Note: Descriptions are shown in the official language in which they were submitted.
~ CURVE 8AWING BAND NILL
Field of the Invention 212 3 7 4 3
This invention relates to devices for sawing lumber
from logs and cants, and in particular relates to a cant cutting
device for cutting a third cant face according to an optimized
profile so as to prepare the cant for optimum cutting in a curve
sawing gang.
Background of the Invention
A canted log, or "cant", by definition has first and
second opposed cut planar faces. In the prior art, cants were
fed linearly through a canter or gang saw so as to produce at
least a third planar face either approximately parallel to the
center line of the cant, so called split taper sawing, or
approximately parallel to one side of the cant, so called full
taper sawing, or at a slope somewhere between split and full
taper sawing. For straight cants, use these methods volume
recovery of the lumber can be close to optimal. However, logs
typically have a curvature and in these cases a curved log will
be cut to a shorter length than what might otherwise be preferred
to reduce the effect of the curvature on the lumber recovery.
Consequently in the prior art curve sawing techniques have been
used.
Curve sawing typically uses a mechanical centering
system that guides a cant into a secondary break-down machine
close to chipping heads or saws. This centering action results
in the cant following a path very closely parallel to the center
line of the cant, thus resulting in split taper sawing of the
cant. Cants that are curve sawn by this technique generally
produce longer, wider and stronger boards than is typically
possible with a straight sawing technique where the cant has
significant curvature.
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`~ Curve sawing techniques have also been applied to cut
parallel to a curved face of a cant, i.e. full taper sawing. See
for example Kenyon, United States Patent No. 4,373,563 and
Lundstrom, Canadian Patent No. 2,022,857. Both the Kenyon and
Lundstrom devices use mechanical means to center the cant during
curve sawing and thus disparities on the surface of the cant such
as scars, knots, branch stubs and the like tend to disturb the
machining operation and produce a "wave" in the cant. Also, when
full taper techniques are employed, the typical use of chipping
heads to machine faces on the cant tend to cause snipeing or
bevelling of the ends of the cant due to non-symmetrical chipping
forces on the cant. Further, cants subjected to these curve
sawing techniques tend to have straight sections on each end of
the cant. This results from the need to center the cant on more
than one location through the machine. That is, when starting
the cut the cant is centered by two or more centering assemblies
until the cant engages anvils behind the chipping heads. When
the cant has progressed to the point that the centering assem-
blies in front of the machine are no longer in contact, the cant
is pulled through the remainder of the cut in a straight line.
It has also been found that full taper curve sawing techniques,
because the cut follows a line approximately parallel to the
convex or concave surface of the cant, tend to produce lumber
that is overly bowed.
Thus in the prior art, so called arc-sawing was
developed. See for example United States Patent No. 5,148,847.
Arc sawing was developed to saw irregular swept cants in a semi-
circular arc. The technique employs an electronic evaluation and
control unit to determine the best semi-circular arc solution to
machine the cant, based, in part, on the cant profile informa-
tion. Arc sawing techniques solve the mechanical centering
problems encountered with curve sawing but limit the recovery
possible from a cant by constraining the cut solution to a semi-
circular form.
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~ It has been found that optimized lumber recovery isbest obtained for most if not all cants if a unique cutting
solution is determined for every cant. Thus for each cant a
"best" curve is determined, which in some instances is merely a
straight line parallel to the center line of the cant, and in
other instances a complex polynomial curve that is only vaguely
related to the physical surfaces of the cant.
Thus it is an object of the present invention to
improve recovery of lumber from cants and in particular irregular
or crooked cants. It is an objective to provide a machining
center in the form of a two degree of freedom articulated
vertical band mill to cut a third face from a cant according to
an optimized curve sawing solution so that the optimized third
face on the cant serves as a sawing guide for a curve sawing gang
cutting the cant parallel to the third face.
In the prior art the cutting of an optimized third cant
face is disclosed in United States Patent No. 4,947,909 entitled
"Process and Apparatus for Optimizing Volume of Boards Cut from
a Log" which issued to Stroud on August 14, 1990. Stroud
discloses a scanner positioned to scan a log and determine an
optimum cut surface profile, a cutting head positioned to cut the
top surface of the log, the cutting head being a chipping head
having relative vertical movement to the top surface. Stroud
discloses a conveyor to convey the log past the scanner and
chipping head, and a controller to control the relative movement
of the chipping head in accordance with a signal from the scanner
to produce a pre-determined optimum cut surface profile for the
top surface of the log. It has been found that the use of
chipping heads in this manner, which are typically constrained
to vertical movement, would produce an undesirably rough third
face on a cant. Consequently, in the present invention it was
desired to use a band mill to provide a smoother third cant face.
Further, it has been found that vertical chipping heads downward
force causes movement of the cant during cutting of the third
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face, consequently reducing the accuracy of replication of an
optimized curve in the cut face.
Applicant is also aware of United States Patent No.
5,243,888 which issued to Bowlin on September 14, 1993 for a
device entitled "Pivoting Carriage and Saw" which teaches an
articulated band saw and log carriage for cutting an optimized
face from a cant carried in the carriage. In particular, Bowlin
teaches a pivotally mounted band saw mounted on a fixed base
adjacent a log carriage, and log positioning means located on the
carriage and band saw. Movement of the carriage and band saw is
orchestrated by a computer interfacing with a scanner so as to
cut pre-selected curved paths through the cant. It has been
found that the Bowlin technique of moving both the log carriage
as well as the band mill causes a loss of through-put.
Applicant is also aware of United States Patent No.
4,144,782 which issued to Lindstrom on March 20, 1979 for a
device entitled "Apparatus for Curved Sawing of Timber".
Lindstrom teaches that when curve sawing a log, the log is
positioned so as to feed the front end of the log into the saw
with the center of the log exactly at the saw blade. In this
manner the tangent of the curve line for the desired cut profile
of the log extends, starting at the front end, parallel with the
direction of the saw blade. Thus, as with the Bowlin teaching,
Lindstrom discloses log movement to position logs for band mill
cutting.
Summary of the Invention
The invention provides a band mill which may be moved
linearly along a pair of tracks and also which may be pivoted
horizontally about a pivot pin mounted to a base. The base has
a flat top surface, four adjustable jack bolts under the corners
of the base, the pivot pin being a fixed upright pivot pin
mounted rigidly thereon. A pivot frame is rotatably mounted on
the pivot pin. The pivot frame includes a plurality of rollers
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~that run on the flat surface of the base. There is a hydraulic
cylinder connecting the base and the pivot frame which when
actuated causes the pivot frame to pivot horizontally about the
pivot pin. Pivoting is selectively actuable as directed by a
computer which has computed an optimized curved cutting profile
for the curve sawing of a third vertical face on a cant. The
cutting profile is determined in part based on profile informa-
tion of the cant supplied by a scanner of a type known in the
art. Selectively actuable pivoting keeps the band mill blade
following in the optimized cutting path as the cant is conveyed
into cutting engagement with the band mill blade and as the third
face is cut into the cant.
Mounted on top of the pivot frame are a pair of linear
tracks to guide a carriage along a linear path. The band mill
is mounted vertically on the carriage and thus positioning the
carriage on the tracks along with pivoting the pivot frame, both
as directed by the computer, allows the band mill blade to follow
the optimized cutting curve. A second hydraulic cylinder
connects the carriage with the pivot frame and is selectively
actuable for moving the carriage back and forth along the linear
tracks. The carriage has depending therefrom a plurality of
rollers that have concave running surfaces to guide the carriage
along the linear tracks.
The carriage supports the band mill and in particular
supports a band wheel support frame including band guides, bottom
bearing mounts, upper band wheel bearing mounts, and band mill
band tensioning means. A pair of band wheels are mounted on the
bearing mounts of the support frame. The band mill band is
mounted on the band wheels and is driven by a drive shaft on the
lower band wheel.
A cant transfer means such as a spiked transfer chain
and a plurality of cant hold-down rollers feeds the cant into
cutting engagement with the band mill and during the cutting of
the third face. The cant is then conveyed into a curved sawing
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-gang where the newly cut third face of the cant is used as a
guide for the gang saws.
Compared with apparatus in the prior art, the present
invention provides a band mill which follows an optimized curve
sawing profile without having to move the cant laterally or
rotationally as the cant is conveyed past the band mill.
Brief Description of the Drawings
Figure 1 is a side elevation view of the curve sawing
band mill of the present invention.
Figure 2 is a plan view of the device of Figure 1.
Figure 3 is a schematic in plan view of a scanner and
curve saw bandmill arrangement incorporating the curve sawing
bandmill of the present invention.
Figure 4 is a side elevation view of the schematic of
Figure 3.
Figure 5 is a fragmentary view of the curve sawing band
mill of the present invention depicted in Figure 4.
Detailed Description of the Preferred Embodiment
As illustrated in Figures 1 and 2, band mill 10 is
supported on a three-tier frame arrangement, the top two tiers
movable relative to each other and to the lower-most tier. In
the lower-most tier, base frame 12 is anchored by base jack bolts
14. Pivot frame pivot pin 16 rotatably connects pivot frame 18
to base frame 12, pivot frame 18 rotatable about pivot pin 16 on
rollers 20. Rollers 20 may run on the top surface of base frame
12. Carriage 22, to which band mill 10 is vertically mounted,
travels linearly over pivot frame 18 on tracks 24. Tracks 24 may
be mounted to the top surface of pivot frame 18. Selectively
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~actuable hydraulic cylinder 26 selectively rotates and positions
pivot frame 18 about pivot pin 16. Selectively actuable
hydraulic cylinder 28 translates and positions carriage 22 along
tracks 24 by rolling carriage 22 on carriage rollers 30.
Cant 32 is conveyed on transfer chain 34 so that band
mill 10 and in particular band mill band 36 may cut a third face
from cant 32 as cant 32 is conveyed in cutting engagement past
band mill band 36.
Band mill 10 has conventional components, namely, band
36, rotatably supported by band mill band wheels 38 rotating
about wheel shafts 40, and band mill support frame 42. Band 36
is tensioned by band tensioner 44 and guided by band guides 46.
Drive motor 48 drives the lower of band wheels 38 via drive belt
50.
As illustrated in Figures 3 and 4, cant 32 is conveyed
in direction A over scanner 52 onto transfer chain 34 and
thereafter conveyed in direction B so as to engage band 36 on
band mill 10. Transfer chain 34 may be a spiked transfer chain.
As cant 32 is conveyed in cutting engagement with band 36 past
band mill 10 on transfer chain 34, band mill 10 rotates in
direction C about pivot pin 16 and linearly translates in
direction D along tracks 24 so as to keep band 36 aligned tangen-
tially to an optimized curve sawing path. The optimized curve
sawing path is determined by an optimizing algorithm computer
processing data from scanner 52. The third face of cant 32 cut
by band 36 along the optimized curve sawing path provides a guide
surface for gang saws 54. Cant 32 may be conveyed as illustrated
from band mill 10 so as to be fed into gang saws 54.
As illustrated in Figure 5, as cant 32 is fed in
cutting engagement past band 36, cant 32 is held down onto
transfer chains 34 by hold-down rollers 56. Hold-down cylinders
58 urge hold-down rollers 56 down against cant 32. Transfer
chains 34 are supported by support frames 60 on sprockets 62.
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~ In operation, cant 32 is loaded on transfer chain 34
approximately centered with the major convex sweep of cant 32
oriented to a preferred side. Cant 32 is held by conventional
means fixed relative to chain 34 and fed longitudinally through
an electro-optical sensing array such as scanner 52 that measures
the geometry of cant 32 relative to the center line of chain 34.
The geometric data is electronically evaluated by an optimizing
algorithm to determine the best value recovery curve sawing
solution. Cant 32 then proceeds longitudinally on chain 34 to
band mill 10 which is numerically controlled to cut the desired
curved profile as a third face of cant 32 by translating band
mill 10, and in particular band 36, to follow the shape of the
desired curve and rotating band mill 10 about pivot pin 16 to
match the instantaneous slope of the desired curve. Once the
third face is cut, cant 32 is fed into a conventional curve
sawing gang saw by known techniques.
In an alternative embodiment tracks 24 are mounted on
base 12 so that carriage 22 runs linearly along base 12,
selectively positionable on tracks 24. Pivot pin 16, rigidly
depending from pivot frame 18, is mounted to carriage 22 so that
pivot frame 18 is selectively rotatable on carriage 22. Band
mill 10 is mounted on pivot frame 18.
In further alternative embodiments a twin band mill is
provided to cut simultaneously third and fourth cant faces. To
assist the movement of pivot frame 18, band guides 46 may be
articulated to steer or twist band 36 to thereby align band 36
tangentially with the requisite curve profile.
As will be apparent to those skilled in the art in the
light of the foregoing disclosure, many alterations and modifica-
tions 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.
