Abstract:
A printed circuit board retaining device for use in securing a printed circuit board in an elongated slot of a rack provides an efficient design allowing for the utilization of an off-the-shelf screw in the device. A screw having a head located within a first end piece interconnects the first end piece, at least one elongated wedge, and a second end piece. A clutch assembly, also retained within the first end piece, is coupled to the screw by a tool configured to engage the screw head. The clutch assembly has a first and second clutch head. The second clutch head being attached to the opposite side of the tool configured to engage the screw head.

Description:
FIELD OF THE INVENTION 
     This invention relates to devices for retaining and fastening printed circuit boards within a rack or chassis. 
     BACKGROUND OF THE INVENTION 
     Elongated wedge-type devices for retaining printed circuit boards (“PCBs”) within elongated slots in racks or chassis are in common use. The devices typically include a center wedge having sloped surfaces at opposite ends and two end pieces having sloped surfaces that abut against the sloped surfaces of the center wedge. The retaining devices are typically constructed with three or five wedges. A screw or shaft extends lengthwise through and connects the end wedges and the center wedge. In operation, a PCB is typically fastened to the backside of the center wedge. The PCB, with the retaining device attached thereto, is placed within the desired slot of the rack. Rotating the screw or shaft in one direction draws the two end wedges toward each other, causing them to deflect transversely on the sloped abutting surfaces of the center wedge. This results in increasing the device&#39;s effective width and wedging the PCB into the desired location. Rotating the screw in the opposite direction moves the two end wedges apart from each other bringing them back into longitudinal alignment with the center wedge and, thereby, releasing the PCB. Examples of such devices are described in greater detail in U.S. Pat. Nos. 4,775,260, 5,607,273, and 5,779,388, which are hereby incorporated by reference. 
     PCB retaining devices are preferably designed to limit the amount of force applied to the PCB while held in a slot. One solution to this problem has been to integrate clutch assemblies into the retaining device. The clutch is typically configured to have a first and second clutch head having cooperating teeth. By manipulating the angle of the clutch head teeth and the force in which the clutch heads are urged together, the torque applied to the screw and, in turn, the wedging force generated by the retaining device may be controlled. Unfortunately, the integration of the clutch assembly into the retaining device has typically led to the use of custom components in the retaining device. Utilization of custom components results in increased design and manufacturing costs and limits the number of suppliers from which the components can be sourced. It would be desirable to develop a PCB retaining device that maximizes the use of off-the-shelf parts without sacrificing utility. If custom components are used, it would be desirable to limit them to small, relatively affordable components. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     In view of the foregoing, one aspect of the present invention is to provide a PCB retaining device that overcomes the shortcomings of the prior art. More particularly the present invention is to provide a PCB retaining device that incorporates a clutch design configured to allow for the use of a standard, off-the-shelf type screw in the retaining device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other aspects, features and advantages of which embodiments of the invention are capable of will be apparent and elucidated from the following description of embodiments of the present invention, reference being made to the accompanying drawings, in which 
         FIG. 1  is a perspective view of a PCB retaining device according to the present invention; 
         FIG. 2  is a perspective view of a wedge assembly and screw of a PCB retaining device according to the present invention; and, 
         FIG. 3  is perspective view of a clutch assembly and screw of a PCB retaining device according to the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Specific embodiments of the invention will now be described with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The terminology used in the detailed description of the embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, like numbers refer to like elements. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     In accordance with the present invention, a PCB retaining device  10  is depicted in  FIGS. 1 through 3 . The retaining device  10  may be attached to a PCB (not shown) at a backside  26  of the center wedge  20  by screws or rivets. The center wedge  20  includes the sloped surfaces  22  and  24  at its opposite ends. The retaining device  10  may further include the wedges  30  having sloped surfaces  32  and  34  on opposite sides. The sloped surfaces  32  of the wedges  30  abut the sloped surface  22  and  24  of the center wedge  20 . The first and second end pieces  40  and  50  include the sloped surfaces  42  and  52 , respectively that abut against the sloped surfaces  34  of the wedges  30 . A screw  60  engages a clutch assembly  100  positioned within a recess  44  formed in the first end piece  40 . The screw  60  passes through a first wedge  40 , the center wedge  20 , and a second wedge  30 . A threaded bore  54  of the second end piece  50  receives a distal end  64  of the screw  60 . 
     In a manner analogous to that described with respect to the prior art, drawing the two end pieces  40  and  50  toward each other by rotating the screw  60  causes the two wedges  30  to move together transversely relative to the center wedge  20 . An elongated channel through the center wedge  20  and the wedges  30  (not shown) is sized and shaped to accept the screw  60  and permit this relative transverse movement of the screw  60 . This transverse movement effectively increases the width of the retaining device  10 , and thereby locks the attached PCB into a slot. It would be appreciated by one skilled in the art that a PCB retaining device according to the present invention may incorporate any odd number of wedging components. For example, a retaining device in accordance with the present invention may alternatively comprise only the center wedge  20  and the two end pieces  40  and  50 . 
     The retaining device  10  also includes a clutch assembly  100  for limiting the maximum forward torque that can be applied to the screw  60 . This, in turn, controls the clamping force of the retaining device  10 , and thus prevents possible physical or functional damage to the PCB being retained. With particular reference to  FIG. 3 , the clutch assembly  100  includes (1) a drive head  110  having a proximal recess  112 , a groove  114 , and a distal recess  116 ; (2) a spring  120 ; (3) a shaft  130  having a first clutch head  132 ; and (4) a clutch interface  140 , having a second clutch head  142  and a tool  144 . 
     The proximal recess  112  of drive head  110  is configured to receive a conventional driver tool such as, but not limited to, a Phillips tip driver, square tip driver, triple square tip driver, torx tip driver, nut driver, or hexagonal driver. The groove  114  of the drive head  110  is sized and shaped to engage the pins  70  inserted through the holes  46  of the first end piece  40 . Engagement of the pins  70  by the groove  114  serve to axially, but not rotationally, secure the drive head  110  within the first end piece  40 . The distal recess  116  of drive head  110  serves to receive the shaft  130  which passes through the spring  120 . The shaft  130  and the distal recess  116  are sized and shaped to be complementary to one another, e.g. the shaft  130  is illustrated as a hexagonal shaft and the female recess  116  as a hexagonal recess operable for receiving and engaging the shaft  130 . It will be recognized that the shaft  130  and the distal recess  116  may be sized and shaped in any number of cross sectional shapes operable to facilitate engagement between the two components. Because the drive head  110  is secured in a fixed location within the first wedge  40  by the pins  70 , the spring  120  acts against the drive head  110  and serves to push the shaft  130  away from the drive head  110 , thereby urging the first clutch head  132  of the shaft  130  towards the second clutch head  142  of clutch interface  140 . 
     Of particular significance is the configuration of the clutch interface  140 . The clutch interface  140  serves, in part, to couple the clutch assembly  100  to the screw  60 . As illustrated in  FIG. 3 , the clutch interface  140  comprises the second clutch head  142  on one side and the male tool  144  on the other side. As described with respect to the prior art, the first clutch head  132  and the second clutch head  142  each have a series or pattern of teeth that are complementary to and operable to engage with one another. The tool  144  is sized and shaped to emulate the working portion of a conventional driver tool such as, but not limited to, a Phillips tip driver, square tip driver, triple square tip driver, torx tip driver, nut driver, or hexagonal driver and to thereby engage the screw head recess  62  of the screw  60 . It will be appreciated that the above described configuration of the interface  140  allows for the incorporation of a standard, off-the-shelf type screw that may be purchased from numerous suppliers of fasteners and screws. Alternatively stated, it is preferable that screw  60  not be a custom or specially designed and manufactured screw. For example, screw  60  may be a standard sized and shaped screw with a female hexagonal head. The ability to utilize an off-the-shelf screw  60  aids in reducing manufacturing costs and facilitates component sourcing for the retaining device  10 . 
     In use, a conventional driver tool such as a hex key is used to engage the proximal recess  112  of the driver head  110 , to rotate the driver head  110  and the first clutch head  132  of the shaft  130 . Because the spring  120  biases the first clutch head  132  against the second clutch head  142 , the rotation is coupled to the second clutch head  142  and, ultimately to the screw  60 . 
     The confronting faces of the first clutch head  132  and second clutch head  142  both include a series of ratchet teeth or other form of engageable series of recessions and protrusions. It should be appreciated that the angles selected for the teeth or other form of engageable series of recessions and protrusions may vary according to the torque limits selected, the frictional forces encountered, and the biasing spring force selected. 
     During a forward rotation of the driver head  110 , which tightens the PCB and retaining device  10  against the side walls of a slot, the screw  60  will eventually encounter significant resistance to further rotation. When this occurs, the surfaces of the first clutch head  132  will begin sliding or ramping up on the tooth surfaces of the second clutch head  142 , against the yielding resistance of the compression spring  120 . Eventually, the first clutch head  132  will be unable to overcome the resisting torque of the second clutch head  142  and slide over or cease to engage the teeth of second clutch  142 . At this stage the retaining device  10  will be tightened to a predetermined torque. 
     As shown in  FIGS. 1 and 2 , a threaded nut  80  is used to secure the distal end of the screw  60  that transverses threaded bore  54  of second end piece  50 . This prevents an inadvertent disassembly of the wedges  30  and  20  and end pieces  40  and  50  by excessively unthreading the screw  60 . 
     Although the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention. Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.