Note: Descriptions are shown in the official language in which they were submitted.
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1lIETHOD AND APPARATUS FOR ON-LINE MONITORING OF LOG SAWING
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for the detection of localized
anomalies or other localized features in wood, such as knots, splits, voids,
checks. and
localized decay for the purpose of grading or cutting wood products such as
lumber, and
specifically to an apparatus employing ultrasonic energy to characterize both
dried and
undried wooden members. The wooden members may be trees, logs, beams, planks,
lumber, boards or wood composites and the like.
Ultrasound has been used to characterize the gross properties of wooden
members
through measurement of time of flight, attenuation, and attenuation as a
function of
frequency (broadband ultrasonic attenuation) of ultrasound passing through a
wooden
member. For example, U.S. Patent 5,307,679 to Ross and assigned to the United
States of
America, describes the use of ultrasonic measurements to detect a proclivity
of a wooden
members to degrade during the drying process. Another example includes
identifying
naturally occutring defects to aid in lumber grading for both structural and
non-structural
applications.
The Problem of Localized Defects
It is also desirable to detect, identify and locate smaller anomalies in
wooden
members such as knots, checks and splits. Such defects, when identified, can
be input to
commercially available optimization systems to allow for the sorting or
cutting of the
wooden members in a way so as to maximize their value, for example, by cutting
a log to
produce the maximum number of board feet of clear or higher grade lumber.
Traditionally identification of defects and other features affecting lumber
grade has
been performed visually, for example, by a saw operator visually inspecting
the log or
board prior to determining the necessary cross or rip cuts that will yield the
best product
output or yield. Recently a number of electronic scanning systems have been
produced
using cameras and lasers to automate this visual process. Such optical
techniques are
limited to the detection of superficial defects in the wooden members and even
these
techniques may be defeated by dirt, bark, stain or other markings on the
outside of the
log. More importantly, intemal defects are generally not visible externally,
yet may affect
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product performance or value.
What is needed is an apparatus for detecting and identifying localized
anomalies
even intemal to a wooden member, that is also robust against the harsh
environment of a
typical lumber operation or the like and that is safer, less costly and more
compact than
instruments based on x-rays or other electromagnetic radiation, or which
provide
information which those svstems have difficulty in detecting such as splits
and checks.
The Problem of Splits
When logs are sawn to size in the field using commercial harvesters, they are
often
subject to the creation of splits when cut. This is because one end of the log
is
unsupported during the cutting operation. Splits also occur when the tree is
initially
felled. The splits are undesirable, introduce defects in the lumber that is
sawn from the
logs, and thereby reduce the value of the log itself. A recent examination of
the problem
indicates that up to 70% of logs harvested in this manner contain splits. If
the problem is
detected in the field at the time of sawing, then either the operator can
modify his/her
practice to reduce this incidence, or the logs can be cut longer such that
sufficient material
will remain free of defects. In other words, if a 12 foot long clear log is
desired, and the
harvester detects end splits for a distance of 12 inches, then the next cut
will be made so
as to have the required 12 feet after the defective portion is removed.
Traditionally identification of defects and other features affecting lumber
grade has
been performed visually, for example, by a saw operator visually inspecting
the log or
board prior to determining the necessary cross or rip cuts that will yield the
best product
output or yield. Recently a number of electronic scanning systems have been
produced
using cameras and lasers to automate this visual process. Such optical
techniques are
limited to the detection of superficial defects in the wooden members and even
these
techniques may be defeated by dirt, bark, stain or other marlcings on the
outside of the
log. More importantly, internal defects such as splits are generally not
visible.
What is needed is an apparatus for detecting and characterizing splits
internal to a
wooden member, that is also robust against the harsh environment of a typical
lumber
operation or the like and that is safer, less costly and more compact than
instnunents
based on x-rays or other electromagnetic radiation.
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BRIEF SLTNIlViARY OF THE INVENTION
Detecting Localized Anomalies
The present inventors have discovered that localized defects such as knots,
checks
and splits or other features such as slope of grain may be detected by a
distortion of an
ultrasonic beam when a part of the beam passing through the localized defect
interferes
with a part of the beam passing through clear or sound wood in either the
dried and
undried states. This distortion may be detected by measurement of waveform
spreading,
decorrelation techniques or other similar techniques. If the defect or
condition is of
broader extent than the ultrasound beam, then the defect or condition may be
detected by
comparison of the signals made in clear portions of the wooden member, in
regions where
the ultrasound beam is completely intercepted by the defect or condition, and
in regions at
the edge of the defect or condition wherein the ultrasound beam passes through
both the
condition or defect and clear or sound wood. Multiple transducers and
receivers providing
additional beams coupled to the wooden member and moving relative to it allow
both
detection and more accurate localization of localized anomalies or other
features.
Specifically, the present invention provides an apparatus for detecting
localized
defects in wooden members and includes at least one pair of opposed ultrasonic
transducers positionable about the wooden member so that an axis between the
transducers is oriented substantially perpendicular to the grain of the wooden
member.
Electronic driving circuitry drives one of the ultrasonic transducers so as to
produce an
ultrasonic wave of known characteristics having a beam width through the
wooden
member. A detection circuit connected to the output of another of the
ultrasonic
transducers receives the ultrasonic wave after passage through the wooden
member along
either singular or multiple paths in the beam width. An electronic computer
communicating with the driving and detecting circuits executes a stored
program to
compare the received ultrasonic wave against a standard to detect a distortion
in the
waveform caused by variation in the wooden member within the region defmed by
the
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ultasound beam width. Based on a detection of this distortion, the computer
provides an
output indicating the presence of localized defects or other conditions. The
waveform
pattem can also be used to identify the condition which caused the waveform
distortion,
and to localize that condition as the transducers are moved relative to the
wooden
member.
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Thus, it is one object of the invention to provide an ultrasonic apparatus for
detecting localized conditions within a wooden member useful for
characterizing the
member for sawing or grading.
The comparison performed by the apparatus may address the attenuation of total
energy in the received ultrasonic wave, the change in spectral energy
distribution in the
received ultrasonic wave, the spreading of the temporal distribution of energy
in the
received ultrasonic wave, phase distortion in the received ultrasonic wave or
a
combination of the above.
Thus it is another object of the invention to provide for a multiparameter
measurement so as to improve the accuracy and robustness of the ultrasonic
measurements.
The apparatus may use multiple ultrasonic transducers whose outputs may be
collected or the measurements may be repeated with a single pair of ultrasonic
transducers.
Thus it is another object of the invention to employ multiple transducer
measurements so as to improve the accuracy and robustness of the detecticsn
process.
The apparatus may include a means for measuring the thickness of the wooden
members along the axis and may calculate a time of flight of the ultrasonic
wave between
transducers to determine a sound velocity, or may determine a change in energy
or phase
as a function of thickness.
Thus it is another object of the invention to account for other factors
affecting the
received ultrasonic waveform so as to improve the apparatuses ability to
detect localized
defects or other features within wooden members of varying thickness and type.
The apparatus may include a means for moving the wooden members with respect
to the ultrasonic transducers perpendicular to the axis of the transducers and
the output of
the electronic computer may be a measure of wooden members' quality as a
function of
position.
Thus it is another object of the invention to locate anomalies along the
length of a
wooden member for the purpose of guiding a cutting of the wooden member to
optimize
its usage.
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AMENDED SM
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Split Detection
The present inventors have discovered that splits create an acoustic
discontinuity
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that may be detected by ultrasonic signal transmitted through the wooden
member across
the grain and a number of different angles and comparing the received
waveforms. Even
after the splits have closed and are no longer visible, they create an
acoustic discontinuity
that may be detected. Detection of the splits may be used to control the
operation of a
saw to change cut locations or modify the sawing technique.
Specifically, the present invention provides an apparatus for detecting splits
in
wooden members using at least one pair of opposed ultrasonic transducers
positioned to
contact the wooden members on opposed points along an axis across a grain of
the
wooden member. Driving circuitry drives one of the ultrasonic transducers so
as to
1 o produce an ultrasonic wave of known characteristics and detection
circuitry connected to
an other of the ultrasonic transducers receives the ultrasonic wave after
passage through
the wooden member to provide a measurement. A scanning means repeats the
wooden
member measurement along axes at a plurality of angles about the wooden member
across
the grain of the wooden members and an electronic computer communicating with
the
driving and detection circuits and the scanning means and executes a stored
program to
compare the wooden member measurements at the plurality of angles to detect a
split in
the wooden member indicated by variation in the measurements.
Thus it is one object of the invention to provide a simple and inexpensive of
detecting splits in wooden members.
The scanning means may be multiple pairs of ultrasonic transducers each
positioned to transmit and receive an ultrasonic wave along a different of the
angles or
may use a movable carriage holding at least one pair of ultrasonic transducers
and
movable about the wooden member to position the ultrasonic transducers at the
plurality
of angles.
Thus it is another object of the invention to permit flexibility in selecting
between
an electrical scanning employing multiple transducers or a mechanically
scanning
employing a single or limited number of pairs of transducers.
The comparison performed by the apparatus may address the attenuation of total
energy in the received ultrasonic wave, the change in spectral energy
distribution in the
received ultrasonic wave, the spreading of the temporal distribution of energy
in the
received ultrasonic wave, phase distortion in the received ultrasonic wave or
combinations of the above.
5
r~~flf'~'~TT=Tr P.rr,~re. Tt~ r. .~ i.
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Thus it is another object of the invention to provide for a multiparameter
measurement so as to improve the accuracy and robustness of the ultrasonic
measurements.
The apparatus may include a means for measuring the thickness of the wooden
members along the axis and may calculate a time of flight of the ultrasonic
wave between
transducers to determine a sound velocity, or may determine a change in energy
or phase
as a function of thickness.
Thus it is another object of the invention to account for other factors
affecting the
received ultrasonic waveform so as to improve the apparatuses ability to
detect localized
1 o defects or other features within wooden members of varying thickness and
type.
The apparatus may include a means for moving the wooden members with respect
to the ultrasonic transducers perpendicular to the axis of the transducers and
the output of
the electronic computer may be a measure of wooden members' quality as a
function of
position.
Thus it is another object of the invention to determine the length of splits
for the
purpose of guiding a cutting of the wooden member to optimize its usage.
The foregoing and other objects and advantages of the invention will appear
from
the following description. In the description, reference is made to the
accompanying
drawings which form a part hereof and in which there is shown by way of
illustration a
2 0 preferred embodiment of the invention. Such embodiment does not necessary
represent
the full scope of the invention, however, and reference must be made to the
claims herein
for interpreting the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view in partial cutaway of a wooden member as may be
moved in a translation direction with respect to opposed ultrasonic
transducers
incorporated into wheels and pressed against the opposed sides of the wooden
member,
Fig. 1 further showing other sensing devices for characterizing the wooden
members'
shape and position;
Fig. 2 is a block diagram showing the transducers and wooden member of Fig. 1
together with associated processing circuitry for generating and receiving
ultrasonic
signals and processing the same including an electronic computer having a
standard
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computer monitor and keyboard;
Fig. 3 is a schematic representation of a processing program executed by the
computer of Fig. 2 receiving an ultrasonic waveform through the wooden member
and
comparing it to a transmitted ultrasonic waveform passing through a standard
material to
produce multiple measurement parameters which may be combined to detect
localized
anomalies;
Fig. 4 is a graph of two such parameters , specifically pulse length and
insertion-
loss (defined below), plotted against distance along the transiation axis
showing the
position of local anomalies evident by examination of these two parameters;
Fig. 5 is an alternative embodiment of the transducer assembly of Fig. I
showing
multiple transducers positioned in an array along an x-axis across the grain
of the wooden
member to provide improved localization of the internal anomalies of the
wooden
-
members;
Fig. 6 shows a plan view in cross section of the wooden member and transducers
of
Fig. 1;
Fig. 7 is a figure similar to that of Fig. 3 showing the multiparametric
measurement
of Fig. 3 applied to the additional dimension of x or z (the translation axis)
in the
embodiments of Figs. 5 and 6 to provide a more robust measurement of localized
anomalies;
Fig. 8 is a figure similar to Fig. 5 showing transducers arrayed radially
around the
circumference of the wooden member such as may be useful for the detection of
internal
splits or checks;
Fig. 9 is a block diagram similar to that of Fig. 3 showing the repetition of
the
element of Fig. 3 for each of the transducers of Fig. 8 and collected by a
parameter
extraction block identifying an orientation of a split;
Fig. 10 is a figure similar to that of Fig. 8 showing the use of the
transducer
assembly of Fig. 8 for tomographic analysis of the intemal structure of the
wooden
member,
Fig. 11 is a fragmentary view of Fig. 9 showing a tomographic back projection
block used to replace the parameter extraction block of Fig. 9 when the
assembly of Fig. 8
is used for tomographic analysis;
Fig. 12 is a figure similar to that of Figs. 8 and 10 showing the wooden
member in
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cross section along the x-y plane with a single pair of transducers positioned
for the
_detection of dynamic splits caused by a sawing operation;
Fig. 13 is a view of the wooden member of Fig. 12 along the x-z plane showing
a
development of a dynamic split with respect to the transducers of Fig. 12
during the
cutting operation caused by the cantilevered weight of the end of the wooden
member;
Fig. 14 is a schematic representation of a computer controlled cutoff saw
suitable
for cutting wooden members as characterized by the present invention so as to
optimize
usage of wooden members based on the location of identified anomalies;
Fig. 15 is a cross sectional view of a transducer of Fig. 1 having a spiked
outer
collar for penetration of bark and or for better coupling with the wooden
member;
Fig. 16 is a view similar to that of Fig. 5 showing transducers positioned
along both
the x and y axes about a board;
Fig. 17 is a graph of signal voltage vs. time for a representative waveform of
Fig. 3
passing through the standard material;
Fig. 18 is a graph of signal voltage vs. time for a representative waveform of
Fig.
3 passing through the wooden member being evaluated;
Fig. 19 is a view similar to Fig. 13 showing an alternative embodiment of the
transducers using spiked transducers and a plunge translate and retract
mechanism; and
Fig. 20 is a figure similar to that of Fig. 12 showing mounting of wheeled
transducers for rotational position about the wood.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to Fig. 1, a wooden member 10 such as a log is shown positioned
horizontally so that its grain direction and axis define a z-axis of a
Cartesian coordinate
system with the x-axis directed generally upward and the y-axis horizontal. As
will be
understood from the following description, the term wooden member should be
held to
embrace trees, logs, lumber, boards and wood composites in various stages of
processing.
The wooden member 10 may be moved in a translation direction 12 with respect
to
a measurement assembly 14 by one or more driven rollers 26 that support the
wooden
member 10 from underneath. In some instances (not shown here), the wooden
member
may be rotated.
The measurement assembly 14 includes a first (transmitting) and second
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CTTRQTTTTTTF CNFFT (RTTT r 16\
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(receiving) ultrasonic transducer 16 encased in rollers such as may roll
against the surface
of the wooden member 10 as it moves in the translation direction 12. The
ultrasonic
transducers 16 are opposed along the y-axis to transmit and receive an
ultrasonic signal
through the wooden member 10 radially and perpendicular to the grain, and are
attached
to slide assemblies 18 (only one shown) which are biased toward the wooden
member 10
by an air cylinder 20 or the like. The wheels of the transducers 16 thereby
maintain
contact with the outer surface of the wooden member 10 while being free to
rotate about
their axes.
A linear position sensor 22 may be attached to the slide assembly 18 so as to
provide a measurement of the separation of the transducers 16 and hence a
measurement
of the width of the wooden member 10 along the axis between the transducers
16. An
encoder/roller assembly 24 positioned against the outer surface of the wooden
member 10
provide a measurement of the z-axis position of the wooden member 10 as it
moves in the
translation direction 12. Auxiliary sensors, such as photoelectric proximity
sensors 28,
may be positioned separated along the z-axis and directed downward along the x-
axis to
detect the beginning and end of the wooden member 10 as it moves, and thus to
provide a
measurement of its length. A sensor array 30 having multiple photoelectric
sensors
arrayed along the x-axis may provide a height measurement of the wooden member
10
along the x-axis to further characterize the wooden member 10.
Ultrasonic transducers encased in a wheel and suitable for use in this
application
with regular wooden members such a boards and logs stripped of bark, are
commercially
available from James Instruments of Chicago, IL (Model C-7219) and Dapco
Industries
of Ridgefield, CT. The transducers may be oriented to produce either
longitudinal or
shear waves through the wooden member 10.
2 5 Referring momentarily to Fig. 15, in a preferred embodiment, the
ultrasonic
transducers 16 includes a transducer element 80 held in a coupling fluid such
as oil 82 as
contained by the inner surface of a rotating wheel 86 as is done in the
commercially
available transducers 16 described above. In distinction, however, the outer
surface of the
wheel provides a series of radially extending spikes 84 whose sharpened tips
may embed
themselves in the wooden member to better couple ultrasonic energy into and
out of the
wooden member and to penetrate bark and the like which generally inhibit the
transmission of ultrasonic energy. The sharpened tips of the spikes
concentrate pressure
9
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WO 99/44049 PCT/US99/03919
to provide improved penetration.
Referring now to Fig. 2, the invention operates under the control of a
standard desk
top computer 34 such as a so called "Wintel" computer using the Windows
operating
system and an Intel 133 MHz Pentium processor chip set. Computer 34 includes a
pott
36, a processor 38, and electronic memory 39 of a type familiar to those of
ordinary skill
in the art, all interconnected by an internal bus 40. The port 36 accepts
input digital
signals from devices outside the computer 34 and provides output digital
signals to
devices outside the computer as generated by execution of a stored program as
will be
described. The principal output signal generated is a digitized ultrasonic
pulse waveform,
which is communicated through the port 36 to an amplifier/D to A converter 32.
The
amplifier/D to A converter 32 converts the digitized ultrasonic pulse waveform
to a high
power analog electrical signal that is output to one 'transmitting' ultrasonic
transducer 16
to drive the transmitting ultrasonic transducer 16' to produce a predetermined
broadband
ultrasonic pulse of predetermined phase and frequency content, in the
preferred
2 5 embodiment having a center frequency of substantially 80 kHz. It will be
understood to
those of ordinary skill in the art that other frequencies may also be used.
The port 36 also receives inputs from receiving transducer 16 detecting the
ultrasonic waveform after it has passed through the wooden member 10 as pre-
processed
by a gain-controllable amplifier/A to D converter 42. Gain-controllable
amplifier/A to D
converter 42 preferably provides at least eight-bits of resolution and a
sampling speed of
at least 2.5 times the center frequency of the ultrasonic waveform being
transmitted. The
gain-controllable amplifier/A to D converter 42 provides for amplification
over a fifty dB
range as controlled by the computer 34.
Port 36 also receives inputs from the proximity sensors 28 and 30, the linear
position sensor 22, the encoder/roller assembly 24, and the sensor array 30 so
as to make
their measurements available to the computer 34. A separate port 41 connects
the
computer 34 to the standard computer monitor 44 and keyboard/mouse 47.
During operation of the apparatus of the present invention, the computer 34
executes a stored program held in memory 39 to cause the transmission of the
broadband
ultrasonic pulse from transducer 16' to transducer 16. The computer 34 then
collects and
processes the data from transducer 16 receiving the ultrasound pulse after
transmission
through and modification by the wooden member 10, as well as inputs from the
other
10 --
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sensors to evaluate the wooden member 10. The rate at which the computer
controls the
amplifier/D to A converter 32 to transmit the broadband pulse is determined by
the
desired spatial sampling rate, and the speed of the wooden member 10 as it is
moved into
the translation direction 12. In one embodiment, the computer controls the
amplifier/D to
A converter 32 so as to transmit the broadband pulse thirty-two times per
second
providing a sampling of the wooden member 10 as it is moved in the translation
direction
12, every 0.12 inches, assuming a twenty foot per minute speed of the wooden
member
10.
The effective aperture of the transmitting and receiving ultrasonic
transducers 16'
and 16, and the sound transmission properties of the wooden member 10 define
an
effective beam 48 through the wooden member 10 along which measurements will
be
made. The wooden member 10 may include a localized anomaly 45, such as a knot
or
check, which may or may not significantly affect the overall strength of the
wooden
member 10. In the case shown, the localized anomaly 45 has a size
substantially less than
the width of the beam 48 . Accordingly, it will be expected that a ponion
along path 54
of the beam 48 will miss the localized anomaly entirely, significantly
reducing the
contribution of the localized anomaly 45 on any modification of the beam 48 by
the
wooden member. Thus an interference occurs between the sound of path 54'
traveling
though the anomaly 45 and the sound of path 54 traveling through unaffected
wood.
Alternatively, a narrow beam may be used such as will be substantially
completely
intercepted by the anomaly. Further, for the case in which the wooden member
is a board,
and the ultrasound transducers are disposed on either edge, the anomaly may
encompass
the entire lateral dimension of the wooden member, completely intercepting the
ultrasound beam regardless of the beam width. In either case, signals may be
compared
against a standard signal taken at an earlier or later time of unaffected wood
or derived
from a model of unaffected wood.
Referring now to Fig. 3 and 17, the standard waveform 46 derives from a
digitized
version stored within the memory 39 as ordered pairs of amplitude values (A)
having
distinct times values (t). The standard wavefotm 46 represents a waveform
received
through a standard material without localized anomalies, such as clear wood or
plastic.
The received waveform 50, (shown also in Fig. 18) being an actual measurement
of the
wooden member 10, may be similarly stored in memory 39 as a set of received
amplitude
11
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values (A') at later time values (t) the delay resulting generally from the
transit time in the
passage of the waveform through the wooden member 10.
Referring to Fig. 3 and 6, the two waveforms of the standard waveform 46 and
received waveform 50 are then analyzed according to a number of different
techniques to
produce parameters 52. Specifically, and referring again to Fig. 2, the
present inventors
have recognized that even though the localized anomaly 45 may be relatively
small in
comparison to the total width of the ultrasound beam 48, a portion of the beam
48 passing
along a path 54 through the localized anomaly 45 modifies the remaining ponion
of the
beam 48 passing along a path 54' outside the localized anomaly 45, the
resulting
interference modifying the received waveform 50 in phase and amplitude or
other
characteristics in a manner that may be detected and analyzed. Similarly, the
ultrasound
beam 48 may only pass through a portion of the localized anomaly 45,
irrespective of the
size of the localized anomaly 45, depending upon the orientation of the
ultrasound beam
48, which also results in interference modifying the received waveform 50.
This analysis
involves extracting various parameters 52 from the received waveform 50 each
parameter
52 selected to detect a distortion in the received waveform 50 caused by
interference
between waveforms on different paths 54 and 54'.
A basic parameter is that of the spreading of the received wavefotm 50 with
respect
to the standard waveform 46 caused by variation in the effective path lengths
54 and 54'
(caused both by differences in path length and differences in sound speed)
such as tends
to spread the received waveform 50 in time. Pulse length is defined in the
prefen-ed
embodiment as 1.25 times the time required for the received wave energy
integral to rise
from ten percent to ninety percent of its final value. Wave energy as
understood in the art
is determined by the formula
WE=f v2(t)dt. (1)
where v is the voltage produced by the transducer 16 and t is time. The pulse
length of the received waveform 50 is compared against the pulse length of the
standard
waveform 46 calculated in a similar manner to produce the relevant parameter.
The effect of the localized anomaly 45 may also change the insertion loss
between
the two transducers 16' and 16. This forms a second parameter of the
measurement and is
defined as the ratio of the energy received by the transducer 16' to the
energy input into
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the wooden member 10 by the transducer 16 according to the following formula:
IL(db) =10log[E,IEaG (2)
where Er is the received energy, E, is the transmitted energy and G is the
receiver
gain as may be programmed as described above. Insertion loss may be further
compared
to a reference value taken through a standard of known acoustic properties
such as a clear
wooden members or a standard reference material such as water or homogenous
plastic
block. Insertion loss may be further compared as a function of the distance
that the
ultrasound wave travels through the wooden member (using a width measurement
from
the linear position sensor 22), expressed in Decibels per inch (or decibels
per centimeter).
A third parameter may be the time of flight of the pulse determined by a
correlation
of the standard and received waveforms 46 and 50 such as may provide an
indication of
the overall qualities of the wooden member 10 outside of the localized anomaly
45. This
time of flight value may alternatively be divided by a width measurement from
the linear
position sensor 22 to produce a sound velocity measurement.
A fourth parameter uses a deconvolution of the received waveform 50 by the
standard waveform 46 which may be expressed mathematically as either
FF-l,.i Cross Power(Reference, Unknown)1 (3)
C Power Specvum(Unlanown) J
or .(F1~T'(Unknown)}
F~ IFFT(Reference)) (4)
where FFT and FFT" are the Fourier transform and the inverse Fourier
transform,
respectively, and wherein the Unknown is signal through the wooden member 10
and the
Reference is a signal through a reference standard of known acoustic
properties. This
deconvolution allows the detection of multiple signal paths through the wooden
member
10 whose variation may indicate the presence of a localized anomaly 45 which
creates
effectively a new path through the wooden member 10. Other methods such as
homomorphic filtering known to those of skill in the art may be used for the
same
purpose.
Referring now to Figs. 3 and 4, two or more parameters may be compared over
the
length of the wooden member 10 along the translation direction 12 to detect
localized
13
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anomalies 45. In the example of Fig. 4, peaks in pulse length 52(a) and
troughs in
insertion loss 52(b) correlate to regions 55 in which localized anomalies 45
are found.
Accordingly, an empirically derived rule may be developed bv testing each of
pulse
length 52(a) and 52(b) against a threshold and logically ANDing the test
outcomes
together to produce an output indicating a localized anomaly 45. The rule mav
be
implemented by explicit rules programmed into the computer 34 or may be
performed by
artificial intelligence techniques such as neural networks or fuzzy logic
known in the an.
Such rules are shown by rule application block 55 and may combine two or more
parameters 52.
The benefits of multiple parameter measurement can be further seen in Table I
below for various types of wood conditions.
Table I
Parameter I4ormal Wetwood Knot Honeycomb
Insertion Loss (dB) -50 -70 -66 -78
Pulse Length ( s) 110 235 244 239
Time of Flight 80 90 80 96
Referring now to Fig. 5, an array of ultrasonic transducers 16 and 16' may be
positioned at varying x-axis locations on the side of the wooden member 10
pairs opposed
along different axes both radial and tangential to the wooden member 10 across
the grain
of the wooden member 10 to provide a different parametric reading for each x-
axis
location. These transducer arrays provide additional spatial information about
the
location of a localized anomaly 45 in the x-axis direction. In yet an
alternative
embodiment shown in Fig. 16, transducers 16 mav be placed arrayed along either
or both
of the x and y-axis to locate the localized anomaly 45 with respect to the x
and y-axes.
This embodiment is particularly useful for grading lumber as to strength where
the
location of a knot, as opposed simply to its existence, is important as to its
effect on
strength. Strength grading can be used to determine the location of pieces of
lumber in
the final product, for example a pallet, where stronger pieces of lumber are
used for the
core of the pallet and the weaker pieces of lumber are used for the planking
that serves
merely to provide the pallet surface. In the embodiment of Fig. 16, individual
top
transducers 16 may be excited while readings are taken at all bottom
transducers 16 so as
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to obtain measurements along four simultaneous axes for each excitation and
reading
along sixteen axes for all four top transducers 16. These multiple readings
mav be used to
triangulate the location of the anomaly.
As shown in Fig. 7, the parameter extraction block 51 for any of these
multiple
measurement embodiments of Figs. 6 and 7 will receive a two dimensional array
of
standard waveforms 46-46" and received waveforms 50-50"'. Each corresponding
standard and received waveform 46 and 50 may be compared as described with
respect to
Fig. 3 but in additional cross combinations of the various waveforms may also
be used to
produce new effective particular parameters such as spatial rates of change of
the
1 o parameters in the x or z direction.
As before, these parameters 52 may be provided by rule application block 55 to
produce an output 56 providing an identification of localized anomalies 45 and
further
providing additional spatial location of localized anomalies 45 in the x-axis
or v-axis.
Specifically, the x- and y- axis positions of localized anomalies 45 may be
determined
from the parameters derived from the location of individual transducer pair
satisfying the
rule of rule block 55 in the same way that the z-axis position is determined
as described
with respect to Fig. 4. In this way, a map of the spatial location of
localized anomalies 45
for the entire wooden member 10 may be developed.
Using this map, decisions about length of cuts of the wooden member 10 across
the
z-axis (to remove localized anomalies 45 from boards) may be augmented with
decisions
about rip cuts of the wooden member 10 along the z-axis such as to maximize
the value of
the cut wood by moving localized anomalies 45 among boards.
Referring now to Fig. 8. a set of transducers 16 may be arrayed about the
periphery
of the wooden member 10 so that the plane of the wheels of each transducer 16
includes
the z-axis and extends radially therefrom so as to provide axis 61 between
pairs of
transducers 16 that extend radially through the wooden member 10. This
configuration
may be used to identify splits 60 within the wooden member 10 such as have a
varying
cross section depending on the radial direction along which they are viewed.
Thus such
splits 60 may be localized to lie narrowly along one radial direction while
being relatively
3 o broad in another radial direction.
Referring to Fig. 9, each opposed pair of transducers 16 is connected to a
parameter
extraction block 51 (as described above) so as to provide a plurality of
parameters 52
CA 02597126 2007-08-24
WO 99/44049 PCTIUS99/0391.9
associated with different radial angles. Each parameter extraction block 51 is
associated
with a rule application block 55 to produce an output 56 for each radial
angle. The
outputs may be compared by a parameter extraction block 62 to identify the
plane of the
split as it crosses the x-y axis. In one embodiment, the parameter extraction
block 62 may
be a simple magnitude comparator. Generally the radial angle associated with
the greatest
insertion loss will be perpendicular to the plane of the split 60.
Example I
Measurements were made of a log prior to cutting ("undisturbed") and after
cutting, at various angles with respect to a split as indicated in the
following Table II.
The measurements were time of flight (TOF) as detected by an amplitude
threshold
(TOFa) or an energy threshold (TOFe). Pulse length (PL) using IEC standard
1157 and
insertion loss (II.) were also measured.
Table II
Angle with TOFe TOFa PL IL
Respect to Split
900 501 449.9 306.27 -89.76
450 553.8 434.3 290.87 -81.85
00 220.5 146.9 175.42 -69.26
undisturbed 193.1 146.2 172 -73.93
The zero degree reading corresponds closely to the undisturbed reading however
the 45 and 90 readings differ significantly from the baseline readings. The
changes in
pulse length and times of flight are by factors of 1.5 to 2.5; the insertion
loss change is
over 20db, or 100 to 1.
Table III below provides successive readings of the same parameters taken
along
the log at increasing distances from the cut face.
16
4ZTTT24ZTTTTTTr CT.TT'TT mT'T C 'Ne\
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= WO 99/44049 PCTIUS99/03919
Table III
Distance from TOFe TOFa PL IL
Cut (mm)
at cut face 503.1 331.8 407.05 -93.55
220 239 120.8 435 -95
240 221 141 425 -93.1
280 210 142.2 176 -80.98
300 187 138.9 158 -70.7
330 181 139.5 140.5 -71.66
Undisturbed 177.5 142 147 -70.5
In this case the three parameters change independently. The times of flight
change
quickly as a function of distance from the cut face because any sound
transmission around
the cut will reach the receiver as quickly as in the undisturbed case.
However, the pulse
length and insertion loss indicate reduced amplitude and significant pulse
distortion from
multipath signals. At 280 mm from the cut face, the pulse length has reduced
to near its
original values indicating that the signal is predominantly a direct path from
transmitter to
receiver. The remaining split has caused a reduction ins signal strength, but
has not
affected the other parameters. Finally at 300 mm and beyond, the signals have
retumed to
1 o their original values.
Referring now to Fig. 10, in a altemative embodiment to the embodiment of Fig.
7,
the consideration of the cross terms of the various standard and received
waveforms 46
and 50 and their deduced parameters may be realized with a tomographic
reconstruction.
In this tomographic reconstruction, each ultrasonic transducer 16, for
example, ultrasonic
transducer 16(a) may sequentially serve as a source of ultrasonic energy to be
received by
each of the other ultrasonic transducers (b) through (h). Relatively narrow
effective beam
widths along projection lines 63 may be obtained in this manner. The standard
waveform
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WO 99/44049 PCT/US99/03919
46 of the selected ultrasonic transducer 16a may be compared pairwise to the
received
ultrasonic waveforms 50 of each of the ultrasonic transducers 16b-h to produce
a separate
parameter measurement. The parameters measured may be any of those previously
described or other similar measurements.
Referring to Fig. 11, the parameters themselves or rule based combinations of
parameters derived from measurements along ones of different projection lines
63 are
then provided to a tomographic reconstructor 66 such as is known in the art of
x-ray
tomography to provide an image of a cross sectional cut through the wooden
member 10
in the x-y plane. Such a tomographic reconstructor 66 may use a fan beam,
filtered back
projection algorithm known in the art. This x-y mapping may augment z-axis
information
obtained by taking multiple projections at different z-axis locations along
the wooden
member 10 allowing for multidimensional optimization of the cutting of the
wooden
members.
Referring now to Fig. 12, in a variation on the embodiment of Fig. 8, a single
pair
of transducers 16 and 16' may be placed in vertical opposition about the
wooden member
10 to detect dynamic splits 60 occurring in a horizontal plane as caused by a
cutting of the
wooden member 10. Referring also to Fig. 13, such splits may occur when a cut
by a saw
68 is made in the x-y plane part way through the wooden member 10 upon which
the
cantilevered weight of an end 70 of the wooden member 10 exert a downward
force 71
2 o causing the split 60. Such dynamic splits caused by force 71 may close
after the cut is
complete but may still be identified by the technique of Fig. S. However, by
using a
concurrent transmission of ultrasonic energy adjacent to the cut line of the
saw 68 on the
supported side of the wooden member 10 during the cutting process, the split
may be
detected as it occurs and decisions about the board made in real-time. Again
multiple
transducers displaced as shown in Fig. 6 may be used to characterize the depth
of the
split. Appropriate bandpass and time window filtering and choice of
measurement
parameters may be used to permit the split to be detected without interference
from both
the electronic an vibrational the noise of the cut of the saw 68. Knowing that
the split 60
is occurring may allow saw operator to adjust the sawing procedure to reduce
the
incidence of splitting. Further knowing the depth of the split with a
disposition of the
transducers (not shown) along the z axis or the length of the wooden member
may allow
the operator to adjust the length of the sawn wooden member 70 such that a
desired length
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CTTRCTTTT'TF CHFFT lRTTT F '1Fl
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WO 99/44049 - PCT/US99/03919
of un-split wood is produced.
Referring now to Fig. 14, the present invention provides in the memory 39 of
the
computer 34 a map 72 of the wooden member 10 indicating sites 74 of local
anomalies 45
identified to spatial locations within the wooden member 10. The computer 34
reading
the map 72 and executing commercially available optimization routines may
control a
computer movable saw 76 as are understood in the art to make appropriate cross
cuts and
rip cuts of the wooden members 10 so as to optimize the value of the wooden
members 10
in the commercial market. Altematively or in addition, the computer 34 may
provide
output to a commercial sorting machine to mark or direct the wooden member as
to
strength or grade thereby allowing more efficient use of lumbers of different
strengths and
in particular better use of lower grade lumbers so as to waste less wood.
It will be also understood that the detection method of the present invention
may be
combined with conventional visual or laser type knot and split detection
equipment to
augment those systems to obtain more robust detection or greater detection
range.
Referring now to Fig. 19, in an alternative embodiment, transducer 16a and I
6b
providing opposed transmitting and receiving ultrasonic transducers aligned
along an axis
90 through wooden member 10 may have spike portions 92 presenting a sharpened
tip
that may be plunged into the wood member 10 along axis 90 thereby passing
through an
outer layer of bark 94. Each of transducers 16a and 16b may be mounted to a
bidirectional hydraulic or air cylinder 96 (shown only for transducer 16a)
which when
activated in a first direction may move the transducers 16 toward the wooden
member 10
and when activated in a second direction may retract it away from the wooden
member
10.
The cylinder 96 may be mounted on a z-axis carriage 98 allowing it to move
with
motion of the wooden member 10 in the z direction for continuous processing
and
measurement of the wooden member 10. At the conclusion of the translation of
the log in
the z direction, the transducers 16 may be retracted and a second hydraulic
cylinder 99
may be used to advance the carriage 98 back along the z-axis whereupon the
transducers
16 may be reinserted into the wooden member 10. In this way, the transducer
16a and
16b follow a rectangular cycle 100 permitting continuous motion of the wooden
member
10.
Referring to Fig. 20, in yet another embodiment, transducers 16 may be mounted
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WO 99/44049 PCT/US99/03919
on a carriage 102 extending about the wooden member 10 in the x-y plane
allowing them
to be rotated orbitally about the Z-axis of the wooden member 10 so as to
obtain
measurements along a number of different radial x-y paths through the wooden
member
for use in detection of split 60 or for tomographic-type measurements. The
s transducers may be retracted to allow z axis motion of the wooden member 10
or the
transducers 16 may be canted so as to allow them to roll in a helical path
with respect to
the wooden member 10 as the wooden member 10 moves along the Z-axis for
._ --_.:.~..
substantially continuous processing. The cacriage 102 thus provides a scanning
means
that is an alternative to the extraction block 62 which provides an electronic
scanning.
10 The above description has been that of a preferred embodiment of the
present
invention, it will occur to those that practice the art that many
modifications may be made
without departing from the spirit and scope of the invention. In order to
apprise the
public of the various embodiments that may fall within the scope of the
invention, the
following claims are made.
STTBCT-TTt'1'F cNFFT /RTTT r 26l
