Scissor lift and method for using the same

Details Scissor lift and method for using the same Scissor lift and method for using the same

1999-09-23

2001-07-10

Noland, Kenneth W. (Department: 3651)

Elevator, industrial lift truck, or stationary lift for vehicle

Having specific load support drive-means or its control

Includes scissored supporting levers in drive-means

C254S122000

Reexamination Certificate

active

06257372

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to lifts and more particularly, to scissor lifts having pivotal legs for raising and lowering lift decks.
BACKGROUND OF THE INVENTION
The design of scissor lifts and lifts operating under similar principles via rotating legs is inherently limited by two primary design considerations: the desire for a large vertical travel and the need for lift stability. These two design considerations are generally at odds with respect to one another because increased lift height typically results in decreased lift stability. In conventional scissor lifts such as the scissor lift illustrated in
FIGS. 1-3
, movement of the scissor lift legs causes a change in elevation of the scissor lift deck. In particular, the legs
2
,
3
of the scissor lift
1
are pivotally connected to the scissor lift frame
4
below and to the scissor lift deck
5
above, as shown. When the legs
2
,
3
are pivoted in one direction, the legs
2
,
3
push the deck
5
up to an elevated position shown in
FIG. 3
, and when the legs
2
,
3
are pivoted in an opposite direction, the deck
5
descends to a lowered position shown in FIG.
2
. The vertical movement of the deck
5
is directly dependent upon the horizontal distance traveled by the legs
2
,
3
in their movement. As such, a conventional scissor lift design having increased horizontal leg travel generally has a greater lift range.
As noted above, however, larger lift ranges typically result in decreased lift stability for a given platform length (particularly when the lifts are in their elevated positions). The horizontal distance through which the legs
2
,
3
can pass is therefore limited to a range as shown in
FIGS. 2 and 3
. However, even if the lift
1
is stable at its upper lift range, other factors impact the lift design and the operation and connection of the legs
2
. For example, the deck
5
should be adequately supported by the legs
2
,
3
in every elevational position of the lift
1
. Inadequate support can cause deck deflection, bending, and undesirable stresses in the deck and lift
1
. As another example, the legs
2
,
3
should be smoothly and easily retractable to a position such as that shown in
FIG. 2
in which the legs
2
,
3
are folded and the deck
5
is lowered to a preferably compact position. The legs
2
,
3
should also be smoothly and easily extendable to a fully extended position such as that shown in FIG.
3
. The placement and relationship of the legs
2
,
3
with respect to one another is necessarily restricted by the positions of the legs
2
,
3
in their fully extended and fully retracted positions and their need to move freely through their range of motion without mutual interference. As illustrated in
FIGS. 1-3
, even the shape of the legs
2
,
3
is often selected so that the legs
2
,
3
can perform the above-described functions (e.g., to nest properly when the lift
1
is placed in its lowered position shown in FIG.
2
).
Although conventional scissor lift designs adequately address the above-described design considerations, such designs are typically inefficient. Conventional scissor lifts often are unnecessarily complex, expensive to manufacture, and/or have a lift range which is less than optimal.
In light of the problems and limitations of the prior art described above, a need exists for a scissor lift apparatus and method which more efficiently utilizes movement of scissor lift legs to produce deck lift and which provides for a stable scissor lift, a fully supported scissor lift deck throughout the range of lift positions, and an easy to manufacture scissor lift having a relatively simple design. Each preferred embodiment of the present invention achieves one or more of these results.
SUMMARY OF THE INVENTION
The present invention provides a scissor lift that achieves enhanced vertical travel of the deck for a given amount of horizontal travel of the legs. The present invention achieves this result by overlapping the deck pivot point (i.e., the point at which a leg is pivotally connected to the deck) with the frame pivot point (i.e., the point at which a leg is pivotally connected to the frame) when the deck is in the fully lowered position. That is, the deck pivot point is lower than the frame pivot point when the deck is fully lowered. The pivot points can occur on the same leg or on different legs, thus providing the two different aspects of the invention described below.
In one aspect, the invention is embodied in a scissor lift comprising a frame, a deck movable relative to the frame between a fully elevated position and a fully lowered position, and a leg coupled to the frame for pivotal movement about a first pivot point and coupled to the deck for pivotal movement about a second pivot point. The leg is rotatable between a first position in which the first pivot point is higher than the second pivot point and a second position in which the first pivot point is lower than the second pivot point. The first position corresponds with the fully lowered position of the deck and the second position corresponds with the fully elevated position of the deck. By overlapping the pivot points as described above, the vertical travel of the deck in increased.
The leg can be coupled to the frame for purely pivotal movement about the first pivot point, and can be coupled to the deck for pivotal and translational movement. In this embodiment, the second pivot point translates relative to the deck. For example, a translation element such as a roller can be used to couple the leg to the deck. Alternatively, the leg could be coupled to the deck for purely pivotal movement about the first pivot point, and could be coupled to the frame for pivotal and translational movement. In this embodiment, the second pivot point translates relative to the frame. If desired, two or more legs could be used in the above-described manner.
In another aspect, the benefits of the present invention are achieved by providing a scissor lift comprising a frame, a deck movable relative to the frame between a fully elevated position and a fully lowered position, a first leg coupled to the frame for pivotal movement about a first pivot point, and a second leg coupled to the deck for pivotal movement about a second pivot point. The first and second legs are pivotable between a first position in which the first pivot point is higher than the second pivot point and a second position in which the first pivot point is lower than the second pivot point. The first leg can be coupled to the frame for pivotal and translational movement and the second leg can be coupled to the deck for pivotal and translational movement. Alternatively, the first leg can be coupled to the deck for purely pivotal movement, and the second leg can be coupled to the frame for purely pivotal movement.
The above-described overlapping of the pivot points can be achieved in a number of ways. For example, the deck pivot point can be spaced from the deck surface, and the frame pivot point can be spaced from the base of the frame. When both pivotal and translational movement is utilized, a deck rail can be spaced from the deck surface to provide a surface upon which a translation element (e.g., a roller) can be positioned, and a frame rail can be spaced from the base of the frame to provide a surface upon which a translation element (e.g., a roller) can be positioned.
The above-described scissor lifts can be utilized to perform corresponding methods of lowering a scissor lift. In one aspect, the method includes the steps of pivoting a leg relative to the frame about a first pivot point and relative to the deck about a second pivot point that is higher than the first pivot point, thereby causing the deck to be lowered, and lowering the second pivot point until the second pivot point is lower than the first pivot point. The pivoting steps can be purely pivotal movement or a combination of pivotal and some other type of movement (e.g., translational movement).
In another aspect, the method includes the steps of pivoting a f

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