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
• • 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
  • G01N21/8851—Scan or image signal processing specially adapted therefor, e.g. for scan signal adjustment, for detecting different kinds of defects, for compensating for structures, markings, edges
  • G01N2021/8854—Grading and classifying of flaws
  • G01N2021/8867—Grading and classifying of flaws using sequentially two or more inspection runs, e.g. coarse and fine, or detecting then analysing
• • 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
  • G01N21/8851—Scan or image signal processing specially adapted therefor, e.g. for scan signal adjustment, for detecting different kinds of defects, for compensating for structures, markings, edges
  • G01N2021/8887—Scan or image signal processing specially adapted therefor, e.g. for scan signal adjustment, for detecting different kinds of defects, for compensating for structures, markings, edges based on image processing techniques
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2201/00—Features of devices classified in G01N21/00
  • G01N2201/10—Scanning
  • G01N2201/102—Video camera

Definitions

• the present invention relates to a method of controlling the surface condition of a face of a solid. It also relates to a device for implementing this method and intended both for assistance equipment for an operator and for an automatic control installation.
• a variety of nuclear fuel for experimental reactors consists of aluminum sandwich plates inserting a core made of a mixture of uranium and aluminum.
• the manufacturing process for these plates consists of laminating four components together: a compacted core of aluminum and uranium embedded in a frame and covered with two plates forming a cover.
• the control is carried out automatically and gives rise to reports integrating quantitative and calibrated measures. External control has so far been carried out visually by qualified operators.
• the implementation technique consists in observing the two surfaces of a plate in grazing light, while handling this plate, and in identifying surface defects. These are holes or scratches whose depth must not exceed 100 ⁇ m. When a surface defect appears suspicious to the operator, he places the plate under the objective of a microscope and assesses the maximum depth of the hole or the scratch that he previously spotted. Plates with unusual characteristics are discarded. Some users have particularly strict requirements, which implies an additional check carried out by another team.
• the invention makes it possible to improve the control of surface conditions and applies both to equipment used by an operator and to an automatic control installation.
• the observation conditions are improved by shots of the surfaces to be inspected, these shots being either presented on a video screen at a control station, either processed digitally in the case of an automatic control installation.
• the use of an optoelectronic probe makes it possible to obtain objective and quantitative depth measurements, these measurements being recordable.
• the subject of the invention is therefore a method of controlling the surface condition of a face of a solid in order to identify the shape defects likely to be there, consisting in: - observing the face of the solid in order to identify the areas likely to constitute faults,
• the size of the areas liable to constitute faults is assessed by measurement using an optoelectronic probe.
• the observation of the face of the solid is advantageously done under grazing and multidirectional lighting.
• the shots are taken on video and in two successive stages, a first stage known as wide field analysis making it possible to quickly identify all the zones liable to constitute defects and a second stage known as small field analysis which does not concerns only the areas identified in the first step, the small field analysis constituting observation by the magnification means.
• the measurement made by means of the optoelectronic probe can be recorded.
• the subject of the invention is also a device for implementing this control method comprising:
• control means receiving said information.
• This device may further comprise means for eliminating the dust likely to be on said face.
• the receiving means may include a solid translation plate allowing the movement of said face along two crossed axes.
• the translation plate can move said face along one of the two axes for the wide field video camera and along the two axes for the small field video camera and for the optoelectronic probe.
• the means for processing the output signals delivered by the video cameras may include two monitors, one for viewing the view filmed by the wide field video camera and the other for viewing the view. filmed by the small field video camera.
• the device can include means for displaying the values measured by the optoelectronic probe.
• the receiving means comprising a solid translation plate allowing the movement of said face along two crossed axes
• the device may include means for controlling this plate along these axes operating in manual mode or in automatic mode. it may include means for recording the positions of the zones liable to constitute shape defects and measurements of the probe.
• the device can be provided with a computer management system which processes the output signals delivered by the video cameras, identifies from these signals the areas likely to constitute defects in shape, controls the optoelectronic probe and analyzes the measurements given by the probe.
• a computer management system which processes the output signals delivered by the video cameras, identifies from these signals the areas likely to constitute defects in shape, controls the optoelectronic probe and analyzes the measurements given by the probe.
• FIGS. 2 and 3 are views, respectively in profile and from above, of a plate to be checked, illuminated in grazing light in one direction,
• FIG. 4 is a block diagram of a device for implementing the control method according to the invention and usable for assistance to an operator
• - Figure 5 is a block diagram of a device for implementing the control method according to the invention and usable for automatic control.
• FIG. 1 shows a plate 1 for which the surface condition of its face 2 is to be checked by first observing the face. According to the invention, this observation is made by means of shots. A satisfactory solution is to use two video cameras, one to perform a wide field analysis and the other to perform a small field analysis.
• the wide field camera 3 makes it possible to identify and locate each potential fault quickly and with an accuracy for example of the order of 200 ⁇ m.
• the small field camera 4 only processes the areas of the wide field image comprising suspected areas. It allows very precise analysis and localization, for example an accuracy of the order of 20 ⁇ m.
• the face to be observed is illuminated by low-angle and multidirectional lighting equipment made up of several light sources creating homogeneous lighting. This acts on the discontinuities of the surface state in over-illumination or in shadow, forming local contrasts which will be indications of location.
• Figures 2 and 3 illustrate this type of lighting for a single lamp 5.
• the camera 3 captures an image of the defect 6, subjected to this lighting, comprising a dark area 7 and a bright area 8.
• the wide field video camera 3, in this exemplary embodiment, covers the width of the plate 1, that is to say a surface such as that carrying the reference 9 in figure 1. This surface can be 100 mm by 70 mm.
• the small field video camera 4 covers an area 10 smaller than the area 9. This area can be 12 mm by 9 mm.
• the device comprises an optical probe 11 of the focodyne type (that is to say with focal spot servoing of a laser diode) whose diameter of the measurement beam is much smaller than the size of the zones considered as defects.
• the plate is arranged on a translation plate 12 with two motorized perpendicular axes X and Y, which makes it possible to know precisely the position of the plate with respect to a reference point. You can use the angle of rotation of the axis drive motors or an incremental encoder for this.
• the movement of the plate 12 is regulated by an axis control member.
• the plate can be held on the plate 12 by vacuum. It can be moved along the X axis under the wide field camera 3 and along the X and Y axes under the small field camera 4 as well as under the probe 11.
• the device can be supplemented by two different video monitors, a monitor 13 for the image transmitted by the wide field camera 3 and a monitor 14 for the image transmitted by the small field camera 4.
• a display device 15 makes it possible to read the values measured by the probe 11. The control then takes place in the following manner.
• the operator observes the illuminated plate on the "wide field” video monitor and put it into rapid scrolling by the axis 18 steering member, in front of the wide field camera 3 which is fixed. When it detects a suspicious trace, it stops scrolling and points to the location 13 on the screen 13. Then it continues the rapid scrolling to the end of the plate.
• the plate automatically positions the previously pointed locations in the small field of the camera 4.
• the operator observing the "small field” video monitor 14 confirms or not the faults and launches the measurement procedure using the control member 16 of the optical probe 11.
• the measurement values and the location of the faults are recorded by the recorder 17 for editing a test report.
• a first rapid scrolling is carried out following a succession of shots whose field corresponds to that of the wide field camera.
• the defects and the remaining dust appear in white on a gray background.
• a first treatment by mathematical morphology consists in extracting the background of the image. This is then subtracted from the original image, which only reveals the defects.
• a second scroll positions faults under the small field camera. Each image is processed to precisely locate these faults and position the probe. The probe then reads the profile of the fault and a maximum calculation is carried out on the series of measurements.
• an automatic control installation has been made from the following elements.
• a 25 MHz INTEL 80386 type computer was used, to which was added a card allowing the acquisition and processing of 512 x 512 images coded on 8 bits (ie 256 gray levels).
• the motorized stage enabling wide field movement consists of two perpendicular tables having a stroke of 120 mm, a resolution of 1 ⁇ m and a displacement speed of 2 mm / s.
• the plate is lit by two cold light generators coupled to two optical fibers. Four homogeneous light sources are thus obtained.
• test plate measuring 70 x 780 mm, it was necessary to treat eight large fields per side. Before each wide field analysis, the plate was cleaned with alcohol and then blown with compressed air to remove the maximum amount of traces and dust.
• the purpose of the wide field analysis is to locate the faults that may exist on the plate.
• the camera acquires a field of 100 x 70 mm. In this image, the faults appear in white on a gray background.
• the binarization of the image (white defects on a black background) is carried out by methods of mathematical morphology.
• the image is first eroded (N times) then expanded (N times). Image 2 is thus obtained, from which the defects have been eliminated. This image is subtracted from the initial image, then the result is thresholded.
• the number N of erosions and expansions as well as the height of the threshold are parameters that can easily be modified by the user.
• the binarized image is filtered so as to eliminate stains whose surface is less than a determined threshold. If the binary image thus obtained does not show any defect (white spots), the next field is brought under the camera and the wide field analysis phase is restarted. Otherwise, the center of each spot is calculated and then positioned under the lens of the small field camera.
• the small field analysis is used to determine with great precision the displacement of the optical micro-probe.
• the small field camera is equipped with a lens examining a field with a surface of 12 x 9 mm (i.e. a resolution of the order of 20 ⁇ m).
• the small field acquisition is carried out in a similar way to the large field acquisition.
• the treatment of small fields takes two distinct forms depending on the type of image.
• the image includes a large defect (wide stripe or large diameter hole)
• its histogram has two distinct peaks, the first in the low gray levels corresponding to the defects, the second in the white corresponding to the background of the picture.
• This algorithm works by comparison of zones. Twenty-five horizontal integrated profiles of twelve partially overlapping lines are calculated on the image. These profiles allow you to define a maximum and minimum profile of the image. A thresholding on the difference of the maximum and minimum profiles makes it possible to calculate the position of the fault on the X axis. A vertical integrated profile of the window [(Xd, 0); (Xf, 512)] is then calculated on the Y axis. The window [(Xd, Yd) (Xf, Yf)] surrounding the fault is thus determined with precision.
• a defect is assimilated to a hole if its length / width ratio is between 1-a and 1 + a.
• the value of a is a user-defined system parameter.
• two perpendicular depth measurements passing through the center of the hole are calculated thanks to the displacement via a motorized stage of an optical micro-probe.
• Defects that are not assimilated to holes are taken into account as scratches.
• the search for the depth of a scratch is carried out by calculating the maximum depth of a series of measurements. If the length of the stripe is less than 5 mm, a profile is calculated every millimeter, otherwise every 2.5 mm.
• the binarization of the small field image carried out, an analysis of the surface and roundness of the defects makes it possible to classify them and to select an optimum search mode for their depth.

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

Applications Claiming Priority (3)

Publications (1)

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Family Applications (1)

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• 1993
  • 1993-11-04 FR FR9313128A patent/FR2712080B1/fr not_active Expired - Fee Related
• 1994
  • 1994-11-04 US US08/436,349 patent/US5606410A/en not_active Expired - Fee Related
  • 1994-11-04 EP EP95900190A patent/EP0677167A1/fr not_active Ceased
  • 1994-11-04 WO PCT/FR1994/001277 patent/WO1995012810A1/fr not_active Application Discontinuation
  • 1994-11-04 JP JP7513055A patent/JPH08505478A/ja active Pending
  • 1994-11-04 CA CA002149516A patent/CA2149516A1/en not_active Abandoned

Non-Patent Citations (1)

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