Abstract:
In a first aspect of the invention, there is provided a new method for edging a wood board. This method comprises the steps of constructing from the scanned images of a wood board, a virtual entity of the wood board; determining from the scanned images an optimized cut line along the virtual entity; displacing the forward edge of the virtual entity ahead of the leading edge of the wood board; displacing the rear edge of the virtual entity behind the trailing edge of the wood board and sawing the wood board along the optimized cut line on the virtual entity. In another feature, the saw blades inside the board edger are mounted in saw collars and are shifted along the arbor by an electric setworks mounted on the top of the saw box and a shifting arm extending vertically between the setworks and a respective saw collar.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention pertains to sawmill edgers and more particularly, it relates to a board edger having a movable saw box controlled by a scanner and a computer to maximize the recovery of lumber from wood cants.  
         BACKGROUND OF THE INVENTION  
         [0002]    As the processing speed increases in sawmill machinery, wood pieces tend to bounce back from bumpers and alignment gates and are not always presented to the sawmill equipment in an ideal position. This inherent disadvantage with the handling of wood pieces is particularly apparent in wood cants or flitches. Wood cants have irregular and nonparallel sides which make them difficult to align along the longitudinal axis of an infeed conveyor for example. Consequently, increasing the processing speed of machinery often results in less recovery.  
           [0003]    In the present description, the words; wood piece, cant, flitch and board are used interchangeably to designate a lengthwise strip of wood cut from a tree trunk.  
           [0004]    In view of increasing both the processing speed and recovery, lineal scanners and computers have been developed to precisely measure the dimensions and the position of a wood board on a conveyor. These scanners and computers generate three-dimensional images of the cant, and calculate a sawing solution that represents the highest value combination of products which can be produced from the cant.  
           [0005]    Similarly, sawmill edgers have been developed to operate with lineal scanners and computers. These edgers have a saw box that is adjustable about a vertical axis, and saw blades that are movable sideways along the arbor. The positions of the saw blades are continuously adjusted to track the realtime position and alignment of a wood board being fed there through and to follow the optimized cutting profile defined by the computer.  
           [0006]    Examples of optimized edgers available in the prior art are disclosed in the following documents;  
           [0007]    U.S. Pat. No. 4,239,072 issued Dec. 16, 1980 to H. Meriläinen;  
           [0008]    U.S. Pat. No. 5,722,474 issued Mar. 3, 1998 to C. Raybon et al.;  
           [0009]    U.S. Pat. No. 5,816,302 issued Oct. 6, 1998 to W. R. Newnes;  
           [0010]    U.S. Pat. No. 5,884,682 issued Mar. 23, 1999 to J. B. Kennedy et al.;  
           [0011]    U.S. Pat. No. 5,946,995 issued Sep. 7, 1999 to S. W. Michell et al.;  
           [0012]    U.S. Pat. No. 6,178,858 issued Jan. 30, 2001 to M. P. Knerr et al.;  
           [0013]    U.S. Pat. No. 6,202,526 issued Mar. 20, 2001 to M. Dockter et al.  
           [0014]    It will be appreciated that in a continuous wood edging process, the cants to be trimmed must be located precisely such that the saw blades can track the optimized cut lines in one cant and reposition quickly to track the optimized cut lines in a next cant. It has been found, however, that when the leading edge of a saw blade is made to focus on the leading edge of a cant approaching at high speed, there is a certain amount of wandering of the saw blade before it is set to track the optimized cut line. The saw blade enters the leading edge of the cant in a milling mode rather than a sawing mode, thereby increasing the kerf width at the leading edge of the cant. Similarly, when the optimized cut line stops at the trailing edge of the cant, the saw blade stops tracking the optimized cut line before it has completely exited the cant, causing an aftercut and also increasing the kerf width at the trailing edge of the cant.  
           [0015]    In the machines of the prior art, several methods are used to locate the leading and trailing edges of a cant to control the tracking of optimized cut lines. For example, the machine described in U.S. Pat. No. 4,239,072 uses several measuring gates on the infeed side of the cutter heads to determine the position of the cant relative to the cutter heads and to adjust the cutter heads prior to entering into the cant. The position of the cant is measured relative to a feeding line. The cutter heads are correspondingly positioned on both sides of the feeding line, and the tracking of the optimized cut lines starts as the cant passes through the edger. The cutter heads are inclined in relation to each other in such a manner that the cutter heads are closer to each other at their cutting side than at the exit side to prevent aftercut.  
           [0016]    The machine disclosed in U.S. Pat. No. 5,722,474 uses photodetectors to detect the location of a cant relative to a reference point. Then the movement of the saw blades is correlated by computer with the longitudinal movement of the cant past the reference point.  
           [0017]    The machine described in U.S. Pat. No. 5,884,682 uses another approach. The machine uses mechanical positioning devices to position the cant and to present it tangentially to the saw blades.  
           [0018]    As it was explained, there are drawbacks in adjusting the saw blades to follow optimized cut lines which start at the leading edge of the wood board and end at the trailing edge of the board. As such, it may be appreciated that there continues to be a need for a new and improved method to operate a board edger to prevent these surface defects. There is also a need for a better board edger in which the saw blades are shifted with greater speed and precision.  
         SUMMARY OF THE INVENTION  
         [0019]    In the present invention, however, there is provided an optimized board edger in which the structure of the saw blade moving mechanism has a low inertia, for rapid positioning of the saw blades. The saw box in the optimized board edger follows optimized cut lines on a virtual entity of the wood board to be trimmed. This virtual entity is made longer than the wood board such that the tracking of the optimized cut lines starts before the saw blades enter the leading edge of the wood board and ends after the saw blades have completely exited the wood board.  
           [0020]    In the present disclosure, the expression “virtual entity” is used to describe a set of data inside a computer memory corresponding to the dimensions, position and speed of a wood board in motion relative to one or more space and time references that are assignable to a board edger.  
           [0021]    Broadly, in accordance with a first feature of the present invention, there is provided a new method for edging a wood board. This method comprises the following steps:  
           [0022]    a) providing a board edger having a movable saw box and a saw blade mounted in that saw box;  
           [0023]    b) scanning a wood board and obtaining images of this wood board;  
           [0024]    c) constructing from the images, a virtual entity of the wood board;  
           [0025]    d) determining from the images, a position, alignment and travelling speed of the wood board;  
           [0026]    e) determining from the images an optimized cut line along the virtual entity;  
           [0027]    f) superimposing the virtual entity in space and time over the wood board;  
           [0028]    g) displacing the forward edge of the virtual entity ahead of the leading edge of the wood board;  
           [0029]    h) displacing the rear edge of the virtual entity behind the trailing edge of the wood board;  
           [0030]    i) extending the optimized cut line to the forward and rear edges of the virtual entity;  
           [0031]    j) simultaneously moving the virtual entity and the wood board through the board edger, and  
           [0032]    k) sawing the wood board along the optimized cut line on the virtual entity.  
           [0033]    The method according present invention for edging a wood board reduces the defects and disadvantages of the prior art by incorporating buffer zones ahead and after the wood board, in which the saw blade adjustments are effected. The lengths of these buffer zones are determined by the response time of the board edger for repositioning the saw blades, the desired speed of the transport conveyor and the desired spacing between the boards.  
           [0034]    In accordance with another feature of the present invention, there is provided a board edger for edging wood cants, comprising a saw box having an arbour mounted therein. At least one saw collar assembly is adjustably mounted on the arbor and a saw blade is mounted in the saw collar assembly. The saw box also has a setworks mounted thereon above the arbor. The setworks has a displacement parallel to the arbor. A saw shifting arm extends at right angle from the arbor, between the saw collar assembly and the setworks for moving the saw blade along the arbor in response to a movement of the setworks. This saw shifting arrangement is advantageous over other board edgers of the prior art in that it is compact, light, frictionless and precise.  
           [0035]    Other advantages and novel features of the present invention will become apparent from the following detailed description of the preferred embodiment. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0036]    One embodiment of the present invention is illustrated in the accompanying drawings, in which like numerals denote like parts throughout the several views, and in which:  
         [0037]    [0037]FIG. 1 is a plan view of a board edging installation comprising the optimized board edger according to the preferred embodiment of the present invention;  
         [0038]    [0038]FIG. 2 is an enlarged plan view of the optimized board edger and partial views of the upstream transport conveyor and downstream discharge conveyor;  
         [0039]    [0039]FIG. 3 is a partial plan view of a board or a cant entering the saws of an edger in a prior art installation;  
         [0040]    [0040]FIG. 4 is a plan view of a cant and of a virtual entity of this cant as generated by the computer system comprised in the preferred installation of the optimized board edger;  
         [0041]    [0041]FIG. 5 is a plan view of the saw box in the optimized board edger according to the preferred embodiment;  
         [0042]    [0042]FIG. 6 is a cross-section view of the saw box, as seen along line  6 - 6  in FIG. 5;  
         [0043]    [0043]FIG. 7 is a side view of the saw box in the optimized board edger;  
         [0044]    [0044]FIG. 8 is a perspective exploded view of a saw blade, a saw collar assembly and a saw shifting arm comprised in the saw box in the optimized board edger;  
         [0045]    [0045]FIG. 9 is a cross-section view of the saw blade, the saw collar assembly and the shifting arm illustrated in FIG. 8;  
         [0046]    [0046]FIG. 10 is an enlarged view of the saw collar assembly, and in particular of the portion of the hub as seen in detail circle  10  in FIG. 9. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0047]    While this invention is susceptible of embodiments in many different forms, there is shown in the drawings and will be described in details herein one specific embodiment of the board edger according to the present invention, with the understanding that the present disclosure is to be considered as an example of the principles of the invention and is not intended to limit the invention to the embodiment illustrated and described. Similarly, the preferred installation of the optimized board edger and its method of operation are provided as examples to explain a general concept. These descriptions should not be used to limit the scope of the invention.  
         [0048]    Referring firstly to FIGS.  1 - 4 , a preferred method for operating an optimized board edger will be described. The preferred board edging installation comprises an in-line arrangement of an infeed conveyor  20 , a lineal scanner  22 , a transport conveyor  24 , an optimized board edger  26 , and a discharge conveyor  28 . The preferred infeed conveyor  20  has a board pre-locating device  30  which function is to position each board as straight as possible along the transport conveyor  24 . The infeed conveyor  20  can be fed manually or from a sorting table as it is customary in sawmills. Numerous components of the machines mentioned above and of the preferred optimized board edger are not illustrated herein because these components belong to known technology and do not constitute the focus of the present invention.  
         [0049]    In the preferred board edging installation, a computer system is provided between the lineal scanner  22  and the optimized board edger  26 . This computer system comprises a personal computer (PC)  32  containing an optimizing software, a programmable logic controller (PLC)  34  communicating with the PC  32  and with one or more servo modules  36  and one or more servo drive translators  38  to control the tracking functions of the optimized board edger  26 . A two-way ethernet 100 MB/sec. connection  40  is provided between the PC  32  and the PLC  34 .  
         [0050]    The lineal scanner  22  is preferably a 3-D True-Shape Scanner manufactured by Perceptron Inc., a company having its headquarters at Plymouth, Mich., USA. The PC  32  preferably has a high speed processor and optimizing software to receive a 3-D image from the lineal scanner  22  and to compute a breakdown solution in 250 millisecond or less for softwood applications and in 400 millisecond or less for hardwood applications.  
         [0051]    The length of the transport conveyor  24  is determined according to the desired travel speed of this transport conveyor and the processing time for each sawing solution. A travel speed of 800-1200 feet/minute is believed achievable with the installation described herein.  
         [0052]    The optimized board edger  26  according to the preferred embodiment has an active saw box  42  which is movable about a vertical axis and in which the saw blades are movable along the arbor. In order to reduce the inertia of the saw box  42 , the arbor is driven by an electric motor  44  through sheaves and belts under the guard  46  and a flexible drive shaft under the guard  48 .  
         [0053]    In use, an untrimmed wood board  50  is scanned while in motion through the scanner  22 . The longitudinal axis  52  of the board relative to the longitudinal axis  54  of the optimized board edger, as well as the optimized cut lines  56  are determined while the wood board is moving toward the optimized board edger  26 .  
         [0054]    The saws are set apart a same distance A as the spacing between the optimized cut lines  56 . The saw box  42  is rotated to align the saw blades  60  parallel to the longitudinal axis  52  of the wood board, and the saw blades are set in motion along the arbor  62  to follow the optimized cut lines  56  as the wood board  50  travels through the optimized board edger  26 .  
         [0055]    Referring now to FIG. 3, the problems with high speed positioning of a saw box will be described. When the longitudinal axis  52  of a wood board  50  to be trimmed is skewed a few degrees from the feeding direction  54 , it will be appreciated that an initial adjustment to a proper spacing and alignment of the saw blades  60  must be made before the saw blades enter the wood piece. As the saw blades  60  enter the wood piece  50 , the saw blades  60  must move in unison along the arbor  62  to follow the optimized cut lines  56 .  
         [0056]    In the machines of the prior art, the leading edge  70  and the rear edge  72  of the wood board  50  are detected and used to designate the beginning and the ending of the optimized cut lines  56 . The leading and trailing edges are used as targets with which the saw blades must aim. However, it will be appreciated that the saw box has a certain inertia and its actuators have acceleration, deceleration, elasticity and dampening factors, incorporated in each of their movements. These motion factors cause a certain delay in positioning the saw blades  60  at the entrance and exit of a board. As a result, the positioning of the saw blades  60  is not instantaneous. The saw blades might still oscillate around their programmed position as they enter the leading edge  70  of the wood board. The tracking of the saw blades in unison to follow the optimized cut lines  56  may only start an instant after the saw blades have actually entered the board. Similarly, the movement of the saw blades in tracking the optimized cut lines throughout to the trailing edge  72  stops prematurely before the saw blades have completely exited the wood board.  
         [0057]    This dragging in the positioning of the saw blades to follow the optimized cut lines causes the kerf width near the leading and trailing edges of a wood board to be generally larger than normal, causing defects in the recovered lumber and side stresses on the saw blades.  
         [0058]    In the preferred method of operating the optimized board edger  26 , the PC  32  is configured to construct a virtual entity  80  of each wood board  50 . This virtual entity  80  has all the dimensions of the physical wood board  50 . This virtual entity  80  is superimposed in space and time over the physical wood board  50 .  
         [0059]    Depending upon the operating speed and the length of the transport conveyor  24 , the virtual entity  80  is assigned excess length L ahead of the leading edge  70  of the wood board  50 , and excess length T following the trailing edge  72  of the wood board  50 . The optimized cut lines  56  are projected along both excess lengths L, T.  
         [0060]    In the preferred method of operation, the angle of the saws  60  relative to the longitudinal axis  52  of the wood board  50  and the spacing A of the saw blades  60  are adjusted, and the displacement of the saw blades in unison along the arbour  32  is set in motion by the PC  32  according to the position, alignment and travelling speed of the virtual entity  80 . The target set points between which precise tracking of the saw blades  60  is maintained are set at the forward edge  70 ′ and the rear edge  72 ′ of the virtual entity  80 . By aiming the saw blades  60  at the forward edge  70 ′ of the virtual entity  80 , the inherent oscillation of the saw blades  60  during positioning occurs along the excess length L, such that uniform side edges are obtained from the leading edge  70  of the actual wood board  50 . Similarly, the tracking of the optimized cut lines back to the rear edge  72 ′ of the virtual entity  80  ensures that the saw blades are out of the wood board  50  when tracking stops. In the preferred edging installation, having the response and computing time as mentioned hereinbefore, the lengths L and T are set at  24  inch each.  
         [0061]    Referring now to FIGS.  5 - 7 , the saw box  42  in the preferred optimized edger  26  will be described in some details. The saw box consists of a frame  90 , an arbor  92  mounted in bearings  94 ,  96 , a pair of saw blades  60  mounted on the arbor  92 . The saw box has a setworks  98  mounted on top of the frame  90 . There is provided three circular ball bearings  100  on the bottom of the frame  90 . The bearings  100  are set on a circular rail  102 , represented by a dashed line in FIG. 5. This circular rail is mounted on the base of the edger  26 . The preferred angular adjustment B of the saw box  42  is 7-{fraction (1/2)} 0  to the left and to the right of the longitudinal axis  54  of the optimized board edger  26 , for a total angular displacement of  15 °.  
         [0062]    The rotation of the saw box  42  to the right or the left of the longitudinal axis  54  is effected by a DC servo drive actuator controlled by the PC  32 . This DC servo drive actuator and its mounting have not been illustrated herein for being known to those skilled in the art.  
         [0063]    The setworks  98  also comprises two DC servo drive motors  104  respectively linked to a linear slide  106 , and also being controlled by the PC  32 . Each linear slide  106  encloses a ball screw and a ball nut connected to a yoke plate  108 . Each DC servo drive motor  104  drives the yoke plate  108  along the linear slide  106  with precision. A shifting arm  110  is affixed to the yoke plate  108  and extends to a respective saw collar assembly  112  for moving one of the saw blades  60  along the arbor  92 . Both saw blades  60  are movable independently of each other along the arbor  92  for board width adjustment, and in unison with each other during the edging of a wood board.  
         [0064]    The arbor  92  has splines thereon as it is customary with board edgers. Each saw blade  60  is supported in a collar assembly  112 , which is adapted to engage with, and to slide along these splines. This collar assembly  112  is better illustrated in FIGS.  8 - 10 . The saw collar assembly  112  comprises a hub  114  which has grooves  116  therein to engage with the splines  118  on the arbor  92 , with a loose sliding fit. The hub  114  has a flange  120  on its circumference, to which is clamped the saw blade  60 , by means of a blade lock ring  122  with bolt holes  124  and machine screws  126  through these holes. Next to the flange  120 , there is an inner bearing seat  128  on the outside surface of the hub, and an adjoining threaded portion  130 . A bearing  132  is held to the inner bearing seat  128  of the hub by a lock nut  134  engaged over the threaded portion  130 . This bearing  132  affords a frictionless rotation of the hub  114  relative to the shifting arm  110 .  
         [0065]    The outer race of the bearing  132  is clamped into an outer bearing seat  136  inside an opening  138  in the lower end of the shifting arm  110 . The outer race of the bearing  132  is held to the outer bearing seat  136  by means of an outer lock ring  140  having bolt holes  142  and machine screws  144  through these holes. Where possible, the components of the saw collar assembly  112  are made of aluminum to ensure a minimum weight and inertia.  
         [0066]    The preferred shifting arm  110  has a conduit  146  therein to which is connected a nozzle  148 . This conduit  146  and nozzle  148  are advantageous for periodically pumping lubricant to the surface of the arbor  92  for lubricating the hub  114  and the arbor  92 .  
         [0067]    Referring particularly to FIG. 10, the grooves  116  inside the hub  114  do not extend the full length of the hub. A brass ring  150  is mounted on each end of the hub  114 , inside the hub, and both rings  150  complement with the grooves, the full length of the hub. Each brass ring  150  is press fitted into a shoulder at each end of the hub  114 . The inside diameter of each ring  150  is a loose fit over the crest of the splines  118  on the arbor  92 . The brass rings  150  are advantageous for preventing a binding of the grooves  116  into the splines  118  and facilitate to a considerable extent the movement of the collar assembly  112  along the arbor  92 .  
         [0068]    As to other manner of usage and operation of the present invention, the same should be apparent from the above description and accompanying drawings, and accordingly further discussion relative to the manner of usage and operation of the invention would be considered repetitious and is not provided.  
         [0069]    While one embodiment of the present invention has been illustrated and described herein, it will be appreciated by those skilled in the art that various modifications, alternate constructions and equivalents may be employed without departing from the true spirit and scope of the invention. Therefore, the above description and the illustrations should not be construed as limiting the scope of the invention which is defined by the appended claims.