Abstract:
An insertion extraction device (IED) ( 100 ) is suitable for use in attaching a movable object ( 40 ) to a fixed structure ( 20 ) with a limited amount of force. The IED ( 100 ) includes a mandrel ( 120 ) and a flexible sleeve ( 140 ). The mandrel ( 120 ) is constructed of a relatively hard material such as a metal and has a first section ( 126 ) with an elliptical, oval, or similar shape and a second section ( 128 ) for attaching to the fixed structure ( 20 ). The flexible sleeve ( 140 ) is constructed of a material such as nylon or urethane plastic. An operator is able to turn the mandrel ( 120 ) by turning the sleeve ( 140 ) with less than a certain amount of torque. When the operator applies an excessive amount of torque to the sleeve ( 140 ), the sleeve ( 140 ) slips over the mandrel ( 120 ), thereby limiting the maximum amount of force that can be applied to insert the movable component ( 40 ) into the fixed structure ( 20 ).

Description:
FIELD OF THE INVENTION 
     This invention relates generally to insertion extraction devices, and more particularly to insertion extraction devices for use in inserting and extracting movable modules to and from fixed structures such as integrated modular avionics cabinets and the like. 
     BACKGROUND OF THE INVENTION 
     Airplanes contain various electronic systems such as avionics systems, cabin control systems, energy maintenance systems, flight entertainment systems, and the like. The electronic components are typically disposed on printed circuit board (PCB) modules. These PCB modules have a fixed size and are attached, both electrically and mechanically, to a supporting structure such as, for example, an integrated modular avionics (IMA) cabinet. The PCB modules must be periodically removed for service and re-inserted into the IMA cabinets. 
     When inserting a PCB module into an IMA cabinet, it is necessary to make proper electrical connections between banks of pins on the PCB module and corresponding sockets attached to the cabinet. In addition the PCB module itself may be delicate. Thus it is necessary to make the connection with an appropriate degree of force. The application of excessive force during insertion can damage or break the pins or sockets, or break the PCB module itself. 
     An insertion extraction device (IED) is an apparatus that is adapted to mechanically attach the PCB module to the IMA cabinet with a limited amount of force. An IED allows the PCB to be fully seated in the IMA cabinet, providing a mechanical advantage to engage and reseat the PCB. It also keeps the PCB engaged by pre-loading the unit in place. Finally it allows the PCB to be properly disengaged from the IMA cabinet. 
    
    
     There are many known IEDs suitable for use with IMA cabinets. Unfortunately these devices rely on the use of expensive elements including a multitude of washers, ball bearings, and detentes. For certain valuable equipment such as avionics systems the cost of the IED may be acceptable, but for others, such as consumer entertainment systems, the cost is relatively high. What is needed is a lower cost IED which is suitable for the task of inserting and extracting delicate modules to and from fixed structures. Such IED is provided by the present invention, whose features and advantages will be more clearly understood from the following detailed description taken in conjunction with accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a perspective view of an integrated modular avionics (IMA) cabinet housing printed circuit board (PCB) modules having insertion extraction devices (IEDs) according to the present invention. 
     FIG. 2 illustrates a perspective view of an IED of FIG.  1 . 
     FIG. 3 illustrates a cut-away view of the IED of FIG.  2 . 
     FIG. 4 illustrates a side view of the mandrel of FIG.  2 . 
     FIG. 5 illustrates a top view of the mandrel of FIG.  2 . 
     FIG. 6 illustrates a top view of the flexible sleeve of FIG.  2 . 
     FIG. 7 illustrates a side view of the insertion extraction device of FIG. 1 in which a retaining plate is used to captivate the mandrel to the printed circuit board module. 
     FIG. 8 illustrates a side view of the insertion extraction device of FIG. 1 in which a keeper member is used to captivate the mandrel to the printed circuit board module. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a perspective view of an integrated modular avionics (IMA) cabinet  10  housing printed circuit board (PCB) modules  40  having insertion extraction devices (IEDs)  100  according to the present invention. IMA cabinet  10  includes a chassis  20  suitable for housing a PCB module in each of eight slots such as a first slot  30 . Each slot includes a corresponding guide rail  50 . Shown in FIG. 1 is a representative set of three PCB modules  40 . Each PCB module  40  includes electrical connectors at a back end thereof (not shown) for coupling to corresponding connectors at the interior side of the back end of chassis  20 . Each PCB module  40  also includes two IEDs  100  located at top and bottom sides of a front panel portion. Alternatively a single IED would be sufficient for proper engagement and extraction. Chassis  20  also includes two threaded holes  60  for each slot  30  corresponding to the positions of IEDs  100  on each PCB module  40 . 
     FIG. 2 illustrates a perspective view of an IED  100  of FIG.  1 . IED  100  includes generally a mandrel  120 , a flexible sleeve  140 , a retaining plate  160 , a captivating washer  180 , and a retaining screw  200 . Retaining plate  160  attaches IED  100  to the front plate of a PCB module  40  through holes at both ends. Screw  200  secures flexible sleeve  140  and washer  180  to mandrel  120 , leaving flexible sleeve  140  free to rotate. 
     Now considering FIGS. 1 and 2 together, in order to insert PCB module  40  into chassis  20 , an operator slides PCB module  40  into a slot  30  along guide rail  50  until the end of mandrel  120  contacts a corresponding threaded hole  60 . At this time the electrical connectors on PCB module  40  and chassis  20  are in close proximity but have not yet engaged. The operator then turns flexible sleeve  140  in a clockwise direction. Flexible sleeve  140  is adapted to turn mandrel  120  with no more than a limited amount of torque, thereby limiting the force by which the electrical connectors of PCB module  40  engage the corresponding connectors at the interior side of the back end of chassis  20 . By the time the front plate of PCB module  40  contacts the front of chassis  20 , PCB module  40  has moved inward along slot  50  deeply enough to have made sufficient electrical contact with the electrical connectors in chassis  20 . 
     The operation of IED  100  can be better understood from FIG. 3, which illustrates a cut-away view  300  of IED  100  of FIG.  2 . Shown in FIG. 3 is a mandrel portion  320  of mandrel  120 , a sleeve portion  340  of flexible sleeve  140 , and retaining plate  160 . Mandrel portion  320  is elliptical in shape and has two discontinuities located at ends of the major diameter thereof. These discontinuities form a step along the perimeter in the counter-clockwise direction. Located in a center of mandrel portion  320  is a threaded hole  330  suitable for coupling to screw  200 . Sleeve portion  340  has a smooth inner perimeter that distorts to assume an elliptical shape similar to the elliptical shape of mandrel portion  320 . Sleeve portion  340  has an outer perimeter with a set of ribs (or flutes) that enhance its gripability. 
     The operation of IED  100  can be understood by considering FIGS. 1-3 together. An Ad operator turns sleeve  140  in a clockwise direction to insert PCB module  40  into the corresponding slot of chassis  20 , and in a counterclockwise direction to extract PCB module  40  from the corresponding slot of chassis  20 . Mandrel  120  will rotate to insert PCB module  40  into a corresponding slot  60  when an operator imparts a moderate amount of torque on sleeve  140  in the clockwise direction. However once the torque exceeds a predetermined amount, sleeve  140  slips freely (cams) over the outer perimeter of mandrel  120 . Thus IED  100  ensures that PCB module  40  is inserted into the slot with no more than a predetermined maximum amount of force. A designer can select this predetermined maximum amount by varying the size and shape of mandrel  120  and the elasticity of the material forming sleeve  140 , and can estimate it using commercially available computer aided design (CAD) modeling packages. 
     When the operator turns sleeve  140  in the counterclockwise direction, flexible sleeve  140  will distort to grip the steps of mandrel  120 , allowing the operator to impart a large amount of torque to mandrel  120 . This feature is advantageous because the extraction force from the chassis is not critical. 
     IED  100  has numerous advantages over conventional devices constructed of coil springs, spherical balls, detente plates, spring washers, drive clutches, disc springs, and the like. IED  100  minimizes the quantity of moving parts. It may be calibrated when flexible sleeve  140  is fabricated, and will never require calibration after assembly. “Recalibration” can be achieved by simply replacing the existing sleeve with a substitute sleeve calibrated to another desired maximum amount of torque. In addition to being suitable for new designs, IED  100  may also be substituted for an existing clutch configuration. Mandrel  120  can be fabricated from a hard material such as metal. It can be die-cast around a threaded post, and a tapped hole can be later installed. Mandrel  120  can also be notched in the opposite direction, gripping in the clockwise direction and slipping in the counter-clockwise direction. Flexible sleeve  140  is durable yet flexible and is easily replaced if damaged. It can be easily manufactured by extruding it and cutting it to length as needed. Flexible sleeve  140  may be fabricated from materials such as nylon or urethane plastic, which are capable of many flexures yet are durable enough not to flake, chip or permanently dent in any appreciable amount when the sleeve rotates around the mandrel or grips the notch. Flexible sleeve  140  may also be conveniently modeled using modern computer aided design (CAD) techniques, allowing the designer to calibrate IED  100  using the properties of the flexible material and a three-dimensional modeling system. 
     FIGS. 4-8 describe further details and properties of the components of IED  100 . FIG. 4 illustrates a side view of mandrel  120  of FIG.  2 . Mandrel  120  has a circular base  122  near the center having a length  130  along a horizontal axis of 0.130 inches and a diameter  131  of 0.775 inches. Adjacent to a right surface of base  122  is a thin circular portion  124  having a length  132  of 0.05 inches and a diameter  133  of 0.576 inches. On the right side of base  122  to the right of thin circular portion  124  and along the honzontal axis is a first section  126  having a length  134  of 0.82 inches, a major diameter of 0.576 inches, and a minor diameter of 0.404 inches. On the left side of base  122  along the horizontal axis from a left surface of base  122  is a second section  128  having a length  135  of 0.75 inches and a diameter  136  of 0.164 inches. Second section  128  is threaded post for mating with a corresponding threaded hole  60  of chassis  20 . It should be apparent that in other embodiments other. suitable attachments adapted to couple to a corresponding member on chassis  20  may be used. For example second section  128  may be a threaded hole which engages a corresponding threaded post on chassis  20 . 
     Mandrel  120  is constructed of a relatively-hard material such as metal. It is preferably die-cast around a threaded post with a tapped hole subsequently installed and thus is inexpensive to manufacture. 
     FIG. 5 illustrates top view of mandrel  120  of FIG. 2, as viewed from the end of first section  126 . A threaded hole  500  extends inward from the surface of mandrel  120 . The cross-sectional shape of first section  126  is characterized by a major diameter  502  and a minor diameter  504 . The relative sizes of major diameter  502  and minor diameter  504  in part determine the maximum amount of torque by which an operator can turn mandrel  120  before the flexible sleeve slips. Major diameter  502  has a size  510  equal to 0.576 inches. Minor diameter  504  has a size  512  equal to 0.404 inches. In the illustrated embodiment the shape of first section  126  is elliptical. However other suitable shapes including oval, rectangular with rounded edges, and the like may be substituted for the illustrated oval shape. Section  126  is not perfectly elliptical and includes two steps  506  and  508  at each end of major diameter  502 . Each of these steps is 0.05 inches in size. When the operator turns IED  100  in the counterclockwise direction, the inside surface of flexible sleeve  140  will catch the steps, allowing a large amount of torque to be applied. In other embodiments in which the maximum extraction force must similarly be limited, steps  506  and  508  may be eliminated. Furthermore only one of steps  506  and  508  is required to allow a large amount of torque in the counterclockwise direction. Also the direction of the step could be reversed to allow a maximum amount of torque in the counterclockwise direction but a large amount of torque in the clockwise direction. 
     FIG. 6 illustrates top and side views of flexible sleeve  140  of FIG.  2 . Preferably, flexible sleeve  140  is fabricated with black nylon and has a height  600  of 0.75 inches. Viewed from a top thereof, flexible sleeve  140  assumes the approximate elliptical shape of the first section of mandrel  120 . Such an ellipse has a length  606  between the two foci defining the ellipse of 0.190 inches. Flexible sleeve  140  is smooth along an inner perimeter thereof, and has eight ribs positioned evenly around the outer perimeter thereof. The area between adjacent ribs forms eight flutes. The distance  604  between the deepest position of the cavity of a flute and the inner perimeter is equal to 0.025 inches. When flexible sleeve  140  rotates such that the deepest part of a flute is aligned with the end of the ellipse, an angle  608  equal to sixty degrees is formed between the deepest part of this flute and the deepest part of an adjacent flute. A flute has a radius  610  equal to 0.172 inches, whereas the end of the ellipse has a radius  612  of 0.202 inches. 
     FIGS. 7 and 8 illustrate two different methods of attaching IED  100  to PCB module  40 . FIG. 7 illustrates a side view of a portion of IED  100  of FIG. 1 (without flexible sleeve  140  and retaining hardware) in which retaining plate  160  is used to captivate mandrel  120  to PCB module  40 . In this embodiment thin circular section  124  fits within a central hole of retaining plate  160 . The central hole has a diameter of 0.609 inches which provides enough clearance to allow mandrel  120  to rotate freely. FIG. 8 illustrates a side view of a portion of IED  100  of FIG. 1 (without flexible sleeve  140  and retaining hardware) in which a keeper member  802  is used to captivate a mandrel  800  to PCB module  40 . As shown in FIG. 8 mandrel  800  is made without a thin circular portion. Keeper member  802  may be formed by an E-ring or snap-ring keeper or the like. 
     While the invention has been described in the context of a preferred embodiment, various modifications will be apparent to those skilled in the art. For example an IED according to the present invention can be used advantageously in any system which requires insertion and/or extraction subject to a maximum force. Thus it may be used in non-electrical systems. While such an IED is particularly useful in avionics and other airline systems, it may also be used in applications such as test equipment. Also flexible sleeve  140  may be constructed using any of a variety of materials with sufficient flexibility and strength, including nylon, urethane plastic, and the like. It may be uniform so to allow it to be extruded and cut to the appropriate length, or non-uniform. Also the mandrel can assume a variety of shapes such as elliptical, oval, rectangular with rounded corners, and the like. A threaded hole could be substituted for the threaded post of the mandrel. Accordingly, it is intended by the appended claims to cover all modifications of the invention which fall within the true scope of the invention.