WO2016055213A1 - Procédé de détermination d'un champ de vecteurs de déplacement spatial d'un objet de test - Google Patents

Procédé de détermination d'un champ de vecteurs de déplacement spatial d'un objet de test Download PDF

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Publication number
WO2016055213A1
WO2016055213A1 PCT/EP2015/069413 EP2015069413W WO2016055213A1 WO 2016055213 A1 WO2016055213 A1 WO 2016055213A1 EP 2015069413 W EP2015069413 W EP 2015069413W WO 2016055213 A1 WO2016055213 A1 WO 2016055213A1
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WO
WIPO (PCT)
Prior art keywords
test object
projection pattern
displacement vector
image
pattern image
Prior art date
Application number
PCT/EP2015/069413
Other languages
German (de)
English (en)
Inventor
Bernhard Wieneke
Original Assignee
Lavision Gmbh
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 Lavision Gmbh filed Critical Lavision Gmbh
Publication of WO2016055213A1 publication Critical patent/WO2016055213A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
    • G01B11/167—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge by projecting a pattern on the object
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T7/00—Image analysis
    • G06T7/20—Analysis of motion
    • G06T7/246—Analysis of motion using feature-based methods, e.g. the tracking of corners or segments

Definitions

  • the invention relates to a method for determining a spatial
  • Displacement vector field of a test object in which the test object at least one projection pattern image, the recording of which the test object is illuminated with a spatially modulated, projected on the test object projection pattern, is recorded and compared with a reference.
  • a common problem occurring, for example, in material testing technology is the determination of the three-dimensional deformation of a test object under mechanical stress.
  • Surface point of the test object assigns a three-dimensional vector, which represents its displacement at the time of measurement relative to a time-spaced reference state of the test object.
  • Displacement vector field should be synonymous synonymous as 3D deformation addressed.
  • the 3D deformation is using a stereo DIC
  • the projection pattern image is characterized in that the test object is illuminated with a known projection pattern for its recording.
  • Projection pattern is a preferably periodic, spatial intensity modulation of the illumination light.
  • a bar, grid or wave pattern can be projected onto the test object, whereby sharp edges or continuous transitions can be realized between light and dark areas of the pattern. Is this
  • test object is illuminated substantially uniformly in the process of the cited document, so that one on his
  • This may be a natural surface structure of the test object, an artificially applied structure, such as randomly distributed drops of paint or the like.
  • This plane displacement vector field is synonymous here synonymous as 2D deformation.
  • the term of the self-pattern image is to be interpreted broadly and includes any image from which the self-pattern of the test object can be derived. It does not necessarily, as in the last-mentioned method, one with uniform
  • Own pattern image and the projection pattern image typically have to be recorded at different times.
  • the determination of the 3D deformation thus becomes the 2D deformation representative of the recording time of the self-pattern image and the recording time of the image which is different for it
  • Projection pattern image representative form of the test object is based.
  • the determined 3D deformation is therefore not representative of a specific point in time, but rather of the time interval between the two acquisition times of the own pattern image and the projection pattern image with the corresponding measurement uncertainty. For fast-running processes in the test object, such as fracture or cracking processes, this significantly reduces the cognitive value of the measurement.
  • the second mathematical function is a mathematical model of a second plane displacement vector field distorted
  • the plane shift vector fields are varied by means of a mathematical error minimization method until a match is achieved between the mathematical model of the projection pattern image and the recorded projection pattern image, and
  • step b calculating the spatial displacement vector field from those varied planar displacement vector fields which have led to said coincidence in step b.
  • the method according to the invention only requires the acquisition of a single image at the time of measurement, namely a projection pattern image, upon which the test object is illuminated with the spatially modulated projection pattern projected onto the test object.
  • a pattern of a natural pattern at the same or a closely adjacent time is within the scope of the
  • This model consists of the combination of two mathematical functions, which should be referred to here as the first mathematical function P and as the second mathematical function S.
  • the "combination" of the mathematical functions P and S, which both describe surface intensity distributions, is essentially essentially a multiplication.
  • the functions P and S are each spatially two-dimensional functions, ie they depend on two surface variables, which are to be referred to here as x and y.
  • the Area parameters x and y preferably correspond to the area variables of the recorded projection pattern image.
  • the first mathematical function P follows from a function P (x, y) representing the intensity of the undistorted projection pattern. Therefore, according to a two-dimensional distortion that can be represented by a first plane displacement vector field (dx p , dy p ), it has P (x-dx p , y-dy p ). The two-dimensional distortion results from the projection of the projection pattern onto the three-dimensional shape of the test object.
  • the second mathematical function S follows from a function S (x, y) which determines the intensity of a self-pattern image of the self-image taken at a reference time t ref
  • Test object represented Therefore, after a two-dimensional distortion that can be represented by a second plane displacement vector field (dx s , dy s ), it has the form S (x-dx s , y-dy s ).
  • the two-dimensional distortion results from the deformation of the test object between the reference and the measurement time.
  • the spatial displacement vector field i.e. the two plane displacement vector fields, can be determined. determine the SD deformation, which was subjected to the test object between the reference time point and the recording time t.
  • the superposition of a projection pattern distortion and a self-pattern distortion can be achieved by 3D imaging alone by taking a single image at the time of measurement, namely one
  • Self-pattern image at the time of measurement or the isolation of the self-pattern information by means of spectral filtering or other methods, as is done in the known method, is unnecessary due to the present invention.
  • the associated advantages in terms of time and equipment costs are obvious.
  • a scalar field is determined, which represents for each point of the first plane displacement vector field, the underlying displacement of the respective corresponding surface point of the test object perpendicular to the plane spanned by the surface variables plane, and the spatial
  • Displacement vector field and the scalar field Displacement vector field and the scalar field.
  • Test object known at the reference time t is also known because of the known optical structure of the apparatus, as projected onto this reference form
  • Displacement vector field describes the distortion that lies between the projection pattern and a (hypothetical) projection pattern image of the reference form.
  • the second displacement vector field inherited unchanged from step b represents the surface displacement in the x-y plane, so that a vectorial complement of this second planar displacement vector field around the scalar field representing the z-component of the displacement explained above to the desired spatial
  • Displacement vector field i. to the desired 3D deformation, leads.
  • Reference object projected reference projection pattern is illuminated.
  • the mental steps described above as purely mathematical are used for Determination of the reference form in this variant practically implemented, so that in addition to the recording of a reference pattern of self-image here also the inclusion of a reference projection pattern image is required.
  • the combination of the first and the second mathematical functions made for constructing the mathematical model essentially comprises their multiplication.
  • a scaling by a scaling factor is favorably included, which is likewise varied within the scope of the mathematical error minimization method.
  • the fitting method is extended by an additional degree of freedom, which may lead to better matching, e.g. in the case of changing intensities of illumination.
  • the self-pattern of the test object extends over its entire surface.
  • the projection pattern has a modulation depth of 100%, all of the self-pattern information is lost in the dark areas of the projection pattern. This complicates the error minimization method.
  • the projection pattern has a modulation depth ⁇ 100%, in particular a modulation depth between 40% and 60%. This modulation depth can also represent a parameter to be adopted.
  • the modulation depth is determined by a parameter in the mathematical model of the
  • Projection pattern image is represented and the parameter representing the modulation depth is optionally varied within the mathematical Whyinimierungsvons. This also represents an extension of the error minimization method by an additional degree of freedom.
  • error minimization methods can be performed as global or local methods.
  • the fitting process is essentially applied simultaneously to the entire image.
  • the fitting process is successively applied to sections of the image to be inserted.
  • the plane displacement vector fields are successively, partially varied to match a corresponding portion of the recorded projection pattern image, wherein additionally shear and / or rotation parameters are varied, the relative orientation of the respective sections of the plane displacement vector fields to the respective
  • the self-pattern image of the inspection object used as a reference image is a "pure" self-image image, that is, an image of the uniform illumination light test object, however, because it greatly simplifies the calculation.
  • the method according to the invention makes it particularly suitable for a multiple, successive application to the deforming under mechanical stress
  • the behavior of a stressed and deforming test object can be measured or monitored very tightly clocked.
  • very rapid processes, such as crack formation can be observed with such a fast process.
  • FIG. 1 shows a schematic representation of a structure for carrying out the method according to the invention
  • FIG. 2 is a schematic representation to illustrate a preferred embodiment
  • FIG. 1 shows, in a greatly simplified schematization, the construction of a device for carrying out the method according to the invention.
  • a projector 10 By means of a projector 10, either a projection pattern 16 (for recording a projection pattern image) or a uniform light (for recording a self-pattern image) is projected onto the test object 12.
  • the projector 10 may be e.g. a conventional one
  • White light projector (slide projector) act, the light is sent as needed by a projection pattern 16 wearing mask.
  • a projection pattern 16 wearing mask Alternatively, a can
  • programmable projector eg a so-called DMD (Digital Micromirror Device) projector with which mask-independent any projection pattern can be realized, find use.
  • DMD Digital Micromirror Device
  • Image detector 1 1 arranged, e.g. a CCD camera with which images of the suitably illuminated test object can be recorded.
  • FIG. 2 shows a diagram for illustrating a preferred embodiment of the method according to the invention.
  • a method for measuring the three-dimensional deformation of a test object that is under tension and deforms by way of example is selected.
  • the test object points to his
  • Reference numeral 12 designates the test object at a reference time, for which, in the context of the present description, it is assumed to be undeformed for the sake of simplicity.
  • the self-pattern on the surface of the test object 12 appears as a given two-dimensional one
  • a projection pattern 16 on the test object 12 leads to a distortion of the projection pattern 16 on the surface of the test object 12, a projection pattern, for example represented by a projection mask used Image of the test object 12 with projected projection pattern shows a projection-related two-dimensional intensity distribution.
  • test object 12 has deformed from its undeformed to a deformed state. In this state it carries in Figure 2 the
  • test object 12 The deformation of the test object 12 also creates a
  • a model M of such a projection pattern image is created, the parameters of which are varied until the mathematical model M matches the actually recorded projection pattern image of the deformed test object 12 'within a predetermined tolerance.
  • an advantageous embodiment of the mathematical model M is shown. This is the multiplication of two mathematical functions P and S scaled by the scaling factor 1 / I 0.
  • P, S are two-dimensional intensity distributions whose variables x and y preferably correspond to the dimensions correspond to the recorded projection pattern image.
  • the functions P and S additionally flow in dependence on a respective plane displacement vector field (dx p , dy p ), or (dx s , dy s ).
  • the intensity distributions P and S in the model M are shown as a result of a distortion around (dx s , dy s ) or (dx s , dy s ) of an undistorted intensity distribution P (x, y) and S (x, y), respectively.
  • dx s , dy s a distortion around (dx s , dy s ) or (dx s , dy s ) of an undistorted intensity distribution P (x, y) and S (x, y), respectively.
  • Displacement vector fields (dx p , dy p ) and (dx s , dy s ) will be further explained below.
  • the basic idea of the present invention is these levels
  • Shift vector fields ie the parameters (dx p , dy p ) or (dx s , dy s ) to vary until the model M within the given accuracy with the recorded projection pattern image matches.
  • other parameters such as the intensity scaling factor 1 / l 0 to vary, if necessary.
  • the first plane displacement vector field (dx p , dy p ) represents the distortion of the projection pattern 16 resulting from its projection onto the deformed test object 12 ', ie the transition from the pure projection pattern 16 to the twice distorted projection pattern 16 ".
  • dx s , dy s the distortion that the eigenpattern 14 experiences as a result of the deformation of the test object 12, ie the transition from the eigenpattern 14 on the undeformed test object 12 to the distorted eigenpattern 14 'on the deformed test object 12'.
  • both displacement vector fields are not known to those skilled in the art in advance.
  • planar result shift vector fields (dx p , dy p ) and (dx s , dy s ) leading to the said match are used in a next method step to calculate a spatial displacement vector field (dx, dy, dz) which is the
  • the shape z (x, y) of the test object at the time of measurement can be calculated from the result shift vector field (dx p , dy p ) determined above. From these parameters, the desired spatial displacement vector field (dx, dy, dz) can then be calculated in a manner known to those skilled in the art.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Multimedia (AREA)
  • Computer Vision & Pattern Recognition (AREA)
  • Theoretical Computer Science (AREA)
  • Length Measuring Devices By Optical Means (AREA)

Abstract

L'invention concerne un procédé de détermination d'un champ de vecteurs de déplacement spatial ((dx, dy, dz)) d'un objet de test, dans lequel au moins une image de motif de projection, lors de l'enregistrement de laquelle l'objet de test est éclairé avec un motif de projection modulé spatialement et projeté sur l'objet de test, est enregistrée par l'objet de test et comparée à une référence. L'invention est caractérisée en ce que a) une combinaison d'une première fonction mathématique (P(x-dxpy-dy<sb />p)) et d'une seconde fonction mathématique (S(x-dxs, y-dys)) de variables de surface (x, y) est créée comme modèle mathématique de l'image de motif de projection, a1) la première fonction mathématique (P(x -dxp, y-dyp)) étant un modèle mathématique du motif de projection déformé d'un premier champ de vecteurs de déplacement plan ((dxp, dyp)) est et a2) la seconde fonction mathématique (s(x-dxs, y-dys)) étant un modèle mathématique d'une image de référence, déformée d'un second champ de vecteurs de déplacement plan ((dxs, dys)), qui a été enregistrée à un instant de référence (tref) en tant qu'image d'image de motif propre de l'objet de test, en ce que b) les champs de vecteurs de placement plans ((dxp, dyp), (dxs, dys)) sont modifiés au moyen d'une méthode mathématique de minimisation d'erreurs jusqu'à obtenir une concordance entre le modèle mathématique de l'image de motif de projection et l'image de motif de projection enregistrée, et en ce que c) le champ de vecteurs de déplacement spatial ((dx, dy, dz)) est calculé à partir des champs de vecteurs de déplacement plans ((dxp, dyp), (dxs, dys)) qui sont varié et qui ont conduit à la dite concordance à l'étape b.
PCT/EP2015/069413 2014-10-08 2015-08-25 Procédé de détermination d'un champ de vecteurs de déplacement spatial d'un objet de test WO2016055213A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102014114616.6A DE102014114616B3 (de) 2014-10-08 2014-10-08 Verfahren zur Ermittlung eines räumlichen Verschiebungsvektorfeldes eines Prüfobjektes
DE102014114616.6 2014-10-08

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Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19509962A1 (de) 1995-03-18 1996-09-19 Univ Karlsruhe Verfahren und Vorrichtung zur Erfassung von dreidimensionalen Verschiebungsvektorfeldern

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19509962A1 (de) 1995-03-18 1996-09-19 Univ Karlsruhe Verfahren und Vorrichtung zur Erfassung von dreidimensionalen Verschiebungsvektorfeldern

Non-Patent Citations (5)

* Cited by examiner, † Cited by third party
Title
B. BARRIENTOS ET AL: "Three-dimensional displacement measurement by fringe projection and speckle photography", AIP CONFERENCE PROCEEDINGS, vol. 992, 1 January 2008 (2008-01-01), pages 828 - 833, XP055027081, ISSN: 0094-243X, DOI: 10.1063/1.2926979 *
BARRIENTOS, B. ET AL.: "Three-dimensional displacement fields measured in a deforming granular-media surface by combined fringe projection and speckle photography", J. OPT.A: PURE APPL. OPT., vol. 10, 2008, pages 104027
NGUYEN T. NAM, HUNTLEY JONATHAN M., BURGUETE RICHARD L., COGGRAVE C. RUSSELL: "Shape and displacement measurement of discontinuous surfaces by combining fringe projection and digital image correlation", OPTICAL ENGINEERING, vol. 50, no. 10, 14 June 2011 (2011-06-14), pages 101505 - 101505-9, XP060020363, Retrieved from the Internet <URL:http://opticalengineering.spiedigitallibrary.org/article.aspx?articleid=1158389> [retrieved on 20151111], DOI: 10.1117/1.3572190 *
QUAN, C. ET AL.: "3-D deformation measurement using fringe projection and digital image correlation", OPTIK, vol. 115, no. 4, 2004, pages 164 - 168
TAY, C. J. ET AL.: "Integrated method for 3-D rigid-body displacement measurement using fringe projection", OPT. ENG., vol. 43, no. 5, May 2004 (2004-05-01), pages 1152 - 1159

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