Abstract:
A ladder incorporating a vertical support structure and a set of removable rungs. The vertical support structure is formed by stacking a series of interlocking sticks. The sticks incorporate features allowing the removable installation of the rungs. The rungs are small and light, so that a set of such rungs may be easily carried by a user. The vertical sticks generally remain attached to the object to be climbed—such as a tree or pole. When the user wishes to climb the object, the user installs the rungs as he or she climbs. The rungs are then removed upon descent. In this manner, unauthorized climbing of the object is inhibited. Locking features are also included to prevent unauthorized access by another person having a set of removable rungs. Several different embodiments of the removable rungs are disclosed. The application of the invention to different types of hunting tree stands is also disclosed in detail, although the application of the invention extends far beyond hunting products.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]    This application is a continuation in part of application Ser. No. 10/058,901, having a filing date of Jan. 30, 2002 (also naming Timothy Scott Skipper as sole inventor). 
     
    
     
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not Applicable  
         MICROFICHE APPENDIX  
         [0003]    Not Applicable  
         BACKGROUND OF THE INVENTION  
         [0004]    1. Field of the Invention  
           [0005]    This invention relates to the field of ladders. More specifically, the invention comprises a modular ladder having removable steps.  
           [0006]    2. Description of the Related Art  
           [0007]    The incorporation of removable rungs into various structures is well known in the prior art. As one example, U.S. Pat. No. 6,247,553 to Jones (2001) discloses a removable rung (or step) designed to be applied to a steel T-post of the type commonly used for cattle fencing. It allows a user to step over a modem fence line without having to put weight on the strands of barbed wire. The Jones device is not easily removable, however. It is designed to be installed and left in place. Thus, it is ill suited for the type of application encompassed by the present invention.  
           [0008]    U.S. Pat. No. 3,833,090 to Georgianna (1974) discloses a removable step designed to be locked into a steel support column. This invention is directed to warehouse racks, whose vertical columns already include slots for the mounting of shelves and the like. The step design in the &#39;090 patent takes advantage of these pre-existing slots. The step is quite large and cumbersome, however. It would be difficult to store a set of such steps on the user&#39;s person, and quite cumbersome to carry them over long distances.  
           [0009]    A similar device is disclosed in U.S. Pat. No. 4,450,936 to Strom (1984). The Strom device also takes advantage of the pre-existing slots found in warehouse columns. Unlike the Georgianna device, though, it is formed of simple bar stock components. The &#39;936 device should therefore be easier to fabricate. It is still quite bulky, however. In addition, it requires a support column having a large interior cavity so that the step can be “snaked” into position. While such a large cavity is often found in warehouse columns, it is rarely found elsewhere.  
           [0010]    Accordingly, the prior art devices are limited in that they:  
           [0011]    1. Are difficult to apply and remove;  
           [0012]    2. Are heavy;  
           [0013]    3. Are bulky; and  
           [0014]    4. Require a vertical column having a large interior cavity. Require the deployment  
         BRIEF SUMMARY OF THE INVENTION  
         [0015]    A ladder is composed of a vertical support structure and a set of rungs. In the present invention, the vertical support structure is formed by stacking a series of interlocking sticks. The sticks incorporate features allowing the removable installation of a set of rungs. The rungs are small and light, so that a set of such rungs may be easily carried by a user. The vertical sticks generally remain attached to the object to be climbed—such as a tree or pole. When the user wishes to climb the object, the user installs the rungs as he or she climbs. The rungs are then removed upon descent. In this manner, unauthorized climbing of the object is inhibited.  
           [0016]    Several different embodiments of the removable rungs are disclosed. The common feature of all these embodiments is the fact that the rungs cannot come loose from the vertical stick while they are under load (some embodiments cannot come loose, whether loaded or not). The application of the invention to different types of hunting tree stands is also disclosed in detail, although the application of the invention extends far beyond hunting products.  
           [0017]    A locking mechanism, which allows the user to lock the device in a position where it cannot be climbed by an unauthorized user, is also provided. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is an isometric view, showing a prior art tree stand and ladder.  
         [0019]    [0019]FIG. 2 is an isometric view, showing a prior art climbing stick in greater detail.  
         [0020]    [0020]FIG. 3 is an isometric view, showing the vertical support element of the proposed invention.  
         [0021]    [0021]FIG. 4 is an isometric view, showing the details of the angled holes piercing the vertical support element.  
         [0022]    [0022]FIG. 4B is an isometric view, showing the alternating nature of the angled holes in the vertical support element.  
         [0023]    [0023]FIG. 5 is an isometric view, showing a removable rung.  
         [0024]    [0024]FIG. 6 is an isometric view, showing the installation of a removable rung.  
         [0025]    [0025]FIG. 7 is an isometric view, showing the installation of a removable rung.  
         [0026]    [0026]FIG. 8 is an isometric view, showing the installation of a removable rung.  
         [0027]    [0027]FIG. 9 is an elevation view, showing the installation of a removable rung.  
         [0028]    [0028]FIG. 10 is an elevation view, showing the installation of a removable rung.  
         [0029]    [0029]FIG. 11 is an isometric view, showing the removable rungs in place on the vertical support element.  
         [0030]    [0030]FIG. 12 is an isometric view, showing two of the vertical support elements stacked together, with rungs attached.  
         [0031]    [0031]FIG. 13 is an isometric view, showing the vertical support elements attached to a tree.  
         [0032]    [0032]FIG. 14 is an isometric view, showing the details of the base stick.  
         [0033]    [0033]FIG. 15 is an isometric view, showing the locking slide.  
         [0034]    [0034]FIG. 16 is an isometric view, showing the operation of the locking mechanism.  
         [0035]    [0035]FIG. 17 is an isometric view, showing the operation of the locking mechanism.  
         [0036]    [0036]FIG. 18 is an isometric view, showing an alternate embodiment of the removable rung.  
                                         REFERENCE NUMBERALS IN THE DRAWINGS                                10   tree       12   tree stand       14   climbing stick       16   fixed rung       18   securing strap       20   standoff       26   inclined hole       30   strap lock       38   removable rung       40   step       42   insertion cylinder       52   ladder stand       56   base       60   transverse hole       90   lock hole       96   pierced stick       98   strap anchor       100   extension       102   receptacle       104   admission slot       106   leading protrusion       108   trailing protrusion       110   first side wall       112   second side wall       114   base stick       116   locking handle       118   locking hole       120   slot       122   locking slide       124   inclined notch       126   horizontal hole       128   alternate rung                  
 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0037]    The proposed invention allows a user to climb many types of vertical objects. One particular application of the invention is in the field of hunting, where tree stands are often employed to provide the hunter an elevated and stationary position. FIG. 1 shows a prior art tree stand  12  attached to a tree  10 . As installing a tree stand requires considerable effort, hunters often wish to leave them in place. This requires a device for climbing the tree. FIG. 1 also discloses a prior art tree-climbing device. A series of climbing sticks  14  are linked together and attached to tree  10 . Each climbing stick  14  has a series of fixed rungs  16 .  
         [0038]    [0038]FIG. 2 shows an individual climbing stick  14  in more detail. The reader should be aware that the square vertical member is hollow, so that a second climbing stick  14  can be placed on top of the one shown and linked together using the smaller square section located on top of the climbing stick  14 . Two stand offs  20  are provided to separate climbing stick  14  from the tree  10 , thereby allowing clearance for the user&#39;s boots on fixed rungs  16 . A pair of securing straps  18  are passed tightly around the tree  10  and locked in position by toggle clamps or other prior art means.  
         [0039]    The prior art devices shown in FIGS. 1 and 2 are effective in allowing access to the tree stand  12 . Unfortunately, when the user leaves the tree stand  12  unattended, other persons may use the ready access to steal the tree stand. In addition, many landowners are concerned about the safety of unsecured ladders in position on their property. If children or persons unfamiliar with tree climbing climb the unsecured ladders, they may be injured. Thus, it is desirable to create a ladder which cannot be climbed without specialized equipment.  
         [0040]    [0040]FIG. 3 discloses one embodiment of the present invention. Pierced stick  96  is similar in its general configuration to the prior art climbing stick  14 , except that it includes no fixed rungs  16 . Two stand offs  20  are provided, along with securing strap  18 , which is attached via strap anchor  98 . Strap  18  is locked in place around the object to be climbed by actuating strap lock  30 .  
         [0041]    Pierced stick  96  incorporates features allowing a series of such sticks to be assembled vertically. The lower portion of the device incorporates extension  100 . The upper portion encompasses, via the hollow nature of the material used, receptacle  102 . Those skilled in the art will readily appreciate that a second pierced stick  96  could be mated to the one shown in FIG. 3 via inserting the extension  100  of the second pierced stick  96  into the receptacle  102  of the pierced stick  96  shown. Additional pierced sticks  96  could then be added to create a column of desired height.  
         [0042]    The vertical support column of pierced stick  96  is modified over the prior art. Like the prior art device, it is formed primarily of a hollow square section. However, it is also pierced by a series of inclined holes  26 . FIG. 4 shows a detailed view of one of these inclined holes  26 . The reader will observe that they are substantially inclined from the horizontal. In addition, one side of the hole incorporates admission slot  104 .  
         [0043]    [0043]FIG. 4B shows another view of pierced stick  96 . The reader will observe that alternating inclined holes  26  are actually inclined in opposite directions. In addition, the admission slots  104  alternate as well, with admission slot  104  being always located on the upper extreme of inclined hole  26 . The reasons underlying these features will be explained in the following.  
         [0044]    [0044]FIG. 5 shows removable rung  38 . It comprises two main components: insertion cylinder  42  and step  40 . Insertion cylinder  42  includes two protrusions, separated by linear distance and  180  degrees of rotation. The first of these, leading protrusion  106 , descends from the lower extreme of insertion cylinder  42 , just aft of its leading end (the right-hand extreme, in the view shown). The second of these, trailing protrusion  108 , ascends from the upper extreme of insertion cylinder  42 , near where it joins step  40 .  
         [0045]    [0045]FIGS. 6 through 8 illustrate the sequence of inserting removable rung  38  into pierced stick  96 . First, removable rung  38  is inverted by rotating insertion cylinder  42  180 degrees. The reader will observe that leading protrusion  106  is now extending upwards. This orientation allows leading protrusion  106  to pass through admission slot  104  and into the interior of pierced stick  96  (which, as explained previously, is hollow). The user then advances insertion cylinder  42  into the hollow interior until trailing protrusion  108  comes up against the outer surface of pierced stick  96 .  
         [0046]    Next, as shown in FIG. 7, the user rotates removable rung  38  (in either direction)  180  degrees, so that trailing protrusion  108  aligns with admission slot  104 . The user then advances insertion cylinder  42  further into inclined hole  26 —as shown in FIG. 8  
         [0047]    Turning now to FIG. 9, the reader will observe that further progress of insertion cylinder  42  through inclined hole  26  has been arrested by the fact that leading protrusion  106  has come up against second side wall  112  (where admission slot  104  was found in first side wall  110 ). Second side wall  112  has no admission slot—it only has the inclined hole. Thus, the removable rung is locked in place.  
         [0048]    The geometry of removable rung  38  reveals that it is locked in place under load. The reader will also observe, however, that trailing protrusion  108  rests within admission slot  104 . Thus, whether loaded or not, removable rung  38  is restrained from rotating and is thereby locked in place. Only through deliberate manipulation is it possible to remove it  
         [0049]    Step  40  extends out from the side of pierced stick  26  Since it forms the stepping surface for a user climbing the device, it may be knurled or coated with a non-slip surface to promote traction. As illustrated previously in FIG. 4B, successive inclined holes  26  are actually inclined in opposite directions. This alternating orientation is provided so that alternating steps can be inserted on opposite sides of pierced stick  26 . FIG. 10 shows an elevation view of a removable rung  38  inserted from the right-hand side (in the view as shown). The reader will observe that the inclined hole  26  shown is inclined in the opposite direction from the one shown in FIG. 9. Likewise, it has admission slot  104  located on second side wall  112  rather than first side wall  110 . This mirror-imaging of the previously disclosed features allows removable rung  38  to be inserted from the right rather than the left. Removable rung  38  is absolutely identical; i.e., the same rung can be inserted from the right or the left, depending on the incline of inclined hole  26 .  
         [0050]    [0050]FIG. 11 shows pierced stick  96  with four removable rungs  38  locked in position. The reader will now understand why successive inclined holes  26  must be inclined in opposite directions in order to allow removable rungs  38  to be inserted in alternating sides.  
         [0051]    [0051]FIG. 12 shows two pierced sticks  96  locked together—as previously described. FIG. 13 shows a column of pierced sticks  96  attached to a vertical object to be climbed—in this case tree  10 . Although a tree has been used for the illustration, those skilled in the art will realize that the invention can also be easily attached to utility poles, walls (using different attaching means), or other types of vertical objects.  
         [0052]    In actual use, a stack of four or more pierced sticks  98  would be placed on the tree  10  or other object to be climbed. The sticks  98  are attached to the tree  10  using the securing straps  18  which are well known in the prior art. All removable rungs  38  would be removed before leaving the device unattended. A user wishing to climb the device would need to bring along a set of removable rungs  38 . The user would then progressively install removable rungs  38  as he or she ascends the ladder. When the user later descends the ladder, removable rungs  38  would be progressively removed.  
         [0053]    A rung to rung spacing of  9  to  18  inches is typical for this type of device. Accordingly, in order to ascend a twelve foot object, the user would need to bring approximately eight to sixteen removable rungs  38 . These rungs  38  can be made of aluminum alloy, resulting in a modest weight, even for a set of sixteen.  
         [0054]    [0054]FIG. 13 also discloses another type of vertical support element—base stick  114 . Base stick  114  is not strictly necessary. A normal pierced stick  96  can be used instead. However, as it incorporates additional features, base stick  114  is desirable.  
         [0055]    [0055]FIG. 14 shows base stick  114  in greater detail. The reader will observe that it is longer than pierced stick  96 , encompassing one additional inclined hole  26 . It also has a flat lower extreme (lacking the extension). This lower extreme is typically placed on the ground.  
         [0056]    It is desirable to prevent unauthorized persons from using the invention to climb an object to which it is secured. Some unauthorized persons may have access to removable rungs  38 . Thus, an additional security measure is advantageous. FIG. 15 discloses locking slide  122 . It is also formed from a hollow square section. It is sized to slidably fit within the hollow interior of base stick  114 . Locking slide  122  is cut by a series of inclined notches  124 . Locking hole  118  also passes transversely through locking slide  122  (it is also inclined).  
         [0057]    Locking handle  116  is attached to the rear surface of locking slide  122  It allows the user to move locking slide  122  up and down within the interior of base stick  114 , as will be explained in the following.  
         [0058]    [0058]FIG. 16 is a hidden-line view showing locking slide  122  inside base stick  114 . The reader will observe that inclined notches  124  within locking slide  122  align with inclined holes  26  in base stick  114 . In the position shown, locking slide  122  does not interfere with the addition or removal of removable rungs  38 . Thus, the position shown is the “unlocked” position.  
         [0059]    Locking handle  116  passes through the rear wall of base stick  114  through slot  120 . Of course, locking handle  116  must be made removable from locking slide  122  (such as by a threaded engagement), in order to allow assembly. During assembly, locking slide  122  is typically slipped into base stick  114 . The threaded hole for receiving locking handle  116  is then aligned with slot  120 . Locking handle  116  is then threaded into position, where it remains.  
         [0060]    The view in FIG. 16 shows that locking hole  118  is positioned well below the upper inclined hole  26 . Gravity maintains locking slide  122  in this position, by pulling locking handle  116  to the lower extreme of slot  120 .  
         [0061]    In FIG. 17, the user has grasped locking handle  116  and pulled locking slide  122  upward until locking handle  116  stops against the upper extreme of slot  120 . The reader will observe that inclined notches  124  no longer align with inclined holes  26 . In fact, the solid side walls of locking slide  122  now completely obstruct inclined holes  26  in base stick  114 . This fact prevents the installation of any removable rungs  38 , rendering the device inoperable. The reader will also observe that locking hole  118  in locking slide  122  now aligns with the upper inclined hole  26  (upper in this particular view). This fact allows a user to pass a lock through the aligned holes, thereby securing the device in an inoperative state.  
         [0062]    Although the use of the removable rung  38  having an inclined cylinder  42  is preferable, it is by no means the only manner of implementing the invention. FIG. 18 shows a simplified version employing a straight alternate rung  128 . The hole through pierced stick  96 , in the embodiment shown, is horizontal. Alternate rung  128  has leading protrusion  106  and trailing protrusion  108 , again separated by distance and  180  degrees of rotation. To install alternate rung  128 , the user aligns leading protrusion  106  with admission slot  104 , then pushes the right-hand portion of the rung into the hollow interior of pierced stick  96 . The user then rotates alternate rung  128  to align trailing protrusion  108  with admission slot  104 . By this point, the right hand (in the view) portion of alternate rung  128  will be seated within the right hand hole in pierced stick  96 .  
         [0063]    The embodiments described have been modular; i.e., they can be broken down into reasonable short segments to aid portability. However, those skilled in the art will also realize that the invention could be made non-modular. As an example, a long version of pierced stick  96  (perhaps  20  feet long) could be bolted to a utility pole. Such a pierced stick  96  would have  26  or more inclined holes  26 . The application of the device to a utility pole would prevent unauthorized climbing, while allowing service personnel to easily climb the pole. A long version of pierced stick  96  could also be attached to the vertical walls of manholes and other construction features.  
         [0064]    Likewise, those skilled in the art will know that many hunting stands are free-standing—such as tripod stands. The removable rung features could be incorporated into one of the legs of the tripod. The removable rung features could also be incorporated into the legs of a ladder stand.  
         [0065]    Although the preceding description contains significant detail, it should not be construed as limiting the scope of the invention but rather as providing illustrations of the preferred embodiment of the invention. Thus, the scope of the invention should be fixed by the following claims, rather than by the examples given.