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.