Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SYSTEM AND METHOD FOR THE DETECTION
OF BLUESTAIN AND ROT ON WOOD
FIELD OF THE INVENTION
The present invention relates to a system and method for the detection of
bluestain and rot on wood. More specifically, the present invention concerns
such
a system and method where the detection is made by spectrally analysing tight
reflected off the wood.
DESCRIPTION OF THE PRIOR ART
The quantity of wood that is stained with bluestain is constantly increasing,
particularly since the forests of British Columbia have been infested with an
insect
known as mountain pine beetle. This type of wood is easily distinguished from
other woods by its blue colour, due to the fungi carried by the insect. The
volume
of bluestain wood treated by mills increases, but consumers are reluctant to
use
this wood, even though studies have demonstrated that the physical properties
of
the wood are unaffected. Mill operators would like to the able to grade
bluestain
wood during the early stages of classification, either at the planing step or
at the
cutting step. The colour of bluestain wood, varying from grey to black, is
also akin
to that of rot. Hence, a sensor for detecting bluestain must detect not only
bluestain but also rot, without being affected by the other natural defects of
the
wood.
There is not presently technology available in sawmills (and particularly
those of
first transformation) which permits the detection of bluestain. There are
scanners
that exist, but they are used in mills of secondary transformation. Most of
the
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scanners are based on 2D colour cameras, the image of which is then analysed
by
a computer program. The problem is that the colour of the bluestain is
difficult to
determine with any certainty from a colour image, and is easily mistaken for
other
defects. Furthermore, the computer programs are based on complicated
algorithms which compare regions of the image in order to make a
determination,
which makes the processing of the image heavy and difficult to implement in
real
time. The detection level being low, human intervention is generally required
to
make a final classification of the wood.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a system and method for
detecting bluestain and rot on a piece of wood which is based on a spectral
analysis of the piece of wood.
In accordance with one aspect of the invention, there is provided a system for
detecting bluestain and rot in wood in a wood processing plant, said wood
processing plant including a conveyor for conveying a piece of wood through a
scanning area, said system comprising:
a scanning unit comprising a plurality of scanners arranged to scan a face
of said piece of wood in a direction perpendicular to a conveying direction of
said
piece of wood, each of said scanners comprising:
a light for illuminating a point on said piece of wood;
a collector for collecting light reflected from said piece of wood;
a splitter for splitting said collected light into at least two beams;
a filter for filtering out of each of said beams a wavelength associated
with each of said beams, each of the wavelengths being different;
a collector for collecting the filtered light, said collector being adapted
to output a signal related to an intensity of said filtered light; and
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a comparator for comparing the output of each of the collector, said
comparator being adapted to output a signal when a ratio between said signal
between each of said collector exceeds a predetermined threshold.
In accordance with another aspect of the invention, there is provided a system
for
grading a piece of wood based on the detection of bluestain and rot, said
system
comprising:
a first scanning unit according to claim 1 for scanning a top of said piece of
wood;
a second scanning unit according to claim 1 for scanning a bottom of said
piece of wood;
a data collector which synchronizes said output of said comparator with the
passage of said wood piece through said scanning area in order to scan said
wood piece at a predetermined interval, for collecting said output of each of
said
comparator; and
a grading computer for grading said piece of wood according to data
collected by said data collector.
In accordance with yet another aspect of the invention, there is provided a
method
for detecting bluestain and rot in wood comprising the steps of:
(a) providing a scanning unit comprising a plurality of
scanners arranged to scan a face of said piece of wood
in a direction perpendicular to a conveying direction of
said piece of wood;
(b) with said scanning unit:
(i) illuminating a point on said piece of wood;
(ii) collecting light reflected from said piece of wood;
(iii) splitting said collected light into at least two
beams;
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(iv) filtering out of each of said beams a wavelength
associated with each of said beams, each of the
wavelengths being different;
(v) collecting the filtered light with a collector
adapted to output a signal related to an intensity
of said ~Itered light;
(vi) comparing the output of each of the collector;
and
(vii) outputting a signal when a ratio between said
signal between each of said collector exceeds a
predetermined threshold.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in more detailed in the following description
of a
preferred embodiment of the invention, made with reference to the following
drawings in which:
Figure 1 is schematic representation of a system for grading a piece of wood
conveyed in a longitudinal direction, consisting of two scanning units, a data
collector and a grading computer;
Figure 2 is cross-sectional view of Figure 1 showing only the top scanning
unit;
Figure 3 is a schematic representation of the arrangement of the light, the
lens and
the filters and detectors;
Figure 4 is a bottom view of a scanning unit;
Figure 5 is a detailed view of the scanner, showing details different from
those of
Fig. 3; and
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Figure 6 is a schematic view of two scanning units for each surface of the
piece of
wood, offset from each other.
5 DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
As mentioned previously, the present invention is based on a spectral analysis
of
the piece of wood. This provides the advantage that the detection does not
depend on the interpretation of an image, as in the scanners of the prior art,
but
rather depends on the reaction of the wood to certain specific wavelengths of
light
reflected off the piece of wood.
More specifically, the present invention concerns a system for detecting
bluestain
and rot in wood in a wood processing plant, the wood processing plant
including a
conveyor 10 for conveying a piece of wood through a scanning area 12.
The system includes a scanning unit 20 comprising a plurality of scanners 22
arranged to scan a face of the piece of wood in a direction perpendicular to a
conveying direction of said piece of wood. The scanning unit can be
monolithical,
in that it is made of a single piece, or could be made of a plurality of
individual
scanners mounted together. In Fig. 1, the scanners are individual.
Referring now to Figs. 2, 3 and 5, each of the scanners includes a light 23
for
illuminating a point on said piece of wood. There is also provided a collector
25 for
collecting light reflected from the piece of wood; a splitter 27 for splitting
the
collected light into at least two beams 29, 31; and a filter 33, 34 for
filtering out of
each of the beams 29, 31 a wavelength associated with each of the beams, each
of the wavelengths being different. The scanners further include a collector
35, 36
for collecting the filtered light, the collector being adapted to output a
signal related
to an intensity of said filtered light; and a comparator 37 for comparing the
output
of each of the collector, the comparator being adapted to output a signal when
a
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ratio between the signal between each of said collector exceeds a
predetermined
threshold.
As better shown in Figs. 3 and 5, the light 23 is preferably LEDs. More
preferably,
the LEDs are arranged in a line (which is parallel to the conveying direction
of the
piece of wood). In order to provide better results, the LEDs are further
disposed on
either side of the collector 25, which is in a preferred embodiment a lens.
Further
preferably, the LEDs are selected to emit light in the spectrum of 900 to 1200
nm.
Given the fact that pieces of wood have varying thicknesses, the LEDs are
adapted to illuminate the piece of wood with a stable intensity for a depth of
3
inches (see Fig. 2). Thus, the scanning unit 22 is preferably placing 6 inches
away
from the conveyor 10.
As shown in Fig. 3, the splitter 27 and filter 34 are a single component, as a
person skilled in the art of optics would readily understand. The detectors
35, 36,
as shown in Fig. 5, are preferably mounted on PCBs, which further include the
electronic components required to output the signal related to the intensity
of light.
Such detectors are well known, and are readily available.
The comparator 27 is also a well known component, and details of its
construction
are not included herein. However, the output of the comparator is preferably
an
analog signal, varying for example between 0-10 V, indicative of the strength
of
the signals received by the collectors.
As mentioned previously, the present invention is based on a spectral analysis
of
the light reflected from the piece of wood. It has been found that although a
single
wavelength may be used for the purpose of detecting bluestain and rot, the
efficiency and accuracy of the system is further increased by comparing a
ratio
between the intensity of at least two wavelengths. It should be noted that the
ration
can compare three or more wavelengths, but accuracy does not necessarily
increase.
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The inventors have found that the best results occur in the range of 900-1200
nm.
Two combinations of wavelengths have been found to be the best: the ratio of
985
nm over 965 nm (or 980 nm over 960 nm) and 1140 nm over 955 nm. The choice
will most likely depend on the impact of false detections caused by knots. If
a false
detection would have no impact, then the first pair of wavelengths should be
selected; otherwise the second should be considered.
In order to provide optimal scanning, the wood is conveyed longitudinally, and
the
scanning unit is provided with twelve scanners, separated from each other by a
distance of one inch (see Fig. 4). Of course, if the piece of wood is scanned
transversely, then the scanning unit should have enough scanners to scan the
whole length of the piece of wood.
The system of the present invention is further preferably connected to a data
collector which is operatively associated with the conveyor. This enables the
data
collector to synchronize the collection of data as the piece of wood passes
through
the scanning area 12. Preferably, the piece of wood is scanned at every 0.125
to
every 0.500 inch, depending on the accuracy required.
As is typical in sawmills, there are also grading computers, which permit the
grading of a piece of wood according to a variety of surface defects, etc. The
data
collector can then be integrated into a grading system.
In order to provide even greater accuracy, as shown in Fig. 6, two scanning
units
can be placed over each surface of the piece of wood. In such a case, the
scanning units on one side a offset by approximately'/2 inch.
Although the present invention has been explained hereinabove by way of a
preferred embodiment thereof, it should be pointed out that any modifications
to
this preferred embodiment within the scope of the appended claims is not
deemed
to alter or change the nature and scope of the present invention.
