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CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the priority of U.S. Provisional Patent Application Ser. No. 61/830,534 filed Jun. 3, 2013, which application is incorporated in its entirety herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to extension ladder accessories and in particular to a paint can shelf attachable to a sliding extension ladder fly section. 
     Painters have been faced with the problem of supporting a paint can on an extension ladder for many years. Various holders have been developed and marketed, but none have succeeded to provide a good solution. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention addresses the above and other needs by providing an extension ladder paint can shelf which attaches to a sliding extension ladder fly section and slides against a fixed extension ladder section. The shelf includes two parallel arms which reach through hollow rungs of the sliding extension ladder fly section, whereby the shelf is raised and lowered with the sliding extension ladder fly section. Slides are attached to the arms on each side of the sliding extension ladder fly section and include low friction surfaces facing the fixed extension ladder section. The slides allow somewhat loose tolerances in the engagement of the arms with the ladder preventing the ladder sections from binding when the ladder is extended or lowered. 
     In accordance with one aspect of the invention, the extension ladder paint can shelf includes a slide residing against a face of an extension ladder base section side rail. The hollow rungs of the fly section of the extension ladder are only slightly displaced outward from the face and typical extension ladder tolerance do not facilitate an extension ladder paint can shelf spaced outward from the face of the base section side rail. To prevent binding when the ladder is extended or lowered, a low friction material is attached to the side of the slider facing the rail face. The material may be, for example, metal, plastic, TEFLON® material, TURCITE® material, and the like. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
         FIG. 1  shows a perspective view of a prior art extension ladder. 
         FIG. 2  shows a perspective view of a paint can shelf according to the present invention for use with the extension ladder. 
         FIG. 3  shows an exploded perspective view of the paint can shelf according to the present invention with the extension ladder. 
         FIG. 4A  shows a perspective view of the assembled paint can shelf according to the present invention attached to the extension ladder. 
         FIG. 4B  shows a front view of the assembled paint can shelf according to the present invention attached to the extension ladder. 
         FIG. 5A  is a side view of a bent elbow of the paint can shelf according to the present invention. 
         FIG. 5B  is a front view of the bent elbow of the paint can shelf according to the present invention. 
         FIG. 6  shows a perspective view of a slide member of the paint can shelf according to the present. 
         FIG. 7A  shows a side view of the slide member of the paint can shelf according to the present. 
         FIG. 7B  shows a rear view of the slide member of the paint can shelf according to the present. 
         FIG. 8  shows a cross-sectional view of arms of the paint can shelf according to the present residing in ladder rungs. 
         FIG. 9  shows a compressible ring according to the present invention around a top edge of a paint can recess in the paint can shelf. 
     
    
    
     Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing one or more preferred embodiments of the invention. The scope of the invention should be determined with reference to the claims. 
     A perspective view of a prior art extension ladder  10  is shown in  FIG. 1 . The extension ladder  10  includes a stationary base section  12  and an extending fly section  16 . The base section  12  include a base section side rails  14   a , and the fly section  14  includes fly section slide rails  14   b , and hollow rungs  18 . The fly section  16  can be lowered to generally align with the base section  12  for a minimum ladder length, or can be extended with respect to the base section  12  to obtain a longer ladder  10 . The ladder  10  is leaned at an angle A 1  during use to provide stability. The angle A 1  is preferably 13 to 17 degrees from vertical. 
     A perspective view of a paint can shelf  20  according to the present invention, for use with the extension ladder  10 , is shown in  FIG. 2 , an exploded perspective view of the paint can shelf  20  is shown in  FIG. 3 , a perspective view of the assembled paint can shelf  20  attached to the extension ladder  10  is shown in  FIG. 4A , and a front view of the assembled paint can shelf  20  attached to the extension ladder  10  is shown in  FIG. 4B . The paint can shelf  20  includes a first slide  24   a  on a left side of the paint can shelf  20 , parallel upper arm  22   a  and lower arm  22   b , a second slide  24   b  opposite to the first slide  24   a , a bent leg  26 , and a shelf  28 . The arms  22   a  and  22   b  may be permanently attached to the first slide  24   a , or attachable to the first slide  24   a , and when attached to the first slide  24   a , extends a length L from the first slide  24   a , the length L preferably about 18 and ¾ inches. The arms  22   a  and  22   b  extend through the hollow rungs  18  of the extending fly section  16 , passages  40   a  and  40   b  respectively (see  FIG. 5A ) of the second slide  24   b , and through the bent leg  26  far enough to attach locks  32  to exposed ends of the arms  22   a  and  22   b , retaining the bent leg  26 , while positioning the slides  24   a  and  24   b  facing the faces  15  (see  FIG. 4 ) of the base section side rail  14   a  (see  FIG. 1 ), and sandwiching the extending fly section  16  of the ladder  10  between the slides  24   a  and  24   b . The locks  32  may be pins, lynchpins, nuts, or any apparatus attachable to exposed ends of the arms  22   a  and  22   b . A cylindrical recessed area  30  is configured to accept a paint can provided in the shelf  28 . Additional features may be provided in the shelf  28 , the features including a slot  31  accepts a scraping or putty knife or the like, and various passages  33  accept brushes and tools of various types, and the like. The arms  22   a  and  22   b  preferably have a diameter D 1  of preferably one inch. 
     A side view of the bent elbow  26  is shown in  FIG. 5A  and a front view of the bent elbow  26  is shown in  FIG. 5B . The bent elbow  26  includes two passages  40   a  and  40   n  for the arms  22   a  and  22   b , the passages  40   a  and  40   b  spaced apart by a separation S of preferably between ten and fourteen inches and more preferably about twelve inches. The bent elbow  26  has a vertical centerline CL and the passages  40   a  and  40   b  are connected by a second centerline CL 2 . The centerlines CL and CL 2  are separated by the angle A 2  preferably matching the angle A 1  of the extension ladder  10  to provide a generally horizontal shelf  28 . A diagonal brace  27  provides support for the shelf  28 . The angle A 2  is preferably between 13 and 17 degrees and more preferably about 15 degrees. The recessed area  30  had a depth D 1  and diameter D 2  for receiving and holding the paint can. The depth D 1  is preferably at least about three inches deep to prevent the paint can from escaping from the recess  30  when the ladder  10  is moved, and is more preferably about three inches deep, for example, between 2.5 and 3.5 inches deep. The diameter D 2  is preferably between 6.5 and seven inches and more preferably at least about 6.5 inches and more preferably about 6.75 inches. 
     A perspective view of the slide member  24   b  is shown in  FIG. 6 , a side view of the slide member  24   b  is shown in  FIG. 7A , and a rear view of the slide member  24   b  is shown in  FIG. 7B . The slide member  24   b  includes two passages  41   a  and  41   b  for the arms  22   a  and  22   b , the passages  41   a  and  41   b  spaced apart by a separation S. A low friction plate  42  is attached to the rear surface of the slide member  24   b , the plate  42  faces, or lays against, a face  15  (see  FIG. 4 ) of the base section side rail  14   a . A ramp  50  may be present at one or both ends of the slide member  24   b  and helps the slide member  24   b  to slide along the face  15 . 
     The passages  41   a  and  41   b  have a diameter D 2  of preferably about one inch and allow the arms  22   a  and  22   b  to slide through the passages  41   a  and  41   b . The centers of the passages  41   a  and  41   b  are offset a distance O, of preferably about one inch, from the rear surface of the plate  42 . The diameter D 2  and offset O allow the paint can shelf  20  to slide on, or avoid contact with, the face  15  (see  FIG. 4 ) of the base section side rail  14   a  when the ladder  10  is extended or lowered. The slide member  24   b  has a width W of preferably about 2¼ inches and a height H of preferably about fifteen inches. The slide member  24   a  preferably has the same dimensions D 2 , O, S, W, and H as the slide member  24   a  and may include a low friction plate  42 . The low friction plate  42  may be made from TEFLON® material, TURCITE® material, a hard metal material, or the like. The slide member  24   a  (see  FIG. 3 ) may have all or some of the features of the slide member  24   b  shown in  FIGS. 6 ,  7 A, and  7 B. 
     A cross-sectional view of the arms  22   a  and  22   b  residing in the ladder rungs  18  is shown in  FIG. 8 . In one popular ladder  10  the arms are preferably spaced apart a separation S 2  of about eleven inches, and the arms  22   a  and  22   b  are preferably about one inch in diameter. 
     A compressible ring  60  is insertable into the recess  30  in the shelf  28 . The ring  60  provides an interference fit to better hold a one gallon paint can in the recess  30 . 
     The paint can shelf  20  described above is a preferred design for a right handed painter, another embodiment for a left handed painter is a mirror image of the paint can shelf  20 . An example of a suitable material for the paint can shelf  20  is polycarbonate sold under the trademark LEXAN. 
     While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.

Summary:
A paint can shelf attaches to a sliding extension ladder fly section. The shelf includes two parallel arms which reach through hollow rungs of the sliding extension ladder fly section, whereby the shelf is raised and lowered with the sliding extension ladder fly section. Slides are attached to the arms on each side of the sliding extension ladder fly section and include low friction surfaces facing the fixed extension ladder section. The slides allow somewhat loose tolerances in the engagement of the arms with the ladder preventing the ladder sections from binding when the ladder is extended or lowered.