JPH0318059Y2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Technical Field This invention relates to miniaturization, cost reduction, and improvement in control responsiveness, etc. of a power supply device for a plasma arc welding machine.

(b) Prior art and its drawbacks A circuit diagram of a conventional power supply device for a plasma arc welding machine is shown in Fig. 5. Transformer T that transforms three-phase alternating current
1 is a primary winding Ta connected to a three-phase AC power supply,
It has a pilot arc winding Tb and a plasma arc winding Tc. The pilot arc winding Tb is connected to the pilot arc current rectifier circuit RE via a switch A1. The pilot arc current rectifier circuit RE includes diodes D1 to D6.
It is configured as a three-phase full-wave rectifier circuit. The negative terminal of the output of this pilot arc current rectifier circuit RE is connected to the electrode EL of the plasma torch through a terminal O1. Further, the positive electrode is connected to the terminal O3 via the current limiter R2 and the coupling coil CC of the high frequency generator HF, and the restraint nozzle N of the plasma torch is connected to the terminal O3. The high frequency generator HF is used to facilitate arc generation by superimposing a high frequency voltage on the DC voltage output from the pilot arc current rectifier circuit RE and applying it to the restraint nozzle N when a pilot arc is generated. A plasma arc current rectifier circuit RC is connected to the plasma arc winding Tc. The plasma arc current rectifier circuit RC is a three-phase AC full-wave rectifier circuit composed of thyristors TH1 to TH3 and diodes D7 to D9, and this rectifier circuit is opened and closed by opening and closing of the thyristors TH1 to TH3. This thyristor
The opening/closing of TH1 to TH3 is done by the phase control circuit PS, which will be described later.
controlled by. The negative electrode of the output of this plasma arc current rectifier circuit RC is connected to the electrode EL through the terminal O1, similar to the negative electrode of the pilot arc current rectifier circuit RE, and the positive electrode is connected to the terminal O2 through the smoothing reactor L and the current detector CT. It is connected. A base material M for welding is connected to the terminal O2. The current detector CT converts the detected value into an error amplifier.
Outputting to CA. A reference battery E is connected to the error amplifier CA in advance, and the error between the detected value of the current detector CT and the reference voltage is amplified and the phase control circuit is activated.
Output to PS. Phase control circuit PS is error amplifier
Based on the output of CA, the timing of opening and closing of thyristors TH1 to TH3 is controlled in phase so that the current flowing through the current detector CT is constant. The positive terminal of the pilot arc current rectifier circuit RE is a diode D1.
0, is connected to the positive pole of the plasma arc current rectifier circuit RC via resistor R1 and switch A2,
When switch A2 is closed, the voltage of the pilot arc current rectifier circuit RE is applied to the base material M via terminal O2.

When using the power supply device for a plasma arc welding machine with the above configuration, first close the switch A1 and ignite the pilot arc between the welding electrode EL and the restraint nozzle N to generate plasma, then the phase control circuit At the same time as operating the PS, switch A2 is closed only at the moment of plasma arc ignition, and the voltage of the pilot arc current rectifier circuit RE is applied to the base material M.
Assists arc ignition between electrode EL and base metal M.

By the way, in such a power supply device for a plasma arc welding machine, phase control is performed by opening and closing semiconductor rectifying elements (thyristors TH1 to TH3) of AC at commercial frequency, but when the plasma arc is started, the current control of the control system Due to this delay, a temporarily excessive plasma arc current flows. This current often caused damage to the welding electrode EL and the transformer T1. Further, during welding or cutting work, the plasma arc is repeatedly ignited and stopped, and it is desirable to leave the pilot arc ignited during the work to facilitate ignition. However, if the pilot arc continues to be ignited with the same current as when it is stopped while the plasma arc is ignited, power consumption will increase, and the secondary winding Tb
However, the current capacity of the pilot current rectifier RE had to be increased, making it larger and more expensive. Furthermore, in order to prevent the welding electrode EL and restraint nozzle N from being worn out due to insufficient smoothing of the voltage applied to the welding electrode EL and restraint nozzle N, a smoothing reactor L with a large induction coefficient is used. This also has the drawback of making the device larger and more expensive.

(c) Purpose of the invention In view of the above-mentioned drawbacks, the object of this invention is to provide a power supply device for a plasma arc welding machine that is small and capable of constantly igniting a pilot arc and sufficiently smoothing the applied voltage.

(d) Structure and effect of the invention This invention consists of a power supply rectifier circuit that rectifies AC input to obtain a DC voltage, a high-frequency switching circuit that converts this DC voltage into a high frequency, and a secondary side that is connected to this high-frequency switching circuit. a transformer having a pilot arc winding and a plasma arc winding, and a pilot arc current rectifier circuit that rectifies the output of the pilot arc winding and supplies the rectified output between the welding electrode and the restraint nozzle. , a plasma arc current rectifier circuit that switches open/close the output of the plasma arc winding, rectifies it, and supplies the rectified output between the welding electrode and the base metal; and plasma flowing between the welding electrode and the base metal. A current detector that detects arc current, an error amplifier that determines the error between the detected value of the current detector and a preset reference potential, and a high frequency switching circuit that controls the high frequency switching circuit based on the output of the error amplifier. A control unit.

With the above configuration, the following effects can be achieved according to this invention.

The AC power source is first converted to DC, then converted to high frequency, transformed, rectified and smoothed into DC for arcing. By using high frequency, transformers,
The smoothing reactor and capacitor can be made smaller, and the rectified direct current has high smoothness. Therefore, the device can be made smaller and cheaper, welding work can be performed with high braking, and since a direct current with less ripple flows, there is less wear and tear on the electrodes and restraint nozzle.
In addition, since feedback control of the plasma arc current is performed by switching the high frequency waveform, it is possible to perform quick and highly accurate control with little time lag. In addition, since plasma arc current control is performed on the high frequency before voltage transformation, this control is also applied to the pilot arc current, making it possible to reduce the pilot arc current during plasma arc ignition, thereby reducing power consumption. It is possible to reduce the current capacity of the pilot arc winding, pilot arc current rectifier circuit, etc.

(e) Embodiment FIG. 1 is a circuit diagram of a power supply device for a plasma arc welding machine which is an embodiment of this invention. The power supply rectifier circuit RF is a three-phase AC full-wave rectifier circuit composed of six diodes D11 to D16. The voltage rectified by the power rectifier circuit RF is supplied to high frequency switching transistors Q1 and Q2. Capacitors C1 and C2 connected in series are connected between the DC output terminals of the rectifier RF, and the high frequency switching transistors Q1 and
Q2 is connected. A primary winding Td of a transformer T3 is connected between capacitors C1 and C2 and between transistors Q1 and Q2. transistor Q
1 and Q2 are turned on alternately, so that an alternating current flows through the primary winding Td. The on/off state of the transistors Q1 and Q2 is controlled by a high frequency switching circuit control section SC1. The transformer T3 has a pilot arc winding Te.
Two secondary windings are wound: and a plasma arc winding Tf. The transformed output of the pilot arc winding Te is full-wave rectified by the pilot arc current rectifier circuit RH consisting of diodes D17 and D18, and its positive output is smoothed by the smoothing reactor L2 and then passed through the current limiter R3 and the high frequency generator HF. The signal is supplied to the terminal O3 via the coupling coil CC. A restraint nozzle N of a welding machine is connected to the terminal O3. The negative pole of the pilot arc current rectifier circuit RH is connected to the electrode EL of the welding machine via the terminal O1. The high-frequency generator HF is used to apply a high-frequency voltage superimposed on the DC voltage supplied to the restraint nozzle N at the time of ignition of the plasma arc, thereby facilitating generation of a pilot arc. The transformer output of the winding Tf for plasma arc is thyristor TH4, TH
Plasma arc current rectifier circuit RG consisting of 5
full-wave rectification. The positive electrode is connected to a terminal O2 via a plasma arc current detector CT, and a base material M for welding is connected to the terminal O2. The negative electrode is connected to terminal O1 via smoothing reactor L1. Thyristors TH4 and TH5 are opened and closed by a plasma switch circuit SC2. The positive terminal of the pilot arc current rectifying circuit RH is connected to the positive terminal of the plasma arc current rectifying circuit RG via a diode D19, a current limiter R4, and a switch A3. This causes the pilot arc voltage to be applied to the base metal when switch A3 is closed. The detected value of the plasma arc current detector CT is output to the error amplifier circuit CA. A reference potential is previously set in the error amplification circuit CA by the battery E, and the error amplification circuit CA amplifies the error between the detected value and the reference potential and outputs it to the high frequency switching circuit control section SC1. The high frequency switching circuit control unit SC1 controls the transistor Q to maintain the plasma arc current at a constant value set by the reference potential based on the input from the error amplifier circuit CA.
1. Controls on/off of Q2.

When performing plasma arc welding using this circuit, when the power is turned on, a pilot arc current flows and a pilot arc is generated between the electrode EL and the restrained nozzle N. Arc ignition instantaneous high frequency generator
HF applies high frequency voltage to assist in ignition. When the welding machine approaches the base metal M to start welding, turn on the torch ignition foot switch (not shown), and the plasma switch circuit SC
2 turns on thyristors TH4 and TH5 and the base material M,
Apply voltage between electrodes EL. At this time, the switch A3 is closed for a certain period of time and the voltage for the pilot arc is also applied to the base material M, so that the already generated pilot arc and the superimposed voltage can easily ignite the plasma arc. I can do it. When interrupting welding work, simply turn off the foot switch to stop the plasma arc and return to only the pilot arc.

FIG. 2 is a graph showing the current and signal voltage of each part during operation of the above embodiment, and FIG. 3 is a graph showing the voltage and current characteristics of the pilot arc. Figure 2A
B shows the switch signal of the power supply of the device, and B shows the pilot arc current. When the power switch is turned on, the pilot arc current continues to flow, and the pilot arc is always ignited. The same figure C shows thyristor TH4 of plasma arc switch circuit CS2,
The ON signal of TH5, D in the same figure shows the plasma arc current. When the thyristors TH4 and TH5 are turned on, a plasma arc is immediately ignited and a plasma arc current flows, but at this time the pilot arc current decreases as shown in FIG. this is,
For the pilot arc circuit load characteristic shown in graph c in Fig. 3, the error amplifier CA and the high frequency switching circuit control unit SC1 cause the switching circuit S to output the maximum output since the current detector CT detects zero when the plasma arc is stopped. While the no-load voltage of the winding Te is maximized, while the plasma arc current is flowing,
The switching circuit S is controlled so that the output of the current detector CT becomes a constant value.
This is because the no-load voltage of Te decreases, and the pilot arc current decreases accordingly. The no-load characteristic shown by a in FIG. 3 shows the case where no plasma arc current is flowing, and the no-load characteristic shown by b shows the case when the plasma arc current is flowing. As a result, the pilot arc current value when the plasma arc is ignited can be made smaller than the current value when the plasma arc is stopped.
The current capacity of the device can be reduced, which can promote miniaturization and cost reduction of the device.

FIG. 4 is a circuit diagram of another embodiment of this invention. This embodiment differs from the embodiment shown in FIG. 1 in that a winding without an intermediate tap is used for the pilot arc winding, and a diode bridge is used for the rectifier. L3 is a reactor for preventing surge current. This makes it possible to further reduce the weight of the transformer. The operation and functions are exactly the same as the embodiment shown in FIG.

In this way, if you use this power supply device for plasma arc welding machines, the commercial power supply is first converted to DC, then converted to high frequency, transformed, and rectified and smoothed to DC for arc, so the transformer, The smoothing reactor and capacitor can be made smaller, and the rectified DC has a high degree of smoothness. Therefore,
The equipment can be made smaller and cheaper, welding work can be performed with high braking, and since direct current with less ripple flows, there is less wear on the electrodes and restraint nozzles. Furthermore, since feedback control of the plasma arc current is performed by switching the high frequency waveform, it is possible to perform quick and highly accurate control with little time lag. In addition, since plasma arc current control is performed on the high frequency before voltage transformation, the pilot arc current is also controlled, making it possible to reduce the pilot arc current during plasma arc ignition and reduce power consumption. It is possible to save money and reduce the current capacity of the pilot arc Te, pilot arc current rectifier, etc.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a power supply device for a plasma arc welding machine that is an embodiment of this invention, Figure 2 A, B,
C and D are diagrams showing graphs of the power-on signal, pilot arc current, plasma arc-on signal, and plasma arc current of the above embodiment, and Fig. 3 shows when the plasma arc current of the above embodiment is flowing and when it is not flowing. FIG. 4 is a circuit diagram of another embodiment of this invention, and FIG. 5 is a circuit diagram of a conventional power supply device for a plasma arc welding machine. RF...Power rectifier, S...High frequency switching circuit, T3...Transformer, RH...Pilot arc current rectifier, RG...Plasma arc current rectifier, SC1...High frequency switching circuit control unit.

Claims (1)

[Scope of utility model registration request] A power supply rectifier circuit that rectifies AC input to obtain a DC voltage, a high frequency switching circuit that converts this DC voltage to high frequency, and a pilot arc winding and a plasma arc winding connected to this high frequency switching circuit on the secondary side. a pilot arc current rectifier circuit that rectifies the output of the pilot arc winding and supplies the rectified output between the welding electrode and the restraint nozzle; a plasma arc current rectifier circuit that rectifies and supplies the rectified output between the welding electrode and the base metal; a current detector that detects the plasma arc current flowing between the welding electrode and the base metal; A plasma arc welding device comprising: an error amplifier for determining an error between a detection value of a device and a preset reference potential; and a high-frequency switching circuit control section that controls the high-frequency switching circuit based on the output of the error amplifier. Machine power supply.