You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a lockable protective cap that may be secured to a post to prevent people or animals from being injured on the post.  
       BACKGROUND OF THE INVENTION  
       [0002]     Metal posts having a “T” cross-section are often used as fence posts or supports for plants, such as newly planted trees. These posts are often manufactured by extrusion or rolling and then sheared to length. The shearing process typically leaves a sharp edge or burr on the top of the post. Additionally, as the post is driven into the ground, the top of the post is flattened and creates a sharp edge around the perimeter of the post. Injuries to people or livestock from the sharp edges on a post range from small scratches or cuts to deep lacerations or impalement.  
         [0003]     Where metal posts have been installed in public areas, such as around schools and playgrounds, children have been injured by exposed sharp edges on the tops of the posts. Even where protective caps have been placed on the posts, children or teenagers often remove the caps from the posts leaving the sharp edges exposed.  
       SUMMARY OF THE INVENTION  
       [0004]     The present invention comprises a lockable, protective cover or cap for the top of posts. The cap comprises a sidewall having a first end and a second open end, the sidewall forming a post receiving opening; a cover at least partially closing the first end of the sidewall; and a locking member extending inwardly from the sidewall for engaging the engageable surface of the post.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]      FIG. 1  shows a perspective view of a first embodiment of a lockable protective cap of the present invention installed on a post;  
         [0006]      FIG. 2  shows a broken perspective view of the embodiment of a lockable protective cap of  FIG. 1  installed on a post;  
         [0007]      FIG. 3  shows a cross-sectional view of the embodiment of a lockable protective cap of  FIG. 1 ;  
         [0008]      FIG. 4  shows a partially-sectional perspective view of a second embodiment of a lockable protective cap of the present invention;  
         [0009]      FIG. 5  shows a cross-sectional view of the embodiment of a lockable protective cap of  FIG. 4 ;  
         [0010]      FIG. 6  shows a cross-sectional view of the embodiment of a lockable protective cap of  FIG. 4  installed on a post taken along section line  6 - 6 ;  
         [0011]      FIG. 7  shows a partially-sectional perspective view of a third embodiment of a lockable protective cap of the present invention;  
         [0012]      FIG. 8  shows a cross-sectional view of the embodiment of a lockable protective cap of  FIG. 7  installed on a post taken along section line  8 - 8 ;  
         [0013]      FIG. 9  shows a cross-sectional view of the embodiment of a lockable protective cap of  FIGS. 7 and 8  taken along section line  9 - 9 ;  
         [0014]      FIG. 10  shows a partially-sectional perspective view of a third embodiment of a lockable protective cap of the present invention;  
         [0015]      FIG. 11  shows a cross-sectional view of the embodiment of a lockable protective cap of  FIG. 10  installed on a post taken along section line  11 - 11 ; and  
         [0016]      FIG. 12  shows a cross-sectional view of the embodiment of a lockable protective cap of  FIGS. 10 and 11 . 
     
    
     DETAILED DESCRIPTION  
       [0017]      FIGS. 1 and 2  show a typical “T-shaped” metal post  10 . The post  10  comprises an elongated shaft  12  having laterally extending flanges  14 . A series of protruding studs  16  extend along a front surface of the post  10 . The precise location of the studs  16  along any particular post is somewhat random depending on where the post has been cut. Therefore, a first stud may be positioned directly at the top edge of the post  10 , it may be spaced apart from the top edge, or only a partial stud may be present at the top of the post, all depending upon where the post is cut during the manufacturing process. Although the present invention is generally described with respect to such a “T-shaped” post, one skilled in the art would readily understand that the invention may also be used with respect to posts of other shapes as long as the posts comprise a structure that may be engaged, such as the studs  16  of the “T-shaped” posts described herein.  
         [0018]      FIGS. 1 through 3  show a first embodiment of a lockable protective post cap  20  of the present invention that may be used with a post, such as the “T-shaped” post shown in  FIGS. 1 and 2 . The cap  20  comprises a sidewall  22  forming a post-receiving opening  24  and a cover  26 . The cover  26  may be integrally formed with the sidewall  22  (see, e.g.,  FIGS. 4, 5 ,  10  and  12 ) or may be separately formed and attached to the sidewall  22  (see, e.g,  FIGS. 1 through 3 ), such as via adhesion, fusion, heat staking or the like. Where the cover  26  and the sidewall  22  are separately formed and attached, such as shown in  FIGS. 1 through 3 , the cover  26  and sidewall  22  may be formed such that the outer wall of the cover and the outer wall of the sidewall fit flush with each other or either the cover  26  or the sidewall  22  may overlap one another. The cover  26  is preferably rounded, as shown in  FIGS. 4 and 5 , so that the cap  20  does not provide any exposed sharp edges.  
         [0019]     The cap  20  further comprises a locking member  28  for engaging a stud  16  of the post  10 . In this embodiment, the locking member  28  protrudes inwardly at an angle A from the sidewall  22  of the cap  20 . In one embodiment, for example, the angle A may comprise an angle from about 30 degrees to about 60 degrees, from about 40 degrees to about 50 degrees or about 45 degrees. The locking member  28  may be formed unitarily with the sidewall  22  as shown in  FIGS. 1 through 3  or may comprise a separate portion that is attached to the sidewall  22  of the cap  20 . The locking member  28  may be formed unitarily with the sidewall  22 , for example, such as via molding or extruding, or may be formed of a separate portion attached to the body, such as via adhering, fusing, heat staking or the like. In one embodiment of the present invention, for example, the locking member  28  may be punched or cut out of the sidewall  22  and bent to form the locking member  28 . Alternatively, the locking member  28  may be molded or otherwise formed at an angle from the sidewall  22 .  
         [0020]     The locking member  28  provides an angled surface  30  for sliding over an engaging surface of the post  10 , such as a stud  16 , as the cap  20  slides over the end of the post  10 . In this embodiment, the locking member  28  may be flexible enough to deform over a stud  16  as the cap  20  slides over the end of the post  10 . As the locking member  28  slides past the stud  16 , however, the locking member  28  is sufficiently resilient to engage the stud  16  of the post  10 . Thus, the locking member  28 , after passing the stud  16 , rebounds and the distal end  32  of the locking member  28  provides a surface for engaging the stud  16  and prevents the cap  20  from being removed from the post  10 . In another embodiment, the sidewall  22  of the cap  20  may deform along with or instead of the locking member  28  as the cap  20  slides over the end of the post  10  and the angled surface  30  comes into contact with the stud  16 . In this embodiment, after the locking member  28  passes the stud  16 , the sidewall  22  and/or the locking member  28  of the cap  20  rebound and the distal end  32  of the locking member  28  provides a surface for engaging the stud  16  and prevents the cap from being removed from the post  10 .  
         [0021]     The sidewall  22  may comprise a generally cylindrical shape as shown in  FIGS. 1 through 12  or may comprise any other shape for receiving a post  10 . For a T-shaped post  10 , such as shown in  FIGS. 1 and 2 , for example, the sidewall  22  may comprise a generally T-shaped configuration for receiving the post within the post-receiving opening  24 . In this embodiment, for example, the generally T-shaped configuration of the sidewall  22  prevents the cap  20  from being twisted with respect to the post  10 . This, in turn, prevents the locking member  28  from being disengaged from the stud  16  of the post  10  by turning the cap  20  with respect to the post  10 . In another embodiment, after the cap  20  is placed onto the end of the post  10 , the sidewall  22  may be deformed around at least a portion of the post  10  to prevent the cap  20  from being twisted with respect to the post  10  and, in turn, prevent the locking member  28  from being disengaged from the stud  16  of the post  10  by turning the cap  20  with respect to the post  10 .  
         [0022]     Since the position of the studs  16  with respect to a post may vary with respect to the top of the post  10 , the distance between the inner surface of the cap  20  and the distal end  32  of the locking member  28  preferably is long enough to ensure that at least one stud is located above the distal end  32  of the locking member  28  when the cap  20  is placed over the top of the post  10 . Thus, the distance between the inner surface of the cap  20  and the distal end  32  of the locking member  28  is preferably at least equal to the center-to-center spacing of the studs on a post  10 . Where a post  10  includes two inch center-to-center spacing between studs, for example, the cap  20  preferably comprises a length from the inner surface of the cover  26  to the distal end  32  of the locking member  28  of at least two inches. Even more preferably, since a stud or a partial stud may be located at the very top of the post  10  and may be damaged when the post is driven into the ground, the cap  20  comprises a length from the inner surface of the cover  26  to the distal end  32  of the locking member  28  of at least the center-to-center spacing of the studs  16  plus the length of a stud  16  so that the locking member  28  of the cap  20  may engage a stud displaced from the top edge of the post  10 . In the example above where the center-to-center spacing of the studs is two inches and where the length of a stud is about 0.75 inches, for example, the length of cap from the inner surface of the cover  26  where the top edge of a post could abut the cover to the distal end  32  of the locking member is preferably at least about 2.75 inches.  
         [0023]     As shown in  FIGS. 4 and 5 , the cap  20  may comprise a cover  27  that does not completely enclose the top end of the cap  20 . In this embodiment, the cover  27  comprises a protective lip  29  that extends around the cap and covers at least the periphery of the post  10 . The protective lip  29  prevents the cap from sliding down the post and exposing the top end of the post. While potentially sharp edges of the post  10  may be accessed through the opening in the cover  27 , the protective lip  29  reduces the likelihood of accidental contact with those edges.  
         [0024]      FIGS. 7 through 9  show another embodiment of a cap  40  of the present invention. The cap  40  further comprises channel  54  for receiving an elongated shaft  12  or flange  14  of the post  10 . The channel  54  may, for example, extend the length of the sidewall  42  as shown in  FIG. 9  or may extend only a portion of the length of the sidewall  42 . The channel  54  may be formed unitarily with the sidewall  42  of the cap  40 , such as via molding or extruding, or may comprise one or more separately formed portion that is attached to the sidewall  42  of the cap  40 , such as via adhering, fusing, heat staking or the like, or may comprise an opening in the sidewall (e.g., a slot) through which the elongated shaft  12  or a flange  14  of a post may be extended. In the embodiment shown in  FIGS. 7 through 9 , for example, the elongated shaft  12  or flange  14  of the post extends into the channel  54  and the channel walls  56  prevent the cap  40  from being twisted with respect to the post  10 . Thus, the locking member  48  remains aligned with the stud  16  of the post  10  and prevents the locking member  48  from being disengaged from the stud  16  of the post  10  by turning the cap  40  with respect to the post  10 .  
         [0025]      FIGS. 10 through 12  show yet another embodiment of a cap  60  of the present invention. The cap  60  comprises a locking member  68  extending from the interior of the sidewall  62  of the cap  60 . In this embodiment, the locking member  68  may be unitarily formed with the sidewall or may comprise a member separately formed and attached to the sidewall  62 . The locking member  68  may further comprise a rib  76  that extends around an arc of the sidewall  62 . The rib  76  may extend around the entire perimeter, or substantially around the entire perimeter, of the post-receiving opening  64 , or may extend around only a portion of the perimeter of the post-receiving opening  64 . In an embodiment in which the locking member  68  comprises a rib  76  extending around the entire or a substantial portion of the perimeter of the post-receiving opening  64 , the rib  76  may be used to engage a post where the studs extend further from the shaft than the flanges of the post or where a particular post does not include flanges. In this embodiment, the rib  76  provides a locking member  68  that is more easily aligned with a stud  16  of the post and allows the cap  60  to be turned substantially completely around the post without disengaging the locking member  68  of the cap  60  from the stud  16  of the post  10 .  
         [0026]     A cap of the present invention may be manufactured at least partially comprising a sufficiently resilient material to allow the locking member to engage a portion of a post. Preferably, the cap is manufactured using a low-cost resilient plastic such as poly vinyl chloride (PVC), acrylonitrile-butadienestyrene (ABS), or a styrene-acrylonitrile copolymer (SAN). Alternatively, other resilient materials may be used.  
         [0027]     While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various other changes in the form and details may be made without departing from the spirit and scope of the invention.

Summary:
A lockable protective cap for a post is disclosed. The protective cap comprises a sidewall having a first end and an open second end. The sidewall forms a post receiving opening for receiving a post through the open second end. The cap further comprises a cover at least partially closing the first end of the sidewall and a locking member extending from the sidewall for engaging an engageable surface of the post.