Abstract:
A platform lift apparatus enables the safe movement of objects to and from an attic storage space. The platform lift apparatus includes a frame, a drive mechanism, and a platform. The frame includes internal and external mounting surfaces. The drive mechanism is substantially disposed within the frame and is coupled to the internal mounting surfaces. The drive mechanism includes a plurality of rotatable, parallel shafts with each shaft further including at least one lift drum having an associated lift tether at least partially wound thereon and having an end hanging therefrom. The platform is coupled to each lift tether end and is thereby suspended from the frame. The platform is selectively movable by operation of the drive mechanism within in a vertical dimension between raised and lowered positions. The drive mechanism further comprises an electric motor operatively coupled to the plurality of parallel shafts.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to residential or commercial storage, or more particularly, to a platform lift apparatus for raising or lowering objects relative to an upper storage location such as an attic storage space located above a garage or living quarters.  
         [0003]     2. Description of Related Art  
         [0004]     Many homes have attic spaces above garages and living quarters, and these attic spaces often provide a storage location for various items. While some attic spaces are finished and have access via a stairwell, most attic spaces remain unfinished and have more rudimentary access systems. The most basic access system is a simple opening or scuttle hole formed in the ceiling dividing the attic space from the room below. The scuttle hole is commonly located in a closet or main hallway, and may be covered by a hatch that comprises a removable portion of ceiling, such as formed from plywood or drywall. A user would position a ladder below the opening and access the storage space by carrying storage objects up and down the ladder. An improvement over this basic access system is a pull-down ladder that is built into a hingedly attached door covering the opening. The pull-down ladder may be folded into a plurality of sections to provide a compact structure when stowed. The user opens the door and unfolds the ladder to bring it into an operational position. This pull-down ladder has improved convenience since the user does not have to transport a ladder to and from the access location, and the ladder is anchored to the opening to thereby provide an increased degree of safety for the user.  
         [0005]     Nevertheless, a drawback of each of these access systems is that it is difficult to transport objects up and down the ladder. The user cannot easily carry the object and grasp the ladder at the same time, thereby forcing a dangerous tradeoff between carrying capacity and safety. Moreover, the size and weight of the objects that may be transported is limited to that which could be manually carried and fit through the dimensions of the access opening. Users of such access systems have a substantial risk of injury due to falling and/or dropping objects, and the objects themselves can be damaged as well.  
         [0006]     Thus, it would be advantageous to provide an improved way to transport objects to and from an attic storage space without the drawbacks and safety risks of the known access systems. Additionally, there are many other applications in which it would be desirable to transport objects to and from a raised position. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     A more complete understanding of the platform lift system will be afforded to those skilled in the art, as well as a realization of additional advantages and objects thereof, by a consideration of the following detailed description of the preferred embodiment. Reference will be made to the appended sheets of drawings, which will first be described briefly.  
         [0008]      FIG. 1  is an isometric view of a platform lift system in accordance with an embodiment of the invention;  
         [0009]      FIG. 2  is a top view of the platform lift system and associated platform;  
         [0010]      FIG. 3  is a sectional view of the platform lift system as taken through the section C-C of  FIG. 2 ;  
         [0011]      FIG. 4  is a sectional view of the platform lift system as taken through the section A-A of  FIG. 2 ;  
         [0012]      FIG. 5  is a sectional view of the platform lift system as taken through the section B-B of  FIG. 2 ;  
         [0013]      FIG. 6  is a side view of a lift pulley having a belt tensioner;  
         [0014]      FIG. 7  is a front view of the lift pulley of  FIG. 6 ;  
         [0015]      FIG. 8  is a top view of an embodiment of a platform including an integrated basket;  
         [0016]      FIG. 9  is a side view of the platform of  FIG. 8 ;  
         [0017]      FIG. 10  is a rear view of the platform of  FIG. 8 ;  
         [0018]      FIG. 11  is a side view of an alternative embodiment of a platform lift system that does not include a ceiling opening;  
         [0019]      FIG. 12  is a front view of a drop down storage system in accordance with another embodiment of the invention;  
         [0020]      FIG. 13  is a sectional view of the drop down storage system as taken through the section D-D of  FIG. 12 ;  
         [0021]      FIG. 14  is a top view of an alternative embodiment of the platform lift system that includes an integrated ladder;  
         [0022]      FIG. 15  is a side view of the platform lift system of  FIG. 14 ;  
         [0023]      FIG. 16  is a front view of the platform lift system of  FIG. 14 ;  
         [0024]      FIG. 17  is a top view of another embodiment of the platform lift system that includes a pull-down ladder;  
         [0025]      FIG. 18  is a side view of the platform lift system of  FIG. 17 ;  
         [0026]      FIG. 19  is an end view of the platform lift system of  FIG. 17 ;  
         [0027]      FIG. 20  is a cross-sectional side view of another embodiment of the platform lift system that includes a pull-down ladder;  
         [0028]      FIG. 21  is a cross-sectional side view of the platform lift system of  FIG. 20 ;  
         [0029]      FIG. 22  is a top view of the platform lift system of  FIG. 20 ;  
         [0030]      FIG. 23  is a top view of the platform lift having traversed partly downward along the guide affixed to the ladder;  
         [0031]      FIG. 24  is a side cutaway view of the platform pulley length adjust assembly;  
         [0032]      FIG. 25  is an end view of the platform pulley length adjust assembly;  
         [0033]      FIG. 26  is a sectional view of the reduction gears as taken through the section C-C of  FIG. 22 ;  
         [0034]      FIG. 27  is a side view of an embodiment of the platform lift having an impact detection system;  
         [0035]      FIG. 28  is an enlarged side view of a portion of the impact detection system of  FIG. 27 ;  
         [0036]      FIGS. 29   a - c  are side views of an alternative transition mechanism to permit the lift platform of  FIG. 22  to transition to the ladder guide;  
         [0037]      FIGS. 30   a - c  are an alternative drive system for the platform lift system;  
         [0038]      FIGS. 31   a - c  are an another alternative drive system for the platform lift system;  
         [0039]      FIG. 32   a - b  are yet another alternative drive system for the platform lift system;  
         [0040]      FIG. 33  is an alternative embodiment of a platform lift system adapted to move a load between interior and exterior structures;  
         [0041]      FIG. 34  is another alternative embodiment of a platform lift system adapted to engage a window ledge;  
         [0042]      FIG. 35  is a side view of another alternative embodiment of a platform lift system movable along a monorail;  
         [0043]      FIG. 36  is a front view of the platform lift system of  FIG. 35 ;  
         [0044]      FIG. 37  is a perspective view of another alternative embodiment of a platform lift system having an expandable frame assembly;  
         [0045]      FIG. 38  is a side view of another alternative embodiment of a platform lift system used in connection with an overhead rail;  
         [0046]      FIG. 39  is a front view of another alternative embodiment of a lift system used to raise an enclosed compartment;  
         [0047]      FIG. 40  is a top view of the lift system of  FIG. 39 ; and  
         [0048]      FIG. 41  is a side view of the lift system of  FIG. 39 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0049]     The present invention satisfies the need for an improved way to transport objects to and from an attic storage space without the drawbacks and safety risks of the known access systems. In the detailed description that follows, like element numerals are used to describe like elements illustrated in one or more figures.  
         [0050]     More particularly, the invention provides a platform lift system that enables objects to be moved between an attic space and a room below. The platform lift system includes a frame that is mounted into a scuttle hole formed in an attic ceiling and a platform that is supported by the frame. The platform may be selectively raised or lowered in order to transport objects to/from the attic space. When in a raised position, the platform engages the frame and seals the attic space to provide a thermal barrier. The frame lies substantially flush with the ceiling floor, so as to maximize available storage space within the attic ceiling and minimize interference between the lift system and objects moved on and off the platform. The frame further includes a drive system that controls the movement of a plurality of belts that are coupled to the platform. The platform is raised by withdrawing the belts, and is lowered by paying out the belts.  
         [0051]     Referring first to  FIG. 1 , an isometric view of a platform lift system is illustrated in accordance with an embodiment of the invention. The platform lift system is installed in a ceiling structure that is supported by horizontally extending joists  21 . A rectangular scuttle hole is formed within the ceiling structure that is bounded on two sides by joists  21  and on the other sides by crosspieces that abut the joists. As shown in  FIG. 1 , a section of an intermediary joist is removed for the length of the scuttle hole, such that the width of the scuttle hole corresponds to twice the separation between adjacent joists plus the width of one joist. As will be understood to persons skilled in the art, the platform lift system maintains the structural integrity of the ceiling notwithstanding the removal of a section of joist.  
         [0052]     The platform lift system further comprises a vertically oriented frame  11  having a rectangular shape adapted to fit into the scuttle hole formed in the ceiling. The frame  11  may include mounting brackets  12  or integral flanges (not shown) that engage upper surfaces of the joists and crosspieces to facilitate attachment thereto. The frame  11  may be constructed of wood, metal, plastic, or other high strength, lightweight material capable of supporting a suitable load carried by the platform lift system.  
         [0053]     A drive system coupled to the frame raises and lowers a platform (described below). In an embodiment of the invention, the drive system includes shafts  31 ,  32 , shaft drive gear  34 , motor  41 , motor drive gear  46 , belt drive gears  51 , and drive belts  56 . The shafts  31 ,  32  are rotatably mounted in parallel at opposite ends of the frame  11 . Each end of the shafts  31 ,  32  includes a belt drive gear  51  mounted thereto in substantial alignment. This way, the respective belt drive gears on the left end of the shafts  31 ,  32  are aligned and the respective belt drive gears on the right end of the shafts are similarly aligned. The left and right belt drive gears  51  carry respective right and left drive belts  56 . Shaft  31  further carries shaft drive gear  34 . Motor  41  is mounted to the frame  11  using suitable brackets and is adapted to drive motor drive gear  46 , which is in turn arranged in mesh with the shaft drive gear  34 . Accordingly, motor  41  drives shaft  31  to rotation by cooperation of the motor drive gear  46  and shaft drive gear  34 , and shaft  32  is driven to rotation in unison with shaft  31  by cooperation of the belt drive gears  51  and drive belts  56 . In a preferred embodiment of the invention, the shafts  31 ,  32  are keyed to match associated keying of the belt drive gears  51  and shaft drive gear  34  so as to maintain synchronized movement of the shafts. Further, the drive belts  56  may include teeth that engage associated sprockets of the belt drive gears  51  to further maintain synchronized shaft movement. Motor  41  may further include speed reduction gearing  42  and bearings  44  to achieve a desired rotational rate of the shafts  31 ,  32 .  
         [0054]     The shafts  31 ,  32  further carry a plurality of pulleys  52  for raising and lowering lift belts  55 . Each shaft has lift pulleys  52  disposed at both ends such that one pulley is located adjacent to each corner of the frame  11 . The lift pulleys  52  carry a respective lift belt  55  that winds onto the pulley. A first end of each lift belt  55  is fixedly attached to a respective lift pulley  52 , and a second end of the lift belt  55  hangs vertically from the pulley and is attached to the platform (described below). With respect to shaft  32 , the drive system further includes idler pulleys  57  that serve to move the respective lift belts toward the outer periphery adjacent to the frame  11 . It should therefore be understood that when motor  41  is driven to rotation in a clockwise direction, shaft drive gear  34  and shafts  31  will each be driven to rotation in a counter-clockwise direction to unwind the lift belts  55  and thereby lower the platform. Conversely, when motor  41  is driven to rotation in a counter-clockwise direction, shaft drive gear  34  and shafts  31  will each be driven to rotation in a clockwise direction to rewind the lift belts  55  and thereby raise the platform. It will be appreciated that the platform lift system will include suitable control circuitry for activating the motor  41  in forward and reverse directions.  
         [0055]      FIG. 2  illustrates a top view of the platform lift system and associated platform  60 . Likewise,  FIGS. 3, 4  and  5  illustrate sectional views of the platform lift system as taken through the section C-C, A-A, and B-B of  FIG. 2 , respectively. As best shown in  FIGS. 4 and 5 , the platform  60  includes a base  64  comprising a generally rectangular board having a shape corresponding to the scuttle hole. The platform  60  may further include vertically extending fences that define a carrying basket (described below). As shown in  FIG. 4 , the base  64  may further include a seal  65  disposed on an upper surface therefore adjacent to an outer periphery of the base so as to form a thermal barrier and also to cushion the engagement of the platform  60  with the frame  11  when the platform is in the fully raised position. The frame  11  and the base  64  may further be provided with respective guide ramps  62 ,  61  that facilitate the engagement of the platform  60  with the frame.  FIG. 5  shows the engagement between the lift belts  55  and the platform  60 . In a preferred embodiment of the invention, the ends of the lift belts  55  are provided with a fastening device  66 , such as a quick release fastener, that engages a corresponding receptacle  63  coupled to the platform  60 . This permits the platform  60  to be disconnected from the lift belts  55 , such as to facilitate loading of objects onto the platform. It should be appreciated that a permanent connection between the platform  60  and the lift belts  55  could also be advantageously utilized.  
         [0056]     Although the frame  11  is illustrated as a fixed rectangular shape, it should be appreciated that the frame may be adjustable to achieve different widths and/or lengths. The shafts  31 ,  32  may be provided with adjustable length, such as using telescoping shaft segments that are fixed in position by tightening a set screw.  
         [0057]      FIGS. 6 and 7  illustrate an embodiment of the lift pulleys  52  having a belt tensioner. More particularly, the belt tensioner includes a tension spring  71  mounted to a portion of the frame  11 . The tension spring  71  may be formed of a flexible band, such as a leaf spring. The tension spring  71  further includes a collar  70  that carries an axle  69 . A tension drum  68  is rotatably coupled onto the axle  69 . The tension drum  68  is biased into physical engagement with the lift belt  55  that has wound onto the lift pulley  52 , such that a constant pressure is applied to the lift belt  55  as it is either played out or re-wound onto the lift pulley  52  as the platform  60  is selectively lowered or raised. It should be appreciated that each of the four lift pulleys  52  would have a like belt tensioner.  
         [0058]      FIGS. 8, 9  and  10  illustrate an embodiment of a platform  60  that includes an integrated basket. The platform  60  further includes a plurality of folded fences  75 ,  76 ,  77  and  78 . The fences are each hingedly attached to respective outer edges of a basket region, and are pivotable between horizontal and vertical positions. In the horizontal (or collapsed) position, fences  77  and  78  are nested below fences  75 ,  76 . Each fence comprises a generally rectangular shape corresponding to roughly one-half of the area defined by the basket region. With the fences disposed in the horizontal or collapsed configuration, a flat surface is defined onto which objects may be carried. Alternatively, with the fences deployed to the vertical position, a generally rectangular basket is formed into which objects may be placed. A latching mechanism may be included that attaches the fences together in the vertical position in order to maintain the basket. It should be appreciated that the basket may be advantageous for transporting small objects that might otherwise fall off the platform while it is being raised or lowered. The platform  60  may also include a fixed position or fold-down ramp that facilitates loading of objects thereon.  
         [0059]      FIG. 11  illustrates a side view of an alternative embodiment of a platform lift system. Unlike the preceding embodiments in which the platform carried objects through a scuttle hole formed in an attic ceiling, the embodiment of  FIG. 11  carries objects to a storage location disposed below the ceiling. This embodiment might be advantageous in a garage or loft in which there is a high ceiling but no attic space above the ceiling. Objects could be carried up to this storage location, thereby clearing floor space below. The frame  11  of the platform lift system would be mounted to the ceiling, such as using angle brackets  80 . In the same manner as described above in any of the foregoing embodiments, lift belts  55  would carry a platform  83 . The platform  83  may have vertically extending alignment guides  81  that engage corresponding stops  82 , which serve the purpose of defining the vertical extent of travel of the platform and guiding the platform into an aligned position.  
         [0060]      FIG. 11  also illustrates a retractable wheel assembly affixed to a bottom surface of the platform  83 . The wheel assembly includes a rotable wheel or caster  91  that rotates about an axle  90 . The wheel assembly is shown in a retracted (or horizontal) position. By pivoting the wheel assembly 90° about a pivot point  88 , the wheel assembly can be moved to an operational position with the wheel  91  oriented vertically. The retractable wheel assembly enables the platform  83  to serve as a dolly for the purpose of moving objects around the floor, after disengaging the lift belts  55 . It should be appreciated that all four corners of the platform  83  may include like retractable wheel assemblies. Moreover, the retractable wheel assemblies could also be used with any of the foregoing embodiments of the invention.  
         [0061]      FIGS. 12 and 13  illustrate yet another embodiment of the invention providing a drop down storage system. Unlike the preceding embodiments, the drop down storage system provides a storage unit  100 , such as a pantry or cabinet, which can be lowered down from the ceiling to enable access. When not in use, the storage unit  100  can be raised back through the ceiling, with the bottom surface of the storage unit ending flush with the ceiling. The storage unit  100  may include a plurality of shelves or drawers or rolling pantry trays  102  (as shown in  FIGS. 12 and 13 ). The storage unit  100  would be raised or lowered substantially as described above, except that the frame  11  is disposed above the ceiling rather than flush with the ceiling. In addition to the lift belts  55  described above, the drop down storage system may also include a scissor stabilizer assembly formed from a plurality of scissor linkages  111  coupled at pivot points  112 . An uppermost linkage  114  and lowermost linkage may have ends that travel in respective tracks  114  that permit the scissor stabilizer assembly to expand and retract. The scissor stabilizer assembly provides smooth, controlled motion of the storage unit  100  as it raises and lowers.  
         [0062]      FIGS. 14-16  illustrate yet another embodiment of the invention providing a lift platform system that includes a pull-down ladder. The pull-down ladder may be folded into a plurality of sections to provide a compact structure when stowed, and may be hingedly attached to a door that seals a scuttle hole formed in the ceiling. When in the unfolded configuration, the rails of the ladder provide a track to guide the movement of a platform. The platform includes wheels extending from one edge thereof, with the wheels adapted to engage the track provided by the ladder. The platform would be raised and lowered substantially as described above, except that rather than traveling vertically between raised and lowered positions, the platform travels diagonally along the track provided by the ladder. This embodiment is advantageous since a user would only have to provide a single scuttle hole through the ceiling to provide for human access and movement of stored objects.  
         [0063]     More particularly,  FIG. 15  illustrates fold-down ladder  125  installed in a ceiling structure that is supported by horizontally extending joists  21 . The ladder  125  comprises a plurality of horizontal steps  126  and may be folded into a plurality of sections that permit the ladder to be stowed in the scuttle hole and enclosed in the ceiling when not in use. The ladder  125  is attached to an edge of the scuttle hole by a hinge  129 . When the ladder  125  is fully deployed, it extends downward at an angle of roughly 45-75° and comes into contact with the floor at the bottom of the ladder. The supporting frame (not shown) for a platform lift is installed above the scuttle hole, such as supported by rafters substantially above the floor of the attic space. The platform  64  may be raised above the scuttle hole to a height sufficient to permit users to climb the ladder  125  and access the attic space without being impeded by the platform.  
         [0064]     As shown in  FIGS. 14-16 , the platform  64  is suspended by lift belts  55  in the same manner as described above with respect to the preceding embodiments. The platform  64  of this embodiment further includes a pair of portal guide rollers  132  and a pair of ladder guide rollers  133  supported by roller support brackets  131  that extend substantially horizontally from an end of the platform. The portal guide rollers  132  are arranged to engage respective roller guides  130  disposed in a vertical orientation at opposite corners of an end of the scuttle hole. The ladder  125  further includes a roller guide  127  that extends the length of the ladder. Accordingly, when the platform  64  is lowered from the overhead stowed position, the portal guide rollers  132  engage the roller guides  130 , which guides the platform downward in a substantially vertical direction. Then, when the guide rollers  132  reach the bottom of the roller guides  130 , the ladder guide rollers  133  engage the roller guide  127  on the ladder  125 . As the platform  64  descends, its direction of travel transitions from substantially vertical to the angle defined by the position of the ladder  125 . The platform  64  will continue to descend along a track defined by the roller guide  127  until reaching the floor or selectively stopped by the user. A pair of guide rollers  144  may also be disposed at an end of the scuttle hole opposite the roller guides  130 . The guide rollers  144  engage an end of the platform  64  as it descends through the scuttle hole.  
         [0065]      FIGS. 17-19  illustrate another embodiment of the invention providing a lift platform system that includes a pull-down ladder. In this embodiment, the platform system moves laterally along an overhead rail system. When it is desired to use the ladder to access the attic space, the platform is moved laterally to a position out of the way of the scuttle hole. But, when it is desired to use the platform lift system, the platform is moved laterally to a position aligned with the scuttle hole. From this position, the platform can be raised and lowered diagonally along the track provided by the ladder in the same manner as described above in the preceding embodiment. More particularly, a pair of platform frame tracks  135  are coupled to the floor of the attic space with corresponding mounting assemblies  138 . The platform assembly includes a plurality of sleeves  136  that engage the tracks  135 , permitting horizontal movement of the entire platform assembly. The platform assembly may thereby be moved horizontally between an operational position aligned with the scuttle hole and a non-operational position moved out of the way of the scuttle hole.  
         [0066]      FIGS. 20-22  illustrate another embodiment of the invention providing a lift platform system that includes a pull-down ladder. In this embodiment, the platform system moves laterally along a rail disposed on the floor of the attic space. As in the preceding embodiment, when it is desired to use the ladder to access the attic space, the platform is moved laterally to a position out of the way of the scuttle hole. But, when it is desired to use the platform lift system, the platform is moved laterally to a position aligned with the scuttle hole. From this position, the platform can be raised and lowered diagonally along the track provided by the ladder in the same manner as described above in the preceding embodiment.  
         [0067]     The lift platform system includes three main subsections: (a) a joist sleeve frame structure that engages a scuttle hole formed in a ceiling; (b) an unfoldable ladder and hatch door that is hingedly attached to the joist sleeve frame structure; and (c) a movable platform carriage assembly with platform lift. All three of these subsections are shown in  FIG. 20 . A scuttle hole is bounded by joists  21  that form the ceiling. A joist sleeve frame  151  is inserted into and fixedly engaged with the scuttle hole so as to provide structural integrity for other subsections of the lift platform system. The sleeve frame  151  is coupled to track  159  using angle brackets  160 . The track  159  lies horizontally on the floor of the ceiling to provide a guide path for the movable platform carriage assembly. A roller guide  245  extends from a side of the sleeve frame  151  via bracket  243  to guide movement of the platform through the scuttle hole. Ladder  225  is shown in an unfolded configuration extending diagonally downward from the joist sleeve frame  151 . The ladder includes a roller guide  227  extending along the length thereof for engagement with a corresponding roller of the movable platform. The movable platform frame  211  is shown above the joist sleeve frame  151 . The moveable platform is shown in a fully raised position  264   a  and partly lowered position  264   b.  As in the foregoing embodiments, the platform  264  is supported by a plurality of lift belts  55  that unwind from respective lift pulleys  52  and idler pulleys  156 .  
         [0068]      FIGS. 21 and 22  shown the moveable platform carriage assembly in greater detail. The drive mechanism for lifting the platform includes a motor  41  that drives an associated motor shaft  150 , and a plurality of helical gears driving a main shaft  270  with desired speed reduction. The platform frame  211  further includes a plurality of track roller wheels  271  that permit lateral movement of the platform carriage assembly along the track  159  (described above). The track roller wheels  271  are coupled to the platform frame  211  using axles  272 .  
         [0069]     In an embodiment of the invention, the lift pulleys  52  further include torsional springs  269  that couple the pulleys to the main shaft  270 . The torsional springs  269  allow for differential stretch length of the lift belts  55 . Since two pulleys at one end of the platform lift the platform directly, while two others guide the lift belts laterally across the width of the platform to the pulleys at the other end before dropping down to lift the platform, differential stretching of the lift belts can result in the platform being moved unevenly. The amount of this differential stretching will also depend on the amount of loading of the platform. The torsional springs  269  are selected to have a spring constant k that matches the expected stretching, and will allow relative motion of the lift pulleys  52  with respect to the shaft  270  no matter what force is applied to the platform.  FIG. 21  further shows a platform pulley length adjustment mechanism  152  that enables the connection between the lift belts  55  and the platform to be adjusted. Tightening the set screw of the platform adjustment mechanism  152  serves to change the length of the lift belts. The adjustment mechanism  152  is described in greater detail below with respect to  FIGS. 24 and 25 .  
         [0070]      FIG. 23  shows the platform of the preceding figures having traversed downward through the scuttle hole in the ceiling. In this embodiment, the platform includes a ladder guide bracket  154  that is coupled to the side of the platform  260  using a rotating joint  153 . The guide bracket  154  carries guide rollers  232 ,  233  that engage the roller guide  227  affixed to the ladder.  
         [0071]      FIGS. 24 and 25  show the pulley belt adjustment mechanism  152  in greater detail. An end of the belt  55  enters a slot  276  formed in an upper surface of the movable platform and enters an interior chamber. A threaded bolt  277  extends the length of the chamber and a slide block is threadingly coupled to the bolt. The belt  55  is affixed to the slide block. Turning the bolt  277  in a clockwise direction causes movement of the slide block within the chamber toward the head of the bolt, thereby loosening the belt  55 . Conversely, turning the bolt  277  in a counter-clockwise direction causes movement of the slide block within the chamber away from the head of the bolt, thereby tightening the belt  55 . It is anticipated that all four corners of the platform include a like mechanism for adjusting the belt length. The platform may also be equipped with a bubble level to enable the operator to accurately adjust the pulley belt adjustment mechanisms to level the platform. Instead of a manual adjustment, the same mechanism could be adapted to automatically level the platform each time it is operated.  
         [0072]      FIG. 26  shows the gear train used to drive the main shaft, taken through the section C-C of  FIG. 22 . The motor  41  drives a helical gear  290 , which is in mesh with helical gear  291  affixed to a worm shaft  292  oriented 90° to the motor shaft. The worm shaft  292  carries worm  293 , which drives worm gear  294  coupled to main shaft  270 . As discussed above, the main shaft  270  drives the pulleys  52  that raise and lower the lift belts  55 . It is anticipated that the gear train achieve a generally high gear reduction ratio (approximately 30:1).  
         [0073]      FIG. 28  illustrates a side view of the lift platform having an impact detection system for the platform lift system. A contact plate  301  is coupled to the underside of the platform deck  360  using a plurality of pins  302 . The pins  302  are fixed to corresponding compression springs  304 , which are fixedly attached at an end to the platform deck  360 . The arrangement permits the contact plate  301  to be movable against the bias applied by the compression springs  304 . Electrical contacts disposed within the compression springs  304  make contact when the contact plate  301  causes one or more of the pins  302  to compress the associated compression springs  304 . Accordingly, if the platform deck  360  comes into contact with an object as the lift platform is descending, the signal electrical signal formed by the closed contacts could trigger a halt to the movement of the lift platform.  
         [0074]      FIGS. 29   a - c  illustrate a transition mechanism that enables the movable platform to transition from vertical movement to the diagonal movement along the ladder.  FIG. 29   a  shows the transition mechanism in a deployed configuration, with the ladder  225  extended downward from the pivot axle  247  that is fixed to the joist sleeve frame  151 . Roller guide  227  is coupled to the ladder  225  and provides a guide path for movement of the platform lift. A folding roller track mechanism  306  includes a track segment  309  that provides a continuous path with the roller guide  227  to enable transition from vertical to diagonal movement. The track segment  309  and roller guide  227  are oriented to engage the guide roller  233  coupled to the platform via bracket  154 . As shown in  FIG. 29   a,  the guide roller  233  first moves vertically in contact with the track segment  309 . Then, upon reaching an elbow defined by the intersection of track segment  309  and roller guide  227 , the guide roller  233  transitions to a diagonal path. Fence  311  keeps the guide roller  233  in contact with the track segment  309 . Spring  312  biases the folding roller track mechanism  306  into position when the ladder is deployed. It should be appreciated that the fence  311  contains the guide roller  233  on the outside as the guide roller moves vertically. Following the transition to diagonal movement, the ladder  225  provides an inner fence for the guide roller  233 . Accordingly, the guide roller  233  is controlled throughout its travel.  
         [0075]      FIG. 29   b  shows the transition mechanism in a stowed configuration, with the ladder  225  folded up and the attic hatch closed. The roller track mechanism  306  is moved out of the way to permit the ladder  225  to move upward as it is stowed.  FIG. 29   c  shows a sectional view of the roller track mechanism  306  as taken through the section A-A of  FIG. 29   b.  An advantage of using the folding roller track mechanism  306  of  FIGS. 29   a - c  is that it avoids the need for redundant sets of guide rollers on the platform.  
         [0076]      FIGS. 30   a - c  illustrate an alternative embodiment of the drive system for the platform lift system. Instead of a continuous loop, the drive belt  456  has a first end fixedly attached to the first belt drive gear  452  and a second end fixedly attached to the second belt drive gear. The drive belt  456  is wound onto the belt drive gears, such that when the platform is fully raised the drive belt is completely wound onto the first belt drive gear  452  and when the platform is fully lowered the drive belt is completely wound onto the second belt drive, gear. By fixedly attaching the ends of the drive belts  456  to the belt drive gears  452 , the belt provides a limit to the amount of vertical travel of the platform. Also, the shaft  432  is offset vertically with respect to shaft  431 , and the drive belt  456  is wound onto the belt drive gears in opposite directions. Thus, the first belt drive gear rotates counterclockwise while the second belt drive gear rotates clockwise, and vice versa. This arrangement has the advantage of paying out the lift belts from the outer periphery of the pulleys, thereby eliminating the need for separate idler pulleys (see  FIG. 1 ) to manipulate the lift belt to the periphery. It should be appreciated that only the belt drive gears at one end of the shafts  431 ,  432  are illustrated in  FIGS. 30   a - c,  and that the other ends would have a like construction.  
         [0077]      FIGS. 31   a - c  illustrate another alternative embodiment of the drive system for the platform lift system. In this embodiment, two of the lift pulleys are eliminated and the belt  556  provides both driving and lifting. Particularly, the drive belt  556  has a first end fixedly attached to the first belt drive gear  552  and a second end that is carried partly by the second belt drive gear and then extends vertically to provide a lift belt. Pulley  551  provides a second lift belt in the same manner described above with respect to  FIG. 1 . When the platform is fully raised, the drive belt  556  is completely wound onto the first belt drive gear  552  and when the platform is fully lowered the drive belt is completely paid out. As in the preceding embodiment, the shaft  532  is offset vertically with respect to shaft  531 , and the drive belt  556  causes the belt drive gears to rotate in opposite directions. Thus, the first belt drive gear rotates counterclockwise while the second belt drive gear rotates clockwise, and vice versa. This arrangement has the advantage of reducing the number of lift pulleys and associated belts. It should be appreciated that only the belt drive gears at one end of the shafts  531 ,  532  are illustrated in  FIGS. 31   a - c,  and that the other ends would have a like construction.  
         [0078]      FIGS. 32   a - b  illustrate yet another alternative embodiment of the drive system for the platform lift system. In this embodiment, all of the lift pulleys are eliminated and the belt  656  provides both driving and lifting. Particularly, the drive belt  656  has a first end fixedly attached to the first belt drive gear  652  and a second end that is carried partly by the second belt drive gear and then extends vertically to provide a lift belt. The first belt drive gear  652  also includes a separate lift belt  655  that is wound onto the drive gear along with the drive belt  656 . When the platform is fully raised, the drive belt  656  and lift belt  655  are completely wound onto the first belt drive gear  652  and when the platform is fully lowered the drive belt  656  and lift belt  655  are completely paid out. As in the preceding embodiment, the shaft  632  is offset vertically with respect to shaft  631 , and the drive belt  656  causes the belt drive gears to rotate in opposite directions. It should be appreciated that only the belt drive gears at one end of the shafts  631 ,  632  are illustrated in  FIGS. 32   a - b,  and that the other ends would have a like construction.  
         [0079]      FIG. 33  is an alternative embodiment of a platform lift system adapted to move items from outside a structure to an interior raised position. For example, the platform lift system could raise a load disposed on ground level outside a building and transport the load through an upper window into an interior of the building. As shown in  FIG. 33 , the structure includes an exterior wall  703  and a raised room having floor  707 . A modular frame assembly  702  provides vertical support for a platform lift mechanism having wheels  771  that engage track  759 . The platform lift mechanism Includes platform  760  that is raised and lowered using belts that attach at lift points  766 . A load  704  may be strapped to the platform using restraints  705 . Pulleys  752  raise and lower the belts as substantially described above. With the load  704  and platform  760  in the raised position, the entire platform lift mechanism may be moved laterally along the track  759  to a position outside a window or balcony. The load  704  may then be lowered to the exterior floor by operation of the platform lift. The same process in reverse would be used to move a load into the structure.  
         [0080]      FIG. 34  illustrates another alternative embodiment of a platform lift system adapted to move items from a window ledge. A frame assembly  802  is positioned in an interior space, and has foldable members that extend along an interior wall and out through a window. The frame assembly  802  supports a vertical rail  859  on which a platform lift mechanism travels. The platform lift mechanism includes wheels  871  that engage the vertical rail to permit the platform to be transferred between interior and exterior positions. As in the preceding embodiments, the platform lift mechanism includes a platform  860  that is lifted using belts coupled to pulleys  852 . It is anticipated that the frame assembly  802  not be permanently installed, but rather be merely secured in place ballast. This way, the platform lift mechanism can be deployed when it is need to move an object, and can otherwise be disassembled and put away.  
         [0081]      FIGS. 35 and 36  illustrate another alternative embodiment of a platform lift system that is movable along a monorail  901 . The monorail  901  is coupled to the ceiling  958  using periodic mounting brackets  902  that are spaced along a travel path. A platform lift system includes a platform frame  911  having brackets  903  holding roller wheels  971 . The monorail  902  includes a track that engages the roller wheels  971 , enabling the platform frame  911  to be transported along the travel path. As in the foregoing embodiments, the platform frame  911  supports a platform that is lifted using belts. This way, an object could be picked up using the platform and transported anywhere along the travel path. Alternatively, the platform frame  911  may not include a platform, but rather the lift belts would directly engage an object to be transported, such as a wheelchair or gurney within a hospital.  
         [0082]      FIG. 37  illustrates another alternative embodiment of a platform lift system having an expandable frame assembly. The expandable frame assembly enables the lift platform of the present invention to be modified to accommodate any size load. The frame assembly includes a frame formed from tubular sections  1068 ,  1067 ,  1069 , and  1070 . The tubular sections are telescoping such that end sections  1070  are movable within vertical sections  1068  to change the length dimension of the frame, and sections  1067  are movable over horizontal sections  1068 ,  1069  to change the width dimension of the frame. Locking screws  1074  rigidly fix the sections in place after a desired frame shape is selected. The frame assembly carries a sling  1073  that is connected to the frame using quick-disconnect latches  1072 .. The entire frame assembly may be raised or lowered using a platform lift system as described in the previous embodiments.  
         [0083]      FIG. 38  illustrates another alternative embodiment of a platform lift system used in connection with an overhead rail. Transverse frame tracks  1075  are suspended from a ceiling  1162  of an interior structure, such as a garage. A movable track segment  1059  extends between the transverse frame tracks  1075  and is movable along the transverse frame tracks using rollers. A platform lift system is movable on the movable track segment  1059  such that the platform lift system could be moved to any position within a space bounded by the transverse frame tracks  1075 . The platform lift system could lift any sized object, such as using the expandable frame assembly of  FIG. 37 .  
         [0084]      FIGS. 39 through 41  illustrate an alternative embodiment of the drop down storage system of  FIGS. 12 and 13  used to lift a compartment  1060 .. The compartment  1060  may include a hingedly attached gate  1078 . The compartment  1060  may be suitable to transport a wheelchair.  
         [0085]     Having thus described a preferred embodiment of a platform lift system, it should be apparent to those skilled in the art that certain advantages of the described system have been achieved. It should also be appreciated that various modifications, adaptations, and alternative embodiments thereof may be made within the scope and spirit of the present invention.