Abstract:
Apparatus for raising and lowering objects. In accordance with some embodiments, a winch motor is adapted to rotate a winch member in opposing first and second directions to wrap/unwrap a portion of a cable on/from the winch member to raise and lower a lifting platform assembly, respectively. A tension detection switch assembly includes an on/off switch connected to the winch motor and a biasing member which exerts a bias force upon the winch member to nominally deflect the winch member to a first position which sets the switch to deactivate the winch motor in an absence of tension in the cable from the lifting platform assembly. A presence of tension in the cable from the lifting platform assembly deflects the winch member to a second position which sets the switch to facilitate activation of the winch motor.

Description:
RELATED APPLICATIONS 
     The present application is a continuation of co-pending parent U.S. application Ser. No. 11/732,282 filed Apr. 3, 2007, which in turn makes a claim of domestic priority under 35 U.S.C. 119(e) to U.S. Provisional Application No. 60/788,660 filed Apr. 3, 2006. 
    
    
     BACKGROUND 
     The present disclosure relates generally to the field of lifting systems used to raise and lower objects and more particularly, but not by way of limitation, to a lifting system configured to raise and lower objects to and from an attic for storage of objects therein, for example in a building such as a residential structure. 
     The need to move storage items up stairs or ladders to a second level floor in a home, such as an attic floor or second floor living space, is common among home owners. As stairs are narrow and steep, moving large or heavy boxes and other bulky items up stairs presents a difficult and often dangerous task. 
     Home owners commonly store seasonal items in their attic to save space in their garages or closets. Seasonal items, including items like artificial Christmas trees, wreaths, wrapping paper, holiday lights, yard decorations, candles, garlands, centerpieces and dishes, to name a few, are all desirable to store out of sight in the attic until the next seasonal use. Other storage items include hobby supplies, keepsakes, seasonal clothing, seasonal sporting goods like skis, sleds, and hunting gear, for example. 
     It has become common practice to install flooring in the attic space to provide a place to store these items. The problem that has long existed is that attic storage space is normally accessible only by a fold-down ladder (which is often flimsy or unstable) or stairway that is both steep and narrow and sometimes slick. Climbing one of these ladders is dangerous enough with both hands free. Trying to carry boxes and other heavy or bulky items up or down is virtually impossible to do and usually requires two persons: one pushing from below and the other pulling from above. The person above must try to back up the ladder while using both hands to pull the storage item. This is extremely dangerous and can result in serious accidental injury. The consumer Products Safety Commission reports, “Each year there are over 164,000 emergency room-treated injuries in the U.S. relating to ladders.” Undoubtedly, some portion of this number involves injuries obtained while using attic ladders. 
     For these reasons there has been a longstanding need for a way for home owners to safely move or retrieve storage items to or from a second level (such as an attic, second floor, or basement) without lifting or carrying them up or down stairs or ladders. One solution is to install an elevator in the home. However, elevators are complex devices that must be installed by skilled engineers, electricians and contractors and are therefore very expensive. The cost is too high to be afforded by the average home owner. 
     In particular, there are a number of specific problems associated with the lift systems of the prior art which are encountered by the users of such systems. These are identified below and bear on issues of safety, affordability, effectiveness, simplicity, and installability.
         1. Prior art lift systems often require an excessive amount of skilled labor to install. Often, installation requires hiring an electrician to install special wiring, which can be costly. The systems often require specially trained persons to make custom modifications to the apparatus to fit each individual installation.   2. Prior art systems are seldom readily adaptable to a wide variety of ceiling heights, and rafter (joist) dimensions. Home ceilings typically range from 8 to 11 feet high, even 15 feet high, especially in the garage. Ceiling joists range from 2×4 inches to 2×12 inches in lumber and from 2×14 inches to 2×36 inches in fabricated joists and laminated beams, thus causing wide variation in the thickness of the ceiling opening that the lift device must be adapted to fit through.   3. Prior art systems often require roller guide tracks, telescoping columns, rails or other expensive and cumbersome guide means. Telescoping columns are inherently costly. Guide track and rails are also costly as well as unsightly. These devices are not readily adaptable to widely different ceiling heights and other structural variations and often require the device to be custom built or to be specifically modified to fit each particular installation.   4. Prior art systems lacking such guide means, however, cannot reliably guide themselves and the maximum load into and out of the ceiling opening. The platform assembly of the prior art systems often incur misalignment between the ceiling opening and the platform assembly when loaded to capacity so that the platform or cargo thereon catches on the edge of the ceiling opening and cannot pass through the opening.   5. Systems of the prior art are often not completely installable with ordinary tools and often do not include a reliable means to adjust the length of the cables for each installation using ordinary tools. Typically, cables used in these systems must be modified to have permanently swaged sleeves forming loops at each end and are not adjustable. It requires special tools to swage sleeves or lugs for lifting applications. These systems do not include a secure and easily adjustable means to connect the cables which depends only ordinary tools common to home owners.   6. Most prior art systems leave the opening in the ceiling open whenever it is not in use (in the raised position). This is esthetically unpleasing and leads to loss of heating or cooling into the attic space, and allows access by unwanted entry of insects and small animals from the attic space into the home.   7. Other prior art systems that close the opening in the ceiling do not elevate the storage items level with the floor above the opening and would require lifting of the storage items manually merely to remove them from the platform and onto the floor surface or vice versa. The home owner is then required to lift each storage item out of (or lower each storage item into) a recessed hole in the upper floor that can very in depth from a few inches to over 2 feet, depending on the joist height and ceiling thickness as previously discussed. This increases the chance of back injuries, and is inconvenient to the home owner, substantially reducing the usefulness of such a lifting device.   8. Prior art systems often provide unstable lifting platforms thus rendering them less capable of safely lifting a variety of objects of different sizes and weights. For example the lifting platform of these systems is often designed in such a way to increase the risk of becoming top heavy when loaded with large objects, creating a potential hazard of tipping over and spilling the load off of the platform.   9. Systems of the prior art may not stop automatically when raised to the highest position, sometimes causing the system to be stressed or jammed when it reaches the uppermost limit of its travel. Similarly these systems may not automatically stop as close to level (flush) with the attic floor as possible, unless the operator releases the switch at an exactly optimal instant. Devices of the prior art systems used to stop the upward travel of the platform usually require user intervention or must be preset by a trained installer.   10. The prior art systems generally do not stop automatically when lowered to the lowest (floor) position and the platform often comes into contact with the lower floor abruptly so that the motor may not stop instantly, allowing the cable (or other connecting means) to continue to spool out. This can lead to tangling or fouling and may leave the cable requiring repair. Systems which do have automatic downward stopping mechanisms require a mechanism of considerable complexity and expense due to the necessity of routing wires to a moving platform or employing a wireless remote switching device and may require installation and setting by a trained installer.   11. Typically, in prior art systems, if the platform assembly becomes lodged or caught in the ceiling opening when traveling downward, motor action of the apparatus is not immediately stopped. This causes a vitally unsafe situation. If the platform becomes lodged while the cable continues to pay out the cables will accumulate slack, possibly becoming fouled or jammed. Then if the platform is dislodged while the cables are slack, it can free-fall some distance from the opening, possibly spilling the load or even breaking the cable, causing costly damage and possible serious personal injury.   12. The platform assembly of prior art systems tend to flip over and thereby spill the load whenever one of the cables becomes jammed while the other cables continue to pay out. If this occurs, costly damage and serious personal injury is possible.   13. Many prior art systems do not include a momentary switch for safety so that the lifting mechanism will stop immediately when the switch is released by the operator and do not include a security locking device to prevent unauthorized use, for example, by children.   14. Systems which are installed where the upper floor is a living space occupied by or accessible to small children, often leave the opening in the upper floor open when the platform is lowered, potentially allowing a person or child to inadvertently step or fall through the opening to the floor below likely suffering serious injury or death.   15. Prior art systems are often too costly to be affordable to the average home owner, while still meeting the stated minimum needs and requirements and may be unnecessarily complex thereby adding cost without adding benefits or usefulness.       

     As indicated above, a variety of mechanical lifting systems have been proposed in the prior art, but all have shortcomings, problems, and disadvantages. A number of prior art systems require tracks or telescoping columns to guide the platform and would be inherently complex and costly while not readily adapting to different heights and locations. Other propose controlling the lifting platform using only cables to provide support and stability. This arrangement will support vertical loads but lacks dynamic stability. Large loads on such systems will inherently become unstable if the platform becomes tipped due to an obstruction or any fouling or jamming of one of the supporting cables. Once the platform and load thereon become unbalanced, the platform could flip completely over, dumping the load. This is because cables or tethers can resist downward forces but cannot resist the upward forces created by an unbalanced platform. In addition to the balance problem, supporting the platform directly with four cable attachment points as taught in the prior art, leaves another important safety problem unsolved. Such a cable attachment configuration naturally allow some swaying of the lifting platform as it moves upward. 
     When the platform carries a load that approaches the maximum load dimensions, then any swaying of the upwardly moving platform can allow misalignment of the load and the ceiling opening. When this occurs, the load and platform can become jammed or the load spilled. In order to provide adequate lifting platform stability or guidance of the load into the ceiling opening, the prior art systems require telescoping columns, tracks or rails or the like. 
     While some of the prior art systems make vague references to limit switches that would stop the lifting platform when it reaches the lower floor, none have provided a specific solution to the problem of how to implement these lower limit switches while suitably managing the associated wiring. For example, Penn suggests placing limit switches in the underside of the lifting platform in one application and in another application he suggests putting them at the bottom of a folding ladder having tracks to guide the platform. Penn fails to demonstrate a plausible means to connect the switches in the underside of the movable platform with the drive mechanism above. Penn also fails to show how to mount a switch on the lowest end of a folding ladder and how to safely manage the wiring through a series of joints in the ladder that fold and could pinch or cut the wires. Both of these approaches would be inherently problematic, difficult and costly to implement. 
     The prior art systems also leave open the opening in the ceiling after raising the loaded platform level with the upper floor. Also, the platforms of the prior art systems often leave the raised, loaded platform substantially below the upper floor surface, causing the user to lean over the opening and lift out the storage items. This could be difficult and dangerous with heavy items. Most recently or newly constructed garages use fabricated joists to support large ceilings without support columns in double and triple car garages. These joists are typically 16 inches to 24 inches tall. The platforms of the prior art systems are made as low as possible for easy loading on the lower floor, but require loads to be lifted out of recesses 12 inches to 20 inches deep on the upper floor where 16-24 inch joists have been used. Conversely if the platform in the prior art system is built to be tall enough to reach the upper floor when raised, then the platform would be 16 inches to 24 inches high when resting on the lower floor. That would require the user to do much lifting to load and unload the elevated platform causing much inconvenience to the home owner while increasing the risk of back injury. 
     Further, none of the prior art systems has provided a practical means to automatically halt the apparatus in the event the platform assembly becomes jammed or lodged in the ceiling opening while descending. Moreover, none of the prior art has provided a practical means to automatically halt the apparatus in the event one cable should become jammed or fouled while the platform is descending. 
     It is to providing a lifting and closure system which solves these problems and deficiencies that the present disclosure is directed. 
     SUMMARY 
     Various embodiments of the present disclosure are generally directed to a lifting system suitable for use in safely and securely lifting/lowering an object between a lower floor surface and an upper floor surface. 
     In accordance with some embodiments, a winch motor is adapted to rotate a winch member in opposing first and second directions to wrap/unwrap a portion of a cable on/from the winch member to raise and lower a lifting platform assembly, respectively. 
     A tension detection switch assembly includes an on/off switch connected to the winch motor and a biasing member which exerts a bias force upon the winch member to nominally deflect the winch member to a first position which sets the switch to deactivate the winch motor in an absence of tension in the cable from the lifting platform assembly. A presence of tension in the cable from the lifting platform assembly deflects the winch member to a second position which sets the switch to facilitate activation of the winch motor. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows a perspective view of a lifting system constructed and operated in accordance with the present invention, wherein the lifting system is in a lowered position. 
         FIG. 2  shows the lifting and closure system of  FIG. 1  in a partially raised configuration. 
         FIG. 3  shows the lifting system of  FIG. 1  in a fully raised position. 
         FIG. 4  is a perspective view of a platform assembly of the system of  FIGS. 1-3 . 
         FIG. 5  is a perspective view of a support and drive assembly of the system of  FIGS. 1-3 . 
         FIG. 6  shows an end view of the lifting system of  FIGS. 1-3  with a lifting platform (upper platform) thereof supported on a lower floor surface, such as in a garage. 
         FIG. 7  shows a partial side view of the platform assembly of  FIG. 6 . 
         FIG. 8  shows a side view of the lifting system of  FIG. 6 . 
         FIG. 9  shows an end view of the lifting system of  FIG. 1  with the platform system raised and aligned with an upper floor surface, such as in an attic over a garage. 
         FIG. 10  shows a partial side view of the platform assembly of  FIG. 9  in the raised position. 
         FIG. 11  shows a side view of the lifting system as shown in  FIG. 9 . 
         FIGS. 12A and 12B  show side and end views, respectively, of an embodiment of the present invention having an alternate biasing mechanism when the platform assembly is in a raised position. 
         FIGS. 13A and 13B  shown side and end views of the biasing mechanism of  FIGS. 12A and 12B  when the platform assembly is in a lowered position. 
         FIGS. 14A and 14B  show side and end views, respectively, of an alternate embodiment of the invention having a biasing mechanism comprising a constant force spring, wherein the platform assembly is in a raised position. 
         FIGS. 15A and 15B  show side and end views, respectively, of the embodiment of  FIGS. 14A and 14B  when the platform assembly is in a lowered position. 
         FIG. 16  shows an end view of a lifting system of the present invention which utilizes a portal closure door wherein the portal closure door is in a raised position. 
         FIG. 17  is an end view of the embodiment of  FIG. 16  wherein the portal closure door is in a partially lowered position. 
         FIG. 18  is an end view of the embodiment of  FIG. 16  wherein the portal closure door is in a fully lowered position and rests against an attic floor. 
         FIGS. 19A and 19B  are fragmentary views of a cable clamping system of the present invention. 
         FIG. 20  is a perspective view of a control module of the present invention. 
         FIG. 21  is a bottom perspective view of a drive assembly of the present invention. 
         FIG. 22  is an end view of the drive assembly of  FIG. 21 . 
         FIG. 23  is a side view taken through the drive assembly of  FIG. 21 . 
         FIG. 24  is a side view of an alternate embodiment of the drive assembly of the present invention. 
         FIG. 25  is a perspective view of a platform assembly of the present invention which has sidewalls. 
         FIG. 26  is a perspective view of a platform assembly of the present invention having sidewalls, a back wall and a front door assembly. 
         FIG. 27  is an isometric view of a prior art lifting system in a swaying condition. 
         FIG. 28  is an isometric view of a prior art lifting system in a tilted condition. 
         FIG. 29  is a side view of the lifting system of the present invention showing the platform assembly swaying end to end. 
         FIG. 30  is a side view of the lifting system of the present invention showing the platform assembly swaying side to side. 
         FIG. 31  is a perspective view of a platform assembly of the present invention indicating the cargo maximum center of gravity in relation to the points of attachment of the cable arms. 
         FIG. 32  is a side view of the present invention showing the platform assembly in an unbalanced state, hanging by a single cable arm. 
         FIG. 33  is a side view of the present invention showing the platform assembly in an unbalanced state, hanging by the alternate cable arm. 
         FIG. 34  is a side view of an alternate embodiment of the platform frame of the present invention. 
         FIG. 35  is a side view of an alternate embodiment of the platform frame of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments set forth herein are generally directed to a storage lifting system suitable for use in safely and securely lifting an object from a lower floor surface to an upper floor surface and/or lowering an object from the upper surface to the lower floor surface. 
     One embodiment of the lifting system of the present invention is shown in  FIGS. 1-11  and is designated therein by the general reference numeral  10 . The lifting system  10  preferably comprises two main components which are operatively connected: a support and drive assembly  12 , and a movable platform assembly  14 . Preferably the lifting system  10  is not integrally associated with a retractable ladder system. 
     For purposes of disclosing a particular environment in which the lifting system  10  can be advantageously used,  FIG. 1  shows selected interior portions of a residential structure  16  having a garage  18  and an attic  20  above the garage  18 . The garage  18  has a garage floor  22  and a ceiling  24 . The attic  20  has an attic floor  26  and a portal  28 , having a portal depth  28   a , an upper entrance  29   a , and a lower entrance  29   b,  positioned between and extending completely through the ceiling  24  to the attic floor  26  which allows access to the attic  20  from the garage  18  and through which the movable platform assembly  14  is raised into the attic  20  and lowered to the garage floor  22  as described below in greater detail. 
     The lifting system  10  is configured to move cargo items including objects such as boxes, trunks, barrels, containers, building materials, equipment, or even persons or animals, from the garage floor  22  of the garage  18  to the attic floor  26  of the attic  20 , and vice versa, although it will be appreciated that the lifting system  10  can readily be used to transfer cargo items or persons or animals from locations other than a garage and can be used in other environments as long as there are two separate spaces separated by a floor, ceiling, or other such support structure. For example, the invention can be used to carry objects into a stilted home from below the stilted home, and as an elevator to provide human transport from a lower floor to an upper residential floor, and can be used as well in non-residential applications such as in a manufacturing facility or the like. A typical item for transport is a cargo item  46  (e.g., see  FIG. 6 ), which may be for example a box, trunk or luggage, or any other object desired to be transferred in the manner contemplated herein. In general, the lifting system  10  can be employed to move cargo items  46  between any two adjacent levels in a residence, including the basement level, the ground level, any higher level above ground level, the attic  20 , the garage  18  and outdoor levels like decks, balconies, and even rooftops. 
     The movable platform assembly  14  in a preferred embodiment comprises a closure (lower) platform  30  (for portal closure) and a lifting (upper) platform  32  (for lifting and support), and a platform frame  34  to which both the closure platform  30  and lifting platform  32  are connected, either directly or indirectly. In a key feature of the invention, when the lifting system has a closure platform  30 , the platform assembly  14  further comprises a biasing mechanism  35  which provides a biasing force for adjusting the position of the closure platform  30  relative to the position of the lifting platform  32  in a manner described in more detail below. 
     The support and drive assembly  12  comprises a support frame  36  and a drive mechanism  38 . In a preferred embodiment, the drive mechanism  38  is connected to the support frame  36  and is supported thereby over the attic floor  26  and over the portal  28  in a position above the platform assembly  14 . The drive mechanism  38  may alternately be attached directly to a portion of the attic floor  26 , or to a roof over the attic  20  rather than to the support frame  36 . A cable (also referred to herein as a tether, strand or webbing)  40  is connected to and extends from the drive mechanism  38  of the support and drive assembly  12  to the platform frame  34  of the platform assembly  14 . The support and drive assembly  12  is thereby engagingly connected to the platform assembly  14  via the cable  40  (which may be made of wire, cable, plastic, rope, webbing or any other suitable material). As noted, cable  40  may also be referred to herein as a tether. 
       FIGS. 1 ,  4 ,  6 ,  7  and  8  show the lifting system  10  in a lowered position wherein the platform assembly  14  is resting on the garage floor  22 , either after the cargo item  46  has been placed on the lifting platform  32  for lifting or after the cargo item  46  has been removed therefrom after lowering.  FIG. 2  shows the lifting system  10  in operation, wherein the platform assembly  14  is suspended in an intermediate position between the garage floor  22  and the ceiling  24 .  FIGS. 3 ,  9 ,  10  and  11  show the lifting system  10  in a raised position wherein the platform assembly  14  has been raised through the portal  28  so the lifting platform  32  is substantially flush with the attic floor  26  and the upper entrance  29   a  and portal attic floor edge  29   d , and the closure platform  30  abuts the ceiling  24  thereby closing the lower entrance  29   b.    
     As is evident from the description herein and particularly  FIGS. 3 ,  9 ,  10  and  11 , it can be seen that two of the main platform components of the platform assembly  14 , i.e., the closure platform  30  and the lifting platform  32 , function substantially independently and have separate purposes. The function of the lifting platform  32  is to support and carry cargo items  46  up to the attic  20  for storage therein, or for delivery of cargo items  46  from the attic  20  to the garage floor  22  (or other similar surface in a room or enclosure below the attic  20  or other such area, such as a second floor at a home). The function of the closure platform  30  is to act as a door or cover which contactingly engages and abuts the ceiling  24  and closes the lower entrance  29   b  of the portal  28  where it opens into the ceiling  24 . Closure of the lower entrance  29   b  of the portal  28  in this way provides a number of benefits, including but not limited to, (1) substantially preventing movement of heat and/or cooled air from the attic  20  to the garage  18  and vice versa, thereby maintaining the insulative capacity of the ceiling  24 , (2) preventing debris from falling through the portal  28  from the attic  20  into the garage  18 , (3) preventing small animals and insects from gaining entrance to the attic  20  or garage  18  via an open portal  28 , and (4) concealing a visible aperture (lower entrance  29   b ) in the ceiling  24  when the lifting platform  32  is in a fully raised position thus cosmetically improving the appearance of the ceiling  24 . Furthermore, as will be explained in more detail below, in the raised position of the platform assembly  14 , the distance between the lifting platform  32  and the closure platform  30  is automatically adjustable due to the action of the biasing mechanism  35  thereby enabling the closure platform  30  to self-adjust to the portal depth  28   a  (the vertical distance between the attic floor  26  (i.e., upper surface) and the ceiling  24  (i.e., lower surface)) in the portal  28  in a site-specific and situational manner, thereby enabling secure closure of the portal  28  by the closure platform  30  in virtually any circumstance. As will be understood, the present invention differs from some prior art systems in that the door or platform which closes the lower opening  29   b  of the portal  28  is not connected to the ceiling  24 , but rather is independent of the ceiling  24 . 
     Referring now to the platform assembly  14  as shown in  FIG. 4 , in one embodiment, the closure platform  30  has a first end  50 , a second end  52  which opposes the first end  50 , a first side  54 , a second side  56  which opposes the first side  54 , an outer peripheral edge  58  which extends about the circumference of the closure platform  30 , an upper surface  60 , and a lower surface  62 . Similarly, the lifting platform  32  has a first end  64 , a second end  66  which opposes the first end  64 , a first side  68 , a second side  70  which opposes the first side  68 , an outer peripheral edge  72  which extends about the circumference of the lifting platform  32 , an upper surface  74 , and lower surface  76 . 
     The platform assembly  14  is preferably configured so that the lifting platform  32  is as close as practical to the garage floor  22  when in the lowered position as shown in  FIGS. 1 ,  4 ,  6 ,  7  and  8 . 
     The platform frame  34  in this embodiment (e.g.,  FIG. 4 ) is constructed of a first end frame  80  having a first leg  82  having an upper end  84  and a lower end  86 , a second leg  88  having an upper end  90  and a lower end  92 , and a first side frame connector  94  which connects the upper end  84  of the first leg  82  to the upper end  90  of the second leg  88 . The platform frame  34  is also constructed of a second end frame  80   a  which has a first leg  82   a  having an upper end  84   a  and a lower end  86   a , a second leg  88   a  having an upper end  90   a  and a lower end  92   a , and a second side frame connector  94   a  which connects the upper end  84   a  of the first leg  82   a  to the upper end  90   a  of the second leg  88   a . In a preferred embodiment the platform frame  34  optionally comprises a reinforcing cross bar  96  having a first end  98  and a second end  100 , wherein the first end  98  is connected to the first side frame connecter  94  and the second end  100  is connected to the second side frame connector  94   a . The platform frame  34  is optionally enclosed with a removable chain, strap, band, webbing, net or tether  97  or other such barrier device such as a sidewall (discussed in further detail below). The platform frame  34  is constructed of any suitable material which has the strength and stability required to support operation of the present invention and may include metals such as aluminum, steel and titanium and/or thermoplastic polymeric materials, or other carbon-based materials such as graphite or composite materials or wood. It will be apparent to a person of ordinary skill in the art that the first end frame  80  and second end frame  80   a  could each be of unitary construction wherein the first and second legs  82 ,  88  and the associated connector  94 , for example, could be made in one piece, such as by sheet metal stamping, die cast metal, molded thermoplastic polymer, wood or other suitable construction. In any event, each first leg  82  and second leg  88  is connected at or near first end  64  of the lifting platform  32  and each first leg  82   a  and second leg  88   a  is connected at or near second end  66  of the lifting platform  32 . 
     As indicated above, both the closure platform  30  and the lifting platform  32  are connected to the platform frame  34 . The lifting platform  32  preferably is rigidly connected to the platform frame  34 , directly by screws, bolts, clamps, or other fastening devices for example, such that the first end frame  80  is connected to or adjacent the first end  64  (or first side  68 ), and the second end frame  80   a  is connected to or adjacent the second end  66  (or second side  70 ) wherein the first end frame  80  and second end frame  80   a  face and oppose each other. Alternatively an lifting platform support assembly  101  may be connected to the platform frame  34 , and the lifting platform  32  connected to the lifting platform support assembly  101 , wherein the lifting platform  32  is attached indirectly to the platform frame  34  via the lifting platform support assembly  101 , rather than directly. 
     The first end frame  80  and second end frame  80   a  may be connected to or are adjacent to portions of the outer peripheral edge  72  of the lifting platform  32  wherein the lower end  86  of the first leg  82 , the lower end  92  of the second leg  88 , the lower end  86   a  of the first leg  82   a , and the lower end  92   a  of the second leg  88   a  are exposed and downwardly oriented. In one embodiment, at least a lower portion of each leg  82 ,  88 ,  82   a  and  88   a  is hollow for containing a portion of the biasing mechanism  35 . Preferably an upper portion of the first end frame  80  is slanted inwardly toward the cable attachment points forming a first end converging portion  95 , and an upper portion of the second end frame  80   a  is slanted inwardly forming a second end converging portion  95   a . First end converging portion  95  has a first end frame apex  136  and second end converging portion  95   a  has a second end frame apex  138 . 
     In the embodiment of  FIGS. 1-11 , the biasing mechanism  35  comprises a plurality of individual coiled tension springs comprising biasing springs  102   a ,  102   b,    102   c  and  102   d , each of which has a first end  104   a ,  104   b ,  104   c  and  104   d , respectively, which is attached to or substantially contained within the leg  82 ,  88 ,  82   a  and  88   a,  respectively, and a second end  106   a ,  106   b ,  106   c  and  106   d  which protrudes from or extends from the leg  82 ,  88 ,  82   a  and  88   a , respectively. The protruding second ends  106   a - 106   d , each are attached via a fastening device  108   a - 108   d , respectively, to the closure platform  30  of the platform assembly  14 . When the biasing springs  102   a - 102   d  are fully retracted within each leg  82 ,  88 ,  82   a  and  88   a , respectively, the closure platform  30  is urged (biased) in a fully retracted position such that the closure platform  30  is substantially adjacent to the lifting platform  32  ( FIGS. 1 ,  4 ,  6 ,  7  and  8 ). The closure platform  30  is usually in the fully retracted position when the platform assembly  14  is resting on the garage floor  22  in preparation for loading items onto or unloading items from the lifting platform  32  as shown in  FIGS. 1 ,  4 ,  6 ,  7  and  8 , or when the platform assembly  14  is in a partially elevated (raised) position (as shown in  FIG. 2 ) before the closure platform  30  engages the ceiling  24 . When the platform assembly  14  is raised such that the lifting platform  32  is lifted through the portal  28  into the raised position as shown in  FIGS. 3 ,  9 ,  10  and  11 , the closure platform  30  engages and abuts the ceiling  24  and the biasing springs  102   a - 102   d  of the biasing mechanism  35  are extended under tension such that the biasing springs  102   a - 102   d  urge the closure platform  30  against the ceiling  24  as the lifting platform  32  is raised into an attic loading or attic unloading position wherein the closure platform  30  fits against and abuts the ceiling  24  thereby stopping further upward advancement of the closure platform  30  and closing the lower entrance  29   b  of the portal  28  in accordance with the present invention. 
     As the lifting platform  32  and platform frame  34  of the platform assembly  14  are raised through the portal  28 , the upwardly directed force supplied by the cable  40  will overcome the biasing force supplied by the biasing springs  102   a - 102   d  of the biasing mechanism  35  so that distal separation will occur between the closure platform  30  and the lifting platform  32 . In other words, the biasing mechanism  35  will enable continued upward movement of the lifting platform  32  while retaining the closure platform  30  in place under tension against the ceiling  24 . In this embodiment, the biasing springs  102   a - 102   d  will telescope out of the legs  82 ,  88 ,  82   a  and  88   a,  respectively during this operation, as shown in  FIGS. 3 ,  9 ,  10  and  11 . The upper surface  60  of the closure platform  30  may have a gasket (not shown) which lines the outer peripheral edge  58  of the upper surface  60  for engaging the ceiling  24  for forming a more tight fit therebetween. While it is shown herein that the coiled springs  102   a - 102   d  are substantially enclosed within the legs  82 ,  88 ,  82   a , and  88   a  in the foregoing preferred embodiment, other embodiments are also contemplated wherein the coiled springs  102   a - 102   d  are outside of, partially enclosed by, adjacent-to, or parallel-to, the legs  82 ,  88 ,  82   a , and  88   a , yet still connected to the frame  34  at their upper ends  104   a - 104   d  and to the closure platform  30  at their lower ends  106   a - 106   d.    
     The presence of the biasing mechanism  35 , a novel feature of the present invention, allows the final elevational height of the lifting platform  32  to be set independently of the elevational height of the closure platform  30  (at least to the extent allowed by the extendability of the biasing springs  102   a - 102   d ). Preferably, the lifting platform  32  is raised until such time that the upper surface  74  of the lifting platform  32  is substantially even (flush) with the elevation of the attic floor  26 . This advantageously allows the user to easily slide or otherwise move the cargo items  46  laterally from the lifting platform  32  and onto the attic floor  26 , or alternatively from the attic floor  26  to the lifting platform  32 . It is therefore generally unnecessary for the user, as in prior art systems, to step onto or otherwise reach down into the portal  28  below the level of the attic floor  26  in order to access the cargo item  46  on the lifting platform  32 , or to lift the cargo item  46  up and over one or more platform obstructions (e.g., rims) to remove the cargo item  46  therefrom. Substantially heavier and bulkier loads can thus be readily accommodated by the platform assembly  14 . 
     As previously noted, the support and drive assembly  12  comprises a support frame  36  and a drive mechanism  38 . As shown in  FIG. 5 , in one embodiment, the support frame  36  is constructed of a first end frame  110  having at least a first leg  112  (which may be of unitary construction) having an upper end  114  and a lower end  116 , and second leg  118  (which may be of unitary construction) having an upper end  120  and a lower end  122 . The support frame  36  is also constructed of a second end frame  110   a  which has at least a first leg  112   a  (which may be of unitary construction) having an upper end  114   a  and a lower end  116   a , and a second leg  118   a  (which may be of unitary construction) having an upper end  120   a  and a lower end  122   a . It is also contemplated herein that the first end frame  110  and second end frame  110   a  can each be of unitary construction wherein, for example, the first and second legs  112 ,  114 , and optionally the floor rail  124 , can be made in one piece, such as by sheet metal stamping, die cast metal, molded thermoplastic polymer, wood or other suitable construction. 
     The support frame  36  is constructed of any suitable material which has the strength and stability required to support operation of the present invention and may include metals such as aluminum, steel and titanium and/or thermoplastic polymeric materials, or carbon-based materials such as graphite or composite materials or even wood. In an alternate embodiment, first leg  112  and second leg  118  of first end frame  110  each may be of non-unitary construction, i.e., constructed from more than one element, and first leg  112   a  and second leg  118   a  of second side frame  110   a  each may also be non-unitary of non-unitary construction, as noted above. In any event each first leg  112  and  112   a  and second leg  118  and  118   a  is, in one embodiment, attached to a floor rail assembly  124  which is securely attached to the attic floor  26  adjacent to the portal  28  (e.g.,  FIGS. 5 ,  6 , and  8 - 11 ). Alternatively, each leg  112 ,  112   a ,  118 , and  118   a  may be individually directly attached to the attic floor  26 . The function of the support frame  36  is to support the drive mechanism  38  in a position in the attic  20  above the portal  28 . 
     As shown in  FIG. 5 , the support frame  36  optionally further comprises a plurality of spacers  126  which may be attached either to the legs  112 ,  112   a ,  118  and  118   a  near the lower ends  116 ,  116   a ,  122 , and  122   a  thereof, respectively, or, as shown in  FIG. 5 , to portions of the floor rail assembly  124  in positions near the floor  26  and adjacent the legs  112 ,  112   a ,  118 , and  118   a  of the support frame  36 . The spacers  126  are preferably constructed of a durable yet smooth material such as nylon or other thermo-plastic material, or metal. The spacers  126  are preferably attached such that they are able to roll when exposed to a surface pressure and function to maintain separation between the platform frame  34  and the portal attic floor edge  29   d  and the support frame  36 , and to properly align, guide and center the platform frame  34  within the portal  28  as shown for example in  FIGS. 9 ,  10 ,  12 B,  14 B,  16  and  17 . 
     As shown in  FIGS. 11 and 21 , the drive mechanism  38  is constructed of a winch housing  130  transversely connected at one end to the first end frame  110  and at an other end to second end frame  110   a  of the support frame  36 . A winch tube assembly  132  extends longitudinally within the winch housing  130  and is operatively connected to a winch motor  134  which causes rotation of the winch tube assembly  132  for raising and lowering the cable  40  which is attached to the winch tube assembly  132 . 
     Any number of suitable motors are commercially available for use as the winch motor  134 . One particularly suitable motor is Electric Hoist Motor Model 40765 by Chicago Electric, Inc., which has a rated lifting capacity of 250 lbs. 
     The cable  40  (also referred to herein as a tether) has a first cable arm  42  (also referred to herein as tether arm  42 ) and a second cable arm  44  (also referred to herein as tether arm  44 ) (e.g., see  FIGS. 1 ,  2 ,  4 ,  5 ,  8 ,  21 ) which are coupled to the movable platform assembly  14  and which extend from the winch tube assembly  132 . A center portion of the cable  40  is preferably secured to the winch tube assembly  132  at a medial position thereof (as shown in more detail in  FIG. 21 ), and first cable arm  42  and second cable arm  44  of the cable  40  each extends from the winch tube assembly  132  downwardly, where the first cable arm  42  is attached to the first side frame connector  94  of the first side frame  80 , and the second cable arm  44  is attached to the second side frame connector  94   a  of the second side frame  80   a.    
     As shown in  FIGS. 8 and 11 , each first cable arm  42  and second cable arm  44  of cable  40  preferably extends at a slightly off-vertical angle with respect to vertical when the platform assembly  14  is in the lowermost position. As the winch tube assembly  132  is rotated, the cable  40  wraps about the winch tube assembly  132  thereby raising the first cable arm  42  and second cable arm  44  of the cable  40  and the platform assembly  14 . In this way, the off-vertical angle approximates the winding pitch of the cable  40  on the winch tube  132  as the platform assembly  14  is raised, and the first cable arm  42  and second cable arm  44  of cable  40  will be either vertically aligned or remain off-vertical when the platform assembly  14  is in an uppermost position. This cable configuration advantageously reduces the likelihood that rubbing contact will occur between portions of the cable  40  and edge portions of the portal  28  and enhances level winding of the cable  40  onto the winch tube  132 . 
     While the platform assembly  14  is preferably only supported by the cable  40  at two opposing ends of the platform assembly  14 , stability is nevertheless enhanced due to the configuration of the platform frame  34  with respect to the length and width dimensions of the lifting platform  32  of the platform assembly  14 . 
     More specifically, the upwardly directed forces supplied by the cable  40  are transferred to the first end  64  and second end  66  of the lifting platform  32 . Thus, even if the center of gravity of the cargo item  46  is significantly offset from a centerline of the lifting platform  32 , it is contemplated that relatively little tilting of the lifting platform  32  will take place as the lifting platform  32  is raised. 
     The platform frame  34  is preferably configured to engage a portal ceiling edge  29   c  of the portal  28  to correct any twisting or other misalignments of the lifting platform  32  as it is raised, thereby ensuring that the platform assembly  14  is guided properly into the portal  28  in the upright position shown in  FIGS. 3 ,  9 ,  10  and  11 . Thus, to the extent that any tilting or other misalignment of the platform assembly  14  occurs during lifting, such will be corrected as the platform frame  34  enters the portal  28 , providing alignment before the cargo  46  and the lifting platform  32  enter the portal  28 . 
     Another advantage of the platform frame  34  of the present invention is that the legs  82 ,  88 ,  82   a  and  88   a  stabilize the lifting platform  32  against both upward and downward relative motion of the respective corners of the lifting platform  32 . For example, in an apparatus wherein four separate cables are attached directly to a platform with one at each corner (as in the prior art), it can be readily seen that each of said corners would be secured against downward motion due to the respective tension in the associated cable. However, if an event occurred during lifting of such a 4-cable platform, such as a shift in the center of gravity of the cargo or an obstruction such as with the ceiling surface, there may be nothing to prevent one side of the prior art platform from rising (i.e., advancing upwardly faster than the draw rate of the associated cables) and causing the platform to undergo a tilt to substantially vertical orientation, thereby allowing the cargo to fall off the 4-cable platform. Further, if one cable becomes fouled, tangled, or jammed while the 4-cable platform is being lowered, then one corner would be halted while the others proceed downward causing the platform to progressively tilt to a substantially vertical orientation, spilling the cargo. 
     Thus, the respective legs  82 ,  88 ,  82   a  and  88   a  of the platform frame  34  of the present invention significantly enhance the stability of the lifting platform  32  by resisting both compressive and tension forces upon the corners of the first end  64  and second end  66  of the lifting platform  32  that would otherwise tend to move the lifting platform  32  out of the stable orientation. 
     As shown in  FIGS. 1-3 ,  6 , and  8 - 11 , the attic floor  26  and ceiling  24  form an upper surface and a lower surface, respectively (having a portal depth  28   a  therebetween) of an upper support structure  140  which has a plurality of joists  142  perpendicularly oriented to the attic floor  26  and ceiling  24 . In a preferred embodiment the joists  142  are contemplated as comprising conventional 2×12 lumber members located on 16 inch spacings, although other configurations, including different types and sizes of joist members and/or spacings, can readily be accommodated as understood by a person of ordinary skill in the art. 
     Another advantage of the platform assembly  14  as contemplated herein is that it readily adapts to different portal depths  28   a  of the portal  28  in the upper support structure  140  (i.e., wherein portal depth  28   a  is defined herein as the distance between the attic floor  26  (upper surface) and ceiling  24  (lower surface) as determined by the dimensions of the joists  142 ). For example, if the joists  142  comprise 2×10 boards or planks instead of 2×12s, the overall thickness of the upper support structure  140  (i.e., distance between the attic floor  26  and ceiling  24  and equivalent to the portal depth  28   a ) would be accordingly reduced by almost two inches. If the joists  142  were 2×16s, the thickness would be increased by about 4 inches. 
     Nevertheless, the platform assembly  14  would operate substantially as before with the closure platform  30  engaging and abutting the ceiling  24  and the lifting platform  32  continuing upwardly to the final position level with the attic floor  26  since the biasing springs  102   a - 102   d  are automatically adjustable. In this case (wherein the joists  142  are 2×10s), the only substantive operational difference would be that the biasing springs  102   a - 102   d  would generally undergo a reduced amount of extension, so that the final separation distance between the lifting platform  32  and the closure platform  30  would be reduced. 
     The closure platform  30  preferably comprises a series of small support members (not shown), such as elastomeric cushion members at each corner of the lower surface  62 . These support members of closure platform  30  support the weight of the platform assembly  14  and the loaded cargo item  46  when the platform assembly  14  is in the lowermost (resting) position on the garage floor  22  (see e.g.,  FIGS. 1 ,  6  and  7 ), thus preventing contact between the closure platform  30  and the garage floor  22 . This advantageously prevents the transfer of oil, dirt or other contaminants from the garage floor  22  to the closure platform  30  (oil stains on garage floor  22  may be acceptable, while oil stains on ceiling  24  are generally not). Alternately, fasteners  109  used to attach fastening device  108   a - 108   d  to the closure platform  30 , such as shown in  FIGS. 7 ,  9 ,  10 ,  11 ,  12 B and  14 A, may be provided with well-known plastic screw head covers or other devices that can serve the same purposes as the aforementioned elastomeric cushion members. 
     Referring now to the support and drive assembly  12 , as shown in  FIGS. 6 ,  8 ,  9  and  11 , an upper limit switch lever  146  extends from the winch motor  134  adjacent the winch tube assembly  132 . As the lifting platform  32  reaches the final desired elevation, the uppermost portion of the second side frame connector  94   a  of platform frame  34  (or other appropriate portion of the platform frame  34 , such as the reinforcing cross bar  96 ) toggles the upper limit switch lever  146  upwardly, activating an internal limit switch of the winch motor  134  to turn the winch motor  134  off. Preferably, the upper limit switch lever  146  has an enclosed aperture (shown in  FIG. 21 ) through which the cable  40  extends. In this way, the cable  40  is captured by the upper limit switch lever  146 , ensuring that the second side frame connector  94   a  will remain properly aligned with the upper limit switch lever  146 . 
     As shown in  FIGS. 8 and 11 , power is supplied to the lifting system  10  such as by way of a power cord  148 . Alternatively, the lifting system  10  can be hardwired using a dedicated electrical junction box, or powered by a removable extension cord. User control inputs are preferably provided by way of a control module  150 . It is contemplated that the control module  150  may be configured to require the user to be physically located within a radius defined by the length of the control module cord  151 , in order to operate the lifting system  10 . Alternatively the support and drive assembly  12  may be operated remotely by a wireless controller, such as used for garage door openers and well known in the art. 
     Suitable lockout and safety precautions are preferably enacted to prevent unauthorized use of the system, such as by unattended children. In one preferred embodiment shown in  FIG. 20 , the control module is disabled electrically by a key-locking switch  151   b . Other preferred embodiments are also contemplated. For example, the control module  150  can be made to be removable from the rest of the lifting system  10  and safely stored or locked up elsewhere by a responsible adult. Similarly, the lifting system  10  can be configured to accommodate keyed padlocks or other mechanisms (such as on the upper limit switch lever  146 ) to ensure that the lifting system  10  is not operated by unauthorized personnel. 
     As mentioned previously, the upper support structure  140  is contemplated in the present example to comprise a series of joists  142  on 16 inch centers, which can be a commonly employed residential construction configuration. A preferred configuration for the lifting system  10  provides the lifting platform  32  with a width of nominally 32 inches or slightly less, or about two 16 inch spans. In this way, during original construction or retrofit of an existing structure, a portion of one of the joists  142  in the upper support structure  140  can be removed and a pair of end boards  152  secured perpendicularly between two adjacent joists  142  to define the portal  28 , as shown in  FIGS. 8 and 11 . 
     In another alternative residential construction configuration, joists  142  may be positioned on 24 inch centers. In this case, the lifting platform may have a width of nominally 24 inches, sufficient to fit within a single span. A pair of end boards  152  can be supplied as before to define and enclose the portal  28  between adjacent joists  142 . While 24 and 32 inch widths of portal  28  provide particular advantages, it will be understood by a person of ordinary skill in the art that this is merely illustrative and is in no way limiting; rather, any number of different widths and lengths for the lifting platform  32  can be employed depending on the requirements of a given application. 
     As desired, the lifting system  10  or any lifting system described herein can be provided as a kit able to accommodate both the 24 and 32 inch (or other) sizes. Adjustment mechanisms can readily be configured by the skilled artisan to permit either size to be erected by the installer or end user. For example, the lifting platform  32  can comprise 8 inch wide planks (laid transversely to the direction shown in  FIGS. 1-3 ), such that three planks will provide a 24 inch width, and four such planks will provide a 32 inch width of the lifting platform  32 . Similarly, extension pieces can be configured to expand or contract the sizes of components of the platform frame  34  and/or support frame  36  to meet the 24 or 32 inch version, and so on. In an alternate embodiment of the present invention, a lifting system  10   a  is similar in all ways to lifting system  10  or any other lifting system described herein except in having an alternate configuration of a platform assembly  14   a  which has an alternate biasing mechanism such as that shown in  FIGS. 12A ,  12 B,  13 A and  13 B and designated therein by the general reference numeral  160 . Biasing mechanism  160  is constructed of a plurality of biasing springs (e.g., tension springs)  162   a ,  162   b ,  162   c  and  162   d , each of which is attached to both lifting platform  32  and closure platform  30  of the platform assembly  14 . In other words, the biasing mechanism is not directly attached to portions of the legs  82 ,  82   a ,  88  and  88   a  of the platform frame  34  and to the closure platform  30 , but rather to the lower surface  76  of the lifting platform  32  and to the upper surface  60  of the closure platform  30 . In particular, biasing springs  162   a,    162   b ,  162   c , and  162   d  have first ends  164   a ,  164   b ,  164   c , and  164   d , respectively and second ends  166   a ,  166   b ,  166   c , and  166   d , respectively. Biasing spring  162   a  opposes and is adjacent to biasing spring  162   b , and biasing spring  162   c  opposes and is adjacent to biasing spring  162   d , in a manner such as that shown in  FIGS. 12A-13B . Biasing spring  162   a  is attached at its first end  164   a  to closure platform  30  by a mounting bracket  170  and at its second end  166   a  to lifting platform  32  by a fastening device  172  and is entrained and supported at an intermediate position by a roller  168   a  which is secured to the lower surface  76  of the lifting platform  32 . Similarly, biasing spring  162   b  is opposingly secured at its first end  164   b  to closure platform  30  by the mounting bracket  170  and at its second end  166   b  to lifting platform  30  by a fastening device  174  and is entrained and supported at an intermediate position by a roller  168   b  which is secured to the lower surface  76  of the lifting platform  32 . 
     Biasing spring  162   c  is similarly attached at its first end  164   c  to closure platform  30  by a mounting bracket  176 , and at its second end  166   c  to lifting platform  32  by a fastening device  178  and is entrained and supported at an intermediate position by a roller  168   c  which is secured to the lower surface  76  of the lifting platform  32 . Similarly, biasing spring  162   d  is opposingly secured at its first end  164   d  to closure platform  30  by the mounting bracket  176  and at its second end  166   d  to lifting platform  32  by a fastening device  180  and is entrained and supported at an intermediate position by a roller  168   d  which is secured to the lower surface  76  of the lifting platform  32 . Each biasing spring  162   a ,  162   b ,  162   c , and  162   d  is substantially parallel to the lower surface  76  of the lifting platform  32  from its connection at the fastening device  172 ,  174 ,  178  and  180 , respectively, to the roller  168   a ,  168   b ,  168   c,  and  168   d , respectively, where each biasing spring  162   a - 162   d  is turned approximately 90 degrees toward the closure platform  30 , where each biasing spring  162   a - 162   d  is attached as described above. In this manner, the biasing springs  162   a - 162   d  extend and roll over the rollers  168   a - 168   d  to provide the biasing force, as described elsewhere herein such that the closure platform  30  is abuttingly urged against the ceiling  24  to close the lower entrance  29   b  when the platform assembly  14  is raised through the portal  28  ( FIGS. 12A-12B ), and then retracts to urge the closure platform  30  in a position against the lifting platform  32  when the platform assembly  14  is lowered again below the portal  28  ( FIGS. 13A-13B ). 
     In an alternate version of the present invention, a lifting system referred to in  FIGS. 14A ,  14 B,  15 A and  15 B by the general reference numeral  10   b  is similar to lifting system  10  or  10   a  or any other lifting system contemplated herein except in having an alternate configuration of a platform assembly  146 , which has an alternate version of a biasing mechanism, referred to therein by general reference numeral  190 . Biasing mechanism  190  is similar to biasing mechanism  160  of lifting system  10   a  except biasing mechanism  190 , instead of comprising coiled tension springs, comprises a first pair of biasing springs  190   a  and a second pair of biasing springs  190   b  which are constant force springs. Each pair of biasing springs  190   a  and  190   b  comprise two constant force springs which are positioned in parallel on opposing sides of the platform assembly  14   b . First pair of biasing springs  190   a  has a left hand spring  192   a  having a first end  194   a  attached to the closure platform  30  and a second end  196   a  attached to a pickup roller  198   a  which is secured to the lifting platform  32 , and which is entrained over a payout roller  200   a , also attached to lifting platform  32 . First pair of biasing springs  190   a  further comprises an opposing right hand spring  192   b  having a first end  194   b  attached to the closure platform  30  and a second end  196   b  attached to a pickup roller  198   b  which is secured to lifting platform  32  and which is entrained over a payout roller  200   b , also which is secured to the lifting platform  32 . The second pair of biasing springs  190   b  is parallel to first pair of biasing springs  190   a  and is constructed in exactly the same configuration. The biasing mechanism  190  may comprise more than two pairs of constant force biasing springs. The biasing mechanism  190  functions to cause the closure platform  30  to be extended ( FIGS. 14A and 14B ) or retracted ( FIGS. 15A and 15B ) in a manner similar to that for the previously described lifting systems  10 - 10   a  and indeed the biasing mechanism  190  can be used in substitution of biasing mechanisms  35  or  160  in lifting systems  10 - 10   a,  or any other such lifting and closure system described or contemplated herein. 
     In an alternate embodiment the biasing mechanism may be a “scissor-type” mechanism (not shown) in which the biasing force tends to try keep the “scissor-type” mechanism in a closed (retracted) position, as with the other biasing mechanisms described herein. 
       FIGS. 16-18  show an alternate embodiment of the present invention wherein lifting system  10  or any other lifting system contemplated herein is additionally equipped with a portal closure door  206 . As noted above, lifting system  10  has a support and drive assembly  12  (having a support frame  36  and a drive assembly  38 ) and a platform assembly  14  having a closure platform  30 , an lifting platform  32  and a platform frame  34 . The portal closure door  206  is attached by a hinge  208  or other suitable movable attachment device to the attic floor  26  and is sized to substantially cover the upper entrance  29   a  of the portal  28 . The platform frame  34  in one preferred embodiment has a horizontal bar  210  which extends between first leg  82  and first leg  82   a  of the platform frame  34 . When the platform assembly  14  is in the raised position as shown in  FIG. 16 , the portal closure door  206  leans upwardly against the horizontal bar  210 , such that the lifting platform  32  is exposed and available for use in the attic  20  in the manner described elsewhere herein. As the platform assembly  14  is lowered through and below the portal  28 , the portal closure door  206  is lowered until it lays flat on the attic floor  26 , substantially covering the upper entrance  29   a  of the portal  28  ( FIGS. 17 and 18 ), thereby serving as a safety feature to prevent individuals in the attic  20  from stepping or falling accidentally into the portal  28 , or preventing objects or small animals in the attic  20  from entering or falling into the portal  28 , and additionally to provide a further insulative effect to minimize heat gain or heat loss from the attic  20  into the garage  18 , or vice versa. It will be understood further that the portal closure door  206  may be raised and lowered by features other than the horizontal bar  210  on the platform frame  34 , for example, the portal closure door  206  may be raised and lowered by a pulley system (not shown) which is activated as the platform assembly  14  is raised and lowered. Alternatively, the horizontal bar  210  may be absent and the portal closure door  206  may be raised and lowered by the edges of the first leg  82  and first leg  82   a  of the platform frame  34 . The portal closure door  206  may be a feature of any of the lifting systems described or contemplated herein. 
     The novel manner of the attachment of the cable  40  to the platform frame  34  provides a number of benefits. As shown in  FIG. 4 , and in further detail in  FIGS. 19A-19B , the cable  40  is attached via separate cable arms  42  and  44  thereof to the first side frame connector  94  and to the second side frame connector  94   a , respectively. Referring to  FIGS. 19A and 19B , the second side frame connector  94   a  has an inner surface  220   a , an upper cable opening  222   a  and a lower cable opening  224   a . The second side frame connector  94   a  further comprises a cable clamping system  226   a  secured to the inner surface  220   a . Although not shown herein the first side frame connector  94  also has a cable clamping system exactly the same as cable clamping system  226   a . The cable clamping system  226   a  is constructed of a plurality of posts or studs  228   a  which extend from the inner surface  220   a . A pressure clamping plate  230   a  has a plurality of holes  232   a  therein which are positioned in complement with the pattern of posts  228   a  such that the pressure clamping plate  230   a  can fit over the posts  228   a  (as shown in  FIG. 19B ). When the posts  228   a  have threads, the pressure clamping plate  230   a  can be secured (bolted) to the inner surface  220   a  of the second side frame connector  94   a  with a plurality of washers  234   a  and lock nuts  236   a  in a conventional and well understood manner, as shown in  FIG. 19B . When the posts  228   a  are not threaded the pressure clamping plate  230   a  may be secured to the second side frame connector  94   a  by other means known in the art, such as by screwing the pressure clamping plate  230   a  directly to the inner surface  220   a.    
     The cable clamping system  226   a  functions to adjustably secure the cable arm  44  to the platform frame  14 . The cable arm  44  inserted through the upper cable opening  222   a  and through the lower cable opening  224   a  and is threaded around and through the posts  228   a  such that the cable arm  44  is frictionally and non-slippingly secured by the plurality of posts  228   a  ( FIG. 19A ). The pressure clamping plate  230   a  is then secured against the portion of the cable arm  44  threaded among the posts  228   a  ( FIG. 19B ). In typical prior art systems, cables used for lifting have permanently swaged sleeves forming loops at each end and are not adjustable. It requires special tools to swage sleeves or lugs for lifting applications. Thus, in prior art systems the cable length cannot be adjusted without cutting and re-swagging the cable. In the present system, the length of cable arm  42  or  44  which is passed through the first or second side frame connector  94  or  94   a , respectively, can be easily and readily adjusted with ordinary tools such as wrenches common to home owners. In another aspect of the invention, each cable arm  42  and  44  enters the upper cable opening  222   a  from the outside of the first or second side frame connector  94  and  94   a , respectively. This is, each cable arm  42  and  44  is essentially outside of the platform frame  34  which prevents any edge of the platform frame  34  from becoming caught on a portion of the portal  28  such as the portal ceiling edge  29   c , thus promoting the efficient movement of the platform frame  34  through the portal  28  as discussed in further detail below. 
       FIG. 20  shows the control module  150  which is, in a preferred embodiment, connected by a cord  151  to the drive mechanism  38  or winch motor  134 . The cord  151  is preferably from 10 to 20 feet in length but may be any length suitable for a particular application. The control module  150  has a control module momentary switch  151   a  which immediately turns off and stops the winch motor  134  when the user&#39;s finger is removed from the control module momentary switch  151   a  thereby enhancing the safe use of the lifting and closure system claimed herein. Further, the control module  150  preferably includes a locking mechanism  151   b  for preventing unauthorized or accidental operation of the system, and which can be unlocked, for example with a key  151   c.    
     Shown in  FIG. 21  (and in side views in  FIGS. 22-23 ) is a bottom perspective view of an embodiment of the drive mechanism designated by the reference numeral  38   b . The drive mechanism  38   b  comprises, as for drive mechanism  38 , a winch housing  130 , a winch tube assembly  132 , a winch motor  134 , an upper limit switch lever  146  and a power cord  148  leading to a power source. Cable  40  is secured to the winch tube assembly  132  via a cable clamp assembly  240  attached to a medial portion of the cable  40  and first cable arm  42  and second cable arm  44  are passed through holes  241  in the winch tube assembly  132  and extend downwardly therefrom. The drive assembly  38   b  has a tension detection switch assembly  242  which causes the winch tube assembly  132  to stop paying out cable automatically when the weight (tension) of the platform assembly  14  is removed from the cable arm  42 . The tension detection switch assembly  242  comprises a momentary switch  244  and a spring bracket  246  which is attached to the winch housing  130  and to the winch tube assembly  132 . The spring bracket  246  is upwardly biased and supports the end of the winch tube assembly  132 . 
     The tension detection switch assembly  242  serves a plurality of functions which enhance the safe and dependable operation of the present invention. A first function is to limit the downward travel of the platform assembly  14 , stopping the drive mechanism  38  instantly when the platform assembly  14  comes to rest on the garage floor  22 . A second function provided is to sense if the lifting platform  32  and the cargo item  46  thereon becomes lodged in the portal  28  while descending thereby stopping the drive mechanism  38  instantly upon sensing this condition. A third function provided is to sense a jammed or fouled condition of the cable arm  44  while descending which produces slack in cable arm  42 , and thereupon stopping the drive mechanism  38  instantly upon sensing this condition. A fourth function provided is to instantly stop the drive mechanism  38  upon the breakage or disconnect of cable arm  42  while descending. 
     When the winch tube assembly  132  is weighted by the cable arm  42  and the platform assembly  14 , the spring bracket  246  depresses the momentary switch  244  and enabling the downward motor circuit and the winch motor  134  can be downwardly actuated with the control module switch  151   a  causing the winch tube assembly  132  to lower the cable arm  42 . When the weight of the cable arm  42  is released from the winch tube assembly  132 , for example when the platform assembly  14  rests on a floor, or when the opposing cable arm  44  is jammed or caught or otherwise ceases being spooled out, the winch tube assembly  132  becomes unweighted via the cable arm  42  whereupon the momentary switch  244  opens the downward motor circuit and the winch motor  134  is automatically and immediately stopped causing cessation of movement of the platform assembly  14  and of the cable arm  42  wherein the cable arm  42  does not continue to spool out, even when the control module switch  151   a  continues to be depressed for downward travel. This prevents the cable arm  42  from becoming tangled or fouled which could require repair. This system enables the cable arm  42  to be stopped without requiring the control module momentary switch  151   a  to be released at the exact instant that the platform assembly  14  reaches the floor. Further, since the tension detection switch assembly  242  is contained entirely within the drive assembly  38   b , and not upon some element of the platform assembly  14 , the tension detection switch assembly  242  can be preset, for example at the factory, for reliable operation without user intervention or requiring a trained installer. The lifting system  10  (or any other lifting system contemplated herein) will stop immediately if the platform assembly  14  becomes lodged in the portal  28  when traveling downward. This is a vital safety issue. If the platform assembly  14  becomes lodged while the cable  40  continues to pay out, at least one cable arm would accumulate slack, possibly becoming fouled or jammed. Then if the platform assembly  14  were to suddenly dislodge while the cable arm was slack, it could free-fall some distance from the portal  28  possibly spilling the cargo item  46  or even breaking the cable  40 . This event could cause costly damage and possible serious personal injury. In the present invention, since the tension detection switch assembly  242  causes cable movement to cease immediately, the movement of the platform assembly  14  will cease immediately, thus the platform assembly  14  will resist spilling the cargo item  46  from the lifting platform  32 . 
     Shown in  FIG. 24  is an alternate version of a drive mechanism of the present invention designated by the general reference numeral  38   c  which not only has tension detection switch assembly  242  for detecting when weight is released from cable arm  42 , but also has a second tension detection switch assembly  250  at the opposing end of the winch tube assembly  132  and which functions to stop movement of the drive assembly  38   b  when weight is released from cable arm  44  in a manner similar to the operation of tension detection switch assembly  242 . The drive assembly of the present invention may be constructed without a tension detection switch assembly, with only a single tension detection switch assembly, or with a pair of tension detection switch assemblies. 
     In an alternate embodiment of the invention as shown in  FIG. 25 , the platform assembly  14  may be modified with the addition of a first sidewall  260  and a second sidewall  262 . The first sidewall  260  is attached to an inwardly facing surface of first side frame  80  and second sidewall  262  is attached to an inwardly facing surface of second side frame  80   a  by screws, bolts, clips, adhesives, cements, wire, or any other appropriate fastening means known to a person of ordinary skill in the art. The first and second sidewalls  260  and  262  may be attached to outwardly facing surfaces of the first and second end frames  80  and  80   a , respectively, as well. The sidewalls  260  and  262  are shown in  FIG. 25  as extending entirely from near the lifting platform  32  to near a point of angular change of each of legs  82  and  88  of first end frame  80  and each of legs  82   a  and  88   a  of second end frame  80   a , respectively. The size of the sidewalls  260  and  262  is not limited to the size shown in  FIG. 25  however and may in fact be a lesser size, or even may be larger. 
     Alternatively, the platform assembly  14  of the embodiment of  FIG. 25  may be further equipped with a backwall  264 , and a front door assembly  266 , as shown in  FIG. 26 . The backwall  264  is constructed in a manner similar to that of sidewalls  260  and  262  except the backwall  264  extends between first leg  82  of the first end frame  80  and first leg  82   a  of the second end frame  80   a . The front door assembly  266  comprises a first hinged door  268  and a second hinged door  270  which both can be opened outwardly for unloading or loading cargo items  46  onto the lifting platform  32 . The first and second hinged doors  268  and  270  can be securely closed via door closure device  272 . Such door closure devices are well known to those of ordinary skill in the art. Optionally, the backwall  264  may be constructed to have a pair of opening doors in a manner similar to that of front door assembly  266 . Alternatively, the platform assembly  14  may be constructed only with sidewalls  260  and  262 , and with backwall  264 , and without a front door assembly  266 . 
     As noted above, certain prior art lifting systems propose controlling the lifting platform using only cables to provide support and stability. This arrangement will support vertical loads but lacks dynamic stability. In such systems, the cables attach at or near the platform and therefore the cable attachment points are always below the center of gravity of any load placed on the platform as shown, for example in  FIG. 27 . It is easy to see that any large load would inherently become unstable if the platform tipped due to an obstruction or any fouling or jamming of one of the supporting cables. Once the platform and load become unbalanced, the platform can flip completely over, dumping the load, e.g., as shown in  FIG. 28 . This is because cables or tethers can resist downward forces but cannot resist the upward forces created by an unbalanced platform. In addition to the balance problem, supporting the platform directly with four cable attachment points as taught in the prior art, leaves another important safety problem unsolved. The cables naturally allow some swaying of the lifting platform as it moves upward (see  FIG. 27 ). When the platform carries a load that approaches the maximum load dimensions, then any swaying of the upwardly moving platform can allow misalignment between the load and the ceiling opening. When this occurs, the load and platform can become jammed as shown in  FIG. 27  or the load spilled as exemplified in  FIG. 28 . Further, as depicted in  FIG. 28 , if one of the cables in a prior art system becomes fouled, tangled, or jammed while the 4-cable platform is being lowered, then the one corner supported by the fouled, tangled or jammed cable would be halted while the other corners would continue to proceed downward causing the lifting platform to progressively tilt to a substantially vertical orientation, spilling the cargo. 
     The configuration of the platform assembly  14  of the present invention solves the instability problems associated with the prior art, and solves the problems of swaying which occur when the loading platform of the prior art is raised, and solves the problems which occur in prior art systems due to the center of gravity of the load being above the point of attachment of the cables (i.e., the “top heaviness”). The present invention provides a platform frame  14  that not only protects and guides the load through the portal  28 , but also provides cable attachment points well above the center of gravity of any load, creating an extremely stable platform that substantially resists tipping over and spilling the load. 
     As shown in  FIG. 29 , in some instances, when the platform assembly  14  is raised toward the portal  28 , the platform assembly  14  will begin to sway in an end-to-end direction  280 . In such an instance, as the platform assembly  14  is raised, the cable arm  42  (or  44 ) will tend to engage the portal ceiling edge  29   c  and will self-align and guide the platform frame  34  into the portal  28 , thereby overcoming the tendency of the platform frame  34  to be caught at the portal ceiling edge  29   c . Similarly, as shown in  FIG. 30 , as the platform assembly  14  is raised, it may begin to sway in a side-by-side direction  282 . In such an instance, the slanted portion  95  of the platform frame  34  will engage the portal ceiling edge  29   c  at the lower entrance  29   b  and will cause the platform frame  34  to become aligned with and guided into the portal  28 , thereby overcoming the tendency of the platform frame  34  to be caught at the portal ceiling edge  29   c . Recalling  FIG. 27 , which shows a cargo item on a prior art system about to become caught on a portal ceiling edge, it is clear how the configuration of the platform frame  34  of the present invention solves this problem of swaying and misalignment by the platform. This configuration of the lifting and closure system of the present invention eliminates the need for costly, complicated roller guide tracks, telescoping columns, rails and the like while maintaining substantially all of the benefits of stability and guidance normally provided by these devices. This is accomplished with a novel platform frame structure that substantially improves stability of the loaded platform while automatically correcting misalignment between the loaded platform and the portal while reliably guiding the platform assembly safely into the opening. 
     As noted above, and as graphically demonstrated in  FIG. 31 , the platform assembly  14  and platform frame  34  of the present invention places a maximum center of gravity  284  of the cargo item  46  well below attachment points  286  and  288  of the cable arms  42  and  44 . As demonstrated in  FIG. 31 , this configuration substantially stabilizes the cargo item  46  and prevents the lifting platform  32  and platform frame  34  from imbalance, even when one cable arm  42  or  44  becomes jammed and the other cable arm is completely slack. The platform frame  34  defines a cargo space (cargo volume)  290 , preventing impact between the cargo item  46  and the portal ceiling edge  29   c , so long as the cargo item  46  is within the defined cargo space  290 . 
     As described above, the present invention has significant advantages, particularly regarding preventing tipping or spillage of the cargo item  46  from the lifting platform  32  in the event of a malfunction of the cable  40  or support and drive assembly  12 .  FIGS. 32 and 33  show situations in which one cable arm becomes jammed or caught while a second cable arm continues to spool out. For example, in  FIG. 32  the cable arm  42  is shown jamming at point  292  on the winch tube assembly  132  wherein the cable arm  44  has continued to spool out, causing the platform frame  34  to tilt downwardly toward second side frame  80   a  and causing the cargo item  46  to slide downwardly and be arrested by second sidewall  262  thereby preventing it from spilling from the lifting platform  32 . Slack in the cable arm  44  is detected by the second tension detection switch assembly  250 , thereby automatically stopping the drive mechanism  38 . As indicated in the figure, center of gravity  296  of cargo item  46  is well below the cable attachment point  286  and the platform frame  14  hangs at an angle θ of about 45 degrees to the floor. 
     Similarly, as shown in  FIG. 33 , the cable arm  44  is shown jamming at point  294  on the winch tube assembly  132  wherein the cable arm  42  has continued to spool out, causing the platform frame  34  to tilt downwardly toward first end frame  80  and causing the cargo item  46  to slide downwardly and be arrested by first sidewall  260  preventing it from spilling from the lifting platform  32 . Slack in the cable arm  42  is detected by the first tension detection switch assembly  242  thereby automatically stopping the drive mechanism  38 . As indicated in the figure, center of gravity  296  of cargo item  46  is well below the cable attachment point  288  and the platform frame  14  hangs at an angle θ of about 45 degrees to the floor. 
     Shown in  FIG. 34  and designated therein by reference numeral  14   c  is an alternate version of a platform assembly of the present invention. Platform assembly  14   c  comprises a platform frame  34   c  which is the same in all regards to the other platform frames contemplated herein except that platform frame  34   c  comprises a first end frame  300  which is slanted at an angle θ inwardly (toward the cargo area) from a vertical axis  302 , and a second end frame  304  which is slanted at angle θ inwardly (toward the cargo area) from a vertical axis  306 . Angle θ is preferably from 0° to 30°, more preferably from 1° to 25°, though may be greater than 30°. 
     Shown in  FIG. 35  and designated therein by reference numeral  14   d  is an alternate version of a platform assembly of the present invention. Platform assembly  14   d  comprises a platform frame  34   d  which is the same in all regards to the other platform frames contemplated herein except that platform frame  34   d  comprises a first end frame  310  having a lower portion  312  which is substantially vertical and an upper portion  314  which is slanted at an angle  0  inwardly (toward the cargo area) from a vertical axis  316 . Platform frame  34   d  further comprises a second end frame  318  having a lower portion  320  which is substantially vertical and an upper portion  322  which is slanted at angle θ inwardly from a vertical axis  324 . Angle θ is preferably 0° to 30°, more preferably from 1° to 25°, but may be greater than 30°. 
     The slanted configurations of platform frames  34   c  and  34   d  enhance the ability of the platform assemblies  14   c  and  14   d , respectively, to be guided into the portal  28  without rubbing or becoming caught against any portion of portal  28 , thereby enhancing the safety and ease of use of the lifting system as constructed with either of platform assemblies  14   c  or  14   d.    
     It will now be appreciated that the various embodiments discussed herein (and other versions easily contemplated by persons of ordinary skill in the art) regarding the lifting systems of the present invention offer several advantages over the prior art. The novel configurations of the platform frames and support frames advantageously provide greater platform stability and effectively align and guide the lifting platforms through the portal in the attic floor. The novel closure platform of some embodiments advantageously operates to provide a ceiling cover to close the lower opening of the portal in the ceiling while still facilitating any number of desired final elevational placements of the lifting platform in its uppermost position, including level with or slightly above the adjacent attic floor. The lifting system of the present invention is also inexpensive, reliable and easy to install. In view of the foregoing, preferred embodiments of the present invention can be characterized without limitation as a method and apparatus for manipulating the elevational height of an object such as a cargo item. In accordance with preferred embodiments, such as described below, the lifting systems described herein are constructed to have a stationary support and drive assembly and movable platform assembly as contemplated herein. 
     In one preferred embodiment, the invention is a lifting and closure system, comprising a platform assembly comprising a lifting platform, a closure platform positioned below and facing the lifting platform, and a biasing mechanism attached to the closure platform for urging the closure platform toward the lifting platform, and a support and drive assembly positioned on a support structure, the support structure having an upper surface, a lower surface and a portal, the support and drive assembly positioned above the platform assembly and operatively connected to the platform assembly for raising the platform assembly into the portal, the portal having an upper entrance extending through the upper surface of the support structure, and a lower entrance extending through the lower surface of the support structure in a position below the upper entrance, and wherein the portal has a portal depth comprising a distance between the upper surface and the lower surface of the support structure, and wherein when the platform assembly is raised into the portal, the closure platform engages and is urged against the lower surface of the support structure by the biasing mechanism causing the closure platform to cover the lower entrance of the portal, and wherein the biasing mechanism is self-adjustable to enable the closure platform to be positioned a variable distance from the lifting platform for adjusting to differences in portal depths among different support structures. 
     In this embodiment, the platform assembly is operatively connected to the support and drive assembly, for example by a tether system. The lifting and closure system may further comprise a portal closure door for closing the upper entrance of the portal when the platform assembly is in a lowered position. The support and drive assembly may comprise a drive mechanism for raising and lowering the platform assembly and a support frame for supporting the drive mechanism. The platform assembly may comprise a platform frame for supporting the lifting platform and closure platform, the platform frame connected to the support and drive assembly, and wherein the lifting platform is secured to the platform frame. The biasing mechanism may be connected to the platform frame and to the closure platform, thereby connecting the closure platform to the platform frame. The biasing mechanism may be connected to the lifting platform and to the closure platform, thereby connecting the closure platform to the lifting platform. The biasing mechanism may comprise at least one pair of springs. The at least one pair of springs may comprise coiled tension springs. The at least one pair of springs may comprise constant force springs. The biasing mechanism may comprise two pairs of springs. The platform frame may comprise two pairs of legs having lower ends, each pair of legs having an upper end, wherein the lifting platform is attached near the lower ends of the two pairs of legs. The platform assembly may be attached to the support and drive assembly via a tether system attached to the upper ends of the two pairs of legs of the platform frame. Each leg of each pair of legs may have a lower vertical portion and an upper slanted portion wherein the upper slanted portions of each leg terminate at the upper end of the pair of legs. The tether system may be adjustably connected to the platform assembly at attachment points on the platform assembly such that the positions of attachment of the tether to the platform assembly are adjustable without affecting the length of the tether system. The lifting and closure system may comprise a tension detection switch positioned within the drive mechanism for immediately stopping the motion of the drive mechanism upon detection of a reduction in tension on at least one tether arm of the tether system. The tension detection switch may have a pre-set setting for detecting the reduction in tension. The platform assembly may further comprise one or more barriers for constricting movement of a cargo item on the lifting platform. The barrier may be a wall, a chain, a rope, a web, a net, a cable, a brace, a band, a bar, and combinations thereof. When a cargo item having a center of gravity is placed on the lifting platform of the platform assembly, the center of gravity of the cargo item is preferably below the point of operative connection between the support and drive assembly and the platform assembly. 
     The platform assembly may comprise a platform frame supportingly connected to the lifting platform which is substantially horizontal, and having a first end and a second end opposite the first end, said platform frame having a first end frame connected to the platform first end, and a second end frame opposite the first end frame and connected to the platform second end, each first end frame and second end frame having a width at least as wide as the first end and second end, respectively, of the lifting platform, wherein the first end frame and the second end frame each extend upwardly from the lifting platform, and the first end frame and second end frame defining a cargo space therebetween, and each first and second end frame having an inner side facing toward the other and each first end frame and second end frame having an outer side facing away from the other, and each first end frame and second end frame having a first side and a second side of substantially equal length and extending upwardly from the lifting platform for a lower portion of their length and converge toward each other for an upper portion of their length thereby forming a first side converging portion of the first end frame, the first side converging portion having an upper end forming a first end frame apex and a second end converging portion of the second end frame, the second side converging portion having an upper end forming a second end frame apex. 
     The support and drive assembly may be operatively connected to the platform assembly by at least two tethers, each of which is attached to the platform frame through an outer opening in the opposite outer side of each first end frame and second end frame at a point at or below the first frame apex and second frame apex, respectively, and the at least two tethers fastened securely within the platform frame for the purpose of raising the platform assembly and any cargo placed on the lifting platform into the portal, the portal having an upper entrance extending through the upper surface of the support structure, and a lower entrance extending through the lower surface of the support structure in a position below the upper entrance, and wherein the portal has a portal depth comprising a distance between the upper surface and the lower surface of the support structure, and wherein when the platform assembly is raised to the portal, the first frame apex of the first end frame and the second frame apex of the second end frame are drawn and guided into the portal lower entrance by the at least two tethers which extend from the outer sides of the first and second end frames of the platform frame and which thereby inhibit the first and second frame apexes from impacting the lower portal entrance as they are drawn in by the at least two tethers, and wherein as the platform assembly advances upward into the portal, the first side converging portion and the second side converging portion of each first end frame and second end frame can engage a portion of the lower portal entrance to progressively urge the platform frame into a proper alignment for entering the portal as the platform frame is drawn upwardly into the portal thereby preventing contact between a portal edge and the lifting platform or cargo disposed thereon and within the cargo space. 
     The support and drive assembly may have a drive mechanism comprising an electrically operated winch mechanism for winding up or paying out the tether to raise or lower the platform assembly upwardly or downwardly through the portal, the winch mechanism having an upward bias within the drive mechanism so that when the tether is weighted by the platform assembly, the winch mechanism moves against the upward bias closing a tension detection switch and causing the winch mechanism to pay out of the tether, and wherein when the tether is not weighted by the platform assembly, the winch mechanism moves toward the upward bias thereby opening the tension detection switch and disabling the winch mechanism and stopping pay out of the tether, thereby halting movement of the platform assembly immediately when the platform assembly comes to rest on a floor surface below the portal opening, or when the platform assembly or tether becomes lodged or caught in the portal or is otherwise arrested from movement. 
     The present invention further contemplates a method of vertically transferring an object between locations, comprising providing a lifting and closure system, comprising a platform assembly comprising a lifting platform, a closure platform positioned below and facing the lifting platform, and a biasing mechanism attached to the closure platform for urging the closure platform toward the lifting platform and wherein the biasing mechanism is self-adjustable to enable the closure platform to be positioned a variable distance from the lifting platform, and a support and drive assembly positioned on a support structure, the support structure having an upper surface, a lower surface and a portal, the support and drive assembly positioned above the platform assembly and operatively connected to the platform assembly for raising the platform assembly into the portal, the portal having an upper entrance extending through the upper surface of the support structure, and a lower entrance extending through the lower surface of the support structure in a position below the upper entrance, and wherein the portal has a portal depth comprising a distance between the upper surface and the lower surface of the support structure, orienting the platform assembly in a loading position on a surface below the portal and disposing an object on the lifting platform of the platform assembly, and actuating the support and drive assembly to raise the platform assembly into the portal wherein the closure platform engages and is urged against the lower surface of the support structure by the biasing mechanism causing the closure platform to cover the lower entrance of the portal. 
     The platform assembly of the lifting and closure system of this method is preferably operatively connected to the support and drive assembly by a tether system. The lifting and closure system of the method may further comprises a portal closure door for closing the upper entrance of the portal when the platform assembly is in a lowered position. The support and drive assembly of the lifting and closure system of the method may comprise a drive mechanism for raising and lowering the platform assembly, and a support frame for supporting the drive mechanism in a position above the portal. The platform assembly of the lifting and closure system of the method may comprise a platform frame for supporting the lifting platform and closure platform, the platform frame connected to the support and drive assembly, and wherein the lifting platform is secured to the platform frame. The biasing mechanism of the platform assembly of the method may be connected to the platform frame and to the closure platform, thereby connecting the closure platform to the platform frame. The biasing mechanism of the platform assembly of the method may be connected to the lifting platform and to the closure platform, thereby connecting the closure platform to the platform. The biasing mechanism of the platform assembly of the method may comprise at least one pair of springs. The at least one pair of springs of the biasing mechanism may comprise coiled tension springs. The at least one pair of springs of the biasing mechanism may comprise constant force springs. The biasing mechanism of the platform assembly may comprise two pairs of springs. The platform frame of the platform assembly of the method may comprise two pairs of legs having lower ends, each pair of legs having an upper end, wherein the lifting platform is attached near the lower ends of the two pairs of legs. The platform assembly of the lifting and closure system of the method may be attached to the support and drive assembly via a tether system attached to the upper ends of the two pairs of legs of the platform frame. Each leg of each pair of legs of the platform frame has a lower vertical portion and an upper slanted portion wherein the upper slanted portions of each leg terminate at the upper end of the pair of legs. The tether system of the lifting and closure system of the method may be adjustably connected to the platform assembly at attachment points on the platform assembly such that the positions of attachment of the tether to the platform assembly are adjustable without affecting the length of the tether system. The lifting and closure system of the method may further comprise a tension detection switch positioned within the drive mechanism for immediately stopping the motion of the drive mechanism upon detection of a reduction in tension on at least one tether arm of the tether system. The tension detection switch of the drive mechanism of the method may have a pre-set setting for detecting the reduction in tension. The platform assembly of the lifting and closure system of the method may further comprise one or more barriers for constricting movement of a cargo item on the lifting platform. The barrier of the platform assembly may be a wall, a chain, a rope, a web, a net, a cable, a brace, a band, a bar, and combinations thereof. When a cargo item having a center of gravity is placed on the lifting platform of the platform assembly, the center of gravity of the cargo item is below the point of operative connection between the support and drive assembly and the platform assembly. 
     In one embodiment the invention is a kit for assembling a lifting and closure system, wherein the kit comprises platform components comprising an lifting platform, a closure platform, a biasing mechanism, and platform frame components which when assembled comprise a platform assembly having a platform frame for supporting the lifting platform, with the closure platform positioned below and facing the lifting platform, and wherein the biasing mechanism is attachable to the closure platform in a configuration for urging the closure platform toward the lifting platform, support and drive components comprising support frame components and a drive assembly comprising a motor, and a winch assembly, which when assembled comprise a support and drive assembly able to be positioned on a support structure, the support structure having an upper surface, a lower surface and a portal, and a tether for operatively connecting the platform assembly to the support and drive assembly, wherein the tether can be connected to the winch assembly such that a first tether arm and a second tether arm of the tether can extend from the winch assembly of the drive assembly to connect to the platform frame of the platform assembly, wherein in use the support and drive assembly can be positioned on the support structure above the platform assembly and when in operation is able to raise the platform assembly into the portal and lower the platform assembly through the portal, the portal having an upper entrance extending through the upper surface of the support structure, and a lower entrance extending through the lower surface of the support structure in a position below the upper entrance, and the portal having a portal depth comprising a distance between the upper surface and the lower surface of the support structure, wherein when the platform assembly is raised into the portal, the closure platform engages and is urged against the lower surface of the support structure by the biasing mechanism causing the closure platform to cover the lower entrance of the portal and fit against the lower surface of the support structure, and wherein the biasing mechanism is self-adjustable to enable the closure platform to be positioned a variable distance from the lifting platform for adjusting to differences in portal depths among different support structures. 
     The lifting platform of the kit is preferably attachable to the platform frame. The biasing mechanism of the kit may be connectable to the platform frame and to the closure platform. The biasing mechanism of the kit may be connectable to the lifting platform and to the closure platform. The biasing mechanism of the kit may comprise at least one pair of springs. The at least one pair of springs of the kit may comprise coiled tension springs. The at least one pair of springs of the kit may comprise constant force springs. The biasing mechanism of the kit may comprise two pairs of springs. The platform components of the kit may comprise two pairs of legs having lower ends, each pair of legs having an upper end, wherein the lifting platform is attachable near the lower ends of the two pairs of legs. The platform assembly of the kit may be attachable to the support and drive assembly via the first tether arm and the second tether arm wherein each is attachable to the upper ends of the two pairs of legs of the platform frame. Each leg of each pair of legs of the platform components may have a lower vertical portion and an upper slanted portion wherein the upper slanted portions of each leg terminate at the upper end of the pair of legs. The tether of the kit may be adjustably connectable to the platform assembly at attachment points on the platform assembly such that the points of attachment of the tether to the platform assembly are adjustable without affecting the length of the tether system. The kit may comprise a tension detection switch positioned within the drive mechanism for immediately stopping the motion of the drive mechanism upon detection of a reduction in tension on at least one tether arm of the tether system. The tension detection switch of the kit may have a pre-set setting for detecting the reduction in tension. The kit may comprise one or more barriers for attachment to the platform frame for constricting movement of a cargo item on the lifting platform. The barrier may be a wall, a chain, a rope, a web, a net, a cable, a brace, a band, a bar, and combinations thereof When a cargo item having a center of gravity is placed on the lifting platform of the assembled platform assembly, the center of gravity of the cargo item is below the point of operative connection between the support and drive assembly and the platform assembly. The kit may comprise a portal closure door for closing the upper entrance of the portal when the platform assembly is in a lowered position. 
     In one embodiment, the invention is a lifting system comprising a platform assembly comprising a platform frame supportingly connected to a lifting platform which is substantially horizontal, and having a first end and a second end opposite the first end, said platform frame having a first end frame connected to the first end of the lifting platform, and a second end frame opposite the first end frame and connected to the second end of the lifting platform, each first end frame and second end frame having a width at least as wide as the first end and second end, respectively, of the lifting platform, wherein the first end frame and the second end frame each extend upwardly from the lifting platform, and the first end frame and second end frame defining a cargo space therebetween, and each first end frame and second end frame having an inner side facing toward the other and each first end frame and second end frame having an outer side facing away from the other, and each first end frame and second end frame having a first side and a second side of substantially equal length and extending upwardly from the lifting platform for a lower portion of their length and converge toward each other for an upper portion of their length thereby forming a first end converging portion of the first end frame, the first side converging portion having an upper end forming a first end frame apex and a second end converging portion of the second end frame, the second side converging portion having an upper end forming a second end frame apex; and a support and drive assembly positioned on a support structure, the support structure having an upper surface, a lower surface and a portal, the support and drive assembly positioned above the platform assembly and operatively connected to the platform assembly by at least two tethers, each of which is attached to the platform frame through an outer opening in the opposite outer side of each first end frame and second end frame at a point at or below the first frame apex and second frame apex, respectively, and the at least two tethers fastened securely within the platform frame for the purpose of raising the platform assembly and any cargo placed on the lifting platform into the portal, the portal having an upper entrance extending through the upper surface of the support structure, and a lower entrance extending through the lower surface of the support structure in a position below the upper entrance, and wherein the portal has a portal depth comprising a distance between the upper surface and the lower surface of the support structure, and wherein when the platform assembly is raised to the portal, the first frame apex of the first end frame and the second frame apex of the second end frame are drawn and guided into the lower entrance of the portal by the at least two tethers which extend from the outer sides of the first end frame and second end frame of the platform frame and which thereby inhibit the first frame apex and second frame apex from impacting the lower entrance of the portal as they are drawn in by the at least two tethers, and wherein as the platform assembly advances upward into the portal, the first side converging portion and the second side converging portion of each first end frame and second end frame can engage a portion of the lower entrance of the portal to progressively urge the platform frame into a proper alignment for entering the portal as the platform frame is drawn upwardly into the portal thereby preventing contact between a portal edge and the lifting platform or cargo disposed thereon and within the cargo space. 
     The lifting system may further comprise a closure platform positioned below and facing the lifting platform, and a biasing mechanism attached to the closure platform for urging the closure platform toward the lifting platform wherein when the platform assembly is raised into the portal, the closure platform engages and is urged against the lower surface of the support structure by the biasing mechanism causing the closure platform to cover the lower entrance of the portal, and wherein the biasing mechanism is self-adjustable to enable the closure platform to be positioned a variable distance from the lifting platform for adjusting to differences in portal depths among different support structures. 
     The biasing mechanism may be connected to the platform frame and to the closure platform, thereby connecting the closure platform to the platform frame, or the biasing mechanism may be connected to the upper platform and to the closure platform, thereby connecting the closure platform to the lifting platform. The biasing mechanism may comprise at least one pair of springs, and in one embodiment comprises two pairs of springs. The at least one pair of springs may comprise coiled tension springs, or the at least one pair of springs may comprise constant force springs. The tether system is preferably adjustably connected to the platform assembly at attachment points on the platform assembly such that the positions of attachment of the tether to the platform assembly are adjustable without affecting the length of the tether system. The lifting system further comprises a tension detection switch positioned within the drive mechanism for immediately stopping the motion of the drive mechanism upon detection of a reduction in tension on at least on tether arm of the tether system. The tension detection switch may have a pre-set setting for detecting the reduction in tension. The platform assembly may further comprise one or more barriers for constricting movement of a cargo item on the lifting platform. The barrier may be a wall, a chain, a rope, a web, a webbing, a net, a cable, a brace, a band, a bar, and combinations thereof. In the lifting system described above when a cargo item having a center of gravity is placed on the lifting platform of the platform assembly, the center of gravity of the cargo item is below the point of operative connection between the support and drive assembly and the platform assembly. The lifting system may further comprise a portal closure door for closing the upper entrance of the portal when the platform assembly is in a lowered position. 
     The support and drive assembly may have a drive mechanism comprising an electrically operated winch mechanism for winding up or paying out the tether to raise or lower the platform assembly upwardly or downwardly through the portal, the winch mechanism having an upward bias within the drive mechanism so that when the tether is weighted by the platform, the winch mechanism moves against the upward bias closing a tension detection switch and causing the winch mechanism to pay out of the tether, and wherein when the tether is not weighted by the platform, the winch mechanism moves toward the upward bias thereby opening the tension detection switch and disabling the winch mechanism and stopping pay out of the tether, thereby halting movement of the platform assembly immediately when the platform assembly comes to rest on a floor surface below the portal opening, or when the platform assembly or tether becomes lodged or caught in the portal or is otherwise arrested from movement. 
     The invention also contemplates a kit for supplying the components of this system and a method utilizing this system. 
     In another embodiment, the invention is a lifting system comprising a platform assembly comprising a lifting platform, and a support and drive assembly positioned on a support structure, the support structure having an upper surface, a lower surface and a portal, the support and drive assembly positioned above the platform assembly and operatively connected to the platform assembly by at least one tether for raising the platform assembly into the portal, and the support and drive assembly having a drive mechanism comprising an electrically operated winch mechanism for winding up or paying out the tether to raise or lower the platform assembly upwardly or downwardly through the portal, the winch mechanism having an upward bias within the drive mechanism so that when the tether is weighted by the platform assembly, the winch mechanism moves against the upward bias thereby closing a tension detection switch and causing the winch mechanism to pay out the tether, and wherein when the tether is not weighted by the platform assembly, the winch mechanism moves toward the upward bias thereby opening the tension detection switch and disabling the winch mechanism and stopping pay out of the tether, thereby halting movement of the platform assembly immediately when the platform assembly comes to rest on a floor surface below the portal opening, or when the platform assembly or tether becomes lodged or caught in the portal or is otherwise arrested from movement. 
     The lifting system may further comprise a closure platform positioned below and facing the lifting platform, and a biasing mechanism attached to the closure platform for urging the lower platform toward the lifting platform. The portal has an upper entrance extending through the upper surface of the support structure, and a lower entrance extending through the lower surface of the support structure in a position below the upper entrance, and a portal depth comprising a distance between the upper surface and the lower surface of the support structure and, wherein when the platform assembly is raised into the portal, the closure platform engages and is urged against the lower surface of the support structure by the biasing mechanism causing the closure platform to cover the lower entrance of the portal, and wherein the biasing mechanism is self-adjustable to enable the closure platform to be positioned a variable distance from the lifting platform for adjusting to differences in portal depths among different support structures. 
     The platform assembly may comprise a platform frame supportingly connected to the lifting platform which is substantially horizontal, and having a first end and a second end opposite the first end, said platform frame having a first end frame connected to the platform first end, and a second end frame opposite the first end frame and connected to the platform second end, each first end frame and second end frame having a width at least as wide as the first end and second end, respectively, of the lifting platform, wherein the first end frame and the second end frame each extend upwardly from the lifting platform, and the first end frame and second end frame defining a cargo space therebetween, and each first and second end frame having an inner side facing toward the other and each first end frame and second end frame having an outer side facing away from the other, and each first end frame and second end frame having a first side and a second side of substantially equal length and extending upwardly from the lifting platform for a lower portion of their length and converge toward each other for an upper portion of their length thereby forming a first end converging portion of the first end frame, the first side converging portion having an upper end forming a first end frame apex and a second end converging portion of the second end frame, the second side converging portion having an upper end forming a second end frame apex. The support and drive assembly may be operatively connected to the platform assembly by at least two tethers, each of which is attached to the platform frame through an outer opening in the opposite outer side of each first end frame and second end frame at a point at or below the first frame apex and second frame apex, respectively, and the at least two tethers fastened securely within the platform frame for the purpose of raising the platform assembly and any cargo placed on the lifting platform into the portal, wherein when the platform assembly is raised to the portal, the first frame apex of the first end frame and the second frame apex of the second end frame are drawn and guided into the portal lower entrance by the at least two tethers which extend from the outer sides of the first and second end frames of the platform frame and which thereby inhibit the first and second frame apexes from impacting the lower portal entrance as they are drawn in by the at least two tethers, and wherein as the platform assembly advances upward into the portal, the first side converging portion and the second side converging portion of each first end frame and second end frame can engage a portion of the lower portal entrance to progressively urge the platform frame into a proper alignment for entering the portal as the platform frame is drawn upwardly into the portal thereby preventing contact between a portal edge and the lifting platform or cargo disposed thereon and within the cargo space. 
     The biasing mechanism may be connected to the platform frame and to the closure platform, thereby connecting the closure platform to the platform frame, or the biasing mechanism may be connected to the upper platform and to the closure platform, thereby connecting the closure platform to the lifting platform. The biasing mechanism may comprise at least one pair of springs, and in one embodiment comprises two pairs of springs. The at least one pair of springs may comprise coiled tension springs, or the at least one pair of springs may comprise constant force springs. The tether system is preferably adjustably connected to the platform assembly at attachment points on the platform assembly such that the positions of attachment of the tether to the platform assembly are adjustable without affecting the length of the tether system. The lifting system further comprises a tension detection switch positioned within the drive mechanism for immediately stopping the motion of the drive mechanism upon detection of a reduction in tension on at least on tether arm of the tether system. The tension detection switch may have a pre-set setting for detecting the reduction in tension. The platform assembly may further comprise one or more barriers for constricting movement of a cargo item on the lifting platform. The barrier may be a wall, a chain, a rope, a web, a webbing, a net, a cable, a brace, a band, a bar, and combinations thereof. In the lifting system described above when a cargo item having a center of gravity is placed on the lifting platform of the platform assembly, the center of gravity of the cargo item is below the point of operative connection between the support and drive assembly and the platform assembly. The lifting system may further comprise a portal closure door for closing the upper entrance of the portal when the platform assembly is in a lowered position. 
     The invention also contemplates a kit for supplying the components of this system and a method utilizing this system. 
     Although the present disclosure and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, means, kits, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, means, kits, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, means, kits, methods, or steps.