Classifications

• • 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
  • G01N21/89—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
  • G01N2021/9513—Liquid crystal panels

Definitions

• the invention relates to a device for analyzing the optical quality of a transparent substrate, in particular for detecting deforming optical defects present either on the surface of this substrate or in its mass.
• optical defects of the transparent substrates are characterized by the optical deformations that they cause when these substrates are in a situation of use, such as, for example, automotive glazing, building glazing, plasma or LCD screens, etc.
• the techniques usually used to detect and evaluate defects typically consist of:
• the method of this US patent requires to know or to adapt the characteristics of the sight (its dimensions, its forms, its position) and the camera (number of pixels, distance to the sight, ...) to ensure a proper alignment of the pattern of the target with the pixels of the camera, which is restrictive, and rarely possible in an industrial environment (bad regularity of the sight, dilation of the sight in function of the variations of temperature in the day, vibrations of the ground, ).
• US 6 208 412 proposes another method of measurement by observation in transmission of a one-dimensional test pattern.
• the measuring device of this document uses a projector to generate a pattern by forming, on a large screen, always substantially greater than the dimensions of the glazing to be measured (typically 2 ⁇ 3 m), a time-varying unidirectional periodic pattern, as well as a matrix camera which visualizes the pattern through the glazing to be analyzed.
• the test pattern should be gradual gray, ie it should not have high local contrasts.
• This device described in the latter document if it can give satisfaction in the laboratory or on the edge of the production line for a sampling control, can not be used against a line control, on a ribbon scrolling continuously, in the framework of a control that must be exhaustive without the possibility of stopping the glass momentarily.
• 6,208,412 and its measurement process are incompatible with a measurement on an industrial line, on a continuously moving continuous substrate, with the constraint of exhaustive control.
• the applicant has thus set himself the task of designing a device for analyzing the optical quality of a transparent substrate, which does not have the drawbacks of the techniques mentioned above and makes it possible to detect and quantify the defects of this substrate in transmission, in an easy, precise, and repetitive manner by responding to all the constraints of an implementation on an industrial line for a control of the glass over its entire length, on a substrate in continuous scrolling or not, and by ensuring in particular the reduction of glass compliance costs on a production line.
• This innovative device must also allow the use of measurement methods that lead to optimize the analysis time.
• the subject of the invention is a device for analyzing a transparent surface of a substrate comprising a pattern formed on a support disposed opposite the surface of the substrate to be measured, a camera for taking at least one image of the target deformed by the measured substrate, a lighting system of the sight, and image processing and numerical analysis means which are connected to the camera, characterized in that the support is of oblong shape of small and large extensions, the pattern being monodirectional and consisting of a pattern that extends in the smallest extension of the support, the pattern being periodic transverse to the small extension, and that the camera is linear and positioned to acquire a linear image in transmission of the test pattern through the substrate according to the large extension of the support.
• the device comprises one or more of the following characteristics, taken separately or in any technically possible combination:
• the ratio between the large extension of the support and the small extension of the support is for example greater than or equal to 10, preferably greater than or equal to 20;
• the pattern comprises at least one line which has, according to the small extension of the support, a width between 0.1 mm and 5 cm, preferably between 1 mm and 2 mm;
• the pattern consists of an alternating succession of light and dark lines
• the support of the test pattern consists of a panel backlit by the lighting system
• the support is, at its face facing the glazing to be measured, translucent and diffusing such as a white plastic plate;
• the lighting system is formed of a multitude of light-emitting diodes
• the substrate is arranged between the test pattern and the camera for a measurement in transmission;
• the support of the test pattern is movably mounted relative to the substrate perpendicular to the substrate running plane;
• the device comprises a mechanical system for raising and lowering to move the support closer to and closer to the target relative to the substrate while maintaining a sufficient sharpness in the image of the pattern picked up by the camera;
• the device comprises a memory on which programs adapted to:
• linear camera to take a linear image in transmission of the illuminated target, the substrate or the target being displaced relative to each other in a single direction of travel parallel to the direction of the defects and to the lines of the test; • (1) to acquire the line of pixels of the linear image taken following the great extension of the sight, without moving the camera relative to the target;
• the acquisition period of the lines is greater than the acquisition duration of each line, for example 0.1 seconds or more;
• each line is displayed after each step (2) so that the reconstituted image of a portion of the substrate simulates a continuous scrolling effect which will correspond to the real-time display of a 2D mapping of the defects;
• a linear camera comprises a single video sensor providing as output signal a single line of pixels.
• the sensor comprises a single receiver composed of several juxtaposed sensitive elements respectively corresponding to the pixels of the output signal, the sensitive elements being aligned on a single line.
• Linear cameras are space-saving and achieve fast acquisition.
• the oblong shape of the support of the sight accompanied by the use of a linear camera makes it possible to reduce the area occupied by the sight and thus limit the location necessary for the device on a production line.
• the size of the patterns of the test pattern and the position of the sight, the glass and the camera are of course to be adapted to each type of measurement, this device being able to adapt to the control of samples a few centimeters wide as to the control a glass ribbon several meters wide in permanent scrolling. In the latter case we will associate several camera-test systems to cover the entire width of the ribbon to be analyzed. For smaller substrates, the large extension of the support may correspond to the width of the substrate to be measured.
• the ratio between the large extension of the support and the small extension of the support is for example greater than or equal to 10, preferably greater than or equal to 20.
• the perceived deformations expressed in terms of optical magnification by a fixed observer placed on one side of the substrate observed in transmission vary with the distance separating the substrate from the pattern which acts as an optically speaking object.
• the optical power is in a known manner defined as the inverse of the focal length of the equivalent optical lens which would, if it were positioned in place of the defect, give the same magnification as that perceived by the observer.
• the pattern of the pattern consists of an alternating succession of light and dark lines, preferably strongly contrasting (for example white and black) and respectively of equal widths.
• the width of the lines forming each pattern is in fact adapted to the measurement and width conditions of the defects.
• the width of the lines can thus be between 0.1 mm and 10 mm, preferably between 1 mm and 2 mm.
• the support panel of the test pattern may then not exceed 5 cm wide, which therefore greatly reduces the dimensions useful for implantation of the device of the invention compared to those existing.
• the panel is, at its face facing the substrate to be measured, translucent and diffusing.
• This is for example a white plastic plate. It can also be a transparent substrate on which the pattern is printed.
• a second translucent plate associated with the illumination will ensure the bright background necessary for a backlight almost homogeneous of the test pattern although this homogeneity is not critical.
• the lighting system is formed of a multitude of light-emitting diodes. This lighting can be judiciously modulated in intensity over time, for example, to increase the life or to adapt to the transmission of a more or less absorbent substrate.
• the substrate is disposed between the test pattern and the camera.
• the invention also relates to a method for analyzing a transparent or specular surface of a substrate using a device comprising a pattern formed on an oblong support of small and large extensions, a linear camera to take at least one image of the pattern deformed by the measured substrate, a target lighting system, and image processing and digital analysis means which are connected to the camera, the method comprising steps consists in :
• the method also has one or more of the following characteristics, taken separately or according to any one of the technically possible combinations:
• each line is displayed after each step (2) so that the reconstituted image of a portion of the substrate simulates a continuous scrolling effect which will correspond to the real-time display of a 2D mapping of the defects;
• the substrate is a continuous glass ribbon; the acquisition period of the lines is greater than the acquisition duration of each line, for example 0.1 seconds or more.
• the rate of shooting of each line will be slaved to the speed of relative movement of the substrate relative to the test pattern to prevent overlap, in the direction of scrolling, an image of a pixel line with the next.
• the analysis will then concern only the defects of a passage time under the camera of the order of one second, the point defects, a passage of time typically of tenth of a second will be detected only randomly.
• the device and method according to the invention it is possible to perform a fast and reliable control on a representative sample of lines regularly spaced from the substrate.
• the entire substrate can thus be controlled quickly, even if the spaces between the lines are not.
• it would be advantageous to multiply the device by placing one or more identical downstream devices, all of which are synchronized to analyze a different part of the substrate, i.e. the spaces between the lines analyzed by the other devices, all the devices preferably being synchronized on the same periodicity of image acquisition.
• each line is done in a known manner. It is for example to extract local phases of the pixel line acquired using the linear camera and to deduce phase variations, to deduce the position of the defect but also to quantify by a measure deformation of the lines of the test pattern from which it is possible to provide, by means of an optical calculation model, a dimensioned quantity of the deformation or an optical power representative of the defect.
• the digital phase extraction processing can be carried out thanks to the well-known method of Fourier transform. It appears that the method according to the invention leads to satisfactory results on industrial lines without modification thereof, for reduced costs and allows much faster control than in the prior art.
• the device of the invention and the method of implementation can be applied to transparent substrates such as monolithic or laminated glazing, flat or curved, of any size for various uses (building, automobile, aeronautic, railway).
• the device and the method can be advantageously applied to the flat glass ribbon on a float line. They can also be applied to flat glazing for building applications or special glazing for electronic applications (plasma or LCD screens, etc.) and other transparent substrates.
• FIG. 1 shows a schematic sectional view of an analysis device according to the invention for a transmission measurement
• FIG. 2 illustrates an example of a test pattern according to the invention
• FIG. 3 illustrates a reconstituted image of the substrate showing at its center a defect.
• 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 electroluminescent diodes which are arranged at the rear of the translucent panel.
• the lighting system 4 is formed of a light source arranged on the front of the test pattern, for example a spot oriented to illuminate the front face of the support panel of the test pattern.
• the camera 3 is linear; it generates a frame of shots which, by digital processing, is stacked with the previous ones to form a global image in two dimensions of the moving substrate. Since the test pattern is of small dimensions relative to the substrate as we shall see, the substrate 2 or the test pattern is able to move in translation relative to one another to ensure the necessary number of shots over the entire picture. substrate.
• the trigger frequency of the camera for each shot is slaved to the frame rate.
• the camera is positioned at a distance d adapted to view all or a fraction of the extension of the substrate that is transverse to the direction of travel of the substrate or the test pattern. Thus, if scrolling is in a horizontal plane, the camera is arranged vertically.
• the camera 3 could make an angle with respect to the vertical which would be adapted to the conditions of implantation on the industrial line.
• the pattern 10 as shown in Figure 2, is formed on a support 11 of oblong shape. It is monodirectional and consists of a pattern 10a.
• the test pattern according to the invention has a small extension of small size relative to the substrate to be measured.
• the pattern extends over 5 cm by 1.0 m.
• the pattern 10a of the pattern extends along the smallest extension of the support, being periodic transversely to the small extension, that is to say according to the large extension of the support.
• Pattern 10a consists of an alternating succession of clearly contrasting dark and light lines.
• the processing and calculation means 5 are connected to the camera to develop the mathematical treatments and analyzes that follow the successive shots.
• FIG. 3 illustrates an image recorded by the camera, the image of the pattern being deformed by the presence of defects in one direction.
• the implementation of the device consists in:
• the intensity of the optical defects can be calculated. It is not necessary, with this method, to know the state of the previous line, nor that of the next one.
• a pattern is a spatially periodic signal.
• the mathematical analysis consists in a known way of characterizing this signal by its local phase modulo 2 ⁇ , at the level of a pixel of the camera, and one thus defines a two-dimensional mapping of the phases (corresponding to all the pixels) of the image in two dimensions seen by transmission, called map of the phases.
• This method is commonly described in the literature. It breaks down as follows: acquisition of a linear image of the target deformed by the sample;
• This image is a complex image comprising a real part R and an imaginary part I; calculation of the local phase at a pixel, modulo 2 ⁇ , of the image.
• This phase is obtained by calculating, pixel by pixel, the value of arctg (I / R).
• the step of calculating the modulo 2 ⁇ phase of the image performed for each pixel it is easy to deduce the map of the derivatives of the phase, also called map gradients.
• This calculation of the phase gradient of the image is obtained by simple difference of the pixel to pixel phase, the phase jumps of 2 ⁇ being easily eliminated.
• This calculation can be carried out after the acquisition of each of the lines or on a group of lines.
• After deduction of the phase map of the complete image reconstructed from the series of linear images taken by the camera it is then possible to connect the value of the derivative of the phase in each point of the image to the optical power Pi of the defects of the glazing at the origin of these local phase variations using an optical calculation model which makes it possible to calculate the optical power Pi from the derivative of this phase.
• the evaluation of the optical power and its comparison with a threshold value makes it possible to quantify the defect.
• the derivative of the phases may rather be compared to a local calibration width which will provide a deformation width representative of the extent of the defect.
• Quantification of the defect thus makes it possible to establish the optical quality of a substrate directly on the production line.
• the method according to the invention for analyzing the substrate consists in: taking, with the aid of a linear camera, a series of linear images in transmission of a narrow single pattern on said substrate, without the necessity, such as in the prior art, a studied coupling of the test pattern with respect to the camera or the use of a projector and a large screen; extracting by digital processing of the local phases, calculating the derivative of these phases, and mathematically calculating the intensity profile of the defects (preferably according to a calculation of the optical power and its comparison with a threshold value);
• the proposed measuring device allows control over the entire length of the substrates present on an industrial line, without sampling of the substrate, without stopping or slowing down of the substrate, without changing its position on the conveying system, without the use of a system of projection of successive patterns, without any constraint of optical or mechanical adjustment. It generates a reduced area of use compared to the dimensions of the sight which are much lower than existing ones; typically the support panel of the test pattern of the invention is 1 meter long by 5 cm wide.

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

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• 2010
  • 2010-04-01 FR FR1052477A patent/FR2958404B1/fr not_active Expired - Fee Related
• 2011
  • 2011-03-28 CN CN201180017405.0A patent/CN103097879B/zh active Active
  • 2011-03-28 ES ES11717302T patent/ES2751989T3/es active Active
  • 2011-03-28 KR KR1020187003691A patent/KR20180018829A/ko not_active Ceased
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  • 2011-03-28 US US13/637,318 patent/US8736688B2/en active Active
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  • 2011-03-28 JP JP2013501904A patent/JP2013524192A/ja active Pending
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