Abstract:
A stick or boom for a work machine. The stick or boom has a box portion including a first and second end and a first and second pivot point position at respective ends. A truss portion having an offset pivot point is attached to said stick or boom.

Description:
TECHNICAL FIELD 
     This invention relates to a work machine, such as an excavator, backhoe, front shovel or material handler, more particularly to the structure of a stick and/or boom for use with the work machine. 
     BACKGROUND 
     In a typical arrangement, the boom and stick have an enclosed, box like configuration. For example, U.S. Pat. No. 3,220,578 discloses a stick having an enclosed, box-like shape. 
     Structural members for work machines such as backhoes, excavators and front shovels typically include a boom pivotally attached to a machine frame at a first end, a stick pivotally attached to the boom at a second end and a bucket or material handling device further attached to the stick. Drive mechanisms, often hydraulic cylinders, are coupled to the machine in manner that moves the boom relative to the machine frame, the stick relative to the boom and the material handler relative to the stick. 
     In order to achieve the desired movement of structural members, sticks and booms are typically have three pivot (attachment) points. Two of the three pivot points are typically disposed at the first and second end, respectively, of the boom or stick. The first and second pivot points typically define a first longitudinal axis. The third pivot point is typically disposed at a predetermined distance from the first longitudinal axis. A second axis can be defined by extending a line from the first pivot point to the offset pivot point and a third axis can be defined by extending a line from the second pivot point to the offset pivot point. The first longitudinal axis, the second axis and the third axis form a triangle. 
     A problem with the box-like configuration is that such a structure is high in cost to manufacture and heavy in weight. When the boom or stick is unnecessarily heavy, the amount of material such as dirt or rock that can be carried by a bucket is reduced, thus requiring extra bucket loads to fill a truck. The additional weight also induces additional stress into other components of the work machine; this may adversely effect the life of the work machine. The power requirements to lift or move the additional weight increases the engine and related component size, resulting in increased machine cost. Unnecessary weight, generally, reduces efficiency and increases operating costs of the machine. 
     The present invention is directed toward overcoming one or more of the problems set forth above. 
     SUMMARY OF THE INVENTION 
     In an embodiment of the present invention, a work machine having at least one of a boom and a stick. A material-handling device is attached to the boom or stick. The boom or stick being constructed of a box portion and an attached truss portion. 
     In another embodiment of the present invention, a structural member for a work machine is disclosed. The structural member has a first end and a second end, a first pivot point disposed adjacent the first end and a second pivot point is disposed adjacent the second end. The structural member comprises an offset pivot point having a plurality of longitudinal members extending to the box section, forming a rigid structure. 
     In yet another embodiment of the present invention, a method of reducing the weight in one of a stick and boom of a work machine. The method includes constructing a box portion having a first pivot point, a second pivot point and a first longitudinal axis extending therethrough. A truss portion is constructed having a plurality of longitudinal members intersecting a third pivot point. Attaching the truss section to the box section completes the stick or boom. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a portion of a work machine, according to one aspect of the present invention. 
     FIG. 2 is a side view of a boom of a work machine, according to another aspect of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, a work machine  10  includes a boom  12 , a stick  14  and a material-handling device  16 . In this application an excavator is used to define the work machine  10 , the material handling device  16  is a bucket  18 . However, the invention may be applied to other types of work machines, such as a wheel loader, backhoe, or telescopic material handler. In the case of a wheel loader, one material-handling device could have a mechanism for grasping the material, such as a grapple. The stick  14  is pivotally connected to the boom  12  at stick pivot point  20  and the bucket  18  is pivotally connected the stick  14  at bucket pivot point  22 . 
     According to one aspect of the present invention, the stick  14  includes a first portion (box portion)  24  that is constructed from a plurality of plate sections attached to one another to create a box or rectangular cross-section. The box portion  24  is substantially enclosed around its periphery, as illustrated in FIG.  1 . According to this embodiment, the truss portion  26  includes a pair of triangular truss members  28  that are spaced apart from each other and interconnected by cross members  30 . The truss portion  26  is pivotally connected to the box portion  24  at base pivot point  32  so that it is free to rotate with respect to the box portion  24 . More specifically, a base plate  34  is secured to the box portion  24  and the truss portion  26  is pivotally attached to the base plate  34  at base pivot point  32 . However, it is important that the truss portion  26  be generally fixed in relation to the box portion  24 . Therefore, a pair of support members  36  extend from the end of the truss portion  26  to the box portion  24  to prevent the truss portion  26  from rotating with respect to the box portion  24  about pivot point  32 . As a result of this arrangement, the truss portion  26  is able to withstand forces created during operation of the machine. However, it should be understood that the invention is not limited to having the truss portion  26  pivotally secured to the base plate  34 . One suitable alternative would be to have the truss portion  26  solidly attached (e.g., integrally attached) to the box portion  24 . Another alternative is to mount the truss portion  26  using the current stick  14  to boom  12  connecting pin  20 . 
     It should be noted that the base plate  34  may either be integrally secured to the box portion  24  or, alternatively, the base plate  34  may be removably attached using bolts, screws, or the like. Further, it should be understood that this is just one example of a suitable truss portion  26  and the invention is not limited to any particular truss design. 
     A first drive mechanism  38  is provided for pivoting the stick  14  with respect to the boom  12 . A second drive mechanism  40  is provided for pivoting the bucket  18  or material handling device  16  with respect to the stick  14 . A third drive mechanism (not shown) is provided for pivoting the boom  12  with respect to a machine frame. In this application, a typical drive mechanism includes a hydraulic cylinder  44  and rod  46 . A number of drive mechanisms may be used in place of the cylinder  44  and rod  46 , including cables and pulleys. 
     With respect to the first drive mechanism  38 , the base end of the cylinder  44  is pivotally connected to the boom  12  at pivot point  48  and distal end of the rod  46  is pivotally attached to the truss portion  26  at a first truss pivot point  50 . With respect to the second drive mechanism  40 , a base end  52  of the cylinder  44  is pivotally connected to the truss portion  26  at a second truss pivot  54  and the distal end of the rod  46  is pivotally connected to a linkage  56  at a linkage pivot point  58 . The linkage  56  includes a first pair of link members  60  which are pivotally connected at one end to the distal end of the rod  46  at the first linkage pivot point  58  and at the other end to the stick  14  at a second linkage pivot point  62 . The linkage further includes a second pair of link members  64  which are connected at one end to the first linkage pivot point  58  and at the opposite end to a back of the bucket  18  at a third linkage pivot point  66 . The linkage and drive mechanisms are conventional and the invention is not intended to be limited to any particular linkage or drive mechanism. 
     According to another aspect of the invention, the boom  12 ′ may included a truss portion  26 ′ in combination with a box portion  24 ′. More specifically and with reference to FIG. 2, the boom  12 ′ may include the first portion (box portion)  24 ′ and the second portion (truss portion)  26 ′. The truss portion  26 ′ includes a first pair of truss members  70 ,  72  which, together with the box portion  24 ′ forms a triangle. Although not shown, a second pair of truss members may be laterally spaced from the first pair of truss members  70 ,  72 , and suitably interconnected by one or more connecting members, as with the truss portion  22  discussed in regard to the stick  14 . 
     The boom  12 ′ is pivotally attached to the machine  10  and the stick  14 ′ is pivotally attached to the boom  12 ′. More specifically, a first end  74  of the boom  12  includes a boom pivot point  76  for pivotally attaching the boom  12  to a machine frame  78 . Correspondingly, a second end  80  of the boom  12  includes the stick pivot point  18 ′ for pivotally attaching the stick  14  to the boom  12 . The truss portion  16 ′ includes the pivot point  48 ′ for attaching the first drive mechanism  36 ′. The first drive mechanism  36 ′ further attaches to a stick. 
     Industrial Applicability 
     In operation, the apparatus of the present invention operates in a conventional manner. For example, the first drive mechanism  38  is operable to pivot to stick  14  with respect to the boom  12 . The second drive mechanism  40  is operable to pivot the bucket  18  or material handling device  16  with respect to the stick  14  and the third drive mechanism  42  is operable to pivot the boom with respect to the machine frame (not shown). 
     The present invention provides a stick  14  and boom  12  that is constructed with less steel, therefore reducing the weight and cost of the structure. The reduced structure weight additionally increases the amount of material that the bucket  18  can lift. Fuel efficiency is also improved due to the reduced weight, because the machine is not required to move the excess weight. In some cases, the amount of weight reduction of the structure may increase payload capacity enough to reduce the horsepower requirement for the engine, allowing the use of a lower cost engine. In other cases the increase payload capacity may permit use of a smaller machine, saving the customer some capital expense. 
     In addition, it is possible to have a variety of truss designs adapted to fit different machine configurations. A single machine may be reconfigured for different functions by changing the material handling device  20 , the stick  14  or the boom  16 . 
     It should be understood that while one embodiment is described in connection with an excavator, the present invention if readily adapted to provide similar functions for other work machines. Other aspects, objects and advantages of the present invention can be obtained from a study of the drawings, the disclosure and the appended claims.