JPH0442076Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a device for detecting the center position of a laser weld bead shape, which is used in quality inspection of a laser weld bead.

[Prior Art] Radiographic testing and ultrasonic testing are commonly used as non-destructive testing methods for detecting internal defects in welded parts. For example, Japanese Patent Application Laid-Open No. 55-50998 discloses a method using a radiographic examination. Further, Japanese Patent Application Laid-Open No. 56-53898 discloses a device that uses a fiberscope to monitor a welded part from a position where there is no radiation exposure, but the test itself is based on a radiographic examination. Also, JP-A-58-
Publication No. 157596 discloses a welding part monitoring device for laser welding, etc. When a welded part is irradiated with a laser and imaged by an ITV camera, the amount of incident light is narrowed down by a combination of multiple variable temperature filters. Disclosed is a device designed to prevent image tube burn-in. However, none of the conventional publications teaches the image processing technique of the present invention for determining the center of the weld bead from images taken with an ITV camera.

[Problems to be solved by the invention] However, laser butt welding using a laser beam has the following unique problems.

Since laser beam welding allows high-speed welding using a concentrated heat source, it is possible to obtain a good welded joint with a narrow welded area and a welded heat-affected zone. However, on the other hand, because the width is narrow, that is, the spot diameter of the focused laser beam is minute (about φ0.3 mm), the tolerance for deviation of the laser beam with respect to the butt groove is as high as ±0.2 mm. Accuracy is required. On the other hand, it is difficult to satisfy the above-mentioned accuracy 100% in actual welding due to problems such as the accuracy of the welding machine, the accuracy of the steel plate that is the object to be welded, and the fluctuation of the optical axis of the laser beam. As a result, a defect called fusion failure occurs because the welding interfaces do not fully fuse together due to beam misalignment, and especially when welding with a laser beam, the cross-sectional shape of the bead becomes constricted at the center like a wine cup. This results in an internal defect that cannot be determined from the appearance of the weld. Conventionally, two non-destructive testing methods, the above-mentioned radiographic examination and ultrasonic flaw detection test, have been conventionally used to detect this defect. However, with the former test method, it is impossible in principle to perform online automatic inspection, and with the latter test method, although it is possible in principle and there are examples, the scale of the equipment is extremely large, and water, etc. There are many restrictive conditions, such as the need to scan the contact through a couplant, making it difficult to construct an online automatic inspection device.

In order to solve such problems, the following invention was filed by the present applicant on August 6, 1986, under the title "Quality Inspection Device for Laser Butt Welding", although it is not yet publicly known. (Unexamined Japanese Patent Publication No. 1983-
Publication No. 40692).

That is, as shown in FIG. 8, a means 3 for irradiating a slit-shaped light 2 from diagonally above onto a weld bead 1 by laser butt welding with the welding line direction and the longitudinal direction of the slit-shaped light 2 perpendicular to each other; A visual sensor consisting of a means for photographing reflected light from vertically above the welding bead using an ITV camera 4, and a position of the optical axis center of the laser beam and a welding position determined from the image obtained by the visual sensor. This is a quality inspection device for laser butt welding, which includes an image processing device 5 that determines the deviation and determines the quality of welding.

In the above device, a weld bead 1 (three-dimensional shape) formed by laser butt welding is irradiated with slit light 2 (slit-shaped light) diagonally from above with the welding line direction and the longitudinal direction of the slit light at right angles, and the reflected light is A flat image representing the cross-sectional shape of the bead 1 can be obtained by photographing it from vertically above the bead 1 with the ITV camera 4 (light cutting method). The above part is called a visual sensor, and the slit light 2 is produced by a semiconductor laser 6, a collimating lens 7, and a cylindrical lens 8. The camera 4 is a small CCD camera, and these are housed in a sealed case.
It is attached to the processing head (welding torch) of a laser welder. By processing the image obtained from this visual sensor at high speed by a dedicated image processing device 5 consisting of an image input device and a computer,
The center position of the weld bead, that is, the center of the optical axis of the laser beam, can be determined while welding.
On the other hand, when positioning the workpieces 9 and 10 for butt welding, in most cases, one of the workpieces is longer than the total welding length, the other workpiece is equal to the total welding length, and the former workpiece is pressed against the positioning reference pin, and the latter workpiece is It will be pressed against the workpiece to position it. Therefore, edges of the workpiece exist at both ends or at either end of the entire weld length. The edge position of the workpiece, that is, the position of the welding line (butt groove) can be determined by photographing and processing the image using the aforementioned visual sensor and dedicated image processing device before or after welding has finished. By comparing this with the optical axis center of the laser beam determined in the same manner as described above, the deviation of the laser beam with respect to the welding line can be determined, and the quality of the welding (presence or absence of poor fusion) can be determined.

The present invention provides the above-mentioned quality inspection apparatus for laser butt welding, which is not yet known and which was previously filed.
This invention relates to an idea for further improving the video processing calculation part that determines the center of the weld bead from the output video signal determined by the ITV camera.

Specifically, the video processing calculation section used in the device of the earlier application was as shown in FIG. That is, the comparator 12 detects bright areas of the output video signal (FIG. 9) from the ITV camera 11, the front edge detection 13 and the rear edge detection 14 detect each edge, and the center detection is performed. The center position (FIG. 10) is determined by a circuit 15, and the data output circuit 16 outputs the signal to the outside as a position output. The outputs E1 to E5 of each stage are shown in FIG.

However, this configuration has the following problems that should be improved.

The ITV camera output 17 in Fig. 12 is not constant depending on the shape and condition of the work surface, and is unstable near the weld bead, making it difficult to set the level of the comparator.

With the settings in Figure 13A, the settings shown in Figure 13B
When the ITV camera output is low, there is no comparator output and the position cannot be detected.

Furthermore, when the waveform is not symmetrical as in the case of FIG. 13C, the center changes depending on the setting of the compart level, so it is desirable to raise the comparator level so that the brightest part becomes the center as much as possible.

As mentioned above, at a certain comparator level,
It is difficult to detect the center position.

This invention uses an ITV camera to capture an image of the three-dimensional shape of the weld bead converted into a flat one using the optical cutting method.
An object of the present invention is to provide a device for determining the center of a weld bead image from the obtained image, which can determine and output the center even if the weld bead image changes in various ways and the center becomes difficult to discern. .

[Means for Solving the Problems] As shown in FIG. 1, the laser weld bead shape inspection device according to the present invention to achieve the above object measures the three-dimensional shape of the weld bead in a flat plane using an optical cutting method. ITV camera 21 that shoots and outputs the converted image
and; a plurality of comparators 24, 25, which are connected to the ITV camera in parallel, have different setting levels, and each detects a video at or above the respective setting level from the output video signal of the ITV camera.
26, 27 (any number greater than or equal to 2, the same applies hereinafter); connected in series to each comparator,
A plurality of position detection circuits 28, 29, 30 detect the front edge and rear edge of each image detected by the comparator, detect the center position of the front edge and the rear edge, and output the center of the weld bead. ,31
and an output circuit 32 that is connected in series to all of the plurality of position detection circuits and selectively outputs output signals from the plurality of position detection circuits; and; connected in series to all of the plurality of position detection circuits. and a priority circuit 33 which determines which of the output signals of the plurality of position detection circuits should be outputted with priority and instructs the output selection circuit.

In Figure 1, the petestal clamp 23 is used to stabilize the DC level of the video signal, and the LPF 22 is used to stabilize the DC level of the video signal.
(Low pass filter) was added to remove signal changes (mainly noise, etc.) smaller than the position resolution of the position detection circuit, but both 22 and 2
All three are not required.

[Function] Comparator 1, 24 to comparator n,
27 and position detection circuit 1, 28 to position detection circuit n,
31 is selected by the priority circuit 33, and based on the signal, the output selection circuit 32 selects position data and outputs it. The comparator level settings at this time are as shown in Figure 3, for example, comparator 1, 24 > comparator 2,
25>comparator 3, 26>comparator n, 27. An example of the priority conditions of the priority circuit 33 is shown in FIG.

Under this condition, even in the case shown in FIG. 13B, there are multiple comparators, so even if comparators 1 and 24 are OFF, comparator 2,
Since 25, 3, 26, 7, and 27 are turned on, the data of the position detection circuits 2 and 29 can be output in this case. Details of the position detection circuits 28-31 are shown in FIG. The center of the signal is determined by the center detection 43 based on the position information obtained by the front edge detection 41 and the rear edge detection 42. In order to check whether the position can be detected correctly using the input signal at this time, the signal is checked in the signal abnormality detection 44, and if the position can be detected correctly, an OK signal is output. In other cases, an NG signal is output.

[Example] Below, preferred embodiments of the laser weld bead shape inspection device according to the present invention are shown in FIGS. 5 to 7.
The operation will be explained with reference to the drawings.

The configuration of the embodiment is shown in FIG. In this example, comparators 1, 55, 2, 56, 3, 57, 4,
58 and position detection circuits 1, 59, 2, 60, 3,
Although four circuits of 61, 4, and 62 are used, the number of circuits n is not limited to 4, and may be any number of circuits as long as it is 2 or more. Position detection circuit 1, 59, 2, 60, 3, 6
The details of 1, 4, 62, 1 are as shown in FIG.

Comparator 1, 55, 2, 56, 3, 5
The level setting conditions for 7, 4, and 58 are as follows.

Comparator 1 > Comparator 2 > Comparator 3 > Comparator 4 If the comparator settings are other than the above conditions, the priority order will be lost, so a setting abnormality detection circuit 70 is provided.

The operating conditions for priority circuit 65 are shown in FIG. In the figure, OK indicates good, NG indicates defective, and × indicates either OK or NG, and indicates a condition under which the signal of the OK position detection circuit is output preferentially.

The video signal of the ITV camera 51 is passed through an LPF (low pass filter) 53 to remove signal components that adversely affect noise and equal position detection, and furthermore, a petestal clamp 54 is used to keep the DC level constant for the comparators 55, 56, 57, and 58. is input. Its output is comparator 1~4,55
58, and are further input to each of the position detection circuits 59 to 62, and the position output and the determination output whether the position output is OK or NG are sent to the priority circuit 65, respectively. The priority circuit 65 is
The optimum position output is selected based on the conditions shown in FIG. 6, the data selector 63 is controlled, a signal is sent to the output interface 64, and the data is sent to an external device. At this time, each comparator 66 to 69
The settings are the comparators 55, 56, 57,
It must be set based on 58 level setting conditions. A setting abnormality detection circuit 70 detects a setting abnormality. 71 is a power supply that supplies electricity to each part.

The effects of using four comparators 55, 56, 57, 58 and position detection circuits 59, 60, 61, 62 will be explained with reference to FIGS. 7 and 5. In the case of FIG. 7A, the waveform is symmetrical and all the comparators 55, 56, 57, 58 detect it, so in this case, the position detection circuits 1 to 4, 5
Since the position outputs of 9 to 62 are almost the same, it is not necessary to have four comparator and position detection circuits.
However, when the level is low as in the case of Fig. 7B, comparators 1, 2, 3, and 55 to 57 cannot be detected, so if there is only one comparator and position detection circuit, the level setting is set to comparator 1, 55, the position cannot be detected, but if four circuits are prepared, even if it cannot be detected in the case of Fig. 7C, in the case of Fig. 7B, comparators 4 and 58 and the position detection circuit 4 and 62, the position can be detected even if the level drops to a certain extent.

If the waveform is not symmetrical as shown in Fig. 7, the values output by the position detection circuits 1 to 4 and 59 to 62 are different, so we would like to detect the value of the peak of the mountain, which is the brightest part of the image. In this case, if there are multiple comparators 55, 56, 57, 58, the one closest to the peak of the mountain will be output due to the priority order, so the position output will be lower than when there is only one comparator and position detection circuit. Errors are reduced.

In the case of Fig. 7E, comparators 3, 57, and 4, 58 are detected twice, so it is not known which position is correct, so accurate values cannot be detected, but 1, 55 and 2, 56 are detected successfully. Since the signals are detected, the signals of the position detection circuits 1, 59 and 2, 60 at the correct positions can be output, and the values of the position detection circuits 1, 59 are output based on the priority relationship.

In this way, comparators 55, 56, 57,
58 and position detection circuits 59, 60, 61, 62
By preparing multiple positions, prioritizing them, and using the best position output, accurate values can be obtained and undetectable signals can be significantly reduced.

[Effects of the invention] As explained above, when using the laser welding bead shape inspection device of the invention, multiple comparators and position detection circuits are provided, the setting levels of the comparators are mutually changed, and the output signal is prioritized. I decided to output it in order, so
Even if there are various instabilities such as size, smallness, asymmetry, etc. in the flat image of the weld bead taken by the ITV camera,
The center of the weld bead can be determined and output, contributing to improved welding quality.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a laser weld bead shape inspection device according to the present invention, and FIG.
Figure 3 is a diagram of the output conditions of the priority circuit; Figure 3 is a comparator level diagram showing the relationship between the setting level of each comparator with respect to the ITV camera output in Figure 1; and Figure 4 is a position detection diagram in Figure 1. FIG. 5 is a block diagram showing the internal configuration of the circuit; FIG. 5 is a block diagram of an embodiment of the laser weld bead shape inspection apparatus according to the present invention; FIG. 6 is a diagram of the output conditions of the priority circuit in FIG. 5; The figure is a comparator level diagram showing the relationship between the set level of each comparator with respect to the ITV camera output. A is when the ITV camera output video is normal, B is when the video level is a little low, and C is when the video level is low. If it is too low, D is a diagram showing a case where the waveform of the image level is not symmetrical, E is a diagram showing a case where there are two peaks in the image level, and FIG. 8 is a perspective view showing the entire laser welding bead shape inspection device together with a block diagram. , Figure 9 shows the ITV of the weld bead used in the earlier application of the applicant for utility model registration.
A monitor TV image of the image taken by the camera, Fig. 10 is a diagram of the center position of the weld bead determined from the image of Fig. 9, Fig. 11 is a block diagram of the inspection device used in the apparatus of Fig. 9, and Fig. 12 is a diagram of the center position of the weld bead determined from the image of Fig. 9. A relationship diagram of the ITV camera output E1, comparator output E2, front edge detection output E3, rear edge detection output E4, and center output E5 detected by the device shown in Fig. 11. Fig. 13 shows the comparator level in the device shown in Fig. 11. ,
It is a diagram showing the relationship between the ITV camera output and the comparator output, where A shows a normal case, B shows a case where the ITV camera output is low, and C shows a case where the waveform is not symmetrical. 21...ITV camera, 24, 25, 26, 2
7...Each comparator, 28, 29, 30, 3
1...Each position detection circuit, 32...Output selection circuit,
33...Priority circuit.

Claims (1)

[Claims for Utility Model Registration] An ITV camera that captures and outputs an image obtained by converting the three-dimensional shape of a weld bead into a flat image using an optical cutting method; The ITV camera is connected in parallel to the ITV camera and has different setting levels. , a plurality of comparators, each of which detects an image above a respective set level from the output image signal of the ITV camera; connected in series to each comparator,
a plurality of position detection circuits that detect the front edge and rear edge of each image detected by the comparator, detect the center position of the front edge and the rear edge, and output the center of the weld bead; an output circuit that is connected in series to all of the multiple position detection circuits and selectively outputs output signals from the multiple position detection circuits; A laser weld bead shape inspection device comprising: a priority circuit which determines which of the output signals of the circuit should be output with priority and instructs the output selection circuit;