JPS6068173A - Detection of profiling for welding - Google Patents

Abstract

PURPOSE:To obtain high control accuracy and stability with a titled method in automatic arc welding in which the projecting length of a wire is maintained constant by utilizing the impedance of a welding arc for controlling the position of a welding torch. CONSTITUTION:Welding is performed while maintaining the projecting length of a welding wire constant by an automatic arc welding device which feeds a consumable electrode at a constant speed or an arc welding robot. The position of a torch 2 in the central axis direction thereof is automatically followed up in this case. The impedance Za of the arc which is the characteristic value obtd. by dividing arc voltage E by current I is calculated by a circuit 4 and is used as an input signal for controlling automatically the torch position for the purpose of the above-mentioned automatic follow-up. The magnitude of the change rate of the arc characteristic value with a change in the distance (h) between the torch 2 and the materials 1 to be welded is E<I<Za and therefore the improvement in the accuracy and prevention of malfunction in the stage of relational discrimination are effectively accomplished.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a welding trace detection method, and more particularly to a welding trace detection method that can be applied to arc welding robots, automatic arc welding equipment, various earth welding application devices, and the like.

When performing arc welding using automatic arc welding equipment or a teaching/regeneration type arc welding robot, even if installation errors, dimensional errors, or deformation of the welded material occur during welding, the amount of variation can be detected. However, many methods have been proposed and put into practical use to automatically correct the welding process to always perform proper welding. So-called arc sensors, which serve as input signals, are also frequently used. The operating principle of arc sensors that have been mainly used in the past is shown in Figures 1 and 2.
Figures (A), (13), and (C) will be explained. Fig. 1 shows the current/voltage characteristics in general consumable electrode constant-speed gas-shielded arc welding and an example of the external characteristics of a general welding power source. As shown in the figure, the distance between the welding torch and the material to be welded. However, the characteristic curves move up and down while remaining substantially similar.

On the other hand, when the arc is loaded with a welding power source having external characteristics (close to constant voltage characteristics) as shown in the figure, h
PN for =ho, PL for h=h0+Δh, h=ho-
At Δh, stable energization is performed at each intersection of Ps, and a steady welding state is obtained. In other words, in response to changes in the distance between the welding torch and the workpiece, the operating point changes to PN,
Pr, , ps, etc. change, and this fluctuation Nyosimi flow,
Voltage fluctuates. As is clear from the figure, h=h, to h
=ho+Δh, the current ■ changes from Io to Io−
In ΔI, the voltage E changes from Eo to E0+ΔE, and if h=ho changes to h=ho−Δh, I=I, +
Δ■.

It can be seen that each changes as E=Eo−ΔE.

In this way, a change in h causes both 9I and E to change, but as can be seen from the figure, the change in E...
Since the change in 9I is much larger, it is actually possible to use the change in I to control the target value of h, and so-called arc sensors utilize this phenomenon.

Fig. 2 (4), (B), and (C) utilize the phenomenon shown in Fig. 1 to change the distance between the welding torch and the workpiece by changing the welding current while keeping the wire protrusion length EX constant. This is an example of the current method for controlling the welding torch position to automatically follow the direction of the welding process. Figure 2 (6) shows the positional relationship of the welding torch to a grooved fillet welded joint, Figure 2 (B) shows the positional relationship of the welding torch to a fillet welded joint, and Figure C) foil A.
) (or the same applies to (B)), a block configuration example of a control device for automatically tracking the distance between the welding torch and the workpiece by using the welding current as a control input signal is shown.

As mentioned above, due to the phenomenon shown in Figure 1, the phenomenon shown in Figure 2 (
As shown in 4), (B), and (C), changes in current I are skillfully used to control the position of the welding torch.
This method has the following drawbacks.

(1) Although the change in machining due to the change in h is much larger than the change in E, when performing delicate control in the Z-axis direction or Y-axis direction, the input due to the change in Stable comparative discrimination may be difficult for signals.

(2) In order to make the droplet transfer into a stable spray transfer, a sharp pulsed current may be superimposed on the welding current. may be superimposed and the operation of the control circuit may become unstable. Changes in the axial direction also change h, so when moving in the Y-axis direction (X-axis direction), the welding current signal is used as a control input signal to control the same height of the welding torch in the Z-axis direction. It is difficult to expect high control accuracy just by using it as is.

In addition, Figure 1 L and Figure 2 (4), (B), (C
), 01 is the material to be welded, 02 is the welding torch, 03
is a current signal input, 04 is a low-pass filter, 05 is a shaping circuit, θ6 is a discrimination circuit, 07 is a servo amplifier, 08 is a servo motor, 09 is a two-axis drive mechanism, 010 is a wire protrusion length signal input, 01 is a discrimination circuit. The threshold setting circuit Q12 is a dead band width setting circuit.

The present invention was proposed in view of the above circumstances, and its purpose is to eliminate the above-mentioned drawbacks, produce high-precision, low-cost welding that has little noise interference, and can reliably respond to minute changes. The present invention provides a copying detection method.

The welding tracing detection method according to the present invention uses a consumable electrode constant-rate feed automatic arc welding device or a consumable electrode constant-rate feed arc welding robot to keep the protrusion length of the welding wire constant while moving the welding torch in the direction of the center axis. In the welding tracing detection method for automatically tracking the position, the impedance of the welding arc is detected and used as an input signal for automatic control of the welding torch position for automatically tracking the position in the center axis direction of the welding torch. Characteristics and control input signals.

By using the arc impedance Za, which is a characteristic value obtained by dividing the arc voltage E by the current I, the following effects can be obtained.

(1) The magnitude of the change rate of the arc characteristic value due to the change in the distance between the welding torch and the welded material is E(I(Za), and if Za is used as the control input signal, the conventional A larger rate of change can be obtained than in the case where this method is used, which is effective in improving accuracy in comparison and discrimination and preventing malfunctions.

(2) When a pulsed current flows from the pulse generator built into the welding power source, the voltage changes along the arc load characteristic curve with the same sign and sign as the current change, regardless of the external characteristics of the power source. Therefore, the impedance does not change much, and therefore, noise interference due to sharp pulsed current is reduced accordingly, and control accuracy can be improved. (3) Impedance Za is calculated by dividing voltage E by current factor. Since it can be obtained by using the same method, the circuit configuration is easy and can be realized at low cost.

An embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Figures 3 (G), (B), and (C) are diagrams each showing the configuration of an embodiment used to carry out the method of the present invention, and Figures 4 (A), (ω), and (C) are diagrams, respectively. FIG. 5 is a diagram showing a specific circuit configuration example of the impedance calculation circuit in FIG. Figure 7 shows changes in welding current, voltage, and impedance with changes in the distance between the welding torch and the workpiece. Diagram for explaining changes in arc voltage and impedance, No. 8
Figures (A), (B), and (C) are for explaining changes in welding current and impedance when the welding torch is moved in the X-axis direction while riving in the Y-axis direction in the method of the present invention. It is a diagram.

Figures 3 (4), (B), and (C) show arc impedance detection in general thin-electrode constant-speed gas-shielded arc welding, and the wire protrusion length Eχ being kept constant using the impedance signal. This is an example of a block configuration for controlling the welding position to automatically follow the distance between the welding torch and the workpiece while maintaining the same distance.
Figure (B) shows the positional relationship of the welding torch to the fillet weld joint, where 1 is the material to be welded, 2 is the welding torch, and h
is the distance between the welding torch and the workpiece, E is the voltage, X is the welding current, 0 is the polarity of the welding current, and Z and Y are the drive shafts to be controlled in the welding torch position, respectively. FIG. 3 (q is an example of the block configuration of the control device in the positional relationship of FIG. 3 (A) (or (B) is the same);
is a current input signal, 3b is an arc voltage input signal, 4 is an arc impedance calculation circuit, 5 is an impedance signal, 6 is a low-pass filter, 7 is a peak hold circuit, 8
9 is a comparison discrimination circuit, 9 is a wire protrusion length signal input, 10 is a wire protrusion length signal amplification circuit, 11 is a comparison discrimination threshold setting circuit, 12 is a servo amplifier circuit, 13 is a dead band width setting circuit for the servo amplifier circuit, 14 15 represents a servo motor, and 15 represents a 2@ drive mechanism, respectively. Next, Figure 4 Prisoner (B)
, (C) are specific examples of the arc impedance detection/arithmetic circuit, which is the basis of the present invention, among the functional components in FIG. 3(C)l=. Figure (A) shows an example of the circuit configuration when calculating diimpedance from the arc voltage and current using a divider and an operational amplifier. Impedance calculation circuit, 5 is impedance signal, 8 is current shunt, VR is variable resistor, OP is operational amplifier, D is divider,
COM indicates a common baseline. FIG. 4(B) is an example of a circuit configuration when calculating the rainbow impedance of a multiplier and an operational amplifier from arc voltage and current, and M among the functional elements in the figure represents a multiplier, and Note that the same reference numerals as in (4) in the same figure are the same elements. FIG. 4(C) is an example of a circuit configuration when calculating the rainbow impedance of an operational amplifier and a transistor from arc voltage and current. In the figure, TR indicates a transistor, and other elements are 4), Those with the same symbols as in (B) mean the same elements.

A method according to an embodiment of the present invention will be described.

(1) Effects related to detection of arc impedance Functional elements 1° 2.3a, 3b, 4, 5 in Figures 3 (G), (B), and (C). and Fig. 4 (A'), (
B).

The impedance of the arc of the functional element with the same sign in (C) is detected. First, the arc impedance Za is defined as follows.

za: Arc impedance (Ω): Current (
A) E: Arc voltage (V) Hereinafter, the effect will be explained using specific circuit examples shown in FIGS. 4(A), (B), and (C).

Fig. 4 (5) Basic arithmetic function of divider v
o': Divider output (quotient) z' Second-side divider input (dividend) x' Second-side divider input (divisor) The circuit is configured so that Za is calculated as ①o'. In the figure, OP functions as a linear amplification or sign inversion function, and VR functions as a level adjuster for the component and the E component.

Fig. 4 (B) Basic calculation function of multiplier M ■
. :Multiplier output (product) The circuit is configured to calculate za=1-, and in the figure, OP functions as a linear amplification or sign inversion function, and VR functions as a level adjuster for the I and E components.

FIG. 4(C) shows a circuit configured to calculate Za-' using logarithmic conversion and anti-logarithmic conversion functions using operational amplifiers and transistors.

In the figure, OP is linear amplification, and sign and transformation are transistors TR.
In addition, the VR functions as a level adjuster for the I component and the E component.

(2) Effect of arc impedance Za as a control input The effect when the impedance as a characteristic value of the arc is used as an input signal for controlling the distance between the welding torch and the welded material will be explained.

Figure 5 shows the current/voltage characteristics in general consumable electrode constant-speed feed gas shielded arc welding and an example of the external characteristics of a general welding power source. The distance is wide. The arc voltage characteristic curves fluctuate vertically by Δh around , and the arc voltage characteristic curves fluctuate vertically while remaining substantially similar. On the other hand, when the arc is loaded by a welding power source with external characteristics (close to constant voltage characteristics) as shown in the figure, PN is applied when h = ho, and PL is applied when h = ho + Δh.

When h = ho - Δh, stable energization is performed at each intersection of ps, and a steady welding state is obtained. That is, the operating point changes as PN, Pl, Ps, etc. in response to a change in the distance between the welding torch and the workpiece, and this fluctuation causes the stain current and voltage to change. As is clear from the figure, hh.

If it changes from h=hIllH−Δh, the current I becomes .

From I. - For Δ, the voltage E is E. GaraE. Each changes to 10ΔE, and h=ho. It can be seen that -Δh (-If it changes, engineering changes to I. +ΔI, and E changes to Eo - ΔE. In this way, both I and E change due to the change in h, as can be seen from the figure. Since the change in She is much larger than the change in E, using the change in ■, h
Target value deviation has been carried out in the past, and so-called arc sensors are based on this principle.

On the other hand, in the present invention, the arc impedance Za
The target value of h is controlled using the change in
For example, in FIG. 5, the curve shown by the broken line is the current/impedance characteristic curve corresponding to the current/voltage characteristic curve shown by the solid line, and h=h0 (I=I., E=EO).
The operating point at which l is released is pN/, and the corresponding impedance Za is Z a = Za ao * h = ho + Δh (I = I. - ΔI, E = Eo + Δ
The operating point in E) is PL', and za is za. ten Δ
Za.

h=ho-Δh (I=I. 10ΔI, E=E, -ΔE)
Then Ps', Za=Za・. −∆Za, and such impedances Za as h
The characteristics when used as a control input signal will be explained with reference to FIG. Figure 6 shows I, E, and
This figure shows the results of comparing the changes in Za, and as can be seen from the figure, h is equal to ha. +Δh or ho−Δh, the current change rate is 1/or the voltage change rate is E/. . In any case, the rate of change in impedance is a/Za#.

This means that as an input signal for h control, Za has a higher degree of discrimination than E or Niji, that is, by using Za as an input signal, it is possible to stabilize the control and improve accuracy. It turns out that it is possible.

Next, in order to stabilize droplet transfer (spraying), a pulsed current may be superimposed on the welding current. In such a case, the ratio of pulse waves included in the input signal differs depending on whether the current, voltage E, or impedance Za is used as a control signal. The situation is shown in Figure 7.
In Figure 7, the welding electrician is the reference electrician. and pulse current ip
0 As can be seen from the same figure, the current Karako. +IF, the operating point Po moves to Pp, and the voltage E changes from Eo to E, +
TDP (changes by 1. In this case, the current change rate is 1/0. The voltage change rate is 0/. and the impedance change rate is Za/2.
If you compare 'o, a/za,. It can be seen that the number is closest to 112. In other words, if Za is used as a human input signal for control, even if a sharp pulse current is superimposed on the current, the pulse ratio in the input signal is small compared to using other characteristic values (: Accuracy can be improved and stabilized.

Next, in the configurations shown in Fig. 3 (A> and (B)), not only changes in the Z-axis direction but also changes in the Y-axis direction change h. direction), the impedance z8 of the welding current and arc is the 8th
The process of change is as shown in Figure (c), O)). 8th
Figure (A) shows the riping situation of a welding torch for a butt welded joint with a groove, and Figure (B) shows the same case for a fillet welded joint. (C) of the same figure shows the change in the welding current in (5) or (B), and (c) also shows the change in the arc impedance Za. As can be seen from the figure, as the welding torch moves in the Y-axis direction, the welding current I has a minimum value near the center of the riving (YO).

The arc impedance Za has a maximum value near both ends of the riping (YL or YR), whereas the arc impedance Za has a very thick value near the center of the ribbing (Yo) and a minimum value near both ends of the riping (YL or YR). However, when the welding torch advances while riving in the Y-axis direction with this configuration, a characteristic value signal near the riping center is required for height follow-up control in the two-axis direction. By employing the peak hold value ZaφPEAK of the impedance Za of 0 or more, which can be easily solved, the method of the present invention provides the following excellent effects: 0 (1) Consumable electrode (Welding wire) Constant speed feed automatic arc welding equipment or consumable electrode (welding wire) Constant speed feed arc welding robot, the wire protrusion length EX is constant (while maintaining the welding torch and material to be welded) By switching the welding torch position control input signal for automatically following the separation from the conventional welding current I to the arc impedance Za, signal discrimination is improved compared to control using the welding current I or arc voltage E. The capacity is large, and high control accuracy and stability can be obtained5.Furthermore, when a pulsed current is superimposed on the welding current, by using za as the control input (i month), it is possible to The pulse wave ratio can be minimized,
Control stability is improved.

Furthermore, when welding a butt-welded joint or a fillet-welded joint with a groove, not only changes in the direction of the welding torch center axis (two axes), but also changes in the direction perpendicular to the welding line (Y-axis) are caused by changes in the welding torch and the workpiece. Since the distance between materials is changed, when riving in the Y-axis direction and progressing (welding line direction: It is thought that it is most effective to use the arc characteristic value signal of Control can be carried out extremely easily and reliably.

(2) The method of the present invention can be applied to existing automatic arc welding equipment or welding robots with almost no modification or modification.

(3) Since the main parts are constructed using simple analog circuits, it can be realized at low cost.

(4) Provide a powerful clue to realizing labor savings through automation and robotization of welding-related equipment.

(5) Improving the functionality of welding robots or automatic welding equipment.

Market competitiveness will be strengthened by reducing costs.

[Brief explanation of the drawing]

Figure 1 is a diagram showing examples of current/voltage characteristics and external characteristics in conventional arc welding, and Figures 2 (4) and (B). (C) is a diagram showing the configuration of a conventional example, and FIG. 3 (A)
. (B) and (C) are diagrams showing the configuration of an embodiment used to implement the method of the present invention, respectively, and FIG. 4 (4)
. (B) and (C) are diagrams showing specific circuit configuration examples of the impedance calculation circuit in Figure 3 and Figure 5, respectively.
The figure shows the current-impedance characteristic curve obtained by the method of the present invention, and Figure 6 shows the change in the distance between the welding torch and the workpiece (= accompanying change in welding current, voltage, and impedance) in the method of the present invention. Figure 7 is a diagram for explaining changes in arc voltage and impedance when the welding current is composed of a reference current and a pulse current superimposed in the method of the present invention, Figure 8 (5), (especially C)
, (D) are diagrams for explaining changes in welding current and impedance when the welding torch is moved in the X-axis direction while riving in the Y-axis direction in the method of the present invention. DESCRIPTION OF SYMBOLS 1... Material to be welded, 2... Welding torch, 3a... Current input signal, 3b... Arc voltage input signal, 4...
Impedance calculation circuit, 5... Impedance signal, 6... Low pass filter, 7... Peak hold circuit, 8... Comparison discrimination circuit, 9... Wire protrusion length signal input, 10... Wire protrusion Long signal amplification circuit, 11.
... comparison discrimination threshold value setting circuit, 12 ... servo amplification circuit, 13 ... dead band width setting circuit for servo amplification circuit,
14... Servomorph, 15... 2-axis drive mechanism.

Claims (1)

[Claims] For welding using a consumable electrode constant speed feed automatic arc welding device or a consumable electrode constant speed feed arc welding robot to automatically follow the position of the welding torch in the direction of the center axis while keeping the protruding length of the welding wire constant. A tracing detection method for welding, characterized in that the impedance of a welding arc is detected and used as an input signal for automatic control of the welding torch position for automatically following the position of the welding torch in the central axis direction.