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TECHNICAL FIELD  
       [0001]     The disclosure relates generally to a folding ladder configured for installation in an opening, such as an opening in a ceiling of a house (e.g., attic ladder), an opening in a ceiling of a building floor, or an opening to a suspended storage space (e.g., an elevated garage storage area) to provide temporary access between one floor or space and another floor or space. The disclosure particularly relates to a positioning system for a folding ladder and a method for installation of a folding ladder.  
       BACKGROUND  
       [0002]     Examples of attic ladders or “disappearing stairways” are shown, for example, in U.S. Pat. Nos. 2,649,237 and 2,852,176. These ladders normally fold and retract upwardly into a frame secured between adjacent joists of the attic, and the folded ladder is covered by a door which normally extends substantially flush with the finished ceiling of the room in which the ladder is mounted. Attic ladders thus take up no floor space except when actually extended and are also inexpensive to construct, as compared with fixed stairways typically constructed on-site.  
         [0003]     U.S. Pat. No. 4,281,743 issued to Fuller on Aug. 4, 1981 shows another conventional attic ladder. As shown in  FIG. 1  attic ladder  11  includes an outside frame  12  mounted between adjacent floor joists  13  of the attic floor  14 . Cross braces  15  are mounted between a pair of adjacent floor joists  13  to provide end support for the frame  12  of the disappearing stairway. Ladder  11  is mounted in the ceiling by securing frame  12  to the joists  13  and the cross braces  15 . A cover panel  16  forms part of ladder  11  and is hinged to the outer frame  12 , so that the door becomes substantially flush with the ceiling  17  when the ladder  11  is folded. A first ladder portion  17  is affixed to the inner face of cover panel  16  and a second ladder portion  18  is pivotally hinged to the first ladder portion so as to be unfolded or folded when the ladder is opened or closed. While commercially available attic ladders or disappearing stairways typically come in a number of sizes, most come in several standard widths and lengths adaptable to fit conventional constructions.  
         [0004]     U.S. Pat. No. 4,541,508 issued to Lundh on Sep. 17, 1985 shows yet another conventional attic ladder. In  FIG. 2 , a foldable ladder is shown to consist of a lower section  11 , a central section  12  and an upper section  13 . The central section  12  is hingedly connected to the two remaining sections  11 , 13  by a hinge so that the central section  12  and the lower section  11  can be folded up on the upper section  13 . Upper section  13  is hingedly attached to a frame  14  by hinges  15 , with the folding down movement of the upper ladder section  13  being limited by a pair of toggle joints  16 , 17 , attached to the upper ladder section and to the frame  14 . Toggle joints  16 , 17  are rigidly connected to each other at the lower arms by means of an axle  18  extending in parallel with the rungs of the ladder and are attached to the axle outside the side rails of the ladder. The ladder is spring-biased to a closed position by a gas spring  19  connected at one end to an outside of one side rail and connected at its other end, via piston rod  19   a , to moment arm  18   a , which is rigidly connected to the axle  18  at such an angle that a maximum moment is generated when the door is almost entirely closed. When the point of connection between the gas spring  19  and the moment arm  18   a  has passed the line for moment center (i.e. the connecting line between the attachment of the gas spring  19  to the ladder  13  and the axle  18 , which passing takes place when the door is opened entirely), the gas spring  19  actuates the door so that it is locked in folded-down position, which is necessary because the “weight” of the door decreases as soon as the ladder sections are folded out.  
         [0005]     As far as methods of installation are concerned, a typical method of installation of the folding ladder is shown in FIGS.  3 ( a )- 6 ( b ), described below.  
         [0006]      FIG. 3 ( a ) shows preparation of an opening  51  to receive a folding ladder, such as in an attic. An area is selected that is clear of wiring and plumbing and a rough opening is cut for the ladder next to at least one joist  50 . A sub-frame is then created on-site using lengths of wood cut to fashion headers/footers  52  and spacers  54 .  FIG. 3 ( b ) shows headers/footers  52  nailed to joists  50  at both ends and to the joist that was cut. Spacers  54  are nailed to the headers/footers  52  and an adjoining joist  50 . The ladder&#39;s frame box  58  will be attached to this sub-frame.  
         [0007]      FIG. 4 ( a ) shows installation of temporary support brackets  56 . Temporary support brackets are formed from pieces of wood, such as 5″×5″ pieces of wood, attached to the ceiling at each corner of the opening by screwing them into the ceiling joists  50 . A kit-made frame box  58  is assembled and lifted up through the opening  51  and then lowered to rest on the temporary support brackets  54 .  FIG. 4 ( b ) shows attachment of the frame box  58 . Shims (not shown) are used to center the frame box  58  in the subframe and to make sure it is level. The frame box  58  is then nailed to the sub-frame at a variety of points to secure the frame box and the temporary support brackets  56  are removed. The hatch door  62  is then attached to the frame box by a hinge  61  in such a manner as to provide a hatch that closes flush with the ceiling.  
         [0008]      FIG. 5 ( a ) shows both the installation of an individual wooden step  64  in a corresponding pair of grooves  65  in the left and right ladder rails  66 ,  68  and installation of all of the wooden steps  65  in the corresponding pairs of grooves in the left and right ladder rails, such as by inserting screws through the outside of the left and right ladder rails and into the steps.  FIG. 5 ( b ) shows the assembled folding ladder being folded about hinges  86 , in the directions of the arrows, for installation.  FIG. 5 ( c ) shows that the folded ladder  70  is tied together with a string or strap  72  to prevent inadvertent unfolding of the ladder during installation. Following this step, a hand rail is attached to the uppermost (as-installed) ladder rail sections with a metal bracket and lower hanger arms are attached to selected ladder-to-hatch brackets  74 .  
         [0009]      FIG. 6 ( a ) shows the conventional folding ladder assembly  70  following attachment of the folding ladder assembly to the hatch door  62  via ladder-to-hatch brackets  74 . To set the ladder angle a string  75  is tied to a ladder step and is secured, at another end, to a footer portion  52  of the frame box  58  or support frame, as shown. A length of this string  75  is selected so as to provide and maintain the folding ladder at a desired angle during cutting of the ladder  70  to form a ladder foot  80 . Alternatively, a second workman may hold the ladder at the desired angle during the ladder foot formation step. To create a foot  80  that is level with the floor, measuring sticks are used (labeled herein as “A” and “B” for descriptive purposes). Stick “B”  77  is placed on the front side of the ladder rail&#39;s second section  78  and stick “A”  76  is placed on the back of the ladder rail&#39;s third section  79 , keeping the bottom of the stick level with the bottom of the rail (e.g.,  66 ). A horizontal line may then be drawn across the rail (e.g.,  66 ) that joins the marks on sticks “A” and “B”  76 ,  77  to denote the appropriate angle and the sticks  76 ,  77  are then translated up the ladder rails to intersect a lower portion of the lower ladder rail  79  and the horizontal line is transferred to the lower portion of the lower ladder rail. The sticks  76 ,  77  may also be used to determine an appropriate length of the lower portion of the lower ladder rail  79 . The lower portion of the lower ladder rail  79  is then cut to form the foot.  
         [0010]      FIG. 6 ( b ) depicts downward rotation of the upper hanger arms  60 , which are spring-loaded, and connection thereof to the lower hanger arms  85  at joint  87  to complete the conventional folding ladder assembly  70 . Finally, an eyebolt, rope, or some other access device may be installed so as to protrude from, or to be accessible from, an underside of the hatch, to thereby permit a person in the space below the ladder to rotate and open the hatch and the folding ladder by means of, for example, a hook.  
         [0011]     However, additional improvements can be realized in the structure of the attic ladder support frame as well as the methods by which the attic ladder is installed. Efficiency and man power improvements can also be realized, as the conventional methods of installation require two people to assemble the ladder.  
       SUMMARY  
       [0012]     In one aspect, there is provided a support frame for a foldable ladder configured for installation in an opening between one floor or space and another floor or space, including a plurality of separable support frame plates collectively configured to circumscribe the opening and a plurality of connection sites are disposed at opposing ends of each of the plurality of separable support frame plates to facilitate connection of each support frame plate to adjacent support frame plates. The connection sites include, for example, mating locking connectors or a plurality of matching through-holes, which permit insertion of a fastening means therethrough.  
         [0013]     In yet another aspect, there is provided a strut positioning system for a foldable ladder configured for installation in an opening defined between one floor or space and another floor or space, the opening having a distal side to which a ladder is rotatably attached, a proximal side to which an opening or closing torque is applied to open or close the foldable ladder, and a first and a second lateral side, the gas strut positioning system comprising: a gas strut or a hydraulic strut having a proximal end and a distal end; a track configured for mounting in a fixed position relative to and along one of the first lateral side and the second lateral side of the opening defined between one floor or space and another floor or space; a rack plate comprising gear teeth configured to matingly engage corresponding pinion gear teeth and comprising a connector for connecting to the proximal end of the gas or hydraulic strut, the rack plate being configured for translational movement within the track from a first position to a second position, wherein the first position corresponds to a non-compressed state of the gas or hydraulic strut and the second position corresponds to a compressed state of the gas or hydraulic strut; a locking device configured to lock the rack plate in the second position; a pinion gear comprising teeth configured to matingly engage corresponding rack plate gear teeth and comprising a torque application member configured to matingly engage a torque application tool, the pinion gear being rotatably mounted in a fixed position on the lateral side of the opening within the track; wherein, upon connection of the distal end of the gas or hydraulic strut to one of a ladder and a link member attached to a ladder and compression of the gas or hydraulic strut by application of a torque to the pinion gear, the rack plate is locked in the second position.  
         [0014]     In another aspect of the strut positioning system for a foldable ladder configured for installation in an opening defined between one floor or space and another floor or space, the opening having a distal side to which a ladder is rotatably attached, a proximal side to which an opening or closing torque is applied to open or close the foldable ladder, and a first and a second lateral side, there is provided a gas strut positioning system comprising: a gas strut or a hydraulic strut having a proximal end and a distal end; a track configured for mounting in a fixed position relative to and along one of the first lateral side and the second lateral side of the opening defined between one floor or space and another floor or space; a slide plate configured for translational movement within the track from a first position to a second position, wherein the first position corresponds to a non-compressed state of the gas or hydraulic strut and the second position corresponds to a compressed state of the gas or hydraulic strut; a means for locking the rack plate in the second position; wherein, upon connection of the distal end of the gas or hydraulic strut to a ladder or a link member attached to a ladder and compression of the gas or hydraulic strut, the slide plate is locked in the second position.  
         [0015]     In still another aspect, there is provided a method for installing a foldable ladder configured for installation in an opening defined between one floor or space and another floor or space, the method comprising: defining an opening having a distal side to which a ladder is rotatably attached, a proximal side to which an opening or closing torque is applied to open or close the foldable ladder, and a first and a second lateral side; installing a strut positioning system within a perimeter of the opening, the strut positioning system comprising a track configured for mounting in a fixed position relative to and along one of the first lateral side and the second lateral side of the opening defined between one floor or space and another floor or space; a rack plate comprising gear teeth configured to matingly engage corresponding pinion gear teeth and comprising a connector for connecting to an end of a strut, the rack plate being configured for translational movement within the track from a first position to a second position, wherein the first position corresponds to a non-compressed state of the strut and the second position corresponds to a compressed state of the strut; a locking device configured to lock the rack plate in the second position; and a pinion gear comprising teeth configured to matingly engage corresponding rack plate gear teeth and comprising a torque application member configured to matingly engage a torque application tool, the pinion gear being rotatably mounted in a fixed position on the lateral side of the opening within the track; positioning a folded ladder assembly at least partially within the opening and securing the folded ladder assembly relative to the opening; pivoting the folded ladder assembly forwardly until the folded ladder is sufficiently close to the support frame to permit attachment of curved brackets connecting upper lateral ends of the folded ladder to connectors provided on the first and second lateral sides of the opening attaching one end of a strut, comprising at least one of a gas strut and a hydraulic strut, to one of the folded ladder and an extension member attached to the folded ladder and attaching another end of the strut to the rack plate connector when the rack plate is positioned at the first position, wherein the strut is in an non-compressed state; applying a torque to the pinion gear to corresponding move the rack plate along the track from the first position to the second position and to thereby compress the strut; and securing the rack plate at the second position.  
         [0016]     In another aspect of a method for installing a foldable ladder configured for installation in an opening defined between one floor or space and another floor or space, the method includes defining an opening having a distal side to which a ladder is rotatably attached, a proximal side to which an opening or closing torque is applied to open or close the foldable ladder, and a first and a second lateral side; assembling a support frame assembly; installing the support frame assembly along an inner perimeter of the opening; installing a strut positioning system along at least lateral side of the support frame assembly, the strut positioning system comprising a track configured for mounting in a fixed position relative to and along one of the first lateral side and the second lateral side of the opening defined between one floor or space and another floor or space; a rack plate comprising gear teeth configured to matingly engage corresponding pinion gear teeth and comprising a connector for connecting to an end of a strut, the rack plate being configured for translational movement within the track from a first position to a second position, wherein the first position corresponds to a non-compressed state of the strut and the second position corresponds to a compressed state of the strut; a locking device configured to lock the rack plate in the second position; and a pinion gear comprising teeth configured to matingly engage corresponding rack plate gear teeth and comprising a torque application member configured to matingly engage a torque application tool, the pinion gear being rotatably mounted in a fixed position on the lateral side of the opening within the track; positioning a folded ladder assembly at least partially within the opening and securing the folded ladder assembly to the support frame assembly; pivoting the folded ladder assembly forwardly until the folded ladder is sufficiently close to the support frame to permit attachment of curved brackets connecting upper lateral ends of the folded ladder to connectors provided on lateral sides of the support frame; attaching one end of a strut, comprising at least one of a gas strut and a hydraulic strut, to one of the folded ladder and an extension member attached to the folded ladder and attaching another end of the strut to the rack plate connector when the rack plate is positioned at the first position, wherein the strut is in an non-compressed state; applying a torque to the pinion gear to corresponding move the rack plate along the track from the first position to the second position and to thereby compress the strut; securing the rack plate at the second position.  
         [0017]     In yet another aspect of a method for installing a foldable ladder configured for installation in an opening defined between one floor or space and another floor or space, the method comprising: defining an opening having a distal side to which a ladder is rotatably attached, a proximal side to which an opening or closing torque is applied to open or close the foldable ladder, and a first and a second lateral side; installing a strut positioning system along at least lateral side of the support frame assembly, the strut positioning system comprising a track configured for mounting in a fixed position relative to and along one of the first lateral side and the second lateral side of the opening; a slide plate configured for translational movement within the track from a first position to a second position, positioning a folded ladder assembly at least partially within the opening and securing the folded ladder assembly relative to the opening; attaching curved brackets connecting upper lateral ends of the folded ladder to connectors provided at the first and second lateral sides of the opening; attaching one end of a strut, comprising at least one of a gas strut and a hydraulic strut, to one of the folded ladder and an extension member attached to the folded ladder and attaching another end of the strut to the slide plate when the rack plate is positioned at the first position, wherein the strut is in an non-compressed state; moving the slide plate from the first position toward the second position along the track to compress the strut; and securing the rack plate at the second position.  
         [0018]     Additional advantages will become readily apparent to those skilled in this art from the following detailed description, wherein only the a preferred example of the present concepts are shown and described. As will be realized, the disclosed concepts are capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the spirit thereof. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     Reference is made to the attached drawings, wherein elements having the same reference numeral designations represent like elements throughout, and wherein:  
         [0020]      FIG. 1  is a perspective view of a conventional folding ladder disposed in an opening;  
         [0021]      FIG. 2  is a perspective view of another conventional folding ladder disposed in an opening;  
         [0022]      FIG. 3 ( a ) shows preparation of an opening to receive a conventional folding ladder;  
         [0023]      FIG. 3 ( b ) depicts a step in the preparation of a conventional folding ladder subframe;  
         [0024]      FIG. 4 ( a ) depicts a step in the installation of a conventional folding ladder including installation of temporary support brackets;  
         [0025]      FIG. 4 ( b ) shows another step in the installation of a conventional folding ladder including attachment of the frame box;  
         [0026]     FIGS.  5 ( a )-( c ) show additional steps in the installation of a conventional folding ladder including the installation of an individual wooden step, securement of the steps, folding the ladder for installation, and tying the folded ladder to prevent inadvertent unfolding of the ladder during installation;  
         [0027]      FIG. 6 ( a ) illustrates a conventional folding ladder assembly following attachment to the hatch door via the ladder-to-hatch brackets and intermediate steps of setting the ladder angle and creating a ladder foot that is level with the floor;  
         [0028]      FIG. 6 ( b ) depicts connection of the upper hanger arms to the lower hanger arms to complete the conventional folding ladder assembly.  
         [0029]     FIGS.  7 ( a )- 7 ( d ) are, respectively, a perspective view of the support frame, an exploded perspective view of a head portion of the support frame, a top view of the support frame, and a side view of the support frame in accord with the present concepts;  
         [0030]      FIG. 8  is a top-perspective view of a gas strut positioning system for a folding ladder and support frame in accord with the present concepts;  
         [0031]      FIG. 9  is a side views of a gas strut positioning system for a folding ladder and support frame in accord with the present concepts wherein the gas strut in a fully compressed position;  
         [0032]      FIG. 10  is a side views of a gas strut positioning system for a folding ladder and support frame in accord with the present concepts wherein the gas strut in a fully extended position;  
         [0033]     FIGS.  11 ( a )-( b ) is a side view of a gas strut positioning system and exploded isometric view of a ratchet system thereof in accord with the present concepts;  
         [0034]     FIGS.  12 ( a )-( d ) respectively show isometric, side, front, and exploded detail views of a gas strut positioning system rack plate in accord with the present concepts;  
         [0035]     FIGS.  13 ( a )-( c ) respectively show a top view of a ratchet spring plate, a top view of a ratchet, and a side view of a ratchet of a gas strut positioning system in accord with the present concepts;  
         [0036]     FIGS.  14 ( a )-( c ) respectively show an isometric view, a front view, and an exploded detail view of a gear for use in the gas strut positioning system in accord with the present concepts; 
     
    
     DETAILED DESCRIPTION  
       [0037]     With reference to the attached drawings, there is described a folding ladder and various features including but not limited to locking mechanisms, positioning mechanisms, and movable steps, as well as a support frame and methods of installation of the support frame and folding ladder in an opening to provide access between spaces on opposite sides of the opening.  
         [0038]     In one aspect of the folding ladder support frame, shown in FIGS.  7 ( a )- 7 ( d ), the support frame is made up of four sections comprising a separate head plate  210 , a right side plate  220 , a left side plate  230 , and a foot plate  240 . These plates may be assembled at ajob-site together and fastened together, such as by screws or rivets, or snapped together through an appropriate snap-lock connection to thereby form a unitary frame. It is preferred that the frame comprise a metal or metal alloy, such as but not limited to a commercial-grade steel, which permits the frame sections to be manufactured using cost effective and reliable techniques, such as stamping and rolling. Such non-limiting techniques (e.g., any conventional casting method could also be utilized) permit features, such as the openings  202 , tabs  201 , and hinge slots  212  to be easily incorporated into the support frame  200  to facilitate the addition or operation of other mechanisms which, as discussed below, enable installation of the frame more quickly and with less tools and installers than required by conventional installations.  
         [0039]     Side plates  220 ,  230 , shown in  FIG. 7 ( a ), are each 1347.8 mm long in the depicted example and are 88.9 mm high (see  FIG. 7 ( d )). Top and bottom edges of the side plates  220 ,  230  are bent inwardly as shown in  FIG. 7 ( d ) into a roughly U-shaped or C-shaped section defining a gap of about 3.8 mm between the edges of the bent portion. The shaped section (e.g., U-shaped or C-shaped) or bend provides a track within which the rack plate  610 , depicted in FIGS.  7 ( a )-( b ), can be guided as it moves during the installation process, as described below. The bend or shaped section also provides a track within which the ends of the head plate  210  and the foot plate  240  may be inserted and moved during installation thereof. In another aspect of the invention, the ends of the head plate  210  and the foot plate  240  need not be bent as shown in  FIG. 7 ( b ) and may instead be substantially planar. Such aspect permits additional variability in lateral placement of the head plate  210  and the foot plate  240  relative to the side plates  220 ,  230 . Lateral adjustments may be realized, for example, by flanged connectors on side plates  220 ,  230 , which bear through-holes positionable with respect to slots in the head and foot plates  210 ,  240 .  
         [0040]      FIG. 7 ( c ) shows a strut positioning system  600  attached to opposing sides of the support frame  200  along a major longitudinal axis of the frame. Each strut positioning system  600  comprises a rack plate  610 , a gear  615  and ratchet system  620 . The gear  615  is rotatably affixed to the support frame assembly  200  by means of a shaft or gear pin disposed in an opening or hole  203  formed at a point about 757.3 mm from the rightmost edge of the example shown in FIGS.  7 ( a )-( c ). Hole  203  is, in the illustrated example, displaced downwardly from a top edge of the support side plate (e.g.,  230 ) by about 40.1 mm and up from a longitudinal centerline by about 13.4 mm. Openings  202  are, in the illustrated example, about 9.53 mm deep and 15.88 mm high. In one aspect, gear  615  is supported by a C 1006  steel gear pin having a proximal base diameter of 19.05 mm, a shaft diameter of 9.53 mm, and a groove configured to receive a retaining clip or ring at a distal portion thereof. Thus, the rack plates  610  are configured to move along a major longitudinal axis of the frame  200  during installation of the strut positioning system  600 , described below, and the gears  615  are adapted to facilitate alignment and smooth motion of the rack plates  610  during such installation.  
         [0041]      FIG. 8  shows a top-perspective view of one strut positioning system  600  for a folding ladder and support frame in accord with the present concepts. The strut may comprises a gas strut or a hydraulic strut (i.e., the actual fluid(s) employed by the strut may vary)). Strut  602  is, in one aspect, a Suspa  445  N gas strut with a stroke length of 200 mm (compressed length of 300 mm and extended length of 500 mm)(Part No. C16-08054). Generally speaking, the strut  602  is used to control the force required to open or close the folding ladder  100 . Strut  602 , which maintains a fully open position unless forced into compression, provides several advantages over the common lever and spring mechanisms use in conventional attic ladders (e.g., occupying less space) and confers a smooth force distribution and permits improved control over the force and velocity of the ladder  100  during opening or closing.  
         [0042]      FIGS. 9 and 10  respectively show side views of a strut positioning system  600  for a folding ladder and support frame in accord with the present concepts wherein the gas strut  605  is in a fully extended position and a fully compressed position, as is more fully described below.  
         [0043]      FIG. 11 ( a ) shows a side view of an example of a strut positioning system  600  comprising a rack plate  610  attached to the support frame  200 , gear  615 , and ratchet system  620 . Rack plate  610 , shown in greater detail in FIGS.  12 ( a )-( d ), advantageously comprises a zinc or cadmium plated commercial quality 1020 steel with a yield strength of 50,000 psi or greater. Gear  615  is shown in greater detail in FIGS.  14 ( a )-( c ) and, in one aspect, made from Zinc Zamac  3 .  FIG. 11 ( b ) shows an exploded isometric view of a ratchet system  620  including a ratchet spring plate  621  (see  FIG. 13 ( a )), ratchet  622  (see FIGS.  13 ( b )-( c )), and ball socket  623 . Ratchet spring plate  621  is made, in one aspect, from a C1095 spring steel about 0.76 mm thick. Ratchet  622  is made, in one aspect, from Zinc Zamac 3. Ball socket  623  is made from stainless steel and has a ball radius dimensioned to receive a corresponding socket of a strut  602  extension arm. In one aspect, the ball socket  623  has a threaded base having a diameter of 0.38 inches and a depth of 0.25 inches capped by a hex nut having a diameter of about 0.56 inches, upon which the ball is situated. Any of the rack plate  610 , gear  615 , or ratchet system  620  members could comprise other metals, alloys, materials (e.g., thermoplastic/thermosetting resins or composite materials), surface treatments or coatings in accord with the present concepts.  
         [0044]      FIG. 12 ( a ) shows an isometric view of a strut positioning system rack plate  610  in accord with the present concepts depicting rack teeth  611  and mounting sections  612 . Rack teeth  611  are shown, in the example illustrated by  FIG. 12 ( d ), to have an addendum of 4.26 mm and dedendum of 5.29 mm with a pressure angle of 14.5° and a pitch of about 13.3 mm. In the example of  FIG. 12 ( d ), the gear  615  is expected to have a pressure angle of 14.5°, a diametral pitch of 6 with 12 teeth, a pitch diameter of 50.8 mm, an outside diameter of about 59.3 mm, a root diameter of about 40.2 mm, and a circular tooth thickness of about 0.66 mm, as shown in FIGS.  14 ( a )-( c ). However, as known to those of ordinary skill in the art, numerous other tooth profiles and rack/pinion configurations could be utilized to the same effect and the illustrated example is not to be taken as limiting the concepts expressed herein.  
         [0045]      FIG. 13 ( a ) shows one example of ratchet spring plate  621  wherein the ratchet spring plate is about 53.98 mm long, about 0.76 mm thick, and about 15.88 mm wide. Four through-holes  624 ,  625  are provided therein. In the example depicted, the left-most through-holes  624  are disposed to enable connection of the ratchet spring plate  621  to the rack plate  610  and the right-most through-holes  625  are disposed to enable connection of the ratchet spring plate  621  to the ratchet  622 . The ratchet  622  is thereby cantilevered from the side of the rack plate  610  as shown, for example, in  FIG. 11 ( b ) and is subjected to a downward bias upon upward deflection of the ratchet  622  and spring plate  621 .  
         [0046]     FIGS.  11 ( b )-( c ) depict one example of a ratchet  622  in accord with the present concepts. Ratchet  622  comprises through holes  626  corresponding to the right-most through-holes  625  of ratchet spring plate  621  to enable affixation thereto by conventional fasteners. Alternative means of connection between the ratchet spring plate  621  and ratchet could also be employed, such as but not limited to a welded or bonded connection, a unitary structure, or clamping device. Ratchet  622  includes, at a distal end, an engagement portion  627  configured to engage tabs  201  and openings  202  in the support frame. In one aspect, the engagement portion  627  has a first surface  628  inclined 30° from the horizontal and a second surface  629  inclined 70° from the horizontal. The second surface  629  is adapted to correspond to an aspect of the tabs  201  in which the tab is similarly inclined 70° from the horizontal, so as to permit positive engagement of the second surface to a respective tab as described in more detail below.  
         [0047]     In another aspect, a strut positioning system  600  could comprise a track configured for mounting in a fixed position relative to and along one of a first lateral side or a second lateral side of an opening defined between one floor or space and another floor or space. Such track could be mounted, for example, on a support frame, such as described above, or on a conventional frame box, framing attached to a joist, or directly to a joist itself. In this aspect, a slide plate is provided that is configured for translational movement within the track from a first position to a second position, wherein the first position corresponds to a non-compressed state of the strut (e.g., a gas strut, a hydraulic strut, or a spring strut) and the second position corresponds to a compressed state of the strut. A locking member for locking the slide plate in the second position is also provide such that, upon connection of a distal end of the strut to a ladder or to a link member attached to a ladder and upon compression of the strut, the slide plate is locked in the second position by the locking member.  
         [0048]     As with the first example of a strut positioning system  600 , it is preferred that such track comprises a plurality of landings disposed between the first position and the second position and configured to prevent reverse translation of the slide plate in a direction toward the first position past the landing under a bias of the strut. In one aspect, the landings may comprise a tooth having at a rearwardly slanted front face and a rear face having a perpendicular attitude or a forwardly slanted face. The slide plate would correspondingly possess a ratchet tooth front face having a perpendicular or a forwardly slanted face complementing a shape of a rear face of the track landing tooth and having a forwardly slanted rear face having a shape substantially complementing a shape of the track landing tooth front face. It is preferred, in this example, that the slide plate comprises an outwardly biased ratchet tooth extending from at least one side thereof (e.g., a top and/or a bottom side). Thus, the slide plate tooth is biased into engagement with the track landing tooth to thereby permit motion of the slide plate in only one direction. A plurality of track landings may be provide substantially contiguous to one another to comprise, in combination, a linear pawl. Such linear pawl may be provided along only along a top or a bottom of the track, or may be provided along both the top and the bottom of one or more tracks. Once the slide plate is appropriately oriented in the second position, the slide plate may be fixed by a conventional mechanical fastener (e.g., screw, rivet) or may be locked in place by the action of the aforementioned ratchet tooth and linear pawl.  
         [0049]     The strut positioning system  600  provided herein further significantly permits a single person installation.  
         [0050]     Prior to installation, a rough opening must be made in the ceiling roughly corresponding to and larger than that of the folded ladder. If the folding ladder is wider than a spacing between ceiling joists, appropriate reinforcements and bracing should be provided prior to cutting the ceiling joists so as to prevent sagging and to maintain structural integrity. For example, two headers and a stringer could be constructed of 2″ lumber and nailed securely to the ceiling joists, in a manner to those of ordinary skill in the art. In accord with the example herein, a rough opening that is 22 ½″×54″ is formed at a position eight feet off the ground.  
         [0051]     As previously noted, one aspect of the folding ladder support frame provides a support frame comprising four sections (head plate  210 , a right side plate  220 , a left side plate  230 , and a foot plate  240 ) which may be assembled at a job-site together and fastened together, such as by screws or rivets, to form a continuous frame. In some instances, installation of a support frame or of a complete perimeteral support frame is not necessary and this step may be omitted, as appropriate. Once assembled, as necessary, the support frame  200  is lifted into the rough opening in the ceiling and positioned with framing hooks (not shown) on the head plate  210 . The head-plate  210  of the frame  200  should be pushed as far forward against the frame as possible and the frame should be installed with the bottom of the frame located about 0.150″ from the bottom of the drywall on the ceiling so as to provide a flush transition between the ceiling and the panel  300 . The center of the head plate  210  should be centered within the framed hole, such as by sliding the head plate by tapping on the edges of the frame hooks. The support frame  200  is then fastened to the wooden joists by a mechanical fastener, such by using ¼″×1 ½″ lag screws. The lag screws are driven into the wood through four lag screw holes disposed on each side plate of the support frame  200 . Although the positioning of these holes is relatively arbitrary, in one aspect four holes are located on the centerline of the support frame side plate  220 , one hole being located at the foot plate  230 , one located in the center of the side plate  220  and two holes located near the support frame head plate  210 . The lag screws should be driven in fully to secure the frame to the joists.  
         [0052]     The folded ladder  100  assembly may then be positioned within the door hinge slots  212  located on the frame head plate  210 . When this step is complete, the folded ladder  100  will be hanging straight down from the hooks (a strap still holds the ladder sections together at this point). The ladder  100  may then be fastened to the frame  200  head plate  210  using a mechanical fastener, such as ¼″×1 ½″ lag screws by fastening the lag screws into the wood through a number (e.g., four) of lag screw holes that provided on the door hinge  215  and on the head plate  210  of the frame  200  until the door hinge and frame head plate are tight against the wooden joist. Then, using a ladder (such as a 6 foot ladder facing the folding ladder assembly  100 ), ascend the ladder (e.g., to the 3 rd  or 4 th  step) to temporarily remove the nuts and spacers from the bolts attached to the frame. The ladder assembly  100  is then pivoted forwardly until the folded ladder is at about a 65° angle from the ceiling to permit attachment of two curved brackets  216 . Each curved bracket  216  will be placed over the bolt, pin or river protruding from the frame. Once the brackets are in place, a spacer and nut are fastened to each bracket the nut tightened to the bracket in such a manner as to enable the bracket to slide freely. A post bearing a ball joint is provided at a top of the ladder assembly  100 . This post is adapted to be pivoted and fits into a respective attachment slot in the curved bracket  216 . The post is preferably configured (e.g., rounded) so as to minimize friction between the post and the curved bracket attachment slot. Once in position, the nut to the bolt that holds the post in place is tightened.  
         [0053]     To attach the struts, a proximal or base end (i.e., a larger diameter end) of each strut  602  is snapped into place over a respective post ball joint located on a side of the ladder assembly  100 . A distal or terminal end of each strut  602  is attached to the rack plate  610  ball socket  623  that slides inside the frame side plate  230 . Once the strut has been attached, a wrench (e.g., a {fraction (7/8)}″ wrench) is used to turn the gear  615  until the strut is compressed, with the rack plate  610  snapped into its fourth and final position. For example, if looking at the head plate  210  of the support frame  200 , the gear  615  on the left frame side plate  230  will be turned in a counter-clockwise direction, while the gear  615  on the right frame side plate  230  will be turned in a clockwise direction.  
         [0054]     Rack plate  610  and ratchet system  620 , such as shown in FIGS.  7 ( a ) and  11 ( b ) are configured to sequentially encounter, deflect, and pass over each of the tabs  201  as the strut  602  is compressed. The tabs  201  serve as backstops or locks against inadvertent and sudden extension by the strut  602 , which could otherwise cause injury to the installer or damage to the folding ladder  100  or related components. Once the strut  602  has been substantially fully compressed, in a location corresponding to the fourth tab  201 , the rack plate  610  may then be secured to the support frame side  230 , such as by a ¼″×1 ½″ lag screw through a hole on the rack  610  above the ratchet system and into the wood joist.  
         [0055]     The proximal end of each strut  602  is adapted to slide, by virtue of the post, within the attachment slot in the curved bracket  216  and the distal end of each strut  602  is fixed in the configuration noted above. Thus, the struts  602  are initially installed in the fully open position with a distal end of each gas strut attached to ratchet system  620  ball socket  623  and a proximal end of each gas strut to a bracket  108  attached to a ladder rail  105 ,  106 , whereafter the strut  602  may then be compressed to a set final position.  
         [0056]     Without the above-described positioning system, a folding ladder employing a gas strut would require a strut distal end to be fixed to the support frame through a suitable connection and the strut proximal end to be secured to the ladder. Such folding ladder configuration would have to be installed at a position rotated backward substantially past its 90° resting position to place the system in the proper position to rotate the ladder back sufficiently to compress the strut. The need to rotate the entire ladder assembly in this manner would require a substantial amount of open space around where the folding ladder is to be installed, which would be detrimental to some space-limited applications. Moreover, unlike conventional folding ladder systems, which require the use of at least two individuals to install the strut, the above-described positioning system permits installation of a folding ladder by a single person.  
         [0057]     Once the ladder is secured in place, a strap or other mechanical fastener holding that ladder sections closed would can be removed and the ladder assembly may safely be unfolded and locked in an unfolded position. To accurately position the ladder with respect to the floor or other base surface, the foot assembly  500  out of the bottom rail section until the foot rests on the floor. The foot assembly  500  may then be secured in position by an appropriate mechanical fastener. For example, a sheet metal screw may be inserted provided through the bottom section  130  rail  105 ,  106  and into the closest hole on the foot assembly  500  rail.  
         [0058]     FIGS.  14 ( a )-( c ) respectively show an isometric view, a front view, and an exploded detail view of a gear  615  for use in the gas strut positioning system in accord with the present concepts. As previously noted, the example presented herein provides a pressure angle of 14.5°, a diametral pitch of 6 with 12 teeth  616 , a pitch diameter P D  of 50.8 mm (2.00″), an outside diameter of about 59.3 mm (2.33″), a root diameter of about 40.2 mm (1.58″), a thickness of about 9.53 mm (0.375″), and a circular tooth thickness of about 0.66 mm (0.262″). A hub  617  having a width of 22.23 mm (0.875″) and a depth of 12.7 mm (0.50″) is provided to facilitate application of a wrench thereto (e.g., a {fraction (7/8)}″ wrench) to manually turn the gear  615  to compress the strut  602  during installation of the gas strut positioning system  600 . Hub  617  could alternately comprise a protruding hub or recessed opening having any shape used to permit external application of torque thereto and could include, for example, a hex-shaped hub or recess, a rectangular or square slot, cross-shaped intersecting slots. This gear configuration is specific to the particular example of the rack system described above and is not to be taken as limiting the broader concepts expressed herein.  
         [0059]     The invention disclosed herein can be practiced by employing conventional materials, methodology and equipment. Accordingly, the details of such materials, equipment and methodology are not set forth herein in detail. In the previous descriptions, numerous specific details of one preferred example, such as specific materials, structures, etc., are set forth to provide a grounding in the present invention. However, it should be recognized that the present invention can be practiced without resorting to the details specifically set forth. In other instances, well known processing structures have not been described in detail, in order not to unnecessarily obscure the present invention. It is to be understood that the present invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein.

Summary:
A support frame for a folding ladder, a folding ladder positioning system, and a method for installing a folding ladder, are disclosed and pertain to folding ladders disposable within an opening, such as openings in a ceiling of a house, to provide temporary access between one floor or space and another floor or space. In one aspect, a support frame includes a plurality of separable support frame plates collectively configured to circumscribe the opening and a plurality of connection sites are disposed at opposing ends of each of the plurality of separable support frame plates to facilitate connection of each support frame plate to adjacent support frame plates. The connection sites include, for example, mating locking connectors or a plurality of matching through-holes, which permit insertion of a fastening means therethrough.