Abstract:
An apparatus for positioning an electronic printed circuit board within a electronic chassis is disclosed. The PCB includes at least one connector and the chassis backplane includes at least one connector adapted for electrically connecting to the PCB connector when the PCB is latched within the chassis. The apparatus comprises a lever and a rod. The lever includes a first pivot means that is rotated about the edge of the chassis. The lever is movable between a first position and a second position to allow the connector mounted on the back end of the PCB to engage the backplane connector by actuating the lever downward, or to disengage the PCB connector from the backplane connector by actuating the lever upward. The rod is pivotally coupled to the PCB by a rod pivot and pivotally coupled to the lever by a lever pivot that enables movement of the rod along the same plane in which the lever is actuated.

Description:
BACKGROUND OF INVENTION  
         [0001]    1. Technical field  
           [0002]    The present invention relates in general to mechanical fasteners, and in particular, to a mechanism for positioning an electronic assembly within a housing, such as, for example, a printed circuit board within an electronic chassis.  
           [0003]    2. Background  
           [0004]    Printed circuit boards (PCB) are used in many electronic devices, such as telecommunications equipment. In these devices, PCBs are often electrically connected to a back-plane using connectors that extend from the printed circuit card and that mate with connectors located on the backplane.  
           [0005]    Generally, mechanical systems used for insertion and extraction of PCBs comprise a handle secured to the front end of the PCB or a pair of cam levers that cooperate with the front end of the chassis and slotted rail guides dedicated to each PCB mounted in an electronic chassis assembly.  
           [0006]    Insertion and extraction handles present the advantage of being very simple. However, the disadvantage of these systems is that they are not usable with connectors requiring a high insertion and retention force to overcome mechanical resistance to properly mate the connector.  
           [0007]    For this type of connector, a cam lever based mechanism is better suited. Some cam lever systems further comprise a snap latch system that cooperate with a mechanical part secured to the PCB to insure an automatic latching of the PCB in the chassis. The two following patents illustrate some prior art solutions.  
           [0008]    U.S. Pat. No. 4,233,646 from Leung discloses an improved latching lever for use with a PCB. The latching mechanism comprises a hooked portion flexibly connected to the body portion of the latching lever, an actuating member solidly connected to the hooked portion for moving the hooked portion relative to the body portion, and a stop portion, solidly connected to the body portion for limiting the movement of the actuating member. A stud carried by the PCB is engaged by the hooked portion of the lever to enable the lever to latch. Moving the actuating member to contact the stop portion disengages the hooked portion from the stud, thereby unlatching the lever, and leaving the lever free to pivot about its pivot point.  
           [0009]    In commonly assigned U.S. Pat. No. 6,058,579, a snap latch insertion and removal lever is described. The snap latch device has a handle with a pair of cam members extending from a lower end. The device also has a flexible snap which protrudes from the handle. The front end of the snap has a barbed lip. The device is designed to interlock a shuttle assembly to a stationary chassis. The device is pivotally mounted to the shuttle which carries a board with connectors. The device is movable between an engaged position and a retracted position. In the engaged position, the cam members engage an end wall on the chassis and the snap inserts through and engages a hole in the shuttle. The mechanical interlock between the cam members and the end wall rigidly secures the shuttle in the chassis. The device is moved to the retracted position by pulling back on the snap to dislodge the barbed lip. This release allows the device to rotate so that the cam members disengage the end wall. After the snap and cam members are clear of the hole and end wall, respectively, the shuttle may be completely removed from the chassis. The shuttle may be inserted and locked into the chassis by reversing these steps. The snap provides visual and audible feedback to the installer to insure a proper connection between the mating connectors on the shuttle and chassis.  
           [0010]    One drawback of prior art designs is that the force required to mate the PCB is applied on the front end of the card while connectors are located on the back end. This results in undesired flexing of the PCB during insertion, thereby decreasing its reliability and utility by creating a heightened risk of micro cracks within the internal signal layers of the PCB.  
         SUMMARY OF INVENTION  
         [0011]    The present invention relates to an apparatus for easy insertion, latching and removal of a PCB into a chassis.  
           [0012]    In a preferred embodiment, the apparatus for positioning an electronic PCB assembly within a chassis housing comprises a lever and a rod. The electronic PCB assembly includes at least one connector and the chassis backplane includes at least one connector adapted for electrically connecting to the PCB connector when the PCB is latched within the housing. The lever includes a mechanical pivot joint that is rotated about the edge of the chassis housing. The lever is movable between a first position and a second position to allow the connector mounted on the PCB to engage the backplane connector by actuating the lever downward, or to disengage the PCB connector from the backplane connector by actuating the lever upward. The rod is coupled to the PCB by a rod pivot and coupled to the lever by a lever pivot that enables movement of the rod along the same plane in which the lever is actuated.  
           [0013]    The arrangement of the mechanical pivot joint, the rod pivot and the lever pivot is such that the electronic assembly is latched within the housing when the lever is set in the second position.  
           [0014]    The lever preferably comprises a handle and the mechanical pivot joint comprises an upper cam lever and a lower cam lever that contact the housing when the handle is moved from the first position to the second position. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0015]    [0015]FIG. 1. Illustrates a front view of the printed circuit board, the chassis, the backplane and the apparatus according to an embodiment of the present invention.  
         [0016]    [0016]FIG. 2. Shows an enlarged front view of the right side of the printed circuit board, the chassis, the backplane and the apparatus according to the invention in the engaged position.  
         [0017]    [0017]FIG. 3. Illustrates an enlarged front view of the right side of the printed circuit board, the chassis, the backplane and the apparatus according to the invention in the released position.  
         [0018]    [0018]FIG. 4. Shows a profile view of a rod and a cut view of a lever. 
     
    
     DETAILED DESCRIPTION  
       [0019]    Referring to FIG. 1, a general front view of a PCB  130  is shown. A backplane  110  is secured into a chassis  120  preferably with screws (not shown). A backplane connector  111  extends perpendicularly from backplane  110 . A PCB connector  113  extends longitudinally from PCB  130 .  
         [0020]    One mechanism  100  for inserting, extracting and latching the PCB into the chassis is shown mounted on the right and the left sides, respectively, of the PCB  130 . As shown in FIG. 1, mechanism  100  is comprised of a combination of a lever  102  coupled to a rod  104 , extending from the lever and coupled to a holder  106  secured to the PCB. In the described embodiment, the PCB  130  is coupled to the rod  104  through the holder  106 . Although this illustrates a commercial application, a person skilled in the art would appreciate that any form of coupling the rod to the PCB would allow the mechanism to operate. Specifically, a direct coupling of the rod  104  to a printed circuit card would be suitable for phone cards or single in-line module (SIM) cards.  
         [0021]    When operated, mechanism  100  moves from an engaged or locked position (shown on FIG. 2) to a released or retracted position (shown in FIG. 3).  
         [0022]    Referring to FIG. 2, lever  102  has an elongated body in the form of a handle  250 , an upper cam lever  280 , a lower cam lever  281  and a transverse lever pivot through hole  201  located near the lower cam lever. Handle  250  extends perpendicularly to the lever pivot  201  and to both cam levers. As shown on cut view A-A of FIG. 4, lever  102  looks like a reversed U and is preferably made of steel sheet. Lever  102  may further include an open circular slot  251  to guide the rotation of the lever. A swell  252  may be further welded on handle  250  to stiffen lever  102 .  
         [0023]    In the described embodiment, the PCB  130  is guided perpendicularly to backplane  110  with pin guides  220  that are secured either to the backplane  110  or to the chassis  120 . The pin guides  220  may be cylindrical metal parts having a cone-shaped upper end to engage facing pin holes  221  located on the bottom part of the PCB. [ 0024 ] The holder  106  is secured to the PCB  130  with screws (as illustrated on FIG. 1) or by any other conventional technique. The rod is positioned relative to the holder, by insertion into a hole of the holder that acts as a rod pivot.  
         [0024]    The holder is then pivotally coupled to the rod  104  through the rod pivot  202 .  
         [0025]    To insert the PCB  130  within the chassis  120 , mechanism  100  is moved in engaged position by pushing on handle  250 . The description herein is made in reference to one mechanism located on one side of the PCB but the principles described are identical for a second mechanism located on the opposite side of the PCB  130 .  
         [0026]    Referring to FIG. 2, upper cam lever  280  contacts chassis  120  on an upper contact area  260 . Lever  102  rotates around upper contact area  260  until lower cam lever  281  contacts the chassis  120  on a lower contact area  261 . Lever  102  and lever pivot  201  then rotate around lower contact zone  261  actuating rod  104  downwards. Rod  104  pulls holder  106  secured to the PCB  130  downward into the chassis.  
         [0027]    As rod  104  rotates also around holder  106  with rod pivot  202  and as pin hole  221  contacts pin guide  220 , holder  106  and PCB  130  move downward vertically. The mechanical force required to mate PCB connector  113  with backplane connector  111  is applied at a point much closer to the PCB connector then prior art solutions, thereby reducing the risk of damage coincident with PCB insertion and extraction.  
         [0028]    If the operator continues pushing on handle  250 , PCB  130  is moved further downward until lower contact zone  261 , pivot  201  and pivot  202  are aligned. The mechanism  100  then reaches a static position where lever  102  and handle  250  are substantially horizontal.  
         [0029]    If counterclockwise pressure on handle  250  is exerted after PCB  130  is fully seated in the chassis, lower cam lever  281  continues to rotate around lower contact zone  261 , actuating lever pivot  201  and causing rod  104  to move upward. As a consequence, rod pivot  202 , holder  106  and PCB  130  are moved upward slightly, thereby avoiding damage to PCB  130 . Movement of handle  250  is stopped when it contacts the upper boundary  272  of holder  106 . The physical tolerance between the handle  250  and upper boundary  272  of holder  106  is very small since a larger dimension would cause the PCB to disengage PCB connector  113  from backplane connector  111 . The angle formed between rod pivot  202  and lower contact zone  261  is less than 180° when mechanism  100  is in the engaged position and PCB  130  is latched into chassis  120 . An upward vertical force applied to the PCB  130  will tend to move lever  102  counterclockwise. As it contacts upper boundary  272 , mechanism  100  is in the locked position. The only way to extract the PCB  130  is to pull handle  250 , which provides the assurance that PCB connector  113  will not unintentionally disengage from backplane connector  111  and eliminates the need for a screw or other supplemental fastening device.  
         [0030]    Rod  104  preferably bends a little during the insertion operation for two reasons. First, it will accommodate the physical clearances and tolerances associated with a particular installation and second, rod  104  will act as a spring reinforcing the latching effect of mechanism  100 .  
         [0031]    Another advantage of the invention is that when lever  102  is actuated counterclockwise, the operator applies a certain force to mate PCB connector  113  with the backplane connector  111  but once pivot  201  passes beyond the position where pivot  201 , contact zone  261  and pivot  202  are aligned, the applied force is significantly reduced. This is due to the spring effect of lever  102 , until handle  250  comes in contact with an upper boundary  272 . This provides the installer, who cannot see the back end of the PCB a positive feedback indicating that the card is fully seated in the backplane connector.  
         [0032]    Another main advantage of the present invention already mentioned is that the force required to mate PCB and backplane connectors is applied at a point near the back end side of the PCB. This approach reduces the bending of the PCB when inserting it into the chassis. Consequently, the risk of damage to an electrical component, trace, solder joint or the connectors is lessened considerably. Neither is a heavy holder required or in some implementations no holder at all may be required. Similarly, a heavy guiding system designed to reduce flexing and deformation of the PCB may be eliminated. However, depending on the system operating environment, a light weight rail guide may be provided. For example, in the case where the system environment subjects the chassis assembly to pronounced accelerative forces or thermal stress.  
         [0033]    Accordingly, the invention is directed toward a mechanism that allows a PCB to be firmly secured into the chassis and provides positive feedback to the user indicating the circuit board is fully seated in the chassis and the connectors are securely coupled.  
         [0034]    Referring now to FIG. 3, the mechanism  100  is shown in the retracted position. To extract PCB board  130  from chassis  110 , the operator pulls handle  250 . Lever  102  moves clockwise and lower cam lever  281  and lever pivot  201  rotate around lower contact zone  261 . Rod  104  moves rod pivot  202 , holder  106  and PCB  130  downward until upper contact zone  260 , lever pivot  201  and rod pivot  202  are aligned vertically. Then upper cam lever  280  of lever  102  contacts upper contact zone  260  of chassis  110  and rotates around it. Lever pivot  201  rotates now clockwise around upper contact zone  260 . Rod  104 , rod pivot  202 , holder  106  and PCB  130  continue moving upward vertically. This disengages PCB connector  113  from backplane connector  111 . In this position, pin guide  220  is still engaged in pin hole  221 , however, at this point the PCB may be extracted manually by the operator from the chassis.  
         [0035]    Referring to FIG. 3, swell  252  protruding from lever permits easy manual extraction of the PCB  130 . As the operator continues moving handle clockwise, the swell contacts chassis  110  on the upper contact zone  260  and the PCB  130  is further released.  
         [0036]    Holder  106  may further comprise a pin  271  to guide the rotation of lever  102  within the open circular slot  251 . The circular slot  251  and pin  271  are not required elements for insertion, extraction or latching of the PCB  130 , but serve to reduce mechanical stress during insertion and extraction of the PCB. As lever  102  rotates either around upper contact zone  260  or lower contact zone  261  a large clearance is present between open circular slot  251  and pin  271 .  
         [0037]    [0037]FIG. 4 a  illustrates a profile view (B-B) of a rod  104  utilized in the embodiment described above. The first end of the rod  104  is coupled to the lever  102  at the lever pivot  201  and the second end of the rod  104  is coupled through the holder  106  at the rod pivot  202 . FIG. 4 b  shows a cut view (A-A) of lever  102 , including the swell  252 , handle  250  and lever pivot  201 .  
         [0038]    An advantage of the invention is to apply the force necessary to mate the PCB connectors with the backplane connectors at the most optimal location. The invention also provides a positive feedback to the installer that the printed circuit card is fully seated and the connectors are coupled securely. In addition, the invention provides a method for easy securing of the PCB whatever the retention force of the connectors.  
         [0039]    The present invention has been described in preferred embodiments that present various advantages, such as smooth latching of the PCB in a chassis and positive feedback for a complete fit. While the invention has been described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is understood that numerous other modifications and variations can be devised without departing from the scope of the invention.