JPH0530858Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to an arc welding power source suitable for use in, for example, TIG (tungsten inert gas) welding.

[Prior Art] Fig. 4 is a circuit diagram showing the configuration of a conventional arc welding power source. In the figure, 1 is a DC power source such as a battery (voltage is E), D1, D2 and D3, D.
4 are diodes connected in reverse to both ends of the power source E, respectively. Each diode D1, D2, D
Switching elements S1, S2, S3, and S4 are interposed between the anodes and cathodes of No. 3 and D4, respectively. In this case, the inverter is activated by the diodes D1 to D4 and the switching elements S1 to S4.
INV is configured. A smoothing reactor (including stray inductance in wiring) L, an arc starter AS, an electrode T, an arc A, and a base material W are inserted in series between the output ends of the inverter INV. Then, while the control unit (not shown) detects the welding current Iw, the welding current Iw is
On/off of each of the switching elements S1 to S4 is controlled as appropriate so that the average value of the switching elements coincides with the target value.

FIG. 5 is a diagram showing the relationship between the general on/off control timing of the switching elements S1 to S4 in the above circuit and the welding current Iw. In this figure, a section Ta is a section where the welding current Iw flows in the direction of the arrow shown in FIG. 4, and a section Tb is a section where the welding current Iw flows in the direction opposite to the above arrow (negative direction). Furthermore, energy is stored in the reactor L while the switching element S2 is on in the interval Ta, and similarly, while the switching element S4 is on in the interval Tb, the reactor L
Energy is stored in the opposite direction. And the section
T ₁ , T ₁ ... are sections in which the energy stored in the reactor L circulates through the switch S3 and the diode D1, and sections T ₂ , ₂ ... are the sections in which the energy stored in the reactor L circulates through the switch S3 and the diode D1.
The energy stored in the switching element S1,
This is the section where the current circulates through the diode D3.

As can be seen from FIG. 5E, if the above-mentioned switch control is performed, the ripples in the welding current Iw are reduced due to the smoothing effect of the reactor L, and the welding current Iw at a substantially constant level flows alternately in forward and reverse directions.

[Problems Solved by the Invention] Incidentally, when welding materials that are easily oxidized, such as aluminum, AC welding, which has a cleaning effect to remove oxide films, is often applied.

However, AC welding has the drawback that the average value of the welding current must be lowered when welding thin materials, resulting in unstable arc.
That is, for example, in the circuit of the AC welding power source shown in FIG. 4, there is a smoothing reactor L,
Due to the influence of this reactor L (and other wiring stray inductance), the waveform of the welding current Iw does not become a perfect rectangular wave, but becomes a triangular wave as shown by the solid line in FIG. In this case, if the value of di/dt is large, a certain effect can be achieved, but if the value of reactor L is small, the smoothing effect disappears,
If the average value of the welding current Iw becomes small, there will be a section where the welding current Iw is 0, as shown by the dashed-dotted line in FIG. 6, resulting in a problem of arc breakage.

This invention has been made in consideration of the above-mentioned circumstances, and has as its object to provide an AC welding power source which does not cause arc interruption even when the average welding current value becomes small, and which can always generate a stable arc.

[Means for solving the problem] This invention was made to solve the above problem, and includes a reference pulse generating means for generating a reference pulse for generating an arc at every predetermined period, and a circuit. a switching means for switching from a regeneration mode to a circulation mode; a welding current detection means for detecting a welding current flowing through the circuit; and a peak value command means for commanding a peak value of the welding current based on a detection result of the welding current detection means. Setting means for setting the minimum arc sustaining current value that allows the arc to sustain at the end of one cycle in the arc welding power source provided;
a triangular wave generating means for generating a triangular wave that rises from the start point of the regeneration mode and falls at the start point of the next cycle; a deviation detecting means for detecting a deviation between the peak command value of the welding current and the arc sustaining minimum current; A switching signal that compares the deviation value output from the deviation detection means with the output value output from the triangular wave generation means, and switches the circuit from regeneration mode to circulation mode when the output value becomes equal to the deviation value. and switching signal generating means for supplying the switching means to the switching means.

[Operation] According to the above configuration, the setting means sets the minimum arc sustaining current value that allows the arc to continue at the end of one cycle. Then, the deviation detection means detects the deviation between the minimum arc sustaining current value and the peak command value of the welding current, and this deviation value is compared with the triangular wave generated by the triangular wave generation means at the time of starting the regeneration mode. When the value of this triangular wave becomes equal to the deviation value, the regeneration mode is switched to the circulation mode at that point. In this way, the period during which regeneration mode is switched to circulation mode changes depending on the deviation between the minimum arc sustaining current value and the peak command value of welding current, so welding in which the final value of each cycle of welding current is always constant is achieved. Current can be obtained. Therefore, even if the welding current becomes small, arc breakage does not occur and a stable arc can be generated.

[Example] Hereinafter, an example of this invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing the configuration of an embodiment of this invention. In this figure, the same reference numerals are given to the parts corresponding to those in FIG.

In Figure 1, 6 indicates that the primary coil is an inverter.
This is a high frequency transformer connected to the output end of INV, and the cathode of diode 13 is connected to one end of the secondary coil, and the anode of diode 11 is connected via switching element S7. The anode of the diode 13 is connected to the base material W via the switching element 9 and the current detector 15 sequentially, and the cathode of the diode 11 is connected to the cathode of the diode 12 and the current detector 1.
5 and to the anode of a diode 14 via a switching element S10. The other end of the secondary coil of the transformer 6 is connected to the anode of the diode 12 via the switching element S8, and the high frequency transformer 1
It is connected to the electrode T via the secondary coil 6, and also to the cathode of the diode 14.

Reference numeral 18 denotes a control unit that performs on/off control of the switching elements S1 to S4 and switching elements S7 to S10, and drive control of the arc starter 17, and controls each setting device 22-1 to 22 in the setting unit 22.
On/off control of each switching element is performed based on the set value of -3 and the welding current Iw detected by the current detector 15. Further, an oscillator is provided in the control unit 18,
To turn on/off each switching element,
This is performed based on the period of the output signal (frequency is 15kHz) of this oscillator. Here, a control system for controlling on/off of each of the above-mentioned switching elements will be explained with reference to FIG.

In this figure, 24 is the voltage corresponding to the instantaneous value of the welding current Iw detected by the current detector 15.
This is a terminal to which Vif (absolute value) is supplied, and the voltage Vif is supplied to the inverting input terminal of the comparator 25 via this terminal 24, and the average value converter 2
6. The average value converter 26 converts the voltage Vif
(hereinafter referred to as average voltage Vif'). Average voltage output from average value converter 26
Vif′ is supplied to the deviation detection point 27 and setter 22
The deviation from the average voltage value Vwa set by -1 is detected. In this case, the setting device 22-1 is for setting the average value of the welding current Iw. The deviation detected at the deviation detection point 27 is supplied to an integrator 28, where it is integrated. Then, the value obtained by integrating the deviation, that is, the voltage Vp, is determined by the comparator 2.
It is supplied to the non-inverting input terminal of No. 5 and also to the deviation detection point 29. At the deviation detection point 29, the output of the integrator 28 and the voltage set by the setting device 22-2
Deviation from Vb is detected. In this case, setting device 2
2-2 is a bias circuit that cancels the voltage Vp ₀ corresponding to the current ip ₀ . In this case, the current ipo is the value at time t ₁ of the current downward slope during circulation of the welding current Iw. The output of the deviation detection point 29 is then supplied to the inverting input terminal of the comparator 32.
Next, a switch 30 is used to reset the integral value of the integrator 31 at a predetermined timing. In this case, when the output of the SR (set/reset) latch 36 is inverted to the "H" level, both terminals of the switch 30 become conductive. The SR latch 36 is set by a one-shot multivibrator 34 triggered by the rising edge of the 15kHz oscillator 33, and is reset when Vif>Vp or when the output of the oscillator 33 is inverted to "L" level. The integrator 31 integrates the voltage Vt set by the setter 22-3, and its output is supplied to the non-inverting input terminal of the comparator 32. In this case, the setting device 22-3 is for setting the regeneration period. Then, the output of the comparator 32 controls the switching element S8 or S10.

The above-mentioned average value converter 26, deviation detection point 27,
29, integrator 28, 31, comparator 25, 3
2 constitutes an on/off control system 18a.

Next, the operation of this embodiment with the above configuration will be explained with reference to FIG.

First, from the setting unit 22, the average current setting value Vwa,
Setting value to cancel voltage Vp ₀ equivalent to current ip ₀
Vb (-Vp ₀ ) and regeneration period setting value Vt in the control unit 1.
Supply to 8. The control unit 18 then drives the arc starter 17 to generate the arc A. Further, at the rising time t ₁ of the reference pulse P ₁ (FIG. 3A) generated within the control unit 18, the switching elements S1, S4, and S7 are turned on (all other switching elements are turned off). As a result, on the secondary side of the transformer 6, switching element S7→
Welding current Iw flows through the path of diode D11→current detector 15→base material W→electrode T. here,
Inductance L2 of the secondary wiring of the transformer 6,
The number of turns of the primary coil and secondary coil of transformer 6 is
If N ₁ , N ₂ and the voltage between the electrode and the base metal are Va, the welding current Iw is expressed by the following formula.

Iw=(E×(N ₂ /N ₁ )−Va)×t/L2 ...(1) Next, in the on/off control system 18a, the deviation between the average voltage Vif' and the voltage Vwa is integrated, and this The voltage Vp ₁ , which is the integrated value, is compared with the voltage Vif, and when the voltage Vif exceeds the voltage Vp ₁ (time t ₂ shown in the figure (b)), the output of the comparator 25 is inverted to "L" level. and switching element S1,
S4 is turned off. In this case, voltage Vp ₁ has a value corresponding to the peak of welding current Iw. Then, when the switching elements S1 and S4 are turned off, the energy stored in the secondary side of the transformer 6 regenerates the current to the power source 1 through the same path as in the period _t1 to _t2 , and the welding current Iw rapidly increases. decreases to

On the other hand, when the output Q of the SR latch 36 is inverted to "L" level, the switch 30 becomes non-conductive.
As a result, the voltage set by the setting device 22-3
Vt is supplied to an integrator 31. Then, the output of the integrator 31 (FIG. 3C) is supplied to the non-inverting input terminal of the comparator 32, and compared with Vp-Vb (Vp ₀ ), which has already been supplied to the inverting input terminal of the comparator 32. Then, at time _t3 when the output of the integrator 31 exceeds Vp-Vb, the output of the comparator 32 (FIG. 3D) is inverted to the "H" level, and the switching element S8 is turned on.

The welding current Iw during the period t ₂ to _{t 3} described above is expressed by the following formula.

Iw=｜ip ₁ ｜−(E×(N ₂ /N ₁ )+Va)(t ₃ −t ₂ )/
L2...(2) (ip ₁ is the peak current value at time t ₂ ) Then, when switching element S8 is turned on, welding current Iw circulates. In this case, switching element S7 may remain on or may be switched off.

As described above, when the switching element S8 is on, the welding current Iw sequentially flows through the switching element S8 and the diode 12, which are the bypass path. Therefore, the period t ₃ shown in FIG.
When the welding current Iw at t ₄ decreases, this slope, that is, the value of di/dt decreases, and the welding current during this period decreases.
The value of Iw is the lowest current value at which arc breakage does not occur. Then, when one cycle of the output signal of the oscillator in the control unit 18 is completed, the control unit 18 turns each switching element S1 to S4, S7 to S10 on and off again in the same manner as in the period _t1 to t/ ₂ . state.

Subsequently, each of the above-mentioned periods _t1 to _t2 , _t2 to _t3 , _t3 to _t4
The same operation as above is repeated, but the operation of this circuit will now be described for cases in which the peak value of the welding current Iw following the period t ₁ to _{t 4} is small and large. First, when the peak value ip ₂ (FIG. 3 b) of the welding current Iw detected by the current detector 15 is small, the voltage Vp ₂ output from the integrator _{28 is} The period t ₅ to _{t 6} until the voltage becomes smaller than the value of Vp ₁ and the comparator 32 is inverted to “H” level is the period mentioned above.
It will be shorter than t ₂ - _{t 3} . Then, switching element S8 is turned on at time _t6 , and welding current Iw circulates. Therefore, when the peak value of the welding current Iw becomes smaller, the period until the switching elements S1 and S4 are turned off becomes shorter, and the regeneration period also becomes shorter. At the same time, the perfusion period becomes longer. This control means that if the switching element S8 is turned on at the same value as the welding current Iw at time _t3 , the welding current Iw will circulate at the slope indicated by _l1 in FIG. Become. As a result,
The current value corresponding to the hatched portion indicated by the symbol _A1 decreases, and the probability of arc breakage etc. occurring at time _t7 increases. On the other hand, as mentioned above, when the peak value of welding current Iw is small,
By controlling the regeneration period to be short, the final value of the welding current Iw in each cycle can be kept constant. Therefore, even if the peak value of the welding current Iw decreases, arc breakage does not occur and stable arc discharge is performed.

Next, when the peak value ip ₃ (Fig. 3 B) of the welding current Iw increases, the voltage output from the integrator 28 increases.
When Vp ₃ becomes larger than the voltage Vp ₁ during the period t ₁ to _{t 2} described above, the period (t ₇ to t ₈ ) until switching elements S1 and S4 are turned off becomes longer, and the comparator 32 is inverted to “H” level. The period until t ₈
~ _t9 is also longer than the aforementioned period _t2 ~ _t3 . and,
Switching element S8 is turned on at time _t9 , and welding current Iw circulates. Therefore, the welding current
As the peak value of Iw increases, the period until the switching elements S1 and S4 are turned off becomes longer, and the regeneration period also becomes longer. At the same time, the perfusion period becomes shorter. Controlling in this way means that if the value of the welding current Iw is the same as that at time _t3 ,
When the switching element S8 is turned on, the welding current Iw circulates at the slope indicated by the reference numeral ₂ in FIG. As a result, the current value corresponding to the hatched portion indicated by the symbol _A2 becomes excessive. On the other hand, as described above, when the peak value of the welding current value Iw is large, if the switching element S8 is controlled to be turned on for a longer period, the average value of the welding current Iw is reduced by a portion corresponding to _A2 . be able to. Therefore, even if the peak value of the welding current Iw increases, the average current is low and stable arc discharge is performed.

Next, after the above-described series of operations has been performed several times, switching elements S3 and S2 are turned on,
Switch the direction of welding current Iw. And period
During the period _t10 to _t11 , only the switching element S9 is turned on, and during the period _t11 to _t12 , the switching element S9 is turned off while the switching element S9 is turned off.
3. With S2 turned off, during the period t ₁₂ to t ₁₃ ,
Switching element S9 is turned on or off, and switching element S10 is turned on. In this case, the switching of the switching elements in each section _t10 to _t12 is exactly the same as that in the above-described section _t1 to _t4 , and the only difference is the direction of the peak value of the welding current Iw. That is, each interval t ₁₀ ~
The value of welding current Iw at t ₁₂ is also expressed by the above-mentioned equations (1) and (2). Further, the operation of the control unit 18 in each section t ₁₀ to _{t 12} is also the same as in the above case.

In this embodiment, the above periods have the following relationship:

Td/(Td+Te+Tf)<(1/2)...(3) (Td is t ₁ to t ₂ , Te is t ₂ to t ₃ , and Tf is t ₃ to t ₄ ) Such a relationship was set. This is due to the following reasons. That is, during period Td, E is applied to transformer 6.
(V), and -E(V) may be applied to the transformer 6 during the regeneration periods of periods Te and Tf. in this case,
If the regeneration period is shorter than the period Td, biased magnetization will occur in the transformer 6, and it will eventually become saturated. However, if the regeneration period is longer than the period Td, the transformer 6 will be magnetized in the opposite direction by the amount that is excited in the positive direction. This is because since the transformer 6 is excited, biased magnetization does not occur, and saturation of the transformer 6 is thereby avoided.

Furthermore, since switching elements S7 and S9 are switched only when switching polarity, and switching elements S8 and S10 forming a bypass path are switched only when low current is present, losses are small in both cases.

[Effects of the invention] As explained above, according to this invention, there are provided a reference pulse generating means for generating a reference pulse for generating an arc at predetermined intervals, and a switching means for switching the circuit from regeneration mode to circulation mode. , an arc welding power source comprising a welding current detecting means for detecting a welding current flowing in the circuit, and a peak value commanding means for commanding a peak value of the welding current based on a detection result of the welding current detecting means; a setting means for setting a minimum arc sustaining power supply value that allows the arc to last at the end; a triangular wave generating means for generating a triangular wave that rises from the start of the regeneration mode and falls at the start of the next cycle; and a peak of the welding current. a deviation detection means for detecting a deviation between a command value and the arc sustaining minimum current, and a deviation value outputted from the deviation detection means and an output value outputted from the triangular wave generation means, and a deviation detection means for detecting a deviation between the command value and the arc sustaining minimum current; and switching signal generating means for supplying a switching signal to the switching means for switching the circuit from the regeneration mode to the circulation mode when the deviation value becomes equal to the deviation value, so that the final value of each cycle of the welding current is always constant. A stable arc can be generated without arc breakage even when the welding current becomes small.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing the configuration of an embodiment of this invention, Figure 2 is a block diagram showing the electrical configuration of a control signal generation circuit used in the embodiment, and Figure 3 is an implementation of this invention. FIG. 4 is a circuit diagram showing the configuration of a conventional welding power source; FIGS. 5 and 6 are waveform diagrams explaining the operation of a conventional welding power source. . S8, S10... Switching element (switching means), 15... Current detector (welding current detection means),
22-1... Setting device, 26... Average value converter, 2
7... Deviation detection point, 28... Integrator (22-1,
26, 27, 28 are peak value command means), 22-
2... Setting device (setting means), 22-3... Setting device,
25, 32... Comparator, 29... Deviation detection point (deviation detection means), 31... Integrator (22-3,
31 is triangular wave generating means), 32... comparator (switching signal generating means), 33... oscillator (reference pulse generating means).

Claims (1)

[Claims for Utility Model Registration] Reference pulse generation means for generating a reference pulse for generating an arc at predetermined intervals; switching means for switching a circuit from regeneration mode to circulation mode; and detection of welding current flowing in the circuit. and peak value command means for commanding a peak value of the welding current based on the detection result of the welding current detection means, the arc welding power source comprising: a setting means for setting a minimum sustained current value; a triangular wave generating means for generating a triangular wave that rises from the start of the regeneration mode and falls at the start of the next cycle; a peak command value of the welding current and the minimum arc sustaining current; a deviation detection means for detecting a deviation of the deviation value; and a deviation value outputted from the deviation detection means and an output value outputted from the triangular wave generation means are compared, and when the output value becomes equal to the deviation value, the An arc welding power source, comprising switching signal generating means for supplying a switching signal for switching a circuit from regeneration mode to recirculation mode to the switching means.