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

Definitions

• the invention relates to the field of automatic industrial inspection and more particularly relates to a process, and the corresponding device, for the inspection of glass.
• the purpose of glass inspection is to detect and locate faults, called “inclusions", generated during the manufacturing phase in pieces of glass.
• inclusions generated during the manufacturing phase in pieces of glass.
• the impact of these defects on the quality of the glass produced depends on their number, their shape, and the standards imposed on glassmakers according to the intended application. These defects are of two types:
• - "broth” type the defects are gas bubbles which remain in the molten material
• - "stone” type the defects are defects in the homogeneity of the basic constituents, leading to the formation of a visible particle in the glass.
• the size of these inclusions is generally less than a millimeter and their measurement must be carried out with great precision, at least for certain applications, the required precision possibly ranging from 1 / 10th to 1 / 100th of a millimeter.
• the subject of the invention is a method of inspecting glass, and the corresponding device, which makes it possible to avoid the drawbacks of conventional methods by making it possible both to locate the defects on the surface as in the thickness of the glass and to know approximately their positions in the thickness of the glass, which allows very good discrimination between surface defects and inclusions.
• the inspection method uses a three-dimensional treatment and for this performs localized lighting of the glass by a laser beam, and suitable detection which makes it possible to view the upper face of the glass and its lower face separately. and, between the two, its thickness.
• a method of inspecting a glass by illumination by means of a light source external to its illuminating surface characterized in that it consists in illuminating the illuminating surface by an applied laser beam in a direction approximately perpendicular to the illumination face to form a light curtain in the form of a plane passing through the glass in its thickness, for detecting by a camera the reflected radiation emerging from the piece of glass in a direction of oblique observation with respect to the direction of the plane formed by the light curtain when inclusions are presented in the glass at the location of the light curtain, and visualize by the camera the image of the inclusions thus obtained, between two lines representing respectively the rays light weakly reflected by the entry and exit surfaces of the light beam during its passage through the thickness of the glass.
• the invention also relates to the inspection device intended for the implementation of the method as described above.
• the invention will be better understood and other features will appear with the aid of the description which follows with reference to the appended figures.
• FIG. 1 is a diagram of the inspection device according to the invention
• FIG. 2 is a detailed diagram of the device
• the glass inspection device comprises, in one embodiment illustrated schematically in plan view in FIG. 1, two stations, a station 1 for detecting and locating faults in three dimensions, X, Y, Z and a station 2 for classification and measurement of these faults.
• the piece of glass 3 is placed on a conveyor 4 and analyzed as it passes vertically from station 1 for the detection and location of faults, the movement of the conveyor taking place along the X axis.
• Station 1 provides an image of successive sections of the piece of glass (in the YZ plane), such as that shown in Figure 1 where an inclusion has been represented between two lines corresponding respectively to the upper surface and the lower surface of the glass .
• the first station is constituted as follows. It comprises a lighting source 10 of the neon helium laser type, HeNe illustrated in FIG. 2.
• the beam emitted by the laser source is widened by an optical bar disposed at the output of this source so as to constitute a kind of light curtain , of suitable thickness, as illustrated in FIG. 2, which corresponds at all times to a YZ section of the piece of glass.
• This light curtain therefore illuminates the glass perpendicular to the plane of the conveyor and therefore encountered successively:
• a camera 20 placed above the glass and obliquely to the light curtain, as shown in section in FIG. 3, is intended to capture the radiation emerging from the piece of glass in its direction, called the direction of observation, and therefore sees these interruptions respectively as:
• the corresponding lines can be lines if the intersection of the light curtain and the upper face of the glass is a straight line, or curved lines for a spherical or cylindrical face if the curvature extends in the direction of the light curtain.
• the method of inspecting a piece of glass consists of scrolling this piece of glass over the conveyor belt 4 under the station 1 comprising the laser source and the camera system, the carpet being animated by a uniform translational movement.
• the laser beam is chosen to be sufficiently spread; if the width of the room exceeds the possible width of expansion of the beam, the optical laser lighting device will be reproduced as many times as necessary.
• station 1 is equipped with additional cameras to cover the useful field.
• the images are acquired by the camera system at video frequency; the sequence of images thus obtained is processed in a computer processing device which makes it possible to detect and follow the two lines associated with the surfaces as well as one or more inclusions between these two lines.
• the information provided by the station 1 is therefore a location by imaging of the defects in three dimensions X, Y and Z.
• the luminance information of the defect also makes it possible to approximately quantify the size of the defects, and this information can be used by item 2 for classification and measurement.
• the characteristics of the lighting system are such that the source is a neon helium laser source as indicated above, the means for expanding the beam from the source laser consist of an optical bar or a divergent lens, half cylinder plan / concave, so as to spread the laser beam in one direction; the thickness of the laser curtain must be greater than the size of the defects so as to guarantee detection of the defect in all cases.
• the sensors used are of the CCD type; the number of sensors depends on the width of the piece of glass to be inspected and on the desired resolution.
• the number of cameras is doubled so as to overcome parasitic phenomena due to multiple reflections of the laser beam in the glass , capable of generating on the image light lines of lesser energy inside the two lines described above.
• the duplication of information processing makes the device more robust, especially in the case of a dusty atmosphere.
• two cameras are placed symmetrically with respect to the laser whose axis is vertical.
• the angle of incidence (i) between the laser and the optical axis of the camera is chosen so that one of the axes of the two cameras is always located on the side opposite the laser beam relative to the normal to the surface glass.
• the camera 21 will be used while for the right part of the room the camera 22 will be used.
• the camera's optical system at station 1 the problem is not precision but simply the detection and location of faults whose coordinates along the X, Y and Z axes are then communicated to station 2 for precise measurement.
• the camera optics are therefore chosen as follows.
• the camera's optical system includes an anamorphic element: in practice it is not necessary to have the same resolution along the two axes of the image. Good precision is required along the vertical axis so as to correctly separate the inclusions from the two surface lines (which are the two horizontal lines in the images in FIGS. 4a to 4d; on the other hand, it is desired to be able to cover the widest band possible glass along the horizontal axis (Y) in order to limit the number of cameras required and the power of computer processing. This is why an anamorphic optical system is used to ensure an anisotropic magnification in the image in both directions orthogonal X and Z.
• the invention is not limited to the method and device for inspecting glass as described in detail above.
• it was describes a conveyor on which is driven a piece of glass which scrolls vertically from an observation post.
• a mobile observation post the material to be inspected remaining fixed. This arrangement is particularly interesting for large pieces of glass to be inspected.
• the camera was provided in the example to form an image from the radiation emerging in the direction of observation.
• an optic which would facilitate the formation of the useful image, in particular an optical filter transmitting to the detector the radiation emerging at the length d wave of the laser source used.

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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)

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• 1991
  • 1991-09-13 FR FR9111315A patent/FR2681429B1/fr not_active Expired - Fee Related
• 1992
  • 1992-09-14 EP EP92920289A patent/EP0603311A1/de not_active Ceased
  • 1992-09-14 RU RU94026774/25A patent/RU94026774A/ru unknown
  • 1992-09-14 US US08/196,212 patent/US5459330A/en not_active Expired - Fee Related
  • 1992-09-14 WO PCT/FR1992/000859 patent/WO1993006467A2/fr not_active Application Discontinuation
  • 1992-09-14 JP JP5505828A patent/JPH06510856A/ja active Pending

Non-Patent Citations (1)

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