Note: Descriptions are shown in the official language in which they were submitted.
CA 02933490 2016-06-16
CHARGER SCANNER SYSTEM
Field of the Invention
The present invention concerns apparatus and methods for analyzing the
geometry and other
attributes of a log block in three dimensions, more specifically generating a
plurality of scan points for
collection within a measurement system used to compute the optimum yield axis
of the log block.
Background of the Invention
Veneer sheets are generated from tree logs. Logs are ultimately positioned in
a veneer lathe
charger and it is desirable to calculate, as close as possible, an optimum
yield axis of the log veneer
when, subject to peeling. Current industry practice is to acquire measurements
surrounding a log
circumference at multiple stationary locations spaced along the length of the
log. The measurements are
used to obtain only an approximate center of the log in both a lathe charger
and veneer lathe prior to the
peeling operation.
The logs, blocks, or log blocks as they are often designated can exceed 40
inches in diameter
and over 106 inches in length when received by the veneer lathe. When in the
lathe, the block is turned
at a high speed and is engaged along its entire length by a lathe knife, which
strips the veneer away,
ideally in uninterrupted sheets. The sheets are typically 0.015"-0.25" inches
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thick, and the log is typically turned until the diameter of the block is less
than six inches. Breaks in the
sheets of the veneer occur most often when the spindles turning the block are
not located about an
optimum yield axis. Such breaks equate to waste resulting in undesirable cost
and expense. Significant
research and development has been allocated to improving equipment and methods
for extracting veneer
from log blocks. The assignee of the present invention has several patents
involving such improvements.
Such patents include, United States Patent Nos. 6,116,306, issued September
12, 2000 and 4,884,605,
issued December 5, 1989, which describe noncontact scanning using
triangulation measurement
techniques and multiple single point laser scanners for determining diameter
cross-sections of the log
block.
Quantities of 5 to 32 independent single point scanners are current common
practice for a
typical eight foot lathe charger. Installation, alignment, cleaning, and
maintenance of large quantity
independent scanners are costly and inefficient. Although the techniques
described in the
aforementioned patents for noncontact scanning an approximate center axis is
generally effective, the art
lacks the ability to calculate an optimum yield axis. Thus, less than a
maximum yield is achieved by
employing the techniques currently practiced in the industry as described in
the above patents. Anything
less than an accurate calculation of the log's optimum yield axis creates
waste resulting in costs to the
overall product.
Summary of the Invention
The present invention is a new and improved method and apparatus for scanning
and analyzing
a log block profile for determining an optimum yield axis using a series of
block profile scanners.
According to one example embodiment, four block profile scanners are employed.
Each block profile
scanner is capable of measuring 512 scanned distances.
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In summary then, the present invention may be characterized in one aspect as
including a measurement system for computing a geometric center of a log block
in three
dimensions where the system includes a charger apparatus; at least one block
scanner mechanism
having an illumination source for projecting light along the length of the
surface of the log block
forming a plurality of scan points and an imaging device such as a two-
dimensional pixel array for
receiving the plurality of scan points that are reflected from the surface of
the log block; and a
processing unit such as a computer that compiles information from the imaging
device
representative of a three-dimensional image of the log block, the processing
unit calculating an
optimum yield axis from the three-dimensional image. The system may include a
plurality of
block scanners mechanisms in a spacial alignment such that some of the
plurality of scan points
from adjacent scanners overlap.
In one embodiment the imaging device includes a two-dimensional pixel array
having a scan density of at least 512 x 512 pixels and is a charged couple
device, that is includes
two dimensional CCD arrays.
The imaging device may be a complementary metal oxide semiconductor device.
The block scanner may be a triangulation type measuring scanner. The
processing unit may
further advantageously include a scan overlap algorithm for analyzing the
overlapping scan points
of adjacent block scanners, for example wherein the scan overlap algorithm
uses the scan point
having the longer distance of any two or more overlapping scan points when
compiling the
information representative of the three-dimensional image of the log block to
calculate the
optimum yield axis. Yet further advantageously, the processing unit may
further include a range
threshold algorithm such that any scan point having a value less than the
threshold is negated when
compiling the information representative of the three-dimensional image of the
log block to
calculate the optimum yield axis.
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=
The method for scanning a profile of a log block according to a further aspect
ofthe
present invention may include the steps of:
a) transmitting illumination from an illumination source located
within at least one
block scanner along the length of the surface of the log block;
b) receiving reflected illumination from along the length of the surface of
the log
block in the block scanner onto an imaging device, the reflected illumination
forming a plurality of scan points;
c) rotating the log block about its axis while transmitting
illumination and receiving
the reflected illumination;
d) generating a plurality of scan paths from the scan points collected by
the imaging
device;
e) triangulating the scan points for each of the scan paths to produce a
numerical
model of the block; and
f) computing the geometric center of the block from the numerical model of
the
block.
The method may further include a preliminary and secondary scanning process,
and
the log block may remain stationary during the preliminoty scanning process.
The method may
include filtering out the scan points having a value less than a range
threshold value when
triangulating the scan points for each ofthe scan paths to produce a numerical
model of the block,
or filtering out overlapping scan points captured by more than one block
scanner when
triangulating the scan points for each of the scan paths to produce a
numerical model of the block.
Brief Deacription of the Drawings
The foregoing and other features of the present invention will become apparent
to
one skilled in the art to which the present invention relates upon
consideration of the following
description of the invention with reference to the accompanying drawings, in
which:
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Figure lA is an isometric view of a scanner used in the prior art;
Figure 1 is a front elevation view of a charger and scanners where the log
block is
in a first or rest position for a preliminary scanning process;
Figure 2 is a side elevation view of Figure 1 and of a veneer lathe;
Figure 3A is an isometric view showing the operation of a block profile
scanner in
one example embodiment;
Figure 38 is a diagrammatical view of one example embodiment of a block
profile
scanner;
Figure 4 is a front elevation view of the charger and scanners where the log
block is
in a second or yield scan position;
Figure 5 is a partial perspective view of Figure 4;
Figure 6 is a linear representation of a block circumference through 3600 as
shown
in Figure 5;
Figure 7 is a partial front elevation view of a charger positioning a block
such that
the scanners are used for calculating an optimum yield axis;
Figure 8 is a magnified view of a block exposed to overlapping scanner regions
encountering a shadowing condition in the block profile;
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Figure 9 is a flow diagram representing a logic process of analyzing a
shadowing condition in a
log block profile; and
Figure 10 is an illustration representing a filtering process used when
scanning a
block profile.
Figure 11 is a diagrammatic view of a block in cross section and the
corresponding
representations of the r, bõ, and h dimensions.
Detailed Description of Embodiments of the Invention
Turning to the drawings, a lathe charger apparatus is shown in phantom
generally at 10 in
Figures 1 and 2. The lathe charger 10 holds a log block 12 in a rest or first
position supported by a first
vee 13 and a second vee 14. The block 12 comprises a first end 15 and second
end 16, as supported by
the vees upon loading into the charger apparatus 10 from a conveyor (not
shown). Depicted in Figure 1
are block profile scanners or cameras 20a - 20d suspended above the log block
12 by a fixture 11.
Although four scanners 20a - 20d are shown, it should be appreciated by those
skilled in the art that any
number of scanners can be used. A block profile scanner 20 is a triangulation
type-measuring scanner
=
capable of capturing a two-dimensional image. The block profile scanner can be
for example, a type of
scanner that employs a charged couple device (CCD) or complementary metal
oxide semiconductor
(CMOS) based imaging technology. A suitable block profile scanner will have an
illumination source
that is projected along the length of the surface of the log block 12,
reflecting a surface image profile of
the block surface along its length onto a high density two-dimensional pixel
array 26.
Figure 1 A an isometric view of a scanner system used in the prior art. The
scanner system
includes an illumination source projecting light along the circumference of a
block. The
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camera or scanner in Figure 1 A is limited to imaging the surface of the block
at a single circumferential
location along the block.
Figure 3A illustrates one example embodiment of a scanner system having an
illumination
source 23 separated from a camera 32. The illumination source 23 projects a
light path 24 upon the
block 12. The light path 24 is reflected from the top surface of the block
forming a reflected image 29
that is received by a lens 25 on the camera 32. An analysis of the reflected
image 29 is performed by a
processor (not shown) that can either be internal or external to the camera 32
or scanner 20. A separate
example embodiment is shown in Figure 3B. Structures of Figure 3B that are the
same or similar to
structures of Figure 3A and are labeled with the same reference number with
the addition of a prime.
Figure 3B features an illumination source 23' and receiving lens 25' contained
within a scanner 20'. The
reflected image 29' is ultimately projected through the lens 25' onto the high
density two-dimensional
pixel array 26. In one embodiment, the pixel array has a scan density
resolution of 512 x 512 pixels per
scanner.
An example of a suitable commercial block profile scanner includes a camera
made by IVP
Integrated Vision Products Inc. under model number NP Ranger M20 OEM-1.
Further discussion on
this type of scanner technology is disclosed in U.S. Patent No. 6,313,876
issued to Eklund.
The scanner 20' of Figure 3B further includes a housing 21 with a window 22
from which the
illumination source 23' projects a light path 24' upon the surface of the
block 12. The illumination
source 23' can be one or more light emitting diodes or laser diodes lensed to
project a narrow line of
light. The light path 24' results in a reflected image 29' of the block
surface and is received through a
lens 25' located in the scanner 20'. The lens concentrates the reflected image
29' upon the two-
dimensional pixel array 26. The data image captured on the pixel array is then
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analyzed and converted into a value that corresponds to a linear scan distance
from the scanner 20
that is associated with a specified scan point or position r. along the block
12.
Employing a 512 x 512 pixel array, approximately 512 scan distances are
measured
by each scanner along the profile of the block 12 at rotational increments
ofthe log block at 1.50 or
less. Each scan distance is correlated to the simultaneous angle of log block
rotation and to the
simultaneous distance from scanner face to axis of the log block rotation,
thereby providing the
three-dimensional data for calculating an optimum yield axis.
Preliminary Scanning Operation
A preliminary scanning process occurs while the block 12 is in a first
position in
order to calculate an approximate center 30, as shown in Figure 2. During the
preliminary
scanning operation, the four block profile scanners 20a 20d analyze and scan
the block 12 from
the first end 15 to the second end 16, as best seen in Figure 1.
Each of the block profile scanners generate 512 scan points represented by the
values n, = 1'0 in Equation (1) and shown in Figure 3B. The values rõ
correspond to a
particular pixel in the pixel array 26 that is analyzed and converted into a
corresponding scan
distance. Each scan distance corresponding to each scan point is collected and
stored in a central
processing unit (CPU) or computer 40. A variable h of Equation (1) represents
a known distance
from the scanners less the distance from the calculated scan point. Knowing
the values for hand
each scan distance corresponding to each scan point r0 along the profile 12 of
the block allows for
a distance b. to be calculated, which represents the approximate center 30, as
demonstrated by the
equations and Figure 11.
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h=r+b Equation (1)
rappwõ b. cos (45 ) Equation (2)
b = h /1 + cos (45 ) Equation (3)
$econdary Scanntng Operation for Calculating the Optimum Yield Axis
After the completion of the preliminary scan and the calculation of the
approximate
center 30, a pair of charger spindles shown in Figure 4 as 17a and 17b, are
independently moved
into engagement with the first and second ends of the log block 12 at the
approximate center 30
calculated during the preliminary scanning operation. A pair of hydraulic
cylinders 18a and 18b
lift block 12 from the first rest position to a second or yield position, as
best seen in Figures 4, 5,
and 7.
While block lifts from first rest to yield position or while in the yield
position, log
block 12 assumes an orientation for determining a precise three-dimensional
geometric
configuration from which the optimum yield axis can be calculated by rotating
the log block 12 via
charge spindles 17a and 17b. Simultaneously, four light paths represented by
24a - 244 are
generated by the illumination source 23 in each respective scanner and are
projected along the
length profile of the block 12. Each light path contains 512 scan points
represented by rõ that
provide a reflected image on the pixel array 26, which is equated to a
corresponding scan distance
to the block 12. The four light paths 24a ¨ 24d combine to form a single scan
path 31. As the
block rotates, multiple scan paths 31a, 31 b... are generated along a
longitudinal direction
represented by X in Figures 5 and 6 through the 360 degree rotation. Log block
12 is typically
accelerated into a spin col at an approximate rate of 2 revolutions per second
and using the
described block profile scanners allow for scan paths to occur every 1.5
degrees over the 360
degree rotation of the block 12, thereby generating at least 240 scan paths.
The number and
frequency of the scan paths could be even greater during the acceleration and
deceleration of the
block rotation, most typically as the rotational speed decreases. By using
four block profile
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scanners each having 512 x 512 two-dimensional pixel array and generating a
scan path along the
block approximately every 1.5 degrees results in approximately 419,520 scan
points rõ that are
measured by the scanner and thus provide a corresponding scan distance SD for
each scan point, as
shown in Figure 7. Such a significant number of scan points along multiple
scan paths provides an
elevated scan density, allowing a clear three dimensional analytical depiction
of a log block,
including detection of any excrescences or discontinuities 28 in the block
that often result from
knots in the wood. Typically, the larger to the mass of the block 12 the
slower the rotational
speed, resulting in an even greater number of scan point rõ than the 419,520
points discussed
above.
Knowing the scan distances SDõ based on pixel data from the scan points r,,
provide
corresponding scan point radii "Re" that collectively form the optimum yield
axis of the block 12
represented by line 50 in Figure 7. For example, knowing SD and the height H
from the center of
the spindle 17 to the corresponding scanner 20, and the angle that a given
light beam 24 is
projected from scanner center represented by allows the scan point radius 11õ
to be calculated,
which corresponds to a radius of the block at that particular scan point.
Although H is a variable
distance it is known value, since the distance traveled for each spindle 17
can be tracked by the
CPU 40 by, for example encoders (not shown). The scan point radius Rõ is the
distance from the
surface of the block 12 to the optimum yield axis 50 for each scan point rõ.
This is shown and
calculated for scan point radius 11512 that corresponds to scan point 1.512 in
Figure 7 and Equation
(4).
H512 = H - X
X = cos (13) * SD
H512 = H - cos() * SD Equation
(4)
The locus of the scan point radii Rõ from the data stream generated by 512
scan points from
each scanner along every 1.5 degrees of rotation of the block 12 provides a
precise three
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dimensional shape of log block 12. The three dimensional shape provides
approximately 419,520
scan point radii from which the optimum yield axis 50 is calculated. Once the
optimum yield axis
50 is computed, such location is used to position block 12 for the highest
yield value in the
removal of veneer by receiving a pair of pendulum clamps for transferring the
log block 12 into a
veneer lathe 60 shown generally in phantom in Figure 2. The process executed
by the veneer lathe
60 is described in further detail in the '306 patent.
Scan Path Overlap
1.0 Spacing of the scan points I.. from each scanner along log
block length varies with
distance from scanner to log surface, typically ranging from 0.050" to 0.100"
over the operating
range of each scanner. When scanners overlap the result is more dense or
closer spaced data and
sometimes (with reference to Figures 7 and 8) two X readings may
coincidentally apply to the
same Y position. An optimizing algorithm 100 will use the smaller indicated
radius for
calculating optimum yield axis 50. An added advantage of overlap is more
accurate surface
definition by eliminating shadowing that may result from surface protrusions
and recesses.
Each scan distance SD is converted into distance X (perpendicular distance
from
face of scanner to stuface of log as shown in Figures 7 and 8) and distance Y
along length of log
12 to a horizontal center location. For each scanner, Y is first expressed as
distance from vertical
centerline of the scanner, negative to right of center and positive to left.
The scanner interface
computer 40 combines data from all four scanners and passes all range readings
to the optimizing
computer in the form of X (perpendicular distance from face of scanners to
surface of log) and Y
(distance along length of log) with Yr.:iat center of material flow, negative
Y to right and positive
Y to left. For example, (assume X is constant 63"), the last SD at each end of
a block 100" long
would be reported to the optimizing computer as X = 63", Y = -50" right end
and X = 63" and Y
+50" left end.
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Shown in Figure 1 are three overlap regions represented by 27a, 27b, and 27c.
Each overlap region 27 results from each respective scanner light path 24
extending beyond the
adjacent scanner's light path. The amount of surface area of the block 12
subjected to the overlap
regions 27 vary depending on the diametrical size and location of the block.
The overlapping
regions are smaller as the diameter of the block 12 increases or the closer
the proximity of the
block to the scanner, as depicted when comparing Figure 1 (the block located
in a preliminary scan
position) with Figure 4 (the block located in a secondary scan position).
The overlap regions 27 provide an advantage in analyzing areas susceptible to
a
shadowing condition along the block resulting from projections or
protuberances along the block
profile as best seen in Figure 8, which is a magnified portion of a log block
12. The overlapping
regions, for example in Figure 8 using scanner 20b and 20c provide two
different scan distance
values for scan point I'. represented by SD1 and SD2, respectively. The
optimization algorithm
100 constructed in programs or source code resolves which scan distance to use
for overlapping
scan points, which is represented generally, by the flow chart in Figure 9.
Referring now to Figure 9, the optimization algorithm source code 100 is
initiated
at 110. The scan distance reflected onto the pixel array 26 for each scanner
is assigned a value at
120 and assigned a coordinate position at 130 relating to the value 120. A
decision point 140
evaluates whether the coordinate points are within an overlapping region and
assigned the same
position. If the points do not overlap the scan point radius R, of the block
12 is calculated for that
particular scan point I-. at 145. If the scan points do overlap and are
assigned the same position, a
comparison is made at 150. The scan distances are compared for each common
scan point at 150.
The scan point having the greater scan distance is selected for calculating
the block scan point
radius R. at 160. Referring again to Figure 8, SDI is greater than SD2,
therefore the value for
SDI will be used to calculate the scan point radius R. for scan point rA in
accord with the program
100. As a result, the programming and overlapping regions 27 provide a smaller
diameter and
more accurate image of the log block 12 when encountering shadowing
conditions.
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Steam Penetration Filtering
The scanning environment frequently includes airborne steam, or any other
airborne material, of
random intensity between the camera or scanner 20 and the block 12 being
scanned. The steam is
typically emitted from the block 12 being scanned and/or from peeling veneer
from the previously
scanned block. Even though laser illumination and reflection from the block
surface penetrate the steam,
random reflections from the steam can cause multiple extraneous range
readings.
Figure 10 is an illustration representing a filtering process used when
scanning a block profile.
The cameras 20 are scanned from the farthest range to closest. Only the
farthest range reading
represents the block surface thus only the farthest reading is used for
calculating optimum yield axis. A
threshold 70 is provided to remove background ambient light and allow for
accurate range
measurement. Stated another way, if the scan distance measures an object such
as random reflections,
airborne material or steam clouds 72, the measured scan distance will be
smaller than the threshold 70,
and as such, the scan distance measurement is dismissed or filtered from the
central processing unit or
computer 40 when calculating the optimum yield axis 50. The scope of the
claims should not be
limited by the embodiments set forth in the examples, but should be given the
broadest interpretation
consistent with the description as a whole.
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