WO1994025838A1 - Procede et appareil permettant de detecter des couleurs d'articles et de classer ces derniers - Google Patents

Procede et appareil permettant de detecter des couleurs d'articles et de classer ces derniers Download PDF

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Publication number
WO1994025838A1
WO1994025838A1 PCT/CA1994/000233 CA9400233W WO9425838A1 WO 1994025838 A1 WO1994025838 A1 WO 1994025838A1 CA 9400233 W CA9400233 W CA 9400233W WO 9425838 A1 WO9425838 A1 WO 9425838A1
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WO
WIPO (PCT)
Prior art keywords
lines
articles
line
signal
threshold value
Prior art date
Application number
PCT/CA1994/000233
Other languages
English (en)
Inventor
Gilles Allaire
Gratien Beauchemin
Roger Garceau
Bruno Leclerc
Original Assignee
Centre De Recherche Industrielle Du Quebec
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Priority claimed from CA002095154A external-priority patent/CA2095154C/fr
Priority claimed from CA002095155A external-priority patent/CA2095155C/fr
Application filed by Centre De Recherche Industrielle Du Quebec filed Critical Centre De Recherche Industrielle Du Quebec
Priority to AU67181/94A priority Critical patent/AU6718194A/en
Publication of WO1994025838A1 publication Critical patent/WO1994025838A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/46—Measurement of colour; Colour measuring devices, e.g. colorimeters
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
    • B07C—POSTAL SORTING; SORTING INDIVIDUAL ARTICLES, OR BULK MATERIAL FIT TO BE SORTED PIECE-MEAL, e.g. BY PICKING
    • B07C5/00—Sorting according to a characteristic or feature of the articles or material being sorted, e.g. by control effected by devices which detect or measure such characteristic or feature; Sorting by manually actuated devices, e.g. switches
    • B07C5/04—Sorting according to size
    • B07C5/12—Sorting according to size characterised by the application to particular articles, not otherwise provided for
    • B07C5/14—Sorting timber or logs, e.g. tree trunks, beams, planks or the like
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
    • B07C—POSTAL SORTING; SORTING INDIVIDUAL ARTICLES, OR BULK MATERIAL FIT TO BE SORTED PIECE-MEAL, e.g. BY PICKING
    • B07C5/00—Sorting according to a characteristic or feature of the articles or material being sorted, e.g. by control effected by devices which detect or measure such characteristic or feature; Sorting by manually actuated devices, e.g. switches
    • B07C5/34—Sorting according to other particular properties
    • B07C5/342—Sorting according to other particular properties according to optical properties, e.g. colour
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/46—Measurement of colour; Colour measuring devices, e.g. colorimeters
    • G01J3/462—Computing operations in or between colour spaces; Colour management systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/46—Measurement of colour; Colour measuring devices, e.g. colorimeters
    • G01J3/50—Measurement of colour; Colour measuring devices, e.g. colorimeters using electric radiation detectors
    • G01J3/502—Measurement of colour; Colour measuring devices, e.g. colorimeters using electric radiation detectors using a dispersive element, e.g. grating, prism
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/46—Measurement of colour; Colour measuring devices, e.g. colorimeters
    • G01J3/50—Measurement of colour; Colour measuring devices, e.g. colorimeters using electric radiation detectors
    • G01J3/501—Colorimeters using spectrally-selective light sources, e.g. LEDs
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/46—Measurement of colour; Colour measuring devices, e.g. colorimeters
    • G01J3/50—Measurement of colour; Colour measuring devices, e.g. colorimeters using electric radiation detectors
    • G01J3/51—Measurement of colour; Colour measuring devices, e.g. colorimeters using electric radiation detectors using colour filters
    • G01J3/513—Measurement of colour; Colour measuring devices, e.g. colorimeters using electric radiation detectors using colour filters having fixed filter-detector pairs

Definitions

  • the present invention pertains to a method and apparatus for sensing the color of articles and for classification thereof, and more specifically for sensing the color of wood parts for the purpose of classification as required in wood products manufacturing.
  • wavelengths are typically chosen such that, for a given range of colors characterizing these articles, a maximum variation of reflected light intensity values corresponding to the wavelengths is observed. Therefore, wavelengths are generally selected to correspond to some peaks on light reflection curves, and such peaks should be characterized by
  • SUBSTITUTE SHEET relatively high amplitude variations depending on the color of the articles, so as to properly carry out color sensing and classification.
  • each chosen peak wavelength corresponds to a dominant color component which characterizes color of articles to be inspected, the relative amount of such a color component being considered as a basis for color sensing and classification.
  • red oak is a such species of wood, being characterized by a very high range of color hues, from light gray to dark red, and thus requiring a very high resolution color sensing and classification technique to classify in appropriate categories wood pieces giving substantially the same color perception to a person viewing at these pieces. Furthermore, high resolution has to be achieved while keeping the processing time required by the color sensing method as short as possible so as to implement such a method in a high volume automatic color article sensing apparatus, through minimizing the number of wavelength measurements and calculations.
  • Another feature of the present invention is to provide an apparatus for sensing the color of articles and for classification thereof.
  • Another feature of the present invention is to provide an apparatus for sensing the color of articles made of wood and for classification thereof, especially for articles made of red oak.
  • the present invention provides a method for sensing the color of articles comprising the steps of (a) selecting a first pair of wavelengths on a plurality of light reflection curves in terms of a reflected light wavelength spectrum, these curves being associated with a plurality of articles constituting a sample representative of the color range to be sensed, wherein said first pair of wavelengths delimits a first range of wavelengths corresponding to light reflection values in these curves, the light reflection values in each of the curves being in a substantially linear relationship over said first range of wavelengths, (b) illuminating with light
  • SUBSTITUTE SHEET comprising the first pair of wavelengths a first area of one of the articles, (c) measuring light reflected from this first area of the inspected article at the first pair of wavelengths to detect light reflection values corresponding to the first pair of wavelengths, and (d) producing a primary signal representing either a difference between or a ratio of said detected light reflection values, this signal being indicative of the color of the inspected article.
  • the present invention provides a method for classifying articles according to their color comprising the steps of: (a) selecting a first pair of wavelengths on a plurality of light reflection curves in terms of a reflected light wavelength, spectrum; (b) illuminating with light comprising the first pair of wavelengths an area of an article to be inspected; (c) measuring light reflected from this area at the first pair of wavelengths to detect corresponding light reflection values; (d) producing a primary signal representing either a difference between or a ratio of the detected light reflection values, this signal being indicative of the color of the inspected article; (e) selecting at least one secondary wavelength on the reflected light wavelength spectrum; (f) illuminating with light comprising this secondary wavelength the area of the inspected article; (g) measuring light reflected from this area at this secondary wavelength to produce a secondary signal which is further indicative of the color of the inspected article; (h) providing a classification frame comprising a first pattern consisting of first and second crossing sets of lines respectively defined by mathematical analysis, this
  • an apparatus for sensing the color of articles comprises means for placing each of said articles at a viewing location in the apparatus.
  • an illumination means emitting a light output comprising a first pair of wavelengths, the light output being directed toward the viewing location for illuminating a first area of one of those articles passing at the viewing location.
  • the first pair of wavelengths is selected from a plurality of light reflection curves in terms of a reflected light wavelength spectrum, said curves being associated to a plurality of articles constituting a sample representative of the color range to be sensed. This first pair of wavelengths thus delimits a first range of wavelengths corresponding to light reflection values in the light reflection curves.
  • the light reflection values in each of these curves must be in a substantially linear relationship over the first range of wavelengths.
  • the apparatus comprises means for producing a first primary signal which represents either a difference between or a ratio of the detected light reflection values, this signal being indicative of the color of the inspected article.
  • an apparatus for classifying articles according to their color comprises a means for placing each of said articles at a viewing location in the apparatus.
  • an illumination means emitting a light output comprising a pair of wavelengths selected from a plurality of light reflection curves in terms of a reflected light wavelength spectrum, and at least one secondary wavelength selected from theses curves.
  • the light output is directed toward the viewing location for illuminating an area of an inspected article passing at said viewing location.
  • a computer means for producing a primary signal representing either a difference between or a ratio of said detected light reflection values corresponding to the pair of wavelengths, and a secondary signal corresponding the secondary wavelength, those signals being indicative of the color of the inspected article.
  • the computer means defines a classification frame comprising a first pattern consisting of first and second crossing sets of lines respectively defined by mathematical analysis, this classification frame defining a plurality of color classes.
  • the computer means then classifies the inspected article in one of the plurality of color classes defined by the frame, whenever the primary signal and the secondary signal comply with a specific condition.
  • the computer means rejects the inspected article whenever the primary and secondary signals do not comply with this specific condition.
  • FIG. 1 is a graph showing reflection curves for a representative sample of articles, and providing as ordinate, the light reflection values as measured, and as abscissa, wavelengths over the reflected light spectrum, according the present invention.
  • FIG. 2 is a two dimensional graph showing position of the color indicating points as provided by the method according to the invention and presenting, as abscissa on a first axis, the first primary color signal as produced for each article inspected, as ordinate on a second axis, the second primary or secondary color signal for each of those articles, and a proposed classification frame whereby color signals can be classified so as to assign corresponding articles to a specific one of a plurality of the color classes.
  • FIG. 3 is a three dimensional graph showing position of color indicating points provided by the method according to this invention and presenting, on a first axis, the primary reflection signal as produced for each article inspected, on a second axis, the second primary or secondary reflection signal for each of those articles, on a third axis, a tertiary signal for each of those articles, and a proposed classification frame whereby color signals can be classified so as to assign corresponding inspected articles to a specific one of a plurality of color classes.
  • FIG. 4 is a schematic diagram of an example of the apparatus according to this invention showing a complete article classifying apparatus using a spectrophotometer as light measuring device.
  • FIG. 5 is a schematic diagram showing a dual gratings spectrophotometer that could be used according to the present invention.
  • FIG. 5a is a plan view of the article conveyer as shown in FIG. 5.
  • FIG. 6 is a schematic diagram showing an alternate light measuring device according to the present invention which comprises a beam splitter followed by a series of optical filters respectively connected thereto.
  • FIG. 7 is a schematic diagram showing an alternate light illumination and measuring device according to the present invention which respectively comprises a series of light sources respectively providing a plurality of light outputs, and a series of photodetectors for respectively detecting these light outputs.
  • FIG. 7a is a plan view of the article conveyer as shown in FIG. 7. MODES OF CARRYING OUT THE INVENTION
  • FIG. 1 there is shown a graph presenting a set of reflection curves, as generally designated at 10, which are expressed in terms of the wavelength spectrum of reflected light.
  • Each curve of the set 10 corresponds to a respective article which has been selected from a batch of articles to be inspected, so as to constitute a sample of articles that is representative of the color range to be sensed.
  • reflection measurements have been made on a group of articles made of red oak, and six articles and corresponding reflection curves were selected by visual inspection of all articles in the batch.
  • Each of the chosen articles is associated with a particular category among a given number of color categories, which are in the particular instance identified by grade 1 to grade 6, respectively corresponding to curves, 12, 14, 16, 18, 20 and 22.
  • the reflection measurement has been accomplished using a light source, the output of which has been directed to a given area of the articles to be inspected, this light output being characterized by a near flat emission spectrum in the working spectrum portion, and using a spectrophotometer system which is readily available in the marketplace. It is pointed out that more than one area on the same article can be illuminated so as to measure light reflection values associated thereto, as will be later described with reference to the apparatus as shown in FIGS. 5A and 7A.
  • the reflection values have been measured in terms of the percentage of the reflected light intensity over the light intensity as received at the article under inspection, a parameter commonly known as the reflectance value.
  • the resolution achieved is generally not sufficient to properly segregate inspected articles characterized by a very similar type of color signature.
  • the pair of wavelengths is selected so to correspond to near linear curves portions respectively starting and ending at points 13 and 24, 15 and 26, 17 and 28, 19 and 30, 21 and 32, 23 and 34, for the example as hereabove explained, it has been found that the best result is achieved when the pair of wavelengths is selected in a such way that the curve portion defined between chosen wavelengths substantially fits over a straight line drawn therebetween, as shown by respectively starting and ending points 13' and 24', 15* and 26', 17* and 28', 19' and 30', 21' and 32', 23' and 34', which respectively correspond to pair of wavelengths ⁇ 'i and ⁇ '2 in the particular example as shown in FIG.
  • the pair of wavelengths should be preferably in the range of about 450 to about 500 nm, which corresponds to ⁇ ' ⁇ and ⁇ '2 in a particular example as shown in FIG. 1.
  • the pair of wavelengths in the range of about 430 to about 520 nm, corresponding to ⁇ i and ⁇ 2 in the same example as shown in FIG. 1.
  • the light reflection curves could present more that one region of curves showing linear portions, as happens with articles made of red oak and as illustrated in FIG. 1.
  • pairs of wavelengths ⁇ 3 - ⁇ 4 and ⁇ '3 - ⁇ '4 represent ranges of wavelength delimiting respectively near linear and linear curves portions, which are similar to the ranges and corresponding curves portions as delimited by pairs of wavelengths ⁇ i - ⁇ 2 and ⁇ 'l - ⁇ '2- Therefore, for article color sensing purposes, either curve regions associated to ⁇ i - ⁇ 2 and ⁇ 'l - ⁇ '2 or curve regions associated to ⁇ 3 - ⁇ 4 and ⁇ '3 - ⁇ '4, can be considered in selecting the working pair of wavelengths.
  • illumination and reflection measurements associated with the first and the second pair of wavelengths can be carried out either on a single area of the inspected article, or on a respective distinct area on the same article.
  • the pair of wavelengths selected in this second curve regions should be preferably in a range of about 550 to about 630 nm, which corresponds to ⁇ '3 and ⁇ '4 in a particular example as shown in FIG. 1.
  • the red oak experience has shown that reasonably good results can also be achieved using a pair of wavelengths comprised in a range of about 530 to about 650 nm, corresponding to ⁇ 3 and ⁇ 4 in the same example as shown in FIG. 1.
  • the measurement of light reflected from the article at a pair of wavelength selected according to the present invention provide light reflection values that are then processed by an electronic calculating device or computer, as will be described later in greater detail, to produce a primary signal representing either a difference between or a ratio of the detected light reflection values.
  • This primary signal is indicative of the color of the inspected article and could be fed to an electronic classification device to sort inspected articles according to predetermined color categories, as will be explained later in greater detail.
  • refection value measurements and calculations can be carried out for more than one area on the article, and a mean primary signal can be so produced.
  • a primary signal is then calculated for each of these additional areas, this primary signal representing either a difference between or a ratio of the detected light reflection values associated with respective wavelength of the first pair.
  • the sum of all primary signals so produced are then produced, this result being finally divided by the total number or areas illuminated so as to obtain the desired mean primary color signal.
  • the luminance parameter of reflected light can be evaluate by measuring the reflection values associated with a minimum of one given wavelength, and preferably with a set of three wavelengths, respectively comprised in the red, green and blue regions of the spectrum.
  • a single wavelength is preferably selected so as to maximize amplitude variation of signal associated with the range of luminance to be evaluated, while affording appropriate signal level.
  • illumination and reflection measurements associated with the first pair of wavelengths, and with this or these secondary wavelengths can be carried out either on a single area of the inspected article, or on different areas on the same article.
  • a mean secondary signal can be produced using the same method as earlier explained for the mean primary signal derivation.
  • color sensing applied to articles made of red oak it has been found that a good result is also achieved when at least one of these secondary wavelengths is preferably in the range of about 530 to about 650 nm.
  • the light reflected from the article is then measured to produce a tertiary signal which is further indicative of the color of the inspected article, by providing a better indication of the luminance thereof.
  • the secondary signal only approximating the true luminance value, this tertiary signal, which is derived using a different wavelengths, provide a better color resolution.
  • illumination and reflection measurements associated this tertiary wavelength can be carried out either on the same area of the inspected article as illuminated for measurements corresponding to the first pair of wavelengths and secondary wavelength, or on a different area on the same article.
  • a mean tertiary signal can be produced using the same method as earlier explained for the mean primary signal derivation. For color sensing applied to articles made of red oak, it has been found that a good result is achieved when at least one of these tertiary wavelengths is preferably in the range of about 430 to about 520 nm.
  • the first primary signal can be added a second primary signal, the combination thereof also giving a better color resolution.
  • a second primary signal it is suggested to select a second pair of wavelengths on the same light refection curves as earlier used for selecting the first pair of wavelengths, as those shown in FIG. 1, but considering another region of curves showing linear portions rather than considering the one as initially chosen, such another region of curves preferably respecting the linearity condition as earlier proposed. For instance, referring to FIG. 1, if a first pair of wavelengths is selected in such a manner to be in the range delimited by ⁇ i - ⁇ 2 or in the range delimited by ⁇ 'l and ⁇ '2 as shown in FIG.
  • a second pair of wavelengths can be selected in a such manner to be in the range delimited by ⁇ 3 - ⁇ 4 or in the range delimited by ⁇ '3 ⁇ ⁇ '4.
  • a first pair of wavelengths is selected in a such manner to be in the range delimited by ⁇ 3 - ⁇ 4 or in the range delimited by ⁇ '3 - ⁇ '4
  • a second pair of wavelengths can thus be selected to be in the range delimited by ⁇ i - ⁇ 2 or in the range delimited by ⁇ ' l ⁇ ⁇ 1 2-
  • illumination and reflection measurements associated with this second pair of wavelengths can be carried out either on the same area of the inspected article as illuminated for measurements corresponding to the first pair of wavelengths, or on a different area on the same article.
  • a mean second primary signal can be produced using the same method as earlier explained for the mean first primary signal derivation.
  • the use of same preferred wavelength values ranges as those hereabove mentioned are suggested.
  • the article under inspection is illuminated with light comprising this second pair of wavelengths, and the light reflected from the article is then measured to provide light reflection values, which are then processed by an electronic calculating device or computer, as will be described later in greater detail, to produce this second primary signal representing either a difference between or a ratio of the detected light reflection values.
  • a mean tertiary signal can be produced using the same method as earlier explained for the mean first primary signal derivation.
  • at least one of these tertiary wavelengths is preferably in the range of about 430 to about 650 nm.
  • a further aspect of this invention concerns the color classification of articles in one of a plurality of color categories.
  • This aspect will be hereabove described in reference to FIGS. 1, 2 and 3.
  • a similar sensing method as earlier described is preferably applied.
  • a first pair of wavelengths is selected on a plurality of light reflection curves in terms of reflected light wavelength, as those shown in FIG. 1.
  • An area on each of articles to be inspected is then illuminated with light comprising the first pair of wavelengths.
  • the light reflected from the illuminated area of each article is measured to detect corresponding light reflection values, which are then processed to produce a primary color signal representing either a difference between or a ratio of said detected light reflection values.
  • the so produced primary color signal is indicative of the color of the article being inspected.
  • One or more secondary wavelengths on the reflected light wavelength spectrum are then selected.
  • An area on each of articles to be inspected is then illuminated with light comprising this or these wavelengths.
  • the light reflected from the illuminated area of each article is measured to detect light reflection values corresponding to a secondary wavelength, from which a secondary color signal is produced by addition of these light reflection values.
  • this secondary signal is further indicative of the color of the article being inspected.
  • a second primary signal can be produced so as to give a better indication of the color of the article being inspected, as already provided by the first primary signal.
  • a second pair of wavelengths is selected on a plurality of light reflection curves in terms of reflected light wavelength, as those curves shown in FIG. 1.
  • An area on each of articles to be inspected is then illuminated with light comprising this second pair of wavelengths.
  • the light reflected from the illuminated area of each article is measured to detect corresponding light reflection values, which are then processed to produce a second primary color signal representing either a difference between or a ratio of said detected light reflection values.
  • the so produced second primary color signal is further indicative of the color of the article being inspected.
  • the first or second pair of wavelengths, with which the first and second primary signals are respectively associated are selected from a plurality of light reflection curves in terms of reflected light wavelength spectrum, said curves being associated with a plurality of articles which constitute a sample representative of the color range to be sensed.
  • the first or second pair of wavelengths delimits respectively a first or second range of wavelengths corresponding to light reflection values in said curves, the light reflection values in each of said curves being in a substantially linear relationship over the first or second range of wavelengths.
  • a two dimensional graph representing, as abscissa, the first primary color signal Rl produced for each article inspected, and as ordinate, the second primary or secondary color signal R2 for each of those articles, these signals being provided by the method as earlier explained.
  • a given number of articles are selected from a batch of articles to be inspected, so as to form a sample of articles that is representative of the color range to be sensed.
  • a representative sample of articles made of red oak has been selected by visual inspection, and reflection measurements have been made for each article of this sample.
  • Color signals associated with each article of the sample has been graphically represented, as shown in the graph of FIG. 2.
  • the associated first primary color signal rl and the second primary or secondary signal r2 form a given point designated at numeral 41 on the graph, each point having respective coordinates (rl, r2) .
  • a classification frame, generally designated at numeral 42 is then drawn over all of points 41, in a such manner that substantially each of these points are included in the classification frame 42. More specifically, the frame 42 comprises a first pattern consisting of a first an a second crossing set of lines designated as 44 and 46 on the system of axis Rl and R2, which sets of lines are respectively defined by following relations :
  • R2j -m2(Rlj-Rloj)+R2oj
  • Rl 0 i is the origin threshold value for the first primary color signal on the axis Rl and corresponds to a line i of the first set of lines;
  • Rio j is the origin threshold value for the first primary color signal on the axis Rl and corresponds to a line j of the first set of lines;
  • R2 0 i is the origin threshold value for the second primary or secondary color signal on the axis R2 and corresponds to a line i of the second set of lines;
  • R2o j is the origin threshold value for the second primary or secondary color signal on the axis R2 and corresponds to a line j of the second set of lines;
  • mi is a slope parameter for said line i, and is a positive value
  • Cj j is the class delimited by lines i, i+1, j and j+1 of the classification frame, wherein i ⁇ . m-1, j ⁇ . m-1; rl is the first primary color signal indicative of the color of each one of articles to be inspected;
  • r2 is the second primary of secondary color signal further indicative of the color of each one of articles to be inspected.
  • FIG. 3 there is shown a three dimensional graph representing, on a first axis, the primary color signal Rl as produced for each article inspected; on a second axis, the second primary or secondary color signal R2 for each of those articles; on a third axis, a tertiary color signal R3 for each of those articles; and a proposed classification frame whereby color signals can be classified so as to assign corresponding articles to a specific one of a plurality of color classes, as will be hereunder described.
  • Primary and secondary color signals are provided by the method as earlier explained.
  • the tertiary signal could be produced using at least one tertiary wavelength that must be different from a previously selected secondary wavelength, and according essentially to the same method as earlier exposed.
  • FIG. 3 a representative sample of articles made of red oak has been selected by visual inspection, and reflection measurements have been made for each article of this sample.
  • Color signals associated with each article of the sample has been graphically represented, as shown in the graph of FIG. 3.
  • the associated first primary color signal rl, the second primary or secondary signal r2 and the tertiary signal r3 form a given point designated at numeral 48 on the graph, each point having respective coordinates (rl, r2, r3).
  • a classification frame, generally designated at numeral 50 is then drawn inside the tridimensional space defined by axis Rl, R2 andR3.
  • the frame 50 comprises a first pattern consisting of first and second crossing sets of lines, designated at 52 and 54, which are respectively defined by the following relations :
  • R2i m 1 (Rli-Rloi)+R2 oi and
  • R2 j -m 2 (Rl j -Rl 0j )+R2 0j
  • Rl 0 i is the origin threshold value for the first primary signal on said first axis Rl and corresponds to a line i of said first set of lines;
  • Rio j is the origin threshold value for the first primary signal on the first axis Rl and corresponds to a line j of said first set of lines;
  • R2 0 i is the origin threshold value for the second primary or secondary signal on said the axis R2 and corresponds to a line i of said second set of lines;
  • R2 0 j is the origin threshold value for the second primary or secondary signal on the axis R2 and corresponds to a line j of said second set of lines;
  • mi is a slope parameter for said line i, and being a positive value
  • This first pattern lays in a plane intersecting third axis R3 at a point R3 0 which is a first threshold value for the tertiary signal produced.
  • FIG. 3 there is provided a second pattern consisting of a third and a fourth crossing set of lines designated at 56 and 58, which sets of lines are respectively defined by the following relations :
  • Rl o i is the origin threshold value for the first primary signal on the axis Rl and corresponds to a line i of the third set of lines;
  • Rloj is the origin threshold value for the first primary signal on the axis Rl and corresponds to a line j of the third set of lines;
  • R2o i is the origin threshold value for the second primary or secondary signal on the axis R2 and corresponds to a line i of the fourth set,of lines;
  • R2o j is the origin threshold value or the second primary or secondary signal on the axis R2 and corresponds to a line j of the fourth set of lines;
  • m 3 is a slope parameter for said line i, and being substantially equal to said slope parameter mi;
  • the second pattern lays in a plane intersecting the third axis R3 at a point R3 0 >R3o which is a second threshold value for the tertiary signal, as earlier explained. Moreover, the following relation must be generally satisfied:
  • the classification frame 50 further comprises first and second sets of surfaces respectively designated at 60 and 62, only a portion of one of these surfaces being shown in FIG. 3 for the sake of clarity.
  • the first set 60 comprises surfaces respectively intersecting lines i of the first set of lines 52, with corresponding lines i of the third set of lines 56.
  • the second set 62 comprises surfaces respectively intersecting lines j of the second set of lines 54 with corresponding lines j of the fourth set of lines 58.
  • Such a configuration of crossing sets of surfaces defines a first stage of (n-l)*(m-l) color classification cells 63, each of those cells delimiting a respective classification space therein. It is noted that only one of these cells is represented in FIG. 3 for the sake of clarity.
  • the classification step of the method then consists of classifying each of the articles to be inspected in a color class j associated with a respective one of the cells, whenever the first primary signal, the second primary or secondary signal and the tertiary signal corresponding to the area of the inspected article define a point located inside the corresponding classification cell. Furthermore, whenever the primary signal, the second primary or secondary signal and the tertiary signal define a point located in one or more of the surfaces defining adjacent cells, the corresponding article will be arbitrarily classified in the color class j having the lowest value of i and j associated with a respective one of adjacent cells.
  • j is the class delimited by lines i, i+1, j and j+1 of the second pattern of the classification frame, and wherein i ⁇ . n-1, j ⁇ . m-1;
  • rl is the first primary signal is indicative of the color of the article under inspection
  • r2 is the second primary or secondary signal is further indicative of the color of this article
  • r3 is the tertiary signal further indicative of the color of this article.
  • the apparatus comprises a handling unit generally designated at 72, a light measurement unit 74, a power and electronic unit 76 and a computer 78.
  • the handling unit comprises a roll conveyer 80 on which articles 82 to be inspected are disposed to feed the input end 84 of the apparatus. As herein shown, articles 82 are disposed in an end-to-end relationship.
  • An incoming article 82 is disposed at the input end 84 of the apparatus, and an upper belt conveyer 86, which is driven through pulley 89 by an electric motor 91, then moves the incoming article 82 along the upper surface 87 of an elongated flat bed plate 88 secured to the housing of the apparatus (not shown).
  • a guide 85 provided on the bed plate 88 keeps aligned articles moving thereon, as better shown in FIG. 5A.
  • the bed plate 88 comprises a viewing aperture 90 extending therethrough and above which articles 82 pass, whereby the undersides of articles 82 are presented to the viewing aperture 90 at a viewing location 93.
  • An optical sensing block 92 having an upper surface 94 being flush with the upper surface 87 of bed plate 88 is mounted in the aperture 90, the upper surface 94 being made of light transparent material.
  • the optical sensing block 92 is connected to the light measuring unit 74 as will be hereunder explained.
  • This light measuring unit consists of a spectrophotometer comprising a light source 96 providing a light output 98 which is conducted toward upper surface 87 of optical sensing block 92 by a first light guide (not shown), such as a fiber optic cable, such a light guide being well known in the art.
  • the light source is chosen in such a manner that the light output 98 comprises the pair of wavelengths selected from a plurality of light reflection curves in terms of a reflected light wavelength spectrum, as earlier explained in reference to FIG. 1.
  • the light output then reaches upper surface 94 of the sensing block 92, preferably at an angle of 45 degrees with reference to the upper surface 94.
  • a second light guide (not shown) collects and directs the a reflected light beam 100 from an area 101 of the underside of article 82 under inspection toward to a spectrophotometer grating 102.
  • the grating 102 spreads the reflected light beam 100 in wavelength components forming the continuous reflected light spectrum.
  • wavelength components are then directed to a respective photodetector of an array of photodetectors 103, a CCD linear array in one particular instance, and a plurality of analog signals, which are proportional to the intensity values of reflected light corresponding to a respective wavelength component, are fed to an electronic interface 106 through cable 104.
  • the electronic interface 106 processes and converts analog reflected light signals to digital serial or parallel signals which are then fed to the computer 78 through link 108.
  • a power unit 110 connected to an electrical power source 112 supplies appropriate voltage levels for the operation of the electronic interface 106 and computer 78 through link 109.
  • the computer 78 selects those digital reflected light signals corresponding to each wavelength of the selected pair of wavelengths, and produces a signal representing either a difference between or a ratio of said detected light refection values, such a signal being indicative of the color of the inspected article.
  • Such color signal can then be displayed on a display (not shown) connected to the computer 78, or fed to another electronic device for further processing.
  • an example of such further processing consists of classifying articles to be inspected in a respective one of a plurality of the color classes.
  • the computer is used to carry out the classification method as earlier described in detail, to produce primary, secondary and tertiary color signals, so as to define a classification frame, and to classify each inspected article in a respective one of the color classes.
  • the computer 78 sends a signal representing the selected color class to a marking head 116 securely mounted in a second aperture 117 provided through the bed plate 88 of the apparatus.
  • the marking head 116 immediately prints an identification mark, e.g., an alphanumeric code and/or bar code, on the inspected article, which corresponds to the selected class for this specific article that can be later manually or automatically sorted.
  • FIG. 5 shows a partial schematic diagram of another example of the apparatus according to the present invention, wherein measurement unit 74 comprises a dual gratings spectrophotometer as designated at numerals 119A and 119B.
  • the light source 96 provides two light outputs 120 and 122 which are conducted toward upper surface 94 of optical sensing block 92 respectively by first and second light guides (not shown), such as fiber optic cables. Light outputs 120 and 122 then reach upper surface 94 of sensing block 92 preferably at an angle of 45 degrees with reference to the upper surface 94.
  • Third and fourth light guides respectively collect and direct reflected light beam 124 and 126 from areas 128 and 130 of the underside of article 82 under inspection, as better shown in FIG. 5A, toward gratings 119A and 119B.
  • Gratings 119A and 119B respectively reflected light beams 124 and 126 in wavelength components constituting the continuous reflected light spectrum.
  • the spread wavelength components are then directed to a respective array of a pair of linear arrays of optical sensors 132 and 134, a pair of CCD linear arrays in the particular instance, and the two groups of analog signals so produced are directed to the electronic interface through cables 136 and 138, as indicated by arrows 140 and 142.
  • the apparatus configuration as shown in FIGS. 5 and 5A provides color sensing associated with areas which are not aligned in the moving direction of the article under inspection, as clearly shown in FIG. 5A. Therefore, in the case when articles to be inspected are characterized by a non uniform color over their surface, more representative color signals can be obtained through averaging reflected light measurements based on a plurality of areas on the inspected articles, which areas need not absolutely be aligned thereon.
  • a beam splitter 144 is provided for receiving the reflected beam of light 100 from the area 101 of the article underside to be inspected, and for splitting the incoming beam in a plurality of substantially identical reflected light beams 146.
  • Each of these beams is directed to a respective one of a plurality of bandpass optical filters, identified in the particular instance at numerals 147, 148, 149 and 150, the bandwidth of which are centered at a respective wavelength, namely ⁇ i, ⁇ 2, I3 and ⁇ 4, these wavelengths being selected as earlier explained.
  • bandpass optical filters identified in the particular instance at numerals 147, 148, 149 and 150, the bandwidth of which are centered at a respective wavelength, namely ⁇ i, ⁇ 2, I3 and ⁇ 4, these wavelengths being selected as earlier explained.
  • a different number of these filters could be required depending upon the sensing or classifying method used.
  • Beams of reflected light passing through filters 147, 148, 149, and 150 are then directed to a respective one of a plurality of photodetectors 151, 152, 153, and 154, such as photodiodes or equivalent semiconductor devices. Reflected light analog signals produced by theses photodetectors are then directed to the electronic interface through link 155, as indicated by the arrow 156.
  • a plurality of light sources such as laser diodes, as indicated in the particular instance at numerals 156, 157, 158 and 159, are provided. These light sources are chosen in a such manner their respective bandwidth comprises one of wavelengths associated with a selected pair of wavelengths or one of the secondary or tertiary wavelengths as selected according to the method as earlier explained, namely ⁇ i, ⁇ 2, ⁇ 3 and ⁇ 4- Each of these light sources is aligned with a respective filter of a series of bandpass optical filters 160, 161, 162 and 163, the bandwidth of which are respectively centered on ⁇ i, ⁇ 2, ⁇ 3 and ⁇ 4- It is noted that a different number of these light sources and associated optical filters could be required depending upon the sensing or classifying method as used.
  • the light sources 156, 157, 158 and 159 provide respectively four light outputs 164', 165', 166' and 167', which are conducted toward upper surface 94 of optical sensing block 92 respectively by a first series of four light guides (not shown), such as fiber optic cables. Light outputs 164, 165, 166, and 167 then reach upper surface 94 of sensing block 92 preferably at an angle of 45 degrees with reference to the upper surface 94.
  • a second series of light guides respectively collect and direct reflected light beams 164, 165, 166, and 167 from areas 168, 169, 170 and 171 of the underside of article 82 under inspection, as better shown in FIG. 7A, toward photodetectors 172, 173, 174, and 175. Reflected light analog signals produced by theses photodetectors are then directed to the electronic interface through link 176, as indicated by the arrow 177.

Abstract

Un procédé et un appareil (70) permettent de détecter des couleurs d'articles (82) et de classer ces derniers. Deux premières longueurs d'onde sont sélectionnées sur plusieurs courbes de réflexion lumineuse (11-22) en fonction d'un spectre de longueurs d'onde de lumière réfléchie. Un article (82) à inspecter est éclairé par une lumière (98) qui comprend ces deux premières longueurs d'onde et la lumière (100) qu'il réfléchit est mesurée pour permettre la détection des valeurs de réflexion lumineuse correspondant à ces deux premières longueurs d'onde. Il en découle un signal primaire qui représente soit une différence soit un rapport existant entre ces valeurs de réflexion lumineuse détectées et qui indique la couleur de l'article inspecté (82). Une longueur d'onde secondaire au moins est sélectionnée sur le spectre des longueurs d'onde correspondant à la lumière réfléchie et l'article inspecté est éclairé avec une lumière comprenant cette longueur d'onde secondaire, puis la lumière qu'il réfléchit est mesurée pour donner un signal secondaire qui précise sa couleur. Un ordinateur (78) offre une grille de classement (42) qui comprend un premier motif consistant en deux jeux de lignes qui se croisent (44, 46) et qui sont chacun définis par analyse mathématique, cette grille définissant plusieurs classes de couleurs (Cij). L'ordinateur (78) classe l'article inspecté dans l'une des classes de couleur définies par cette grille (42) quand les signaux primaire et secondaire correspondent à une situation spécifique, et il rejette l'article inspecté (82) quand ces signaux primaire et secondaire ne correspondent pas à cette situation spécifique.
PCT/CA1994/000233 1993-04-29 1994-04-28 Procede et appareil permettant de detecter des couleurs d'articles et de classer ces derniers WO1994025838A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU67181/94A AU6718194A (en) 1993-04-29 1994-04-28 Method and apparatus for sensing the color of articles and for classification thereof

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CA002095154A CA2095154C (fr) 1993-04-29 1993-04-29 Appareil de classement par couleurs d'articles divers et methode connexe
CA002095155A CA2095155C (fr) 1993-04-29 1993-04-29 Appareil de definition de la couleur d'articles divers et methode connexe

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WO1999037413A1 (fr) * 1998-01-23 1999-07-29 Centre De Recherche Industrielle Du Quebec Procede et dispositif servant a classifier des lots de copeaux de bois
WO2019201786A1 (fr) * 2018-04-20 2019-10-24 Bühler Uk Limited (Bukl) Machine d'inspection et de tri optiques, et procédé correspondant
FR3101144A1 (fr) * 2019-09-23 2021-03-26 Odesyo Système et procédé de contrôle de la couleur d’un article en déplacement

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WO1999037413A1 (fr) * 1998-01-23 1999-07-29 Centre De Recherche Industrielle Du Quebec Procede et dispositif servant a classifier des lots de copeaux de bois
US6175092B1 (en) 1998-01-23 2001-01-16 Centre de Recherche Industrielle du Qu{acute over (e)}bec Method and apparatus for classifying batches of wood chips or the like
WO2019201786A1 (fr) * 2018-04-20 2019-10-24 Bühler Uk Limited (Bukl) Machine d'inspection et de tri optiques, et procédé correspondant
GB2587511A (en) * 2018-04-20 2021-03-31 Buehler Uk Ltd Optical inspection and sorting machine, and corresponding method thereof
GB2587511B (en) * 2018-04-20 2022-06-08 Buehler Uk Ltd Optical inspection and sorting machine, and corresponding method thereof
FR3101144A1 (fr) * 2019-09-23 2021-03-26 Odesyo Système et procédé de contrôle de la couleur d’un article en déplacement
WO2021058172A1 (fr) 2019-09-23 2021-04-01 Odesyo Système et procédé de contrôle de la couleur d'un article en déplacement
US11940328B2 (en) 2019-09-23 2024-03-26 Veoria System and method for controlling the colour of a moving article

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