Note: Descriptions are shown in the official language in which they were submitted.
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TITLE: OPTIMIZED BOARD EDGER AND
METHOD OF OPERATION THEREOF
FIELD OF THE INVENTION
This invention pertains to sawmill edgers and more particularly, it
relates to a board edger having a movable saw box controlled by a scanner
and a computer to maximize the recovery of lumber from wood cants.
BACKGROUND OF THE INVENTION
As the processing speed increases in sawmill machinery, wood
pieces tend to bounce back from bumpers and alignment gates and are not
always presented to the sawmill equipment in an ideal position. This
inherent disadvantage with the handling of wood pieces is particularly
apparent in wood cants or flitches. Wood cants have irregular and non-
parallel sides which make them difficult to align along the longitudinal axis
of an infeed conveyor for example. Consequently, increasing the processing
speed of machinery often results in less recovery.
In the present description, the words; wood piece, cant, flitch and
board are used interchangeably to designate a lengthwise strip of wood cut
from a tree trunk.
In view of increasing both the processing speed and recovery, lineal
scanners and computers have been developed to precisely measure the
dimensions and the position of a wood board on a conveyor. These
scanners and computers generate three-dimensional images ofthe cant, and
calculate a sawing solution that represents the highest value combination
of products which can be produced from the cant.
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Similarly, sawmill edgers have been developed to operate with lineal
scanners and computers. 'These edgers have a saw box that is adjustable
about a vertical axis, and saw blades that are movable sideways along the
arbor. The positions of the saw blades are continuously adjusted to track
the realtime position and alignment of a wood board being fed there
through and to follow the optimized cutting profile defined by the
computer.
Examples of optimized edgers available in the prior art are disclosed
in the following documents;
US Patent 4,239,072 issued December 16, 1980 to H. Merilainen;
US Patent 5,722,474 issued March 3, 1998 to C. Raybon et al.;
US Patent 5,816,302 issued October 6, 1998 to W. R. Newness
US Patent 5,884,682 issued March 23, 1999 to J. B. Kennedy et al.;
US Patent 5,946,995 issued September 7, 1999 to S. W. Michell et al.;
US Patent 6,178,858 issued January 30, 2001 to M.P. Knerr et al.;
US Patent 6,202,526 issued March 20, 2001 to M. Dockter et al.
It will be appreciated that in a continuous wood edging process, the
cants to be trimmed must be located precisely such that the saw blades can
track the optimized cut lines in one cant and reposition quickly to track the
optimized cut lines in a next cant. It has been found, however, that when
the leading edge of a saw blade is made to focus on the leading edge of a
cant approaching at high speed, there is a certain amount of wandering of
the saw blade before it is set to track the optimized cut line. The saw blade
enters the leading edge of the cant in a milling mode rather than a sawing
mode, thereby increasing the kerf width at the leading edge of the cant.
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Similarly, when the optimized cut line stops at the trailing edge of the cant,
the saw blade stops tracking the optimized cut line before it has completely
exited the cant, causing an aftercut and also increasing the kerf width at the
trailing edge of the cant.
In the machines of the prior art, several methods are used to locate
the leading and trailing edges of a cant to control the tracking of optimized
cut lines. For example, the machine described in US Patent 4,239,072 uses
several measuring gates on the infeed side of the cutter heads to determine
the position of the cant relative to the cutter heads and to adjust the cutter
heads prior to entering into the cant. The position of the cant is measured
relative to a feeding line. The cutter heads are correspondingly positioned
on both sides of the feeding line, and the tracking of the optimized cut lines
starts as the cant passes through the edger. The cutter heads are inclined in
relation to each other in such a manner that the cutter heads are closer to
each other at their cutting side than at the exit side to prevent aftercut.
The machine disclosed in US Patent 5,722,474 uses photodetectors
to detect the location of a cant relative to a reference point. Then the
movement ofthe saw blades is correlated by computer with the longitudinal
movement of the cant past the reference point.
The machine described in US Patent 5,884,682 uses another
approach. The machine uses mechanical positioning devices to position the
cant and to present it tangentially to the saw blades.
As it was explained, there are drawbacks in adjusting the saw blades
to follow optimized cut lines which start at the leading edge of the wood
board and end at the trailing edge of the board. As such, it may be
appreciated that there continues to be a need for a new and improved
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method to operate a board edger to prevent these surface defects. There is
also a need for a better board edger in which the saw blades are shifted with
greater speed and precision.
SUMMARY OF THE INVENTION
In the present invention, however, there is provided an optimized
board edger in which the structure of the saw blade moving mechanism has
a low inertia, for rapid positioning of the saw blades. The saw box in the
optimized board edger follows optimized cut lines on a virtual entity of the
wood board to be trimmed. This virtual entity is made to be longer than the
wood board such that the tracking of the optimized cut lines starts before
the saw blades enter the leading edge of the wood board and ends after the
saw blades have completely exited the wood board.
In accordance with a broad aspect of the present invention, there is
provided a new method to reduce saw kerf defects while parting a wood
piece in motion. This method consists of determining a parting line along
the wood piece, extending the parting line beyond an edge of the wood
piece, and parting the wood piece along the parting line.
In another broad aspect of the present invention, there is provided
an installation for parting wood boards in motion and avoiding or
substantially reducing kerf defects. This installation comprises a wood
parting apparatus having a wood parting tool mounted therein. There is
also provided, a means to determine a parting line on a wood board, to
extend the parting line beyond an edge of the wood board, and to move the
parting line with the wood board through the wood parting apparatus. The
new installation also has means to cause the wood parting tool to track the
parting line along its extended length.
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In the present disclosure, the expression "virtual entity" is used to
describe a set of data inside a computer memory corresponding to the
dimensions, position and speed of a wood board in motion relative to one
or more space and time references that are assignable to a board edger.
In another feature of the present invention, there is provided a new
method for edging a wood board. This method comprises the following
steps:
a) providing a board edger having a movable saw box and a saw blade
mounted in that saw box;
b) scanning a wood board and obtaining images of this wood board;
c) constructing from the images, a virtual entity of the wood board;
d) determining from the images, a position, alignment and travelling
speed of the wood board;
e) determining from the images an optimized cut line along the virtual
entity;
f) superimposing the virtual entity in space and time over the wood
board;
g) displacing the forward edge of the virtual entity ahead of the leading
edge of the wood board;
h) displacing the rear edge of the virtual entity behind the trailing edge
of the wood board;
i) extending the optimized cut line to the forward and rear edges of the
virtual entity;
j) simultaneously moving the virtual entity and the wood board
through the board edger, and
k) sawing the wood board along the optimized cut line on the virtual
entity.
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The method according present invention for edging a wood board
reduces the defects and disadvantages of the prior art by incorporating
buffer zones ahead and after the wood board, in which the saw blade
adjustments are effected. The lengths ofthese buffer zones are determined
by the response time of the board edger for repositioning the saw blades,
the desired speed ofthe transport conveyor and the desired spacing between
the boards.
In accordance with another feature of the present invention, there is
provided a board edger for edging wood cants, comprising a saw box
having an arbour mounted therein. At least one saw collar assembly is
adjustably mounted on the arbor and a saw blade is mounted in the saw
collar assembly. The saw box also has a setworks mounted thereon above
the arbor. The setworks has a displacement parallel to the arbor. A saw
shifting arm extends at right angle from the arbor, between the saw collar
assembly and the setworks for moving the saw blade along the arbor in
response to a movement of the setworks. This saw shifting arrangement is
advantageous over other board edgers of the prior art in that it is compact,
light, frictionless and precise.
Other advantages and novel features of the present invention will
become apparent from the following detailed description of the preferred
embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
One embodiment of the present invention is illustrated in the
accompanying drawings, in which like numerals denote like parts
throughout the several views, and in which:
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FIG. 1 is a plan view of a board edging installation comprising the
optimized board edger according to the preferred embodiment of the
present invention;
FIG. 2 is an enlarged plan view of the optimized board edger and partial
views of the upstream transport conveyor and downstream discharge
conveyor;
FIG. 3 is a partial plan view of a board or a cant entering the saws of an
edger in a prior art installation;
FIG. 4 is a plan view of a cant and of a virtual entity of this cant as
generated by the computer system comprised in the preferred
installation of the optimized board edger;
FIG. 5 is a plan view of the saw box in the optimized board edger
according to the preferred embodiment;
FIG. 6 is a cross-section view of the saw box, as seen along line 6-6 in
FIG. 5;
FIG. 7 is a side view of the saw box in the optimized board edger;
FIG. 8 is a perspective exploded view of a saw blade, a saw collar
assembly and a saw shifting arm comprised in the saw box in the
optimized board edger;
FIG. 9 is a cross-section view of the saw blade, the saw collar assembly
and the shifting arm illustrated in FIG. 8;
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FIG. 10 is an enlarged view of the saw collar assembly, and in particular
of the portion of the hub as seen in detail circle 10 in FIG. 9.
DESCRIPTION OF THE PREFERRED EMBODIMENT
While this invention is susceptible of embodiments in many
different forms, there is shown in the drawings and will be described in
details herein one specific embodiment of the board edger according to the
present invention, with the understanding that the present disclosure is to
be considered as an example of the principles of the invention and is not
intended to limit the invention to the embodiment illustrated and described.
Similarly, the preferred installation of the optimized board edger and its
method of operation are provided as examples to explain a general concept.
These descriptions should not be used to limit the scope of the invention.
Referring firstly to FIGS. 1-4, a preferred method for operating an
optimized board edger will be described. The preferred board edging
installation comprises an in-line arrangement of an infeed conveyor 20, a
lineal scanner 22, a transport conveyor 24, an optimized board edger 26,
and a discharge conveyor 28. The preferred infeed conveyor 20 has a
board pre-locating device 30 which function is to position each board as
straight as possible along the transport conveyor 24. The infeed conveyor
20 can be fed manually or from a sorting table as it is customary in
sawmills. Numerous components ofthe machines mentioned above and of
the preferred optimized board edger are not illustrated herein because these
components belong to known technology and do not constitute the focus of
the present invention.
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In the preferred board edging installation, a computer system is
provided between the lineal scanner 22 and the optimized board edger 26.
This computer system comprises a personal computer (PC) 32 containing
an optimizing software, a programmable logic controller (PLC) 34
communicating with the PC 32 and with one or more servo modules 36 and
one or more servo drive translators 38 to control the tracking functions of
the optimized board edger 26. A two-way ethernet 1 OOMB/sec. connection
40 is provided between the PC 32 and the PLC 34.
The lineal scanner 22 is preferably a 3-D True-Shape ScannerTM
manufactured by Perceptron Inc., a company having its headquarters at
Plymouth, Michigan, USA. The PC 32 preferably has a high speed
processor and optimizing software to receive a 3-D image from the lineal
scanner 22 and to compute a breakdown solution in 250 millisecond or less
for softwood applications and in 400 millisecond or less for hardwood
applications.
The length of the transport conveyor 24 is determined according to
the desired travel speed of this transport conveyor and the processing time
for each sawing solution. A travel speed of 800-1200 feetlminute is
believed achievable with the installation described herein.
The optimized board edger 26 according to the preferred
embodiment has an active saw box 42 which is movable about a vertical
axis and in which the saw blades are movable along the arbor. In order to
reduce the inertia ofthe saw box 42, the arbor is driven by an electric motor
44 through sheaves and belts under the guard 46 and a flexible drive shaft
under the guard 48.
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In use, an untrimmed wood board 50 is scanned while in motion
through the scanner 22. The longitudinal axis 52 ofthe board relative to the
longitudinal axis 54 of the optimized board edger, as well as the optimized
cut lines 56 are determined while the wood board is moving toward the
optimized board edger 26.
The saws are set apart a same distance A as the spacing between the
optimized cut lines 56. The saw box 42 is rotated to align the saw blades
60 parallel to the longitudinal axis 52 of the wood board, and the saw
blades are set in motion along the arbor 62 to follow the optimized cut lines
56 as the wood board 50 travels through the optimized board edger 26.
Referring now to FIG. 3, the problems with high speed positioning
of a saw box will be described. When the longitudinal axis 52 of a wood
board 50 to be trimmed is skewed a few degrees from the feeding direction
54, it will be appreciated that an initial adjustment to a proper spacing and
alignment of the saw blades 60 must be made before the saw blades enter
the wood piece. As the saw blades 60 enter the wood piece 50, the saw
blades 60 must move in unison along the arbor 62 to follow the optimized
cut lines 56.
In the machines of the prior art, the leading edge 70 and the rear
edge 72 of the wood board 50 are detected and used to designate the
beginning and the ending of the optimized cut lines 56. The leading and
trailing edges are used as targets with which the saw blades must aim.
However, it will be appreciated that the saw box has a certain inertia and
its actuators have acceleration, deceleration, elasticity and dampening
factors, incorporated in each of their movements. These motion factors
cause a certain delay in positioning the saw blades 60 at the entrance and
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exit of a board. As a result, the positioning of the saw blades 60 is not
instantaneous. The saw blades might still oscillate around their
programmed position as they enter the leading edge 70 of the wood board.
The tracking of the saw blades in unison to follow the optimized cut lines
56 may only start an instant after the saw blades have actually entered the
board. Similarly, the movement of the saw blades in tracking the optimized
cut lines throughout to the trailing edge 72 stops prematurely before the
saw blades have completely exited the wood board.
This dragging in the positioning of the saw blades to follow the
optimized cut lines causes the kerf width near the leading and trailing edges
of a wood board to be generally larger than normal, causing defects in the
recovered lumber and side stresses on the saw blades.
In the preferred method of operating the optimized board edger 26,
the PC 32 is configured to construct a virtual entity 80 of each wood board
50. This virtual entity 80 has all the dimensions of the physical wood board
50. This virtual entity 80 is superimposed in space and time over the
physical wood board 50.
Depending upon the operating speed and the length of the transport
conveyor 24, the virtual entity 80 is assigned excess length L ahead of the
leading edge 70 of the wood board 50, and excess length T following the
trailing edge 72 of the wood board 50. The optimized cut lines Sb are
projected along both excess lengths L, T.
In the preferred method of operation, the angle of the saws 60
relative to the longitudinal axis 52 of the wood board 50 and the spacing A
of the saw blades 60 are adjusted, and the displacement of the saw blades
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in unison along the arbour 32 is set in motion by the PC 32 according to the
position, alignment and travelling speed of the virtual entity 80. The target
set points between which precise tracking of the saw blades 60 is
maintained are set at the forward edge 70' and the rear edge 72' of the
virtual entity 80. By aiming the saw blades 60 at the forward edge 70' of
the virtual entity 80, the inherent oscillation of the saw blades 60 during
positioning occurs along the excess length L, such that uniform side edges
are obtained from the leading edge 70 of the actual wood board 50.
Similarly, the tracking of the optimized cut lines back to the rear edge 72'
of the virtual entity 80 ensures that the saw blades are out of the wood
board 50 when tracking stops. In the preferred edging installation, having
the response and computing time as mentioned hereinbefore, the lengths L
and T are set at 24 inch each.
Referring now to FIGS. 5-7, the saw box 42 in the preferred
optimized edger 26 will be described in some details. The saw box consists
of a frame 90, an arbor 92 mounted in bearings 94, 96, a pair of saw blades
60 mounted on the arbor 92. The saw box has a setworks 98 mounted on
top of the frame 90. There is provided three circular ball bearings 100 on
the bottom of the frame 90. The bearings 100 are set on a circular rail 102,
represented by a dashed line in FIG. 5. This circular rail is mounted on the
base of the edger 26. The preferred angular adjustment B of the saw box
42 is 7-1/2° to the left and to the right of the longitudinal axis 54
of the
optimized board edger 26, for a total angular displacement of 15°.
The rotation of the saw box 42 to the right or the left of the
longitudinal axis 54 is effected by a DC servo drive actuator controlled by
the PC 32. This DC servo drive actuator and its mounting have not been
illustrated herein for being known to those skilled in the art.
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The setworks 98 also comprises two DC servo drive motors 104
respectively linked to a linear slide 106, and also being controlled by the
PC 32. Each linear slide 106 encloses a ball screw and a ball nut connected
to a yoke plate 108. Each DC servo drive motor 104 drives the yoke plate
108 along the linear slide 106 with precision. A shifting arm 110 is affixed
to the yoke plate 108 and extends to a respective saw collar assembly 112
for moving one of the saw blades 60 along the arbor 92. Both saw blades
60 are movable independently of each other along the arbor 92 for board
width adjustment, and in unison with each other during the edging of a
wood board.
The arbor 92 has splines thereon as it is customary with board
edgers. Each saw blade 60 is supported in a collar assembly 112, which is
adapted to engage with, and to slide along these splines. This collar
assembly 112 is better illustrated in FIGS. 8-10. The saw collar assembly
112 comprises a hub 114 which has grooves 116 therein to engage with the
splines 118 on the arbor 92, with a loose sliding fit. The hub 114 has a
flange 120 on its circumference, to which is clamped the saw blade 60, by
means of a blade lock ring 122 with bolt holes 124 and machine screws 126
through these holes. Next to the flange 120, there is an inner bearing seat
128 on the outside surface of the hub, and an adjoining threaded portion
130. A bearing 132 is held to the inner bearing seat 128 of the hub by a
lock nut 134 engaged over the threaded portion 130. This bearing 132
affords a frictionless rotation of the hub 114 relative to the shifting arm
110.
The outer race of the bearing 132 is clamped into an outer bearing
seat 136 inside an opening 138 in the lower end of the shifting arm 110.
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The outer race of the bearing 132 is held to the outer bearing seat 136 by
means of an outer lock ring 140 having bolt holes 142 and machine screws
144 through these holes. Where possible, the components of the saw collar
assembly 112 are made of aluminum to ensure a minimum weight and
inertia.
The preferred shifting arm 110 has a conduit 146 therein to which
is connected a nozzle 148. This conduit 146 and nozzle 148 are
advantageous for periodically pumping lubricant to the surface of the arbor
92 for lubricating the hub 114 and the arbor 92.
Referring particularly to FIG. 10, the grooves 116 inside the hub
114 do not extend the full length of the hub. A brass ring 150 is mounted
on each end of the hub 114, inside the hub, and both rings 150 complement
with the grooves, the full length of the hub. Each brass ring 150 is press
fitted into a shoulder at each end of the hub 114. The inside diameter of
each ring 150 is a loose fit over the crest of the splines 118 on the arbor
92.
The brass rings 150 are advantageous for preventing a binding of the
grooves 116 into the splines 118 and facilitate to a considerable extent the
movement of the collar assembly 112 along the arbor 92.
As to other manner of usage and operation of the present invention,
the same should be apparent from the above description and accompanying
drawings, and accordingly further discussion relative to the manner of
usage and operation of the invention would be considered repetitious and
is not provided.
While one embodiment ofthe present invention has been illustrated
and described herein, it will be appreciate d by those skilled in the art that
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various modifications, alternate constructions and equivalents may be
employed without departing from the true spirit and scope of the invention.
Therefore, the above description and the illustrations should not be
construed as limiting the scope of the invention which is defined by the
appended claims.
