JP3469078B2 - Arc igniter for plasma processing equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a plasma processing apparatus,
That is, an arc igniter for a plasma fusing machine or a plasma welding machine, which does not cause radio interference during its operation, is provided.

[0002]

2. Description of the Related Art As a conventional arc igniting method for a plasma processing apparatus, a high frequency high voltage is applied at the time of starting the arc to cause a discharge between a nozzle electrode for pilot arc and a main electrode to start the pilot arc. , This is transferred to the main arc between the main electrode and the base material. FIG. 6 shows an example of a device for this purpose. Reference numeral 4 is a main power supply for the main arc, which supplies a large DC current. The negative side of the output of the main power source is the main electrode 2 of the torch 1.
, And the positive side is connected to the base material 5. Reference numeral 6 is a DC power supply for pilot arc, which supplies a small current, the negative side of the output of which is connected to the main electrode 2 similarly to the main power supply, and the positive side is connected to the nozzle electrode 3.

By the way, in order to generate the main arc, it is necessary to start the pilot arc first. For this, a method of starting the arc by discharging by a high frequency high voltage has been conventionally used. 30 in FIG.
Is a high-frequency high-voltage circuit, which discharges in the spark gap 32 by the voltage from the step-up transformer 31 to generate a high-frequency voltage, which is superposed on the pilot arc DC power supply 6 via the coupling coil 33. It is supposed to do. Due to this high frequency high voltage, a discharge is generated between the nozzle electrode 3 and the main electrode 2 at the time of starting the arc, thereby inducing a pilot arc.
In FIG. 6, reference numerals 34 and 35 are a choke coil and a bypass capacitor, respectively, for preventing a high frequency high voltage from being applied to the pilot arc power source 6 and causing a failure. When the pilot arc is generated in this manner, the torch 1 can be moved to a steady-state plasma arc between the main electrode 2 and the base material 5 by bringing the torch 1 close to the base material while applying the voltage from the main power supply 4. it can.

The above high frequency high voltage is necessary only when the pilot arc is started. Therefore, generally, the operation of the high-frequency generator is automatically stopped when the pilot arc or the main arc is generated, while the operation is automatically started when the arc is broken. As described above, the high frequency is not continuously generated, but the arc blinking frequency of the welding device or the like is very high, and a considerably strong noise electric wave is radiated each time the arc is started. Therefore, in order to use a plasma welding machine or a plasma fusing machine in a factory close to a private house, it is necessary to install a line filter, an electromagnetic shield or the like as a measure against noise interference to a television or a radio.
Further, for the purpose of automating welding and the like, an automatic device such as a robot using a microcomputer is combined, but there is a possibility that high frequency noise may cause these electronic devices to malfunction or be destroyed.

As a measure against the above problem, Japanese Patent Publication No. 8-1341
In Japanese Patent No. 6 and Japanese Patent No. 2631178, a direct current high voltage power source is connected in parallel with the main power source of the direct current arc welding device, and a high voltage is applied between the electrode of the welding torch and the base metal at the time of starting the arc. A device has been proposed in which a discharge is caused to occur, and thereby an arc is started. However, when such an arc ignition method is applied to a plasma welding machine or a plasma fusing machine, the insulation resistance is low due to the water cooling method of the torch, and a DC high voltage power source with a large current capacity must be used. I understood it. For example, Japanese Patent Publication No. 8-13416 discloses that a no-load voltage is 1000 V or more and a DC high voltage generating circuit having a short circuit current of 100 mA or less is used as a condition, and Japanese Patent No. 2631178. As an example, the publication discloses a DC high-voltage power supply having a drooping characteristic with a no-load voltage of about 4 kV and a short-circuit current of about 10 mA. However, in the plasma processing apparatus, the leakage current when a high voltage is applied may be about 1 A, and it has been found that arc ignition of the plasma processing apparatus is difficult with a DC high voltage power supply having a current capacity as shown here. did.

[0006]

SUMMARY OF THE INVENTION The present invention provides an arc igniter for a plasma processing apparatus that does not cause radio interference, which is a problem of the conventional method of applying a high frequency voltage. For this reason, in the method of applying a DC high voltage, there is provided a method of enabling this with an inexpensive device without requiring a DC high voltage power supply with a large current capacity.

[0007]

Means for Solving the Problems The present invention is to solve the above problems and is a plasma in which a negative output of a DC power source for pilot arc is connected to a main electrode and a positive output is connected to a nozzle electrode for pilot arc. In an arc igniter of a processing apparatus, a DC high-voltage power supply having a no-load voltage of 1400 V or more and a capacitor for charging an output voltage of the DC high-voltage power supply are provided, and a resistor and a high-voltage switch closed at the time of arc ignition. A positive output of the capacitor is connected to the nozzle electrode for the pilot arc, a negative output is connected to the main electrode, respectively, and a rectifying element having a reverse blocking voltage equal to or higher than the no-load voltage of the DC high voltage power source is It is an arc igniter for a plasma processing apparatus, which is connected in series with a pilot arc DC power supply. Here, the resistance value of the resistor is 500Ω or more and 3 kΩ
It is also characterized in that the DC high-voltage power supply and the capacitor are constituted by a multistage cascade rectification circuit.

[0008]

1 is a conceptual diagram showing an example of a plasma processing apparatus provided with an arc ignition device of the present invention.
Has a main electrode 2 and a nozzle electrode 3 which are not consumed by a plasma torch, and a high-speed shield gas is jetted from a gap between the main electrode and the nozzle electrode. Reference numeral 4 denotes a main power source, which is mainly composed of a transformer, a rectifier, and a current control device, which are not shown, and outputs a large direct current. The current control device is implemented, for example, by using a saturable reactor or by controlling the phase by using a thyristor, a power transistor or the like for the rectifier itself. The output of this main power source is connected to the base material 5 on the positive side and to the main electrode 2 on the negative side. 6 is a direct current power source for pilot arc, which is designed to output a small current direct current,
The internal structure is the same as that of the main power source 4. The positive side of the output of the pilot arc power supply is the rectifying element 7 which will be described later.
To the nozzle electrode 3, and the negative side is connected to the main electrode 2 as well as the main power source 4.

Reference numeral 8 is a DC high-voltage power supply, the output of which is charged in a capacitor 9, and the voltage of this capacitor is applied between the main electrode 2 and the nozzle electrode 3 when the pilot arc is started. Is caused to generate a spark discharge,
Induce a pilot arc. Spark discharge is possible if the voltage applied between the main electrode and the nozzle electrode is about 1000 V or more, but in the plasma processing apparatus, the insulation resistance is low and the voltage drops at the torch tip as described above. , The charging voltage of the capacitor, that is, the no-load voltage of the DC high-voltage power supply is 1400 V or more, preferably 1
Make it 700V or more. Even if the voltage of the DC high-voltage power supply is high, there is no problem in causing spark discharge, but if it is too high, the withstand voltage of peripheral devices such as wiring must be increased, which is uneconomical. Therefore, it is not necessary to set the voltage of the DC high-voltage power supply to 3000 V or more in the normal case. The current capacity of the DC high-voltage power supply may be smaller than the current flowing when a high voltage is applied between the nozzle electrode 3 and the main electrode 2.
That is, in the present invention, even when the insulation resistance is low and the leak current is large like a plasma torch, a large current can be instantaneously flown by discharging the capacitor without providing a power source with a large current capacity, and the nozzle electrode and the main electrode The voltage required for spark discharge can be secured between and.

Reference numeral 10 denotes a high-voltage switch, which is a contact such as an electromagnetic contactor. The high-voltage switch is normally open, and the arc start switch of the plasma processing apparatus is turned on and the capacitor 9 is charged and then closed. Reference numeral 11 is a resistor that limits the discharge current from the capacitor to prevent damage to the contacts and torch of the high-voltage switch due to a large current, and when a pilot arc causes a decrease in load resistance, etc. Moreover, it is for preventing the DC high voltage power supply from being short-circuited. For this purpose, the resistance value of the resistor is usually 500Ω or more. On the other hand, if the resistance value is too high, the voltage applied to the torch becomes low and spark discharge becomes difficult, so a range of 3 kΩ or less is appropriate.

The rectifying element 7 is for preventing a high voltage from the capacitor 9 from being applied to the direct-current power source 6 for pilot arc and causing dielectric breakdown. Therefore, it is necessary that the reverse blocking voltage is equal to or higher than the no-load voltage of the DC high voltage power source 8 and the current capacity is equal to or higher than the pilot arc current. In the arc ignition method using high-voltage direct current discharge as in the present invention, it is necessary to provide a rectifying element so that the high voltage is not applied to the arc power source in any case. With respect to 4, the rectifying element for this purpose is unnecessary because the voltage of the capacitor 9 is not applied. That is, in the plasma processing apparatus of the type in which the main arc is generated via the pilot arc, a rectifying element of a small current corresponding to the pilot arc current is sufficient, and thus the arc ignition method using a high DC voltage is particularly suitable.

FIG. 2 is a time chart for explaining the operation of the above-mentioned device of the present invention. When the arc start switch is turned on, the supply of shield gas is started, and after the gas reaches the tip of the torch, power is supplied to the arc power supply, that is, the pilot arc power supply 6 and the main power supply 4. At the same time, the DC high-voltage power supply 8 is also fed to charge the capacitor 9, and after the capacitor is charged, the high-voltage switch 9 is closed and the high voltage of the capacitor is applied between the nozzle electrode 3 and the main electrode 2. When applied, a spark discharge is generated. At this time, since the output voltage has already been applied from the pilot arc DC power supply 6, a spark arc induces a pilot arc between the nozzle electrode 3 and the main electrode 2. Referring to the transition of the voltage of the nozzle electrode in FIG. 2, first, the no-load voltage of the pilot arc power source is applied, and then the high voltage DC is applied, the pilot arc is generated and becomes the arc voltage. The high voltage is shown schematically in this figure,
Actually, it is instantaneous as described later. Although not shown in FIG. 2, since the direct current voltage from the main power source 4 is further applied, the pilot arc is brought between the main electrode 2 and the base material 5 by bringing the torch 1 close to the base material 5. Move to.

Since the high DC voltage between the nozzle electrode and the main electrode is necessary only when the arc is started, the high voltage switch 9 detects the pilot arc when it occurs and opens it. Further, when spark discharge occurs between the nozzle electrode and the main electrode, the capacitor discharges and the terminal voltage drops, so the high voltage switch 9 is closed and then opened to charge the capacitor to the no-load voltage of the DC high voltage power supply. It is preferable to do so. In other words, even when the pilot arc does not occur at one time, it is preferable that the high voltage switch is not left closed and is repeatedly opened and closed at a constant cycle.
The high-voltage switch monitors the current of the main arc and pilot arc with a current transformer, etc., and if there is a break in both the main arc and pilot arc during use of the plasma processing device, it automatically closes the pilot arc. It is preferable to re-ignite.

When a multi-stage cascade rectifier circuit as described below is adopted as the DC high voltage power source of the present invention, the
It is preferable that the secondary voltage can obtain high DC voltage without being too high. Moreover, as described above, in the present invention, the output of the DC high-voltage power supply is once charged into the capacitor and then discharged all at once during pilot arc ignition.However, in the multistage cascade rectification circuit, the DC voltage in the present invention is not required even if a separate capacitor is provided. The function of the high-voltage power supply and the function of the capacitor can be combined. FIG. 3 shows an example of a multi-stage cascade rectification circuit, which has a peak value V _m of the secondary voltage of the power transformer 21 of 6 _m .
The case where a double voltage is obtained is shown. That is, since each capacitor 22 is charged with a voltage obtained by adding the voltage V _m of the power source to the voltage of the capacitor at the previous stage, it is possible to obtain a voltage that is twice the voltage V _m of the power source depending on the number of stages in which the rectifier 23 and the capacitor are combined. You can

FIG. 4 shows another example of the multi-stage cascade rectification circuit, and shows a case where a voltage six times the peak value V _m of the secondary voltage of the power transformer 21 is obtained as in the circuit of FIG. . Twice the voltage V _m to the capacitors 25 of V _m, 2 stage and thereafter to the capacitor 24 of the first stage is charged in this circuit. Thus 6 V _m at three times the 2V _m in this example
Double voltage can be obtained. Since the capacitors are connected in series in this circuit, the effective capacitance is reduced as compared with the circuit shown in FIG. However, FIG.
In the circuit (1), the capacitors at each stage must have sequentially higher withstand voltages as the number of stages is increased, but this circuit has an advantage that the withstand voltage of each capacitor is twice the voltage V _m of the power supply.

FIG. 5 is a graph of the oscilloscope recording the phenomenon when the pilot arc of the plasma processing apparatus is generated by the arc ignition apparatus of the present invention. In this example, the multistage cascade rectifier circuit shown in FIG. 4 is used, the number of stages is 18, and the capacitance of each capacitor is 0.01.
˜0.02 μF and no-load voltage is 1800V. As the resistor 11, a resistor having a resistance of 1 kΩ was used.
FIG. 5A shows changes in voltage and pilot arc current measured at the output side of the high voltage switch 10. The voltage rises when the high-voltage switch is closed, but it drops instantaneously due to the discharge of the capacitor. FIG. 5B shows the voltage transition at this time measured with the time axis expanded,
The application time of the high voltage is about several μs.

In the present invention, as shown in FIG. 5 (b), it can be seen that the pilot arc can be activated if it is applied to the torch for several μs which is the discharge time of the capacitor. That is, as shown in FIG. 5 (a), it takes about 10 ms for the pilot arc current to rise and reach a steady state, but the DC high voltage itself has a sufficient effect if applied for a much shorter time. be able to. This is probably because the plasma generated by the spark discharge due to the high DC voltage, that is, the ionized gas remains even when the discharge current disappears, and the pilot arc path can be generated in the gas due to the conductivity of this plasma. To be

[0018]

According to the arc igniter of the plasma processing apparatus of the present invention, unlike the apparatus for applying a high frequency, which has been generally practiced in the past, the discharge by the high DC voltage is used, and therefore the radio wave interference is not generated. . Further, in the device of the present invention, even if the current capacity of the DC high-voltage power source itself is small, a large current can be flown by discharging the capacitor, and even if the insulation resistance is low and the leak current is large like a plasma torch, it does A voltage required for spark discharge can be secured between the electrodes.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a plasma processing apparatus provided with an arc ignition device of the present invention.

FIG. 2 is a time chart explaining the operation of the arc ignition device of the present invention.

FIG. 3 is a circuit diagram showing an example of a multistage cascade rectification circuit used in the arc ignition device of the present invention.

FIG. 4 is a circuit diagram showing an example of a multistage cascade rectification circuit used in the arc ignition device of the present invention.

5 (a) and 5 (b) are graphs of an oscilloscope measuring the operation of the arc igniter of the present invention.

FIG. 6 is a diagram showing an example of a conventional arc ignition device using a high-frequency high voltage.

[Explanation of symbols]

1 torch 2 main electrode 3 nozzle electrodes 4 main power supply 5 Base material 6 DC power supply for pilot arc 7 Rectifying element 8 DC high voltage power supply 9 capacitors 10 High voltage switch 11 resistors 21 power transformer 22 Capacitor 23 Rectifier 24, 25 capacitors 30 high frequency high voltage circuit 31 step-up transformer 32 Spark Gap 33 Coupling coil 34 choke coil 35 Bypass capacitor

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kazuyuki Tsuchiya, No. 1 Shin-Nakahara, Isogo-ku, Yokohama-shi, Kanagawa Ishi, Kawashima Harima Heavy Industries, Ltd. Technical Research Institute (72) Katsura Owaki 1 Shin-Nakahara, Isogo-ku, Yokohama, Kanagawa Address Ishi Kawashima Harima Heavy Industries Co., Ltd. Technical Research Institute (72) Inventor Keiji Onda 1-39 Hikisawa, Kamiyacho, Kasugai City, Aichi Prefecture Toyo Denki Co., Ltd. Kamiya Factory (56) Reference JP-A-4-249096 (JP, A) ) JP-A-5-92267 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B23K 10/00 B23K 9/06 B23K 9/067

Claims (3)

(57) [Claims] 1. An arc igniter of a plasma processing apparatus, wherein a negative output of a pilot arc DC power source is connected to a main electrode and a positive output is connected to a pilot arc nozzle electrode, respectively. A voltage power supply and a capacitor for charging the output voltage of the DC high voltage power supply are provided, and the positive output of the capacitor is applied to the nozzle electrode for the pilot arc through a resistor and a high voltage switch that closes during arc ignition. , A negative output is connected to each of the main electrodes, and a rectifying element having a reverse blocking voltage equal to or higher than the no-load voltage of the DC high-voltage power supply is connected in series to the pilot arc DC power supply. Arc ignition device for plasma processing equipment. 2. The resistance value of the resistor is 500Ω or more and 3k.
The arc ignition device of the plasma processing apparatus according to claim 2, wherein the arc ignition device has an Ω or less. 3. The arc igniter for a plasma processing apparatus according to claim 1, wherein the DC high-voltage power supply and the capacitor are configured by a multistage cascade rectification circuit.