JP2707016B2 - DC TIG arc welding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC TIG arc welding machine.

[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 between the electrode and a base material.

[0003] The conventional DC TIG arc welding machine used for this welding supplies a constant current controlled DC to the welding load of the electrode and the base material by feedback control of the output current.

In the case where only the DC power supply controlled by the constant current is carried out, the current value is set so as to secure a sufficient arc current. When the arc is started by contacting with the electrode, the tip of the electrode melts into the base material and is welded due to the excessive current controlled by the constant current at the time of the transition to the short circuit, and an arc start mistake is likely to occur.

Therefore, in recent years, this type of DC TIG arc welding machine often includes a DC power supply for supplying the DC power and a high frequency (2 to 3 MHz) for arc start.
z), a high-frequency power supply of high voltage (2-3000 V) is provided. When starting the arc, a gap is provided between the electrode and the base material, an arc is generated by applying the high frequency and high voltage of a high frequency power supply to the gap, and after the arc is generated, the operation is switched to DC power supply. This also prevents an arc start mistake from occurring.

[0006]

The conventional DC TIG arc welding machine which performs only DC power supply can be used only for welding with a relatively small current in order to avoid an arc start mistake. When the number is small, there is a problem that an arc start mistake is likely to occur due to a shortage of current at the time of arc transfer, and an applicable current range is limited.

On the other hand, a direct current TI equipped with a conventional high frequency power supply
In the case of a G arc welding machine, not only a direct current power source but also a high frequency power source is required, so that there is a problem that miniaturization and weight reduction cannot be achieved. In addition, there is a problem in that high-frequency noise generated by the high-frequency power supply causes malfunction of other electric devices and the like.

[0008] Further, further miniaturization and weight reduction are required, and the digitization of electric devices and control devices has been progressing.
At present, when the operating voltage is low, a welding technique of performing only DC power supply and short-circuiting a base material and an electrode to start an arc is being reviewed.

According to the present invention, in a DC TIG arc welding machine which performs only constant-current controlled DC power supply, an excessive current at the time of transition to a short circuit and a shortage of current at the time of arc transition are prevented, and the applicable current range is reduced. The purpose is to expand.

[0010]

In order to achieve the above object, a DC TIG arc welding machine according to the present invention comprises a current detector for detecting a current of a welding load, and a voltage detector for detecting a voltage of the welding load. A current determining unit that forms a determination signal of the presence or absence of a current based on a current detection signal of a current detector; a voltage determination unit that forms a determination signal of the presence or absence of a voltage based on a voltage detection signal of a voltage detector; Gate processing of the signal, the gate section where the output signal is inverted by the change from open to short circuit in the no-current state and the change from short circuit to open in the current state at arc start, and the output signal of this gate section is differentiated. A differential circuit for forming a differential signal for current correction, and an error amplifier for forming an error signal between a signal obtained by adding the 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, a current discriminating unit based on the current detection signal of the current detector and the voltage detection signal of the voltage detector, and the current and voltage of the voltage discriminating unit. The presence / absence discrimination signal is processed by the gate unit, and when the arc starts to open by short-circuiting the electrode and base material,
An output signal is formed which is inverted by a change in a short-circuit transition from no to a current without a voltage due to a short circuit, and a change in an arc from a non-existence to a voltage with a current due to opening (arc generation).

Then, the output signal is differentiated by a differentiating circuit to form a differential signal for current correction having a different polarity between a change in short-circuit and a change in arc, and this differential signal is added to a set signal for constant current control. You.

By this addition, the setting signal of the constant current control is
The correction is made in the decreasing direction when the short-circuit shifts, and is increased in the increasing direction when the arc shifts. Then, based on this signal correction, the output current is corrected to decrease from the value of the set signal at the time of transition to short-circuit, thereby preventing an overcurrent at the time of welding with a large current and increasing the correction at the time of transition to an arc, resulting in insufficient current at the time of welding at a small current. Is prevented.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment 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 three-phase AC input power of input terminals 1a to 1c, and 3 is an input-side smoothing capacitor. Reference numerals 4 and 4 denote inverters to which a DC power supply smoothed by the capacitor 3 is supplied, and which includes internal transistors, MOS-FETs, and IGBTs.
A DC power supply is converted into a high-frequency AC by switching of a control element such as a DC power supply.

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

Reference numeral 11 denotes the current (output current) I of the welding load 10.
, A current-to-voltage converter 12 to which the current detection signal of the detector 11 is input, a conversion unit that converts the current detection signal into a voltage signal (hereinafter referred to as a conversion detection signal) Si, and an output current It has a current discriminating unit that forms the presence / absence discrimination signal Di.

Reference numeral 13 denotes a steady current setter for dividing the voltage of the positive power supply terminal + B to form a setting signal α for constant current control at the time of 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 the time of arc start (short circuit), 15, 1
Reference numeral 6 denotes two analog switches for setting signal switching.

An error amplifier 17 generates a power supply control signal Sc for constant current control.
8, a voltage signal Si via the input resistor 19 and the analog switch 15 and a setting signal β via the input resistor 20 and the analog switch 16 are input in parallel to the non-inverting input terminal.

Reference numeral 21 denotes the voltage (output voltage) V of the welding load 10
Is a voltage discriminating unit to which the voltage detection signal Sv of the detector 21 is inputted, and forms a discrimination signal Dv for the presence or absence of the output voltage. 23 is a discrimination signal Di, Dv
Is an input and gate, and the analog switch 1
6 are formed. An inverter gate 24 inverts an output signal of the AND gate 23 to form a control signal for the analog switch 15, and forms a gate unit 25 together with the AND gate 23.

Reference numeral 26 denotes a differentiating circuit formed by providing 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 a differential circuit for current correction. A signal γ is generated.

Reference numerals 29 and 30 denote resistors for dividing the control signal Sc, and reference numeral 31 denotes an analog switch controlled by the discrimination signal Dv, which controls the division of the control signal Sc. Reference numeral 32 denotes an inverter drive circuit for driving a control element of the inverter 4, to which a control signal Sc is supplied via resistors 29 and 30 and a voltage dividing circuit of the switch 31. The discrimination signal Di is "1" (high level) or "0" depending on the presence or absence of the output current.
(Low level), and the discrimination signal Dv changes to “0” or “1” depending on the presence or absence of the output voltage.

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

The AC power is rectified and smoothed by the rectifier 2 and the capacitor 3, converted into a DC power, and supplied to the inverter 4. The inverter 4 converts the DC power into a high-frequency AC by the drive control of the drive circuit 32.

Further, the 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 is applied to the electrode 8, the base material having a polarity with the base material 9 being positive. 9.

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".

On the basis of 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. 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", and the analog switch 16 is turned off.
As shown in FIG. 7, the output signal of the inverter gate 24 is "1".
And the analog switch 15 is turned on.

When the analog switch 15 is turned on,
The reference input signal shown in FIG. 2E supplied to the non-inverting input terminal of the error amplifier 17 is a setting signal α via a resistor 19.
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 also becomes the minimum 0, the control signal Sc becomes the 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 characteristics at the time of a steady arc, and supplied to the drive circuit 32.

Then, the control signal Sc is output from the drive circuit 32.
Is driven to be 0, and 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, at the time t to start the arc,
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 discrimination signal Dv is inverted to “1” due to the disappearance of the output voltage V, the analog switch 31 is turned off, and the discrimination 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 section 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 "".
As a result, the output signal of the inverter gate 24 is inverted to "0".
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, when the analog switches 15 and 16 are turned 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 output. Switch. In addition, when the output signal of the inverter gate 24 is differentiated by the differentiating circuit 26 and the output signal of the inverter gate 24 transitions from a short to an inversion from “1” to “0”, the discharge of the capacitor 27 is performed. The differential signal γ for current correction having the 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 the transition to the short circuit is changed from the setting signal β to the differential signal γ, as is apparent from FIG. And the signal is corrected for the decrease.

The corrected signal (β + γ) and the voltage signal S
drive circuit 3 based on a power supply control signal Sc based on an error with respect to i.
2 drives the inverter 4 to control the output current I at a constant current. Therefore, the output current I (short-circuit current) at the time of transition to short-circuit is corrected to decrease from the current based on the setting signal β, and the setting signal β is gradually defined from 0. Rise to value. Note that the analog switch 3
By turning off 1, the power supply control signal Sc is directly supplied to the drive circuit 32 without adjusting the voltage division. Further, due to a delay in the control response or the like, the output current I rises and changes slightly later than the differential signal γ.

Next, at time t2, when the electrode 8 is separated from the base material 9 and opened to shift to an arc, the output voltage V is changed with the output current I flowing due to the occurrence of an arc between the electrode 8 and the base material 9. As a result, the determination 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, and 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". . The analog switch 16 is turned off and the analog switch 15 is turned on by the inversion of the output signals of the AND gate 23 and the inverter gate 24.
The setting signal α is supplied to the error amplifier 17 instead of the setting signal β.

The differential signal γ becomes a signal having a rising differential characteristic due to the differentiation of 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 the setting signal α by the differential signal γ.

The corrected signal (α + γ) and the 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 at the time of arc transition (arc transition current) increases from the current based on the setting signal α. After being corrected and rising sharply, it gradually converges to the specified value of the setting signal α.

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

Further, since the arc transfer current is forcibly increased and corrected by the differential signal γ, even when the arc current is set to be smaller than the short-circuit current and small current welding is performed, there is no shortage of current at the time of arc transfer. Arc start mistake is prevented. As a result, the applicable current range is greatly expanded as compared with the conventional case.

Further, in this embodiment, the setting signal of the constant current control is switched between the time of the short circuit and the time of the arc, and the set value of the short circuit current and the set value of the arc current are changed. The loss at the start can be reduced.

It is needless to say that the present invention can be applied to a case where the setting signal for constant current control is not switched between a short circuit and an arc. In addition, 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, the following effects can be obtained. The gate unit 25 outputs the current detection signal of the current detector 11 and the current determination unit (current-voltage converter 12) based on the voltage detection signal of the voltage detector 21 and the current / voltage presence / absence determination signal of the voltage determination unit 22 by the gate unit 25. At the time of the arc start in which the electrode 8 and the base material 9 are short-circuited and opened, the change of the short-circuit transition from the absence of the current with no voltage due to the short-circuit to the presence of the short-circuit, and the absence of the voltage with the current due to the opening (arc generation). An output signal which is inverted by the change of the arc transition to "yes" is formed, and the output signal is differentiated by the differentiating circuit 26 to form a differential signal for current correction having different polarities between the short-circuit transition change and the arc transition change. In order to add the signal to the setting signal of the constant current control, the setting signal of the constant current control supplied to the error amplifier 17 is corrected in the decreasing direction at the time of the transition of the short circuit and is corrected in the increasing direction at the transition of the arc.

Based on the signal correction, the output current is corrected to be smaller than the value of the set signal at the time of transition to the short circuit, thereby preventing an overcurrent of the large current welding, and increasing at the time of the arc transition to the small current welding. Current can be prevented, a DC TIG arc welding machine that supplies only a constant current controlled direct current to the welding load 10 and opens an electrode 8 and a base material 9 from a short circuit to generate an arc can be applied. The current range can be greatly extended to significantly improve performance.

[Brief description of the drawings]

FIG. 1 is a connection diagram of one embodiment of a DC TIG arc welding machine of the present invention.

2 (a) to 2 (f) are waveform diagrams of respective parts for explaining the operation of FIG.

[Explanation of symbols]

 Reference Signs List 8 electrode 9 base material 10 welding load 11 current detector 12 current-voltage converter forming current discriminating section 17 error amplifier 21 voltage detector 22 voltage discriminating section 25 gate section 26 differentiating circuit

Continued on the front page (72) Masahiro Aoyama 2-14-3 Awaji, Higashi-Yodogawa-ku, Osaka-shi Inside Sansha Electric Manufacturing Co., Ltd. (72) Inventor Haruo Moriguchi 2- 14-3 Awaji, Higashi-Yodogawa-ku, Osaka-shi (72) Inventor Kunio Kano 2-14-3 Awaji, Higashi-Yodogawa-ku, Osaka City In-house Sansha Electric Works (56) References JP-A-53-95155 (JP, A)

Claims (1)

(57) [Claims] 1. A DC TIG arc welding machine that supplies only a constant-current controlled DC current to a welding load of an electrode and a base material and opens the electrode and the base material from a short circuit to start an arc. A current detector that detects a current; a voltage detector that detects a voltage of the welding load; a current determination unit that forms a determination signal of the presence or absence of a current based on a current detection signal of the current detector; A voltage discriminator for forming a discrimination signal of the presence or absence of a voltage based on the voltage detection signal; A gate for inverting an output signal due to a change; a differentiation circuit for differentiating 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 for forming an error signal from the current detection signal as a power supply control signal for the constant current control. A DC TIG arc welding machine characterized in that the waveform has been corrected.