Abstract:
A flanged link cross tube ( 1 ) for use in pivotal connections of beams ( 10 ) that locates weld roots ( 5 ) to the outer mating surface of beam ( 10 ) and flange ( 4 ). As the beams ( 10 ) rotate about a pivot connection, high torque loading occurs along the common plane (Z) between adjacent beams ( 10 ). Locating weld roots ( 5 ) on the outer mating surface of beams ( 10 ) and flanges ( 4 ) reduces loading on weld roots ( 5 ) and extends the useful life of a scissors lift ( 20 ).

Description:
FIELD OF THE INVENTION 
     This invention relates to scissors-type lifting devices, and, more particularly, to cross tubes used to receive the pivot pins at the juncture of rectangular cross-section linkages for scissors-type lifts. 
     BACKGROUND OF THE INVENTION 
     Aerial work platforms provide access to elevated areas so that workers may easily and safely perform routine maintenance on elevated fixtures, or gain access to elevated construction or storage areas. Generally, a scissors-type aerial work platform consists of a work platform, a scissors lift, and a support base. The scissors lift is extended vertically, usually by a hydraulic actuator mounted on the support base, to raise the work platform to a desired height. The support base may be a mobile structure, such as a small cart or a truck, or a stationary structure. 
     A scissors lift is a series of pivotally connected scissors-type linkages. Each scissors linkage is formed by pivotally connecting rectangular cross-section elongate beams (“rectangular link tubes”) at central axes. Typically, two of the rectangular link tubes are welded together so as to form an “inner link weldment.” Another pair of rectangular link tubes are connected together and extend outside the inner link weldment. These two rectangular link tubes form an “outer link weldment.” The connected inner and outer link weldments are called a “stack.” The outer and inner link weldments are connected at their centers and are rotatable to a first formation in which the two link weldments form an “X,” and a second formation in which the two link weldments extend substantially along one another. The stack is connected in series to another stack by pivotally connecting the lower end pair of the outer and inner link weldments to the upper end pair of the outer and inner link weldments of another stack. Additional stacks can be added to form a scissors lift of a desirable size. The uppermost stack is connected to a work platform, with one of the inner and outer link weldments pivotally connected, usually by a hinge, and the other end slidably attached to the work platform. The lowermost stack is similarly connected to the support base. 
     Typically, at each pivotal connection of the link weldments, each rectangular link tube has a cross tube welded into a hole within the link tube, the cross tube positioned perpendicular to the beam&#39;s longitudinal axis. The rectangular link tubes of the inner link weldment are rigidly connected by a central link cross tube. Shorter cross tubes extend through holes in the rectangular link tubes of the outer link weldment. A pivot pin extends through the cross tubes. 
     Applying a force to one beam of a scissors linkage causes the inner and outer link weldments to rotate relative to one another about their central axes. This rotation displaces the ends of the inner and outer link weldments, which are pivotally connected to the inner and outer link weldments in another stack. The inner and outer link weldments of the adjacent stack also rotate relative to one another. Thus, applying a force to at least one stack in the scissors lift transfers the force to the entire scissors lift structure. As a result, each stack extends or retracts, which in turn elevates or lowers the work platform. 
     A common problem in scissors-type lifting devices is that the adjoining rectangular link tubes of the inner and outer link weldments undergo opposite moments of torque as they rotate about the pivot connections. This loading fatigues the weld joints between the cross tubes and the rectangular link tubes. Fatigue is most severe at the inside weld joints on the facing surfaces of the rectangular link tubes. At this location, a weld root is formed between the outer surface of the cross tubes and the inner surface of the cross tube hole in the rectangular link tubes. Repetitive loading eventually results in fatigue fractures along these weld roots after 20,000-30,000 operational cycles. As the fractures significantly degrade the structural integrity of the scissors lift, extensive repairs or replacement of parts must be accomplished before the scissors lift can be safely used again. 
     As will be readily appreciated from the foregoing discussion, there is a need for a cross tube section that reduces the transfer of the torque loading force to the weld joints between the cross tube section and the rectangular link tube, which in turn reduces metal fatigue and thus increases the useful life of the scissors lift apparatus. The present invention is directed to fulfilling this need. 
     SUMMARY OF THE INVENTION 
     The present invention provides a link connection having a first hollow beam and a second hollow beam. A first cross tube extends through the first hollow beam and has a first radially-extending annular flange at one end connected to a side of the first hollow beam. A second cross tube extends through the second hollow beam. A pivot pin extends through the first cross tube and the second cross tube so that the first radially-extending annular flange is located between the first and second hollow beams. 
     In accordance with one aspect of the invention, the first cross tube includes a raised inner bearing surface for mounting a bearing. 
     In accordance with another aspect of the invention, the first radially-extending annular flange is welded to the side of the first hollow beam. 
     In accordance with still another aspect of the invention, the second cross tube includes a second radially-extending annular flange at one end connected to a side of the second hollow beam and arranged such that the second radially-extending annular flange is located between the first and second hollow beams. 
     In accordance with still another aspect of the invention, the first cross tube includes a link section and a flange section, the flange section including the first radially-extending annular flange, and the flange section and the link section being connected together so as to form the cross tube. 
     The present invention further provides a scissors linkage assembly having two stacks of linkages. The scissors linkage assembly includes first and second hollow beams in the first stack of linkages and third and fourth hollow beams in the second stack of linkages. A first cross tube extends through the first hollow beam. The first cross tube preferably includes a first radially-extending annular flange at one end connected to a side of the first hollow beam. 
     A second cross tube extends through the second hollow beam and the third hollow beam. Preferably, the second cross tube includes a second radially-extending annular flange at one end connected to a side of the second hollow beam and arranged such that the second radially-extending annular flange is located between the first and second hollow beams; and a third radially-extending annular flange at the opposite end connected to a side of the third hollow beam and arranged such that the third radiallyextending annular flange is located between the third and fourth hollow beams. 
     A third cross tube extends through the fourth hollow beam; and preferably includes a fourth radially-extending annular flange at one end connected to a side of the fourth hollow beam and arranged such that the fourth radially-extending annular flange is located between the third and fourth hollow beams. A pivot pin extends through the first cross tube, the second cross tube, and the third cross tube. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a side perspective view of a scissors-type personnel lift having a scissors linkage assembly that incorporates flanged cross-tubes formed in accordance with the present invention. 
     FIG. 2 is a perspective view of the scissors linkage assembly of the scissors-type personnel lift in FIG.  1 . 
     FIG. 3 is a detail view of one end of the scissors linkage assembly of FIG.  2 . 
     FIG. 4 is a sectional view taken along the section lines  4 — 4  of FIG. 2, showing an adjacent pair of flanged cross-tubes formed in accordance with this invention. 
     FIG. 5 is a cross-sectional view of an alternate embodiment of a flanged link cross-tube formed in accordance with this invention, wherein the cross tube is formed as a single piece. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawing, in which like reference numerals represent like parts throughout the several views, FIG. 1 shows a scissors lift  20  incorporating the present invention. The scissors lift  20  includes a base  22  connected by a scissors linkage assembly  24  to a work platform  25 . During use, the scissors linkage assembly  24  is extended so as to raise the work platform  25 . 
     FIG. 2 shows the scissors linkage assembly  24 . The scissors linkage assembly  24  is formed from inner link weldments  26  pivotally attached to and nested inside of outer link weldments  28 . The outer link weldments  28  are formed from a pair of outer rectangular link tubes  34 . Each of the inner link weldment  26  is constructed from a pair of inner rectangular link tubes  36 . The outer and inner rectangular link tubes  34 ,  36  are hollow and rectangular in cross-section (FIG.  4 ). The inner and outer link weldments  26 ,  28  are rotatably connected at their centers so that they can be configured from a position in which the two weldments form an “X,” to a position where the two beams are substantially parallel. The connected inner and outer link weldments  26 ,  28  form a stack  30  (only one indicated in FIG. 2, but four stacks shown). 
     A series of the stacks  30  are connected together by pivotally connecting the lower end pair of the inner and outer link weldments  26 ,  28  of a stack  30  to the upper end pair of the inner and outer link weldments  26 ,  28  of another stack. The connected series of stacks  30  forms linkage assembly  24 . 
     Adjacent stacks  30  share end pivot points and are connected at those end pivot points by end link sections  39 . Inner and outer link weldments  26 ,  28  are pivotably connected by similar central link sections  38  to form each stack  30 . The present invention is directed to unique cross tubes  40 ,  42  (FIG. 4) for use in the central and end link sections  38 ,  39 . Because the construction of the end link sections  39  and central link sections  38  are similar, only one end link section  39  will be described in detail. 
     FIG. 3 illustrates one end of an end link section  39  formed in accordance with the present invention. As shown in FIG. 4, the end linkage  39  extends from one outer rectangular link tube  34  of the outer link weldment  28 , through both inner rectangular link tube  36  of an adjacent stack  30 , and on through the adjacent other outer rectangular link tube  34  of the outer link weldment  28 . The end link section  39  includes outer cross tubes  42  that extend through each of the outer rectangular link tubes  34 . The central cross tube  40  extends through and rigidly links the inner rectangular link tube  36  of the inner link weldment  26 . 
     As can be seen in FIG. 4, the outer and inner rectangular link tubes  34 ,  36  are each substantially of rectangular cross-section. The outer rectangular link tubes  34  include holes  46  for receiving the outer cross tubes  42 . Likewise, the inner rectangular link tubes  36  include holes  48  for receiving the central cross tubes  40 . The central cross tube  40  extends through and is connected to both of the inner rectangular link tube  36  of the inner link weldment  26  (best shown in FIG.  4 ). 
     Referring again to FIG. 4, the outer cross tube  42  includes two separate pieces: a flanged section  50  and a link section  52 . The flanged section  50  is cylindrical in shape and has a uniform internal diameter. An inner end of the flanged section  50  includes an annular flange  54  that extends radially outward and is formed integral with the end of the flanged section  50 . The distal end of the flanged section  50  includes a male coupling  56 . The male coupling tapers inward from the outer diameter of the flanged section  50 . 
     The link section  52  is cylindrically shaped with a uniform outer diameter. The outer portion of the link section  52  includes a uniform inner diameter. Spaced inwardly from the outer portion of the link section  52  and located inside the cylinder of the link section is a raised bearing mounting surface  58  having a uniform, shorter diameter than the remainder of the link section. A female coupling  60  is formed on the distal end of the link section  52 . The female coupling  60  includes an outer diameter that substantially matches the diameter of the remainder of the link section  52 . However, the inner diameter is slightly larger than the remainder of the link section, and is tapered to match and fit over the male coupling  56  of the flanged section  50 . 
     In practice, the flanged section  50  is attached to the link section  52 , either by placing the two pieces together, or by welding or attaching the two pieces in some suitable manner. The two sections  50 ,  52  are then inserted through the holes  46  in the outer rectangular link tube  34  until the distal end of the link section  52  extends slightly out of the outer side of the outer rectangular link tube  34 , and the annular flange  54  of the flanged section  50  abuts against the inner side of the outer rectangular link tube. The flanged section  50  is then welded to the inner side of the outer rectangular link tube  34  so as to form a weld root  62  between the inner edge of the outer rectangular link tube  34  and the annular flange  54 . The outer side of the outer rectangular link tube  34  is then welded to the link section  52  at the juncture of the hole and the link section  52  so as to form a weld root  64 . 
     In the end link section  39 , the central cross tube  40  is used to link two inner rectangular link tubes  36 , as is shown in FIGS. 2 and 4. As shown in FIG. 4, the central cross tube  40  includes two flanged sections  50  that are identical to the flanged section  50  described with reference to the outer cross tube  42  above. In addition, the central cross tube  40  includes an elongate link section  66 , each end of which is shaped like the link section  52  for the outer cross tube  42 , except the elongate link section  66  does not include raised bearing mounting surfaces at each end. However, the elongate link section  66  includes female couplings  70  (similar to female coupling  60 ) at each end. 
     In practice, one of the flanged sections  50  is welded, otherwise connected, or just placed on one of the female couplings  70  of the elongate link section  66 , and the combined elongate link section and flanged section are inserted through the holes  48  on one of the inner rectangular link tubes  36 . The annular flange  52  is aligned against the outer surface of the inner rectangular link tube  36  and is welded in place so as to form a weld root  72  similar to the weld root  62 . A second weld root  74  is formed at the juncture of the hole  48  at the inner side of the inner rectangular link tube  36  and the elongate link section  66 . 
     The opposite flanged section  50  is welded in place against the outer surface of the opposite inner rectangular link tube  36  so that flange is connected by a weld root  72  to the inner rectangular link tube, and the male coupling  56  extends inside the inner rectangular link tube. The unwelded end of the elongate link section  66  is then inserted through the hole  48  on the inner side of the inner rectangular link tube  36  and the female coupling  70  is fitted over the male coupling  56  of the flanged section  50 . The elongate link section  66  is then welded to the inner side of the inner rectangular link tube  36  at the junction of the hole  48  and the elongate link section  66  so as to form a second weld root  74 . 
     After the outer cross tubes  42  have been mounted in the outer rectangular link tubes  34  and the central cross tube  40  has been mounted through adjacent inner rectangular link tubes  36 , a pivot pin  76  is extended through the pair of outer cross tubes and the central cross tube  40  so as to create a pivot for the adjacent stacks  30 . Similar outer cross tubes  42  and central cross tubes  40  are used at each of the end link sections  39  and central link sections  38 . Pivot pins  76  also extend into each one of these link sections. If desired, internal plastic bearings (not shown, but well known in the art) can be mounted within the flanged sections  50  that abut against the raised bearing mounting surfaces  58  and receive the pivot pin so as to reduce rotational friction. 
     The central and outer cross tubes  40 ,  42  provide the advantage of moving the weld roots  62 ,  72  away from the joints formed by the interface of the cross tubes  40 ,  42  and the holes  46 ,  48 . During operation, adjoining inner and outer rectangular link tubes  34 ,  36  undergo opposite moments of torque as they rotate about the pivot connection of the end link sections  39  or central link sections  38 . The load is most severe on the inside weld joints (that is, the weld joints at the inner portions of the outer rectangular link tubes  34  and the outer portion of the inner rectangular link tubes  36 ). The annular flanges  54  rest against these surfaces of the inner and outer rectangular link tubes  36 ,  34 , thereby removing the weld roots away from the joints formed by the interface of the cross tubes  40 ,  42  and the inner surface of the holes  46 . Moving the flange weld roots  62 ,  72  to the outer surfaces of the inner and outer rectangular link tubes  34 ,  36  reduces the load on the weld roots, thus making the weld roots less susceptible to fatigue and cracking. 
     Although the outer cross tubes  42  are shown as made of two separate pieces, an outer cross tube  80  can also be constructed of a single piece, having a flange  154  and a raised bearing mounting surface  158  as is shown in FIG.  6 . The outer cross tube  80  constructed in this manner can be used as an outer cross tube in the outer rectangular link tube  34 . Additionally, the central cross tube  40  could be formed by providing an integral flanged section with the elongate link section, and then adjoining a separate flanged section  52  with the integral piece. However, using the flanged sections  50  and the link sections  52 ,  66  described allows the flanged sections  50  to be standardized, thus providing a less expensive manner of manufacturing the central and outer cross tubes  40 ,  42 . 
     While the preferred embodiment of the invention has been illustrated and described with reference to preferred embodiments thereof, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention as defined in the appended claims.