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WO2007131723A1 - Procédé de mesure d'un corps solide - Google Patents

Procédé de mesure d'un corps solide Download PDF

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Publication number
WO2007131723A1
WO2007131723A1 PCT/EP2007/004201 EP2007004201W WO2007131723A1 WO 2007131723 A1 WO2007131723 A1 WO 2007131723A1 EP 2007004201 W EP2007004201 W EP 2007004201W WO 2007131723 A1 WO2007131723 A1 WO 2007131723A1
Authority
WO
WIPO (PCT)
Prior art keywords
measuring
solid
surveying
values
threshold
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/EP2007/004201
Other languages
German (de)
English (en)
Inventor
Dirk Neumayer
Martin Stotz
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Werth Messtechnik GmbH
Fraunhofer Gesellschaft zur Foerderung der Angewandten Forschung eV
Original Assignee
Werth Messtechnik GmbH
Fraunhofer Gesellschaft zur Foerderung der Angewandten Forschung eV
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Werth Messtechnik GmbH, Fraunhofer Gesellschaft zur Foerderung der Angewandten Forschung eV filed Critical Werth Messtechnik GmbH
Priority to EP07725121A priority Critical patent/EP2016369A1/fr
Publication of WO2007131723A1 publication Critical patent/WO2007131723A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T11/00—2D [Two Dimensional] image generation
    • G06T11/003—Reconstruction from projections, e.g. tomography
    • G06T11/005—Specific pre-processing for tomographic reconstruction, e.g. calibration, source positioning, rebinning, scatter correction, retrospective gating
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2223/00—Investigating materials by wave or particle radiation
    • G01N2223/045—Investigating materials by wave or particle radiation combination of at least 2 measurements (transmission and scatter)

Definitions

  • the invention is in the field of surveying methods, by means of which the shape of solids can be detected multi-dimensionally.
  • test pieces for example in the manufacture of cast parts, in which the shape and dimensional accuracy of castings must be checked by three-dimensional measurement and compared with specifications. In this step, in addition to the external shape accuracy and the presence of voids or material distortions is checked. Overall, the actual geometry data is with
  • target data for example, from a CAD system.
  • a radiographic method for example an X-ray computer tomographic method.
  • a solid to be measured is successively irradiated from several different directions, wherein usually the x-ray source is fixed and the solid body is rotated about a fixed axis.
  • a detector for example as a two-dimensionally resolving detector in the form of a CCD matrix, which detects the X-rays after passing through the solid.
  • gray values which are calculated in a known manner, taking into account the between the individual
  • Measurements completed angle of rotation can be further processed.
  • consistency limits of the solid so for example, material or density limits or outer contours and boundaries of cavities can be determined.
  • the present invention has the object to increase the reliability and accuracy of the measurement of solids by combining different surveying.
  • the invention relates to a method for measuring a solid using a first surveying method (computed tomography method) radiating through the solid in conjunction with a second measuring method for measuring at least one point of at least one surface or at least one surface of the solid.
  • Such a method using the combination of two surveying methods is basically already known from the prior art.
  • Such is already in the patent Abstract of Japan, Pub. No. 2002071345 A describes a method in which so-called surveying paths are determined by means of a first measuring method for a solid, by means of which and along which the measurement takes place by means of a second measuring method.
  • DE 10 2004 026 357 A1 discloses a device which is used for measuring an object and has an X-ray sensor system and another tactile or optical sensor system, wherein both sensor systems deliver evaluatable data in a common coordinate system.
  • the X-ray sensor system is positioned according to the detection by the other sensor. Excellent points of the object to be measured are measured by means of the further sensor system and from this geometry features are determined which are used to calibrate the X-ray sensor system.
  • CT point cloud is generated and these data are corrected with the data acquired in another way.
  • the present invention has the object to improve the interaction of such different surveying methods in terms of the result and a facilitated and accelerated implementation.
  • the object is achieved by assigning a local segmentation threshold value for the evaluation of the data obtained by the first measurement method to points of the surface of the solid body by means of the measured values obtained by the second method.
  • these threshold values are each used as a basis for the determination of further local segmentation threshold values of the surroundings of the points.
  • the result of a computed tomography is normally in the form that intensity units or gray values are assigned to specific volume units (voxels) and that edges, surfaces or material boundaries of a solid body are represented by jumps in the gray value between the voxels.
  • Such jumps are not ideal and there are often blurred or gray scale transitions in real measurement results.
  • such a computed tomography image is evaluated by defining a threshold value of the gray values representing the boundary surfaces of the solid.
  • the concept of a global threshold is generally abandoned in favor of local thresholds. These are determined by local comparison of the data determined by the second measuring method with the data determined by the first measuring method. sets. That is, by means of the second assessment method, for example, an interface of the solid is detected at one point and it is determined where the local threshold value would have to lie so that the evaluation of the measured values determined by the first method would yield the correct result.
  • This threshold value is defined as a local threshold value and also serves as a threshold value in the immediate vicinity of said location, or at least the threshold value prevailing in the immediate vicinity is determined from the threshold value defined as described. This can also be done, for example, by interpolation of the threshold values at different locations.
  • measurements are carried out by means of the second measurement method at two spaced-apart locations, from which threshold values corresponding to threshold values determined by comparison with the first measuring method are determined and defined as local threshold values. Thereupon, at the positions lying between the two measuring points, further local threshold values are defined by interpolation, which serve for the further evaluation of the data obtained by the first measuring method.
  • Threshold values can also be determined, for example, in the interior region of the solid to be measured, where no measurement data can be acquired by the second measurement method, insofar as this is a surface measurement method, for example a strip projection method.
  • the combined evaluation of the data according to the invention is possible without any problems, as long as the surveying devices for the first and the second surveying methods remain in a defined position relative to one another or are moved against each other in a defined manner.
  • the method according to the invention is particularly advantageous if the first measuring method is an X-ray computer tomography method by means of which an intensity value is assigned to each of the individual volume units.
  • the method can be advantageously applied to other types of computed tomography, such as neutron beam computer tomography.
  • the local threshold is partly known by matching the measurements from the second surveying method.
  • the same threshold value can also be used in areas in the immediate vicinity by means of the measuring point measured in the second measuring method.
  • the measuring points which are measured by means of the second measuring method can thus be spatially less densely distributed than the measuring points of the first measuring method.
  • local threshold values are determined by interpolation between known local threshold values.
  • Determination of consistency limits of the solid can be done with an accuracy that exceeds the resolution given by volume units (voxels).
  • volume units voxels
  • a plurality of adjacent volume units (voxels), at least one of which has an intensity above the local threshold and at least one intensity below the local threshold value, the point at which the threshold value is exceeded is set approximately to a range smaller than one unit volume (subvoxel accurate).
  • the local threshold is initially often set only voxel exactly, a higher accuracy can be achieved by using an iterative method. For this purpose, for example, according to the subvoxelge- nauen Determination of the point at which a body boundary is again redefined by interpolation at exactly this point the threshold locally. After the renewed determination of the threshold value, in a further iteration step, the
  • the local threshold values for the volume units are determined individually and stored in a matrix.
  • this matrix corresponds in size to the matrix with the voxel data, in which an intensity value is assigned to each individual voxel.
  • a further advantageous embodiment of the method provides that the local threshold values determined in each case for the same volume units are subtracted from the intensity values determined for the individual volume units (voxels) and that thereafter the segmentation is carried out by means of a global threshold value.
  • the last process step to perform the determination of the body boundaries by means of a global threshold corresponds to the previously common method.
  • the advantage of the invention is shown in the intermediate step, in which local, different threshold values are used. This improves the resolution and accuracy and reduces the susceptibility to errors.
  • a device according to the invention for carrying out the method according to the invention advantageously has a subtraction device which, after determining the local threshold values, reduces the individual elements of the matrix of intensity values from the first memory device by the local threshold values stored in the second memory device , The results are stored in a third memory device.
  • the data stored in the third memory device can now be used for global evaluation, ie for the entire solids constant, threshold value.
  • the nonuniformities and nonlinearities which are unavoidable when using the first measuring device are optimally calculated out in the data thus cleaned up in the third memory device. The evaluation of these data thus results in an adjusted three-dimensional image of the solid to be measured.
  • the second measuring method is a surface-resolution method, in particular a strip projection method.
  • a streak projection method a known pattern, for example, a straight, parallel stripe pattern or grid lines, is projected onto the surface of the solid to be measured by means of an optical image and the image formed on the surface of the solid is taken from an angle that is typically different from the angle of incidence , From the distortions of the ideally straight stripe pattern can be closed by triangulation on the shape of the surface.
  • a stiffener projection method is the ideal supplement to a transmission method, for example a computed tomography X-ray method, in order to achieve overall accurate and reliable data not only for the externally visible surface of a solid to be measured.
  • FIG. 1 shows a flow chart which represents the method according to the invention
  • FIG. 2 shows a combined measuring device
  • FIG. 3 shows a two-dimensional arrangement of voxel data and the corresponding processes during the evaluation of the data.
  • FIG. 1 shows by way of example and schematically simplified three two-dimensional fluoroscopy images 1, 2, 3, which are recorded and stored on a radiographic screen by means of an X-ray tomography method at different transillumination angles with respect to the transilluminated object as transillumination images.
  • these transillumination images which represent the solid to be measured from different angles, can be converted into a three-dimensional image of the object. It is of course possible to use far more than three images for the calculation.
  • the three-dimensional image is in the form of gray values or intensity values in a three-dimensional voxel matrix 4. Each subvolume cube of this matrix 4 is assigned a separate intensity value.
  • this measurement can contain fewer measurement points than the measurement obtained by the first measurement method, but the individual measurement points are more accurate than the computed tomography method.
  • the measurement results 5 of the image obtained by the second measurement method are included in the matrix by setting threshold values for the evaluation of the computed tomography data at the points at which they are determined on the basis of the body boundaries defined by the second measurement method, namely as local, if appropriate locally different thresholds.
  • the local threshold values are determined by interpolation of the remaining, present threshold values.
  • the body boundaries of the solid to be measured can be calculated precisely.
  • the corresponding calculation result is shown symbolically in the matrix 7 and more clearly in the pyramid 8.
  • the advantage of the final measurement result 8 lies in the fact that on the one hand partially measured values are available with the high measurement accuracy of the second measurement method, but on the other hand also where these Measurements are not present, can be obtained by the first surveying reliable values whose accuracy has been increased by using the second measurement method.
  • cavities in the solid body for example, which are not detected by means of the second measuring method, insofar as it detects a surface measurement, can be detected precisely by means of a transmission method.
  • FIG. 2 shows by way of example a device for carrying out the method according to the invention, the individual elements being shown only schematically.
  • a movement device 10 is arranged for the solid 11 to be measured, with a drivable shaft 12, a motor 13 and a gear 14 and a turntable 15.
  • the solid is firmly positioned on the turntable 15 and can be driven by the drive about the vertical axis 16 in small steps, for example, of 0.9 °, rotated and stopped therebetween.
  • an X-ray source 17 for example in the form of a microfocus X-ray tube, which radiates the solid 16 to an X-ray screen 18, and a strip projection device 19 which radiates a geometric pattern onto the solid 11 and the distortions , which result from the shaping of the solid 11, detected.
  • stiffener projection device 19 instead of the stiffener projection device 19, it is also possible to provide another surface imaging device, for example a touch device or a distance measuring device, using running time measurements and an interferometric measuring device.
  • another surface imaging device for example a touch device or a distance measuring device, using running time measurements and an interferometric measuring device.
  • the data captured by the X-ray screen 18 is passed to a computing device 20 which also receives data from the drive means 12, 13, 14 receives about the angular position of the solid 11.
  • the computing device 20 also receives the measurement results of the stiffener projection device 19.
  • the computing device can perform the calculations shown in FIG. 1 and store and process the abovementioned three-dimensional matrices.
  • the computing device 20 determines a representation of the solid 11 in three dimensions, which is for example in different views on the screen 21 d3.rstellba.r.
  • FIG. 3 a simplified schematic two-dimensional example is used to illustrate how the results of the two surveying methods are computationally combined.
  • a global threshold value for determining the shapes of the solid body between the intensity 1 and the intensity 2 could be determined, for example.
  • Measurement errors in the computed tomography measurement can be compensated.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Theoretical Computer Science (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)
  • Apparatus For Radiation Diagnosis (AREA)

Abstract

L'invention concerne un procédé de mesure d'un corps solide (11) au moyen d'un premier procédé de mesure par radiographie du corps solide (tomographie par ordinateur) associé à un second procédé de mesure permettant de mesurer au moins une surface du corps solide (11). L'objectif de cette invention est d'améliorer l'utilisation de ces deux procédés de mesure et d'optimiser le calcul des résultats. A cet effet, une valeur seuil de segmentation locale permettant l'évaluation des données obtenues par le premier procédé de mesure est attribuée à des points de la surface du corps solide à l'aide des valeurs de mesure obtenues par le second procédé. Ces valeurs seuils peuvent servir de base à la détermination d'autres valeurs seuils de segmentation locales dans le voisinage des points.
PCT/EP2007/004201 2006-05-11 2007-05-11 Procédé de mesure d'un corps solide Ceased WO2007131723A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP07725121A EP2016369A1 (fr) 2006-05-11 2007-05-11 Procédé de mesure d'un corps solide

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102006022103.6 2006-05-11
DE102006022103A DE102006022103B4 (de) 2006-05-11 2006-05-11 Verfahren zum Vermessen eines Festkörpers

Publications (1)

Publication Number Publication Date
WO2007131723A1 true WO2007131723A1 (fr) 2007-11-22

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PCT/EP2007/004201 Ceased WO2007131723A1 (fr) 2006-05-11 2007-05-11 Procédé de mesure d'un corps solide

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EP (1) EP2016369A1 (fr)
DE (1) DE102006022103B4 (fr)
WO (1) WO2007131723A1 (fr)

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2014009976A (ja) * 2012-06-28 2014-01-20 Hitachi Ltd ３次元形状計測用ｘ線ｃｔ装置およびｘ線ｃｔ装置による３次元形状計測方法
DE102018105709A1 (de) 2017-03-15 2018-09-20 Werth Messtechnik Gmbh Verfahren zur computertomografischen Messungen von Werkstücken
DE102019131452A1 (de) * 2019-11-21 2021-05-27 Volume Graphics Gmbh Computerimplementiertes Verfahren zur Segmentierung von Messdaten aus einer Messung eines Objekts
DE102019131434A1 (de) * 2019-11-21 2021-05-27 Volume Graphics Gmbh Computerimplementiertes Verfahren zur Segmentierung von Messdaten aus einer Messung eines Objekts
DE102019131437A1 (de) * 2019-11-21 2021-05-27 Volume Graphics Gmbh Computerimplementiertes Verfahren zur Segmentierung von Messdaten aus einer Messung eines Objekts
DE102019220090B3 (de) * 2019-12-18 2021-01-07 Bayerische Motoren Werke Aktiengesellschaft Verfahren und Vorrichtung zum automatisierten Bewerten eines Kernbruchdefektes in einem Hohlraum in einem Gussbauteil

Citations (2)

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EP0366387A2 (fr) * 1988-10-24 1990-05-02 General Electric Company Obtention d'images tridimensionnelles à partir de données tomographiques
WO2005119174A1 (fr) * 2004-05-26 2005-12-15 Werth Messtechnik Gmbh Instrument de mesure a coordonnees et procede de mesure d'un objet

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JP3427046B2 (ja) * 2000-08-29 2003-07-14 株式会社日立製作所 ３次元寸法計測装置及びその計測方法
DE10331419A1 (de) * 2002-07-12 2004-01-22 Mycrona Gesellschaft für innovative Messtechnik mbH Verfahren und Vorrichtung zur Bestimmung der Ist-Position einer Struktur eines Untersuchungsobjektes
DE102004026357B4 (de) * 2004-05-26 2022-11-17 Werth Messtechnik Gmbh Vorrichtung und Verfahren zum Messen eines Objektes
DE102005023376A1 (de) * 2005-05-17 2006-11-23 Carl Zeiss Industrielle Messtechnik Gmbh Verfahren und Vorrichtung zum Bestimmen von Materialgrenzen eines Prüfobjektes

Patent Citations (2)

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Publication number Priority date Publication date Assignee Title
EP0366387A2 (fr) * 1988-10-24 1990-05-02 General Electric Company Obtention d'images tridimensionnelles à partir de données tomographiques
WO2005119174A1 (fr) * 2004-05-26 2005-12-15 Werth Messtechnik Gmbh Instrument de mesure a coordonnees et procede de mesure d'un objet

Non-Patent Citations (2)

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Title
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MULLALLY WILLIAM ET AL: "Segmentation of nodules on chest computed tomography for growth assessment", MEDICAL PHYSICS, AIP, MELVILLE, NY, US, vol. 31, no. 4, April 2004 (2004-04-01), pages 839 - 848, XP012074839, ISSN: 0094-2405 *

Also Published As

Publication number Publication date
DE102006022103B4 (de) 2013-05-29
DE102006022103A1 (de) 2007-11-22
EP2016369A1 (fr) 2009-01-21

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