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BACKGROUND OF INVENTION 
       [0001]    In the operation of trucks and other vehicles, the use of a ladder therewith may be needed for the effective operation of the vehicle. Such vehicles may include trucks used for hauling goods or items, service vehicles, emergency vehicles e.g., fire trucks and emergency medical treatment vehicles. Such ladders are useful in assisting in loading and unloading items from a truck or obtaining access to various regions in a fire truck, ambulance or the like. The landing, door or other area of the vehicle that needs access is not always at the same height above the ground often times because of terrain or there may be multiple areas on a single vehicle that need accessed. This presents problems with ladders having deep treads or steps since the treads or steps will not necessarily be at the correct and preferably level pitch. One solution to this problem is the use of ladders with rungs that have a small depth so that the out of pitch condition is not noticeable. Additionally, such ladders may have curved upper surfaces for engagement with a user&#39;s foot so that any out of pitch condition is not noticed. Small depth and curved contact surfaces can cause user discomfort. 
         [0002]    These solutions, however, have not been acceptable particularly when the ladder is to be used where deep treads are desirable for user comfort and stability. It would also be desirable to have a ladder with adjustable pitch steps which pitch does not depend on the surface on which the ladder rests. Additionally, it would be desirable to have a ladder adapted for adjusting the working height by adjusting the angularity of the ladder relative to the device on which the ladder is resting while providing a user adjustable pitch step. 
       SUMMARY OF INVENTION 
       [0003]    The present invention involves the provision of a collapsible ladder having adjustable pitch steps with at least one use pitch. The ladder includes at least one back rail connected to the steps which steps can selectively pivot relative to the back rail. At least one link is connected to the steps to help simultaneous pivoting movement of the steps relative to the back rail. A base is provided for engaging the ground and the base spans a substantial distance on the ground for stability. A stop mechanism is provided and is operably associated with the link and or steps to selectively limit movement of steps relative to the back rail to fix the pitch of the steps. The stop mechanism may include a ratchet mechanism and/or fixed stops. One or more spacers may also be provided to provide for a space between the link and the back rail to eliminate a pinch point. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0004]      FIG. 1  is a front perspective view of a collapsible ladder showing the ladder in a collapsed configuration. 
           [0005]      FIG. 2  is a perspective view of a preferred embodiment of the ladder with the ladder shown resting on a portion of a vehicle. 
           [0006]      FIG. 3  is an enlarged fragmentary perspective view of a portion of the ladder showing the steps in a collapsed configuration for storage. 
           [0007]      FIG. 4  is an enlarged side fragmentary view of a ratchet mechanism and step with the step latched in a collapsed configuration. 
           [0008]      FIG. 5  is an enlarged side fragmentary view of the ladder of  FIG. 4  with the step latched in a first use position 
           [0009]      FIG. 6  is an enlarged side fragmentary view similar to  FIG. 5  but showing the step in a second use position. 
       
    
    
       [0010]    The same number used throughout the various figures designates like or similar parts and/or structure as described herein. 
       DETAILED DESCRIPTION 
       [0011]    The reference numeral  1  designates generally a ladder for use with a vehicle or other device such as a landing  2  which may be part of a vehicle. The ladder  1  is useful with any vehicle, e.g., a vehicle used for transporting and distributing goods or items, an emergency vehicle such as a fire truck or an ambulance, a maintenance or service truck or the like, where on occasion, a user needs to move to an elevated position to perform acts such as loading and unloading, accessing supplies, equipment and the like. The ladder  1  includes a plurality of steps or treads  4  that are supported by a suitable support structure  5  permitting pivoting movement of the steps  4  on the support structure. The support structure  5 , in the illustrated embodiment, includes at least one back rail  7  and at least one link  8  each connected to each of the steps  4 . A landing (not shown) may also be provided as part of the ladder  1 , if desired, which would be particularly useful when the ladder  1  is to be used for loading and unloading items. The support structure  5  also provides the ladder with a base  10  for engaging the ground. The width of the base  10  spans a sufficient distance to provide stability for the ladder. A stop mechanism  14  is also provided which releasably fixes the steps  4  for use in at least one and preferably more than one pitch independent of the angle of the ground on which the ladder  1  rests. Preferably, the stop mechanism  14  provides for a plurality of fixed use pitches. 
         [0012]    In the illustrated structure, the ladder  1  includes a plurality of vertically spaced apart steps  4 . The description of the ladder  1  herein, unless otherwise specified, is for the ladder being positioned in a use configuration with one end portion resting on the ground and another end portion being supported by a vehicle or loading platform. As shown, the steps  4  have a width “W” and a depth “D.” The steps  4  will have a tread plate  16  that is preferably generally planar on the upper surface and may be provided with plurality of traction enhancing members such as holes, raised diamond patterns, ribs and the like. Preferably the steps  4  are made of an aluminum alloy material for lightness and strength. To provide for strength, without excessive use of material, the moment of inertia of the tread plate  16  may be increased by providing a web structure which is shown as including front and rear web members  18  which may be formed with the tread plate. The tread plate  16  and members  18  may be at least partially formed as by extrusion. Opposite ends of the steps  4  may be provided with additional support members  22  which may be secured to the tread plate  16  as by welding. The steps  4  may also be formed by casting. The supports  22  may be secured to the tread plates  16  as with a screw fastener arrangements  24 . The steps  4  have front-to-rear spaced channels  26  that are preferably an integral part of members  18 . As best seen in  FIG. 3 , the supports  22  may be secured to the tread plate  16  with channel members  26  extending between interior faces  27  of the supports  22  which can be fastened in place with screw fasteners  28  extending through the supports  22  and into the channel members  26 . The channel members  26  may have an open side  29  which will permit for expansion of the channel members  26  during installation of the screw fasteners  28 . The end faces of the web members  18  help secure the supports  22  in perpendicular relationship to the treads  16 . 
         [0013]    The ladder  1  includes a step support structure  5 . The step support structure  5  includes at least one rail  7  and at least one link  8 . The steps  4  are pivotally attached to the rail  7  and the link  8 . The rail  7  provides for load bearing support and the link  8  provides for simultaneous adjustment of the pitch of the steps  4 . A base  10  is also provided as part of the support structure  5  and preferably spans a distance to be outside of the normal stepping area of the steps  4  which is preferably at least about one half of the width W of the steps  4  to provide for a reduction in any outside lateral loading moment about the mounting of the steps to the support structure. It is to be understood that a single rail and a single link can be used. However, it is preferred that the support structure  5  includes a pair of spaced apart rails  7  and a pair of spaced apart links  8 . In a preferred embodiment, the rails  7  and the links  8  are aluminum alloy or composite material such as fiberglass U channels. A U channel shape provides for convenience in assembly of the steps  4  to the rails  7  and links  8 . In the illustrated structure, the base  10  is provided for by the lower end portions  32  of the rails  7  which are held in spaced apart relationship by the steps  4 . If a single rail  7  is used, a U-shaped lower leg structure may be used to provide a wide foot print for stability. 
         [0014]    The steps  4  are pivotally mounted to the support structure  5 . As shown, the steps  4  have fasteners  40  such as shoulder bolts or studs secured thereto that are each received through a respective aperture in the web  36  of the U-channels forming the rails  7  and links  8 . By having U-channels, a recess  38  is provided which allows for shielded securement of the fasteners  40 . As seen, friction reducing spacers  42  are provided on the fasteners  40  to space the rails  7  and links  8  from the side edges of the steps  4  to provide for clearance for the fasteners  40 . The steps  4  and the rails  7  and the links  8  on each side form a parallelogram arrangement of parts such that when the links  8  are moved, they remain in an orientation that is generally parallel to the longitudinal axes of the rails  7 . During movement of the links  8 , the links will either move toward or away from the rails  7  narrowing or widening the gap  44  therebetween. Spacers or stops  45  may be secured to either the rails  7  or links  8  to limit movement of the links and rails toward one another so that the gap  44  is wide enough to prevent finger pinching where the ladder  1  is collapsed. Movement of one step  4  or one link  8  will effect simultaneous movement of the other link  8  and steps. The links  8  have opposite ends  46 ,  47  with end  46  being a top end and the other end  47  being a bottom end. The bottom ends  47  of the links  8 , in a preferred embodiment, do not touch the ground but are retained in an elevated position relative to the ground during ladder use. The bottom ends  32 ,  47  of the rails  7  and the links  8 , respectively, may be provided with an end cap member  50 , for example, a curved foot to provide for good contact with the ground and/or prevent contact of a sharp edge of the end with a user. Often times, such feet are made of a polymeric material and are either fastened with mechanical fasteners, press fit or adhesively joined to a rail or link. 
         [0015]    The ladder  1  is provided with a stop mechanism  14  that will selectively limit at least opening movement of the steps  4  and links  8 . Preferably the stop mechanism  14  is operable for fixing the ladder in at least one of a plurality of selectable open configurations. Further, the stop mechanism 14  is operable to selectively retain the steps  4  and links  8  in a closed configuration for storage and to prevent unintended movement of the links and steps during movement of the ladder from a collapsed configuration to an extended use configuration. The stop mechanism  14  is operably associated with the links or one of the steps to selectively limit movement of the steps  4  relative to the rail  7  to selectively fix the pitch of the steps at a desired pitch. The stop mechanism  14  is preferably operated manually by the user of the ladder  1 . 
         [0016]    As seen in  FIG. 3 , the stop mechanism  14  includes at least one ratchet mechanism  60  preferably associated with at least one of the rails  7  and at least one of the steps  4  to selectively fix the pitch of the steps relative to the rail and the ground. In the illustrated structure, the ratchet mechanism  60  includes a ratchet wheel  62  having a plurality of spaced apart teeth  63  for engagement with a pawl  64 . The wheel  62  is shown as having a generally circular edge  66 , however, the wheel can have a curved exterior edge. As shown, the ratchet wheel  62  has a generally circular exterior ratchet surface with a plurality of notches  67  therein. In a preferred embodiment a pair of ratchet mechanisms  60  are provided and the ratchet wheels  62  are each mounted to a respective rail  7  and extend forwardly toward a respective link  8 . 
         [0017]    The ratchet mechanism  60  further includes a pawl  64  that is preferably biased, as for example, by being spring loaded, for engagement with a respective ratchet wheel  62 . The pawl  64  includes a catch portion  72  adapted to fit within a notch  67  on the ratchet wheel  62 . In the illustrated structure, the biasing is done by a torsion coil spring  75  having one end  76  engaging the pawl and one end  77  engaging a bottom side of the tread plate  16 . Preload in the spring  75  biases the pawl  64  toward and into engagement with the ratchet wheel such that the catch portion  72  engages the peripheral edge  66  of the ratchet wheel  62  and is engagable within a selected notch  67 . Preferably, the pawls  64  are fixed to a common shaft  79  to effect simultaneous movement of each pawl for release from a respective notch  67 . As shown, a release device  81 , such as a lever, is mounted or affixed to the shaft  79  as by set screws  83  to effect rotation thereof and pivoting movement of each of the pawls  64 . The shaft  79  is pivotally mounted to a step  4  and the release  81  is positioned under the tread  16 . The release  81  works against the preload of the spring  75  whereby upon release of the lever  81 , via user release, the pawls  64  each move back into engagement with a respective ratchet wheel  62 . As shown, each ratchet wheel  62  has a plurality of peripherally spaced apart notches  67 . The notches are designated  67 A-E respectively for convenience. The notch  67 A, when the pawl is received therein, will lock the links  8  and the steps  4  in a collapsed configuration ( FIGS. 1 ,  4 ) for storage of the ladder  1 . The notches  67  B-E may be used to releasably lock the ladder  1  in a preselected extended configuration ( FIGS. 2 ,  5 ,  6 ) for use. The notches  67 B-E will allow user to select a desired pitch to adjust for the spacing between the ground on which the ladder will rest and the platform to which the ladder will provide steps to, for example, the interior of a truck, a loading dock or the like. The configuration of the notches  67  and the teeth  63  forming some of the notches is such as to permit free movement from the extended configuration to the collapsed configuration until the pawls  64  are received in a respective notch A which will lock the ladder and its component parts in the collapsed configuration. The notches  67  are also configured to selectively lock the ladder from moving from one extended position to a more downward extended position i.e., a one way ratchet. If the pitch is too high i.e., the steps are sloping downward and inwardly, the pawls  64  may be released from a respective notch  67  to allow the steps to be lowered on their free end. In use, it is more convenient to extend the ladder to its fully extended position and then move the steps upwardly until the desired step pitch is achieved. The pawls  64  are visible to allow a user to ensure that both of the pawls  64  are latched into a respective notch  67  indicating that the ladder  1  is ready to use. 
         [0018]    As shown, the links  8  do not touch the ground during use and serve to effect simultaneous movement of the steps  4  when either a link  8  is moved or a step  4  is moved by a user. However, in an alternative embodiment, it is to be understood that the links  8  may contact the ground if desired when in an extended position. This would be particularly useful for ladders that are to be used on relatively flat and level ground surfaces e.g., a paved parking lot. In another alternate embodiment, the ratchet mechanisms  60  may be eliminated, and a fixed stop structure  85  (seen in phantom in  FIG. 1 ) may be used as the stop mechanism  14  to limit movement of the links  8  and steps  4  to an extended or use configuration. Further, a plurality of such stop structures  85  may be used to provide for a variety of pitches for the steps. As seen in  FIG. 1 , the alternate stop structure  85  is shown as having one stop member on each rail  7 . As shown, a stop member  85  is secured to each of the rails  7  and is engagable with a lower end of a respective link  8  when the links are moved from a collapsed configuration to an extended configuration limiting further movement of the links and fixing the pitch of the steps. The pitch of the steps  4  may be adjusted somewhat by the angle of the ladder when it is leaned against a device such as a truck bed for loading. 
         [0019]    As best seen in  FIGS. 1 ,  2 , the ladder  1  is provided with a securement structure to releasably secure the ladder to the device providing the elevated loading or work surface or storage area. As shown, one or both of the rails  7  may be provided with a hook  90  which can be received within a groove  92  to releasably fix the upper portion of the ladder to the vehicle or the like. The ladder  1  may also be provided with an attached landing (not shown) which may be pivotally mounted to one or both of the rails and suitably constructed for limiting upward movement of the free ends of the landing relative to the rails  7  say, for example, an included angle between the landing and the rails of up to about 120 degrees and preferably more than 90 degrees. 
         [0020]    Thus, there has been shown and described several embodiments of a novel invention. As is evident from the foregoing description, certain aspects of the present invention are not limited by the particular details of the examples illustrated herein, and it is therefore contemplated that other modifications and applications, or equivalents thereof, will occur to those skilled in the art. The terms “having” and “including” and similar terms as used in the foregoing specification are used in the sense of “optional” or “may include” and not as “required”. Many changes, modifications, variations and other uses and applications of the present invention will, however, become apparent to those skilled in the art after considering the specification and the accompanying drawings. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention which is limited only by the claims which follow.

Summary:
The present invention involves a selectively collapsible ladder which permits for adjusting the pitch of the steps between at least two pitches, one pitch being where the ladder collapsed for storage and another pitch whereby the steps are positioned for use by a user. The ladder includes a support structure comprising one or more support rails for extending between the ground and a loading or work surface or storage compartment. The steps are connected together by one or more links for effecting simultaneous movement of the steps. A stop mechanism is provided to releasably fix the step pitch relative to a support rail. The stop mechanism may include a ratchet mechanism that permits setting the pitch of the steps at one of several available pitch settings.