JPH06218548A - Welding control method for welding robot - Google Patents

Abstract

PURPOSE:To correct the deviation of a weld line in the real time by monitoring and detecting the deviation of the actual weld line from the change of a welding current or the welding voltage in accordance with weaving and correcting the tip position of a torch during welding according to this deviation. CONSTITUTION:Both a robot controller 1 to control the operation and position of the welding robot and an arc sensor controller 2 to monitor and detect a welding state are formed of microcomputers. While the torch 4 of the welding robot is moved in the specified weld line direction, the torch tip is vibrated orthogonally to the moving direction periorically by weaving to proceed welding. The deviation of the actual weld line is monitored and detected from the change of the welding current or welding voltage following weaving and according to this monitoring and detection, the tip position of the torch 4 during welding is corrected according to the deviation. Consequently, an image pickup sensor such as a camera is obviated, this is hardly affected by heat and light of an arc and the welding quality is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding control method for welding by a welding robot, and more particularly to control of a welding locus.

[0002]

2. Description of the Related Art Conventionally, in welding using a welding robot,
Numerical control of a microcomputer (NC control) is often used for the control (welding control). In this case, the welding accuracy is easily influenced by the tacking accuracy and the setting accuracy of the welding object, and the welding object is deformed by the heat generated by the welding, and the welding line is also likely to change. Therefore, in order to perform welding correctly along the welding line designated in advance by the NC data, a function of correcting the welding locus of the welding robot in real time is required. This correction is conventionally performed by monitoring the welding state from a photographed image of an ITV scanning sensor or a light-section type sensor.

[0003]

In the case of the welding control method for the conventional welding robot described above, I for correcting the welding locus is used.
TV scanning sensors and optical cutting type sensors are easily affected by heat and light generated by the arc during welding, and it is difficult to use them for a long time near the tip of the torch where the welding arc occurs. Must be placed separately. And if you place these sensors away from the arc,
It becomes difficult to accurately grasp the welding state, the welding copying accuracy is limited, the welding quality cannot be improved, and there is a problem of interference with the object to be welded.

Further, the image sensor using this type of camera is expensive, and moreover, it requires complicated and high-level processing of its image data, and there is a problem that it cannot be controlled in real time in association with the operation of the welding robot. An object of the present invention is to correct the deviation of the welding line in real time by a method that is less susceptible to the heat and light of the arc without using an image sensor such as a camera.

[0005]

To achieve the above object, in the welding control method of the welding robot of the present invention, the torch tip is moved by weaving while moving the torch of the welding robot in the designated welding line direction. Periodically vibrates at right angles to the moving direction to proceed with welding, and the deviation of the actual welding line is monitored and detected from the change in welding current or welding voltage due to weaving, and the deviation is detected by the monitoring and detection. Correct the torch tip position during welding.

[0006]

In the welding control method of the welding robot of the present invention configured as described above, the torch tip vibrates periodically by weaving while moving the torch in the designated welding line direction to perform welding. At this time, the distance between the tip of the torch and the object to be welded (workpiece) changes periodically due to weaving, and the welding current or welding voltage changes with this change.

Then, the deviation of the actual welding line during welding is monitored and detected from the change of the welding current or welding voltage, and the torch tip position is corrected by the result of this detection to correct the welding trajectory in real time. In this case, since the welding state is monitored and detected from the welding current or the welding voltage, a conventional image sensor such as a camera is unnecessary, and is not affected by heat or light generated by the arc. Moreover, the numerical processing is based on the magnitude of the current or voltage, and the deviation of the welding line can be detected more easily and quickly than the image processing, and the real-time correction (control) associated with the operation of the welding robot can be performed.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment will be described with reference to FIGS. FIG. 5 shows a control configuration. The robot control device 1 for controlling the operation and position of the welding robot and the arc sensor control device 2 for monitoring and detecting the welding state are both formed by a microcomputer. The input / output signals of the arc sensor control device 2 include (a) an analog input signal from the welding machine 3 mounted on the welding robot,
There are three types of signals: (b) a digital input signal given from the robot controller 1, and (c) a digital output signal given to the robot controller 1.

Specifically, the three types of signals are composed of the following signals. First, the analog input signal of (a) is the detection signal Sa of the welding current, the welding current supplied to the torch 4 from the welding machine 3 is detected by the shunt resistor 5 and converted into a voltage signal, and the high frequency of this voltage signal is detected. It is formed by removing the noise component by the low-pass filter 6. Next,
The digital input signal of (b) is a command signal Sb ₁ of an expected welding current as an output current value given to the welding machine 3, a weaving reference signal Sb ₂ for position determination of the torch 4 for each weaving cycle, and welding conditions. It is formed by three kinds of signals, which are signals Sb ₃ of various control parameters shown.

The control parameter of the signal Sb ₃ is
It changes every time the welding position (downward horizontal, upward horizontal, upright progress, etc.), the gas used, the welding conditions such as the core wire (wire) 7 protruding from the torch 4, and the like are changed by the robot controller 1. It is transferred from the robot controller 1 while being changed to an appropriate value at any time in conjunction with the driving NC data. The control parameter includes six data P ₁ to P ₆ below. P ₁ : The difference between the maximum value and the minimum value of the welding current in one weaving cycle. P ₂ : The difference between the average value of the welding current in one weaving cycle and the average value of the next cycle. P ₃ : The difference between the upper current value and the lower current value as the coordinate correction determination set value. P _4: the difference between the predicted welding current command value and the welding current average value of one weaving cycle of the coordinate correcting determination setting value. P ₅ : Direction of coordinate correction. P ₆ : Designation of the number of times the welding current is taken in for one weaving cycle. The upper current value and the lower current value are welding current values when the torch 4 in one cycle of weaving is above and below, respectively. Next, the digital output signal of (c) is formed by the coordinate correction signal Sc ₁ for the coordinate correction command of the welding line and the welding abnormality signal Sc ₂ which instructs the welding robot to stop at the time of welding abnormality.

Next, a welding control algorithm will be described. When welding the objects to be welded (workpieces) 8 and 9 arranged in an L shape as shown in FIG. 6A, the tangential direction on the inner wall side of the objects 8 and 9 orthogonal to the paper surface is the proper welding line direction. Become. Then, by the operation and position control of the robot controller 1, the torch 4 repeats weaving while moving in the welding line direction as the welding progresses, and the position of the torch 4 is moved by this weaving every weaving cycle. →→→→ The torch tip periodically vibrates at right angles to the moving direction.

Due to this vibration, the distance between the tip of the torch 4 and the objects to be welded 1 and 2 changes, and the welding current is highest between the tip of the torch 4 and the objects to be welded 8, 9 as shown in FIG. 6 (b). It becomes low at the far position and becomes high at the closest position. That is, when the torch 4 is weaved, the welding current pulsates at a frequency twice that of the weaving, and the size of the welding current is different from that of the objects to be welded 8 and 9.
It changes in the opposite direction to the tip.

When the actual welding line during welding deviates from the proper welding line direction, the symmetry of the waveform of the welding current deviates and the size of the welding current changes. Therefore,
Focusing on the characteristics of this welding current, the arc sensor control device 2
Thus, the deviation of the actual welding line is monitored and detected from the change of the welding current due to the weaving, and the torch tip position is corrected and the welding line is controlled via the robot controller 1 based on this result.

Specifically, this control includes control based on the next average value of the welding current and control based on the difference between the upper current value and the lower current value. Then, the control based on the average value of the welding current consists of the process of FIG. 1, and the arc sensor control device 2 executes the process of the same diagram under the given setting conditions based on the control parameters of the weaving reference signal Sb ₂ and the signal Sb ₃ . Periodically, the welding current is sampled from the detection signal Sa for one period of weaving and integrated,
From the result, the average welding current value for one period of weaving is obtained.

Further, the average value of the measured welding current and the expected welding current (average value) given by the command signal Sb ₁ are compared to obtain a difference, and the coordinate correction for moving the welding robot in the direction in which the difference becomes smaller. The signal Sc ₁ is given to the robot controller 1. As a result, in the case of downward welding in which the upward movement in FIG. 6 is the + Z direction movement and the rightward movement is the −Y direction movement,
For example, as shown in FIG. 2A, when the torch 4 is too far away from the objects to be welded 8 and 9 and the average welding current measured is lower than the expected welding current, the position of the torch 4 is moved in the + Z direction, -Y by the coordinate correction signal. The correction is made so as to approach the origin in both directions, and the torch 4 approaches the welding objects 8 and 9 as shown in FIG.

By repeating this control, the distance between the torch 4 and the objects 8 and 9 to be welded is adjusted so that the actual welding current average value matches the expected welding current, and the tip position of the torch 4 is corrected. . Next, the control based on the difference between the upper current value and the lower current value consists of the process of FIG. 3, and the arc sensor control device 2 grasps the position of the torch 4 during weaving from the weaving reference signal Sb ₂ and detects the detection signal Sa.
Based on the above, the welding current for one cycle of weaving is divided into an upper current value on the side of FIG. 6 (b) where the torch 4 is located above and a lower current value on the side of FIG. 6 (b) where the torch 4 is located below. Divide and total.

Then, the difference between the upper current value and the lower current value obtained by this integration is calculated, and the absolute value of this difference is compared with the appropriate value (set value) of this absolute value given by the control parameter. When the obtained absolute value becomes large and the waveform of the welding current becomes asymmetric, the deviation of the position of the torch 4 on the welding object 8 or 9 side is detected from the positive and negative polarities of the difference, and the difference is detected. A coordinate correction signal Sc ₁ for moving the welding robot in a decreasing direction is given to the robot controller 1. As a result, for example, in the case of downward welding, the actual welding line is displaced as shown in FIG.
If the torch 4 is displaced to the side, the position of the torch 4 is controlled so as to match the proper welding line as shown in FIG.
The tip position of is corrected.

That is, the arc sensor control device 2 periodically obtains a welding current detection signal Sa of the welding machine 3 during welding based on various welding control conditions and settings given by the signals Sb _{1 to} Sb _3. In addition, the deviation of the welding line is monitored and detected from the change of the welding current for one cycle of weaving. As a result, the coordinate correction signal Sc ₁ is given to the robot controller ₁ to correct the tip position of the torch 4 in real time. By the way, when a gap occurs between the objects 8 and 9 to be welded or a burnout or the like occurs and the deviation of the welding line becomes abnormal, the arc sensor control device 2 determines that the welding is abnormal, and the robot control device 1 receives the welding error signal. Apply Sc ₂ and stop welding.

Then, the results of FIGS. 7 to 10 were obtained by applying the method to actual welding. FIGS. 7 and 8 show welding currents and welding beads 10 applied to upward welding and when welding is performed by shifting the position of the torch 4 at the start of welding by a predetermined amount in the −Z direction in advance.
8 (a) is the welding start point, FIG. 8 (b) is during welding,
(C) shows the state of the welding bead 10 at each welding end point.

As is clear from FIG. 7, the welding current had a large amplitude and a low frequency in the first half of the welding, but the amplitude decreased in the latter half of the welding due to repeated correction of the torch tip position. The frequency also increased, and it was automatically corrected to a normal waveform. Based on this modification, the welding bead 10 was also largely deviated to the lower side according to the deviation of the welding line in the first half of the welding as shown in FIG. 8 (a), but in the latter half of the welding, the same figure (b), (c). As shown in Fig. 3, the weld line returned to normal and was evenly formed above and below.

9 and 10 are applied to downward welding,
The welding current and welding bead 10 when the position of the torch 4 at the start of welding is shifted in the + Z direction by a predetermined amount and welding is performed are shown. 10A and 10B show the states of the welding bead 10 at the welding start point and the welding end point, respectively. Then, in the case of this downward welding, the welding current has a smaller amplitude and a higher frequency in the latter half of the welding, is automatically corrected to a normal waveform, and the welding bead 10 is biased downward at the welding start point. At the end of welding, the upper and lower parts were formed normally.

Since the welding locus of the welding robot is corrected by monitoring and detecting the change of the welding current, the welding condition is not affected by the heat and light of the arc as in the case of using the conventional image sensor. Can be accurately grasped and no interference with the welding objects 8 and 9 occurs. Further, since it is sufficient to perform a simple numerical calculation process, it is possible to correct the deviation of the welding line by performing real-time control in association with the operation of the welding robot. Therefore, the welding quality is remarkably improved as compared with the conventional case.

Since there is no interference with the objects 8 and 9 to be welded, it is possible to cope with various welding postures such as upward horizontal, downward horizontal, and vertical advance. In addition, when a gap between the objects 8 and 9 to be welded, a burnout, or the like occurs, a so-called abnormality monitoring function is activated to stop welding and improve safety. When the welding start point and the welding end point are sensed in advance and welding is performed, a good bead can be obtained even if there is a bend during welding or thermal strain due to welding because the deviation of the welding line is automatically corrected. You can Also, even if only the welding start point is sensed and welded, the end point detection function can automatically detect the end point of the welding line. In this case, since it is not necessary to sense the welding end point, the welding takt time is reduced. You can improve and work efficiently.

Further, the control parameters given to the arc sensor control device 2 can be converted into NC data. In this case, the data can be changed easily in the robot control device 1 by being given on a RAM basis. Is also possible. By the way, in the above-mentioned embodiment, the deviation of the welding line is monitored and detected from the change of the welding current, but the deviation of the welding line may be monitored and detected from the change of the welding voltage.

[0025]

Since the present invention is configured as described above, it has the following effects. Welding is performed by periodically vibrating the torch tip by weaving while moving the torch 4 in the designated welding line direction. At this time, the torch tip and the welding object 8, 9 are weaved.
And the welding current or voltage changes with this change, the deviation of the actual welding line during welding is monitored and detected from this change, and the torch tip position is detected based on this detection result. It is corrected and the welding trajectory is corrected in real time. Further, since the welding state is monitored and detected from the welding current or the welding voltage, a conventional image sensor such as a camera is unnecessary, and is not affected by heat or light generated by the arc.

Moreover, since the numerical processing is based on the magnitude of the current or voltage, the deviation can be detected more easily and more quickly than the image processing, and the quick correction (control) associated with the operation of the welding robot can be performed. Therefore, it is possible to correct the deviation of the welding line in real time and improve the welding quality by a method that does not require an image sensor and is less susceptible to the heat and light of the arc.

[Brief description of drawings]

FIG. 1 is a flowchart of control based on an average value of a welding current according to an embodiment of the present invention.

2 (a) and 2 (b) are explanatory views of the torch tip position before and after the control of FIG.

FIG. 3 is a flowchart of control based on a difference between an upper current value and a lower current value according to the first embodiment of the present invention.

4 (a) and 4 (b) are explanatory views of the torch tip position before and after the control of FIG.

FIG. 5 is a block diagram of one embodiment of the present invention.

6 (a) and 6 (b) are explanatory diagrams of changes in the torch position and changes in welding current due to weaving.

FIG. 7 is an actually measured waveform diagram of an example of welding current.

8 (a), (b) and (c) are explanatory views of a welding bead formed by the welding current of FIG.

FIG. 9 is a measured waveform diagram of another example of the welding current.

10 (a) and 10 (b) are explanatory views of a welding bead formed by the welding current of FIG.

[Explanation of symbols]

 1 Robot control device 2 Arc sensor control device 4 Torch 7 Core wire 8, 9 Welding object

Claims (1)

[Claims] 1. A welding robot torch is moved in a designated welding line direction while weaving to periodically vibrate the torch tip at right angles to the moving direction to proceed with welding, and a welding current or welding associated with the weaving is performed. The deviation of the actual welding line is monitored and detected from the change of the voltage,
A welding control method for a welding robot, characterized in that the position of the tip of the torch during welding is corrected according to the deviation by detection.