Abstract:
A grapple skidder for dragging a bundle of logs or trees from one location to a selected site. The grapple skidder comprises a boom and grapple assembly including a grapple suspended from an arched boom arm pivotally mounted to a linear main boom pivotable between forward and rearward inclined positions. A heel is directly mounted on the underside of the main boom to provide an arresting surface against which the butt ends of the trees abut when the boom and grapple assembly is operated to lift a bundle of trees over another bundle of trees lying on the ground. The arresting surface retains the grasped trees against pivotal movement due to gravitational forces, whereby pivotal movement of the main boom in a direction opposite to that which tend to be induced by the gravitational forces results in the trees being completely lifted off the ground.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to grapple skidder suited for moving an elongated load, such as a group of trees or logs, from one location to a selected location on a terrain.  
           [0003]    2. Description of the Prior Art  
           [0004]    It is well known to use grapple skidders to drag loads of logs from one location to a selected site. Conventional grapple skidders typically comprise a grapple suspended at the free distal end of a boom mounted on a tow vehicle. The grapple is usually hydraulically operated to open and close about one end of the load to be skidded. In the open position, the grapple is lowered to surround the butt end portion of a load of logs. Then, the grapple is closed and lifted to a position where the grasped end of the load of logs abut the rear end portion of the vehicle rearwardly of the rear axle thereof. This causes substantial tipping forces on the boom section tending to pivot the same rearwardly.  
           [0005]    To minimize such tipping forces, it has been proposed, as exemplified by U.S. Pat. No. 3,782,567 issued on Jan. 1, 1974 to Likas et al., to use a boom assembly comprising a small linear boom arm pivotally mounted at a distal end of a main C-shaped boom which is, in turn, pivotally mounted to a vehicle.  
           [0006]    Although the structure of the boom assembly disclosed in the above mentioned patent allows to drag an elongated load with one end thereof elevated over the rear axle of the vehicle so as to reduce the couple exerted on the boom by the dragged load, it has been found that there is a need for a new grapple skidder having a boom and grapple assembly offering increased freedom of movement.  
           [0007]    It has also been found that there is a need for a grapple skidder having a boom and grapple assembly which can be operated to stack a bundle of trees or logs over another bundle of trees or logs lying on a ground surface.  
         SUMMARY OF THE INVENTION  
         [0008]    It is therefore an aim of the present invention to provide a new grapple skidder having a boom and grapple assembly adapted to lift an elongated load over a ground surface.  
           [0009]    It is also an aim of the present invention to provide a grapple skidder which offers increased freedom of movement.  
           [0010]    It is a further aim of the present invention to provide a method for completely elevating an elongated load over a ground surface with a grapple skidder.  
           [0011]    Therefore, in accordance with the present invention, there is provided a grapple skidder comprising a vehicle, a boom mounted to a rearward end portion of the vehicle, a grapple articulately suspended from a distal end of the boom for grasping an elongated load, and a heel mounted to the boom at a spaced location from the grapple for providing an arresting surface for the elongated load. The boom is pivotable to a first position to locate the grapple beyond the vehicle for embracing the elongated load at a location comprised between a leading end and the center of gravity thereof, and to a second position for lifting the leading end of the elongated load above a ground surface against the arresting surface to retain the elongated load against pivotal movement due to gravitational forces, whereby further pivotal movement of the boom from the second position thereof in a direction away from the first position results in the elongated load being completely lifted above the ground surface.  
           [0012]    In accordance with a further general aspect of the present invention, there is provided a grapple skidder comprising a vehicle, a boom mounted to a rearward end portion of the vehicle, a grapple suspended from a distal end of the boom for grasping an elongated load, and a heel mounted to the boom for providing an arresting surface for the elongated load. The boom is pivotable from a first position to locate the grapple beyond the vehicle for embracing the elongated load at a location comprised between a leading end and the center of gravity thereof, to a second position in which the elongated load is completely lifted above a ground surface with the leading end thereof abutting against the arresting surface of the heel, thereby precluding pivotal movement of the grapple and the elongated load relative to the boom due to gravitational forces acting on the elongated load at the center of gravity thereof.  
           [0013]    In accordance with a further general aspect of the present invention, there is provided a method of lifting an elongated load over a ground surface with a grapple skidder having an arresting surface, comprising the steps of:  
           [0014]    a) grasping the elongated load with a grapple at a selected location comprised between a first end of the elongated load and a center of gravity thereof,  
           [0015]    b) lifting the first end of the elongated load above the ground surface against the arresting surface of the grapple skidder so as to retain the elongated load against pivotal movement due to gravitational forces, and  
           [0016]    c) applying further lifting forces at the selected location to completely elevate the elongated load above the ground surface.  
           [0017]    In accordance with a further general aspect of the present invention there is provided a grapple skidder comprising a boom assembly including a linear main boom and an arched boom arm. The main boom is mounted to a vehicle for pivotal movement with respect thereto about a substantially horizontal axis. The arched boom arm is pivotally mounted to the main boom. A grapple is mounted at a distal end of the arched boom arm for grasping one end portion of an elongated load to be dragged. At least one arm cylinder extends between the main boom and the arched boom arm for pivoting the same relative to the main boom. The main boom is pivotable relative to the vehicle between first and second positions, wherein in the first position, the main boom is inclined forwardly with respect to a direction of travel of the vehicle during skidding, thereby allowing the elongated load to be dragged with one end portion thereof lifted over the rearward end of the vehicle, while minimizing the overall dimensions of the boom assembly when not in use. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, showing by way of illustration a preferred embodiment thereof, and in which:  
         [0019]    [0019]FIG. 1 is a side view of a grapple skidder illustrating the freedom of movement of a boom and grapple assembly thereof in accordance with a first embodiment of the present invention;  
         [0020]    [0020]FIG. 2 is a top plan view of the boom and grapple assembly of the grapple skidder of FIG. 1;  
         [0021]    [0021]FIG. 3 is a side view of the grapple skidder illustrated in the process of dragging endwise a bundle of trees from on location to another selected location;  
         [0022]    [0022]FIG. 4 is a perspective view of a boom and grapple assembly of the grapple skidder of FIG. 1;  
         [0023]    [0023]FIG. 5 is a side view of the grapple skidder illustrating how the boom and grapple assembly thereof can be operated to lay a bundle of trees on another bundle of trees lying on a ground surface; and  
         [0024]    [0024]FIG. 6 is top plan view of a boom and grapple assembly of a grapple skidder in accordance with a second embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    Now referring to the drawings and in particular to FIG. 1, a grapple skidder  10  suited for transporting loads or drags of logs or trees and embodying the elements of the present invention will be described.  
         [0026]    The grapple skidder  10  generally comprises a log skidder or self-propelled tracked vehicle  12  supported on either side thereof by a track  14 . Each track  14  is driven by a pair of wheels  16  operating in tandem. A rear chassis  18  is articulated to the front chassis of the vehicle  12  and is driven from the power take-off thereof. The rear chassis  18  is provided in the form of a structural frame  26  supported on either side thereof by a track  20 . Each track  20  is driven by front and rear wheels  22  and  24  operating in tandem. It has been found that the use of such an articulated self-propelled tracked vehicle  12  in the context of a grapple skidder is advantageous, as compared to conventional four wheel drive grapple skidders, in that it provides increased traction, floatation, and stability, especially, on soft grounds.  
         [0027]    A base in the form of a turntable  28  is mounted on the frame  26  substantially between the front and rear wheels  22  and  24  for pivotal movement about a vertical axis. A boom mount  30  is secured on the top surface of the turntable  28 . As best seen in FIGS. 1, 2 and  4 , a linear main boom  32  is pivotally mounted at a bottom end thereof to the boom mount  30  by means of a pair of hinge pins  34  extending along a horizontal pivot axis (see FIG. 2). Accordingly, the main boom  32  is capable of swinging on the turntable bearings and pivoting about the hinge pins  34  relative to the boom mount  30 . Likewise, a boom arm  36  is pivotally mounted to the main boom  32  via a horizontal hinge pin  38 .  
         [0028]    A conventional grapple  40  is freely suspended from the free distal end of the arm  36  by an appropriate grapple coupling  42  that pivots about two axes perpendicular to one another. The grapple  40  includes a pair of opposed arcuate jaw members  44  which can be hydraulically operated to open and close tightly about a bundle of logs or trees piled on the ground in stacked relationship, as is well known in the art.  
         [0029]    As seen in FIGS. 1 and 2, a pair of side-by-side hydraulic cylinders  46  are provided for pivoting the main boom  32  relative to the turntable  28 . Each hydraulic cylinder  46  is connected at a first end thereof to the boom mount  30  via a hinge pin  48  located below the hinge pins  34  of the main boom  32 . Each hydraulic cylinder  46  is connected at an opposed rod end thereof to a bracket  50  extending integrally away from a top surface  51  of the main boom  32 , at a pivot point  53  spaced from the main boom  32  itself to provide a lever arm for the movement of the main boom  32 . Hydraulic lines (not shown) provide pressurized hydraulic fluid to retract and extend the boom cylinders  46 , as is well known in the art.  
         [0030]    As seen in FIGS. 2 and 4, the proximal end of the arm  36  is received in a central rectangular cutout portion  52  provided in the main boom  32  at a location spaced lengthwise from the distal end thereof. A single central hydraulic arm cylinder  54  is provided on a top side of the arm  36  for pivoting the same relative to the main boom  32 . The arm cylinder  54  is pivotally connected at a first end thereof to the distal end of the main boom  32  via a hinge pin  56 . Likewise, the arm cylinder  54  is pivotally connected at a second opposed end thereof to the boom arm  36  by means of a hinge pin  58 .  
         [0031]    The boom arm  36  has a proximal linear segment  60  and a distal arched segment  62  extending integrally downwardly from the linear segment  60 . The hinge pin  58  is located substantially adjacent the root of the arched segment  62 , i.e. at the end of the linear segment  60  near the junction of the linear and arched segments  60  and  62 . As to the hinge pins  38  connecting the boom arm  36  to the main boom  32 , they are disposed at a location between the opposed ends of the boom  32  below the point of pivot of the arm cylinder  54  relative to the main boom  32  and immediately above the point of connection of the boom cylinders  46  and the main boom  32 . The shape of the main boom  32  and the boom arm  36  in combination with the emplacement of the arm cylinder  54  between the boom arm  36  and the main boom  32  provide a boom assembly which is foldable upon itself, thereby allowing the overall dimensions of the boom assembly to be minimized for transport and storage purposes. Furthermore, the fact the main boom  32  is displaceable to a forwardly inclined position, as illustrated in full line in FIG. 1, also allows an elongated load, such as a bundle of trees or logs, to be dragged with the leading ends thereof elevated just over the rear wheel  24  of the grapple skidder  10 , thereby minimizing the couple transmitted to the boom  32  by the dragged load.  
         [0032]    The above described relative disposition of the various points of connection between the boom mount  30 , the main boom  32 , the boom arm  36 , the boom cylinders  46  and the arm cylinder  54  has been found suitable to maximize the freedom of movement of the main boom  32  and the boom arm  36  while preserving the lifting capacity thereof.  
         [0033]    As seen in FIG. 1, the boom  32  and boom arm  36  are displaceable between a fully retracted position in which the boom  32  is inclined forwardly with respect to a direction of travel of the tracked vehicle  12 , while the arm  36  extends in a generally vertical direction with the grapple  40  hanging therefrom over the rear chassis  18  between the front and rear wheels  22  and  24  thereof, and a fully deployed position (shown in dotted lines) wherein the boom  32  is inclined rearwardly and the arm  36  extends downwardly therefrom in a generally vertical direction. According to a preferred embodiment of the present invention, the boom  32  extends at about  65  degrees from the vertical when displaced to its retracted position and about  55  degrees when displaced to its deployed position.  
         [0034]    As seen in FIG. 3, the mobility of the main boom  32  and boom arm  36  allows the grapple skidder  10  to drag a bundle of trees T with the butt ends thereof elevated over the rear wheels  24  of the rear chassis  18  and the other ends of the trees remaining in contact with the ground. By skidding the bundle of trees T with the butt ends thereof lifted directly over the rear chassis  18 , the flexural forces exerted on the main boom  32  and the frame  26  by the trees T, which are being dragged, can be advantageously reduced.  
         [0035]    In the vehicle loaded and skidding position illustrated in FIG. 3, the boom cylinders  46  and the arm cylinder  54  are respectively fully and partly retracted so as to position the grapple  40  substantially over the rear wheel  24  of the rear chassis  18 . The grapple  40  tightly grasped the bundle of trees T at an appropriate location adjacent the butt ends of the trees T.  
         [0036]    In the event that the grapple skidder  10  becomes stuck in a soft ground while dragging a bundle of trees T, the boom cylinders  46  can be extended from the retracted position thereof to a fully or partly extended position, as indicated by arrow  64  in FIG. 3, to cause the main boom  32  to pivot in the direction indicated by arrow  66  in order to push the vehicle in a forward direction with the bundle of trees T.  
         [0037]    As seen in FIG. 4, the grapple skidder  10  further includes a heel  68  which is mounted on the main boom  32  near the bottom end thereof. The heel  68  includes a pair of laterally spaced-apart parallel mounting plates  70  which are secured to the underside  72  of the main boom  32 . A square tube  74  extends at right angle from each mounting plate  70  for slidably receiving a corresponding one of a pair of legs  76  extending from a transversal arresting bar  78 . The opposed ends of the arresting bar  78  are curved inwardly to embrace the sides of the bundle of trees T which are being lifted by the grapple skidder  10 . Transversal through bores  80  are distributed along the square tubes  74  and the legs  76  for receiving fasteners  82  in order to secure the legs  76  to the square tubes  74  in one of a selected positions. This thus allows to adjust the spacing between the arresting bar  78  and the underside  72  of the main boom  32 .  
         [0038]    The location of the heel  68  allows the grapple skidder  10  to completely lift a bundle of trees T above the ground over another bundle of trees T′ lying on the ground (see FIG. 5). Accordingly, the grapple skidder  10  can advantageously be used to stack a bundle of trees onto another. The stacking operation is accomplished by first extending the boom cylinders  46  while the arm cylinder  54  remains retracted so as to locate the grapple  40  behind the rear chassis  18  for embracing a bundle of trees T, which lies on the ground, at a location comprised between their butt ends and their center of gravity. The jaw members  44  of the grapple  40  are then caused to close tightly around the bundle of trees T. Thereafter, the boom cylinders  46  are retracted to displace the main boom  32  in a generally vertical orientation so as to lift the butt ends of the bundle of trees T, and the arm cylinder  54  is extended to locate the butt ends of the grasped bundle of trees T under the heel  68 . Once the butt ends have been elevated directly under the heel  68 , further contraction of the boom cylinders  46  will first cause the butt ends of the bundle of trees to engage the arresting bar  78 , thereby preventing pivotal movement of the bundle of trees T due to gravitational forces, and then result in the grasped bundle of trees T being completely lifted off the ground.  
         [0039]    [0039]FIG. 6 illustrates a second embodiment of the present invention which is similar to the first one with the exception that the turntable  28 ′ has been incorporated at the articulation between the boom arm  36 ′ and the main boom  32 ′ rather than being provided on the rear chassis  18  at the bottom of the main boom  32 ′. Accordingly, the arm  36 ′ is adapted to pivot relative to the main boom  32 ′ about two axes perpendicular to one another. The turn table  28 ′ is mounted on the main boom  32 ′ for pivotal movement about a pivot  102 . A pair of lateral cylinders  104  extend between the turntable  28 ′ and the main boom  32 ′ to pivot the turntable  28 ′ about the pivot  102  laterally relative to the main boom  32 ′. The boom arm  36 ′ is pivotally mounted to the turntable  28 ′ for pivotal movement about a pivot  106 . A boom arm cylinder  54 ′ is provided between the boom arm  36 ′ and the turntable  28 ′ to pivot the boom arm  36 ′ about its pivot axis  106 .