JPH0579437B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a constant arc length control method in pulsed arc welding.

[Conventional technology]

In non-consumable electrode type pulsed arc welding, methods for welding while keeping the arc length constant are those described in Japanese Utility Model Publication No. 52-43706 and Japanese Patent Application Laid-Open No. 16345-1983. There are things that have been done.

[Problem that the invention seeks to solve]

In the former method, the arc voltage is controlled 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 range of about 0.5 to 2 Hz, the arc length uncontrollable period increases, and continuous and stable constant arc length control cannot be performed.
If the welding surface of the workpiece is inclined as shown in Figure 4, the locus of the welding torch will vibrate in steps as shown by the solid line in the figure, resulting in poor welding quality and arc length control. If the starting point is in an uncontrolled current period, there is a problem in that control responsiveness decreases.

In addition, the latter converts either the base current or pulse current of the welding current into a voltage, sets the voltage as the reference arc voltage, and adds or subtracts the amount of current change converted to voltage from the reference arc voltage. However, since the welding current is converted into an arc voltage, the linearity between the welding current and the arc voltage is lost in the low current region (the shaded region of the arc voltage V - welding current I characteristic shown in Figure 5). ), there was a problem that resulted in an out-of-control problem.

Furthermore, since the voltage obtained by a current-to-voltage converter such as a shunt is minute, a voltage amplifier or the like is not only necessary, but also there is a problem that noise is easily generated.

[Purpose of the invention]

The present invention has been made in order to solve the above-mentioned conventional problems, and it is possible to reduce the To obtain a constant arc length control method in pulsed arc welding that is continuous and stable even in the frequency domain, has higher responsiveness than conventional methods, and can realize constant arc length control even in the low current domain. With the goal.

[Means to solve the problem]

In pulsed arc welding, the arc voltage also changes as the welding current changes. For this reason, with conventional constant current welding equipment, the welding torch vibrates and welding cannot be performed. However, the difference in arc voltage between high and low current periods is the absolute value of both currents,
Since the current difference has the characteristic that it is constant as long as it does not change, a configuration is adopted in which this voltage difference is used to control the arc voltage at a constant arc length by using an almost DC-like arc length control signal for one cycle after the calculation point. Specifically, during the pulse current period, the arc voltage is compared with the reference arc voltage, and during the base current period, the arc voltage detected and stored during the pulse current period is compared with the arc voltage detected and stored during the base current period.
The difference between the memorized arc voltage and the base current period is added to the arc voltage in the base current period to create a corresponding pulsed arc voltage, and this is compared with the reference arc voltage to calculate the difference in both the pulsed current period and the base current period. The structure is such that the electrode position is controlled.

〔Example〕

A method of matching the arc voltage during the low current period to the arc voltage during the high current period will be described below.

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, etc., and FIG. 3 is a waveform flowchart. In the figure, 1 is a welding power source (pulse current source), and 2 is an arc voltage detector. The arc voltage detector 2 detects the arc voltage V shown in FIG. 2b.
Detect. 3 is a welding torch, 4 is a base material to be welded,
A servo motor 5 drives the welding torch 3 toward and away from the base material 4 to be welded. 6 is a power amplifier, 7 is a differential amplifier, and 8 is a reference arc voltage setter, which generates a reference arc voltage Vo for setting the arc length.

Reference numeral 9 denotes a contact current detector which detects the welding current I shown in FIG.
supply to. Timing signal generator 10 detects the rise and fall of welding current I and generates timing signals A to E shown in FIG. 3. Timing signal A goes to H level in synchronization with the rise of welding current I, and goes to L level in synchronization with the fall of welding current I. Timing signal B goes to H level after a fixed time t delay from the fall of welding current I. The timing signal C is a signal synchronized with the timing signal A, and the timing signal E becomes H level in synchronization with the falling point of the welding current I, and a certain period of time t has passed from that point in FIG. 2. The timing signal D, which is a signal that becomes L level at time Y shown in c, is a signal that becomes H level at time Y when timing signal E falls, and becomes L level when welding current I rises. The above-mentioned fixed time t corresponds to a transient period after the fall of the welding current I. 11 is a filter,
The voltage output of the arc voltage detector 2 is waveform-shaped.
12 and 13 are voltage holders. Voltage holder 12
The arc voltage V and the timing signal A whose waveforms have been shaped as shown in FIG. , the final voltage value Vph (voltage value at time point X shown in FIG. 2c) of the captured pulse arc voltage Vp is held for a period of time when the pulse arc voltage Vp is at the L level. The arc voltage V whose waveform has been shaped and the timing signal B are guided to the voltage holder 13 through the filter 11, and when the timing signal B becomes H level, the arc voltage V, that is, the base arc voltage of the arc voltage V is introduced.
Vb is taken in and the sampled base arc voltage Vbh is held during the period when it is at L level. Here, the values of Vph and Vbh held at the predetermined sampling point are used as they are, but the average value of the arc voltage during the current period and the average value of the previous few cycles of the current period are used as Vph and Vbh.
May be set to Vbh. 14 is a differential amplifier,
The difference (Vph - Vbh) between the pulse arc voltage Vph and the base arc voltage Vbn is output. 15 is an adder which combines the arc voltage V whose waveform has been shaped by the filter 11 and the output of the differential amplifier 14 (Vph-
Vbh), an additional voltage Vd=V+(Vph−Vbh) (1) corresponding to the pulse arc voltage during the base current period is calculated.

16 is a switch device, and switches 16C are opened and closed by timing signals C to E, respectively.
~16E, a differential amplifier 14, a subtracter 15,
The output of the filter 11 is opened and closed at predetermined timing to create an arc length control signal Vc in the form of a substantially DC voltage as shown in FIG. 2e. When the timing signal C is input to the switch device 16, the switch 16C is turned on when the timing signal C is at H level, and supplies the arc voltage V (pulse arc voltage Vp) to the differential amplifier 7 during the pulse current period. When the timing signal E is input, the switch 16E is turned on at the H level, that is, during the above-mentioned transient period t of the welding current I, and the final value Vph of the pulse arc voltage held by the voltage holder 12 is transferred to the differential amplifier 7. supply to. When the timing signal D is input, the switch 16D is turned on during the H level, that is, during the base current period after the above-mentioned transient period t, and the switch 16D is turned on to output the differential voltage Vd to the differential amplifier 7.
supply to. The differential amplifier 7 compares the voltages Vp, Vph, Vd inputted in time series, that is, the arc length control signal Vc shown in FIG. 2e, with the reference arc voltage Vo set by the reference arc voltage setting device 8. and sends out the deviation ε. This deviation output ε=Vo−Vc
is amplified by the power amplifier 6 and then the servo motor 5
The servo motor 5 controls the welding torch 3 so that the deviation ε becomes 0, thereby controlling the arc length between the welding electrode and the base material 4 to be welded to be constant.

In this embodiment, during the pulse current period, the arc length is controlled using the pulse arc voltage Vp of the period as an arc length control signal, and during the base current period, the pulse arc voltage Vph of the pulse current period before the period is controlled.
The difference between the base arc voltage Vbh sampled at a predetermined point in the base current period and the base arc voltage Vbh in the base current period is added to the base arc voltage in the base current period to obtain an additional voltage Vd.
The arc length is controlled using the arc length control signal. In other words, the arc length is controlled not only during the pulse current period but also during the base current period, so the arc length is continuously controlled. ~
Even in a low frequency region of about 2 Hz, the uncontrollable period virtually disappears, and responsiveness improves accordingly.

Therefore, even if the welding surface of the base material 4 to be welded is inclined as shown in FIG. The welding quality improves by drawing and moving.

Further, in this embodiment, the initial transient period t of the base arc voltage Vb is the pulse arc voltage
Since the arc length is controlled using Vph as the arc length control signal, the control will not become unstable. In addition,
During this transition period t, the servo motor 5 may not be driven and the welding torch 3 may be fixed.

In addition, in this embodiment, since the arc voltage or the voltage corrected thereto is used as the arc length control signal,
The arc length can be controlled even in the low current range, and a constant arc length can be ensured over a wide current range of 20 to 300 amperes.

Furthermore, with the control device implementing the present invention, there is no need to set the pulse arc voltage and base arc voltage separately, and the arc length can be controlled with a single voltage setting knob, which has the advantage of improving operability. There is.

In actual welding, the difference between high and low currents is large;
If the arc length is set based on one of these, the welding conditions for the other will not be appropriate, which may cause an arc short circuit or cause problems with the amount of heat input. 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.

Also, in this case, voltage was used as the reference value for setting the arc length, but if the speed feedback signal from the arc length control motor is a pulse train emitted from a pulse encoder, a similar configuration can be obtained by using a pulse train, etc. It will be done.

〔Effect of the invention〕

As explained above, the present invention performs arc length control by using a pulse arc voltage during the pulse current period and a portion corresponding to the pulse arc voltage created by correcting the base arc voltage during the base current period as an arc length control signal. By adopting this configuration, the uncontrollable period can be greatly reduced compared to the conventional method, so continuous, stable, and highly responsive constant arc length control can be achieved even in the low frequency range. In addition, it has the advantage of being able to control the arc length to a constant level even in the low current range, and this is especially effective in the case of sloped workpieces or workpieces with complexly shaped welding surfaces. It becomes noticeable.

[Brief explanation of the drawing]

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 timing, and Fig. 3 is a waveform for explaining the output of the timing signal generator in the above embodiment. A 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 setter, 9...Current detector, 10
...timing signal generator, 12, 13 ... voltage holder, 14 ... differential amplifier, 15 ... adder,
16...Switch device.

Claims (1)

[Claims] 1. In consumable electrode type pulsed arc welding in which welding is performed by changing high and low welding current in pulses, the arc voltage is compared with a reference arc voltage for setting the arc length during the high current period. The welding electrode position is controlled based on the deviation, and during the low current period, the arc voltage is detected and stored at a predetermined sampling point in the low current period from the arc voltage that was detected and stored during the high current period before the low current period. The welding electrode position is controlled by the deviation between the reference arc voltage and the voltage value obtained by subtracting the arc voltage and adding the difference voltage to the arc voltage during the low current period. This is after the transition period when descending, and during this transition period, the welding electrode position is controlled based on the deviation between the arc voltage detected and stored during the high current period before the low current period and the reference arc voltage. A constant arc length control method in pulsed arc welding, characterized by: