Abstract:
A lift having a platform with a substantially level ride is described. The lift reduces the distance between the ground and the platform in the ground position. An extension plate having receiving portions for accommodating portions of the lift when the platform is in a bed level position.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Continuation of co-pending U.S. patent application Ser. No. 11/100,805 filed on Apr. 6, 2005, the entire contents of which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to load lifting and lowering devices and, more particularly, to a lift having a platform which is able to rest on or near the ground and remain substantially level during raising and lowering. 
         [0004]    2. State of the Art 
         [0005]    A common type of load elevator or lift comprises a substantially rectangular platform connected at one edge to the swingable ends of a laterally spaced apart pair of linkage systems. The other ends of the linkage systems are pivotally connected to a support such as the chassis of a vehicle or a loading dock. A power means, usually hydraulic, is interconnected to the pair of linkage systems for moving the platform between ground level and that of the truck or dock or the like. Each of the linkage systems comprises first and second lateral links in the form of an upper arm and a lower arm. The swingable ends of the linkage systems comprise a first vertical link between the upper and lower arms in the form of a shackle against which the weight of the platform and the load thereon are imposed. The other ends of the linkage systems comprise a second vertical link between the upper and lower arms in the form of the support to which the linkage systems are pivotally connected. In this manner, the upper and lower arms, the shackle and the support define a substantially parallelogram-shaped arrangement for each of the linkage systems. 
         [0006]    A problem typically encountered with the above-described linkage systems is that they do not maintain a perfect parallelogram arrangement when moving the platform between a raised and lowered position. Rather, the first vertical link is slightly rotated during translation such that the platform describes an arc as it is being raised or lowered. When located at or near ground level, this causes the outer edge of the platform to be tilted or ramped towards the ground. This may not be suitable for some loads, such as those resting on wheels or other mechanisms allowing for lateral load movement. 
         [0007]    One approach to addressing this problem has been to lower the platform a first distance wherein the linkage systems are maintained in the parallelogram arrangement, i.e. without substantially rotating the first vertical link, and then using additional mechanisms to move the platform a second distance into contact with the ground. This two-step translation method enables the platform to have a substantially level orientation through most of its lifting range, but requires a complex lift assembly that is more difficult to manufacture and maintain. Moreover, the platform may still have to be slightly tilted when translating through the second distance in order to reach the ground. 
         [0008]    What is needed is a lift that has a platform with a substantially level ride through its entire lifting range and that does not require the use of complex mechanisms for lowering the platform to a location on or near the ground. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    The present invention overcomes the above-described problems with prior art lifts by providing a method and apparatus for a lift with a platform which is able to rest on or near the ground and remain substantially level during raising and lowering. The present invention accomplishes this by use of a novel linkage system arrangement having an upper arm and a lower arm coupled between a support frame and a shackle. The shackle is attached to a platform support that holds a lift platform in a level position while touching or very nearly touching the ground. 
         [0010]    In one embodiment according to the present invention, an actuator is positioned above the upper arm and the lower arm of the linkage system, and the lower arm has sides forming a hollow configuration for surrounding the lower arm and attaching to the actuator. Alternatively, the actuator may be positioned below, between or to the side of the upper arm and the lower arm. 
         [0011]    In another embodiment according to the present invention, an active opener arm is connected to the linkage system and assists in stowing and unstowing the lift platform. 
         [0012]    In yet another embodiment according to the present invention, an extension plate cooperates with the lift platform for loading and unloading. The extension plate may have hinged sections, and may also have a removable center section for receiving locking rods. 
         [0013]    Other and further features and advantages will be apparent from the following detailed description of the present invention when read in conjunction with the accompanying drawings. It should be understood that the embodiments described are provided for illustrative and exemplary purposes only, and that variations to, and combinations of, the several elements and features thereof are contemplated as being within the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0014]    In the drawings, which illustrate what is currently considered to be the best mode for carrying out the invention: 
           [0015]      FIGS. 1A-1C  show a prior art lift which tilts or ramps the outboard edge of the platform to the ground. 
           [0016]      FIGS. 2A-2B  show one embodiment of a lift in accordance with the present invention. 
           [0017]      FIGS. 3A-3F  show multiple views of one embodiment of a lift in accordance with the present invention with the platform in a fully stowed, partially stowed, partially unfolded, fully unfolded, and bed level positions. 
           [0018]      FIGS. 4A-4B  show one embodiment of an upper arm and a lower arm in accordance with the present invention. 
           [0019]      FIGS. 5A-5D  show one embodiment of a shackle and platform support in accordance with the present invention. 
           [0020]      FIGS. 6A-6D  show embodiments of extension plates in accordance with the present invention. 
           [0021]      FIGS. 7A-7B  show one embodiment of an underride in accordance with the present invention. 
           [0022]      FIGS. 8A-8B  shows one embodiment of how a lift in accordance with the present invention may be shipped and installed. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]      FIGS. 1A and 1B  show a prior art lift  10  which tilts or ramps its platform  34  to the ground. Lift  10  includes an upper arm  60  and a segmented lower arm  62 . One end of upper arm  60  is rotatably coupled to a main frame  12  by a first upper pin  70 , while the swingable end of upper arm  60  is coupled to a shackle  74  by a second upper pin  72 . The segmented lower arm  62  includes a member  80  rotatably coupled to a plate assembly  96 . Member  80  is rotatably coupled to main frame  12  by a first lower pin  94 , and plate assembly  96  is coupled to shackle  74  by a second lower pin  98 . Lift  10  also includes a cylinder  40  coupled to main frame  12  and to the inside of plate assembly  96 . Platform  34  is rotatably coupled to shackle  74  by second upper pin  72  and includes a support member  78  which rests against shackle  74  to support platform  34  from below. 
         [0024]      FIG. 1B  shows a side view of lift  10  in a lowered position. In this position, plate assembly  96  and/or shackle  74  contacts the ground, and platform  34  is still substantially level. Platform  34  is supported from below by support member  78 , which is in contact with the outboard face of shackle  74 . Cylinder  40  is then made to become shorter, causing member  80  and plate assembly  96  to rotate with respect to each other and “break” and draw in lower pin  98  of shackle  74 . This has the effect of tilting shackle  74  and thus platform  34 .  FIG. 1C  shows a side view of lift  10  with platform  34  in a tilted or ramped position, after cylinder  40  has been made to become shorter. As can be seen in  FIGS. 1A-1C , platform  34  cannot be maintained in a level orientation while contacting the ground. 
         [0025]      FIGS. 2A-2B  show one embodiment of a lift  100  in accordance with the present invention, in assembled and partially exploded views. Lift  100  includes an upper arm  110  and a lower arm  120 . Upper arm  110  is rotatably coupled to a frame  130  by a first upper pin  136 , while the swingable end of upper arm  110  is coupled to a shackle  140  by a second upper pin  142 . Lower arm  120  is coupled to frame  130  by a first lower pin  138  and to shackle  140  by a second lower pin  144 . The points where upper arm  110  and lower arm  120  couple to frame  130  and shackle  140  may substantially form a linkage system defining the sides of a parallelogram. Lift  100  also includes an actuator  150 , for example a hydraulic cylinder, coupled to frame  130  and lower arm  120 . 
         [0026]    Lift  100  includes a platform support  170 . Platform support  170  is positioned adjacent to shackle  140  and rotatably fixed with respect to the swingable end of lower arm  120  by second lower pin  144 . A platform  160  is coupled to and rests on platform support  170 .  FIGS. 2A-2B  show that an extension plate  200  may be installed to cooperate platform support  170  of lift  100 , as described in further detail with respect to  FIGS. 6A-6D , and lift  100  may also include an underride  190 , described in further detail with respect to  FIGS. 7A-7B . Steps (not shown) may also be attached to underride  190 , extension plate  200 , or other parts of lift  100 , as known in the art. 
         [0027]      FIGS. 3A-3F  show side views of lift  100  in various stages of moving from a raised to a lowered position.  FIG. 3A  shows lift  100  in a fully stowed stage, with upper arm  110  and lower arm  120  in a raised position.  FIG. 3B  shows lift  100  in a partially stowed stage, with upper arm  110  and lower arm  120  in a lowered position. Shackle  140  contacts the ground or is very close to the ground. Platform  160  is forced partially outward from the stowed position by an active opener arm  125 , which assists in the stowing and unstowing of platform  160 , as described in further detail with respect to  FIGS. 5C-5D .  FIG. 3C  shows lift  100  with platform  160  being partially unfolded.  FIG. 3D  shows lift  100  with platform  160  being further unfolded.  FIG. 3E  shows lift  100  in the ground position, with platform  160  fully unfolded. Platform support  170  and/or shackle  140  contacts the ground. Platform  160  is substantially level, and is touching or very nearly touching the ground.  FIG. 3F  shows lift  100  subsequently raised with platform  160  at the vehicle bed or loading dock level position. 
         [0028]      FIGS. 4A-4B  show one embodiment of upper arm  110  and lower arm  120  in accordance with the present invention. Actuator  150  is positioned above both upper arm  110  and lower arm  120  and is coupled to frame  130  and lower arm  120 . In the illustrated embodiment, lower arm  120  has a hollow configuration which at least partially encloses or envelopes upper arm  110  and allows actuator  150  to be coupled to the sides of lower arm  120 .  FIG. 4A  also shows that lower arm  120  may include a channel which allows an extension  123  to be coupled to upper arm  110  and to pass through the channel for coupling to active opener arm  125 . 
         [0029]    In an alternative embodiment, lower arm  120  may not have continuous sides forming a hollow configuration, but may instead have discrete extensions which reach around upper arm  110  and allow actuator  150  to be coupled to lower arm  120 . While not a requirement of the present invention,  FIGS. 4A-4B  show that actuator  150  is preferably positioned in substantially the same vertical plane as upper arm  110  and lower arm  120 . Configuring upper arm  110 , lower arm  120 , and actuator  150  to rotate in substantially the same vertical plane reduces binding during operation. 
         [0030]    Other arrangements for positioning actuator  150  with respect to upper arm  110  and lower arm  120  are also contemplated as being within the scope of the present invention. It is possible, for example, that actuator  150  may be positioned below upper arm  110  and lower arm  120 , with actuator  150  coupled to frame  130  and upper arm  110 . It is also possible that actuator  150  may be positioned between upper arm  110  and lower  120 , with actuator  150  coupled to frame  130  and upper arm  110  and/or lower arm  120 . 
         [0031]      FIG. 5A  shows one embodiment of a shackle  140  in accordance with the present invention. Shackle  140  is coupled to upper arm  110  and lower arm  120  by second upper pin  142  and a second lower pin  144 , respectively. Second upper pin  142  may have a cap or head  528  on one end, and a slot  521  on the other end for receiving a fastener  520 . First lower pin  144  has a stop  522  on one end and a slot  524  on the other end. Second lower pin  144  passes through a torsion spring  526 , which includes an outer leg  529  and an inner leg  530 . Torsion spring  526  is coupled to second lower pin  144  by a spring bracket  525  that mates with inner leg  530  and slot  524 , such that inner leg  530  is fixed in place to prevent torsion spring  526  from freely rotating about second lower pin  144 . Second lower pin  144  is prevented from rotating by stop  531  on shackle  140  which is mated with stop  522  on lower pin  144  with a fastener  540 . Shackle  140  may also include a dock bumper  180  ( FIGS. 5C and 5D ). 
         [0032]      FIG. 5B  shows one embodiment of a platform support  170  in accordance with the present invention. Platform support  170  is configured to be coupled to lower pin  144  of shackle  140 , and is capable of rotating about lower pin  144 . As platform  160  is unstowed, platform  160  rotates about lower pin  144  and a channel  172  in platform support  170  slidably engages upper pin  142 . When platform  160  is unstowed to a horizontal position, upper pin  142  stops at the end of channel  172  and allows platform support  170  to hold platform  160  in a substantially level position. Channel  172  may be suitably configured to mate with cap or head  528  of upper pin  142 . Platform support  170  is thus supported from above by upper pin  142  when unstowed. This allows the bottom of platform  160  when unstowed to be at substantially the same level as or lower than the bottom of shackle  140 . 
         [0033]    When lift  100  is in the lowered position, platform  160  is capable of resting on or near the ground. When lift  100  is in the vehicle bed or loading dock level position, platform support  170  may have raised sides  214  ( FIGS. 6A-6D ) which cooperate with extension plate  200  to provide a guide for loading and unloading on platform  160 . When lift  100  is in the stowed position shown in  FIG. 3A , the stowed platform  160  has a lower profile because it is coupled to lower pin  144 . This lower profile may reduce the required length of extension plate  200  needed to provide proper clearance to lift  100 . When platform  160  is in the unstowed position shown in  FIGS. 3D-3E , outer leg  529  of torsion spring  526  are biased against platform support  170  and help in stowing and unstowing of platform  160 . 
         [0034]    In other embodiments within the scope of the present invention, platform support  170  may include a tab or other structure in place of, or in addition to channel  172  that stops against upper pin  142  when platform  160  is unstowed. Shackle  140  may also include one or more structures for coupling of platform  160  and/or for engaging channel  172  or platform  160  itself. Platform support  170  and platform  160  may thus be supported by upper pin  142  or any part of shackle  140 . While not required, it is preferred that platform  160  be supported from a location that is above or at substantially the same level as lower pin  144 . Although shackle  140 , platform  160 , and platform support  170  are shown as separate elements in the embodiments described, any combination of these three elements may be formed as a single piece. In another embodiment, shackle  140  may also be taller or longer than illustrated and support platform  160  with a chain, cable or linkage attached between platform  160  and shackle  140 , in addition to or in place of platform support  170 . 
         [0035]      FIGS. 5C-5D  shows views of one embodiment of dock bumper  180 , with extension plate  200  cut away to show detail. Dock bumper  180  may prevent damage to lift  100  when attached to a vehicle, for example, that is backed into a dock or other structure. Extension plate  200  includes a housing  202  to receive shackle  140 , and shackle  140  is configured to press against the inside of housing  202  when lift  100  is in a stowed configuration, so as to transfer force from dock bumper  180  to extension plate  200  and minimize or prevent damage to other parts of lift  100  such as upper arm  110  and/or lower arm  120 . Extension plate  200  in turn is configured to transfer force from shackle  140  to the vehicle. Mounting dock bumpers  180  on shackles  140  instead of extension plate  200  allows extension plate  200  to be designed with a greater useful width. 
         [0036]    As shown in  FIGS. 5C-5D , the linkage system may also include an active opener arm  125 , which assists in the stowing and unstowing of platform  160 . Active opener arm  125  is coupled to upper arm  110  by an extension  123 . When lift  100  moves from a raised to a lowered position, translation of upper arm  110  and extension  123  causes active opener arm  125  to rotate and exert pressure against platform  160 , forcing platform  160  outward towards its unstowed orientation. Likewise, when lift  100  moves from a lowered to a raised position, active opener arm  125  is caused to rotated in an opposite direction and lower platform  160  resting thereon towards a stowed orientation. Further details regarding the structure and function of such an active opener arm are described in copending U.S. application Ser. No. 10/789,909, the disclosure of which is incorporated herein by reference. 
         [0037]      FIGS. 6A-6B  shows one embodiment of an extension plate  210  in accordance with the present invention. Extension plate  210  includes a surface plate  212  with hinged sections  214 . Hinged sections  214  are capable of lying flush with surface plate  212 , as shown in  FIG. 6A .  FIG. 6B  shows that when platform  160  of lift  100  is raised, shackles  140  will raise hinged sections  214 , which may then cooperate with the raised sides of platform support  170  to provide a guide for loading and unloading. When platform  160  reaches the bed level position, platform  160  will be substantially coplanar with surface plate  212  and the vehicle bed or loading dock surface. When platform  160  is lowered, hinged sections  214  will drop back down. 
         [0038]      FIGS. 6C-6D  show another embodiment of an extension plate  220  in accordance with the present invention that is configured to receive locking rods (not shown) that are known in the art to be found on conventional side-swinging doors. In order to accommodate such locking rods, extension plate  220  includes a surface plate  222  with a center section  224 .  FIG. 6C  shows center section  224  lying flush with surface plate  222 .  FIG. 6D  shows center section  224  moved to allow locking rods to be passed through extension plate  220 . In the embodiment shown, center section  224  is hinged at the outboard edge of extension plate  220  and swings outward. Center section  224  may have a latch  226  to help keep it closed. In other embodiments, center section  224  may be removable, slidable, spring-loaded, hinged at the inboard edge of extension plate  220  and swing inward, or configured with any other suitable mechanism to provide clearance to locking rods. In yet another embodiment, surface plate  222  includes arcuate grooves or channels which provide clearance for the locking rods. 
         [0039]    As seen in  FIGS. 6C-6D , extension plate  220  also includes permanently raised sections  216 , rather than the hinged sections  214  associated with extension plate  210 . It is within the scope of the present invention that hinged sections  214  may be included in extension plate  220 , and center section  224  which accommodates locking rods may also be used with the extension plate  210  shown in  FIGS. 6A-6B . 
         [0040]      FIGS. 7A-7B  show one embodiment of an underride  190  in accordance with the present invention. Underride  190  acts as a rear impact guard and prevents other vehicles from traveling underneath lift  100 . Underride  190  includes an underride bar  191  which may be coupled to frame  130  by plates  192 . Plates  192  may be coupled to frame  130  at the same point as lower arms  120 . This transfers most or all of any impact force to underride  190  to frame  130  and not to lower arms  120 . Plates  192  may include adjustment holes  194  which couple to lower arms  120  and allow underride  190  to be adjusted to a desired height. Underride  190  may also act as a synchronizing or balancing structure which minimizes binding or “walking” of upper arm  110  and lower arm  120  on each side of lift  100  as it is being operated. 
         [0041]      FIGS. 8A-8B  shows how a lift  100  according to the present invention may be shipped as a package with extension plate  200  and then installed on a vehicle. In this manner, lift  100  and extension plate  200  may come pre-adjusted from the factory. Extension plate  200  may be held in the proper position with respect to the rest of lift  100  by a tack-weld  310  (FIG.  8 B), an installation bracket  320  ( FIG. 8A ), or any other suitable fastener or removable coupling. To install lift  100  and extension plate  200 , extension plate  200  is leveled before being welded or otherwise coupled to the vehicle, and then lift  100  is welded or otherwise coupled to the vehicle. After tack-weld  310  is cut and installation bracket  320  is removed, lift  100  has been properly installed. The installation of lift  100  and extension plate  200  are facilitated by the fact that lift  100  and extension plate  200  are shipped pre-adjusted, lift  100  and extension plate  200  do not need to be disassembled before installation, and once extension plate  200  has been properly coupled to the vehicle no further adjustment of lift  100  will typically be necessary before lift  100  can be coupled to the vehicle. 
         [0042]    While the invention has been described in terms of some specific examples and in some specific embodiments, it will be clear that this invention is not limited to these specific examples and embodiments and that many changes and modified embodiments will be obvious to those skilled in the art without departing from the true spirit and scope of the invention as defined in the appended claims. The scope of the invention is, therefore, indicated by the appended claims rather than the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.