JPH0686013B2 - Constant arc length control method in pulse arc welding - Google Patents

Description

The present invention relates to a constant arc length control method in pulse arc welding.

[Conventional technology]

In non-consumable electrode type pulse arc welding, the conventional method for welding while keeping the arc length constant has been the conventional method.
What is described in Japanese Patent No. 3706 and Japanese Patent Laid-Open No. 54-16345
There is one described in the publication.

[Problems to be solved by the invention]

The former controls the arc voltage to the reference arc voltage only during either the low current period (base current period) or the high current period (pulse current period) of the welding current. In this case, in the low frequency region of about 0.5 to 2 Hz, the period in which the arc length cannot be controlled increases and continuous and stable constant arc length control cannot be performed. If it is tilted as shown in Fig. 4, the locus of the welding torch vibrates in a step-like manner as shown by the solid line in the figure, so the welding quality deteriorates, and the starting point of the arc length control is the uncontrolled current part. In that case, there is a problem that the control response is lowered.

The latter is one in which either the base current or the pulse current of the welding current is converted into a voltage, the voltage is set as the reference arc voltage, and the amount of current change converted into the voltage is added to or subtracted from the reference arc voltage. However, since the welding current is converted into an arc voltage, the low current region where the linearity between the welding current and the arc voltage is lost (the arc voltage V shown in FIG. 5).
-There is a problem that control is impossible in the hatched area of the welding current I characteristic).

Furthermore, since the voltage obtained by a current-voltage converter such as a shunt is minute, not only a voltage amplifier is required, but also noise is likely to occur.

[Object of the Invention]

The present invention has been made in order to solve the above-mentioned conventional problems, and by taking the difference between the arc voltage in the high current period and the arc voltage in the low current period and performing the arithmetic processing with the arc voltage in the entire period, To obtain a constant arc length control method in pulse arc welding that is continuous and stable even in the frequency range, has a higher responsiveness than before, and can realize constant arc length control even in the low current range. With the goal.

[Means for solving problems]

In order to achieve the above object, the present invention compares an arc voltage with a reference arc voltage in a base current period, and in a pulse current period, detects an arc voltage detected / stored in the base current period and the pulse current period. The difference with the stored arc voltage is subtracted from the arc voltage in the pulse current period to create a base arc voltage corresponding portion, and this is compared with the reference arc voltage, and in both current periods of the pulse current period and the base current period. It is configured to control the electrode position.

〔Example〕

FIG. 1 is a block diagram of a constant arc length control device embodying the present invention, FIG. 2 is a diagram showing waveforms of welding current, arc voltage and the like, and FIG. 3 is a waveform time chart. In the figure, 1 is a welding power source (power source for supplying a pulse current), and 2 is an arc voltage detector. The arc voltage detector 2 detects the arc voltage V shown in FIG. Reference numeral 3 is a welding torch, 4 is a base metal to be welded, and 5 is a servomotor, which drives the welding torch 3 in a direction to approach / separate from the base metal 4 to be welded. 6 is a power amplifier, 7 is a differential amplifier,
A reference arc voltage setting device 8 generates a reference arc voltage Vo for setting the arc length.

A welding current detector 9 detects the welding current I shown in FIG. 2 (a) and supplies it to the timing signal generator 10. The timing signal generator 10 detects the rising and falling edges of the welding current I and generates the timing signals A to E shown in FIG. The timing signal A becomes H level in synchronization with the falling time of the welding current I and becomes L level in synchronization with the rising time, and the timing signal B becomes H level with a delay of a certain time t from the rising time of the welding current I. Short pulse signal,
Timing signal C is a signal synchronized with timing signal A,
The timing signal E becomes the H level in synchronization with the rising time of the welding current I, and the second time after a certain time t has passed from that time
The timing signal D, which is at the L level at the time point Y shown in FIG. 7C, is at the H level at the rising time point Y of the timing signal E and becomes at the L level at the falling time point of the welding current I. The constant time t corresponds to the rising transient period of the welding current I. Reference numeral 11 is a filter that shapes the voltage output of the arc voltage detector 2. 12 and 13 are voltage holders. The voltage holder 12 passes through the filter 11 and is shown in FIG.
A waveform-shaped arc voltage V and a timing signal A are introduced as shown in FIG. 3, and the arc voltage V during the timing signal A is at the H level, that is, the base arc voltage Vb of the arc voltage V.
Then, the final voltage value Vbh (voltage value at the time point Y shown in FIG. 2C) of the acquired base arc voltage Vb is held during the L level. The voltage holder 13 is a filter
The waveform-shaped arc voltage V and the timing signal B are introduced through 11, and when the timing signal B becomes the H level, the arc voltage V, that is, the pulse arc voltage of the arc voltage V.
Vp is taken in and the sampled pulse arc voltage Vph is held for a period of L level. Here, the values held at the predetermined sampling points for Vph and Vbh were used as they are,
The average value of the arc voltage during the current period or the average value of several cycles before the period may be Vph and Vbh. A differential amplifier 14 outputs the difference (Vph-Vbh) between the pulse arc voltage Vph and the base arc voltage Vbh. Reference numeral 15 is a subtracter, which receives the arc voltage V whose waveform is shaped by the filter 11 and the output (Vph-Vbh) of the differential amplifier 14, and which is the difference voltage Vd = V corresponding to the base arc voltage in the pulse current period. -(Vph-Vbh) --- Calculates (1).

A switch device 16 has switches 16C to 16E which are opened and closed by timing signals C to E, respectively, and opens and closes the outputs of the differential amplifier 14, the subtractor 15 and the filter 11 at a predetermined timing. An almost direct-current arc length control signal Vc shown in (e) is created. When the timing signal C is input, the switch device 16 switches the switch 16 at the H level.
C is turned on, and the arc voltage V (base arc voltage Vb) is supplied to the differential amplifier 7 during the base current period. When the timing signal E is input, the switch 16E is turned on at the H level, that is, during the transient time t of the welding current I, and the base arc voltage final value Vbh held by the voltage holder 12 is supplied to the differential amplifier 7. Supply to. When the timing signal D is input, the switch 16D is turned on at the H level, that is, during the pulse current period after the transient period, and the difference voltage Vd
Is supplied to the differential amplifier 7. The differential amplifier 7 receives the voltages Vb, Vbh, and Vd that are input in time series, that is, the substantially arc-shaped arc length control signal shown in FIG. The deviation ε is sent out in comparison with the voltage Vo. This deviation output ε = Vo−Vc is amplified by the voltage amplifier 6 and then supplied to the servomotor 5. The servomotor 5 controls the welding torch 3 so that the deviation ε becomes 0. The arc length between the welding base materials 4 is controlled to be constant.

In the present embodiment, the base current period, the arc length is controlled by using the base arc voltage Vb of the period as an arc length control signal, the pulse current period, the base arc voltage Vbh of the base current period before the period and the pulse. The arc length is controlled by using the difference voltage Vd obtained by comparing the difference between the pulse arc voltage Vph sampled at a predetermined time point of the current period and the pulse arc voltage, that is, not only the base current period but also the pulse current. Since the arc length is also controlled during the period, the arc length is controlled continuously, and the uncontrollable period virtually disappears even in the low frequency range of 0.5 to 2 Hz, and the response Also improves.

Therefore, even when the welding surface of the base material 4 to be welded is inclined as shown in FIG. 4, the welding torch 3 is prevented from moving in a step-like manner, and the linear locus along the base material 4 to be welded is prevented. Draw and move to improve the welding quality.

Further, in this embodiment, since the arc length is controlled by using the base arc voltage Vbh as the arc length control signal during the transition period t of the rise of the pulse arc voltage Vp, the control does not become unstable. The welding torch 3 may be fixed without driving the servo motor 5 during the transition period t.

Further, in the present embodiment, since the arc voltage or a voltage obtained by correcting the arc voltage is used as the arc length control signal, the arc length can be controlled even in the low current region, and the arc current can be controlled over a wide current region of 20 to 300 amperes. It becomes possible to secure the arc length.

Further, in the control device embodying the present invention, it is not necessary to individually set the pulse arc voltage and the base arc voltage, and the arc length control can be performed with one power setting knob, so that there is an advantage that operability is improved.

In actual welding, the current difference between high and low is large, and if the arc length is set based on one of them, the welding condition of the other becomes incorrect and an arc short circuit occurs or the heat input becomes excessive. I have something to do. In such a case, the electrode position may be controlled using an intermediate value between the arc voltage during the high current period and the arc voltage during the low current period.

In this case, the reference value for setting the arc length is voltage, but in the case of the pulse train in which the speed feed back signal from the arc length control motor is emitted from the pulse encoder, etc., the same configuration can be obtained by using this pulse train. realizable.

〔The invention's effect〕

As described above, according to the present invention, the base arc voltage is controlled during the base current period, and the base arc voltage corresponding portion generated by correcting the pulse arc voltage during the pulse current period is controlled by the arc length control signal. With this configuration, the uncontrollable period can be greatly reduced compared to the conventional one, so it is possible to realize a constant arc length control that is continuous, stable, and highly responsive even in the low frequency range. Moreover, there is an advantage that the arc length can be controlled to be constant even in the low current region.

[Brief description of drawings]

FIG. 1 is a block diagram of a constant arc length control device embodying the present invention, FIG. 2 is a diagram showing waveforms and sampling timings, and FIG. 3 is a waveform for explaining the output of the timing signal generator in the above embodiment. Time chart, FIG. 4 is a diagram for explaining the drawbacks of the conventional method, and FIG. 5 is a welding current-arc voltage waveform diagram. 2 ... Arc voltage detector, 3 ... Welding torch, 5 ... Servo motor, 7 ... Differential amplifier, 8 ... Reference arc voltage setting device, 9 ... Current detector, 10 ... Timing signal generator , 12, 13 …… Voltage holder, 14 …… Differential amplifier, 15 ……
Subtractor, 16 ... Switch device.

Claims (1)

[Claims] 1. In consumable electrode type pulse arc welding in which high and low welding currents are changed in a pulsed manner, the arc voltage is compared with a reference arc voltage to set the arc length during a low current period, and the deviation thereof is compared. The welding electrode position is controlled by the arc voltage detected / stored at a predetermined sampling time in the high current period from the arc voltage detected / stored in the low current period before the high current period in the high current period. The welding electrode position is controlled by the difference between the reference arc voltage and the voltage value obtained by subtracting the difference voltage and adding the difference voltage to the arc voltage in the high current period, and the predetermined sampling time is a transient at the rise of the high current. After the lapse of the period, during this transition period, the welding electrode is affected by the deviation between the arc voltage detected and stored in the low current period before the high current period and the reference arc voltage. Constant arc length control method for a pulse arc welding and controls the location.