JPS6226866B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides controlled rectification of an AC input by one controlled rectifier made of a semiconductor-controlled rectifying element to provide a first output terminal and a second output terminal for supplying plasma arc current. 2
A DC output with drooping characteristics or constant current characteristics is obtained at the output terminal, and the first output terminal or the second output terminal is
The present invention relates to a plasma power supply connected to a third output terminal for supplying pilot arc current via a current limiter.

[Conventional technology]

Normally, a plasma arc has the property that the diameter of its spread shrinks as it is cooled from the surroundings, reaching a high temperature of 1 to 20,000℃. In recent years, plasma welding or plasma cutting has been used to efficiently process metals.

Next, a plasma power supply device conventionally used for plasma welding and plasma cutting will be explained with reference to FIGS. 1 and 2.

In Figure 1, U, V, W are the input terminals of the three-phase power supply, and T1 is the primary winding Ta, which is the input terminal U, V,
Main transformer connected to W, and two secondary windings, one for pilot arc and one for plasma arc.
It has Tb and Tc.

Ts and Ms are torch switches and magnetic contactors for external operation connected in series to the AC power supply terminal AC,
A denotes three first normally open contacts of the electromagnetic contactor MS, each of which has one end connected to the U-phase, V-phase, and W-phase pilot arc secondary windings Tb.

RE is a rectifier configured into a full-wave rectifier circuit by first to sixth semiconductor rectifiers D1 to D6 consisting of diodes, and three AC side terminals are connected to each first normally open contact A of the magnetic contactor MS. The negative DC side terminal (-) is connected to the first output terminal O1.

RC denotes first to third semiconductor controlled rectifiers TH1 to TH3 made of thyristors and seventh to ninth semiconductor rectifiers D7 to D made of diodes.
9 is a controlled rectifier configured into a full-wave rectifier circuit, the three AC side terminals are connected to the plasma arc secondary winding Tc of the main transformer T1, and the negative DC side terminal (-) is connected to the secondary winding Tc for plasma arc of the main transformer T1. 1 output terminal O1.

L, RL1, and CT are a smoothing reactor, a first relay, and a current detector connected in series between the positive DC side terminal (+) of the control rectifier RC and the second output terminal O2, respectively.

R1 is the first current limiter connected between the positive DC side terminals (+) of the rectifier RE and the control rectifier RC, and R2, RL2, CC are the positive DC side terminals (+) of the rectifier RE, respectively. ) and the third output terminal O3 are a second current limiter, a second relay, and a coupling coil connected in series.

HF is a well-known high-frequency generator composed of a spark gap G connected to the primary winding of a coupling coil CC, a high-voltage capacitor C, and a high-voltage transformer T2, and the primary winding of the high-voltage transformer T2 is
Normally closed contact B of second relay RL2 and electromagnetic contactor
AC power supply terminal AC via the second normally open contact A′ of the MS.
It is connected to the.

CA is a comparison amplifier with one input terminal connected to the current detector CT, and S and E are each comparison amplifiers.
These are the normally open switch contact and the reference power supply of the first relay RL1 connected in series between the other input terminal of the CA and the ground terminal.

PS is a phase shifter connected to the output terminal of the comparator amplifier CA, and each semiconductor-controlled rectifier TH1 to TH
Outputs the ignition signal to the gate terminal 3.

EL and N are the first and third output terminals O, respectively.
1, the electrode and restraint nozzle of the plasma torch connected to O3, M is the base material connected to the second output terminal O2.

Next, the operation of the power supply device will be explained with reference to FIG. 2.

At time t1 in Fig. 2, when the torch switch TS is turned on as shown in Fig. 2a, the electromagnetic contactor MS is energized and its first normally open contact A and second normally open contact are connected to each other.
A′ is turned on, and the voltage induced in the pilot arc secondary winding Tb of the main transformer T1 is transferred to the rectifier RE.
The DC output voltage of this rectifier RE is applied to the second current limiter R2 and the second relay RL.
2 and the electrode EL through the coupling coil CC
and the restraint nozzle N.

On the other hand, by turning on the second normally open contact A' of the electromagnetic contactor MS, an AC voltage is applied to the primary winding of the high voltage transformer T2 of the high frequency generating section HF, and the high frequency generating section
At HF, the high voltage on the secondary side of the high voltage transformer T2 is charged to the high voltage capacitor C, and when the charging potential reaches the breakover voltage of the spark gap G, the high voltage is transferred through the primary winding of the coupling coil CC. The battery is discharged, and this operation is repeated to generate a high frequency voltage as shown in FIG.

Furthermore, this high frequency voltage is applied to the coupling coil.
After being boosted to a high voltage by the CC, it is superimposed on the output voltage of the rectifier RE and applied between the restraint nozzle N and the electrode EL, and at time t2, a pilot arc is generated between the restraint nozzle N and the electrode EL, and the voltage of the rectifier RE is increased. The output current is limited to a predetermined current value by the second current limiter R2, and a pilot arc current is supplied to the restraint nozzle N and the electrode EL as shown in FIG. As shown in d, the second relay RL2 operates and its normally closed contact B is opened, and as shown in c of the same figure, the operation of the high frequency generator HF is stopped.

Then, when the plasma torch is brought close to the base material M,
At time t3, as shown in the figure e, the pilot arc moves and a plasma arc is generated between the electrode EL and the base material M, and a plasma arc current flows from the base material M to the electrode EL.

At this time, if we assume that the reference power supply E is connected to the comparator amplifier CA, the detection signal of the current detector CT is zero at the moment when a plasma arc occurs, so the phase shifter PS of the feedback control system , each semiconductor-controlled rectifying element TH1 to TH3 is fully conductive, and an excessive plasma arc current flows from the base material M to the electrode EL. Electrode EL is damaged.

Therefore, when a plasma arc occurs, the reference power source E is disconnected by the normally open switch contact S of the first relay RL1, and when a plasma arc occurs, the output current of the rectifier RE is limited by the first current limiter R1. A small current flows from the base material M to the electrode EL, and a small current plasma arc is generated.

This small current operates the first relay RL1, closing its switch contact S, and the reference voltage of the reference power supply E is applied to the comparator amplifier CA.
In CA, the detection voltage of the current detector CT which detects the plasma arc current, converts it into a voltage proportional to the current and outputs it, and the reference voltage are compared and amplified, and both input voltages are output from the comparator amplifier CA. A signal is output such that the difference between the two becomes zero.

The ignition signal based on this output signal is used by the phase shifter PS.
output from each semiconductor controlled rectifier TH1~
TH3 is phase controlled, the output current of the control rectifier RC is constant current controlled to a constant value set in the reference power source E, and is smoothed by the smoothing reactor L, so that a predetermined plasma arc current is supplied.

Therefore, an excessive hot current is prevented from flowing at the time of arc start, and the plasma torch is protected.

Then, at time t4, as shown in figure a, when the torch switch TS is turned off, as shown in figure b,
Since the pilot current no longer flows, the plasma arc also disappears, as shown in FIG.

[Problem that the invention seeks to solve]

However, in the above power supply device, in addition to the control rectifier RC as a power source for the plasma arc, in order to prevent hot current at the time of arc start, a secondary winding for the pilot arc is installed in the main transformer T1 for generating the pilot arc. Tb must be provided separately, the circuit configuration becomes extremely complicated, the cost is high, and there are disadvantages in that miniaturization is not possible.

[Means for solving problems]

The present invention has been made in consideration of the above-mentioned drawbacks of the conventional art, and provides controlled rectification of alternating current input by one controlled rectifier made of a semiconductor controlled rectifier to provide a first output terminal for supplying plasma arc current and a first output terminal for supplying plasma arc current. 2
A DC output with drooping characteristics or constant current characteristics is obtained at the output terminal, and the first output terminal or the second output terminal is
In a plasma power supply device connected to a third output terminal for supplying pilot arc current via a current limiter, a feedback control system of the control rectifier section includes:
A first reference power source for setting a pilot arc current and a second reference power source for setting a plasma arc current are provided, and the first reference power source and the second reference power source are compared through a normally closed contact and a normally open contact, respectively. A relay is connected to the amplifier and inserted between the control rectifier and either the first output terminal or the second output terminal to detect plasma arc current and operate both the contacts. This is a plasma power supply device featuring:

[Effect]

Therefore, according to the present invention, one circuit of the controlled rectifier is used as a power supply circuit for both the pilot arc and the plasma arc, and as a result, the secondary winding of the main transformer also becomes one winding, and the circuit configuration is improved. This greatly simplifies the process, reduces assembly man-hours, reduces costs, and downsizes the device.

Furthermore, by providing two reference power supplies in the feedback control system and switching both power supplies according to the occurrence of pilot arc and plasma arc, excessive hot current can be prevented when plasma arc occurs.

Furthermore, reliability is improved by simplifying the configuration.

〔Example〕

Next, this invention will be described in the third section showing one embodiment thereof.
This will be explained in detail with reference to FIG.

The circuit configuration of FIG. 3 differs from that of FIG. 1 in the following points.

The pilot arc secondary winding Tb, the rectifier RE and the first current limiter R1 of the main transformer T1 in Fig. 1 are deleted, and the secondary winding of the second relay RL2, second current limiter R2 and coupling coil CC is A series circuit of windings is inserted between the smoothing reactor L and the third output terminal O3.

Furthermore, the feedback control system of the control rectifier RC is provided with a first reference power source E1 for setting the pilot arc current and a second reference power source E2 for setting the plasma arc current.

Further, instead of the first relay RL1 in FIG. 1, a third relay RL3 having two normally open and normally closed contacts A and B is inserted.

Furthermore, one end of the first normally open contact A of the electromagnetic contactor MS is connected to the other input terminal of the comparator amplifier CA, and the first and 2 reference power supply E
Connect each positive side terminal of 1 and E2 to the 3rd relay.
It is connected to the other end of the first normally open contact A of the electromagnetic contactor MS via the normally closed contact B and the normally open contact A of RL3.

Next, the operation of the embodiment will be explained with reference to FIG. 4.

The basic operation is almost the same as that in FIG. 1, and the different points will be explained.

At time t5 shown in FIG. 4, as shown in FIG.
The reference voltage of the first reference power source E1 is applied to the comparison amplifier CA via the normally closed contact B of the relay RL3 and the first normally open contact A of the electromagnetic contactor MS.

However, at this time, since the detected voltage of the current detector CT is zero, each of the semiconductor control rectifiers TH1 to TH3 of the control rectifier RC is fully conductive by the firing signal of the phase shifter PS of the feedback control system, and the torch is turned off. The output voltage of the control rectifier RC is applied between the restrained nozzle N and the electrode EL.

On the other hand, when the second normally open contact A' of the electromagnetic contactor MS is turned on, the high frequency generator HF operates, and as shown in Figure c, the high frequency high voltage is applied to the output voltage of the control rectifier RC by the coupling coil CC. superimposed, t6
At times, a pilot arc occurs between the restricted nozzle N and the electrode EL, and as shown in Figure b, the control rectifier
The output current of RC is limited to a predetermined current value by the second current limiter R2, and a pilot arc current flows from the restraint nozzle N to the electrode EL, and this current causes the second
At time t6 after the relay RL2 is activated, the operation of the high frequency generator HF is stopped, as shown in c in the figure.

Then, when the plasma torch is brought closer to the base material M, the output voltage of the control rectifier RC changes between the base material M and the electrode EL when the torch switch TS is turned on.
As shown in figure e,
At t7, the pilot arc moves and connects the base material M and the electrode.
A plasma arc is generated between the ELs and a plasma arc current flows.

When this plasma arc occurs, the comparator amplifier CA
, the reference voltage of the first reference power source E1 and the detection voltage of the current detector CT are compared and amplified, and the first reference power source E1 is set to a current value equivalent to the pilot arc current as described above. Therefore, the plasma arc starts with a small current equivalent to the pilot arc current set in the first reference power source E1, and an excessive hot current does not flow.

Then, at time t8, as shown in Figure d, the plasma arc current is detected and the third relay RL3 operates, and its normally closed contact B and normally open contact A are opened and closed, respectively, and as a result, the comparator amplifier CA
The reference signal is switched from the first reference power source E1 to the second reference power source E2, and the plasma arc current is controlled to a constant value by the feedback control system based on the reference voltage set to the second reference power source E2.

Then, at time t9, when the torch switch TS is turned off, both the pilot arc and the plasma arc are extinguished.

〔Effect of the invention〕

As described above, according to the plasma power supply device of the present invention, it is possible to obtain a simplified circuit configuration that can prevent excessive hot current when a plasma arc occurs.

Therefore, the number of assembly steps can be reduced, and the cost and size of the device can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a wiring diagram of a conventional plasma power supply device, and Fig. 2 is a time chart of Fig. 1, where a is the on/off of the torch switch, b is the pilot arc current, c is the high frequency voltage, and d is the second The operating state of the relay, e indicates the plasma arc current, FIG. 3 is a wiring diagram of one embodiment of the plasma power supply device of the present invention, FIG. 4 shows the time chart of FIG. 3, and a indicates the torch switch. On, off, b indicates the pilot arc current, c the high frequency voltage, d the operating state of the third relay, and e the plasma arc current, respectively. TH1~TH3...Semiconductor controlled rectifier, RC...
...Control rectifier, O1, O2, O3...first, second
and third output terminal, R2...fault limiter, E1...
1st reference power supply, E2...2nd reference power supply, A...normally open contact, B...normally closed contact, CA...comparison amplifier,
RL3...Relay.

Claims (1)

[Claims] 1. The AC input is controlled and rectified by one control rectifier made of a semiconductor-controlled rectifier to obtain a DC output with drooping characteristics or constant current characteristics at the first output terminal and second output terminal for supplying plasma arc current, and In a plasma power supply device in which the first output terminal or the second output terminal is connected to the third output terminal for pilot arc current supply via a current limiter, the feedback control system of the control rectifier section includes a pilot arc current setting controller. In addition to providing a first reference power source for setting a plasma arc current and a second reference power source for setting a plasma arc current,
The first reference power source and the second reference power source are connected to a comparator amplifier via a normally closed contact and a normally open contact, respectively, and the controlled rectifier, the first output terminal, and the second
A plasma power supply device characterized in that a relay is inserted between one of the output terminals to detect a plasma arc current and operate both of the contacts.