WO1998021550A1 - Dispositif et procede de capture d'image a distance d'une surface reflechissante - Google Patents

Dispositif et procede de capture d'image a distance d'une surface reflechissante Download PDF

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Publication number
WO1998021550A1
WO1998021550A1 PCT/CA1997/000846 CA9700846W WO9821550A1 WO 1998021550 A1 WO1998021550 A1 WO 1998021550A1 CA 9700846 W CA9700846 W CA 9700846W WO 9821550 A1 WO9821550 A1 WO 9821550A1
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WO
WIPO (PCT)
Prior art keywords
image
reflective surface
distance
detector
diffused light
Prior art date
Application number
PCT/CA1997/000846
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English (en)
Inventor
Francois Blais
Original Assignee
National Research Council Of Canada
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 National Research Council Of Canada filed Critical National Research Council Of Canada
Publication of WO1998021550A1 publication Critical patent/WO1998021550A1/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
    • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
    • G01B11/026—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness by measuring distance between sensor and object
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C11/00—Photogrammetry or videogrammetry, e.g. stereogrammetry; Photographic surveying

Definitions

  • the invention relates to three dimensional (3-D) computer vision and more particularly to three dimensional imaging of objects having reflective surfaces.
  • Human vision relies on experience and stereoscopic vision to determine ranges of objects. Each of two eyes capture an image from locations offset by a predetermined distance, and the brain determines a range to at least an object within a field of view. When peering into a mirror, a person sees images within the mirror of objects that are outside the mirror. Stereoscopic vision establishes a distance to the images that is substantially the distance light travels from the objects to the person's eyes. As such, the English language has an expression "tricks with mirrors" wherein mirrors are used to alter a physical space. For example, placing mirrored tile on a wall in a small room, makes the room appear much larger.
  • Two popular techniques currently in use for optical ranging of a target surface are known, respectively, as the standard optical triangulation system and the Biris (bi-iris) system, the latter employing an apertured mask in a converging lens system of an imaging device having a position sensitive detector, e.g. a CCD camera.
  • a sample machine vision system is disclosed in U.S. Patent number 5, 270, 795 entitled Validation of Optical Ranging of a Target Surface in a Cluttered Environment, in the name of F. Blais.
  • the system comprises a collimated laser light source and an image capture means for capturing light diffused by opaque surfaces. It merges the features of standard optical triangulation systems and those of Biris systems.
  • the system uses a laser light source and a detector having two irises distanced apart. Light from the laser diffused from opaque surfaces is detected at the detector through each of the two irises. The resulting images are correlated to determine range.
  • surfaces are reflective or transparent, collimated light sources are often reflected as collimated beams missing the image capture means. As such, many range sensing means relying on optical range sensing are limited to substantially opaque surfaces.
  • the content of U.S. Patent number 5, 270, 795 to F. Blais is hereby incorporated herein by reference.
  • a method of measuring a distance from a first location to a reflective surface comprises the steps of: directing diffused light toward the reflective surface forming an image therein;
  • a range imaging means having a detector, measuring a distance from the detector to the image
  • determining the distance to the reflective surface based on a known relationship between the location of a diffused light source, the location of the detector and the distance from the detector to the image.
  • a method of measuring a distance to a reflective surface comprising the steps of:
  • an imaging means comprising a detector, said detector having a known spatial relation to the object, receiving some of the projected light reflected off of the reflective surface and forming an image of the object;
  • an imaging system comprising
  • a diffused light source for directing diffused light toward a surface and for forming at least an image therein
  • an imaging means comprising at least a detector for receiving diffused light reflected from the surface and having a predetermined spatial relation with the diffused light source;
  • An advantage of the present invention is the ability to model reflective surfaces using an optical range measurement device.
  • Fig. 1 is a simplified diagram of a prior art imaging device imaging a reflective surface
  • Fig. 2 is a simplified diagram of a prior art imaging device failing to image a reflective surface
  • Fig. 3 is a simplified diagram of a device according to the present invention imaging a reflective surface
  • Fig. 4 is a simplified diagram of a device according to the present invention imaging a planar reflective surface and indicating the effect of a field of vision upon a detector;
  • Fig. 5 is a simplified diagram of a device according to the present invention incorporating two detectors and a single diffused light source
  • Fig. 6 is a simplified diagram of a device according to the present invention incorporating two detectors and two diffused light sources;
  • Fig. 7 is a simplified diagram of a device according to the present invention incorporating three detectors and a diffused light source;
  • Fig. 8 is a simplified diagram of a device according to the present invention incorporating two detectors and two diffused light sources;
  • Fig. 9 is a simplified diagram of a device according to the present invention incorporating a plurality of detectors and a single diffused light source and imaging a transparent substrate having a predetermined non-zero thickness;
  • Fig. 10 is a simplified diagram of a device according to the present invention imaging a reflective surface that is non-planar;
  • Fig. 11 is a diagram showing a triangulation method of determining image range
  • Fig. 12 is a simplified diagram of a Biris range system employing a single Biris detector and four diffused light sources; and Fig. 13 is a flow diagram of a method of determining distance and reflective surface geometry according to the present invention.
  • Fig. 1 a reflective surface 5 with an object in the form of a collimated laser light source 2 having an iris with a predetermined shape 3, and a detector 9, on a first side thereof and according to the prior art. On a second side thereof is an image 7 of the object.
  • a reflective surface 5 in the form of a polished mirror is shown having an object, a collimated laser light source 2 having an iris with a predetermined shape 3, and detector 9 according to the prior art on a first side thereof and having an image on a second side thereof. Paths of light are shown for light from the collimated laser light source 2. As can be seen, light reflected by the reflective surface 5 misses the detector 9 and therefore is not used in determining a range for the surface 5. Alternatively, when light is diffused at the object, it is imaged by the detector 9 and is used for determining a range. Resulting range images treat reflective surfaces and transparent surfaces as holes or worse yet, inconsistently treat them as either holes or, when alignment happens to be appropriate, as surfaces. Further, the number of diffused and reflected signals reaching a detector leads to inconsistent range detection.
  • a laser light source 2 is diffused by diffusion means 30 producing a recognizable pattern of light and dark (two diffusing circles and an opaque frame). Diffusion means 30 acts as diffusing irises and results in a plurality of objects.
  • a detector 9 in the form of a CCD is positioned for receiving light from the objects once the light is reflected off a reflective surface.
  • the detector 9 is provided with a frequency selective filter means 56 for filtering frequencies other than a predetermined range of frequencies. This allows use of the invention in lighted conditions.
  • the filter means filters ambient light of predetermined frequencies. Further alternatively, no filter is used.
  • a diffused light source provides illumination of a large percentage of a field of view for the detector.
  • diffused light source thickness is small to result in sharp images at the detector 9.
  • a range detection algorithm executed within a processing means 60 determines a distance between the detector 9 and images 7 of the objects (diffusion means) 30. The processing means 60 then determines a range between the detector 9 and the reflective surface 5 in dependence upon the known relative locations of the objects 30 and the detector 9.
  • At least two data points are required. These points can be acquired by projecting at least two light sources, by projecting an object with at least two discernible features, by capturing an image with at least two detectors or by capturing images with a detector provided with two irises (Biris).
  • Biris two irises
  • a collimated light source and a diffuser allows light within a narrow band of frequencies to be projected and to form several objects 31-36.
  • a distance D is measured between the detector 9 and each image. Each distance corresponds to a series of potential locations and orientations of the reflective surface 5.
  • the resulting equation for each distance Dj is a simple triangulation with an unknown angle at a vertex thereof.
  • the distance D ⁇ is equal to the distance of 4a added to the distance of 4b.
  • the distances of 4a and 4b are interrelated by the distance from the object to the detector (shown in Fig. 10).
  • Associating an image for which a distance is to be calculated with an object determines a value for K.
  • a triangle is formed with a known base K and an unknown height. Relying on the rules of geometry, a unique triangle has been defined. In dependence upon the orientation of the base and an angle defined by a vertex of the triangle, surface orientation is determined. Therefore, by determining a distance to an image and using the known distance from the detector to an associated object, a distance to an imaged point on a surface is determined. The orientation of the surface can be determined using two measurements.
  • FIG. 4 An image is captured by the detector 9 (shown in Fig. 4) of a plurality of images. The number of images (4) is determined and a preliminary association is made. A distance to each image and a corresponding surface is determined. Each surface is then compared to determine whether or not the determined surfaces are consistent.
  • Associating the images with different objects is performed in order to determine a consistency of other associations. Once sufficient associations have been made, a most consistent surface is selected as the surface measured. W en the surface or the detector is moving, the consistency of the surface is measured against other surface shape and distance determinations.
  • a single diffused light source in the form of an LED By capturing an image with each of at least two detectors, A distance to the image can be ascertained.
  • FIG. 5 an embodiment of the present invention is shown opposite a flat reflective surface.
  • a laser light source 2 is diffused by diffusion means 30 producing a recognizable pattern of light and dark.
  • the diffusion means 30 acts as an object.
  • a plurality of detectors 9a and 9b in the form of CCDs are positioned proximate the object.
  • the detectors are provided with a frequency selective filter means 56 for filtering frequencies other than the laser frequency. Alternatively, the filter means filters ambient light at predetermined frequencies. Further alternatively, no filter is used.
  • the use of two detectors results in the capture of two data points for the image (as is shown in Fig. 5) and allows for triangulation to be employed.
  • a system provided with 2 detectors and 2 diffused light sources is shown.
  • the system results in the acquisition of 4 data points.
  • Such a system is useful for range determination and for surface modeling of the reflective surface 5.
  • For each image a distance and surface orientation is calculated. Due to the increased number of data points, a solution is now possible (and unique) for surface distance, surface orientation, and surface curvature (over a section of the surface).
  • Moving the detectors or the surface allows image capture of the entire surface and allows for surface modeling.
  • the relative motion is accurately measured to ensure accurate modeling.
  • Fig. 7 an embodiment wherein a single diffused light source projects images to each of 3 image capture means is shown.
  • the device operates similarly to that of Fig. 6. Triangulation is achieved between each pair of points (three different pairs) to determine information relating to surface distance, surface geometry, and surface orientation.
  • the light sources are diffused light sources in the form of LEDs 21.
  • the light sources 21 can be regular diffused light sources (bulbs) or other diffused lighting means.
  • the elimination of a laser light source reduces the overall cost of the system.
  • a frequency dependent optical filter may be employed to filter out ambient light from light reaching the detector.
  • Transparent surfaces tend to be reflective in part.
  • a transparent surface In Fig. 9, a transparent surface
  • a processing means 60 resolves the images 7 and 7d and calculates image distances in order to determine plate thickness and surface geometry.
  • a laser light source 2 is diffused by diffusion means 30 producing a recognizable pattern of light and dark.
  • the diffusion means 30 acts as a plurality of objects.
  • Detectors 9a and 9b in the form of CCDs are positioned proximate the objects 30.
  • the detectors 9a and 9b are positioned in a location having a known spatial relation to a location of the objects 30.
  • the detectors 9a and 9b are provided with a frequency selective filter means 56 for filtering frequencies other than the laser frequency.
  • the filter means filters ambient light of predetermined frequencies. Further alternatively, no filter is used.
  • a range detection algorithm executed within a processing means 60 determines a distance between the detectors 9a and 9b and an image 7 of the objects (diffusion means) 30. Where, as in this instance, the reflective surface is non-linear, the image 7 is distorted relative to the objects 30 and/or magnified relative to the curvature of the surface.
  • the processing means 60 correlates objects 30 and images 7. Alternatively, points on an object (known) are correlated with points on a captured image (reflected). Using the known spatial relation between the detectors 9a and 9b and the objects 30, the processing means determines a distance to at least some of the points on the reflective surface 5. Locations of these points are then used to determine a surface geometry for the reflective surface 5 and therefore orientation and magnification of the curved surface can be determined. At least 3 captured images are required to determine surface geometry. Preferably, more images are captured. Further images at different angles or from different known locations allow for the construction of a geometric model of the reflective surface 5. Alternatively, a large object with a discernible pattern is used to model the entire surface. Further alternatively, the diffused light source is stationary and only the detectors 9a and 9b move. In this last embodiment, the diffused light source's pattern is used to determine detector angle or location; image overlap is used to construct a model of the reflective surface 5.
  • a detector is spaced a distance Kl from a first object and a distance K.2 from a second object.
  • the detector detects images of each of the first and second objects. The images are at angles of and ⁇ , respectively. Between the images of the first and second objects is a distance K similar to that distance between the objects themselves. Therefore, a triangle is formed with a known base and a known angle opposite the base. This results in a determined triangle. Once determined the values of Dl and D2 are calculated using trigonometric functions or other known methods.
  • a second series of triangles is now formed in which the bases are Kl and K2 respectively. Angles of a corner of each triangle adjacent the base are known. The distance around the perimeters of the two triangles are Dl + Kl and D2 + K2, respectively. This is known because the optical paths from the detector to the images Dl and D2 are equal in length to the optical path from each of the first object and the second object, respectively. As the light travels in a substantially straight line from the object to the reflective surface and from the reflective surface to the detector, the distance D 1 is equivalent to the distance in traversing two sides of a triangle; the third side of the triangle has a length Kl.
  • D2 is equivalent to the distance in traversing two sides of a triangle; the third side of the triangle has a length K2.
  • K2 the two triangles can be evaluated to determine all distances and thereby measure a distance to a point on a substantially flat reflective surface. This method of determining range is known in the art as photogrammetry.
  • FIG. 12 an embodiment of the invention using a Biris detector 9 having two apertures 91 and 92, a lens 96, and a CCD 97 and 4 diffusing light sources 3 is shown.
  • Existing implementations of Biris systems weight standard plane of light range measurement contributions with Biris contributions to increase accuracy of a range measurement.
  • a plane of light measurement forms a large part of a range measurement since it relies on a large triangulation base.
  • a range is calculated by the system.
  • the distance between the apertures 91 and 92 is referred to as b.
  • an angle of incidence of light is determined in dependence upon a point on a CCD within the detector 9 where the light is incident.
  • the point is referred to as p. From these two values (p and b) range can be determined (as explained with reference to Fig. 11 and U.S. Patent 5,270, Validation of Optical Ranging of a Target Surface in a Cluttered Environment to F. Blais).
  • step 3 4. evaluate the surface orientation/curvature and range resulting from each computation in step 3 and correlate them; 5. when the computed values do not correlate, associate the images with different objects and return to step 3; and 6. when the computed values correlate, minimize any range surface curvature errors computed in step 3.
  • the focal length is
  • Anamorphic lenses may increase camera accuracy while retaining field of view. It will be apparent to those of skill in the art that as laser field of view increases, further constraints are imposed upon dimensions of light sources arrays.
  • each object can have a different wavelength or a different shape. Allowing sufficient images to fall within a field of view is a geometrical problem to be solved in dependence upon known criteria regarding a surface.
  • a method of determining distance and reflective surface geometry is shown in a flow diagram.
  • Diffused light is projected at a reflective surface a range for which is to be determined.
  • the diffused light is in the form of at least an object.
  • the diffused light reflects off the reflective surface and is detected by at least a detector. At least two and preferably at least three instances of reflected light are detected by the at" least a detector.
  • a range is calculated to an image (as viewed by the at least a detector) of the at least an object.
  • Each image is associated with an object in the form of a diffused light source.
  • the association is estimated and may be incorrect.
  • a range and orientation are calculated for the reflective surface.
  • the calculated ranges and orientations for each image are compared to determine a surface. When a surface results, it is refined by reducing errors in surface range and curvature. When an inadequate surface results, at least an image is associated with a different object and the range and orientation is recalculated. The method continues from the calculation of range and orientation as set out above.
  • a diffused light source is a primary light source providing diffused light.
  • a diffused light source is a secondary light source transmitting or reflecting light incident thereon in a diffused fashion.
  • a discernible object reflecting some diffused light acts a diffused light source.
  • the primary source of light need not provide diffused light and, in an embodiment, is a collimated laser light source in conjunction with a diffuser acting as a secondary light source.
  • the curvature of the object changes the position of the image of the source. If the curvature is small, then the surface can be considered planar and a direct reflection of the image occurs. If not then the location of the image changes and must be compensated.
  • the distance of the position of the image of the source to the surface is modified by the "focal" of the surface, using the formula: — ⁇ — r_obj is the position of the object f r_ls r_obj r r_ls r_obj
  • the sensor measures the modified position of the image r ⁇ c_r.
  • the compensated position ric is obtained using:
  • cr c curvature of the surface
  • r radial coordinate i x 2 2
  • k conic constant

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Multimedia (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Length Measuring Devices By Optical Means (AREA)
  • Measurement Of Optical Distance (AREA)

Abstract

L'invention a trait à un dispositif ainsi qu'à un procédé permettant une imagerie de surfaces réfléchissantes, procédé au tire duquel une source de lumière diffusée d'une gamme de fréquence prédéterminée dans une configuration prédéterminée est dirigée vers la surface réfléchissante. La lumière se réfléchissant sur la surface traverse un filtre destiné à filtrer la lumière d'ambiance et parvient à un capteur. Celui-ci détecte la lumière. Par triangulation avec deux points dans la configuration, un microprocesseur détermine une distance jusqu'à une image formée en arrière de la configuration. Ce microprocesseur calcule également une distance jusqu'à la surface réfléchissante en fonction de la distance jusqu'à l'image et des emplacements de la source de lumière diffusée et du capteur. Dans une variante, deux capteurs sont utilisés, réclamant une source ponctuelle de lumière diffusée.
PCT/CA1997/000846 1996-11-12 1997-11-12 Dispositif et procede de capture d'image a distance d'une surface reflechissante WO1998021550A1 (fr)

Applications Claiming Priority (2)

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US74649196A 1996-11-12 1996-11-12
US08/746,491 1996-11-12

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WO1998021550A1 true WO1998021550A1 (fr) 1998-05-22

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1211478A2 (fr) * 2000-11-29 2002-06-05 Sick Ag Détermination de distance
WO2003019114A1 (fr) * 2001-08-30 2003-03-06 Centre De Recherches Metallurgiques, A.S.B.L. Procede et dispositif pour la mesure de distances sur des bandes de metal brillant
EP1380811A1 (fr) * 2002-07-03 2004-01-14 Optosys SA Dispositif optique de mesure de distances
CN106257996A (zh) * 2013-12-09 2016-12-28 赫氏公司 测量装置及其测量方法

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4529316A (en) * 1982-10-18 1985-07-16 Robotic Vision Systems, Inc. Arrangement of eliminating erroneous data in three-dimensional optical sensors
US5414517A (en) * 1992-05-01 1995-05-09 Agency Of Industrial Science & Technology Method and apparatus for measuring the shape of glossy objects
US5477332A (en) * 1992-12-17 1995-12-19 Mcdonnell Douglas Corporation Digital image system and method for determining surface reflective and refractive characteristics of objects

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4529316A (en) * 1982-10-18 1985-07-16 Robotic Vision Systems, Inc. Arrangement of eliminating erroneous data in three-dimensional optical sensors
US5414517A (en) * 1992-05-01 1995-05-09 Agency Of Industrial Science & Technology Method and apparatus for measuring the shape of glossy objects
US5477332A (en) * 1992-12-17 1995-12-19 Mcdonnell Douglas Corporation Digital image system and method for determining surface reflective and refractive characteristics of objects

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1211478A2 (fr) * 2000-11-29 2002-06-05 Sick Ag Détermination de distance
EP1211478A3 (fr) * 2000-11-29 2003-04-16 Sick Ag Détermination de distance
EP1722191A1 (fr) * 2000-11-29 2006-11-15 Sick Ag Détermination de distance
WO2003019114A1 (fr) * 2001-08-30 2003-03-06 Centre De Recherches Metallurgiques, A.S.B.L. Procede et dispositif pour la mesure de distances sur des bandes de metal brillant
BE1014355A3 (fr) * 2001-08-30 2003-09-02 Ct Rech Metallurgiques Asbl Procede et dispositif pour la mesure de distances sur des bandes de metal brillant.
US7054013B2 (en) 2001-08-30 2006-05-30 Centre De Recherches Metallurgiques Process and device for measuring distances on strips of bright metal strip
EP1380811A1 (fr) * 2002-07-03 2004-01-14 Optosys SA Dispositif optique de mesure de distances
US6864964B2 (en) 2002-07-03 2005-03-08 Optosys Sa Optical distance measuring device
CN106257996A (zh) * 2013-12-09 2016-12-28 赫氏公司 测量装置及其测量方法
EP3080548A4 (fr) * 2013-12-09 2017-08-09 Hatch Pty Ltd Appareil de mesure et son procédé
AU2014361727B2 (en) * 2013-12-09 2019-07-04 Hatch Pty Ltd Measuring apparatus and method for same
CN106257996B (zh) * 2013-12-09 2019-08-16 赫氏公司 测量装置及其测量方法

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