FR2899965A1 - Optically reflecting surface e.g. mirror, controlling method for e.g. motor vehicle, involves capturing digital image of surface by camera and analyzing parameter related to light intensity of image, for analyzing beam reflected by surface - Google Patents

Abstract

The method involves enlightening an optically reflecting surface (10) e.g. mirror, to be controlled, by a light beam (11) that is emitted by a point light source (12) e.g. laser diode. A digital image (15) of the surface is captured by an optical pick up camera (16) and a parameter corresponding to light intensity of the image is analyzed, for analyzing a light beam (14) that is reflected by the surface, where the light intensity of the image is obtained by reflection. An independent claim is also included for an optically reflecting surface controlling device comprising a light source.

Description

METHOD AND DEVICE FOR OPTICALLY CONTROLLING AN OPTICALLY SURFACE

REFLECTING

  The present invention relates to a method for optically reflecting an optically reflective surface, in which said optically reflecting surface to be illuminated by means of at least one light beam emitted by a light source is monitored, and the light reflected by said surface is analyzed. optically reflective.

  It also relates to a device for optical control of an optically reflective surface, comprising luminous means for illuminating, by at least one light beam emitted by a light source, said optically reflecting surface to be controlled, and analysis means for analyzing the light. reflected by said optically reflective surface. International patent application WO 03/036230 A1 discloses a method and a device for measuring at least one geometrical quantity of an optically reflective surface in order to determine in particular the variations of curvature, the slopes and the reliefs of this surface. . This system makes it possible to control the geometry of the surfaces and in particular to detect defects in the curvature of these surfaces. Nevertheless, this technique only makes it possible to detect small variations of curvature covering a large area. It becomes inoperative for large but very localized variations in curvature, which is the case with most paint defects. Methods known under the trademark DIFFRACTO or ONDULO have the same disadvantages.

  Artificial vision methods based on direct observation of the part to be controlled are difficult to apply because they would require the fine orientation of the surfaces and allow only limited control to small areas.

  In the automotive industry in particular, the appearance of the surface of new vehicles is extremely critical. No defects are tolerated. In low-level lighting, the slightest defects become visible to the naked eye, because the gloss of the paint highlights the slightest defects such as asperities, scratches or bumps of the base support, in particular of the body, on which this painting is deposited. This surface quality problem also exists in other technical fields, for example in the furniture sector or in the production of all kinds of household or industrial appliances whose aesthetic appearance is one of the strengths. of sale. The most common defects include, in particular, paint particles, hollow stampings on the substrate, pits, orange peel paint, paint projections or paint excess thicknesses, the lineage in the material constituting the support. or the like. These defects are characterized by their small size, the cross section is usually between 0.1 mm and 5 mm and the depth is generally between 0.5 and 10 micrometers.

  The detection technique is currently entirely manual and consists in placing the part to be controlled by an operator in particular geometrical positions with respect to artificial lighting or a target to generate illumination under grazing incidence, which enables the eye to be controlled. of the operator to detect defects. This detection is not easy and requires some experience on the part of the operator who, according to the nature of the defect, must focus on the surface or in the vicinity of the light source, which generates a 25 visual fatigue for the operator and makes it inefficient to detect defects after a few hours. In addition, visual detection is not infallible because it remains subjective and does not quantify the defect, which raises the problem of evaluation and can generate conflicts between the producer and the client, when opinions differ in regarding the seriousness of the defect. 30

  In addition, these defects are extremely difficult to detect at the time of manufacture and appear clearly only in certain lighting conditions, for example at sunset or under certain artificial lighting.

  As a result, there is currently no effective and completely reliable way to optimally and automatablely detect small defects on an optically reflective surface, such as a surface coated with glossy paint. In addition, no currently known method makes it possible to quantify bodywork or paint defects on motor vehicles, furniture items, polished pieces or the like, even if occasionally these defects could be identified and located.

  The present invention proposes to overcome these drawbacks by providing an efficient and economical method and device for controlling an optically reflective surface for identifying small defects in recesses or reliefs, locating them geometrically and, at need to quantify them.

  This object is achieved by the method according to the invention, as defined in the preamble, characterized in that for analyzing said reflected light, at least one image of said optically reflecting surface is taken and at least the parameter corresponding to the luminous intensity of said image of this surface.

  The method according to the invention is based on the principles of geometrical optics and in particular the laws of total reflection. The surface to be controlled is considered to be a perfectly reflective mirror in such a way that an incident beam which makes a given angle with respect to the vector normal to that surface is reflected at the same angle in a direction symmetrical with respect to this normal vector. In other words, the reflected beam is in the plane of the incident beam and the vector normal to the reflecting surface and the respective angles of the incident beam with the normal vector and the reflected beam with the normal vector are equal and of opposite sign . As a result, the direction of the reflected beam depends on the orientation of the normal vector at the surface at the point in question. If we consider all the reflected beams, this set is carrying information on the mapping of the normal vectors of the surface which allows to deduce the desired information, as will be described below.

  Preferably, said image of said optically reflective surface is taken by means of at least one optical camera.

  According to a first embodiment, said optically reflective surface is directly illuminated by a substantially point source, in that a reflected image of the zone of said optically reflecting surface illuminated by said substantially point source is formed on a screen. , in that the said image is analyzed and in that a relative movement is made between the said substantially point source associated with the screen and the said optically reflecting surface in order to scan at least one zone of the said surface to be checked and analyze the luminous intensity of the images obtained by reflection.

  Said screen may be of the frosted translucent type or of the opaque type.

  According to a particular embodiment, said screen is arranged at a variable distance D.

  This distance D 2 is preferably at least approximately half the radius of a sphere comparable to the geometry of a defect to be identified on said surface to be tested, and between 10 to 150 mm and preferably between 30 and 150 mm. 80 mm to correspond to the dimensions of the defects that one wishes to identify.

  According to another embodiment, it is also possible to interpose between the point light source and the surface to be controlled an opening formed in an opaque mask in order to illuminate only a part of this surface.

  Advantageously, said incident light beam which illuminates said optically reflecting surface to be controlled forms at the point of impact of the beam with a vector normal to this surface at this point, an angle which may vary depending on the applications.

  According to a second embodiment, a translucent frosted screen disposed opposite said optically reflective surface is illuminated by at least one light source which generates at least one light line on said frosted translucent screen, in that one moves said light line for scanning at least one zone of said frosted translucent screen, in that, by means of a camera, a digital image of said light line is taken for each of its geometric positions by reflection on said surface to be inspected and in that the digital images taken by said camera are analyzed.

  In this case, the distance D between said surface to be inspected and said frosted screen is preferably approximately between 100 to 400 mm and preferably between 200 and 300 mm. Advantageously, the digital images taken by said camera are analyzed by examining their intensity and deducing the local reflectivity of the surface to be controlled.

  It is possible to analyze the digital images taken by said camera by examining the width of the corresponding signal and deducing the presence of a very localized variation of curvature of the surface to be controlled.

  It is also possible to analyze the digital images taken by said camera by examining the position (Xo) of the signal and deducing the local orientation of an element of the surface to be controlled.

  The device according to the invention is characterized in that it comprises a light source for generating at least one light beam and illuminating said optically reflecting surface to be controlled, and means for analyzing the light reflected by said optically reflective surface, characterized in that said means for analyzing said reflected light comprises a device for forming at least one image of said optically reflective surface and means for analyzing at least the parameter corresponding to the luminous intensity of said image of that surface.

  Preferably, the device further comprises an optical camera for forming said image of said optically reflective surface and means for analyzing the image taken by said camera.

  According to a first embodiment, the device comprises a substantially point source and a screen for displaying a reflected image of the zone of said optically reflective surface illuminated by said substantially point source, at least one camera arranged to take a digital image of said reflected image, means for performing the analysis of said digital image, means for effecting a relative displacement of said substantially point source and said optically reflective surface for scanning at least one area of said surface to be monitored; means for analyzing the digital images taken by said camera.

  According to this variant, the screen, which may be of the translucent frosted or opaque type, is arranged at a distance D which is at least approximately half the radius of a sphere comparable to the geometry of a defect to be identified on said surface to control, and between 10 to 150 mm and preferably between 30 and 80 mm.

  Advantageously, the device may comprise at least one opening formed in an opaque mask interposed between the point light source 10 and the surface to be controlled in order to illuminate only a part of this surface.

  According to a second embodiment, the device according to the invention comprises means for illuminating said frosted screen disposed opposite said optically reflective surface by at least one light source which generates at least one light line on said frosted screen, means for moving said light line to scan at least one area of said frosted screen, said camera for taking a digital image of said light line for each of its geometric positions by reflection on said surface to be inspected and means for analyzing the images digital cameras taken by said camera. Said distance D between said surface to be inspected and said frosted screen is preferably approximately between 100 to 400 mm and preferably between 200 and 300 mm.

  The device according to the invention advantageously comprises means for analyzing the digital images taken by said camera by examining their intensity and deducing the local reflectivity of the surface to be controlled.

  The device according to the invention preferably also comprises means for analyzing the digital images taken by said camera in

  examining the width of the corresponding signal and deducing the presence of a very localized variation of curvature of the surface to be controlled.

  The device according to the invention advantageously furthermore comprises means for analyzing the digital images taken by said camera by examining the position (Xo) of the signal and deducing the local orientation of an element of the surface to be controlled. .

  The present invention will be better understood and its advantages will emerge more clearly from the following description of various embodiments illustrated by the appended drawings, in which:

  FIG. 1 is a schematic view illustrating a first embodiment of the device for carrying out the method according to the invention; FIG. 2 is a schematic view illustrating a second embodiment of the device for implementing FIG. 3 is a schematic view illustrating the measuring principle 20 according to the method of the invention; FIG. 4 is a schematic view illustrating an image forming model by applying the method; according to the invention, and FIG. 5 represents an image analysis method corresponding to the second embodiment of the device for implementing the method according to the invention.

  FIG. 1 schematically represents a first embodiment of the method according to the invention. An optically reflective surface 10 to be controlled and having a substantially macroscopically constant curvature is illuminated by a light beam 11 emitted by a light source considered, in this case, as approximately point-like 12.

  This light source, known per se, may for example be an optical fiber output, a laser or a laser diode or the like. A defect in said surface to be inspected may be represented by an area of this surface having a substantially spherical shape whose radius is different from the radius of curvature of the perfect surface. A screen, which in this case is a frosted translucent type screen 13, is disposed near the surface 10 to be controlled which emits a reflected beam 14 when illuminated by the source 12, this beam being intercepted by the screen 13, on which a light spot 15 appears. This light spot 15 can be observed directly with the naked eye or, as shown, is photographed by an optical camera 16 for analysis which will be explained in detail. thereafter. The reflected beam 14 forms with the normal vector n at the surface 10 at the points of impact of the rays of the incident beam, an angle equal to that formed by the incident beam with said normal vector n at the surface 10. The screen 13 can also be opaque type.

  For the entire surface 10 to be controlled, it is necessary to scan this surface either by moving the light source 12 associated with the screen 13 and keeping the surface 10 in position, or by moving the 10 and maintaining the light source 12 associated with the screen 13 in position, or by combining the two displacements.

  FIG. 3 schematically illustrates the principles of formation of the images that appear on the frosted translucent screen 13 according to the geometry of the deformations of the surface to be inspected 10. These deformations can be cataloged in two geometrical categories: a deformation of concave geometry 20 assimilated to a spherical cavity, a deformation of convex geometry 21 likened to a spherical hump. As shown precisely in FIG. 3, the concave geometry deformation 20 generates a convergent reflected beam 30 and the convex geometry deformation 21 generates a divergent reflected beam 31. The frosted translucent screen 13 is placed at a variable distance, preferably a short distance D from surface 10 to 10

  control, this distance D being substantially equal to half the radius of the sphere which is assimilated to the defect of the surface to be controlled 10. The laws of reflection of the spherical mirrors specify that the reflected rays are focused at a distance equal to the half of the radius of the sphere. If the translucent frosted screen is disposed at this distance D of the reflecting surface having a concave defect, there will be a significant overcurrent at the point of focus. If the frosted translucent screen is disposed too far from the surface to be monitored, overcurrent will not be observed. Conversely, the rays arriving on a defect of convex type, are reflected with a divergence, and to generate on the frosted 13 a low intensity spot which appears well if the frosted translucent screen 13 is disposed at a small distance from the surface to be controlled 10. Again, if the frosted translucent screen 13 is disposed too far from the surface to be controlled 10, the area of low intensity will no longer be apparent.

  In practice, the defects have extremely small dimensions and the working distance D which corresponds to the difference between the surface to be controlled and the ground surface is typically between 10 and 150 mm and preferably of the order of 30. at 80 mm. The geometric model shown is theoretically valid only for incident angles close to 0 degrees from the normal vector at surface 10 at the point of impact of the incident ray. However, in practice, the method is applicable at angles up to 60 degrees to the normal vector at the surface 10. Beyond these angles, the image formed on the frosted translucent screen 13 only reveals defects of large spatial size, which does not correspond to the defects of small size sought in the context of the present invention.

  The image that appears on the frosted translucent screen 13 when the surface to be inspected 10 is scanned by an incident beam 11 with substantially parallel radii, for example emitted by a moving light source (not shown), is shown schematically by FIG. 4. A deformation of concave geometry 20 emits a convergent reflected beam which forms on the 2899965 <<

  frosted 13, disposed at a small distance as mentioned above, a substantially punctual spot 33. A deformation of convex geometry 21 emits a divergent beam which forms on the frosted translucent screen 13, arranged at a small distance as mentioned above, a spread stain 34. The substantially point spot 33 has increased brightness because the reflected light is focused on a reduced area. In contrast, the spread spot 34 has a reduced brightness because the reflected beam is divergent and the reflected light is distributed over a larger area. Flawless areas 25 emit an approximately parallel beam 35 which forms on the frosted translucent screen 13 a constant intensity light 36 whose brightness is intermediate between that of the substantially point spots 33 and that of the spread spots 34.

  It should be noted that a mask may be interposed between the substantially point source of light 12 and the surface to be controlled 10, which has an opening which limits the lighting zone of this surface. This variant makes it possible to improve the quality of the images obtained because the analyzed zone is not disturbed by the parasitic rays which, in the absence of the mask, would have originated from the defects present in the other zones of said surface. FIG. 2 diagrammatically represents a second embodiment of the method according to the invention. In this variant, the position of the light source and of the image analysis camera is reversed. The device represented by this figure comprises, as in the case of the device represented by FIG. 1, a surface 50 to be controlled, optically reflective, and having a substantially constant curvature, a frosted translucent screen 53 which is disposed near the surface 50 to control, a light source 52 and a camera 56 for detecting the optical consequences caused by the small defects of the surface to be controlled 50. In this case, the camera 56 visualizes the frosted translucent screen 53 by reflection on the surface to control 50. In practice, it projects on the screen 53 frosted at least one light ray 55 which

  sweeps the entire surface to be controlled 50. The interest of this variant is twofold. On the one hand the working distance D can be increased significantly without loss of quality. For example, it is possible to work without difficulty at a working distance D of 200 to 300 mm to control an area of about 150x150 mm. On the other hand, in addition to an image characterized by intensity variations induced by the defects of the surface to be controlled 50, additional information can be obtained which makes it possible to quantify more precisely the optical characteristics of the surface.

  In this variant, the camera takes an image for each position of the projected line. For a complete scan of the frosted, a succession of n images corresponding to each scanning position is obtained. The values of the luminous intensity received for a camera pixel correspond schematically to the curve represented by FIG. 5. For a glossy surface, the collected signal can be in the form of: l = I min + (I0 I min) .e (x-x0) 2 2a 2 From this curve, it is therefore possible for each camera pixel to draw the following main information: .- intensity received (lo Imin): this intensity provides information on the local reflection of the surface .- width of the signal: for a perfect mirror the parameter width a must be exactly the same as that of the projected line. An increase or decrease in a reflects the presence of a very localized variation in curvature, which corresponds to the defect sought. .- X0 position of the signal: the Xo parameter provides information on the local orientation of the surface element corresponding to the pixel in question. After calibration, this parameter makes it possible to obtain the components of the vector normal to the surface and thus to reconstruct the 3D shape of the surface. other information characterizing the signal: other information can be derived from the analysis of the temporal signal obtained such as min or I o used alone, such as the possible presence of several peaks. All this information characterizes the optical property of the surface to be controlled, visualized by the considered pixel of the camera. The basic information (lo Imin), a, Xo being obtained for each camera pixel, it is possible to reconstruct three images of the surface, each image corresponding to one of the parameters above.

  FIG. 5 illustrates a curve 60 which represents the light intensity of the image received by the camera pixels as a function of the offset order number of the projected line. An intensity peak 61 is observed which makes it possible to precisely position a defect identified on the surface to be controlled 10.

  The device and the method according to the invention are in particular but not exclusively adapted to an application in the automotive industry. The control of the state of the surface of the bodywork and in particular of the quality of the paint can be automated, which makes it possible to avoid the risk of errors due to the fatigue of a controller operating in direct vision.

Of course, the present invention is not limited to the described embodiments but extends to any modification and variation obvious to a person skilled in the art while still within the scope of the protection defined in the appended claims. 25

Claims (28)

claims   A method of optically reflecting an optically reflective surface (10, 50) in which at least one light beam (11, 51) emitted from a light source (12, 52) is irradiated with said surface ( 10, 50) and the reflected light (14) is analyzed by said optically reflective surface (10, 50), characterized in that for analyzing said reflected light (14) at least one image of said optically reflective surface (10, 50) and analyzing at least the parameter io corresponding to the luminous intensity of said image of this surface (10, 50).   2. Method according to claim 1, characterized in that one takes said image of said surface (10, 50) optically reflective by means of at least one camera (16, 56) optical shooting. 15   3. Method according to any one of claims 1 or 2, characterized in that one directly illuminates said surface (10) optically reflective by a source (12) substantially punctual, in that one forms on a screen ( 13) an image (15) reflected from the area of said optically reflective surface (10) illuminated by said substantially point source (12), in that said image (15) is analyzed and in that that a relative movement is made between said source (12) substantially punctual associated with said screen (13) and said surface (10) optically reflective to scan at least one area of said surface (10) to be controlled to carry out the analysis of the light intensity of the images (15) obtained by reflection.   4. Method according to claim 3, characterized in that said screen (13) is of the frosted translucent type. 3o   5. Method according to claim 3, characterized in that said screen (13) is of the opaque type.   6. Method according to claim 3, characterized in that said screen (13) is arranged at a variable distance D.   7. Method according to claim 6, characterized in that said screen (13) is arranged at a distance D which is at least approximately half of the radius of a sphere comparable to the geometry of a defect to be identified. on said surface (10) to be controlled.   8. Method according to claim 6, characterized in that said distance D is approximately between 10 to 150 mm and preferably between 30 and 80 mm.   9. Method according to claim 3, characterized in that is interposed between the light source (12) point and the surface (10) to control an opening in an opaque mask to illuminate only part of this surface .   10. Method according to claim 3, characterized in that said incident light beam (11) which illuminates said optically reflective surface (10) to be controlled forms at the point of impact of the beam with a vector normal to this surface at this point, a angle that can be varied depending on the applications.   11. A method according to claim 2, characterized in that one illuminates a screen (53) translucent frosted disposed opposite said surface (50) optically reflective by at least one source (52) light that generates at least one bright harbor. (55) on said frosted translucent screen (53), in that said light line (55) is moved to scan at least one area of said frosted translucent screen (53) by taking, by means of a camera (56), a digital image of said light line (55) for each of its geometric positions by reflection on said surface (50) to be controlled and in that the digital images taken by said camera (56).   12. The method of claim 11, characterized in that the distance D between said surface (50) to be controlled and said screen (53) translucent frosted is approximately between 100 to 400 mm and preferably between 200 and 300 mm.   13. Method according to claim 11, characterized in that the digital images taken by said camera (56) are analyzed by examining their intensity and deducing the local reflectivity of the surface (50) to be controlled.   14. Method according to claim 11, characterized in that the digital images taken by said camera (56) are analyzed by examining the width of the corresponding signal and deducing the presence of a very large variation of curvature. localized surface (50) to control.   15. Method according to claim 11, characterized in that the digital images taken by said camera (56) are analyzed by examining the position (Xo) of the signal and deducing the local orientation of a element of the surface (50) to be controlled.   16. Control device, for implementing the method according to any one of the preceding claims, comprising a light source (12, 52) for generating at least one light beam (11, 51) and illuminating said surface (10). 50) optically reflective to be monitored, and means for analyzing the light reflected from said optically reflective surface (10, 50), characterized in that said means for analyzing said reflected light comprises a device for forming at least one image of said 30 optically reflecting surface (10, 50) and means for analyzing at least the parameter corresponding to the light intensity of said image of this surface (10, 50).   17. Device according to claim 16, characterized in that it further comprises an optical camera (16, 56) for forming said image of said optically reflective surface (10, 50) and means for analyzing the image taken by said camera (16, 56).   18. Device according to any one of claims 16 or 17, characterized in that it comprises a source (12) substantially punctual and a screen (13) for displaying a reflected image (15) of the area of said surface ( 10) optically reflective illuminated by said source (12) substantially punctual, at least one camera (16) arranged to take a digital image of said reflected image (15), means for performing the analysis is said digital image, means for effecting a relative displacement between said substantially point source (12) associated with the screen and said optically reflective surface (10) for scanning at least one area of said surface (10) to be monitored and means for performing analyzing digital images taken by said camera (16). 20   19. Device: according to claim 18, characterized in that said screen (13) is a frosted translucent type screen.   20. Device according to claim 18, characterized in that said screen (13) is a screen of the opaque type.   21. Device according to claim 18, characterized in that said screen (13) is arranged at a variable distance D of said surface (10) to be controlled.   22. Device according to claim 21, characterized in that said variable distance D is approximately between 10 to 150 mm and preferably between 30 and 80 mm.   23. Device according to claim 18, characterized in that it comprises at least one opening in an opaque mask interposed between the point light source and the surface to be controlled to illuminate only part of this surface. io   24. Device according to claim 17, characterized in that it comprises means for illuminating a frosted translucent screen (53) disposed opposite said optically reflective surface (50) by at least one light source (52) which generates at least a light stripe (55) on said frosted screen (53), means for moving said light stripe (55) to scan at least one area 15 of said frosted screen (53), a digital camera (56) for taking a digital image of said light line (55) for each of its geometric positions by reflection on said surface (50) to be controlled and means for analyzing the digital images taken by said camera (56). 20   25. Device according to claim 24, characterized in that the distance D between said surface (50) to be controlled and said screen (53) is approximately between 100 to 400 mm and preferably between 200 and 300 mm. 25   26. Device according to claim 24, characterized in that it comprises means for analyzing the digital images taken by said camera (56) by examining their intensity and deducing the local reflectivity of the surface (50) to control, regulate. 3o   27. Device according to claim 24, characterized in that it comprises means for analyzing the digital images taken by the camera (56) by examining the width of the corresponding signal and deducing the presence of a variation of curvature very localized surface (50) to control.   28. Device according to claim 24, characterized in that it comprises means for analyzing the digital images taken by said camera (56) by examining the position (Xo) of the signal and deducing the local orientation d an element of the surface (50) to be controlled.