JPH0446673B2 - - Google Patents

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention is a consumable welding process in which V-shaped, L-shaped or similar grooves are welded by weaving the welding torch left and right along the welding line. The present invention relates to an electrode arc welding method, and particularly to a welding method using automatic welding line tracing control that causes a welding torch to accurately follow the welding line.

"Prior Art" Conventionally, methods that utilize welding phenomena have often been used as a method for copying weld lines. This method detects the weld line in the groove by using the correlation between the protruding length of the welding wire and the welding current, and has the advantage of not requiring a dedicated detector.

Japanese Patent Publication No. 52-107703 and Japanese Unexamined Patent Application Publication No. 1983-10770 disclose methods for automatically tracing welding lines using this type of welding phenomenon.
A method described in the specification of Publication No. 78654 is known. This method detects and compares welding current values at both left and right end positions of periodic weaving, and controls movement of the center of the weaving so that both welding current values become equal.

Another known method is the consumable electrode type arc welding method described in Japanese Patent Laid-Open No. 58-5337. In short, this method compares the maximum and minimum welding current values in each half period of periodic weeping, calculates the difference, and calculates the maximum and minimum current values for each adjacent half period. By comparing the difference and controlling the movement of the center of the weaving in the direction where the difference between the left and right sides becomes smaller, the weaving is made to move in a way that accurately follows the welding line.
The above-mentioned Japanese Patent Publication No. 52-100773 and Japanese Patent Application Laid-open No. 52-78654
Compared to the method described in the above publication, this method has the advantage that the detection resolution of deviations from the weld line is superior, and precise weld line tracing control can be performed.

Next, an example of the welding line tracing method which is the basis of the present invention will be explained with reference to the welding method described in the above-mentioned Japanese Patent Laid-Open Publication No. 58-53375.

Now, for example, using a welding current with constant voltage characteristics, weld the welding torch 3 to the horizontal plate 1 and the vertical plate 2, which are the base materials, in a horizontal direction with respect to the welding line _SW , as shown in Fig. 5. Horizontal fillet welding shall be performed by proceeding welding in the direction of the welding line _SW (perpendicular to the finger surface). When the welding wire 4 is fed at a constant speed, the protruding length l of the wire 4 changes along the groove shape.

FIG. 5 shows a case where the center position _S2 of the weaving width of the welding torch 3 coincides with the welding line _SW , and the welding line is correctly followed. FIG. 6 shows the forward stroke of weaving in which the torch 3 reaches the right end position S ₃ from the left end position S _{1 of the weaving via the weaving center S 2 and} vice versa in the case of FIG. ₅ .
3 is a graph showing changes in welding current during the backward stroke of weaving from 1 to ₁ to the left end S1. The details are leg length
This is a waveform diagram showing the results of measuring and recording the welding current when performing horizontal fillet welding of 7.5 mm using an optical electrode oscilloscope. The welding conditions were shielding gas composition Ar + 20% CO ₂ , wire diameter 2 mm. ,
Average welding current 305A, welding voltage 29V, welding speed 35
cm/min, weaving cycle approximately 150 times/min, and weaving width L=6 mm. In addition, when measuring the welding current, a low-pass filter with a cutoff frequency fc of 10 Hz is used to remove high frequency components caused by the commercial frequency of the welding power source and components caused by irregular short circuits of the arc. .

The left and right end positions of the weaving are detected by a proximity switch attached to the weaving device.

As is clear from Fig. 6, when the center _S2 of the weaving width of the welding torch 3 coincides with the welding line _SW and the welding line is correctly followed, the wire protrusion length l and the welding current are From the correlation characteristics, the weaving left end current value IL ₁ and the weaving right end current value IR ₁ are equal to each other, and furthermore, the minimum welding current value IL ₂ in the forward stroke of weaving and the minimum welding current value IR ₂ in the backward stroke of weaving are equal to each other. .

In addition, the left end current value IL ₁ is from the time when the weaving left end position S ₁ is reached, and the right end current value IR ₁ is from the time when the weaving right end position S ₃ is reached by the phase delay time τ of the welding current signal due to the low-pass filter. It can be seen that an appropriate response can be obtained if the detection is performed at each delayed time point.

Furthermore, the minimum welding current value IL ₂ is the left end current value IL ₁
After detecting the welding current, the welding current in the forward process leading to the weaving right end position S ₃ was measured, and the minimum value between them was detected. Similarly, the welding current minimum value IR ₂ was detected as the right end current value IR ₁ . Thereafter, the welding current during the backward stroke to the weaving left end position _S1 may be measured and the minimum value during that period may be detected.

Next, Fig. 7 shows the weaving state when the center position _S2 of the weaving width is shifted toward the vertical plate 2 side with respect to the welding line _SW , and Fig. 8 shows the forward and reverse weaving strokes in this case. This is a specific example showing a change in welding current during a process.

Figure 8 shows the results of measuring and recording the welding current using an optical electromagnetic oscilloscope when horizontal fillet welding was performed under the welding conditions explained in Figure 6, and the deviation from the weld line S _W was D = 2 mm. FIG.

From FIG. 8, when it shifts toward the vertical plate 2 side, a deviation occurs between the right end current value IR ₁ and the left end current value IL ₁ .
It can be seen that IR ₁ > IL ₁ .

By the way, what should be noted in Figure 8 is that
Minimum value of welding current in the forward stroke of weaving
IL ₂ is not equal to the minimum value IR ₂ of the welding current in the backward stroke, and IR ₂ <IL ₂ . That is, even though IR ₂ should be equal to IL ₂ by simply applying the correlation between the wire protrusion length and the welding current, they are not equal. The reason for this is not necessarily clear, but if we estimate from the arc observation results during the experiment, if the center _S2 of the weaving width deviates from the welding line _SW as described above, the Since the behavior of the molten pool at the weld line is different from that in the case where there is no deviation, the behavior of the arc with respect to the molten pool is different, and it is presumed that a change in the welding current as shown in FIG. 8 occurs.

Furthermore, in the experiment, the minimum value in the above outgoing process was
In contrast to IL ₂ , the minimum value IR ₂ in the backward stroke is always small, and the difference between the two minimum values (IL ₂ - IR ₂ ) is
It was confirmed that the value was proportional to the size of the deviation between the weaving width center position S ₂ and the weld line _SW .

Conversely, if the center position _S2 of the weaving width shifts toward the horizontal plate 1 side, the result will be opposite to that shown in Figure 8.
The magnitude relationship between IL ₁ >IR ₁ and the minimum value of the welding current in the forward and backward steps is IR ₂ >IL ₂ .

To summarize the above relationship, let IL ₁ be the current value at the left end of the weaving in the forward stroke of weaving from the left end position S ₁ of the weaving to the right end position S ₃ via the weaving center S ₂ , and the minimum value of the welding current.
Assuming that IL ₂ is the current value at the right end of weaving in the return process from right end position S ₃ to left end position _{S 1} and IR ₂ is the minimum welding current value, (IL ₁ − _{IL 2} )=(IR ₁ − IR ₂ ), it may be determined that the weaving center S ₂ and the welding line _SW coincide.

If (IL ₁ −IL ₂ )>(IR ₁ −IR ₂ ), it is determined that the weaving center S ₂ is shifted to the left with respect to the welding line _SW .

If (IL ₁ −IL ₂ )<(IR ₁ −IR ₂ ), it is determined that the weaving center S ₂ is shifted to the right with respect to the welding line _SW .

This provides a criterion for determining the direction of deviation.

In addition, the difference current values (IL ₁ - _{IL 2} ), (IR ₁ - IR ₂ ) and the deviation of the two difference currents | (IL ₁ - IL ₂ ) - (IR ₁ - IR ₂ )| are the welding center S ₂ of the weaving center. Proportional to the deflection value relative to the line.

Therefore, the current value in each weaving half cycle
Detect IL ₁ , IL ₂ and IR ₁ , IR ₂ , and then use these detected values to calculate the difference current values (IL ₁ −IL ₂ ) and (IR ₁
−IR ₂ ) and compare the difference current values with each other,
Based on the comparison results, the weaving width center position is controlled to move in the direction that the difference current values become equal to each other or to a constant value based on the deviation direction judgment criteria described above, according to the deviation of the difference current values. For example, automatic tracing of weld lines becomes possible.

``Problems with the prior art'' In arc welding, generally in areas where the arc length is long and the welding current is large, the pinch effect becomes greater than the surface tension of the welding rod, and the droplets separate from the rod end as small particles. A phenomenon called spray migration occurs, where the spray enters the molten pool at high velocity. On the other hand, when the arc length is short, the droplets hanging down at the end of the rod naturally come into contact with the base metal at a small current, and the welding rod and the base metal are bridged by the droplets. In low-current arc welding, a power source with characteristics that allows a large current to flow during such a short circuit is used, and the pinch force generated by this large current breaks the bridge and generates an arc. This phenomenon in which droplets migrate in large clumps is called short-circuit migration, and the short-circuit period is, for example,
It is about 60 to 100 times/second. The interval between such short circuits can be determined by detecting fluctuations in the welding current, but the fluctuations are generally large, and the short circuit period is generally taken as the average value of the intervals between the short circuits.

However, in the short-circuit transition region, the short-circuit and arc are repeated as cycles with considerable fluctuations as described above, and the size of the migrating droplet also fluctuates, so the detected welding current I has a waveform as shown in Fig. 2e. As shown in the figure, sudden fluctuations cannot be avoided. This point is in contrast to the welding current in the spray transition region, which changes approximately smoothly as shown in FIG.

Conventional automatic weld line tracing control using arc tracing detects the peak or bottom value of the welding current as described above, and uses the difference to perform accurate tracing calculations. High accuracy can be obtained when the fluctuations are gradual, but in regions where the welding current fluctuates rapidly, such as in the short-circuit transition region, it is possible to detect changes in the welding current only due to deviation of the welding wire from the welding line. There was a problem in that it was difficult to do so, and the imitation control system was significantly degraded. Particularly in thin plate welding, most of the welding conditions are based on such a short-circuit transition region, and the workpiece shape is complex, distortion, workpiece installation error, etc. are large, and highly accurate tracing control is required.

``Object of the Invention'' Therefore, the object of the present invention is to smooth the changes in welding current in the short-circuit transition region, absorb the changes in welding current due to reasons specific to the short-circuit transition region, and eliminate current fluctuations due to deviation of the welding wire. The objective is to improve the detection accuracy of

"Structure of the Invention" In order to achieve the above object, the main means adopted by the present invention is to correct the welding line at regular intervals based on the detected welding current and to correct the welding line while periodically weaving the welding torch. In a consumable electrode arc welding method in which welding is performed in a short-circuit transition region following a welding line that has been The welding line is corrected based on the maximum and minimum values in the weaving cycle of the values determined, and its scope of application is the arc welding described in the above-mentioned Japanese Patent Application Laid-Open No. 58-53375. Not only the method, but also the
It is applicable to the welding line automatic tracing method described in JP-A-52-10773 and JP-A-52-78654, and all other consumable electrode type arc welding methods, and is particularly suitable for arc welding of thin plates. .

"Embodiments" Next, embodiments embodying the present invention will be described with reference to the accompanying drawings of FIGS. 1 to 4 to provide an understanding of the present invention. Here, FIG. 1 is a diagram showing changes in welding current when a welding method according to an embodiment of the present invention is implemented, and FIGS. Figure e is a diagram showing the original waveform of the welding current, Figure 3 is a side view of the entire robotic device for carrying out the welding method according to the same embodiment, and Figure 4 is a block diagram showing the signal flow in the robot device. It is a diagram. In this embodiment, the same reference numerals will be used for the same elements as those in the conventional example.

Figure 3 shows the V of the base material M being welded by the welding robot R.
A state in which arc welding is being performed on the shaped groove portion 5 with the welding torch 3 is shown, and the current flowing through the welding wire 4 is detected by the shunt 6 and transmitted to the robot control panel 7. The robot control panel 7 is a welding robot R.
A control unit for driving the welding torch 3 along a predetermined welding line, a robot body control unit 8 for specifying the attitude and position of the welding robot R, and furthermore, a weaving waveform, and a shunt 6. It consists of a tracing control section 9 which samples the welding current inputted from the controller and sends a correction command signal to the robot main body control section 8 in order to correct and move the welding torch 3 in the direction of a proper welding line Sw. Fourth
figure).

The welding robot R is driven by a servo control unit 10 (FIG. 4) of the robot main body control unit 8, driven by a signal from the servo control unit 10, is attached to a foundation 11, and is rotated around a vertical axis by an arrow θ. ₁ , a vertical arm 13 mounted on the swivel base 12 that performs a driving motion in the direction of the arrow θ ₂ in a vertical plane, and a swivel base 12 that is mounted on the tip of the vertical arm 13. A horizontal arm 14 that is driven to swing in the direction of arrow θ ₃ within the same driving vertical plane.
and a wrist portion 15 that is attached to the tip of the horizontal arm 14 and holds the welding torch ₃ . Wrist part 15 indicated by θ ₅
Therefore, the welding robot R is configured to have five degrees of freedom.

Next, with reference to FIGS. 1, 2, and 4, the control procedure for the arc welding method using the microcomputer will be explained in detail. FIG. 1 is a diagram showing changes in welding current when the present invention is applied to a control method that corrects the welding line every half cycle of weaving, and FIG. 2a shows a control procedure in the robot main body control section 8. Figure b shows the processing procedure in the copying control unit 9, and Figures c and d are shown in Figure 2B.
This is a flowchart showing a subroutine for sampling IL _nsx , IL _nio and IR _nsx , IR _nio .

First, for control, the robot has already been taught the welding line using the PTP method, for example.
It is assumed that the teaching data is stored in a storage device (not shown) within the robot main body control section 8. It is also assumed that the welding conditions are set so that arc welding is performed in the short-circuit transition region.

First, at the start of welding work, the processing procedure on the robot main body control section 8 side shown in Fig. 2a and the processing procedure on the copying control section 9 side shown in Fig. 2b are synchronized and executed in parallel. will be processed. In the program shown in FIG. 2A, the microprocessor first retrieves teaching data from a storage device (not shown), performs interpolation processing on this data, and calculates the position of the weld line based on the teaching data. This calculation is performed in the position calculation section 16 of the robot main body control section 8. In addition, the microprocessor has a weaving pattern (e.g. weaving width, weaving period, etc.)
is specified, and based on this weaving pattern, the weaving waveform calculation section 17 performs weaving waveform calculation, that is, calculation of the weaving locus. Here, in step a, it is determined whether a correction command signal has been transmitted from the copying control section 9 to the copying input section 18 of the robot main body control section 8.

On the other hand, on the side of the scanning control section 9, as shown in FIG. 2b, in step b, the welding torch is in a state of movement of the torch 3 from the left end position _S1 to the right end position _S3 shown in FIG. 5 (rightward process). Determine whether or not.
At this time, assuming that the torch is moving from the left end position _S1 to the right end position, the welding current at that time is during the first half period of the curve P as shown in Figure 1.
It is represented by the part C _1l . As shown in FIG. 4, a weaving left end signal and a weaving right end signal are output from the weaving waveform calculation section 17 of the robot main body control section 8 to the copying calculation section 19 of the copying control section 9. The start and end points of each half cycle and left half cycle, that is, the position of the left end S ₁ and the position of the right end S ₃ are informed.

In the first left half cycle C _1l , the welding torch 3 moves from the left side (L) to the right side (R), so
Processing progresses in the direction of yes at step b,
The welding current maximum value IL _nsx and minimum value IL _nio of the welding current P in the left half period C _1l are sampled.

Sampling of IL _nsx and IL _nio is processed according to the subroutine shown in FIG. 2c. Here, as shown in FIG. 2e, the weaving period is divided into predetermined sampling periods SC, and the welding current I for each sampling period SC is integrated. Let the integral values be S ₁ , S ₂ , S ₃ , ... in order (in the leftward process,
S ₁ ′, S ₂ ′, S ₃ ′, S ₄ ′, …) Next, among the integral values thus obtained, the largest one IL _nsx (maximum welding current value) and the smallest one IL _nio (minimum welding current value) are sampled. Sampling period as above
SC is set to a time that is more than twice the short circuit period and less than 1/4 of the weaving period. The reason for setting it to more than twice the short-circuit period is that if it is 1 times the original waveform itself, the smoothing effect by integration is not strong enough.
In addition, when it is about 1.5 times, there are cases where one short-circuit waveform and two short-circuit waveforms are included in the sampling period SC, resulting in incomplete integration. This is because it is desirable to include the above short circuit waveform. Also, the maximum and minimum values of the welding current are included in one weaving cycle (total of 4 pieces of data), and they occur at approximately equal intervals, so the length of one integration time is one weaving cycle. 1/4 of the period
Must be less than or equal to

In step c, it is determined whether the welding process for half a period of the weaving operation has been completed. This is determined by whether or not the above-mentioned weaving right end signal has been input from the weaving waveform calculation section 17 to the copy calculation section 19. If the determination is NO at this time, the process returns to step b. If the determination is YES, this indicates that the welding torch 3 has arrived at the right end position _S3 , and the process proceeds in the direction of YES to the determination in step d. In step d, it is determined whether the half period determined in step c is the first half period at the start of welding, that is, the left half period _c1l in FIG. 1, and if yes, step b is performed.
Return to At this time, since the welding process has already moved from the right end position _S3 to the left end position _S1 , a negative determination is made in step b, and the maximum value IR _nsx and the minimum value of the welding current P in the leftward process are IR _nio is the second
It is sampled according to the subroutine shown in Figure d. Then, in step c, for half a period,
That is, in this case, after waiting for the end of the right half cycle _c1r , the process goes through step d and then goes to step e. The first one weaving cycle has now passed, and the
It becomes possible to calculate the difference current value described in the -53375 publication. Here, in step e, the difference ΔIL in current values in the left half cycle is calculated by IL _nsx - _{IL nio} , and the difference ΔIL in welding current values in the right half cycle is calculated by IR _nsx - IR _nio , Furthermore, a difference current value ΔO=ΔIL−ΔIR proportional to the deflection value of the weaving center _S2 with respect to the welding line _SW is calculated (step n). Thereafter, in step h, it is determined whether the absolute value of the difference current value ΔO is within the allowable range (dead zone), and if it is far from the dead zone, a correction command signal is copied and the input section 1
Send on 8th. If the absolute value of the difference current value ΔO is within the allowable range, the program is returned to the beginning without modifying the welding trajectory.

On the other hand, the robot main body control section 8 shown in FIG.
If it is determined that there is a correction command after receiving the correction command signal in step a of the side program, the correction command signal is given to the position calculation unit 16, and in response to this, the position calculation unit 16 changes the fixed shift amount to the original position. Add to the target position data. Thereafter, the microprocessor multiplies the data corresponding to the weaving waveform sent from the weaving waveform calculating section 17 and the calculated position data corresponding to the corrected welding line locus, and responds to the signal from the corrected timing generating section 20. The corrected target position signal is sent to the servo control section 10 to servo control the welding robot R.

"Effects of the Invention" As described above, the present invention corrects the welding line at regular intervals based on the detected welding current, and periodically weaves the welding torch to short-circuit the welding line following the corrected welding line. In the consumable electrode arc welding method for welding in the transition region,
The welding line is corrected based on the maximum and minimum values in the weaving cycle of the values obtained by integrating the above welding current at predetermined time intervals that are more than twice the short circuit cycle and less than 1/4 of the weaving cycle. This is a consumable electrode type arc welding method characterized by
Even if the original waveform of the welding current includes sudden fluctuations due to the short circuit transition region, this is smoothed by integration, so fluctuations in the welding current value due to deviation of the welding torch can be accurately detected. Furthermore, since the entire weaving process is sampled, it is possible to accurately capture peak values, exhibiting highly accurate followability, reducing bead meandering, and improving the appearance of the welded part.

[Brief explanation of drawings]

FIG. 1 is a diagram showing changes in smoothed welding current when an arc welding method according to an embodiment of the present invention is carried out, and FIGS. 2 a to 2 d are flowcharts showing the processing procedure of the same embodiment. , FIG. 2e is a diagram showing the original waveform of the welding current in the short-circuit transition region, FIG. The figure is a block diagram showing the signal flow in the same embodiment, Figure 5 is a side view of the welding part showing the welding work state when the weaving center and the weld line are aligned, and Figure 6 is the same as shown in Figure 5. Fig. 7 is a diagram corresponding to Fig. 5 showing a state in which the weaving center is displaced with respect to the welding line, and Fig. 8 is a diagram showing changes in welding current in the state shown in Fig. 7. FIG. 3 is a diagram showing a conventional correction processing procedure. (Explanation of symbols) 3... Welding torch, 4... Welding wire, 7... Robot control panel, 8... Robot main body control section, 9... Copying control section, 10... Servo control section, 1
6... Position calculation section, 17... Weaving waveform calculation section, 18... Copying input section, 19... Copying calculation section, 20
...Correction timing generator, I, IL, IR...Welding current, ΔO...Difference current value, P...Welding current curve, S _W ...Welding line, R...Welding robot, C _l , _Cr ... Half cycle.

Claims (1)

[Claims] 1. In a consumable electrode type arc welding method in which the welding line is corrected at regular intervals based on the detected welding current, and the welding torch is weaved periodically to follow the corrected welding line to weld in the short-circuit transition region. , the welding line is corrected based on the maximum and minimum values in the weaving cycle of the values obtained by integrating the welding current at predetermined time intervals of at least twice the short circuit cycle and at most 1/4 of the weaving cycle. A consumable electrode arc welding method characterized by: