CA2123743A1 - Curve sawing band - Google Patents

Abstract

A curve sawing band mill for cutting a vertical face from a piece of lumber conveyed past the band mill, has a base, a selectively positionable horizontally rotatable frame rotatable about a pivot rigidly mounted to the base, a selectively positionable horizon-tally translatable frame linearly translatable on the horizon-tally rotatable frame, the band mill mounted vertically on the horizontally translatable frame.

Description

~ 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.

- 21237~3 `~ 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.

~ 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 ` 2123743 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 ~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 -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 ~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.

~ 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.

Claims (2)

1. A curve sawing band mill for cutting a vertical face from a cant conveyed past said band mill, comprises a base, a selectively positionable horizontally rotatable frame rotatable about a pivot rigidly mounted to said base, a selectively positionable horizontally translatable frame linearly translatable on said horizontally rotatable frame, said band mill mounted vertically on said horizontally translatable frame.

2. A curve sawing band mill for cutting a vertical face from a cant conveyed past said band mill, comprises a base, a selectively positionable horizontally translatable frame linearly translatable on said base, a selectively positionable horizontally rotatable frame rotatable about a pivot rigidly mounted to said horizontally translatable frame, said band mill mounted vertically on said horizontally rotatable frame.