KR930004107Y1 - Power supply apparatus for plasma arc - Google Patents

Abstract

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Description

Power supply for plasma arc

1 is a connection diagram showing an embodiment of a power supply device for a plasma arc of the present invention.

Figures 2a-c and 3a-c and 4a-c are timing charts for explaining the operation of Figure 1, respectively.

5 is a connection diagram of a conventional example.

* Explanation of symbols for main parts of the drawings

3: base material 4: electrode

5: nozzle 8: high frequency generator

9: 3 phase AC power supply 10: DC conversion circuit

11: current detector 12: first relay

13,24: 1st, 2nd normally closed contact point 14: 2nd relay

15: top contact 16: first resistor

17 series circuit 18 start switch

19: 3rd relay 20,32: 1st, 2nd opening contact

22 condenser 25 fourth relay

36: transistor 28: command part

31: drive, output adjustment circuit 33: normally closed contact

The present invention relates to a power supply device for plasma arc, which is applied to a processing apparatus that performs a welding or cutting of a workpiece by a plasma arc.

2. Description of the Related Art Conventionally, a plasma arc power supply device applied to a processing apparatus for performing welding or cutting of a workpiece by plasma arc is configured as shown in FIG.

In Fig. 5, (1) is an AC power supply, (2) is a DC conversion circuit formed by a combination of a thyristor or a diode and a transistor to rectify the AC output of the AC power supply 1 and output a direct current, (3) and (4) are each a base material and an electrode connected to the positive (+) output terminal of the DC conversion circuit 2, and (5) covers the electrode 4 to cover the inside thereof. (6), (7), (8) are a switch, a resistor, and a high frequency generator provided in series between the conversion circuit (2) and the nozzle (5). The switch 6 is turned on by ON of the start switch other than the drawing, and is turned off by the flow of plasma current between the base material 3 and the electrode 4, and the high frequency generator 8 is connected to the nozzle 5 and the electrode. The high frequency high voltage is applied between (4).

Although not shown in FIG. 1, the DC switch circuit 2 is operated by outputting a drive signal to a gate of a thyristor or a base of a transistor constituting the DC converter circuit 2, by operating the ON switch. A drive and an output adjustment circuit for driving the output and outputting the drive signal of the level set by the operation of the variable setting unit to adjust the output of the DC converter circuit 2 are provided.

When the shield gas is flowed into the nozzle 5 and the above-described start switch is turned on, the drive and output adjustment circuits are operated to drive the DC converter circuit 2 and the switch 6 is turned on to turn the nozzle 5 on. DC voltage by the DC converter circuit 2 is applied between the electrode 4 and between the base material 3 and the electrode 4, but between the nozzle 5 and the electrode 4 and between the base material 3 and the electrode ( 4, no current flows between the nozzle 5 and the electrode 4 and between the base material 3 and the electrode 4 by a gap between them.

Therefore, when the high frequency generator 8 is operated to apply a high frequency high voltage between the nozzle 5 and the electrode 4, the gap between the nozzle 5 and the electrode 4 is broken, and the nozzle 5 and the electrode 4 are broken. A pilot arc occurs between the control circuit 2 and the switch circuit 2, the switch 6, the resistor 7, the high frequency generator 8, the nozzle 5, and the electrode 4. ) Flows.

Next, when the electrode 4 approaches the base material 3, the gap between the base material 3 and the electrode 4 becomes small, and the monitoring arc pulls between the base material 3 and the electrode 4 so that the base material ( Plasma arc A is generated between the 3) and the electrode 4, and a plasma current flows through the DC converter circuit 2, the base material 3, and the electrode 4, and then the switch 6 is turned off so that the nozzle 5 The monitoring current flowing to the over electrode 4 is cut off, and only the plasma current continues to flow through the base material 3 and the electrode 4 to maintain the plasma arc A.

In this case, however, if the generation of the plasma arc A fails, the monitoring current is applied to the switch 6, the resistor 7, the generator 8, the nozzle 5, and the electrode 4 with the switch 6 turned on. There is a problem that there is a risk of damaging the resistance 7 because it continues to flow.

Therefore, in the present invention, even if the generation of the plasma arc fails, it is possible to forcibly block the monitoring current flowing through the nozzle and the electrode to prevent damage to the resistance.

The present invention has been made in view of the above-described points, a DC conversion circuit connected to a current power source, a base material and an electrode connected to positive and negative output terminals of the DC conversion circuit, a nozzle covering the electrode, and A current detector connected to a positive output terminal of a direct current conversion circuit and the base material to detect a current flowing through the conductive path and output a voltage signal proportional to the current, and to two output terminals of the current detector. A first relay connected to the first relay connected in series between the electrostatic source terminal and the ground, a first relay contact and a second relay, and a start switch connected to the AC power supply and a third relay in series A first upper contact and a capacitor of the third relay connected in series between the circuit, the electrostatic source terminal and ground, and the first relay of the first relay connected in series between the electrostatic source terminal and ground. 2 normal closing And a fourth relay and a switch element, and a command portion connected to one end of the capacitor and a control terminal of the switching element to detect an electric potential of one end of the capacitor having a predetermined value or more and output an ON command signal to the control terminal of the switching element. A drive, an output adjustment circuit connected to the electrostatic source terminal through a series circuit between the second open contact of the third relay and the open / close contact of the fourth relay to output a drive signal to the direct current conversion circuit; A power supply device for plasma arc comprising a top contact, a resistance, and a high frequency generator of the second relay connected in series between a positive output terminal of a DC converter circuit and the nozzle.

Therefore, according to the present invention, the third relay is energized by the ON of the start switch, so that the first and second contact points of the third relay are turned ON, and the second upper contact is turned ON to drive the output adjustment circuit. By operating DC drive circuit, DC voltage is applied between base material and electrode and between nozzle and electrode, and high frequency high voltage by high frequency generator is applied between nozzle and electrode to generate monitoring arc between nozzle and electrode. When the monitoring current flows through the nozzle and the electrode, and then the electrode approaches the base metal, a plasma arc is generated between the base material and the electrode, and a plasma current flows through the base material and the electrode, and the plasma current is detected by the current detector so that the voltage signal Output, the first relay is excited, the first normally closed contact of the first relay is turned off, the excitation of the second relay is stopped, and the image of the second relay is stopped. The contact point is turned off, and the monitoring current flowing through the nozzle and the electrode is forcibly cut off.

On the other hand, when the plasma arc does not occur after the occurrence of the monitoring arc, when the first phase contact point of the third relay described above is turned ON, the capacitor is charged so that one end of the potential rises, and one end of the capacitor reaches a predetermined value. The ON command signal is output from the command section to the control terminal of the switching element, the switching element is turned on, and the ON / OFF contact point of the fourth relay is turned OFF by exciting the fourth relay by turning ON the switching element, and the driving and output adjustment circuit By stopping the operation, the DC conversion circuit also stops the operation, and the flow of the monitoring current to the nozzle and the electrode is forcibly cut off, thereby preventing damage to the resistance caused by the continuous flow of the monitoring current.

EXAMPLE

Next, a description will be given in detail with reference to FIGS. 1 to 4 showing an embodiment of the present invention.

In FIG. 1, reference numeral 9 denotes a three-phase AC power supply, reference numeral 10 denotes a base material 3 and an electrode 4 connected to positive and negative output terminals, and a thyristor or a diode. It is formed in combination with a transistor, and is a DC conversion circuit for converting the three-phase AC of the AC power source 9 into direct current, and (11) is an electric current path between the constant output terminal of the DC converter circuit 10 and the base material 3 A current detector which detects a current flowing through the conduction path and outputs a voltage signal proportional to the current; and (12) is a first relay connected to two output terminals of the current detector 11; And (14) are the first normally closed contact and the second relay of the first relay 12 connected in series between the electrostatic terminal (+ B) and the ground, and the positive output of the DC converter circuit 10 An upper contact 15 of the second relay 14, a first resistor 16, and a high frequency generator 8 are provided in series between the terminal and the nozzle 5.

(17) is a series circuit of the start switch 18 and the third relay 19 connected to two terminals of the AC power source 9, and (20), (21) and (22) are electrostatic source terminals (+ NPN transistors as the second phase-closed contact point of the first relay 12 and the fourth relay and the switching element provided in series between B) and ground, and (27) between the base and the emitter of the transistor 26. The upper and lower contact points of the connected third relay 19, 28 are the fourth resistor 29 and the zener diode connected between the connection point of the second resistor 21 and the capacitor 22 and the base of the transistor 25. One end, which is a command portion that becomes a series circuit of (30) and is the width of the second resistor 21 of the capacitor 22 when the Zener diode 30 is equal to or higher than the Zener voltage Vz, detects the potential, The high level ON command signal is output to the base as the control terminal, and the circuit surrounded by the dotted line in the first diagram, that is, the second and third resistors 21 and 23, the capacitor 22, and the contact point 20 ), (24), (27), the 4th relay 25, the transistor 26, and the command part 28 comprise a monitoring current interruption circuit.

In addition, the high frequency generator 8 is driven within the T time period when the charging of the capacitor 22 is started until one end reaches Vz, the potential of which is a predetermined value, and the electrode 4 and the base material 3 are approached. It is assumed that the charging time T of the capacitor 22 is set so that the flow of the plasma current can be started to the base material 3 and the electrode 4 by a series of operations.

(31) is a DC conversion circuit connected to the electrostatic source terminal (+ B) through a series circuit between the second upper contact 32 of the third relay 19 and the upper closed contact 33 of the fourth relay 25. (10) is a drive and output adjustment circuit, operates by turning on the two contacts 32 and 33, and outputs a drive signal to the gate of the thyristor or the base of the transistor constituting the DC converter circuit 10; The DC conversion circuit 10 is driven, and at the same time, the drive signal of the set level is output by the operation of the variable resistor 34 attached to the outside so as to adjust the output of the DC conversion circuit 10.

Next, an operation will be described in the above embodiment.

As shown in FIG. 2A, when the start switch 18 is turned on at time t ₁ , the third relay 19 is excited to turn on the first and second upper opening contacts 20 and 32 and at the same time, the upper and closing contacts. (27) is turned OFF, the drive is driven by the ON of the second phase opening contact 32, the output adjustment circuit 31 is operated so that the DC conversion circuit 10 is driven, and the ON of the first phase opening contact 20 is ON. to be the disclosure by the charging of capacitor 22 at time t ₁ as shown in Figure 2b and the potential of one end of the capacitor begins to rise.

By the way, the direct current voltage is applied between the base material 3 and the electrode 4 by the driving of the DC conversion circuit 10, but because the gap between the base material 3 and the electrode 4 is large, the base material 3 and the electrode No current flows in (4), and the first relay 12 is not excited while the output of the current detector 11 is zero, and the second relay 14 is turned off while the first upper contact 13 is turned off. ) Is kept in the excited state, and the top contact 15 is kept in the ON state, and a DC voltage by the DC converter circuit 10 is applied between the nozzle 5 and the electrode 4, and in this state, the high frequency generator When the high frequency high voltage is applied between the nozzle 5 and the electrode 4 by operating (8), the gap between the nozzle 5 and the electrode 4 is broken and a monitoring arc is formed between the nozzle 5 and the electrode 4. Is generated, and the DC conversion circuit 10 is connected between the nozzle 5 and the electrode 4 through the upper contact 15, the first resistor 16, and the high frequency generator 8 in the ON state. Indicate to The monitor current (I _p) at the time (t ₂₎ flows as.

Next, when a shield gas flows into the nozzle 5 and the electrode 5 approaches the base material 3, the gap between the base material 3 and the electrode 4 becomes small, and the monitoring arc is connected to the base material 3. The plasma arc A is generated between the base material 3 and the electrode 4 by being pulled between the electrodes 4, and a plasma current flows through the DC converter circuit 10, the base material 3, and the electrode 4. The current is detected by the current detector 11 so that a voltage is applied to the first relay 12 and the first relay 12 is excited to turn off the first and second plaque contacts 13 and 24, In addition, the excitation of the second relay 14 is stopped, and the upper and lower contact points 15 are turned off. As shown in FIG. 2C, the monitoring current is cut off at the nozzle 5 and the electrode 4 at time t ₃ to be 0. Only the plasma current flows continuously through the base material 3 and the electrode 4 to maintain the plasma arc A.

At this time, the 2b also be initiating the charge of the capacitor 22 to the time t ₁ and the potential of one end of the capacitor 22 rises, for example, capacitor 22 at time t ₄ after the time T from the time t ₁ as shown in the When the potential of one end of the zener diode 30 reaches the zener voltage Vz of the zener diode 30, the electrostatic source terminal (+ B) is connected to the base of the transistor 26 through the resistor 29 of the command portion 28 and the diode 30. The current from the signal is supplied as a high level ON command signal, and the transistor 26 is turned on. However, as described above, the second phase contact 24 of the first relay 12 is turned off due to the flow of plasma current. Since the fourth relay 25 is not energized, the fourth relay 25 is not excited, and the drive is operated while the upper and lower contacts 33 are turned off, and the output adjustment circuit 31 continues to operate. The plasma current flows continuously to the electrode 4.

As shown in FIG. 2A, when the start switch 18 is turned off at time t ₅ , the excitation of the third relay 19 is stopped to turn off the first and second upper openings 20 and 32. At the same time, the normal closing contact 27 is turned on, the drive and output adjustment circuit 31 is stopped by the OFF of the second phase contact 32, and the DC conversion circuit 10 is also stopped. ) And the current of the capacitor and current to the base of the transistor 26 through the command unit 28 by the OFF of the first upper contact 20 at the same time as the flow of the plasma current between the electrode and the electrode 4 is stopped. Supply of the charging current to 22 is stopped, and as shown in FIG. 2C, the charging charge of the capacitor 22 is discharged through the third resistor 23 at time t ₅ , and the potential of one end of the capacitor 22 is discharged. Begins to degrade.

However, when the start switch 14 is turned on at time t ₆ as shown in FIG. 3a, the charging of the capacitor 22 is started at time t ₆ as shown in FIG. 3b as in the case of FIG. At one end of the capacitor 22, the potential starts to rise, and as shown in Fig. 3c, the monitoring current I _p flows through the nozzle 5 and the electrode 4 at time t ₇ , and then as shown in Fig. 3b. When no plasma arc occurs between the base material 3 and the electrode 4 for some reason until the potential at one end of the capacitor 22 reaches a predetermined value Vz at a time t ₈ from t ₆ to t ₈ hours later. Since the plasma current does not flow in the current detector 11, the output voltage of the current detector 11 is 0, and the first relay 12 is not excited, and the first and second phase-closure contacts 13 of the first relay 12, 24, the second relay 14 is turned off without turning ON. It is kept in the excited state and is kept in the ON state with the upper-closed contact point 15. As shown in FIG. 3B, one end of the capacitor 22 reaches Vz having a predetermined value at time t ₈ and the transistor 26 is turned on. As the fourth relay 25 is excited, the upper and lower contact points 33 are turned off, the driving and output adjustment circuit 31 stops the operation, and the DC converter circuit 10 stops the operation, and the upper and lower contact points 15, 1, the flow of the monitoring current to the resistance 16, the high frequency generator 8, the nozzle 5, and the electrode 4 is forcibly interrupted at time t ₈ as shown in FIG. 3C, and the monitoring current becomes zero. Damage to the first resistor 16 due to the continuous monitoring current flowing for a long time is prevented.

As shown in FIG. 3A, when the start switch 18 is turned OFF at time t ₉ and immediately after the start switch 18 is turned on again at time t ₁₀ , as shown in FIG. 3B, at time t ₉ The capacitor 22 starts to discharge and the potential at one end begins to gradually decrease, but at the time t ₁₀ , charging of the capacitor 22 resumes, and the potential at one end, which has slightly decreased from Vz, starts to rise again. As shown in Fig. 3, even when the monitoring current I _p flows again to the nozzle 5 and the electrode 4 at time t ₁₁ , as shown in Fig. 3b, a very small time has elapsed since the potential of one end of the capacitor 22 has elapsed. After that, since the predetermined value Vz is reached at time t ₁₂ , the transistor 26 is turned on at time t ₁₂ , and the fourth relay 25 is excited, and the upper and lower contacts 33 of the fourth relay 25 are turned off. Drive, output adjustment circuit 31 stops working To stop the direct current conversion circuit 10 operate, and the 3c also the normally closed contact 15 at time t ₁₂ as shown in the first resistor 16 and the high frequency generation section 8, a nozzle 5 and electrode ( 4) be a flow of monitoring current forcibly cut off again monitored to jeonru is zero damage to the first resistance 16 can be prevented and then the start switch 18 at time t ₁₃ as shown in claim 3a Fig. As shown in FIG. 3B, as shown in FIG. 3B, the capacitor 22 starts discharging at time t ₁₃ , and at one end, the potential starts to decrease.

Furthermore, when the first at time t ₁₄ as shown in Fig. 4a Fig start switch 18 is ON, start charging the capacitor 22. At time t _14, as the same manner as in the case above the second-degree shown in the 4b FIG. As a result, the potential of one end of the condenser 22 rises, and as shown in FIG. 4C, the monitoring current I _p flows through the nozzle 5 electrode 4 at time t ₁₅ , and then as shown in FIG. 4A. The start switch 18 is turned off at time t ₁₆ after the time T '(<T) from t ₁₄ , and furthermore, if no plasma arc occurs between the base material 3 and the electrode 4 until time t ₁₆ , the start switch ( 18), the first and second phase opening contacts 20 and 32 of the third relay 19 are turned off, and the capacitor 22 starts discharging at time t ₁₆ as shown in FIG. 4b. at the same time the potential at the one end driven slowly starts to decrease at time t _16, the output adjustment circuit ( By the operation stop of 31), the DC change circuit 10 stops the operation, and the flow of the monitoring current to the nozzle 5 and the electrode 4 is interrupted at time t ₁₆ as shown in FIG. 4C.

At this time, as shown in FIG. 4B, at the time t ₁₆ , the power supply of one end of the capacitor 22 does not reach Vz, which is a predetermined value, so that the transistor 26 is not turned ON.

Then, as shown in FIG. 4A, when the start switch 18 is turned on again at time t ₁₇ after some time from time T ₁₆ , as shown in FIG. 4B, charging of the capacitor 22 is resumed at time t ₁₇ . The potential at one end starts to rise again, and as shown in FIG. 4C, even when the sense current I _p flows again through the nozzle 5 and the electrode 4 at time t ₁₈ , the potential at one end of the capacitor 22 remains at the fourth level. after a short time from the resumption filled cured as shown in Fig because reaches a predetermined politicians Vz at time t ₁₉ due to reaching the predetermined politicians Vz, the transistor 26 at time t _19, the transistor 26 is time t ₁₉ Is turned on, the fourth relay 25 is excited, the upper and lower contact points 33 of the fourth relay 2 are turned off, and the drive and output adjustment circuit 31 is stopped to operate the DC converter circuit 10. Stop, and as shown in Fig. 4C, At each t ₁₉ , the flow of the monitoring current to the upper and lower contact point 15, the first resistor 16 and the high frequency generator 8, the nozzle 5 and the electrode 4 is forcibly cut off again so that the monitoring current becomes zero. Damage to the first resistor 16 is prevented, and then the starter switch 18 is turned off at time t ₂₆ as shown in FIG. 4a, so that the capacitor 22 at time t ₂₀ as shown in FIG. 4b. Discharge starts, and the potential of one end begins to fall.

In addition, the base material 3 may newly install another power supply for the plasma electrode on the electrode 4.

As described above, according to the plasma arc power supply device of the present invention, even if the generation of the plasma arc between the base material and the electrode fails, the monitoring current flowing through the nozzle and the electrode can be forcibly cut off, and the connection between the DC converter circuit and the nozzle It is possible to prevent damage to the upper contact of one second relay, the resistance of the resistance and the series circuit of the high frequency generator.

Claims (1)

DC conversion circuit 10 connected to AC power source 9, base material 3 and electrode 4 and the electrode connected to positive (+) output terminal of DC conversion circuit 10, respectively. (4) connected to the nozzle (5), the constant output terminal of the DC converter circuit 10 and the conductive path between the base material (3) to detect the current flowing through the conductive path and the voltage proportional to the current The current detector 11 for outputting a signal, the first relay 12 connected to the two output terminals of the current detector 11, and the electrostatic source terminal + B connected in series with the ground; The first circuit 12 and the second relay 14 of the first relay 12, and the series circuit 17 of the start switch 18 and the third relay 19 connected to the AC power source (9) And the first phase-closing contact 20 and the condenser 22 of the third relay 19 connected in series between the electrostatic source terminal and ground, and in series between the electrostatic source terminal and ground. Of the connected first relay 12 A second relay contact point 24 is connected to a fourth relay 25 and a switching element, one end of the capacitor 22 and a control terminal of the switching element to detect a potential of one end of the capacitor 22 having a predetermined value or more; A command unit 28 for outputting an ON command signal to a control terminal of the switching element, a second open contact 32 of the third relay 19, and an upper close contact 33 of the fourth relay 25, A drive circuit connected to the electrostatic source terminal via a series circuit 17 of the output circuit to output a drive signal to the DC converter circuit 10. The output adjustment circuit 31 and the constant output terminal of the DC converter circuit 10 An upper contact point 15 of the second relay 14, a resistor 16, and a high frequency generator 8 connected in series with the furnace 5; .