METHOD OF MEASURING A 3D PROFILE OF AN ARTICLE

Abstract

The invention relates to a method of measuring a 3D profile of an article moving on a conveyor in a certain conveying direction, which method includes a step consisting in using an optical sensor to scan, by triangulation, a laser line projected onto the article moving on the conveyor. The method further includes a step of using the optical sensor to scan, by contrast difference, the article moving on the conveyor, and a step of making combined use of the results of the scans by triangulation and of the scans by contrast difference in a data processor unit for the purpose of measuring the 3D profile of the article.

Claims

1. A method of measuring a 3D profile of an article moving on a conveyor in a certain conveying direction, which method comprises: using an optical sensor to scan, by triangulation, a laser line projected onto said article in the field of view of said sensor transversely to said conveying direction, taking a contrast image of a top of said article moving on said conveyor, and making combined use of the results of the scan by triangulation and the contrast image in a data processor unit for the purpose of measuring the 3D profile of said article, wherein the contrast image is formed using the same optical sensor as the optical sensor that performs the scans by triangulation, said optical sensor being arranged to scan, in its field of view, and in contrast difference, a strip that is transverse to said conveying direction, and wherein said data processor unit is arranged to match, in time, the scan by triangulation and the scan by contrast difference in such a manner as to merge them for measuring said 3D profile.

2. A method according to claim 1, wherein the steps of using an optical sensor to scan by triangulation and by contrast difference are performed in alternation.

3. A method according to claim 1, wherein the steps of using an optical sensor to scan by triangulation and by contrast difference are performed simultaneously.

4. A method according to claim 1, further comprising a step of using said optical sensor to scan by triangulation another laser line projected onto said article that is moving.

5. A method according to claim 1, further comprising a step of illuminating said article with white light parallel to the laser line in order to perform the scan of said article by contrast difference.

6. A method according to claim 5, wherein said white light is produced by LEDs.

7. An apparatus for sorting postal articles, said apparatus comprising: a sorting conveyor for conveying postal articles in a certain conveying direction past sorting outlets under the control of a monitoring and control unit in such a manner as to sort them separately into the sorting outlets, a first item of equipment suitable for detecting that articles are mutually superposed on the conveyor, and a second item of equipment suitable for separating and singulating on the conveyor said articles that are detected as being mutually superposed, wherein said first item of equipment comprises: a laser source arranged to project a laser line onto said article transversely to said conveying direction, an optical sensor arranged to scan, by triangulation, the laser line projected onto said article in the field of view of said sensor transversely to said direction, said optical sensor further being arranged to take a contrast image of a top of said article moving on said conveyor, and a data processor arranged to make combined use of the results of the scan by triangulation and the contrast image in a data processor unit for the purpose of measuring the 3D profile of said article, wherein said optical sensor is arranged to scan, in its field of view, and in contrast difference, a strip that is transverse to said conveying direction, and wherein said data processor unit is arranged to match, in time, the scan by triangulation and the scan by contrast difference in such a manner as to merge them for measuring said 3D profile.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention can be better understood and other advantages appear on reading the following description and on examining the accompanying drawings, in which:

[0025] FIG. 1 is a diagrammatic view of a portion of an article conveyor seen in profile and suitable for implementing the method of the invention for measuring a 3D profile of an article;

[0026] FIG. 2 is a diagrammatic view of said conveyor portion as seen from above;

[0027] FIG. 3 is a diagrammatic view of the data processor unit merging a laser scan and a contrast-difference scan to obtain a 3D measurement of superposed articles in an implementation of the invention; and

[0028] FIG. 4 is a highly diagrammatic view of postal article sorting apparatus suitable for implementing the method of the invention for measuring a 3D profile.

DESCRIPTION OF IMPLEMENTATIONS

[0029] In this example, the method of the invention for measuring a 3D profile is implemented in postal article sorting apparatus 40 comprising a sorting conveyor 41 for conveying postal articles such as 2, 2a, 2b in series in a certain conveying direction D1 past sorting outlets 42 under the control of a monitoring and control unit 43, as shown in FIG. 4. In the example shown in FIG. 4, two mutually superposed articles 2a, 2b need to be identified by measuring their 3D profiles (block X) and need to be separated from each other (block S) so as to be sorted separately into the sorting outlets 42.

[0030] FIG. 1 shows a conveyor 1 with a matrix optical sensor 3 suitable for scanning a portion 4 of the conveyor 1 that corresponds to the field of view of the sensor 3 and that extends over the entire width L of the conveyor 1. In this example, the optical axis A of the sensor 3 is preferably perpendicular to the conveyor 1 in such a manner as to facilitate observing the moving postal articles 2, 2a, 2b in plan view, typically from a height of one meter. In this example, the matrix optical sensor 3 is suitable for forming a digital image over a plurality of rows of pixels, and typically over about one hundred rows of pixels, it being possible for this digital image to include, at the same time, a laser line projected onto the moving article and a contrast-difference strip parallel to the laser line and transverse to the direction D1.

[0031] The optical sensor 3 makes it possible to offer digital images of sufficient resolution for dimensional measurements with accuracy to within about one millimeter over the widths and over the heights of the articles.

[0032] The scans by the optical sensor 3 are, inter alia, used to highlight the grayscale contrast differences in the conveyor portion 4. In known manner, a plurality of consecutive scans make it possible, after they have been concatenated by a data processor unit 5 of the conveyor 1, to define all of the outlines of the articles 2a, 2b that are moving in the conveyor portion 4. Contrast difference also makes it possible to determine the presence and the positioning of labels 12 and/or of folds or creases in the articles 2a, 2b. In order to increase the contrast on the portion 4 of the conveyor 1 and to make it more uniform, artificial lighting of the type comprising LEDs 6, which lighting is white in this example, is also mounted between the optical sensor 3 and the belt of the conveyor 1. The LEDs 6 are placed against a lightshade 7 making it possible to restrict the propagation of light LUX to a limited strip of the portion 4 of the conveyor 1 that extends over the width of the conveyor 1.

[0033] Without limiting the scope of the invention, the artificial lighting 6 may also operate in cross-polarized manner in order to reduce the reflections off the articles 2a, 2b, e.g. when they are wrapped in plastics film.

[0034] The conveyor 1 also includes a first laser source 8 suitable for projecting a laser line 9 onto said conveyor portion 4. In this example, the laser line 9 is inclined at an angle (lying in the range 10 to 30, and preferably 20) relative to the axis A of the optical sensor 3, and is directed transversely to the conveying direction D1 so as to extend over the entire width of the conveyor 1. It can thus be understood that the laser line 9 is deformed by the articles 2a, 2b as it crosses the conveyor portion 4. The laser line 9 in the absence of articles 2a, 2b in the conveyor portion 4 is shown in FIG. 2 as a dashed line, and the laser line as deformed by the articles 2a and 2b is shown as offset solid lines.

[0035] In known manner, the profile of the laser line 9 deformed by the articles 2a, 2b and sensed during the successive scans enables the data processor unit 5 to determine the heights of the articles 2a, 2b on the known principle of laser triangulation, or laser scanning.

[0036] Without limiting the scope of the invention, the conveyor 1 includes a second laser source (not shown) that is suitable for projecting another laser line in the conveyor portion 4, which other laser line is distinct from the laser line 9. It can be understood that this other laser line, which, in this example, is projected facing the laser line 9, makes it possible to consolidate the acquisition by laser triangulation by limiting the blind spots when the articles 2a, 2b are of complex shapes are when a plurality of articles 2 are mutually superposed, as shown in FIG. 1. In this situation, the contrast strip Tr2 may be interposed between the two laser lines projected onto the article moving on the conveyor 1. The width of the contrast strip and the spacing between the laser lines projected in the portion 4 is related to the speed of movement of the conveyor 1, which fixed speed of movement is a parameter that is predetermined so that the triangulation scans and the contrast-difference scans match in time so that they can be merged for measuring the 3D profile of the article. Typically, with a sensor of 100 rows of pixels, it is possible to have 20 rows of pixels reserved for scanning the contrast strip and the other rows of pixels reserved for triangulation scanning of the two laser lines while having a separation of about one hundred millimeters between the contrast strip and the laser line in the portion 4.

[0037] The processor unit 5 is also designed to merge all of the data of the laser scans and of the contrast difference scans.

[0038] For this purpose, the unit 5 subdivides the scan including the profiles of the heights 10 and the scan including the profiles of the outlines 11 each into a plurality of columns of pixels of identical size in the conveying direction D1, as shown in FIG. 3.

[0039] Each column is assigned an order number (n1, n2, etc.) corresponding to a scan in the conveyor portion at a time T (t0 to tx) as the articles move. Matching or merging is performed on the columns having an identical order number by the processor unit 5. Once all of the columns have been merged, the measurement of the 3D profile of the article is determined by the data processor unit 5.

[0040] In this example, in order to prevent the laser lines from disturbing the contrast difference scan and vice versa, the optical sensor 3 is designed to scan the articles 2a, 2b in alternation by means of an encoder wheel (not shown). In this example, the encoder wheel makes it possible to scan the portion 4 in segments (Tr1 and Tr2) and at constant pitch. Each segment thus corresponds to a column of pixels of a scan. It can also be understood that the frequency of the scans is defined, inter alia, by the speed of movement of the conveyor 1. In view of the negligible distance between the two acquisition zones, which distance is, in this example, of the order of a few centimeters, the laser scans and the contrast difference scans are considered to have been done at the same time.

[0041] In another implementation of the invention, the laser and contrast scans may be performed simultaneously so that each digital image 4 formed by the optical sensor 3 includes both the profile of the laser line 9 and the contrast difference. In this situation, the data processor unit 11 is designed to detect the disturbances generated by the laser line 9 and to modify accordingly the measurement of the profile of the article 2 by contrast difference. It can be understood that, in this example, the lightshade 7 makes it possible to restrict the light LUX to a limited zone in the portion 4 of the conveyor 1. Thus, the laser and contrast-difference scans can be performed simultaneously without leading to large disturbances to the measurement of the 3D profile of the article 2 by contrast difference.

[0042] When two superposed or juxtaposed articles 2a, 2b are being conveyed on a conveyor, as shown in FIGS. 1 and 2, the method consists, in a first stage, in scanning 100 the articles 2a, 2b by laser triangulation in order to obtain a profile of the heights, as shown in FIG. 3. In a second stage, the method consists in scanning 110 the articles 2a, 2b by contrast difference in order to obtain the outlines of said articles. Then the method consists in using the data processor unit 5 to merge 120 the laser and contrast-difference scans in order to obtain the measurement 130 of the profiles 3D of the articles 2a, 2b.

[0043] In FIG. 4, the equipment represented by block X is specially designed to implement the method of the invention so as to measure the 3D profiles of postal articles such as 2a and 2b that are, in this example, mutually superposed, and so as to detect such superposition (multiple loading of articles on the conveyor 41) in such a manner that equipment represented by block S that is downstream from the equipment X acts on the mutually superposed articles 2a, 2b so as to separate them and singulate them on the conveyor 41 so as to make it possible to sort the articles 2a, 2b into the sorting outlets 42.

[0044] Naturally, the present invention is in no way limited to the above description of one of its implementations, which can undergo modifications without going beyond the ambit of the invention.