Abstract:
An equipment shelf includes circuit board slides being arranged to support edges of circuit boards, whereby the circuit boards are removably retained in a system. First and second end panels are fixed in a spaced apart relationship by a pair of front cross connecting members and by a pair of rear cross connecting members. Each of the circuit board slides is carried between an inner edge of a front cross connecting member and an inner side of a rear cross connecting member. As each board slide is overlapped by only one of the cross connecting members, the cross connecting members are more widely spaced from front to back than would otherwise be the case, whereby greater area for a flow of a ventilating medium is available.

Description:
FIELD OF THE INVENTION 
     The invention is in the field of electronic systems and is concerned with an equipment shelf for retaining circuit boards in an electronic system. 
     BACKGROUND OF THE INVENTION 
     Over the last decade or so, some electronic systems such as telephone switching facilities or main frame computers and the like have demonstrated a convergence of technologies. Likewise, these apparatuses have taken on a general sameness of physical appearance, particularly in the retainment of circuit board elements. Each of the systems of interest is characterized by an equipment shelf having circuit board slides being arranged in parallel one with another, in a row, for receiving edge surfaces of a plurality of circuit boards. A circuit board is inserted from a front side of the equipment shelf into a pair of the circuit board slides where the circuit board is retained, and it is electrically and/or optically connected into the system by conductors carried by a back plane at a back side of the equipment shelf. One example of this structure is found in U.S. Pat. No. 4,787,081, issued on Nov. 22, 1988 and entitled &#34;TIME DIVISION MULTIPLEX EQUIPMENT SHELVES&#34;, which at a glance, may appear to be similar, but have remained distinct because of design variations in circuit board dimensions which of course dictate like differences in slide spacing and depth. Such distinct variations are not limited between systems but may also exist within a system of any one type. One reason for variation is that some circuit boards generate more heat than others, while in operation. It is desirable to arrange circuit boards, in an equipment shelf, with a minimum of space therebetween in order to maximize the use of space in any given system. However the minimum spacing attainable between circuit boards can be dictated by several factors, one of which is providing for adequate ventilation to allow for dissipation of heat generated by normal operation of the circuit boards. 
     My application for patent, entitled &#34;EQUIPMENT SHELF&#34;, was filed in Canada on Sept. 29, 1989, and is identified with Ser. No. 614,700. My application teaches that the expense of inventory associated with the variety and number of piece parts typically required for the manufacture of various equipment shelves used in some electronic systems may be reduced. 
     In one example, the equipment shelf includes a plurality of circuit board slides, each having an elongated body with a groove in one side thereof, for receiving an edge of a circuit board, and a plurality of attachment projections extending from another side thereof. The circuit board slides are grouped in pairs, each for slidably engaging opposite edges of a circuit board. First and second side panels are spaced apart by a plurality of elongated cross connecting members, which receive the attachment projections in retaining means facing the circuit board locations. One of the advantages of this equipment shelf is that each of the elongated spacing members is provided by an extrusion which is cut to length for assembly. In assembly, each of the elongated spacing members is orientated to fit at its location where it is secured in place by screw threaded fasteners. Each extrusion is shaped to receive retaining means in the form of a thin flat strip with holes formed therein at predefined locations, for fastening the board slides. However, this assembly is at some disadvantage, as each spacing member is a little wider than it would otherwise be, in order to facilitate the feature of adaptability. This greater width has been observed to have an adverse effect upon otherwise satisfactory ventilation characteristics of the equipment shelf. Air flow required for cooling during operation is somewhat restricted by the width of each of the cross connecting members. This width is convenient for providing the adaptability of the equipment shelf and may be compensated for by positioning the circuit boards at greater than typical spacing, to obtain adequate ventilation. However, increased spacing of the circuit boards may also increase the amount of floor space required to accommodate the electronic system. 
     It is an object of the present invention to improve ventilation of circuit boards retained in an adaptable equipment shelf. 
     SUMMARY OF THE INVENTION 
     An equipment shelf in accordance with the invention includes circuit board slides being arranged to support edges of circuit boards, whereby the circuit boards are removably retained in a system. The equipment shelf comprises: first and second end panels being fixed in a spaced apart relationship by a pair of front cross connecting members and by a pair of rear cross connecting members, and each of the circuit board slides being carried between an inner edge of a front cross connecting member and an inner side of a rear cross connecting member. 
     As each board slide is overlapped by only one of a front and a rear cross connecting member, the cross connecting members are more widely spaced from front to back than would otherwise be the case. 
     In one example of the invention, the equipment shelf comprises: 
     first and second end panels having front and rear edges being fixed in a spaced apart relationship by a pair of front cross connecting members and by a pair of rear cross connecting members, respectively; 
     a plurality of circuit board slides being carried between an inner edge of a front cross connecting member and an inner side of a rear cross connecting member, each of the circuit board slides comprising: 
     an elongated body including a pair of side walls connected by first and second edge walls, the side and edge walls extending a length between first and second fastening formations, the first fastening formation being fixed to the inner edge, and the second fastening formation being fixed to the inner side; 
     a groove in the first edge wall and being defined by parallel sidewalls connected by a floor, the groove being for receiving the edge of one of the circuit boards; 
     the first fastening formation including a projection extending substantially parallel with respect to a line along said floor; 
     the second fastening formation including a projection extending substantially normal with respect to said line; and 
     each of the front cross connecting members comprises: 
     a fastening element being an elongated flat strip having fastening locations being defined therein spaced apart one from another; 
     a retaining means wherein the fastening element is realisably fixed, the retaining means being a retaining channel extending between the end portions, along the interior edge of the body, and the retaining channel being defined by a pair of side surfaces being connected by a third surface, each of the pair of side surfaces having a groove therein being spaced a first predetermined distance from the third surface, the elongated flat strip is retained therein, the retaining channel including a pair of walls extending from the side surfaces toward one another and terminating at secondary side walls being spaced a predetermined distance apart one from another; and 
     the first fastening formation including a rectangular protrudence being of a dimension to fit between the secondary side walls to restrain the circuit board slide from rotational movement. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An example of an equipment shelf is discussed with reference to the accompanying drawings, in which: 
     FIG. 1 is a perspective view of an equipment cabinet suitable for housing a telecommunications switching system; 
     FIG. 2 is a block schematic diagram illustrating one of many possible examples of typical physical circuit locations within upper and lower equipment shelves in the equipment cabinet illustrated in FIG. 1; 
     FIG. 3 is a simplified perspective view of an equipment shelf, in accordance with the invention, suitable for use in the system illustrated in FIGS. 1 and 2; 
     FIGS. 4a and 4c are inner edge and inner side fragmentary views and FIG. 4b is an end view, illustrating a front cross connecting member used in the equipment shelf in FIG. 3; 
     FIGS. 5a and 5c are outer edge and inner side fragmentary views and FIG. 5b is an end view, illustrating a rear cross connecting member used in the equipment shelf in FIG. 3; 
     FIG. 6 is a partial plan view of a fastening element being insertable in the cross connecting members illustrated in FIGS. 4a, 4b and 4c, and in FIGS. 5a, 5b and 5c for defining lateral spacing of circuit board positions as illustrated in FIG. 2; 
     FIGS. 7a through 7f are views of a circuit board slide, for use in the equipment shelf illustrated in FIG. 3, in accordance with the invention: and 
     FIG. 8 is an illustration of a circuit board slide, similar to the circuit board slide in FIG. 7a  being assembled with the front and rear cross connecting members in FIGS. 4b and 5b. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, the equipment cabinet includes a pedestal 101 which carries lower and upper equipment shelves underneath a louvred cap 102. The lower and upper equipment shelves are hidden behind lower and upper covers 103 and 104. The system illustrated in FIG. 2 shows the lower and upper equipment shelves 203 and 204 being occupied by a combination of circuit units of various lateral dimensions for performing various functions, as labelled, to provide an operating system in accordance with a particular specification. 
     An example of an equipment shelf for holding circuit board slides 70, in accordance with the invention, is that illustrated in FIG. 3. This equipment shelf includes first and second side panels 8 and 9 being fixed apart one from the other by front cross connecting members 21 and 24, and by rear cross connecting members 22 and 23. The front cross connecting members 21 and 24 are cut to length from a standardized front extrusion body, of cross section as illustrated in FIG. 4b, and thereafter fastened by metal screws 27 between respective corners 8a-9a and 8d-9d of the side panels 8 and 9. The rear cross connecting members 22 and 23 are cut to length from a standardized rear extrusion body, of cross section as illustrated in FIG. 5b, and thereafter fastened by metal screws 26 between respective corners 8b-9b and 8c-9c of the side panels 8 and 9. As shown in FIG. 4c, each front cross connecting member carries an elongated thin flat fastening strip 60 adjacent its inner edge, and as shown in FIG. 5c, each rear cross connecting member carries an elongated thin flat fastening strip 60 adjacent its inner side. Each of the fastening strips 60 includes holes 61 as exemplified in FIG. 6 for retaining slippery plastic circuit board slides as illustrated in FIGS. 7a-7e. 
     The circuit board slides 70 are retained by the holes 61 at circuit board slide locations 10, 11, 12 and 16, as exemplified in FIG. 3. Top side and bottom views of one of the circuit board slides are shown in the FIGS. 7a, 7b and 7c respectively. FIG. 7d is a view of the right hand end of the circuit board slide in FIG. 7a. FIG. 7e is a view of the left hand end of the circuit board slide in FIG. 7a. FIG. 7f is a view of a cross section of the circuit board slide in FIG. 7a, taken along a line 7f--7f. Each of the circuit board slides 70 includes an elongated body portion being defined by a pair of side walls 71 connected by first and second edge walls 72 and 73, the first edge wall 72 being broader than the second edge wall 73. The side and edge walls 71-73 extend between front and rear fastening formations at 80 and 90. Part of the side walls 71, along with the edge wall 73 define a reinforcing rib 77 which terminates with an edge 78 next to the rear fastening formation at 80, and abuts at 79 with the front fastening formation at 90. The reinforcing rib 77 underlies a groove 74, in the first edge wall 72, the groove 74 being defined by parallel sidewalls 75 connected by a floor 76. The front and rear fastening formations at 80 and 90 are intended for engagement adjacent the inner edge and the inner side of front and rear ones of the cross connecting members respectively. The front fastening formation at 80 includes a receiving end 84 and is provided where the parallel sidewalls 75 meet with divergent sidewalls 85 and the floor 76 extends into a sloped floor 86 which joins the divergent sidewalls 85 and a base 81. The base 81 is connected with the rib 77 and carries a rectangular projection 82, which has a cylindrical body 83 extending therefrom, along a line parallel to the floor 76. The cylindrical body 83 is terminated with a frustum 83a and is of such dimension to free fit into any of the holes 61. The rear fastening formation at 90 includes a base 91 which is a widened extension of the first edge wall 72 and the groove 74. The base 91 defines a land 97 from which a cylindrical formation 93 extends substantially normal to the land 97 and is bisected by a groove 93b. The cylindrical formation 93 is terminated with an interference fitting formation 93a for resilient forced engagement with any of the holes 61. When the circuit board slide is in assembly in the equipment shelf, the groove 74 is intended to receive an edge of one of the circuit boards, via the receiving end 84. Furthermore, the end portions 80 and 90 are conveniently broad to provide for structural robustness while the majority of the body portion of the circuit board slide along the groove 74 is comparatively narrower to provide greater free space between the card slides 70 as shown in FIG. 3, with the intent of reducing resistance to a flow of a cooling medium. 
     Referring to the FIGS. 4a-4c the front cross connecting member is in the form of an aluminum extrusion having a body portion cut to predetermined length corresponding to the distance between the side panels 8 and 9. A longitudinal channel 42 extends along an inner side 41 of the body portion and a longitudinal channel 44 extends along an inner edge 43 of the body portion. The longitudinal channel 42 is provided for cooperative engagement with a typical circuit board latching lever, not shown. The longitudinal channel 44 is defined by a pair of side surfaces 45 and 46 being connected by a bottom surface 47. The side surface 45 includes a flared groove 48 therein and the side surface 46 includes a similar flared groove 49 therein. Each of the grooves 48 and 49 is spaced a predetermined distance from the bottom surface 47 for slidably receiving a longitudinal edge of a circuit board slide fastening strip 60, which is illustrated in FIG. 6. The front cross connecting member includes a pair of grooves 42a for convenience of fastening with either of the side panels 8 and 9, by means of screw fasteners illustrated at 27 in FIG. 3. 
     Referring to the FIGS. 5a-5c the rear cross connecting member is in the form of an aluminum extrusion having a body portion cut to predetermined length corresponding to the distance between the side panels 8 and 9. A longitudinal channel 52 extends along an outer edge 53 of the body portion and a longitudinal channel 54 extends along an inner edge 51 of the body portion. The longitudinal channel 52 is provided for cooperative engagement with a typical nut and bolt mounting of a back plane circuit board, not shown. The longitudinal channel 54 is defined by a pair of side surfaces 55 and 56 being connected by a bottom surface 57. The side surface 55 includes a groove 58 therein and the side surface 56 includes a similar groove 59 therein. The grooves 58 and 59 are spaced a predetermined distance from the bottom surface 57 for slidably receiving a longitudinal edge of a circuit board slide fastening strip 60, which is illustrated in FIG. 6. The rear cross connecting member includes a pair of grooves 52a for convenience of fastening with either of the side panels 8 and 9, by means of screw fasteners illustrated at 26 in FIG. 3. 
     Referring to FIG. 8, the card slide substantially as illustrated in FIG. 7b is shown in assembly, on the left, with a front cross connecting member as illustrated in FIG. 4b, and on the right, with a rear cross connecting member as illustrated in FIG. 5b. This is facilitated by the strips 60 from FIG. 6 residing in the respective grooves 48, 49 and 58, 59, with circular openings 61 being occupied by the respective cylindrical bodies 83 and 93. The combination of the cylindrical body 93 and the strip 60 being of a polycarbonate material provides sufficient resilience that the body 93 remains substantially unabraded after several insertions into and removals from the circular hole 61. Furthermore substantial tolerance of variation of length of the card slides is permitted by another structural feature, that being the combination of the rectangular projection 82 residing between the walls 45 and 46. This structure accrues two advantages. One advantage is that the holes 61 may be circular and thus less expensively formed than oblong holes usually used for this purpose. The other advantage is that the card slider is restrained from rotation about its length, without stressing the fastening strips 60.