MXPA97005701A

MXPA97005701A - Method and apparatus for following and inspecting a edge or sea

Info

Publication number: MXPA97005701A
Application number: MXPA/A/1997/005701A
Authority: MX
Inventors: Buchmann Christa; Wildmann Daniel
Original assignee: Elpatronic Ag
Priority date: 1996-07-29
Filing date: 1997-07-28
Publication date: 1998-02-01

Abstract

The present invention relates to a system for tracking and inspecting a common edge (13) between the two preforms (6, 7) of sheet metal that are to be welded together, a line pattern (5) is projected across the edge (13) by means of a projector (2) and the image is formed by a camera (3). The captured image is analyzed to derive from the trace of the information of the lines on the clear between the preforms or on the edge rail. The projected pattern has several lines with different light intensities. When the photographed image is processed, then it is possible, even if there is variation in the reflective characteristics of the sheet metal preforms, to select a line that is neither too weak nor too bright in the image obtained and which is therefore can use for meaningful analysis

Description

METHOD AND APPARATUS FOR FOLLOWING AND INSPECTING A EDGE OR MARGIN DESCRIPTION OF THE INVENTION The invention relates to a method according to the introductory part of claim 1, and to an apparatus according to the introductory part of claim 6. The invention also relates to a method and an apparatus according to the introductory parts of the invention. claims 10 and 12, respectively, and to a method and an apparatus according to the introductory parts of claims 13 and 14 respectively. It is known to weld sheet metal to form larger components (called custom made preforms), which are frequently subjected to a forming process. An example of a field in which such "custom-made preforms" are used in the motor vehicle industry. The welding of the metal prefrr ^ a = can be done by mesh welding and laser welding. Because the weld seam is subjected to the forming process together with the preforms, it is essential that the entire seam be of good quality. The preforms that are to be welded are fed to the welding point with the edges that are to be welded together in contact. It is import .- *? - * "the focused laser beam follow the common edge of the juxtaposed preforms as accurately as possible.To achieve this, it makes use of devices that determine the precise lane of the edge ahead of the welding area, thus allowing the laser beam to be guided consistently during welding.A known device does this by projecting a pattern of lines of constant intensity transversely across the edge, the image of this pattern being formed by a camera, and the obtained image is analyzed by computer to derive from the trace of at least one of the lines the common edge rail or the clear between the preforms at that point, in this way, the edge and the clearing are on track throughout The welding beam is controlled in its entire length in front of the weld zone and the laser beam is controlled as the weld is carried out. The welding can be determined in a similar way, allowing the detection of welding defects. Both to follow the edge before welding and, in particular, to inspect the edge or weld seam after welding, the problem arises that there is much variation in the reflectibility of the sheet metal preforms. The individual preforms may have different surface coatings; an oil film, or a film that is not oil, a glossy or opaque finish, traces of smoke, etc. The large differences in brightness due to these factors can go beyond the dynamic scale of the camera used, causing the image lines to be formed to be too bright or too dim and making the image difficult or impossible to achieve. play. If an edge is followed, it may be necessary to reduce the travel speed, or welding defects may occur; If an edge is inspected, it can be difficult to detect the defects in some cases, or it can be assumed that there are defects where there are none. Therefore, the problem that the invention seeks to solve is to improve the method of the class exposed to the principle and / or the apparatus of the type exposed at the beginning to allow the captured image to be analyzed without any problem, even under adverse conditions. According to a first aspect of the invention, this is achieved by the erratic aspects of claim 1 and the claim. respectively. When projecting lines of different brilliance on the preforms, it improves the possibility of interpreting the photograph. On a bright, highly reflective preform, the evaluation unit can use a correctly reflected line, of lower intensity for the evaluation, and to ignore the too bright lines of higher intensity. On a dark, poorly reflective preform, the line with greater intensity can provide good results. In this way, a very good result can be easily obtained both in the edge tracking and in the inspection of the edge. The light intensities of the individual lines may be different and may reside, for example, between 15% and 100%; You can also provide lines with the same intensity. In a preferred example, 5 lines are provided, with intensities of 25% (two lines), 50% (two lines) and 100% (one line). According to another aspect of the invention, the problem is solved by the characteristic aspects of claims 10 and 12 respectively. In this case, each image analysis determines if the brightness of the lines resides within specific limits, if not, a control signal is generated that acts on the exposed control of the camera device for the next shot, in such a way that the next picture is brighter or darker. It is also possible to combine both aspects of the invention, in such a way that the control of the exposure of the camera based on the result of the image just seen is done in addition to using the different brightness lines.

According to a third aspect of the invention, the problem is solved by the characteristic aspects of claims 13 and 14 respectively. By varying the intensity brightness of the total projector, it is possible to compensate the reflectivity of different preforms. The embodiments of the invention given by way of example will now be described in detail with reference to the figures, in which: Figure 1 shows schematically a basic arrangement of the projector and the line camera, and Figure 2 is a schematic illustration with an edge tracking apparatus and two edge inspection or welding devices. Figure 1 shows two preforms 6 and 7 which are juxtaposed and have a common edge 13. These preforms are joined along the edge 13, for example by laser welding. To follow the rail path and c to inspect the weld seam, it is known to project a number of lines 5 of light transversely across the edge 13 on that edge and the adjacent region of the two preforms. In the example shown, only three lines are illustrated, but some other number of lines can be used. The lines extend at an angle of 90 'with respect to, or an oblique angle with respect to the edge 13. A .::. 3 * 1 view of an image-forming device 3, which can be in particular a CCD camera. The projector 2 for projecting the lines 5 is preferably formed by a laser light supply in front of which a diffraction grating is arranged to generate the lines 5 as diffraction lines. The image captured by the camera 3 is analyzed in an image evaluation unit to determine from the rail of at least one of the lines 5, the clear lane between the preforms 6 and 7 along the edge 13, or , as it may be the case, to determine the rail of the weld seam after the preforms are welded. Figure 2 shows such an apparatus in which a number of arrangements according to Figure 1 have been provided, that is, an arrangement 1 ahead of the welding zone and two arrangements 10 and 11 that go behind the welding zone , as can be seen in Figure 2, the preforms 6 and 7, which can be, for example, 2 m long in the direction of the welding, are carried through the apparatus in the direction of the arrows A by means of a conveyor device ( it is not shown) with its position located precisely. A metal reforming device having rollers 8 and 9 can be provided in front of the edge tracking apparatus 1. By deforming the thickest white 6, this device reduces any gap between the preforms to a minimum. The precise lane of the glade is then determined by the edge tracking arrangement 1, as already described, by projecting a pattern of lines across the edge 13 and by observing by means of a camera, and evaluating, the line pattern. For example, five parallel lines can be projected across the edge by a projection device. The camera image of arrangement 1 passes to an evaluation unit 18"which determines the precise lane of the clearing. The evaluation unit 18 transmits control signals to a control unit 14, which, in turn, controls the laser light supply 15 in such a way that the laser light beam (only shown schematically) for welding the preforms 6 and 7 follows exactly the rail of the clearing along the edge 13. After the welding zone (for example in the direction of the conveyor), behind the laser beam, an arrangement 10 similar to that shown * r Figure 1 is disposed above the weld seam, and an additional arrangement 11, similar to that shown in Figure 1 is disposed below the preforms. These two arrangements also project lines through the edge 13, and therefore through the weld seam. From the images of the lines, the evaluation units 17 and 17 are able to determine the lane ie the weld seam and therefore to carry out a welding inspection for various types of defects, as is known per se, and will not be described in detail in the present. The evaluation units 16 and 17 transmit an appropriate signal to the control unit 14 and can transmit a signal to a higher range control 19 to indicate whether the mixed panel consisting of two welded preforms 6 and 7 satisfies, or does not satisfy the quality requirements. According to one aspect of the present invention, the lines 5 are projected in such a way that different lines have different light intensities. For example: of the three lines shown in Figure 1, the brightest line can have a light intensity of 100%, a second line can have a light intensity of 60%, and a third line can have a light intensity of 30%. In a preferred embodiment, 5 lines are projected as diffraction lines. In this mode, the central diffraction line of zero order has, for example, the intensity of 100%. Each of the first order diffraction lines on either side of the first diffraction line has an intensity of 50%, and each of the distant second order diffraction lines have a light intensity of 25%. Line projectors with diffraction gratings and laser beams capable of meeting the requirements are manufactured for example by LASIRIS INCORPORATED of 3549 Ashby, Quebec, Canada. Thanks to the different light intensities of the lines 5, the images captured by the camera 3 can provide good detection of at least one of the lines, even when there are different flexibilities of the preform surfaces along the edge 13, then From the selection of the appropriate line or lines through the evaluation unit, good evaluation of images is possible. In this way the clearance rail, or the rail of the weld seam, can be established accurately even under difficult reflection conditions on the surface of the foil metal. According to another aspect of the invention, the individual cameras receive an exposure control signal 20 which in Figure 2 is shown transmitted by the control unit 14, but which can also be transmitted to the camera directly by the unit I? of associated evaluation or, as the case may be, 16 f 17. The control signal 20 contains the information that the camera must select an exposure time that is greater or less than, or equal to, that of the photograph previous when you capture the next image. If the camera used is a CCD camera, the control signal can regulate the integration time of the CCD element, instead of the time of e i *: t í- Cor. Based on the information that the preceding image of lines 5 has been too dark or too bright, the exposure of the camera in question is modified so for the next shot. Consequently this capacity also allows an improvement of the recognition of the projected lines in the obtained images. Preferably, • the integration is always done over the same edge or seam length, despite the travel speed. Both aspects of the invention can also be used in combination. The lines of different intensity can be projected through the edge 13, and in addition the modification of the exposure of an individual camera can be provided. Suitable cameras, in particular CCD cameras, are commercially available, and need not be described in detail herein. According to a further aspect of the invention, the total brightness of the projected lines can be controlled. In this case, it is not the exposure time of the camera or the integration time of the CCD element which is modified by a signal from the evaluation unit, but the brightness of the line projector. This facility can be combined with either or both of the two aspects described above. Therefore, the brightness of a line projector projecting lines of equal intensity can be controlled, or the brightness of a line projector that produces different intensity line can be controlled, as described above. The brightness control can also be combined with the control of the exposure time or the integration time, with the controller unit in this case taking out the two control signals, one for the projector and one for the camera. The three aspects of the invention can be presented as follows: Stage EFFECT 1. The intensity lines Local differences in the different projected through reflection through the line projector. Edge or seam can be compensated. 2. Integration time or exposure setting and triggering speed of the element therefore the image always modified camera CCD (it prefers the brightness irisma, so that the preferably with resolution is always constant despite the same length of travel speed, edge or seam) 3. Basic intensity control Equal brightness of the output light from the scattered projector and reflected to line despite the general reflection characteristics of the foil metal preform

Claims

1. A method for tracking the edge before welding and / or inspecting the edge or weld seam after welding, in welding together with the sheet metal preforms along a common edge of the preforms, where the light is projected onto the preforms in the form of a plurality of lines that extend transversely across the edge and the image of the lines captured by a camera is evaluated, characterized in that the different light intensity lines are projected onto the preforms .

2. The method according to claim 1, characterized in that the lines have light intensities in the range from 100% to 5%.

3. The caaforwidai method falls from claim 1 or claim 2, characterized by "that the additional lines are projected that are of equal intensity with respect to the lines of such lines of different light intensity.

4. The method of compliance with claim 3, characterized in that the zinc "a * is projected: a line with an intensity of 100%, two lines with an intensity of 50% and two lines with an intensity of 25%.

5. The method according to claim 4, characterized in that the five lines are produced by a diffraction grating, a center line of the order of zero diffraction having intensity of 100%, the lines of first order of diffraction being on either side of the line central having intensity of 50% and the external lines of the second diffraction order having an intensity of 25%.

6. An apparatus for tracking the edge before welding and / or inspecting the welding edge or seam after welding, in welding together with the sheet metal preforms along a common edge, comprising a device for generate a plurality of lines that are extier.de :: through the edge, a camera device to capture an image of the lines and evaluation means to evaluate the image, characterized in that the device to generate the lines is arranged to produce lines of different intensity and the evaluation means are arranged to select lines for evaluation based on the brightness of the scattered or reflected radiation.

7. The apparatus in accordance with the claim 6, characterized in that the device for generating lines comprises a laser light supply and a diffraction grating.

8. The apparatus in accordance with the claim 7, characterized in that the device is designed to generate five diffraction lines, a diffraction line of the order of zero having an intensity of 100%, the diffraction lines of the first order an intensity of approximately 50% and the lines of diffraction of the second order an intensity of approximately 25%.

9. The apparatus according to claim 6, characterized in that the camera device comprises at least one CCD camera.

10. A method for tracking the edge before welding and / or inspecting the edge or weld seam after welding, in welding together with the sheet metal preforms along a common edge, where the light is projected onto the preforms in the form of a plurality of lines extending transversely across the edge and the image of the lines captured by a camera evaluated by evaluation means, characterized in that the evaluation means have a variable exposure control controllable, and because a part of the evaluation of each image is made a determination whether the exposure needs to modify the next image, and if so, a control signal is transmitted to the camera to modify the exposure.

11. The method according to claim 10, characterized in that the CCD camera is used and because the exposure is controlled by modifying the integration time of the CCD element or the firing rate of the camera trigger, the integration in each case being preferably made over an optional constant length of edge or seam.

12. An apparatus for tracking the edge before welding and / or inspection of the welding edge or seam after welding, in welding together with the sheet metal preforms along a common edge, comprising a device for generating a plurality of light lines extending transversely across the edge, a camera device for capturing an image of the lines and evaluation means for evaluating the image, characterized in that the camera device comprises a camera with controllable exposure control, in particular a CCD camera with controllable integration time of the CCD element and / or controllable trigger speed, and in that the evaluation means are arranged to output a control signal for the camera device.

13. A method for tracking the edge before welding and / or inspection of the edge or weld seam after welding, in welding together with the sheet metal preforms along ur. common edge where the light is projected onto the preforms in the form of a plurality of lines that extend transversely across the edge and the image of the lines captured by a camera is evaluated, characterized in that a projector for such projection of the lines it is controllable in its intensity of light, and because as part of the evaluation of each image a determination is made whether the line width of the lines needs sc * - í.car »e for the next image, and if so , a signal co-transmits to the projector to modify the intensity.

14. An apparatus for tracking the edge before welding and / or inspection of the welding edge or seam after welding, in the welding together with the sheet metal preforms to the large ae ur. common device, comprising a device for generating a plurality of lines of light extending transversely across the edge, a camera device for capturing an image of the lines and evaluation means for evaluating the image, characterized in that the device for generating the lines comprises a line projector with a control input for the light intensity of the light supply, and in that the evaluation means are arranged to take out a control signal for the line projector.