JPH05237657A - DC TIG arc welder - Google Patents

Abstract

(57) [Summary] [Purpose] A DC T that supplies only DC current with constant current control.
Prevents excessive current when the IG welder shifts to a short circuit and prevents current shortage when the arc shifts, thereby expanding the applicable current range. [Structure] A current detector 11 and a voltage detector 21 that detect the current and voltage of the welding load 10, and a current discriminating unit (current-voltage converter 12) that forms a discrimination signal for the presence or absence of current based on the current detection signal of the detector 11. ) And a voltage detection signal of the detector 21 to form a voltage presence / absence determination signal.
A gate unit 25 that gates both discrimination signals; a differentiation circuit 26 that differentiates the output signal of the gate unit 25 to form a differential signal for current correction; and a differential signal added to the setting signal for constant current control. Error amplifier 1 for forming an error signal between the generated signal and the current detection signal as a power supply control signal for constant current control
7 is provided, and the current at the start of the arc is corrected by the power supply control signal to a differential waveform in which the short-circuit current decreases and the arc transfer current increases.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a DC TIG arc welder.

[0002]

2. Description of the Related Art Conventionally, in DC TIG arc welding, a tungsten electrode is used, and a rod is arc-welded in a non-contact state of the electrode and the base material.

The conventional DC TIG arc welder used for this welding supplies a constant-current-controlled direct current to the welding load of the electrodes and the base metal by feedback control of the output current.

By the way, in the case of performing only the direct current feeding controlled by the constant current, the current value is set so as to secure a sufficient arc current. When an arc start is made by contacting the electrode, the tip of the electrode is melted and welded to the base material due to an excessive current controlled by a constant current at the time of transition to a short circuit, and an arc start mistake is likely to occur.

Therefore, in recent years, this kind of direct current TIG arc welding machine is often used together with a direct current power source for supplying the direct current power and a high frequency (2 to 3 MH) for arc start.
z), a high-frequency (2-3000 V) high-frequency power source is provided. When starting the arc, a gap is provided between the electrode and the base metal, and the high frequency and high voltage of the high frequency power source is applied to this gap to generate an arc. I try not to make an arc start mistake.

[0006]

In the case of the conventional DC TIG arc welding machine which only supplies DC power, it can be used only for welding with a relatively small current in order to avoid arc start mistakes, and the current When the number of the electric currents decreases, an arc start error is likely to occur due to a shortage of the electric current at the time of the arc transition, and there is a problem that the applicable electric current range is limited.

On the other hand, a direct current TI equipped with a conventional high frequency power source
In the case of the G arc welder, not only a direct current power supply but also a high frequency power supply is required, so that there is a problem in that it cannot be made smaller and lighter. Moreover, there is a problem in that the high-frequency noise generated by the high-frequency power source causes malfunction of other electric devices and the like.

Further, further downsizing and weight saving are required, and further, the digitalization of electric equipment and control equipment is advanced,
Now that the operating voltage is low, the welding method of performing arc start by short-circuiting the base metal and electrodes while performing only DC power supply is being reviewed.

According to the present invention, in a DC TIG arc welding machine which supplies only DC power supply under constant current control, an excessive current at the time of transition to a short circuit is prevented and an insufficient current at the time of transition to an arc is prevented, and an applicable current range is set. Intended to expand.

[0010]

To achieve the above object, in a DC TIG arc welder of the present invention, a current detector for detecting the current of a welding load and a voltage detector for detecting the voltage of a welding load. And a current discriminating unit that forms a discrimination signal for the presence or absence of current based on the current detection signal of the current detector, a voltage discriminating unit that forms a discrimination signal for the presence or absence of voltage based on the voltage detection signal of the voltage detector, and the above-mentioned discrimination The signal is gated to differentiate the output signal of this gate part and the gate part where the output signal is inverted by the change from the open state to the short state at the arc start and the change from the short circuit to the open state with the current. A differential circuit that forms a differential signal for current correction, and an error amplifier that forms an error signal between a signal obtained by adding a differential signal to a setting signal for constant current control and a current detection signal as a power supply control signal for constant current control. Wherein the power supply control signal current at the time of arc start circuit current due to decrease correcting the differential waveform arc transition current increases.

[0011]

In the case of the DC TIG arc welding machine of the present invention configured as described above, the current detection signal of the current detector, the current determination unit based on the voltage detection signal of the voltage detector, the current of the voltage determination unit, and the voltage The presence / absence discrimination signal is processed by the gate, and the electrode and base material are short-circuited and opened. At the time of arc start,
An output signal that is inverted is formed by the change in the short circuit from no current to the current with no voltage due to a short circuit, and the change in the arc transition from no voltage to the current with a current due to opening (arc generation).

Then, this output signal is differentiated by a differentiating circuit to form a differential signal for current correction having different polarities depending on the change in short circuit and the change in arc, and this differential signal is added to the setting signal for constant current control. It

By this addition, the setting signal for constant current control is
It is corrected in the decreasing direction at the time of transition to a short circuit and is corrected in the increasing direction at the time of arc transition. Then, based on this signal correction, the output current is corrected to be smaller than the value of the set signal at the time of transition to a short circuit to prevent overcurrent at the time of large current welding, and is also increased to be corrected at the time of arc transition to make the current shortage at the time of small current welding. Is prevented.

[0014]

EXAMPLE One example will be described with reference to FIGS. In FIG. 1, 1a to 1c are three-phase AC input terminals of a welding machine, 2 is an input side rectifier having a diode bridge configuration for rectifying a three-phase AC input power source of the input terminals 1a to 1c, and 3 is an input side smoothing capacitor. Reference numeral 4 is an inverter to which a DC power source smoothed by the capacitor 3 is fed and which includes an internal transistor, a MOS-FET, an IGBT.
The DC power supply is converted into high-frequency AC by switching control elements such as.

Reference numeral 5 is an output transformer for transforming the high frequency alternating current of the inverter 4, and 6 is an output side rectifier for rectifying the output of the transformer 5, which is a full wave rectifier of diodes 6a and 6b. Reference numeral 7 is a smoothing reactor, 8 is a tungsten electrode for TIG welding, and 9 is a base material, which forms a welding load 10 together with the electrode 8.

Reference numeral 11 denotes a current (output current) I of the welding load 10.
Is a current detector for detecting the current, and 12 is a current-voltage converter to which the current detection signal of the detector 11 is input. The conversion unit for converting the current detection signal into a voltage signal (hereinafter referred to as a conversion detection signal) Si and the output current It has a current discriminator that generates a discrimination signal Di for presence or absence.

Reference numeral 13 denotes a steady current setting device that divides the voltage of the positive power supply terminal + B to form a setting signal α for constant current control during steady arc (opening), and 14 divides the voltage of the positive power supply terminal + B. Arc start current setting device for forming a setting signal β for constant current control at arc start (short circuit), 15, 1
Reference numeral 6 denotes two analog switches for switching setting signals.

Reference numeral 17 denotes an error amplifier which forms a power supply control signal Sc for constant current control, and has an inverting input terminal with an input resistor 1
The voltage signal Si via 8 is input, and the setting signal α via the input resistor 19 and the analog switch 15 and the setting signal β via the input resistor 20 and the analog switch 16 are input in parallel to the non-inverting input terminal.

21 is the voltage (output voltage) V of the welding load 10.
Is a voltage detector for detecting the voltage of the detector 21, and 22 is a voltage discriminator to which the voltage detection signal Sv of the detector 21 is input, and forms a discrimination signal Dv of the presence or absence of an output voltage. 23 is the discrimination signals Di, Dv
Is an AND gate to which is input, and analog switch 1
6 control signals. Reference numeral 24 is an inverter gate that inverts the output signal of the AND gate 23 to form a control signal for the analog switch 15, and forms a gate section 25 together with the AND gate 23.

Reference numeral 26 is a differentiating circuit formed by connecting a differential resistor 27 and a capacitor 28 in series between the output terminal of the inverter gate 24 and the non-inverting input terminal of the error amplifier 17, and the differential circuit for current correction. Generate the signal γ.

Reference numerals 29 and 30 denote resistors for dividing the control signal Sc, and 31 denotes an analog switch controlled by the discrimination signal Dv, which controls the division of the control signal Sc. An inverter drive circuit 32 drives the control element of the inverter 4, and is supplied with the control signal Sc via the voltage dividing circuit of the resistors 29 and 30 and the switch 31. The determination signal Di is "1" (high level) or "0" depending on whether the output current is present or not.
It changes to (low level), and the discrimination signal Dv changes to "0" or "1" depending on the presence or absence of the output voltage.

Further, the analog switches 15 and 16 are connected to the output signals of the AND gate 23 and the inverter gate 24, respectively.
The analog switch 3 is turned on and off by 1 ”and“ 0 ”.
1 is turned on and off according to "0" and "1" of the discrimination signal Dv. Then, first, when the power is turned on, AC power is supplied to the input terminals 1a to 1c with the electrode 8 and the base material 9 being opened.

The AC power supply is rectified and smoothed by the rectifier 2 and the capacitor 3, converted into a DC power supply and fed to the inverter 4. The inverter 4 drives and controls the drive circuit 32 to convert the DC power supply into a high frequency AC.

Further, this high-frequency alternating current is supplied to the rectifier 6 via the transformer 5, and the direct current formed by the rectification and smoothing of the rectifier 6 and the reactor 7 has a polarity in which the base material 9 is positive and the electrode 8 and the base material are positive. 9 is supplied.

At this time, the space between the electrode 8 and the base material 9 is opened,
Since the output current I does not flow as shown in FIG.
The current detection signal of the current detector 11 is held at 0, the conversion detection signal Si of the converter 12 becomes 0, and the discrimination signal D
i becomes "0".

Further, based on the detection of the output voltage V shown in FIG. 2A, the voltage detector 21 outputs a voltage detection signal Sv proportional to the output voltage V, and the voltage discriminating unit 22 based on this signal Sv. The discrimination signal Dv of "0" shown in FIG. 2B is output, and the analog switch 31 is turned on by the discrimination signal Dv of "0".

The discrimination signals Di and Dv are both "0".
Therefore, the output signal of the AND gate 23 is held at "0", the analog switch 16 is turned off, and (c) of FIG.
As shown in, the output signal of the inverter gate 24 is "1".
Then, the analog switch 15 is turned on.

When the analog switch 15 is turned on,
The reference input signal of FIG. 2E supplied to the non-inverting input terminal of the error amplifier 17 is the setting signal α via the resistor 19.
Then, the power amplification control signal Sc of α-Si is formed by the error amplification between the signal α and the voltage signal Si.

At this time, since the output current I is 0 and the conversion detection signal Si is also minimum 0, the control signal Sc is maximum (=
α). Further, when the analog switch 31 is turned on, the control signal Sc is divided by the resistors 29 and 30, adjusted according to the control response characteristic during a steady arc, and supplied to the drive circuit 32.

Then, the drive circuit 32 controls the control signal Sc.
The inverter 4 is driven so that the output voltage V is not the maximum no-load voltage but the control signal S
The voltage has a magnitude determined by c.

Next, in order to start the arc, time t
When the electrode 8 is short-circuited to the base material 9 at 1, the output voltage V disappears to 0, and the output current I starts to flow. Then, the determination signal Dv is inverted to "1" by the disappearance of the output voltage V, the analog switch 31 is turned off, and the determination signal Di is inverted to "1" based on the current detection signal of the current detector 11.

Further, the discrimination signals Di and Dv are both "1".
Therefore, the gate unit 25 detects the change from the open state to the short circuit in the no current state, and the output signal of the AND gate 23 becomes "
It is inverted to "1", and the output signal of the inverter gate 24 is inverted to "0" with this inversion.
The analog switch 16 is turned on by the output signal of "1" of 3 and the analog switch 15 is turned off by the output signal of "0" of the inverter gate 24.

At this time, by turning the analog switches 15 and 16 off and on, the setting signal β is supplied as a reference input signal to the error amplifier 17 via the resistor 20 instead of the setting signal α, and the setting signal for constant current control is supplied. Switch. Further, the output signal of the inverter gate 24 is differentiated by the differentiating circuit 26 and the output signal of the inverter gate 24 is inverted from "1" to "0" at the time of a short circuit transition, based on the discharge of the capacitor 27, (d) of FIG. A differential signal γ for current correction having a falling differential characteristic shown in FIG.

Since the differential signal γ is added to the setting signal β, the reference input signal of the error amplifier 17 at the time of transition to the short circuit is as shown in FIG. The signal will be reduced and corrected with.

This corrected signal (β + γ) and voltage signal S
The drive circuit 3 is driven by the power supply control signal Sc based on the error from i.
Since 2 drives the inverter 4 to control the output current I with a constant current, the output current I (short circuit current) at the time of transition to a short circuit is corrected by decreasing from the current based on the setting signal β, and the setting signal β is gradually regulated from 0. Rise to value. In addition, analog switch 3
When 1 is turned off, the power supply control signal Sc is directly supplied to the drive circuit 32 without being subjected to voltage division adjustment. Further, due to the delay of the control response and the like, the output current I rises slightly later than the differential signal γ.

Next, at time t2, the electrode 8 is separated from the base material 9 and opened, and when the arc 8 is transferred to the arc, the output voltage V is generated while the output current I flows due to the arc between the electrode 8 and the base material 9. The signal rises, the discrimination signal Dv is inverted from "1" to "0", and the analog switch 31 is turned on.

Further, the gate section 25 detects the change from the short circuit to the open state of the current-carrying state, the output signal of the AND gate 23 is inverted to "0", and the output signal of the inverter gate 24 is inverted to "1". .. Then, by inverting the output signals of the AND gate 23 and the inverter gate 24, the analog switch 16 is turned off and the analog switch 15 is turned on,
The setting signal α is supplied to the error amplifier 17 instead of the setting signal β.

Further, the differential signal γ becomes a signal having a rising differential characteristic by differentiating the output signal of the inverter gate 24. Since the differential signal γ is added to the setting signal α, the reference input signal of the error amplifier 17 at the time of arc transition is a signal obtained by increasing and correcting the setting signal α with the differential signal γ.

This corrected signal (α + γ) and voltage signal S
Since the drive circuit 32 drives the inverter 4 by the power supply control signal Sc based on i and controls the output current I at a constant current, the output current I (arc transfer current) at the time of arc transition increases from the current based on the setting signal α. After being corrected and rising steeply, it gradually converges to the specified value of the setting signal α.

Since the short circuit current at the time of arc start short circuit transition is forcibly reduced and corrected by the differential signal γ, the current at short circuit transition does not become excessive even at the time of high current welding, and the tip of the electrode 8 is prevented. Is prevented from welding to the base material 9.

Further, since the arc transfer current is forcibly increased and corrected by the differential signal γ, there is no shortage of current during arc transfer even when the arc current is set smaller than the short circuit current and small current welding is performed. Arc start mistakes are prevented. Therefore, the applicable current range is significantly expanded as compared with the conventional one.

Moreover, in this embodiment, the set signal for constant current control is switched between a short circuit and an arc to change the set value of the short circuit current and the set value of the arc current. Therefore, the short circuit current is selected to be as small as possible. The loss at the start can be reduced.

Of course, it can be applied to the case where the setting signal for constant current control is not switched between the short circuit and the arc. Further, it goes without saying that the configuration of each unit is not limited to the embodiment.

[0044]

Since the present invention is configured as described above, it has the following effects. By the gate unit 25, the current detection signal of the current detector 11, the current determination unit (current-voltage converter 12) based on the voltage detection signal of the voltage detector 21, the current of the voltage determination unit 22 and the determination signal of presence / absence of voltage are made by the gate unit 25. At the time of arc start to process and short-circuit and open the electrode 8 and the base material 9, the short-circuit changes from no current to no current due to the short circuit, and from no current voltage due to opening (arc generation) An output signal that is inverted by the change of arc transition to the present is formed, and this output signal is differentiated by the differentiating circuit 26 to form a differential signal for current correction having different polarities depending on the change of the short circuit and the change of the arc. Since the signal is added to the setting signal for constant current control, the setting signal for constant current control supplied to the error amplifier 17 is corrected in the decreasing direction at the time of transition to the short circuit and is corrected in the increasing direction at the time of transition to the arc.

Based on this signal correction, the output current can be corrected to be smaller than the value of the set signal at the time of transition to the short circuit to prevent overcurrent of the large current welding, and at the same time to be increased to be corrected at the transition to the arc for small current welding. It is possible to apply a DC TIG arc welding machine that can prevent the current shortage and supply the welding load 10 with only the direct current controlled by the constant current and open the electrode 8 and the base material 9 from the short circuit to generate an arc. The current range can be greatly expanded to significantly improve performance.

[Brief description of drawings]

FIG. 1 is a connection diagram of an embodiment of a DC TIG arc welder of the present invention.

2A to 2F are waveform diagrams of respective parts for explaining the operation of FIG.

[Explanation of symbols]

 8 Electrode 9 Base material 10 Welding load 11 Current detector 12 Current-voltage converter 17 forming current discriminating section 17 Error amplifier 21 Voltage detector 22 Voltage discriminating section 25 Gate section 26 Differentiating circuit

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masahiro Aoyama 2-14-3 Awaji, Higashiyodogawa-ku, Osaka City Sansha Electric Manufacturing Co., Ltd. (72) Inventor Haruo Moriguchi 2-3-14 Awaji, Higashiyodogawa-ku, Osaka Stock company Sansha Electric Co., Ltd. (72) Inventor Kunio Kano 2-14-3 Awaji, Higashiyodogawa-ku, Osaka City Sansha Electric Co., Ltd.

Claims (1)

[Claims] 1. A direct current TIG arc welding machine for supplying a constant current controlled direct current to a welding load of an electrode and a base material, and starting an arc by opening the electrode and the base material from a short circuit. A current detector that detects a current, a voltage detector that detects the voltage of the welding load, a current determination unit that forms a determination signal of the presence or absence of current based on the current detection signal of the current detector, and the voltage detector A voltage discriminating unit that forms a discriminating signal of the presence or absence of a voltage based on the voltage detection signal, and gate-processes both discriminating signals to change from the open current state to the short circuit at the arc start and from the short circuit to the open state with the current. A gate unit in which an output signal is inverted by a change, a differentiation circuit that differentiates the output signal to form a differential signal for current correction, and a signal obtained by adding the differential signal to the constant current control setting signal. An error amplifier that forms an error signal with the current detection signal as a power supply control signal for the constant current control, and the short circuit current decreases the arc start current due to the power supply control signal, and the arc transfer current increases. DC TIG arc welding machine characterized by being corrected to a waveform.