Abstract:
A method for providing electrical energy to a self-destruct fuze for submunitions contained in a projectile is provided. The method including: using a firing acceleration of the projectile to deform at least one elastic element to store mechanical energy in the elastic element; converting the stored mechanical energy to electrical energy; and providing the electrical energy at least indirectly to the self destruct fuze for detonation of the self destruct fuze. Alternatively, the firing acceleration can lock the elastic element in the deformed position and an expulsion acceleration of the submunitions from the projectile can be used to unlock the elastic element and convert the stored mechanical energy to electrical energy.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit to earlier filed provisional application Ser. No. 61/131,430 filed on Jun. 9, 2008, the entire contents of which are incorporated herein by reference. 
     
    
     GOVERNMENT RIGHTS 
       [0002]    This invention was made with Government support under Agreement No. DAEE30-03-C-1077 awarded by the Department of Defense. The Government has certain rights in the invention. 
     
    
     FIELD 
       [0003]    The present invention relates generally to power source and safety mechanisms for munitions, particularly an electrically operated self-destruct fuze for submunitions and the like. 
       BACKGROUND 
       [0004]    Heavy guns such as artillery are sometimes used against foot soldiers, particularly where the target is out of range of machine gun bullets, or where there is no line of sight to the target. However, foot soldiers may be spread out over a large area and the damage caused by a conventional shell is too localized to be effective in such scenarios. One known approach for destroying foot soldiers under these conditions is to use a “cargo projectile” loaded with submunition grenades. The cargo projectile is a shell that is designed to be fired from large caliber cannons such as artilleries or tanks over the position of enemy foot soldiers. A plurality of submunition grenades are released and dispersed from the cargo projectile over a large area of ground. Such submunition grenades may be designed to explode in the air or may be designed to explode on impact. 
         [0005]    The use of improved conventional munitions (ICMs) which can deliver a very large number of submunitions by means of an artillery or rocket carrier on a target area has increased the problem of hazardous duds that remain on the battlefield. The danger to follow-up friendly personnel has increased in recent time because of the large quantities of ICM carriers that have been deployed in each mission. Because of the large quantity of submunitions now deployed during each mission, all prior inputs have proven to still leave a prohibitive number of hazardous duds on the battlefield. 
         [0006]    The basic requirements for submunition grenades include (i) a high degree of safety during storage and handling, both prior, during and subsequent to their being packed into cargo projectiles, (ii) reliability during deployment, i.e. that they should explode appropriately after release from the cargo projectile, and not prematurely, prior to their dispersal, (iii) the number of dangerous dud grenades that do not explode on impact should be minimized, and (iv) in certain cases, they should be prevented from explosion if they are dropped off the cargo projectile for any reason, before the projectile is fired. The minimization of dangerous duds is very important since if they are scattered over the battlefield, they would pose hazard to friendly troops and even to civilians or wildlife long after the battle. It will be appreciated that these requirements are to some extent contradictory, and the development of safe but highly explosive ordnance is not trivial. 
         [0007]    Each submunition grenade includes a casing that disintegrates into lethal shrapnel when the submunition grenade explodes, a warhead for exploding the casing, and a fuze for detonating the warhead. To achieve the required safety levels in handling and storage, but reliability of the submunition grenade after releasing, the fuzes thereof are sophisticated devices that generally include chemical, mechanical and occasionally electrical subcomponents. 
         [0008]    Typically the fuze of an impact type of submunition grenade includes a chemical detonator and a firing pin that triggers the detonator on impact. To allow the grenades and the cargo projectiles that contain such grenades to be handled safely, various safety mechanisms have been devised. Typically, in addition to the armed position in which is the grenade&#39;s fuze aligned to trigger the detonator, the firing pin of the submunition grenade also has a safe position, and when the firing pin is in this safe position, the submunition grenade can be handled and even dropped without fear of it detonating. However, once the firing pin is moved to the armed position however, an impact or similar jolt will cause the pin to detonate the detonator, igniting the warhead and thereby causing the submunition grenade to explode. 
         [0009]    A known safety mechanism for submunition grenades is a slider assembly that keeps the detonator in a safe position away from the firing pin, preventing inadvertent detonation. After being detached from the cargo projectile, the centrifugal forces on the submunition grenade cause the slider assembly to slide into the armed position, aligning the detonator with the firing pin. Once aligned, a catch locks the slider in place such that upon appropriate impact, such as an impact with a hard surface, the firing pin is driven forward to strike the appropriately aligned detonator, detonating it, thereby igniting the warhead of the submunition grenade. 
         [0010]    Like all mechanical systems, such slider assemblies are not fail-safe. Occasionally, they do not retract, or do not retract fully. This can happen, for example, when the striker assembly is locked for some reason. 
         [0011]    One disadvantage of the prior art submunition fuzes described above, is that where the submunition grenade impacts with an inappropriate surface, such as a soft surface, or where the angle of impact is wrong, such that the firing pin is not induced to strike the detonator, the grenade is not detonated. Consequently, there is a risk of armed submunition grenades launched at the enemy but not detonated on impact being left scattered over the battlefield. Wherever a submunition grenade does not detonate it is considered as being a “dud”. Armed dud submunition grenades remain dangerous, and pose a risk to friendly troops and even to civilians long after the battle. 
         [0012]    Submunition grenade fuzes are known that have a locked safe position for the firing pin that is designed to prevent the firing pin from being moved to the armed position inadvertently. When the grenades are packed into a cargo projectile carrier, the firing pin of each grenade fuze is unlocked, but it remains in its safe position until the fuze is armed. This only happens after the submunition grenade is ejected from the cargo projectile. In a submunition grenade of this type, one end of the shaft of the firing pin protrudes outside the fuze housing, and to the protruding end a drag producing means is fitted. The cargo projectile warhead spins in flight due to rifling of the barrel of the gun from which it is launched. When the grenades are ejected from the cargo projectile, the drag producing means, typically a nylon ribbon is activated. 
         [0013]    This drag producing means acts in an inertial manner, countering the spin of the submunition grenade around its longitudinal axis, and displaces the firing pin assembly, causing it to assume a striking position. In his manner, the fuze is armed automatically, but only after ejection. On impact, the firing pin assembly is driven into the grenade with a force that causes the detonation of the fuze detonator and explosion of the warhead thereby. 
         [0014]    In certain scenarios, the submunitions may be accidentally ejected from the assembled round due to nearby explosions, fire or other similar events. Following such accidents, the submunitions is usually armed, posing a very serious safety problem. 
         [0015]    Thus, despite the many safety features included in submunition grenades (see for example U.S. Pat. No. 5,387,257 by M. Tari, et al., U.S. Pat. Nos. 6,142,080 and 6,145,439 by R. T. Ziemba, U.S. Pat. No. 6,244,184 by O. Tadmor, and U.S. Pat. No. 7,168,367 by A. Levy, et al.), there is still a risk of armed submunition grenades being dispersed over the battlefield but not detonated. 
         [0016]    A need therefore exists for power source and safety mechanisms for secondary electrically operated self-destruct fuzes for submunitions that function in the event a mechanical or other primary fuze mode fails to function. 
         [0017]    A need also exists for power sources that are not based on chemical batteries, including reserve batteries, that are cost effective and easy to mass produce and that provide for very long shelf life of sometimes over 20 years. 
         [0018]    Furthermore, a need exists for power sources that are simple in design and operation, thereby are easy to manufacture and perform quality control to ensure reliability and long shelf life. 
         [0019]    Furthermore, a need exists for power sources with essentially zero stored power, whether chemical or mechanical or electrical or in any other forms before the projectile firing while the submunitions and/or the cargo projectile packed with the submunitions are in storage. 
         [0020]    Furthermore, a need exists for power sources and safety mechanisms that differentiate accidental acceleration profiles from those that are encountered during projectile firing and can also be during submunitions expulsion from the cargo projectile. 
         [0021]    The present invention provides a method for the development of such power sources with integrated mechanisms to provide for the aforementioned safety requirements. In addition, a number of exemplary embodiments for such power sources with integrated safety mechanisms are disclosed. 
         [0022]    The present invention relates generally to power source and safety mechanisms for munitions. In particular, it relates to secondary electrically operated self-destruct fuze for submunitions that function in the event a mechanical or other primary fuze mode fails to function. 
         [0023]    An objective of the present invention is to significantly reduce the number of hazardous duds in the battlefield, thereby improving battlefield safety conditions for friendly troops passing through a former targeted area and for civilians after the battle. 
         [0024]    A further objective of the present invention is to improve the life/cost saving in explosive ordnance disposal procedures. 
         [0025]    A further objective of the present invention is to significantly reduce the cost of power sources in electrically operated fuzing in general and in self-destruct secondary fuzes in particular. 
         [0026]    A further objective of the present invention is to reduce the complexity of the design, manufacture and testing and quality control of power sources in electrically operated fuzing in general and in self-destruct secondary fuzes in particular, thereby providing power sources that are more reliable. 
         [0027]    A further objective of the present invention is to provide power sources that are less susceptible to environmental conditions such as corrosion, thereby could satisfy very long shelf life of sometimes over 20 years. 
         [0028]    A further objective of the present invention is to provide a power source for self-destruct fuzes that have essentially zero electrical and/or mechanical and/or chemical and/or other types of stored energy prior to the projectile launch and that energy, mechanical and/or electrical is generated at least partially due to the firing acceleration. 
         [0029]    A further objective of the present invention is to provide power sources with primary safety mechanisms that would allow them to initiate power generation essentially only if the projectile experiences an acceleration profile that is expected during the firing or a specified acceleration profile. 
         [0030]    It is yet another objective of the present invention to provide power sources with secondary safety mechanisms for use in self-destruct fuzes for submunitions that would essentially prevent power generation only if the projectile experiences an acceleration profile that is expected during the firing (or a specified acceleration profile) and then experiences an acceleration profile due to the detonation of the submunitions expulsion charges. 
         [0031]    Another objective of the present invention is to remove a source of (duds) booby trap application by an enemy. 
       SUMMARY 
       [0032]    Accordingly, a method is provided for the development of power sources for self-destruct fuzes for submunition with substantially zero power prior to projectile firing, or prior to projectile firing and post projectile firing until submunitions expulsion from the projectile. The aforementioned zero power characteristics is to ensure safe handling and storage during various stages of submunitions production and assembly into the cargo projectile as well as storage of the projectile. The indicated safety features can be integrated into the design of the power source. 
         [0033]    In addition, a number of embodiments for such power sources with integrated safety mechanisms are provided. 
     
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         [0034]    These and other features, aspects, and advantages of the apparatus and methods of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
           [0035]      FIG. 1  illustrates a typical volume available in submunitions for a power source and safety mechanisms. 
           [0036]      FIG. 2  illustrates a first embodiment of a power source with integrated safety mechanism for submunitions. 
           [0037]      FIG. 3  illustrates the power source of  FIG. 3  after experiencing an acceleration of a predetermined magnitude to activate the power source into a power generating configuration. 
           [0038]      FIG. 4  illustrates a second embodiment of a power source with integrated safety mechanism for submunitions. 
           [0039]      FIG. 5  illustrates the power source of  FIG. 4  after experiencing an acceleration of a first predetermined magnitude and/or direction to activate the power source into an intermediate position. 
           [0040]      FIG. 6  illustrates the power source of  FIG. 4  after experiencing an acceleration of a second predetermined magnitude and/or direction to activate the power source into a power generating configuration. 
       
    
    
     DETAILED DESCRIPTION 
       [0041]    In general, the amount of space available for power sources and for the aforementioned safety mechanisms in submunitions self-destruct fuze is very small, making the use of chemical reserve batteries very difficult and costly, and nearly impractical. The use of active chemical batteries is not possible in submunitions due to the up to 20 years of shelf life requirement and also due to safety concerns that an active battery would generate. A typical volume available for a power source and its safety mechanisms is shown in  FIG. 1  together with typical dimensions of this available space (see for example U.S. Pat. No. 5,387,257 by M. Tari, et al.). As can be observed, the available volume is very small and in many cases is a complex shape. 
         [0042]    A method and apparatus are provided for power sources that could be designed to fit inside the available volume of the geometrical shape shown in  FIG. 1  or other similarly complex shapes. In one embodiment, the power sources have substantially zero power prior to firing and begin to generate power after the projectile has been fired. In another embodiment, the power sources have substantially zero power prior to firing, post projectile firing until submunitions expulsion from the projectile has occurred. 
         [0043]    In this method, the firing acceleration is used to deform at least one elastic element, thereby causing mechanical energy be stored in the at least one elastic element. In one embodiment, the stored mechanical energy causes vibration of the elastic element coupled with certain inertial elements, which may be integral to the elastic element. The mechanical energy is then harvested from the vibration system and converted into electrical energy using piezoelectric materials based elements. The harvested electrical energy is then used directly by the self-destruct fuze electrical/electronic circuitry and/or stored in electrical energy storage devices such as capacitors for use in said electrical/electronic circuitry and for detonation of self-destruct fuze charges. In another embodiment, the aforementioned deformed at least one elastic element (and its accompanying inertial element) is locked in its deformed position by certain mechanical locking mechanism and released only by the expulsion acceleration caused by the detonation of charges onboard the projectile during the flight. Once the at least one elastic element and its accompanying inertial element are released, the mechanical energy stored in the said elastic elements is harvested as described above for the previous embodiment. 
         [0044]    As a result, the aforementioned power sources have zero power prior to firing (or prior to firing and prior to expulsion). These characteristics of the power sources ensure safe handling and storage during various stages of submunitions production and assembly into the cargo projectile as well as storage of the projectile and accidental expulsion of the assembled submunitions from the stored projectile. It is noted that the aforementioned safety features are integrated into the design of the power source, which may also be supplemented by other electrical/electronic safety features/logics, etc., to provide for additional safety. 
         [0045]    The schematic of the first embodiment  10  of the power source with integrated safety mechanism is shown in  FIG. 2 . The power source  10  is positioned within the available space  5 . The power source consists of an element mass  15 , to which is attached at least one (primary) spring  12 . In the schematic of  FIG. 2  a second spring element  14  is also shown to be attached to one side of the mass element  15 . The spring  14  is designed for primarily lateral deformation to allow the motion of the mass element  15  in the direction of the arrow  25 , which is the primary direction of deformation (axial deformation in the case of the helical spring  12  shown in the schematic of  FIG. 2 ) of the primary spring  12 . It is noted that the mass element  15  and the primary spring  12  (and the spring  14 , when present) may be integral. In addition, the spring  12  may be an elastic element of an appropriate shape to provide the required deformation to displacement (spring rate) in the direction of deformation as indicated by the arrow  25 . 
         [0046]    During the projectile firing, the direction of acceleration action on the power source is in the direction of the arrow  26 . During the expulsion, the firing charge onboard the projectile accelerates the submunitions out of the back of the projectile, with the direction of the acceleration acting on the power source being in the direction opposite to the direction of the arrow  26 . 
         [0047]    The mass element  15  is attached to the primary spring  12 . The opposite end of the primary spring  12  is then attached to at least one piezoelectric element  11  (which can be a stacked type of piezoelectric element). The piezoelectric element is in turn attached to the submunitions self-destruct fuze structure at the surface  17  (the self-destruct fuze structure not shown in  FIG. 2 ). 
         [0048]    The mass element  15  is provided with a sloped surface  24 , which is engaged with a matching surface  27  of the element  16 . The element  16  is positioned between the mass element  15  on one side (at its sloped surface  27 ) and the surface  21  of the submunitions self-destruct fuze structure, with which it is in contact with the surface indicated as  22 . The element  16  is constrained to motions that are essentially in the direction of the arrow  26  which is provided by either guide on the surface  21  of the submunitions self-destruct fuze structure (not shown for clarity), or by the use of elastic elements (flexures) that provides such guided motions, or other means that are well known in the art. The element  16  may also be provided by elastic elements (such as of the bending type), not shown in  FIG. 2 , that provides a bias force that keeps pushing the element  16  downward (in the opposite direction to the arrow  26 ), pushing the sloped surface  27  of the element  16  against the sloped surface  24  of the mass element  15 . 
         [0049]    While a projectile that houses the submunitions with the self-destruct fuze with the present power sources are being fired, the entire submunitions self-destruct fuze assembly is accelerated in the direction of the arrow  26  in the gun barrel. During this period, the firing acceleration will act on the mass of the element  16  and causes it to be pushed down (in a direction opposite that of the applied acceleration, i.e., in a direction opposite to the direction of the arrow  26 ). This force, if large enough, will overcome the force exerted by any biasing force provided by the aforementioned biasing (such as of the bending type) elastic elements and frictional forces, springs  12  and  14  (if any) and will begin to move downward, thereby causing the mass element  15  to move to the right, thereby deforming the spring  12  in compression. If other elastic elements such as the element  14  shown in  FIG. 2  are also present, they would also deform in their designed manner (in the case of the elastic element  14  in bending) and store additional potential energy. The aforementioned biasing forces (particularly those provided by the aforementioned elastic biasing element of the element  16  and the springs  12  and  14 ) can be designed to minimize the aforementioned motion of the element  16  as a result of accidental events such as dropping of the device or round or vibration and shock during transportation or the like. 
         [0050]    If the acceleration level is high and long enough, which it is when the projectile is fired by a gun, then the element  16  is pushed down past the mass  15  and is pushed to the bottom of the available submunitions self-destruct fuze structure space  5  into the position indicated as  28  in the schematic of  FIG. 3 . The mass element  15  and the spring  12  (and other elastic elements such as the element  14 —if present) assembly will then begin to vibrate. During each cycle of this mass-spring assembly vibration, the primary spring  12  applies a cycle of compressive and tensile forces on the piezoelectric element  11 . The force applied to the piezoelectric element would then generate a charge proportional to the applied force by the spring  12  (cyclic with the frequency of vibration of the aforementioned mass-spring assembly) in the piezoelectric element that is then harvested using a number of well known techniques and used directly in the self-destruct fuze circuitry or stored in a capacitor for later use. 
         [0051]    If the acceleration level is not high and/or long enough, such as may occur if the submunitions or its self-destruct fuze is accidentally dropped, or if the assembled projectile itself is dropped, or if the submunitions are accidentally or due to a nearby explosion expelled from the projectile, then the force acting downward on the element  16  is either not large enough or is not applied long enough to cause the element  16  to be pushed down past the mass  15  and free the mass  15  and primary spring  12  (and other elastic elements such as the element  14 —if present) assembly to begin to vibrate. This feature provides for safe operation of the submunitions self-destruct fuze, i.e., essentially zero power prior to firing of the projectile. It is noted that the (generally small amounts of) pressure exerted on the piezoelectric element  11  during the aforementioned events as the element  16  is pushed down slightly would still generate a small and short duration pulse of charges, which can be readily differentiated from the charges generated during the vibration of the mass-spring (elements  15  and  12 —and  14  if present) assembly. A number of such methods of differentiating short duration (pulse) charges from vibratory charges and or differentiating the maximum (peak) voltage levels reached as the element  16  passes the mass  15  during projectile firing, or by measuring the total amount of electrical energy harvested (e.g., by measuring the voltage of a capacitor that is charged by the harvested electrical energy and providing a small amount of leakage to prevent the charges to be accumulated over a relatively long period of time), or the like are available and well known in the art. 
         [0052]    It is also noted that once the element  16  has been pushed down to the position  28 ,  FIG. 3 , the biasing force provided by the aforementioned biasing (such as of the bending type) elastic elements (indicated as the element  29  in  FIG. 3 ), will hold it down in its position  28 , thereby prevent it from interfering with the vibration of the mass  15  and spring  12  (and spring  14 —if present) assembly. In  FIG. 3 , the biasing elastic element  29  is shown to be of a bending type, which is attached to the element  16  on one end and to the submunitions self-destruct fuze structure at the point  30 . Other types of elastic elements may also be used instead of the bending type  29  shown in  FIG. 3 . The biasing element  29  may also behave elastically while the element  16  is engaged with the mass element  15  and once it has moved down past the mass element  15 , it enters its plastically deforming range and thereby is forced to stay substantially in its position  28 . The biasing elastic element  29  may be integral to the element  16 . 
         [0053]    In another embodiment, a “latching” element (not shown in  FIG. 3 ) is provided on the structure of the submunitions self-destruct fuze to which the biasing elastic (with or without plastically deforming characteristic) is locked once it nears its position  28 , and is thereby prevented from returning to its original position shown in  FIG. 2  or interfering with the vibration of the mass element  16 . It is noted that locking latching elements are very well known in the art and is used extensively to lock various components together, particularly components made with relatively elastic materials such as plastics. 
         [0054]    It is also noted that the piezoelectric element  11  can be preloaded in compression. This is a well known method of using piezoelectric elements since piezoelectric ceramics are highly brittle and can only withstand low levels of tensile forces. Preloading of the piezoelectric element  11  can be made, for example, by either the spring  14  or by adding a separate spring that is fixed to the submunitions self-destruct fuze structure and presses on the piezoelectric element  11  at its free end (not shown), where it is attached to the primary spring  12 . Any other method commonly used in the art may also be used to preload the piezoelectric element in compression. The amount of preload can be to a level that prevents the piezoelectric element to be subjected to tensile loading beyond its tensile strength, for example not more than around  10  percent of its compressive strength. 
         [0055]    The schematic of another embodiment  40  of the power source with integrated safety mechanism is shown in  FIG. 4 . The embodiment  40  has all the components described for the embodiment  10  shown in  FIGS. 2 and 3 , with the following additional features. 
         [0056]    The power source  40  has an additional member  44 , which can be in the form of a beam that is fixed to the submunitions self-destruct fuze structure at the point  45  via a hinge joint  46 , which can be a living joint, that allows the member  44  to rotate upwards and downwards in the direction of the arrow  26 . The free end of the member  44  is provided with a downward bended portion  47 . The mass element  41  in turn is provided with a step  48  that could engage the bended portion  47  of the member  44  if the mass element  41  and the member  44  are both appropriately positioned. Similar to the embodiment  10  shown in  FIGS. 2 and 3 , the mass element  41  is also provided with a sloped surface  42 , which is engaged with a matching surface  27  of the element  16 . 
         [0057]    While a projectile that houses the submunitions with the self-destruct fuze with the present power sources are being fired, the entire submunitions self-destruct fuze assembly is accelerated in the direction of the arrow  26  in the gun barrel. 
         [0058]    During the projectile firing, the direction of acceleration action on the power source is in the direction of the arrow  26 . During the expulsion, the firing charge onboard the projectile accelerates the submunitions out of the back of the projectile, with the direction of the acceleration acting on the power source being in the direction opposite to the direction of the arrow  26 . During the firing, the firing acceleration will act on the mass of the element  16  and causes it to be pushed down (in a direction opposite that of the applied acceleration, i.e., in a direction opposite to the direction of the arrow  26 ). The force resulting from the firing acceleration and acting on the element  16  will then overcome the force exerted by any biasing force provided by the aforementioned biasing (such as of the bending type) elastic elements  29  (shown in  FIG. 5  but not shown in  FIG. 4  for clarity), frictional forces, and spring  12  (and spring  14 —if present) and will begin to move the element  16  downward, thereby causing the mass element  41  to move to the right, thereby deforming the spring  12  in compression. If other elastic elements such as the element  14  shown in  FIG. 2  are also present, they would also deform in their designed manner (in the case of the elastic element  14  in bending) and store additional potential energy. If the acceleration level is high and long enough, which it is when the projectile is fired by a gun, then the element  16  is pushed down past the mass element  41  and is moved to the bottom of the available submunitions self-destruct fuze structure space  5  into the position indicated as  28  in the schematic of  FIG. 5 . The element  16  is then held in its position  28  by the element  29  as was described for the embodiment of  FIGS. 2 and 3 . In the meantime, as the mass element  41  is pushed back enough by the element  16  during its downward motion, the downward bended portion  47  of the element  44  engages the step  48  of the mass element  41 , and as the element  16  passes the mass element  41  towards its position  28 , the mass element  41  is prevented from rebounding to its original position ( FIG. 4 ) by the force of the compressed spring  12  (and spring  14 —if provided). 
         [0059]    If the acceleration level is not high and/or long enough, such as may occur if the submunitions or its self-destruct fuze is accidentally dropped, or if the assembled projectile itself is dropped, or if the submunitions are accidentally or due to a nearby explosion expelled from the projectile, then the force acting downward on the element  16  is either not large enough or is not applied long enough to cause the element  16  to be pushed down past the mass  41 . This feature provides for safe operation of the submunitions self-destruct fuze, i.e., essentially zero power prior to firing of the projectile. It is noted that the (generally small amounts of) pressure exerted on the piezoelectric element  11  during the aforementioned events as the element  16  is pushed down slightly would still generate a small and short duration pulse of charges. These events are, however, readily differentiated from the charges generated during the vibration of the mass-spring (elements  41  and  12 —and  14  if present) assembly. A number of such methods of differentiating short duration (pulse) charges from vibratory charges and or differentiating the maximum (peak) voltage levels reached as the element  16  passes the mass element  41  during projectile firing, or by measuring the total amount of electrical energy harvested (e.g., by measuring the voltage of a capacitor that is charged by the harvested electrical energy and providing a small amount of leakage to prevent the charges to be accumulated over a relatively long period of time), or the like are available and well known in the art may be employed for this purpose. 
         [0060]    At some point during the projectile flight, submunitions expulsion charges are detonated, and the submunitions are accelerated out of the back of the projectile in the direction shown by the arrow  49  as shown in  FIG. 6 , which is in a direction opposite to the projectile firing acceleration as indicated by the arrow  26  in  FIG. 4 . The expulsion acceleration of the submunitions in the direction of the arrow  49  will then act on the mass (inertia) of the member  44 , causing it rotate upwards, thereby releasing the mass element  41 . The mass element  41  and the spring  12  (and other elastic elements such as the element  14 —if present) assembly will then begin to vibrate. During each cycle of this mass-spring assembly, the primary spring  12  applies a cycle of compressive and tensile forces on the piezoelectric element  11 . The force applied to the piezoelectric element would then generate a charge proportional to the applied force by the spring  12  (cyclic with the frequency of vibration of the aforementioned mass-spring assembly) in the piezoelectric element that is then harvested using a number of well known techniques and used directly in the self-destruct fuze circuitry or stored in a capacitor for later use. 
         [0061]    The positioning of the member  44  can be biased downward, which can be by the living joint  46  and its own beam-like member, such that while its downward bent portion  47  is engaged with the step  48  of the mass element  41 , incidental accelerations in the direction of the arrow  49 ,  FIG. 6 , or incidental decelerations in the direction of the arrow  26 ,  FIG. 4 , would not cause the member  44  to release the mass element  41 . 
         [0062]    It is noted that in many projectiles, the projectiles are accelerated in rotation during the firing using rifled barrels to achieve a desired spinning rate upon exit to achieve stability during the flight. In such cases, the spinning acceleration during the firing and the centrifugal forces generated due to the spinning speed of the projectile during the flight can also be considered when calculating the spring rates for the spring  12  (and the spring  14 —if present) and their preloading levels for the proper operation of the power source and its safety features. The above factors can also be considered during the design of the remaining components of the power source and its safety mechanisms to ensure their proper operation. 
         [0063]    While there has been shown and described what is considered to be preferred embodiments of the invention, it will, of course, be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention be not limited to the exact forms described and illustrated, but should be constructed to cover all modifications that may fall within the scope of the appended claims.