EP1459033A2 - Procede de mesure tridimensionnelle d'une surface - Google Patents

Procede de mesure tridimensionnelle d'une surface

Info

Publication number
EP1459033A2
EP1459033A2 EP02804921A EP02804921A EP1459033A2 EP 1459033 A2 EP1459033 A2 EP 1459033A2 EP 02804921 A EP02804921 A EP 02804921A EP 02804921 A EP02804921 A EP 02804921A EP 1459033 A2 EP1459033 A2 EP 1459033A2
Authority
EP
European Patent Office
Prior art keywords
determined
contrast
sensor
optical axis
image
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.)
Withdrawn
Application number
EP02804921A
Other languages
German (de)
English (en)
Inventor
Ralf Christoph
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
Original Assignee
Werth Messtechnik 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 Werth Messtechnik GmbH filed Critical Werth Messtechnik GmbH
Publication of EP1459033A2 publication Critical patent/EP1459033A2/fr
Withdrawn legal-status Critical Current

Links

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
    • G01B11/30—Measuring arrangements characterised by the use of optical techniques for measuring roughness or irregularity of surfaces
    • G01B11/306—Measuring arrangements characterised by the use of optical techniques for measuring roughness or irregularity of surfaces for measuring evenness
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N13/00—Stereoscopic video systems; Multi-view video systems; Details thereof
    • H04N13/20—Image signal generators
    • H04N13/204—Image signal generators using stereoscopic image cameras
    • H04N13/207—Image signal generators using stereoscopic image cameras using a single 2D image sensor
    • H04N13/236—Image signal generators using stereoscopic image cameras using a single 2D image sensor using varifocal lenses or mirrors
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N13/00—Stereoscopic video systems; Multi-view video systems; Details thereof
    • H04N13/20—Image signal generators
    • H04N13/271—Image signal generators wherein the generated image signals comprise depth maps or disparity maps

Definitions

  • the invention relates to a method for three-dimensional measurement of a surface of an object according to the autofocus principle by means of a coordinate measuring device, an optical sensor that detects a measurement area of the surface moving or apparently moving along its optical axis and a parameter that is characteristic of the surface, such as Contrast value is measured, and the spatial coordinate of the measuring point is calculated from the position of the sensor, which corresponds to a focus location, and the position of the measuring point to be measured or its image in a plane perpendicular to the optical axis.
  • optically scanning measuring systems For the surface analysis of material surfaces, optically scanning measuring systems are used that work according to the auto focus principle. For example, individual autofocus points are measured using the contrast method during scanning. This method requires long measuring times to record complete contours. A few seconds are required per measuring point.
  • WO 99/53271 describes a method for point-wise scanning profile determination of a material surface with a coordinate measuring machine according to the auto focus principle.
  • an image processing sensor is moved along an optical axis and, at the same time, the contrast values are determined via an evaluation system.
  • the resulting contrast curve is used to infer the distance between the object surface and the sensor.
  • Another common feature of the known methods is that only one measurement point along the optical axis is obtained for each image field. This results in the disadvantage that a quick measurement of surfaces is not possible. It has already been considered to set several windows simultaneously in the image field of a focus sensor. However, the number of focus values is limited by the size of the windows arranged next to one another, so that only a few windows or focus points with sufficient pixel information are used to determine the contrast.
  • the present invention is based on the problem of developing a method of the type mentioned in the introduction in such a way that a high-resolution description of three-dimensional surfaces is made possible.
  • the problem is essentially solved in that the measuring area is divided into partial areas and the characteristic parameter of each partial area is determined along its optical axis during the movement of the sensor.
  • the optical sensor is a CCD chip or a CCD camera, a focus location being determined for each image processing pixel.
  • a focus location is assigned to the measuring points.
  • the focus location is understood to mean the position relative to the sensor (in sensor coordinates) in which an image section has the optimal sharpness (e.g. maximum contrast).
  • the invention provides that the partial areas, that is to say the windows of the image field of the CCD sensor, overlap for the determination of the characteristic parameter, measuring points being determined from overlapping partial or evaluation areas simultaneously or almost simultaneously.
  • the density of the measured focus locations and thus measurement points is limited by the number of image points of the image processing sensor.
  • the focus location is determined for each measuring point in a partial area to be designated as the operator window.
  • the size of the measuring area is limited overall by the image field.
  • the measuring range is the evaluation range defined by the image processing window, in which measuring points are generated by the method according to the invention.
  • Sub-area is to be understood as the local area in which z.
  • the term field of view of the image processing sensor should also be introduced. This describes the physical limitation of the entire field of view by the camera chip or the chip size.
  • an image processing operator is used in a known manner to convert the gray value into a binary image in order to determine the contrast value for selected image processing pixels from the respective operator window.
  • a stack of images is measured during the process of the optical sensor along its optical axis, the characteristic parameter being determined for each partial area and then the focus location per partial area being determined from the stack of images.
  • the spatial coordinate for each pixel and thus each measuring point can then be calculated.
  • the respective focus locations of the desired measuring points are determined from a few image planes. For example, two or three levels of contrast values can be calculated, which are used to calculate the focus location after determining a measured focus function beforehand.
  • the focus location for each pixel (pixel) can be calculated simultaneously by arranging two or three or more sensor chips, and the coordinate on the optical axis can be determined from this, as disclosed by WO 01/33166 A1.
  • the determination of the contrast values measured in each sensor can result in a predetermined distance the previously known relation of the contrast value curves or parabolas to each other, the contrast value curve of the sensor is calculated, on the working plane of which the point is to be depicted sharply.
  • the point to be measured lies in the focal plane of the optics assigned to the sensor.
  • the invention is also characterized in that the focus location for the respective image point (pixel) is calculated from the neighboring focus location using additional image points located in the evaluation window.
  • the calculation of the focus location for each image processing pixel can also take place by starting from a calculated focus location for a pixel and then calculating the neighboring focus locations differentially from this.
  • the secondary information is used that neighboring pixels are close to each other. can be expected. This additional condition allows the calculation algorithm to be limited to the close range around the focus maximum.
  • An independent proposal of the invention also provides for the calculation of the functional course of the contrast function to be detached in principle from the calculation of the focus locations. This makes it possible to use all amplitudes for the most accurate possible calculation of the functional curve of the contrast function and thus to achieve a low-noise result.
  • the contrast function can be generated from individual profiles for individual pixels by averaging, or can be determined by combining all the contrast profiles of all pixels. This contrast function determined in this way is then used to determine the location of the maximum of the contrast function for each pixel from a few support points when determining the respective local focus location. Three bases are normally sufficient for this. The noise of the corresponding contrast values is no longer received by falsifying the contrast function, but only by directly falsifying the amplitude values. A higher accuracy is thus achieved.
  • the advantage lies in the fact that fewer measuring points have to be recorded in order to determine an exact focus location, which increases the measuring speed or achieves a reliable measuring result (reproducible) with a high number of measuring points.
  • the invention is characterized in that a virtual 2D image is generated from the determined maximum values, the contrast values in the individual pixels (pixels) in such a way that each pixel is assigned the amplitude that corresponds to the image of the maximum contrast. Images captured during the autofocus measurement are searched for high-contrast pixels. An image is then composed of all high-contrast areas (pixels) of the individual images, which improves the depth of field.
  • the three-dimensional surface course determined by the method according to the invention can be overlaid for further evaluation with the 2D image determined according to the invention with a large depth of field such that a joint evaluation of the 2D image curved in space is possible using image processing methods.
  • Fig. 4 Determination of a focus location on the basis of a calibrated
  • FIG. 5 shows a basic illustration of a sensor arrangement for determining a focus location
  • Fig. 7 is a schematic diagram of a coordinate measuring machine.
  • a coordinate measuring machine 10 is shown in principle, with which the surface geometry of an object is to be determined in high resolution.
  • the coordinate measuring machine 10 can be a z. B. from granite base frame 12 with measuring table 14, on which an object, not shown, can be arranged, the surface of which is to be measured.
  • a portal 16 is adjustable in the Y direction along the base frame 12.
  • columns or stands 18, 20 are slidably supported on the base frame 12.
  • a crossbeam extends from the columns 18, 20, along which - in the X direction - a carriage 24 can be adjusted, which in turn receives a quill or column 26 which moves in the Z direction is adjustable.
  • An optical sensor 28 such as a laser distance sensor, emanates from the quill or column 26 and, on the one hand, is adjustable in the X and Y planes to determine the surface geometry and, on the other hand, it can be moved along its optical axis, that is to say in the exemplary embodiment along the Z axis.
  • FIG. 1 shows the optical sensor 28, which comprises a lens 30 and a CCD chip 32 assigned to it, arranged in the image plane of the lens 30.
  • the CCD chip 32 or also called the camera matrix has light-sensitive pixels 42, 44 arranged in lines 34, 36 and columns 38, 40 in order to use the image information to be extracted from them in the form of gray-scale images in the manner described below to assign the surface 46 of an object 48 measure up.
  • the measuring range detected at a predetermined XY coordinate by means of the optical sensor 28 or its image depicted on the camera matrix 32 is divided into partial areas, so-called windows, which are mxn - in the exemplary embodiment by a 3 x 3 Operator - is specified, which scans the entire camera matrix 32, as is symbolized purely in principle by the arrow representations 52, 54 in FIGS. 1 and 2a.
  • the focus location is determined for each pixel 42, 44 from the 3x3 operator, specifically by the fact that, given a predetermined XY position, the optical sensor 28 or the CCD camera along its or its optical axis 50, ie in Z- Direction is moved, wherein a stack of images 56, 58, 60 is generated.
  • Each image 56, 58, 60 is scanned by the corresponding mx n operator, that is to say the 3 ⁇ 3 operator in the exemplary embodiment, in order then to determine a contrast curve 62, 64 for each pixel 42, 44, as is purely in principle shown in FIG. 2a can be seen.
  • the focus location ie the working distance at which a measurement point of the surface 46 is sharply imaged in the image plane 38, corresponds to the maximum of the contrast curve 62, 64. Since, according to the invention, a focus location is fundamentally assigned to each pixel 42, 44, the spatial coordinate of each measurement point can then be assigned and thus the surface profile of the object 48 to be measured can be determined, as the diagram in FIG. 2b illustrates in principle. Knowledge of the XY coordinate of the respective pixel 42, 44 in is used here the coordinate measuring machine 10 and the focus location (Z coordinate) determined from the contrast curves 62, 64.
  • 1 and 2 also show that the measuring points, i. H. the focus locations of the individual pixels 42, 44 are calculated from overlapping evaluation areas which are predetermined by the size of the operator.
  • the contrast values of a total of 9 pixels, which are symbolized by the numbers 1 to 9, are determined and then an average contrast value is determined from these, which corresponds to the pixel in the center of the partial area, that is to say in the exemplary embodiment the pixel with the number “5”.
  • a contrast value curve 70 is reproduced in principle, in which the contrast is plotted against the Z axis.
  • the height profile of an object can also be determined in a direction other than the Z axis of a coordinate measuring machine, depending on the orientation of the optical axis of the optical sensor used in relation to the coordinates of the coordinate measuring machine.
  • a stack with a desired number of images can be evaluated to determine the contrast curves and thus the focus locations
  • FIG. 4 there is the basic possibility according to FIG. 4 of using a stack with three planes or images captured in these, basically per Processing pixels a focus location is determined. Three images are sufficient if a general focus function of the system is determined, the contrast curve then being determined from the position of two or three support points.
  • the con- Trast values Pl, P2 and P3 were determined at different working or image distances Z ', Z' and Z '".
  • the contrast value curve determined in the system was then passed through the measuring points Pl, P2 and P3 in order to then increase the actual focus location 74 determine (vertex).
  • contrast value curves i. H. the contrast values measured from the stack of images are determined by scanning the gray values of the pixels 42, 44 as a function of the working distance of the lens 30 of the CCD camera 28, that is to say at different Z positions of the camera 28 from the surface 46 of the object 48 to be measured, 5 and 6 can be simulated in this regard by replacing the sensor 28 with three sensors 76, 78, 80 in the exemplary embodiment, which work or deviate from one another at a point 82 of an object 84 to be measured. Have image spacing. To the distance of the point 82 z. B.
  • the distance-dependent contrast values that is, the entire contrast curve is approximately on a parabola. If the distance between the sensor 78 and the point 82 to be measured is consequently changed, depending on the imaging plane to the working or image plane, a contrast curve results in the sensor 78 which corresponds to a parabola which is given the reference symbol 86 in FIG. 6 is.
  • the beam path is directed via a lens 88 to the working or image plane of the sensor 78, that is to say a CCD matrix.
  • sensors 76, 80 are assigned to sensor 78, which have a different optical distance from point 82 to be measured.
  • the lens 88 with the deflection devices and the sensors 76, 78, 80 preferably forms a unit and is integrated in a probe of a coordinate measuring machine.
  • the contrast course to be measured is first determined in the sensors 76, 78, 80, so that measurement curves result which can be seen in FIG. 6, the parabola 86 for the sensor 78 and, because of the sensors 76, 80 arranged at different optical distances compared to the sensor 78, the parabolas 100, 102 are offset.
  • the parabola 100 is assigned to the sensor 76 and the parabola 102 to the sensor 80. This spacing offset of the parabolas 100, 86, 102 results from the fact that the sensors 76, 78, 80 have different focus levels, which are identified in FIG. 5 by the reference numerals 104, 106 and 108.
  • the probe head which comprises the sensors 76, 78, 80 and the optics 88, is adjusted to the point 82 in such a way that it is in the focal plane 106 of the sensor 80, a contrast value 110 results, which is the vertex of the parabola 102 corresponds.
  • a contrast value 110 results, which is the vertex of the parabola 102 corresponds.
  • the contrast curves 86, 100, 102 have been determined and placed in relation to one another, it is only necessary to determine the respective contrast values of the sensors 76, 78, 80 at a desired distance of the probe head from a point to be measured, in order to then immediately use them to calculate the vertex of the sensor corresponding to a distance Z - in the exemplary embodiment of the sensor 78 - at which the point to be measured is or would be imaged sharply on the working or image plane of the sensor 78, as a result of which the focus location of the point 82 to be measured can be determined is. This is illustrated with the aid of FIG. 6.
  • the contrast values of the measurement point 82 depicted in the sensors 76, 78, 80 are determined at the distance ZI, measurement values P1, P2 and P3 result, where P3 is the measurement value of the sensor 78.
  • the measured value Pl corresponds to the contrast value that was determined by the sensor 76 and the measured value P3 to the contrast value that was determined by the sensor 80. Since the relation of the contrast value curves 86, 100, 102 to one another is known, it is only necessary to assign measured values on the contrast curve 86 and sensor P3 to the measured values P1 and P3, so that they have a total of three measured values P ', P "and P'" result that lie on the stored measured value curve of the sensor 78.
  • a distance Z is assigned, at which the measuring point 82 is sharply imaged on the working plane or image plane of the sensor 78.
  • the Z distance between the measuring point 82 and the probe and thus the focus location can thus be determined without the probe having to be adjusted to the object 84.
  • the respective CCD matrix is scanned in accordance with the explanations, in particular in connection with FIGS. 1 and 2, by an image processing operator of the desired size.
  • a contrast curve is not determined for the entire area of a CCD matrix, but basically a contrast curve for each pixel itself.
  • An image processing operator is run over the measuring range by means of an algorithm and thereby simulates a large number of small windows.
  • the subareas are thus basically measured simultaneously with each Z setting of the sensor, each contrast value of a subarea being assigned to a pixel encompassed by the subarea.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Length Measuring Devices By Optical Means (AREA)

Abstract

La présente invention concerne un procédé de mesure tridimensionnelle d'une surface (46) d'un objet (48, 84), selon le principe de mise au point automatique au moyen d'un appareil de mesure de coordonnées (10). Pour permettre une description à haute résolution de surfaces tridimensionnelles, la zone de mesure (32) est selon l'invention subdivisée en zones partielles (1, 2, 3, 4, 5, 6, 7, 8, 9) et le contraste de chaque zone partielle est déterminé au cours de l'action d'un capteur optique (28) le long de son axe optique (50), de façon simultanée ou pratiquement simultanée.
EP02804921A 2001-12-19 2002-12-19 Procede de mesure tridimensionnelle d'une surface Withdrawn EP1459033A2 (fr)

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
DE10162663 2001-12-19
DE10162663 2001-12-19
DE10219491 2002-04-30
DE10219491 2002-04-30
PCT/EP2002/014915 WO2003052347A2 (fr) 2001-12-19 2002-12-19 Procede de mesure tridimensionnelle d'une surface

Publications (1)

Publication Number Publication Date
EP1459033A2 true EP1459033A2 (fr) 2004-09-22

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EP02804921A Withdrawn EP1459033A2 (fr) 2001-12-19 2002-12-19 Procede de mesure tridimensionnelle d'une surface

Country Status (3)

Country Link
EP (1) EP1459033A2 (fr)
AU (1) AU2002366374A1 (fr)
WO (1) WO2003052347A2 (fr)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE602005004332T2 (de) 2004-06-17 2009-01-08 Cadent Ltd. Verfahren zum Bereitstellen von Daten im Zusammenhang mit der Mundhöhle
WO2008135530A1 (fr) * 2007-05-02 2008-11-13 Werth Messtechnik Gmbh Procédé pour des appareils de mesure de coordonnées avec capteur de traitement d'image
DE102011114932A1 (de) * 2011-10-06 2013-04-11 Hommel-Etamic Gmbh Verfahren zur Ermittlung einer Kontur einer Oberfläche
DE102012109726A1 (de) 2012-09-04 2014-04-03 Werth Messtechnik Gmbh Verfahren und Vorrichtung zur Bestimmung der Geometrie eines Objektes mit einer Zoomoptik
DE102013105102A1 (de) 2013-03-28 2014-10-02 Werth Messtechnik Gmbh Verfahren und Vorrichtung zur Bestimmung von Merkmalen an Messobjekten
US9675430B2 (en) 2014-08-15 2017-06-13 Align Technology, Inc. Confocal imaging apparatus with curved focal surface
DE102015110289A1 (de) 2015-06-26 2016-12-29 Werth Messtechnik Gmbh Verfahren zur Bestimmung von Messpunkten auf der Oberfläche eines Werkzeugstücks mit einem optischen Sensor

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Publication number Priority date Publication date Assignee Title
JP2928548B2 (ja) * 1989-08-02 1999-08-03 株式会社日立製作所 立体形状検出方法及びその装置
US6407817B1 (en) * 1993-12-20 2002-06-18 Minolta Co., Ltd. Measuring system with improved method of reading image data of an object
JPH1068608A (ja) * 1996-08-28 1998-03-10 Nikon Corp 高さ測定装置
AU1517801A (en) * 1999-11-03 2001-05-14 Werth Messtechnik Gmbh Automatic contrast focussing with three optical paths

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See references of WO03052347A2 *

Also Published As

Publication number Publication date
WO2003052347A2 (fr) 2003-06-26
AU2002366374A1 (en) 2003-06-30
WO2003052347A3 (fr) 2004-03-25
AU2002366374A8 (en) 2003-06-30

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