Patent Publication Number: US-11644286-B1

Title: Vibration resistant initiator assembly having exploding foil initiator

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of Ser. No. 17/395,883 filed Aug. 6, 2021, which claims the benefit of U.S. Provisional Application No. 63/067,416 filed Aug. 19, 2020. The disclosure of each of the above-referenced applications is incorporated by reference as if fully set forth in detail herein. 
    
    
     FIELD 
     The present disclosure relates to a vibration resistant initiator assembly having an exploding foil initiator. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     Initiator assemblies are employed to detonate an input charge to release energy that is subsequently employed to initiate detonation, deflagration or combustion in an output charge. There is a trend in the field of initiator assemblies to employ an exploding foil initiator as the means for initiating detonation of the input charge. Electrical energy input to an exploding foil initiator causes a thin metal bridge to vaporize, which propels a flyer through a barrel and into contact with the input charge. The flyer is typically formed of a relatively thin plastic material and must be accelerated over a relatively short distance (i.e., less than 0.050 inch) to a velocity that is sufficient to initiate the detonation of the input charge. Moreover, the flyer must strike the input charge in a manner that is perpendicular to the axis of the barrel to reduce the risk that contact between the flyer and the input charge will initiate detonation of the input charge. 
     In situations where the initiator assembly is subjected to a relatively large amount of vibration, there is a risk that portions of the output charge will break apart and migrate within the initiator assembly onto the flyer. This situation is detrimental because it greatly increases the risk that the exploding foil initiator will not be able to detonate the input charge. In this regard, if even a relatively small mass of the material that forms the output charge falls onto the flyer, the additional mass could prevent the flyer from being accelerated to a threshold velocity that is needed to cause the input charge to detonate and/or could cause the flyer to tilt relative to the longitudinal axis of the barrel so that the shock produced by contact between the flyer and the input charge is distributed over time (rather than all at once) so that the input charge is not shocked to a degree that initiates detonation of the input charge. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     In one form, the present disclosure provides an initiator assembly that includes a housing, a base, an exploding foil initiator and an input charge assembly. The housing defines a cavity. The base coupled to the housing and closes the cavity. The exploding foil initiator is mounted to the base and has a barrel that defines an initiation axis. The input charge assembly is received in the cavity and includes a holder and an input charge. The holder has a first axial end and a second axial end that are spaced apart along the initiation axis. The first axial end is closer to an output of the barrel than the second axial end. A charge aperture is formed through the first axial end of the holder and does not extend through the second axial end of the holder. The input charge is formed of an explosive material and is received into the charge aperture. 
     In another form, the present disclosure provides an initiator assembly that includes a housing, an output charge, an input charge assembly, and a base/EFI assembly. The housing has a housing member and a cover. The housing member has a first axial end and a second axial end and defines a cavity with a first cavity portion, a second cavity portion and a third cavity portion. The first cavity portion extends through the first axial end of the housing member. The third cavity portion extends through the second axial end of the housing member. The second cavity portion is disposed between the first and third cavity portions. The first cavity is larger in diameter than the second cavity portion so as to define a first annular shoulder on the housing member where the first and second cavity portions intersect one another. The second cavity portion is larger in diameter than the third cavity portion so as to define a second annular shoulder on the housing member where the second and third cavity portions intersect one another. The cover is fixedly coupled to the second axial end of the housing member to close an end of the cavity. The output charge is received in the third cavity portion and is at least partly formed of an explosive material. The input charge assembly has a holder and an input charge. The holder is fixedly coupled to the housing member and has a first holder portion and a second holder portion. The first holder portion defines a charge aperture that does not extend fully through the holder. The second holder portion is smaller in diameter than the first holder portion. A third annular shoulder is formed on the holder radially outwardly of where the second holder portion intersects the first holder portion. The first holder portion is received into the second cavity portion and is located along the initiation axis such that the third annular shoulder is spaced apart from the second annular shoulder on the housing member. The second holder portion is partly received in the third cavity portion. The input charge is received into the charge aperture and is formed of an explosive material. The base/EFI assembly has a base, a plurality of terminals, and an exploding foil initiator. The base is fixedly coupled to the housing member. The terminals extend through the base and are electrically coupled to the exploding foil initiator. The exploding foil initiator is coupled to the base. The base/EFI assembly is slidably received into the first cavity portion and closes the cavity on a side of the housing member opposite the cover. The base/EFI assembly is abutted against either an axial end of the holder or a barrier that is abutted against the axial end of the holder. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG.  1    is a perspective view of an exemplary vibration resistant initiator assembly constructed in accordance with the teachings of the present disclosure; 
         FIG.  2    is a side view of the initiator assembly of  FIG.  1   ; 
         FIG.  3    is an exploded perspective view of the initiator assembly of  FIG.  1   ; 
         FIG.  4    is a section view taken along the line  4 - 4  of  FIG.  2   ; 
         FIG.  5    is a perspective view of a portion of the initiator assembly of  FIG.  1   , illustrating a base and an exploding foil initiator in more detail; 
         FIG.  6    is a section view of a portion of an alternately constructed exploding foil initiator; and 
         FIG.  7    is an enlarged portion of  FIG.  4   . 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     With reference to  FIGS.  1  through  3   , an initiator assembly constructed in accordance with the teachings of the present disclosure is generally indicated by reference numeral  10 . The initiator assembly  10  can include a housing  12 , a base  14 , an exploding foil initiator  16 , an input charge assembly  18 , and optionally an output charge  20 . 
     With reference to  FIG.  4   , the housing  12  can define a cavity  30  that can be configured to receive all or a portion of the base  14 , as well as the exploding foil initiator  16 , the input charge assembly  18  and if included, the output charge  20 . The cavity  30  can have a first cavity portion  32  and a second cavity portion  34  that can be disposed concentrically along an initiation axis  36 . The first cavity portion  32  can be larger in diameter than the second cavity portion  34 . A first annular shoulder  38  can be formed on the housing  12  where the first and second cavity portions  32  and  34  of the cavity  30  intersect one another. Optionally, the housing  12  can further define a third cavity portion  40  that can be sized to house the output charge  20 . The second cavity portion  34  can be disposed along the initiation axis  36  between the first cavity portion  32  and the third cavity portion  40 . If desired, the third cavity portion  40  can be disposed concentrically about the initiation axis  36  and can be smaller in diameter than the second cavity portion  34  such that a second annular shoulder  42  can be formed on the housing  12  where the second and third cavity portions  34  and  40  intersect one another. 
     In the example provided, the housing  12  includes a housing member  50  and a cover  52  that are assembled to one another, but it will be appreciated that the housing  12  could be unitarily and integrally formed as a single, discrete component. The housing member  50  can be a tubular structure having a first axial end  54  and a second axial end  56 . A through-bore  58  can be formed through the housing member  50  that is sized to the diameter of the third cavity portion  40 . A first counterbore  60  can be formed into the first axial end  54  of the housing member  50  and can form the first annular shoulder  38 . A second counterbore  62  can be formed into the first annular shoulder  38  and can form the second annular shoulder  42 . It will be appreciated that the first and second annular shoulders  38  and  42  are spaced apart from one another along the initiation axis  36 . The through-bore  58  that forms the third cavity portion  40  can extend from the second annular shoulder  42  through the second axial end  56  of the housing member  50 . Accordingly, it will be appreciated that the first cavity portion  32  can extend through the first axial end  54  of the housing member  50 , while the third cavity portion  40  can extend through the second axial end  56  of the housing member  50 . 
     The cover  52  can be fixedly coupled to the second axial end  56  of the housing member  50  to close an end of the cavity  30 . In the example shown, the cover  52  is received into a third counterbore  66  that is formed into the second axial end  56  of the housing member  50 . The third counterbore  66  defines a third annular shoulder  68  against which the cover  52  is abutted. Any desired means may be employed to fixedly couple the cover  52  to the housing member  50  to close an end of the cavity  30  on the second axial end  56  of the housing member  50 . In the particular example provided, the cover  52  is laser welded to the housing member  50 . 
     With reference to  FIGS.  4  and  5   , the base  14  can be a structure or assembly to which the exploding foil initiator  16  can be mechanically and electrically mounted and which can secure the exploding foil initiator  16  to the housing  12 . One example of a suitable base is the header that is illustrated and described in commonly assigned U.S. Pat. No. 7,571,679, the disclosure of which is incorporated by reference as if fully set forth in detail herein to the extent that they do not contradict any of the present disclosure. In brief, the base  14  can include a header body  70 , a plurality of terminals  72  and a plurality of seal members  74 . The header body  70  can define a plurality of terminal apertures  76 . Each of the terminals  72  can be disposed through an associated one of the terminal apertures  76 . Each of the seal members  74  can be received in an associated one of the terminal apertures  76  and can be sealingly engaged to the header body  70  and to a respective one of the terminals  72 . If desired, other elements of the header assembly described in U.S. Pat. No. 7,571,679, such as an insulating spacer and a frame member, may be incorporated into the base  14  if desired. At least a portion of the header body  70  can be sized to be received into the first cavity portion  32  of the housing  12 . In the example provided, the header body  70  is shaped as a right cylindrical plinth, having an outer diameter that is sized to fit into the first counterbore  60 . The height of the header body  70  is relatively shorter than the distance between the first axial end  54  of the housing member  50  and the first annular shoulder  38 . 
     The exploding foil initiator  16  can include a foundation structure  90 , a pair of bridge contacts  92 , a bridge  94 , a flyer layer  96  and a barrel  98 . The foundation structure  90  can be formed of any desired electrically insulating material, such as a ceramic material and/or a resin-impregnated fiberglass material. The bridge contacts  92  and the bridge  94  can be mounted onto the foundation structure  90  in a desired manner, such as via vapor deposition in one or more layers. The flyer layer  96  can be disposed over the bridge contacts  92 , the bridge  94  and the foundation structure  90  and can be formed of a suitable material, such as a layer of polyamide. The barrel  98  can be disposed over and abut the flyer layer  96  and can be formed of a suitable material, such as a layer of polyamide. The barrel  98  can define a barrel aperture  100  that can extend fully through the barrel  98  and can be disposed concentrically about the initiation axis  36 . The exploding foil initiator  16  can be mounted to the base  14  and each of the bridge contacts  92  can be electrically coupled to an associated one of the terminals  72 . The base  14  and the exploding foil initiator  16 , together with exploding foil initiator  16  can form a base/EFI assembly  102  that is received at least partly into the first cavity portion  32  of the housing  12 . 
     As shown in  FIG.  6   , the barrel  98  could be overmolded onto the flyer layer  96  and the base  14 . Configuration of an initiator assembly in this manner is described in more detail in commonly assigned U.S. Pat. No. 10,267,604 and commonly assigned U.S. Ser. No. 16/280,069, the disclosures of which are incorporated by reference as if fully set forth in detail herein to the extent that they do not contradict any of the present disclosure. 
     Returning to  FIG.  4   , the input charge assembly  18  includes a holder  110  and an input charge  112 . The holder  110  is fixedly coupled to the housing member  50  and has a first holder portion  116  and an optional second holder portion  118 . The first holder portion  116  is sized to be received into the second counterbore  62 , while the second holder portion  118 , if included, is sized to be received into the through-bore  58 . In the example provided, the through-bore  58  is smaller in diameter than the second counterbore  62  so that the first holder portion  116  is relatively larger in diameter than the second holder portion  118 . Accordingly, a fourth annular shoulder  120  is formed on the holder  110  where the first and second holder portions  118  and  116  intersection one another, with the fourth annular shoulder  120  extending radially outwardly from where the second holder portion  118  intersects the first holder portion  116 . The holder  110  can define a charge aperture  122  that is disposed concentrically about the initiation axis  36  and which is configured to hold the input charge  112 . The charge aperture  122  is formed into a first axial end  126  of the holder  110  and does not extend fully through the holder  110  in an axial direction along the initiation axis  36  (i.e., the charge aperture  122  does not extend through a second axial end  128  of the holder  110  that is opposite the first axial end  126  of the holder  110 ). 
     The input charge  112  is received into the charge aperture  122  and is formed of a suitable explosive material, such as a secondary explosive material. In the particular example provided, the input charge is formed of RSI-007 which is a secondary explosive material that is available from Reynolds Systems Incorporated of Middletown, Calif. Those of ordinary skill in the art will appreciate that the term “input charge” not only connotates that the element is formed of an energetic material, but also that this charge is the first charge (and possibly the only charge) in a line or string of charges that are operated when a “flyer” is discharged during operation of the exploding foil initiator  16 . In this regard, a shockwave produced when the “flyer” impacts against another structure, such as the input charge  112  or a barrier/cover member  130 , is transmitted into the input charge (i.e., either directly or indirectly) to cause the input charge  112  to detonate. Accordingly, it will be understood that the input charge  112  detonates in response to a shockwave that is produced through motion and impact of the “flyer” and not through in response to a shockwave produced by detonation of a charge of an energetic material. 
     With reference to  FIGS.  4  and  7   , the first holder portion  116  is received into the second cavity portion  34  and located axially along the initiation axis  36  such that the fourth annular shoulder  120  is spaced apart from the second annular shoulder  42  on the housing member  50  and the second holder portion  118  is partly received in the third cavity portion  40  and partly received in the second cavity portion  34 . It will be appreciated that orientation of the input charge  112  in this manner relative to the housing  12  positions the open end of the charge aperture  122  so that it faces the exploding foil initiator  16 . 
     With reference to  FIGS.  3  and  7   , an optional barrier or closure member  130  may be received into the first counterbore  60  and abutted against the first axial end  126  of the holder  110  such that the input charge  112  is disposed between the closed end of the charge aperture  122  and the barrier or closure member  130 . Alternatively, the barrier or closure member  130  can be received into the open end of the charge aperture  122 , or mounted to the first axial end  126  of the holder  110  such that the input charge  112  is disposed between the closed end of the charge aperture  122  and the barrier or closure member  130 . The barrier or closure member  130  could be employed for various reasons, including one or more of: a) electrically insulating the base/EFI assembly  102  from the holder  110  and/or the input charge  112 ; b) mechanically separating the base/EFI assembly  102  from the holder  110  and/or the input charge  112 ; c) sealing the input charge  112  within the charge aperture  122 ; and d) modifying (e.g., attenuating, amplifying, concentrating, spreading) the shockwave that is produced by the exploding foil initiator  16  prior to transmission of the shockwave into the input charge  112 . In the example provided, the barrier or closure member  130  has a washer-like configuration having a center hole  132  that is disposed concentrically about the initiation axis  36  in-line with the barrel aperture  100  ( FIG.  5   ). The center hole  132  can be sized in a desired manner but will generally be larger in diameter than the barrel aperture  100  ( FIG.  5   ) so as not to impede the motion of a “flyer” that is produced when the exploding foil initiator  16  is operated. It will be appreciated, however, that the barrier or closure member  130  could be formed without the center hole  132 , in which case the “flyer” produced when the exploding foil initiator  16  is operated is intended to impact against the barrier or closure member  130 , rather than pass through the barrier or closure member  130 . 
     With reference to  FIG.  4   , the output charge  20  is received in the third cavity portion  40  and is disposed along the initiation axis  26  between the housing  12  (i.e., the cover  52  in the example provided) and the second axial end  128  of the holder  110 . The output charge  20  can be at least partly formed of an explosive material. In the example provided, the output charge  20  is formed of a secondary explosive material and is directly abutted against the cover  52  and the second axial end  128  of the holder  110 . 
     With reference to  FIGS.  3  through  5  and  7   , when assembling the initiator assembly  10 , the output charge  20  may be initially fitted into the housing member  50 . In this regard, the output charge  20  may be compacted prior to its insertion into the housing member  50 , and/or could be compacted in the housing member  50 . If the output charge  20  is compacted prior to its insertion into the housing member  50 , the output charge  20  could be fully compacted (i.e., to a desired density, to a desired volume, and to a desired size), or could be compacted to an intermediate level (e.g., to permit the output charge  20  to be received into the through-bore  58  in a slip-fit or press-fit manner) and thereafter fully compacted once it is received into the housing member  50 . Depending upon manufacturing preferences, the cover  52  may be coupled to the housing member  50  prior to or after the output charge  20  has been assembled to the housing member  50 . 
     Likewise, the input charge  112  can be fitted into the charge aperture  122  in the holder  110 . The material that forms the input charge  112  may be compacted prior to its insertion into the holder  110 , and/or could be compacted in the holder  110 . If the input charge  112  is compacted prior to its insertion into the holder  110 , the input charge  112  could be fully compacted (i.e., to a desired density, to a desired volume, and to a desired size), or could be compacted to an intermediate level (e.g., to permit the material that forms the input charge  112  to be received into the charge aperture  122  in a slip-fit or press-fit manner) and thereafter fully compacted once it is received into the holder  110 . If a barrier or closure member  130  is employed in the initiator assembly  10  and is received into the open end of the charge aperture  122  and/or mounted to the holder  110 , the barrier or closure member  130  can be inserted into the charge aperture  122  and/or mounted to the holder  110  as desired. 
     The input charge assembly  18  can be received into the housing  12  such that the second holder portion  118  is at least partly received into the through-bore  58  and the first holder portion  116  is received into the second counterbore  62 . The input charge assembly  18  can abutted against the output charge  20  and can be secured to the housing  12  to inhibit movement of the holder  110  along the initiation axis  36 . In the example provided, a force of a predetermined magnitude is applied to the holder  110  such that the second axial end  128  of the holder  110  is not only abutted against the output charge  20 , but also the output charge  20  is in a force transmission path between the holder  110  and the housing  12 . The holder  110  can be fixedly coupled to the housing  12 , for example by laser welding the holder  110  to the housing  12 , while the force of the predetermined magnitude is applied to the holder  110 , the output charge  20  and the housing  12  to thereby ensure the absence of void space along the initiation axis  36  in the third cavity portion  40  that would potentially permit movement of the output charge  20 , in whole or in part, along the initiation axis  36 . Preferably, a compressive axial load is maintained on the output charge  20  along the initiation axis  36  after the holder  110  has been fixedly coupled to the housing  12 . To ensure that a compressive load can be maintained on the output charge  20  after fixedly coupling the holder  110  to the housing  12 , the spacing of the second annular shoulder  42  away from the first annular shoulder  38  along the initiation axis  36  is larger than the distance between the first axial end  126  of the holder  110  and the fourth annular shoulder  120 , and the spacing between the second annular shoulder  42  and the cover  52  along the initiation axis  36  is smaller than the sum of the distance from the fourth annular shoulder  120  to the second axial end  128  of the holder  110  and the overall length of the output charge  20  along the initiation axis  36 . The holder  110  may be coupled to the housing  12  at one or more discrete points, for example about the circumference of the first holder portion  116 /second counterbore  62 . Alternatively, the holder  110  may be coupled to the housing  12  around the entirety of the circumference of the first holder portion  116 /second counterbore  62 , which may effectively seal the first cavity portion  32  from the third cavity portion  40 . 
     The base/EFI assembly  102  can be received into the housing  12  such that the base  14  is at least partly received into the first counterbore  60  and the base/EFI assembly  102  abutted against the input charge assembly  18  (or against the barrier/closure member  130  if one is employed in the initiator assembly  10 ). To the extent that a barrier or closure member  130  is employed and it is merely disposed between the input charge assembly  18  and the base/EFI assembly  102 , then the barrier or closure member  130  can be received into the cavity  30  in the housing  12  prior to the insertion of the base/EFI assembly  102  into the housing  12 . Once the base/EFI assembly  102  has been abutted to the input charge assembly  18  (if no barrier or closure member  130  is employed in the initiator assembly  10 ) or to the barrier or closure member  130  (if a barrier or a closure member is employed in the initiator assembly  10 ), the base  14  may be coupled to the housing  12  at one or more discrete points, for example about the circumference of the header body  70 /first counterbore  60 , to close the cavity  30  at a first axial end  54  of the housing member  50 . Alternatively, the base  14  may be coupled to the housing  12  around the entirety of the circumference of the header body  70 /first counterbore  60 , which may effectively seal the first cavity portion  32  from the atmosphere. 
     Because neither the holder  110  nor the base  14  engage a hard stop formed on the housing  12 , both the holder  110  and the base  14  are able to move along the initiation axis  36  during the assembly process to ensure that a compressive load of a predetermined magnitude is placed on the output charge  20 , and to ensure that the base/EFI assembly  102  in general, and more specifically, the axial end of the barrel  98  of the exploding foil initiator  16  that is most distant from the bridge  94 , is spaced relative to the input charge  112  or to the barrier or closure member  130  in a desired manner. Where the various components are welded together, for example, the cover  52  and the housing member  50 , the holder  110  and the housing member  50  and/or the base  14  and the housing member  50 , the configuration that is described above and illustrated in the drawings permits the formation of a butt weld between components (i.e., the welds between the cover  52  and the housing member  50 , the holder  110  and the housing member  50 , and the base  14  and the housing member  50  are butt welds in the example illustrated). Given the flexibility in the positioning of the holder  110  and the base  14  within the housing  12 , it will be appreciated that the initiator assembly  10  can be designed such that the first axial end  54  of the housing member  50  is flush with an outer axial end of the base  14  and that the first axial end  126  of the holder  110  can be flush with the second annular shoulder  42 , but that the outer axial end of the base  14  could be recessed below or protrude from the first axial end  54  of the housing member  50  and/or the first axial end  126  of the holder  110  could be recessed into the second counterbore  62  or extend into the first counterbore  60 . 
     In operation, an electrical signal of a predetermined voltage can be applied to one of the terminals  72  to drive electrical current through the bridge  94  to cause the bridge  94  to suddenly convert from a solid into a plasma. The conversion of the material of the bridge  94  into a plasma is associated with a large change in volume that causes a “flyer” to shear from the flyer layer and propel the “flyer” through the barrel  98 . Despite the fact that the “flyer” is relatively thin and can be formed from a material such as polyamide, the “flyer” exits the barrel  98  with sufficient energy to generate a shockwave when it impacts the barrier or cover member  130  (if a solid barrier or cover member is present in the initiator assembly  10 ) or an axial end of the input charge  112  that faces toward the exploding foil initiator  16  (in situations where no barrier or cover member  130  are present in the initiator assembly  10  or when the barrier or cover member  130  is configured to permit the “flyer” to pass through it an impact against the input charge  112 ). The shockwave is sufficiently strong so that it migrates into the input charge  112 , either directly or through the barrier or cover member  130  (if a solid barrier or cover member  130  is present in the initiator assembly  10 ) to cause the material of the input charge  112  to detonate. Energy produced by the detonation of the material of the input charge  112  can be employed to generate a second, more powerful shockwave that can be employed to rupture the closed end of the holder  110  and initiate detonation of the material that forms the output charge  20 . 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.