JPH0160350B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a DC arc welding power source suitable primarily for arc welding using consumable electrodes.

Conventionally, as a power source for DC arc welding, DC power is obtained by converting a commercial AC power source to a voltage suitable for welding using a transformer, and then controlling the phase using a switching element such as a thyristor to control the output and perform rectification. Furthermore, in order to obtain dynamic characteristics of current and voltage suitable for welding, they were supplied to the output terminal via a DC reactor. On the other hand, in a DC arc welding method using a consumable electrode, the consumable electrode and the workpiece may be short-circuited at the start of welding or during welding. In this case, if a short circuit current of an appropriate magnitude with an appropriate rise speed is applied depending on the diameter of the consumable electrode, material, welding current value, resistance value and reactance value of the welding current path, etc., the arc will not occur smoothly. If it is not possible to generate or
This not only impairs workability due to an increase in spatter, but also causes welding defects. moreover,
After arc generation, an important requirement for arc stability is that the current decreases to the set value at a rate of decline appropriate to each welding condition.

In particular, in the short-circuit transitional arc welding method in which a short-circuit and an arc are alternately generated, it is known that the bead shape changes greatly depending on not only welding stability but also the reactance value of the output circuit.
In other words, the current rise speed at the time of a short circuit depends on the amount of excess
Furthermore, since the rate of fall of the current during arc regeneration is related to the arc force, it affects the penetration depth as well as the amount of spatter generated. Therefore, in order to have a bead with the desired bead width, excess buildup amount, and penetration depth in such a welding method, the reactance must be adjusted arbitrarily or in phase relation when the current increases and decreases. If this is possible, ideal welding will be possible. In contrast, in conventional DC arc welding power sources, a DC reactor is provided in the output circuit to adjust the rise speed, magnitude, and fall speed of the output current in the event of a short circuit. However, it is not always easy to design and manufacture a DC reactor with the necessary time constant, and the required time constant for current change is extremely long, and the inductance required for this is several tens of μH or more. It was quite difficult to obtain such a large inductance, reaching several 100 μH. Moreover, the number of currents
Since it has a large value of 100A, it is a very large reactor. Also, if an iron core is used to obtain a large inductance, the problem of saturation will arise.
Furthermore, the appropriate inductance value depends on the diameter, material, welding current, welding voltage of the consumable electrode, or
Since these values change in a complicated manner depending on whether they are increased or decreased, it has been virtually impossible to obtain a DC reactor that is compatible with all of them. In reality, the solution was to use reactors with intermediate characteristics between these.

In order to eliminate these drawbacks of DC reactors, a phase delay element is inserted into the output feedback circuit to create a phase delay in output changes in response to changes in load, essentially creating the effect of a DC reactor. is proposed. However, all of these power supplies rectify commercial AC power to obtain the desired characteristics, so the output contains many low-frequency pulsations of 200Hz or less, and in order to smooth this out, a time constant is required. A long smoothing circuit is required, and since the output current is large, this smoothing circuit must be constructed with a reactor, and this smoothing reactor is required for the stability of welding as explained earlier. It is approximately the same as a DC reactor, and it is common to use both. Therefore, even if a phase delay element is included in the feedback control system to provide the reactor effect necessary for stable welding,
Since it was necessary to provide a smoothing reactor, no significant advantage could be obtained in the end. When such a control system is configured to produce a reactor effect, it is most advantageous when using a DC power source with little pulsation.For example, when polyphase AC is rectified and a Analog control may be performed using analog elements. However, in this case, the analog element always bears the power corresponding to the pulsation, making it necessary to use a high-power transistor.
This not only makes the equipment large and expensive, but also
Even during use, it is inevitable that there will be a lot of power loss and the efficiency will be poor.

The present invention eliminates the drawbacks of each of the conventional examples described above, and uses a switching control method using switching elements to control the output of a DC power supply, and a circuit that provides a phase delay to the output control circuit with respect to load fluctuations. By creating a circuit configuration in which the amount of phase delay can be adjusted independently when the output increases and decreases, an extremely small and inexpensive output smoothing circuit can be used, and The object of the present invention is to provide a high-performance, inexpensive DC arc welding power source that can easily obtain the optimum output rising speed and falling speed for welding.

FIG. 1 is a block diagram showing an embodiment in which the present invention is carried out using chopper control, which is one of the switching control methods. In the figure, 1 is an input terminal and is connected to, for example, a three-phase AC power source. 2 is a DC power supply which converts the AC input from the input terminal 1 into a voltage suitable for welding with a transformer 21, and then converts it to DC with a rectifier circuit 22, and uses three-phase AC as the AC power supply. It is desirable that the rectifier circuit be a multi-phase rectifier circuit such as a three-phase full-wave or six-phase half-wave rectifier. Reference numeral 3 denotes a switching control circuit for adjusting the output of the DC power supply 2 by a switching method, and in the case shown in the figure, a chopper control circuit using series transistors is used. 4 is a smoothing circuit for smoothing the output of the switching control circuit 3, and if the frequency of the chopper control circuit used in the switching control circuit 3 is a high frequency of 300 Hz or more, preferably several KHz or more, the time constant of this smoothing circuit is An extremely short length will suffice, and a small smoothing circuit such as an air-core reactor or a small-capacity capacitor will suffice. Furthermore, when the frequency is set to be sufficiently high, the smoothing circuit can be replaced by inductance or stray capacitance caused by the internal wiring of the switching control circuit 3 and the routing of the output lead wires. The time constants of these smoothing circuits are sufficiently short compared to the time constants of output changes necessary for arc stability, so that the smoothing circuits do not affect arc stability. 5 is a consumable electrode that is fed at a predetermined speed; 6 is an object to be welded;
7 is a welding arc. Reference numeral 8 denotes a phase lag control circuit for causing a phase lag in output changes in response to load fluctuations, and includes a coefficient unit 81 that multiplies the output Ia of the output current detector 85 by a coefficient _k1 , and an output current detector 85.
A differentiating circuit 82 that differentiates the output Ia of the output voltage detector 86, a coefficient unit 83 that multiplies the output Ea of the output voltage detector 86 by a coefficient _k2 , an output Er of the output setting device 9, an output _k1 Ia of the coefficient unit 81, an output of the differentiating circuit 82 and an arithmetic circuit 84 that subtracts the sum of each output of the output k ₂ Ea of the coefficient unit 83. In this case, each coefficient adder may be omitted if a coefficient adder is used in the arithmetic circuit or if each detector is capable of adjusting the output level. The differentiating circuit 82 changes the coefficient depending on the direction of change of the input signal in order to independently adjust the phase delay amount of the phase delay control circuit 8 when the output current increases and when the output current decreases. It is configured. This differential circuit 8
A concrete example of the second embodiment is shown in FIG. In FIG. 2, the differentiating circuit 82 includes a resistor R1 and a capacitor C.
1, C2, operational amplifier OP1 and operational amplifier OP
A diode D provided in the feedback circuit No. 1 for determining increase and decrease of the input signal.
1 and D2, and a phase delay amount adjuster consisting of variable resistors VR1 and VR2 connected in series to these. Note that in the same figure, the resistor R1 and the capacitor C2 are provided to stabilize the differential operation, and may be considered to be excluded in terms of the operating principle. 10 is a phase delay control circuit 8
An output control circuit for driving the switching control circuit 3 according to the output of the switching control circuit 3, which is a drive signal with a constant frequency and a time width corresponding to the input signal, or a drive signal with a constant time width and a frequency corresponding to the input signal. Alternatively, it generates a drive signal whose time width and frequency both correspond to the input signal. The operation of the embodiment shown in FIGS. 1 and 2 will be explained. In the differential circuit shown in Fig. 2, the capacitance of capacitor C1 is C, the resistance values of variable resistors VR1 and VR2 are r ₁ ,
r ₂ and the forward drop of diodes D1 and D2 is negligible, the output signal E ₀ when it increases with respect to the input signal Ei is E ₀ = −r ₁ CdEi/dt = −k ₃ dIa/dt ...(1) When the input signal Ei decreases, the output E ₀ is E ₀ = -r ₂ CdEi/dt = -k ₄ dIa/dt ... (2). Here, Ia is the output current of the device of FIG. 1, and k ₃ and k ₄ are positive constants determined by c, r ₁ , r ₂ and the conversion ratio of the output current detector 85. Furthermore, the negative signs in equations (1) and (2) above are due to the result of using an inverting amplifier circuit as the differentiating circuit, and the output of the differentiating circuit 82 is added to the outputs of the coefficient multipliers 81 and 83 to obtain the sum of the three. When comparing the output signal of the output setting device 9 in the arithmetic circuit 84, the signal is inverted again.
E ₀ ' is set so that a positive output signal is obtained when the output increases and a negative output signal is obtained when the output decreases. In the embodiment shown in FIG _{. 1} when _the differentiating circuit shown in FIG. 3) and Er−(k ₁ Ia+k ₂ Ea+k ₄ dIa/dt=0 ...(4). Therefore, k ₂ Ea=Er−(k ₁ Ia+k ₃ dIa/dt) ...( 5) and k ₂ Ea=Er−(k ₁ Ia+k ₄ dIa/dt) ……(6) or k ₁ Ia=Er−(k ₂ Ea+k ₃ dIa/dt) ……(7) and k ₁ Ia=Er −(k ₂ Ea + k ₄ dIa/dt) ...(8) Here, the coefficient k ₁ is the value corresponding to the resistance value of the output circuit, and k ₃ and k ₄ are the diameter and material of the consumable electrode used. If _{the value} determined _by Therefore, the variable resistors VR1 and VR2
By adjusting the coefficients k ₃ and k ₄ , or by setting the coefficients k ₃ and k ₄ in conjunction with the output setting, the optimum current increase and decrease rates can always be achieved. This reactor effect can be easily obtained. By the way, in arc welding, depending on the object to be welded, the applied welding conditions, and the welding method, the static characteristics of the voltage and current of the power source may drop to a certain extent as the output current increases, compared to those with perfect constant voltage characteristics. In some cases, it may be more convenient to use a device with a falling characteristic, or a device with a constant current characteristic, in which the output current does not change regardless of changes in the output voltage. Therefore, in addition to the coefficients k ₃ and k ₄ , it is desirable that the coefficients k ₁ and k ₂ are not fixed, but are adjustable. In this case, if k ₁ ≪ k ₂ , the characteristic is almost constant voltage, and if k ₁ ≫ _{k 2} , it is almost constant current characteristic.
Further, in the middle between the two, a power source with an intermediate falling characteristic can be obtained. Of course, if only constant voltage characteristics are required, the coefficient k ₁ is set to zero, that is, the coefficient multiplier ₈₁ in FIG. 83 may be excluded from the circuit configuration.

In addition to the embodiment shown in FIG. 2, the differentiating circuit 82 may include a simple differentiating circuit consisting of a capacitor and a resistor, or an amplifier that amplifies the outputs of these differentiating circuits. Furthermore, as a means of adjusting the coefficients k ₃ and k ₄ , two series circuits of a diode and a variable resistor are connected in parallel with opposite polarities, and the signal level can be set to different values depending on the direction of change. A circuit for adjusting the voltage may be provided on the input side or the output side of the differential circuit. Furthermore, two sets of ordinary differentiating circuits using operational amplifiers may be provided, and one of the outputs may be selected in accordance with the polarity of the output signal to provide the total output. In any of these,
It is also possible to replace the variable resistor for adjustment with a transistor. Furthermore, in the case where the welding conditions used are approximately constant, these resistors may be fixed or semi-fixed at optimal values when increasing and decreasing the output, respectively.

In the embodiment shown in FIG. 1, the phase lag control circuit is configured to include a signal obtained by differentiating the output of the output current detector in the output feedback signal, but the phase lag control circuit is not limited to this. Since a change in load also appears as a change in output terminal voltage, this may be used. In this case, a first-order delayed signal of the output voltage may be supplied as the phase delayed signal that is fed back to the output control circuit.

FIG. 3 is a block diagram showing another embodiment of the present invention in this manner. FIG. 3 shows an example of a system in which an inverter is used as a switching control circuit to convert DC power into AC power and then convert it back into DC power to obtain a predetermined DC output. In the figure, 23 is a rectifier circuit that converts AC power from the input terminal 1 into DC, and is of the same type as the rectifier circuit 22 of FIG. 1, except that it handles a different voltage. Switching control circuit 3
An inverter 31 receives the DC output of the rectifier circuit 23, converts it into AC power, and then converts it to a predetermined voltage.
and a rectifier 32 that rectifies the output of the inverter 31 and returns it to direct current. In addition, the phase lag control circuit 8 integrates the output Ea of the output voltage detector ₈₆ in place of the differentiating circuit ₈₂ in FIG. ₅ ∫Eadt or k ₆ ∫Eadt is used, and the arithmetic circuit 88 uses the output Er of the output setter 9, the output k ₁ Ia of the coefficient unit 81, and the output of the integration circuit 87.
k ₅ ∫Eadt or k ₆ ∫Eadt and the output of the coefficient unit 83
This is an arithmetic circuit that subtracts k ₂ Ea. Here, the integrating circuit 87 may be a first-order lag circuit such as a low-pass filter that charges a capacitor provided with a discharge circuit with an appropriate time constant via a resistor together with a discriminator for determining the direction of output change. FIG. 4 shows a concrete example thereof. In the same figure, D3 and D
4 is a diode for determining the direction of change in output voltage, VR3 and VR4 are variable resistors for adjusting the amount of phase delay, C3 is a capacitor, and integration is performed by variable resistors VR3 and VR4 and capacitor C3. It constitutes a circuit. OP2 is an operational amplifier, which is a voltage follower circuit for adjusting the output impedance, and the load connected to the output side of the integrating circuit 87, that is, the operational circuit 8 in FIG.
If the input impedance of step 8 is sufficiently large, it can be omitted. Coefficients k ₅ and k ₆ of the integrating circuit 87, which correspond to the amount of phase delay when the output voltage increases and decreases, are determined by the resistance values of the variable resistors VR3 and VR4 and the capacitance of the capacitor C3.

In the embodiment of FIG. 3, the output control circuit 10 has Er-(k ₁ Ia+k ₂ Ea+k ₅ ∫Eadt)=0...(9) and Er-(k ₁ Ia+k ₂ Ea+k ₆ ∫Eadt)=0...(10) It works as follows. In this case as well, each coefficient k ₁ ,
The method for determining k ₂ , k ₅ and k ₆ is the same as in the case of FIG. Further, the integrating circuit 87 may also be one using an operational amplifier other than the embodiment shown in FIG.
Various modifications can be made to the method of adjusting k ₅ and k ₆ as in the differential circuit shown in FIG. 2. Note that it is convenient to use an inverter 31 in FIG. 3 that takes out its output through transformer coupling. In this case, the built-in transformer adjusts the output voltage to a voltage suitable for arc welding. If the inverter 31 is not connected to a transformer, it will be necessary to install a transformer between the inverter 31 and the rectifier circuit 32, but in this case as well, if the output frequency of the inverter is high, a very small Become something. In FIGS. 1 and 3, only one output setting device 9 is provided, but two output setting devices are provided, one for voltage and one for current, and the current element and voltage element are separately set in the arithmetic circuit 88. You may compare and synthesize the results. Further, in order to provide a phase delay, both the differential signal of the output current tester and the integral signal of the output voltage detector may be fed back.

As described above, in the present invention, by using the switching method, the output smoothing circuit has a very short time constant and is simple, or may not be necessary in some cases. In addition, when the consumable electrode short-circuits to the workpiece, or when a change in load occurs, such as when a short-circuit changes to an arc, by providing a phase delay in the output change, There is no need to use a large DC reactor to stably generate an arc. In addition, the effective reactor effect can be set to different values when the output increases and decreases, which was difficult with conventional equipment, dramatically improving welding stability and reducing the occurrence of spatter. Moreover, the bead shape can be controlled. For this,
Welding in difficult positions, such as facing upward or standing, becomes easier.

[Brief explanation of drawings]

1 and 3 are block diagrams showing embodiments of the present invention, FIG. 2 is a connection diagram showing an embodiment of the differential circuit used in the embodiment of FIG. 1, and FIG. 4 is an implementation of the embodiment of FIG. FIG. 3 is a connection diagram showing an embodiment of an integrating circuit used in the example. 2...DC power supply, 3...Switching control circuit, 4
...Smoothing circuit, 8...Phase delay control circuit, 9...Output setting device, 10...Output control circuit, 81, 83...Coefficient unit, 82...Differentiating circuit, 84, 88...Arithmetic circuit, 8
5... Current detector, 86... Output voltage detector, 87...
Integral circuit.

Claims (1)

[Scope of Claims] 1. A DC power supply, a switching control circuit that adjusts the output of the DC power supply to a desired value using a switching control method, an output setting device, an output of the output setting device, and an output of the switching control circuit. a phase lag control circuit that outputs a signal with a phase lag of a different value depending on when the output increases or decreases in response to a change in load; A DC arc welding power source equipped with an output control circuit that drives the circuit. 2. The phase delay control circuit includes an output current detector, a differentiation circuit that differentiates the output of the output current detector with different coefficients when increasing and decreasing, and a differential circuit that differentiates the output of the output current detector from the output of the output setting device using different coefficients. The DC arc welding power source according to claim 1, comprising an arithmetic circuit that subtracts the sum of the output of the current detector and the output of the differentiating circuit. 3. The phase delay control circuit includes an output voltage detector, an output current detector, a differentiating circuit that differentiates the output of the output current detector with different coefficients when increasing and decreasing, and the output setting. 2. The DC arc welding power source according to claim 1, further comprising an arithmetic circuit that subtracts the sum of the output of the output voltage detector and the output of the differential circuit from the output of the detector. 4. The phase delay control circuit includes an output voltage detector, an output current detector, a differentiating circuit that differentiates the output of the output current detector with different coefficients when increasing and decreasing, and the output setting. The DC arc welding power source according to claim 1, comprising an arithmetic circuit that subtracts the sum of the output of the output voltage detector, the output of the output current detector, and the output of the differential circuit from the output of the device. . 5. The phase delay control circuit includes an output voltage detector, an output current detector, an integration circuit that integrates the output of the output voltage detector with different coefficients when increasing and decreasing, and the output setting. The DC arc welding power source according to claim 1, further comprising an arithmetic circuit that subtracts the sum of the output of the output current detector and the output of the integrating circuit from the output of the detector. 6. The phase delay control circuit includes an output voltage detector, an integration circuit that integrates the output of the output voltage detector with different coefficients when increasing and decreasing, and an output voltage detector that integrates the output of the output voltage detector by applying different coefficients when increasing and decreasing the output. The DC arc welding power source according to claim 1, comprising an arithmetic circuit that subtracts the sum of the output of the voltage detector and the output of the integrating circuit. 7. The phase delay control circuit includes an output voltage detector, an output current detector, an integration circuit that integrates the output of the output voltage detector with different coefficients when increasing and decreasing, and the output setting. The DC arc welding power source according to claim 1, comprising an arithmetic circuit that subtracts the sum of the output of the output voltage detector, the output of the output current detector, and the output of the integrating circuit from the output of the device. . 8. The phase delay control circuit includes an output voltage detector, an output current detector, an integrating circuit that integrates the output of the output voltage detector with different coefficients when increasing and decreasing, and the output current. a differentiating circuit that differentiates the output of the detector with different coefficients when increasing and decreasing; and an output of the output setting device, an output of the output voltage detector, an output of the output current detector, and an integrating circuit. The DC arc welding power source according to claim 1, comprising an arithmetic circuit that subtracts the sum of the output of the differential circuit and the output of the differential circuit. 9. Claims 1 to 8, wherein the phase delay amount of the output change by the phase delay control circuit can be adjusted respectively when the output increases and when the output decreases.
A power source for DC arc welding as described in any of the paragraphs. 10. Claim 1, wherein the switching control circuit is a circuit that performs chopper control using a switching element connected in series to the output side of a DC power source.
The DC arc welding power source according to any one of Items 9 to 9. 11. The switching control circuit comprises an inverter circuit that converts the output of a DC power source into AC power, and a rectifier circuit that converts the output of the inverter circuit into DC power. DC arc welding power source described in . 12. The DC arc welding power source according to any one of claims 1 to 11, wherein the output control circuit is a circuit that determines the output frequency of the switching control circuit according to an input signal. 13. The DC arc welding power source according to any one of claims 1 to 12, wherein the output control circuit is a circuit that determines the conduction time width of the switching control circuit according to an input signal.