JPH0321820Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an AC arc welding machine using constant current feedback control, and more specifically to an AC arc welding machine that reduces excessive current flowing at the time of arc start and stabilizes the arc start. It is related to.

Figure 1 is a circuit diagram of a conventional AC TIG arc welding machine of this type, in which 1 is a reference voltage generator, 2 is a
is an operational amplifier, 3 is a time constant circuit (delay element using a capacitor and a resistor circuit) provided in the feedback circuit of the operational amplifier 2, 4 is an output polarity width control circuit provided in the output section of the operational amplifier 2, and 5 is provided in the output section. 6 is an output current control circuit consisting of a thyristor element, 7 is a consumable electrode, 8 is a base material, 9 is a base material 8
This is an output current detector inserted between the output terminal and one input terminal of the operational amplifier 2, and performs feedback control of the welding current.

According to the circuit configuration, when the welding power source switch (not shown) is operated, the AC power source (also not shown) is connected to the first rectifier circuit, the transformer, the second rectifier circuit, and further to the reactor, as well as to the reactor shown in FIG. A pulse voltage is applied to the consumable electrode 7 via the output polarity width control circuit 4, the phase shifter 5, and the output current control circuit 6,
An arc is generated between the base material 8 and the base material 8. At this time, after comparing and amplifying the detection signal obtained from the output current detector 9 and the reference signal obtained from the reference voltage generator 1, the output set by the output polarity width control circuit 4 is transmitted via the phase shifter 5. The output current control circuit 6 is controlled. When an AC arc welding machine controlled in this manner is started with the output polarity unbalanced as shown in the waveform diagram of FIG. 2, a hunting phenomenon occurs and good welding cannot be obtained. Also,
The welding machine is equipped with a smoothing reactor and a large time delay element in the feedback circuit to stabilize the control system.
Efforts are being made to stabilize the system and prevent hunting.

However, although the system can be stabilized by including a large time delay element, the feedback response at startup is slow, so that an excessive rush current flows at arc startup, as shown in the characteristic diagram of FIG. The time during which this rush current flows is determined by the time constant circuit 3, which is a delay element shown in the circuit of FIG. 1, and is approximately several 100 ms. When such an excessive current flows, not only is the electrode damaged and worn out, but also
Good welding cannot be expected. Further, when a low current is used to suppress the welding, the welded material burns through because the welding is not completed completely, and good welding results cannot be expected.

SUMMARY OF THE INVENTION An object of the present invention is to provide an AC arc welding machine that eliminates the drawbacks of the prior art, reduces excessive current during arc startup, and provides a good arc start.

The feature of this invention is that the constant current control feedback circuit is equipped with a response delay time element dedicated to high speed and low speed, as well as an amplifier circuit, so that the high speed side and the low speed side can be automatically switched according to the detected output current value. The aim is to stabilize the system at arc start and reduce excessive current.

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIGS. 4 to 6. FIG. 4 shows a specific circuit configuration thereof, and components having the same reference numerals as those in FIG. 1 have the same functions. In FIG. 4, two amplifiers 2a and 2b are provided at the output section of the reference voltage generator 1, and a time constant circuit 3 serving as a delay element is connected to the two amplifiers 2a and 2b.
a and 3b are provided. Of these, the amplifier 2a and time constant circuit 3a are activated during low-speed response, and the amplifier 2b and time constant circuit 3b are activated during high-speed response. 10 is a switch for switching between the low-speed response side and the high-speed response side. Switching of the switch 10 is controlled via a timing circuit 11 whose activation is controlled by the output signal of the output current detector 9.

According to the same circuit configuration, when the arc is started as described above, the current is detected by the output current detector 9, and the difference between the detected current (signal) and the signal from the reference voltage generator 1 is detected. Slow response amplifier 2
a and the high-speed response amplifier 3a, the output of which controls the output current control circuit 6 via the switch 10, the output polarity width control circuit 4' and the phase shifter 5, and the output of the output current detector 9. The timing circuit 11 is activated by the signal, and switching control is performed after a predetermined timing has been established.

Now, in a welding machine having a feedback circuit as shown in FIG. 4, when starting an arc, the output polarity width is set to the same positive and negative states as shown in the waveform diagram of FIG. 5. At this time, the amplifier 2b on the high-speed response side is selected and set by the switch 10.

Therefore, when an arc start is performed, the output signal of the output current detector 9 causes the timing circuit 11 to
is activated, and after a predetermined delay time (approximately 0.3 sec) has elapsed, the switch 10 is switched by a signal output from the amplifier 2b on the high-speed response side to the amplifier 2a on the low-speed response side.
Switch to connect. Next, after the aforementioned predetermined delay time (approximately 0.3 sec) has elapsed, a timing signal output from the timing circuit 11 with a further delay of approximately 0.1 sec changes the output polarity width to a preset positive/negative ratio (for example, (see Figure 2).
As a result, when the arc is started, the response is fast, the output is in a balanced state, and a stable arc start as shown in FIG. 6 without excessive current or hunting phenomenon can be obtained.

As is clear from the above embodiments, according to the present invention, a delay element dedicated to high speed and low speed is provided to reduce the excessive current that is switched and controlled at the time of arc start, and the output polarity width is switched. Therefore, it has the advantage and effect that excessive current at the time of arc start can be reduced and stable arc start without hunting phenomenon can be obtained.

[Brief explanation of drawings]

Figure 1 is a schematic circuit configuration diagram of a conventional AC TIG arc welding machine, Figures 2 and 3 are output waveform diagrams to explain the circuit operation of Figure 1, and Figure 4 is a diagram of a conventional AC TIG arc welding machine. A schematic circuit configuration diagram of an AC TIG arc welding machine showing an embodiment, and FIGS. 5 and 6 are output waveform diagrams for explaining the circuit operation of FIG. 4. 1...Reference voltage generator, 2a, 2b...Amplifier, 3a, 3b...Time constant circuit, 4, 4'...Output polarity width controller, 5...Phase shifter, 6...Output current control circuit , 7... Electrode, 8... Base material, 9... Output current detector, 10... Switch, 11... Timing circuit.

Claims (1)

[Scope of utility model registration request] A constant current feedback control circuit is provided in the power supply circuit between the consumable electrode and the base material, and a detection signal obtained from an output current detector forming the constant current feedback control circuit and a reference signal obtained from a reference voltage generator are provided. In an AC TIG arc welding machine, the AC TIG arc welding machine includes an amplifier circuit that amplifies the difference between Two types of amplifier circuits are provided as amplifier circuits, one with a delay element for low-speed response and one for high-speed response, and a switch is provided to select and switch between the two types of amplifier circuits, as well as an output current detection signal when an arc occurs. An AC arc welding machine characterized by comprising a timing circuit that performs switching control of the switching device and switching control of the output polarity width of the output polarity width control circuit.