Traversing hoists – Adjustable to transport or nonuse position – Collapsible or foldable boom
Reexamination Certificate
1998-02-27
2002-05-21
Brahan, Thomas J. (Department: 3652)
Traversing hoists
Adjustable to transport or nonuse position
Collapsible or foldable boom
C212S238000, C212S261000, C212S270000, C182S002900, C182S002110
Reexamination Certificate
active
06390312
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to lift structures and/or load-bearing vehicles.
BACKGROUND OF THE INVENTION
Historically, there have been developed a wide range of lift structures that are arranged in such a manner as to elevate personnel or material in order to provide facilitated access to an elevated location.
Different types of lifts vary in size, shape and function. For example, “vertical pole” lifts generally involve the use of a telescoping mast or sequentially extending mast (in which mast segments are usually “stacked” along a horizontal direction and then propagate upwardly one-by-one), on which is mounted a basket, cage or other platform structure intended to carry one or more individuals. Most “vertical pole” lifts are intended to carry only one individual, however, and are generally designed to elevate solely in a vertical direction. U.S. Pat. No. 3,752,261 (Bushnell, Jr.), U.S. Pat. No. 4,657,112 (Ream et al.) and U.S. Pat. No. 4,015,686 (Bushnell, Jr.) disclose general examples of such lifts.
“Scissors lifts”, on the other hand, involve the use of a scissors-type mechanism for propagating a basket, cage or platform upwardly. Again, the propagation is solely along a generally vertical direction, but in this case the more rigid structure of the scissors mechanism permits greater loads to be propagated and carried. U.S. Pat. No. 5,390,760 (Murphy) and U.S. Pat. No. 3,817,846 (Wehmeyer) disclose general examples of such lifts.
“Boom lifts” involve the use of a pivotable, and often extendible, boom structure to propagate a basket, cage or platform both upwardly and in a variety of other directions. U.S. Pat. No. 3,861,498 (Grove) and U.S. Pat. No. Re. 31,400 (Rallis, et al.) disclose general examples of such lifts.
Other types of lifts, not typically falling into one of the three categories outlined above, can also be used for similar purposes, that is, for propagating personnel or material in a generally upward direction to access an elevated workspace. U.S. Pat. No. 4,488,326 (Cherry), U.S. Pat. No. 3,927,732 (Ooka et al.), U.S. Pat. No. 5,299,653 (Nebel), U.S. Pat. No. 4,154,318 (Malleone), U.S. Pat. No. 4,799,848 (Buckley) and U.S. Pat. No. 4,147,263 (Frederick et al.) disclose general examples of lifts outside of the three categories discussed above.
Many types of vehicles and lift structures, especially boom lifts, excavators, cranes, backhoes, and certain other machines, have centers of mass that migrate significantly during use. In contrast, automobiles and similar vehicles have their lateral centers of mass located at some point substantially along the longitudinal axes thereof and these tend not to migrate significantly at all. Thus, a migrating center of mass has been a perennial problem with certain vehicles or machines, including boom lifts.
For example, as the boom of a boom lift is extended and a load is applied to the platform or bucket thereof, the lift's center of mass moves outwardly toward the supporting wheels, tracks or outriggers. If a sufficient load is applied to the boom, the center of mass will move beyond the wheels and the lift will tip over. The imaginary line along a support surface (e.g., the ground) about which a vehicle tips is known as the “tipline”. A more detailed discussion of the principles of tipping is provided in copending and commonly assigned U.S. patent application Ser. No. 08/890,863, which is hereby incorporated by reference as if set forth in its entirety herein.
By defining the tipline of a vehicle as near to the perimeter of the vehicle's chassis as possible, the stability of the vehicle is increased. This increase in stability permits the vehicle to perform its intended function with the minimum amount of necessary counterbalance weight, which results in lower costs, improved flotation on soft surfaces, easier transport, etc.
In the context of boom lifts, two types of stability are generally addressed, namely “forward” and “backward” stability. “Forward” stability refers to that type of stability addressed when a boom of a boom lift is positioned in a maximally forward position. In most cases, this will result in the boom being substantially horizontal. On the other hand, “backward” stability refers to that type of stability addressed when a boom of a boom lift is positioned in a maximally backward position (at least in terms of the lift angle). In most cases, this will result in the boom being close to vertical, if not completely so.
In a typical boom lift, not only can the boom be displaced (i.e., pivoted) through a vertical plane, but also through a horizontal plane. The horizontal positioning is usually effected via a turntable that supports the boom. As the wheeled chassis found in typical boom lift arrangements will usually not exhibit complete circumferential symmetry of mass, it will be appreciated that there exist certain circumferential positions of the boom that are more likely to lend themselves to potential instability than others. Thus, in the case of a boom lift in which the chassis or other main frame does not exhibit symmetry of mass with regard to all possible circumferential positions of the boom, then a greater potential for instability will exist, for example, along a lateral direction of the chassis or main frame, that is, in a direction that is orthogonal to the longitudinal lie of the chassis or main frame (assuming that the “longitudinal” dimension of the chassis or main frame is defined as being longer than the “lateral” dimension of the chassis or main frame). Thus, when designing the boom lift for safety requirements, these circumferential positions of maximum potential instability must be taken into account.
Historically, it has been the norm to ensure the presence of a counterweight to the boom. In this manner, when the boom is in a maximally forward position, the counterweight, situated on the opposite side of the tipline from the boom, will help counteract the destabilizing moment contributed to by the boom (with personnel or material load).
The use of a counterweight does have somewhat of an opposite consequence, however, when one considers the issue of backward instability. Particularly, when a boom is moved into a maximally backward position, it will be appreciated that a destabilizing moment, contributed to by the boom (with personnel or material load) and counterweight, could act in a backward direction. On the other hand, if a destabilizing moment is not present, even a small net stabilizing moment might be undesirable. Thus, it has been the norm to accord the chassis or other main frame an even greater weight than might be desired, for the purpose of counterbalancing the destabilizing moment that contributes to backward instability.
Although the measures described hereinabove have conventionally been sufficient to reduce the risk of vehicle tipping in either a forward or a backward direction, concern has arisen in the industry over the costs associated with providing an overly massive vehicle chassis. The mass of a vehicle chassis not only has ramifications in manufacturing costs, but also in transport costs or in other factors, such as the load that might be applied to fragile surfaces (e.g. mud). Accordingly, a need has been recognized in conjunction with keeping such additional mass to a minimum.
Therefore, a need has been recognized in conjunction with the provision of a lift structure of reduced weight that does not compromise stability and/or with the provision of a lift structure in which a greater range of movement of the item being moved is provided for a given overall weight of the lift structure.
Other needs have been recognized in conjunction with given lift structures, as discussed herebelow.
An important consideration in the design and manufacture of load-bearing apparatus, such as boom lifts, is the range of motion afforded by the apparatus or lift. Typically, a lift or other type of load-bearing apparatus will have a predetermined “work envelope” based on the components used in manufacturing the apparatus as well as the
Brahan Thomas J.
JLG Industries Inc.
Reed Smith LLP
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