Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Improvements in the secondary breakdown of logs in sawing
mills
The present invention regards log-sawing and particularly
sawing of logs having a curvature.
Log sawing is generally performed in at least two stages,
namely, a primary log breakdown sawing, where two parallel
cuts are made, sometimes combined with chipping, in order
to obtain a block, i.e. a log having two parallel plane
surfaces. The log is then rotated 90 for passing through
a second saw rig for secondary breakdown into planks. The
products of the two breakdown operations are then edged,
sorted, dried, etc. A comprehensive review of the state of
the art is found in IlLumber Manufacturing" by Ed M. Willi-
ston (Miller Freeman Publications, 6econd printing, San
Francisco 1978).
Only an ideal log has the straight form of an elongated
truncated cone, and most logs are more or less curved. In
order to obtain a maximum yield of useful wood, it i6
standard practice to orient the log such that the plane of
the maximum curvature is parallel to the sawing plane when
performing the primary log breakdown sawing. The secondary
breakdown is then performed on a log having two parallel
surfaces, but which is bent in the perpendicular direct-
ion. Most commonly, the secondary breakdown is then madeby straight sawing seams. In this secondary breakdown,
there are in principle two methods in use, namely, full
taper sawing and center sawing, also called half tape
sawing. In full taper sawing, the sawing direction follows
a straightedge or linebar, against which the log is laid
and governed, so that the opposite edge makes the full
taper angle with the sawing direction. In half taper
sawing, also called pith sawing or center sawing, the
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B
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sawing direction follows the straight line approximate of
the pith of the log, such that both edges make half of the
taper angle to the sawing direction. From the point of
view of yield, both systems are defendable. It would,
however, be an advantage if the sawyer could select
between both in order to obtain best individual yield.
Further, for some uses, wood cut along the pith is pre-
ferred by the users.
Presently, center sawing is preferred in northern Europe,
whereas full taper sawing is more common in the USA and in
Canada.
Apparently, the straight sawing of curved logs, regardless
of method, leads to a loss of yield, and therefore, much
inventive effort has been brought to enabling sawing
llaround the curve", a method practiced for some fifty
years in Scandinavia, using pith sawing techniques. The
general principle followed for such curve sawing is to
shorten the length of the steering equipment with two or
more saws. Although the planks come out curved, it is a
fact that after drying, automatically being straightened
by stacking when dried, they come out straighter and with
less warping than with llstraight sawing". Further, the
yield is very much increased, and cases are known where,
depending on the proportion of curved logs, an improvement
in yield of 12% has resulted. However, as far as known,
curve sawing using full taper sawing has not hitherto been
tried.
In principle, curve sawing is made with similar cutting
means and aligning devices as straight sawing, with the
difference that the aligning means must be positioned at
mutually shorter distances. This makes guiding and align-
ing more difficult. The remote end of the log being treat-
ed must be given liberty to move sideways once the log has
been securely entered into the cutting/sawing device
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proper, being guided by fitting guides at short intervals
in the log direction. On the other hand, in order to
obtain proper entry of the near end of the log, it i8
necessary to have pre-aligning devices, which must, how-
ever, be withdrawn once the log has been safely enteredand is guided at two poisitions near to each other and to
the cutting/sawing device.
It is an object of the present invention to obtain a
system with a secondary saw rig which is capable of curve
sawing and in which curve sawing is possible alternative
using pith sawing and full taper sawing, at will, such
that the sawyer can at all times select the sawing scheme
which will give the best economic yield for each log.
Economically best yield is not the same as best yield in
volume and may vary much from a mill to another and even
from season to season, depending on what kind of plank and
board dimensions are in demand. The sawyer is nowadays
often computer assisted, and equipment is known for optic-
ally projecting sawing lines for various models of cuts,
cooperating with automatic settings of the saws. The
sawyer may then try more than one scheme on the log before
selecting one of them.
Automatic setting saws, for instance such prior art
circular saws which are movably mounted on a splines
shaft, are particularly advantageous in combination with a
guiding system for logs for obtaining the objects of the
invention. The invention can however be practised with
different kinds of sawing equipment, also with band saw
equipment, although this will not be described.
The invention shall now be more fully explained by refer-
ence to the drawings, where
Fig. 1 A-D show the principles of secondary sawing as
described above.
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Fig. 2 shows a layout of a curve sawing line.
Fig. 3 A and B show pre-aligning for center and full taper
curve sawing respectively, using a chipper canter.
Fig. 4 A and B show final aligning for center and full
taper curve sawing respectively, using a chipper canter.
Fig. 5 A and B show started curve sawing in a chipper
canter for center and full taper sawing respectively.
Fig. 6 A and B show aligning and sawing respectively in an
edger saw.
Fig. 7 A-C show a roller pair which is guidable by
hydraulic cylinders for centering/aligning purposes.
Fig. 8 shows a hydraulic control system for a chipper
canter and an adjustable roller pair.
Fig. 9 A-B show the control system for a roller pair in
center-sawing and full taper sawing modes respectively.
In Fig. l A-D are shown in schematic horizontal views how
the various kinds of sawings are performed on a curved log
together with views of sawing seams, for curved logs. In
Fig. l A, straight/center sawing is shown. Centering is
made by rollers, and the block is then steered through
linearly. The side cuts will make one board which is thin
at the middle and one which is thick at the middle.
Fig. l B shows straight/full taper sawing, where the block
is steered along a linebar at one side. Fig. l C shows
curve/center sawing, under constant control of two pairs
of rollers, which follow the sides of the block at all
times, moving sideways always with equal amounts. Fig. l D
shows curve/full-taper sawing under control of two pairs
of rollers. One roller in each pair is still, whereas the
other one will move in contact with the block. Thus, the
two rollers kept still will form something resembling the
linebar of Fig. l B.
In Fig. Z is shown schematically a secondary sawing line,
with a scanner l, a chippercanter 2 provided with an
infeed device 3, and an edger 4 provided with infeed
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devices and a set of adjustable circular saws. To this
secondary saw line are fed blocks which are already pro-
vided with two opposite flats parallel to the plane of the
paper, having been chipped and/or sawn in a direction sub-
stantially coplanar with the eventual curve plane of thelogs. The scanner is of well-known type, being able to
establish diameter, taper and curve, for determining how
the following secondary breakdown is to be performed. The
chipper canter will make chips out of some of the edge
material, and the following edger will cut up the result-
ing block into planks. According to the invention, both
those steps can be performed by curve chipping and curve
sawing respectively.
When reaching the infeed device 3, the way the block is to
be sawn is already decided. In particular, it is decided
whether center sawing or full-taper sawing is indicated,
and how the chipper canter is to be set.
For a block to be center-sawed, it is first pre-centered
by two pairs 30 A, B and 31 A, B of vertical rollers
mounted on swing-arms in a mechanism enabling them to move
pairwise to and from a centering line 32 (Fig. 3 A). The
small end of the block is entered first, and the wider end
will swing out in proportion to the curvature, as shown.
The block will move on under the guidance of said two
pairs of rollers until within reach of a third pair of
rollers 33 A, B. As shown in Fig. 4 A, in a final center-
ing step, third rollers 33 A, B will now grip the block,
whereas first rollers 30 A, B will lift off. Chipper heads
40 A and 40 B in the chipper-canter will now be set, norm-
ally at equal distances to center line 3Z, and the block
moves on under guidance of horizontal driven roller pairs
into the gap between chipper-canter rotating heads 40 A
and 40 B. When the block is in a position as in Fig. 5 A,
the guidance is taken over by anvils 42 A, B on the other
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side of the chipper heads and which are fixedly coupled to
the respective chipper heads 40 A, B, and by fourth
rollers 41 A, 41 B.
The fourth roller pair 41 A, B is symmetrically movable
and will be pressed by hydraulic means toward the center
line. The chipper heads are set 61ightly toe in (about one
millimeter, not seen in the drawing), and the anvils 42 A,
B are set at the front edge distance of the chipper heads.
This makes it possible for a curved block to steer through,
maintaining substantially its curvature. The distance
between the fourth roller pair 41 A, B and the anvils
42 A, B is of the order of one meter, and the Figures are
drawn to scale.
The curved block which exits from the chipper canter is
provided with two parallel flats in the horizontal direct-
ion, whereas the "flats" made by the chipper canter in the
vertical direction are vertical and parallel but length-
wise curved. Although the edges may not be filled outeverywhere, the cross section is substantially a right
rectangle, often a right square. For the further division
of this block by curve sawing, the curved vertical sur-
faces are used for guidance, and the previous cutting will
determine if the further sawing is along the pith or
according to the principle of full taper. The guide
rollers of the following edger may therefore be arranged
for symmetrical movement. In order to obtain curve sawing,
it is, however, necessary to use llshort'l guidance.
Fig. 6 A and 6 B show this guidance.
As the logs are treated small end first, the end first
entered in the edger may have its theoretical form less
than filled out, such that it is unsuitable for precise
guiding. Aligning before introduction must therefore be
made using longer guidance than is then used for curve
, s, ~ `
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sawing. As shown in Fig. 6 A and 6 B, there are therefore
two guiding systems comprising a pre-aligner 60 A, 60 B
followed by an aligner 61 A, 61 B, each comprising two
bars with opposing rollers and movable in opposition and
symmetrically. The log is introduced and aligned by means
of all the rollers as shown in Fig. 6 A. Once sawing has
started, the pre-aligner bars 60 A, 60 B are swung away as
shown in Fig. 6 B, and guidance is then assured by the
rollers on bars 61 A, 61 b together with the saws and
eventually by knives 62 a, 62 b which follow cut seams,
particularly in the outermost seams where less than per-
fect side boards are likely to result but the seam will
most likely be at full height. After exiting, curve sawed
planks and boards are obtained, which may be further sawn
and which after proper drying will be straight.
The previous description has mainly regarded the curve
sawing following the pith, i.e. center sawing. As already
mentioned, the inventive machinery makes it possible
alternatively to use the full taper sawing principle in
curve sawing.
The principle of straight full taper sawing is shown in
Fig. 1 B, and the idea then is to let the block be guided
along a material long linebar at one side, which linebar
is parallel to the cutting or sawing direction. In curve
full taper sawing, as shown in Fig. 1 D, the linebar is
then exchanged for a set of rollers which are kept im-
mobile, mounted on one side of the block, with opposite
rollers which move to fit the changing width of the block.
As the distance between the two fixed-axis rollers forming
the "linebar" is short, a curved block will still be cut
along a curve.
In order to obtain the possibility of working with both
methods, it is necessary for the roller pairs of the
chipper canter to either move in a coupled way to and from
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a common center, or let one roller stay fixed, whereas the
opposite roller can move to and from the fixed roller.
Such a roller pair construction will be described.
When the sawing line of Fig. 2 is to perform a full-taper
sawing, the pre-aligning step as shown in Fig. 3 B i8
performed by setting rollers 30 A and 31 A along a non-
-material linebar, outside of the cutoff plane defined by
cutter head 40 A. Also roller 33 A is set colinear with
the same non-material linebar. As shown in Fig. 4B,
rollers 30 A, B are lifted off when the block is final
aligned by roller pairs 31 A, B and 33 A, B. In the sawing
operation (Fig. 5 B), the guidance is given by roller
41 A, fixed on the imaginary ~linebar~, and movable roller
41 B before the chipper canter, and by anvils 42 A, B
after the chipper canter. Roller 41 B will hold the block
by resilience against fixed roller 41 A. The chipper heads
being slightly toe-in (not seen in Figure), the block can
be cut in a curvature, the distance being about one meter
between roller 41 A and first cutting edge of cutter head
40 B. Anvils 42 A and 42 B are following the positions of
the respective chipper heads 40 A, B.
In order to obtain the advantages of the invèntion, it is
necessary to have a roller pair control mechanism which
satisfies the condition that it can either be set to be
movable symmetrically to a center line, or with a first
roller settable to a predetermined position, the second
roller of the pair being resiliently movable toward the
first roller.
In the embodiment disclosed, two different methods are
used for obtaining alternatively the two kinds of move-
ment, one on mechanical principle, the other on hydraulic
principle.
The first method is used for roller pairs 30 A, B, 31 A, B
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and 33 A, B shown in Fig. 3-5. Fig. 7, 8 and 9 show the
method. Two rollers 80 A, B are mounted on links 81 A, B,
which are swingable around swing-points 82 A, B. Fixed on
respective links 81 A, B are arms 83 A, B, the ends of
which are articulately coupled at 83 A, B to respective
ends of a first hydraulic cylinder 84. On link 81 B is
further fixed a further arm 85, to which is articulately
fixed one end of a second hydraulic cylinder 86, the other
end of which is articulately fixed at swinging-point 87.
Swinging-points 82 A, 82 B and 87 are fixed on a carrier
88, which can be linearly displaced by a third hydraulic
cylinder 89.
The advantage of this system is that symmetric movement of
the jaw consisting of rollers 80 A, B can be substantially
obtained, centered on line 32, by actuating only first
cylinder 86, letting second cylinder at constant length
(Fig. 7 A). Center line 32 may be displaced by actuating
third cylinder 89.
For full taper sawing, cylinder 86 is set at a predeter-
mined position as in Fig. 7 B, e.g. at maximum stretch.
Roller 80 B will take a predetermined position. Now,
roller 80 A can be moved independently by means of cylin-
der 84.
In order for the first-mentioned symmetric jaw movement to
be substantially obtained, a certain symmetry is needed.
In Fig. 7 A, the rollers 80 A, 80 B, are shown in a l'mid
position~, corresponding to a mean block size. The first
hydraulic cylinder 84 is set at minimal length and is
articulately joined to arms 81 A, B at joints 83 A~,
83 B', which are at equal distances from the respective
fixed swinging-points 82 A, 82 B. Further, in this mid-
-position, lines joining 82 A - 83 A' and 82 B - 83 B' are
at right angles to the line joining joints 83 A' and
83 B'. It is not difficult to see that if arm 81 B is
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swung a small angle by means of second cylinder 86, arm 81
will swing in the opposite sense and with a substantially
equal angle. The error is surprisingly small within a
swing angle of 12.5, corresponding in Fig. 7 A to a
closing of the ~jaw". With arms 81 A, B of a length of
380 mm, the center line will only move about 0.16 mm.
An analysis shows that what is necessary for such a con-
struction to work is that two minimum conditions must be
satisfied for the position corresponding to the middle of
the working interval, namely, firstly that for that
position, the tierod line drawn between articulate joining
points 83 A', 83 B' intersects the line between swinging-
-points 8Z A, 82 B at its midpoint, and secondly that the
normals drawn from swinging-points 82 A, 82 B to the
tierod line are of equal lengths. Those conditions are
sufficiently approximated for the demands at introduction.
Fig. 7 C shows the positions of the rollers when both
first and second cylinders are at their shortest length.
This is the infeed open position. For centersawing, thus,
the second cylinder 86 is activated and will center a
block relative to center line 32. For linebar full taper
sawing, the second cylinder 86 is set at e.g. its maximum
length, whereas the first cylinder 83 is given a pressure
to bring it to shorten.
The cylinder pair 41 A, 41 B at the immediate entry of the
chipper canter is controlled in another way. Fig. 8 and
9 A-B show the hydraulic system of the chipper-canter. As
recited above, the chipper heads 40 A and 40 B may be
individually adjustable. This is done by setting cylinders
40 A', 40 B', which each move a slide, on which the
respective chipper head is mounted together with roller
mechanisms for rollers 41 A, 41 B and anvils 42 A, 42 B
respectively. The anvils (not shown) are strictly follow-
ing the chipper heads, as they are to contact the llplanes
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cut by the chipper head6. The rollers 41 A, 41 B on the
other hand are to roll against the block edges as they are
before chipping. According to one mode, one of them is to
be held fixed, the other re6iliently pres6ing against the
block, according to the other mode, they should center the
block by moving oppositely in unison.
In Fig. 8, it is shown how the chipper head6 together with
61ides may be di6placed by actuating valve6 40 A", 40 B".
Roller8 41 A, 41 B are di8placed by cylinder8 100 A, 100 B.
Thi6 hydraulic con6truction i6 sufficiently preci6e to
guarantee high-precision sawing to obtain a product which
ha6 good tolerance6.
In order to obtain the two modes of moving by means of
hydraulic means, Fig. 8 and Fig. 9 A-B 6how the general
principle. A hydralic source 101 having a pressure line P
and a return line T is coupled as 6hown in Fig. 8 through
a control device 200 provided with a 6witch 102 and a
one-way valve 105. For each of the hydraulic cylinder6
100 A and 100 B, there are provided further switches 103
and 104 respectively.
The control device receive6 on the input the lines P and T
and outputs via the switch 103, one of the outputs passing
via the one-way valve 105. Said two outputs and a direct
return line coupled to T are coupled via switches 103 and
104 to the respective hydraulic cylinders 100 A and 100 B.
Thereby, the output from the one-way valve 105 is 6plit
into two, making four lines go to the switche6 103 and 104.
In operation, it is po6sible to make the cylinder6 work
either in symmetry for curve/center sawing (Fig. 9 A) or
by keeping one cylinder fixed (Fig. 9 B). For one cylinder
to stand still, it is sufficient for that cylinder to have
both feed lines closed, and switch 104 therefore ha6 one
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position where both are closed, as shown in Fig. 9 B. For
symmetrical inward movement, the respective switches 102,
103 and 104 are set as in Fig. 9 A. In this position,
cylinder 100 B will prolong, the other side of its plunger
displacing equal amounts of oil, which displaced oil will
go to prolong cylinder 100 A, since one-way valve 105 will
prevent that oil from returing to the T line, as shown
with a bar in Fig. 9 A. The oil displaced thereby from
cylinder 100 A will go freely to line T. The rollers moved
by those cylinders will thus move in unison and symmetric-
ally toward a common center. When the rollers are to move
out to their opposite positions, it is sufficient to
change the switch 102 and set switch 104 in its opposite
position (see Fig. 9 A), and the cylinders will move to
their opposite end positions, which are the starting
positions for next operation.
This hydraulic movement is very precise and has further
the advantage of enabling a device which has small
dimensions in the length direction of the log and may
therefore be placed near to each other and to cutting
equipment. This makes it easier to perform curve sawing,
and the hydraulic movement is preferred for the guide
means nearest to the cutting/sawing devices, whereas the
llmechanical" means previously described are preferred for
pre-aligning purposes.
In both cases, it is suitable to have a stabilized/limited
hydraulic pressure to press the rollers toward the log. An
exemplary embodiment of such a stabilization is shown at
110 in Fig. 8 and consists in a bypass valve regulated by
a pressure sensor for setting a suitable pressure for
obtaining resilient pressure of rollers against the log.
There have now been described means for curve sawing in-
cluding guide means whereby both center sawing and full
taper sawing may be performed in the same machinery.
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Obviously, the various mainly hydraulic movements must be
controlled such that they are activated in the right order
in order to perform the described functions. The various
control and sensing devices for performing this task are
obvious to an engineer familiar with standard automatic
control systems and would normally be computer assisted.
This being the case, it has not been seen as suitable to
describe the further control equipment, being well within
the grasp of one familiar with the art of industrial
control.
Not shown in the Figures and not described is the forward
feed. As is conventional, this feed is obtained by meafi of
horizontal driven roller pairs, one in the bottom plane
where the log is moving, another vertically adjustable,
forming a roll nip with the former. As this feed is con-
ventional, it is not described.
