Note: Descriptions are shown in the official language in which they were submitted.
CA 02359698 2001-10-17
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APPARATUS AND METHOD FOR DETERMINING A DRYING TIME OF A PIECE
OF WOOD
FIELD OF THE INVENTION
The present invention relates to an apparatus and a method for determining the
drying time of a piece of wood among wood species, such as fir and spruce.
BACKGROUND OF THE INVENTION
It is standard practice in the lumber industry to dlry or season several
lumber
pieces together for a certain period of time before these can be used or sold
to
customers. In a typical sawmill, once the wood has been cut to a specific
length,
the (umber pieces are put in a dryer. However, since not all lumber pieces
have
the same humidity level, some may be over-dried while others may remain too
humid. Consequently, the quality of the lumber pieces becomes inferior as they
are prone to twist, split or rot. One solution to this problem has been to
sort or
classify the lumber pieces according to their humidity level before the drying
operation. An hygrometer is used to determine the humidity of each piece of
wood.
However, such classification does not yield satisfactory results because the
measurement of humidity before the drying operation is not necessarily
correlated
with its drying time. For example, pieces of wood of different species may
require
different drying times even though their initial humidity levels are
identical.
As seen above, there is a need to determine the dryiing time of a piece of
wood in
a simple and effective manner, which would lead to .a more efficient sorting
of the
lumber pieces before the drying step.
Known in the art, Canadian Patent No. 1,32f,908 (BEAUCHEMIN et al.) provides
a method and an apparatus for detecting the humidity in cut lumber before
sorting
and drying the same. However, the apparatus uses weight sensors that are
inadequate for precisely measuring the humidity level in the lumber pieces.
Indeed, tests have shown that the weight of a piece of wood is not necessarily
related to its humidity level. Furthermore, as mentioned above the
determination of
CA 02359698 2001-10-17
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the humidity level in a piece of wood is not necessarily an indication of its
drying
time.
Also known in the art, Canadian Patent Application 2,270,274 (LEGER et al.)
describes a method and an apparatus for facilitating the separation of lumber
pieces that are of different species. The lumber piecE;s are coated with an
indicator
liquid and are optically scanned to identify their species prior to drying.
The
process is inefficient as it does not determine the drying time of a piece of
wood
and additionally requires the marking of each piece at an earlier step..
Also known in the art are US patents: 5,486,815 (WAGNER); 5,406,378 (JAMROZ
et al.); 5,307,679 (ROSS); 5,317,274 (NAKA.GAWA et al.); 4,876,889
(SHAKKOTTAI et al.); 4,683,418 (WAGNER et al.); 4,377,783 (WAGNER);
4,123,702 (KINANEN et al.); 4,059,988 (SHAW); 3,811,087 (SCHMELZER), which
show various devices for measuring humidity of diffE~rent materials or
determining
a species of a piece of wood, but are all unable to dletermine the drying time
of a
piece of wood in a simple and effective manner.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a~ simpler and more effective
apparatus and method for determining the drying time of a piece of wood and
which does not suffer from the drawbacks of the prior art.
Another object of the invention is to provide a method and an apparatus for
determining the drying time of a lumber piece, which is reliable and adapted
to
large scale sawmills, and can be used in a fully automated implementation.
According to the present invention, there is provided an apparatus for
determining
a drying time of a piece of wood, comprising:
a conveyor adapted to transport the piece of wood along a travelling path;
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a probe mounted aside the travelling path, the probe having first and
second electrodes extending next to one another arnd having spiked ends
directed
toward the travelling path for insertion into the piece of wood when the piece
of
wood transported by the conveyor passes by the probe, the second electrode
having an input for receiving electric power, the first electrode having an
output for
transmission of a current signal having passed through the piece of wood from
the
second electrode to the first electrode;
driving means for selectively driving the probe toward and away from the
piece of wood between a measuring position where the spiked ends of the
electrodes are stuck in the piece of wood and a retracted position where the
spiked ends of the electrodes are withdrawn from the piece of wood;
a control means connected to the driving means, for controlling operation
thereof; and
a measuring means coupled to the outputs of the electrodes, for measuring
the current signal, and determining the drying time of the piece of wood based
on
the current signal.
According to another aspect of the present invention, there is provided a
method
for determining a drying time of a piece of wood, uaing a probe having first
and
second electrodes extending next to one another and having spiked ends in a
same direction, comprising the steps of:
transporting the piece of wood along a travelling path;
driving the probe against the piece of wood into a measuring position where
the spiked ends of the electrodes are stuck in the piece of wood;
applying electric power on the second electrode while the spiked ends of
the electrodes are in the measuring position;
measuring a current signal passing through the piece of wood from the
second electrode to the first electrode;
removing the probe from the piece of wood into a retracted position where
the spiked ends of the electrodes are withdrawn from the piece of wood when
the
current signal has been measured; and
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determining the drying time of the piece of wood based on the current
signal.
According to yet another aspect of the present invention, there is provided an
apparatus for determining a drying time of a piece of wood, comprising:
a 'probe having first and second electrodes extending next to one another
and having spiked ends directed in a same direction for insertion into the
piece of
wood, the second electrode having an input for receiving electric power, the
first
electrode having an output for transmission of a current signal having passed
through the piece of wood from the second electrode to the first electrode;
and
a measuring means coupled to the output of the first electrode, for
measuring the current signal, and determining the drying time of the piece of
wood
based on the current signal.
According to still another aspect of the present invention, there is provided
a
method for determining a drying time of a piece of wood, using a probe having
first
and second electrodes extending next to one another and having spiked ends in
a
same direction, comprising the steps of:
driving the probe against the piece of wood ini:o a measuring position where
the spiked ends of the electrodes are stuck in the piece of wood;
applying electric power on the second electrode while the spiked ends of
the electrodes are in the measuring position;
measuring a current signal passing through the piece of wood from the
second electrode to the first electrode;
removing the probe from the piece of wood when the current signal has
been measured; and
determining the drying time of the piece of wood based on the current
signal.
The invention as well as its numerous advantages will be better understood by
reading of the following non restrictive description of preferred embodiments
made
in reference to the appended drawings.
CA 02359698 2001-10-17
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic block diagram of an apparatus. for determining a drying
time
5 of a piece of wood, according to the present invention.
Fig. 2 is a perspective view of an apparatus for trainsporting pieces of wood
and
determining their drying time, according to the present invention.
Fig. 3 is a perspective view of mechanisms for moving probes vertically and
longitudinally according to the present invention.
Fig. 4 is a perspective view of a guide frame for longitudinal motion of the
probes,
according to the present invention.
Fig. 5 is a perspective view of a base for vertical motion of the probes,
according
to the present invention.
Fig. 6, 7 and 8 are a perspective view, a side view and a top view
respectively of
jaw arrangements moving the probes relative to passing pieces of wood,
according to the present invention.
Fig. 9, 10 and 11 are a perspective view, a side view and a top view
respectively
of a probe according to the present invention.
Fig. 12 is a schematic block diagram of control circuits of the apparatus,
according
to the present invention.
DESCRIPTION OF PREFERRED ENIBODIMENTS
Referring to Fig. 2, there is shown an apparatus for determining the drying
time of
a piece of wood 3, such as fir and spruce or other species, according to the
present invention. The apparatus comprises a conveyor 5 adapted to transport
the
piece of wood 3 along a travelling path in the direction depicted by arrow 7.
The
conveyor 5 may be a conventional conveyor used in sawmills for transporting
pieces of wood after these have been cut to a specific; length.
The apparatus also comprises a probe 9 mounted aside the travelling path 7
along
which path the piece of wood 3 is transported. As bf~st seen in Figs. 9 to 11,
the
probe 9 has first and second electrodes 11, 13 and <~n optional third
electrode 15
CA 02359698 2001-10-17
extending next to one another and having spiked ends 17, 19, 21 directed
toward
the travelling path for insertion into the piece of wood 3 transported by the
conveyor 5 when it passes by the probe 9. The second electrode 13 has an input
23 for receiving electric power. The first and third Electrodes 11, 15 are
spaced
from the second electrode 13 in opposite directions and have outputs 25, 27
for
transmission of current signals having passed through the piece of wood 3 from
the second electrode 13 to the first and third electrodes 11, 15 respectively.
The
first and third electrodes 11, 15 may have different dimensions. The third
electrode
is optional as it is provided for redundancy purposes and to determine the
10 homogeneity of the piece of wood as will be described below.
For example, in use, if one of the spiked ends '17, 21 of the first and third
electrodes 11, 15 is inadvertently inserted into a knot in the piece of wood
3, then
this would probably yield an erroneous measurement which would not be close to
15 the one measured by the other electrode. This exi:raneous measurement could
then be discarded by an appropriate filter or in a software program that
analyses
the results.
Also, by using the three electrodes 11, 13, 15, experimental tests performed
by the
applicant have demonstrated that in addition of detE;rmining the drying time,
one
can determine the homogeneity of the piece of wood 3. Indeed, if the piece of
wood 3 is homogeneous, then the measured current signals are substantially
identical for each of the first and third electrodes 11, 15, whereas if the
piece of
wood 3 is heterogeneous, then the measured current signal are different for
each
of the first and third electrodes 11, 15.
Preferably, the spiked end 17 of the first electrode 11 is shorter than the
spiked
end 21 of the third electrode 15. The spiked end 17 of the first electrode is,
in this
example, 3116 inches (0.476 cm) long, whereas the spiked ends 19, 21 of the
second and third electrodes 13, 15 measures 7/16 inches (1.111 cm) long.
However, all the spiked ends 17, 19, 21 may be of the same length. Also, it is
CA 02359698 2001-10-17
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preferable that the electrodes 11, 13, 15 be aligned with and equally spaced
apart
from one another.
Preferably, the electrodes 11, 13, 15 are made of special steel which is
highly
wear resistant and sufficiently rigid. The electrodes 11, 13, 15 can be
mounted on
an electrode assembly 10 designed for easy replacement of any electrode.
Referring back to Fig. 2, the apparatus also comprises a driving mechanism 29
for
selectively driving the probe 9 toward and away from the piece of wood 3
between
a measuring position where the spiked ends 17, 19~, 21 of the electrodes 11,
13,
are stuck in the piece of wood 3, and a retracted position where the spiked
ends 17, 19, 21 of the electrodes 11, 13, 15 are withdrawn from the piece of
wood
3.
15 Referring to Fig. 1, the apparatus also comprises a control circuit 31
connected to
the driving mechanism 29, for controlling its operation. The control circuit
31 can
be conveniently embodied by a control module in a microprocessor unit 33. A
measuring circuit 35 coupled to the outputs 25, 27 of the electrodes 11, 15 is
provided for measuring the current signals having passed through the piece of
wood 3. The measuring circuit 35, which can be conveniently embodied by a
measuring module in the microprocessor unit 33, determines the drying time of
the
piece of wood 3 based on the current signals.
The measuring circuit 35 that was used in the experiments is a microcomputer
made by the company MOELLER. It receives the current signals and has an
analog to digital converter and microprocessor for computing digital values
corresponding to the measured current signals. The microcomputer can be
programmed to convert these digital values into resistance values. The exact
resistance that corresponds to each digital value is determined by measuring
the
digital values of different nominal resistances with the electrodes 11, 13,
15. The
results are then tabulated and can be integrated in the programming of the
microcomputer or measuring circuit 35 that was mentioned above.
CA 02359698 2001-10-17
In operation, the apparatus of the present invention can provide a drying time
for
each piece of wood that is probed by the electrodes as the measured current
signals are processed by the microcomputer or me<~suring circuit 35. This
drying
time may be displayed by the microcomputer or can be transmitted to another
machine that sorts the pieces of wood according to the drying time data.
The measuring circuit 35 can also determine the homogeneity level of the piece
of
wood 3 based on a difference between the current signals. If a significant
difference between the electrodes is detected by the measuring circuit, then
the
piece of wood is determined to be less homogeneous.
In the embodiment described above, only one probe 9 is needed to take the
current signal measurements. However, if the piece of wood 3 is travelling on
the
conveyor 5 and if the apparatus is not provided with a mechanism for moving
the
probe along the conveyor, it may be necessary to stop or slow down the
conveyor
5 so that the spiked ends 17, 19, 21 of the probe 9 can be inserted and
removed
from the piece of wood 3 without damaging the probe 9. The probe 9 is
preferably
made of a strong material providing high electric insulation resistance
between the
electrodes 11, 13, 15 and the electrode assembly 1 (). The microprocessor unit
33
may be also connected to a master system 36 that controls other mechanisms or
parts in the sawmill.
Preferably, and as best shown in Fig. 9, the probe 9 comprises at least one
set of
first, second and third additional electrodes 11', 11 ", 13', 13", 15', 15"
projecting
on sides of and being connected with the first, second and third electrodes
11, 13,
15 respectively. The additional electrodes 11', 11 ", 13', 13", 15', 15" have
substantially identical shapes to the electrodes connected therewith. These
additional electrodes are useful for improving the reliability of the current
measurements in the event that some of the electrodes run into knots in the
wood,
holes, or rotten parts, which would lead to erroneous measurements.
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Referring to Figs. 2 and 3, the apparatus preferably includes a probe moving
mechanism 37 mounted on a side of the conveyor 5.. As will it be further
described
herein below, at least a portion of the probe movinc,~ mechanism 37 supports
the
driving mechanism 29. The probe moving mechanism 37 moves the probe 9
upstream along the conveyor 5 towards a subsequent piece of wood 39 travelling
on the travelling path once the current signals passing through the piece of
wood 3
have been measured by the measuring circuit 35.
The probe moving mechanism 37 may consist of a guide frame 41 mounted on the
side of the conveyor 5. The guide frame 41, which is best shown on Fig. 4, has
an
arrangement of two parallel slides 43 receiving and guiding the driving
mechanism
29 along the conveyor 5. A chain assembly 45 has a chain element 47 running
around two spaced apart sprocket wheels 49, 50 mounted on the side of the
conveyor 5 at a given distance from the guide frame 41. The chain assembly 45
can be driven by the conveyor 5 by coupling the sprocket wheel 49 to a turning
shaft 52 of the conveyor 5 through a gearing assembly 54. A rod 51 extends
between the guide frame 41 and the chain assembly 45. The rod 51 has an end
pivotally connected to a link 55 of the chain element 47 and an opposite end
5T
pivotally connected to the driving mechanism 29.
In operation, the probe moving mechanism 37 acts as a piston that moves the
probe 9 back and forth linearly along the conveyor 5, and at the speed of the
conveyor 5.
As best shown in Fig. 5, the driving mechanism 29 may be made of a base 59
slidably mounted in the arrangement of two parallel slides 43 of the guide
frame
41. The back of the base 59 has a linear bearing engaging with the parallel
slides
43 of the guide frame 41. The opposite end.57 of the rod 51 (see Fig. 3) can
be
pivotally attached to the base 59. The base 59 has an arrangement of two
parallel
slides 81 extending substantially crosswise to the arrangement of two parallel
slides 43 of the guide frame 41.
CA 02359698 2001-10-17
Referring back to Figs. 2 and 3, a bracket 63 extends over the conveyor 5. The
bracket 63 supports the probe 9 and forms part of the driving mechanism 29.
The
bracket 63 is slidably mounted in the arrangement of two parallel slides 61 of
the
base 59, and can slide toward and away from the conveyor 5. As best shown in
5 Fig. 8, the back of the bracket 63 has a linear tearing 66 engaging with the
parallel slides 61 of the base 59. An actuator 65 is further mounted onto the
base
59 and has an end 67 connected to the bracket 63. The actuator 65 can push or
pull the bracket 63 toward and away the conveyor 5 in response to control
signals
sent by the control circuit 31.
The actuator 65 may consist of a pneumatic piston wvith both a pressure
regulator
and a pneumatic electric valve. The actuator 65 m;ay also consist of a
hydraulic
piston or other suitable actuating device.
Preferably, a detector 69 (see Fig. 1 ) is mounted in front of the probe 9 and
is
connected to the control circuit 31. The detector 69 generates a detection
signal
when the piece of wood 3 approaches the probe 9. The detector 69 may be
formed of a photocell 69 directed across the travelling path 7 upstream of the
probe 9.
An additional probe 9' can be mounted aside the travelling path, with both
probes
9, 9' being identical and facing each other in a closable jaw arrangement 71
(see
Fig. 3) for biting the piece of wood 3 by action of the driving mechanism 29.
In operation, when a current is sent to the actuator 65, the jaw arrangement
71
closes, whereas it opens when there is no current se~~t to the actuator 65.
An additional jaw arrangement 71' with facing probes 9", 9"' as in the other
jaw
arrangement 71 may be provided to process two pieces of wood at a time. Both
jaw arrangements 71, 71' operate identically and in unison. The jaw
arrangements
71, 71' are spaced from each other along the conveyor 5 so that the piece of
wood
3 and a successive piece of wood 73 are processed simultaneously.
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Because the pieces of wood travel on the conveyor at a relatively high speed,
the
measurements must be made quickly enough, e.g. about 150 pieces per minute.
Therefore it is more efficient to use the above pair of jaw arrangements 71,
71' as
two pieces of wood are bitten simultaneously. This configuration has the
advantage of avoiding abrupt movements and undesirable vibrations.
Referring to Fig. 12, there is shown a schematic circuit diagram of the
electrodes
11, 11', 13, 13', 15, 15' being inserted in a piece of wood 3 as the second
electrodes 13, 13' are powered with a 10 volts D.C. source. The spiked ends
17,
21 of the first and third electrodes 11, 15 measure 3/16 inches (0.476 cm) and
7116 inches (1.111 cm) long respectively.
The drying time of a piece of wood is defined in the lumber industry as the
time
that it takes a piece of wood to attain a humidity level that is below 19%. As
will be
shown in the experimental results below, the drying time is correlated with
the
resistance measured by the measuring circuit.
In an experiment, the applicant has noted some measurements reported in the
following table:
Wood Resistance measured Resistance measured Approximat
species between the first between the third a drying
and the and the time hours
second electrodes second electrodes
kohms kohms
Fir 375 375 220
Fir 200 200 262
Fir 150 150 340
Fir 40 40 400
Fir 10 -1 800
Spruce 1 f 5 290 260
Spruce 75 130 240
Spruce 55 95 700
~
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Further and more recent tests done by the applicant have been reported in the
following tables:
Wood Resistance measured Humidity level measured
species between the first and after 222 hours (%)
the
second electrodes kohms
Spruce 120 16
Spruce 118 14
-.-
Spruce 84 15
Spruce 79 16
Spruce 79 15
Spruce 79 16
Spruce 74 15
Spruce 73 17
Spruce 72 18
Spruce 56 18
Spruce 44 19
Spruce 43 18
Fir 42 17
Spruce 42 18
Wood Resistance measured Humidity level measured
species between the first and after 288 hours (%)
the
second electrodes kohms
Spruce 38 13
Spruce 38 13
Spruce 38 15
Spruce 38 14
Spruce 37 15
Spruce 35 - 15
Fir 35 20
Fir 26 15
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Wood Resistance measured Humidity level measured
species between the first and after 288 hours
the (%)
second electrodes kohms
Fir 25 15
Fir 25 15
Fir 23 15
Fir 23 17
Fir 22 -- 18
Wood Resistance measured Humidify level measured
species between the first and after 362 (hours
the {%)
second electrodes kohms
Fir 22 16
Spruce 21 17
Fir 21 16
Fir 20 20
Fir 10 21
Fir 5 _ 25
Fir 5 31
Fir 5 33
Fir 5 34
Fir 5 39
Fir 5 35
Fir 5 49
Fir 5 41
Fir 5 43
The tests where performed. by drying several wood pieces with a fan. The wood
pieces were put outdoors and covered with a plastic so that rain water did not
affect the results. Of course, the ambient humidity level could not be
controlled
and neither was the temperature, which ranged between 25 to 5 degrees Celsius.
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The humidity level was measured by means of a hygrometer made by the
company DELMHORST.
As can be appreciated, these tests tend to show th<~t certain ranges of
measured
resistance yield acceptable drying levels (below 19°/0) after a
predetermined drying
time. For example, measured values of 120 to 42 kohms give a drying time of
222
hours, measured values of 38 to 23 kohms give a drying time of 288 hours,
while
measured values under 22 kohms may yield drying times of longer than 288
hours.
Accordingly, an empirical relationship can be established between the measured
current signals and the drying time of a piece of wood. This empirical
relationship
may be obtained as shown above by tabulating the; measurement results of the
current signals or the corresponding resistance values measured by the
electrodes, and the humidity level measured after .a predetermined drying
time.
This empirical relationship will of course vary depending on the particular
drying
conditions. For example, the empirical relationship will be modified if a more
or
less powerful dryer is used. Other factors affecting the empirical
relationship
depend on whether the drying occurs indoors or outdoors, or if the ambient
humidity and temperature can be controlled or not. Once the empirical
relationship
is established, it can be entered in the program of the microcomputer or
measuring
circuit 35.
Similarly as for the determination of a drying time, an empirical relationship
can be
established for the homogeneity of the pieces of wood. The empirical results
can
be entered into the program of the microcomputer or measuring circuit 35. The
homogeneity level data can be used similarly as above for sorting the pieces
of
wood in combination with the drying times. This hornogeneity level may also be
displayed by the microcomputer or can be transmittE~d to a sorting machine
that
can use the homogeneity data.
CA 02359698 2001-10-17
It should also be noted that the probe 9 may also be used without the conveyor
5
in certain circumstances. Accordingly, the probe 9 can be manually operated by
a
user who inserts the spiked ends of the probe 9 into the piece of wood to take
the
measurements. It goes without saying that such a technique is very time
5 consuming if several pieces of wood are to be inspected. However, the use of
the
probe 9 without the conveyor 5 can be useful, for example, when making tests
on
a limited number of wood pieces. The apparatus would then consist of only the
probe 9 and the measuring circuit 35, both of which being described above.
10 Also, instead of having all the electrodes in an aligned configuration,
other
arrangements of electrodes may possibly be suit<~ble, as long as the current
signals flowing from the second electrode to the first and third electrodes do
not
interfere with each other. For example, a triangular electrode configuration
may be
used.
Although preferred embodiments of the present invention have been described in
detail herein and illustrated in the accompanying drawings, it is to be
understood
that the invention is not limited to these precise embodiments and that
various
changes and modifications may be effected therein without departing from the
scope or spirit of the present invention.
