Note: Descriptions are shown in the official language in which they were submitted.
t
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GONTROL SYSTEM FOR AUTOMATIC ADJUSTMENT
OF LATHE KNI FE P I'rGH
Back round of Invention
The subject matter of the present invention
relates generally to veneer lathe apparatus fox peeling
sheets of veneer from a rotating log by means of a lathe
ZO knife of adjustable pitch and, in particular, to an
electrical control system for automatic adjustment of
lathe knife pitch angle in response to reduction of the
diameter of the log during peeling.
15 As shown in U.S. Fatent 4,708,180 of R. A.
Browning, et al~~ issued November 24, 1987, it has here-
tofore been the practice to provide a veneer lathe with
automatic adjustment of the lathe knife pitch angle by a
mechanical control including a cam follower roller on
~0 the knife carri.age~whicka rolls along a pitch rail cam
member. The slope of the pitch rail is set manually ar
by other mechanical adjustment means prior to the start
of peeling and the knife pitch is then adjusted entirely
by movement of the cam follower roller along the surface
of the pitch rail during peeling. In most cases, the
pitch rail. is linear with a constant slope. However,
such roll may be provided with a custom profiled end
portion of changing slope for small diameter logs as
discussed in the Browning patent. Unfortunately, such a
custom-made pitch rail having an end portion of differ-
ent slope does not apply to all species or types of
wood. In addition, manual adjustment of the pitch rail
to set the slope angle at the start of the peel is tine
consuming and inaccurate. The above-cited Browning
~g patent also discloses the use of an automatic control
means employing a computer for adjusting the gap between
the lathe knife and a nose bar roll engaging the log
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immediately in front of the knife in response to changes in the
log diameter and knife pitch during peeling. However, there is
nothing in this patent which teaches that the pitch angle of
the knife should be adjusted automatically by an electrical
control system including a computer in accordance with knife
pitch profile tables stored in the memory of such computer in
the manner of the present invention.
During the veneer peeling process, better quality
veneer is usually produced when the lathe knife pitch angle is
varied as the radius of the log diminishes during peeling.
Typically, the knife :pi.tch angle, which is the angle the front
cutting edge of the knife makes with a vertical plane passing
through the tip of such knife, varies from a positive angle or
"lead" where the knife is tipped away from the log for logs of
large diameter to a negative pitch angle or "heel" where the
knife blade is inclined toward the log for small diameter log
blocks. The difficulty is that the manner in which the knife
pitch angle should be varied during peeling is different for
different species or types of wood. This requires frequent
manual adjustment of the slope of the pitch rail and
replacement of any custom profile pitch rail with another
profile when such rail is provided with an end portion of
changing slope.
Summary of Invention
It is therefore, one object of the present invention
to provide an improved veneer lathe apparatus having an
electrical control system for automatically adjusting 1_athe
knife pitch angle during peeling as the radius of the 1_og block
diminishes.
63198-1086
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Another object of the invention is to provide
such an apparatus in which the lathe knife pitch angle
is adjusted in a fast, accurate manner by a computer
control system.
A further object of the invention is to provide
an automatic lathe knife pitch adjustment apparatus in
which a plurality of different pitch profiles defined by
pitch data tables are stored in the memory of a digital
computer so that such profiles may be selected in a
rapid and precise manner by the computer for different
wood species.
An additional object of the invention is to
provide such an automatic knife pitch control apparatus
in which the pitch profiles stored in the computer can
be easily defined and revised by data entries in pitch
data tables of knife pitch angles versus knife carriage
positions.
Still another object of the invention is to
provide such an apparatus in which the lathe knife pitch
angle is quickly and easily changed during peeling by
adjusting the height of the cam follower roller on the
knife carriage in response to a computer output signal
corresponding to the desired pitch angle.
A further object of the invention is to provide
a closed loop computer control system for automatically
adjusting a lathe knife pitch angle during peeling in a
fast, accurate manner.
A still further object of the invention is to
provide such a closed loop control system in which elec-
trical signals are produced by a computer corresponding
to a predetermined knife pitch angle and applied to a
servo valve for controlling a cylinder to adjust the
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height of the cam follower on the knife carriage to the proper
height for such pitch angle and a transducer produces a
corresponding cylinder piston position signal which is fed back
to the computer to verify when such height adjustment has been
completed for the desired pitch angle.
The present invention provides electrical control of
the lathe knife pitch angle using a digital computer having
digital data representing different profiles of pitch angle
adjustment provided as a plurality of different knife pitch
tables stored in the memory of the computer.
In the electrical control system of the present
invention, the computer is employed to control the knife pitch
by adjustment of the vertical position or height of the cam
follower roller on the knife carriage to support such carriage
l.'~ at different heights above the pitch rail. In the preferred
embodiment, the height adjustment of the cam follower roller is
accomplished by means of an eccentric which is rotated by a
lever arm connected to the piston rod of a pitch adjustment
cylinder operated by a servo valve in response to the pitch
control output signal of the computer. The cylinder contains a
transducer which produces a piston rod position signal
corresponding to such height which is fed back to the computer
to provide a closed loop feedback control in order to
accurately set the pitch angle within 0.01 degree as a function
2!~ of the horizontal position of the main knife carriage along the
pitch rail during pee:Ling.
The present invention has the advantage that
different pitch angle profiles for adjustment of the lathe
knife pitch angle are easily defined and revised by changing
the data entries stored in the computer memory. In addition,
the computer enables quick selection of the appropriate pitch
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profile from a plurality of pitch profile tables stored in such
memory. Also, the ability to develop more optimum pitch
profiles for different wood species and different wood
conditions is made possible. As a result, the quality of
5 veneer is improved, and the production output of the veneer
lathe is increased.
The invention may be summarized according to a first
broad aspect as veneer lathe appa=ratus with automatic adjust-
ment of the knife pitch angle, comprising: drive means for
1~~ rotating a log; main carriage means for moving the lathe knife
toward said log to peel veneer from the log; knife carriage
means for supporting the lathe knife and being pivotally
mounted on said main carriage means to change the pitch angle
of said knife; pitch :rai.l cam means for guiding the movement of
1.'~ said knife carriage means along a mechanical pitch rail; cam
follower means mounted on said knife carriage means for
engagement with said pitch rail cam means to cause said knife
carriage to pivot as said cam follower means moves along said
pitch rail cam means to adjust the pitch angle of said knife
20 through a range of pitch angles during peeling as the main
carriage is moved toward the .Log; and control means for
automatically adjusting the position of said cam follower means
on said knife carriage means in response to changes in the
position of said main carriage means to vary said range of
25 pitch angles.
According to another broad aspect the invention
provides electrical control system for automatic adjustment of
veneer lathe knife pitch angle, comprising: pitch adjustment
means for adjusting the pitch of a veneer lathe knife by moving
3() an actuation rod in response to a pitch adjustment input
signal; first transduc=er means for producing a pitch angle
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indication signal corresponding to the position of said rod;
second transducer means for producing a lathe carriage position
output signal corresponding to the position of a lathe carriage
moving said knife toward a rotating log block to peel veneer
from said block, said lathe carriage position being related to
the radius of said log block, and computer means for producing
said pitch adjustment signal in response to said lathe carriage
position signal and for terminating said pitch adjustment
signal in response to said pitch angle indication signal when
the desired pitch angle is reached.
Description of the Drawinas
Other objects and advantages of the present invention
will be apparent from the following detailed description of a
preferred embodiment thereof and from the attached drawings of
which:
Fig. 1 is a partially diagrammatic end view of a
veneer lathe knife pitch angle adjustment apparatus in
accordance with the invention;
Fig. 2 is a schematic diagram of a computer control
system which may be employed for the apparatus of Fig. l;
Fig. 3 is an enlarged view of a portion of the
apparatus of Fig. 1 showing adjustment of the knife pitch; and
Fig. 4 is a diagrammatic view of a typical lathe
knife pitch angle profile stored as a pitch data table in the
memory of the computer system of Fig. 2.
Description of Preferred Embodiment
As shown in Fig. l, one embodiment of the veneer
lathe apparatus of the present invention includes a lathe knife
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supported for pivoting movement on a knife carriage 12,
which is pivotally mounted on a main lathe carriage 14. The
main carriage 14 is moved in a
- 6 -
horizontal direction 15 by an electric motor 16 whose
output shift is geared to a pair of drive screws 18 at
the opposite ends of the main carriage. The main car-
riage 14 also supports a nose bar roll 20 whicYz is
mounted by support arms 21 on a roll carriage 22 for
adjustment of the knife gap between such roll and the
knife by sliding movement within a pair of spaced guide
channels 24 and 26 attached to the main carriage 14.
The nose bar roll 20 is urged against the outer surface
of a log block 28 to compress such surface at a position
immediately in front of the knife blade 10 and is spaced
from such knife by a gap corresponding to the thickness
of the veneer to be peeled from such log block. As a
result, the knife blade peels thin sheets of wood veneer
27 from the surface of the log block 28 as such log
block is rotated in a clockwise direction 29 in Fig. 1.
The log block is driven in any suitable manner
such as by a pair of powered spindles 30 which engage
the opposite ends'~f the log at its central axis to
rotate such log about an axis of rotation 32. The lathe
spindles 30 are suitably coupled to a electric motor 34
for rotation in a conventional manner. The nose bar
roll 20 may also be driven by connecting it to another
electric motor 36 for rotating such nose bar roll and
causing it to apply additional torqu a to the log for
rotation thereof during peeling.
During peeling, the knife blade 28 is moved
horizontally toward the axis of rotation 32 of such
block by movement of the main carriage 14 in the direc-
tion 15 with the motor 16 as the diameter of the block
reduces. The knife carriage 12 is adjustably mounted on
a cam follower roller 38, which rolls along a pitch rail
cam member 40. The pitch rail 40 is provided with a
predetermined slope so that as the cam follower roller
38 moves along such pitch rail, it causes the knife
_ 7 _
carriage 12 to pivot in the clockwise and counterclock-
wise directions of arrows 42 about the point of the
knife blade 10. As a result of adjustment of the height
of roller 38 on the knife carriage 12 and the slope of
S the rail 40, the pitch angle of the knife blade between
the blade°s front surface 41 and a vertical plane may be
varied positively and negatively from an angle of zero
degree where the front surface of the knife blade is
vertical, as shown in Fig. 3. The range of variation of
the knife pitch angle is between a positive pitch angle
or "lead" of up to ~-1 degrees in a clockwise direction
away from the log and a negative pitch angle or °'heel"
of about --5 degrees in a counterclockwise direction
toward the log in Fig. 1 when the slope of the rail 40
is zero or parallel to the horizontal direction 15.
Thus, the pitch angle of the knife blade is set by the
slope of the pitch rail cam 40 and by the height of the
cam follower roller 38 on the knife carriage 12. Rail
40 can be set to a background slope enabling total
operating range of pitch adjust from -h10 degrees to -10
degrees.
Normally, the pitch rail 40 has a constant
slope, but it may be provided with an end portion of
changing slope nearest the log which is greater than the
slope of its other portion, as shown by element 120 in
U.S. Patent No. 4,708,180. However, different species
of wood and different wood conditions of the same spe-
cies require changes in the pitch profile for optimum
yield of veneer of substantially uniform thickness and
high quality. This pitch angle profile change for dif-
ferent species of wood is conventionally done manually
lay adjusting the slope of the pitch rail 40 before.peel-
ing through adjustment of a pair of threaded mounts 44
and 45 at the opposite ends of the pitch rail with
wrenches or a manually controlled motor. Thus, the
mounts are rotated to adjust the height of the pitch
8
rail by raising or lowering the ends of such rail in the
direction of arrows 48 and 50 in order to set the rail
slope. This manual adjustment of the slope of the pitch
rail is slow and inaccurate, resulting in lower quality
veneer and reduced production. The electrical control
system of the present invention overcomes this problem
by allowing rapid selection between a plurality of pre-
determined pitch profiles stored in the computer memory
as pitch data tables which can be easily changed by
inputting new data with the computer terminal, as here-
after described.
The electrical control system for adjusting the
knife pitch angle in accordance with the present inven-
tion includes a pitch adjustment cylinder 52 fixed at
one end to the main carriage 14. The piston rod 54 of
the pitch adjustment cylinder is pivotally connected at
pivot 55 to one end of a lever arm 56 to rotate such
lever arm. The lever arm 55 is connected at its other
end to the shaft of an eccentric 58 which causes the
center of the cam follower roller 38 to orbit about the
axis of the eccentric to raise such cam follower roller
to different heights on the knife carriage 12 in re-
sponse to pivotal rotation of the lever arm of about
90 degrees ar less by the pitch adjust cylinder 52.
These adjustments of the height of the cam follower
roller 38 on the knife carriage 12 cause such knife
carriage to rotate the knife to different angles corre-
sponding to such heights at any given position along the
pitch rail 40, Thus, by adjusting the height of the cam
follower roller 38 on the knife carriage 12, several
different effective pitch profiles are provided for a
given pitch rail 40 to change the pitch angle of the
knife blade in accordance with different wood species
and different wood conditions in a fast, accurate manner.
_ g _
The pitch adjustment cylinder 52 is controlled
by a servo valve 60, which is operated by the pitch con-
trol output signal at output terminal 61 of a digital
computer in the computer control system of Fig. 2 as
hereafter discussed. The position of the piston rod 54
in the pitch adjustment cylinder 52 corresponding to the
height of the cam follower roller 38 is sensed by a
transducer 62 to produce a height output signal which is
applied to input terminal 63 of the computer control
lp system. A main lathe carriage position cylinder 64,
fixed to the frame of the lathe and whose movable piston
rod 66 is connected to the main carriage l~ .for movement
with such carriage, causes a transducer 67 coupled to
such piston rod to produce a lathe carriage position
signal corresponding to the log block radius. This main
carriage position signal is applied at an input 68 of
the compLater to indicate the log radius or the position
of the knife blade 10 relative to the axis of rotation
32 of the log during peeling. The transducers 67 and 62
may be sonic pulsW waveguide transducers of the
Temposonics-type described in U.S. Patent ~o. 4,708,180.
The horizontal knife gap 69 between the front
surface 41 of the knife blade ZO and the nose bar roll
20 ahown in Fig. 3 may also be automatically adjusted by
the computer in response to changes in diameter of the
log block 28 by means of a gap adjustment cylinder 70
mounted at pivot 71 on the main carriage 14. The piston
rod 72 of such cylinder is pivotally connected at pivot
7~ to a lever arm 76 which rotates an eccentric 78 that
is pivotally attached to a second cylinder 80 to adjust
the nose bar to knife gap. The second cylinder 80 has
its piston rod 82 connected to the nose bar carriage 22
for..reciprocating the nose bar roll 20 between the con-
tact position shown in Fig. 1 with such roll in contact
with the log during peeling and a retracted position in
which the roll is removed from contact with the log to
10
allow loading of new logs into the lathe. The gap be-
tween the nose bar roll 20 and the knife blade 10 is
adjusted during peeling by means of the gap adjust
cylinder 70 in response to gap control signals trans-
muted from a computer output 84 to a servo valve 86
controlling the cylinder 70. A gap spacing transducer
88 is attached to the gap adjustment cylinder 70 in
order to sense the position of the poston rod 72 in such
cylinder which corresponds to the gap spacing between
the knife blade and the nose bar roll 20. The trans-
ducer 88 produces a gap spacing output signal which is
applied to an input terminal 90 of the computer.
The operation of such nose bar roll gap adjust-
ment in response to reduction in the diameter of the log
block during peeling is described in greater detail in
~J.~. Patent No. 4,708,180 of ~3rowning, et al., issued
November 24, 1987.
It should be noted that a pair of backup rolls
92 and 94 may be provided which are moved into contact
with the surface of the log block 28 on an opposite side
thereof from the knife blade 10 and nose bar roll 20
when the log block has been peeled to a small diameter
on the order of about 8 inches. 'thus, the backup rolls
92 and 94 prevent the bending of log blocks of small
diameter during peeling due to the pressure of the knife
and nose bar. The movement of the backup rolls toward
the center of rotation 32 of the log block may also be
adjusted by the computer.
A computer control system for adjusting the
lathe knife pitch angle in accordance with the present
invention is shown in ~'ig. 2. Such computer control
system includes a central. processing unit (CPU) 96 of a
general purpose digital computer which contains a digi-
tal data memory including a random access memory (RAM)
a, ,
- 11 -
and an electronic programmable read-only memory (EPROal)
in which the comptater program for operating such system
is stored. The CPU 96 is connected to a data bus 98
including parallel lines having a plurality of inputs
and outputs. A digital data storage memory 100, con-
sisting of a RAM and an EPROM is employed to store the
data of several knife pitch angle profiles for different
species of wood, such profiles being stored in the form
of pitch data tables such as that shown in Fig. 4. The
pitch angle profile tables may be each formed by 14
pairs of data points corresponding to the various knife
pitch angles at different log block radii or.distances
from the knife to the axis of rotation 32 of such block.
Four different pitch profiles may be stored in
the computer memory 100 and selectively accessed by the
computer control system by means of a pitch selection
switch 102. The pitch selection switch has four differ-
ent switch positions corresponding to such four pitch
rail profile tables. In addition, a zero pitch angle
control switch 104 is provided to calibrate the pitch
adjust system to the front face bevel 41 ground into
knife 10, as well as two veneer thickness adjustment
settings 106 and 108. These switches all supply input
signals through a parallel input circuit 110 and the
data bus 98 to the computer. Peel thickness signals
"set 1 peel thickness" and "set 2 peel thickness°' cor-
responding to two different veneer thicknesses, such as
0.100 inch and 0.200 inch,. are transmitted from output
111 of a programmable controller 112 through the paral-
lel input 110 to the CPU 96. Such programmable control-
ler also receives input information from the computer,
such. as the knife '°carriage position Noe 2°' signal. at
input 113, through a parallel output circuit 114. The
thickness adjustment switches 106 and 108 are for °°fine
tuning" adjustment of the knife gap between the knife
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blade and the nose bar roll for a selected veneer thick-
ness in order to compensate for knife dullness and other
variables. A computer terminal 116 is provided for
manual input of data and for displaying output informa-
Lion gathered by the computer, such terminal being con-
nected by lead 117 to the central processing unit 96.
A lathe charger computer 118 may also be pro-
vided for controlling the measurement and centering of
l0 logs in a lathe charger tnot shown) and for transmitting
such logs into the lathe with such lathe charger.
Charger computer 118 does not control the knife pitch
adjustment. However, such charger computer may be
connected to the parallel output circuit 114 of the
above-described computer, including CpI~ 96, to receive
control signals including lathe "carriage position
i~o. 1"' signal at input 119 so that the veneer lathe
charger does not transfer logs into the lathe until
peeling of the previous log is finished and the main
lathe carriage has been retracted far enough to allow
clearance for loading next log.
As shown in Fig. 2, the pitch adjustment cylin-
der 52 has its servo control valve 60 connected to the
output 61 of a digital-to-analog converter 120 of the
computer control which converts the digital data re-
ceived from the computer corresponding to a pitch rail
profile table stored in memory 110 into an analog pitch
adjustment signal. The pitch adjustment signal causes
the pitch adjustment cylinder S2 to rotate the pitch
adjustment eccentric 58 to change the height of the cam
follower roller 38 on th a knife carriage 12 to the
proper value of the desired pitch angle for the log
diameter corresponding to the position of such cam fol-
lower roller on the pitch rail 40. The transducer 62 of
the pitch adjustment cylinder 52 transmits a height
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position signal corresponding to the position of the
piston rod 54 to input 63 of a transducer data converter
122. From this transducer signal, the computer can
determine when the selected height of the cam follower
roller corresponding to the desired pitch angle is
reached and then terminate the pitch adjustment signal
applied to valve 60. Thus, a closed-loop feedback
control system is provided.
It should be noted that the position of the
main carriage 14 on the pitch rail 40 corresponding to
the distance of the knife blade 10 from the axis of
rotation 32 of the log or to the radius of such log is
provided by an output signal of the position transducer
67 of the carriage position cylinder 64. The main car-
riage position signal is transmitted from the transducer
67 to input 68 of the transducer data converter 122.
This main carriage position signal enables the CPU to
determine the knife pitch angle from the selected pitch
profile table stored in the computer 100 which has been
selected by the pitch select switch 102.
The nose bar roll gap adjustment cylinder 70 is
also provided with a servo valve 86 connected to the
output 84 of the digital-to-analog converter 120 which
is coupled through the data bus 98 to the CPU 96. As a
result, the nose bar roll gap control cylinder 70 is
caused to rotate lever arm 76 and the eccentric 78 to
adjust the gap between the.nose bar roll 20 and the
knife blade 10 in accordance with the radius of the log
block 28 being peeled which is determined from the
output 68 of the main carriage transducer 67 that is
applied to the transducer data converter 122, as dis-
cussed above~ A gap spacing transducer 88 coupled to
the piston rod 72 of the nose bar roll gap cylinder 70
produces a gap pacing signal which is applied to input
30 of the transducer data converter 124. The converter
- 14 -
124 applies the gap spacing signal through the data bus
98 to the CPU 96 which, when the desired gap spacing as
reacted, terminates the gap adjustment signal applied to
valve 86. Thus, the nose bar roll gap is also adjusted
by a closed-loop control system.
Backup rolls 92 and 94 are moved together into
engagement with the log block 28 when such log block has
been peeled to a small diameter of, for example, about
8 inches diameter by an actuation cylinder 126 con-
trolled by a servo valve 128 connected to an output 129
of the digital-to-analog converter 120. Thus.. the servo
valve 128 controls the cylinder 126 in response to a
computer output signal to move the backup rolls 92 and
94 into engagement with the log when it reaches a diame-
ter of 8 inches. The cylinder 126 continues to move the
backup rolls toward the axis of rotation 34 of such log
during peeling until peeling stops. At this time, a
control signal is generated by the controller 112 and
applied to fast-up valve 130 connected to actuation
cylinder 126 to quickly raise the backup rolls to the
retracted or full-up positions thereby allowing a new
log to be loaded into the veneer lathe. A full-up limit
switch 134 is provided on a support arm 135 for the
backup rolls to produce an output signal which is
applied at an input 136 of the progranunable controller
to tell it that the backup rails have reached the
full-up position. A transducer 138 produces a backup
roll position signal corresponding to the position of
the piston rod 139 of actuation cylinder 126 and sup-
plies such position signal at computer input 140 to the
transducer data converter 124. This tells the computer
the.position of the backup rolls relative to the axis of
rotation of the log so they are maintained in contact
with the surface of the log at the proper pressure
during peeling.
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A knife pitch angle profile 142 which is
exemplary of the type which may be stored in the compu-
ter memory 100 in the control system of Fig. 2 is shown
in Fig. 4. Such profile, Sdhich is typical for Douglas
S fir or hemlock, is in the form of a curve of joined data
points 144, each representing a knife pitch angle at a
given log block radius. The pitch profile curve 142
consists of 13 data points, labeled 144A t:o 144M, cor-
responding to different knife pitch angles for different
log block radius positions. Thus, point 144A has a
positive pitch angle of about -E0.6 degree at a block
radius of 20 inches, point 1448 has a pitch angle of
+0.2 degree for a block radius of about 1b.5 inches,
while data point 144C has a pitch angle of zero degree
at a block radius of 14 inches. Then the pitch angle
decreases to negative angles of progressively greater
magnitude as the block radius decreases. Thus, point
144D has a pitch angle of about -0.1 degree at about
11.2 inch radius, point 144E has a pitch angle of
-0.2 degree at a radius of 8 inches and point 144F has a
pitch angle of -0.35 degree at a radius of about
S.7 inches. The pitch angle decreases rapidly to an
angle of -2.0 degrees at a radius of approximately 1.5
inches at point 144L which corresponds to a log block
2S diameter of 3 inches. The pitch angle would be adjusted
to an even lower pitch angle of -3.5 degrees at a block
radius of 1 inch at point 144M, if peeling to this small
diameter.
An important advantage of the present invention
is that any of the data points 144 on the pitch angle
profile curve 142 may be changed to provide a new pitch
profile curve simply by changing the data in the pitch
profile table stored in the computer 100. This can be
done by manually inputting a new data point by means of
terminal 116. Thus, the present invention is an ex-
tremely versatile and accurate way of changing the pitch
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angle profiles far different wood species and different
log conditions such as moisture content or sap content.
It will be obvious to one having ordinary skill
in the art that many changes may be roads in the above-
described preferred embodiment of the present inven-
tion. Therefore, the scope of the invention should be
determined by the following claims.
15
25
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