Abstract:
In a chassis for holding drawers containing computer components or the like, accurate alignment of each drawer in its corresponding slot is provided by a plurality of alignment features along an edge of an opening for the drawer. Mating alignment features are provided in each drawer, that engage with the alignment features on the chassis to ensure alignment of the drawer in the chassis. Various different types of alignment features are provided. Mating alignment features may additionally be provided along an opposing edge of the chassis and drawers. After being aligned, the drawers may be fastened to the chassis in a conventional fashion.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims priority pursuant to 35 U.S.C. §119(e) to U.S. Provisional Application No. 60/420,924, filed Oct. 24, 2002, which application is specifically incorporated herein, in its entirety, by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to computer chassis for housing computer components, and more particularly, to portions of such chassis as relate to the insertion and removal of modular drawers. 
   2. Description of Related Art 
   Various forms of computer chassis are known in the art, for housing components of a computer system or networked computer systems. Such chassis are typically formed primarily of sheet metal components, such as formed sheet steel components, for strength and EMI shielding. In addition, computer chassis often include slots for sliding removable modular drawers into and out of the computer system. The removable drawers are themselves often housed in formed sheet metal housings. As is known in the art, sheet metal is an economical choice for electronics enclosures, but also entails compromises with respect to achievable tolerances and methods of assembly. 
   Customarily, computer chassis are provided with a plurality of slots, all of which are not necessarily occupied by a removable drawer when the computer system is in use. Often, a plurality of empty slots are available for the insertion of new drawers. A problem arises when drawers are not properly inserted. The first drawer may not be properly aligned in the slot, because of tolerances required to ensure ease of assembly. Consequently, sufficient space may not be left for drawers that will be subsequently inserted, and drawers may need to be removed and realigned to make room for the new drawers. This rearrangement of drawers wastes time, and increases the risk that the computer system will be disrupted by the rearrangement. 
   Also, if drawers are not properly aligned in their slots, electro-magnetic interference (“EMI”) gaskets may not be properly positioned. EMI gaskets may be a part of the drawer and/or chassis design to meet performance and regulatory requirements. If the drawers are not properly aligned to the system chassis, the assembled system may not meet its design specifications for control of EMI, resulting in an unacceptable amount of EMI emanating from the assembled system. 
   Prior-art computer chassis were not designed to solve these problems, which were not heretofore recognized as important. Although the presence of slots inherently involves a degree of guidance, prior-art chassis do not provide the necessary degree of precise guidance to avoid misalignment in a fool-proof fashion. Instead, prior-art systems rely on the skill of the assembler to properly align each drawer in the chassis, and to fasten each drawer in place after it has been aligned. Prior-art threaded fastenings are not desirable for providing precise alignment of each drawer, because of the difficulty of locating and threading fasteners into sheet-metal components in a precise way. 
   It is desirable, therefore, to provide a guide system for a computer chassis to ensure that new drawers are more precisely aligned in one of a plurality of empty slots, without the need for special attention by the person assembling the system. It is preferable that the guide system be independent of the fastening system for fastening the drawers to the chassis, and to require little or no additional cost of materials and assembly. 
   SUMMARY OF THE INVENTION 
   The present invention provides a guide system for a computer chassis, that ensures drawers are properly aligned in a suitable slot. The guide system may easily be implemented on sheet metal chassis and sheet metal drawer housings for little or no additional cost, and is not limited to sheet metal materials. 
   In brief, a system according to the invention comprises alignment features positioned adjacent to the edge of a plurality of slots in a computer chassis. The alignment features correspond to mating features on a plurality of removable drawers that may be inserted into the chassis. The alignment features may be positioned so that each drawer to be inserted is guided into a particular position with respect to the available slots. For example, each drawer may be guided to a position that ensures adequate space will be left for remaining drawers. Optionally, the alignment features may differ from one another, so that only a drawer having a mating feature of a corresponding shape may be inserted into a particular slot. 
   A more complete understanding of the invention will be afforded to those skilled in the art, as well as a realization of additional advantages and objects thereof, by a consideration of the following detailed description of the preferred embodiment. Reference will be made to the appended sheets of drawings which will first be described briefly. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of chassis for a computer system, with two inserted drawers according to an embodiment of the invention. 
       FIG. 2  is a detail view showing a guide tab of the chassis and mating guide cutout of a removable drawer, according to an embodiment of the invention. 
       FIG. 3  is a detail view showing an alignment tab of the chassis and a mating guide flange of a removable drawer, according to an embodiment of the invention. 
       FIG. 4  is a detail view of a lower edge of the chassis, showing protruding alignment prongs attached along a lower edge of the chassis. 
       FIG. 5  is a detail view showing relative positions of an alignment prong and adjacent drawers in a fully inserted position. 
       FIG. 6  shows the exemplary chassis with all slots filled by a plurality of drawers aligned to the chassis according to the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The present invention provides a computer chassis with drawer guides that overcome the limitations of the prior art. In the detailed description that follows, like element numerals are used to indicate like elements appearing in one or more of the figures. 
     FIG. 1  shows a chassis  100  for a network computer system, according to an embodiment of the invention. Chassis  100  may be formed primarily from sheet metal components, as known in the art. In the alternative, chassis  100  may be comprised primarily of materials such as EMI-shielding plastics, or other suitable materials. Chassis  100  may include other suitable components and materials, as known in the art. 
   Chassis  100  has a plurality of slots  102 , three of which are covered by covers  104 , and one of which is occupied by drawer  106 . In reality, each “slot” may merely comprise a portion of an open bay. There need be no dividers between the slots. Whether of not dividers are present, if a drawer is not properly aligned to its allotted slot, it may not be possible to properly insert an adjoining drawer. Drawers are inserted into the slots  102  through an opening in the front of the chassis. The opening is bordered by opposing edges that may serve for positioning each drawer within its slot. Alignment features, as further described below, may be provided along or adjacent to at least one of these opposing edges. 
   In the exemplary embodiment, drawer  106  is a system drawer comprising a plurality of modules  108 ,  110 . Module  108  may be a power supply module. Chassis  100  is designed to hold a plurality of system drawers like drawer  106 . Each system drawer may be connected to network and power connectors at the back of the chassis. In addition, or in the alternative, provisions may be made for connections at the front panels of the drawers, as shown in FIG.  1 . In the alternative, drawer  106  may be a drawer for a system module, instead of for a complete computer system. In such alternative embodiments, each drawer may connect to a system bus at or near the rear of the chassis. 
   Referring to  FIGS. 1 and 2 , conventional fasteners, for example, threaded fastener  101  which threads into threaded hole  103 , may be used to secure drawer  106  to chassis  100 , after the drawer is fully inserted into the chassis. The attachment fasteners are not used to align drawers  106  into slots  102 . Instead, attachment fasteners like  101  may be allowed to “float” within a housing  105  which allows an amount, such as about 1 mm, of free play for the fastener. The fasteners  101  may then more readily be threaded into their respective threaded holes. In the alternative, conventional oversized attachment through holes in an attachment flange of the drawer (not shown) may be used to retain a fastener. Either way, drawer  106  would be subject to becoming misaligned by the amount of free play or free width of the through hole, were it not for the presence of the alignment features described herein. In other words, fasteners  101  may permit a greater amount of free play than the alignment features. Of course, other attachment fasteners, for example, clips, may be used instead of or in addition to threaded fasteners. Some amount of free play may be a desirable property of these alternative attachment fasteners, as well. 
   System drawer  106  should be inserted only into a slot  102 , and should not occupy portions of more than one slot. Accordingly, again referring to  FIGS. 1 and 2 , an edge flange  112  along an edge of chassis  100  bordering an opening for slots  102  is provided with a plurality of guide tabs  114 . Each guide tab  114  is positioned adjacent to one of slots  102 , in a predetermined position relative to the width of the slot. Each guide tab may be formed by creating an opening  116  in the edge flange  112 , and folding a portion of material removed for the opening into a tab so that it is approximately orthogonal to flange  112 . Side edges  118  of the tab may be tapered towards its end  120 , so as to more readily guide the top edge of drawer  106 . When drawer  106  is fully inserted into the chassis, edges  122  of cutout  122  should be closely adjacent to, or in contact with, guide tab  114 . 
   System drawer  106  is provided with a corresponding cutout  122  in an upper flange  123 , adjacent to an upper periphery of drawer  106 . Cutout  122  is sized and positioned so as to guide drawer  106  into slot  102 , by engaging guide tab  114  with edges  124  of cutout  122 . In the alternative, or in addition, other mating guide features may be provided, for example, pins and mating holes. Tabs  114  and cutouts  122  have the advantage of being readily formed using the same sheet metal forming operations as generally used to form components of chassis  100  and drawer housing  106 . 
   In the alternative, or in addition to an edge flange  112  along an edge of the slot  102 , a support bar  126  may be used to define a bottom edge, as shown in  FIGS. 3 and 4 . An alignment feature  128  may be separately provided along support bar  126 , with a corresponding flange  130  on drawer  106 . As shown more clearly in  FIG. 4 , alignment feature  128  comprises a prong  132  and a mounting tab  134  that is attached to the support bar  126  defining a bottom edge. An upper surface of alignment feature  128  is flush with, or below, the upper surface of support bar  126 , so as to facilitate sliding drawers into the chassis. A plurality of alignment features  128  may be provided, each disposed along support bar  126  along the bottom edge to guide drawer  106  by engagement with edge  136  of flange  130  on a corresponding drawer  106 . 
     FIG. 5  shows a more greatly magnified view of the relative positions of prong  132  and edge  136 , when drawer  106  is fully inserted into slot  102 . Essentially, prong  132  provides a precise spacing between adjacent drawers  106 ,  106 ′, thereby ensuring alignment of both drawers along their bottom edges. At the same time, if drawer  106  is not properly aligned in its corresponding slot, interference between flange  130  and prong  132  will prevent full insertion of the drawer into the slot. The leading end of prong  132  may be tapered or chamfered to better guide drawer  106  into its slot by engagement with edge  136 . In addition, or in the alternative, a prong (not shown) may be attached to, or formed in, drawer  106 , configured to engage with a corresponding notch in the bottom edge  126  of the chassis. 
   Thus, drawer  106  may be aligned in slot  102  to a high degree of precision, being guided along both upper and lower ends. It should be apparent that the terms “upper” and “lower” are used herein relative to the orientation of the figures, and are not intended to imply that any particular orientation is required in practice. Drawers  106 , chassis  100 , and the alignment features may be oriented in any desired manner. 
   In an alternative embodiment, a drawer may be configured to fit only in a particular slot or slots by arrangement of complementary alignment features. For example, referring to  FIGS. 1 and 2 , a protruding alignment feature such as a guide tab  114  may be provided at a position on flange  112  that will interfere (not shown) with an upper flange  123  of drawers that are not intended to be inserted into the corresponding slot in the chassis, thereby preventing drawers from being inserted into a wrong slot. In comparison, a drawer that is intended for the slot may be provided with a cutout  122  in an appropriate location, both permitting its insertion into the slot and aligning it with respect to chassis  100 . 
   Referring to  FIG. 6 , an exemplary computer chassis assembly  200  comprising a chassis  201 , a plurality of slots  202 , and a corresponding plurality of drawers  206  is depicted. Chassis  200  has an opening, which in the illustrated embodiment is completely filled by the plurality of drawers, positioned along a side of the chassis. Each of the slots  202  thereby has an opening bounded by opposing edges of the chassis, such as the upper edge  205  and lower edge  207 . Each of the drawers  206  is inserted into a corresponding one of the plurality of slots  202 . A plurality of first alignment features (e.g., guide tabs  214 ) are disposed along at least one of the opposing edges  205 ,  207  of the chassis. A plurality of second alignment features (e.g., cutouts  222 ) are disposed on the plurality of drawers  206 . Each of the plurality of drawers has at least one of the plurality of second alignment features. Each of the first alignment features engages a mating one of the second alignment features, thereby aligning each of the drawers  206  to a corresponding one of the slots  202 . Similar complementary alignment features, such as those described above, may be disposed along lower edge  207  and so as to engage corresponding lower portions of drawers  206 . 
   Having thus described a preferred embodiment of the invention, it should be apparent to those skilled in the art that certain advantages of the within system have been achieved. It should also be appreciated that various modifications, adaptations, and alternative embodiments thereof may be made within the scope and spirit of the present invention. For example, particular shapes of guide features have been illustrated, but it should be apparent that the inventive concepts described above would be equally applicable to other shapes of guide features. The invention is further defined by the following claims.