JPS6316225B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current supply device for arc welding that is powered by alternating current and supplies direct current to a welding electrode.

The object of the invention is to facilitate the welding operation so that even relatively unskilled personnel can perform acceptable welds, and also to provide a more satisfactory welding operation than with conventional welding current devices operating at the mains frequency. The object of the present invention is to provide a new and useful welding current supply device that can perform the following steps.

For this purpose, according to the invention, the average duration of the current and voltage transients caused by a short circuit through a droplet of welding material is longer than the time required for complete charging or discharging of the capacitor, but a controlled frequency converter of the series capacitor type, operating with a short half-period of, for example, 3 ms or less, preferably 1.5 ms or less, and adapted to be connected to the welding electrode via a transformer in series with a rectifier; There is also provided a current supply device for arc welding having a control device for controlling the frequency converter so as to maintain arc power substantially unchanged regardless of changes in load caused by a welding operation. The control device includes a device for controlling the switching device to alternately charge and discharge the capacitor at a frequency approximately inversely proportional to the applied voltage or the square of the voltage applied to the capacitor of the frequency converter. .

With such a welding current supply device, a particularly stable and stationary arc is obtained even with slight variations in the distance between electrode and working part. Furthermore, even if a short circuit occurs due to a droplet of welding material, the arc will be re-ignited smoothly due to the small dynamic effects in the molten material.

Furthermore, some variation in the voltage of the AC power supply, ie the voltage applied to the capacitor, does not adversely affect the welding characteristics.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to more easily understand the present invention and clarify its features, embodiments of the present invention will be described below with reference to the accompanying drawings.

The current supply device shown in FIG. 1 is connected at terminal 10 to a three-phase alternating current network. The input current is rectified by a six-element full-wave rectifier 11, and a conductor 1 forming a DC output terminal
The rectified output voltage at 2, 13 is smoothed with a buffer capacitor 14 and fed to a frequency converter which has a low input impedance as a result of the illustrated configuration of elements 11-14. Elements 11, 14 constitute an intermediate DC voltage source.

In the illustrated embodiment, the switching elements of the frequency converter consist of thyristors 15, 16, which are controlled in such a way that they are activated alternately. The frequency converter is combined with a transformer designated 17, the primary winding 18 of which is connected to a load capacitor 19, which forms part of the frequency converter.
20 in series. The secondary winding 21 of the transformer 17 is connected via a rectifier bridge 22 and a tie yoke 29 to welding electrode terminals 24, 25, which can be connected to the welding electrode holder and to the workpiece to be welded. . In the illustrated embodiment, a capacitor 26 is connected between terminals 24 and 25;
This capacitor 26 is used to maintain the desired open circuit voltage. A shunt 27 may be provided to measure the load current.

If the supply voltage varies and the frequency of the frequency converter is constant, the frequency converter produces an output across terminals 10 that varies approximately proportionally to the square of the supply voltage U ₁₀ . If the output from the current supply remains approximately constant regardless of variations in the supply voltage, the frequency of the frequency converter must be varied proportionally to 1/U ₁₀ .

FIG. 2 shows a controller that controls the frequency converter so that the arc power remains substantially constant regardless of load changes caused by welding operations and changes in input voltage. This control device has a potentiometer 33 and an oscillator 34, said potentiometer 33 being adapted to control the operating frequency of the oscillator 34. Potentiometer 33 is connected between ground and a negative voltage source that varies approximately inversely as the square of the voltage applied to the frequency converter.

In the illustrated embodiment, the controller further includes a potentiometer 3.
3, a constant negative potential section 335 and a load resistor 331 are connected in series. Supply voltage U ₁₀ is applied to the primary winding of transformer 334 and transformer 334
The secondary winding of is connected to a smoothing capacitor 332 and a load resistor 331 via a rectifier bridge 333. The values of these components are such that the voltage across resistor 331 is equal to or greater than the voltage across resistor 331
is chosen to be approximately twice the voltage across it. As a result, the voltage across the load resistor 331 is
This means that as long as the fluctuations in the supply voltage are small, e.g. within ±5%, the voltage across the power regulator ₃₃ will vary approximately in proportion to 1/U ₁₀ ² . It means.

The output from the frequency converter is the load capacitor 1
The energy stored in these capacitors is proportional to the charge/discharge and frequency. That is, output P=f・c・U ₁₀ ²・K1・K2. where f is the frequency of the converter, c is the capacity of capacitors 19, 20, U ₁₀ is the supply voltage,
K1 is a constant related to the high rate, etc., and K2 is a constant related to the ratio between U ₁₀ and the voltage from the intermediate DC voltage sources 11 and 14.

By the way, if the output does not change with fluctuations in the supply voltage, the value of the output P remains constant regardless of the value of U ₁₀ , so by replacing f in the above equation with 1/U ₁₀ ² , it can be easily calculated. You can check.

Therefore, the frequency of the converter must vary in proportion to 1/U ₁₀ ² .

The frequency of the oscillator 34 controlled by the potentiometer 33 therefore also varies in proportion to 1/U ₁₀ ² . Instead of using U ₁₀ as the control voltage signal, it is of course also possible to use the voltage applied to the converter capacitors 19, 20. The oscillator 34 is an amplifier 340
It has an integrating circuit consisting of resistors 341, 342, and a capacitor 343. The oscillator 34 also includes a level discriminator 34 in combination with comparison resistors 345, 346.
4, a resistor 345 is connected to the output of the integrating circuit, and a resistor 346 is connected to a voltage source with a constant negative voltage. Amplifier 340 is controlled in the positive direction by a control signal from potentiometer 33 and in the negative direction by a signal from the output of monostable flip-flop 50, discussed below. A voltage regulator 35 in the form of a voltmeter is provided for regulating the desired maximum output voltage from the current supply device;
It is connected via a comparison resistor 36 to the terminal 25 of the current supply device and to an amplifier 37 serving as a level discriminator.

The state of the thyristors 15, 16 is controlled by a sensing circuit consisting of a transformer 38, the primary side of which is connected via diodes 39, 40 to the anodes A1, A2 and cathodes K1, K2 of the thyristors 15, 16. be done. One end of the secondary winding of the transformer 38 is grounded, and the other end is connected to two resistors 41,
42, and one end of the resistor 42 is connected to a constant negative voltage. Resistance 41, 42
The connection point is further connected to an amplifier 43 which acts as a level discriminator, and the switching point is connected to a resistor 41,
42 and the constant negative voltage mentioned above.
Each of the amplifiers 344, 37, 43 is connected to a respective input 45, 46, 47 of an AND gate 48, which operates in a known manner. Therefore, for AND gate 48 to provide an output signal, the output signal obtained from amplifier 344 must be positive. Correspondingly, it is necessary that the output signal from amplifier 37 is positive, ie the load voltage at terminal 25 is lower than the value set in regulator 35. Furthermore, the output signal from amplifier 43 must be positive, meaning that the anode voltage of one thyristor is negative with respect to the cathode and both thyristors 15, 16 are deactivated. There is.

The output of AND gate 48 is connected to the input of a monostable flip-flop 50, which has a predetermined pulse duration, for example 30 μs, corresponding to the recovery time of thyristors 15,16.
Therefore, a positive voltage pulse is obtained at the output of flip-flop 50 for a period corresponding to the recovery time of thyristors 15 and 16. This voltage pulse is resistor 3
42 to amplifier 340 and also to the trigger input T of JK flip-flop 51, so that JK flip-flop 51 changes the state of its output at the end of the pulse obtained from flip-flop 50. The Q output of the JK flip-flop 51 is connected via capacitors 52 and 53 to the bases of transistors 54 and 55, respectively. The emitters of transistors 54, 55 are grounded and their collectors are connected to the primary windings of ignition transformers 56, 57 of thyristors 15, 16, respectively. The other ends of these primary windings are connected to a terminal with a predetermined positive potential, and the terminals of the secondary windings are connected to the cathode K of the respective thyristor 15, 16.
1, K2 and gates G1, G2, respectively. Elements 48, 50-57 constitute a switching pulse former. The signal from the output of JK flip-flop 51 is connected to capacitors 52 and 53.
transistors 54, 55 alternately conduct through capacitors 52, 53 for a short time determined by , so that thyristors 15, 16 alternately receive short firing pulses, thereby causing 18 alternately to form an alternating current, the frequency of which is determined by input 4 of AND gate 48.
It is determined by the signals at 5, 46 and 47. In this configuration, the desired substantially constant arc power can be set simply by correspondingly adjusting the potentiometer 33.

Figure 3 shows the connection point 60 when a normal load is applied to the output of the current supply device shown in Figures 1 and 2;
The voltages U ₆₀ , U ₆₁ at 61 and the voltage U ₁₈ at the primary winding 18 of the transformer 17 are shown. FIG. 3 also shows the output current I ₂₅ flowing through the terminal 25 and the output currents I ₁₅ and I 16 from the thyristors 15 and ₁₆ (I ₁₆ is indicated by a dotted line). In FIG. 3, the symbol t ₁ designates the moment of firing of the thyristor 15, and t ₂ represents the moment when the thyristor 15 is extinguished and formed by the primary winding 18 of the transformer 17 and the capacitors 19, 20. represents the instant at which a negative voltage is obtained between the anode A1 and the cathode K1 as a result of the resonant circuit, t3 represents the instant at which the thyristor 16 fires, and t4 represents the instant at which the thyristor 16 is extinguished and the resonant circuit represents the point in time when a negative anode voltage is obtained as a result of . Code t5 is thyristor 1
5, and the above operations are repeated if the load does not change substantially.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an AC-operated arc welding current supply device equipped with a frequency converter of the type that may be advantageously used in conjunction with the present invention; FIG. The circuit diagram of the control circuit shown in FIG. 3 is a curve representing the voltage and current occurring during normal operation of the current supply device. In the figure, 11 is a full-wave rectifier, 14 is a buffer capacitor, 15 and 16 are thyristors, 17 is a transformer, 1
9 and 20 are load capacitors, 22 is a rectifier bridge, 24 and 25 are welding electrode terminals, 26 is a capacitor, 27 is a shunt, 29 is a choke, 30 is an amplifier, 31 is a multiplier, 32 is a regulator, and 33 is a power supply A regulator, 34 an oscillator, 35 a voltage regulator, 36
is a comparison resistor, 37 is an amplifier, 38 is an amplifier, 3
9, 40 are diodes, 41, 42 are resistors, 43
is an amplifier, 48 is an AND gate, 50 is a monostable flip-flop, 51 is a JK flip-flop,
52 and 53 are capacitors, 54 and 55 are transistors, and 56 and 57 are ignition transformers.

Claims (1)

[Claims] 1. Intermediate DC voltage sources 11, 14 connected to input terminal 10 and provided with DC output terminals 12, 13;
and a transformer 17 having a primary winding 18 and a secondary winding 21 connected to the welding electrode terminals 24, 25 via a rectifier bridge 22, and one side connected to each of the DC output terminals 12, 13. , at least one capacitor 19, 20 whose other side is connected to one end of the primary winding 18, and the primary winding 1
The other end of 8 is connected to the switching pulse former 48,5.
The DC output terminals 12 and 13 are connected to both of the DC output terminals 12 and 13 through controlled switching devices 15 and 16 which alternately receive switching pulses from a switching control device having a switching control device having a switching control device having switching pulses 0 to 57. a voltage squaring and regulating device 33, 33 connected to a voltage source 334 of a value corresponding to the voltage applied to or to the capacitors 19, 20, the output of which is connected to the input of the oscillator 34;
1 to 333, 335, and the output of the oscillator 34 is connected to the switching pulse generators 48, 50 to 57 that generate trigger pulses. 2. The oscillator 34 is a voltage-controlled oscillator that generates a pulse train output according to the voltage input to the oscillator 34, and the pulse train output determines the switching frequency of the switching devices 15 and 16. The current supply device for arc welding described above. 3 The switching devices 15 and 16 consist of first and second thyristors, and also include first and second capacitors 1
9 and 20 are provided, the first and second thyristors, the first and second capacitors and the primary winding 18 are arranged such that the first capacitor 19 is charged via the second thyristor 16 and the primary winding 18 and the first capacitor 19 is charged via the second thyristor 16 and the primary winding 18 and The second capacitor 20 is charged via the first thyristor 15 and the primary winding 18 and discharged via the second thyristor 16 and the primary winding. The current supply device for arc welding according to claim 1, which is connected so as to be connected to the current supply device. 4 The switching devices 15 and 16 are composed of first and second thyristors, and the first and second capacitors 19,
20 is the second thyristor 1 of the above two thyristors
6 and the first thyristor 15 alternately conduct charging and discharging through the primary winding 18. connected across the first and second capacitors 19,
20 are connected in series with each other and across the intermediate DC power supply, and the primary winding 18 connects the thyristors 15 and 16 to the connection part of the capacitor 1.
The current supply device for arc welding according to claim 1, which is connected between the connecting portions 9 and 20. 5 Intermediate DC voltage sources 11, 14 connected to input terminal 10 and equipped with DC output terminals 12, 13
and a transformer 17 having a primary winding 18 and a secondary winding 21 connected to the welding electrode terminals 24, 25 via a rectifier bridge 22, and one side connected to each of the DC output terminals 12, 13. , at least one capacitor 19, 20 whose other side is connected to one end of the primary winding 18, and the primary winding 1
The other end of 8 is connected to the switching pulse former 48,5.
The DC output terminals 12 and 13 are connected to both of the DC output terminals 12 and 13 through controlled switching devices 15 and 16 which alternately receive switching pulses from a switching control device having a switching control device having a switching control device having switching pulses 0 to 57. a voltage squaring and regulating device 33, 33 connected to a voltage source 334 of a value corresponding to the voltage applied to or to the capacitors 19, 20, the output of which is connected to the input of the oscillator 34;
1 to 333, 335, the output of the oscillator 34 is connected to the switching pulse generators 48, 50 to 57 that generate trigger pulses, and the switching devices 15, 16 are comprised of first and second thyristors. , and the switching control device controls the thyristor 1 according to the applied trigger pulse.
The thyristor ignition circuits 50 to 57 which alternately ignite the thyristor ignition circuits 5 and 16 to make them conductive are connected to the voltage controlled oscillator 34 and the thyristor ignition circuits 50 to 57, and when not blocked, the thyristor ignition occurs. A gate device 4 that supplies pulses of the pulse train output to the circuits 50 to 57 as the trigger pulses.
8. A current supply device for arc welding, comprising: 6. It has first and second capacitors 19 and 20 that are alternately charged and discharged via the primary winding 18 by the alternate conduction of the two thyristors 15 and 16, and the thyristors 15 and 16 are connected in series with each other and have an intermediate capacitor. Claim 5, wherein the DC voltage sources 11, 14 are connected across and the primary winding 18 is connected between the connections of the thyristors 15, 16 and the connections of the capacitors 19, 20. The current supply device for arc welding described in . 7 Intermediate DC voltage sources 11, 14 connected to input terminal 10 and equipped with DC output terminals 12, 13
and a transformer 17 having a primary winding 18 and a secondary winding 21 connected to the welding electrode terminals 24, 25 via a rectifier bridge 22, and one side connected to each of the DC output terminals 12, 13. , at least one capacitor 19, 20 whose other side is connected to one end of the primary winding 18, and the primary winding 1
The other end of 8 is connected to the switching pulse former 48,5.
The DC output terminals 12 and 13 are connected to both of the DC output terminals 12 and 13 through controlled switching devices 15 and 16 which alternately receive switching pulses from a switching control device having a switching control device having a switching control device having switching pulses 0 to 57. a voltage squaring and regulating device 33, 33 connected to a voltage source 334 of a value corresponding to the voltage applied to or to the capacitors 19, 20, the output of which is connected to the input of the oscillator 34;
1 to 333, 335, the output of the oscillator 34 is connected to the switching pulse generators 48, 50 to 57 that generate trigger pulses, and the switching control device further includes thyristors 15, 16.
and the gate device 48, and blocks the gate device 48 at all times, except when the anode voltage of either of the thyristors is negative with respect to the cathode voltage, so that the thyristor that was first conductive is then interrupted. A current supply device for arc welding, comprising first sensing circuits 39 to 43 in which none of the thyristors is allowed to conduct. 8. It has first and second capacitors 19 and 20 that are alternately charged and discharged via the primary winding 18 by the alternate conduction of the two thyristors 15 and 16, and the thyristors 15 and 16 are connected in series with each other and have an intermediate capacitor. Claim 7, wherein the DC voltage sources 11, 14 are connected across and the primary winding 18 is connected between the connections of the thyristors 15, 16 and the connections of the capacitors 19, 20. The current supply device for arc welding described in . 9 intermediate DC voltage sources 11, 14 connected to input terminal 10 and provided with DC output terminals 12, 13;
and a transformer 17 having a primary winding 18 and a secondary winding 21 connected to the welding electrode terminals 24, 25 via a rectifier bridge 22, and one side connected to each of the DC output terminals 12, 13. , at least one capacitor 19, 20 whose other side is connected to one end of the primary winding 18, and the primary winding 1
The other end of 8 is connected to the switching pulse former 48,5.
The DC output terminals 12 and 13 are connected to both of the DC output terminals 12 and 13 through controlled switching devices 15 and 16 which alternately receive switching pulses from a switching control device having a switching control device having an output voltage of 0 to 57. a voltage squaring and regulating device 33 , 33 connected to a voltage source 334 whose value corresponds to the voltage applied to or to the capacitors 19 , 20 and whose output is connected to the input of the oscillator 34 ;
1 to 333, 335, the output of the oscillator 34 is connected to the switching pulse generators 48, 50 to 57 that generate trigger pulses, and the switching control device further controls the welding electrode terminals 24, 2.
A current supply device for arc welding, characterized in that it comprises a second sensing circuit 35, 36, 37 adapted to block the gate device 48 when the voltage to the welding device 5 exceeds a predetermined maximum value. 10 It has first and second capacitors 19 and 20 that are alternately charged and discharged via the primary winding 18 by the alternate conduction of the two thyristors 15 and 16, and the thyristors 15 and 16 are connected in series with each other and have an intermediate capacitor. Claim 9, wherein the DC voltage sources 11, 14 are connected across and the primary winding 18 is connected between the connections of the thyristors 15, 16 and the connections of the capacitors 19, 20. The current supply device for arc welding described in .