Abstract:
A grapple saw includes grapple having downwardly-extending jaws for holding a log therebetween, the jaws moveable between an open position and a closed position in a gripping direction; and a saw carried by the grapple, the saw having a blade moveable between starting and ending positions in a cutting plane generally parallel to the gripping direction, so as to sever a log held in the jaws. The ending position of the saw blade is substantially horizontal, so as to prevent twisting of a free end of the severed log relative to the grapple.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to logging equipment and more particularly to grapples used to lift and move trees and logs.  
         [0002]     In the logging industry, it is a well-known procedure to top, delimb, rough-cut, and otherwise partially process trees very close to the location where they are felled. This saves the cost of transporting entire trees, reduces the amount of waste material generated at the sawmill or processing plant, and also makes transportation easier because the trees are in a more-or-less uniform cylindrical shape and size after topping and delimbing.  
         [0003]     One common type of machinery used in field processing of trees is a “grapple saw”. A grapple is a mechanism with moveable jaws used to grip and move felled trees. Grapples are typically carried by moveable booms mounted on skidder vehicles or independent loaders. Some of these grapples have saws mounted thereto which can be used to cut the trees down to shorter lengths. While these grapple saws are effective, they typically complete the cut in a way that causes the log to twist on completion of the cut. This can pinch the saw and possibly damage or break the saw, and also presents a risk to personnel nearby as the log rolls away.  
         [0004]     Accordingly, it is an object of the invention to provide a grapple saw which avoids twisting of a log as it is cut.  
         [0005]     It is another object of the invention to provide a grapple saw which has minimal ground contact during a cutting operation.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     These and other objects are met by the present invention, which in one aspect provides a grapple saw, including: a grapple having downwardly-extending jaws for holding a log therebetween, the jaws moveable between an open position and a closed position in a gripping direction; a saw carried by the grapple, the saw having a blade moveable between starting and ending positions in a cutting plane generally parallel to the gripping direction, so as to sever a log held in the jaws, wherein the ending position of the saw blade is substantially horizontal, so as to prevent twisting of a free end of the severed log relative to the grapple.  
         [0007]     According to another aspect of the invention, the jaws are moveable about at least one pivot axis, and the saw is moveable about a pivot point disposed substantially below both the at least one pivot axis.  
         [0008]     According to another aspect of the invention, the saw includes a chain carried on a moveable bar.  
         [0009]     According to another aspect of the invention, the saw is enclosed in a saw box mounted to the grapple.  
         [0010]     According to another aspect of the invention, a grapple saw includes: a grapple having at least one pair of downwardly-extending jaws for holding a log therebetween, the jaws pivotable about a common axis to move in a gripping direction between an open position and a closed position; and a saw carried by the grapple, the saw having a blade moveable about a pivot point in a cutting plane generally parallel to the gripping direction between starting and ending positions so as to sever a log held in the jaws, wherein the pivot point is disposed substantially below the common axis of the jaws.  
         [0011]     According to another aspect of the invention, a grapple saw includes: a grapple having a frame and at least one pair of downwardly-extending jaws for holding a log therebetween, the jaws pivotable about spaced-apart jaw pivots to move in a gripping direction between an open position and a closed position; a saw box mounted to the frame and having a first end having a pivot axis and a second ends having a pivot point, the saw box moveable about the pivot axis between a stowed position and a cutting position in which the pivot point is disposed substantially below the jaw pivots; a saw carried by the saw box and pivotable about the pivot point between starting and ending positions in a cutting plane generally parallel to the gripping direction, so as to sever a log held in the jaws.  
         [0012]     According to another aspect of the invention, the ending position of the saw is substantially horizontal, so as to prevent twisting of a free end of the severed log relative to the grapple.  
         [0013]     According to another aspect of the invention, the frame carries a convex saddle adapted to stabilize a log gripped in the jaws.  
         [0014]     According to another aspect of the invention, the saw box includes a concave edge adapted to bear against a log in the cutting position.  
         [0015]     According to another aspect of the invention, a method of cutting a log includes: providing a grapple having jaws for holding a log therebetween, the Jaws moveable between an open position and a closed position in a gripping direction; providing a saw carried by the grapple, the saw having a blade moveable in a cutting path within a plane generally parallel to the gripping direction; gripping the log in the jaws of the grapple; moving the saw blade along the cutting path to engage and progressively sever the log; and directing a terminal portion of the saw movement such that, upon completion of cutting, a free end of the log separates from the remainder of the log substantially free from any twisting motion about a long axis of the log.  
         [0016]     According to another aspect of the invention, the saw blade terminates the cut in a substantially horizontal position. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which:  
         [0018]      FIG. 1  is a side view of a grapple saw constructed in accordance with the present invention;  
         [0019]      FIGS. 2A-2C  are front views showing the grapple saw of  FIG. 1  during a cutting sequence on a first log;  
         [0020]      FIGS. 3A-3C  are front views showing the grapple saw of  FIG. 1  during a cutting sequence on a second log;  
         [0021]      FIGS. 4A-4C  are front views showing the grapple saw of  FIG. 1  during a cutting sequence on a third log;  
         [0022]      FIGS. 5A-5C  are front views showing an alternative grapple saw during a cutting sequence on a fourth log;  
         [0023]      FIGS. 6A-6C  are front views showing the grapple saw of  FIG. 5  during a cutting sequence on a fifth log; and  
         [0024]      FIGS. 7A-7C  are front views showing the grapple saw of  FIG. 5  during a cutting sequence on a sixth log. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]     Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,  FIGS. 1 and 2  illustrate an exemplary grapple  10 . The grapple  10  includes one or more pairs of opposed jaws  12  which are pivoted open and closed about a common axis  14  by hydraulic cylinders  16 , which are in turn mounted to the end of a moveable boom  18  of a known type. The motion of the jaws  12  define a gripping direction which is generally perpendicular to the log or object to be gripped. A saw box  20  having an opening  22  is mounted to one of the outermost jaws  16 . The saw box  20  encloses a saw  24  which is moveable between a retracted position, shown in  FIG. 2A , and an extended position, shown in  FIG. 2C .  
         [0026]     In the illustrated example, the saw  24  is a chainsaw having a bar  26  and a chain  28  driven by a hydraulic motor  30 , or other suitable power source. Means such as a hydraulic cylinder (not shown) or other suitable actuator are provided to pivot the bar  26  about a pivot point “P 1 ”.  
         [0027]     In contrast to prior art practice, the pivot point P 1  is carefully located to achieve a specific cutting motion. This cutting motion is shown in  FIGS. 2A-2C  on a relatively large log “L 1 ”. As used herein, the term “log” is used to refer generally to the workpiece, whether it is an entire tree trunk or a shorter portion already cut therefrom. The process begins by clamping the log L 1  in the jaws  12 , with the saw  24  in the retracted position ( FIG. 2A ). The grapple  10  is primarily used to stabilize the log L 1  during the cut, and  50  it is typically not lifted above the ground. The saw  24  is then started and moved downward to engage and cut the log L 1 . The bar  26  pivots about point P 1  which is positioned relatively low on the jaw  16 . The bar  26  moves within a plane generally parallel to the gripping direction (in other words, it does not intersect a line defining the gripping direction).  FIG. 2B  shows the cut partially completed.  
         [0028]      FIG. 2C  shows the cut at the instant of completion, with a free end “F 1 ” of the log L 1  falling away. As the cut progresses, less and less of the log cross-section remains intact at the cutting plane. At some point, the remaining material will be insufficient to keep the log L 1  intact and the free end F 1  will begin to fall away from the remainder of the log L 1  even though it is not completely severed. In a prior art grapple saw (not shown), with a saw pivoted at a high point on the grapple, the cut is completed with the saw bar close to a vertical position. This causes the log to twist apart about its long axis, which can pinch and possibly damage the saw bar and cause a safety hazard to nearby personnel. The prior art saw bar also extends substantially below the jaws which can cause it to contact the ground during a cut. This is highly abrasive and causes rapid wear of the saw.  
         [0029]     The low pivot point P 1  of the saw  24  causes it to closely approximate a horizontal position at the end of the cut. The twisting tendency of the log L 1 , if any, is greatly reduced. The exact nature of the cut will vary depending upon the size of the log which is cut. Ideally, the saw  24  will be as close to horizontal as possible upon completion.  FIGS. 3A-3C  show the steps in cutting a log L 2  which is smaller than the log L 1 , and  FIGS. 4A-4C  show the steps in cutting another log L 3  which is yet smaller than the log L 2 . In the particular example shown, the saw bar  26  is most nearly horizontal at the cut termination with the smallest log L 3 . In each case, the protrusion of the saw bar  26  below the jaws  16  is limited such that minimal ground contact is experienced.  
         [0030]     The size and shape of the grapple jaws  16  as well as the location of the pivot point P 1  may be chosen so that the greatest reduction of twist is achieved with a log of a specific size. In general, the pivot point P 1  is located substantially below the jaw pivot axis  14 . More specifically, the pivot point P 1  may be positioned below a line “T 1 ” tangent to a top surface  32  of the log L 1 . The greatest reduction in twist will be achieved when the pivot point P 1  is at approximately at the level of a line “T 2 ” tangent to a bottom surface  34  of the log L 1 .  
         [0031]      FIG. 5A  illustrates another exemplary grapple  110  which is intended to be carried by a log skidder of a known type. The grapple  110  includes a frame  112  and one or more pairs of opposed jaws  114  which are pivoted open and closed about spaced-apart pivot axes  116  and  118 . The motion of the jaws  114  define a gripping direction which is generally perpendicular to the log being gripped. A concave saddle  120  is provided to bear against and stabilize a log during the cut.  
         [0032]     A saw box  122  having an opening  124  is mounted to a the frame  112 . The saw box pivots about an axis  126  between a stowed position, shown in  FIG. 5A , and a cutting position, shown in  FIG. 5B . The saw box  122  encloses a saw  128  which is moveable between a retracted position, shown in  FIG. 5B , and an extended position, shown in  FIG. 5C . The saw box  122  has a concave edge  123  adapted to bear against a log and stabilize it during a cut. In the illustrated example, the saw  128  is a chainsaw having a bar  132  and a chain  134  driven by a hydraulic motor  136 , or other suitable power source. Means such as the illustrated hydraulic cylinder  138  are provided to pivot the bar  132  about a pivot point “P 2 ”.  
         [0033]     The pivot point P 2  is carefully located to achieve a specific cutting motion. This cutting motion is shown in  FIGS. 5B and 5C  on a relatively large log “L 4 ”. The process begins by clamping the log L 4  in the jaws  114  and against the saddle  120  with the saw box  122  in the stowed position and the saw  128  in a retracted position ( FIG. 5A ). The grapple  110  is primarily used to stabilize the log L 4  during the cut, and so it is typically not lifted above the ground. The sawbox  122  is lowered until it contacts the log L 4 , and the saw  128  is then started and moved downward to engage and cut the log L 4 . The bar  132  pivots about point P 2  which is positioned a substantial amount below the frame  112 . The motion of the bar  132  lies within a plane that is generally perpendicular to the gripping direction (in other words, the plane does not intersect the cutting direction).  FIG. 5B  shows the cut partially completed.  
         [0034]      FIG. 5C  shows the cut at the instant of completion, with a free end “F 4 ” of the log L 4  falling away. As the cut progresses, less and less of the log cross-section remains intact at the cutting plane. At some point, the remaining material will be insufficient to keep the log L 4  intact and the free end F 4  will begin to fall away from the remainder of the log L 4  even though it is not completely severed.  
         [0035]     The low pivot point P 2  of the saw  128  causes it to closely approximate a horizontal position at the end of the cut. The twisting tendency of the log L 4 , if any, is greatly reduced. The exact nature of the cut will vary depending upon the size of the log which is cut. Ideally, the saw  128  will be as close to horizontal as possible upon completion.  FIGS. 7A-7C  show the steps in cutting a log L 5  which is smaller than the log L 4 , and  FIGS. 8A-8C  show the steps in cutting another log L 6  which is yet smaller than the log L 5 . In the particular example shown, the saw bar  132  is most nearly horizontal at the cut termination with the intermediate size log LS. In each case, the protrusion below the saw box  122  is limited such that minimal ground contact is experienced.  
         [0036]     The size and shape of the saw box  122  as well as the location of the pivot point P 2  may be chosen so that the greatest reduction of twist is achieved with a log of a specific size. In general, the pivot point P 2  is located substantially below the saw box pivot axis  126 . More specifically, the pivot point P 2  may be positioned below a line “T 3 ” tangent to a top surface  140  of the log L 4 . The greatest reduction in twist will be achieved when the pivot point P 2  is approximately at the level of a line “T 4 ” tangent to a bottom surface  142  of the log L 4 .  
         [0037]     The foregoing has described a grapple saw. While specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of the invention. Accordingly, the foregoing description of the preferred embodiment of the invention and the best mode for practicing the invention are provided for the purpose of illustration only and not for the purpose of limitation.