Abstract:
A scissor lift that achieves enhanced vertical travel of the deck for a given amount of horizontal travel of the legs. The enhanced vertical travel is achieved 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. The deck and frame pivot points can provide purely pivotal movement or a combination of pivotal and some other type of movement (e.g., translational movement). The above-described scissor lifts can be utilized to perform corresponding methods of lowering a scissor lift. In the method, the deck pivot is positioned lower than the frame pivot when the deck is in the fully lowered position.

Description:
This application claim benefit to U.S. provisional application No. 60/144,003 Jul. 15, 1999. 
    
    
     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 first leg relative to the frame about a first pivot point, pivoting a second leg relative to the deck about a second pivot point that is higher than the first pivot point, and lowering the second pivot point until the second pivot point is lower than the first pivot point. As with the first method described above, the pivoting steps can be purely pivotal movement or a combination of pivotal and some other type of movement (e.g., translational movement). 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is further described with reference to the accompanying drawings, which show a preferred embodiment of the present invention. However, it should be noted that the invention as disclosed in the accompanying drawings is illustrated by way of example only. The various elements and combinations of elements described below and illustrated in the drawings can be arranged and organized differently to result in embodiments which are still within the spirit and scope of the present invention. 
     In the drawings, wherein like reference numerals indicate like parts: 
     FIG. 1 is a perspective view of a prior art scissor lift, showing the scissor lift in an elevated position; 
     FIG. 2 is a side elevational view, partly broken away, of the prior art scissor lift shown in FIG. 1, with the lift in its fully lowered position; 
     FIG. 3 is a side elevational view, partly broken away, of the prior art scissor lift shown in FIGS. 1 and 2, with the lift in its fully elevated position; 
     FIG. 4 is a perspective view of a scissor lift according to a preferred embodiment of the present invention, showing the scissor lift in its fully elevated position; 
     FIG. 5 is a side elevational view of the scissor lift shown in FIG. 4, with the scissor lift in its fully lowered position; and 
     FIG. 6 is a side elevational view of the scissor lift shown in FIGS. 4 and 5, with the scissor lift in its fully elevated position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The scissor lift of the present invention is indicated generally at  10  in FIGS. 4-6, and has a frame  12 , a deck  14 , and legs  18 ,  20  for supporting the deck  14  in at least two positions above the frame  12 . The frame  12  preferably has a base  16  (e.g., a base plate, or the like) upon which frame elements and other components of the frame  12  are mounted. Preferably, the lift  10  has four legs  18 ,  20  as best seen in FIG.  4 : a pair of crossed legs on either side of the lift  10 . More particularly, scissor lift  10  preferably has a pair of outside legs  18  and a pair of inside legs  20  extending from the frame  12  to the deck  14 . The outside legs  18  are located on the scissor lift  10  exterior to the inside legs  20 . The outside and inside legs  18 ,  20  on each side of the lift  10  are pivotally connected together in a conventional manner about an axis  22  which is preferably shared by all four legs  18 ,  20 . Therefore, respective rotation of the outside legs  18  and the inside legs  20  causes the height of the deck  14  to change. Preferably, a pin, bolt, or other similar pivot element  24  is received through an aperture  26  in each outside leg  18  and in a bearing (not shown) fitted within a bearing housing  28  of each inside leg  20 . The bearing housing  28  can be integral to the inside leg  20  or can be connected thereto in any conventional manner, including without limitation by welding, brazing, gluing or otherwise bonding, bolting, screwing, press fitting, and the like. The pivot connection described herein and illustrated in the figures represents only one possible type of pivot connection between pairs of inside and outside legs  18 ,  20 . One having ordinary skill in the art will appreciate that other well-known pivot connections are possible and fall within the spirit and scope of the present invention. 
     In the preferred embodiment of the present invention shown in the figures, the outside legs  18  are pivotally secured in a conventional fashion at one end  30  to the frame  12 , and the inside legs  20  are pivotally secured in a conventional fashion at one end  32  to the deck  14 . Preferably, the legs  18 ,  20  are secured by and are pivotal about pivot pins or other such elements  34 ,  36 , respectively. As such, the legs  18 ,  20  are pivotal about pivot points coinciding with the pivot elements  34 ,  36 . The pivot elements  34 ,  36  preferably pass through apertures in the legs  18 ,  20  and matching apertures in flanges  38 ,  40  on the frame  12  and deck  14 , respectively. One having ordinary skill in the art will recognize that there are many conventional ways to pivotally secure the legs  18 ,  20  to the frame  12  and deck  14 , such as by rivets, bolts, mating pins and sockets or other similar joints, and the like. In addition to the manner in which the legs  18 ,  20  are coupled to the frame  12  and deck  14  as just described, each of these alternative manners of coupling the legs  18 ,  20  to the frame  12  and deck  14  falls within the spirit and scope of the present invention. 
     Deck rollers  42  are preferably secured for rotation to the opposite ends  44  of the outside legs  18 , and frame rollers  46  are preferably secured for rotation to the opposite ends  48  of the inside legs  20 . When the legs  18 ,  20  are rotated about axis  22 , the outside legs  18  pivot about pivot elements  34  and the inside legs  20  pivot about pivot elements  36 . This motion causes the deck and frame rollers  42 ,  46  to translate horizontally as the distance between the deck and frame rollers  42 ,  46  changes (i.e., as the deck rollers  42  move vertically). 
     The illustrated deck  14  has a downwardly depending skirt  50  extending peripherally from the deck surface  52 . The flanges  40  to which the inside legs  20  are pivotally secured preferably extend from the skirt  50  as shown in the figures. With particular reference to FIG. 4, the skirt  50  preferably defines two deck rails  54  running along the sides of the deck  14  and upon which the deck rollers  42  roll. Preferably, the deck rails  54  are sufficiently wide to support the deck  14  upon the deck rollers  42  and are sufficiently long to provide roller support in a range of lift positions from the fully lowered position shown in FIG. 5 to the fully raised position shown in FIG.  6 . The length of the deck rails  54  selected is therefore dependent upon the range of positions of the legs  18 ,  20  and ultimately upon the range of positions in which the lift  10  can be placed. 
     The illustrated deck rails  54  are turned edges of the skirt  50 , but can instead take many other forms well known to those skilled in the art. For example, the deck rail  54  can be the unturned edges of the skirt  50  if the skirt  50  is made of sufficiently thick members, or can be a set of elongated bars, tracks, rails, or other elements secured to or beside the skirt edges in any conventional manner (such as by welding, brazing, bolting, screwing, riveting, nailing, and the like). The shape of the deck rails  54  can be flat as shown in the figures or can have any other profile desired, including without limitation an H or L-shaped profile, a concave or convex V or U-shaped profile, and longitudinally grooved profiles. Preferably, the rollers  42  are shaped to match such alternatively shaped deck rails  54 . 
     Although rollers  42  upon deck rails  54  are preferred, many other translation elements can instead be used to accomplish the same functions as the rollers  42  and deck rails  54 . For example, the ends  44  of the outside legs  18  can be fitted with low-friction material in the form of blocks, strips, bands, and the like to slide against the deck rails  54  in the movement of the legs  18 ,  20 . Also, the deck rails  54  can be fitted with similar low-friction material to permit the outside legs  18  to slide against the deck rails  54 . The rollers  42  and deck rails  54  can instead be replaced by conventional sliding track assemblies (e.g., ball bearing tracks or glides) attached in a conventional manner to the ends  44  of the outside legs  18  and to the skirt  50  for sliding movement of the outside legs  18  with respect to the deck  14 . The elements enabling translation of the ends  44  of the outside legs  18  can be in limited engagement with the skirt  50  such as the deck rollers  42  rolling upon the deck rails  54 , or can be more fully engaged with the skirt  50 . For example, the deck rollers  42  can be fitted between and slide along a pair of rail members or opposing surfaces of a track on the skirt  50 , can fit and roll along grooves in the deck rails  54 , or can have teeth or apertures which mate with apertures or teeth, respectively, in the deck rail  54 . The various translation elements (rollers, slides, tracks, and the like) and the manner in which they translate along the skirt  50  as described above fall within the spirit and scope of the present invention. In addition to the manner in which the legs  18 ,  20  are coupled to the frame  12  and deck  14  via the rollers  46 ,  42  as just described, each of these alternative manners of coupling the legs  18  to the deck  14  via other translation member falls within the spirit and scope of the present invention. 
     It should be noted that the deck rails  54  often serve to strengthen the skirt  50  and therefore the deck  14  in addition to serving as surfaces upon or over which translation elements of the outside legs  18  move. Therefore, the shape and/or manner of connection of the deck rails  54  is preferably selected to accomplish both functions. Also, the skirt  50  need not necessarily extend about the entire periphery of the deck  14  as shown in FIGS. 4-6. Although a peripheral skirt  50  is preferred to serve as a barrier to entry of foreign matter into the lift  10  when in its fully lowered position, such a skirt is not required to practice the present invention. If desired, the skirt  50  can be replaced by walls, framework, or members which are of sufficient size and serve only to support the deck rails  54  and the pivot elements  36  in their positions disposed a distance from the underside of the deck surface  52 . 
     The ends  48  of the inside legs  20  preferably are coupled to the frame for translation across the frame  12  in a manner similar to the ends  44  of the outside legs  18  translating across the deck  14 . Specifically, the frame rollers  46  on the ends  48  of the inside legs  20  preferably roll along a frame rail  56  secured to the frame  12 . The frame rails  56  are preferably elongated members having C-shaped cross-sections as shown in the figures. The frame rollers  48  therefore preferably roll between upper and lower surfaces of the frame rails  56 . Although this frame rail and roller design is preferred, many other translation elements can be used to smoothly translate the ends  48  of the inside legs  48  along the frame  12 . For example, the frame rail  56  can be flat such as the deck rails  54  on the deck skirt  50 , can be H, V, or L-shaped, or can take the shape of any of the alternative rail types discussed above with reference to the deck rails  54  of the deck skirt  50 . Also, the frame rails  56  and frame rollers  46  can be replaced by many other conventional translation elements permitting sliding or rolling movement of the inside leg ends  48  along the frame  12  as discussed above with reference to the deck rails  54  and the deck rollers  42 . 
     For reasons that will be discussed in more detail below, the frame rails  56  are preferably elevated a distance over the base  16  of the frame  12  in a conventional manner. For example, the frame rails  56  can be located upon elevating bars  78  attached in a conventional manner to the base  16  of the frame  12 , the frame rails  56  themselves can be made relatively high to elevate the surface upon which the frame rollers  46  roll, the frame  12  can be shaped to have an elevated portion or portions located beneath the frame rails  56 , etc. 
     The above-described arrangement between the legs  18 ,  20 , the deck  14  and the frame  12  permits smooth and steady vertical movement of the deck  14  with respect to the frame  12 . With reference to FIGS. 4-6, when the inside legs  20  are pivoted about the pivot elements  24 ,  36  in a clockwise direction and when the outside legs  18  are pivoted about the pivot elements  24 ,  34  in a counter-clockwise direction, the deck rollers  42  roll along the deck rails  54  toward their positions shown in FIG.  6  and the frame rollers  46  roll along the frame rails  56  toward their positions also shown in FIG.  6 . It should be noted that the legs  18 ,  20  pivot about pivot points coinciding with the deck and frame rollers  42 ,  46  as the legs  18 ,  20  rotate and translate. The legs  18 ,  20  therefore push the deck  14  upward as they rotate in this manner. When the inside legs  20  are pivoted about the pivot elements  24 ,  36  in a counter-clockwise direction as seen in FIGS. 4-6 and when the outside legs  18  are pivoted about the pivot elements  24 ,  34  in a clockwise direction, the deck rollers  42  run along the deck rails  54  back to their positions in FIG.  5  and the frame rollers  46  roll along the frame rails  56  back to their positions also shown in FIG.  5 . The legs  18 ,  20  therefore pull the deck  14  downward and/or permit the deck  14  to fall under its own weight as the legs  18 ,  20  rotate in this manner. 
     The preferred embodiment of the present invention has a pair of connecting elements  58 ,  60  to increase the stability of the lift  10  and to help maintain the legs  18 ,  20  of each pair of outside and inside legs  18 ,  20  in the same rotational positions. The outside legs  18  are preferably connected to one another by connecting element  58 , and the inside legs  20  are preferably connected to one another by connecting element  60 . The connecting elements  58 ,  60  are preferably beams or bars which are connected to the legs  18 ,  20  in any conventional manner, such as by being welded, brazed, bolted, riveted, screwed, nailed, or glued thereto. In the preferred embodiment of the present invention, the connecting element  58  connecting the outside legs  18  together is an L-shaped beam or a pair of plates welded (or otherwise secured together in a conventional manner) in an L-shape, and is located at the upper ends  44  of the outside legs  18  when viewed in FIGS. 4 and 6. Also in the preferred embodiment of the present invention, the connecting element  60  connecting the inside legs  20  together is a hollow tube having a square cross-sectional shape, and is located just above the axis of rotation  22  of the inside legs  20  as viewed in FIGS. 4 and 6. 
     It will be appreciated by one having ordinary skill in the art that the connection elements  58 ,  60  can take virtually any hollow or solid cross-sectional shape and can be secured to their respective leg pairs  18 ,  20  in a number of other locations along the lengths of the legs  18 ,  20 . For example, the connection element  58  between the outside legs  18  can instead be in a location which is on the opposite side and opposite ends of the legs  18  from the connection element location illustrated in the figures. As another example, the connection element  60  between the inside legs  20  can instead be located on the opposite side of the rotation axis  22  or further up on the inside legs  20  on the same side of the rotation axis  22 . However, the locations of the connection elements  58 ,  60  described above and illustrated in the figures is preferred in light of the preferred location and orientation of the actuator  62  described below. 
     To rotate the legs  16  in the manner described above, an actuator  62  is preferably secured between the connection elements  58 ,  60  and can be actuated to push and pull the legs  18 ,  20  into different rotational positions with respect to one another. The actuator  62  is therefore indirectly secured at one end to the outside legs  18  and at another end to the inside legs  20 . When the actuator  62  is actuated (e.g., extended or retracted), the connection points  64 ,  66  at which the actuator  62  is connected to the legs  18 ,  20  are forced apart or together to thereby rotate the legs  18 ,  20  about the pivot elements  24 ,  34 ,  36 . As best understood with reference to FIG. 6, to produce torque about the axis of rotation  22  sufficient to rotate the legs  18 ,  20  about the axis of rotation  22 , the line through which the actuator  62  exerts force should not be aligned with the axis of rotation  22 , nor should that line ever cross the axis of rotation  22  because doing so would bring the legs  18 ,  20  into a position in which the actuator  62  cannot exert any appreciable torque between the legs  18 ,  20 . Therefore, the actuator  62  in the preferred embodiment of the present invention shown in the figures is not aligned with respect to the axis of rotation  22  and is instead skewed with respect thereto. 
     The actuator  62  is preferably rotatably attached in a conventional manner (e.g., via a pivot pin, bolt, hinge, or other conventional connection element or elements) to the middle of the connecting element  58  and to the middle of the connecting element  60 . Specifically, the actuator base  68  is preferably mounted for rotation via a pivot  64  on the connecting element  58 , and the actuator shaft  67  is preferably mounted for rotation via a pivot  66  on the connecting element  60 . More preferably, the actuator shaft  67  is mounted for rotation to a pivot bracket  70  extending or connected in a conventional fashion to a middle location of the connecting element  60 . With reference to FIGS. 3 and 4, force applied by the actuator  62  against the pivot  66  creates a torque on the inside legs  20  about the pivot elements  24  to thereby change the rotational position of the legs  18 ,  20  and to raise or lower the deck  14 . Similarly, force applied by the actuator  62  against the pivot  68  creates a torque on the outside legs  18  about the pivot elements  24  also to change the rotational position of the legs  18 ,  20  and to raise or lower the deck  14 . Preferably, the connecting elements  58 ,  60  are reinforced in a conventional manner by reinforcement gussets, braces, or other such elements indicated in the figures at  71 . Such reinforcement members can be integral to the connecting elements  58 ,  60  and/or legs  16  or connected thereto in a conventional manner such as by welding, bolting, riveting, screwing, and the like. 
     One having ordinary skill in the art will appreciate that the location and points of attachment of the actuator  62  can be different than that described above and illustrated in the figures. With reference to FIG. 6 for example, the actuator  62  can instead be attached to the lower ends  30  of the outside legs  18  either directly or indirectly (e.g., to a connecting member which is itself connected to the outside legs  18 ) and attached either directly or indirectly in a location along the length of the inside legs  20 . Depending upon the manner in which the actuator  62  is connected (i.e., to connecting elements  58 ,  60 , directly to the legs  18 ,  20  as described below, or otherwise), such connection can require moving the location of the connecting elements  58 ,  60  and/or adding one or more connecting elements  58 ,  60  to the lift  10 . As indicated above, the actuator  62  should be positioned between the legs  18 ,  20  so that the axis of rotation  22  of the legs  18 ,  20  never crosses or becomes aligned with a line extending through the actuator&#39;s points of connection. If the axis of rotation  22  were to cross or become aligned with this line, the actuator  62  would be unable to exert torque upon the legs  18 ,  20 . 
     The actuator  62  can take many forms, including without limitation a hydraulic or pneumatic piston actuator, jack-type actuators employing threaded rod, ratchet, and other conventional jacking mechanisms, and the like. Preferably however, the actuator  62  is a hydraulic piston actuator. Actuator and jacking mechanisms capable of changing and maintaining the distance between elements are well known to those skilled in the art and are therefore not discussed further herein. 
     The actuator  62  is powered and controlled in a conventional manner dependent upon the type of actuator employed. For example, the actuator  62  can be directly powered by electricity, by pressurized gas, fluid or air, by one or more motors, etc. In the preferred embodiment of the present invention, hydraulic fluid is pumped to and returned from the hydraulic piston actuator  62  via hydraulic lines  72  and a pump  74  driven by a motor  76  (shown only in FIG. 4) controlled by one or more user-operable controls (not shown). The pump  74  can instead be replaced by a compressor driven by the motor  76  to supply the actuator  62  with pressurized gas on demand. Such systems and their manner of connection and operation are well known to those skilled in the art. 
     An important feature of the present invention is the locations of the pivot elements  34 ,  36 , the deck rollers  42 , and the frame rollers  46  with respect to the deck  14  and the frame  12 . Conventional lift designs typically locate the pivot elements close to the base of the lift frame  4  and close to the surface of the deck  6 , respectively, as shown in FIGS. 1-3. With particular reference to FIGS. 1 and 3, conventional lifts typically have legs mounted for pivotal movement to the deck  5  about an uppermost location of the legs, such as in the upper left-hand corner of the legs  3  in FIGS. 1 and 3. Similarly, conventional lifts typically have legs mounted for pivotal movement to the frame  4  about a lowermost location of the legs, such as in the lower left-hand corner of the legs  2  in FIGS. 1 and 3. Also with reference to FIGS. 1 and 3, conventional lifts typically have legs with translation elements (e.g., rollers and the like) located in an uppermost location of the legs, such as in the upper right-hand corner of the legs  2  in FIGS. 1 and 3. Similarly, conventional lifts typically have legs with translation elements located in a lowermost location of the legs, such as in the lower right-hand corner of the legs  3  in FIGS. 1 and 3. 
     In contrast, the illustrated deck pivot elements  36  are located a distance from the deck surface  52 , and the frame pivot elements  34  are located a distance from the base  16  of the frame  12 . This change permits the inside legs  20  to be pivotally secured to the deck  14  about a lower position on the inside legs  20 , such as in upper left-hand corner of the inside legs  20  illustrated in FIG. 6, and permits the outside legs  18  to be pivotally secured to the frame  12  about a higher position on the outside legs  18 , such as in the lower left-hand corner of the outside legs  18  illustrated in FIG.  6 . Also, this change permits the inside legs  20  to translate via deck rollers  46  located at a higher position on the inside legs  20 , such as in the lower right-hand corner of the inside legs  20  illustrated in FIG. 6, and permits the outside legs  18  to translate via frame rollers  42  located at a lower position on the outside legs  18 , such as in the upper right-hand corner of the outside legs  18  illustrated in FIG.  6 . Preferably, the frame pivot elements  34  and the frame rollers  46  are therefore located in a higher position with respect to the base  16  of the frame  12 , and the deck pivot elements  36  and the deck rollers  42  are therefore located in a lower position with respect to the deck surface  52 . As discussed in more detail above, the deck rollers  42  preferably roll along the deck rails  54  of the skirt  50  (located a distance from the underside of the deck surface  52 ). Similarly, the frame rollers  46  preferably roll along the frame rails  56  (located a distance from the base  16  of the frame  12 ). 
     In the preferred embodiment of the present invention, the deck pivot elements  36  and the deck rollers  42  are located in the same horizontal plane  80  throughout the range of positions of the legs  18 ,  20 , and the frame pivot elements  34  and the frame rollers  46  are located in the same horizontal plane  82  throughout the range of positions of the legs  18 ,  20 . These relationships help to ensure that the deck  14  remains horizontal and level in all positions of the lift  10 . 
     With reference to FIGS. 1-3, it should be noted that conventional lifts  1  have deck pivots  6  and deck rollers  7  which remain above the frame pivots  8  and the frame rollers  9  throughout the range of movement of the lift  1 . The deck pivots  6  and the deck rollers  7  are typically co-planar in such lifts  1 , as are the frame pivots  8  and the frame rollers  9 . In contrast, it should be noted that when the lift  10  of the present invention is lowered to the position shown in FIG. 5, the deck pivot elements  36  and/or the deck rollers  42  drop below the elevation of the frame pivot elements  34  and/or the frame rollers  46 . Most preferably, the deck pivot elements  36  lie in the same horizontal plane  80  as the deck rollers  42  and the frame pivot elements  34  lie in the same horizontal plane  82  as the frame rollers  46 . When the lift  10  is lowered to the position shown in FIG. 5, the horizontal plane  80  is lowered beneath the horizontal plane  82 . This relationship is facilitated at least in part by the locations of the pivot elements  34 ,  36 , the deck rollers  42 , and the frame rollers  46  as described above. Specifically, by virtue of the locations of the pivot elements  34  and the deck rollers  42  on the outside legs  18 , the outside legs  18  fit between the frame  12  and the deck  14  behind the skirt  50  when the lift  10  is in its fully lowered position. Also, by virtue of the locations of the pivot elements  36  and the frame rollers  46  on the inside legs  20 , the inside legs  20  also fit between the frame  12  and the deck  14  behind the skirt  50  when the lift  10  is in its fully lowered position. 
     The locations of the pivot elements  34 ,  36 , the deck rollers  42 , and the frame rollers  46  with respect to the deck  14  and the frame  12  as just described offers a number of advantages over prior art lifts. Due to the roller and pivot locations disposed from the underside of the deck surface  52  and from the base  16  of the frame  12  as discussed above, an amount of roller travel along the deck rails  54  and the frame rails  56  in the present invention produces a larger amount of vertical deck travel than the same amount of horizontal roller travel in prior art lifts. Therefore, the lift  10  of the present invention is capable of increased vertical movement for the same horizontal movement of the legs when compared to prior art lifts. Depending upon the vertical location of the deck pivot elements  36  and the deck rollers  42  with respect to the underside of the deck surface  52 , and depending upon the vertical location of the frame pivot elements  34  and the frame rollers  46  with respect to the base of the frame  12 , the increase in vertical travel can be 10-25% over that of prior art lifts. In other words, the distance between the horizontal plane  80  and the underside of the deck surface  52  determines where the deck pivot elements  36  and/or the deck rollers  42  are located and the amount of additional vertical travel produced by horizontal movement of the deck rollers  42  on the deck rails  54 . Likewise, the distance between the horizontal plane  82  and the base  16  of the frame  12  determines where the frame pivot elements  34  and/or the frame rollers  46  are located and the amount of additional vertical travel produced by horizontal movement of the frame rollers  46  on the frame rails  56 . 
     It should be noted that the increase in lift range resulting from the above-described arrangement is not limited to movement in the vertical direction, but includes applications in which the lift  10  moves upward and forward or backward, and applications in which the lift moves upward while tilting forward or backward. For example, changing the location of the bearing housing  28 , the pivot element  24 , the aperture  26 , and the axis of rotation  22  of the legs  18 ,  20  to a location upward or downward on the legs  18 ,  20  as viewed in FIGS. 5 and 6 will cause the deck  14  to move forward or rearward as the deck  14  is raised or lowered. Likewise, moving the location of these elements to the left or right on the legs  18 ,  20  as viewed in FIGS. 5 and 6 will cause the deck  14  to tilt forward or backward as the deck  14  is raised or lowered. The teachings of the present invention apply equally to alternative lift types such as these. 
     The above-described locations of the pivot elements  34 ,  36 , the deck rollers  42  on the outside legs  18  and deck rails  54 , and the frame rollers  46  on the inside legs  20  and inwardly-disposed frame rails  56  results in a lift design having less interference between legs  18 ,  20  as the lift  10  is raised and lowered. As a result, tapered or shaped legs such as those found in prior art lifts are no longer needed, thereby permitting wider, larger, and stronger legs  18 ,  20  to be used (see FIGS.  4 - 6 ). This provides for a stronger and more stable lift  10  and reduces manufacturing costs of the legs  18 ,  20 . Also, because the legs  18 ,  20  of the lift  10  are in less extended positions for each lift height, the legs  18 ,  20  of the present invention provide a wider support and a more stable lift  10  for comparable lift heights. The lift  10  of the present invention can also lift higher than prior art lifts having comparable leg lengths. 
     The lift  10  preferably has a safety latch  84  and a latching pin  86  (see FIG. 4) that cooperate to latch the lift  10  in an elevated position in manner well known to those skilled in the art. For example, the safety latch  84  of the preferred embodiment is an arm pivotally secured in a conventional manner to one of the inside legs  20 . The safety latch  84  has a hooked end, and can be pivoted on the inside leg  20  to latch with a pin  86  on an outside leg  18  corresponding to the inside leg  20 . When latched, the safety latch  84  preferably prevents the legs  18 ,  20  from movement with respect to one another, thereby preventing the lift  10  from unexpected lowering. One having ordinary skill in the art will recognize that a number of other conventional safety latch designs can be used to accomplish the same function, including without limitation a safety bar positioned between a leg and the frame to be compressed therebetween in the event of unexpected lift drop, a latch connected between the deck or frame and a leg when the lift is in an elevated position, one or more stops releasably secured to one or more of the deck rails  54  and/or the frame rails  56  adjacent the rollers  42 ,  46  when the lift  10  is elevated, etc. Also, the safety latch  84  can be made adjustable, for example, by a number of pins  86  located to latch with the safety latch  84  at different lift heights. Other such adjustment mechanisms are well known to those skilled in the art and are therefore not discussed further herein. 
     The present invention can be provided with a shroud  88  (shown only in FIG. 4) attached in a conventional manner to at least part of the periphery of the deck  14  and the frame  12 . The shroud  88  preferably has bellow-type folds therein to collapse into a relatively small size when the lift  10  is lowered. The bellow-type folds preferably unfold when the lift  10  is raised to obstruct access to the area between the frame  12  and the deck  14  regardless of the lift position. The shroud  88  can be made from any number of materials found in sheet form, such as rubber, plastic, nylon and other synthetics, fabric, foil and paper. Most preferably, the shroud  88  is made from folded vinyl sheeting or can also be a roller curtain. 
     The frame  12 , deck  14 , legs  18 ,  20 , connecting elements  58 ,  60 , and the safety latch and pin  84 ,  86  can each be made of any number of materials capable of bearing load without significant deflection, including without limitation metal, plastics and other synthetics, wood, composites, and refractory materials. Preferably however, these elements are made from a strong rigid material such as steel, iron, or aluminum. Most preferably, these elements are all made of steel. 
     The embodiments described above and illustrated in the figures are presented by way of example only and are not intended as a limitation upon the concepts and principles of the present invention. As such, it will be appreciated by one having ordinary skill in the art that various changes in the elements and their configuration and arrangement are possible without departing from the spirit and scope of the present invention as set forth in the appended claims. For example, the lift  10  of the present invention described above and illustrated in the drawings preferably has four legs, two outside legs  18  and two inside legs  20 . Many different lift applications and lifting devices can employ the principles of the present invention while having fewer or more legs than the preferred embodiment lift  10 . For example, one outside leg  18  and one inside leg  20  can be substantially centered beneath the deck  14  and operate in a similar manner to the legs  18 ,  20  of the preferred embodiment lift  10 . In such a case, the deck rail  54  can be a beam, wall, or other such element running down the center of the deck&#39;s underside, and the deck  14  would preferably have additional support along one or more of its ends or sides to lessen the chance of lift tipping or bowing. 
     In another embodiment, the deck  14  is supported by only one outside leg  18  and one inside leg  20  located on one side of the deck  14  much in the same way as one outside and inside leg pair appears in FIGS. 4-6. The opposite side of the deck  14  would preferably be supported for vertical travel in any conventional manner. In yet another embodiment, legs in addition to those shown in FIGS. 4-6 can be employed, such as an additional inside leg or legs  20  located between the inside legs  20  shown, an additional outside leg or legs located on either side of the outside legs  18  shown (with additional deck rails  54  and frame rails  56  as necessary), and the like. It is even possible to stack legs  18 ,  20  atop one another for an extended scissor-like device. For example, the tops of the outside and inside legs  18 ,  20  illustrated in FIGS. 4-6 can instead be attached to the bottoms of additional outside and inside legs which themselves have top ends coupled to the deck  14  as shown in FIGS. 4-6. Of course, the connecting elements  58 ,  60  in many of these alternative embodiments might need to be moved to accommodate full lowering and raising of the lift  10  as shown in the figures. In other such embodiments such as the stacked legs just described, additional connecting elements are preferably employed between the legs  18 ,  20 . 
     Where alternative embodiments of the present invention do not have connecting elements  58 ,  60 , the actuator  62  of the present invention can be connected directly to and between outside and inside leg pairs  18 ,  20 . Specifically, the ends of the actuator  62  can be rotatably connected to an outside leg  18  and an inside leg  20  in any conventional fashion. If desired, multiple actuators  62  can even be used for the same pair of outside and inside legs  18 ,  20 , such as an actuator rotatably connected substantially horizontally and below the axis of rotation  22  to an outside leg  18  and an inside leg  20  and an actuator rotatably connected substantially horizontally and above the axis of rotation  22  to the outside leg  18  and inside leg  20 . Alternatively, an actuator  62  can be rotatably connected substantially vertically and left of the axis of rotation  22  (with reference to the views of FIGS. 5 and 6) to an outside leg  18  and an inside leg  20  and an actuator  62  can be connected substantially vertically and right of the axis of rotation  22  to the outside leg  18  and to the inside leg  20 . The particular connection locations for the actuator(s) used should be selected to permit the legs  18 ,  20  to rotate from a fully lifted position to a fully retracted position. 
     The legs  18 ,  20  in the preferred embodiment lift of the present invention can also be reversed as desired. For example, it is possible to have a lift of the same general construction shown in FIGS. 4-6, but with the legs  18 ,  20  and associated elements substantially upside down so that the inside legs  20  ride upon frame rails  56  or other such elements on the underside of the deck  14  and the outside legs  18  ride upon rail surfaces or other such elements on the sides of the frame  12 . 
     In the preferred embodiment of the present invention, the legs  18 ,  20  are secured for pivotal rotation at one end of the frame  12  and deck  14  and for translation toward and away from an opposite end of the frame  12  and deck  14 . One having ordinary skill in the art will appreciate that the legs  18 ,  20  need not necessarily be secured for pivotal rotation in any particular location between the ends of the frame  12  and deck  14  (e.g., at one end of the frame  12  and deck  14  as shown in the figures) to achieve the advantages of the present invention. As long as the legs  18 ,  20  have sufficient deck and frame length to translate in their pivoting movements, the legs  18 ,  20  can be located virtually anywhere between a frame  12  and a deck  14  having any desired shape, length, and width. However, it may be necessary in certain cases to provide additional support to other portions of the deck  14  in a conventional manner, such as by one or more vertical guide posts passing through the deck  14 , a conventional cable and counterweight system providing a lifting force at the distal ends, corners, or edges of the deck  14 , and the like. 
     It is even possible to use the scissor lift of the present invention only as a lifting force and to employ other well-known elements and devices to provide the necessary support to the deck  14  against tipping or bowing. Such well-known elements and devices include without limitation those just mentioned for providing additional support to the deck  14 . In such cases, the legs  18 ,  20  need not necessarily be pivotally attached to the frame  12  and the deck  14  as described above and illustrated in the figures. Instead, both ends of the legs  18 ,  20  can be provided with rollers to roll and translate upon the frame  12  and beneath the deck  14  in the same manner described above with respect to the deck rollers  42  and the frame rollers  46 . The location of the legs  18 ,  20  between the frame  12  and deck  14  in such alternative embodiments can be controlled in a number of other manners, including without limitation roller stops on the deck rails  54  and/or the frame rails  56 , restraining the pivot element  24  in a conventional manner to only move in a vertical direction, securing the legs  18 ,  20  to the frame or to the deck via only one or two pivots, etc. 
     The legs  18 ,  20  of the present invention need not necessarily be flat or plate shaped as shown in the preferred embodiment of FIGS. 4-6. Instead, the legs  18 ,  20  can have a round, square, rectangular, or other cross-sectional shape and can be solid or tubular as desired. Additionally, the outside legs  18  and the inside legs  20  need not necessarily be rotatably secured to one another about their midpoints as illustrated in FIGS. 4-6. Although such connection is preferred, the axis of rotation  22  can be moved to a location down or up the lengths of the legs  18 ,  20 , but preferably is located the same length from each bottom end  30 ,  48  of the legs  18 ,  20 .