Abstract:
A modular electronic assembly includes a chassis, a housing supported by the chassis having an access opening through a first wall of the housing, a removable access panel or releasable member at least partially covering the opening, and a midplane supported by the chassis and slidably removable from the chassis through the opening when the housing is mounted on the chassis. A method of constructing a modular electronic assembly is also disclosed.

Description:
FIELD OF THE INVENTION 
   The present invention is directed toward an electronic assembly with a removable midplane, and more specifically, toward an electronic assembly comprising a chassis for supporting a plurality of electronic components and a modular removable midplane electrically connectable to electronic components supported by the chassis. 
   BACKGROUND OF THE INVENTION 
   Assemblies for supporting a plurality of electrical components and connecting them to various power supplies, inputs, outputs and/or to one another are well known. The electrical components are often modular and can be individually connected to and removed from the assembly. Such assemblies may be referred to, for example, as electrical cabinets or racks and generally comprise a structural frame or chassis that supports the electrical components. The assembly may be at least partially surrounded by a housing to protect the electrical components. 
   The housing, in some instances, may comprise individual panels secured to the chassis. In other cases, a housing may include structural supports integrated therewith and lack a distinct chassis. As used herein, “chassis” will generally refer to structural elements of an electronic assembly and “housing” will refer to elements provided primarily for protecting or covering the electronic modules whether these elements are separately provided or integrally formed. 
   It is also known to provide such assemblies with a midplane. A midplane is frequently a printed circuit board (PCB) having a plurality of connectors connectable to the electronic modules supported by the assembly. A midplane is generally provided toward the middle of an assembly and often includes electrical connectors on front and rear surfaces thereof so that modules can be connected to both sides. 
   Typical assemblies include a chassis that is constructed around a midplane, which essentially makes the midplane an integral part of the chassis. This is especially true in the case of “dual bay” or “multi-bay” assemblies which are arranged to support multiple levels of electronic modules stacked vertically and thus have at least two bays on their front and rear sides. If a midplane requires repair or if an upgrade to the midplane is needed, the chassis must be disassembled to a significant degree to access the midplane. This is often difficult to do at a site where the assembly is installed because it may be difficult or impossible to properly realign the midplane with the chassis when it is reinstalled in the assembly. Moreover, employees or contractors skilled in assembling sheet metal chassis may not be adept at handling printed circuit boards, and a printed circuit board may be damaged when a chassis is assembled around it. Electrostatic discharge, for example, can damage the PCB if care is not taken during chassis assembly. 
   It would therefore be desirable to provide an electrical assembly to which a midplane may be added after chassis assembly is complete and which allows for the easy removal and replacement of a midplane. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various aspects of the invention will become apparent after a reading of the following detailed description of the invention in connection with the following drawings wherein: 
       FIG. 1  is a perspective view of a chassis for an assembly according to an embodiment of the present invention; 
       FIG. 2  is a partially exploded perspective view of an assembly including the chassis of  FIG. 1 , a midplane, and a housing; 
       FIG. 3  is a perspective view of the assembly of  FIG. 2  including a plurality of electronic modules mounted in bays of the assembly; 
       FIG. 4  is a rear elevational view of the midplane of  FIG. 2 ; 
       FIG. 5  is a side elevational view of the midplane of  FIG. 2 ; 
       FIG. 6  is a side elevational view, partly in section, of the assembly of  FIG. 2 ; 
       FIG. 7  is a sectional view taken along line VII—VII of  FIG. 3  illustrating a first midplane mounting arrangement; 
       FIG. 8  is a sectional front elevational view of an assembly according to an embodiment of the present invention illustrating a first alternate midplane mounting arrangement; 
       FIG. 9  is a sectional front elevational view of an assembly according to an embodiment of the present invention illustrating a third alternate midplane mounting arrangement; 
       FIG. 10  is a side elevational view of an assembly according to a second embodiment of the present invention; and 
       FIG. 11  is a flow chart illustrating a method of assembling an electrical assembly according to an aspect of the present invention. 
   

   DETAILED DESCRIPTION 
   Referring now to the drawings, wherein the showings are for purposes of illustrating preferred embodiments of the invention only and not for the purpose of limiting same,  FIG. 1  illustrates a chassis  10  formed from a plurality of vertical framing members  12  and horizontal framing members  14  interconnected to form an enclosure in the shape of a rectangular parallelepiped having a front  16 , a rear  18 , a first side  19  and a second side  20 . Chassis  10  also includes guide plates for guiding and supporting a number of electronics modules  21  (illustrated in  FIG. 3 ) including a lower front guide plate  22  having a flange  23  and a lower rear guide plate  24  having a flange  25  and four middle guide plates, namely, a first side front guide plate  26  having a flange  27 , a second side front guide plate  28  having a flange  29 , a first side rear guide plate  30  having a flange  31  and second side rear guide plate  32  having a flange  33 . A first gap  34  extending from first side  19  of chassis  10  to second side  20  of chassis  10  is defined by the pair of middle front guide plates  26 ,  28  and middle rear guide plates  30 ,  32  for receiving a midplane  36  illustrated, for example in  FIG. 2 . A second gap  35  running from front  16  of chassis  10  toward rear  18  of chassis  10  is defined by first side guide plates  26 ,  30  and second side guide plates  28 ,  32  and may be used to accommodate an added guide plate  43  as illustrated in  FIGS. 2 and 3 . 
   In this embodiment, an end plate  38  is provided on first side  19  of chassis  10  at one end of gap  34  and a frame plate  40  is provided on second side  20  of chassis  10  on the end of gap  34  opposite end plate  38 . A U-shaped channel support  41  is mounted beneath lower guide plates  22  and  24  and helps guide and support midplane  36  as described hereinafter. Upper guide plates  37 ,  37 ′ having flanges  39 ,  39 ′ further define slot  34 . While guide plates  37 ,  37 ′ are illustrated as solid plates, they may alternately be formed with vents such as those formed in lower guide plates  22 ,  24  and middle guide plates  26 ,  28 ,  30 ,  32 . 
   It should be noted that while a multi-bay assembly having two bays, upper and lower bays  72 , on each side is illustrated, an assembly having three or more levels of bays could also be provided. Moreover, the size of the bays is determined by the size of the various electronic modules  21  to be mounted therein, and could differ from what is shown. In addition, while the middle front guide plates  26 ,  28  and middle rear guide plates  30 ,  32  (and lower front guide plate  22  and lower rear guide plate  24 ) are illustrated as lying in substantially the same plane, they could just as readily lie in different planes. 
     FIGS. 2 and 3  illustrate a housing  42  attached to chassis  10 . Housing  42  comprises a top panel  44 , a first side panel  46  on first side  19  of chassis  10 , and a second side panel  48  on the second side  20  of chassis  10 . Second side panel  48  includes an opening  50  aligned with frame plate  40  of chassis  10  through which midplane  36  can be inserted into and removed from chassis  10 . Housing  42  provides protection for components  21  and may also contribute to the rigidity of the overall assembly. Various openings are provided in housing  42  for cooling and wiring connections in a well known manner. 
   Midplane  36  comprises a PCB that includes a front side  52 , illustrated in  FIG. 3 , and a rear side  54  illustrated in  FIG. 5 . Midplane  36  further comprises an upper edge  56 , a lower edge  58 , a first side edge  60  and a second side edge  62 . A plurality of connectors  64  are provided on front side  52  and rear side  54 , the size, type and wiring of which will depend on the types of electronic modules  21  to be used in the assembly. As illustrated in  FIGS. 4 and 5 , midplane  36  further includes first and second braces or stiffeners  66  running between first side edge  60  and second side edge  62  which are formed from a material such as steel, for example, and are designed to increase the rigidity of midplane  36 . 
   As will be appreciated from  FIGS. 1 and 2 , midplane  36  can be inserted into chassis  10  through opening  50  in second side panel  48  of the housing and through frame plate  40  of the chassis  10  through gap  34  between front guide plates  26 ,  28  and rear guide plates  30 ,  32  until first side edge  60  of midplane  36  abuts end plate  38  of chassis  10 . Lower edge  58  of midplane  36  is supported by support  41  while the middle guide plate flanges  27 ,  29 ,  31  and  33  and flanges  39 ,  39 ′ on upper guide plate  37  help guide the midplane along slot  34 . 
   With regard to  FIGS. 1 and 7 , in this embodiment, end plate  38  includes a plurality of projections  68  which will help to properly align midplane  36  with respect to chassis  10 . These projections  68  may comprise pins secured to end plate  38  or screws or other fasteners inserted through openings formed in end plate  38 . In a presently preferred embodiment, a combination of alignment pins and screws is used. The specific nature of the alignment mechanism is not critical so long as projections are provided that can be received into alignment openings  70  formed at opposite ends of stiffeners  66 . 
   The alignment openings  70  and projections  68  are arranged and configured so that midplane  36  will assume a predetermined relationship to guide plates  26 ,  28 ,  30  and  32 , and hence any electrical modules  21  supported by those guide plates, when electrical modules are inserted into the bays  72  defined by the chassis  10 , guide plates  26 ,  28 ,  30  and  32 , and any auxiliary dividers  74  as illustrated in  FIGS. 2 and 6 . Additional fasteners  73  extend through openings  75  in the flange  23  of lower guide plate  22 , though openings  75  in flanges  27  and  29  of middle front guide plates  26  and  28 , and through flange  39 ′ of upper guide plate  37 ′ into openings (not shown) in midplane  36  to further secure midplane  36  to the chassis. Additional fasteners  73  are also provided in the flange  25  of lower rear guide plate  24  and in the flanges  31 ,  33  of middle rear guide plates  30 ,  32  and in flange  39  of upper guide plate  37  to further align and secure midplane  36 . 
   To accommodate variations in the thickness of midplane  36 , slot  34  will generally be slightly wider than the nominal thickness of midplane  36 . Therefore, the midplane will be rigidly fastened to only one set of flanges, such as rear flanges  25 ,  31 ,  33 ,  39 . Fasteners  73  extending through front flanges  23 ,  27 ,  29  and  39 ′ will extend into openings in the midplane to help hold the midplane in proper position, but the midplane will generally be slightly spaced from these front flanges. 
   With projections  68  inserted into the alignment openings  70  near first side edge  60  of midplane  36 , alignment openings  70  near second side edge  62  of midplane  36  remain exposed through opening  50  in second side panel  48 . An access panel  76  is provided that is sized to cover opening  50  and attach to second side panel  48  and/or frame plate  40 . Access panel  76  includes an EMI gasket  77  to provide an EMI seal around opening  50 , and openings  78  aligned with alignment openings  70  near second side edge  62  of midplane  36 . Suitable fasteners  80 , such as pins or screws are inserted through openings  78  and into alignment openings  70  of midplane  36 . When access panel  76  is then secured to housing  42 , midplane  36  will be secured in a proper orientation with respect to the chassis  10 . Because midplane  36  is locked in place in this manner, it not only maintains a necessary orientation with respect to the chassis  10  and supported electronic elements  21 , but it, together with stiffeners  66 , braces and contributes to the rigidity of chassis  10 . As will appreciated from the foregoing, this arrangement simplifies the removal and repair or replacement of midplane  36  as well. 
   In a variation of the above embodiment, end plate  38  can be omitted and projections  68  may be supported by first side panel  46  of housing  42 . Likewise, frame plate  40  can be omitted and the access panel  76  may be connected directly to second side panel  48  of housing  42 . 
   An additional variation of this embodiment of the invention is illustrated in  FIG. 8 . Elements identical to those in the first variation are identified with like reference numerals. In this embodiment, a guide channel  80  is provided on end plane  38  (or directly mounted on housing first side panel  46 ), and first side edge  60  of midplane  36  is inserted into this guide channel  80  to hold the midplane  36  in proper orientation with respect to chassis  10 . Access panel  76  is also provided with a guide channel  82  which is placed over second side edge  62  of midplane  36  as access panel  76  is secured to housing  42 . Guide channel  80  and access panel guide channel  82  hold midplane  36  securely in place within chassis  10  this secure interconnection allows midplane  36  to increase the rigidity of chassis  10 . 
     FIG. 9  illustrates an alternate variation of the invention in which elements common to the earlier variations are identified with the same reference numerals; elements related to previously identified elements are identified with the same reference numeral and a prime. In this embodiment, end plate  38  (or first side panel  46  of housing  42 ) is provided with openings  84  that receive projections  86  of stiffeners  66 ′. Openings  88  on access panel  76 ′ receive projections  86  near the second side edge  62  of midplane  36 . Projections  86  and openings  84 ,  88  are arranged such that midplane  36  is properly positioned within chassis  10  when the projections are received within the openings and access panel  76  is secured to housing  42 . 
     FIG. 10  illustrates a second embodiment of the present invention in which elements common to the earlier embodiments are identified with like reference numerals. In this embodiment, chassis  10  is open and not covered with panels forming a housing as in the first embodiment. A lower bracket  90  is provided on lower guide plate  24  while an upper bracket  92  is provided between two of the horizontal framing members  12  forming chassis  10 . Lower bracket  90  and upper bracket  92  define, with gap  34 , an opening into which a midplane  36  can be inserted into chassis  10 . A first member, such as plate  96  is removably connected between second side front guide plate  28  and second side rear guide plate  32  and a second member, such as plate  98  is removably connected to lower guide plate  24  to hold midplane  36  in place. The end of gap  34  at first side  19  of chassis  10  may be blocked by a portion of one of the horizontal framing members  14  that form chassis  10  or by an additional plate  96 . This arrangement allows the benefits of embodiments of the present invention to be enjoyed even in rack arrangements with an open chassis. 
   A method of practicing an embodiment of the present invention is illustrated in the flow chart of  FIG. 11 . In a first step  100 , a chassis is formed for supporting a plurality of electronic elements. A housing comprising at least one panel having an opening is attached to the chassis at a step  102 . At a step  104 , a midplane is slid through the opening into the chassis, and at a step  106 , a cover is attached over the opening to hold the midplane in a predetermined position with respect to the chassis. 
   The present invention has been described herein in terms of several embodiments. Numerous modifications and additions to these embodiments will become apparent to those skilled in the relevant arts upon a reading and understanding of the foregoing description. It is intended that all such modifications and additions form a part of the present invention to the extent they fall within the scope of the several claims appended hereto.