JP5263051B2 - Laser irradiation point detection device and seam position detection device in laser welding machine - Google Patents

Description

  The present invention relates to an apparatus for detecting a laser irradiation position and a seam position in a laser welding machine that welds a butted portion (seam portion) of a welding material using a laser beam as a heat source.

  Conventionally, as one method for producing a welded steel pipe, a laser welding method is used in which a hot-rolled steel sheet or the like is bent into a pipe shape and a butted portion (hereinafter referred to as a seam portion) is welded using a laser beam as a heat source. In such a welding method, accurate alignment is always required so that the laser irradiation position accurately hits the seam portion. Moreover, the seam position and the laser irradiation position fluctuate depending on the production line conditions, heat input conditions, and the like even during welding. Therefore, it has been performed to monitor the laser irradiation position and the position of the seam portion in the laser welded portion and perform position control so that the two coincide with each other.

  As a method for monitoring a laser welded portion, as already disclosed in Patent Document 1 (electron beam or laser beam welding method and apparatus thereof), the laser welded portion is directly observed with a television camera, and the weld line (seam position) is melted. A method for detecting the pond center position is known. In this method, when the welded part is illuminated with external illumination and observed, the seam part is dark and the molten pool is observed brightly, assuming the horizontal direction on the screen (the direction perpendicular to the traveling direction of the welded steel pipe). ), The position of one line is determined for each of seam detection and weld pool detection, and the luminance pattern of the horizontal line is binarized to detect the positions of the seam portion and the molten pool.

Japanese Patent Publication No.55-18439

  However, for example, a welded part image at the time of manufacturing a laser welded pipe is not necessarily symmetrical with respect to the center of the weld line due to fluctuations in the edge shape of the welding material butting part or dirt on the edge part, and Since the reflectance varies depending on the surface properties of the base material, it is difficult to detect a stable seam position simply by binarization. Similarly, the shape of the molten pool is not a symmetrical shape around the molten pool center, and therefore sufficient reliability cannot be obtained. That is, there has been a problem that sufficient reliability and measurement accuracy cannot be obtained simply by determining the center position of the weld line and the weld pool by binarizing the brightness from one line of data.

  The present invention has been made in view of such circumstances, and provides an apparatus capable of accurately detecting a laser irradiation point position (that is, a molten pool position) and a seam position even under actual welding conditions. Let it be an issue.

  A first means for solving the above-described problem is an apparatus for detecting a laser irradiation point in a laser welding machine that welds a butt portion (seam portion) of a welding material using a laser beam as a heat source, and images a welded portion. Laser welding comprising: an imaging device; means for binarizing a captured image; and means for calculating a center position of a binarized high-brightness portion and detecting it as a laser irradiation point It is a laser irradiation point detection apparatus in the machine.

  Since high-luminance plasma is generated at the laser irradiation point, in the imaging apparatus, the luminance of the pixel corresponding to this portion is higher than that of other portions. Therefore, by providing a high-level threshold value, binarizing the pixels of the imaging device, obtaining the position of the center of gravity of the pixel (two-dimensional) corresponding to high luminance, and setting this position as the center of the laser irradiation point, laser irradiation Can detect points accurately. Since a molten pool is formed at the laser irradiation point, determining the laser irradiation point is equivalent to determining the position of the molten pool.

  A second means for solving the above-mentioned problem is an apparatus for detecting a laser irradiation point in a laser welding machine for welding a butt portion (seam portion) of a welding material using a laser beam as a heat source, the laser in the laser welding machine. An apparatus for detecting an irradiation point, an image pickup device for picking up an image of a welded portion, and a minimum luminance extraction means for extracting the luminance of the minimum one of the pixels of an image picked up within a predetermined time, and extracted And a means for detecting a laser irradiation point on the basis of an image constituted by pixels having the minimum luminance.

  The plasma light is flame-like light, and in an actual welding machine, the shape and size of the plasma light change with time. Therefore, when the position of the plasma light is obtained using an image of a certain momentary plasma light, an error in position measurement occurs due to the shape of the flame.

  In this means, the brightness of each pixel of the image captured within a certain time is extracted, and an image having the extracted brightness as the brightness of each pixel is obtained. Based on this, the laser irradiation point is detected. Thereby, accurate position detection can be performed. The detection method of the laser irradiation point applied may be a known method or an invention described in this specification.

  Third means for solving the problem is the second means, wherein the means for detecting the laser irradiation point binarizes an image constituted by the pixels having the minimum luminance; And a means for calculating a barycentric position of the binarized high luminance part and detecting it as a laser irradiation point.

  This means is a combination of the first means and the second means, and has both functions in combination, so that accurate laser irradiation point position detection is possible.

  A fourth means for solving the above-mentioned problem is an apparatus for detecting the position of a seam before welding in a laser welding machine for welding a butt portion (seam portion) of a welding material using a laser beam as a heat source, An illuminating device that illuminates the image, an imaging device that images the welded portion, a minimum luminance extracting means that extracts the luminance of the minimum one of the pixels of the image captured within a predetermined time, and the extracted minimum luminance A seam position detecting device in a laser welding machine, comprising: means for detecting a seam position before welding based on an image formed by pixels having.

  The detection of the seam part before welding is performed by illuminating the welded part with an illuminating device and imaging the welded part with an imaging device. The seam part appears dark because there is no reflected light, and the welded part appears brighter with reflected light. It is done using. However, during welding, a phenomenon called spatter in which the material melted by the laser flies may occur. Since the melted material flies, if the scattering position coincides with the seam portion, the seam portion that should be dark is imaged brightly, which may cause noise when measuring the seam position. In addition, the seam portion may also change in luminance due to material stains and plasma light luminance change.

  In this means, the brightness of each pixel of the image captured within a certain time is extracted, and an image having the extracted brightness as the brightness of each pixel is obtained. The seam position is determined based on this. Therefore, the influence of the sputtering can be removed and the seam portion can be recognized as an image in the darkest state, so that the seam portion is emphasized and accurate position determination is possible. The applied seam portion position determination method may be a known method or an invention described in the present specification.

  A fifth means for solving the above-mentioned problem is an apparatus for detecting the position of a seam before welding in a laser welding machine for welding a butt portion (seam portion) of a welding material using a laser beam as a heat source, An illumination device for illuminating the image, an image pickup device for picking up an image of the welded portion, and integration of the luminance of each pixel of one line in a direction perpendicular to the traveling direction of the welding material within a certain time among the pixels of the picked-up image A seam position detecting device in a laser welding machine, comprising means for calculating a value and means for detecting a seam position before welding based on the calculated integrated value.

  Since the seam before welding has no reflected light from the lighting device, the brightness is lower than that of the welding material. The seam part is detected using this, but the brightness of the seam part and the brightness of the welding material change with time. Therefore, if the measurement is performed based on the measurement data for one line, accurate position measurement cannot be performed. There is a case.

  This means calculates the integral value within a certain time of the brightness of each pixel in one line in the direction perpendicular to the welding material traveling direction, and detects the seam position before welding based on the calculated integral value. Like to do. This is equivalent to detecting the seam position based on the average value of multiple lines in the direction perpendicular to the direction of travel of the welded steel pipe, and variations in each line (time) can be suppressed. The position can be detected. The applied seam portion position determination method may be a known method or an invention described in the present specification.

  A sixth means for solving the above-mentioned problem is an apparatus for detecting the position of a seam before welding in a laser welding machine for welding a butt portion (seam portion) of a welding material using a laser beam as a heat source, An illuminating device that illuminates the image, an imaging device that images the welded portion, and a temporal moving average of the luminance of each pixel in one line in a direction perpendicular to the traveling direction of the welding material among the pixels of the captured image A seam position detecting device in a laser welding machine, comprising means for calculating a value and means for detecting a seam position before welding based on the calculated moving average value.

  In this means, a temporal moving average is used instead of the integral value of the fifth means. Therefore, unlike the fifth means, the seam position can be detected continuously, and the seam position can be detected accurately.

  A seventh means for solving the above-mentioned problem is an apparatus for detecting the position of a seam before welding in a laser welding machine for welding a butt portion (seam portion) of a welding material using a laser beam as a heat source. An illuminating device that illuminates the image, an imaging device that images the welded portion, means for integrating the luminance of the pixels of the captured image in a direction parallel to the traveling direction of the welding material over a predetermined range, and A seam position detecting device in a laser welding machine, comprising means for detecting a seam position before welding based on an integrated value.

The traveling direction of the welder is represented by the y coordinate, and the direction perpendicular thereto is represented by the x coordinate. Each pixel is represented by (x _i , y _j ), and the luminance of each pixel is B (x _i , y _j ). In this means, within the range of a ≦ j ≦ b, B (x _i , y _j ) is integrated with respect to j to obtain an integrated value S _B (x _i ). Based on this S _B (x _i ), the seam position before welding is detected. Therefore, similarly to the fifth means and the sixth means, the seam position can be detected based on the average value for a plurality of lines in the direction perpendicular to the traveling direction of the welded steel pipe. An accurate seam position can be detected.

Note that S _B (x _i ) calculated by this means is used instead of “the luminance of each pixel in one line in the direction perpendicular to the traveling direction of the welding material” in the fifth means or the sixth means. It is also possible to obtain an integral value or a temporal moving average within a certain time and detect a seam position before welding based on these values, and such a thing is also included in the scope of this means. .

An eighth means for solving the above-mentioned problem is an apparatus for detecting the position of a seam before welding in a laser welding machine for welding a butt portion (seam portion) of a welding material using a laser beam as a heat source, and laser irradiation. It also has a point detection device, and has a function of searching for a seam position only within a certain range from the laser irradiation point based on the laser irradiation point obtained by the laser irradiation point detection device. It is a seam position detection apparatus in a laser welding machine.

  In a steady state in actual equipment, the laser irradiation point and the seam position before welding are controlled to coincide with each other. Therefore, by detecting the laser irradiation point and searching for the seam assuming that the seam position is within a certain range based on it, the seam position can be determined without the influence of noise. it can. In particular, when the seam position detection device detects the seam by illuminating the welded portion with an illuminating device and detecting reflected light from the welded portion with an imaging device, the seam position is detected depending on how the illumination light strikes. Parts other than the part may appear dark, and in the case of a welded steel pipe, the peripheral part of the field of view of the imaging device may appear dark together with the seam part, resulting in noise in detecting the seam part. In this means, even in such a case, the seam position can be detected without being affected by noise.

  A ninth means for solving the above-mentioned problem is the eighth means, in which an illuminating device that illuminates the welded portion, an imaging device that images the welded portion, and a pixel of the imaged image are welded. Means for obtaining a pixel having a minimum luminance within a certain range from the laser irradiation point for one line or a plurality of lines in a direction perpendicular to the traveling direction of the material, and constant from the laser irradiation point on both sides around the pixel Means for separately obtaining a pixel having the maximum luminance within the range, and binarizing the image using the lower luminance of the two obtained pixels as a threshold, and calculating the center of gravity of the pixel having the luminance equal to or lower than the threshold A seam position detecting device in a laser welding machine comprising means for determining a position and determining the position of the center of gravity as a seam center position.

  In this means, in order to determine the seam portion, a threshold value for binarizing the image is automatically determined. When the reflected light that illuminates the welded portion is received, in many cases, the reflected light from the welded material portion tends to have a maximum value in the immediate vicinity of the seam portion. Therefore, as will be described in detail later, the pixel having the minimum luminance within a certain range from the laser irradiation point is obtained, and the pixel having the maximum luminance within the certain range from the laser irradiation point is obtained on both sides around the pixel. Obtained separately, the image is binarized using the lower of the two obtained pixels as a threshold, and the center of gravity of the pixel having the luminance equal to or lower than the threshold is determined, and this center of gravity is defined as the seam center position. By determining, the seam center position can be obtained accurately regardless of the change in the amount of reflected light.

Note that “determining a pixel having a minimum luminance within a certain range from the laser irradiation point for a plurality of lines” means that S _B (x _i ) is calculated for a plurality of lines as described in the seventh means. This is equivalent to calculating _i that minimizes S _B (x _i ) within a certain range from the laser irradiation point. Further, instead of obtaining S _B (x _i ), the integral value within a fixed time described in the fifth means and the temporal moving average value described in the sixth means may be used.

  A tenth means for solving the problem is either the eighth means or the ninth means, wherein the laser irradiation point detection device is any one of the first means to the third means. It is characterized by being.

  In this means, since any one of the first means to the third means is used as the laser irradiation point detection device, the laser irradiation point can be accurately obtained, and the seam position can be accurately obtained accordingly. become.

  The eleventh means for solving the problem is any one of the fifth means to the tenth means, wherein the minimum of the luminance of each pixel of the image captured by the imaging device within a predetermined time. Characterized in that, instead of using the captured image as it is for the subsequent signal processing, the image having the extracted minimum luminance is used for the subsequent signal processing. To do.

  In this means, since the subsequent signal processing is performed based on the extracted image having the minimum luminance, as described in the fourth means, it is possible to remove the influence of the spatter, and the seam. The portion can be recognized as an image in the darkest state, the seam portion is emphasized, and accurate position determination is possible.

  In the present invention, a high-level threshold is provided, the pixels of the imaging device are binarized, the barycentric position of the pixel (two-dimensional) corresponding to high luminance is obtained, and this position is set as the center of the laser irradiation point. The laser irradiation point can be accurately detected.

  Further, in the present invention, the luminance of each pixel of the image captured within a predetermined time is extracted, and an image having the extracted luminance as the luminance of each pixel is obtained. Since the laser irradiation point is detected based on the image, the position of the laser irradiation point can be accurately detected.

  In the present invention, since the above-mentioned inventions are combined, accurate laser irradiation point position detection is possible.

  Further, in the present invention, the luminance of each pixel of the image captured within a predetermined time is extracted, and an image having the extracted luminance as the luminance of each pixel is obtained. Since the seam position is determined based on the image, the influence of sputtering can be removed, and the seam portion is emphasized, and accurate position determination is possible.

  In the present invention, the integral value within a predetermined time of the luminance of each pixel of one line in a direction perpendicular to the traveling direction of the welding material is calculated, and the seam position before welding is calculated based on the calculated integral value. Is detected so that the seam position can be accurately detected.

  In the present invention, since the temporal moving average is used, the seam position can be continuously detected, and the seam position can be accurately detected.

  Further, in the present invention, the luminance of the pixels of the captured image is integrated in a direction parallel to the traveling direction of the welding material over a predetermined range, and the seam position before welding is calculated based on the calculated integrated value. Since it detects, the effect equivalent to the invention mentioned above is acquired.

  Further, in the present invention, by detecting the laser irradiation point and searching for the seam assuming that the seam position is within a certain range with reference to the laser irradiation point, the seam position can be determined without the influence of noise. A decision can be made.

  In the present invention, since the binarization threshold is automatically determined, the seam center position can be accurately obtained regardless of the change in the amount of reflected light.

  In the present invention, since the laser irradiation point detecting apparatus according to the above-described invention is used, the laser irradiation point can be accurately determined, and the seam position can be accurately determined accordingly.

  Further, in the present invention, instead of using the captured image as it is for the subsequent signal processing, the extracted image having the minimum luminance is used for the subsequent signal processing. In addition, the seam portion can be recognized as an image in the darkest state, and the seam portion is emphasized, and accurate position determination is possible.

FIG. 1 is a schematic diagram showing the configuration of an apparatus which is an example of an embodiment of the present invention. FIG. 2 is a diagram for explaining a laser irradiation point detection method by binarization processing. FIG. 3 is a schematic diagram showing a configuration of an apparatus as another example of the embodiment of the present invention. FIG. 4 is a diagram for explaining a method of calculating the minimum luminance image. FIG. 5 is a diagram for explaining a seam position detection method by integration processing. FIG. 6 is a diagram illustrating an example of a seam position detection method. FIG. 7 is a diagram illustrating an image in the case where the welding material is a pipe material, and a distribution of luminance integration values. FIG. 8 is a diagram for explaining a processing method when the seam search range is limited. FIG. 9 is a diagram illustrating a change in the integrated value of luminance when the luminance of the seam portion changes. FIG. 10 is a diagram for explaining an automatic threshold setting processing method.

  Hereinafter, examples of embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of an apparatus which is an example of an embodiment of the present invention. In FIG. 1, 1 is a steel plate as a welding material, 2 is a laser, 3 is a laser beam, 4 is a seam before welding, 5 is a weld bead, 6 is a projector, 7 is an imaging device, 8 is a laser irradiation position detection means, 9 is a seam position detecting means, and 10 is an automatic threshold setting means.

  The steel plate 1 is bent into a pipe shape, and a laser beam 3 is irradiated from the laser 2 to the attached portion (seam portion). As a result, the temperature of the seam portion 3 rises in the laser light irradiation portion, and the steel plate is melted and plasma is generated. The seam portion 3 is melted and welded to form a weld bead 5 to produce a welded steel pipe. The welded steel pipe travels to the right side of the figure, and welding is performed continuously.

  The light from the projector 6 is irradiated to the welded part (near the laser light irradiation part). The imaging device 7 images the irradiation light reflected by the steel plate 1 and the light from the plasma. Since the light from the plasma is much stronger than the reflected light from the steel plate 1, if the sensitivity of the imaging device is such that the imaging device is not saturated by the light from the plasma, the reflected light from the steel plate 1 is It becomes impossible to observe sufficiently.

  Therefore, the irradiation light from the projector 6 is changed to ultraviolet light, and an ultraviolet transmission filter is provided in front of the imaging device 7 to reduce the laser light and the visible and infrared light amounts of the plasma light emitted from the material melted at high temperature. Let As a result, the irradiating laser itself becomes invisible, but the plasma light emitted from the melted material can be attenuated and detected. Since the position of the plasma light is generated at the position of the material melted by the laser irradiation, detecting the position of the plasma light is equivalent to detecting the position of the laser irradiation position and the position of the molten pool.

  The laser irradiation position detection means 8 detects the laser irradiation position from the plasma light imaged by the imaging device 7. As described above, the plasma light is generated from the position where the laser is irradiated and the material is melted, and the brightness is higher than that of the reflected light from the surrounding steel plate 1, so that the reflected light from the surrounding steel plate is not extracted. When a threshold is set and binarization is performed, only plasma light is extracted. By obtaining the position of the center of gravity of this binary image, the plasma light, that is, the laser irradiation position can be obtained.

  An example of this detection method is shown in FIG. In the following figures, the same elements as those shown in the previous figures are denoted by the same reference numerals and description thereof is omitted. In FIG. 2, 12 is plasma light, and 13 is a binarized image. FIG. 2A shows an example of a captured image, where the seam portion 4 before welding is the darkest, then the steel plate 1 surface and the weld bead 5 are light and the plasma light 12 is the brightest. By binarizing this image, the binarized image is as shown in FIG. 2B, and only the portion corresponding to the plasma light 12 is extracted as the binarized image 13. The laser irradiation position detection means 8 calculates the center of gravity of the binarized image 13 and sets it as the laser irradiation position.

  By the way, the plasma light 12 is actually flame-like light, and its size, shape, and brightness are constantly changing. Therefore, the laser irradiation position may be erroneously detected simply by binarizing the captured image and obtaining the position of the center of gravity as described above. A schematic diagram of an embodiment of the present invention that prevents the occurrence of such problems is shown in FIG. The embodiment shown in FIG. 3 is different from the embodiment shown in FIG. 1 in that the minimum luminance image calculation means 11 is provided after the imaging device 7.

The minimum luminance image calculation means 11 obtains the minimum luminance for a certain time for each pixel of the captured image and sets it as the minimum luminance of the pixel. That is, the coordinates of the pixel is (i, j), and the A _t (i, j) and the luminance in the imaging timing t, the said predetermined time is 10 imaging timing, minimum brightness image calculation unit 11, A ₁ ( The smallest of i, j) to A ₁₀ (i, j) is selected for each pixel. Then, this is _defined as A _min (i, j), and an image formed by A _min (i, j) is formed. This operation is repeated every 10 imaging timings. Instead of obtaining the minimum value at every 10 imaging timings, the smallest _one of A ₁ (i, j) to A ₁₀ (i, j) is first used, and A ₂ (i, j) is used at the next imaging timing. It is also possible to shift the targets for obtaining the minimum value one by one, such as the smallest one of .about.A ₁₁ (i, j), and to obtain the minimum value at every imaging timing.

In FIG. 3, the image formed by A _min (i, j) is given to the laser irradiation position detecting means 8, and the laser irradiation position detecting means 8 is the same as in the embodiment shown in FIG. The laser irradiation position is detected by binarizing the image and obtaining the center of gravity of the binarized image. According to this method, the laser irradiation position can be stably detected even if the size, shape, and brightness of the plasma light 12 change every moment.

  This is shown in FIG. 4, (a) to (c) are actual captured images, (a) is when the plasma light 12 is small, (b) is when the plasma light is large and flows like a flame, (c) Shows the case where the plasma light is large but almost circular. (d) is an output image of the minimum luminance image calculating means 11, and it can be seen that the plasma light 12 becomes the minimum, and the flowing image as shown in (b) is erased. For this reason, if the minimum luminance image calculation means 11 is provided, the laser irradiation position can be detected stably. Even when the image after passing through the minimum luminance image calculation device 11 is processed by another method to obtain the laser irradiation position, this effect can be obtained similarly.

  In order to perform optimum welding, it is necessary to detect the laser irradiation position and simultaneously detect the position of the seam 4 to control the positional relationship. The seam portion 4 before welding is in a state where there are some gaps between the materials to be welded, and even when light is applied, the light hardly reflects from the position of the seam 4. By utilizing this property, light is applied to the material around the seam 4 position by the projector 6 in FIGS. 1 and 3, the irradiated surface is imaged by the imaging device 7, and the seam position is imaged by the seam position detecting means 9. It is detected as a dark place on the screen.

  The seam position detection device 9 inputs the luminance of pixels for one line in a direction perpendicular to the direction of the welded steel pipe away from the position where the plasma light 12 is imaged on the captured image plane. This is shown in FIG. In FIG. 5, (a) shows a captured image. In the figure, the welded steel pipe is traveling in the lower direction of the screen, and is located at a position slightly away from the light receiving surface of the plasma light 12, one line 14 minutes in a direction perpendicular to the steel pipe traveling direction (horizontal direction in the figure). The luminance is input to the seam position detection device 9.

  Examples of the input luminance are shown in FIGS. 5 (b) and 5 (c). In these figures, the horizontal axis represents the horizontal position, and the vertical axis represents the luminance of the pixel corresponding to each position. In these figures, since the luminance is greatly reduced at the position of the seam 4, the position of the seam 4 can be detected by detecting this position. However, as can be seen by comparing (b) and (c), the rate of decrease in luminance at the seam portion 4 changes with time, and the luminance of the steel plate 1 portion also changes, although not clearly shown in the figure. Therefore, detecting the position of the seam 4 with only one line of information may lead to erroneous detection.

  Therefore, the seam position detecting device 9 integrates the luminance of each pixel for one line for a certain time for each pixel. Thereby, an integral value as shown in FIG. 5 (d) is obtained. In FIG. 5 (a), since the steel pipe is moving downward, the luminance within a predetermined length range of the seam portion is integrated. This eliminates short-term noise and small fluctuations. Although not shown, the same result can be obtained by taking a temporal moving average instead of integration. Also, instead of integrating the luminance of each pixel for one line for each pixel for a certain period of time or taking a moving average, the luminance of the pixel in the portion indicated as the luminance integration range in FIG. The same effect can be obtained by integrating in the length direction of the steel pipe (longitudinal direction in FIG. 5 (a)).

  The seam position detection device 9 detects the position of the seam 4 by processing the integrated value. An example is shown in FIG. In FIG. 6A, the point where the luminance is lowest is determined as the seam position (seam center). In FIG. 6B, a threshold value is provided and binarization is performed thereby, and the position of the center of gravity of the portion A where the luminance is equal to or lower than the threshold value is determined as the seam position (seam center).

  When the welding object is a steel pipe, as shown in FIG. 7 (a), the image is picked up with the luminance at the periphery of the image lowered. In such a case, the time integral value of the pixels of one line for seam detection is as shown in FIG. 7B, and portions below the threshold value occur at the seam portion and at both ends, and in some cases the luminance at both ends. May be lower than the brightness of the seam portion. Therefore, in such a case, if the calculations shown in FIGS. 6A and 6B are performed, there is a risk of erroneous detection.

  As a countermeasure against this, the seam position detection device 9 has a function of searching for the seam position only within a certain range from the laser irradiation point with reference to the laser irradiation point (same as the plasma light position). This function will be described with reference to FIG. FIG. 8 corresponds to FIG. 7B, where the horizontal axis represents the horizontal position of the image, and the vertical axis represents the integral of the brightness of each pixel for one detected line within a certain time. Indicates the value. The plasma light position is detected by, for example, the method described above.

  As shown in FIG. 8, the data to be subjected to the seam position detection process is limited to data within a certain distance from side to side with respect to the plasma light position. In the steady welding state, the laser beam irradiation position and the seam position do not deviate so much, so by limiting the range that is subject to data processing in this way, it is possible to detect the point where the brightness of the surrounding area decreases. The seam position can be accurately detected even in the situation shown in FIG. As the seam position detection method, for example, the process shown in FIG. 6 may be performed only for the data to be processed.

  However, even if such a measure is taken, the detection of the seam portion may be unstable. This is shown in FIG. FIGS. 9A, 9B, and 9C correspond to FIG. 5D, and show the integrated values within a certain time of the brightness of each pixel that is detected for one line. As described above, the brightness of the reflected light amount reflected from 1 part of the steel sheet and the brightness of the seam part greatly change depending on the case, and the binarization based on the threshold shown in FIG. It may not be clear whether the point indicates the seam center.

  As a countermeasure against this, as shown in FIG. 1, automatic threshold value determination means 10 is provided, and the output is given to the seam position detection device 9. The operation of the automatic threshold value determination means 10 will be described with reference to FIG. In FIG. 10, the position S at which the luminance is minimum is obtained within the seam position detection processing target range (between P and P ′) determined by the method shown in FIG. 8 with reference to the plasma light detection position. Next, the luminance is observed in the directions from S to P and P ', respectively, and the positions A and A' where the maximum luminance is first obtained are obtained. Next, the smaller one of the luminances of A and A ′ is determined as a threshold value and applied to the seam position detecting means 9. After that, the seam position detection means 9 determines the seam position C by determining the center of gravity position C of the seam portion area B that is equal to or less than the threshold, as in the method shown in FIG. This makes it possible to accurately and stably measure the laser irradiation position and the seam position even if there is a change in luminance, surface property, or intensity of plasma light on the material surface.

  During welding, a phenomenon called spatter in which the material melted by the laser flies may occur. If the material melted by sputtering flies over the seam position, noise may occur when measuring a seam position with low brightness. In addition, the seam portion also changes in luminance due to contamination of the material and luminance change of the plasma light. In order to remove these influences, as shown in FIG. 3, it is preferable to use a signal that has passed through the minimum luminance image calculation means 11 used in the laser irradiation point detection device as an input signal of the seam position detection device 9.

  That is, as shown in FIGS. 4A to 4C, even if the luminance of the seam portion 4 varies depending on the location, the signal that has passed through the minimum luminance image calculation means 11 is shown in (d). Since the signal having the lowest luminance is selected as described above, the darkness of the seam portion is emphasized. Further, even if the material melted by sputtering crosses over the seam 4, the influence is erased in the minimum luminance image calculation means 11. Therefore, the position of the seam 4 can be measured accurately.

DESCRIPTION OF SYMBOLS 1 ... Steel plate 2 which is welding material ... Laser 3 ... Laser beam 4 ... Seam part 5 before welding ... Weld bead 6 ... Projector 7 ... Imaging device 8 ... Laser irradiation position detection means 9 ... Seam position detection means 10 ... Automatic threshold setting Means 11 ... Minimum luminance image calculation means 12 ... Plasma light 13 ... Binary image 14 ... Detection target line

Claims (5)

  An apparatus for detecting the position of a seam before welding in a laser welding machine that welds a butt portion of a welding material using a laser beam as a heat source, and also includes a laser irradiation point detection device, and is obtained by the laser irradiation point detection device. A seam position detection device in a laser welding machine having a function of searching for a seam position only within a certain range from a laser irradiation point on the basis of the laser irradiation point, an illumination device that illuminates a welded portion, and welding An image pickup device for picking up an image of a portion and a pixel having a minimum luminance within a certain range from the laser irradiation point with respect to one line or a plurality of lines in a direction perpendicular to the traveling direction of the welding material among pixels of the picked-up image A means for obtaining, a means for separately obtaining a pixel having a maximum luminance within a certain range from the laser irradiation point on both sides of the pixel; Means for binarizing the image using the lower one of the luminances of the pixels as a threshold value, obtaining a centroid position of a pixel having a luminance equal to or lower than the threshold value, and determining the centroid position as a seam center position. A seam position detecting device in a laser welding machine. An apparatus for detecting the position of a seam before welding in a laser welding machine that welds a butt portion of a welding material using a laser beam as a heat source, and also includes a laser irradiation point detection device, and is obtained by the laser irradiation point detection device A seam position detection device in a laser welding machine having a function of searching for a seam position only within a certain range from the laser irradiation point with respect to the laser irradiation point,
An apparatus for detecting a laser irradiation point in a laser welding machine that welds a butted portion of a welding material using a laser beam as a heat source, an imaging device for imaging a welded portion, means for binarizing the captured image, 2 A laser welding machine having a laser irradiation point detecting device in a laser welding machine, characterized in that it comprises means for calculating a centroid position of a digitized high-intensity part and detecting it as a laser irradiation point Seam position detector. A seam position detecting device in a laser welding machine according to claim 2 ,
An apparatus for detecting a laser irradiation point in a laser welding machine that welds a butt portion of a welding material using a laser beam as a heat source, and an imaging device that images a welded portion and each pixel of an image captured within a predetermined time And a minimum luminance extracting means for extracting the lowest luminance among the luminances, and a means for detecting a laser irradiation point based on an image constituted by the extracted pixels having the minimum luminance. A seam position detecting device in a laser welding machine, comprising a laser irradiation point detecting device in a laser welding machine. A seam position detecting device in a laser welding machine according to claim 2 ,
An apparatus for detecting a laser irradiation point in a laser welding machine that welds a butt portion of a welding material using a laser beam as a heat source, and an imaging device that images a welded portion and each pixel of an image captured within a predetermined time And a minimum luminance extracting means for extracting the lowest luminance among the luminances, and a means for detecting a laser irradiation point based on an image constituted by the extracted pixels having the minimum luminance. A laser irradiation point detection device in a laser welding machine,
The means for detecting the laser irradiation point is a means for binarizing an image constituted by the pixels having the minimum luminance, and a means for calculating the center of gravity position of the binarized high luminance portion and detecting it as a laser irradiation point And a seam position detecting device in a laser welding machine. A seam position detector in a laser welding machine as claimed in any one of claims 1 to 4, the smallest of the brightness of each pixel of the image captured by the imaging device within a predetermined time Laser having minimum luminance extraction means for extracting luminance, and using an image having the extracted minimum luminance for subsequent signal processing instead of using the captured image as it is for subsequent signal processing Seam position detection device for welding machines.

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