SYSTEM AND METHOD FOR CONTROLLING THE COLOR OF A MOVING OBJECT

Description

[0001] The present invention relates to the control of the color of a moving article and applies in particular to the control of color in the field of industrial printing. State of the art

[0002] Driven by new digital technologies, industrial printing is developing in many sectors such as packaging, textiles, automotive, cosmetics, pharmaceuticals, chemicals, food processing, furniture, etc.

[0003] Print quality and color accuracy are essential to avoid customer dissatisfaction; therefore, color print conformity control is a competitive issue for new users of digital printing technologies, who are demanding automation in industrial print quality control processes. The rejection / acceptance threshold resulting from automatic control must be positioned between sub-quality, which allows non-compliant objects to leave and leads to costly returns, and over-quality, which rejects objects acceptable to the customer, again with additional costs.

[0004] Human color control can easily achieve closeness to customer validation criteria; however, operator color control requires extensive experience to train a control specialist. Furthermore, the subjectivity of operator control and visual fatigue make human controls unreliable or repeatable.

[0005] Automatic color control methods have thus been developed.

[0006] For example, color control is known based on the use of "RGB" cameras (RGB, an English acronym for "Red", "Green", "Blue"). White incident light illuminates the printed article to be controlled and the reflected light is analyzed by the RGB camera in at least 3 spectral bands: red, green, blue. Such automatic color control is described, for example, in patent EP 2172171, which describes a system for controlling the color of an image printed on a printing strip during movement.

[0007] From the RGB components, it is possible to determine a "color profile", for example determined in a CIE 1976 L*a*b* space, which can be compared to a reference color profile. However, the light that illuminates colored surfaces participates in the formation of the light spectrum perceived by the eye. Two surfaces can appear identical under a given lighting and appear different colors with another lighting. This is the case of metameric colors whose physical spectrum is different but which have identical RGB values ​​under a given lighting. They become different if the lighting spectrum is changed. Thus, color control using an RGB camera only allows a relative measurement of the color, useful for measuring drifts but requiring prior calibration that will have to be redone if the external conditions change.

[0008] The use of a spectrophotometer for automatic color control is also known. A spectrophotometer allows a complete analysis of the spectrum of light reflected by the illuminated article in white light. More precisely, it allows, compared to an RGB camera, to convert energy bands of the spectrum into an absolute measurement in L*a*b* space independent of the source profile and thus to access a "true color" control.

[0009] However, the spectrophotometer control is carried out by sampling on printed solid areas with a minimum surface area of ​​5 mm x 5 mm. The control can therefore only be carried out in uniform areas (same color, without gradient), which limits the quality control for printed characters and more generally all surfaces whose size is less than 5 mm x 5 mm.

[0010] Other methods are disclosed (see for example WO 94 / 25838 or US 2007 / 0139735) comprising illuminating a sample to be analyzed by means of beams of different wavelengths. However, in the methods described, only one or more point areas of a sample can be analyzed. An objective of the present description is to propose a system for monitoring the color of a moving article which allows in particular an absolute measurement of the color, in real time, and over the entire surface of a moving article. Summary of the invention

[0011] In this description and in the claims that follow, the term "comprise" is synonymous with (means the same as) "include", "contain", and is inclusive or open and does not exclude other elements not described or shown. Furthermore, in this description, the term "about" is synonymous with (means the same as) a lower and / or upper margin of 10%, for example 5%, of the respective value.

[0012] According to a first aspect, the present description relates to a system for controlling the color in real time of an article on a support moving in a given direction of movement, comprising: a lighting device configured to illuminate said moving article according to successive lighting cycles, each lighting cycle comprising the successive formation, at a given frequency, of a given number N of lighting lines having distinct spectral bands, N ≥ 4, said lighting lines being substantially perpendicular to the direction of movement, all of the N lighting lines formed during a lighting cycle defining on the moving article a lighting band of given dimension in the direction of movement;a detection device configured to detect, during each lighting cycle, the light backscattered by the article illuminated successively by each of said lighting lines, so as to form, during each lighting cycle, at each point of a given number of points of an observation band perpendicular to the direction of movement, a number N of signals corresponding respectively to the light backscattered by said point in each of the spectral bands; a processing unit configured to determine, at each of the points of the observation band and from said N signals, at least one value representative of the color of said point.;

[0013] According to one or more exemplary embodiments, the system is configured for the control of articles arranged on a scrolling support and the movement is a translational movement; the direction of movement is thus parallel to the translational direction.

[0014] According to one or more exemplary embodiments, the system is configured for the control of articles arranged on a rotating support, for example a rotating cylinder; the direction of movement is then perpendicular to a generatrix of the cylinder.

[0015] In this description, "backscattered light" means all light re-emitted by the article when illuminated by an illumination line, whether by a reflection mechanism, a diffusion mechanism or a combination of both.

[0016] The color control system thus described allows in particular, compared to known state-of-the-art systems, an absolute measurement of the color, in real time, over the entire surface of the article and allows a differentiation of colors less than or equal to the sensitivity of the eye.

[0017] According to one or more exemplary embodiments, said at least one value representative of the color comprises coordinates defined on the Lab sphere defining a “hue angle” and a luminance, for example the sphere called “1976 CIE L*a*b*” adopted by the International Committee on Illumination (CIE) in 1976 and defined according to the ISO 11664-4 standard.

[0018] According to one or more exemplary embodiments, said at least one value representative of the color comprises a color difference (or distance between colors) determined in relation to a reference object. The reference object is for example an article of the same type as that whose color is to be controlled (standard), or a reference file comprising the data which enabled printing.

[0019] The color difference is for example determined in the CIE L*a*b* space for example by one or other of the formulas: ΔE76 called "Delta 1976" or ΔE00 called "Delta 2000", these two formulas being defined in the ISO 12647-2 standard version 2013. In practice, the ΔE76 formula calculates a Euclidean distance between two colors defined in the CIE L*a*b* space and the ΔE00 formula takes into account the observation conditions (such as for example the differences in sensitivity of the cones of the human eye according to the colors and the brightness) to get even closer to human perception.

[0020] According to one or more exemplary embodiments, the number N of lighting lines of distinct spectral bands is between 4 and 36, advantageously between 8 and 12. The applicant has shown that in this range, a good compromise is obtained between a sufficient number of distinct spectral bands to have good precision in the characterization of the color and a reduced measurement time for the control.

[0021] According to one or more exemplary embodiments, the lighting device comprises a plurality of light sources configured for the successive emission of one or more beams in each of said spectral bands, and one or more optical elements configured to form, from said beam(s) emitted in each of said spectral bands, a lighting line in said spectral band. Said optical element(s) comprise for example one or more lenses, including for example one or more cylindrical lenses, and / or one or more reflective elements, in particular for the concentration of the lighting light power.

[0022] According to one or more exemplary embodiments, said optical element(s) further comprise a diffuser for homogenizing each of the lighting lines.

[0023] The said optical element(s) aim to form, from the light emitted by the said light source(s) in each of the spectral bands, a lighting line perpendicular to the direction of movement, and of given width in the direction of movement.

[0024] According to one or more exemplary embodiments, said optical element(s) are configured to form the plurality of N lighting lines corresponding to the plurality of spectral bands at substantially the same position on the support of the article.

[0025] According to one or more exemplary embodiments, the frequency of formation of the lines and / or the optical device for the formation of the lighting lines are configured such that said N lighting lines formed on said moving article during a lighting cycle are juxtaposed.

[0026] According to one or more exemplary embodiments, the frequency of formation of the lines and / or the optical device for the formation of the lighting lines are configured such that said N lighting lines formed on said moving article during a lighting cycle are at least partially superimposed.

[0027] According to one or more exemplary embodiments, the lighting source(s) comprise a set of multiplexed point sources, for example LED (“Light Emitting Diode”) type sources or laser diodes.

[0028] According to one or more exemplary embodiments, the detection device comprises at least one fixed sensor and one or more optical elements configured to form, during each cycle, an image of each line of illumination backscattered by the article on said sensor.

[0029] According to one or more exemplary embodiments, said at least one sensor is monochrome.

[0030] According to one or more exemplary embodiments, said at least one sensor is linear, i.e. formed from a line of photosensitive elements (“pixels”).

[0031] For example, said at least one sensor comprises a CCD camera or a CMOS camera, comprising for example between 4096 (4k) and 16384 (16k) photosensitive elements with a pitch of 3.5 µm.

[0032] According to one or more exemplary embodiments, the dimension of the observation strip in a direction parallel to the direction of movement is between 0.1 mm and 1 mm, advantageously between 0.1 mm and 0.7 mm, for example between approximately 0.1 mm and approximately 0.5 mm.

[0033] According to one or more exemplary embodiments, the dimensions of a point in the observation strip are substantially identical in the direction of movement and in the transverse direction (perpendicular to the direction of movement). In practice, the dimension of a point in the direction of movement (or "longitudinal resolution") is equal to the dimension of the observation strip in the direction of movement and the dimension of a point in the transverse direction (or "transverse resolution") is given by the dimensions of the photosensitive elements of the sensor(s). Thus, to obtain identical resolution in both directions, the signal from a plurality of adjacent photosensitive elements whose dimension in one direction is usually a few tens of microns can be averaged.

[0034] According to one or more exemplary embodiments, the observation strip is defined by the lighting strip.

[0035] According to a second aspect, the present description relates to a method for controlling the color of an article on a support moving in a given direction, comprising: the illumination of said moving article, by means of a lighting device and according to successive lighting cycles, each lighting cycle comprising the successive formation, at a given frequency, of a given number N of lighting lines having distinct spectral bands, N ≥ 4, said lighting lines being substantially perpendicular to the direction of movement, all of the N lighting lines formed during a lighting cycle defining on the moving article a lighting band of given dimension in the direction of movement;the detection, by means of a detection device, during each lighting cycle, of the light backscattered by the article illuminated successively by each of said lighting lines, so as to form, during each lighting cycle, at each point of a given number of points of an observation band perpendicular to the direction of movement, a number N of signals corresponding respectively to the light backscattered by said point in each of the spectral bands; the determination, at each of the points of the observation band and from said N signals, of at least one value representative of the color of said point. ;

[0036] According to one or more exemplary embodiments, said at least one value representative of the color comprises a hue angle and a luminance defined on the Lab sphere, for example the sphere called “1976 CIE L*a*b*”.

[0037] According to one or more exemplary embodiments, said at least one value representative of the color comprises a color difference (or distance between colors) determined relative to a reference object.

[0038] According to one or more exemplary embodiments, the determination of said at least one value representative of the color comprises one or more averaging steps, including for example the weighted averaging of signals acquired by the detection of several lighting lines of the same spectral band and of consecutive lighting cycles. Such weighted averaging makes it possible to improve the precision of the color characterization, to the detriment of the longitudinal resolution.

[0039] According to one or more exemplary embodiments, the control method comprises a prior step of calibrating the detection device. For example, the calibration is carried out using a calibrated target. Brief description of the figures

[0040] Other advantages and characteristics of the invention will appear on reading the description, illustrated by the following figures: [ Fig. 1 ] represents a functional diagram of an exemplary color control system according to the present disclosure. [ Fig. 2A ] illustrates an example of an object on a scrolling medium, for implementing a color control method according to the present description. [ Fig. 2B ] illustrates an example of an object on a rotating support, for implementing a color control method according to the present description. [ Fig. 3 ] depicts block diagrams of exemplary lighting line formations, during a lighting cycle, in a color control method according to the present disclosure. [ Fig. 4] represents a block diagram illustrating the formation of the lighting lines and the detection of the corresponding light signals, during a given number of lighting cycles, according to an example of implementation of a color control method according to the present description. [ Fig. 5A ] represents a functional diagram of an exemplary lighting device in a color control system according to the present disclosure. [ Fig. 5B ] represents a functional diagram of an exemplary detection device in a color control system according to the present disclosure. [ Fig. 6 ] represents a functional diagram of examples of color control systems according to the present description, with two examples of illumination and detection respectively. [ Fig. 7] represents spectral curves (normalized intensity as a function of wavelength) of lighting lines, according to an example of implementation of a color control method according to the present description. [ Fig. 8 ] represents a functional diagram of an exemplary light source in a color control system according to the present disclosure. [ Fig. 9 ] represents a functional diagram of an exemplary lighting device in a color control system according to the present disclosure. [ Fig. 10 ] represents a diagram illustrating the CIE Lab sphere (or “1976 CIE L*a*b*”) adopted by the International Committee on Illumination (CIE) in 1976 and defined according to the ISO 11664-4 standard. Detailed description of the invention

[0041] In the following detailed description of embodiments of the present invention, numerous specific details are set forth in order to provide a more thorough understanding of the present disclosure. However, it will be apparent to those skilled in the art that the present disclosure may be implemented without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the disclosure.

[0042] There Fig. 1 represents a functional diagram of an exemplary color control system 100 of an article 10 arranged on a moving support, according to the present description.

[0043] The color control system 100 comprises a lighting device with one or more lighting sources 101 and an optical device 105 comprising one or more optical elements for forming lighting lines from lighting beams from said lighting source(s). The color control system 100 further comprises a detection device with at least one sensor 102 and a second optical device 106 comprising one or more optical elements for forming images of the lighting lines on said at least one sensor. The color control system 100 further comprises in this example a unit 103 for synchronizing the lighting and the detection with the movement and a processing unit 104.

[0044] As illustrated in the Fig. 2A, the article 10 can be arranged on a scrolling support 201. The movement is then a translation in a direction Y parallel to the translation direction.

[0045] This configuration applies, for example, to an article such as a strip of paper, fabric, or plastic film coming out of a printing machine, but also to bulk articles such as rectangular boxes, etc.

[0046] As illustrated in the Fig. 2B , the object 10 can also be arranged on a rotating support 202, for example a cylindrical support. The direction of movement Y is then perpendicular to a generatrix of the cylinder.

[0047] This configuration applies, for example, to an item such as a dispensing tube or printed cylindrical box.

[0048] The lighting device is configured to successively form, on the moving article, a plurality of lighting cycles. Each lighting cycle comprises the successive formation, at a given frequency, of a given number N of lighting lines having distinct spectral bands, N ≥ 4. Each lighting line results from the shaping by the optical device 105 of a lighting beam emitted by said source(s) 101 of a given spectral band or “color”, referenced C 1 , C 2 , C 3 , C 4 in the example of the Fig. 1 .

[0049] The detection device 102, 106 is configured to detect, during each lighting cycle, the light backscattered by the article illuminated successively by each of said lighting lines.

[0050] The lighting lines formed by said lighting source(s) 101 and the optical device 105 are substantially perpendicular to the direction of movement. They define during a lighting cycle a lighting strip whose width (or direction in the direction of travel, i.e. in the direction of movement) depends on the width of each lighting line, the frequency of formation of the lighting lines during a lighting cycle and the speed of movement of the support (translation speed in the example of the Fig. 2A or tangential velocity in the example of the Fig. 2B ).

[0051] There Fig. 3 thus illustrates 3 examples (31 - 33) of formation of lighting lines L 1 - L 4 , corresponding respectively to the beams C 1 - C 4 . The example of the Fig. 3 illustrates the case of an article on a scrolling 201 support but also applies to the case of an article on a rotating support.

[0052] In the example of the Fig. 3 , only 4 lighting lines are shown for the sake of simplification but in practice, between 8 and 12 lighting lines of distinct spectra are preferred to obtain a better determination of the color. Each lighting line has a width δl. The lighting band 20 is formed by all the lighting lines and has a width Δl.

[0053] In the example referenced 31, the frequency of line formation is low compared to the speed of movement. This results in a strip of illumination with areas of the article not illuminated.

[0054] In the example referenced 32, the frequency of formation of the lines is adapted to the speed of movement of the article, such that two lines are juxtaposed.

[0055] In the example referenced 33, the frequency of formation of the lines and / or the optical device for the formation of the illumination lines are configured such that two lines are at least partially superimposed. This configuration is not problematic since in practice, the illumination lines are formed one after the other and acquired in a synchronized manner. Thus, the illumination strip can have a width which will be at least equal to the width of an illumination line.

[0056] In practice, the detection device comprising the sensor(s) 102 and the optical device 106 for imaging the illumination lines on the sensor(s) may be configured to enable the acquisition of a line whose dimensions are at least as large as those of a illumination line so as not to reduce the dimensions of the band actually observed. Thus, an observation band corresponding to a illumination cycle may be defined, merged with the illumination band. However, if the optical field defined by the detection device (or “acquisition line”) has smaller dimensions than the illumination line, an effective observation band may be defined by all of the acquisition lines during a illumination cycle, or, more generally, by the surface common to the sets formed on the one hand by the illumination lines and on the other hand by the acquisition lines.In the remainder of the description, however, it will be assumed that the effective observation band is limited by the illumination band.

[0057] Thus, during each lighting cycle, for each point P k of the observation band, the detection device allows the acquisition of N signals corresponding respectively to the light backscattered by the article in each of the spectral bands, and from which it will be possible to determine at least one value representative of the color of said point.

[0058] As illustrated for example in diagrams 32 and 33 of the Fig. 3, a point P k has dimensions determined in the direction of movement by the width Δl of the observation strip and in the transverse direction (i.e. in the X direction perpendicular to the Y direction of movement), by a dimension δp defined by the opto-geometric characteristics of the sensor(s) 102 and of the optical device 105. Thus, for example, for a sensor 102 formed from a linear arrangement of photosensitive elements (or pixels) of given dimensions, the dimension δp of a point P k will be equal to the dimension of one or more pixel(s) of the sensor, divided by the magnification of the optical device 106.

[0059] We can then define a resolution of the system in the direction of travel (or longitudinal resolution), defined by the width Δl of the observation strip and a resolution of the system in the transverse direction (or transverse resolution), defined by the dimension δp of a point P k .

[0060] Due to the original arrangement of the elements of the system according to the present description, the applicants have shown that it is possible to achieve a longitudinal resolution of less than 1 mm, typically between 0.1 mm and 1 mm, 0.1 mm corresponding to the resolution of a human observer observing at a distance of 30 cm. Advantageously, it will be possible to obtain a longitudinal resolution of between 0.1 mm and 0.5 mm, typically around 0.5 mm. The transverse resolution is fixed by the dimensions of the pixels, but in practice it will be possible to seek to have identical longitudinal and transverse resolutions.

[0061] There Fig. 4 illustrates according to an example the formation of the lighting lines and the detection of the corresponding light signals, during a given number of lighting cycles (in this example 3), according to an example of implementation of a color control method according to the present description.

[0062] In this example, 4 lighting lines are formed by means of the lighting device and during a first lighting cycle, respectively referenced L [1, 1], L [2, 1], L [3, 1], L [4, 1]. The lighting lines all have the same width δl. As in the example shown in diagram 32, Fig. 3 , the lighting is synchronized with the movement of the support by means of the synchronization unit 103 so that the lighting lines are juxtaposed and form an observation strip B 1 . The lighting is furthermore synchronized with the detection so that the sensor(s) 102 successively detect each of the lines, which results in N acquisition signals referenced A[1,1], A[2,1], A[3,1], A[4,1] on the Fig. 4 .

[0063] For example, if we are looking for a given longitudinal resolution Δl for the color control system, which corresponds to the width of the observation band, and if we are working with N different spectral bands, in this example 4, we can choose an incremental displacement δs of the support equal to Δl / N and synchronize the displacement with the lighting so that with each displacement of the support, we illuminate with the following line.

[0064] The operation is repeated with a sufficient number of cycles to cover the item whose color is to be controlled.

[0065] So in the example of the Fig. 4 , we generally note L[i, j] the lighting line corresponding to the color i of the cycle j , A[i, j] the acquisition of the light backscattered by the lighting line corresponding to the color i of the cycle j and Bj the observation band associated with a lighting cycle j.

[0066] The detection device sends to the processing unit 104, for each point P k (see Fig. 3 ) of an observation band Bj a number N of signals A k [i, j] corresponding to the light backscattered by said point P k in each of the N spectral bands i of the lighting cycle j. From these signals it is possible to determine at least one value representative of the color of the point.

[0067] For example, we can determine the hue angle h ab and the luminance L on the CIE Lab sphere.

[0068] As a reminder, the Fig. 10shows a diagram illustrating the CIE Lab sphere adopted by the International Committee on Illumination (CIE) in 1976 and defined according to ISO 11664-4. The hue angle h ab indicates the color; it evolves from red (angle 0°) to yellow (90°) then to green (180°) then to blue (270°). On the sphere, the luminance L is indicated on the ordinate, the colors evolving from the lightest (L = 100) to the darkest (L = 0).

[0069] To calculate an L*a*b* value from the N light energy measurements of each of the bands of the lighting spectrum, the following steps can be implemented.

[0070] As explained above, and for each point Pk of each observation band, a spectral reflectance curve of the article is determined, i.e. a curve giving, as a function of the wavelength, a value corresponding to the backscattered light. This reflectance curve is corrected by the light spectrum of the lighting device formed from the sum of the light spectra of each source of the lighting device. From the corrected spectrum, we can first calculate the "absolute" color in the CIE XYZ space (1931) defined by the ISO / CIE 11664-3:2019 and ISO / CIE 11664-4:2019 standards, then deduce the perceived color in the CIE Lab space (1976).

[0071] According to one or more exemplary embodiments, it is also possible to gain in precision on the color, to the detriment of a loss on the longitudinal resolution, by averaging the acquisitions A[i,j] and A[i, j+1] of two lighting lines of the same color i but of two consecutive bands B j and B j+1.

[0072] Thus, we can determine an acquisition signal A' k [i,j] of a point P k (j) of an observation band Bj by: A ′ k i j = N − i N A k i j + 1 − N − i N A k i , j + 1

[0073] This formula gives, in a simplified example of lighting comprising 4 color bands (N=4) and therefore i varying from 0 to 3: [Math 2] A ′ k 0 j = 1 ∗ Ak 0 j + 0 ∗ Ak 0 , j + 1 [Math 3] A ′ k 1 j = 3 4 ∗ Ak 1 j + 1 4 ∗ Ak 1 , j + 1 [Math 4] A ′ k 2 j = 1 2 ∗ Ak 2 j + 1 2 ∗ Ak 2 , j + 1 [Math 5] A ′ k 3 j = 1 4 ∗ Ak 3 j + 3 4 ∗ Ak 3 , j + 1

[0074] Generally, the synchronization unit 103 and the processing unit 104 referred to in the present description may be included in one or more physical entities, for example one or more computers or electronic cards.

[0075] When in this description, reference is made to calculation or processing steps for the implementation in particular of method steps, it is understood that each calculation or processing step can be implemented by software, hardware, firmware, microcode or any appropriate combination of these technologies. When software is used, each calculation or processing step can be implemented by computer program instructions, software code or programmable logic. These instructions can be stored or transmitted to a storage medium readable by the synchronization unit and / or the processing unit and / or be executed by the synchronization unit and / or the processing unit in order to implement these calculation or processing steps.

[0076] There Fig. 5A depicts a block diagram of an exemplary lighting device in a color control system according to the present disclosure and the Fig. 5B represents a functional diagram of an example detection device.

[0077] A lens of the lighting device as illustrated in the Fig. 5A is to standardize the lighting and concentrate it to form lighting lines of desired dimensions and sufficiently bright. It thus comprises, in addition to the source(s) 101, convergence optics 51, 53 and deflection optics 52.

[0078] The convergence optics 54, 56 and deflection optics 55 of the detection device illustrated in the Fig. 5B allow the images of the lighting lines to be formed on the sensor(s) 102, for example linear cameras of the CMOS or CCD type.

[0079] There Fig. 6 represents a functional diagram of examples of color control systems according to the present description, with respectively two lighting and detection configurations making it possible to form observation bands referenced respectively 61 and 62.

[0080] The configuration for forming the observation band 62 corresponds to illumination at an angle of approximately 45° and detection in a plane substantially perpendicular to the support (geometry 0-45). This standardized configuration makes it possible to measure only the scattered light. The configuration for forming the observation band 61 corresponds to illumination at substantially normal incidence and detection at approximately 45°. This configuration also makes it possible to measure part of the specular radiation.

[0081] There Fig. 7 represents spectra (normalized intensity curve as a function of wavelength) of lighting lines, according to an example of implementation of a color control method according to the present description.

[0082] Lighting lines are obtained, for example, using LEDs. Independent control of the emission power of each LED makes it possible to model any type of standardized lighting (D50, D65, etc.) or not by simple parameterization. The juxtaposition of the emission spectra of the LEDs makes it possible to cover all frequencies of the visible spectrum and to obtain very good precision in color control.

[0083] Table 1 below illustrates, as an example, 12 types of LEDs whose spectra overlap. [Table 1] Colors Max Frequency Band 1. Purple 440 420 - 445 2. Marine 460 440 - 465 3. Blue 475 460 - 480 4. Cyan 500 485 - 515 5. Green 530 510 - 550 6. Light Green 550 530 - 565 7. Lime 560 545 - 575 8. Amber 590 580 - 600 9. Orange 610 595 - 625 10. Red 630 620 - 640 11. Bright Red 670 660 - 680 12. Red Far 735 720 - 750

[0084] One objective of lighting is, for example, to create from incoherent sources a light strip that is as homogeneous as possible in the transverse direction and sufficiently concentrated in the direction of travel (or movement) to increase the light output and gain precision in color control.

[0085] A set of lighting sources, an example of which is illustrated in the Fig. 8 can be used.

[0086] In this example, the light sources, for example LEDs whose spectra are represented on the Fig. 7 , form point sources combined in the form of a matrix 80. The matrix 80 comprises a set of cells 81, each cell comprising all the lighting sources 801, in this example 12 in number. Thus, in the example of the Fig. 8 , the lighting sources are distributed in each module in a matrix of 3 columns and 4 rows.

[0087] When forming a lighting line i, all point sources i of the different modules are lit, which allows for lighting in the corresponding spectral band that is homogeneous across the entire area to be illuminated.

[0088] Note that it is also possible to distribute the point lighting sources randomly in the matrix of each of the modules to further homogenize the lighting.

[0089] There Fig. 9represents a functional diagram seen in section of an exemplary lighting device in a color control system according to the present description, in a 0-45 geometry (illumination at 45° relative to the surface). The lighting device comprises in addition to the sources 101 a diffuser 91. A shutter 92 has been added at the outlet of the diffuser to reduce the angle on the concentration device consisting of two inverted semi-cylindrical lenses 93, 94 of the same focal length. Although described through a certain number of exemplary embodiments, the color control systems and methods according to the present description include different variants, modifications and improvements which will be obvious to those skilled in the art, it being understood that these different variants, modifications and improvements are part of the scope of the invention as defined by the claims which follow.

Claims

1. A color control system (100) for controlling, in real time, the color of an article (10) positioned on a carrier (201, 202) moving in a given direction of movement (Y), comprising: - an illuminating device (101, 105) configured to illuminate said moving article in successive illuminating cycles, each illuminating cycle comprising successively generating, at a given frequency, a given number N of lines of light having distinct spectral bands, N ≥ 4, said lines of light being substantially perpendicular to the direction of movement, the set of N lines of light generated during an illuminating cycle defining, on the moving article, an illuminating strip of given dimension in the direction of movement; - a detecting device (102, 106) configured to detect, during each illuminating cycle, the light backscattered by the article successively illuminated by each of said lines of light, such as to generate, during each illuminating cycle, for each dot (Pk) of a number of given dots of an observation strip (20) perpendicular to the direction of movement, a number N of signals corresponding to the light backscattered by said dot in each of the spectral bands, respectively; - a processing unit (104) configured to determine, for each of the dots of the observation strip and on the basis of said N signals, at least one value representative of the color of said dot.

2. The color control system as claimed in claim 1, wherein the number N of lines of light of distinct spectral bands is comprised between 8 and 12.

3. The color control system as claimed in any one of the preceding claims, wherein the illuminating device comprises a plurality of light sources (101) configured to successively emit one or more beams in each of said spectral bands, and one or more optical elements (105) configured to generate, from said one or more beams emitted in each of said spectral bands, a line of light in said spectral band.

4. The color control system as claimed in any one of the preceding claims, wherein a dimension of the observation strip in a direction parallel to the direction of movement is comprised between about 0.1 mm and about 1 mm.

5. The color control system as claimed in any one of the preceding claims, wherein the detecting device comprises at least one fixed sensor (102) and one or more optical elements (106) configured to generate, during each cycle, an image of each line of light backscattered by the article on said sensor.

6. The color control system as claimed in claim 6, wherein said at least one sensor is monochrome.

7. A color control method for controlling the color of an article on a carrier (201, 202) moving in a given direction, comprising: - illuminating the moving article, by means of an illuminating device (101, 105) and in successive illuminating cycles, each illuminating cycle comprising successively generating, at a given frequency, a given number N of lines of light having distinct spectral bands, N ≥ 4, said lines of light being substantially perpendicular to the direction of movement, the set of N lines of light generated during an illuminating cycle defining, on the moving article, an illuminating strip of given size in the direction of movement; - detecting, by means of a detecting device (102, 106), during each illuminating cycle, the light backscattered by the article successively illuminated by each of said lines of light, such as to generate, during each illuminating cycle, for each dot of a number of given dots of an observation strip (20) perpendicular to the direction of movement, a number N of signals corresponding to the light backscattered by said dot in each of the spectral bands, respectively; - determining, for each of the dots of the observation strip and on the basis of said N signals, at least one value representative of the color of said dot.

8. The color control method as claimed in claim 7, wherein said at least one value representative of the color comprises a color difference determined with respect to a reference object.

9. The color control method as claimed in either one of claims 7 and 8, wherein the determination of said at least one value representative of the color comprises a step of computing the weighted average of signals acquired via detection of a plurality of lines of light of same spectral band in consecutive illuminating cycles.

10. The color control method as claimed in any one of claims 7 to 9, further comprising a prior step of calibrating the detecting device.