JPS6216743B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is capable of adjusting the time constant of a change in the output current of a welding machine in response to a change in the welding machine load, that is, a change in the output voltage, without using a DC reactor. This invention relates to a DC arc welding control device.

[Prior art] A consumable electrode is fed to the joint of the workpiece, and the weld grains at the tip of the consumable electrode are transferred onto the surface of the molten pool formed on the workpiece, thereby filling the joint with melt. In a DC arc welding control device for welding, a consumable electrode and a workpiece are short-circuited at the start of or during welding. In this case, if a short-circuit current with an appropriate current value with an appropriate rising speed is not applied depending on the consumable electrode diameter, material, welding current value, resistance value and reactance value of the welding current carrying line, etc., a smooth arc will not occur. Otherwise, the welding process may not be able to occur, or spatter may increase, impairing workability or causing welding defects. For this reason, in conventional DC arc welding methods, a DC reactor is used to adjust the rise and magnitude of the short circuit current. This is because the DC reactor has the function of suppressing changes in current.

[Problems to be solved by the invention] However, it is not always easy to design and manufacture a DC reactor with a desired time constant.
It has been difficult to obtain a DC reactor with particularly large inductance. In addition, the problem of saturation of the iron core occurs, and as mentioned above, the appropriate reactance value changes depending on the resistance value and reactance value of the consumable electrode, so select a DC reactor that is suitable for various welding conditions and short circuit. In practice, it has been extremely difficult to properly control the rise and magnitude of the current.

Therefore, in Japanese Patent Application No. 51-130098 (see Japanese Patent Application Laid-Open No. 53-55447), the inventor of the present invention previously proposed a method for determining the output current Ia (jω) with respect to the change in the output voltage Ea (jω).
We proposed that the delay in the change in ω) be realized by changing the time constant of the voltage feedback circuit without using a DC reactor. However, in the control device of the invention proposed earlier,
It was not possible to increase the value of equivalent inductance when the change in output voltage was small. Also,
Actual inductance has the property of generating a back electromotive force proportional to the change in current and suppressing the change in current, but in the invention proposed earlier, when the amount of voltage feedback is zero, for example, it is completely constant. When using current characteristics, it was not possible to produce an equivalent inductance effect even if the current value changed.

An object of the present invention is to propose a DC arc welding control device that can obtain an inductance effect closer to the actual inductance than the previously proposed DC arc welding control device.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides an output setting circuit 6 for setting the output current, an output current detection circuit 41 for detecting the output current, and an output current detection circuit 41 for detecting the output current. a differentiating circuit 46 for differentiating the output signal Ei of
The output signal Er of the output setting circuit 6, the signal ei corresponding to the output signal Ei of the output current detection circuit 41, and the output signal ed of the differentiating circuit 46 are input (Er-ei-
ed) is provided, and the output current of the welding machine is controlled by the output of the amplifier circuit 30.

[Example] Hereinafter, a control device of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an equivalent circuit of a welding current supply circuit in a conventional DC arc welding control device including an inductance L. In the figure, E ₀ is the no-load output voltage, Ea is the arc voltage with a substantially constant value, R is the resistance value of the equivalent circuit, and L is the inductance value of the equivalent circuit. It also includes the inductance of the welding cable and welding cable.

If the current flowing through the circuit shown in the figure is Ia, E ₀ −Ea=RIa+L(dIa/dt) (1) holds true.

Figure 2 shows an implementation of the DC arc welding control device of the present invention in which changes in the output current of the welding machine follow changes in the welding machine load according to a set time constant without using a DC reactor. This is an example. In the figure, 1 is a power source, 2 is a welding transformer that receives power from the power source 1, and 30 is a rectifier/amplifier 3 connected to the secondary side of the welding transformer.
1 and an arithmetic element 32 constituting an arithmetic circuit. Rectifier/amplifier 31 is rectifier 31
A and the amplifier 31b may be integrally constructed using a thyristor, or may be constructed by combining a silicon rectifier and a transistor amplifier that are separately constructed. 40 is a current feedback circuit, and this circuit includes an output current detection circuit 41;
Signal ei = aEi obtained by multiplying the output signal Ei of the output current detection circuit 41 by an arbitrarily settable coefficient a.
A differential waveform signal ed=b is obtained by multiplying the output signal Ei of the detector output amplifier circuit 42 and the output current detection circuit 41 by an arbitrarily settable coefficient b.
The differential circuit 43 outputs (dEi/dt). Further, 50 is a welding machine load consisting of a welding electrode 51, an arc 52, and a workpiece 53, and 6 is a predetermined output setting signal for setting the output current of the welding machine.
This is an output setting circuit that generates Er.

In FIG. 2, the output voltage of the arithmetic element 32 is
If Ee, Ee=Er−ei−ed =Er−aEi−b(dEi/dt) ……(2) Also, since the output current Ia is proportional to Ee, the constant is K ₁
Then, Ia=K ₁ Ee = K ₁ [Er−aEi−b(dEi/dt)] ...(3) Furthermore, if the output current detection circuit 41 is a shunt with a resistance value r, Ei=rIa ... ...(4) dEi/dt=r(dIa/dt) ...(5) Substituting these equations (4) and (5) into equation (3), we get Ia=K ₁ [Er−arIa−br(dIa/dt), and rearranging this, we get K ₁ br(dIa/dt)+ (1+K ₁ ar) Ia = K ₁ Er ...(6). Here, if k ₁ ar≫1, then (1+K ₁ ar)
Since Ia≒K ₁ arIa, equation (6) can be transformed into equation (7) below.

br (dIa / dt) + arIa = Er ... (7) If we set br = L, ar = R, Er = E ₀ - Ea in equation (7), then equation (7) becomes L (dIa / dt) + RIa =E ₀ −Ea ...(8). This equation (8) is the same as equation (1) established from the equivalent circuit of the conventional DC arc welding control device using an inductance, and even in the DC arc welding control device of the present invention that does not use an inductance. This shows that the same effect as a DC arc welding control device using an inductance can be obtained.

Moreover, the general solution to equation ( ₇ ) is Ia=(Er/ar)+K ₂ ε ^-(b/a)t ...(9), where K 2 is the constant.

The time constant T is expressed as a/b and exhibits an equivalent inductance effect. This time constant T is the coefficient a, b
It can be changed by changing any of them, but as shown in equation (9), the coefficient a determines the steady value of the welding machine output current Ia together with the output signal Er of the output setting circuit. Therefore, it is better to adjust the time constant T by changing the coefficient b than to change the time constant T by changing the coefficient a.The transient value K ₂ ε having an equivalent inductance effect with the steady value Er/(ar) is better if the time constant T is adjusted by changing the coefficient b. ^{-(b/a
) and t} can be adjusted separately, which is desirable.

FIG. 3 shows an embodiment of the differential circuit 43 used in the DC arc welding control device of the present invention, in which AMP ₁ and AMP ₂ are operational amplifiers, R ₁ to R ₄ are resistors, C ₁ and C ₂ are capacitors.
The output signal Ei of the output current detection circuit 41 is connected to the resistor R ₁
When inputted to the operational amplifier AMP ₁ through the capacitor C ₁ , an inverted differential waveform output is obtained to the variable resistor VR, and a normally rotated differential waveform signal b (dEi/dt) is obtained to the output terminal of the operational amplifier AMP ₂ . It will be done. The coefficient b can be varied by adjusting variable resistor VR or resistor _R2 . Capacitor C ₂ together with resistor R ₁ has the effect of reducing unnecessary high frequency noise. In the above embodiment, the resistor R ₄ and the operational amplifier AMP ₂ are not necessarily required.

In this way, in the DC arc welding control device of the present invention, as shown in equation (8), ar can be set equal to R and br can be set equal to L, and the static The characteristic and the dynamic characteristic determined by br=L can be set individually, and the value of L can also be used as a direct reading scale.

Further, the control device of the present invention is not limited to the above embodiment, and a voltage feedback circuit may be added. In addition, when the output Ei of the output current detection circuit 41 is not amplified, that is, the coefficient a
In the case where is set to 1, the detector output amplification circuit 42 can be omitted. Furthermore, the arithmetic element 32 and the amplifier 31b may be integrated, or various modifications may be made. Further, the control device of the present invention is applicable not only to consumable electrode arc welding but also to non-consumable electrode arc welding.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide an appropriate time constant for changes in output current in response to changes in welding machine load without using a DC reactor that is difficult to design, manufacture, and adjust. In addition to this effect, a large equivalent inductance value can be obtained even when the change in output voltage is small, and even when the amount of voltage feedback is zero, the equivalent inductance effect can be obtained by changing the current in the same way as the actual inductance. It has the advantage of being able to demonstrate Furthermore, the present invention provides many advantages such as being able to set dynamic characteristics independently of static characteristics and using inductance values as direct reading scales.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an equivalent circuit of the output current energization circuit of a conventional DC arc welding control device, Fig. 2 is a block diagram showing an embodiment of the DC arc welding control device of the present invention, and Fig. 3 is a circuit diagram of the present invention. FIG. 2 is a connection diagram showing an example of a differential circuit used in the DC arc welding control device of the invention. 6... Output setting circuit, Er... Output signal of output setting circuit, 30... Amplifying circuit, 41... Output current detection circuit, Ei... Output signal of output current detection circuit, 43...
Differential circuit, ed...output signal of the differentiating circuit, 50...welding machine load, Ia...output current of the welding machine.

Claims (1)

[Claims] 1. In a DC arc welding control device that feeds back an output current to control the output to a set value, an output setting circuit that sets the output current, an output current detection circuit that detects the output current, and an output current detection circuit that controls the output current to a set value. A differentiation circuit that differentiates the output signal Ei, and an output signal Er of the output setting circuit, a signal ei corresponding to the output signal Ei of the output current detection circuit, and an output signal ed of the differentiation circuit are input (Er-
1. A DC arc welding control device comprising: an arithmetic circuit that obtains a control signal Ee (ei-ed); and an amplifier circuit that controls the output current using the control signal Ee.