JPH0580310B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is applicable to short-circuit transitional arc welding machines that perform 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 short circuit period is detected by detecting the welding voltage and comparing the detected voltage with a predetermined reference voltage, since the welding voltage generally changes quite clearly between arcing and short circuit. It was determined by

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 is output terminal 4
9 is a reference voltage setter that determines the voltage threshold for distinguishing between a short circuit and an arc, and 10 is the output of the welding voltage detector 8 and the reference. This is a comparator that compares the output of the voltage setter 9 with the output of the output setter 11, and is supplied to the control circuit 12 of the power converter 2 together with the output of the output setter 11.

In the welding machine shown in the figure, the voltage e a between the output terminals 4a and 4b detected by the welding voltage detector 8 _is
is compared with the output e _r of the reference voltage setter 9 in the comparator 10, and when e _a > e _r , it is determined that it is an arc generation period, and when e _a ≦ e _r , it is determined that it is a short circuit generation period. The determination result is output to the control circuit 12. Therefore, in the example shown in the figure, the welding voltage detector 8, reference voltage setter 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, Japanese Patent Publication No. 51-36230) is equivalent. Furthermore, by controlling the feeding speed of the consumable electrode 7 by this control circuit, it is possible to adjust the short circuit time rate by changing the ratio of each period between short circuit and arc (for example, Japanese Patent Publication No. 52-11289). .

Problems to be Solved by the Invention 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. A method that discriminates by comparing a reference voltage and a welding voltage will also be practical. 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 connect 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 indicates the case where the detection is near the arc occurrence point, b indicates the case where the detection is relatively far from the arc occurrence point, Ta indicates the arc occurrence period, and Ts indicates the short circuit occurrence period. ing. Each a in Figures 4 and 5
As shown in the waveform diagram, if the change in welding voltage is measured near the point where the arc occurs, it will change depending on the set value of the welding voltage when an arc occurs, but when there is a short circuit, it will hardly affect the magnitude of the set value of the output voltage. The voltage will be low and will not be affected. For this reason, setting the reference voltage e _r for short circuit detection to a constant value, that is, a value E ₁ that is approximately halfway between the lowest set value of the output voltage and the voltage at the time of short circuit occurrence, will ensure sufficient stability. Short circuits can be detected. However, when the welding voltage is detected at a location away from the arc generation point, a voltage drop due to the welding current caused by a cable 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 is set to a high value even when a short circuit occurs due to the voltage drop in the cable caused by this large current. Sometimes the short circuit current also takes on a large value, so it shows a considerably high value as shown in period Ts in FIG. 5b. Depending on the set value of the output voltage, this value can 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 short circuit detection is set to an approximately constant value,
If E is set to ₁ , a short circuit may not be detected at all depending on the set value of the output voltage.

Means for Solving the Problems In order to solve the above drawbacks of the conventional detection circuit, the present invention uses the output setting value of the welding power source as a reference signal for detecting a short circuit, and compares this with the welding voltage. However, 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 higher reference value is compared with the detected value, and if the output voltage is set low and the detected voltage is low when an arc occurs, a commensurately low voltage is set as the reference value. Therefore, it is 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. 1, the output e _a of the welding voltage detector 8 and the signal e _r obtained by level-adjusting the output of the output setter 11 by the coefficient unit 13 are inputted to the comparator 10, and the output of the welding voltage detector 8 is inputted to the comparator 10. It is configured to output a signal corresponding to the magnitude relationship to the control circuit 12. The embodiment shown in FIG. 2 will be explained with reference to the waveform diagram in FIG. Second
In the figure, a shows the situation when the output setting value is set to a low value e ₀₁ , and b shows the situation when the output setting value is set to a high value e ₀₂ . Also, Ta in the figure
and Ts 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 _e01 , as shown in Figure 2a, the welding voltage at Ta is low when an arc occurs, but the current flowing through _T6 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, the reference value e _r for short circuit detection is set as ke ₀₁ ( _where 0<k<1
Short circuits can be detected accurately if the constant is set to . On the other hand, when the setting value of the output setting device 11 is high as e ₀₂ , the current that flows during a short circuit also increases, and therefore the detection voltage during the short circuit period Ts becomes a considerably high value as shown in Figure 2b, but in this case Since the reference voltage for detecting a short circuit is also a high value of ke ₀₂ , the occurrence of a short circuit can be reliably detected.

In the above, we have described a welding power source that sets the output voltage, but as a welding power source for short-circuit transitional arc welding, the output voltage current characteristics are set to increase the output current compared to those with approximately constant voltage characteristics. Therefore, a method is used that limits the short-circuit current as 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. Sometimes. 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 1 and the comparator 10. The coefficient multiplier 13 may be one that multiplies the input signal by k, or may be one that subtracts a constant voltage Δe 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. In addition, 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, which improves operability and prevents accidents such as disconnection. There will be no more outbreaks.

[Brief explanation of the drawing]

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, Fig. 2 a and b are waveform diagrams for explaining the operation of the embodiment of Fig. 1, and Fig. 3 The figure is a connection diagram showing an example of a conventional welding machine using a conventional short circuit detection circuit, and Figures 4a and b and Figures 5a and b are waveform diagrams for explaining the operation of the conventional example in Figure 3. It is. 2... Power conversion unit, 5... Welding torch, 6...
Object to be welded, 7...Consumable electrode, 8...Welding voltage detector, 9...Reference voltage setting device, 10...Comparator,
11... Output setting device, 12... Control circuit, 13...
...Coefficient unit.

Claims (1)

[Claims] 1. Used in a short-circuit transfer 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 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.