Method for testing welds and device for photographing welds, in particular for carrying out the aforementioned method

Abstract

Method for inspecting welds or other structural details, wherein the welds are photographed with a camera system to record image data, wherein a camera system with two or more cameras is used and image data generated with this camera system are used to calculate a 3D point cloud using a photogrammetric matching method, for example Least Squares Matching (LSM) and Structure from Motion (SfM), whereby a digital 3D model of the photographed weld seam (2) is created, characterized by that in each position a partial surface is already reconstructed and several partial surfaces are transformed to each other via the ICP algorithm or are directly fused together if the camera orientation is known, and that the assignment of the point clouds to each other is carried out via visual odometry and an algorithm such as the Iterative Closest Point (ICP) algorithm.

Description

[0001] The invention relates to a method for inspecting weld seams or other structural details, in which the weld seams are photographed with a camera system in order to record image data, wherein a camera system with two or more cameras is used and image data generated with this camera system is used to calculate a 3D point cloud with the aid of a photogrammetric assignment method, for example least squares matching (LSM) and structure from motion (SfM), wherein a digital 3D model of the photographed weld seam (2) is created.

[0002] The invention further relates to a device for photographing weld seams or other structural details, comprising at least one housing carrying at least one camera whose camera lens is directed outwards, in particular for carrying out the aforementioned method.

[0003] Welds are used to connect technical structures. This can occur, for example, in pipeline construction, both in air and underwater. Other structural details may also need to be examined in air or underwater.

[0004] Welds are regularly inspected and assessed by experienced individuals. Their experience is crucial for detecting defects, particularly in welds. This visual inspection is considered highly important. However, underwater, this visual inspection can only be performed by a person who is also underwater, such as a diver. Their vision is limited by their eyesight and the external conditions. External conditions include factors such as diving equipment, currents, water turbidity, and (artificial) lighting. Other factors, such as water turbidity, also play a role.

[0005] The results of the visual inspection cannot be verified by third parties.

[0006] For this reason, inspection using a camera system has already been proposed. In the specialist article Ekkel, T. [et al.]: Precise laser-based optical 3D measurement of welding seams under water. The international archives of the photogrammetry, remote sensing and spatial information sciences. Underwater 3D recording and modeling, 16 - 17 April 2015, Piano di Sorrento, Italy, Vol. XL-5 / W5, 2015, pp. 117-122. DOI: 10.5194 / isprsarchives-XL-5-W5-117-2015, a camera system and a linear laser were used to record a laser line projected onto the components to be inspected using a stereo camera system, which in turn is positioned in space using control points. Here, a camera system was used, and a reference field was used to locate the camera system in space. The cameras, which are installed in an underwater housing, for example, are moved over the weld seam and take images. The reference field serves to locate the camera with high precision.At each camera position, a 3D profile of the laser line is calculated, resulting in a complete 3D point cloud of the scanned surface along the travel path. The known system therefore relies on the external reference provided by the reference field for positioning. The disadvantage of this is that the frame is comparatively far away. Furthermore, the system's accuracy is limited, and it can only be used under good visibility conditions.

[0007] A generic method is known from the technical article by Nietiedt, S.; Kahmen, O.; and Luhmann, T.: Investigation of orientation and matching methods for high-precision 3D surface detection of weld seams with a mobile camera system. Publications of the DGPF, Volume 28, 2019, pp. 711-719. WO 2021 / 080498 A1 describes a method for inspecting a weld seam using a triangulation sensor, while US 2019 / 0 204 715 A1 and DE 20 2006 001 267 U1 describe anti-glare devices for camera housings. Further prior art is available from the publications Kang, L., Wu, L., and Yang, YH.: Two-View Underwater Structure and Motion for Cameras under Flat Refractive Interfaces. Computer Vision – ECCV 2012. ECCV 2012. Lecture Notes in Computer Science, Vol. 7575. Springer, Berlin, Heidelberg. https: / / doi.org / 10.1007 / 978-3-642-33765-9_22 and US 2018 / 0 174 327 A1.

[0008] The invention is based on the object of providing a method of the type mentioned above that further improves the inspection of weld seams and other structural details. Furthermore, a device for imaging weld seams of the type mentioned above is to be provided.

[0009] With regard to the method, this object is achieved according to the invention in that a partial surface is already reconstructed in each position and several partial surfaces are transformed to one another via the ICP algorithm or are directly fused with one another if the camera orientation is known, and that the assignment of the point clouds to one another is carried out via a visual odometry and an algorithm, such as the Iterative Closest Point (ICP) algorithm.

[0010] When testing weld seams underwater, for example, a diver can record data that can later be viewed by one or more inspectors at any time and in any location. This is advantageously done with high quality because the cameras have a better resolution than the human eye and are based on optimized lighting. The welded joint is inspected digitally, using automatic analysis, or visually using interactive analysis on the screen, and leads to a classification of the joint in accordance with applicable standards. The test can be repeated at any time, e.g. in the event of a later failure, which cannot be done underwater. The results are recorded and archived digitally and can be partially automated. The data basis also enables a 3D change analysis of the test object after multiple tests over a certain period of time.

[0011] With the method according to the invention, a 3D model of the surface of the welded joint can be generated by analyzing two or more images. This model can then be used to digitally inspect the weld. Measurements that, for example, a diver would manually record and document on-site using state-of-the-art technology can be interactively digitally recorded and documented after the 3D measurement using the method according to the invention, independent of time and location. The high-resolution image data of the weld used to calculate the 3D model are archived, providing additional visual and objective evidence.

[0012] In the method according to the invention, the camera system is located in space from the camera system and can be additionally supported by a reference frame.

[0013] According to the invention, a camera system with two or more cameras is used for this purpose. Image data generated by this camera system is used to calculate a 3D point cloud using a photogrammetric image matching method, in particular least-squares matching (LSM) and structure from motion (SfM). A reference frame can then be dispensed with, as the camera's location is advantageously determined from the image data. The point clouds can be assigned to one another, for example, using visual odometry and the so-called iterative closest point (ICP) algorithm. The measurement principle for calculating a single point cloud remains the same (LSM, SfM).

[0014] According to the method according to the invention, a partial surface is reconstructed at each position. Multiple partial surfaces can then be transformed to one another using a method such as the (ICP) algorithm, or, if the camera orientation is known, directly merged.

[0015] With the method according to the invention, inspection-relevant geometries, such as the A dimension or the height of a penetration undercut, can be automatically determined from the surface data. An inspector can receive the automatically pre-evaluated data and then, based on their experience and all image and 3D data, decide how to evaluate the weld seam. This can be done in a dry office environment. It can also be done using machine learning (AI) methods. With the help of learning methods, 2D image and 3D geometric data can be used to inspect the seam for features (cracks, pores, etc.). Another advantage of the entire image (in contrast to the individual laser line) is that cracks are very clearly visible, even if they may not be resolvable in the 3D model. 2D image data and 3D surface data can also be combined for this purpose.In particular, the flexibly controllable lighting allows effects such as pores as local elevations to be highlighted in the image, which benefits the inspection process using the aforementioned methods.

[0016] With regard to the device-side solution to the stated problem, it is provided that a glare protection for the lens is arranged on the housing, wherein the glare protection is formed from separately mounted rod elements and wherein the rod elements are aligned parallel to one another and arranged in at least one row surrounding the lens.

[0017] The images required for the method described above are recorded using preferably two cameras with corresponding lenses. The evaluation of the images can only be as good as the quality of the images provided. Therefore, when recording a weld seam, care must be taken to ensure that extraneous light and external clouding do not impair the recording of the image. According to the invention, an anti-glare screen is provided which runs around the lens of the camera or cameras like a curtain. If there are two lenses, the curtain runs around both lenses. The anti-glare screen is made of individual rod elements that are mounted separately. The rod elements are aligned parallel to one another and arranged in a row that runs around the lens. If the lens has a circular circumference, the row that runs around the lens can run on a circular line.Other geometries are of course possible; for example, two lenses can be orbited with an approximately elliptical line.

[0018] The rod elements can be arranged discretely from one another, or each rod element can be connected to neighboring rod elements with connecting elements. Especially when the rod elements are connected or overlapped, a light-tight curtain can be created, which thus achieves good shading of the lens.

[0019] The connecting elements for the rod elements are preferably designed as sleeve elements that can be inserted into the rod elements. Sleeve elements and rod elements can be pushed into one another, while the rod elements can also be moved within the sleeve elements.

[0020] This makes it possible for some of the rod elements to be mounted on the housing at adjustable heights. Underwater images are regularly taken from a relatively short distance (< 10 cm). The lens must therefore be brought close to the object being photographed. Rod elements can be placed on the object and the lens moved closer to the object. The rod elements move due to their height-adjustable mounting on the housing of the device. The device can be flexibly aligned along the weld seam. The height-adjustable rod elements can each be loaded with a spring force. If the camera is positioned slightly further from the object, the rod elements can be returned to their original position by the spring force. Each height-adjustable rod element can, for example, be held in a spring element, with this spring element being attached to the housing of the device.

[0021] However, a further development also provides for some rod elements on the housing to be arranged at a fixed height. These rod elements are not movable, but fixed. They serve as spacers for moving the camera closer to, for example, a weld seam, in order to position the camera and its lens at the correct distance for the best imaging results. The height-adjustable rod elements therefore make it possible to adapt the device to the substrate at a defined shooting distance. A weld seam is surrounded by structures; the camera must be optimally positioned relative to the weld seam, and the rod elements of the curtain can then rest on the components surrounding the weld seam.

[0022] To further develop the invention, it is also provided that sections with low-friction geometries, such as spherical sections, are arranged at the free ends of the rod elements. These can be guided over objects with little friction, and spherical sections can more easily overcome cracks or protrusions. The rod elements can be made of plastic or stainless steel, while the sections can be made of rubber, PVS, or latex.

[0023] The lens(es) can be assigned a ring-shaped, individually controllable light source to illuminate the object being photographed. The light source is mounted eccentrically.

[0024] The lighting can generally be positioned either stationary or camera-mounted. It can be integrated into the glare shield in a ring-like manner (e.g., using individual LEDs). This makes the lighting part of the glare shield. Multiple, individually controllable LEDs provide uniform light and enable different illumination angles. This also enables other techniques such as Reflectance Transformation Imaging (RTI), which further enhances the quality of the visual, digital inspection of weld seams.

[0025] To further develop the device according to the invention, it can be provided with at least one device for introducing a medium into the area of ​​the glare shield in front of the lens. The existing medium can be displaced by introducing a medium into the glare shield. The existing medium can be, for example, a cloudy liquid underwater, which can be displaced by fresh, clean water by introducing it into the area in front of the lens in the area of ​​the glare shield.

[0026] By introducing a medium into the area of ​​the glare shield, a habitat is created in front of the lens and maintained permanently by a slight overpressure and the tightness of the habitat. This enables trouble-free image acquisition with at least one camera.

[0027] Embodiments of the device according to the invention are illustrated in the drawings. They show: Fig. 1: a schematic perspective view of a first embodiment of a device according to the invention for imaging weld seams, Fig. 2: a perspective view of a single part of the device according to Fig. 1, Fig. 3: two sectional views of the individual part according to Fig. 2, Fig. 4: further sectional views of the detail according to Fig. 2, Fig. 5: a schematic partial view of a second embodiment of a device according to the invention for imaging weld seams, Fig. 6: a scaled enlarged perspective view of a detail of the device according to Fig. 5, Fig. 7: a perspective view of a detail according to Fig. 5, Fig. 8: two sectional views of the detail according to Fig. 7, and Fig. 9: two perspective views of the detail according to Fig. 7.

[0028] Fig. 1 shows a housing 1 of a camera (not shown in detail). The camera has a lens that is held by the housing 1 and extends from the housing 1 toward a weld seam 2. The weld seam 2 is a fillet weld connecting two surface elements 3, 3'. The housing 1 of the camera supports a glare shield 4. The glare shield 4 is formed from rod elements 5.

[0029] The rod elements 5 are arranged parallel to each other and encircle the lens (not shown) in a circular line.

[0030] The rod elements 5 form a tight glare shield 4. The rod elements 5 are mounted in bearings 6, and the height of the rod elements 5 is adjustable within the bearings 6. The bearings 6 are attached to the camera housing.

[0031] Some rod elements 7 are not height-adjustable. These rod elements 7 are fixed; they serve as spacers for the camera housing 1 and thus for the camera itself. The rod elements 7 are directly attached to the weld seam 7.

[0032] Fig. Figure 2 shows a movable rod element 5. The rod element 5 is housed in a bearing 6, and a spring 8 is arranged within the bearing 6. This spring presses on the rod element 5. The mobility of the rod element 5 is indicated by a double arrow 9. A spherical section 10, particularly made of rubber, is arranged at the free end of the rod element 5.

[0033] Fig. 3 and Fig. 4 each show rod elements 5 in their receptacle in bearings 6. The pins 5 are rotatably arranged in the bearings 6, as indicated by double arrows 9. Fig. 4 and Fig. 5 shows that connecting elements 11 are assigned to the rod elements 5. These connecting elements 11 serve to connect the rod elements 5 to one another. The connecting elements 11 can be made of flexible materials, for example, thermoplastic polymer, polyethylene, rubber, or latex. Both the rotatable receptacle of the pins 5 in the bearings 6 and the specific design of the connecting elements 11 as spherical ends and C-shaped sleeve elements 12 enable the rod elements 5 to be laid along a circular, or geometrically flexible, line. This line is closed by the connecting elements 11.

[0034] In the second embodiment, a camera housing 1 is also assigned a mount 6. The camera is again positioned near a weld seam 2 for connecting surface elements 3. A glare shield 4 is again provided, which is formed from movable rod elements 5 and fixed rod elements 7.

[0035] Fig. Figure 6 shows how the glare shield 4 is positioned close to a surface element 3 with a butt-welded seam 2. The fixed-height rod element 7 is positioned close to the seam 2 and thus forms a spacer element for the camera. The other rod elements 5 rest tightly on the surface element 3 or on the seam 2. Here, too, the surface elements 5, 7 have spherical sections 10 at their ends closest to the surface element 3 or the weld 2.

[0036] Fig. 7 shows that the rod element 5 with spherical section 10 is again accommodated in a bearing 6, the height changeability is symbolized by the double arrow 9.

[0037] The two representations of the Fig. 8 show the bearing 6 and the rod element 5. Double arrows 9 show that the rod element 5 can be rotated within the bearing 6. The rod elements 5 carry lamellae 13 that protrude from the bearing 6. This results in Fig. 5 provides a large-area seal against light and ambient media. The bar elements 5, which are located in close proximity, can be rotated relative to each other so that their slats 13 abut or overlap. This seals the gap between adjacent slats 13.

Claims

[1] A method for inspecting welds or other structural details, in which the welds are photographed with a camera system to record image data, whereby a camera system with two or more cameras is used and image data generated with this camera system is used to calculate a 3D point cloud using a photogrammetric matching method, for example Least Squares Matching (LSM) and Structure from Motion (SfM), whereby a digital 3D model of the photographed weld seam (2) is created, characterized by , that a partial surface is already reconstructed in each position and several partial surfaces are transformed to each other using the ICP algorithm or, if the camera orientation is known, are directly fused with each other and that the assignment of the point clouds to each other is carried out using visual odometry and an algorithm such as the Iterative Closest Point (ICP) algorithm. [2] Device for photographing weld seams or other structural details, comprising at least one housing (1) which carries at least one camera whose camera lens is directed outwards, in particular for carrying out the method according to claim 1, characterized by , that a glare protection device (4) for the lens is arranged on the housing (1), wherein the glare protection device (4) is formed from separately mounted rod elements (5, 7) and wherein the rod elements (5, 7) are aligned parallel to one another and are arranged in at least one row surrounding the lens. [3] Device according to claim 2, characterized by that the rod elements are arranged discretely from one another. [4] Device according to claim 3, characterized by that each rod element (5) is connected to adjacent rod elements (5) with connecting elements (11). [5] Device according to claim 4, characterized by that the connecting elements (11) are sleeve elements (12) into which the rod elements (5, 7) can be inserted. [6] Device according to one of claims 2 to 5, characterized by that some rod elements (5) are mounted on the housing (1) in a height-adjustable manner. [7] Device according to claim 6, characterized by that the height-adjustable rod elements (5) are each loaded with a spring force. [8] Device according to claim 7, characterized bythat each height-adjustable rod element (5) is accommodated in a bearing element (6), wherein the bearing elements (6) are fastened to the housing (1). [9] Device according to one of claims 2 to 8, characterized by that some rod elements (7) are arranged at a fixed height on the housing (1). [10] Device according to claim 9, characterized by that the rod elements (5, 7) are received or arranged so as to be rotatable about their longitudinal axis. [11] Device according to one of claims 2 to 10, characterized by that sections with low-friction geometries (10) are arranged at the free ends of the rod elements (5, 7). [12] Device according to one of claims 2 to 11, characterized by that the rod elements (5, 7) are made of plastic or stainless steel. [13] Device according to one of claims 2 to 11, characterized by that a ring-shaped illumination is assigned to the lens. [14] Device according to one of claims 2 to 13, characterized by that it has at least one device for introducing a medium into the area of ​​the glare protection (4) in front of the lens.

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