Abstract:
A system and method for improving the process of mechanical translation of projectiles by a spring mechanism that is built of a smart material and that is activated by an electric pulse, to provide a controlled translation of a projectile before firing or, in case of pre-firing termination, in order to restore the projectile to its original position after translation. The pre-firing translation using the spring mechanism provides a more controlled process and reduces the risk associated with the conventional propulsion charge translation design. The ability to return the projectile to its initial state after translation affords a significant advantage over the conventional propulsion charge design since it enables the projectile firing to be terminated even after translation, unlike in the conventional design whereby the projectile firing is irreversible upon a mechanical translation by setting off the propulsion charge.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 USC 119e of U.S. provisional patent application serial No. 60/319572 filed on Sep. 24, 2002, and Ser. No. 60/319,692 filed Nov. 13, 2002 which application is expressly incorporated by reference. 
    
    
     FEDERAL RESEARCH STATEMENT 
     The invention described herein may be manufactured and used by or for the Government of the United States for governmental purposes without the payment of any royalties thereon. 
    
    
     BACKGROUND OF INVENTION 
     Ammunition is an essential part of the arsenals of the Armed Forces. A vast array of different types of ammunition are currently in use in the Armed Forces. Conventional ammunition refers to ammunition whereby the projectile is held by and partly extends from the cartridge case. Another type of ammunition is termed Cased Telescoped Ammunition (CTA). 
     In general, CTA is comprised of individual rounds containing a projectile, fitted inside a cartridge case with seals at both ends, held by an internal steel or composite sleeve. The sleeve itself is internal to the CTA cartridge case and is attached to the front seal by threads. Furthermore, it is designed to prevent the projectile from unwanted movement and also to maintain a necessary alignment with the gun tube once the CTA is fully chambered in the gun. 
     CTA is being developed by the US Army for use in rapid auto-loader small, medium and large caliber systems up 120 mm range. Presently, a 105-mm CTA is being developed for use in the 105-mm Multi-Role Armament Ammunition System (MRAAS). The term CTA therefore comes from the projectile being telescoped back into the cartridge case. Thus, the CTA ammunition resembles a cylindrical article that houses the projectile, sleeve, and energetics (propellant and primer) internally, hence hidden from view. In contrast, a conventional ammunition is discernible by the aft seal, cartridge case and most of the projectile. Similar to CTA, the energetics are stored inside the cartridge case. 
     A unique benefit can be provided to both conventional and CTA ammunition by translating the projectile in the gun just before the main propellant charge goes off. Translation means that the projectile is moved or moving just before the main propellant charge provides the energy to fire the projectile from the gun. In brief, the translation process is a mechanism whereby the projectile is displaced a small distance forward in the gun before the main propulsion charge ignites. 
     The translation affords the projectile a number of advantages. One such advantage is that the projectile is set in motion momentarily before the main propulsion charge ignites, thus reducing the recoiling action of the gun and the setback force on the projectile. Consequently, the impulsive stress on the projectile significantly decreases, thereby improving the performance margin by allowing less robust projectiles to survive gun launch. As a result, the projectile can be made lighter using less robust designs. A lighter projectile will have a higher velocity, and for Kinetic Energy (KE) rounds it will enhance its ability to defeat the target. 
     Moreover, for ammunition with very high propellant density pack and/or large projectile volume to propellant volume space, high differential pressure waves can occur during propellant ignition. These high differential pressure waves can increase the pressure to dangerous levels that may damage the projectile or the gun. Translation may correct this problem by moving the projectile and correcting the density and volume problem. By translating the projectile, the ullage volume increases, thereby reducing the amplitude of the pressure wave. 
     Typically, the conventional translation process can be accomplished by an energetic means utilizing a secondary propulsion charge or propellant pre-charge as part of the propulsion system. The secondary propulsion charge is set off, generating a sufficient gas pressure to propel the projectile forward. After a short timing delay following the ignition of the secondary propulsion charge, the main propulsion charge is then ignited, resulting in an ensuing ballistic event of the projectile as it continues to travel along the gun tube and out of the gun to target. 
     While the conventional propulsion translation design provides the translation objective, such a design involving a dual propulsion charge system is usually difficult to achieve and furthermore presents some risks in maintaining the correct timing. If the timing is too long, then the projectile will travel too far down the tube. Consequently, the propellant gases from the main charge will not impart enough velocity on the projectile to defeat its target. Conversely, if the timing is too short, then the secondary and main charge may go off nearly at the same time, thereby creating a large pressure wave that may damage the projectile or gun. 
     Another disadvantage with the conventional design using the energetic translation method is that the process is irreversible. Once the secondary propulsion charge is ignited, a ballistic event is eventual and committal. In some cases when a pre-firing termination is commanded, this energetic translation method is not an enabling technology. 
     Thus, there remains an unsatisfied need for an improved design of a translation process or mechanism for use in conventional and CTA ammunition. Preferably, the enhanced translation design should be easy to achieve in field operation and does not present a risk due to the timing factor. Moreover, the enhanced translation design should be reversible to allow the projectile to return to its initial state after translation in an event of a pre-firing termination. 
     SUMMARY OF INVENTION 
     It is a feature of the present invention to provide an improved design method for achieving a translation process for the projectiles of small, medium and large caliber ammunition including both conventional and CTA. The improved method of translation embodied in the present invention utilizes a spring mechanism built of smart material as part of a mechanism to translate the projectiles. 
     These smart materials are materials that may be trained to change shape at certain temperatures or when electricity is passed through. They are known as shape memory alloys. Exemplary materials are Nitinol (Nickel-Titanium) and CAN (Copper-Aluminum-Nickel). They can be trained to change to a particular shape at a set temperature or applied current and change back to the original shape. The shape change takes place almost instantaneously and with substantial force to accomplish the work needed to translate a projectile or work a mechanism to translate the projectile. In addition, since they can return to the original shape as needed, the projectiles may be moved back to their pre-translated position if needed. Shape memory alloys have been known to be able change shape thousands of times without loss of properties and ability to do work. 
     The present invention provides numerous other features, among which are the following: 
     1. A shape-memory alloy, such as Nitinol, is used for the spring mechanism. The shape-memory alloy retains the information of the spring undeflected state even after undergoing a deflection. 
     2. For translation of a CTA projectile, the spring mechanism is attached between the steel sleeve on the cartridge housing and the CTA projectile. 
     3. For translation of a conventional projectile, the spring mechanism is attached between the rear of the projectile and the aft seal at the rear of the cartridge. This same mechanism is also applicable to a CTA projectile. 
     4.The spring is initially compressed. Upon electrically activating the shape-memory spring mechanism, the spring expands to translate the projectile forward for both the conventional and CTA projectiles. 
     5. In an event that a pre-firing termination is ordered, an electric charge activates the shape-memory spring mechanism to return it to the initial compressed state, thus restoring the position of the CTA projectile to its non-translated state. 
     6. Upon firing, the high pressure causes the spring mechanism to separate from the projectile and sleeve or aft seal (case base and seal), and travel up the gun tube and be expelled without interference to the projectile. 
     The improved method of translation of the present invention affords significant advantages over the conventional design in that the translation mechanism is simple and does not require a propulsion charge, which eliminates the potential risks due to incorrect timing. More importantly, the shape-memory material utilized in the improved translation method of the present invention permits a projectile firing to be terminated before a ballistic event. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The features of the present invention and the manner of attaining them, will become apparent, and the invention itself will be understood by reference to the following description and the accompanying drawings, wherein: 
     FIG. 1 is a cutaway view of a CTA cartridge comprising of a CTA projectile and a smart material translation spring mechanism, made according to a preferred embodiment of the present invention, shown prior to a translation of the CTA projectile 
     FIG. 2 is a cutaway view showing the CTA cartridge of FIG. 1 loaded into the gun; 
     FIG. 3 is a cutaway view of the translation spring mechanism of FIG.  1  and shows how the spring is attached to the projectile, aft sleeve and low voltage activation wire; 
     FIG. 4 is a cutaway view of the projectile, with the translation spring mechanism, loaded into the front seal/sleeve assembly without the rear part of the sleeve, a low voltage activation wire attached to the spring and subsequently to the aft seal for controlling the smart spring; 
     FIG. 5 is a cutaway view showing the activation wire and containing the components of FIG. 4 with the aft sleeve attached to the front sleeve by threads; 
     FIG. 6 is a cutaway view of the cartridge case attached to the components of FIG.  5 . 
     FIG. 7 is comprised of FIGS. 7A and 7B, and represents a partly exploded cutaway view of the components of FIG. 6 with the propellant added and the rear seal assembled with the primer and propellant bag charge to form the cartridge of FIG. 1 containing the translation spring assembly by snapping these assemblies together with the activation wire attached to the aft seal; 
     FIG. 8 is a cutaway view of the translation spring mechanism activated. This may be compared with FIG. 3 showing the translation spring before activation; 
     FIG. 9 is a cutaway view of the CTA cartridge loaded in the gun showing the translation of the projectile into the gun tube upon activation of the translation spring mechanism; 
     FIG. 10 is a cutaway view of the CTA cartridge with the translation spring mechanism in an alternate location, wherein the spring is attached to the rear of the projectile and the aft seal; 
     FIG. 11 is a cutaway view of the CTA cartridge of FIG. 10 with the spring mechanism activated and the projectile translated into the gun tube; 
     FIG. 12 is a cutaway view of a conventional ammunition cartridge, loaded into the gun, with the spring translation mechanism attached to the rear of the projectile and the case base; 
     FIG. 13 is a cutaway view of a conventional ammunition cartridge with the spring translation mechanism activated and the projectile translated into the gun tube; 
     FIG. 14 illustrates the launch of the CTA projectile in the gun, upon an ignition of the propulsion charge following the translation by the spring mechanism as shown in FIG. 9; 
     FIG. 15 illustrates the launch of the conventional projectile in the gun, upon an ignition of the propulsion charge following the translation by the spring mechanism as was shown in FIG. 13; and 
     FIG. 16 illustrates how conventional translation of the projectile is done using a propellant pre-charge that is ignited before the main propellant charge. 
    
    
     Similar numerals in the drawings refer to similar elements. It should be understood that the sizes of the different components in the figures might not be in exact proportion, and are shown for visual clarity and for the purpose of explanation. 
     DETAILED DESCRIPTION 
     With reference to FIG. 1, a Cased Telescoped Ammunition (CTA) cartridge  10  made according to a preferred embodiment of the present invention is generally comprised of an aft seal  11 , primer  12 , cartridge case  13 , front seal  14 , front sleeve  15 , aft sleeve  16 , projectile  17 , obturator  18 , translation spring mechanism  19 , propellant  20 , propellant bag charge  21 , low voltage control wire  22  and control wire link  23 . Each of these major components is further described as follows: The projectile  17  is constructed of metal or composite material of various shapes (usually cylindrical) that is either a solid or a tactical projectile containing explosives or other lethal cargo. The translation spring mechanism  19  is constructed of a smart material, such as nitinol, and is attached to the projectile  17 , metal or composite aft sleeve  16 , and the control wire  22 . 
     The metal or composite aft sleeve  16  is threaded into the metal or composite front sleeve  15 , which in turn is threaded into the metal front seal  14 . The projectile  17  is held in the front sleeve  15  by the plastic obturator  18 . The composite or combustible cartridge case  13  snaps into the metal front seal  14  and aft seal  11 . 
     The Propellant  20 , propellant bag charge  21  control wire  22 , projectile  17 , translation spring mechanism  19 , obturator  18 , front and aft sleeve  16  and  15  are all internal to the cartridge case  13 , front and aft seal  14  and  11 , respectively. 
     A primer  12  is threaded into the aft seal  11 . The metal control wire link  23  is threaded into the aft seal  11  and is attached to the control wire  22  before the aft seal is snapped onto the case  13 . The assembly of the CTA is detailed in the FIGS. 4-7 that follow. 
     FIG. 2 shows the CTA cartridge  10  loaded into the gun tube  101  with a closed breech  102 . 
     FIG. 3 shows how the spring  19  is attached to the projectile  17  by means of a groove  24  in the projectile  17 . The spring  19  is attached to the rear sleeve  16  and the low voltage control wire  22  by an epoxy layer  25 . 
     FIG. 4 illustrates the first step in the assembly of the CTA cartridge  10  with the translation spring mechanism  19 . The front sleeve  15  is threaded into the front seal  14 . The translation spring mechanism  19  and obturator  18  are then attached to projectile  17 . The obturator  18  is pressed on until it goes into a seat (not shown) on the projectile  17 . Thereafter, the spring  19  is slipped onto the projectile until the front of the spring  19  is in the groove  24  in the projectile  17 . The projectile  17  is then pressed into the forward sleeve  15  until the obturator  18  snaps into a groove in the sleeve (not shown). The assembly is now complete and the low voltage control wire  22  is attached with the epoxy  25  to rear of the spring  19 . 
     FIG. 5 illustrates the second step in the assembly of the CTA cartridge  10  with the spring translation mechanism  19 . The aft sleeve  16  has the epoxy  25  applied to a position where the rear part of the spring  19  would be in contact. The aft sleeve  16  is then threaded onto the front sleeve  15 . This would allow the back of the spring  19  to be anchored to the aft sleeve  16  and attached to the control wire  22 FIG. 6 illustrates the third step in the assembly of the CTA cartridge  10 . The cartridge case  13  is pressed onto and snaps onto the front seal  14 . The two surfaces have matching grooves that allow them to snap together. The projectile  17 , aft sleeve  16 , front sleeve  15  and wire  22  are now all internal to the cartridge case  13  and front seal  14 . 
     FIG. 7 shows the final step in the assembly of the CTA cartridge  10 . Propellant  20  is added to the cartridge case  13 . The propellant bag charge  21  is glued or attached to the aft seal  11 . The primer  12  is threaded into the aft seal  11 . The wire  22  is pulled through a hole in the aft seal  11  and attached to the control wire link  23 . The control wire link  23  is then threaded into the aft seal  11 . The aft seal  11  is now pressed onto the cartridge case  13  and snaps together as a complete CTA cartridge  10  as shown in FIG.  1 . 
     FIG. 8 shows the spring  19  activated and expanded which moves the projectile  17  forward. 
     FIG. 9 shows the CTA cartridge  10  in the gun with the translation spring mechanism  19  activated and the projectile  17  translated into the gun tube  101 . This may be compared with FIG. 2 that shows the spring  19  not activated and projectile  17  not translated. 
     The translation spring mechanism  19  is activated by low voltage electricity that comes through the control wire link  23  in the aft seal  11  and then through the wire  22  to the spring  19 . The voltage activates the spring  19  to expand and move the projectile  17  forward causing projectile translation into the gun tube. If a second voltage is sent, the spring  19 , which is secured to the aft sleeve  16  and the projectile  17 , will compress and pull the projectile back to its pre-translated state shown in FIG.  2 . 
     FIG. 10 shows an alternate translation spring mechanism  19  location for the CTA cartridge  100 . The spring  19  is placed between the aft seal  11  and the projectile  17 . The spring  19  is attached by the epoxy  25  to the rear of the projectile  17  and to the control link  23  in the aft seal  11 . The loading of this CTA cartridge  100  is the same as that of the CTA cartridge  10 , except the spring  19  is not placed in the sleeve  26  but is attached to the projectile  17  by the epoxy  25 . 
     The sleeve  26  is made of an integral, single-unit construction without the control wire  22 . After loading the propellant  20 , the epoxy layer  25  is applied on the back and front of the spring  19  that contacts the aft seal  11  and projectile  17 . Thereafter, the aft seal  11  is snapped onto the case. The spring  19  is now attached by the epoxy  25  to the aft seal  11  and projectile  17 . The epoxy  25  is applied on the inside of the control wire link  23  thread in the aft seal  11  and contacts the spring  19 . The control wire link  23  is threaded into the aft seal  11  and is now affixed by the epoxy  25  to the rear of the spring 19 . 
     FIG. 11 shows the spring  19  in the alternate location activated to translate the projectile  17  into the gun tube  101 . The propellant  20  may or may not be placed inside the spring  19  but is not shown here for clarity sake. The spring  19  is activated as before by low voltage electricity passing from the control wire link  23  to the spring  19 . If a second voltage is sent, the spring  19 , which is secured by the epoxy  25  to the aft seal  11  and the projectile  17 , will compress and pull the projectile back to the pre-translated state, as shown in FIG.  10 . 
     FIG. 12 illustrates the use of the translation spring mechanism  19  on conventional ammunition, which is loaded into a gun  101  with a closed breech  102 . The translation spring mechanism  19  is attached to the rear of the projectile by the epoxy  25  and the case base and seal  27  also by the epoxy layer  25 . 
     The conventional ammunition with the translation spring mechanism  19  of the present invention can be built as follows: The obturator  18  is snapped onto the projectile  17 . A case adapter  29  is snapped onto the obturator  18 . The propellant  20  is attached to the projectile  17  by tape to the outer row of propellant sticks  20 . The spring  19  is attached by the epoxy  25  to the rear of the projectile  17 . The primer  12  is then threaded into the case base and seal  27 . 
     A cartridge case  28  is snapped into the case base and seal  27 . The epoxy  25  is applied to the rear of the spring  19 . The case  28  is slid over the propellant  20  and glued to the case adapter  29 . The control wire link  23  is then threaded into the case base and seal  27  and makes contact with the spring  19 . 
     FIG. 13 shows the spring  19  activated on conventional ammunition and the projectile  17  translated into the gun tube  101 . The spring  19  is activated as before by low voltage electricity passing from the control wire link  23  to the spring  19 . If a second voltage is sent, the spring  19 , which is secured to the case base and seal  27  and the projectile  17  by the epoxy  25 , will compress and pull the projectile  17  back to the pre-translated state shown in FIG.  12 . 
     FIG. 14 illustrates the CTA projectile  17  traveling up the gun tube  101  after the translation by the spring  19  and the propellant  20  being ignited to form high pressure gases  30 . The propellant gases  30  propel the projectile  17  down and out of the gun tube  101 . The spring  19  either remains attached to aft sleeve  16  or the aft seal  11  (depending on the spring  19  location) or is broken into pieces and exits out of the gun tube  101  after the projectile  17  exits the gun tube  101 . The plastic obturator  18  usually breaks up into pieces as the projectile  17  travels down-range. 
     FIG. 15 illustrates the conventional ammunition projectile  17  traveling up the gun tube  101  after the translation by the spring  19  and the propellant  20  being ignited and turned into high pressure propellant gases  30 . The propellant gases  30  propel the projectile  17  down and out of the gun tube  101 . The spring  19  either remains attached to case base and seal  27  or is broken into pieces and exits out of the gun tube  101  after the projectile  17  leaves the gun tube  101 . The obturator  18  breaks up into pieces as the projectile  17  travels down-range. 
     FIG.16 illustrates how a conventional translation works using a propellant pre-charge  31  for translation of the projectile  17  and the regular propellant  20  to continue the motion of the projectile  17  out of the gun tube  101  to its intended target. The propellant pre-charge  31  is placed behind the projectile  17  as shown in FIG.  16 . Upon ignition, only this pre-charge  31  burns and turns into high pressure gases  30  for translating the projectile  17 . 
     Should the pre-charge  31  gases  30  ignite the propellant  20  before the projectile  17  has translated, the pressure of propellant gas  20  may exceed the pressure limit of the gun tube  101 , thus posing as a safety issue. 
     As shown in FIG. 16, a CTA cartridge  10  was used for purposes of illustration. A conventional cartridge  100  would make no difference to the illustration since both have the pre-translation charge  31  behind the projectile  17  and the functioning of translation and safety issues are the same for the CTA  10  or conventional cartridge  100 . Once the propellant  20  is properly ignited, after the translation has taken place, FIGS. 14 and 15 illustrate the projectile  17  traveling down the gun tube for the CTA  10  and conventional ammunition  100 . 
     It should be understood that the geometry, compositions, and dimensions of the elements described or illustrated herein can be modified within the scope of the invention and are not intended to be the exclusive; rather, they can be modified within the scope of the invention. Other modifications can be made when implementing the invention for a particular environment.