JP2738006B2 - AC arc welding machine - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an arc welding machine, and more particularly to an AC arc welding machine suitable for arc welding of aluminum-based workpieces having a strong oxide film on the surface. is there.

[Conventional device]

FIG. 6 is a connection diagram of a conventional polarity-switchable AC arc welding power source. In FIG. 1, reference numeral 1 denotes a DC power supply having a constant current characteristic. For example, power is obtained from a commercial AC power supply (not shown), converted into a voltage suitable for arc welding, rectified, and the output current is set to a constant value according to the reference signal Ir. A known DC power supply that controls so as to maintain the voltage is used. Reference numerals 2a to 2d denote switching elements such as bridge-connected transistors. The DC terminal side of the bridge circuit is connected to the output terminal of the DC current 1 as an input terminal, and the AC terminal side is an output terminal. Connect to the workpiece 4. Reference numeral 6 designates a pair of switching elements 2a to 2d, 2a and 2b or 2c and 2d, which are a pair, of the bridge-connected switching elements 2a to 2d. A positive / reverse period signal generating circuit for supplying a signal Sp for switching the electrode 3 to a positive potential output) and a positive polarity period Tsp
Is a variable resistor VRsp and the reverse polarity period Trp is a variable resistor VR
A repeat timer circuit set by rp is used. Reference signal generation circuits 7 and 8 output reference signals Isp and Irp for determining the output current value during the positive polarity period and the output current value during the reverse polarity period, respectively, and are each composed of a DC power supply and a variable resistor. I have. Reference numeral 9 denotes a reference signal switching circuit composed of an analog switch. The output of either the reference signal generation circuit 7 or 8 is switched by the output signal Sp of the forward / reverse period signal generation circuit 6 to the DC power supply 1 as an output current reference signal Ir. Supply. Reference numeral 10 designates an output signal Sp of the forward / reverse period setting circuit 6 as an input and a switching element 2 according to the input signal.
This is a switching element drive circuit for simultaneously turning on any of a, 2b or 2c, 2d.

In the device shown in FIG. 7, when the polarity is positive, the period is controlled by the variable resistor VRsp, and the current value is controlled by the output Isp of the reference signal generation circuit 7.
In the case of reverse polarity, the period is independently set by the variable resistor VRrp, and the current value is independently set by the output Irp of the reference signal generating circuit 8. Therefore, the positive polarity current, the reverse polarity current, and the duration in the case of both polarities are independently adjusted.

On the other hand, the penetration depth for obtaining the required welding quality is substantially determined by the positive polarity current, and the range in which the surface oxide film of the workpiece is removed (so-called cleaning width) is the reverse polarity current value and the length of the reverse polarity period. It is known that it depends on Sato. In other words, the length of the positive polarity period is Tsp, the length of the reverse polarity period is Trp, and the peak values of each period are Isp and Irp in a waveform in which the current of the positive polarity and the reverse polarity is almost a rectangular wave.
When, the bead width Bw is And the cleaning width Cw obtained at this time is (Where 1 ≦ n ≦ 3, k1 and k2 are proportional constants determined by welding conditions). Here, it is essential that the cleaning width Cw required for the bead width Bw is wider than this, and this bead width
Since it is a value obtained by adding the margin Co to Bw (where Co is a constant value almost independently of the bead width), Cw = Bw + Co (3) Therefore, from the above equations (1), (2) and (3), The relationship between the period in polarity and the current value is Becomes Thus, the proper current value in both forward and reverse polarities is
They have a close relationship with each other, and even if any of them is excessive or insufficient, a welding result of a required quality cannot be obtained. Therefore, in the above-described conventional apparatus, adjustment is not easy, and individual differences among workers tend to increase.

The present inventors have previously made one of the reference signal generation circuits for determining the output current to be provided two sets in order to solve the above-mentioned problems of the conventional device the output signal of the other reference signal generation circuit as an input, An AC arc welding machine comprising a function generator that generates a signal corresponding to an input signal, wherein the output signals of the two reference signal generating circuits determine the output current at the time of both forward and reverse polarities is disclosed in Japanese Patent Application No. Sho 61 -244763.

FIG. 7 shows an example of this type of apparatus. FIG. 7 shows the output Isp of the first reference signal generating circuit 7 and the output of the forward / reverse period setting circuit 6 in place of the reference signal setting device 8 for setting the output current at the time of reverse polarity in the conventional device of FIG. FIG. 6 shows a second reference signal generating circuit 11 comprising a function generator which receives an output as an input and outputs a signal Irp = f (Isp, Trp, Tsp) corresponding to the input signal. Therefore, the same reference numerals are given to those having the same functions. Here, as the second reference signal generation circuit 11, a circuit that outputs a signal proportional to the above-described equation (4) may be used. Such a function generator can be easily realized by combining an adder using an operational amplifier and a multiplier (for example, a multiplication / division integrated circuit of product No. 4452 of Teledyne, USA).

In actual welding, these elements Isp, Tsp, T
If all rps are variable, not only will control become extremely difficult, but it will also cause confusion in selecting conditions. Therefore, assuming that A is a constant determined by the welding conditions such as the work to be welded and the shielding gas as the function generator 11, Furthermore, even if a circuit for performing a simple operation such as Irp = A.Isp + b is used, it is unlikely that this will cause a practical problem. In this case, only the output Isp of the first reference signal generation circuit 7 needs to be input to the second reference signal generation circuit 11. In the apparatus shown in FIG. 7, by setting the output of the first reference signal generating circuit 7 so as to obtain a required positive polarity current, a reverse polarity current suitable for this positive current value is obtained. Is obtained from the second reference signal generation circuit 11. The reference signals Isp and Irp thus obtained are output from the forward / reverse period setting circuit 6.
The reference signal Ir is supplied to the DC power supply 1 via a reference signal switching circuit 9 that switches according to sp. Accordingly, the switching elements 2a and 2b conduct between the electrode 3 and the workpiece 4 only during a period in which the positive current having a value determined by the output signal Isp of the first reference signal generating circuit 7 is set by the variable resistor VRsp. The reverse polarity current of a value determined by the output signal Irp of the second reference signal generation circuit 11 which receives the output signal of the first reference signal generation circuit 7 and outputs a signal related thereto is then supplied to the variable resistor. The switching elements 2c and 2d conduct and flow repeatedly for the period set by VRrp.

[Problems to be solved by the invention]

In the above-described conventional device, since the reverse polarity current is calculated and determined with respect to the positive polarity current, the necessary output current can be easily set. However, as the value of the positive polarity current increases, the value of the required reverse polarity current also increases, so when this reverse polarity current reaches the maximum value that can be output from the DC power supply, Reference signal Irp for determining current
However, the actual reverse polarity current will not increase no matter how large the cleaning width required for this will not be obtained.
Weld defects will result.

[Means for solving the problem]

The present invention has been developed in order to solve the above-described problems of the conventional device.
Until the value of the reverse polarity current reaches the maximum output value of the DC power supply, the length of the reverse polarity period or the ratio of the reverse polarity period in one cycle consisting of the positive polarity and the reverse polarity is fixed and the reverse polarity current value is positive. After the value of the reverse polarity current reaches the maximum value due to the increase in the positive polarity current, the length of the reverse polarity period or the reverse polarity period in one cycle is determined according to the positive polarity current. It is designed to change the occupancy rate.

[Action]

According to the present invention, an accurate reverse polarity output for obtaining a required cleaning width in accordance with an increase or decrease of the positive current can be realized by a simple control circuit.

〔Example〕

FIG. 1 is an explanatory view showing an embodiment of the present invention. In the figure, reference numerals 1 to 11 denote elements having the same functions as those of the conventional apparatus shown in FIG. Reference numeral 12 denotes a third reference signal generation circuit for determining the maximum value Irm of the reverse polarity current, which comprises a DC power supply and a variable resistor, like the first reference signal generation circuit 7. Reference numeral 13 designates an output Irp of the second reference signal generation circuit and an output Irm of the third reference signal generation circuit 12 as inputs, and outputs a constant output Trp = To while Irm ≧ Irp (or Irm> Irp). Irm <
When Irp (or Irm ≦ Irp), Trp = B · f (Ir
p) + To... where B is a constant and f (Irp) is a function of Irp, which is a comparison operation circuit that outputs Trp when Tsp = constant in the above equation (4). Reference numeral 14 denotes a V / R conversion circuit that receives the output Trp of the comparison operation circuit 13 and converts the input voltage into a resistance value. In the case where the forward / reverse period signal generating circuit 6 is not a variable resistor but uses a voltage signal as an input and outputs a polarity switching signal having a time width corresponding to the input signal, the output of the comparison operation circuit 13 is directly or It may be supplied via a coefficient unit or an amplifier.

In the apparatus shown in the figure, when the first reference signal generation circuit 7 determines a reference signal Isp for determining a positive polarity current for obtaining a necessary penetration depth, the reference signal Irp for determining a reverse polarity current is determined by this signal. Is determined by the function generator 11 according to a predetermined function. The reference signal Irp of the reverse polarity current is also supplied to the comparison operation circuit 13 and compared with the output Irm of the third reference signal generation circuit 12. The comparison operation circuit 13 outputs a constant output Tp while the input signal Irp is smaller than Irm, and outputs an output Trp which becomes a function corresponding to Irp when Irp becomes larger than Irm. As a result, the reverse polarity current increases as the positive polarity current increases.

After the reverse polarity current increases and reaches the limit Irm of the capability of the DC power supply 1, even if the signal Irp further increases, the actual value of the reverse polarity current cannot increase, but the output of the comparison operation circuit 13 is inverted. The required cleaning width is secured by increasing the polarity period signal Trp.

In FIG. 1, since the width of the weld bead generated by the positive polarity current changes depending on both the positive polarity period and the positive polarity current, the first function generator used as the second reference signal generator 11 is the first. If not only the output Isp of the reference signal generating circuit 7 but also the output of the variable resistor VRsp that determines the length of the positive polarity period is input as a part of the variable, a more accurate cleaning width can be obtained. Similarly, by inputting the output of the variable resistor VRsp to the comparison operation circuit 13 as a part of the variable, the optimum cleaning width can be automatically secured even when the positive polarity period Tsp is changed. .

FIG. 2 (a) is a connection diagram showing a specific example of the second reference signal generating circuit 11 in the embodiment of FIG. 1, in which the input signal Isp and the voltage of the DC power supply E2 are connected to an operational amplifier A1, Vessel r1
And Irp = A · I
sp + C ... where A and C are constants determined by welding conditions ...
Is what you get. A2 is an operational amplifier for inverting the polarity, and is provided when necessary depending on the polarity of each signal.

FIG. 2 (b) is a diagram showing the relationship between the input and output signals of the circuit of FIG. 2 (a). In this case, the output signal Irp is from an initial value Irp = C determined by the output voltage of the DC power supply E2. From the beginning, it shows a linear change that is directly proportional to the input signal Isp.

FIG. 3 (a) is a connection diagram showing a specific example of the comparison operation circuit 13. In the figure, Def1 is a subtractor which subtracts the output Irm of the third reference signal setting unit 12 from the output signal Irp of the second reference signal generation circuit 11 to obtain a difference signal ΔI. D1, D2
Is a diode, and when the polarity of the output ΔI of the subtractor Def1 is positive (that is, when Irp> Irm), this is transmitted to the next stage.
When ΔI is negative (that is, Irp <Irm), it is grounded. r4 to r6 are resistors and constitute an adder together with the amplifier A3, and the output of the DC power source E3 and the output Δ of the subtractor Def1
I is added. A4 is an operational amplifier for polarity inversion provided as needed. FIG. 3 (b) is the same as FIG.
3 shows the relationship between the output signal Trp and the input signal Irp obtained by the circuit of FIG.
A constant voltage To determined by E3 is output, and when Irp> Irm, a difference voltage ΔI = Irp−Irm between both input signals and a DC power supply
The output signal Trp = B · determined by the sum with the output voltage of E3
(Irp-Irm) + To ... B outputs a constant ...

FIGS. 2 and 3 show examples in which the input signal is changed in direct proportion to the input signal. Alternatively, a characteristic such as Trp = A. (Isp-Irm) ⁿ + To may be obtained by combining a multiplier or a divider instead of the adder shown in each example.

FIG. 4 is a connection diagram showing a specific example of the V / R conversion circuit 14. In the figure, Comp2 is a comparator, A5 is an amplifier, M
Reference numeral 1 denotes an electric motor, and the sliders of the variable resistors VRp and VR1 are simultaneously moved in the same direction by the electric motor.

A voltage is supplied to the variable resistor VR1 from the DC power supply E4, and the output voltage of the slider is negatively fed back to the comparator Comp2. In the figure, when an input signal Trp (output Trp of the comparison operation circuit 13 in FIG. 1) is supplied, the comparator Comp2 supplies a voltage difference between the output of the variable resistor VR1 and the amplifier A5,
The amplifier A5 amplifies the input voltage and drives the electric motor M1. The rotation of the motor M1 causes the slider of the variable resistor VR1 to move.If the rotation direction of the motor M1 is set to a direction in which the output of the comparator Comp2 decreases, the motor M1 receives an input. It stops when the signal Trp matches the output voltage of the variable resistor VR1. At this time the variable resistor
Since the slider is driven in conjunction with the variable resistor VR1, the resistance value of the variable resistor VRp at this time is determined by the input signal Trp.
It is a value proportional to. This variable resistor Vrp is connected to the first
If it is used as a variable resistor for setting the reverse polarity period of the forward / reverse period signal generation circuit 6 in the embodiment of the figure, a reverse polarity period corresponding to the input signal Trp can be set.

In the embodiment of FIG. 1, when the forward / reverse period generating circuit 6 is a circuit for generating a timed signal corresponding to an input signal with a voltage signal as an input, the V / R conversion circuit 14 is of course unnecessary. .

Since the input of the comparison operation circuit 13 may be a signal corresponding to the current in the reverse polarity period, the signal is in a functional relationship corresponding to the output Irp of the second reference signal generation circuit 7 instead of the output Irp. The output Isp of the first reference signal generation circuit 11 may be used.

FIG. 5 is a connection diagram showing another embodiment of the present invention;
In FIG. 1, reference numeral 1 denotes a DC power supply having three terminals of positive, negative and zero as output terminals. Reference numerals 2e and 2f denote switching elements, and an alternating current output is obtained by alternately conducting both switching elements. 3,
Reference numerals 4, 7, 9, 11, and 12 denote elements having the same functions as those of the embodiment of FIG. 1, respectively. Reference numeral 15 denotes an output I of the first reference signal generation circuit 7.
When the input signal sp and the output Irm of the third reference signal generating circuit 12 are input and Isp <Irm (or Isp ≦ Irm), a constant signal α = αo... where 0 <α <1.
(Or Isp> Irm), α = D · f (Isp) +
αo, that is, α = B · f (Irp) + αO, where B and D are constants, and f (Isp) and f (Irp) are functions of Isp and Irp, respectively. Is a comparison operation circuit that outputs ...
It can be easily obtained by combining a subtractor and an operational amplifier similarly to the comparison operation circuit 13 of the embodiment of FIG. Reference numeral 16 denotes a polarity switching period setting circuit for setting the length T of one cycle including a positive polarity period and a reverse polarity period, and includes, for example, a DC power supply and a variable resistor. 17 is a comparison operation circuit 15
And an output T of the polarity switching period setting circuit 16 as inputs, and outputs a positive polarity period signal Tsp = (1−α) T and a reverse polarity period signal Trp = αT. And a subtractor. The output signal Tsp of the forward / reverse period signal generating circuit 17 is a switching element.
2f is made conductive and supplied to the reference signal switching circuit 9, and during the period of Tsp, the output current of the DC power supply 1 is determined using the output Isp of the first reference signal generation circuit 7 as the reference signal Ir. The signal Trp is supplied to the switching element 2e to make it conductive, so that a reverse polarity current flows from the electrode 3 to the workpiece 4.

In the embodiment shown in FIG. 5, a constant reverse polarity time rate α is maintained until the positive polarity current Isp reaches a constant value (the peak value of the reverse polarity current determined corresponding thereto is the maximum value of the DC power supply 1).
= Αo, and is repeated in the forward / reverse period cycle T. During this time, the reverse polarity current increases (for example, in direct proportion) in response to the increase in the positive polarity current. As the positive polarity current increases, the reverse polarity current determined corresponding to this increases in the third reference signal setting circuit 12.
Is larger than the output Irm, the comparison operation circuit 15 sets the reverse polarity period rate α as α = D · f (Isp) + αo, that is, α = B ·
It operates to output f (Irp) + αo and increase α in accordance with an increase in the positive current. As a result, the reverse polarity period increases, and a cleaning width commensurate with the increase in the positive current can be secured. Note that the function f (Isp) or f
(Irp) may be a direct proportional or monotonic increase curve with respect to the increase of Isp or Irp for the reason of the above equation (4).

In the embodiment of FIG. 5, since the ratio of the reverse polarity period is determined in accordance with the current in the positive polarity period, welding can be always performed at a constant period unlike the embodiment of FIG. This is a particular advantage in high speed welding. The reason is that in AC arc welding, the weld bead is formed mainly when the polarity is positive, and when the polarity is reversed, only the so-called cleaning action that destroys the oxide on the surface of the workpiece is performed. If the length of the reverse polarity period increases and the welded object does not melt during this period,
This is because when welding is performed at high speed, the welding torch moves considerably during this time, so that the bead shape becomes non-uniform, and in extreme cases, the bead may be interrupted.

In the embodiment shown in FIG. 5, as in the embodiment shown in FIG.
The output signal Irp of the second reference signal generation circuit 11 may be used instead of the output signal Isp of 11.

〔The invention's effect〕

According to the present invention, in a device for welding a workpiece having an oxide film such as aluminum by alternately flowing currents of both positive and reverse polarities, the reverse polarity current value is increased in correlation with the increase in the positive polarity current. After the reverse polarity current reaches the capacity limit of the device, the period of the reverse polarity current or its ratio is increased, so even when the positive polarity current is increased, there is a shortage of the reverse polarity current. Insufficient cleaning width is eliminated. For this reason, the adjustment only requires setting the positive polarity current alone, and the operation is simplified. Further, the control becomes extremely simple as compared with the method of calculating the reverse polarity current and the reverse polarity period from the positive polarity current and the positive polarity period, so that the apparatus is inexpensive.

[Brief description of the drawings]

FIG. 1 is a connection diagram showing an embodiment of the present invention, FIG. 2 (a) is a connection diagram showing an example of a second reference signal generating circuit 11 used in the embodiment of FIG. 1, and FIG. 2 (b). 3 is a diagram showing the relationship between input and output signals of the circuit of FIG. 2 (a), FIG. 3 (a) is a connection diagram showing an example of the comparison operation circuit 13 used in the embodiment of FIG. 1, and FIG. 3B is a diagram showing the relationship between input and output signals of the circuit of FIG. 3A, FIG. 4 is a connection diagram showing an example of the V / R conversion circuit 14 used in the embodiment of FIG. Is a connection diagram showing another embodiment of the present invention, and FIGS. 6 and 7 are connection diagrams showing an example of a conventional apparatus. 1. DC power supply, 2a to 2a ... Switching element, 6, 17 ...
... Forward / reverse period signal generation circuit, 7 first reference signal generation circuit, 9 reference signal switching circuit, 11 second reference signal generation circuit, 12 third reference signal generation circuit, 13 , 15… Comparison circuit, 14… V / R converter circuit, 16… Polarity switching cycle setting circuit

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Hiroyuki Ishii 2-1-1-11 Tagawa, Yodogawa-ku, Osaka-shi, Osaka Daihen Co., Ltd. (56) References JP-A-63-97364 (JP, A) 61-92463 (JP, U)

Claims (2)

(57) [Claims] 1. A polarity comprising a DC power supply for outputting a current having a peak value corresponding to a supplied reference signal, and a switching element for switching the output of the DC power supply between positive polarity and reverse polarity and transmitting the output to an output terminal. A switching circuit, a first reference signal generation circuit for determining an output current value in the positive polarity period, and a function determined in advance according to an input signal with an output I _sp of the first reference signal generation circuit as an input. A second reference signal generating circuit for determining an output current value during a reverse polarity period comprising a function generator for generating a signal; and a signal _Irm corresponding to a maximum value of the reverse polarity current that can be output from the DC power supply. A third reference signal generating circuit, an output signal I _{rp of} the second reference signal generating circuit (or an output I _{sp of} the first reference signal generating circuit) and an output I _{sp of} the third reference signal generating circuit. input and _rm And, I _rp <I _rm (or I _sp <
(I _rm ), a constant signal T _rp = T ₀ is output, and I _rp ≧ I
T _rp = B · f (I _rp ) + while _rm (or I _sp ≧ I _rm )
T ₀ (or T _rp = B · f (I _sp ) + T ₀ ) where B is a constant and f (I _rp ) and f (I _sp ) are the output signals of the second and first reference signal generation circuits. A comparison operation circuit for outputting functions of I _rp and I _sp , a positive polarity period setting device,
A forward / reverse period signal generation circuit that receives the output T _sp of the positive polarity period setter and the output T _rp of the comparison operation circuit, and outputs a polarity switching signal that defines a positive polarity period and a reverse polarity period to the polarity switching circuit; A reference signal switching circuit that supplies an output signal of the first or second reference signal generation circuit to the DC power supply as a reference signal for setting an output current to the DC power supply in synchronization with an output signal of the forward / reverse period signal generation circuit; AC arc welding machine equipped with 2. A DC power supply for outputting a current having a peak value according to a supplied reference signal, and a polarity comprising a switching element for switching the output of the DC power supply between positive polarity and reverse polarity and transmitting the output to an output terminal. A switching circuit, a first reference signal generation circuit for determining an output current value in the positive polarity period, and a function determined in advance according to an input signal with an output I _sp of the first reference signal generation circuit as an input. A second reference signal generating circuit for determining an output current value during a reverse polarity period comprising a function generator for generating a signal; and a signal _Irm corresponding to a maximum value of the reverse polarity current that can be output from the DC power supply. A third reference signal generating circuit, an output signal I _{rp of} the second reference signal generating circuit (or an output I _{sp of} the first reference signal generating circuit) and an output I _{sp of} the third reference signal generating circuit. input and _rm And I _rp <I _rm (or I _sp <I _rm)
Between outputs a constant signal α = α ₀ ...... However 0 <α <1 ......, during the I _rp ≧ I _rm (or _{I sp ≧ I rm) α =} B ·
f (I _rp ) + α ₀ (or α = B · f (I _sp ) + α ₀ )
Where B is a constant, f (I _rp ) and f (I _sp ) are comparison operation circuits for outputting functions of the output signals I _rp and I _sp of the second and first reference signal generation circuits, A polarity switching period setting circuit that determines one cycle T consisting of a polarity period and a reverse polarity period; an output T of the polarity switching period setting circuit and an output α of the comparison operation circuit; T _sp = (1−α) T and reverse polarity period T _rp = αT
A forward / reverse period signal generating circuit that outputs a polarity switching signal that determines the following. An output signal of the first or second reference signal generating circuit is supplied to the DC power supply in synchronization with an output signal of the forward / reverse period signal generating circuit. An AC arc welding machine comprising a reference signal switching circuit for supplying a reference signal.