Geometric target arrangement for the precise determination of the position of fasteners during 3D scanning

Abstract

Geometric target arrangement (100) for the precise determination of the position of a fastening element (112, 114) during 3D scanning, comprising a geometric target object (102) with a simple geometric, three-dimensional shape, wherein the geometric target object (102) has an opening for receiving a target adapter (200) or a part of the fastening element (112, 114).

Description

Technical area

[0001] The invention relates to a geometric target arrangement for precisely determining the position of a fastening element during 3D scanning. State of the art

[0002] When developing replacement solutions for parts of third-party industrial equipment, 3D scanning is a promising tool for capturing the existing solution as a reference for the design. For large machines such as engines and generators, a scan ideally captures the surrounding area and the entire machine, i.e., a volume of more than 5 m x 10 m x 5 m. For such large objects, LiDAR scanners are preferred because they offer a possible scanning distance of over 10 m and a customer site can be scanned with only approximately 10 viewpoints in about an hour. A limitation of this technology is the limited spatial resolution of such scanners, typically 3 to 10 mm.

[0003] One crucial piece of information for designing a replacement solution is the exact position of the foundation bolts. This information is required with an accuracy of less than + / -3 mm, as the use of slotted holes for these bolts is highly undesirable. This accuracy cannot be achieved by manually extracting the bolt position from the 3D point cloud, as often only the outer half of the bolt or fastener is accessible for scanning, and the point cloud resolution is too low.

[0004] Generally, black-and-white targets or conventional spherical targets can be applied to the screw or fastener. However, manual placement and the uneven surface of the screw head or nut often prevent placement accuracy of more than a few mm, especially for larger screws (M30+).

[0005] Manual measurement is also possible, but the screws are often recessed into the motor feet and not directly accessible for linear measurement, introducing additional errors. This increases the total measurement error to several millimeters and requires the cooperation of at least two people.

[0006] The use of structured light or laser line scanners would be possible to extract the screws from a much higher-resolution scan. Due to the short working distance of such scanners, an additional scan of the surrounding area and inaccessible parts such as cooling water pipes or structures on the ceiling would be required. Typically, a large number of additional targets must be set to allow the scanner to orient itself. Disclosure of the invention

[0007] An object of the invention could therefore be to provide an improved target arrangement.

[0008] The object is achieved by the subject matter of the independent claims. Advantageous embodiments are the subject matter of the dependent claims, the following description, and the figures.

[0009] Technical terms are used according to their general meaning. Where certain terms have a specific meaning, definitions are provided below in the context in which they are used.

[0010] According to a first aspect, a geometric target arrangement for precisely determining the position of a fastening element during 3D scanning is provided, comprising a geometric target object with a simple geometric, three-dimensional shape, wherein the geometric target object has an opening for receiving a target adapter or a part of the fastening element.

[0011] The fastener to be scanned and whose position is to be determined is, for example, a screw with a screw head and a thread, a threaded rod or any fastener or other object where the exact size and position are important, e.g. nuts, rivets, nails, buttons.

[0012] The target object, sometimes called a target mark, has a primitive shape that can be easily computed as a 3D object, describing a shape that produces a global minimum of the residuals when fitted to the 3D data. The position of this object can then be automatically adjusted to minimize the squared residuals with respect to the data points.

[0013] According to embodiments, the geometric target object consists of two separately manufactured parts.

[0014] According to one embodiment, the opening is a cylindrical recess that projects from the surface of the target object into its interior and is radially delimited by a wall that optionally has a thread.

[0015] The geometric target object sits firmly on the threaded rod or screw thread, for example, through the opening of the geometric target object and is centered on the surface of the rod end. It could also have a corresponding thread for screwing onto the rod or be additionally fixed in the axial direction by one or more integrated magnets.

[0016] The geometric target object is larger than the part of the fastener being scanned. This means that the geometric target object, for example, encloses the part of the fastener being scanned. In another example, the target adapter is placed on a part of the fastener being scanned, such as a bolt head or nut, and the geometric target object is larger than the bolt head. One effect of this is to increase the size of the object being scanned, which is now the target object instead of the fastener or target adapter, allowing more data points to be captured on the surface.

[0017] According to one embodiment, the opening extends only partially, preferably approximately halfway, into the geometric target object.

[0018] The geometric target object covers or extends beyond the original target to be scanned, e.g., a screw or threaded rod. The original target is thus raised from, for example, the screw / rod position or the screw head position to the position of the new target, the geometric target object, in order to be accessible from a wider angular range during 3D scanning. This also increases the amount of acquired data and thus the position information.

[0019] According to one embodiment, the target assembly further comprises the target adapter, wherein the target adapter has a cylindrical shape whose diameter corresponds to the opening of the geometric target object in order to be able to be received by the latter.

[0020] In an alternative embodiment, the target adapter and the target object have a matching thread along the cylindrical surface so that the target adapter can be connected to the target object by screwing it in.

[0021] According to one embodiment, the target adapter has a second flat side due to the cylindrical shape, and one or more magnets on the second flat side, and is configured to be removably attached to the target object by the magnet(s).

[0022] This includes that the target object can contain a magnet or a ferromagnetic inset, as well as that the target object can contain a magnet so that it magnetically adheres to the attachment object.

[0023] According to a second aspect, a geometric target assembly for precisely determining the position of a fastener during 3D scanning is provided, comprising a geometric target object having a simple geometric, three-dimensional shape and a target adapter, wherein the target adapter has an opening for receiving a portion of the fastener.

[0024] According to one embodiment, the opening of the target adapter is a cylindrical recess which is radially delimited by a wall and which optionally has a thread to receive a part of the fastening element.

[0025] According to one embodiment, the geometric target object and the target adapter are plugged, magnetically or glued together or are made from one piece, e.g. in one piece by a 3D printer or by casting.

[0026] Manufacturing it in two parts allows for easier and more efficient transport of the target object, such as a bullet. However, it can also be manufactured in one piece.

[0027] According to one embodiment, the geometric target object is a sphere, a cylinder, a hollow cylinder, a cone, a cuboid, a prism, a cone or a cube.

[0028] A sphere is preferred. Using a spherical target allows data to be collected at all angles of incidence of the measuring laser. This results in very precise data, especially at 90° AOI (Angle of Incidence), and eliminates the potential for discretization of the distance or scanning angle by averaging over many points.

[0029] According to one embodiment, a texture and / or further geometric information is printed or glued onto the target object.

[0030] According to one embodiment, the geometric target object has any color and / or any size.

[0031] According to one embodiment, the geometric target object has a color coding for coding a thread diameter of the fastening element, a screw diameter, the shape of the screw head, a material of the screw, a length of the screw, a screw standard, and / or a strength of the screw.

[0032] The characteristic target size is defined by the thread diameter of the screw or threaded rod, or another characteristic size of the fastener, and indicated by the target color (e.g., M30: yellow, M42: purple, M48: red). This allows the basic size of the 3D shape to be used as a constraint for adapting the geometric surface to the scanned data during digital post-processing of the 3D data. This further increases the accuracy of the determined position.

[0033] According to one embodiment, the target adapter has a first flat side due to the cylindrical shape, and on the flat first side one or more magnets, and is configured to be removably mounted on the fastening element by means of the magnet(s).

[0034] According to one embodiment, the target adapter has a hollow base that is shape compatible with the fastener or a part of the fastener, e.g. a screw head or a nut.

[0035] The hollow base can be pulled over the screw head or nut and adheres to the base using one or more magnets. Ideally, the base is colorless, but rather white, black, or gray, so that it can be separated from the target object, for example, by color filtering.

[0036] According to one embodiment, the target adapter is a part manufactured by 3D printing, casting or machining.

[0037] The following demonstrates a method for precisely determining the position of a fastener during 3D scanning using the geometric target arrangement described herein: In a first step, the colored geometric target objects, e.g. colored spheres, are attached to threaded rods, screw threads or screw heads.

[0038] In the case of a threaded rod or screw thread, a cylindrical hole or matching thread in the geometric target object, exemplified below by the sphere, is used to fasten it, and a magnet holds it in place so that the center of the sphere lies on the cylinder or thread axis of the fastener. In the case of a screw, a target adapter is used, which is inserted into the sphere and sits tightly on the screw head or a nut so that the sphere is centered over the screw and the sphere lies half a diameter above the head surface. Ideally, the adapter is held on the ferromagnetic screw head by one or more magnets with almost no play. For each nominal thread diameter, a sphere with a color that differs from the colors of spheres with other thread diameters is used.Once all relevant screws have been marked, the scene is 3D scanned using a LiDAR scanner, and the data is then imported into post-processing software. The software allows the user to determine the correct sphere size based on the color information obtained from the 3D scan. The markers / spheres can even be separated from the scene using color filtering. When using the target adapter, color filtering can be used to separate the markers / spheres from the non-colored (i.e., white, gray, or black) hollow base.

[0039] In a second step, for each screw, a sphere of the appropriate size is adapted to the separated 3D point clouds of the individual target spheres.

[0040] In this way, an average value from a large number of 3D measurements is used to determine the sphere position. This greatly reduces the errors of a single measurement. Fitting with a sphere of defined diameter also overcomes the discretization limit, as measurement noise and data points at different angles of incidence are taken into account. This leads to a sub-resolution position of the sphere center. Since the distance from the sphere center to the screw or rod center is known and defined by the target assembly, the screw or rod position can also be determined with a similar sub-resolution accuracy of typically < 3 mm, often < 1 mm, and used for design.

[0041] The invention thus presents attachments (the target assembly) with defined, primitive geometry and size (such as spheres, cylinders, etc.) that can be attached to important objects, e.g. screws or other fastening elements of heavy machinery.

[0042] The fixture is automatically aligned so that its center point is on the axis of the fastener, defining its position in 2D.

[0043] The top of the fastener has a defined position relative to the center of the target object, e.g. the center of the sphere, which completely defines the position of the fastener.

[0044] The color of the fixture encodes its size and the size of the underlying fastener. Knowing this size, the position of the fixture and fastener can be determined with sub-resolution accuracy by fitting a 3D primitive to the extensive point cloud data collected from the fixture's surface.

[0045] Thus, the invention enables the precise determination of the position and size of important small objects in a 3D scan that would otherwise be difficult or impossible to locate.

[0046] The invention is explained in more detail with reference to the following figures and exemplary embodiments. Short description of the characters Fig. Figure 1a shows a diagram of a threaded rod with a nut in a 3D representation. Fig. Figure 1b shows a diagram of a geometric target object mounted on the fastener. Fig. Figure 1c shows a diagram of the geometric target object in a cross-sectional view. Fig. Figure 2a shows a 3D diagram of a target adapter mounted on a fastener. Fig. Figure 2b shows a diagram of a geometric target object attached to a fastening element using a target adapter in a 3D representation. Fig. Figure 2c shows a diagram of the geometric target object attached to a fastener using a target adapter in a sectional view. Fig. Figure 2d shows another diagram of the geometric target object mounted on a fastener using a target adapter in a sectional view. Fig. 3 shows a diagram of a geometric target arrangement in another embodiment. Detailed description

[0047] The same reference symbols refer to the same elements in all figures.

[0048] Fig. Figure 1a shows a 3D diagram of a threaded rod 112 as a fastener 112 with a nut 113. The position of the threaded rod 112 is to be precisely determined by 3D scanning. However, the fastener 112 to be scanned does not have to be a screw or threaded rod, but can be any fastener or other important small object where the precise size and position are important, e.g., nuts, rivets, nails, buttons.

[0049] Fig. Figure 1b shows a diagram of a target arrangement 100 for precisely determining the position of a threaded rod 112 as a fastening element 112. For this purpose, an object 102 with a simple geometric, three-dimensional shape is mounted on the threaded rod 112. In the embodiment shown, the geometric target arrangement 100 consists of the geometric target object 102, which in this and the other examples is expressed as a sphere 102. When using a spherical target object 102, the data is acquired at all angles of incidence of the measuring laser. This leads to a. very precise data, especially when the laser hits the target object at an angle of 90°, and b. Elimination of possible discretization of the distance or the sampling angle by averaging over many points.

[0050] The geometric target object 102 does not necessarily have to be a sphere, but can also be any other geometric primitive, e.g., a cylinder, a hollow cylinder, a cone, a cuboid, a prism, a cone, or a cube. The target object 102 can be easily calculated as a 3D object using the primitive shape and describes a shape that produces a global minimum of the residuals when fitted to the 3D data. The position of this object can then be automatically adjusted to minimize the quadratic residuals with respect to the data points.

[0051] Fig. Figure 1c shows a diagram of a geometric target object 102 mounted on the threaded rod 112 as a fastening element in a sectional view. The sphere 102 has an opening for receiving a target adapter 200 shown below or a part of the fastening element 112, here a part of the threaded rod 112, which fills the opening. The opening and thus the threaded rod 112 in Fig. 1c extends only partially, preferably halfway, into the ball 102, so that the other half of the ball 102 covers or projects beyond the threaded rod 112. This essentially raises the ball 102 from the screw / rod position, allowing it to be accessed from a wider angular range. This also increases the amount of recorded data and thus the position information.

[0052] The ball 102 has an internal magnet 106 in its center that holds and centers it either on a threaded rod 112 or the target adapter 200, which may also be referred to as a "rod adapter." This eliminates the need to screw on the target adapter 200, and no thread is required. Alternatively or additionally, the ball 102 may also have an internal thread 104 on the radial wall of the opening so that the ball 102 can be screwed onto the threaded rod 112. The target object 102 is firmly seated on the threaded rod 112 by the magnet 106 or the thread 104 and is centered on the surface of the rod end.

[0053] The ball 102 can, in principle, have any color and any size. Fig. 1b and Fig. 1c shows that the sphere 102 is at least radially larger than the part of the fastening element 112 to be accommodated, i.e., the threaded rod 112. The size and surface of the object 112 to be scanned are thus enlarged, allowing more data points to be captured on the surface. The characteristic target object size is defined by the thread diameter of the screw or rod and indicated by the target color (e.g., M30: yellow, M42: purple, M48: red). In this way, the basic size of the 3D shape can be used as a constraint for adapting the geometric surface, which further increases accuracy.

[0054] Fig. 2a shows a diagram of the geometric target arrangement 100, which has a target adapter 200 mounted on the screw head 114 as a fastening element 114, in a 3D representation. The target adapter 200 fits tightly onto the corresponding screw head 114 for a specific thread size, so that the underside of the ball 102 is aligned with the top of the screw head 114. The target adapter 200 can also have an external thread to receive the ball 102, which then has a corresponding internal thread. The target adapter 200, also referred to herein as "adapter" 200 for short, has in this embodiment and the Fig. 2b - 2d, a hollow base 300 which serves as a screw head adapter 300

[0055] Fig. 2b shows a diagram of a geometric target arrangement 100 attached by means of a target adapter 200, including the ball 102 on a screw head 114 as a fastening element 114 in a 3D representation.

[0056] Fig. Figure 2c shows a diagram of the geometric target object 102 attached to a screw head 114 as a fastening element 114 by means of the target adapter 200, in a sectional view. The target adapter 200 does not necessarily have to be 3D printed, but can also be manufactured in other ways, e.g., by casting or machining. The target adapter 200 and the geometric object 102 can also be manufactured as a single part, although this is not the preferred solution. Fig. 2c further shows the magnets 106, 202 for attaching the ball 102 to the target adapter 200 and the magnet 306 for attaching the target adapter 200 to the screw head 112.

[0057] Fig. 2d shows a further diagram of the geometric target object 102 attached by means of the target adapter 200 on a screw head 114 as a fastening element 114, in which the adapter 200 and the ball 102 have a thread 104 and the adapter 200 is fixed to the screw head 114 with a magnet 306.

[0058] Fig. Figure 3 shows a diagram of a geometric target arrangement in another embodiment. The design is optimized for FDM (Fused Deposition Modeling) printing and eliminates overhangs and supports for the best dimensional accuracy. The sphere 102 is assembled from two parts, which, in the example shown, interlock with three centering pins 108. Fig. 3, the magnet 106 can still be seen in the center. In this embodiment, the target adapter 200, in addition to the cylindrical part 304, also has a hollow base 300, which serves as a screw head adapter 300, in this example for a hexagon screw. The base is ideally a different color than the target object, e.g., white or black. The cylindrical part 304 of the target adapter (in Fig.3 (indicated by circles) has two magnets 202, 306. Magnet 306 is used to attach the target adapter 200 to the screw head, and the other magnet 202 is used to hold the ball 102. The screw head adapter 300 has three centering holes 302 into which the three aforementioned centering pins of the cylindrical part 304 fit. The parts 300, 304 can thus be plugged together, or held together magnetically, glued together, or otherwise joined together in a form-fitting manner. They could also be 3D-printed in one piece. The ball 102 or the target adapter 200 could each also be printed as a single part.

[0059] The presented target arrangement offers the following advantages over conventional geometric targets: - Typically, geometric targets are often used as input for reference positions or constraints for the registration of multiple scan positions or data sets. In the present invention, the targets are intended for the position determination of objects in post-processing (and not as a constraint or position input for an optimization process). - The target arrays are attached not by a protruding but by an embossed feature. - The geometric object is not white, but colored according to the screw diameter. - The target arrays are developed and manufactured (e.g. for 3D printing) in different sizes and colors. - The target assemblies can be separated for compact transport and are held together by magnets or plugs rather than screws.

[0060] Other variations of the disclosed embodiments may be understood and practiced by those skilled in the art in practicing the claimed invention, based on the drawings, the disclosure, and the appended claims. In the claims, the indefinite article "a," "an," or "a," does not exclude a plurality. The mere fact that certain measures are recited in dependent claims does not mean that a combination of those measures cannot be advantageous. Any reference signs in the claims are not to be understood as limiting the scope of the claims. Reference symbol 100 Geometric Target Arrangement 102 geometric target object, e.g. sphere 104 threads 106 Magnet of the geometric target object 108 pin, centering pin 112 Threaded rod / screw thread 113 Mother 114 screw head 200 target adapters 202 Target adapter magnet 300 hollow base, screw head adapter of the target adapter 200 302 centering holes 304 cylindrical part of the target adapter 200 (target adapter 200 without base / screw head adapter) 306 additional magnet of the target adapter

Claims

[1] Geometric target arrangement (100) for precisely determining the position of a fastening element (112, 114) during 3D scanning, comprising a geometric target object (102) with a simple geometric, three-dimensional shape, wherein the geometric target object (102) has an opening for receiving a target adapter (200) or a part of the fastening element (112, 114). [2] The geometric target assembly (100) of claim 1, wherein the opening is a cylindrical recess extending from the surface of the target object (102) into its interior and is radially defined by a wall optionally having a thread (104). [3] Geometric target arrangement (100) according to one of the preceding claims, wherein the opening protrudes only partially, preferably halfway, into the geometric target object (102). [4] Geometric target arrangement (100) according to one of the preceding claims, wherein the geometric target arrangement (100) comprises the target adapter (200), wherein the target adapter (200) has a cylindrical shape whose outer diameter corresponds to the opening of the geometric target object (102) in order to be able to be received thereby. [5] Geometric target arrangement (100) according to one of the preceding claims, wherein the target adapter and the target object have a matching thread along the cylindrical surface so that the target adapter (200) can be connected to the target object (102) by screwing it in. [6] Geometric target arrangement (100) according to one of claims 4 to 5, wherein the target adapter (200) has a second flat side due to the cylindrical shape, and has one or more magnets (202) on the second flat side and is adapted to be removably attached to the target object (102) by means of the magnet(s) (202). [7] Geometric target arrangement (100) for precisely determining the position of a fastening element (112, 114) during 3D scanning, comprising a geometric target object (102) with a simple geometric, three-dimensional shape, and a target adapter (200), wherein the target adapter (200) has an opening for receiving a part of the fastening element (112, 114). [8] The geometric target assembly (100) of claim 7, wherein the aperture of the target adapter (200) is a cylindrical recess radially defined by a wall optionally having a thread (104) to receive a portion of the fastener. [9] Geometric target arrangement (100) according to one of the preceding claims, wherein the geometric target object and the target adapter are plugged, magnetically or glued together or are made of one piece, e.g. are manufactured in one piece by a 3D printer or by casting. [10] Geometric target arrangement (100) according to one of claims 1 to 8, wherein the geometric target object (102) consists of two separately manufactured parts [11] Geometric target arrangement (100) according to one of the preceding claims, wherein the geometric target object (102) is a sphere, a cylinder, a hollow cylinder, a cuboid, a prism, a cone, a cone or a cube. [12] Geometric target arrangement (100) according to one of the preceding claims, wherein a texture and / or further geometric information is printed or glued onto the target object (102). [13] Geometric target arrangement (100) according to one of the preceding claims, wherein the geometric target object (102) has any color and / or any size. [14] Geometric target arrangement (100) according to one of the preceding claims, wherein the geometric target object (102) has a color coding for coding a thread diameter of the fastening element, a screw diameter, the shape of the screw head, a material of the screw, a length of the screw, a screw standard, and / or a strength of the screw. [15] Geometric target arrangement (100) according to one of claims 4 to 14, wherein the target adapter (200) has a first flat side due to the cylindrical shape, and has one or more magnets (306) on the first flat side and is adapted to be removably attached to the fastening element (112, 114) by means of the magnet(s) (306). [16] Geometric target arrangement (100) according to one of claims 4 to 15, wherein the target adapter (200) has a hollow base (300) which is shape compatible with the fastening element (112, 114) or a part of the fastening element, eg a screw head (114) or a nut (114). [17] Geometric target arrangement (100) according to one of the preceding claims, wherein the target adapter (200) according to claims 4 to 16 and / or the target object according to claims 1 to 16 is a part manufactured by 3D printing, by casting or by machining.

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