Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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LUMBER MOISTURE CONTENT SORTER
Field of the Invention
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Present invention relates to the measurement of
lumber moisture content, more particularly the present
invention relates to the measuring of the moisture content
of lumber and sorting the lumber based on moisture
content.
Background of the_Present Invention
The idea of sorting lumber based on moisture
content so that one may operate a kiln more efFiciently by
tailoring the drying cycle more accurately with the known
moisture content of the wood has been known for a number
of years, however, no effective means for properly sensing
the moisture content of the wood having a moisture content
of above about 30% moisture has been available.
It has been proposed to sense moisture content
based on infrared reflections. This technique seems to
work reasonably well with veneer but is not particularly
effective with thick sections as normally found in lumber,
~; particularly following storage after sawing.
It is known to measure the dimensions of
elements by sensing reflected light or other means such as
reflected infrared light or by means of x-rays so that the
physical dimensions of an article can be determined.
It is also known to utilize load cells to deter-
mine the weight of any given object.
Brief Descriction of the Present Invention
It is an object of the present invention to
provide a new technique for sensing the moisture content
of wood elements such as lumber pieces.
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It is a further object of the present invention
to provide a system for sensing the moisture or percent
moisture of pieces of lumber and to sort the lumber in
accordance with the moisture or percent moisture content.
Broadly, the present invention comprises means
for sensing at least the major dimension of the lumber
article, means for sensing the weight said lumber article,
means for determining the density of said lumber article
and means for comparing the determined density with a pre-
selected mass density for determining the percent moisture
in the said wood element or sorting the wood elements.
In many cases the means for sensing the ma~or
dimension will comprise means for sensing the length of
the lumber article and wherein the width and thickness
dimensions will be preset (i.e. when the moisture content
of reasonably accurate dimensional lumber is being deter-
mined) so that the volume of the element can be calculated
based solely on the measurement of its length. Also in
- some case the thickness dimension will vary significantly
and must be sensed while the widths remain substantially
constant, in these cases the volume of the element can be
calculated based solely on the measurement of its thick-
ness and length.
Preferably the wood articles will then be separ-
ated on the basis of moisture content with those wood
articles having a percent moisture above a preset limit
being collected in one area and those with a moisture
content below said preset limit being collected in another
area.
Brief Description of the Drawinqs
Further features, objects and advantages will be
evident from the following detail description of the pre-
ferred embodiments of the present invention taken in
conjunction with the accompany drawings in which:
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Figure 1 is a schematic illustration of the
various elements forming the present invention.
Figure 2 is a schematic arrangement illustrating
the sensing devices feeding the microprocessor.
Figure 3 is a graph of number of lumber pieces
versus mass density (percent moisture) to indicate the
distribution of lumber pieces having various moisture
contents O
Description of the Preferred Embodiments
An investigation of clear lumber substantially
free of knots or rot proved conclusively that for a given
species the mass density based on green volume and oven
dry weight of the wood was substantially more uniform than
that of normal run of the mill wood from that species.
Based on this finding, it was concluded that the mass
density moisture content relationship for a given species
is reasonably constant for clear lumber.
Based on this observation, a moisture meter was
produced for lumber wherein the dimensions of each lumber
piece were sensed and the individual lumber pieces were
weighed to find their weights and based on these values
the volume and the density for each piece of lumber was
calculated. Based on this calculated mass density and the
predetermined mass density of the clear oven dry wood, the
percent moisture could be calculated for each wood piece.
- Obviously once the mass density for a selected moisture
content is known to separate on moisture content, one need
only determine the mass density of the lumber and compare
that with the mass density for the selected moisture
content.
Such a device is shown in Figure 2 wherein a
thickness measuring means 10 is used to determ~ne the
thickness of each lumber element 12, a width measuring
~ 35 device 14 senses the width of the lumber and a length
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measuring device 16 senses the length of each lumber
element 12. The output of all of these sensors is sent to
a computer or microprocessor 18 which deterrnines the -
volume of each lumber element 12. These dimension sensors
10, 14 and 16 may be selected from any of a number of well
known sensors.
Load cells 20 (two shown) sense the weight of
each lumber piece 12. This sensed weight is fed to the
microprocessor 18 which then calculates the density of the
lumber element 12, compares this density with a preset
value for density for the preselected moisture content for
that particular species of lumber and based thereon gener-
ates a signal to operate the sorter 22 in accordance with
the mass density (moisture content) determined by pro-
cessor 18. If the moisture content of each piece is
desired the calculated mass density may be compared with
the predetermined mass density for clear lumber of that
; species with difference being attributable to moisture
differences and moisture content calculated. Normally the
invention will be used for sorting and the moisture
content of individual pieces need not be determined.
In many cases it will be unnecessary to sense
the thickness and width since for nominal sized lumber
these dimensions are reasonably accurately known and the
size of the lumber particularly the width and thickness
can be assumed from the nominal size being produced. In
such cases, only length need be measured. In some mills,
only length and thickness need to be sensed, i.e. where
the mill run has significant variations in thickness but
width is uniform.
Figure 1 shows a layout of a typical installa-
tion incorporating the present invention. As shown lumber
elements 12 are removed from a stack 24 onto a conveyor 26
having spaced lugs 28 adapted to move the lumber elements
along with the conveyor with the lumber elements being at
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uniformly spaced intervals therealong. If it is desired
to sense the thickness of the lumber a suitable thickness
sensor 10 will be provided, simllarly if it is desired to
sense the width of the lumber a suitable sensor such as
the sensor 14 may be used. The length is sensed by the
sensor as schematically indicated at 16. In some install-
ations, a single sensor instrument may be used to deter-
mine all the required dimensions of the lumber pieces.
Discreet lumber elements 12 move off the end of
the conveyor 26 onto a roller chute 30 and the weight of
each element 12 is sensed by the sensor which in the
arrangement in Figure 2 is comprised of a pair of load
cells 20. The discreet lumber elements 12 are then
elevated by a conveyor 32 having spaced lugs 39 which
~5 engage and elevate the various lumber pieces 12 in spaced
regimented relationship up to the sorter bin generally
indicated at 22.
In the schematic arrangement shown in Figure 1,
the bin 22 includes a gate 36 that is pivoted between a
close position as illustrated and an open position as
shown by the dotted line. The position of this gate 36 is
determined by the microprocessor 18 which determines the
mass density of each lumber element which, as above
described, provides a sufficiently accurate indication of
the moisture content of each of the lumber pieces 12. The
location oF each of these lumber pieces is accurately
known since each lumber piece is carried by the lugs up
the conveyor 32 and it is known which lugs pick up each
lumber piece. The gate 36 is activated depending on the
mass density of the lumber element 12 such that if the
lumber element is to proceed into the top bin 38 the gate
36 is closed when the lumber element 12 is deposited in
the bin 22 and the lumber element slides over the gate 36
into the bin 38. On the other hand, if the mass density
(moisture content) is significantly different, i.e. on the
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opposite side of a preset mass density cut of-f point, then
the microprocessor 1~ controls the mechanism to open the
gate 36 to the dotted line position and permit the element
12 of this moisture content to pass into bin section 40 of
the sorter 22.
The control or cut off point for the separation
in the illustrated arrangement is a single selected mas
density (cut off point) so that lumber with a mass density
(moisture content) higher proceeds to one bin while lumber
elements with a lower mass density (moisture content)
proceed to a second bin. It will be apparent that more
than one cut off point may be set, i.e. there may be an
intermediate range so that all lumber in an intermediate
range of mass density (moisture content) falls into a
third bin with lumber elements of higher and lower mois-
ture contents going into their own separate bins. However,
since the degree of accuracy of the moisture content
determination (determination by mass density) decreases
with decreasing moisture content, it is preferred to use a
single cut off point at a relatively high mass density
(moisture content).
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In Figure 3, a preselected cut off point has
been indicated by the line AA. This cut off point is pre-
set into the microprocessor 18 so that all the lumber
pieces having a mass density to the left of the line AA
would be sorted into one bin and the high moisture content
lumber indicated by that portion of the curve to the right
~ 30 of the line AA would be received in a second bin.
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Generally, if a single separation line is to be
used that line should coincide with a speciFic moisture
content that generally will be in the range of 80%-110%,
preferably 90%-100% moisture and as above indicated lumber
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pieces with a moisture content above the prescribed limit
will be separated from lumber below that level. It has
been found that for western red cedar 100% moisture coin-
cides with a mass density of about 620 kilograms/cubic
meter. Obviously this does not provide a precise measure-
ment of 100% moisture but is sufficiently accurate such
that separation of pieces with mass density above or below
the selected density results in a very significant
improvement in drying efficiency. For hemlock which
includes what is called sinker stock and contains wood
with very high moisture two separation lines may be used,
one in the range of 160%-190%, preferably 170%-180% and
the other in the range described above for a single separ-
ation line.
15It will be apparent from the position of line AA
in Figure 3 that by far the majority of the lumber falls
to the left of AA, however, the lumber to the right though
small in quantity would in a conventional system govern
the drying cycle. This small quantity of lumber having
moisture above the cut off point when dried together with
the rest of the lumber controlled the drying cycle for all
the lumber. This drying cycle, in some cases, caused
' damage to those lumber pieces having low moisture content.
With the present invention, the high mass
density (moisture content) material will be dried separ-
ately from the major portion of the lumber, each portion
will be kiln dried using a selected drying cycle specific
to that particular portion of the lumber. It has been
found following this practice for western cedar lumber
where line AA is at 100% moisture the majority of lumber,
i.e. the lumber to the left of the line AA in Figure 3 can
be dried in a significantly shorter period of time than if
all the lumber were kiln dried simultaneously (the time to
complete the drying cycle has been reduced by almost 50%
35 in some cases1. It has also b;en found that i~ the portion
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above the separation line AA, i.e. to the right of the
separation line AA, is separately kiln dried, its drying
cycle can also be keyed to its particular moisture content
and the time for drying this portion also reduced signifi-
cantly relative to when all of the lumber was driedsimultaneously.
While it is possible to separate into more than
two groups it is been found that the single separation
provides a very significant improvement and further separ-
ations while they can be used to advantage probably are
not economically justified.
Having described the invention modifications
will be evident to those skilled in the art without
departing from the spirit of the invention as defined in
the Claims.
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