Abstract:
A mechanical coupling arrangement includes first and second pins and a sphere. When coupled, the pins are longitudinally aligned and include partial portions that face one another. The second pin&#39;s partial portion includes a recess formed therein that faces the first pin&#39;s partial portion. The recess is spherically-shaped to be smaller than a hemisphere. A sphere is ring-staked into the first pin&#39;s partial portion and is seated in the recess.

Description:
ORIGIN OF THE INVENTION 
   The invention described herein was made in the performance of official duties by an employee of the Department of the Navy and may be manufactured, used, licensed by or for the Government for any governmental purpose without payment of any royalties thereon. 

   FIELD OF THE INVENTION 
   The invention relates generally to mechanically actuated devices, and more particularly to a mechanical coupling arrangement that can be used to mechanically couple an initiator pin to a firing pin in a secure fashion and reliably provide for the separation of the two pins during a firing sequence. 
   BACKGROUND OF THE INVENTION 
   Some pyrotechnic devices use a percussion primer to begin the device&#39;s ballistic event. Typically, the percussion primer is actuated by a high pressure gas or by a mechanical firing mechanism. In terms of mechanical firing mechanisms, the hook-type sear design is frequently used because of its simplicity and minimal space requirements. A conventional hook-type sear mechanical firing mechanism is shown in its cocked position if  FIG. 1  and in its release position in  FIG. 2 . In both figures, the firing mechanism is referenced generally by numeral  10 . 
   Firing mechanism  10  includes an annular housing  12  that is centrally bored to define two diameters at  13 A and  13 B to support a firing pin  14  and initiator pin  16  that share a common longitudinal axis with that of the housing&#39;s bore  13 . A spring  18  is disposed between an outer annular shoulder  12 A of housing  12  and an annular flange  14 A of firing pin  14 . In the cocked position ( FIG. 1 ), spring  18  is slightly compressed to thereby apply opposing forces F C  to flanges  12 A and  14 A. In this position, spring  18  is held in place as a flange  16 A (formed on initiator pin  16 ) that is larger in diameter than smaller bore  13 A abuts housing  12  as shown. Firing pin  14  and initiator pin  16  are locked together by the combination of (i) complementary hooks  14 B and  16 B, respectively, and (ii) the narrowly-bored region  13 A of housing  12  that constrains firing pin  14  and initiator pin  16  from radial movement. In operation, initiator pin  16  is pulled longitudinally in the direction indicated by arrow  20  in  FIG. 2 . During this process, spring  18  undergoes further compression. Once hook  16 B clears narrowly bored region  13 A and enters the larger bored region  13 B, initiator pin  16  can disengage from firing pin  14 . Once this occurs, the force of spring  18  is released and firing pin  14  moves in the direction of arrow  22  to start a ballistic event. 
   One problem with the hook-type sear design is the fabrication cost associated with the manufacture of hooks that will perform reliably, e.g., not break, not jam together when they are supposed to separate, etc. Conversely, if short cuts are take in the manufacturing process to save money, the result is an unreliable coupling/release assembly. Further, the hook-type design has an inherent weakness since material must be notched out to create the hook. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide a mechanical coupling arrangement. 
   Another object of the present invention is to provide a mechanical coupling arrangement suitable for use in a mechanical firing device. 
   Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings. 
   In accordance with the present invention, a mechanical coupling arrangement includes first and second pins and a sphere. The arrangement is particularly useful in a mechanical firing mechanism where the first pin is a firing pin and the second pin is an initiator pin. The first pin has a first central longitudinal axis, and has a first partial portion extending longitudinally therefrom. The second pin has a second central longitudinal axis, and has a second partial portion extending longitudinally therefrom and adjacent to the first pin&#39;s first partial portion. The second partial portion has a recess formed therein that faces the first partial portion. The recess is spherically-shaped to be smaller than a hemisphere. A sphere is ring-staked into the first partial portion and is seated in the recess such that the first longitudinal axis is aligned with the second longitudinal axis. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and advantages of the present invention will become apparent upon reference to the following description of the exemplary embodiments and to the drawings, wherein corresponding reference characters indicate corresponding parts throughout the several views of the drawings and wherein: 
       FIG. 1  is a cross-sectional view of a conventional mechanical firing mechanism in its cocked position; 
       FIG. 2  is a cross-sectional view of the conventional mechanical firing mechanism in its released position; 
       FIG. 3  is a cross-sectional view of a mechanical firing mechanism in its cocked position using an embodiment of the novel mechanical coupling arrangement of the present invention; 
       FIG. 4  is a cross-sectional view of the mechanical firing mechanism in its released position using the novel mechanical arrangement of the present invention; and 
       FIG. 5  is an isolated view of a ball ring-staked in the firing pin illustrating geometrical relationships important to the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring again to the drawings, simultaneous reference will be made to  FIGS. 3 and 4  where the novel mechanical coupling arrangement of the present invention is illustrated in the context of a mechanical firing mechanism  100  that performs the same function as firing mechanism  10  ( FIGS. 1 and 2 ) described above. Since housing  12 /bore  13  and spring  18  are common between firing mechanism  10  and firing mechanism  100 ,  FIGS. 3 and 4  will use the same reference numerals for these elements and a description thereof will not be repeated. 
   At the heart of firing mechanism  100  is a firing pin  104 , an initiator pin  106 , and ball  108 . Each of these three elements is made from a rigid material such as a metal. Briefly, ball  108  mechanically couples firing pin  104  to initiator pin  106  in bored region  13 A as the ball  108  is intermediate the firing pin  104  and the initiator pin  106  so as to be in contact with the firing pin  104  and the initiator pin  106 , and facilitates the uncoupling of initiator pin  106  from firing pin  104  in larger bored region  13 B. The structure and relationships between these three elements will now be described with additional reference to  FIG. 5  where needed. 
   Firing pin  104  has a main body  104 A sized for sliding engagement with bored region  13 A, and an extension  104 B that extends longitudinally from main body  104 A while only partially filling bored region  13 A. Main body  104 A has a central longitudinal axis  104 C that is coaxially aligned with the central longitudinal axis  13 C of bore  13 . Extension  104 B has a recess  104 D (also shown in  FIG. 5 ) that is sized to receive and hold ball  108  therein. More specifically, recess  104 D is sized/shaped such that it ring-stakes ball  108  in extension  104 B. In an exemplary embodiment, that is, recess  104 D defines a partial spherical region that is larger than a hemisphere so that the center  108 A of ball  108  resides in recess  104 D. If desired, ball  108  may be rigidly coupled to recess  104 D using adhesive. As a result, a portion  108 B of ball  108  (that is smaller than a hemisphere) is exposed when ball  108  is ring-staked in extension  104 B. 
   Initiator pin  106  also has a main body  106 A sized for sliding engagement with bored region  13 A, and an extension  106 B that extends longitudinally from main body  106 A while only partially filling bored region  13 A. Main body  106 A has a central longitudinal axis  106 C that is coaxially aligned with longitudinal axes  13 C/ 104 C when main body  106 A is in bored region  13 A. Extension  106 B is sized/shaped to oppose extension  104 B. Extension  106 B has a recess  106 D formed therein that opposes recess  104 D and is sized/shaped to allow some portion of exposed portion  108 B to seat therein, in an exemplary complementary fashion. In an exemplary embodiment, the ball  108  is simultaneously seated in recess  104 D and opposed recess  106 D. The amount of exposed portion  108 B that seats in recess  106 D defines a contact angle θ that will be explained with reference to  FIG. 5 . 
   In the present invention, the contact angle θ is defined between the following two lines: (i) a central axis  108 C of ball  108  that is parallel to or coincident with (as shown) longitudinal axis  104 C, and (ii) a line  108 D between center  108 A of ball  108  and the starting edge  106 E of recess  106 D. For reasons that will be explained further below, contact angle θ is, in an exemplary embodiment, in the range of approximately 10° to approximately 20°. Note that choosing a contact angle in this range can result in extensions  104 B and  106 B abutting one another ( FIGS. 3 and 4 ), or a gap being formed between extensions  104 B and  106 B ( FIG. 5 ). Either option is acceptable and does not depart from the scope of the present invention. 
   Operation of firing mechanism  100  is similar to the operation of firing mechanism  10 . Briefly, initiator pin  106  is pulled longitudinally in the direction indicated by arrow  20  in  FIG. 4  to thereby further compress spring  18 . Once extension  106 B clears bored region  13 A and enters bored region  13 B, initiator pin  106  is free to more radially and disengages from ball  108  thereby allowing the force of spring  18  to be released so that firing pin  104  can move in the direction of arrow  22  to start a ballistic event. The above-described small contact angle (i.e., between approximately 10-20°) will insure that extension  106 B/initiator pin  106  will slide away from ball  108  as extension  106 B enters bored region  13 B. 
   The advantages of the present invention are numerous. The precision, hardness and surface finish required for reliable release of a coupling arrangement is provided by a hard ball. Since precision ball bearings are readily available, the mechanical coupling arrangement of the present invention can provide reliability and low cost. Further, the receiving spherical recesses in the initiator and firing pins are easy to machine and will not cause the inherent weakness generated by the notches in the current hook-type sear design. 
   Although the invention has been described relative to a specific embodiment thereof, there are numerous variations and modifications that will be readily apparent to those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described. 
   Finally, any numerical parameters set forth in the specification and attached claims are approximations (for example, by using the term “about” or “approximately”) that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of significant digits and by applying ordinary rounding.