Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02305850 2000-OS-10
METHOD AND APPARATUS FOR BUCKSAWING LOGS
This application is a division of Canadian patent application
Serial No. 2,131,056 filed 29 August, 1994
Technical Field
The invention relates to apparatus for cross-
cutting or "bucksawing" long logs to produce logs of
shorter length. More particularly the invention relates to
a method and apparatus for feeding, positioning and holding
a log for bucksawing to the desired length.
Background Art
It is important in the sawing of logs into lumber
that the selection of saw cuts be made to maximize the
quantity and quality of lumber which is yielded by the log,
depending on the length, thickness and quality of the log,
such as the presence of knots, defects and the like. As the
first step in this process, the tree-length log is cut into
shorter lengths, or "bucked", prior to further processing.
There are two commonly used methods of carrying this out in
a sawmill . A first method is a transverse system whereby
the tree-length log is moved sideways through a battery of
buck saws where it is segmented simultaneously into shorter
logs. This method is not particularly well suited to
modifying the position of the cross cut to maximize the
value and recovery from the log. A second method is the
lineal bucking system whereby the tree-length log is moved
endwise down the conveyor to a saw which bucks the log into
shorter lengths one cut at a time. This method is better at
maximizing the value and recovery from the log, but in both
this method and the transverse method the speed of the
transport conveyor is necessarily f fixed at the speed the
log moves through the sawing station, resulting in low
throughput. For example, since the feed conveyor in the
lineal bucking system must be stopped while the log is
being bucked, there is no opportunity for closing the gaps
between the logs on the feed conveyor.
There is therefore a need for a log bucksawing
system in which the speed of the infeed and outfeed
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conveyors can be operated independently of the progress of
the log at the sawing station.
Disclosure of Invention
The present invention provides a method for buck-
sawing a log comprising the steps of a) advancing the log
endwise along an infeed conveyor; b) raising the log above
the level of said infeed conveyor while advancing the log;
c) measuring the advance of the log while raised; d)
stopping the log at the desired length; e) sawing the log
to produce a forward log segment; and f) lowering the for-
ward log segment onto an outfeed conveyor while advancing
the remaining log segments.
Brief Description of Drawings
In drawings which disclose a preferred embodiment of
the invention:
Fig. 1 is a schematic diagram showing the ap-
paratus of the invention in top view with the log on the
infeed conveyor;
Fig. 2 is a schematic diagram showing the ap
paratus of the invention in top view with the log being
positioned in the sawing station;
Fig. 3 is a schematic diagram showing the ap-
paratus of the invention in top view with the log being
sawn in the sawing station;
Fig. 4 is a schematic diagram showing the ap
paratus of the invention in top view with the sawn segment
of the log on the outfeed conveyor;
Fig. 5 is a plan view of the feeding and bucking
according to the invention;
Fig. 6 is an end view, partially cut-away and
partially in section, of the cut-off saw and feed rolls of
the invention, with the rest position of the cut-off saw
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shown in phantom r.;~utline, and the saw blade removed for
purposes of illustration;
Fig. 7 is an elevation of the cut-off saw and
feed rolls of the invention, with the lowered position of
the bottom roll shown in phantom outline;
Fig. 8 i.s a plan view of the feed rolls of the
invention, showing a portion of the cut-off saw;
Fig. 9 i::~ s. plan view of the cut.-off saw of the
invention, showing a portion. of the feed rolls;
Fig. 10 is an elevation view, partly in section,
of the encoders of the invention; and
Fig. 11 is a plan view of the encoding disc used
in the encoders of the invention.
Best Models) For Carrying Out the Invention
Looking at Fig. 1, the bucksawing apparatus,
designated generally as 10, has a log 12 moving in the
direction of arrow A on infeed conveyor 14 towards a
powered hourglass roll 16, horizontal bottom feed roll 18
and vertical side feed rolls 20, 2'1. Feed rolls 18, 20 and
21 are provided with spikes 25 (see Fig. 6 and 7) to grip
the log 12 without slippage, and are rotatably driven by
hydraulic motors JO (see F'ig. 6, 7) such as REXROTHTM fixed_
displacement motors Model AA2FM (series 61), 40 degree bent
axis design, and <:~ Trasmital Bonfiglioli planetary gearbox
(two-stage) Model 303L230MZ-WOA-SSBA-2T, 30:1. Preferably
feed rolls 18, 20 and 21 are all formed of extra strong
steel pipe approximately 2 (two) feet in diameter. The
bottom feed roll :l8 is preff~~rably 1 (one) foot 10 inches in
length, whi7_e the vertical. rolls are preferably 2 (two)
feet long. Pointed spikes 25 are preferably 3/4-inch in
diameter and are welded on the pipe at. 15 degree inter
vals.
Vertical side feed rolls 20, 21 are pivotally
mounted on the ends ofarms 22, 23 which are supported on
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frame 44 and pivoted by cylinders 40, 42. The outfeed
conveyor is indicated at 24 and the cut-off saw is provi-
ded at 26 on a pivoting arm 27 (Fig. 7) or some other
conventional means for swinging the cut-off saw 26 perpen-
dicularly across the path of the log 12. Saw 26 has a saw
guard 30, and is driven by electric motor 32 through drive
belt 35 and sheave 36 on shaft 38. Saw 26 is held on shaft
38 by collar 39. A belt guard 34 is provided. Arm 27 is
pivoted by a position-sensing hydraulic cylinder 41 such as
an REXROTH PRESSURE MASTERT~ MT4-HH complete with TEMPOSONIC
IIT~ probe TTS-RB-U-0240. Horizontal feed roll 18 is
pivotally mounted on frame 45.
Photocells 28, 29 detect the passage of the
forward and rear ends of the log 12. Photocells 28, 29
provide a signal to a computer, central processing unit or
programmable logic controller (not shown) which controls
the operation of the horizontal and vertical feed rolls 18,
20, 21 and cut-off saw pivot arm 27.
The infeed and outfeed conveyors 14 and 24, which
may be belts or chains, are normally run at a fixed,
constant speed, although a variable speed may be used. When
the feed system is not feeding or bucking a log, the verti
cal and horizontal rolls 18, 20, 21 can be run at the same
speed as the infeed or outfeed conveyors. The log 12 will
have been scanned prior to arrival at the infeed conveyor
14 and this scanning information is used to determine the
location of the cuts made by cut-off saw 26. As the infeed
conveyor 14 conveys log 12 towards the cut-off saw 26, the
vertical feed rolls 20, 21 are in the open position shown
in Fig. 1, swung away from the bottom feed roll 18. As
shown in Fig. 2, as the log 12 is conveyed towards cut-off
saw 26, it is centred along the axis of the feed line by
hourglass roll 16. The surface of hourglass roll 16 and
horizontal bottom roll 18 are about 1/2 inch to 1 (one)
inch higher than the surface of the infeed conveyor, and as
the forward end 11 of log 12 makes contact with hourglass
roll 16 and bottom feed roll 18, it is lifted slightly
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above the level of infeed conveyor 14. When the forward
end 11 of log 12 trips the photocells 28 located above and
between hourglass roll 16 and the bottom feed roll 18,
vertical feed rolls 20, 21 are pivoted inwardly and pre-
y positioned on arms 22, 23 to the approximate diameter of
the log 12. As the forward end 11 of log 12 progresses to
a position between the vertical feed rolls 20, 21, full
hydraulic pressure is applied to hydraulic cylinders 40, 42
so that the vertical rolls 20, 21 are pivoted inwardly on
arms 22, 23 to make full contact with the ,surface of log
12. As the forward end 11 of log 12 progresses and trips
the second group of photocells 29 located just past the
cut-off saw 26, the controller will activate the encoders
80 mounted on the hydraulic motor 70 output shafts driving
the vertical feed rolls 20, 21, and activates the pivoting
arm 27 on which cut-off saw 26 is mounted to index the cut-
off saw in position directly behind feed roll 20. The
length of the log which has passed the plane of the cut-
off saw 26 is determined by the controller based on the
number of encoder pulses received from the hydraulic motors
70, and once the desired length of the log has been reached
based on the scanned information, the rolls 18, 20, 21 are
stopped automatically and the log is bucked by pivoting the
cut-off saw across the log as shown in Fig. 3 and 6. With
the aid of the encoder information the log is then consecu-
tively moved forward and stopped by the rolls 18, 20, 21 at
the desired locations according to the scanner information
to cut the log at the optimum lengths. The feed rolls are
able in this way to move the log rapidly between successive
cutting positions. The system can also be manually over-
ridden by.an operator and defects, which are picked up by
the operator, can be manually bucked out of the logs.
The throughput speed of the sawing or bucking
step is increased by the sensing of the log diameters
during the sawing process. The hydraulic cylinders 40, 42
which control the arms 22, 23 which pivot the vertical feed
rolls 20, 21 are equipped with TEMPOSONICT~ linear
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positioners which sense the length of the stroke on the
hydraulic cylinders which control the arms 22, 23 and
thereby generate a signal indicative of the diameter of the
log, which is also used for pre-positioning of the vertical
feed rolls 20, 21 as the log moves forward. This informa-
tion is compared to the scanning information to confirm
that the log is being scanned at the proper location. The
log diameter information is also used to pre-position the
cut-off saw 26 as well as control the stroke of the saw
when the log is bucked. For example, as the diameter of the
log changes, the rest position of the cut-off saw will be
moved towards or away from the log to reduce the distance
the cut-off saw must swing to saw the log. The length of
the stroke or swing of the cut-off saw is also determined
by the measured diameter of the log so that the cut-off saw
can complete its stroke and return to its start position in
the minimum time, thereby maximizing throughput.
Predetermined desired lengths for the log seg
ments to be cut from a tree-length log can be pre-pro
grammed into the system so that as the next programmed
length is approached the hydraulics automatically start to
slow the log down and stop at the desired length. The cut-
off saw is then automatically activated and cycled to cut
the log. Once the first segment is bucked from the log, the
feed rolls advance the log at very high speeds to the next
programmed length for bucking. Meanwhile the segment of the
log which has been bucked can be advanced at high speed on
the outfeed conveyor 24 to the next processing stage (see
Fig. 4) .
Existing lineal bucking systems do not have any
method for quickly rejecting or disposing of short log ends
or other debris in the system. At present this material
must be sawn into very short lengths by the bucking saw so
that it can drop onto refuse conveyors under the cut-off
saw. In the present invention, the horizontal feed roll is
mounted on pivot shaft 46 (Fig. 6) whereby hydraulic
cylinder 48 holds feed roll 18 up in the normal operating
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position. If a short. chunk or other piece of reject ma-
terial develops at the cut--off~saw, the bottom horizontal
feed roll. 18 can be depressed and the material deposited
directly into a refuse conveyor. This el.im:inates the need
to cut the debris into shorter pieces to remove it, thereby
increasing the overall throughput.
Since the infeed conveyor continues to feed
during the intervals when rolls 18, 20, 21 are stopped to
buck the log, gaps between the logs are reduced and the
throughput is increased. The higher throughput speed during
sawing :is also achieved through the use of the hydraulic
motors and encoders on the feed rolls.
The encoding of the hydraulic motors for the
vertical feed rolls is achieved by providing encoders 80 as
shown in Fig. 10. Two inductive proximity sensors 82,
which are preferably OMRON;MModel TL-X281-GL are mounted on
encoder housing .B4 by adjustable mounting plates 86. They
pick up the reflected light from the encoder discs 88
coupled to the output shafts of the hydraulic motors 70.
The pulses are converted by the central processing unit
into a corresponding distance of travel of the log 12. A
splined shaft 90 couples the motor output to a planetary
gearbox. Windows 92, 94 permit viewing of the interior of
the housing. The encoding disc 88, shown in Fig. 11, has
a number of lobes 96 which interact with the proximity
sensors, the sides 98 of which are cut. away to provide a
more accurate reading.
The preferred form of the invention uses tandem
pneumatic/hydraulic cylinders 40, 42 REXROTHTM MXO-PP/ME6
HH with a TEMPOSONIC IIT" probe system to move the arms 22,
23. Since the tree-length logs coming into the .feed system
may be either top or but~t~ first, the feed rolls must move
with the taper of the log as it advances through the
system. As the rolls move with the taper, they must still
maintain constant pressure on the log, preventing the rolls
from Slipping and producing inaccurate log lengths. The
hydraulic circuit is designed such that a constant pressure
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is maintained on the log at all times. However irregular-
ities in the log such as knots or burls will~also be
encountered by the feed rolls moving at considerable speed,
which will tend to cause the rolls to lose contact with the
surface of the log. To reduce this effect the hydraulic
cylinders are provided with associated pneumatic cylinders.
The pneumatic cylinders (Fig. 6 and 7), operating at low
air pressures, are mounted in tandem with the hydraulic
cylinders 40, 42 to absorb and dampen any sudden lateral
movement to maintain contact of the feed rolls on the log.
Another aspect of the control system for the
hydraulic cylinders is a feature to maintain accurate log
positioning at high speed throughput. As the speed of the
log increases, considerable momentum or inertia is built
up, so that when the system tries to stop the log at the
desired position, there is a tendency for the log to
overshoot. This tendency is overcome by decreasing the
hydraulic pump pressure in the hydraulic line serving
motors 70 as the log is slowed so that the hydraulic system
provides a braking action to help slow the log as it
approaches the selected position.
Conventional scanning arrangements are unsuitable
for the present invention which not only reduces gaps
between logs in the system but also increases the through-
put speed through the cut-off saw. In conventional systems,
loge are transported transversely on a log deck to a point
where they are singulated into a conveyor that moves the
loge longitudinally through a log scanner and from there to
the cut-off saw. Each log is transported separately through
the scanner with a gap of two to four feet between consecu-
tive logs. This conventional arrangement cannot provide an
adequate supply for the high throughput of the present
invention. Consequently, a modified scanning arrangement is
preferred for the present invention as illustrated in Fig.
5. Logs are transported transversely on log deck 50 to a
diverter gate 52 where they are diverted onto one of two
parallel conveyors 54, 55 which transport the logs longi-
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tudinally through two parallel log scanners 56, 57. and
from there by parallel conveyors 60, 62 to a deck 58 where
two log sweeps 59 alternately sweep the logs onto infeed
conveyor 18 and from there to the cut-off saw 26. This
arrangement reduces gaps between logs as they enter the
present bucking system.
As will be apparent to those skilled in the art
in the light of the foregoing disclosure, many alterations
and modifications are possible in the practice of this
invention without departing from the spirit or scope
thereof. Accordingly, the scope of the invention is to be
construed in accordance with the substance defined by the
following claims.
