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
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/8806—Specially adapted optical and illumination features
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/89—Investigating the presence of flaws or contamination in moving material, e.g. running paper or textiles
  • G01N21/8901—Optical details; Scanning details
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/89—Investigating the presence of flaws or contamination in moving material, e.g. running paper or textiles
  • G01N21/892—Investigating the presence of flaws or contamination in moving material, e.g. running paper or textiles characterised by the flaw, defect or object feature examined
  • G01N21/896—Optical defects in or on transparent materials, e.g. distortion, surface flaws in conveyed flat sheet or rod
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/95—Investigating the presence of flaws or contamination characterised by the material or shape of the object to be examined
  • G01N21/958—Inspecting transparent materials or objects, e.g. windscreens
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/8806—Specially adapted optical and illumination features
  • G01N2021/8829—Shadow projection or structured background, e.g. for deflectometry

Definitions

• the invention relates to a method and a device for analyzing a surface of a specular substrate, said analysis notably making it possible to detect local flatness defects by measuring the altitude profile of the substrate.
• the first technique consists in measuring the flatness of an object by interferometry.
• the measurement is made by exploiting the interferences intervening between two waves coming from the reflections of an incident wave on the surface to be measured and on a known surface (standard).
• this technique is difficult to apply to online measurements on industrial sites of large substrates. Indeed, interferometric methods, composed of many optical elements, are very sensitive to external disturbances (vibrations, temperature, etc.).
• the second technique consists in measuring the flatness of an object by reflectometry.
• this technique nevertheless requires the use of large components (projector, screen) and / or the use of complex optical components to project and collect light.
• the integration of such a device on an industrial line is rarely possible or desirable, for lack of space.
• the third technique consists in measuring the flatness of an object by deflectometry.
• the analysis of the deformation of a virtual image created by reflection makes it possible to go back to the shape of the object.
• a pattern consisting of a periodic pattern, generally consisting of an alternation of white and black lines, is observed in reflection on the surface of the substrate to be measured.
• a local variation of the surface deforms the observed image locally.
• the measurement of the local phase of the observed image makes it possible to determine the local slopes.
• the shape of the substrate is then reconstructed from the local slopes by integration.
• EP-A-1 336 076 discloses a measurement method for detection of optical and surface defects based on the analysis of the deformation of a two-dimensional pattern observed in reflection. This method consists in taking at least one image in reflection of at least one pattern on the surface using a matrix camera, to extract numerically the local phases, and to determine the variations of local slopes (the variations of curvatures or the variations of altitudes being then deduced).
• This method has the disadvantage of having to control the positioning of the substrate during its displacement to ensure the reproducibility of the measurement. Indeed, in order to extract the phase, the method must include a step of superposition of the image in reflection of the target on a reference pattern and then compare these phases to reference phases in order to deduce phase variations and correct these variations after a sensitivity factor that strongly depends on the observation conditions and the measurement tools used.
• US 6,392,754 discloses a method for determining the profile of a specular surface based on the analysis of a reflection pattern.
• the deformation of the pattern observed in reflection, using a matrix or linear camera makes it possible to evaluate the altitude profile.
• the method consists in determining the local phases of the image by comparing the observed pattern with a perfect theoretical image.
• the altitude profile is then determined by integrating the local slopes, knowing a reference point.
• WO 2010/037956 also relates to the continuous analysis of deforming optical defects present either on the surface of the substrate or in its mass.
• the method consists in acquiring, using a matrix camera, a series of several images of a bidirectional pattern seen in transmission through a substrate, or in reflection on the substrate.
• the image reconstituted by gluing is then analyzed by digital processing to deduce the position of optical defects and quantify their intensities, from the variation of the local phases of the image. This method quantifies optical defects but not flatness defects.
• No. 7,345,698 is concerned with the measurement of optical power, in particular for specular surfaces from a plurality of circular images projected onto the substrate and reflected. This method is not interested in flatness defects either.
• An object of the invention is to provide a robust method of measuring the flatness of a specular substrate.
• an aspect of the invention particularly relates to a method of analyzing a surface of a specular substrate comprising:
• the method has one or more of the following characteristics, taken alone or in any technically possible combination:
• the altitude profile is obtained by integration from the local optical powers
• the method uses a calculation of local slopes from the local optical powers to calculate the altitude profile
• the analysis is carried out during the movement of the substrate
• the substrate is specular and transparent.
• the calculation of the altitude profile as a function of the local optical powers obtained from the local phase derivatives does not require calculation of the local phases. This method makes it possible to use relative measurements, and thus to be less sensitive to external vibrations.
• this method does not require calibration during measures.
• the method is thus robust.
• the proposed invention also has the advantage of avoiding the use of large patterns, allowing acquisition during the displacement of the substrate and limiting the number of cameras, avoiding referencing by an additional camera (a calibration by an additional camera being useless).
• the subject of the invention is also a device for measuring the flatness of a substrate, comprising at least one camera, at least one test pattern, digital image processing means, characterized in that the processing means comprise a calculator and a memory on which are stored programs able to implement a method as described above.
• FIG. 1 shows a schematic sectional view of an analysis device according to the invention for a reflection measurement
• FIG. 2 illustrates an example of a pattern used.
• the device 1 illustrated in FIGS. 1 and 2 makes it possible to analyze by reflection the defects of a specular substrate 2, such as glazing, by calculating the elevation profile of the specular surface of this glazing.
• the device comprises a test pattern 10, means 3 which are for example a matrix camera, a lighting system 4 of the test pattern, and suitable means of processing and calculation 5.
• the pattern 10 is formed on one side of a support panel 1 1, facing the substrate to be measured. It will be described in more detail later for illustrative purposes.
• the specular surface substrate 2 i.e. the glazing, is arranged in front of the sight 10 and the camera 3, the objective of the camera being in the same plane as that of the target and being directed toward the surface of the substrate.
• the lighting system 4 may be a backlight system when the support panel 1 1 is translucent, such as a white plastic plate.
• the lighting system 4 then consists of a multitude of light-emitting diodes which are arranged at the rear of the translucent panel.
• the camera 3 is matrix; it generates frames of shots which, by digital processing, are concatenated to form an overall image of the substrate.
• the substrate 2 or the pattern is able to scroll in translation relative to each other to ensure the necessary number of shots on the entire substrate.
• the trigger frequency of the camera for each shot is slaved to the frame rate.
• the camera 3 is positioned at a distance "d" adapted so as to display all of the reflection of the pattern on the substrate.
• the monodirectional pattern is positioned perpendicular to the axis of travel of the specular substrate.
• the focus of the camera is on the image of the reflected virtual pattern.
• the camera 3 is positioned to attenuate the impact of the potential reflection of the pattern on the underside of the substrate.
• the pattern 10 as shown in Figure 3, is arranged on a support 11 of oblong shape. It is unidirectional.
• the pattern of the pattern consists of an alternating succession of light and dark lines.
• the pattern is small in relation to the substrate to be measured.
• the test pattern extends for example 15 cm by 1.8 m for a zero inclination of the glazing.
• the pattern has for example a periodic pattern in at least one direction of dark and light areas.
• the frequency is variable according to the desired accuracy. Several frequencies may be present on the test pattern.
• the shooting devices (camera, lens) are connected to the processing and calculation means 5 to perform the mathematical treatments and analyzes that follow the successive shots.
• FIG. 4 illustrates an image recorded by the camera, the image of the pattern being deformed by the presence of defects in one direction.
• the invention relates more particularly to the calculation making it possible to obtain flatness from the images.
• the method described in the invention based on deflectometry consists in determining the flatness of a specular substrate from the measurement of the local optical powers.
• the spherical mirror defect modeling allows us, using the proposed method, to link the local optical power to a local curvature of the substrate. From this information, the altitude profile is calculated by integration.
• the calculation of the optical power is made from a two-dimensional image of a monodirectional pattern.
• the mathematical analysis consists in obtaining the value of the local magnification from the local phase derivative in any "point" (or "pixel") of the image, then in calculating the local optical powers.
• a one-dimensional mapping of the local optical powers of each of the images acquired in reflection, called map of the local optical powers, is thus defined.
• One of the possible methods is based on transform processing of
• the altitude profile is obtained by integrating the local radii of curvature.
• the invention thus comprises:

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• General Health & Medical Sciences (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Textile Engineering (AREA)
• Engineering & Computer Science (AREA)
• Length Measuring Devices By Optical Means (AREA)
• Investigating Materials By The Use Of Optical Means Adapted For Particular Applications (AREA)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

Country Status (4)

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• 2013
  • 2013-12-13 FR FR1362601A patent/FR3015033B1/fr not_active Expired - Fee Related
• 2014
  • 2014-12-10 CN CN201480003036.3A patent/CN105008903A/zh active Pending
  • 2014-12-10 EP EP14827494.7A patent/EP3080592A1/de not_active Withdrawn
  • 2014-12-10 WO PCT/FR2014/053262 patent/WO2015086998A1/fr not_active Ceased

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