JPS61176474A - Short-circuit detection circuit - Google Patents

Abstract

PURPOSE:To make the short-circuit detection correct by using the output set value of welding power source as the reference signal for detecting short-circuit and by discriminating the short-circuit period and arc generated period based on the comparison between this set value and welding voltage. CONSTITUTION:The coefficient multiplier 13 to adjust the level between the output signal of a welding voltage detector 8 and the output signal of output setter 11 is set up. The short-circuit detection circuit is composed of the welding voltage detector 8, output voltage setter 11, coefficient multiplier 13 and comparator 10. The signal (er) which the output (ea) of the detector 8 and the output of the output setter 11 are adjusted on the level by the coefficient multiplier 13 is inputted into the comparator 0. The signal corresponding to the size relation of both signals is then outputted from the comparator 10 to a controlling circuit 12. Therefore when the welding conditions are changed, the reference signal for short-circuit detection varies as well and a correct short-circuit detection enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a short-circuit transitional arc welding machine that performs welding while alternating short-circuiting and arcing between a consumable electrode and a workpiece. The present invention relates to an improvement in a short-circuit detection circuit used to obtain a desired welding result by controlling the welding voltage, current, feeding speed of the consumable electrode, etc. to different values in the welding process.

Generally, in short-circuit transition arc welding, short-circuit and arc are regularly repeated, and in order to obtain the desired welding result, the time, welding current, welding voltage, etc. are controlled to appropriate values separately for the short-circuit period and the arc period. Therefore, it is important to accurately detect the short circuit period.

Conventional technology The above short circuit period can be detected by detecting the welding voltage and comparing it with a predetermined reference voltage, since the welding voltage generally changes quite clearly between arcing and short circuit. It was determined based on the comparison results.

FIG. 3 is a schematic configuration diagram showing an example of a short-circuit transition arc welding machine using such a conventional short-circuit detection circuit. In the figure, 1 is a power source, and a general commercial AC power source, a motor drive generator, a battery, etc. are used. 2 is a power conversion unit for converting the output of power source 1 into voltage, current, and characteristics suitable for welding, and obtains DC output using a combination of a transformer and a thyristor, a combination of an inverter and a rectifier circuit, etc. This is a known power conversion method. 3 is a DC reactor for obtaining the transient characteristics of the output current necessary for short-circuit transitional arc welding, 4a and 4b are output terminals, and 5 is a welding torch, which is sent toward the workpiece 6 by a feeding means (not shown). Welding power is supplied to the consumable electrode 7. 8
9 is a welding voltage detector that inputs the voltage between output terminals 4aa4b, 9 is a reference voltage setter that determines a voltage threshold for distinguishing between a short circuit and an arc, and 10 is the output of the welding voltage detector 8. This is a comparator that compares the output of the reference voltage setter 9 with the output of the output setter 11 and the power converter 2.
is supplied to the control circuit 12 of.

In the welding machine shown in the figure, a comparator 10 detects the voltage ea between output terminals 4a and 4b detected by a welding voltage detector 8.
It is compared with the output er of the reference voltage setter 9 at
When >er, it is the arc generation period, and e <g=e
At this time, it is determined that it is a short circuit occurrence period a - r , and the result of this determination is output to the control circuit 12 .

Therefore, in the example shown in the figure, welding voltage detector 8, reference voltage setting device 9, and comparator 10 constitute a short circuit detection circuit. The control circuit 12 determines a drive signal for the power converter 2 based on a signal obtained by modifying the output of the output setter 11 by the output of the comparator 10. As this control circuit, for example, the welding condition setting device 11 determines the short circuit time rate, that is, the proportion of the short circuit time in one cycle of repeated short circuits and arcs.
and adjusts the output voltage and output current of the power converter 2 so that the short-circuit time rate obtained by the output of the comparator 10 matches this set value (for example, the
6230) corresponds to this. Further, by controlling the feeding speed of the consumable electrode 7 by this control circuit, the ratio of each period of short circuit and arc can be changed to adjust the short circuit time rate (for example, Japanese Patent Publication No. 11289/1989).

The conventional short circuit detection circuit configured as described above has the following drawbacks. In other words, if the true welding voltage in short-circuit transition arc welding can be detected, the welding voltage during the short-circuit period will be sufficiently low and it will be easy to distinguish it from the arc period.
Even a circuit such as the conventional short circuit detection circuit described above, which makes a determination simply by comparing a predetermined reference voltage and a welding voltage, can be put into practical use. However, in order to detect the true welding voltage, it is necessary to detect the voltage close to the arc generation point. It is necessary to separately provide a dedicated cable for detection, which poses a major obstacle to operability.

For this reason, voltage signals are usually obtained from near the output terminal of the welding power source. For this reason, the waveform of the detected voltage takes on a different appearance depending on the magnitude of the output voltage and output current.

Figure 4 shows the detected voltage waveform when the output voltage is set to a relatively low value, and Figure 5 is a waveform diagram showing the detected voltage waveform when the output voltage is set to a relatively high value. The horizontal axis indicates time. In both figures, (a) shows the case where the detection is near the arc generation point, (b) shows the case where the detection is relatively far from the arc generation point, and Ta is the arc generation period and Ts
indicates the short circuit occurrence period. As shown in the waveform diagrams (a) in Figures 4 and 5, if the change in welding voltage is measured near the arc generation point, it will change depending on the set value of the welding voltage when an arc occurs, but when a short circuit occurs. This results in a low voltage 'that is almost unaffected by the magnitude of the output voltage setting value. For this reason, even if the reference voltage Cr for short circuit detection is set to a constant value, that is, a value E1 that is approximately halfway between the lowest output voltage setting value and the voltage at the time of short circuit occurrence, short circuits can be detected stably. can be detected.

However, when the welding voltage is detected at a location away from the arc generation point, a voltage drop due to a couple due to the welding current from the arc generation point to the welding voltage detection point is added to the welding voltage. Since this welding current is extremely large during a short circuit compared to when an arc occurs, the detected welding voltage will show a high value during a short circuit. Depending on the set value of the output voltage, the value can quickly reach a value corresponding to the welding voltage during the arc generation period when the output voltage is set to the lowest value. For this reason, if the reference voltage for detecting a short circuit is set to a substantially constant value El, a short circuit may not be detected at all depending on the set value of the output voltage.

In order to solve the drawbacks of the above-mentioned conventional detection circuit, the present invention has the following features:
The output setting value of the welding power source is used as a reference signal for detecting a short circuit, and this is compared with the welding voltage, and the short circuit period and the arc generation period are determined based on the magnitude relationship between the two.

Effect In the present invention, the reference voltage for short circuit detection changes in accordance with the output setting value of the welding power source, so the output setting is high, and therefore the current at the time of a short circuit is large and the detectable welding voltage is low. If the voltage is not low enough even during a short circuit, a high reference value is compared with the detected value, and if the output voltage setting is low and the detected voltage is low when an arc occurs, a commensurately low voltage is set as the standard. This value makes it possible to reliably discriminate between an arc period and a short circuit period no matter which output voltage is set.

Embodiment FIG. 1 shows a connection diagram of an embodiment of a short-circuit transition arc welding machine using the short-circuit detection circuit of the present invention. In the figure, numerals 1 to 8 and 10 to 12 indicate those having the same functions as the conventional example shown in FIG.

Reference numeral 13 denotes a coefficient multiplier, which adjusts the levels of the output signal of the welding voltage detector 8 and the output signal of the output setting device 11, and is provided as necessary. In the embodiment shown in the figure, a welding voltage detector 8, an output voltage setter 11, a coefficient unit 13, and a comparator 10 constitute a short circuit detection circuit.

In the embodiment shown in FIG.
The control circuit 12 is configured to receive the signal Cr whose level has been adjusted in step 3 and output a signal corresponding to the magnitude relationship between the two signals to the control circuit 12. The embodiment shown in FIG. 2 will be explained with reference to the waveform diagram in FIG.

In Figure 2, (a) shows that the output setting value is set to a low value eol.
(b) shows the situation when the output setting value is set to a high value of 602. Further, Ta and Tg in the figure indicate the arc generation period and the short circuit generation period, respectively, as in FIGS. 4 and 5.

Now, when the output of the output setting device 11 is a low value of eol, as shown in Fig. 2(a), the welding voltage at Ta is low when an arc occurs, but the current flowing at Ts at the time of a short circuit is also small, so the detection voltage at the time of a short circuit is also low. It is at a sufficiently low value.

Therefore, if the reference value er for short-circuit detection is set to keol (provided that it is a constant of O>k<1) with respect to the low setting value eot of the output setter, accurate short-circuit detection can be achieved. - When the setting value of the force output setting device 11 is as high as 602, the current that flows during a short circuit also becomes large, and therefore the detected voltage during the short circuit period T6 becomes a considerably high value as shown in FIG. 2(b). In this case, since the reference voltage for detecting a short circuit also has a high value of keo2, the occurrence of a short circuit can be reliably detected.

In addition, although the above description describes a welding power source in which the output voltage is set, a welding power source for performing short-circuit transitional arc welding has an output voltage current characteristic that changes as the output current increases rather than a nearly constant voltage characteristic. It is possible to use a method that limits the short-circuit current with an appropriate falling characteristic that causes the output voltage to drop slightly, or a method that has a nearly constant voltage characteristic during arcing and limits the short-circuit current to an appropriate waveform when a short circuit occurs. be. In these cases, an output setting device is used that sets the short circuit current, that is, the maximum output current. For such a welding power source, the output current setting value is used as the output setting signal, but the operation is the same. Further, the coefficient unit 13 may be provided between the welding voltage detector 8 and the comparator 10 instead of being provided between the output setting device 11 and the comparator 10. The coefficient multiplier 13 may be one that excludes the input signal from the input signal, or may be one that subtracts a constant voltage ΔC from the input signal. Furthermore, as described in the explanation of the conventional device shown in FIG. Any type of control, such as one that controls both the feeding speed and the feeding speed, can be applied.

Effects of the Invention As described above, in the present invention, the output signal of the output setting device or a signal corresponding thereto is used as a reference signal for detecting a short circuit and is compared with the welding voltage, so that the welding conditions are not changed. However, since the reference signal for short circuit detection also changes accordingly, accurate short circuit detection is always possible. Since the influence of the welding current is eliminated, the welding voltage can be detected at the output terminal of the welding power source, and there is no need to run the detection cable close to the arc generation point.
It has excellent operability and eliminates accidents such as wire breakage.

[Brief explanation of drawings]

FIG. 1 is a connection diagram showing an example of a short-circuit transition arc welding machine using the short-circuit detection circuit of the present invention, and FIGS. 2(a) and (b) are waveform diagrams for explaining the operation of the embodiment of FIG. (M)#(Excitation~1) This is a waveform diagram for explaining the operation of the conventional example shown in the lid 3. 2... Power converter section, 5... Welding torch, 6... Welded object , 7... Consumable electrode, 8... Welding voltage detector, 9... Reference voltage setting device, 10... Comparator, 11...
... Output setting device, 12... Control circuit, 13... Coefficient unit.゛Representative Patent Attorney Hiroshi Nakai volunteered to write the procedural amendment) March 4, 1985 Patent Application No. 17775 of 1985 2, Title of Invention Short Circuit Detection Circuit 3, Relationship with the Amended Person Case Patent Applicant 2-1-11 Tayo, Yodoyo-ku, Osaka (026) Osaka Transformer Co., Ltd. 4, Agent

Claims (1)

[Claims] 1. A short-circuit transition arc welding machine that performs welding by repeatedly creating a short circuit and an arc between a consumable electrode and a workpiece using a welding power source whose output is determined by an output setting device. The short circuit detection circuit used includes a welding voltage detection circuit and a comparison circuit that uses the output voltage of the output setting device as a reference signal and compares the output voltage of the welding voltage detection circuit with the reference signal to determine an arc generation period and a short circuit period. A short-circuit detection circuit used in a short-circuit transitional arc welding machine equipped with. 2. The short circuit detection circuit according to claim 1, wherein the welding voltage detection circuit is a circuit that detects the voltage at the output terminal of the welding power source or a portion near the output terminal.