Abstract:
An inertial igniter including: a body having a base and three or more posts, each post having a hole; a locking ball corresponding to each post, wherein a portion of the locking balls are disposed in the hole; a striker mass movably disposed relative to the posts and having a surface corresponding to the posts, the striker mass further having a concave portion corresponding to the locking balls, wherein a second portion of each locking ball is disposed in a corresponding concave portion for retaining the striker mass relative to the posts; a collar movable relative to the posts; and a biasing element for biasing the collar in a first position which retains the striker mass, the biasing element permitting movement of the collar to a second position to release the striker mass relative to the posts upon a predetermined acceleration profile.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/239,048 filed on Sep. 1, 2009, the entire contents of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to mechanical igniters, and more particularly to compact, low-volume, reliable and easy to manufacture mechanical igniters and ignition systems for thermal batteries and the like. 
         [0004]    2. Prior Art 
         [0005]    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. 
         [0006]    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. 
         [0007]    Thermal batteries generally use some type of igniter to provide a controlled pyrotechnic reaction to produce output gas, flame or hot particles to ignite the heating elements of the thermal battery. 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. The 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 general, the inertial igniters, particularly those that are designed to operate at relatively low impact levels, have to be provided with the means for distinguishing events such as accidental drops or explosions in their vicinity from the firing acceleration levels above which they are designed to be activated. This means that safety in terms of prevention of accidental ignition is one of the main concerns in inertial igniters. 
         [0009]    In recent years, new improved chemistries and manufacturing processes have been developed that promise the development of lower cost and higher performance thermal batteries that could be produced in various shapes and sizes, including their small and miniaturized versions. However, the existing inertial igniters are relatively large and not suitable for small and low power thermal batteries, particularly those that are being developed for use in miniaturized fuzing, future smart munitions, and other similar applications. 
         [0010]    The need to differentiate accidental and initiation accelerations 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. 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. An inertial igniter that combines such a safety system with an impact based initiation system and its alternative embodiments are described herein together with alternative methods of initiation pyrotechnics. 
         [0011]    Inertia-based 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. 
         [0012]    In addition to having a required acceleration time profile which will actuate the device, requirements also commonly exist for non-actuation and survivability. For example, the design requirements for actuation for one application are summarized as: 
         [0013]    1. The device must fire when given a [square] pulse acceleration of 900 G±150 G for 15 ms in the setback direction. 
         [0014]    2. The device must not fire when given a [square] pulse acceleration of 2000 G for 0.5 ms in any direction. 
         [0015]    3. The device must not actuate when given a ½-sine pulse acceleration of 490 G (peak) with a maximum duration of 4 ms. 
         [0016]    4. The device must be able to survive an acceleration of 16,000 G, and preferably be able to survive an acceleration of 50,000 G. 
         [0017]    A schematic of a cross-section of a conventional thermal battery and inertial igniter assembly is shown in  FIG. 1 . In thermal battery applications, the inertial igniter  10  (as assembled in a housing) is generally positioned above the thermal battery housing  11  as shown in  FIG. 1 . Upon ignition, the igniter initiates the thermal battery pyrotechnics positioned inside the thermal battery through a provided access  12 . The total volume that the thermal battery assembly  16  occupies within munitions is determined by the diameter  17  of the thermal battery housing  11  (assuming it is cylindrical) and the total height  15  of the thermal battery assembly  16 . The height  14  of the thermal battery for a given battery diameter  17  is generally determined by the amount of energy that it has to produce over the required period of time. For a given thermal battery height  14 , the height  13  of the inertial igniter  10  would therefore determine the total height  15  of the thermal battery assembly  16 . To reduce the total volume that the thermal battery assembly  16  occupies within a munitions housing, it is therefore important to reduce the height of the inertial igniter  10 . This is particularly important for small thermal batteries since in such cases the inertial igniter height with currently available inertial igniters can be almost the same order of magnitude as the thermal battery height. 
         [0018]    With currently available inertial igniters, a schematic of which is shown in  FIG. 2 , the inertial igniter  20  may have to be positioned within a housing  21  as shown in  FIG. 3 , particularly for relatively small igniters. The housing  21  and the thermal battery housing  11  may share a common cap  22 , with the opening  25  to allow the ignition fire to reach the pyrotechnic material  24  within the thermal battery housing. As the inertial igniter is initiated, the sparks can ignite intermediate materials  23 , which can be in the form of thin sheets to allow for easy ignition, which would in turn ignite the pyrotechnic materials  24  within the thermal battery through the access hole  25 . 
         [0019]    A schematic of a cross-section of a currently available inertial igniter  20  is shown in  FIG. 2  in which the acceleration is in the upward direction (i.e., towards the top of the paper). The igniter has side holes  26  to allow the ignition fire to reach the intermediate materials  23  as shown in  FIG. 3 , which necessitate the need for its packaging in a separate housing, such as in the housing  21 . The currently available inertial igniter  20  is constructed with an igniter body  60 . Attached to the base  61  of the housing  60  is a cup  62 , which contains one part of a two-part pyrotechnic compound  63  (e.g., potassium chlorate). The housing  60  is provided with the side holes  26  to allow the ignition fire to reach the intermediate materials  23  as shown in  FIG. 3 . A cylindrical shaped part  64 , which is free to translate along the length of the housing  60 , is positioned inside the housing  60  and is biased to stay in the top portion of the housing as shown in  FIG. 2  by the compressively preloaded helical spring  65  (shown schematically as a heavy line). A turned part  71  is firmly attached to the lower portion of the cylindrical part  64 . The tip  72  of the turned part  71  is provided with cut rings  72   a , over which is covered with the second part of the two-part pyrotechnic compound  73  (e.g., red phosphorous). 
         [0020]    A safety component  66 , which is biased to stay in its upper most position as shown in  FIG. 2  by the safety spring  67  (shown schematically as a heavy line), is positioned inside the cylinder  64 , and is free to move up and down (axially) in the cylinder  64 . As can be observed in  FIG. 2 , the cylindrical part  64  is locked to the housing  60  by setback locking balls  68 . The setback locking balls  68  lock the cylindrical part  64  to the housing  60  through holes  69   a  provided on the cylindrical part  64  and the housing  60  and corresponding holes  69   b  on the housing  60 . In the illustrated configuration, the safety component  66  is pressing the locking balls  68  against the cylindrical part  64  via the preloaded safety spring  67 , and the flat portion  70  of the safety component  66  prevents the locking balls  68  from moving away from their aforementioned locking position. The flat portion  70  of the safety component  66  allows a certain amount of downward movement of the safety component  66  without releasing the locking balls  68  and thereby allowing downward movement of the cylindrical part  64 . For relatively low axial acceleration levels or higher acceleration levels that last a very short amount of time, corresponding to accidental drops and other similar situations that cause safety concerns, the safety component  66  travels up and down without releasing the cylindrical part  64 . However, once the firing acceleration profiles are experienced, the safety component  66  travels downward enough to release balls  68  from the holes  69   b  and thereby release the cylindrical part  64 . Upon the release of the safety component  66  and appropriate level of acceleration for the cylindrical part  64  and all other components that ride with it to overcome the resisting force of the spring  65  and attain enough momentum, then it will cause impact between the two components  63  and  73  of the two-part pyrotechnic compound with enough strength to cause ignition of the pyrotechnic compound. 
         [0021]    The aforementioned currently available inertial igniters have a number of shortcomings for use in thermal batteries, specifically, they are not useful for relatively small thermal batteries for munitions with the aim of occupying relatively small volumes, i.e., to achieve relatively small height total igniter compartment height  13 ,  FIG. 1 . Firstly, the currently available inertial igniters, such as that shown in  FIG. 2 , are relatively long thereby resulting in relatively long total igniter heights  13 . Secondly, since the currently available igniters are not sealed and exhaust the ignition fire out from the sides, they have to be packaged in a housing  21 , usually with other ignition material  23 , thereby increasing the height  13  over the length of the igniter  20  (see  FIG. 3 ). In addition, since the pyrotechnic materials of the currently available igniters  20  are not sealed inside the igniter, they are prone to damage by the elements and cannot usually be stored for long periods of time before assembly into the thermal batteries unless they are stored in a controlled environment. 
       SUMMARY OF THE INVENTION 
       [0022]    A need therefore exists for novel miniature inertial igniters for thermal batteries used in gun fired munitions, particularly for small and low power thermal batteries that could be used in fuzing and other similar applications, thereby eliminating the need for external power sources. The innovative inertial igniters can be scalable to thermal batteries of various sizes, in particular to miniaturized igniters for small size thermal batteries. Such inertial igniters must be safe and in general and in particular they should not initiate if dropped, e.g., from up to 7 feet onto a concrete floor for certain applications; should withstand high firing accelerations, for example up to 20-50,000 Gs; and should be able to be designed to ignite at specified acceleration levels when subjected to such accelerations for a specified amount of time to match the firing acceleration experienced in a gun barrel as compared to high G accelerations experienced during accidental falls which last over very short periods of time, for example accelerations of the order of 1000 Gs when applied for 5 msec as experienced in a gun as compared to for example 2000 G acceleration levels experienced during accidental fall over a concrete floor but which may last only 0.5 msec. 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. 
         [0023]    To ensure safety and reliability, inertial igniters should not initiate during acceleration events which may occur during manufacture, assembly, handling, transport, accidental drops, etc. Additionally, once under the influence of an acceleration profile particular to the firing of ordinance from a gun, the device should initiate with high reliability. In many applications, these two requirements often compete with respect to acceleration magnitude, but differ greatly in impulse. For example, an accidental drop may well cause very high acceleration levels—even in some cases higher than the firing of a shell from a gun. However, the duration of this accidental acceleration will be short, thereby subjecting the inertial igniter to significantly lower resulting impulse levels. It is also conceivable that the igniter will experience incidental low but long-duration accelerations, whether accidental or as part of normal handling, which must be guarded against initiation. Again, the impulse given to the miniature inertial igniter will have a great disparity with that given by the initiation acceleration profile because the magnitude of the incidental long-duration acceleration will be quite low. 
         [0024]    Those skilled in the art will appreciate that the inertial igniters disclosed herein may provide one or more of the following advantages over prior art inertial igniters: 
         [0025]    provide inertial igniters that are significantly shorter and smaller in volume than currently available inertial igniters for thermal batteries or the like, particularly relatively small thermal batteries to be used in munitions without occupying very large volumes; 
         [0026]    provide inertial igniters that can be mounted directly onto the thermal batteries without a housing (such as housing  21  shown in  FIG. 3 ), thereby allowing even a smaller total height and volume for the inertial igniter assembly; 
         [0027]    provide inertial igniters that can directly initiate the pyrotechnics materials inside the thermal battery without the need for intermediate ignition material (such as the additional material  23  shown in  FIG. 3 ) or a booster; 
         [0028]    provide inertia igniters that could be constructed to guide the pyrotechnic flame essentially downward (in the direction opposite to the direction of the firing acceleration—usually for mounting on the top of the thermal battery as shown in  FIG. 3 ), or essentially upward (in the direction opposite of the firing acceleration—usually for mounting at the bottom of the thermal battery), or essentially sidewise (lateral to the direction of the firing); 
         [0029]    provide inertial igniters that allow the use of standard off-the-shelf percussion cap primers instead of specially designed pyrotechnic components; and 
         [0030]    provide inertial igniters that can be sealed to simplify storage and increase their shelf life. 
         [0031]    Accordingly, inertial igniters and ignition systems for use with thermal batteries for producing power upon acceleration are provided. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    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: 
           [0033]      FIG. 1  illustrates a schematic of a cross-section of a thermal battery and inertial igniter assembly. 
           [0034]      FIG. 2  illustrates a schematic of a cross-section of a conventional inertial igniter assembly known in the art. 
           [0035]      FIG. 3  illustrates a schematic of a cross-section of a conventional inertial igniter assembly known in the art positioned within a housing and having intermediate materials for ignition. 
           [0036]      FIG. 4  illustrates a schematic of a cross-section of a first embodiment of an inertial igniter in a locked position. 
           [0037]      FIG. 5   a  illustrates a schematic of the isometric drawing of a first embodiment of an inertial igniter together with the top cap of a thermal battery to which it is attached. 
           [0038]      FIG. 5   b  illustrates a second view of the isometric drawing of the first embodiment of the inertial igniter of  FIG. 5   a  showing the openings that are provided to exit the ignition sparks and flames into the thermal battery. 
           [0039]      FIG. 5   c  illustrates a schematic of the isometric drawing of a first embodiment of an inertial igniter of  FIG. 5   a  without the outer housing (side wall and top cap) of the inertial igniter. 
           [0040]      FIG. 6  illustrates the inertial igniter of  FIG. 4  upon a non-firing accidental acceleration. 
           [0041]      FIG. 7  illustrates the inertial igniter of  FIG. 4  upon a firing acceleration. 
           [0042]      FIG. 8  illustrates the inertial igniter of  FIG. 4  upon the striker mass impacting base, causing the initiation of ignition of the two-part pyrotechnic compound. 
           [0043]      FIG. 9  illustrates a schematic of a cross-section of a second embodiment of an inertial igniter in a locked position. 
           [0044]      FIG. 10  illustrates a schematic of a cross-section of a third embodiment of an inertial igniter in initiation position. 
           [0045]      FIGS. 11   a  and  11   b  illustrate an isometric and a schematic of a cross-section, respectively, of a fourth embodiment of an inertial igniter in initiation position. 
           [0046]      FIG. 12  illustrates a schematic of a cross-section of a fifth embodiment of an inertial igniter in a locked position. 
           [0047]      FIG. 13  illustrates an isometric cut away view of a sixth embodiment of an inertial igniter. 
           [0048]      FIG. 14  illustrates a full isometric view of the inertial igniter of  FIG. 13 . 
           [0049]      FIGS. 15   a  and  15   b  illustrate first and second variations of thermal battery and inertial igniter assemblies. 
           [0050]      FIG. 16  illustrates a first variation of the inertial igniter of  FIG. 13 . 
           [0051]      FIG. 17  illustrates a second variation of the inertial igniter of  FIG. 13 . 
           [0052]      FIG. 18  illustrates a third variation of the inertial igniter of  FIG. 13 . 
           [0053]      FIG. 19  illustrates a thermal battery/inertial igniter assembly in which more than one inertial igniter is used. 
           [0054]      FIG. 20   a  illustrates a top view and  FIG. 20   b  illustrates an isometric view of a bottom plate and posts for a gang of three inertial igniters. 
           [0055]      FIG. 21   a  illustrates a top view and  FIG. 21   b  illustrates an isometric view of a bottom plate and posts for a variation of the gang of three inertial igniters of  FIGS. 20   a  and  20   b.    
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0056]    A schematic of a cross-section of a first embodiment of an inertia igniter is shown in  FIG. 4 , referred to generally with reference numeral  30 . The inertial igniter  30  is constructed with igniter body  31 , consisting of a base  32  and at least two posts  33 , and a housing wall  34 . The base  32  and two posts  33 , which may be integral or may have been constructed as separate pieces and joined together, for example by welding of press fitting or other methods commonly used in the art. In the schematic of  FIG. 4 , the igniter body  31  and the housing wall  34  are shown to be joined together at the base  32 ; however, the two components may be integrated as one piece and a separate top cap  35  may then be provided, which is then joined to the top surface of the housing  34  following assembly of the igniter (in the schematic of  FIG. 4  the top cap  35  is shown as an integral part of the housing  34 ). In addition, the base of the housing  32  may be extended to form the cap  36  of the thermal battery  37 , the top portion of which is shown with dashed lines in  FIG. 4 . 
         [0057]    The inertial igniter  30  with the thermal battery top cap  36  is shown in the isometric drawings of  FIGS. 5   a  and  5   b . The inertial igniter without its housing  34  and top cap  35  is shown in the isometric drawing of  FIG. 5   c . The base of the housing  32  is also provided with at least one opening  38  (with corresponding openings in the thermal battery top cap  36 ) to allow the ignited sparks and fire to exit the inertial igniter into the thermal battery  37  upon initiation of the inertial igniter pyrotechnics  46  and  47 ,  FIG. 4 , or percussion cap primer when used in place of the pyrotechnics  46  and  47  (not shown). 
         [0058]    A striker mass  39  is shown in its locked position in  FIGS. 4 and 5   c . The striker mass  39  is provided with vertical recesses  40  that are used to engage the posts  33  and serve as guides to allow the striker mass  39  to ride down along the length of the posts  33  without rotation with an essentially pure up and down translational motion. In its illustrated position in  FIGS. 4 and 5   c , the striker mass  39  is locked in its axial position to the posts  33  by at least one setback locking ball  42 . The setback locking ball  42  locks the striker mass  39  to the posts  33  of the inertial igniter body  31  through the holes  41  provided in the posts  33  and a concave portion such as a dimple (or groove)  43  on the striker mass  39  as shown in  FIG. 4 . A setback spring  44  with essentially dead coil section  45 , which is preferably in compression, is also provided around but close to the posts as shown in  FIGS. 4 and 5   c . In the configuration shown in  FIG. 4 , the locking balls  42  are prevented from moving away from their aforementioned locking position by the dead coil section  45  of the setback spring  44 . The dead coil section  45  can ride up and down beyond the posts  33  as shown in  FIGS. 4 and 5   c , but is biased to stay in its upper most position as shown in the schematic of  FIG. 4  by the setback spring  44 . 
         [0059]    In this embodiment, a two-part pyrotechnics compound is shown to be used,  FIG. 4 . One part of the two-part pyrotechnics compound  47  (e.g., potassium chlorate) is provided on the interior side of the base  32 , preferably in a provided recess (not shown) over the exit holes  38 . The second part of the pyrotechnics compound (e.g., red phosphorous)  46  is provided on the lower surface of the striker mass surface  39  facing the first part of the pyrotechnics compound  47  as shown in  FIG. 4 . The surfaces to which the pyrotechnic parts  46  and  47  are attached are roughened and/or provided with surface cuts, recesses, or the like as commonly used in the art (not shown) to ensure secure attachment of the pyrotechnics materials to the applied surfaces. 
         [0060]    In general, various combinations of pyrotechnic materials may be used for this purpose. One commonly used pyrotechnic material consists of red phosphorous or nano-aluminum, indicated as element  46  in  FIG. 4 , and is used with an appropriate binder (such as vinyl alcohol acetate resin or nitrocellulose) to firmly adhere to the bottom surface of the striker mass  39 . The second component can be potassium chlorate, potassium nitrate, or potassium perchlorate, indicated as element  47  in  FIG. 4 , and is used with a binder (preferably but not limited to with such as vinyl alcohol acetate resin or nitrocellulose) to firmly attach the compound to the surface of the base  32  (preferably inside of a recess provided in the base  32 —not shown) as shown in  FIG. 4 . 
         [0061]    The basic operation of the disclosed inertial igniter  30  will now be described with reference to  FIGS. 4-8 . Any non-trivial acceleration in the axial direction  48  which can cause dead coil section  45  to overcome the resisting force of the setback spring  44  will initiate and sustain some downward motion of only the dead coil section  45 . The force due to the acceleration on the striker mass  39  is supported at the dimples  43  by the locking balls  42  which are constrained inside the holes  41  in the posts  33 . If an acceleration time in the axial direction  48  imparts a sufficient impulse to the dead coil section  45  (i.e., if an acceleration time profile is greater than a predetermined threshold), it will translate down along the axis of the assembly until the setback locking balls  42  are no longer constrained to engage the striker mass  39  to the posts  33  of the housing  31 . 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 dead coil section  45  will return to its start (top) position under the force of the setback spring  44 . The schematic of the inertial igniter  30  with the dead coil section  45  moved down certain distance d 1  as a result of an acceleration event, which is not sufficient to unlock the striker mass  39  from the posts  33  of the housing  31 , is shown in  FIG. 6 . 
         [0062]    Assuming that the acceleration time profile was at or above the specified “all-fire” profile, the dead coil section  45  will have translated down full-stroke d 2 , allowing the striker mass  39  to accelerate down towards the base  32 . In such a situation, since the locking balls  42  are no longer constrained by the dead coil section  45 , the downward force that the striker mass  39  has been exerting on the locking balls  42  will force the locking balls  42  to move outward in the radial direction. Once the locking balls  42  are out of the way of the dimples  43 , the downward motion of the striker mass  39  is impeded only by the elastic force of the setback spring  44 , which is easily overcome by the impulse provided to the striker mass  39 . As a result, the striker mass  39  moves downward, causing the parts  46  and  47  of the two-part pyrotechnic compound to strike with the requisite energy to initiate ignition. The configuration of the inertial igniter  30  when the balls  42  are free to move outward in the radial direction, thereby releasing the striker mass  39  is shown in the schematic of  FIG. 7 . The configuration of the inertial igniter  30  when the part  46  of the two-part pyrotechnic compound is striking the part  47  is shown in the schematic of  FIG. 8 . 
         [0063]    In another embodiment, the dead coil section  45  may be constructed as a separate collar and positioned similarly over the setback spring  44 . The collar replacing the dead coil section  45  may also be attached to the top coil of the setback spring  44 , e.g., by welding, brazing, or adhesives such as epoxy, or the like. The advantage of attaching the collar to the top of the setback spring  44  is that it would help prevent it to get struck over the posts  33  as it is being pushed down by the applied acceleration in the direction of the arrow  48 ,  FIGS. 6-8 . 
         [0064]    Alternatively, the dead coil section  45  and the setback spring  44  may be integral, made out of, for example, a cylindrical section with spiral or other type shaped cuts over its lower section to provide the required axial flexibility to serve the function of the setback spring  44 . The upper portion of this cylinder is preferably left intact to serve the function of the dead coil section  45 ,  FIGS. 6-8 . 
         [0065]    It is appreciated by those skilled in the art that by varying the mass of the striker  39 , the mass of the dead coil section  45 , the spring rate of the setback spring  44 , the distance that the dead coil section  45  has to travel downward to release the locking balls  42  and thereby release the striker mass  39 , and the distance between the parts  46  and  47  of the two-part pyrotechnic compound, the designer of the disclosed inertial igniter  30  can match the 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. 
         [0066]    Briefly, the safety system parameters, i.e., the mass of the dead coil section  45 , the spring rate of the setback spring  44  and the dwell stroke (the distance that the dead coil section  44  has to travel downward to release the locking balls  42  and thereby release the striker mass  39 ) must be tuned to provide the required actuation performance characteristics. Similarly, to provide the requisite impact energy, the mass of the striker  39  and the separation distance between the parts  46  and  47  of the two-part pyrotechnic compound 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. 
         [0067]    In addition, since the safety and striker systems each require a certain actuation distance to achieve the necessary performance, the most axially compact design is realized by nesting the two systems in parallel as it is done in the embodiment of  FIG. 4 . It is this nesting of the two safety and striker systems that allows the height of the disclosed inertial igniter to be significantly shorter than the currently available inertial igniter design (as shown in  FIG. 2 ), in which the safety and striker systems are configured in series. In fact, an initial prototype of the disclosed inertial igniter  30  has been designed to the fire and no-fire and safety specifications of the currently available inertial igniter shown in  FIG. 2  and has achieved height and volume reductions of over 60 percent. It is noted that by optimizing the parameters of the disclosed inertial igniter, both height and volume can be further reduced. 
         [0068]    In another embodiment, the two-part pyrotechnics  46  and  47 ,  FIG. 4 , are replaced by a percussion cap primer  49  attached to the base  32  of the inertial igniter  60  and a striker tip  50  as shown in the schematic of a cross-section of  FIG. 9 . In this illustration, all components are the same as those shown in  FIG. 4  with the exception of replacing the percussion cap primer  49  and the striker tip  50  with striker assembly. The striker tip  50  is firmly attached to the striker mass  39 . 
         [0069]    The striker mass  39  and striker tip  50  may be a monolithic design with the striking tip  50  being a machined boss protruding from the striker mass, or the striker tip  50  may be a separate piece pressed or otherwise permanently fixed to the striker mass. A two-piece design would be favorable to the need for a striker whose density is different than steel, but whose tip would remain hard and tough by attaching a steel ball, hemisphere, or other shape to the striker mass. A monolithic design, however, would be generally favorable to manufacturing because of the reduction of part quantity and assembly operations. 
         [0070]    An advantage of using the two component pyrotechnic materials as shown in  FIG. 4  is that these materials can be selected such that ignition is provided at significantly lower impact forces than are required for commonly used percussion cap primers. As a result, the amount of distance that the striker mass  39  has to travel and its required mass is thereby reduced, resulting in a smaller total height (shown as  15  in  FIG. 1 ) of the thermal battery assembly. This choice, however, has the disadvantage of not using standard and off-the-shelf percussion cap primers, thereby increasing the component and assembly cost of the inertial igniter. 
         [0071]    The disclosed inertial igniters are seen to discharge the ignition fire and sparks directly into the thermal battery,  FIGS. 4-9 , to ignite the pyrotechnic materials  24  within the thermal battery  11  ( FIG. 3 ). As a result, the additional housing  21  and ignition material  23  shown in  FIG. 3  can be eliminated, greatly simplifying the resulting thermal battery design and manufacture. In addition, the total height  13  and volume of the inertial igniter assembly  10  and the total height  15  of the complete thermal battery assembly  16  are reduced, thereby reducing the total volume that has to be allocated in munitions or the like to house the thermal battery. 
         [0072]    The disclosed inertial igniters are shown sealed within their housing, thereby simplifying their storage and increase their shelf life. 
         [0073]      FIG. 10  shows the schematic of a cross-section of another embodiment  80 . This embodiment is similar to the embodiment shown in  FIGS. 4-8 , with the difference that the striker mass  39  ( FIGS. 4-8 ) is replaced with a striker mass  82 , with at least one opening passage  81  to guide the ignition flame up through the igniter  80  to allow the pyrotechnic materials (or the like) of a thermal battery (or the like) positioned above the igniter  80  (not shown) to be initiated. In addition, the top cap  35  ( FIG. 4-8 ) is preferably eliminated or replaced by a cap  83  with appropriately positioned openings to allow the flames to enter the thermal battery and initiate its pyrotechnic materials. The openings  38  ( FIG. 5   b ) are obviously no longer necessary. 
         [0074]      FIG. 11   b  shows the schematic of a cross-section of another embodiment  90 . This embodiment is similar to the embodiment shown in  FIGS. 4-8 , with the difference that the openings  38  ( FIG. 5   b ) for the flame to exit the igniter  30  is replaced with side openings  91 ,  FIG. 11   a , to allow the flame to exit from the side of the igniter to initiate the pyrotechnic materials (or the like) of a thermal battery or the like (not shown) that is positioned around the body of the igniter  90 . Alternatively, the igniter housing  92  may be eliminated, thereby allowing the generated ignition flames to directly flow to the sides of the igniter  90  and initiate the pyrotechnic materials of the thermal battery or the like. 
         [0075]      FIG. 12  shows the schematic of a cross-section of another embodiment  100 . This embodiment is similar to the embodiment shown in  FIGS. 4-8 , with the difference that the dead coil section  45  ( FIGS. 4-5 ) is replaced with a solid, preferably relatively very rigid, cylindrical section  101 . The advantage of using a rigid cylindrical section  101  is that the balls  42  ( FIGS. 4-5 ) would not tend to cause the individual coils of the dead coil section  45  to move away from their cylindrically positioned configuration, thereby increasing the probability that the dead coil section could get stuck by the friction forces due to the pressure exerted by the balls  42  to the interior of the housing  34  ( FIG. 4 ) or other similar possible scenarios. 
         [0076]    In certain applications, the required reliability levels for initiation of inertial igniters are extremely high. In certain cases, the igniters should be designed and manufactured to perform their function with extremely high reliability of nearly 100 percent. Some cases may even require the use of multiple and redundant inertial igniters to obtain nearly 100 percent reliability. 
         [0077]    The cost issue is also another important consideration since in small thermal batteries that have to be initiated by inertial igniters, the cost of inertial igniters may easily be a significant portion of the total cost. However, to significantly reduce the cost, inertial igniters have to be designed with fewer and easy to manufacture parts and be easy to assemble. In addition, the inertial igniters must use mass produced and commercially available parts. 
         [0078]    The embodiments of the inertial igniters disclosed below are to provide the aforementioned advantages of the embodiments shown in  FIGS. 4-12  and in addition: (1) provide inertial igniters that are significantly more reliable and easy to manufacture than currently available inertial igniters for thermal batteries or the like, particularly for relatively small thermal batteries that are used in munitions; (2) provide highly reliable and at the same time very small inertial igniters that do not occupy a significant volumes of small thermal batteries; (3) provide inertial igniters that are easy to manufacture and assemble into thermal batteries; and (4) provide inertial igniters that are readily modified to satisfy a wide range of no-fire and all-fire requirements without requiring costly engineering development and manufacturing equipment changes. 
         [0079]    A need exists for novel miniature inertial igniters for thermal batteries used in gun fired munitions, that are extremely reliable, low cost (such as having fewer easy to manufacture parts that are not required to be fabricated to very low tolerances), easy to manufacture and assemble, and easy to assemble into a thermal battery (such as simply “drop-in” component during thermal battery assembly). Such inertial igniters can also be adaptable to a wide range of all-fire and no-fire requirements without requiring a significant amount of engineering development and testing. Such inertial igniters can also be capable of allowing multiple inertial igniters to be readily packed into thermal batteries as redundant initiators to further increase initiation reliability when such extremely high initiation reliability are warranted. Such inertial igniters are particularly needed for small and low power thermal batteries that could be used in fuzing and other similar applications. Such inertial igniters must be safe and in general and in particular they should not initiate if dropped, e.g., from up to 5-7 feet onto a concrete floor for certain applications; should withstand high firing accelerations and do not cause damage to the thermal battery, for example up to 20-50,000 Gs or even more; and should be able to be designed to ignite at specified acceleration levels when subjected to such accelerations for a specified amount of time to match the firing acceleration experienced in a gun barrel as compared to high G accelerations experienced during accidental falls which last for very short periods of time, for example accelerations of the order of 1000 Gs when applied for over 5 msec as experienced in a gun as compared to, for example 2000 G acceleration levels experienced during accidental fall over a concrete floor but which may last only 0.5 msec. 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. 
         [0080]    An isometric cross-sectional view of a sixth embodiment of an inertia igniter is shown in  FIG. 13 , referred to generally with reference numeral  200 . The full isometric view of the inertial igniter  200  is shown in  FIG. 14 . 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 percussion cap primer when used in place of the pyrotechnics, similar to the primer  49  in the embodiment  60  shown in  FIG. 9 . Although illustrated with the opening  204  in the base, the opening (or openings) can alternatively be formed in a side wall as is shown in  FIG. 11   a  or in the striker mass as is shown in  FIG. 10 . 
         [0081]    The base  202  of the housing may be extended to form a cap for the thermal battery, similar to the cap  36  of the thermal battery  37  shown for the embodiment  30  in  FIGS. 4 and 5 . 
         [0082]    A striker mass  205  is shown in its locked position in  FIG. 13 . The striker mass  205  is provided with guides for the posts  203 , such as vertical surfaces  206  (which may be recessed as shown in the embodiment  30  in  FIGS. 4 and 5 ), 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. However, the surfaces  206  minimize the chances of the striker mass  205  jamming as compared to the recesses  40 . Further, manufacturing precision is reduced (for both the posts  203  and the striker mass  205 ) when the surfaces  206  are used in place of the recesses  40 . Consequently, both the striker mass  205  and the inertial igniter structure (which includes the posts  203 ) is easier to produce and less costly when the surfaces  206  are used in place of the recesses  40 . 
         [0083]    In its illustrated position in  FIGS. 13 and 14 , 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. 13 . A setback spring  210 , which is preferably in compression, is also provided around but close to the posts  203  as shown in  FIGS. 13 and 14 . In the configuration shown in  FIG. 13 , 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. 
         [0084]    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. 13 and 14 , or may be provided as an internal surface over the entire inner surface of the collar  211  (not shown). 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 makes the collar stronger and more massive. The advantage of providing a continuous inner recess guiding surface for the locking balls  207  is that it would require fewer machining processes during the collar manufacture. Although only one locking ball  207  is illustrated in  FIG. 13 , more than one can be provided, such as a locking ball  207  associated with each post  203 . More than one locking ball  207  can also be associated with each post  203 . 
         [0085]    The collar  211  rides up and down on the posts  203  as can be seen in  FIGS. 13 and 14 , but is biased to stay in its upper most position as shown in  FIGS. 13 and 14  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. 13 and 14 , the setback spring  210  which is biased (preloaded) to push the collar  211  upward away from the igniter base  201 , 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 can (similar to the top cap  35  in the embodiment  30  of  FIG. 4 ) to prevent the collar  211  from being pushed up and allowing the locking balls  207  from moving out and releasing the striker mass  205 . 
         [0086]    In the sixth embodiment, a one part pyrotechnics compound  215  (such as lead styphnate or other similar compound) can be used as shown in  FIG. 13 . The surfaces to which the pyrotechnic compound  215  is attached can be roughened and/or provided with surface cuts, recesses, projections, or the like and/or treated chemically as commonly done in the art (not shown) to ensure secure attachment of the pyrotechnics material to the applied surfaces. The use of one part pyrotechnics compound makes the manufacturing and assembly process much simpler and thereby leads to lower inertial igniter cost. 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. 13 ), 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 . 
         [0087]    Alternatively, a two-part pyrotechnics compound as shown and described for the embodiment  30  of  FIG. 4  can be used. One part of the two-part pyrotechnics compound  47  ( FIG. 4 ), e.g., potassium chlorate, can be provided on the interior side of the base  32 , such as in a provided recess (not shown) over the exit holes  38 . The second part of the pyrotechnics compound (e.g., red phosphorous)  46  can be provided on the lower surface of the striker mass surface  39  facing the first part of the pyrotechnics compound  47 , as shown in  FIG. 4 . In general, various combinations of pyrotechnic materials can be used for this purpose. One commonly used pyrotechnic material consists of red phosphorous or nano-aluminum, indicated as element  46  in  FIG. 4 , and is used with an appropriate binder (such as vinyl alcohol acetate resin or nitrocellulose) to firmly adhere to the bottom surface of the striker mass  39 . The second component can be potassium chlorate, potassium nitrate, or potassium perchlorate, indicated as element  47  in  FIG. 4 , and is used with a binder (such as, but not limited to vinyl alcohol acetate resin or nitrocellulose) to firmly attach the compound to the surface of the base  32  (such as inside of a recess provided in the base  32 —not shown) as shown in  FIG. 4 . 
         [0088]    Alternatively, instead of using the pyrotechnics compound  215 ,  FIG. 13 , a percussion cap primer or the like (similar to the percussion cap primer  49  used in the embodiment  60  of  FIG. 9 ) can be used. A striker tip (similar to the striker tip  50  shown in  FIG. 9  for the embodiment  60 ) can be provided at the tip  216  of the striker mass  205  (not shown) to facilitate initiation upon impact. 
         [0089]    The basic operation of the embodiment  200  of the inertial igniter of  FIGS. 13 and 14  is similar to that of embodiment  30  ( FIGS. 4-8 ) as previously described. Here again, 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 time in the axial direction  218  imparts a sufficient impulse to the collar  211  (i.e., if an acceleration time profile is greater than a predetermined threshold), 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 . 
         [0090]    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 impeded only by the elastic force of the setback spring  210 , which is easily overcome by the impulse provided to the striker mass  205 . As a result, the striker mass  205  moves 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 (similar to the configuration shown for the embodiment  30  in  FIG. 8 ). 
         [0091]    In the embodiment  200  of the inertial igniter shown in  FIGS. 13 and 14 , 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.). This is in contrast with the helical springs with circular wire cross-sections used in the embodiments of  FIGS. 4-12 . The use of the aforementioned 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 in  FIGS. 13 and 14 ), 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 the present 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. 
         [0092]    It is appreciated by those skilled in the art that 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. 
         [0093]    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. 
         [0094]    The striker mass  205  and striker tip  216  may be a monolithic design with the striking tip  216  being formed, as shown in  FIG. 13 , or as a boss protruding from the striker mass, or the striker tip  216  may be a separate piece, possibly fabricated from a material that is significantly harder than the striker mass material, and pressed or otherwise permanently fixed to the striker mass. A two-piece design would be favorable to the need for a striker whose density is different than steel, but whose tip would remain hard and tough by attaching a steel ball, hemisphere, or other shape to the striker mass. A monolithic design, however, would be generally favorable to manufacturing because of the reduction of part quantity and assembly operations. 
         [0095]    The use of three or more posts  203  in the embodiment  200  of  FIGS. 13 and 14  has several significant advantages over the two post designs of the embodiments of  FIGS. 4-5 . namely, unlike the embodiment  30  of  FIGS. 4 and 5  in which the striker mass  39  is provided with vertical recesses  40  that are used to engage the posts  33  and serve as guides to allow the striker mass  39  to ride down along the length of the posts  33  without rotation, the use of at least three posts  203  in the embodiment  200  of  FIGS. 13 and 14  eliminates the need for the aforementioned vertical recesses in the striker mass  205 . As a result, the chances that the striker mass  203  gets jammed at the interface between the aforementioned vertical recesses ( 40  in  FIGS. 4 and 5 ) and the posts ( 33  in  FIGS. 4 and 5 ) are almost entirely eliminated. As a result, the reliability of the inertial igniter is significantly increased. Furthermore, the design of the striker mass and the igniter posts and their required manufacturing process are significantly simplified and the required manufacturing precision is also reduced. As a result, the manufacturing cost of the striker mass as well as the igniter body is significantly reduced. Still further, the contacting surfaces between the striker mass  205  and the posts  203  is increased, thereby allowing for a smoother up and down movement of the striker mass  205  along the inner surfaces of the posts  203 . 
         [0096]    In the embodiment  200  of  FIGS. 13 and 14 , following ignition of the pyrotechnics compound  215 , the generated flames and sparks are designed to exit downward through the opening  204  to initiate the thermal battery below. Alternatively, if the thermal battery is positioned above the inertial igniter  200 , the opening  204  can be eliminated and the striker mass could be provided with at least one opening similar to the passage  81  of the striker mass  82  of the embodiment  80  of  FIG. 10  to guide the ignition flame and sparks up through the striker mass  205  to allow the pyrotechnic materials (or the like) of a thermal battery (or the like) positioned above the inertial igniter  200  (not shown) to be initiated. 
         [0097]    Alternatively, in a manner similar to that shown in the embodiment  90  of  FIGS. 11   a  and  11   b , side ports (openings  91 ) may be provided to allow the flame to exit from the side of the igniter to initiate the pyrotechnic materials (or the like) of a thermal battery or the like that is positioned around the body of the inertial igniter. Alternatively, the igniter housing  261  ( FIG. 16 ) may be eliminated, thereby allowing the generated ignition flames to directly flow to the sides of the igniter  200  and initiate the pyrotechnic materials of the thermal battery or the like. 
         [0098]    In  FIGS. 13 and 14 , the inertial igniter embodiment  200  is shown without any outside housing. In many applications, as shown in the schematics of  FIG. 15   a  ( 15   b ), the inertial igniter  240  ( 250 ) is placed securely inside the thermal battery  241  ( 251 ), either on the top ( FIG. 15   a ) or bottom ( FIG. 15   b ) of the thermal battery housing  242  ( 252 ). This is particularly the case for relatively small thermal batteries. In such thermal battery configurations, since the inertial igniter  240  ( 250 ) is inside the hermetically sealed thermal battery  241  ( 251 ), there is no need for a separate housing to be provided for the inertial igniter itself. In this assembly configuration, the thermal battery housing  242  ( 252 ) is provided with a separate compartment  243  ( 253 ) for the inertial igniter. The inertial igniter compartment  243  ( 253 ) is preferably formed by a member  244  ( 254 ) which is fixed to the inner surface of the thermal battery housing  242  ( 253 ), preferably by welding, brazing or very strong adhesives or the like. The separating member  244  ( 254 ) is provided with an opening  245  ( 255 ) to allow the generated flame and sparks following the initiation of the inertial igniter  240  ( 250 ) to enter the thermal battery compartment  246  ( 256 ) to activate the thermal battery  241  ( 251 ). The separating member  244  ( 254 ) and its attachment to the internal surface of the thermal battery housing  242  ( 252 ) must be strong enough to withstand the forces generated by the firing acceleration. 
         [0099]    For larger thermal batteries, a separate compartment (similar to the compartment  10  over or possibly under the thermal battery hosing  11  as shown in  FIG. 1  can be provided above, inside or under the thermal battery housing for the inertial igniter. An appropriate opening (similar to the opening  12  in  FIG. 1 ) can also be provided to allow the flame and sparks generated as a result of inertial igniter initiation to enter the thermal battery compartment (similar to the compartment  14  in  FIG. 1 ) and activate the thermal battery. 
         [0100]    The inertial igniter  200 ,  FIGS. 13 and 14  may also be provided with a housing  260  as shown in  FIG. 16 . The housing  260  is preferably one piece and fixed to the base  202  of the inertial igniter structure  201 , preferably by soldering, laser welding or appropriate epoxy adhesive or any other of the commonly used techniques to achieve a sealed compartment. The housing  260  may also be crimped to the base  202  as shown in  FIG. 16  for the inertial igniter embodiment  30 . The housing  260  may also be crimped to the base  202  at its open end  261 , in which case the base  202  is preferably provided with an appropriate recess  262  to receive the crimped portion  261  of the housing  260 . The housing can be sealed at or near the crimped region via one of the commonly used techniques such as those described above. 
         [0101]    In addition, as shown in  FIG. 17 , the base  202  of the inertial igniter  200  may be extended to form the cap  263 , which could be used to form the top cap of the thermal battery as is shown in  FIG. 5   c  and identified with the numeral  36  for the inertial igniter embodiment  30 . 
         [0102]    The inertial igniter embodiment  200  of  FIGS. 13 and 14  as provided with the aforementioned housing  260  and shown in  FIG. 16  may also be hermetically sealed. To this end, and as shown in  FIG. 18 , the opening  204  can be covered, preferably with a thin membrane  264 . The membrane  264  can be an integral part of the base  202  and is scorched on its bottom surface (not seen in the view of  FIG. 18 ) to assist it to break open by the pressure generated by the initiation of the pyrotechnics compound  215  ( FIG. 13 ) upon initiation of the inertial igniter to allow the generated flame and sparks to enter the thermal battery through the resulting opening. 
         [0103]    In another embodiment, more than one inertial igniter, preferably inertial igniters of the embodiment  200  type are used in a thermal battery to significantly increase the overall reliability of the thermal battery initiation under all-fire condition. As a result, if for any reason one of the inertial igniters fails to initiate or fails to initiate the thermal battery, then there would be one or more (redundant) inertial igniters to significantly reduce the chances that the thermal battery would fail to be activated. The more than one inertial igniters (preferably of embodiment  200  or any other of the aforementioned embodiments) may in general be assembled in any appropriate configuration in the thermal battery. For the case of small thermal batteries, however and if the thermal battery size allows, the inertial igniters are preferably ganged up together in one location, for example on the top or bottom compartments shown in  FIGS. 15   a  and  15   b  or in the compartment  10  shown in  FIG. 1 , to minimize the total volume and size occupied by the inertial igniters. For example, when three inertial igniters of the embodiment  200  are to be assembled within a thermal battery, for example of the type shown in  FIG. 15   a , assuming that the amount of space available in the compartment  243  is appropriate, the three inertial igniters  200  may be ganged up inside the compartment  243  as shown in the top view of  FIG. 19  (the top cap is removed to show the inertial igniters  200  inside the compartment  243 ). 
         [0104]    When more than one inertial igniter  200  (or of other embodiment types) are ganged up in a compartment similar to that of  243  as shown in  FIG. 19 , the body  201  of two or more of the inertial igniters  200  may be integral. For example, the bodies  201  of the three inertial igniters  200  shown in  FIG. 19  may be integral as shown in the top and isometric views of  FIGS. 20   a  and  20   b , respectively, and identified with reference numeral  265 . 
         [0105]    In certain applications, it is desired that the inertial igniters ganged up in a compartment such as  243  as shown in  FIG. 19  be separated by a wall so that their operations and/or failure (such as flying pieces following initiation or break up of one igniter) would not interfere with the operation of the remaining inertial igniters. In such cases, the inertial igniter bodies (such as the bodies  201  of the inertial igniters  200 ,  FIGS. 13 and 19 ) and the separation walls  206  between at least two of the inertial igniters may be integral as shown in the isometric and top views of  FIGS. 21   a  and  21   b , respectively, and indicated by reference numeral  266 . In the drawings of  FIGS. 21   a  and  21   b , all three inertial igniters  200  are intended to be separated from each other by the walls  267 . 
         [0106]    The present inertial igniters are designed such that when ganged up as shown in  FIG. 20   a  or  FIG. 21   a , their integral bodies  201  can be readily machined, for example from a solid rod, using commonly used CNC machining centers or the like. 
         [0107]    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.