The present invention relates to saw mill apparatus and method and, more particularly, to saw mill apparatus and method for cutting logs of constant and varying diameter using band saws and an improved band saw blade guide system.

In prior art saw mills, it is known to utilize a pair of circular saws or a pair of band saws to cut the sides of a log while it is advanced longitudinally through the saw system. It also is known in the art to utilize blade guides to stabilize lateral movement or "wobble" of the band saw blades while a log is being cut. Such blade guides restrict lateral movement of the blades and minimize stress on the blades.

One problem encountered in typical saw mill apparatus having band saws is that although such band saws generally utilize blade guides, such saw mills generally are unable to optimize cutting and are unable to prevent band saw blade wobble when logs of varying diameter are cut.

One prior art system which attempts to overcome this problem utilizes four photocells to detect the approximate diameter (or width) of a log and utilizes an "air-operated stack cylinder" to adjust the height of a blade guide of each band saw to one of four positions prior to cutting that log. The photocells are arranged on top of one another at a distance of 6 inches between adjacent photocells, and each of four light sources supplies a light beam to a respective photocell.

Depending on the photocells that receive a light beam, the diameter of the log is ascertained to within a 6 inch range. Then, a four position air-operated stack cylinder establishes each blade guide to be located at that position (of the four positions) that is immediately above the detected range of the log's diameter. For example, if the photocells ascertain the log's diameter

to be within the range of 12 to 18 inches, the position of each blade guide is set to the one of four positions that is at least 18 inches above the bottom surface of the log so as to prevent the log from hitting the guides. One difficulty encountered in such prior art saw mill apparatus is its general inability to accurately saw a log which has substantially different diameters along the length thereof. That is, given a particular log having a diameter of, for example, 11 inches at one end and a diameter of 19 inches at its other end, the above-mentioned prior art saw mill may determine that the log has a diameter in a first range (e.g., the 6 to 12 inch range), or a diameter in a second range (e.g., the 12 to 18 inch range) , or a diameter in a third range (e.g., the 18 to 24 inch range) . Since this prior art apparatus selects only a single position of the blade guides for each log to be cut, either the blade guides will be located at a position too far above the log to provide an accurate cut thereof, or will be located at a position too low which would result in the hitting of the guides by the log, thereby damaging the guides. Furthermore, even if a particular log to be cut had a constant diameter throughout its entire length, the prior art apparatus still is capable of positioning the blade guides unacceptably too far from the log (e.g., 6 inches) to provide an accurate cut thereof.

OBJECTS OF THE INVENTION Therefore, it is an object of the present invention to provide saw mill apparatus and method which overcome the shortcomings of the above-described devices. Another object of the present invention is to provide saw mill apparatus and method which tracks the diameter of a log while it is being cut.

A further object of the present invention is to provide saw mill apparatus and method which displaces the band saw blade guides at positions which are in close proximity to the log throughout cutting thereof.

An additional object of this invention is to provide a saw mill apparatus which accurately senses the diameter of a log at plural longitudinal positions thereof so that the blade guides are able to continuously track the log as it is being cut.

Various other objects, advantages and features of the present invention will become readily apparent to those of ordinary skill in the art, and the novel features will be particularly pointed out in the appended claims.

SUMMARY OF THE INVENTION In accordance with one embodiment of the present invention, a sawmill apparatus includes an endless log carrier which supports a log, drive means for advancing the endless log carrier along a given path so as to advance the log supported thereby longitudinally through the saw mill's saw assembly, a band saw which includes a parallel endless band saw blade positioned in the path of the log and which cuts longitudinally the log moving through the apparatus, a blade guide which engages the band saw blade and which is mounted to the band saw in a manner that allows movement of the blade guide along the band saw blade toward and away from the log being cut, a sensing device which senses the diameter of the log at plural longitudinal positions thereof, and a blade guide displacer which displaces the blade guide along the band saw blade in response to the sensed diameters so that the guides are positioned in close proximity to the log while it is being cut. As one aspect of the present invention, the blade guides are displaced plural times during the cutting of the log.

As another aspect of the present invention, the blade guides are positioned at a predetermined distance above the log throughout cutting thereof.

As yet a further aspect of the present invention, the diameter of the log is sensed at predetermined intervals along the length of the log.

As yet another aspect of the present invention, a scanner located upstream from the saw assembly supplies a sensed diameter of a particular longitudinal position of the log to a control device which controls the displacement of the blade guide at a time when that particular position of the log is proximally near the band saw.

In accordance with another embodiment of the present invention, sawmill apparatus includes an endless log carrier which supports a log, drive means for advancing the log carrier along a given path to advance the log supported thereby longitudinally through a saw assembly, a band saw which includes first and second parallel endless band saw blades that are both positioned in the path of the log and that cut longitudinally the log as it moves through the apparatus, a first blade guide which is engaged to the first band saw blade and which is mounted to the band saw in a manner that allows movement of the first blade guide along the first band saw blade toward and away from the log, a second blade guide which is engaged to the second band saw blade and which is mounted to the band saw in a manner that allows movement of the second blade guide along the second band saw blade toward and away from the log, a sensing device which senses the diameter of the log at a plurality of longitudinal positions thereof, and a blade guide displacer which displaces both the first and second blade guides in response to the sensed diameters so that they are positioned along the first and second bands at a predetermined distance from the log while it is being cut. As an aspect of this invention, a first blade guide displacer displaces the first blade guide along the first band saw blade and a second blade guide displacer

displaces the second blade guide along the second band saw blade .

In accordance with a further embodiment of the present invention, an improved method of cutting logs in a sawmill is carried out by advancing a log longitudinally towards a band saw apparatus, cutting the log longitudinally by a band saw blade while the log is advanced therethrough, guiding the band saw blade using a blade guide that is engaged thereto, and displacing the blade guide along the band saw blade a predetermined distance above the log while it is being cut. BRIEF DESCRIPTION OF THE DRAWINGS The following detailed description, given by way of example and not intended to limit the present invention solely thereto, will best be appreciated in conjunction with the accompanying drawings, wherein like reference numerals denote like elements and parts, in which:

Fig. 1 is a partial side view of the saw mill apparatus in accordance with the present invention;

Fig. 2 is a three-dimensional expanded view of the band saw assembly of the present invention; and

Fig. 3 is another side view of the saw mill apparatus of the present invention.

DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS Referring now to the drawings, Fig. 1 is a partial side view of saw mill apparatus 10 in accordance with the present invention, and Fig. 2 is an expanded view of the saw assembly of the present invention. As shown in both Figs. 1 and 2, a log 12 is advanced towards a saw assembly, which includes a first band saw 14 and a second band saw 16 (shown in Fig. 2) , by a carrier 18 in the direction shown. Carrier 18 is, for example, a sharp chain or any other appropriate device which supports, orients, and advances a log to a saw assembly. Such a log carrying device is well-known in the art, for

example, such as disclosed in U.S. Patent No. 4,250,937, issue _d to Detjen on February 17, 1981, or U.S. Patent No. ₄ ,2 ₀₆ ,673, issued to Detjen on June 10, 1980, which are incorporated herein by reference, and therefore, further _d escription thereof is omitted herein except where necessary for an understanding of the present invention. Prior to being cut, log 12 is advanced past a scanning device 20 which ascertains, at a 1/4 inch resolution, the diameter (or width) of the log every 6 inches longitudinally. Scanning device 20 includes a beam array emitter unit 20a which emits to a receiver unit 20b a beam array 20c. Beam array 20b converts the received beam (i.e., that part of the beam that is not blocked by log 12) into a signal representative of the diameter of log 12. It is appreciated that other suitable devices that accurately detect the height (i.e., diameter) of a log and that are known in the art may be used herein.

As log 12 is advanced on carrier 18 towards the saw assembly, scanning device 20 is controlled by an appropriate control system (not shown) to detect the diameter of the log every 6 inches of travel, or alternatively, is controlled to detect the diameter of log 12 at predetermined intervals of time (e.g., every 0.25 second) . The detected diameters are supplied via a control signal (not shown) to the control system which then operates to control the height of first and second blade guides 26, 28 (to be discussed) so that the guides properly track the diameter of log 12 as it advances through the assembly.

As previously stated, the saw mill's saw assembly includes first and second band saws 14, 16. Band saws 14, 16 include respective band saw blades 22, 24 which are supported on their respective wheels or pulleys 30, 32, 34 and 36, and means are provided for rotating the wheels in a conventional manner to cause the band saws to cut log 12 as it is advanced longitudinally

t _h eret _h rough. Log 12 is thereby cut in a conventional manner. That is, the sides of log 12 are cut by the adjacent vertical portions of blades 22, 24 which pro _d uces two slabs and a center hard piece which is known in t _h e art as a flitch or cant. The saw assemblies are pre _f erably shifting saws for producing a center piece _h aving an adjustable thickness, and since the shifting of band saws 14 and 16 is well known in the art, further description thereof is omitted. Blade guides 26 and 28 are mounted to band saws

14 and 16, respectively, by means of hydraulic positioners 38 and 40. It is appreciated, however, that other types of suitable positioning devices may be used herein to position blade guides 26 and 28. Fixed blade guide assemblies (not shown) are utilized to engage band saw blades 22 and 24 at a position immediately below log 12. Fixed blade guides are well known in the art and form no part of the present invention.

Control signals indicative of the diameter of various positions of log 12 are supplied from the control system to hydraulic positioners 38 and 40 so as establish the height (i.e., position) of blade guides 26 and 28 on blades 22 and 24, respectively, in accordance with the present invention. A description of the displacement of blade guides 26 and 28 on blades 22 and 24, respectively, so that they track the width of log 12, in accordance with the present invention, will now be described with reference to Fig. 3 of the drawings. As can be appreciated, Fig. 3 is quite similar to Fig. 1 except the diameter of log 12 is shown to substantially change throughout its length. As various portions of log 12 (e.g., every 6 inches along the log) are advanced past scanning device 20, the diameter of the log is detected and supplied to the control system. Then, at the appropriate time, blade guide 26 is displaced, by means of hydraulic positioner 38, to a position on band saw

_bl ade 22 that is approximately 3 inches above the log, and since scanning device 20 has a 1/4 inch resolution and the diameter of log 12 is measured at least approximately every 6 inches, blade guide 26 properly tracks log 12 along a track path "A". Thus, log 12 is accurately cut and, in addition, the strain on blade 22 is minimized. Similarly, blade guide 28 tracks log 12 by establishing a position that follows path "A" . It is seen, therefore, that although log 12 has substantially different diameters along its length, blade guides 26 and 28 accurately track the log by being positioned at a relatively short distance from the top surface of the log, but are not placed too low so as to risk the possibility of being damaged by any contact between the guides and the log.

In an alternative embodiment of the present invention, blade guides 26 and 28 are coupled together to ensure that they are positioned at the same height relative to log 12. However, Fig. 2 illustrates the preferred embodiment of the invention wherein blade guides 26 and 28 are positioned by respectively different hydraulic positioners 38 and 40.

While the present invention has been particularly shown and described in conjunction with a preferred embodiment thereof, it will be readily appreciated by those of ordinary skill in the art that various changes may be made without departing from the spirit and scope of the invention.

Therefore, it is intended that the appended claims be interpreted as including the embodiments described herein, the alternatives mentioned above and all equivalence thereto.