JPS61273260A - Controlling circuit for arc welding voltage - Google Patents

Abstract

PURPOSE:To increase the welding quality by providing the steady error correcting circuit to eliminate the steady errors of welding voltage and welding target voltage and by deciding the welding current based on the outputs of this correcting circuit and error amplifier. CONSTITUTION:The difference Vepsilon in the welding voltage VO and welding aiming voltage VR is detected by providing an error amplifier 3. A steady error correcting circuit 9 and welding current setting circuit 10 are arranged by linking with the error amplifier 3. The welding current setting circuit 10 is formed by PWM modulation circuit 4 and adder 5. When the welding voltage VO is fed to the error emplifier 3, the amplifier 3 outputs the difference Vepsilon from the target voltage VR as Ves via the steady error correcting circuit 9, which is added to the output Vepsilon. The correcting circuit 9 stabilizes the control circuit by making the output Vepsilon always in zero by an integrator, etc. The welding voltage and current are thus allowed to coincide with the target value and the welding quality is increased because of the steady error being enabled to be eliminated.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to an arc welding voltage control circuit for a consumable electrode type arc welding machine that performs welding while feeding an electrode wire to a welding part. ] FIG. 2 is a block diagram showing a conventional arc welding voltage control circuit. In this figure, numeral 1 is a first-flow supply device constituted by a chopper or an inverter, 2 is a welding load, 3 is a target voltage V, and an output voltage (welding voltage) Vo
4 is a PWM modulation circuit that outputs a voltage with a pulse width proportional to the output Vε of the error detector; 5 is a PWM modulation circuit that outputs a pace current command I! to the waterfall-modulated output Vp; I
This is an adder for adding B.

Next, the operation will be explained. The output Vε is the difference between the target voltage vR detected by the error amplifier 3 and the output voltage vo.
is pulse width modulated by the PWM modulation circuit 4. That is, as shown in FIG. 3, when the output v6 of the error detector 3 is large, the current target value IR added with the pace current command IB has a wide pulse width, and the current target value Ink is Output 1 of said current supply device 1 in operation. The pulse width of is also widened. Therefore, even if there is an average fluctuation in the welding load 2, such as a fluctuation in the protrusion length, the output current is 1. Since the pulse width of the welding beam changes to keep the average welding voltage constant, it is possible to make the welding beam uniform.

A control block diagram of the above operation is shown in FIG.

In FIG. 4, numeral 6 is the error amplification gain A1 of the control system.
7 is the change ratio formula between the current target value IR and the output current 〇, 8 is the average impedance Z of the welding load, 9 is the detection ratio g of the output voltage (welding voltage) Vo, IB + 'f6 * V
O indicates the average value of IR# I6*V6 in FIG.

[Problem that the invention seeks to solve]

Since the conventional arc welding voltage control circuit is configured as described above, as can be seen from FIG. 4, the output average current is given by equation (1).

That is, as can be seen from equation (1), the output average voltage? , is A
Or as long as the dog is a finite value, it is affected by the average load impedance 2. In other words, if the protrusion length changes significantly or if a short circuit occurs during spray welding, the steady-state error between the output average voltage vo and the target voltage vR becomes impossible to ignore.For example, if the protrusion length becomes short, the output Since the voltage V is lower than the target voltage VB, the wire penetrates into the base metal, making the arc unstable, causing non-uniformity in the welding beam, and deteriorating welding quality.

This invention was made to solve the above-mentioned problems, and aims to improve welding quality by eliminating the difference between the average output voltage and the target voltage in any case.

[Means for solving problems]

The arc welding voltage control circuit according to the present invention detects the difference between the welding voltage and the welding target voltage using an error amplifier, and supplies the output of the error amplifier to a welding current setting circuit for determining the welding current, and A steady error correction circuit is provided to which the output of the amplifier is supplied, and the output of the steady error correction circuit is supplied to the welding current setting circuit.

[Effect]

The arc welding voltage control circuit of this invention is provided with a steady error correction circuit that works to eliminate the steady error between the welding voltage and the welding target voltage, so if there is an error between the welding voltage and the target voltage, it will be corrected. The output average current is changed until the error becomes zero, and when the error disappears, the previous output average current is maintained.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, reference numeral 9 is a steady-state error correction circuit, and 10 is a welding current setting circuit.The welding current setting circuit includes a PCM modulation circuit 4 and an adder 5, which were explained with the same reference numerals in the conventional circuit.
It is made up of.

In addition, the same reference numerals as in FIG. 2 indicate the same or corresponding parts.

Next, the operation will be explained. Output voltage (welding voltage) V
The output Vε of the error amplifier 3, which is the difference between o and the welding target voltage vR, is outputted as Vε8 through the steady error correction circuit 9, and is added for each output V.

As an example of this steady-state error correction circuit 9, a specific circuit using an integrator 11 is shown in FIG. In FIG. 5, as long as the output Vε is not zero, it is integrated by an integrator 11, and when the output Vε becomes zero, the previous value is maintained. Therefore, since the control circuit is in a stable state when the output Vε is zero, it can be seen that steady-state errors do not occur under any load conditions.

In order to explain this in terms of control theory, the control configuration shown in FIG. 1 is shown in a block diagram in FIG. 6. In FIG. 6, the symbol 1
2 shows the total error amplification gain in which the transfer function of the steady-state error correction circuit 9 is expressed by Laplace's S. In Figure 6, the output voltage Vo is given by, and its average value is given by setting Laplace's S to 0, so it is given by (3), and vo is No longer affected by load impedance 2.

Note that in the above embodiment, the waterfall modulation method is used to control the output voltage, but a PfM frequency modulation method may also be used.

Further, in the above embodiment, the integrator 11 is included in the steady error correction path 9.
was used, but other means may also be used.

〔Effect of the invention〕

As described above, according to the present invention, a steady-state error correction circuit is provided to eliminate the steady-state error between the output voltage (welding voltage) and the target voltage. However, since the welding voltage matches the target value and there is no penetration, the welding beat is uniform and the overall welding quality can be improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG.
The figure is a block diagram showing a conventional arc welding voltage control circuit, FIG. 3 is a waveform diagram for explaining the operation of the circuit in FIG. 2, and FIG. 4 is a control block diagram showing the operation in FIG. 2. Fifth
The figure is a block diagram showing a specific example of the steady-state error correction circuit of the present invention, and FIG. 6 is a block diagram showing the control configuration of the present invention using a transfer function. 1: Current supply device, 2: Welding load 1.3: Error amplifier,
4: PWM modulation circuit, 5: adder, 9: steady error correction circuit, 10: welding current setting circuit, 11: & divider. Note that the same reference numerals in the figures indicate the same or equivalent parts. Agent Patent Attorney Masaru Sato Figure 3 0-11111----------11111--34 Figure 5 Figure 6

Claims (1)

[Claims] In an arc welding voltage control circuit of a consumable electrode type arc welder that performs welding while feeding an electrode wire to a welding part, an error amplifier that detects a difference between a welding voltage and a welding target voltage is supplied, and the output of the error amplifier is supplied. , a steady-state error correction circuit that operates to eliminate a steady-state error between the welding voltage and the welding target voltage, and a welding current setting circuit that is supplied with the output of the error amplifier and the output of the steady-state error correction circuit and that determines the welding current. An arc welding voltage control circuit characterized by: