Abstract:
An all-plastic light duty shelf unit includes rectangular shelf modules and vertical spacers. Each shelf module has four corner joints that can either be mated directly with each other or coupled together using cylindrical vertical spacers. This allows the user to customize the configuration of the shelf unit to meet his or her specific needs. It also reduces the cost to manufacture the shelf unit because the vertical spacers can be extruded rather than injection-molded. The corner joints also hold a shelf off the floor, thereby reducing part count and manufacturing cost.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to shelf units, and more particularly relates to light-duty shelf units. In its most immediate sense, the invention relates to inexpensive, light-duty all-plastic shelf units such as are sold in knocked-down form in mass market outlets. 
   Conventionally, a shelf unit of this type has a plurality of shelf modules. Each module has a joint at each corner. When the shelf unit is assembled, tubular vertical spacers must be fitted into corresponding joints of adjacent modules. As a result, a conventional shelf unit can only be assembled to form a vertical stack of shelves. This has little visual interest and does not allow the customer to customize the configuration of the shelf unit to meet his or her specific needs. 
   It would be advantageous to provide a shelf unit that would be more versatile and would have a more attractive appearance. 
   One object of the invention is to provide a shelf unit that would be more versatile and would also have a more attractive appearance. 
   Another object is, in general, to improve on known shelf units of this general type. 
   In accordance with the invention, a unitary all-plastic corner joint for a light-duty modular shelf unit is provided. The corner joint comprises a generally cylindrical housing having open top and bottom ends, a cylindrical central bore with a central stop region therein, an annular recess located inside the housing at the top end thereof concentric with and above the central bore, and an annular projection at the bottom end of the housing, the projection being dimensioned to mate with the recess. 
   With such a corner joint, shelf modules can either be interlocked directly (without using vertical spacers) or coupled together using vertical spacers. This makes it possible to build the shelf unit in customized and attractive configurations that meet the user&#39;s specific needs. Additionally, with such a corner joint, cost advantages are also brought about. This is because the vertical spacers that support the shelf modules in a stack can be cylindrical, and can be extruded rather than injection-molded. This substantially reduces the capital investment required to make the shelf unit. 
   In further accordance with the invention, a unitary all-plastic shelf module for a light-duty modular shelf unit is provided. The shelf module comprises at least one corner joint located at a corner and at least two peripheral pieces joined to the corner joint at the corner. Each joint has a generally cylindrical housing having open top and bottom ends located respectively above and below the peripheral pieces, a cylindrical central bore with a central stop region therein, an annular recess located inside the housing at the top end thereof concentric with and above the central bore, and an annular projection at the bottom end of the housing, the projection being dimensioned to mate with the recess. A shelf unit made from such a shelf module has the above identified advantages, and additionally has the advantage that each corner joint serves as a leg that supports the shelf unit above the floor, thereby making separate leg parts unnecessary and reducing manufacturing cost. 
   Although the shelf module can be of any shape (e.g. triangular, half-round, quarter-round), in accordance with the preferred embodiment the shelf module is rectangular. In such a case, there will be four peripheral pieces made up of two end pieces and two side pieces. If the shelf module is square, the end pieces and the side pieces will all be identical. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood with reference to the following illustrative and non-limiting drawings, in which: 
       FIG. 1  is an exploded view of a prior art shelf unit; 
       FIG. 2  shows the corner joint and other parts of the prior art shelf unit; 
       FIG. 3  is an exploded view of a preferred embodiment of the invention; 
       FIG. 4  shows two corner joints in accordance with a preferred embodiment of the invention, together with a tube that connects them; 
       FIG. 5  shows a cross-sectional view of a corner joint and finial in accordance with a preferred embodiment of the invention; 
       FIG. 6  shows two corner joints in accordance with a preferred embodiment of the invention, mounted together; and 
       FIG. 7  shows a preferred embodiment of the invention configured horizontally. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   In the drawings, the same element is always indicated by the same reference numeral. The drawings are not necessarily to scale; portions may be enlarged for clarity. 
   In a known shelf unit illustrated in  FIG. 1 , rectangular all-polypropylene shelf modules  10  each have two side pieces  12  and two end pieces  14 . At each corner of each shelf module is a corner joint  16 . 
   The shelf unit is held off the floor by four polypropylene legs  18 . Each leg  18  is a tube. To prevent the legs  18  from e.g. making annular depressions in carpeting, and to prevent foreign matter from entering them, the bottom end of each of the legs  18  is sealed off by a cap  20 . The shelf modules  10  are supported in a vertical stack by vertical spacers  22 . Each of the vertical spacers is a tube made of polypropylene, and each of the legs  18  and vertical spacers  22  has an annular recess  24  at its top end. The legs  18  and vertical spacers  22  differ only in their length; their top ends and bottom ends are identical. 
     FIG. 2  shows the relationship between a leg  18 , the lower end of a spacer  22 , and a corner joint  16 . As can be seen there, the recess  24  is dimensioned so the top end of the leg  18  fits into the open bottom end of the corner joint  16 , and the bottom end of the vertical spacer  22  fits into the open top end of the corner joint  16 . Because the legs  18  and vertical spacers  22  have differently-shaped top and bottom ends dimensioned to mate only into the bottom and top ends respectively of the corner joints  16 , it is impossible to assemble the shelf unit otherwise than in the illustrated vertical configuration. 
   This brings about the disadvantage that the shelf unit is visually uninteresting and cannot be assembled in a customized manner to meet the user&#39;s needs. Furthermore, because of the recesses  24 , the legs  18  and  22  must be injection-molded. This requires the manufacturer to invest in a mold, which is a substantial capital cost. Additionally, the legs  18  and caps  20  are necessary to keep the lowest shelf module  10  off the floor. These components increase the part count and the cost of the shelf unit. 
   Referring now to  FIGS. 3 and 4 , in accordance with a preferred embodiment of the invention, a corner joint  30  has a generally cylindrical housing  32  and also has open top and bottom ends  34  and  36  respectively. A central bore  38  extends through the corner joint  30 . An annular recess  40  is located inside the housing  32  at the top end  34 . The recess  40  is located above the central bore  38  and is concentric with it. An annular projection  42  is located at the bottom end  36 , and is dimensioned to mate with the recess  40  of another corner joint  30  located immediately beneath it ( FIG. 6 ). A central stop region  44  ( FIG. 5 ), which in this example is an annular flange but could be a constriction of any shape, extends radially inwardly into the central bore  38 . 
   Because (see  FIG. 6 ) the projection  42  mates with the recess  40  of another corner joint  30 , two corner joints  30  can if desired be fitted together without the need for an intervening vertical spacer  46  (although it is of course perfectly possible to couple them together using a vertical spacer  46  if desired). This permits the user to customize the configuration of the completed shelf unit to meet his or her specific requirements; the completed shelf unit can be configured vertically (see  FIG. 3 ) or horizontally (see  FIG. 7 ) or both, by combining components from two or more shelf units. 
   Additionally, it will be noted ( FIG. 7 ) that the central bore  38  is cylindrical. As a result, in accordance with a preferred embodiment of the invention, the vertical spacer  46  can be a cylindrical tube. This is significant because cylindrical tubes can be extruded, and the cost of an extrusion die is negligible as compared with the cost of an injection mold. 
   In accordance with the preferred embodiment of the invention, a rectangular shelf module  48  is provided. Each shelf module  48  has two side pieces  50  and two end pieces  52 , and a corner joint  30  is located at each of the four corners of the shelf module  48 . In the center of each shelf module  48  is a flat shelf region  54  that is supported by the side pieces  50 , the end pieces  52 , and the corner joints  30 . 
   As can best be seen in  FIGS. 4 ,  6 , and  7 , the top end  34  and bottom end  36  of each corner joint  30  extend respectively above and below the side pieces  50  and end pieces  52 . One consequence of this design is that (see  FIG. 7 ) the bottom ends  36  of the corner joints  30  can support a shelf module  48  off the floor. Hence, no separate legs and caps (such as legs  18  and caps  20 ) are required, which reduces costs. 
   Although in accordance with the preferred embodiment the shelf module  48  is rectangular, it need not be an elongated rectangle. The shelf module  48  can alternatively be square, in which case the side pieces  50  and the end pieces  52  will all be identical. Furthermore, the shelf module need not be rectangular. It can alternatively be of another shape, e.g. triangular, half-round, quarter round, etc.; the shape of the periphery of the shelf module can be arbitrarily selected. The shelf module need have only one corner joint  30  located at a corner thereof and two peripheral pieces joined to the corner joint at the corner. And, although in accordance with the preferred embodiment there will normally be four such corner joints  30 , there is no limit to the number of corner joints  30  that can be used in a particular shelf module. Furthermore, differently shaped shelf modules can be used in a single shelf unit; there is no requirement that all the shelf modules in a single shelf unit be identical. 
   In preferred embodiments, the vertical spacers  46  are extruded from polypropylene. Likewise in preferred embodiments, the shelf modules  48  and joints  30  are unitary, and are injection-molded from polypropylene. In the preferred embodiment, the side pieces  50  and end pieces  52  provide rigidity for the shelf region  54 , but this is not strictly necessary. If the shelf region  54  sufficiently reinforced and/or made sufficiently thick, the side pieces  50  and end pieces  54  can be eliminated and each shelf module can be made of a shelf region and four corner joints. Alternatively, if open-centered shelves are desired, the shelf region  54  can be eliminated and each shelf module can be made up of side pieces, end pieces, and corner joints. 
   In the preferred embodiment, each of the open top ends  34  of the highest shelf module  48  may be closed off by a finial formed of two identical mating halves  56  (shown in detail in  FIG. 5 ). This improves the appearance of the assembled shelf unit, but is not necessary and is not a part of the invention. 
   Although at least one preferred embodiment of the invention has been described above, this description is not limiting and is only exemplary. The scope of the invention is defined only by the claims, which follow: