right in FIG. As shown in FIG. 1, the right end of the output current smoothing reactor 27 is grounded, and the positive voltage and negative voltage are taken out from the left end and input to the arc/short circuit detection device 30 according to the present invention. In this example,
The arc/short circuit detection device @30 includes a diode 31 and a peak hold circuit 32 as a first means, a diode 33 and a peak hold circuit 34 as a second means, and an inverting amplifier 35 and a comparator 36 as a third means. It consists of

This device operates as follows.

The positive voltage induced during energy storage in the output current smoothing reactor 27 is input to the peak hold circuit 32 through the diode 31, and the peak value Vp of the positive voltage output from the peak hold circuit 32 is directly input to the non-conducting voltage of the comparator 36. Applied to the inverting input terminal.

- On the other hand, the negative voltage induced when the output current smoothing reactor 27 releases the stored energy is input to the peak hold circuit 34 through the diode 33, and the peak value VN of the negative voltage output from the peak hold circuit 34 is controlled by the inverting amplifier. The polarity of the signal is inverted at 35, amplified, and applied to an inverting input terminal of a comparator 36. Here, the amplification factor of the 1-inverting amplifier 35 is set to the same value as the predetermined value of VP/VN, which is a criterion for arc/short circuit.

By doing this, when the ratio of VP/VN is equal to or higher than a predetermined value, the comparator 36 receives a short-circuit detection signal ``H''.
When a level output is generated and the ratio of VP/VN is less than a predetermined value, the arc state detection signal LL
An output of L I+ level is generated. As mentioned above, V
The ratio of P/VN is unrelated to the output current smoothing reactor 27 and the inductance LO+L11 of the distribution cable 8. Therefore, if this arc/short circuit detection device 30 is used, arcs/short circuits will be detected regardless of the inductance of the distribution cable 8. It is possible to detect The output signal of the comparator 36 is input to the control circuit 29, and is used for current control during touch start, current control during the arc period and short circuit period in short arc welding, etc., as described at the beginning of the specification.

〔Effect of the invention〕

According to the present invention, it is possible to detect arcs/short circuits during welding regardless of the inductance of the wiring cable between the welding power source and the torch. Even in welding machines, the arc/short circuit detection device does not operate due to the influence of disturbances such as changes in cable length, and therefore the output of the welding power source is controlled based on the output signal of this arc/short circuit detection device. This allows for stable welding.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram showing one embodiment of the present invention, and FIG.
The figure is an explanatory diagram showing the output voltage waveform of a DC rectified power supply controlled by an inverter and the induced voltage waveform of the output current smoothing reactor. Figure 3 is a circuit block diagram of a conventional arc/short circuit detection device, and Figure 4 is its FIG. 3 is an operation sequence diagram. 20: Inverter controlled welding power source 24: High frequency inverter 27: Output current smoothing reactor 30: Arc/short circuit detection device 31. 32: First means (31: diode, 32:
33. 34: Second means (33: diode, 34: peak hold circuit) 35. 36: Third means (35: inverting amplifier, 36: comparator) Patent attorney Junnosuke Nakamura 8 :a;e 稗Y-fu5L 23:Da'4t
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Claims (1)

[Claims] 1. In an arc welding machine equipped with an inverter-controlled welding power source whose output is controlled by a high-frequency inverter, a first a second means for holding the peak value of the negative voltage induced when the stored energy of the reactor is released; and whether the ratio of the absolute values of the outputs of the first means and the second means is equal to or greater than a predetermined value. an arc welding machine, comprising: a third means for determining an arc welding machine; and an arc/short circuit detection device that uses the output of the third means as a detection signal for an arc state and a short circuit state during welding.