Abstract:
A screw-type fastener includes an internal cinching mechanism that physically locks exposed threads of a screw outside a housing after a certain number of turns. The fastener may for example, be affixed to a faceplate of a printed circuit board. The exposed threads may then be rotated to threadably engage corresponding threads of a sub-rack or other enclosure in a manner that prevents movement of the faceplate relative to the enclosure as the screw engages the enclosure. When the internal cinching mechanism is locked, the physical relationship (e.g., distance) between the faceplate and the sub-rack is retained until the fastener is unscrewed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. App. No. 61/032,691 filed on Feb. 29, 2008, the entire content of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     This application relates generally to fasteners and more specifically to threaded fasteners that secure an item at a fixed distance from another item. 
     Fasteners such as screws and bolts are commonly used to mechanically couple hardware. In some electronics applications, such as where a printed circuit board is attached to an enclosure, it may be preferable to secure the board to the enclosure in a manner that ensures that the board remains seated in an edge connector without imposing stress on the board that might cause electrical or mechanical failure. There remains a need for an improved fastener for use in such applications. 
     SUMMARY 
     A screw-type fastener includes an internal cinching mechanism that physically locks exposed threads of a screw outside a housing after a certain number of turns. The fastener may for example, be affixed to a faceplate of a printed circuit board. The exposed threads may then be rotated to threadably engage corresponding threads of a sub-rack or other enclosure in a manner that prevents movement of the faceplate relative to the enclosure as the screw engages the enclosure. When the internal cinching mechanism is locked, the physical relationship (e.g., distance) between the faceplate and the sub-rack is retained until the fastener is unscrewed. 
     In one aspect, a device disclosed herein includes a screw with a screw head, a first threaded portion, a second threaded portion, and a central axis, the first threaded portion nearer to the screw head along the central axis and having a first pitch and the second threaded portion farther from the screw head along the central axis and having a second pitch; a nut including interior threads corresponding to the first threaded portion, the nut positioned around the central axis of the screw; and a housing having a first opening that exposes the screw head while retaining the screw head within an interior of the housing, and the housing having a second opening through which the second threaded portion can extend, the interior of the housing rotationally retaining the nut and providing a translational stop for the nut that prevents the nut from traveling closer than a predetermined distance toward the first opening when the first threaded portion engages the nut. 
     In some embodiments the first pitch may be different from the second pitch and the second pitch may be finer than the first pitch. The nut may have an interior diameter greater than an outside diameter of the second threaded portion of the screw. A spring may bias the nut toward the screw head. Another spring may bias the screw toward the first opening of the housing. A partition between the screw head and the nut may be included where the nut may be securely cinched and the screw head engaged with the first threaded portion. 
     In one aspect, a fastener disclosed herein includes a screw having a threaded portion; a housing around the screw, the housing having a first opening that exposes a screw head of the screw and the housing having a second opening that exposes the threaded portion; and an internal threading mechanism that permits the threaded portion to progressively extend out of the housing to engage a separate threaded screw hole, and that rotationally cinches the screw within the housing after the threaded portion has extended a predetermined distance out of the housing. 
     The housing may be a two-part housing having a first half and a second half. The first half may press fit to the second half. The first half may be rotationally coupled to the second half by corresponding threaded regions. 
     In one aspect, a fastener disclosed herein includes a screw with a screw head, a first threaded portion and a second threaded portion; a housing around the screw, the housing having an interior with a partition between a first opening in the housing that exposes the screw head and a second opening in the housing that exposes the second threaded portion; and a nut within the interior and adjacent to the partition, the nut capable of engaging the first threaded portion of the screw to rotationally cinch the screw to the partition with the screw in a position having the second threaded portion extending out of the interior of the housing. 
     The second threaded portion may be smaller diameter than the first threaded portion. The first threaded portion may have a different pitch than the second threaded portion. A coil spring may be around the screw and positioned between the screw head and the partition to bias the screw head toward the first opening. A washer may be around the screw and positioned between the nut and the partition. A return spring may bias the nut toward the partition. The nut may be keyed to an interior portion of the housing to prevent a rotation of the nut upon an application of rotational force thereto. The screw head may be retained within the first opening by at least one of a lip and a crimp. The housing may have an external feature keyed to an insert in a module faceplate. The second threaded portion may have a pitch corresponding to a threaded screw hole of an enclosure sub-rack. The enclosure sub-rack may be a MicroTCA sub-rack. The screw head may include one or more of a Phillips head, a hex head, a flat head, a hexalobular head, an internal hexalobular head, and a square head. The screw head may include one or more of a thumb screw and a wingnut. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention and the following detailed description of certain embodiments thereof may be understood by reference to the following figures wherein: 
         FIG. 1  shows an exploded view of a fastener. 
         FIG. 2  shows a cross-section of a fastener disengaged from a sub-rack. 
         FIG. 3  shows a cross-section of a fastener engaged to a sub-rack. 
     
    
    
     DETAILED DESCRIPTION 
     The following disclosure relates generally to a threaded fastener that secures an object to another at a fixed distance. 
     As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Further, unless expressly stated to the contrary, “or” is intended to mean “and/or” unless otherwise stated to the contrary, and references to elements in the singular (“a”, “an”, “the”, “one”, etc.) are intended to also refer to such elements in the plural unless otherwise stated or clear from the context. 
     Reference will now be made in detail to several embodiments, examples of which are illustrated in the accompanying figures. The figures depict embodiments of the present invention for purposes of illustration only, and are not intended to limit the scope of this disclosure. One skilled in the art will readily recognize that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the invention. 
       FIG. 1  shows an exploded view of a fastener  10  that may be used to secure a module such as an AMC (Advanced Mezzanine Card) module or other circuit board or the like in a rack such as an ATCA (Advanced Telecommunications Computer Architecture) sub-rack. In general, the fastener may include a screw  100 , a compression spring  110 , a housing top  120 , a nut  130 , a wave washer  140 , and a housing bottom  150 , all substantially centered on a central axis  160  of the fastener (which is, in the depicted embodiment, also the central axis  160  of the screw  100 ). 
     The screw  100  may have a screw head  102  shaped to receive a Phillips head, hex head, flat head, square head, hexalobular head, internal hexalobular head, or other screwdriver or tool shape, and may generally includes two threaded portions. A first threaded portion  104  may match the threads of the nut  130  within the housing  120 . The second threaded portion  106  may extend through the housing bottom  150  when the fastener is assembled, and may have threads that match a target for the fastener, such as a nut or threaded through-hole of a sub-rack. The first threaded portion  104  may have a larger diameter than the second threaded portion  106 . The first and second threaded portions  104 ,  106  may have different thread pitches. In some embodiments the second threaded portion  106  may have a finer pitch than that of the first threaded portion  104  so that the nut  130  travels along an axis of the screw  100  more quickly than the second threaded portion  106  displaces the screw  100  while engaging corresponding threads of a sub-rack (not shown) or the like. As a result of this relationship, the nut  130  may travel toward the screw head  102  without applying force to a sub-rack that is threadably engaged to the second threaded portion  106 . In some embodiments, the screw  100  may also, or instead, be adapted for manual operation in the form of a thumb screw, wingnut, or the like. 
     A spring  110  such as a compression spring or a coil spring may serve to bias the screw  100  away from the nut  130  and washer  140  or toward an opening  122  that exposes the screw head  102 . Within the assembled fastener  10  this bias may prevent the screw  100  from floating loosely along the axis of the fastener  10  and may maintain the screw head  102  near the opening  122  when the fastener  10  is not in use. 
     The nut  130  may be threaded with interior threads to match the first threaded portion  104  of the screw  100 . The nut  130  may have an interior diameter sufficiently large to permit the second threaded portion  106  of the screw  100  to pass through unrestricted. In other embodiments, the nut  130  may have a smaller interior diameter. In such embodiments, the nut  130  may be threaded past the second threaded portion  106  during assembly or the nut  130  may be fabricated in a position between the threaded portions  104 ,  106 . The nut  130  and/or washer  140  may be keyed to an interior of the housing bottom  150  or otherwise rotationally retained in order to prevent rotation of the nut  130  when the screw  100  is being screwed into or out of a sub-rack or other threaded component. While this keying is depicted in  FIG. 1  as a square shape with rounded corners, it will be understood that any shape may be employed that prevents rotation of the nut  130  within the housing bottom  150  when rotational force is applied by the screw  100 . 
     A spring or the like may also be positioned between the nut  130  and the housing bottom  150  in order to bias the nut  130  toward the screw  100 . This return spring may push the nut  130  toward the upper housing  120 . It will be understood that the washer  140  may also or instead provide as similar biasing to the nut  130 . The washer  140  may be a wave washer or a crescent washer and may be considered a spring since these type washers may provide biasing. The springs discussed above may be coil springs, torsion springs, leafs springs, biasing springs, or some combination of these, or any other hardware that provides suitable mechanical biasing of components of the fastener  100 . The nut  130  may be allowed to float slightly so that the threaded portion  106  of the screw  100  can rotate into proper alignment with the nut  130  before the respective threads engage. As will also be further appreciated with reference to  FIG. 3  below, the top housing  120  may present a surface smaller than the nut  130  (and the screw head  102 ) where the top housing mates with the bottom housing  150  to form a partition against which the nut  130  and screw  100  can cinch. While the surface of the top housing  150  may provide this mechanical stop for the nut  130 , it will be understood that any suitable partition within the fastener  10  may similarly be employed. In one embodiment, such a partition permits the screw  100  to pass through (e.g., toward a second opening  152  in the bottom housing  150  to engage threaded hardware) while providing a mechanical stop for the nut  130  so that screw  10  can be rotationally cinched within the fastener  10  after a number of turns. In other embodiments, the screw  100  may directly cinch the nut  130 , with suitable modifications to permit an appropriate degree of movement by the nut  130  within the fastener  10 . One or more lock washers or other components for improved rotational operation may also be included at a number of locations along the central axis  160  of the fastener  10 . The washers discussed above may include crescent washers, waver washers, split washers, lock washers, flat washers, or some other type or combination of washers. 
     The housing top  120  and housing bottom  150  may retain the screw  100 , spring  110 , nut  130 , and washer  140  as an assembled unit. For example, the opening  122  in the housing top  120  may include a crimp, lip, or other edge or the like to retain the head  102  of the screw  100  within an interior region of the fastener  10 . A washer may also be positioned between the nut  130  and the top housing  120 . Similarly, the housing bottom  150  may seat and retain the nut  130  and the washer  140 . The housing top  120  may be attached to the housing bottom  150  using a friction fit, a press fit, a weld, an adhesive, or any other attachment technique suitable for a mechanical assembly. The housing top  120  may also, or instead, be threaded onto the housing bottom  150  to permit disassembly and re-assembly of the multi-part fastener. 
     While the two-part housing assembly described above provides for relatively simple assembly and disassembly from easily manufactured parts, it will be understood that other forms of construction may be employed without departing from the scope of this invention. For example, a single housing may be provided, and after a screw is inserted into the housing, one opening may be crimped or otherwise finished to retain the screw head, while a partition may be inserted into the other opening to retain the screw in the opposing axial direction. The partition may be secured, e.g., using an adhesive, a weld, retaining pins, or any other suitable hardware. Thus, with a wide variety of manufacturing options available, it will be understood that the particular embodiments described in detail herein are intended to provide illustrative examples, and do not limit the scope of this disclosure. 
     Although not depicted in  FIG. 1 , it will be further understood that the housing bottom  150  may include a mechanically keyed exterior adapted to fit into a corresponding insert in a module, module faceplate, rack, sub-rack or other hardware such that the housing cannot rotate about its axis (such as in response to rotational force applied to the screw  100 ). For example, the housing bottom  150  may be keyed to insert into a module faceplate to retain the fastener  10  and prevent rotation of the bottom housing  150  (and more generally, the fastener  10 ) when the screw  100  has rotational force applied. 
     Additionally, in some embodiments of the fastener  10  the second threaded portion  106  of the screw  100  may be replaced with other attachment structures. For example, the screw  100  may include an “L” shaped structure on an end thereof, where the “L” includes an arm that engages a flange or other surface when the fastener  10  is cinched to retain the fastener  10  and any related hardware against axial movement. 
       FIG. 2  shows a cross-section of a fastener  200  such as the fastener of  FIG. 1  positioned to secure a module  210  in a sub-rack  220 , which may be an electronics enclosure sub-rack or the like. As shown in  FIG. 2 , the fastener  200  has not yet engaged the sub-rack  220 . A second threaded portion  230  of a screw  235  is aligned with a threaded portion  240  of the sub-rack  220  such that the respective threads can be engaged by applying an axial force to the screw head  255  in the direction of an arrow  257  and rotating the screw head  255  with a screwdriver or other tool. A lip  260  may retain the screw  235  in a top housing  233  of the fastener  200 , with the screw head  255  biased toward an opening  259  in the top housing  233  by a spring  250 , such as a compression spring or the like. In this manner, the screw  235  may be loosely immobilized in a suitable position so that it does not axially float within the fastener  200 , while permitting the screw  235  to travel axially upon an application of force, such as due to a force applied directly along the arrow  257  or an axial force that is created as the screw  235  rotationally engages a nut within the fastener  200 . 
     By way of example, the fastener described herein may be used with a module and enclosure conforming to the PCI Industrial Computer Manufacturers Group (“PICMG”) standards for enclosures such as AdvancedTCA, AdvancedMC, MicroTCA, and the like. MicroTCA is a PICMG standard targeted at providing an off-the-shelf chassis for use with Advanced Mezzanine Cards. The MicroTCA standard defines a specific spacing between an AMC module and a sub-rack into which it is placed. Using the fastener described herein, a screw  235  may be retained within the top housing  233  and a bottom housing  234  of the fastener  200 , with the second threaded portion  230  aligned with threads in the MicroTCA sub-rack, which may be the sub-rack  220  described above. As the screw  235  is tightened (as shown below in  FIG. 3 ), the internal cinching mechanism of the fastener  200  may lock the screw  235  after a certain number of turns. At the same time that the screw  235  is cinching a nut  130  or the like internally, the second threaded portion  230  may engage threads in the sub-rack  220 . Thus the module  210  may be secured at a fixed distance from the sub-rack  220  by the threads of the fastener  200 , which are rotationally secured by the internal cinching mechanism. While an AMC module  210  and a MicroTCA Sub-Rack  220  are depicted in  FIG. 2 , it will be understood that the fastener disclosed herein may be usefully employed in any environment where a screw-type fastener is desired to secure an item a fixed distance from a threaded mount without applying force along the screw axis as a result of threading into or cinching against the threaded mount. 
       FIG. 3  shows a cross-section of a fastener  300  securing a module  310  to a sub-rack  320 . As shown, the screw  330  is cinched in position by a screw head  335  (after application of rotational force with a screwdriver or similar tool) against a bottom lip  350  of a top housing  352  with an opposing force applied by a nut  340 , which is similarly bottomed out against a partition or translational stop formed by the bottom lip  350  between the screw head  335  and the nut  340 . This translational stop may secure the nut  340  and the screw head  335  at a predetermined translational location within the fastener  300 , e.g., with the nut  340  and the screw head  335  each a predetermined distance from the first opening and the second opening of the fastener  300 . A second threaded portion  360  of the screw  335  may be threaded into the sub-rack  320  without applying a substantial axial force (left or right in  FIG. 3 ) to the sub-rack  320 . That is, as a first threaded portion  337  of the screw  330  engages the nut  340 , the screw  330  may continue to move axially toward the sub-rack  320  so that the second threaded portion  360  can continue threading into the sub-rack  320 . This may result in a no-load attachment of the module  310  to the sub-rack  320  in which the two parts are attached by a screw without imposing a substantial load on the module  310  or the sub-rack  320  in order to cinch the screw  330 . This may relieve loading and/or stress under conditions where the application of a lateral force might cause warping, cracking, or other electrical or mechanical damage. 
     Thus as described above the screw head  335 , partition (as formed, for example, by the bottom lip  350  of the top housing  352  in  FIG. 3 ), and nut  340 , and any suitable washers, springs, and other supplemental hardware may cooperate to form an internal threading mechanism that permits the second threaded portion to progressively extend out of the housing  352 , such as by axial force applied to the screw head  335  or as the screw  330  engages an external screw hole, and that rotationally cinches the screw  330  after the second threaded portion  360  has extended a predetermined distance out of the housing. While embodiments are shown and described above, it will be understood that any internal threading, locking, or other mechanism may be similarly employed in a fastener without departing from the scope of this disclosure. 
     The fastener may be designed to meet any of a variety of functional specifications. For example, a minimum number of turns on the second threaded portion  360  may be required for the screw  330  to fully engage the sub-rack  320 , and where this is a design requirement, the fastener  300  may be adapted to permit that minimum number of turns before cinching. Likewise, a maximum number of turns on the second threaded portion  360  may be desired, and the fastener  300  may be adapted to prevent more than such a maximum number of turns. The design may similarly be specified as a minimum or maximum distance that the second threaded portion  360  extends from the fastener  300 . 
     The disclosed fastener may be useful in a variety of applications. For example, the fastener may be used to secure a chassis, shelf, or rack a fixed distance from a component with the fastener. The disclosed fastener may also be usefully employed in high vibration environments where a load between components (due to conventional threaded fasteners or other attachment means) is undesirable. The disclosed fastener may more generally be used in any application where two objects are to be held at a fixed distance or in a fixed relationship without actually being bound to one another through a load-bearing connection. 
     While the invention has been disclosed in connection with the preferred embodiments shown and described in detail, various modifications and improvements thereon will be readily apparent to those skilled in the art. Accordingly, the spirit and scope of the present invention is not to be limited by the foregoing examples, but is to be understood in the broadest sense allowable by law.