Abstract:
A subrack ( 1 ) for use in industrial electronics includes two parallel sidewalls  10 , bottom and top walls ( 40, 30 ) cooperatively defining a space therebetween for receiving plug-in units ( 50 ) therein. Each of the bottom and top walls includes a first plate ( 35 ) defining a number of spaced slide channels, and a second plate ( 31 ) fixed to the first plate. After the plug-in units slide into the subrack along the slide channels, mounting panels ( 52 ) of the plug-in units engage with fronts of the bottom and top walls thereby securing the plug-in units in the subrack. The first and second plates can be produced from sheet steel having a same thickness, which significantly reduces the manufacturing costs.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to component mounting apparatuses, and particularly to a subrack having plate members for mounting plug-in units therein. 
   2. Related Art 
   Subracks for receiving plug-in units therein have been known in the electronics industry for a long time. A typical subrack comprises two sidewalls each having four corners, and four module rails fixed between the sidewalls, the module rails conventionally being screwed to the corresponding corners of the sidewalls. Bottom, top and back walls are attached to the subrack, and cooperate with the sidewalls to define a receiving space therebetween and an open side. The plug-in units can be inserted into and removed from the receiving space via the open side. The plug-in units typically comprise mounting panels engaging with two front module rails to thereby hold the plug-in units in place. For a thorough understanding of this kind of subrack, refer to the IEEE (International Electrical and Electronics Engineers) Standard 1101.10 established in 1996. 
   To enable fastening of the mounting panels, the module rails are required to have rather elaborate structures. Typically, the module rails consist of extruded aluminum. P.R. China Pat. No. 99201828.5, U.S. Pat. No. 6,134,119 and U.S. Pat. No. 6,474,479 disclose a variety of such extruded aluminum module rails. The extruded aluminum module rails generally each comprise a transverse rail defining a plurality of longitudinal grooves therein, and a centering strip and a threaded strip received in respective of the grooves. A row of equidistant centering holes is defined longitudinally in the centering strip, and a row of equidistant threaded holes is defined longitudinally in the threaded strip corresponding to the centering holes. For production of these rather elaborate components, complicated tools are required. Manufacturing of the module rails is quite expensive. In addition, assembling the discrete components (i.e., the sidewalls, and the bottom, top and back walls) and the module rails to complete a subrack is unduly laborious. 
   Thus, a new subrack for plug-in units which overcomes the above-mentioned problems is desired. 
   SUMMARY OF THE INVENTION 
   Accordingly, an object of the present invention is to provide a subrack for a plurality of plug-in units, the subrack having low manufacturing costs. 
   Another object of the present invention is to provide a subrack which has a simple structure and can be easily assembled. 
   To achieve the above-mentioned objects, a subrack in accordance with a preferred embodiment of the present invention comprises a pair of parallel sidewalls, identical bottom and top walls fixed between the sidewalls to cooperatively define a receiving space therebetween adapted to accommodate the plug-in units therein. Each of the bottom and top walls comprises first and second plates. The first plate comprises a main portion and a recessed edge portion. The main portion defines a plurality of spaced slide channels, and a plurality of alignment grooves adjacent the slide channels respectively. The recessed edge portion defines a plurality of through apertures therein. The second plate comprises a vertical portion defining a plurality of threaded apertures corresponding to the through apertures of the recessed edge portion, first and second horizontal portions extending from bottom and top sides of the vertical portion in respective opposite directions. At least one of the first and second horizontal portions is attached to the recessed edge portion thereby fixing the first and second plates together. 
   Other objects, advantages and novel features of the present invention will be drawn from the following detailed description of the preferred embodiment of the present invention with the attached drawings, in which: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an isometric view of a subrack in accordance with the preferred embodiment of the present invention, together with a plug-in unit received therein; 
       FIG. 2  is an enlarged, isometric view of a part of a bottom wall of the subrack of  FIG. 1 ; 
       FIG. 3  is similar to  FIG. 2 , but showing the bottom wall inverted; 
       FIG. 4  is an exploded view of the bottom wall of  FIG. 2 ; 
       FIG. 5  is an enlarged view of a part of the plug-in unit of  FIG. 1 , but viewed from another aspect; and 
       FIG. 6  is a schematic cross-sectional view of the bottom wall of  FIG. 2 , corresponding to line VI—VI thereof, and showing the plug-in unit engaged therewith. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIG. 1 , a subrack  1  of the present invention is for receiving a plurality of spaced plug-in units  50  therein. For the sake of simplicity, only one plug-in unit  50  is shown and described hereafter. The subrack  1  of the preferred embodiment has two levels for plug-in units  50 . It should be appreciated that the subrack  1  may alternatively be configured to have only one level, or three or more levels. For the sake of describing the preferred embodiment simply, only the upper of the two levels is described hereafter. The subrack  1  comprises two parallel sidewalls  10 , and opposite top and bottom walls  40 ,  30  fixed between the sidewalls  10 . The sidewalls  10  and top and bottom walls  40 ,  30  cooperatively define a space therebetween for receiving the plug-in units  50 . 
   Referring also to  FIG. 5 , the plug-in unit  50  comprises a printed circuit board (PCB)  51 , and a mounting panel  52  attached to a front end of the PCB  51 . A pair of handles  56  is attached to top and bottom ends of the mounting panel  52  respectively. Each handle  56  is known in the art as an “injector/extractor handle,” and is used for inserting or extracting the plug-in unit  50  into or from the subrack  1 . The handle  56  at a top end of the mounting panel  52  comprises a pair of upwardly-facing claws  57  at top side thereof. The handle  56  at a bottom end of the mounting panel  52  comprises a pair of downwardly-facing claws  57  at a bottom side thereof. For the sake of simplicity, only the latter of the handles  56  is described hereafter. Each claw  57  comprises a front nail  58   a  and a rear nail  58   b . An alignment pin  54  extends inwardly from an inside of each end of the mounting panel  52 . A screw  55  is movably retained in the mounting panel  52  adjacent each alignment pin  54 . Each screw  55  comprises a threaded shank portion  554  located at an inside of the mounting panel  52 , a smooth shank portion  552  coaxially extending from the threaded shank portion  554  and extending through a corresponding hole (not labeled) of the mounting panel  52 , and a screw head  550  located at an outside of the mounting panel  52 . Prior to attachment of the plug-in unit  50  in the subrack  1 , the screw  55  can be freely moved forward and rearward in the hole. A maximum travel of the screw  55  is defined by a length of the smooth shank portion  552  of the screw  55 . 
   The top and bottom walls  40 ,  30  are made from corrosion-protected sheet steel, and are identical in the preferred embodiment. For the sake of simplicity,  FIGS. 2 through 4  illustrate only the bottom wall  30 . The bottom wall  30  comprises first and second plates  35 ,  31 , which have a same thickness and are attached together by fastening devices such as rivets  33   a ,  33   b . Alternatively, other fastening means such as soldering can be used for connecting the first and second plates  35 ,  31  together. To prevent accumulation of static electricity, a plurality of conductive gaskets  32  is attached between the first and second plates  35 , 31 . 
   The first plate  35  comprises a main portion  350 , and a recessed edge portion  355 . A plurality of parallel, evenly spaced slide channels  351  is defined in the main portion  350 , for slidingly receiving respective PCBs  51  therein. Preferably, the slide channels  351  are formed by a stamping process. That is, parts of the main portion  350  are stamped upwardly to form a plurality of pairs of vertical tabs  351   a ,  351   b . Each pair of vertical tabs  351   a ,  351   b  cooperatively defines one slide channel  351  therebetween. Rear and front ends of each pair of vertical tabs  351   a ,  351   b  are flared. A pair of spaced, divergent protrusions  352  is formed on the main portion  350  in front of each slide channel  351 . The protrusions  352  cooperatively form a V-shaped entrance for guiding a corresponding PCB  51  into the slide channel  351 . An alignment hole  353  is defined in the main portion  350  adjacent each pair of protrusions  352 , corresponding to the alignment pin  54  of a respective plug-in unit  50 . A part of the main portion  350  adjacent each alignment hole  353  is stamped upwardly to define an underside alignment groove  354 , the alignment groove  354  being in communication with the alignment hole  353 . A pair of side flanges  359  depends from opposite ends of the main portion  350  respectively. The side flanges  359  each define a screw hole (not labeled) and a hooking structure (not labeled), for connection of the first plate  35  to the sidewalls  10 . Alternatively, other suitable joining means may instead be provided on the side flanges  359  for connection of the first plate  35  to the sidewalls  10 . 
   The recessed edge portion  355  sequentially comprises first, second and third bent plates  355   a ,  355   b ,  355   c  integrally joined together at respective perpendicularly bent junctions therebetween. The first and third bent plates  355   a ,  355   c  define a row of spaced rivet holes  357 ,  358  respectively. A row of spaced through apertures  356  is defined in the second bent plate  355   b.    
   The second plate  31  comprises a vertical portion  315 , and first and second horizontal portions  316 ,  310  extending from bottom and top sides of the vertical portion  315  in respective opposite directions. A row of screw apertures  314  is defined in the vertical portion  315 , corresponding to the row of through apertures  356  of the first plate  35 . A plurality of pairs of rectangular openings  318  is defined in a front part of the first horizontal portion  316 . Each pair of rectangular openings  318  can engagingly receive the rear nails  58   a  of the claw  57  of the handle  56  respectively. A plurality of rivet holes  317  is defined in a rear part of the first horizontal portion  316 , corresponding to the rivet holes  358  of the third bent plate  355   c . A plurality of extensions  311  is formed at a rear side of the second horizontal portion  310 , for aligning with the alignment holes  353  and creating corresponding spaces for receiving the gaskets  32 . A plurality of rivet holes  312  is defined in a front part of the second horizontal portion  310 , corresponding to the rivet holes  357  of the first bent plate  355   a . A plurality of through openings  319  is defined in the vertical portion  315 , for providing spaces for insertion of protrusions of the third bent plate  355   c  that correspond to the rivet holes  358 . Rivets  33   a ,  33   b  are extended through the rivet holes  357 ,  312  and through the rivet holes  358 ,  317 , thereby securely joining the first and second plates  35 ,  31  together. 
   Each gasket  32  comprises a flat mounting portion  32   a  attached to a corresponding extension  311  of the second plate  31 , and an arcuate contact portion  32   b  extending obliquely from a side of the mounting portion  32   a . The contact portion  32   b  is for resiliently abutting the alignment pin  55  of the handle  56  of the plug-in unit  50 . In the preferred embodiment, the mounting portion  32   a  of the gasket  32  is adhered to the extension  311 . Other suitable attachment means such as screw jointing can alternatively be adopted. 
     FIG. 6  shows assembly of the plug-in unit  50  into the subrack  1 . For the sake of simplicity, only the bottom wall  30  and the corresponding handle  56  of the plug-in unit  50  are shown and described hereafter. The plug-in unit  50  is positioned adjacent a corresponding pair of protrusions  352 . The plug-in unit  50  is pushed inwardly to slide through the entrance of the protrusions  352  and into the corresponding slide channel  351 . When the PCB  51  almost reaches a connector (not shown) located at a rear of the subrack  1 , the alignment pin  54  extends into the alignment hole  353  and the alignment groove  354  to guide the PCB  51  to accurately engage with the connector. Once the PCB  51  engages with the connector, the pair of rear nails  58   a  of the handle  56  engage in the corresponding pair of rectangular openings  318 . Thus the plug-in unit  50  is prevented from being accidentally withdrawn from the subrack  1 . In this state, the contact portion  32   b  of the gasket  32  resiliently abuts against the alignment pin  54  to form a grounding path between the bottom wall  30  and the plug-in unit  50 . Finally, the screw  55  is extended through the corresponding through aperture  356  of the first plate  35  and engaged in the corresponding screw aperture  314  of the second plate  31 . The plug-in unit  50  is thus secured in the subrack  1 . 
   To remove the plug-in unit  50  from the subrack  1 , the screw  55  is disengaged from the screw aperture  314 . The handle  56  is rotated downwardly so that it disengages from the rectangular openings  318 . The plug-in unit  50  can then be easily slid out from the subrack  1 . 
   In the present invention, all elements of the subrack  1  are made of sheet steel. Therefore, manufacturing costs of the subrack  1  are significantly reduced, and assembly of the subrack  1  is simplified. 
   It is understood that the invention may be embodied in other forms without departing from the spirit thereof. Thus, the present examples and embodiments are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein.