Abstract:
A packaging jacket featuring an integral flexible flange. The packaging jacket includes a cylindrical sleeve and a component sub-section that stacks within the sleeve. When stacked, the component sub-section encloses one or more interior chambers that can house an IMU sensor, or other devices. The component sub-section is uniquely held within the sleeve by a flange at one end and a snap ring at the other.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Technological innovation has led to a reduction in the size and weight of many electrical hardware components. This is particularly true in the field of inertial measurement unit (IMU) sensors, where the application of micro-electromechanical systems (MEMS) fabrication techniques has dramatically reduced the size and weight of IMU sensor components compared with their predecessors. 
         [0002]    In aviation, the size and weight of flight hardware is a critical consideration. This has driven the application of MEMS fabrication techniques to aviation-application IMU sensors. The resulting reduction in sensor size has caused the overall size of an IMU package to be dictated more and more by the size of the packaging than by the functionally performing sensing components themselves. The reduction in sensor size provides a corresponding opportunity to reduce package size by reducing the bulk of the packaging materials that house those sensing components. 
       SUMMARY OF THE INVENTION 
       [0003]    The present invention provides a packaging jacket that provides a simple and compact enclosure for inertial measurement unit (IMU) sensors, or other devices. A first part of the jacket is made up of a thin-walled cylindrical sleeve. A second part of the jacket is made up of one or more cylindrically-shaped component sub-sections that stack sequentially inside the length of the cylindrical sleeve. 
         [0004]    At one end of the cylindrical sleeve is a flexible flange that circumscribes at least a portion of the sleeve&#39;s interior edge. At the sleeve&#39;s opposite end, on its interior face, is a snap ring groove to accept an internal snap ring fastener. Component sub-sections are stacked one on top of the other inside the sleeve, forming a component sub-section stack. 
         [0005]    The component sub-section stack is of a height that in order for a snap ring to be installed into the snap ring groove while the stack is within the sleeve, the flexible flange at the sleeve&#39;s opposite end must be displaced. Because the flange is flexible, a force applied to the component sub-section stack at the snap ring end displaces the flange. Displacement of the flange allows the component sub-section stack to move forward in the sleeve, providing room for the snap ring to be installed in the snap ring groove. At the same time, mechanical energy from the applied force becomes stored in the compressed flange. 
         [0006]    After installing the snap ring in its groove, the applied force is removed. The displaced flange rebounds, moving the component sub-section stack backward in the sleeve in the direction of the snap ring. When the component sub-section stack can move no further due to the installed snap ring, the remaining unrelieved energy stored in the flexible flange remains applied against the component sub-section stack. A constant compressive force is left on the component sub-section stack, which is trapped between the flexible flange and the snap ring. Within the component sub-section stack is one or more interior chambers, which are available for housing IMU sensors, or other devices. 
         [0007]    The benefits afforded by this invention are simplification in packaging, a reduction in the number of parts, removal of bulk, and a reduction in cost. All four of these benefits are accomplished mainly by elimination of machine threads and a controlled-torque locking nut system traditionally used in many IMU sensor housings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings: 
           [0009]      FIG. 1  is a perspective view of a MEMS IMU sensor package formed in accordance with an embodiment of the present invention; 
           [0010]      FIG. 2  is a cross-sectional view of the MEMS IMU sensor package of  FIG. 1 ; 
           [0011]      FIG. 3  is an exploded cross-sectional view of the MEMS IMU sensor package of  FIG. 2 ; 
           [0012]      FIG. 4  is a perspective view of a cross-section of a component of the present invention; 
           [0013]      FIG. 5  shows a cross-sectional view of a portion of the package shown in  FIG. 1 ; and 
           [0014]      FIG. 6  is a cross-sectional zoom view of a portion of a flexible flange formed in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]      FIG. 1  illustrates an assembled embodiment of a thin-walled inertial measurement unit (IMU) packaging jacket  10  that includes a cylindrical sleeve  12 . The cylindrical sleeve  12  hold in place multiple interior package components  14 . 
         [0016]      FIGS. 2 and 3  illustrate cross-sectional views of the thin-walled IMU packaging jacket  10 .  FIG. 2  shows the packaging jacket  10  in assembled form and  FIG. 3  shows the jacket  10  in exploded form. The multiple interior package components  14  include an upper component sub-section  15 , a middle component sub-section  16 , a lower component sub-section  18 , upper and lower seals  20 ,  21  and a snap ring  24 . The cylindrical sleeve  12  includes an integral flexible flange  13  and a snap ring groove  22 . Upper component  15  includes a ledge  19 . Within the component sub-section stack  14  is an interior chamber  27 . 
         [0017]    In one embodiment, the sleeve  12  is an elongated cylinder, hollow in the center, and open at each end. The sleeve  12  has sufficient length and inside diameter to accept the component sub-sections  15 ,  16 ,  18 . The wall thickness of the sleeve  12  is of a thickness that provides rigidity, plus a desired level of mechanical impact protection to prevent a physical object from piercing the sleeve  12 . At an open end of the sleeve  12  is the flexible flange  13 . 
         [0018]    The three component sub-sections  15 ,  16 ,  18  have nominally the same outside diameter, which is slightly less than the inside diameter of the sleeve  12 . The diameter facilitates the insertion of the three component sub-sections  15 ,  16 ,  18  snugly but easily within the sleeve  12 . In other embodiments, a different number of component sub-sections could be used. By stacking the component sub-sections components  15 ,  16 ,  18  inside the sleeve  12 , the interior chamber  27  is formed. Optimally the interior chamber  27  is of a size which volumetrically contains micro-electromechanical system (MEMS) sensor parts and supporting electronics (not shown) in the most compact size possible. 
         [0019]    In one embodiment, the upper and lower seals  20 ,  21  are located in cavities formed between the upper and middle component sub-sections  15 ,  16  and middle and lower component sub-sections  16 ,  18 , sealing the interior chamber  27  from the outside atmosphere. 
         [0020]    As shown in  FIG. 4  the flexible flange  13  appears as a lip, or curled element, that circumscribes the interior rim of one end of the sleeve  12 . In one embodiment, the flange  13  is integrally formed with the sleeve  12  and made of the same material as the bulk of the sleeve  12 . In a further refinement of this embodiment, the flange  13  is of a composition that furnishes the flange  13  with flexibility in a direction axial to the cylindrical sleeve  12 . In an alternative embodiment, the flange  13  is formed separately from the sleeve  12 , but is fastened to an end of the sleeve  12 . In yet another embodiment, the flange  13  circumscribes only a portion of the interior rim of one end of the sleeve  12 . 
         [0021]      FIG. 5  shows a cross-sectional view of the component sub-section stack  14  installed in the sleeve  12 . The upper component sub-section  15  has an outside diameter that is less than the inside diameter of the sleeve  12 , but greater than the inside diameter of the flexible flange  13 . Furthermore, the upper component sub-section  15  includes the ledge  19  along its radial edge that, on insertion of the upper component sub-section  15  into the sleeve  12 , meets the flexible flange  13 . Travel of the upper component sub-section  15  within the sleeve  12  is limited by collision of the ledge  19  with the flange  13  inside the sleeve  12 . 
         [0022]    In one embodiment, the height of the component sub-section stack  14  at the ledge  19  slightly exceeds the length of the sleeve  12  measured from the inside tip of the flexible flange  13  in an un-flexed state to the inside edge of the snap ring groove  22 . As a result of these dimensions, with installation of the snap ring  24  into the snap ring groove  22 , the component sub-section stack  14  flexes the flexible flange  13 . 
         [0023]    Initial flexure of the flange  13  is achieved by application of an external force to the component sub-section stack  14  on the exterior face of the lower component sub-section  18 . The applied force moves the component sub-section stack  14  toward the flange  13  in the sleeve  12  until the ledge  19  collides with the flexible flange  13 , causing the flange  13  to flex. Flexure of the flange  13  causes mechanical energy from the applied external force to be transmitted to and stored in the flexible flange  13 . 
         [0024]    With installation of the snap ring  24  and removal of the externally applied force, the component sub-section stack  14  rebounds away from the flange  13  and toward the interior face of the snap ring  24 . The immobility of the snap ring  24  in the snap ring groove  22  causes the exterior face of the lower component sub-section  18  to come to rest against the interior face of the snap ring  24 . The energy left stored in the flange  13  from flexure remains in the flange  13 , and therefore becomes applied to the component sub-section stack  14 . This maintains the component sub-sections  15 ,  16 ,  18  in a compressed state for as long as the snap ring  24  remains installed in the snap ring groove  22 . 
         [0025]    The snap ring groove  22  is integral with the sleeve  12  and circumscribes the sleeve  12  substantially close to the sleeve&#39;s end at the end opposite the flange  13 . The snap ring groove  22  and the snap ring  24  fit together according to standards well-known in the art. 
         [0026]    The middle component sub-section  16  has outside and inside diameters that nominally match the outside and inside diameters of the upper component sub-section  15 . The interior of the middle component sub-section  16  is substantially hollow, and its thickness in the axial direction is variable from embodiment to embodiment. The lower component sub-section  18  is substantially similar to the upper component sub-section  15  in its diameters (inside and outside), thickness in the axial direction, and in the shape and dimensions of its interior face. 
         [0027]    To create the interior chamber  27  for housing an IMU sensor, the component sub-sections  15 ,  16 ,  18  are assembled into the component sub-section stack  14 , as shown in  FIG. 2 . In the component sub-section stack  14 , individual sub-section components are ordered so that on insertion of the component sub-section stack  14  into the sleeve  12 , the exterior face of the upper component sub-section  15  faces the flange  13  and the exterior face of the lower component sub-section  18  faces the snap ring  24 . The middle component sub-section  16  is positioned between the upper component sub-section  15  and the lower component sub-section  18 . 
         [0028]    The interior chamber  27  is formed by stacking together the component sub-sections  15 ,  16  and  18 . In  FIG. 5 , for purposes of sealing the interior chamber  27  from the outside atmosphere, the upper and lower seals  20  and  21  are positioned at upper and lower mating joints  32  and  34  between the upper and middle component sub-sections  15 ,  16 , and middle and lower component sub-sections  16 ,  18 . In one embodiment, the mating joints  32  and  34  are located near the radial edge of the component sub-sections  15 ,  16 ,  18  in order to maximum the potential volume of the interior chamber  27 . Furthermore, for convenience the upper and lower seals  20 ,  21  resemble an O-ring of circular profile and an overall diameter slightly less than the outside diameter of the upper component sub-section  15 . 
         [0029]    The upper component sub-section  15  contains on its interior face a narrow upper sub-section channel  36  concentric with the upper component sub-section  15 , and of a width and diameter substantially matching the width and diameter of the upper seal  20 . The depth of the upper sub-section channel  36  is somewhat greater than the profile of the upper seal  20 . 
         [0030]    Opposite the upper sub-section channel  36 , on the middle sub-section  16 , is a narrow top-facing ridge  40  concentric with the edge of the middle component sub-section  16 . The top-facing ridge  40  on the middle component sub-section  16  is positioned so that when the upper and middle component sub-sections  15 ,  16  and the upper seal  20  are concentrically located about a given axis, the top-facing ridge  40  of the middle component sub-section  16 , the upper sub-section channel  36  of the upper component sub-section  15 , and the upper seal  20  mutually align. Furthermore, the dimensions of the top-facing ridge  40  are such that the top-facing ridge  40  substantially occupies the width of the upper sub-section channel  36  in the upper component sub-section  15 . On stacking the upper and middle component sub-sections  15 ,  16  and the upper seal  20 , the height of the top-facing ridge  40  interferes with the upper seal  20  to a degree that provides optimal sealing between the upper seal  20 , and the upper and middle component sub-sections  15  and  16 . 
         [0031]    The lower seal  21 , a lower sub-section channel  38 , and the bottom-facing ridge  42  are substantially identical to the upper seal  20 , the upper sub-section channel  36 , and the top-facing ridge  40 . The lower seal  21  mates and seals the faces of the middle and lower component sub-sections  16 ,  18  in substantially the same manner as the upper seal  20  seals the upper and middle component sub-sections  14 ,  16 . 
         [0032]    The upper and lower seals  20  and  21  become compressed by the same force that displaces the flange  13 . The compliance of the upper and lower seals  20 ,  21  is high relative to the compliance of the flange  13 , so that the amount of force taken up by the upper and lower seals  20 ,  21  compared with that taken up by the flange  13  is insignificant. The upper and lower seals  20 ,  21  become compressed until the upper and lower mating joints  32 ,  34  of the component sub-sections  15 ,  16 ,  18  meet, providing the twin benefit of a complete seal and a rigid structure to deliver the balance of the applied force to the flange  13 . 
         [0033]    Alternative embodiments for sealing a cavity from an outside atmosphere while using a flexible flange are still considered within the scope of this invention. The possibility for an embodiment where no sealing components are used is also within the scope of invention, for example in applications where only mechanical protection, but not atmospheric isolation, is needed. 
         [0034]      FIG. 6  illustrates the flexible flange  13  in an un-flexed state. In particular, the flange  13  has a flange lip  28  and a flange stiffness tuning feature  30 . The flange lip  28  extends inward from the sleeve  12  into the opening of the sleeve  12 . The lip  28  interferes with the ledge  19  when the upper component sub-section  15  is slid within the sleeve  12 . 
         [0035]    The flange stiffness tuning feature  30  is a channel that circumscribes the interior face of sleeve  12  in the region where the lip  28  meets the sleeve  12 . The flange stiffness tuning feature  30  can be cupped, notched or any shape that relaxes the stiffness of the flange  13 . The depth, the fraction of the circumference circumscribed, and the location of the stiffness tuning feature  30  can vary as would be obvious to one skilled in the art to alter the flexibility of the flange  13 . In one embodiment, the tuning feature circumscribes only 50% of the full circumference, distributed in ten even segments. In another embodiment, the tuning feature  30  is on the outside of the sleeve  12 . 
         [0036]    In one embodiment, the flange  13  is integral with the sleeve  12 , and is a spring steel or similar metallic composition that provides a flexural characteristic to the flange lip  28 . Considered included within the scope of the invention are alternative embodiments of any size, shape or thickness, or embodiments of alternative material compositions, that could provide the flange  13  with the capability of being displaced in an axial direction, and absorb and store a portion of any energy imparted on the flange  13  by an applied force. In another embodiment, the flange  13  does not include the flange relief groove  30  as a feature to decrease the mechanical resistance of the flange  13 . 
         [0037]    As the described electronics packaging invention could be used to package any number of different electronic components in a wide variety of different applications, the fact that the invention disclosed is applied to an inertial measurement unit (IMU) packaging application for aviation purposes in no way limits this invention to aviation applications or to the packaging of IMU sensors and electronics. 
         [0038]    While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.