JPH11347741A - Plasma cutting machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power loss of pilot current suppressing resistance by repeatedly generating/ceasing a pilot arc current at an arbitrary period, outputting a pilot arc current having a high peak current, facilitating transfer from a pilot arc to a plasma arc, and simultaneously setting the effective electrode of the pilot arc low. SOLUTION: For example, the output signal of an oscillation circuit 16 constituted of multi-vibrators and the like is set to be 0.1 second 'H' and 0.2 second 'L'. Relating to the oscillation circuit 16, a plasma arc current flows, the signal of a current detector 11 is received, the oscillation is stopped and the 'H' signal is held while the plasma arc current is flowing. The control circuit 14 controls the start/stop of a driving circuit 15 synchronously with the signal of the oscillation circuit 16. After the transfer to the plasma arc, the operation of a high frequency voltage generating circuit 9 is stopped by the signal of the current detector 11, the oscillating operation of the oscillator 16 is stopped and, the control signal of the control circuit 14 is maintained in the normal continuous controlled state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma cutting machine which generates a pilot arc between an electrode of a plasma cutting torch and a nozzle tip, and generates a plasma arc by inducing the pilot arc.

[0002]

2. Description of the Related Art Conventionally, a pilot arc of a plasma cutting machine has been configured to generate an arc between an electrode and a tip of a plasma cutting torch by flowing an output voltage of the plasma cutting machine through a pilot current suppressing resistor.

For example, FIG. 4 shows a circuit configuration of a conventional inverter-controlled plasma cutting machine.

In FIG. 4, reference numeral 1 denotes an AC power supply, which uses a three-phase or single-phase power supply. Reference numeral 2 denotes a rectifier circuit for converting an AC power supply to a DC power, and 3 denotes an output adjustment power supply circuit of the plasma cutting machine. Here, the output adjustment power supply circuit 3 is a circuit obtained by combining a control rectifier circuit including an insulating transformer, a transistor, a thyristor, a diode, and the like. 4 is a pilot arc current suppression resistor, 5 is an electrode of a plasma cutting torch,
6 is a nozzle tip, 7 is a material to be cut, 8 is a pilot arc generated between the electrode 4 and the tip 5, 9 is a high frequency voltage generating circuit, 10 is a coupling coil for superimposing a high frequency voltage on an output circuit, 11 is a plasma arc. This is a current detector that detects that current has flowed between the electrode and the workpiece. When the current detector 11 operates, the switch 12 connected to the input circuit of the high-frequency voltage generation circuit 9 is opened to stop generating the high-frequency voltage. 13 is a start switch of the plasma cutting machine, 14 is a control circuit which receives a signal of the start switch 13 and controls the output of the plasma cutting machine, and 15 is a drive circuit which receives a control signal of the control circuit and drives the output adjustment power supply circuit 3. .

In the above-mentioned conventional configuration, the pilot arc of the plasma cutting machine outputs the output voltage of the output adjusting power supply circuit 3 via the pilot arc suppressing resistor 4 and is generated between the electrode 5 of the cutting torch and the nozzle tip 6. . that time,
A high frequency voltage is simultaneously generated for starting the pilot arc, and the insulation between the electrode 5 and the chip 6 is broken to generate a pilot arc. For example, in the case of an air plasma cutting machine, since the ionization voltage of the arc is high, even if a high-frequency voltage is generated only at the time of starting the arc, the pilot arc is not maintained. The aim was to stabilize the arc. When the pilot arc is generated, the pilot arc is brought into contact with the workpiece to induce a plasma arc between the electrode 5 and the workpiece 7. After the plasma arc is generated, the plasma arc current detection circuit 11 is activated.
The switch 12 connected to the input circuit of the high-frequency voltage generation circuit 9 is opened by the operation signal of (1) to stop the operation of the high-frequency voltage generation circuit.

[0006]

In the above-mentioned conventional plasma cutting machine, the pilot arc is generated in synchronization with the generation of the high-frequency voltage. Had occurred. The pilot arc current is usually set to a peak current value of 10 A to several tens of amperes. Even in some cases, the insulation is broken by the pilot arc, and the transition to the plasma arc can be easily performed. However, if the pilot arc current value is too large, the loss of the pilot current suppressing resistor becomes excessive, and it is necessary to use a resistor having a large allowable loss.

An object of the present invention is to solve these conventional problems.

[0008]

In order to achieve these objects, the present invention provides a pilot arc current having a high peak current by repeating generation and extinction of a pilot arc current at an arbitrary period. The power loss of the pilot current suppression resistor is reduced by setting the effective current of the pilot arc current low while facilitating the transition from the plasma arc to the plasma arc.

[0009]

(Embodiment 1) Next, a specific example of the present invention will be described.

FIG. 1 shows an embodiment of the present invention. The schematic configuration of the first embodiment is the same as that shown in the conventional example (FIG. 4), and description of overlapping symbols will be omitted.

In FIG. 1, reference numeral 16 denotes an oscillation circuit composed of a multivibrator or the like. Here, the output signal of the oscillation circuit 16 is set to "H" for 0.1 second and "L" for 0.2 second. Set. The oscillation circuit 16 stops the oscillation when the plasma arc current flows and receives the signal of the current detector 11, and maintains the "H" signal while the plasma arc current flows. The control circuit 14 controls the operation / stop of the drive circuit 15 in synchronization with the signal of the oscillation circuit 16.

In this configuration, when the pilot arc current is generated, that is, when the current detector 11 does not detect the plasma arc current, the control circuit 14 operates the drive circuit 15 in synchronization with the signal of the oscillator 16. The output of the plasma cutting machine repeats the operation of generating an output for 0.1 seconds and stopping the output for 0.2 seconds. At this time, the pilot arc current shown in FIG. 5 is in the intermittent state shown in FIG.

After the transition to the plasma arc, the current detector 11
The control circuit 1 stops the operation of the high-frequency voltage generation circuit 9 and the oscillation operation of the oscillator 16
The control signal of No. 4 is kept in a normal continuous control state, and the output of the plasma cutting machine is kept stable.

(Embodiment 2) Next, Embodiment 2 of the present invention will be described with reference to FIG. FIG. 2 shows a configuration in which a switch (or a switching element) is provided in a pilot arc current circuit so that a pilot arc current is generated intermittently at a constant period during the generation of a pilot arc. In FIG.
Reference numeral 17 denotes a switch (or a switching element) provided in the pilot current circuit, which operates in synchronization with the oscillator 16 so as to be closed for 0.1 second and open for 0.2 second during generation of the pilot arc.

In this configuration, when a pilot arc current is generated, that is, when the current detector 11 does not detect the plasma arc current, the switch 17 opens and closes in synchronization with the signal of the oscillator 16 to cut off the pilot arc current circuit.・ Repeat energization. That is, the pilot arc is in an intermittent state in which generation of 0.1 seconds and stop of 0.2 seconds are repeated as shown in FIG.

After the transition to the plasma arc, the current detector 11
With this signal, the operation of the high-frequency voltage circuit 9 is stopped, the oscillation operation of the oscillator 16 is stopped, the switch 17 is kept open or closed, and the output of the plasma cutting machine is kept stable. That is, the same result as in the first embodiment can be obtained.

[0017]

According to the first and second embodiments, when the pilot arc is generated at such an intermittent cycle, the pilot arc current execution value is reduced by one as compared with the case where the pilot arc is continuously generated. / 3, the resistance loss can be reduced to 1/9,
The pilot arc current suppression resistor having a small allowable loss can be used. The pilot arc current value is increased in order to extend the possible distance from the pilot arc to the plasma arc. A pilot arc current suppression resistor can be used.

It should be noted that there is no problem in operability even if the pilot arc is intermittently set in a short cycle such as 0.1 second generation and 0.2 second stop.

By repeating generation and extinction of the pilot arc at an arbitrary cycle as described above, it is possible to provide a low-cost plasma cutting machine using a pilot current suppressing resistor having a small allowable loss. Further, even if the peak current value of the pilot arc current is increased in order to improve the operability, it is possible to sufficiently cope with the same pilot arc current suppression resistance as in the related art.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing a second embodiment of the present invention.

FIG. 3 is a diagram showing a pilot current waveform according to the present invention.

FIG. 4 is a configuration diagram showing an embodiment of a conventional example.

FIG. 5 is a diagram showing a pilot current waveform in a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 AC power supply and three-phase or single-phase AC power supply 2 Rectifier circuit which converts AC power supply to DC 3 Output power supply circuit of plasma cutting machine 4 Pilot arc current suppression resistor 5 Electrode of plasma cutting torch 6 Nozzle chip of plasma cutting torch Reference Signs List 7 material to be cut 8 pilot arc 9 high frequency voltage generation circuit 10 coupling coil 11 plasma arc current detector 12 input switch of high frequency voltage generation circuit 13 start switch of plasma cutting machine 14 control circuit of plasma cutting machine 15 output adjustment power supply circuit Drive circuit 16 Oscillation circuit 17 Pilot arc current switch or switch

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Katsumi Handa 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A plasma cutting machine for generating a pilot arc between an electrode of a plasma cutting torch and a nozzle tip and generating plasma by inducing the pilot arc, wherein the pilot arc is generated at an arbitrary cycle.
A plasma cutting machine characterized by being repeatedly extinguished. 2. The plasma cutting machine according to claim 1, wherein the output of the plasma cutting power supply is started and stopped at an arbitrary cycle during the pilot arc generation period, and the generation and extinction of the pilot arc are intermittently repeated. 3. The plasma cutting machine according to claim 1, wherein during the pilot arc generation period, the power output for the pilot arc is output / stopped at an arbitrary cycle, and the generation / extinction of the pilot arc is intermittently repeated. The plasma cutting machine according to claim 1.