Optical computing methods and systems for inspecting a glass container in transmitted light

1 . An optical computing method for inspecting in through light a glass container moving along a movement trajectory, wherein:

the method includes illumination of the container by an illumination device comprising at least one two-dimensional emitting surface which is arranged on one side of the movement trajectory and which is made up of elementary emitting areas each emitting a polarized emitted light with an emitted polarization property of interest which varies according to a law of periodic variation as a function of a position of the elementary emitting area in the emitting surface;

the method includes an observation of the container, by at least one digital camera having a two-dimensional photoelectric sensor comprising photoelectric elements which each comprise a photoelectric cell corresponding to a pixel in an image acquired by the digital camera, the at least one digital camera being located, with respect to the movement trajectory, on a side opposite to that of the illumination device, so as to collect, by the at least one digital camera, an emergent light emanating from the container and having crossed at least one wall thickness of the container;

the method includes the acquistion, with the at least one digital camera, of partial digital images, each containing an image of the same inspected area of the container, each partial digital image having N partial pixels each of which is the image of a corresponding elementary area of the container, and each partial digital image being acquired with interposition, between the container and the photoelectric cells of the at least one digital camera, of a linear analyzer having a given axis of polarization, for a partial digital image;

the acquisition further includes another acquisition of at least one series comprising at least a first partial digital image and a second partial digital image, for which the axes of polarization of the linear analyzers are distinct from each other, the partial digital images of the same series being superimposable such that each elementary area of the inspected area of the container is imaged by a corresponding partial pixel in each of the partial digital images of the series;

for a primary series, the partial digital images of the primary series each contain, in the background, the image of the same primary inspection portion of the emitting surface, the primary inspection portion being observed through the container by the digital camera, and, on the primary inspection portion of the emitting surface, the law of periodic variation of the emitted polarization property of interest having, along a primary direction, a primary periodic variation, and having several primary periods over the extent of the primary inspection portion along the primary direction;

wherein, over a primary period, the emitted polarization property of interest of the lights emitted by the elementary emitting areas of the primary inspection portion of the emitting surface follows a triangular variation as a function of the position of the elementary emitting area along the primary direction,

and in that the method includes a computer calculation of at least one primary raw refraction image, from the partial digital images of the primary series, by calculating, for each of the elementary areas of an inspected area of the container, a primary raw refraction pixel whose value is representative of the refraction undergone by the light having crossed at least one wall thickness of the container and emerging from the elementary area, from the value of the corresponding partial pixels which are the image of the elementary area in the partial digital images of the primary series.

2 . The method according to claim 1 , wherein, for the same inspected area of the same container, the method includes the acquisition, for the primary series, of a third partial digital image and of a fourth partial digital image for which the axes of polarization of the linear analyzers are distinct from each other and distinct from the axes of polarization of the linear analyzers for the first partial digital image and the second partial digital image of the primary series, preferably orthogonal to each other and offset by 45 angle degrees of the axes of polarization of the linear analyzers for the first partial digital image and the second partial digital image of the primary series.

3 . The method according to claim 1 , wherein, for the same inspected area of the same container, the acquisition includes the acquisition of at least one secondary series of partial digital images;

in that, for the secondary series, the partial digital images each contain, in the background, the image of the same secondary inspection portion of the emitting surface, the secondary inspection portion being observed through the container by the digital camera, and, on the secondary inspection portion of the emitting surface, the law of periodic variation of the emitted polarization property of interest having, along a secondary direction of the emitting surface, different from the primary direction, a secondary periodic variation, and having several secondary periods over the extent of the secondary inspection portion along the secondary direction;

in that, over a secondary period, the emitted polarization property of interest of the lights emitted by the elementary emitting areas of the secondary inspection portion of the emitting surface follows a triangular variation as a function of the position of the elementary emitting area along the secondary direction, and

in that the method includes the computer calculation of at least one secondary raw refraction image, from the partial digital images of the secondary series, by calculating, for each of the elementary areas of an inspected area of the container, a secondary raw refraction pixel whose value is representative of the refraction undergone by the light having crossed at least one wall thickness of the container and emerging from the elementary area, from the value of the corresponding partial pixels which are the image of the elementary area in the partial digital images of the secondary series.

4 . The method according to claim 1 , wherein it comprises the calculation, from at least two partial digital images, of an intensity image it in which the value of each intensity pixel is calculated as an averaged value of the value of at least two partial pixels and corresponding to the same elementary area.

5 . The method according to claim 1 , characterized in that it comprises the acquisition of at least one complementary master image (IM′) so as to calculate a stress image of the inspected area and/or an intensity image for the inspected area.

6 . The method according to claim 1 , wherein the at least one digital camera is a polarimetric digital camera, having a two-dimensional photoelectric sensor comprising photoelectric elements which each comprise a photoelectric cell in front of which is arranged an individual linear analyzer associated with the photoelectric cell of this photoelectric element, the photoelectric sensor including a number N of distinct groups of 4 contiguous photoelectric elements whose individual linear analyzers have each an an axis of polarization, the four axes of polarization of a given group of 4 photoelectric elements forming two pairs, of orthogonal axes of polarization, the two pairs being offset from each other by 45 angle degrees;

and in that the acquisition of the 4 partial digital images of the same series is performed, with the photoelectric sensor of the polarimetric camera, by the acquisition of a master digital image containing an image of the container, the master digital image having a number 4*N of master pixels grouped into N composite pixels each corresponding to a group of contiguous photoelectric elements, each composite pixel having 4 master pixels each corresponding to one of the elements of the group of contiguous photoelectric elements corresponding to this composite pixel, and each master digital image comprising the 4 distinct partial digital images each having N partial pixels, the partial pixels of each of the partial digital images corresponding, for a given partial digital image, to the photoelectric elements of the photoelectric sensor whose individual linear analyzers have a common axis of polarization for this partial digital image.

7 . The method according to claim 1 , wherein the triangular variation is such that each primary period is divided into only two parts, an increasing part and a decreasing part, in that, in the increasing part, the emitted polarization property of interest is an increasing linear function of the position of the elementary emitting area along the primary direction, the emitted polarization property of interest increasing from a primary lower value to a primary upper value, and in that, in the decreasing part, the emitted polarization property of interest is a decreasing linear function of the position of the elementary emitting area along the primary direction, the emitted polarization property of interest decreasing from the primary upper value to the primary lower value.

8 . The method according to claim 1 , wherein the inspection portion of the emitting surface is made up of elementary emitting areas each emitting an elliptically polarized emitted light having an ellipticity ratio less than or equal to 0,7, and in that the emitted polarization property of interest of the light emitted by an elementary emitting area is the orientation of the main axis of polarization of the light emitted by said elementary emitting area.

9 . The method according to claim 1 , wherein the primary inspection portion of the emitting surface is made up of elementary emitting areas each emitting a polarized emitted light according to an elliptical polarization with a phase shift between the two orthogonal components of the electric field vector of the polarized emitted light, and in that the emitted polarization property of interest corresponds to the phase shift between the two orthogonal components of the electric field vector of the polarized emitted light.

10 . The method according to claim 1 , wherein the illumination device includes, in the direction of propagation of the light, a primary two-dimensional source of diffused light, an upstream linear polarizer having a axis of polarization, and a two-dimensional matrix of liquid crystal cells.

11 . The method according to claim 10 , wherein it includes the control of the two-dimensional matrix of liquid crystal cells such that the polarized light derived from each of the liquid crystal cells has an elliptical polarization with, for each liquid crystal cell, the orientation of the main axis of polarization and/or a phase shift between the two orthogonal components of the electric field vector of the light derived from the liquid crystal cell, and in that, for the acquisition of the primary series of partial digital images, the at least one among the orientation of the main axis of polarization and/or the phase shift follows a triangular variation as a function of the position of the liquid crystal cell along the primary direction.

12 . The method according to claim 1 , wherein it includes a step of analyzing refraction anomalies comprising a step of computer calculation based on the raw refraction image.

13 . An optical computing system for inspecting in through light, by using at least one digital camera, a glass container moving along a movement trajectory, in which:

the system includes an illumination device comprising at least one two-dimensional emitting surface, arranged on one side of the movement trajectory and which is made up of elementary emitting areas each emitting a polarized emitted light having a polarization property;

the system includes at least one digital camera with a two-dimensional photoelectric sensor comprising photoelectric elements which each comprise a photoelectric cell, the at least one digital camera, being located, with respect to the movement trajectory, on the side opposite to that of the illumination device, so as to collect, by the at least one digital camera, an emergent light emanating from the container and having crossed at least one wall thickness of the container;

the system is configured to acquire, with the at least one digital camera, at least one series including two partial digital images, each containing an image of the same inspected area of the container, each partial digital image having N partial pixels each of which is the image of a corresponding elementary area of the container, and each partial digital image being acquired with interposition, between the container and the photoelectric cells of the at least one digital camera, of a linear analyzer with a given axis of polarization for a partial digital image, the axes of polarization of the linear analyzers for the at least two partial digital images being distinct from each other, the partial digital images of the same series being superimposable such that each elementary area of the inspected area of the container is imaged by a corresponding partial pixel in each of the partial digital images of the series;

wherein the illumination device includes, in the direction of propagation of the light, a primary two-dimensional source of diffuse light, an upstream linear polarizer having an axis of polarization, and a two-dimensional matrix of liquid crystal cells, wherein a quarter-wave retarder plate is arranged in the light path between the container and the linear analyzers for the at least two partial digital images.

14 . The system according to claim 13 , wherein the system includes means for controlling the two-dimensional matrix of liquid crystal cells such that the polarized light derived from each of the liquid crystal cells has an elliptical polarization with, for each liquid crystal cell, an orientation of the main axis of polarization and/or a phase shift between the two orthogonal components of the electric field vector of the light derived from the liquid crystal cell, and in that the illumination device is controlled such that the at least one among the orientation of the main axis of polarization and/or the phase shift follows a variation as a function of the position of the liquid crystal cell along a primary direction of the emitting surface.

15 . The system according to claim 14 , wherein the illumination device is controlled such that at least one among the orientation of the main axis of polarization and/or or the phase shift follows a triangular variation as a function of the position of the liquid crystal cell along a primary direction of the emitting surface.

16 . The system according to claim 13 , wherein it includes, in the light path between the two-dimensional matrix of liquid crystal cells and the linear analyzers for the at least two partial digital images, the quarter wave retarder plate which has a fast axis oriented parallel or perpendicular to the axis of polarization of the upstream linear polarizer.