Fire escape – ladder – or scaffold – Having transpositioning base and erecting means – Erecting means actuated by lazy tong
Reexamination Certificate
1999-02-10
2001-08-21
Chin-Shue, Alvin (Department: 3634)
Fire escape, ladder, or scaffold
Having transpositioning base and erecting means
Erecting means actuated by lazy tong
C182S069100
Reexamination Certificate
active
06276489
ABSTRACT:
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'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.
REFERENCES:
patent: 1815236 (1931-07-01), Carlson
patent: 2972392 (1961-02-01), Kurvers
patent: 3157430 (1964-11-01), Hamilton
patent: 3172696 (1965-03-01), De Vos
patent: 3279734 (1966-10-01), Kramer
patent: 3713495 (1973-01-01), Redford
patent: 3767236 (1973-10-01), Horgan, Jr.
patent: 3920096 (1975-11-01), Fisher
patent: 4466509 (1984-08-01), Kishi
patent: 4741413 (1988-05-01), Kishi
patent: 4890692 (1990-01-01), Oakman
patent: 4930598 (1990-06-01), Murrill et al.
patent: 5099950 (1992-03-01), Kishi
patent: 5113972 (1992-05-01), Haak, Sr.
patent: 5139110 (1992-08-01), Kishi
patent: 5145029 (1992-09-01), Blasdell
patent: 5560582 (1996-10-01), Beelen
Busuttil John
Davis Michael F.
Lynch Patrick J.
Chin-Shue Alvin
Genie Industries Inc.
Perkins Coie LLP
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