Abstract:
A command to arm apparatus includes a housing having a hollow interior. A pivotally-mounted rotor is disposed in the hollow interior. The rotor has a first, safe position of rotational adjustment that prevents detonation of an explosive and a second, armed position of rotational adjustment that enables detonation of an explosive. A locking cam is pivotally mounted to the rotor and has a rotor-locking position of repose. The rotor is free to rotate from its safe position to its armed position when the locking cam is rotated out of the rotor-locking position by a piston that extends from a piston actuator. The rotor abuts a flat formed in a sidewall of the housing and can rotate no further when the device is in the armed configuration.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to command to arm devices for bullets and rockets. 
         [0003]    2. Description of the Prior Art 
         [0004]    Conventional safe and arm (S&amp;A) devices have a large spread in the distance between “no arm” and “all arm.” Typically, the “all arm” distance is three (3) to four (4) times the “no arm” distance. The “all arms” distance may therefore be hundreds of feet, a distance that is unacceptable in urban warfare. 
         [0005]    Much of the large-spread-in-distance problem resides in the use of mechanical timers that employ verge escapements. 
         [0006]    A verge escapement typically includes a star wheel. The assembly is somewhat bulky and its use results in a safe-and-arm device that occupies an unacceptable amount of space. More importantly, the mechanical structure of such escapements is subject to the effects of friction. Accordingly, such mechanisms are inherently inaccurate. 
         [0007]    Electrical timers in rounds have been used to explode a warhead after the lapse of a predetermined time after firing so that the explosion occurs when the round arrives at the target. They have not been used to arm a safe and arm device after a prescribed time. 
         [0008]    There is a need, therefore, for an improved safe-and-arm device having a thin profile so that it occupies a minimal amount of space. More particularly, there is a need for such a device that does not require a verge escapement mechanism. 
         [0009]    There is also a need for a device having an electrical timer that arms a safe-and-arm device after a prescribed time. More particularly, there is a need for a device that substantially eliminates the distance between the “no arm” and the “all arm” states. 
         [0010]    However, in view of the art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in this art how the identified needs could be met. 
       SUMMARY OF INVENTION 
       [0011]    The long-standing but heretofore unfulfilled need for am improved safe and arm device is now met by a new, useful, and nonobvious invention. 
         [0012]    Missiles that carry warheads include safe and arm (S&amp;A) devices that prevent the warhead from exploding during the flight of the missile to a target. The flight time from launch to impact is the “no arm” time. At the end of the “no arm” time, the S&amp;A device reconfigures itself into an “all arm” configuration, thereby arming the warhead so that it can explode at the target site. It is thus understood that it is important to minimize the amount of time that passes between the respective “no arm” and “all arm” configurations. 
         [0013]    The novel device arms the warhead microseconds after it receives an electrical signal to arm after a flight time equivalent to the “no arm” distance. The “no arm” and “all arm” distances are therefore made substantially equal to one another. 
         [0014]    The electrical signal initiates an explosive actuator at the “no arm” distance. The explosion causes mechanical movement of an actuator piston. The moving piston bears against and releases a mechanical lock of the rotor that contains an explosive lead or detonator. The rotor is held in its safe position by said lock during flight. The rotor moves from the safe position to the armed position in microseconds due to centrifugal force and the absence of an escapement. 
         [0015]    An important object of the invention is to eliminate the spread between “no arm” and “all arm” distances of conventional safe and arm devices. 
         [0016]    These and other important objects, advantages, and features of the invention will become clear as this description proceeds. 
         [0017]    The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the description set forth hereinafter and the scope of the invention will be indicated in the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    For a fuller understanding of the invention, reference should be made to the following detailed description, taken in connection with the accompanying drawings, in which: 
           [0019]      FIG. 1  is a top plan view depicting the novel command-and-arm system with the cover of its housing removed and with the rotor in the safe position; 
           [0020]      FIG. 2  is a top plan view of the rotor, piston actuator, explosive lead, setback pin/spring system, and release cam pivot pin; 
           [0021]      FIG. 3  is a side elevational view of the novel assembly; 
           [0022]      FIG. 4  is a top plan view depicting the locking cam engaging the locking post after the rotor has rotated a very small amount in a clockwise direction; 
           [0023]      FIG. 5  is a top plan view depicting the locking cam engaging the locking post after the rotor has rotated a very small amount in a counterclockwise direction; 
           [0024]      FIG. 6  is a top plan view depicting the actuator piston in its extended position, said configuration being caused by firing the piston actuator in response to an electrical signal delivered by a timer at the instant the round achieves the no arm distance; 
           [0025]      FIG. 7  is a top plan view depicting partial rotation of the rotor toward the armed position; 
           [0026]      FIG. 8  is a top plan view depicting the rotor in the fully rotated, fully armed position; 
           [0027]      FIG. 9  is an isometric view of the assembled device with the rotor in the safe position; and 
           [0028]      FIG. 10  is a transverse sectional view of the assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0029]    The command to arm/safe and arm device assembly ensures that a warhead can not explode until after a round has reached the specified no arm distance for the round. 
         [0030]    Referring now to  FIGS. 1 and 2 , it will there be seen that an illustrative embodiment of the novel command to arm system is denoted as a whole by the reference numeral  10 . Command to arm housing  10  has a hollow interior defined by cover  11 , depicted in  FIG. 3 , bottom wall  13 , and substantially circular sidewall  15 . Flat  15   a  and opening  15   b  are formed in said sidewall  15 . Center point  17  is the longitudinal axis of symmetry of housing  10 . It is indicated by vertical line  17   a  and horizontal line  17   b  that pass through said longitudinal axis of symmetry. 
         [0031]    Rotor  12  is depicted in  FIG. 1  in the safe position as manufactured. It is held by two different locks as required by governmental safety regulations. These locks unlock the rotor upon gun launch. 
         [0032]    First lock  14  is a centrifugal lock spring that releases rotor  12  when the revolutions per second (rps) of a round has reached three hundred revolutions per second (300 rps). The round achieves six hundred revolutions per second (600 rps) at muzzle exit at which time there are ample revolutions per second to release spring  14  which requires only 300 rps to unlock the rotor. Spring  14  does not release before muzzle exit because the setback forces are sufficiently high prior to round exit to deflect spring  14  aft and the friction from this aft force prevents said spring from unlocking rotor  12  until gun exit when the setback force is no longer present. 
         [0033]    Second lock  16  is a conventional Objective Crew Served Weapon (OCSW) standard setback/spring system positioned in a standard location that unlocks rotor  12  when it is subjected to thirty thousand times the force of gravity (30,000 Gs) in the gun barrel. Setback system  16  includes setback pin  16   a , setback spring  16   b  and spacer ring  16   c . An OSCW receives a setback acceleration of at least sixty thousand times the force of gravity (60,000 Gs) in the gun barrel. Setback pin/spring system  16 , like first lock  14 , is released when the gun is fired. 
         [0034]    Explosive piston actuator  18  is unique in its small diameter and small weight of explosive. It has a positive electrode  18   a  that is adapted to contact an electrical contact attached to the housing. It has no “O” rings. 
         [0035]    Piston actuator  18  is mounted close to longitudinal axis of symmetry  17  of the round because at six hundred fifty revolutions per second (650 rps) the centrifugal acceleration is so high that the forces acting on piston actuator  18  make it impossible to operate if it is not near said longitudinal axis of symmetry  17 , it being understood that said axis is the axis of rotation of the round. The size of the charge must be increased if piston actuator  18  is mounted too far from said longitudinal axis  17 , and such charge could damage said piston actuator. 
         [0036]    Accordingly, the center of gravity of rotor  12  is positioned at its optimal location, denoted  20  in this embodiment. Said center of gravity is southwest of longitudinal or rotational axis  17 . Rotor  12  pivots about rotor pivot pin  21  which is positioned southeast of center of gravity  20  and due south of axis  17 . The mass of rotor  12 , when optimally positioned as illustrated, therefore generates a small but adequate counterclockwise torque that drives rotor  12  from the safe,  FIG. 1  position, to the armed,  FIG. 8  position when the locking cam, hereinafter disclosed, unlocks said rotor. 
         [0037]    A five foot (5 ft) drop spring  22  restrains the above-mentioned locking cam  24  in a locked position after a five foot drop and vibration. The amount of restraint thereby provided may be overcome by piston actuator  18 . 
         [0038]    Locking cam  24  is pivotally mounted about locking cam pivot pin  26  but locking post  28  limits to a small amount the rotation of locking cam  24  that is possible prior to actuation of piston actuator  18 . The abutting engagement between locking cam  24  and locking post  28  has sufficient play to allow a small amount of clockwise or counterclockwise rotation of rotor  12  when piston actuator  18  is not actuated as more fully disclosed below. 
         [0039]    The novel structure is depicted in side view of  FIG. 3 . It has a thickness equal to about sixty percent (60%) of the thickness of a conventional runaway. More particularly, the thickness is about 0.190 inch. This reduction in thickness is a result of several factors, including but not limited to elimination of a mechanical star wheel and verge escapement structure of the type commonly found in prior art safe-and-arm devices, positioning piston actuator  18  closer to longitudinal axis  17  so that it can be smaller and operate with a smaller charge as mentioned above, the provision of low profile locking cam  24 , and so on. 
         [0040]      FIG. 4  depicts a first locked position. The clockwise rotation of rotor  12  about rotor pivot point  21  from the safe configuration of  FIG. 1  to the locked configuration of  FIG. 4  is a small rotation, limited by locking post  28 . Said locking post is formed integrally with and depends from cover  11  as best understood in connection with  FIG. 3 . This rotation is caused by a round spinning in a clockwise direction. Rotor center of gravity  20  is still northwest of rotor pivot point  21  in  FIG. 4 , but the small clockwise rotation brings said center of gravity  20  closer to vertical centerline  17   a.    
         [0041]      FIG. 5  depicts a second locked position. The small counterclockwise rotation of the rotor from the safe configuration of  FIG. 1  to the locked configuration of  FIG. 5  is a small rotation, limited by locking post  28 . This rotation is caused by a round spinning in a counterclockwise direction. Rotor center of gravity  20  is still northwest of rotor pivot point  21  in  FIG. 5 , but the small counterclockwise rotation moves said center of gravity  20  further from vertical centerline  17   a.    
         [0042]    Piston  18   b  has a retracted position, as depicted in  FIGS. 1-5 , and an extended position, as depicted in  FIGS. 6-8 . Electrical initiation of piston actuator  18  in response to a signal from a timer causes piston  18   b  to extend to the left as drawn in  FIG. 1 , i.e., to travel from its retracted position to its extended position. Such displacement of piston  18   b  rotates locking cam  24  in a counterclockwise direction, indicated by directional arrow  25  in  FIG. 6 , thereby unlocking rotor  12  as depicted in  FIGS. 6-8 . The timer measures the time from the moment of firing to the moment the round reaches a predetermined no arm distance. 
         [0043]    Explosive lead  30  ignites the warhead when the electric detonator in the fuze, not depicted, ignites said explosive lead when rotor  12  is in the  FIG. 8 , armed position. 
         [0044]    Partial rotation of rotor  12  as a result of the unlocking by cam lock  24  is depicted in  FIG. 7 . Note the rotation of rotor  12  about rotor pivot point  21  from the  FIG. 6  position to the  FIG. 7  position and note further how center of gravity  20  of rotor  12  rotates counterclockwise about rotor pivot pin  21 . 
         [0045]      FIG. 8  depicts rotor  12  in its fully rotated, fully armed position with explosive lead  28  centered on longitudinal axis  17  of command-and-arm device  10 . Note the further rotation of rotor  12  about rotor pivot point  21  from the  FIG. 7  position to the  FIG. 8  position. Flat  15   a , formed in a radially inwardly facing side of sidewall  15 , blocks further rotation of rotor  12 . Opening  15   b , formed in said sidewall  15 , accommodates locking cam  24  by providing clearance space when rotor  12  is in said fully rotated, fully armed position. Significantly, the centrifugal forces generated by spinning of the round also operate to urge rotor  12  against flat  15   a.    
         [0046]      FIG. 9  is an isometric view of the novel assembly with rotor  12  in its safe position. 
         [0047]      FIG. 10  is a transverse sectional view of housing  10 . 
         [0048]    It will be seen that the advantages set forth above, and those made apparent from the foregoing description, are efficiently attained and since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matters contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 
         [0049]    It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween. Now that the invention has been described,