JPH06643A - Weld seam detecting method of automatic welding equipment - Google Patents

Abstract

PURPOSE:To correctly judge the weld seam position by detecting the surface temperature in the vicinity of the weld seam of a work to be welded, and judging that the direction where the reduction ratio of the surface temperature is largest is the weld seam position. CONSTITUTION:Butt welding of works 5, 7 to be welded is executed. The surface temperature of the works 5, 7 to be welded in the vicinity of the weld seam L which is the groove is detected by a surface temperature detector 15. The welding heat is radially transmitted from a molten pool P immediately below a welding torch 13, and shows the temperature distribution whose shape is like the contour of a longitudinally-cut apple as demonstrated like the isothermal lines a1, a2.... The reduction ratio of the surface temperature becomes largest in the direction of the weld seam L due to the groove. The position can correctly be judged by making a judgement that the direction where the reduction ratio of the surface temperature is the largest is the weld seam L. Since this detecting method is of non-contact type, and no effects are made on the welding heat and wears, and the durability is also excellent. Correct judgement can be made even when the plate thickness is small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding line detecting method for automatically controlling the position of a welding torch in an automatic welding apparatus.

[0002]

2. Description of the Related Art In an automatic welding apparatus such as a welding robot, the position of a welding torch is controlled on a welding line (for example, a groove formed by butt welding in butt welding) in order to perform a precise welding operation. For example, a welding line detection method and an apparatus using various sensors such as an image sensor using a CCD camera, an arc sensor, a laser sensor, and a touch sensor have been proposed.

[0003]

Since the CCD camera receives the arc light of extremely strong welding, it is difficult to accurately catch the welding line having a low surface temperature.

The arc sensor detects the deviation of the welding torch from the welding line based on the change of the welding current value. In the case of thick plate welding, since the rate of change in the welding current value due to the deviation of the welding torch is large, it is possible to accurately catch the welding line and it is widely used. However, in the case of thin plate welding, the change rate of the welding current value due to the deviation of the welding torch is small, the welding line cannot be accurately caught, and practical application is difficult.

The laser sensor, like the CCD camera, receives an extremely strong arc light, so that it is difficult to accurately catch a welding line having a low surface temperature.

The touch sensor detects the gap groove of the welding line by bringing the pin into contact with the surface of the workpiece.
Since it is a contact method, it lacks durability due to welding heat and wear, and in the case of thin plate welding, the gap width is narrow and it is difficult to trace with a pin.

The object of the present invention was proposed in view of the above-mentioned problems of the prior art. The object of the present invention is to detect the surface temperature in the vicinity of the welding line of a work piece, thereby relating to the plate thickness of the work piece. It is an object of the present invention to provide a welding line detection method for an automatic welding device that can accurately catch a welding line without using it.

[0008]

In order to solve the above problems, the present invention detects the surface temperature near the welding line of a workpiece to be welded and determines the position of the welding line according to the state of this surface temperature. It is characterized in that the position of the welding torch is automatically controlled after the judgment.

In determining the welding line position based on the surface temperature state, the direction of the greatest decrease in surface temperature is determined as the welding line position.

Further, in determining the position of the welding line based on the state of the surface temperature, the direction in which the isotherm of the surface temperature is discontinuous is determined to be the position of the welding line.

[0011]

With respect to the surface temperature near the welding line of the workpiece, since there is a groove due to the groove at the welding line, the state of change in the surface temperature is significantly different between the welding line and the left and right sides thereof. The position of the welding line can be determined from the state of the detected surface temperature, and the automatic position control of the welding torch is extremely accurate.Because of non-contact detection, there is no lack of durability due to welding heat or wear, and the There is no inaccuracy due to the thin plate thickness.

The position of the welding line based on the state of the surface temperature is judged to be the welding line position in the direction in which the decrease rate of the surface temperature is the largest, or the position of the welding line based on the state of the surface temperature is judged to be the isothermal surface temperature. The welding line position can be accurately determined by determining the direction in which the line is discontinuous as the welding line position.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 5 is a perspective view of a welding robot 1 which is an example of an automatic welding apparatus. This is a groove (welding line) formed by grooved workpieces 5 and 7 on a work table 3 placed horizontally.
The part is to be automatically welded. The robot arm 9 is rotatable and bendable, and a welding head 11 provided at the tip of the robot arm 9 has a welding torch 13 which will be described later.
And a surface temperature detector 15 are provided. The signal output from the surface temperature detector 15 is a detection signal image processing device 17
Or the control device 19 converts the control signal into a control signal to control the operation of the welding robot 1 by a servo mechanism or the like. A welding power supply device 21 for supplying power to these devices is provided.

Next, the first method of detecting the welding line will be described with reference to FIG. 1 which is a perspective view of the vicinity of the welding head 11. When the illustrated left and right workpieces 5 and 7 are butt-welded together, the surface temperature of the workpieces 5 and 7 near the welding line L, which is a groove formed by the groove, is measured by the surface temperature detector 15, for example, infrared rays. Detect with a radiation thermometer.

Since the welding heat is radially conducted from directly below the welding torch 13 (molten pool P) in the directions A, B, C, ..., The surface temperatures of the work pieces 5, 7 are melted. With the pond P as the maximum temperature, the isotherms a ₁ , a ₂ ,
a _3, shows a ... temperature distribution in the form similar to the contour longitudinally, for example apples as. When the relationship between the surface temperature and the distance from the molten pool P is illustrated with the direction A, the direction B, and the direction C as parameters, the surface temperature changes and decreases as the distance from the molten pool P increases as shown in FIG. This decrease rate of the surface temperature is the largest in the direction A which is the direction of the welding line L, and as it deviates from the direction of the welding line L, the decrease rate of the surface temperature is decreased in the directions B and C. It is getting smaller.

That is, in front of the molten pool P, because of the welding line L which is a groove formed by the groove, the surface temperature drops drastically when it is a little away from the molten pool P. This is because the bead 23 allows the workpieces 5 and 7 to be integrated in terms of heat conduction and uniform in heat conduction, and the surface temperature is gradually lowered even at a position considerably distant from the molten pool P.

From this result, it is possible to determine the direction A, which is the direction in which the lowering ratio of the surface temperature is the largest, as the welding line L position. Thus, as a first method for determining the position of the welding line, the temperature signal detected by the detector 15 is detected by the detection signal image processing device 17 in the direction A in which the rate of decrease in surface temperature is the largest, The operation of the welding robot 1 can be automatically controlled in this direction A by being converted into a control signal by the control device 19.

As described above, the surface temperature of the workpieces 5 and 7 near the welding line L is detected and the position of the welding line L is judged based on the state of the surface temperature.
In this embodiment, there is no defect such as the lack of durability due to welding heat and abrasion unlike the touch sensor, and the difficulty in tracing with a pin due to a narrow gap width.

Further, the strong arc light does not hinder the accurate catching of a welding line having a low surface temperature, as in the case of image processing such as a CCD camera or a laser sensor.

In the case of thin plate welding like an arc sensor, the change rate of the welding current value due to the deviation of the welding torch is small,
The problem of not being able to accurately catch the welding line does not exist in the above-described embodiment, and the position of the welding line can be determined by the state of the detected surface temperature, and the automatic position control of the welding torch is extremely accurate.

A second welding line detection method will be described.
The temperature distribution chart of FIG. 2 is shown again in FIG.
In the rear of the molten pool P, the surface temperature of 7 is an isotherm a ₁ ,
, a ₂ , a ₃ , ... Appear in a generally concentric shape around the molten pool P. That is, in the rear of the molten pool P, the welding beads 2
This is because the work pieces 5 and 7 are integrated with each other in terms of heat conduction by 3 and the heat is evenly transferred to the work pieces 5 and 7 by cutting the welding bead 23 longitudinally.

On the other hand, in front of the molten pool P, the isotherms a ₁ , a ₂ , a ₃ , ... Are discontinuous points b ₁ , b ₂ , b ₃ , ... In a shape similar to the contour of the apple. Is appearing. Welding line L
This is because there is a groove due to the groove at the portion of (1), and therefore heat conduction between the workpieces 5 and 7 is not uniform at the position of the welding line L.

From this result, the surface temperature isotherm a ₁ ,
The positions at which a ₂ , a ₃ , ... Are discontinuous (discontinuous points b ₁ , b
It is possible to determine the direction A connecting ₂ , ₂ , b ₃ , ...) As the welding line L position.

The welding line detection method in this embodiment is based on the above-mentioned two methods, but since the welding heat has not yet been generated when starting welding, the above-mentioned surface temperature detection method is used. The method using the vessel 15 cannot detect the conveyance of the welding line L. Therefore, in practical use, an image sensor or laser sensor using the CCD camera, which is a conventional technique, is additionally provided to the welding head 11, and the welding line L is detected by the image sensor or laser sensor at the start of welding. When the welding heat is generated and the heat conduction in the workpieces 5 and 7 becomes a steady state (for example, when a predetermined time has elapsed from the start of welding), the surface temperature detector 15 automatically detects the welding line L. It is desirable that the detection signal image processing device 17 be controlled so as to be switched selectively.

The present invention is not limited to the above-mentioned embodiments, but can be implemented in other modes by making appropriate changes. For example, as the surface temperature detector 15, various non-contact type surface thermometers can be applied without trouble in addition to the infrared radiation thermometer shown in the figure.

[0026]

As described above, according to the present invention, the surface temperature near the welding line of the work piece has a groove due to the groove at the portion of the welding line. The state of change in surface temperature is significantly different. The position of the welding line can be determined from the detected surface temperature state, and the automatic position control of the welding torch is extremely accurate.Because of non-contact detection, durability loss due to welding heat and wear, and the workpiece There is no inaccuracy due to the thin plate thickness.

The welding line position is determined based on the surface temperature state, the direction in which the decrease rate of the surface temperature is the largest is determined to be the welding line position, or the welding line position based on the surface temperature state is determined based on the isothermal surface temperature. The welding line position can be accurately determined by determining the direction in which the line is discontinuous as the welding line position.

[Brief description of drawings]

FIG. 1 is a perspective view of the vicinity of a welding head of a welding robot used in the present invention.

FIG. 2 is an explanatory diagram showing a distribution of the surface temperature of the workpiece in FIG.

FIG. 3 is a characteristic diagram of the surface temperature of the workpiece in FIG.

FIG. 4 is an explanatory view showing a distribution of the surface temperature of a workpiece similar to FIG.

FIG. 5 is a perspective view of a welding robot which is an example of an automatic welding apparatus used in the present invention.

[Explanation of symbols]

 5,7 Work piece 13 Welding torch L Weld line

Claims (3)

[Claims] 1. A position of a welding torch is automatically controlled by detecting a surface temperature near a welding line of a work to be welded, determining a position of the welding line based on a state of the surface temperature. A method for detecting a welding line of an automatic welding device, which is characterized in that: 2. The welding line detection of the automatic welding apparatus according to claim 1, wherein the determination of the welding line position based on the state of the surface temperature determines that the direction in which the rate of decrease of the surface temperature is the largest is the welding line position. Method. 3. The welding of the automatic welding apparatus according to claim 1, wherein the determination of the welding line position based on the state of the surface temperature is performed by determining the direction in which the isotherm of the surface temperature is discontinuous as the welding line position. Line detection method.