Measurement system for a model and method for scanning a model

Abstract

Measuring system (100), comprising: - a frame (110) designed to support a model (105) to which a number of optical markers are attached; - several reference bodies (115) that can be removed from the frame (110) and attached to the frame (110) in a repeatable and / or reproducible manner; - an optical detection system (125) configured to scan the model (105) and the reference bodies (115); and - a processing facility (130) which is equipped to, - to determine an alignment of the frame (110) with respect to the detection system (125) based on a scanning of the reference bodies (115) and - to align a scanning of the model (105) based on the specific orientation of the frame (110); characterized in that the processing device (130) is further configured to - to align two overlapping scans of the model (105) with respect to the position of optical markers detected in both scans relative to each other.

Description

[0001] The present invention relates to a measuring system for scanning a model and a method for scanning a model. In particular, the invention relates to a measuring system for a model representing a part of a motor vehicle.

[0002] During the development of a motor vehicle, a model must be created for a part, assembly, or section of the vehicle to test its functional or aesthetic effect. The model may consist of a flexible material such as clay, which can be molded to replicate the surface of the vehicle. Once a suitable mold is found, the model is scanned so that its shape can be archived or further processed using computer-aided methods.

[0003] Scanning can be performed using an optical measuring device or measuring system that captures multiple points on the model's surface. However, a shape found in this way has no defined orientation in space. For example, to compare surfaces of the model in two different revisions, it is necessary that the scans are referenced to the same coordinate system.

[0004] It is common practice to mount the model in a defined manner on a scanning plate for a scanning process. The scans taken by the measuring system can then be referenced to a coordinate system defined with respect to the scanning plate. By establishing a fixed reference between the model's coordinate system and the measuring plate, the scans can also be referenced to a coordinate system of the model.

[0005] However, this approach requires repeatable attachment of the model to the measuring plate for each individual scanning operation. This requires the model to be moved to the scanning plate and precisely aligned with it. Transporting and adjusting the model relative to the measuring plate can be complex and time-consuming. This can delay the model design process, potentially resulting in increased development costs.

[0006] DE 10 2006 016 677 A1 discloses a measuring system comprising a frame for supporting a model, a plurality of reference bodies, an optical detection system for detecting the model and the reference bodies, and a processing device. The reference bodies are mounted on the frame, without providing any further details regarding the manner of their attachment to the frame.

[0007] Reference bodies as such are also known from the Internet publication "Kinematic Coupling for Precision Fixturing & Assembly", MIT Precision Engineering Research Group, April 2013, accessed via the URL: https: / / web.archive.org / web / 20220401144735 / http: / / pergatory.mit.edu / kinematiccouplings / documents / Presentations / Kinematic %20Coupling%20for%20Precision%20Fixturing%20and %20Assembly.pdf, archived by http: / / www.archive.org on April 1, 2022.

[0008] DE 10 2004 023 033 A1 shows a measuring system according to the preamble of claim 1.

[0009] An object underlying the present invention is to provide an improved technique for providing a scan of a model. The invention achieves this object by means of the subject matter of the independent claims. Subclaims specify preferred embodiments.

[0010] According to the invention, a measuring system is proposed, comprising: - a frame adapted to support a model to which a number of optical markers are applied; - several reference bodies that can be removed from the frame and attached to the frame in a repeatable and / or reproducible manner; - an optical detection system configured to scan the model and the reference bodies; and - a processing facility designed to - to determine an orientation of the frame with respect to the detection system on the basis of a scan of the reference bodies and - to align a sample of the model based on the determined orientation of the frame.

[0011] According to the invention, the processing device is further configured to - to align two overlapping scans of the model with respect to the position of optical markers captured in both scans.

[0012] Using the measuring system, a coordinate system can be easily established that is referenced to the frame. Subsequent scans of the frame or an associated model can be referenced to the established coordinate system without requiring the frame to be aligned in a predetermined manner. The use of a measuring plate may only be required once to establish the frame-fixed coordinate system.

[0013] Sufficient repeatability is generally achieved when scans from the acquisition system before and after the removal and reattachment of the reference bodies are comparable within a predetermined measurement accuracy. In other words, after being removed from the frame, the reference bodies should be able to be reattached to the frame in the same positions so precisely that any deviation from specific positions of a point relative to the frame before and after temporary removal is below a predetermined amount. This amount can correspond to the measurement accuracy.

[0014] The removable reference bodies ensure that the design process of a model on the frame is not disrupted. The reference bodies can only be attached to the frame when scanning is required. Scanning a model can be performed more quickly overall and with fewer technical resources.

[0015] The frame is configured to support a model. The acquisition system is configured to scan the model, and the processing device is configured to align a scan of the model based on the determined orientation of the frame.

[0016] In other words, the processing device can relate a point on the surface of the model sampled by the acquisition system to a coordinate system that has been defined once with respect to the frame.

[0017] The model can have a variable shape. The model material can be chosen arbitrarily, and the model shape can be as complex as desired, as long as it can be scanned by the acquisition system. The size of the model can essentially be determined only by the manageability of the frame. A further limitation may be a stationary acquisition system. Alternatively, a mobile or handheld acquisition system can be used.

[0018] A number of optical markers are applied to the model. According to the invention, the processing device is configured to align two overlapping scans of the model with respect to the position of the markers captured in both scans. A marker can also be referred to as a reference point.

[0019] Markers can be applied to the model before a scan and then removed again afterwards. It may be sufficient if the markers are distributed pseudo-randomly across the surface of the model. The distribution of the reference points on the model can depend on the measurement volume and / or the scanning system used. Information from a manufacturer of the scanning system can be used to distribute and place reference points. Using the acquisition system, a series of scans can be created, whereby two adjacent scans should partially overlap in order to establish a common context for the scans. In this way, a chain or series of scans can be created whose acquired reference points all lie in the same coordinate system.The entire series can be referenced to the frame's coordinate system if a sufficient number of reference bodies can be detected in the scans taken together. It is preferable for multiple reference bodies to be captured in a single scan.

[0020] In one embodiment, a reference body carries an individual optical marking that can be detected by the detection system.

[0021] This prevents confusion of reference bodies during evaluation by the processing device. Ambiguities in the reference of a scan to the frame-fixed coordinate system can be resolved. It is further preferred that the reference bodies be assigned to predetermined positions on the frame. This allows the position of scanned points on the model's surface to be related more accurately and unambiguously to the frame-fixed coordinate system.

[0022] The positions are preferably selected such that a constellation of reference bodies on the frame results in an advantageous geometric shape. For example, an area spanned by the reference bodies or a volume spanned by the reference bodies can be maximized as much as possible. To correctly align the frame in space, three rotational and three translational degrees of freedom are usually defined. It may be sufficient to use at least three reference bodies. However, it is preferred to use at least six reference bodies to provide sufficient reference points for referencing the frame-fixed coordinate system.

[0023] It is further preferred that predetermined mechanical interfaces are provided between the reference bodies and the frame for tool-free separation and connection.

[0024] Equipping the frame with the reference bodies can be completed by a single person in a short time. The interface is designed to hold the reference body to the frame with sufficient repeatability.

[0025] The reference bodies are preferably attached to the frame only for the purpose of, and for the duration of, a scanning operation. Therefore, the interfaces do not need to be so robust that they can withstand accidental contact during model processing. Tool-free connection and separation of the reference body from the frame can reduce setup time before or after scanning.

[0026] If a reference body is individually assigned to a position on the frame, the interface can include a mechanical coding that prevents another reference body from being attached to that position. However, interfaces of multiple reference bodies can also be interchangeable.

[0027] It is generally preferred that a portion of the interface be mounted on the frame in such a way that the reference body can be connected to it without touching the model. For example, the frame can be configured so that the model lies on an upper side of the frame, with an interface located on the underside. In another embodiment, the interface can be located in an area where the model has a recess or cavity.

[0028] Preferably, an interface comprises two surfaces for mutual contact, wherein mutually corresponding sections for mutual positive engagement are formed on the surfaces. The surfaces are assigned to different sections of the interface and can be removed from one another when the interface is opened. By means of the surfaces, a reference body can be reproducibly and precisely brought into a predetermined position relative to the frame. The positive-locking sections can prevent movement of the surfaces relative to one another. The surfaces can comprise flat or curved surfaces. Mutually corresponding concave or convex sections can comprise, for example, a hemisphere, a prism, a cylinder, an elongated hole, or a cone. Several sections for positive engagement can be distributed in a predetermined manner on the surfaces.The position of the reference body relative to the frame can be determinate or overdetermined.

[0029] In a further preferred embodiment, the interface comprises a magnetic fixation between the reference body and the frame. The fixation is preferably designed to bring the reference body closer to the frame. This allows a positive connection to be established or maintained by corresponding sections. The magnetic fixation can be quickly established or broken. In the event of overload, the fixation can open, separating the reference body from the frame.

[0030] It is further preferred that a cantilever is provided between the reference body and the frame. This allows the reference body to protrude beyond the outline of the model without a frame-fixed part of the interface hindering the impression or work on the model when the reference body is removed.

[0031] In a further development, an auxiliary frame is movably mounted on the frame. At least one additional reference body can be mounted on the auxiliary frame. Depending on the number of degrees of freedom of the auxiliary frame relative to the frame, multiple reference bodies can also be provided. To fully determine the orientation of the auxiliary frame relative to the frame-fixed coordinate system, at least three reference bodies are preferably used.

[0032] The movable subframe can support a function of the model. For example, the subframe can represent a door of a vehicle, whereby the door is movable relative to the vehicle in the same way as the subframe is relative to the frame. This can be used, for example, to check whether independently defined shapes of the vehicle and the door are compatible with each other with regard to a predetermined mobility. A subframe can be designed so that it can be separated from the frame. An interface between the frame and the subframe can ensure repeatable reattachment after separation. In a further development of this idea, several subframes can also be movably attached to the frame. The concept can also be cascaded by having another subframe movably attached to the subframe.

[0033] According to the invention, a method for scanning a model carried by a frame is further provided, the method comprising the following steps: - Attaching several reference bodies to the frame; - optical scanning of the model and the reference bodies, wherein a number of optical markers are applied to the model and wherein two overlapping scans of the model are aligned with each other by means of a processing device with respect to the position of optical markers detected in both overlapping scans; - Establishing a frame-fixed coordinate system based on a scan of a predetermined number of reference bodies; - temporarily removing the reference bodies from the frame; - reattaching the reference bodies to the frame; and - Repeat the scan.

[0034] The method can be carried out, in particular, using a measuring system described herein. The temporary removal of the reference bodies can allow the model to be edited to any extent. In contrast to a conventional method, an external device for defining the coordinate system may only be required once. Any number of subsequent scans can then be aligned with respect to the already defined coordinate system.

[0035] The method makes it possible to perform scans of different revisions of the same model on a frame with reduced effort. This allows for easier cross-referencing between different scans of the model. In a further development of the method, different scans of the model can be compared with each other. Differences between two revisions or versions of the model can thus be more effectively identified and quantified. Unchanged parts of the model can be identified.

[0036] The invention will now be described in more detail with reference to the accompanying drawings, in which: Fig. 1 a measuring system; Fig. 2 a flow diagram of a process; Fig. 3 a frame with a model for an interior; Fig. 4 a reference body on a frame; Fig. 5 an exemplary reference body with a mechanical interface; and Fig. 6 a reference body in a further embodiment illustrated.

[0037] Fig. 1 shows a measuring system 100. The measuring system 100 is configured to provide scans of a model 105, which is preferably used in the development process of a motor vehicle. Although smaller elements can also be processed with the measuring system 100, the model 105 is illustrated as a complete motor vehicle for illustrative purposes.

[0038] The measuring system 100 comprises a frame 110 configured to support the model 105 and to which a plurality of reference bodies 115 can be attached. The reference body can be extended from the frame 110 via a boom 118. A mechanical interface 120 is preferably provided between the frame 110 and the reference body 115. Furthermore, the measuring system 100 comprises an optical detection system 125 and a processing device 130. A data storage device 135 is optionally provided.

[0039] The frame 110 is dimensioned to support the model 105 without being excessively deformed, which would affect the measurement result. For larger models 105, the frame 110 is typically constructed of tubular steel. The model 105 can be made of a flexible or hardenable material such as clay or plastic. For weight reasons, a filler material, such as a hardened plastic foam, can be provided between the model 105 and the frame 110.

[0040] Frame-side interfaces 120 are preferably attached to the frame 110 such that they are located outside an area in which the model 105 can be accommodated. Furthermore, the interfaces 120 are further preferably designed such that they cannot be repositioned on the frame 110 or cannot be repositioned inadvertently. A non-repositionable interface 120 can, for example, be firmly attached to the frame 110. A repositionable interface 120 can require the use of a key, a predetermined tool, or the breaking of a seal to change its position relative to the frame 110.

[0041] The frame 110 can be configured to be mechanically aligned with a base plate (not shown). For this purpose, an adapter can be inserted into the base plate, which can engage positively with a corresponding structure on the frame 110. Such an adapter can also be called a quill.

[0042] The detection system 125 is configured to determine the position of at least one point on a surface of an object in a non-contact and, in particular, optical manner. Typically, a plurality of several hundred or several thousand points on a surface can be detected by the detection system 125 with just one recording or measurement run. A position of the detection system 125 relative to the frame 110 can be determined at least initially when both the frame 110 and the detection system 125 are positioned relative to the measuring plate. For this purpose, a frame-fixed coordinate system, i.e., one related to the frame 110, can be defined.

[0043] An example is Fig. 1 depicts a Cartesian coordinate system defined relative to the frame 110. An x-axis extends horizontally rearward, opposite a normal direction of travel of the vehicle. A y-axis runs horizontally from left to right. A z-axis extends vertically upward. An origin of the coordinate system lies on an axis about which both front wheels of the vehicle can rotate, halfway between the left and right wheels. A different definition can also be made. Optionally, a system other than a right-hand system or a system other than a Cartesian system can be used.

[0044] Before starting a scan, the processing unit 130 can generate a coordinate system in the detection range of the detection system 125, which is also referred to as the sensor coordinate system. Once the detection is complete, this coordinate system can be transformed to another one. In the representation of Fig. 1, no sensor coordinate system is shown and it is assumed, without loss of generality, that all measurements are transformed into the x / y / z coordinate system shown before further processing.

[0045] Specific points can be stored in data storage 135. Optionally, the points can also be processed by processing device 130, for example, by smoothing, converting to another data format, or creating a model based on other geometric constructs, such as NURBs (Non-Uniform Rational B-Splines). The points or a processing result can be made available externally.

[0046] In various embodiments, the detection system 125 can be fixed in a hall, mobile, or handheld. In a fixed-in-hall detection system 125, a device is provided that can mechanically control or limit the position of the detection system 125. The orientation of the detection system 125 relative to its surroundings, and in particular to a measuring plate, can thus always be known. A mobile detection system 125 can be mounted on an autonomous platform that the model 105 can, for example, move around.

[0047] Fig. 2 shows a flowchart of a method 200 for scanning a model 105. The method 200 can be carried out in particular by means of a measuring system 100.

[0048] In a step 205, the frame 110 can be provided for the model 105. Preferably, the model 105 is not yet attached to the frame 110 at this time.

[0049] In a step 210, reference bodies 115 can be attached to the frame 110. Positions for the reference bodies 115 on the frame 110 can be determined at this time. It is preferred that at least six reference bodies 115 be used. The reference bodies 115 can be located in a plane or any other geometric structure relative to one another. Further preferably, the reference bodies 115 are positioned on the frame 110 such that they can be viewed from the largest possible angular range. The angular range can be determined horizontally and / or vertically.

[0050] In a step 215, the frame 110 can be measured. A frame-fixed coordinate system can be defined. A later determined position on the surface of the model 105 can be referenced to the frame-fixed coordinate system. The frame-fixed coordinate system is a prerequisite for the comparability of different scans of the model 105 in possibly different states or shapes.

[0051] For calibration, the relative positions of the reference bodies 115 to each other can be determined. The coordinate system can, for example, be set manually. It is preferred that a Cartesian right-hand system be used. Fig. In the embodiment illustrated in Figure 1, the coordinate system can be defined such that a first axis corresponds to a longitudinal axis, a second axis to a transverse axis, and a third axis to a vertical axis of a motor vehicle represented by the model 105. Directions and zero points of the axes can be defined freely or according to an existing convention. In one embodiment, a 3-2-1 alignment is performed using geometric elements of the measuring plate. Subsequently, a zero point of the coordinate system can be shifted to a predetermined position, for example, as shown in the center of the front axle.

[0052] In one embodiment, the coordinate system is defined automatically by exploiting a predetermined geometric relationship between reference bodies 115. For example, two reference bodies can each define an axis. The axes can intersect at a point that can be determined as the origin of the coordinate system.

[0053] In another embodiment, the coordinate values ​​of the reference bodies are acquired and, after an optional corrective alignment, entered as target coordinate values ​​into software running on the processing device 130. The data scanned by the acquisition system 125 can then be stored in the form of coordinate values ​​of the pattern of acquired reference points, as well as a position of an origin and an orientation of the coordinate system.

[0054] In a step 220, the reference bodies 115 can be removed from the frame 110. The reference bodies 115 can be stored in a secure location so that they are available at a later time for the present frame 110 or the model 105 it supports.

[0055] In a step 225, the model 105 can be attached to the frame 110 or processed. The processing can include changing the surface of the model 105. There is no fundamental limit to the extent or scope of a change.

[0056] In a step 230, the reference bodies 115 can be reattached to the frame 110. The reference bodies 115 can be individually marked. A first marking can be readable by a person, and a second marking can be scanned by the detection system 125 and recognized by the processing device 130. During attachment, it is preferably ensured that the reference bodies 115 each assume the same positions on the frame 110 that they had in step 215.

[0057] In a step 235, the model 105 can be measured. For this purpose, the surface of the model 105 can be scanned using the detection system 125. At the same time, one or more reference bodies 115 can be scanned. Typically, a scan comprises a plurality of points that lie within a predetermined measurement range. Multiple scans that partially overlap each other can be combined to form an enlarged scan.

[0058] Each point of the scan can be referenced to the frame-fixed coordinate system by determining its position relative to a reference body 115 recognizable on the scan and taking into account its position relative to the frame-fixed coordinate system. Referencing a scan to the frame-fixed coordinate system can be done in a known manner by transposing using appropriate matrices.

[0059] If the scanned pattern of reference points includes three or more reference bodies, a transformation of all actual data to the previously stored target data can be determined. All data in the project can be transformed. The scan data, i.e., the recorded positions of the reference points, can then be available in the vehicle's coordinate system without the physical model 105 having to be rebuilt on quills on the base plate.

[0060] After measuring the model 105, the method 200 can continue in step 225 to make another change to the model 105 and determine its result. In a step 240, the model 105 can be evaluated based on its scan. The evaluation can be performed in any desired manner. For example, the scan can be used as the basis for a simulation of the model 105 in a wind tunnel. In another embodiment, a computer graphic can be created based on the scan, which can be colored, animated, or otherwise developed in subsequent processing steps. In step 240, different revisions of the model 105 can also be compared with one another. For this purpose, sections of the model 105 that have changed between two predetermined revisions can be identified.

[0061] Fig. 3 shows a frame 110 with a model 105 for a motor vehicle interior. The frame 110 is shown from an outside, and the model 105 is located on a side of the frame 110 facing away from the viewer. A subframe 310 is attached to the frame 110 and can be moved relative to the frame 110 in a predetermined manner. In the illustrated embodiment, the subframe 310 is pivotally mounted relative to the frame 110 about a predetermined axis 305. Optionally, the subframe 310 can also be removed from the frame 110. The mobility of the subframe 310 relative to the frame 110 in the illustrated embodiment represents the mobility of a door of a motor vehicle simulated by the model 105.

[0062] Preferably, several reference bodies 115 are attached to the subframe 310. The reference bodies 115 can be detected from the outside, which is not relevant for the model 105. This allows the position of the modeled door relative to the rest of the motor vehicle to be determined.

[0063] Fig. 4 shows an exemplary reference body 115 on a frame 110. A model 105 can be located on the upper side of the frame 110 facing away from the viewer. A mechanical interface 400 is provided between the reference body 115 and the frame 110, which includes a section 405 fixed to the frame and a section 410 fixed relative to the reference body 115. The extension arm 118 is located between the reference body 115 and the second section 410 and is shaped such that it does not extend into the area of ​​the model 105 and can be easily detected by the detection system 125 on the model 105.

[0064] In the illustrated embodiment, an adjustment mechanism 415 is provided with which a position of the first section 405 of the mechanical interface 400 can be adjusted. The mechanism 415 is preferably used only once to initially define a position of the reference body 115. For subsequent measuring or machining operations on the model 105, the mechanism 415 can be removed or locked. Optionally, the height of the reference body 115 on the frame 110 can be adjusted by attaching a spacer plate. Here, too, no change in the relative position is intended after the initial definition.

[0065] Fig. 5 shows an exemplary reference body 115 with a mechanical interface 400 for attachment to a frame 110. The first section 405 is implemented as a plate that can be attached to the frame 110. A mounting hole 502 or another structure can be provided for attachment. The second section 410 is formed directly on the reference body 115, which, for example, has the shape of a cuboid.

[0066] Exemplary optical markings 505 are shown on the surface of the reference body 115. The markings 505 can be applied to the five surfaces of the cuboid-shaped reference body 115 that are not covered by the second section 410 of the mechanical interface 400.

[0067] Sections 405 and 410 can each have a surface 510 configured to engage one another. To secure sections 405, 410 to one another, a magnetic fixture 515 can be provided, which can comprise a combination of two permanent magnets or one permanent magnet and a suitable metal piece. Fixation 515 is preferably configured to press surfaces 510 together.

[0068] For the clear positioning of the second section 410 on the first section 405, structures can be formed on both sides which are designed to engage with each other in a form-fitting manner.

[0069] A first exemplary structure 520 comprises a spherical portion and a ball socket. In this case, the ball socket 520 is formed on the first portion 405, and the ball portion 520 is formed on the second portion 410. If the ball portion engages the ball socket, lateral displacement of the portions 405, 410 along the surfaces 510 is prevented.

[0070] A second exemplary structure 525 comprises a prism and a slot. The slot is formed, in this example, on the first section 405, and the prism is formed on the second section 410. The second structure 525 also defines a rotational position of the sections 405, 410 about a rotation axis that runs perpendicular to the surfaces 510.

[0071] A third exemplary structure 530 comprises a cylinder and a corresponding hollow cylinder. In the illustrated embodiment, the cylinder is formed on the first section 405, and the hollow cylinder is formed on the second section 410.

[0072] It is preferred that a plurality of structures 520 to 530 are included in the mechanical interface 400 in order to adjust an alignment of the reference body 115 relative to the first section 405 or the frame 110 in a reproducible and unambiguous manner with respect to existing degrees of freedom.

[0073] Fig. 6 shows a reference body 115 in a further embodiment. The illustrated reference body 115 is essentially plate-shaped with, for example, a pentagonal base. The second section 410 is connected to the reference body 115 via an extension arm 118. The second section 410 is also designed in the manner of a plate and, in the illustrated embodiment, comprises a surface 510 for contact with a corresponding first section 405 and three structures 605 formed in the surface 510 of the second section 410.

[0074] The structures 605 are designed as three spaced-apart truncated cones that extend upward from the surface 510. Matching concave receptacles can be formed in the corresponding first section 405 of the mechanical interface 400. The truncated cones 605 are spaced from each other essentially in the manner of an equilateral triangle. Optionally, a magnetic fixation 515 can be formed between a truncated cone and a receptacle. In another embodiment, a fixation 515 can also be formed between the structures 605. Reference symbol 100 measuring system 105 Model 110 frames 115 reference bodies 118 booms 120 interface 125 Recording system 130 processing facility 135 data storage 200 procedures 205 Provide frames 210 Attach reference body 215 Measure frame, define frame-fixed coordinate system 220 Remove reference body 225 Create / edit model 230 Attach reference body 235 Model measured 240 Model rating 305 Axis 310 subframe 400 mechanical interface 405 first section, frame-fixed 410 second section, frame-fixed 415 adjustment mechanism 502 mounting hole 505 optical marking 510 area 515 magnetic fixation 520 first structure, spherical section and ball socket 525 second structure, prism and slot 530 third structure, cylinder and hollow cylinder 605 fourth structure, truncated cone and receptacle

Claims

[1] Measuring system (100), comprising: - a frame (110) adapted to support a model (105) to which a number of optical markers are applied; - a plurality of reference bodies (115) which are removable from the frame (110) and can be attached to the frame (110) in a repeatable and / or reproducible manner; - an optical detection system (125) configured to scan the model (105) and the reference bodies (115); and - a processing device (130) which is arranged to - to determine an orientation of the frame (110) with respect to the detection system (125) on the basis of a scan of the reference bodies (115) and - align a scan of the model (105) based on the determined orientation of the frame (110); characterized by that the processing device (130) is further configured to - to align two overlapping scans of the model (105) with respect to the position of optical markings detected in both scans. [2] Measuring system (100) according to claim 1, wherein the reference bodies (115) carry respective individual optical markings (505) which can be detected and / or optically scanned by means of the detection system (125). [3] Measuring system (100) according to claim 1 or 2, wherein the reference bodies (115) are assigned to predetermined positions on the frame (110). [4] Measuring system (100) according to one of the preceding claims, wherein predetermined mechanical interfaces (400) for tool-free separation and connection are provided between the reference bodies (115) and the frame (110). [5] Measuring system (100) according to claim 4, wherein a mechanical interface (400) comprises two surfaces (510) for mutual engagement, wherein mutually corresponding sections (520-530, 605) are formed on the surfaces (510) for mutual positive engagement. [6] Measuring system (100) according to claim 4 or 5, wherein a mechanical interface (400) comprises a magnetic fixation (515) between the reference body (115) and the frame (110). [7] Measuring system (100) according to one of the preceding claims, wherein a boom (118) is provided between the reference body (115) and the frame (110). [8] Measuring system (100) according to one of the preceding claims, wherein an auxiliary frame (310) is movably mounted on the frame (110); wherein at least one further reference body (115) is mounted on the auxiliary frame (310). [9] Measuring system (100) according to claim 8, wherein a further subframe is movably mounted on the subframe (310). [10] A method (200) for scanning a model (105) carried by a frame (110), the method (200) comprising the following steps: - attaching (210) a plurality of reference bodies (115) to the frame (110); - optical scanning (215) of the model (105) and the reference bodies (115), wherein a number of optical markers are attached to the model (105) and wherein two overlapping scans of the model (105) are aligned with each other by means of a processing device (130) with respect to the position of optical markers detected in both overlapping scans; - defining (215) a frame-fixed coordinate system on the basis of a scan of a predetermined number of reference bodies (115); - temporarily removing (220) the reference bodies (115) from the frame (110); - reattaching (230) the reference bodies (115) to the frame (110); and - Repeat (235) the scan. [11] The method (200) of claim 10, further comprising comparing (240) the samples.

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