Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N7/00—Television systems
  • H04N7/18—Closed-circuit television [CCTV] systems, i.e. systems in which the video signal is not broadcast
• • 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
  • G01B11/24—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures
  • G01B11/25—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures by projecting a pattern, e.g. one or more lines, moiré fringes on the object
  • G01B11/2513—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures by projecting a pattern, e.g. one or more lines, moiré fringes on the object with several lines being projected in more than one direction, e.g. grids, patterns

Definitions

• the invention relates to a device for measuring the shape of a mirror or a specular surface (reflecting surface).
• the invention is more particularly intended for surfaces that are not flat but having a convex shape whose concavity is strongly marked in a direction, hereinafter referred to as "main direction", and much less marked in the direction perpendicular to the main direction , called “secondary direction”. More precisely, "the direction of a concavity” is understood in this way and as illustrated in FIGS. 1a and 1b: by positioning a surface A on a horizontal plane support B with the domed portion opposite this support, the concavity with respect to the plane of the support is distinct according to its comparison with said plane in one and the other of the directions of the plane, directions corresponding to the X and Y axes in a two-dimensional orthogonal reference plane.
• concavity with respect to the other is that which is least parallel to the support plane.
• the concavity is more pronounced along the axis X, so called principal direction, than along the Y axis, said secondary direction.
• measuring the shape means estimating the slope and the altitude for a multitude of points of the surface to be measured with respect to a reference surface, and this in the two corresponding measurement directions. to the main and secondary directions of the bending.
• the invention will be more particularly described with reference to a curved glazing, without being limited thereto.
• the device also applies to flat surfaces that are very slightly deformed, whether in laminated glass or tempered glass.
• Another useful application of the device concerns the measurement of shape of parabolic solar mirrors, for which the concavity of the surface is much more accentuated.
• it is indeed appropriate to measure the shape of a specular surface for example to detect glass defects at the outer surface of a car glazing. The detection and measurement of these defects make it possible to provide the aesthetic appearance of the automobile glazing if it was observed in reflection from the outside of the motor vehicle with which it is associated.
• the shape of the mirror In a parabolic mirror application, it is generally preferable to know the shape of the mirror just after its manufacture, by comparing it to the perfect shape of a reference mirror. Indeed, the good focus of light rays by a mirror depends on the energy efficiency of the mirror. However, the focus is directly related to the ideal profile of the concavity of the mirror, which profile is precisely appreciated by the measurement of slope and altitude of a multitude of points of the surface.
• Various shape measurement techniques are known, such as the probe process, photogrammetry, deflectometry, or laser scanning.
• the probe process consists in mounting a probe at the end of a mechanical arm coming into contact with the surface of the glazing at numerous points (typically 1000 points regularly distributed for a glazing 1500x1500 mm). This measuring device gives direct access to the altitude of each point. The local slope is then calculated from the altitude by digital derivation. The acquisition and processing time is of the order of 100 minutes.
• Photogrammetry consists in sticking on the entire surface to measure a pattern consisting of a white sheet on which is drawn a large number of precisely positioned black spots. Several shots of this pattern are made from different angles (typically eight angles), then these shots are processed by appropriate software to reconstruct the two-dimensional shape of the surface and thus provide a map of the altitude. The local slope is calculated from this altitude by derivation. The acquisition and processing time is of the order of 120 minutes.
• the deflectometry technique is on the other hand much faster, of the order of 5 minutes. It consists in analyzing the deformations of a test pattern after reflection on the surface to be measured. By knowing the state of the undeformed pattern, and in a known manner by ray tracing, the local slope of the surface at any point on this surface can be calculated. The mathematical integration of the local slope into consecutive points leads to the altitude of these different points.
• Laser scanning also faster technique, consists of scanning the surface to be analyzed in two perpendicular directions with a laser precisely aligned in each direction. A camera observes the point of impact of the beam after reflection on a target placed in the plane of focus of the surface and checks the quality of the centering of the point of impact of the beam on this target. The duration of the measurement, for a surface of 1500x1500 mm is, typically, 5 minutes.
• deflectometry and laser scanning techniques are difficult to implement on an industrial line because they require adjustments, extremely fine positioning or calibrations of the measuring systems as soon as a new surface is to be measured.
• an alignment error or inclination of the laser for example 1 milliradian, or 1 mm over a distance of 1 m completely distorts the measurement and estimation results.
• the object of the invention is therefore to provide a device for measuring the shape of a specular surface associated with a volume such as a glazing unit or a mirror, this device not having the aforementioned drawbacks and combining the performances both when the time of implementation and acquisition and processing of data, and the reproducibility of measurement on industrial line.
• the device for measuring the shape of a mirror or a specular surface comprises a first planar pattern of one-way pattern intended to be at a distance from the surface to be measured, a camera for the shooting of the image intended to be reflected in the specular surface, information processing means which are recorded by the camera, first means of illumination of the whole target, and is characterized in that it comprises additional means of lighting which are arranged in the immediate vicinity and parallel to the plane of the test pattern, or in the plane of the test pattern, and facing the surface to be measured, the first lighting means and the additional lighting means alternately so as to visualize respectively that the first test pattern or a second pattern of one-way pattern generated from additional lighting means.
• the additional lighting means by their arrangement are intended to illuminate in the plane of the test pattern towards the surface to be measured.
• the device thus makes it possible, from two distinct patterns, to provide measurements at a time, in the direction of the surface that requires the most precision and resolution, namely the direction of the greatest deformation, and in the secondary direction perpendicular to the main direction.
• the alternating illumination shows either a first monodirectional pattern test pattern which ensures to measure the shape in the main direction, or a second pattern of one-way pattern and perpendicular to the pattern of the first pattern to measure the deformation of the surface. in his secondary direction.
• This device avoids the use of a bi-directional pattern, such as a chessboard pattern, which is difficult to process and has too low spatial resolution.
• the device of the invention by-passes these difficulties by making cohabit on the same surface supporting the first pattern, two separate patterns that are visible only in an appropriate implementation of the lighting conditions.
• the lighting time respectively of the first lighting means and additional lighting means lasts the time of a respective shooting of the entire surface by the camera.
• this device allows an extremely fast measurement of the shape of the surface according to an acquisition and processing time of at most 20 seconds, which is particularly suitable for an industrial line.
• the first pattern comprises an alternation of dark and light parallel lines of identical width, such as 10 mm.
• width is meant the smallest dimension of a line.
• the second pattern provided by the additional illumination means comprises a multiplicity of point light sources, such as light-emitting diodes or optical fiber terminations, which are regularly spaced in an alignment parallel to the lines of the first pattern.
• point light sources such as light-emitting diodes or optical fiber terminations
• the light sources are aligned centrally in the width of at least one dark line.
• the device comprises a panel carrying the first sight, this panel comprising a central orifice which accommodates the objective of the camera, preferably the orifice being dimensioned so that the ratio between its surface and the total area of the target is less than 1/1000.
• the distance between the first sight and the surface to be measured, and the dimensions of the target are adapted so that the whole of the target is reflected on the entire surface to be measured, and in that the objective of the camera is adapted to record in a single shot the entire surface to be measured.
• the device is advantageously associated with a plane support carrying the surface to be measured, this support extending parallel to the first target, and the surface to be measured being intended to be arranged centrally with respect to the optical axis of the objective from the camera.
• the opposite edges of the surface to be measured and perpendicular to the main direction are placed substantially at the same distance from the support so that the curvature in the main direction is substantially symmetrical with respect to the optical axis constituted by the axis of the camera.
• the concavity of said surface must be directed opposite the target, and said surface is arranged on said support so that the unidirectional pattern of the first target is oriented perpendicular to the main direction of the bending.
• the surface is deposited on the support so that the camera can capture the entire surface in one shot, but no precise centering of the surface is necessary, nor calibration or calibration step, which allows very advantageously to save time on industrial line.
• FIG. 2 shows a schematic sectional view of the measuring device of the invention associated with a support carrying the surface to be measured;
• FIG. 3 is a perspective view of the support of FIG. 2;
• FIG. 4 is a front view of an example of a first pattern with a one-way pattern used by the device of the invention.
• FIG. 5 is a partial front view of an example of a second pattern used by the invention.
• FIG. 2 diagrammatically illustrates the measuring device 1 of the invention for estimating the shape of a specular surface 2, such as one of the main faces of a curved glazing having distinct curvatures along mainly two directions; bending being more pronounced in one of the directions.
• a specular surface 2 such as one of the main faces of a curved glazing having distinct curvatures along mainly two directions; bending being more pronounced in one of the directions.
• the device comprises a support 3 on which the glazing is deposited and a more detailed view of which is illustrated in FIG. 3, a pattern 4 with a monodirectional pattern which is more particularly illustrated with reference to FIG. 4, the surface 2 of the glazing being next to the sight, a camera 5, processing means 6 connected to the camera and able to process the recordings recorded by the camera, the first illumination means 7 of the sight, and additional means of illumination 8 implemented when the first lighting means are extinguished.
• the additional lighting means 8 are configured and arranged to illuminate in the plane of the target towards the surface to be measured 2 by generating a second pattern 9 monodirectional pattern perpendicular to the pattern of the first pattern.
• the device of the invention makes it possible, thanks to the first pattern 4, to produce an image in the surface in high resolution, and by the second pattern which is concealed in the first when the additional illumination means are extinguished, to create an image of lower but sufficient resolution for measurement result requirements.
• Changing camera lighting and shooting conditions make it easy to switch between instantly and take two shots successively, one shot per image of each of the staffs reflecting.
• the measurement is therefore made in two perpendicular directions, considering that the most convex shape should be measured more accurately than the less curved shape, or considering that the knowledge of the shape in the second direction is negligible or that this form is flat in this direction.
• the support 3 with reference to FIGS. 3 and 4 forms a plane surface table and on which are arranged a plurality of support pads 30, here visible by transparency through the surface and four in number, as well as lateral stops 31 and 32.
• the curved glazing is deposited on the support 3 according to one of its main faces 20, opposite the surface 2 to be measured, the convex portion 21 of the glazing being turned towards the support 3.
• the glazing thus rests by its face 20 on the support pads 30 which are spaced appropriately to properly distribute the weight of the glazing to maintain a stable equilibrium.
• the lateral stops 31 and 32 make it possible to wedge the glazing by its lateral edges 20 and 22.
• the studs 30 and the stops 31 and 32 also serve to correctly position the glazing, and therefore the surface 2, relative to the target 4 which is intended to be reflected in this surface.
• the positioning of the glazing on the measurement support can be done via a robot arm. It can more simply be done through two operators. More commonly, the positioning of the glazing under the test is done during the conveying of the glazing on line by stopping the glazing under the test pattern, then focusing (by centering) with the aid of removable cylinders acting as stops 31 and 32 associated with an elevator system ensuring vertical translation up or down, and placed under the glazing instead of the support pads 30 to bring the glazing at the right distance from the test pattern. After the shots, the glazing is redeposited on the conveyor and evacuated before the arrival of the next glazing.
• the first pattern 4 illustrated in FIG. 4 is a pattern with a one-way pattern forming a regular periodic signal.
• the pattern consists of a regular alternation of dark lines 40 and lines 41 and clear, preferably black and white lines to provide a strong contrast between them.
• the width of each line is constant, for example 10 mm.
• Each line is an object, optically speaking.
• Each line has an upstream edge and a downstream edge whose positioning is referenced in the processing means 6.
• the camera 5 is intended to take the image of the pattern in reflection on the surface, and therefore the image of each upstream and downstream edge of the lines; the processing means will establish a comparison of the positioning of the edges of each of the lines between the image and the reference, providing the optical magnification of each line.
• the treatment process will be seen in more detail later.
• the target 4 faces the surface 2 to be measured and is arranged at a distance. It extends along a square or rectangular surface.
• the dimensions of the test pattern and its separation distance from the surface 2 are adapted so that the whole of the test pattern can be reflected in the surface 2, these magnitudes also taking into account the type of objective (viewing angle ) assigned to the camera.
• viewing angle the type of objective assigned to the camera.
• the distance sight-surface is 2500 mm
• the dimensions of the target are of 3600 x 1800 mm.
• the objective 50 of the camera 5 (FIG. 2) is located in the same plane as that of the target 4 and pointed towards the surface 2.
• the type of objective and the distance to the surface allow to measure in full field, that is to say on the entire surface in a single shot.
• the target 4 is for example supported by a rigid panel 42 of white PVC on which are screen printed black lines of identical width and regularly spaced.
• the panel 42 has in its center an orifice 43 accommodating the camera lens.
• the orifice will be as small as possible because the portion of the surface 2 facing it can not be measured.
• care must be taken to have a ratio between the surface of the orifice and the surface of the target less than 1/1000.
• the missing part of the pattern corresponding to this orifice may however be artificially reconstituted by a suitable technique so as not to alter the measurement in this area.
• the target is illuminated by its front face (facing the surface 2) with the first lighting means 7, such as projectors.
• the lighting means are in a number and arrangement that are suitable for providing uniform illumination of the entire pattern.
• the whole of its image reflecting in the specular surface 2 is intended to be photographed in a single take by the camera which covers by its objective the whole of the glazing area.
• the camera 5 is for example a matrix camera of known type comprising a decomposition of square pixels according to 1700 columns on 1200 lines. Each pixel is associated with a specific area of the image of the reference pattern which allows the position of each of the line edges of the pattern to be referenced. Each pixel also corresponds to a zone (point) of the surface to be measured.
• the comparison between the acquired pattern is on a perfect glazing, or on a flat glazing and in measurement geometric conditions identical to that of the glazing to be measured, and its image reflected by the glazing to be measured will allow to deduce the optical magnification of each of lines at each pixel and therefore each point of the surface 2. Thanks to the processing means 6, the measured optical magnification will be deduced, the slope in each of the points and consequently the altitude to establish finally the profile of the surface (its form).
• the glazing in order to have the best resolution for measuring the shape corresponding to the most pronounced concavity (principal direction), it is advisable to orient the glazing with respect to the sight so that the lines of the sight are arranged perpendicular to this principal direction.
• the pattern 4 arranged vis-à-vis the surface 2 will be such that the lines 40 and 41 will be perpendicular to the X axis and parallel to the orthogonal Y axis.
• this pattern pattern in parallel lines corresponds to measuring the deformations observed according to the width of each of the lines, which ensures a higher resolution of measurement than with the other type of pattern whose motive will be seen further, and is therefore adapted to the profile of the most pronounced concavity.
• the shooting of the image of the test pattern and its processing to deduce the shape of the surface 2 according to the main direction of the bending are performed in a very short time, of the order of 10 s.
• the device makes it possible to measure extremely rapidly also the shape corresponding to the secondary direction of the bending without moving the glazing.
• a second pattern is thus created in a monodirectional pattern perpendicular to the pattern of the first pattern, the first being then somehow "erased” (no longer being visualized) to take an image in reflection in the first pattern. surface 2 than the only second sight.
• the additional lighting means 8 are provided and put into operation by control means 80, while the first illumination means 7 are extinguished controlled by means of control. 70.
• the control means 70 and 80 are controlled jointly to provide illumination and control. concomitant extinction.
• the exposure time of the camera in particular can also be adapted to the luminous intensity of the second sight, much brighter than the first sight that is no longer illuminated in order to "erase" even more effectively this first sight.
• the additional lighting 8 is arranged at the plane of the test pattern, in the plane of the facade precisely the target or in its immediate vicinity. In addition, this lighting is located in the space of the dark lines of the first monodirectional pattern 4.
• the additional lighting means 8 consist, with regard to FIG. 5, in a plurality of light points regularly spaced along each of the dark lines 41 of the pattern 4 forming the second pattern 9.
• the lighting elements consist of a multiplicity of point light sources 90, such as light-emitting diodes or optical fiber terminations.
• the pattern of the second pattern thus created generates a multitude of objects, formed optically speaking by the separation width between two consecutive light spots for each of the lines.
• This second pattern once reflected in the surface 2, returns an image for which is measured in the direction parallel to the secondary direction the possible deformation (optical magnification) of the separation distance from one light point to another.
• This pattern 9 makes it possible to measure the shape in the secondary direction of the bending, that is to say in the direction Y.
• Such a pattern of the pattern because of its resolution less than that of the pattern of the first, is in effect used for the less curved profile of the surface.
• the processing and calculation means 6 are connected to the camera 5 to develop the mathematical treatments and analyzes that follow the two shots.
• the processing method consists, from the optical magnification measured ⁇ , at a point on the surface (corresponding to the pixel i of the camera), while knowing the distance target-surface d sm to be measured, to calculate the focal distance fi ' equivalent spherical mirror which would give a magnification ⁇ of the test pattern at the distance d sm .
• the local curvature (at each point) can be deduced in a known manner, and then by integrating the local curvature a first time, the local slope is deduced, which then gives access after another mathematical integration at the altitude of each of the points of the surface, and consequently to the shape of this surface.
• the device of the invention thus provides, by its two monodirectional patterns visualizable alternately very quickly, by shooting only two images, and by an easy calculation method, an extremely fast measurement system, reproducible, requiring only a brief shutdown time of the glazing (no more than 10 seconds) followed by a processing time of not more than 10 seconds when it advances on an industrial line.

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• Engineering & Computer Science (AREA)
• Computer Vision & Pattern Recognition (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
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• Signal Processing (AREA)
• Length Measuring Devices By Optical Means (AREA)

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• 2010
  • 2010-09-17 FR FR1057466A patent/FR2965045A1/fr not_active Withdrawn
• 2011
  • 2011-09-14 EP EP11773081.2A patent/EP2616764A1/fr not_active Withdrawn
  • 2011-09-14 CN CN2011800441437A patent/CN103189714A/zh active Pending
  • 2011-09-14 WO PCT/FR2011/052100 patent/WO2012035257A1/fr active Application Filing
  • 2011-09-14 US US13/820,198 patent/US20130162816A1/en not_active Abandoned

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