Abstract:
A method for actuating an inertial igniter. The method including: moving a mass contained within an interior of a body towards one of a pyrotechnic material or primer when an all-fire acceleration profile is experienced; hermetically sealing the interior of the body from an outside environment; restraining the movable mass from contacting the one of the pyrotechnic material or primer for acceleration profiles less than the all-fire acceleration profile; at least indirectly blocking the movable mass from movement towards the one of the pyrotechnic material or primer under acceleration profiles equal to or greater than the all-fire acceleration profile; and manually removing the blocking such that the movable mass can move towards and contact the one of the pyrotechnic material or primer when the all-fire acceleration profile is experienced to actuate the inertial igniter.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present disclosure relates generally to inertial igniters and more particularly to inertial igniters for thermal batteries or other pyrotechnic type initiated devices for munitions such as gun fired or mortar rounds or rockets with safety arm. 
         [0003]    2. Prior Art 
         [0004]    Thermal batteries represent a class of reserve batteries that operate at high temperature. Unlike liquid reserve batteries, in thermal batteries the electrolyte is already in the cells and therefore does not require a distribution mechanism such as spinning. The electrolyte is dry, solid and non-conductive, thereby leaving the battery in a non-operational and inert condition. These batteries incorporate pyrotechnic heat sources to melt the electrolyte just prior to use in order to make them electrically conductive and thereby making the battery active. The most common internal pyrotechnic is a blend of Fe and KClO 4 . Thermal batteries utilize a molten salt to serve as the electrolyte upon activation. The electrolytes are usually mixtures of alkali-halide salts and are used with the Li(Si)/FeS 2  or Li(Si)/CoS 2  couples. Some batteries also employ anodes of Li(Al) in place of the Li(Si) anodes. Insulation and internal heat sinks are used to maintain the electrolyte in its molten and conductive condition during the time of use. Reserve batteries are inactive and inert when manufactured and become active and begin to produce power only when they are activated. 
         [0005]    Thermal batteries have long been used in munitions and other similar applications to provide a relatively large amount of power during a relatively short period of time, mainly during the munitions flight. Thermal batteries have high power density and can provide a large amount of power as long as the electrolyte of the thermal battery stays liquid, thereby conductive. The process of manufacturing thermal batteries is highly labor intensive and requires relatively expensive facilities. Fabrication usually involves costly batch processes, including pressing electrodes and electrolytes into rigid wafers, and assembling batteries by hand. The batteries are encased in a hermetically-sealed metal container that is usually cylindrical in shape. Thermal batteries, however, have the advantage of very long shelf life of up to 20 years that is required for munitions applications. 
         [0006]    Thermal batteries generally use some type of igniter (initiator) to provide a controlled pyrotechnic reaction to produce output gas, flame or hot particles to ignite the heating elements of the thermal battery. 
         [0007]    There are currently two distinct classes of igniters that are available for use in thermal batteries. The first class of igniter operates based on electrical energy. Such electrical igniters, however, require electrical energy, thereby requiring an onboard battery or other power sources with related shelf life and/or complexity and volume requirements to operate and initiate the thermal battery. The second class of igniters, commonly called “inertial igniters”, operates based on the firing acceleration. These (mechanical) inertial igniters do not require onboard batteries for their operation and are thereby often used in high-G munitions applications such as in gun-fired munitions and mortars. 
         [0008]    In munitions, the need to differentiate accidental and initiation accelerations, i.e., the so-called no-fire and all-fire (set-back) accelerations, respectively, by the resulting impulse level of the event necessitates the employment of a safety system which is capable of allowing initiation of the igniter only during high total impulse levels. In mechanical inertial igniters, the safety mechanism can be thought of as a mechanical delay mechanism, after which a separate initiation system is actuated or released to provide ignition of the pyrotechnics. Such mechanical inertial igniters that combines such a safety system with an impact based initiation system of different types are described, for example, in U.S. Pat. Nos. 7,437,995; 7,587,979; 7,587,980; 7,832,335; 8,042,469; and 8,061,271; U.S. Patent Application Publication Nos. 2010/0307362; 2011/0171511; 2012/0180680; 2012/0180681; 2012/0180682; 2012/0205225 and 2012/0210896 and U.S. patent application Ser. Nos. 12/794,763; 12/955,876 and 13/180,469; the disclosures or each of which are incorporated by reference. 
         [0009]    Inertia-based (mechanical) igniters must therefore comprise two components so that together they provide the aforementioned mechanical safety (delay mechanism) and to provide the required striking action to achieve ignition of the pyrotechnic elements. The function of the safety system is to fix the striker in position until a specified acceleration time profile actuates the safety system and releases the striker, allowing it to accelerate toward its target under the influence of the remaining portion of the specified acceleration time profile. The ignition itself may take place as a result of striker impact, or simply contact or proximity. For example, the striker may be akin to a firing pin and the target akin to a standard percussion cap primer. Alternately, the striker-target pair may bring together one or more chemical compounds whose combination with or without impact will set off a reaction resulting in the desired ignition. 
         [0010]    As an example, the isometric cross-sectional view of an inertial igniter described in U.S. Patent Application Publication No. 2011/0171511 is shown in  FIG. 1 , referred to generally with reference numeral  200 . The full isometric view of the inertial igniter  200  is shown in  FIG. 2 . The inertial igniter  200  is constructed with igniter body  201 , consisting of a base  202  and at least three posts  203 . The base  202  and the at least three posts  203 , can be integrally formed as a single piece but may also be constructed as separate pieces and joined together, for example by welding or press fitting or other methods commonly used in the art. The base  202  of the housing can also be provided with at least one opening  204  (with a corresponding opening(s) in the thermal battery—not shown) to allow ignited sparks and fire to exit the inertial igniter and enter into the thermal battery positioned under the inertial igniter  200  upon initiation of the inertial igniter pyrotechnics  215 , or initiation of a percussion cap primer when used in place of the pyrotechnics. 
         [0011]    A striker mass  205  is shown in its locked position in  FIG. 1 . The striker mass  205  is provided with guides for the posts  203 , such as vertical surfaces  206 , that are used to engage the corresponding (inner) surfaces of the posts  203  and serve as guides to allow the striker mass  205  to ride down along the length of the posts  203  without rotation with an essentially pure up and down translational motion. 
         [0012]    In its illustrated position in  FIGS. 1 and 2 , the striker mass  205  is locked in its axial position to the posts  203  by at least one setback locking ball  207 . The setback locking ball  207  locks the striker mass  205  to the posts  203  of the inertial igniter body  201  through the holes  208  provided in the posts  203  and a concave portion such as a dimple (or groove)  209  on the striker mass  205  as shown in  FIG. 1 . A setback spring  210 , which is preferably in compression, is also provided around but close to the posts  203  as shown in  FIGS. 1 and 2 . In the configuration shown in  FIG. 1 , the locking balls  207  are prevented from moving away from their aforementioned locking position by the collar  211 . The setback spring  210  can be a wave spring with rectangular cross-section. The rectangular cross-section eliminates the need to fix or otherwise retain the striker spring  210  to the collar  211 , which is an expensive process; the flat coil spring surfaces minimizes the chances of coils slipping laterally (perpendicular to the direction of acceleration  218 ), which can cause jamming and prevent the release of the striker mass  205  (preventing the collar to move down enough to release the locking balls). Furthermore, wave springs generate friction between the waves at contact points along the spring wire, thereby reducing the chances for the collar  211  to rapidly bounce back up and preventing the striker mass  205  from being released. 
         [0013]    The collar  211  is preferably provided with partial guide  212  (“pocket”), which are open on the top as indicated by the numeral  213 . The guide  212  may be provided only at the location of the locking balls  207  as shown in  FIGS. 1 and 2 , or may be provided as an internal surface over the entire inner surface of the collar  211 . The advantage of providing local guides  212  is that it results in a significantly larger surface contact between the collar  211  and the outer surfaces of the posts  203 , thereby allowing for smoother movement of the collar  211  up and down along the length of the posts  203 . In addition, they prevent the collar  211  from rotating relative to the inertial igniter body  201  and make the collar stronger. 
         [0014]    The collar  211  rides up and down on the posts  203  as can be seen in  FIGS. 1 and 2 , but is biased to stay in its upper most position as shown in  FIGS. 1 and 2  by the setback spring  210 . The guides  212  are provided with bottom ends  214 , so that when the inertial igniter is assembled as shown in  FIGS. 1 and 2 , the setback spring  210  which is biased (preloaded) to push the collar  211  upward away from the igniter base  202 , would “lock” the collar  211  in its uppermost position against the locking balls  207 . As a result, the assembled inertial igniter  200  stays in its assembled state and would not require a top cap to prevent the collar  211  from being pushed up and allowing the locking balls  207  from moving out and releasing the striker mass  205 . 
         [0015]    In the embodiment  200 , a one part pyrotechnics compound  215  (such as lead styphnate or other similar compound) can be used as shown in  FIG. 1 . The striker mass can be provided with a relatively sharp tip  216  and the igniter base surface  202  is provided with a protruding tip  217  which is covered with the pyrotechnics compound  215 , such that as the striker mass is released during an all-fire event and is accelerated down (opposite to the arrow  218  illustrated in  FIG. 1 ), impact occurs mostly between the surfaces of the tips  216  and  217 , thereby pinching the pyrotechnics compound  215 , thereby providing the means to obtain a reliable initiation of the pyrotechnics compound  215 . Alternatively, a two-part pyrotechnics, e.g., potassium chlorate (first part), can be provided on the base  202  over the exit hole  204  and a second part consisting of red phosphorus can be provided on the lower surface of the striker mass surface  205  over the area of the sharp tip  216 . 
         [0016]    Alternatively, instead of using the pyrotechnics compound  215 ,  FIG. 1 , a percussion cap primer or the like can be used. A striker tip is generally provided at the tip  216  of the striker mass  205  to facilitate initiation upon impact. 
         [0017]    The basic operation of the embodiment  200  of the inertial igniter of  FIGS. 1 and 2  is as follows. If the inertial igniter is subjected to any non-trivial acceleration in the axial direction  218  which can cause the collar  211  to overcome the resisting force of the setback spring  210  will initiate and sustain some downward motion of the collar  211 . The force due to the acceleration on the striker mass  205  is supported at the dimples  209  by the locking balls  207  which are constrained inside the holes  208  in the posts  203 . If an acceleration amplitude and duration in the axial direction  218  imparts a sufficient impulse (i.e., an impulse greater than a predetermined threshold) to the collar  211 , it will translate down along the axis of the assembly until the setback locking balls  205  are no longer constrained to engage the striker mass  205  to the posts  203 . If the acceleration event is not sufficient to provide this motion (i.e., the acceleration time profile provides less impulse than the predetermined threshold), the collar  211  will return to its start (top) position under the force of the setback spring  210 . 
         [0018]    Assuming that the acceleration time profile was at or above the specified “all-fire” profile, the collar  211  will have translated down past the locking balls  207 , allowing the striker mass  205  to accelerate down towards the base  202 . In such a situation, since the locking balls  207  are no longer constrained by the collar  211 , the downward force that the striker mass  205  has been exerting on the locking balls  207  will force the locking balls  207  to move outward in the radial direction. Once the locking balls  207  are out of the way of the dimples  209 , the downward motion of the striker mass  205  is no longer impeded. As a result, the striker mass  205  is accelerated downward, causing the tip  216  of the striker mass  205  to strike the pyrotechnic compound  215  on the surface of the protrusion  217  with the requisite energy to initiate ignition. 
         [0019]    In the embodiment  200  of the inertial igniter shown in  FIGS. 1 and 2 , the setback spring  210  is illustrated as a helical wave spring type fabricated with rectangular cross-sectional wires (such as the ones manufactured by Smalley Steel Ring Company of Lake Zurich, Ill.). The use of such rectangular cross-section wave springs or the like has the following significant advantages over helical springs that are constructed with wires with circular cross-sections. Firstly and most importantly, as the spring is compressed and nears its “solid” length, the flat surfaces of the rectangular cross-section wires come in contact and generate minimal lateral forces that would otherwise tend to force one coil to move laterally relative to the other coils as is usually the case when the wires are circular in cross-section. Lateral movement of the coils can, in general, interfere with the proper operation of the inertial igniter since it could, for example jam a coil to the outer housing of the inertial igniter (not shown), which is usually desired to house the igniter  200  or the like with minimal clearance to minimize the total volume of the inertial igniter. In addition, the laterally moving coils could also jam against the posts  203  thereby further interfering with the proper operation of the inertial igniter. The use of such wave springs with rectangular cross-section eliminates such lateral movement and therefore significantly increases the reliability of the inertial igniter and also significantly increases the repeatability of the initiation for a specified all-fire condition. The second advantage of the use of the aforementioned wave springs with rectangular cross-section, particularly since the wires can and are usually made thin in thickness and relatively wide, the solid length of the resulting wave spring can be made to be significantly less than an equivalent regular helical spring with circular cross-section. As a result, the total height of the resulting inertial igniter can be reduced. Thirdly, since the coil waves are in contact with each other at certain points along their lengths and as the spring is compressed, the length of each wave is slightly increased, therefore during the spring compression the friction forces at these contact points do a certain amount of work and thereby absorb a certain amount of energy. The presence of such friction forces ensures that the firing acceleration and very rapid compression of the spring would to a lesser amount tend to “bounce” the collar  211  back up and thereby increasing the possibility that it would interfere with the exit of the locking balls from the dimples  209  of the striker mass  205  and the release of the striker mass  205 . The above characteristic of the wave springs with rectangular cross-section therefore also significantly enhances the performance and reliability of the inertial igniter  200  while at the same time allowing its height (and total volume) to be reduced. 
         [0020]    In the prior art inertial igniters similar the one illustrated in  FIGS. 1 and 2 , by varying the mass of the striker  205 , the mass of the collar  211 , the spring rate of the setback spring  210 , the distance that the collar  211  has to travel downward to release the locking balls  207  and thereby release the striker mass  205 , and the distance between the tip  216  of the striker mass  205  and the pyrotechnic compound  215  (and the tip of the protrusion  217 ), the designer of the disclosed inertial igniter  200  can match the all-fire and no-fire impulse level requirements for various applications as well as the safety (delay or dwell action) protection against accidental dropping of the inertial igniter and/or the munitions or the like within which it is assembled. 
         [0021]    Briefly, the safety system parameters, i.e., the mass of the collar  211 , the spring rate of the setback spring  210  and the dwell stroke (the distance that the collar  210  has to travel downward to release the locking balls  207  and thereby release the striker mass  205 ) must be tuned to provide the required actuation performance characteristics. Similarly, to provide the requisite impact energy, the mass of the striker  205  and the aforementioned separation distance between the tip  216  of the striker mass and the pyrotechnic compound  215  (and the tip of the protrusion  217 ) must work together to provide the specified impact energy to initiate the pyrotechnic compound when subjected to the remaining portion of the prescribed initiation acceleration profile after the safety system has been actuated. 
         [0022]    The inertial igniters of the type described above have been shown to be capable of being miniaturized and provide highly reliable means of initiating thermal batteries or the like. In certain applications, particularly in applications in which the firing (setback) acceleration for initiating the thermal battery is relatively low and/or its duration is relatively short, then the acceleration levels that the inertial igniter could accidentally be subjected to might be even higher than the intended all-fire (setback) acceleration and/or duration. This would also be the case if the munitions in which the inertial igniter is used are required to survive shock loading due to drops from relatively high heights of the order of  40  feet or nearby explosions without the thermal battery (inertial igniter) initiation. In such situations, the aforementioned safety mechanisms would not prevent inertial igniter initiation since shock impulse that could be experienced by the inertial igniter could be higher than that of the firing setback. In such applications, it is highly desirable to provide the inertial igniter integrated thermal battery with safing arm (pin) that has to be removed (actuated or inserted or the like) to make the inertial igniter operational in response to the prescribed all-fire shock profile. 
       SUMMARY OF THE INVENTION 
       [0023]    A need therefore exists for novel miniature inertial igniters for thermal batteries used in munitions such as certain gun fired and mortar rounds and rockets, which require safing arms (pins) to prevent them from being accidentally initiated by dropping or nearby explosions or the like relatively high and long duration shock loading. The innovative inertial igniters can be scalable to thermal batteries of various sizes. Such inertial igniters must be safe in general and in particular they should not initiate when subjected to certain prescribed no-fire shock loading profile; should not initiate with the safing arm (pin) on; should be able to be designed for high firing accelerations, for example up to 20-50,000 Gs or higher; and should be able to be designed to ignite (initiate) at specified acceleration levels when subjected to such accelerations for a specified amount of time as specified by the firing (all-fire) acceleration profile. Reliability is also of much concern since the rounds should have a shelf life of up to 20 years and could generally be stored at temperatures of sometimes in the range of −65 to 165 degrees F. This requirement is usually satisfied best if the igniter pyrotechnic is in a sealed compartment. The inertial igniters must also consider the manufacturing costs and simplicity in design to make them cost effective for munitions applications. 
         [0024]    Accordingly, inertial igniters and ignition systems for use with thermal batteries or the like that are equipped with safing arms (pins) that when in place would prevent the inertial igniter and thereby the thermal battery from being activated are provided. In the disclosed embodiments of the present invention, the basic method used to provide the inertial igniters with safe arming capability is based on using certain mechanisms that in the presence of the “safing arms” (pins), the full operation of the aforementioned safety mechanism (delay mechanism) in releasing the striker mass is prevented by mechanical interference, i.e., by providing stops in the path of movement of the safety (striker release) mechanism. Thereby, even if the inertial igniter is subjected to the prescribed all-fire (or higher) acceleration time profile, the safing arm would prevent the safety mechanism from releasing the striker mass, thereby preventing the inertial igniter from activation. 
         [0025]    The disclosed safing arm equipped inertial igniter embodiments of the present invention have the following highly desirable characteristics:
       They provide hermetically sealed inertial igniters that are readily integrated with thermal batteries to form a hermetically sealed thermal battery;   The safing arm (pin) will prevent inertial igniter activation even when it is subjected to acceleration levels that are significantly higher than the all-fire acceleration levels even if the applied acceleration duration is also infinitely long;   The safing arm (pin) can be readily removed to make the inertial igniter, thereby the thermal battery, operational;   Once the safing arm is removed, the safing arm mechanism does not interfere with proper and reliable operation of the inertial igniter.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]    These and other features, aspects, and advantages of the apparatus of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
           [0031]      FIG. 1  illustrates an isometric cut away view of an inertial igniter assembly known in the art. 
           [0032]      FIG. 2  illustrates a full isometric view of the inertial igniter assembly of  FIG. 1 . 
           [0033]      FIG. 3  illustrates the plane of the cross-sectional view C-C of the prior art inertial igniter assembly of  FIGS. 1 and 2 . 
           [0034]      FIG. 4  is the view of the C-C cross-section of  FIG. 3  of the prior art inertial igniter assembly of  FIGS. 1 and 2 . 
           [0035]      FIG. 5  illustrates the first embodiment of inertial igniter with safing arm (pin) of the present invention as assembled on a thermal battery with the safing arm in position. 
           [0036]      FIG. 6  illustrates the first embodiment of inertial igniter with safing arm (pin) of the present invention as assembled on a thermal battery following the safing arm removal and arming of the inertial igniter. 
           [0037]      FIG. 7  illustrates a second embodiment of inertial igniter with safing arm (pin) of the present invention as assembled on a thermal battery with the safing arm in position. 
           [0038]      FIG. 8  illustrates the second embodiment of inertial igniter with safing arm (pin) of the present invention as assembled on a thermal battery following the safing arm removal and arming of the inertial igniter. 
           [0039]      FIG. 9  illustrates a third embodiment of inertial igniter with safing arm (pin) of the present invention as assembled on a thermal battery with the safing arm in position and removed. 
           [0040]      FIG. 10  illustrates an example of the use of different safing arm geometries in the disclosed embodiments of the inertial igniter of the present invention. 
           [0041]      FIG. 11  illustrates one embodiment of a normally non-operational (inert) inertial igniter of the present invention shown in its non-operational state without the inserted arming pin. 
           [0042]      FIG. 12  illustrates the embodiment of the normally non-operational (inert) inertial igniter of  FIG. 11  in its armed state with the inserted arming pin. 
           [0043]      FIG. 13  illustrates an example of a “U” shaped arming pin that can be used to arm the normally non-operational (inert) inertial igniter of  FIGS. 11 and 12 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0044]    The aforementioned inertia-based (mechanical) igniters were shown to comprise of two basic components (mechanisms) and together they provide the aforementioned mechanical safety (delay mechanism) and provide the required striking action to achieve ignition of the pyrotechnic elements. As it was previously described, the function of the safety system (mechanism) is to fix the striker in position until a specified acceleration time profile actuates the safety mechanism and releases the striker, allowing it to accelerate toward its target under the influence of the remaining portion of the specified acceleration time profile. The ignition itself may take place as a result of striker impact, or rubbing action or simply contact or proximity. For example, the striker may be akin to a firing pin and the target akin to a standard percussion cap primer. 
         [0045]    The following embodiments operate based on the use of certain type of mechanisms that are actuated by the provided safing arm (pin) to prevent the aforementioned mechanical safety (delay) mechanism to fully operate, thereby preventing the striker element of the inertial igniter to be released (become operational) for the required striking action to achieve ignition of the pyrotechnic elements. In the following, the different safing arm embodiments, their methods of design and their operation are described using the prior art inertial igniter of  FIGS. 1 and 2 . 
         [0046]    The section C-C ( FIG. 3 ) of the inertial igniter of  FIGS. 1 and 2  is shown in  FIG. 4 . The schematic of the first embodiment  100  of inertial igniter with safing arm (pin) as attached to a thermal battery  103  is shown in  FIG. 5 . The inertial igniter uses the basic inertial igniter  200  of  FIGS. 1 and 2 , the cross-sectional C-C ( FIG. 3 ) of which is shown in  FIG. 4 . In this embodiment of the inertial igniter with safing arm, the mechanical safety (delay) mechanism of the inertial igniter  200  is modified by adding a flange  101  ( FIG. 5 ) to the safety mechanism collar  211  ( FIGS. 2 and 4 ), as shown in  FIG. 5  and enumerated as  102 . The modified inertial igniter would otherwise function as previously described for the inertial igniter  200  of  FIGS. 1 and 2 . 
         [0047]    The base  202  of the modified inertial igniter  200  shown in the schematic of  FIG. 5  is attached and sealed to the top surface  104  of the thermal battery  103 . A housing element, such as a “bellow” element  105  is assembled over the modified inertial igniter  200 , and is attached and sealed preferably to the side  106  of the base  202  of the modified inertial igniter  200  as shown in the schematic of  FIG. 5 . Alternatively, the “bellow” element  105  may be attached directly to the top  104  of the thermal battery  103 . The “bellow” element  105  thereby forms an enclosed sealed volume within which the modified inertial igniter  200  is positioned. The “bellow” element  105  has an extended rigid ring portion  108 , which is positioned between a top elastic portion  109  and a bottom elastic portion  110 . The inertial igniter with safing arm embodiment  100  is provided with a (preferably) “U-shaped” safing arm  111 , the two prongs of which are shown in the schematic of  FIG. 5 . The safing arm  111  may be provided with a pulling handle or string (not shown) for ease of removal. 
         [0048]    In the “safe” configuration shown in  FIG. 5 , the safing arm  111  is positioned under the exterior portion of the ring  108 , thereby placing the bottom elastic portion  110  of the bellow element  105  in tension and the top elastic portion  109  of the bellow element  105  in compression. As a result, if the inertial igniter  100  and the thermal battery  103  assembly is accelerated (i.e., subjected to shock loading) in any direction including the direction of the inertial igniter activation shown by the arrow  112 , the safety mechanism collar  102  can displace downward only until its flange  101  comes into contact with the top surface of the rigid ring  108  of the bellow element  105 . 
         [0049]    However, if the safing arm  111  is removed, the bellow  105  returns to its configuration shown in the schematic of  FIG. 6 . The rigid ring  108  is then moved down to the indicated position in  FIG. 6 , thereby freeing the safety mechanism collar  102  to travel down when subjected to the specified acceleration time profile (for gun-fired munitions, all-fire setback acceleration), causing the striker mass  205  to be released and activate the inertial igniter pyrotechnic material  215  ( FIG. 2 ) as was previously described for the inertial igniter  200  of  FIGS. 1 and 2 . The ignition flame and sparks are generally passed through a provided opening ( 204  in  FIG. 2 ) into the thermal battery  103  through an opening  113  on the surface of its housing (top surface  104  for the thermal battery  103 ) to activate the thermal battery. 
         [0050]    The schematic of a second embodiment  170  of inertial igniter with safing arm (pin) as attached to a thermal battery  114  is shown in  FIG. 7 . The inertial igniter uses the basic inertial igniter  200  of  FIGS. 1 and 2 , the cross-sectional C-C ( FIG. 3 ) of which is shown in  FIG. 4 . In the embodiment  170  of the inertial igniter with safing arm, the mechanical safety (delay) mechanism of the inertial igniter  200  is modified as was described for the embodiment  100  of  FIG. 5  by adding the flange  101  to the safety mechanism collar  211  ( FIGS. 2 and 4 ), which is enumerated  102  in the schematic of  FIG. 7 . The modified inertial igniter would otherwise function as previously described for the inertial igniter  200  of  FIGS. 1 and 2 . 
         [0051]    The base  202  of the modified inertial igniter  200  shown in the schematic of  FIG. 7  is also attached and sealed to the top surface  115  of the thermal battery  114 . A housing element  116  is used to enclose the modified inertial igniter  200 , and is attached and sealed preferably to the side  106  of the base  202  of the modified inertial igniter  200  as shown in the schematic of  FIG. 7 . Alternatively, the housing element  116  may be attached directly to the top  115  of the thermal battery  114 . The housing element  116  thereby forms an enclosed sealed volume within which the modified inertial igniter  200  is positioned. 
         [0052]    The housing element  116  is provided with at least one and preferably two laterally flexible and axially relatively rigid curved surface portions  117  on its opposite sides as shown in  FIG. 7 , which in their free configuration spring out (bulge out) to the positions  118  as shown in  FIG. 8 . The laterally flexible and axially relatively rigid curved surface portions  117  may, for example, be formed as a section of a sphere or similar curved surface with relatively thin walls out of materials such as stainless steel that is usually used in the construction of bellow type elements. The inner surfaces of the flexible curved surface portions  117  ( 118  in its free configuration) are provided with relatively rigid stops  119 . The inertial igniter with safing arm embodiment  170  is provided with a (preferably) “U-shaped” safing arm  120 , the two prongs of which are shown in the schematic of  FIG. 7 . The safing arm  120  may be provided with a pulling handle or string (not shown) for ease of removal. 
         [0053]    In the “safe” configuration shown in  FIG. 7 , the two prongs of the safing arm  120  are used to press against the laterally flexible and axially relatively rigid curved surface portions  117  to force them into the configuration shown in  FIG. 7 , in which configuration, the relatively rigid stops  119  are positioned below the flange  101  of the safety mechanism collar  102  as shown in  FIG. 7 . As a result, if the inertial igniter  170  and the thermal battery  114  assembly is accelerated (i.e., subjected to shock loading) in any direction including the direction of the inertial igniter activation shown by the arrow  121 , the safety mechanism collar  102  can displace downward only until its flange  101  comes into contact with the top surface of the relatively rigid stops  119 . 
         [0054]    However, if the safing arm  120  is removed, the laterally flexible and axially relatively rigid curved surface portions  117  will spring back to its free configuration  118  shown in  FIG. 8 , and the relatively rigid stops  119  are moved laterally away from the flange  101  of the safety mechanism collar  102  as shown in  FIG. 8 , thereby freeing the safety mechanism collar  102  to travel down when subjected to the specified acceleration time profile (for gun-fired munitions, all-fire setback acceleration) in the direction of the arrow  121 , causing the striker mass  205  to be released and activate the inertial igniter pyrotechnic material  215  ( FIG. 2 ) as was previously described for the inertial igniter  200  of  FIGS. 1 and 2 . The ignition flame and sparks are generally passed through a provided opening ( 204  in  FIG. 2 ) into the thermal battery  114  through an opening  122  on the surface of its housing (top surface  115  for the thermal battery  114 ) to activate the thermal battery. 
         [0055]    The schematic of a third embodiment  140  of inertial igniter with safing arm (pin) as attached to a thermal battery  123  is shown in  FIG. 9 . The inertial igniter uses the basic inertial igniter  200  of  FIGS. 1 and 2 , the cross-sectional C-C ( FIG. 3 ) of which is shown in  FIG. 4 . In the embodiment  140  of the inertial igniter with safing arm, the mechanical safety (delay) mechanism of the inertial igniter  200  is modified as was described for the embodiment  100  of  FIG. 5  by adding the flange  101 to the safety mechanism collar  211  ( FIGS. 2 and 4 ), which is enumerated  102  in the schematic of  FIG. 9 . The modified inertial igniter would otherwise function as previously described for the inertial igniter  200  of  FIGS. 1 and 2 . 
         [0056]    The base  202  of the modified inertial igniter  200  shown in the schematic of  FIG. 9  is also attached and sealed to the top surface  124  of the thermal battery  123 . A housing element  125  is used to enclose the modified inertial igniter  200 , and is attached and sealed preferably to the side  106  of the base  202  of the modified inertial igniter  200  as shown in the schematic of  FIG. 9 . Alternatively, the housing element  125  may be attached directly to the top  124  of the thermal battery  123 . The housing element  125  thereby forms an enclosed sealed volume within which the modified inertial igniter  200  is positioned. 
         [0057]    The housing element  125  is provided with at least one and preferably two laterally positioned cavities  126  on its opposite sides as shown in  FIG. 9 . Inside each cavity  126  a translating element  127  is positioned, which is free to move laterally, and which is provided with a spring element (not shown for clarity) that biases the translating element  127  laterally away from the flange  101  of the modified inertial igniter. As a result, the translating element  127  would normally be “pulled” away from the path of downward travel of the safety collar  102  and its flange  101 . Each translating element  127  is provided with a magnet element  128 , which is oriented such that its N (S), i.e., its North (South), pole is facing the outer surface of the cavity  126 . 
         [0058]    The inertial igniter with safing arm embodiment  140  is provided with a (preferably) “U-shaped” safing arm  129 , the two prongs of which are provided with a “U” shaped end (the sides of which are enumerated  130  in  FIG. 9 ), which engage the outer surface of the cavities  126  as shown in the schematic of  FIG. 9 . Each prong of the safing arm  129  is also provided with a magnet  131 , the N (S) pole of which faces the N (S) pole of the magnet element  128  of the translating element  127 . As a result, when the safing arm  129  engages the inertial igniter  140  as shown in  FIG. 9 , the magnets  131  of the safing arm  129  repulse the magnets  128  of the translating elements  127 , thereby pushing the translating elements  127  under the flange  101  of the safety collar  102  (shown in broken lines). 
         [0059]    The safing arm  129  may be provided with a pulling handle or string (not shown) for ease of removal. 
         [0060]    It is appreciated that since all components of inertial igniters are constructed with nonmagnetic materials, usually stainless steel and brass, therefore they would not interfere with the operation of the disclosed safing arm mechanism of the inertial igniter  140 . 
         [0061]    In the “safe” configuration shown in  FIG. 9 , the two prongs of the safing arm  129  position the N pole of the magnets  131  against the outer surfaces of the cavities  126 , thereby repelling the facing N pole of the magnet  128  of the translating elements  127 , thereby forcing the translating elements  127  towards the inertial igniter body and under the flange  101  of the safety collar  102  as shown with broken lines in  FIG. 9  and indicated by the numeral  132 . As a result, if the inertial igniter  140  and the thermal battery  123  assembly is accelerated (i.e., subjected to shock loading) in any direction including the direction of the inertial igniter activation shown by the arrow  133 , the safety mechanism collar  102  can displace downward only until its flange  101  comes into contact with the top surface of the translating elements  127 . 
         [0062]    However, if the safing arm  129  is removed, the aforementioned biasing spring (not shown) would return the translating elements  127  to the position shown in solid lines in  FIG. 9 , i.e., away from under the flange  101  of the safety collar  102 , thereby freeing the safety mechanism collar  102  to travel down when subjected to the specified acceleration time profile (for gun-fired munitions, all-fire setback acceleration) in the direction of the arrow  133 , causing the striker mass  205  to be released and activate the inertial igniter pyrotechnic material  215  ( FIG. 2 ) as was previously described for the inertial igniter  200  of  FIGS. 1 and 2 . The ignition flame and sparks are generally passed through a provided opening ( 204  in  FIG. 2 ) into the thermal battery  123  through an opening  134  on the surface of its housing (top surface  124  for the thermal battery  123 ) to activate the thermal battery. 
         [0063]    It is appreciated by those skilled in the art that the safing arms used in the embodiments of  FIGS. 5-9  may have different geometries and that those shown in the illustrations are for presenting the basic operating features of these embodiments without intending to indicate limitation to a single geometrically shaped and operating safing arm. As previously indicated, the function of the safing arm (pin) is to prevent the operation of the safety element (safety collar  102  in the embodiments of  FIGS. 5-9 ). It is appreciated by those skilled in the art that such safing arms (pins) can be designed in various geometries to perform the same function as those shown in said embodiments. For example, the safing arm  111  may be replaced by the safing arm  135  as shown for the embodiment  150  in the schematic of  FIG. 10 . In the schematic of  FIG. 10 , the safing arm  135  has “C” shaped ends, the top portion  137  of which engages the top surface  107  of the bellow  105  and the bottom portion  136  of which engages the bottom surface of the rigid ring portion  108  of the bellow  105 , thereby preventing the safety collar  102  from moving down enough (in response to accelerations in the direction of the arrow  112 ) to release the striker mass  205 , thereby rendering the inertial igniter  150  non-operational (safe). The inertial igniter is rendered operational with the removal of the safing arm  135  ( FIG. 6 ) as was previously described for the embodiment  100  ( FIGS. 5-6 ). 
         [0064]    In the above embodiments of the inertial igniter with safing arm (pin) illustrated in the schematics of  FIGS. 5-9 , the inertial igniters become operational, i.e., can be initiated when subjected to the prescribed all-fire condition (setback acceleration) if the safing arm (pin) has been removed. In other words, the inertial igniter embodiments of  FIGS. 5-9  are “normally operational” and are rendered non-operational (inert) with the insertion of the safing arm (pin). 
         [0065]    Alternatively, such inertial igniters may be designed such that they are normally non-operational (inert) and become operational only following insertion of the “safing arm (pin)”. Such normally non-operational inertial igniters are particularly useful for applications in which there is a chance that the safing arm of the aforementioned normally operational inertial igniters be accidentally pulled or drop out during transportation, etc. In general, the basic design of any one of the aforementioned normally operational inertial igniters and those that are disclosed below can be readily modified to make them normally non-operational. As examples, such modifications to the normally operational inertial igniter embodiments of  FIGS. 7-8  and  9  are described below. It is, however, appreciated by those skilled in the art that such modifications can also be made to any of the disclosed embodiments. 
         [0066]    The schematic of the inertial igniter embodiment  170  of  FIG. 7  without the safing arm  120  as attached to a thermal battery  114  is reconfigured in  FIG. 11  and indicated with the numeral  160 . Similar to the embodiment  170  of  FIG. 7 , the housing element  116  which encloses and seals the modified inertial igniter  200  is provided with at least one and preferably two laterally flexible and axially relatively rigid curved surface portions  117  on its opposite sides, which in their free configuration are in the configuration shown in  FIG. 11  in contrast to the embodiment  170 , in which they are in the configuration shown in  FIG. 8 . The inner surfaces of the flexible curved surface portions  117  are similarly provided with relatively rigid stops  119 . In addition, “T” shaped elements  161  are also provided on the outside surface of the flexible curved surface portions  117 , preferably opposite to the inner stops  119  as shown in  FIG. 11 . 
         [0067]    In its free state, the laterally flexible and axially relatively rigid curved surface portions  117  are in the configuration shown in  FIG. 11 , therefore the relatively rigid stops  119  are positioned below the flange  101  of the safety mechanism collar  102 . As a result, if the inertial igniter  160  and the thermal battery  114  assembly is accelerated (i.e., subjected to shock loading) in any direction including the direction of the inertial igniter activation shown by the arrow  121 , the safety mechanism collar  102  can displace downward only until its flange  101  comes into contact with the top surface of the relatively rigid stops  119 , thereby the striker mass  205  is prevented from being released and cause the inertial igniter to be initiated as was previously described. Thus, in the state shown in  FIG. 11 , the inertial igniter is non-operational or inert. 
         [0068]    For the normally non-operational (inert) inertial igniter of  FIG. 11 , the arming pin (arm)  162  is preferably a “U” shaped element similar to the arming pin  162  shown in the schematic of  FIG. 13 . The arming pin  162  may be provided with a pulling handle or string (not shown) for ease of removal. The “U” shaped arming pin  162  is provided with slots  163  that would engage the “T” shaped elements  161  on outside surface of the flexible curved surface portions  117  as shown with dashed lines in  FIG. 11  and solid lines in  FIG. 12 . The front side  164  of the “U” shaped arming pin  162  is sized to engage the “T” shaped elements  161  on outside surface of the flexible curved surface portions  117  in their position shown in the schematic of  FIG. 11  (dashed lines). On the back side  165 , the prongs of the “U” shaped arming pin  162  are spaced wider such that as the arming pin  162  engages the “T” shaped elements  161  and is pushed forward against the inertial igniter casing  116 , the “T” shaped elements  161  and thereby the opposing flexible curved surface portions  117  are pulled apart, thereby bring them into the configuration shown in dashed lines in  FIG. 12 . 
         [0069]    As a result, with the insertion of the arming pin  162 , the laterally flexible and axially relatively rigid curved surface portions  117  are forced to the configuration shown in  FIG. 12  with dotted lines, moving the relatively rigid stops  119  laterally away from the flange  101  of the safety mechanism collar  102 , thereby freeing the safety mechanism collar  102  to travel down when subjected to the specified acceleration time profile (for gun-fired munitions, all-fire setback acceleration) in the direction of the arrow  121 , causing the striker mass  205  to be released and activate the inertial igniter pyrotechnic material  215  ( FIG. 2 ) as was previously described for the inertial igniter  200  of  FIGS. 1 and 2 . The ignition flame and sparks are generally passed through a provided opening ( 204  in  FIG. 2 ) into the thermal battery  114  through an opening  122  on the surface of its housing (top surface  115  for the thermal battery  114 ) to activate the thermal battery. 
         [0070]    As another example, the inertial igniter embodiment  140  of  FIG. 9 , which is a normally operational inertial igniter, i.e., with the safing arm  129  removed, the inertial igniter can be initiated when subjected to the aforementioned prescribed all-fire setback acceleration. The inertial embodiment  140  can be readily turned into a normally non-operational inertial igniter by firstly modifying the biasing spring of the translating element  127  to instead bias the said translating elements  127  laterally towards the flange  101 . As a result, with the safing arm  129  removed, the translating elements  127  are in the position indicated by  132  in  FIG. 9 , and the inertial igniter  140  in non-operational (inert). The second required modification is the switching of the N pole of the magnet  131  with its S pole (or placing the S pole of the magnet attached to the translating element instead of its N pole to face the magnet  131  of the safing arm  129 ). As a result, when the safing arm  129  (in this case the arming arm or pin  129 ) is positioned on the inertial igniter  140  as shown in the schematic of  FIG. 9 , then the translating elements  127  are pulled away from under the flange  101 of the safety collar  102 , thereby rendering the inertial igniter operational. 
         [0071]    In the embodiments of  FIGS. 5-12 , translating elements (vertically translating element  108  in the embodiment  100  of  FIG. 5 ; and laterally translating elements  119  and  127  in the embodiments of  FIG. 7  and  FIGS. 9 and 11 , respectively) are used to position these mechanically blocking elements in the path of motion of the safety element (collar in the present embodiments) to prevent the release of the striker mass that function to initiate the igniter pyrotechnic material. It is, however, appreciated by those in the art that the mechanically blocking elements may be similarly positioned via mechanisms undergoing other types of motions such as by undergoing rotational motion or flextural bending motion or the like, all actuated similarly by the motion of the bellows, flexural surfaces, magnets, or the like as in the disclosed embodiments of the present invention. 
         [0072]    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.