JPH0615457A - Plasma arc power source equipment - Google Patents

Abstract

PURPOSE:To make the output voltage of a start time high enough for transforming it to a plasma arc by chopping a direct current output of a output circuit with the control of a semiconductor chopper element and controlling an energizing current of a pilot power feeding path. CONSTITUTION:A series circuit of a diode 22 and a transistor 23 as a semiconductor chopper element is provided between a joining point P of an output rectifier 5 consisting of an output circuit and an output terminal 8b, and a semiconductor chopper element is provided on a nozzle tip side of the pilot power feeding path. An error amplifier 25 outputting an error signal between a detecting signal Si of an electric current detector 6 and a reference signal Sra of a pilot reference power source 19 and a chopper driving circuit 26 are provided on a chopper controlling circuit 24. A high frequency alternating current of an inverter 3 is controlled so as to be maximum based on the output signal of an error amplifier 17. The output voltage (no load voltage) of an output rectifier 5 can be made sufficiently higher than the no load voltage based on the conventional pilot current reference signal Sra.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma arc power supply device used for plasma cutting and plasma welding.

[0002]

2. Description of the Related Art Conventionally, a plasma arc power supply device of this type is constructed as shown in FIG. 5, in which an AC power supply of an input terminal 1 is rectified by an input rectifier 2 and an output of the rectifier 2 is IGBT.
The inverter 3 having a bridge circuit configuration of switching elements such as T and transistors converts the high frequency alternating current into the high frequency alternating current and supplies it to the output rectifier 5 through the output transformer 4. The output rectifier 5 comprises a full-wave rectifier of diodes 5a to 5d. The node p of the cathodes of the diodes 5c and 5d is positive, and the node n of the anodes of the diodes 5a and 5b is n.
Generates a rectified output in the negative direction.

The connection point p is connected to the positive output terminal 8a for the plasma arc through the current detector 6 and the current relay 7, and the current detector 6, the switch 9 and the current limiting resistor 10 are connected. Is connected to the positive output terminal 8b for the pilot arc via the smoothing reactor 11, and the connection point n is connected to the negative output terminal 8c via the smoothing reactor 11. Furthermore, the output terminal 8a
The base material 13, the nozzle tip 14 of the welding torch, and the electrode 15 are connected to 8 and 8b and 8c, respectively.

At the time of startup, the switch 9 is closed, and the direct current formed by the smoothing of the reactor 11 is used as the base material 13.
It is applied between the electrodes 15 and between the nozzle tip 14 and the electrodes 15. Further, in this state, a high frequency high voltage of a high frequency generating circuit (not shown) is applied between the nozzle tip 14 and the electrode 15, and a pilot arc is generated during this period.

From the connection point p of the output rectifier 5, the current detector 6, the switch 9, the resistor 10, the output terminal 8b, the nozzle tip 14, the electrode 15, the output terminal 8c, and the reactor 11 are connected.
A pilot arc current of a relatively small current flows through the connection point n of the output rectifier 5 via the, and the pilot arc continues.

Further, the current detector 6 detects the pilot arc current, and the detector 6 supplies a detection signal Si proportional to the pilot arc current to the error amplifier 17 of the inverter control unit 16. At this time, the current relay 7 is kept de-energized, and the reference power source changeover switch 18 moves the pilot contact 1
8a, the reference signal Sra for the pilot arc current of the pilot reference power supply 19 is supplied to the error amplifier 17.

Then, the error amplifier 17 receives the reference signal Sra.
The error signal between the detection signal Si and the detection signal Si is supplied to the inverter drive circuit 20 as an output control signal, and the drive circuit 20 makes the detection signal Si equal to the reference signal Sra.
Drive the data. By this driving, the pilot arc current is controlled to a constant current according to the reference signal Sra.

Next, the welding torch approaches the base metal 13,
When a plasma arc is generated between the base material 13 and the electrode 15, the current detector 6, the current relay 7, the output terminal 8a, the base material 13, the electrode 15, the output terminal 8c, from the connection point p of the output rectifier 5. Connection point n of output current unit 5 via reactor 11
A high-current plasma arc current flows through the. At this time, the current relay 7 switches the reference power source changeover switch 18 to the plasma contact 18b, and instead of the reference signal Sra, the reference signal S for the plasma arc current of the plasma reference power source 21.
rb is supplied to the error amplifier 17.

Then, based on the detection signal Si of the current detector 6 and the reference signal Srb, the plasma arc current is controlled to a constant current according to the reference signal Srb, and based on the plasma arc current of this constant current. Base material 1 by plasma arc
3 cutting and welding are performed. By the way, pilot pilot
The general magnitude of the arc current and plasma arc current is 20
A, 300 to 500 A, respectively.

When the pilot arc current continues to flow while cutting and welding by the plasma arc,
Since the resistor 10 consumes a large amount of power and cannot save power, when the plasma arc occurs, the switch 9 is opened to cut off the pilot arc current.

[0011]

In the case of the conventional device shown in FIG. 5, a large-capacity and large mechanical switch 9 is required to supply and cut off the pilot arc current, and the device is made compact and electronic. There is a problem that cannot be achieved.

Further, since the inverter 3 is constant-current-controlled at the time of starting to output a pilot arc current of a relatively small capacity, the output voltage (no-load voltage) of the inverter 3 at starting is sufficiently high. As a result, the voltage (no-load voltage) between the nozzle tip 14 and the electrode 15 becomes low. Therefore, after the pilot arc is generated, the welding torch is
However, if the distance (distance) between the base material 13 and the electrode 15 is not made sufficiently small even if it is brought close to, it is easy to cut or weld easily because the plasma arc does not move or the transfer is delayed. There is a problem that occurs.

If the shift to the plasma arc is delayed, it becomes extremely difficult to control the operation timing, especially when an automatic machine is used for feeding the base metal 13, moving the welding torch, and the like. SUMMARY OF THE INVENTION It is an object of the present invention to provide a plasma arc power supply device which can be miniaturized and made electronic, and at the same time, the output voltage of the output circuit at the time of start-up becomes a high no-load voltage which is sufficiently high for plasma arc transfer. And

[0014]

In order to achieve the above object, the plasma arc power supply device of the present invention supplies a DC output of an output circuit between a nozzle tip of a welding torch and an electrode. , A pilot feed line that maintains a small current pilot arc between the nozzle tip and the electrode at startup, and the DC output between the base material and the electrode, and after the pilot arc occurs A plasma feed line that maintains a high-current plasma arc generated between the base material and the electrode when the torch approaches the base material, and a pilot arc inserted in the nozzle tip side of the pilot feed line. A semiconductor chopper element for current control, and controlling the semiconductor chopper element based on the detection of the output current of the output circuit or the energization current of both the power supply paths, and the energization current of the pilot power supply path is a predetermined pilot arc current at startup. Set to Flow control to plasma A - and a chopper control circuit for interrupting the transition to click.

[0015]

The plasma arm of the present invention constructed as described above.
In the case of a power supply device, the current output of the pilot power supply line is controlled by choppering the DC output of the output circuit by controlling the semiconductor chopper element by the chopper control circuit instead of opening and closing the mechanical switch as in the conventional case. By the control, the current between the nozzle tip of the welding torch and the electrode is constant-current-controlled to a predetermined pilot arc current at the time of starting, and is cut off by the shift to the plasma arc. Since the DC output of the output circuit is controlled by the chopper operation of the semiconductor chopper element, the DC output of the output circuit can be set to a sufficiently high no-load voltage at startup.

[0016]

EXAMPLES Examples will be described with reference to FIGS. 1 to 4.

(First Embodiment) First, a first embodiment will be described with reference to FIGS. 5, the same reference numerals as those in FIG. 5 denote the same or corresponding ones, and the points different from FIG. 5 are the following points (a) to (f). (A) The point that the current relay 7 and the changeover switch 18 of FIG. 5 are omitted. (B) The reference signal of the error amplifier 17 of the inverter control unit 16 is fixed to the reference signal Srb of the plasma reference power source 21.

(C) Between the connection point p of the output rectifier 5 forming the output circuit and the output terminal 8b, a diode 22 and a semiconductor chopper element are used instead of the conventional switch 9 and resistor 10 series circuit. The semiconductor chopper element is provided on the nozzle chip side of the pilot power supply path.

(D) A chopper control circuit 24 for base drive of the transistor 23 is provided, and an error signal between the detection signal Si of the current detector 6 and the reference signal Sra of the pilot reference power source 19 is output to this circuit 24. Error amplifier 25
And a point provided with a chopper drive circuit 26 to which the output signal of the amplifier 25 is supplied.

(E) The current detector 6 is provided between the output terminal 8c and the reactor 11. (F) End of the reactor 11 on the connection point n side and the output terminal 8
A point where a flywheel diode 27 for the energy circulation of the reactor 11 is provided between it and b.

Then, the connection point p, the diode 22, the transistor 23, the output terminal 8b, the nozzle tip 12, the electrode 15, the output terminal 8c, the current detector 6, the reactor 11,
The loop of the connection point n forms the pilot feed line. Further, the connection point p, the output terminal 8a, the base material 13, the electrode 15, the output terminal 8c, the current detector 6, the reactor 11, the connection point n.
Loop forms a plasma feed line.

When AC power is supplied to the input terminal 1 by turning on a main switch (not shown) or the like, this AC power is rectified by the input rectifier 2, and the rectified output is converted by the inverter 3 into a high frequency AC. And supplies the high frequency alternating current to the output rectifier 5 through the output transformer 4, rectifies it by this rectifier 5 and returns it to direct current again, and the output terminals 8a, 8
and between the output terminals 8b and 8c.

At this time, since neither the pilot arc nor the plasma arc is generated, no current flows through the current detector 6, and the detection signal Si is kept at the minimum 0. Since the detection signal Si is 0, the error amplifiers 17 and 25 output the maximum amount of error signals based on the reference signals Srb and Sra, respectively.

Further, based on the output signal of the error amplifier 17, the inverter drive circuit 26 PWM-controls the inverter 3 to a substantially maximum output state, and based on this control, the high frequency alternating current of the inverter 3 is as shown in FIG. It becomes the maximum as shown in (a). When the high frequency alternating current of the inverter 3 becomes maximum, the output voltage (no-load voltage) of the output rectifier 5 becomes sufficiently higher than the no-load voltage based on the conventional pilot current reference signal Sra.

Further, based on the output signal of the error amplifier 25, the chopper drive circuit 26 also controls the transistor 23 to the maximum output state by chopper control. Based on this control, the output of the transistor 23 is also as shown in FIG. It will be maximum. Therefore, at start-up, a sufficiently high no-load voltage is applied between the output terminals 8b and 8c, that is, between the nozzle tip 14 and the electrode 15.

When a high frequency high voltage is applied between the nozzle tip 14 and the electrode 15 by a high frequency generating circuit (not shown) to generate a pilot arc, a pilot arc current flows through the pilot power feeding path, This current is detected by the current detector 6, and the detection signal Si supplied to the error amplifiers 17 and 15 rises from 0.

At this time, the reference signal Srb for setting the plasma arc current is sufficiently larger than the reference signal Sra for setting the pilot arc current, and the error amplifier responds to the change of the detection signal Si based on the pilot arc current. Although the output signal of 25 changes following, the output signal of the error amplifier 17 hardly changes.

Then, based on the output signal of the error amplifier 25, the chopper drive circuit 26 changes the ON period of the transistor 23 so that the detection signal Si becomes equal to the reference signal Srb, and the output of the transistor 23 is changed to (c) of FIG. ), The chopper output having a predetermined pulse width is controlled, and the pilot arc current is controlled to a constant current based on the reference signal Sra. Since the output signal of the error amplifier 17 hardly changes, the inverter 3 is maintained at the maximum output state while the pilot arc is generated.

Next, when the welding torch approaches the base metal 13 and a plasma arc is generated between the base metal 13 and the electrode 15,
A plasma arc current flows through the plasma power supply path, and the detection signal Si becomes sufficiently higher than the reference signal Sra.
At this time, the error amplifier 26 has a minimum error signal, and the chopper control circuit 26 sets the transistor 23 in the minimum output state based on this error signal.

Therefore, the pilot arc current is insufficient and the pilot arc disappears, and this disappearance interrupts the pilot arc current. On the other hand, since the detection signal Si based on the plasma arc current approaches the reference signal Srb,
When shifting to the plasma arc, the output signal of the error amplifier 25 changes following the detection signal Si.

Then, based on the output signal of the error amplifier 17, the inverter drive circuit 20 controls the inverter 3 so that the detection signal Si becomes equal to the reference signal Srb, and the plasma arc current is controlled by this control. Is controlled to a constant current based on the reference signal Srb.

Therefore, in the case of FIG. 1, a small electronic circuit using the semiconductor chopper element of the transistor 23 in place of the conventional mechanical switch 9 causes the pilot arc current when the plasma arc is started. Power can be saved by shutting off the power. Moreover, the output voltage (no-load voltage) of the output rectifier 5 at the time of start-up is sufficient as compared with the case where the inverter 3 is driven at the time of start-up based on the reference signal Srb and driven at the time of the conventional reference signal Sra. As a result, the pilot arc is maintained well, and there is no erroneous transition to the plasma arc or delay in transition due to the gap between the base material 13 and the electrode 15.

(Second Embodiment) Next, a second embodiment will be described with reference to FIG. In FIG. 3, FIG.
The same reference numerals denote the same or corresponding ones, and the points different from FIG. 1 are the following points (g) to (i). (G) A diode 5 for pilot power feeding to the output rectifier 5
A point with p and 5n added. (H) The semiconductor chopper element is a transistor 23p, 33
n and two transistors 23p are diode 5p,
It is provided between the output terminals 8b and the transistor 23n is connected to the diode.
Point provided between the terminal 5n and the output terminal 8b.

(I) The chopper drive circuit 26 alternately drives the transistors 23p and 23n every half cycle of the high frequency output of the inverter 3. In addition, the dio of FIG.
The transistor 22 and the transistor 23 are omitted.

The diode 5p through which the positive output of the output rectifier 5 flows, the transistor 23p, the output terminal 8b,
Nozzle tip 14, electrode 15, output terminal 8c, current detector 6, reactor 11, positive loop of diode 5b,
The diode 5n through which the negative output of the output rectifier 5 flows, the transistor 23n, the output terminal 8b, the nozzle tip 14, the electrode 15, the output terminal 8c, the current detector 6, the reactor 1
1, the negative loop of the diode 5a forms a pilot power supply path.

Further, according to the error signal of the error amplifier 25,
The chopper drive circuit 26 drives the transistor 23p in one half cycle in which the output of the output rectifier 5 becomes positive, and drives the transistor 3n in the other half cycle in which the output of the output rectifier 5 becomes negative. Therefore, in the case of this embodiment, the pilot arc current at the time of startup is the transistor 23p,
23n, which is suitable when a relatively large current is required as a pilot arc current.

(Third Embodiment) Next, a third embodiment will be described with reference to FIG. In FIG. 4, FIG.
The same reference numerals denote the same or corresponding ones, and the different points are the following points.

That is, in place of the current detector 6 of FIG. 1, a current detector 6a for pilot arc current and a current detector 6b for plasma arc current are provided, and the current detector 6a is provided.
Is provided between the transistor 23 and the output terminal 8b, and the current detector 6b is provided between the connection point p and the output terminal 8a.

Then, the current detector 6a detects the pilot arc current at the time of startup, which flows through the pilot power feeding path, and supplies the detection signal Sia proportional to this current to the error amplifier 25. Further, the current detector 6b detects a plasma arc current flowing through the plasma power supply path, supplies a detection signal Sib proportional to this current to the error amplifier 17, and at the same time, issues a stop command when the plasma arc current starts to flow. The control signal SW that is inverted to is supplied to the chopper drive circuit 26.

Therefore, at the time of start-up, the pilot arc current is controlled to a constant current based on the detection signal Sia. When the plasma arc is started, the chopper drive circuit 26 is stopped by the control signal SW and the pilot arc current is stopped. Is cut off, and the plasma arc current is controlled to a constant current based on the detection signal Sib. In the case of this embodiment, the pilot arc current and the plasma arc current are respectively detected by the separate current detectors 6a and 6b, so that the plasma arc current is not so large and the pilot arc current is not so large. And the plasma arc current is small, the pilot arc current control shifts accurately to the plasma arc current control as the pilot arc shifts to the plasma arc current. It has the advantage that good cutting and welding can be performed.

By the way, in each of the above embodiments, in order to miniaturize the device, an inverter 3 is provided on the input side of the output transformer 4, and the output of the inverter 3 is rectified and smoothed to provide a load power supply output. However, the present invention can be applied to the case where the AC power source is rectified by the phase control of the thyristor to form the load power supply output, and the configuration of the output circuit and the like is not limited to the embodiment.

[0042]

Since the present invention is configured as described above, it has the following effects. The chopper control circuit 24 controls the semiconductor chopper element (transistor 2
3, 23p, 23n) is electronically controlled to chopper the DC output of the output circuit (output rectifier 5) to control the energizing current of the pilot power feeding path. Based on this control,
The current between the nozzle tip 14 of the welding torch and the electrode 15 is constant-current-controlled to a predetermined pilot arc current at the time of start-up, and is interrupted by the transition to the plasma arc. It can be formed electronically in a smaller size than when a switch is used.

Moreover, since the pilot arc current is controlled by the chopper control which is separate from the output circuit, the no-load voltage of the output circuit at the time of start-up can be made sufficiently high, so that the shift to the plasma arc can be prevented. It is possible to prevent a delay in transition and provide a suitable power supply device even when an automatic machine is used.

[Brief description of drawings]

FIG. 1 is a connection diagram of a first embodiment of a plasma arc power supply device of the present invention.

2A, 2B, and 2C are waveform diagrams for explaining the operation of FIG.

FIG. 3 is a connection diagram of a second embodiment of the present invention.

FIG. 4 is a wiring diagram of a third embodiment of the present invention.

FIG. 5 is a connection diagram of a conventional device.

[Explanation of symbols]

5 Output Rectifier 13 Base Material 14 Nozzle Chip 15 Electrodes 23, 23p, 23n Transistor 24 Forming Semiconductor Chopper Element 24 Chopper Control Circuit

Front page continued (72) Inventor Kenzo Danjo 2-14-3 Awaji, Higashiyodogawa-ku, Osaka City Sansha Electric Manufacturing Co., Ltd. (72) Inventor Kunio Kano 2-14-3 Awaji, Higashiyodogawa-ku, Osaka City Sansha Electric Co., Ltd.

Claims (1)

[Claims] 1. A pilot for supplying a direct current output of an output circuit between a nozzle tip and an electrode of a welding torch, and maintaining a small current pilot arc between the nozzle tip and the electrode at start-up. A power supply line, and supplies the DC output between the base material and the electrode, and after the pilot arc is generated, the torch approaches the base material and between the base material and the electrode. A plasma power supply path that sustains the generated large current plasma arc, a semiconductor chopper element for pilot arc current control inserted into the nozzle tip side of the pilot power supply path, and the output current of the output circuit or the The semiconductor chopper element is controlled based on the detection of the energization currents of both power supply lines, and the energization current of the pilot power supply line is controlled to a predetermined pilot arc current at the time of start-up so as to shift to the plasma arc. A plasma arc power supply device comprising a chopper control circuit for further shutting off.