Abstract:
A housing for an electrical device including opposed supports or ribs receiving thereon a circuit board having first and second sides separated by a width “a”. A first board support is attached to the housing and has a first side surface, a first support surface substantially perpendicular to the first side surface for supporting the circuit board, and a first recess in the first support surface. A second board support is attached to an opposing side surface of the housing. The side surfaces of the board supports are separated by a distance “b”. When distance “a” is greater than distance “b”, the circuit board is retained in an interference fit. Scrapings that are formed during the insertion of the circuit board into the housing can be collected in the support recesses, which provide relief areas, to avoid interfering with the proper seating of the circuit board on the board supports.

Description:
FIELD OF THE INVENTION 
     This invention relates to a shearable rib or support in a housing for an electrical device. More specifically, the invention supports and retains a circuit board, and prevents sheared plastic shavings, formed when the circuit board is inserted into the housing and scrapes along the ribs, from interfering with proper seating of the circuit board during assembly. This interference is avoided by use of a relief or recess in the rib that collects the shavings. 
     BACKGROUND OF THE INVENTION 
     A need exists for a means to prevent sheared plastic shavings or scrapings from interfering with the proper seating of a circuit board in the housing of an electrical device. 
     One common way to retain a circuit board in an electrical device is to attach the circuit board to the housing using screws or clips. A screw is typically passed through a hole in the circuit board and received in the housing. Circuit board size and shape is generally optimized in order for the circuit board to fit within the dimensions of the housing for the electrical device. Supports or ribs for the circuit board are variously located throughout the housing, and can be located along the side walls. Uses for the supports include cooling for the device, as well as for the prevention of undesirable contact between components mounted on the circuit board and other components, wires and the like located near the circuit board. 
     When the supports are located along the side walls of the housing, sides of the circuit board scrape along the sides of the supports during assembly. When the supports are made of plastic, shavings or scrapings may be generated during the installation of the circuit board. By the time the circuit board reaches the resting destination on the supports, sheared plastic shavings may have accumulated between the supports and the circuit board. These plastic shavings can interfere with the proper and full seating and retention of the circuit board within the housing, and cause misalignment of critically located components and parts to be snap fitted together. 
     Consequently, there is a need for a circuit board support rib that can accommodate the shavings, resulting in proper seating of the circuit board within the housing. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to provide a support for a circuit board in an electrical device capable of both retaining the circuit board and collecting scrapings caused by insertion of the circuit board in the electrical device. 
     Another object of the invention is to provide a means for frictionally retaining a circuit board and collecting scrapings that can interfere with the proper seating of the circuit board. 
     The foregoing objects are basically attained by providing a housing for an electrical device, the housing supporting a board having first and second sides separated by a width “a”, having a housing body; a first board support attached to the housing body having a first side surface, a first support surface substantially perpendicular to the first side surface for supporting the board, and a first recess in the first support surface; a second board support attached to the housing body having a second side surface, a second support surface substantially perpendicular to the second side surface for supporting the board, and a second recess in the second support surface, a distance “b” separating the second side surface and the first side surface being less than the width “a” of the board; wherein the board is inserted into the housing body, the first side of the board scrapes along the first side surface, and the second side scrapes along the second side surface resulting in scrapings that can collect in the first and second recesses, and wherein the board is frictionally retained between the first and second board supports. 
     The foregoing objects are also attained by providing a housing for an electrical device, the housing supporting a board having first and second sides, the combination comprising means, coupled to the housing, for frictionally retaining the board in the housing; means for collecting scraped material, the scraped material resulting when the board is inserted into the housing and the first and second sides scrape along the means for frictionally retaining; wherein some of the scraped material is collected in the means for collecting so as not to interfere with the seating of the circuit board on the means for frictionally retaining. 
     Other objects, advantages and salient features of the invention will become apparent from the following detailed description, which, when taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring to the drawings which form a part of the original disclosure: 
     FIG. 1 is an exploded perspective view of the electrical device of the present invention, showing a housing, a circuit board for insertion into the housing, and a cover for covering the circuit board and housing; 
     FIG. 2 is a cross-sectional end view of the housing with the circuit board inserted taken along  2 — 2  in FIG. 1; 
     FIG. 3 is a rear perspective view of the housing with the inserted circuit board cut away; 
     FIG. 4 is a cross-sectional side view of the housing and circuit board with the cable removed taken along  4 — 4  in FIG. 3; 
     FIG. 5 is an end view similar to FIG. 2 prior to insertion of the circuit board into the housing body; 
     FIG. 6 is an end view similar to FIG. 2 with the circuit board partially inserted into the housing body; and 
     FIG. 7 is a close-up of one side of the circuit board properly seated on a support within the housing and sheared plastic scrapings collected in a recess in the support rib. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As seen in FIGS. 1-7, an electrical wiring device  10  in accordance with the first embodiment of the present invention is illustrated, and includes a housing  12 , a circuit board  14  received in the housing  12 , a cover  16  for covering the circuit board  14 , a grommet  18  also received in the housing  12 , and conduit  20  which is received through the grommet  18  and into the housing  12 . 
     Housing  12  is substantially rectangular, having two side walls  24 ,  26  parallel to the longitudinal axis, and two transverse walls  28 ,  30  which are substantially perpendicular to the two side walls  24 ,  26 . The two side walls  24 ,  26  and the two transverse walls  28 ,  30  are perpendicular to and attached to a substantially planar front wall  31  forming the housing  12 . 
     Housing  12  can be fabricated from any plastic generally used for electrical devices, and may be formed using injection molding, or any other technique known in the art. 
     Circuit board  14  is any circuit board known in the art, and can be a printed circuit board. Circuit board  14  is preferably substantially rectangular with substantially smooth and flat first and second side edges  52  and  54 , which are substantially parallel to one another. Circuit board  14  can be fabricated from fiberglass, cardboard, wood, plastic, ceramic or other materials commonly used in the art of circuit boards and printed circuit boards. Electronics  15  can be transistors, resistors, switches, diodes, wires, or other suitable electronics adapted to be attached to the circuit board  14 . 
     Cover  16  is used to cover one side of the circuit board  14  and a portion of the housing  12 . The cover can be fabricated from paper, cardboard, plastic, fiberglass, or other materials commonly used as covers for electronic devices. The cover can be attached to the circuit board  14  and/or the housing  12  by means of screws, nails, adhesive, glue, hook and loop fasteners, or other means commonly used to attach, either removably or permanently, the cover to an electrical device. The cover can be used to protect the circuit board  14  and the electronics  15  from environmental contamination and undesirable electrical contact with devices outside of this invention. 
     Grommet  18  is received in side wall  30  for the guiding of and passing through of conduit  20 . The grommet  18  can be flexible and fabricated from rubber or plastic, or any other material known in the art to be used as a grommet. Grommet  18  is retained in the traverse wall  30 . Conduit  20  passes through grommet opening  19 , which is sized to be close-fitting about the conduit  20  while preventing environmental contaminants such as dust and debris from entering housing  12 . It is preferable that grommet  18  be flexible and pliable in order to allow conduit  20  of various sizes and types to pass through. 
     Conduit  20  carries information and/or power, for example, electrical or optical, to the electrical wiring device. Conduit  20  can be a shielded cable containing multiple wires or optical fibers or any other electrical or optical conduit known in the art. One end of conduit  20  can be attached to a source of information or power, while the other end is attached to the circuit board  14  and components  15 . It is preferable that conduit  20  be able to pass through grommet opening  19 . 
     A first board support or rib  32  is attached to the first side wall  24  of housing  12 . The first board support  32  can be fabricated from the same material as the first side wall  24  or any other compatible material, and may be integral with the first side wall  24 . The first board support  32  can also be fabricated independently of the first side wall  24  and attached using, for example, adhesive, hot melt, glue, solvent welding, fusion, or other methods known in the art for attaching the board support  32  to the first side wall  24 . 
     The first board support  32  has a first substantially smooth and flat side surface  34  and a first support surface  36  substantially perpendicular to the first side surface  34 . When the circuit board  14  is fully inserted into the housing  12 , a portion of the circuit board  14  rests on the first support surface  36 . A first recess  38  is situated in the first support surface  36 , preferably adjacent the side surface  34 , and prevents debris from interfering with proper seating of the circuit board  14  on the first support surface  36 . 
     A second board support or rib  40  is situated on the second side wall  26  and is substantially opposite the first board of support  32 . The second board support  40  has a second substantially smooth and flat side surface  42  similar to and substantially parallel to the first side surface  34 , a second support surface  44  similar to the first support surface  36 , and a second recess  46  similar to the first recess  38 . The second board support  40  is preferably fabricated from the same material as the first board support  32 . 
     The first board support  32  and the second board support  40 , with the first and second side surfaces  34 ,  42  substantially opposing each other, are separated by a distance such that the circuit board  14  can be frictionally retained between the first and second supports  32 ,  40  by way of an interference, or pressure fit. 
     The interference fit and the frictional retention of the circuit board between the first and second supports  32 ,  40  results when the circuit board  14  is inserted into the housing  12 . During insertion, the first and second side edges  52 ,  54  of circuit board  14  scrape along the first and second side surfaces  34 ,  42  of the first and second board supports  32 ,  40 . The scraping of side surfaces  34 ,  42  results in pieces of the first and second board supports  32 ,  40 , and possibly edges  52  and  54  of the circuit board  14 , being scraped off, forming scrapings  56 . These scrapings  56  fall either into the first and second recesses  38 ,  46  or off to the side of the first and second board supports  32 ,  40  and land elsewhere in housing  12 . With scrapings  56  removed from side surfaces  34 ,  42 , the resulting distance between the first and second board supports  32 ,  40  nearly equals the width of the circuit board  14 , and exerts a retaining force to retain the circuit board  14  in position. 
     FIG. 3 shows a rear view of the circuit board  14  inserted into housing  12 . Circuit board  14  is cut away to view the seating of the circuit board  14  on board supports  32  and  40 . A third board support  48  and a fourth board support  50 , similar to the first and second board supports  32 ,  40  are also shown. The third and fourth board supports  48 ,  50  are also attached to the first and second side walls  24 ,  26  in opposing configuration. In this manner, the circuit board  14  is retained by two substantially opposing pair of board supports. 
     FIG. 5 shows the circuit board  14  prior to insertion into housing  12 . FIG. 6 shows circuit board  14  inserted into housing  12 , but not yet seated on the first and second support surfaces  36 ,  44 . FIGS. 5 and 6 have the same view as FIG.  2 . In FIG. 5, width “a” represents the width from the first side edge  52  of circuit board  14  to the second side edge  54  of circuit board  14 . Width “b” indicates the distance between the first side surface  34  of the first board support  32  and the second side surface  42  of the second board support  40 . In the preferred embodiment, distance “b” separating the second side surface  42  and the first side surface  34  is less than width “a” of the circuit board  14 . 
     By having the distance “b” less than width “a”, circuit board  14  can be retained between the first board support  32  and the second board support  40  by means of an interference, or pressure fit. 
     The difference between width “a” and distance “b” should be sufficient to form an interference fit between the board  14  and the first and second side surfaces  34 ,  42 . It is preferable that distance “b” be about 0.005 inches to about 0.100 inches less than the width “a”. In the preferred embodiment, distance “b” is about 0.060 inches less than width “a”. It should be recognized by one skilled in the art that width “a” must be greater than distance “b” in order to have an interference fit, and the amount by which width “a” must be greater than distance “b” can vary with the flex of both the housing  12  and the circuit board  14 . The flex of housing  12  and circuit board  14  will vary with the materials used to fabricate them. However, while it is desirable that the circuit board  14  be frictionally retained in housing  12  by means of an interference fit, it is undesirable that the first and second side walls  24 ,  26  of housing  12  be spread apart, resulting in an increase in distance “b” rather than a scraping of the material from the first and second side surfaces  34 ,  42 . 
     Recesses  38 ,  46  are generally U-shaped or channel shaped, and are designed to accommodate scrapings  56 . That is, when scrapings  56  are contained in recesses  38 ,  46 , the scrapings  56  do not interfere with the proper seating of the circuit board  14  on the first and second support surfaces  36 ,  44 , as seen in FIGS. 2 and 7. 
     While it is desirable that scrapings  56  are captured in recesses  38 ,  46 , it is not undesirable that some of the scrapings will land elsewhere in housing  12 . Recesses  38 ,  46  are preferably designed to prevent scrapings  56  from interfering between circuit board  14  and support surfaces  36 ,  44 . 
     While only one advantageous embodiment has been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.