Method and device for detecting, in particular, refracting defects

1. A method of an in-line method of optically inspecting transparent or translucent containers ( 3 ) traveling along a determined path F 1 at a high rate between a light source ( 7 ) and an image-taking system ( 9 ) for taking images of the containers and for analyzing the images taken, in order to determine as a characteristic of the container ( 3 ) at least the presence of a defect that refracts light or the quality with which the material constituting the container is distributed, the method being characterized by the following steps:

illuminating each container ( 3 ) traveling at a high rate by means of the light source ( 7 ) that presents light intensity variation in a periodic pattern ( 7 1 ) of period T 1 along at least a first variation direction (D);

for each container ( 3 ), taking a number N greater than or equal to three of images of the container traveling in front of the light source and occupying N different respective positions along the travel path;

between taking successive images, creating a relative shift between the container and the periodic pattern in a variation direction (D) of the periodic pattern ( 7 1 );

determining and applying a geometrical transformation in at least N−1 images of the same container for at least a set of points belonging to the container in order to put the pixels belonging to the container in the N successive images of the same container into coincidence;

for each container ( 3 ) using the N registered images of the container, constructing a phase image; and

analyzing the phase image in order to deduce therefrom, as a characteristic of the container ( 3 ), at least the presence of a defect that refracts light or the quality of the distribution of the material constituting the container.

2. A method according to claim 1 , characterized by the following steps:

for each container ( 3 ), using the N registered images of the container to construct an intensity image; and

analyzing the intensity image in order to deduce therefrom as a characteristic of the container ( 3 ), the presence of a defect that absorbs light and/or the dimensions of the container.

3. A method according to claim 1 , characterized in that the analysis of the phase image consists in determining the speed and/or the amplitude of variation and in comparing said speeds and/or amplitudes with thresholds in order to determine the presence of a defect that refracts light or the quality of the distribution of the material constituting the container.

4. A method according to claim 1 , characterized in that it consists in:

illuminating each container ( 3 ) to be inspected with the help of a light source ( 7 ) presenting light intensity variation in a periodic pattern of period T 2 in a second variation direction different from the first variation direction;

for each container, taking a number N greater than or equal to three of additional images of the article traveling in front of the light source and occupying three N respective different positions along the travel path;

between taking successive images, creating a relative shift between the container and the periodic pattern along the second variation direction of the periodic pattern of period T 2 ;

for each container, using the N registered images of the article to construct a second phase image; and

analyzing the second phase image in order to determine, as a characteristic of the container ( 3 ) the presence of a defect that refracts light or the quality of the distribution of the material constituting the container.

5. A method according to claim 1 , characterized in that it consists in selecting the period T 1 , T 2 of the periodic pattern and the occurrences of the images taken in such a manner that the relative shifts of the container ( 3 ) and of the periodic pattern ( 7 1 ) along the variation direction of the periodic pattern are equal fractions of the period of the pattern under consideration.

6. A method according to claim 1 , characterized in that it consists in obtaining the relative shift between the periodic pattern ( 7 1 ) and the containers ( 3 ) by the containers ( 3 ) traveling relative to the periodic pattern ( 7 1 ) that remains stationary.

7. A method according to claim 1 , characterized in that it consists in obtaining the relative shift between the periodic pattern ( 7 1 ) and the containers ( 3 ) by causing the periodic pattern to shift between taking successive images.

8. A method according to claim 1 , characterized in that it consists in triggering the taking of images and/or the shifting of the illumination pattern as a function of the positions of the containers ( 3 ) traveling relative to the image-taking system ( 9 ) so as to obtain predefined shifts.

9. A method according to claim 1 , characterized in that it consists in selecting a periodic pattern ( 7 1 ) presenting a function in the variation in the level of the emitted light along the variation direction (D) that is sinusoidal.

10. A method according to claim 1 , characterized in that it consists in positioning the periodic pattern in such a manner that a variation in light intensity occurs in at least one direction parallel to the travel direction of the containers.

11. A method according to claim 1 , characterized in that it consists in selecting a periodic pattern that is rectilinear.

12. An installation for in-line inspection of transparent or translucent containers ( 3 ) in order to detect characteristics of the containers, the installation comprising conveyor means ( 2 ) for conveying the containers ( 3 ) so that they travel through an inspection station ( 5 ) made up of at least one light source ( 7 ) placed on one side of the traveling containers and at least one image-taking system ( 9 ) for taking images of the containers arranged on the other side of the containers, together with a unit for analyzing the images taken, the installation being characterized in that:

the light source ( 7 ) presents light intensity variation with a periodic pattern of period T 1 along at least a first variation direction (D);

a first image-taking system ( 9 ) is suitable for taking a number N greater than or equal to three of images of each container placed in front of the light source, with a relative shift being created between the container ( 3 ) and the periodic pattern ( 7 1 ) along a variation direction (D) of the periodic pattern ( 7 1 ) between taking successive images; and

the control and processor unit ( 13 ) comprises:

means for determining and applying a geometrical transformation in at least N−1 images of the same container coming from the first image-taking system in order to put into coincidence pixels of the container in the N successive images of the same container as put into register in this way;

means for calculating at least one phase image from N registered images of the container; and

means for analyzing the phase images in order to deduce therefrom, as a characteristic of the container, ( 3 ) at least the presence of a defect that refracts light or the quality of the distribution of the material constituting the container.

13. An inspection installation according to claim 12 , characterized in that the control and processor unit ( 13 ) also includes means for calculating at least one intensity image from N registered images of the container obtained from the first image-taking system, and means for analyzing intensity images in order to deduce therefrom, as a characteristic of the container ( 3 ), the presence of a defect that absorbs light, and/or its dimensions.

14. An inspection installation according to claim 13 , characterized in that it includes:

a filter interposed between the containers ( 3 ) and the light source ( 7 ) to polarize light linearly in a first polarization direction or circularly in a first direction of circular polarization;

a second image-taking system ( 9 ) suitable for taking a number N greater than or equal to three of images of each container placed in front of the light source;

a filter interposed between the containers and the second image-taking system for polarizing light linearly in the polarization direction orthogonal to the first or circularly in the direction of circular polarization that is opposite to the first; and

a control and processor unit ( 13 ) comprising:

means for determining and applying a geometrical transformation in at least N−1 images of the same container coming from the first image-taking system in order to put into coincidence pixels of the container in the N successive images of the same container as put into register in this way;

means for calculating at least one intensity image from N registered images of the container coming from the second image-taking system; and

means for analyzing the intensity images in order to deduce therefrom, as a characteristic of the container ( 3 ), the presence of a defect that modifies the polarization state of light.

15. An installation according to claim 12 , characterized in that the periodic pattern ( 7 1 ) of the light source ( 7 ) is stationary, such that the relative shift between the periodic pattern ( 7 1 ) and the containers ( 3 ) is obtained by the containers ( 3 ) traveling relative to the periodic pattern ( 7 1 ).

16. An installation according to claim 12 , characterized in that the periodic pattern ( 7 1 ) of the light source ( 7 ) is shifted between taking successive images in order to obtain the relative shifts between the periodic pattern ( 7 1 ) and the containers ( 3 ).

17. An installation according to claim 12 , characterized in that the periodic pattern ( 7 1 ) of the light source ( 7 ) is positioned in such a manner that a variation in light intensity occurs along at least one direction parallel to the travel direction of the containers.

18. An inspection installation according to claim 12 , characterized in that the light source ( 7 ) is suitable for presenting a periodic pattern ( 7 ) presenting a function for variation in the level of emitted light along its variation direction that is sinusoidal.

19. An inspection installation according to claim 12 , characterized in that the image-taking system ( 9 ) is associated with synchronizing means in order to be triggered as a function of the positions of containers relative to the periodic pattern of the light source ( 7 ).

20. An inspection installation according to claim 12 , characterized in that the control and processor unit ( 13 ) controls the light source ( 7 ) in such a manner that the periodic light pattern ( 7 1 ) is shifted in a given direction for taking each image.