JPH0349808Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an AC arc welding machine for TIG welding that has constant current characteristics through feedback control.

[Background of the idea]

A conventional example of this type of AC arc welding machine is shown in FIG. In this conventional example, when an arc occurs, an output current flowing from a welding transformer 10 through an output current control section 11 and a reactor 12 between an electrode 13 and a base metal 14 is detected by an output current detector 8, and the detection signal is and the reference signal given from the reference voltage generator 1 is amplified by an amplifier 2 having a response time delay element 3, and the output of the amplifier is converted into a positive half wave of the welding machine output current by an output polarity width controller 6. By converting the control signal into a control signal corresponding to the output polarity width of the reverse polarity half wave and inputting it to the phase shift circuit 7, the output current control section 11 consisting of a control rectifier is controlled in phase.

In an AC arc welding machine equipped with such a feedback circuit that performs constant current control, during TIG welding, the output polarity width of positive half wave and reverse polarity half wave is shown in Figure 8.
When starting with t _S and t _R unbalanced, hunting (oscillation) in the control system is likely to occur. In addition, since the welding machine main circuit has a delay element such as a reactor 12, a response time advance element 3 with a large time constant is inserted in the feedback circuit to stabilize the control system and prevent hunting. .

However, when the response time advance element 3 with a large time constant is inserted, although the control system is stabilized, the feedback response at startup becomes slow, so that an excessive current (rush current) flows as shown in FIG.

The time during which this excessive current flows is determined by the time constant of the delay element 3, and is approximately several hundred milliseconds. If such an overcurrent flows, the electrode 13 will be severely damaged and worn out, and the object to be welded will likely burn through when welding thin plates.

[Purpose of invention]

An object of the present invention is to provide an AC arc welding machine for TIG welding that suppresses excessive current at startup due to a delay in feedback response and enables stable arc starting.

[Summary of the idea]

The present invention includes an amplifier that amplifies the difference between the detection signal of the output current detector and the reference signal from the reference voltage generator, and the output of the amplifier is used to output a positive half-wave and a reverse half-wave of the welding machine output current. An alternating current that is equipped with a feedback circuit that includes an output polarity width controller that converts the control signal into a control signal corresponding to the polarity width, and a phase shift circuit that provides an ignition signal to an output current control section consisting of a control rectifier based on this control signal. In the arc welding machine, the feedback circuit is provided with a response time delay element, a response time advance element, and a response time switch for turning on and off the response time advance element, and the output polarity width controller is provided with an output polarity width. A switching means is provided, and the response time switching device and the output polarity width switching means are switched by a time circuit inputting the output current detection signal, thereby inserting the response time advance element into the feedback circuit, and switching the response time advance element into the feedback circuit. The welding machine is started with the output polarity width of the reverse polarity half wave being the same as that of the reverse polarity half wave, and after a predetermined period of time has elapsed since the arc is generated, the response time advance element is disconnected from the feedback circuit, and the output polarity width is set to the same value as in the steady state. This feature is characterized in that the width can be switched to a set width.

[Example of idea]

An embodiment of the present invention will be described below with reference to FIGS. 1 to 5.

In FIG. 1, the feedback circuit includes a reference voltage generator 1, an amplifier 2 having a response time delay element 3 such as a CR delay circuit, a response time advance element 4 such as a differentiating circuit, and a response time advance element placed before the amplifier 2. It consists of a response time switch 5 that can be inserted or disconnected, an output polarity width controller 6, a phase shift circuit 7, and an output current detector 8. For example, as shown in FIG. 2, the output polarity width controller 6 has two resistors 63 and 64 connected in parallel between input terminals 61 and 62 to which the output voltage of the amplifier 2 is applied. The voltage at the equilibrium point A that equally divides the resistor 63 is extracted as a control signal corresponding to the output polarity width of the reverse polarity half wave, and the voltage at the equilibrium point B and the voltage at the unbalanced point B' of the other resistor 64 are output polarity. A switch 65 serving as a width switching means switches and outputs a control signal corresponding to the output polarity width of the positive half wave.These control signals cause the phase shift circuit 7 to output the positive half wave and the reverse half wave. Determine firing angle. The output current controller 11 provided on the secondary side of the welding transformer 10 is constructed by connecting control rectifier elements in a symmetrical bridge configuration, with the control rectifier element flowing a positive half-wave current and the control rectifying element flowing a half-wave current of the opposite polarity. An ignition signal is applied from the phase shift circuit 7 to each control rectifier element through which current flows. Direct current is passed through the reactor 12 via an output current controller 11 to shape the waveform of the output current. In FIG. 1, reference numeral 9 denotes a time limit circuit which inputs the detection signal of the output current detector 8, and this time limit circuit 9 switches the response time switch 5 and the switch 65 in the output polarity width controller 6. It is becoming.

First, when starting the welding machine, the response time changer 5 inserts the response time lead element 4 into the feedback circuit, and the changer 65 in the output polarity width controller 6 changes the voltage at the equilibrium point A and the voltage at the equilibrium point B into the control signal. so that it is given to the phase shift circuit 7 as follows. In this state, electrode 1
3 and the base metal 14, the detection signal of the output current detector 8 is inputted to the amplifier 2 having the response time delay element 3 via the response time advance element 4 and the response time switch 5, and reference voltage generator 1
The difference with the reference signal input from Phase control of the control rectifying elements constituting the is performed. After an arc occurs, a time limit circuit 9 inputting the detection signal of the output current detector 8 switches the response time switch 5 after a certain period of time (approximately 0.3 seconds) to switch the response time advance element 4 from the feedback circuit. After the disconnection and after a certain period of time (approximately 0.1 sec) has passed, the switch 65 in the output polarity width controller 6 is operated to switch the voltage at the balanced point A and the voltage at the unbalanced point B' as control signals to the phase shift circuit 7. be given to

By doing this, the response time advance element 4 is inserted into the feedback circuit at startup, so there is little response delay in the control system, and the output current is opposite to the positive half wave as shown in Figure 4. Since the output polarity widths t _{s and tr} of the polarity half-wave are in a balanced state, excessive current can be suppressed without causing a hunting phenomenon in the control system. In addition, during steady state, the response time advance element 4 is disconnected from the feedback circuit, which increases the response delay of the control system. Therefore, as shown in Fig. 5, the output polarity width T _s , T _r
The control system operates stably even in an unbalanced state, and stable welding can be performed with the set output polarity width during steady state as shown in Figure 3.

[Effects of the invention] According to the invention, excessive current at startup due to delay in feedback response, which was a problem with the conventional technology, is suppressed, and damage to the electrode due to excessive current, wear and tear, and burn-through of the welded object are prevented. At the same time, arc start can be stabilized.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention.
Figure 2 is a detailed circuit diagram of the output polarity width controller in Figure 1, Figure 3 is a response characteristic diagram at startup, Figure 4 is an illustration of the output polarity width at startup, and Figure 5 is the output during steady state. FIG. 6 is a block diagram of the conventional example, FIG. 7 is a response characteristic diagram at startup, and FIG. 8 is a diagram explaining the output polarity width. 1...Reference voltage generator, 2...Amplifier, 3...
Response time delay element, 4...Response time advance element, 5
...Response time switch, 6...Output polarity width controller,
65... Output polarity width switching means, 7... Phase shift circuit,
8... Output current detector, 9... Time limit circuit, 11...
...Output current control section.

Claims (1)

[Scope of utility model registration request] An amplifier is provided with a response time delay element that amplifies the difference between the detection signal of the output current detector and the reference signal from the reference voltage generator, and the output of the amplifier is connected to the positive half wave of the welding machine output current and the opposite polarity. A feedback circuit including an output polarity width controller that converts into a control signal corresponding to a half-wave output polarity width, and a phase shift circuit that provides an ignition signal to an output current control section consisting of a control rectifier based on this control signal. An AC arc welding machine equipped with a timer circuit comprising a first and second timer, a response time advance element, a first switch for switching the response time advance element, and a positive half wave of the welding machine output current. A fixed terminal of the output polarity width controller that outputs a signal with a one-to-one output polarity width of the reverse polarity half-wave, and an output that outputs the output of the amplifier of the output polarity width controller as a signal corresponding to the output polarity width. A second switch is provided to switch between the control signal output terminal of the polarity width controller and the fixed terminal, and the detection signal output terminal of the output current detector is connected to the time limit circuit, one of the first switches and the response time advance element. and the input terminal, and one of the output terminals of the timer circuit is connected to the first switching device, and the other is connected to the switching control terminal of the second switching device, respectively.
connecting the output terminal of the response time advance element and the other terminal of the first switch, the output terminal of the first switch and the input terminal of the amplifier, and further connecting one of the input terminals of the second switch; is connected to the fixed terminal of the output polarity width controller, and the other is connected to the control signal output terminal, a response time advance element is inserted into the feedback circuit, and the output polarity width of the positive polarity half wave and the reverse polarity half wave is one pair. 1, the welding machine is started, and after a predetermined period of time has elapsed since the arc is generated, the response time advance element is disconnected from the feedback circuit, and the output polarity width is then switched to the set width during steady state. Characteristic AC arc welding machine.