Abstract:
An inertia igniter including a mechanical delay mechanism having two or more members which are movable under different acceleration conditions to sequentially move a movable member upon sequential movement of the two or more members and an ignition member actuatable by the movable member such that movement of the movable member by the two or more members ignites the ignition member. The movable member can be movable by one of translation and rotation. The inertia igniter can further comprise an impact mass releasably movable in the housing, wherein the impact mass is released and movable by movement of the movable member to impact the ignition member. The inertia igniter can also further comprise a stop member for preventing movement of the impact mass until the movable member has moved a predetermined distance.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to U.S. provisional patent application, Ser. No. 60/835,023, filed on Aug. 2, 2006, 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 multi-stage acceleration (deceleration) operated mechanical delay mechanisms, and more particularly for inertial igniters for thermal batteries used in gun-fired munitions and other similar applications. 
         [0004]    2. Prior Art 
         [0005]    Thermal batteries represent a class of reserve batteries that operate at high temperatures. 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]    A schematic of a cross-section of a thermal battery and inertial igniter assembly of the prior art is shown in  FIG. 1 . In thermal battery applications, the inertial igniter  10  (as assembled in a housing) is either positioned above the thermal battery housing  11  as shown in  FIG. 1  or within the thermal battery itself (not shown). When positioned outside the thermal battery 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. When the inertial igniter is positioned inside the thermal battery itself, the total volume of the igniter must be reduced to minimally add to the total volume of the thermal battery. 
         [0011]    With currently available inertial igniters of the prior art (e.g., produced by Eagle Picher Technologies, LLC), a schematic of which is shown in  FIG. 2 , the inertial igniter  20  has to be positioned within a housing  21  as shown in  FIG. 3 . 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 . 
         [0012]    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). 
         [0013]    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. 
         [0014]    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  ( 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 
       [0015]    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 described herein is a mechanical delay mechanism, which responds to acceleration applied to the inertial igniter. If the applied acceleration reaches or passes the designed initiation levels and if its duration is long enough, i.e., larger than any expected to be experienced as the result of accidental drops or explosions in their vicinity or other non-firing events, i.e., if the resulting impulse levels are lower than those indicating gun-firing, then the delay mechanism returns to its original pre-acceleration configuration, and a separate initiation system is not actuated or released to provide ignition of the pyrotechnics. Otherwise, the separate initiation system is actuated or released to provide ignition of the pyrotechnics. 
         [0016]    Inertia-based igniters must therefore comprise two components so that together they provide the aforementioned mechanical safety (mechanical delay mechanism) and to provide the required striking action to achieve ignition of the pyrotechnic elements. The function of the safety system is to prevent the striker mechanism to initiate the pyrotechnic, i.e., to delay full actuation or release of the striker mechanism until a specified acceleration time profile has been experienced. The safety system should then fully actuate or release the striker, allowing it to accelerate toward its target under the influence of the remaining portion of the specified acceleration time profile and/or certain spring provided force. The ignition itself may take place as a result of striker impact, or simply contact or proximity or a rubbing action. 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 or a rubbing will set off a reaction resulting in the desired ignition. 
         [0017]    Herein is described multi-stage mechanical delay mechanisms that provide very long time delays (as compared to prior art mechanisms) when subjected to acceleration in a specified direction in very small size and volume packages (as compared to prior art mechanisms). The mechanisms take advantage of the quadratic nature of time and the distance traveled under an applied acceleration. The mechanisms are particularly suitable for inertial igniters. Also disclosed are a number of inertial igniter embodiments that combine such mechanical delay mechanisms (safety systems) with impact or rubbing or contact based initiation systems. 
         [0018]    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: 
         [0019]    1. The device must fire when given a [square] pulse acceleration of 900 G±150 G for 15 ms in the setback direction. 
         [0020]    2. The device must not fire when given a [square] pulse acceleration of 2000 G for 0.5 ms in any direction. 
         [0021]    3. The device must not actuate when given a ½-sine pulse acceleration of 490 G (peak) with a maximum duration of 4 ms. 
         [0022]    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. 
         [0023]    A need therefore exists for the development of novel methods and resulting mechanical delay mechanisms for 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 that occupy very small volumes and eliminate the need for external power sources. The development of such novel miniature inertial ignition mechanism concepts also requires the identification or design of appropriate pyrotechnics and their initiation mechanisms. The innovative inertial igniters would preferably be scalable to thermal batteries of various sizes, in particular to miniaturized igniters for small size thermal batteries. Such inertial igniters must in general be safe 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 and in certain cases over 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. 
         [0024]    To ensure safety and reliability, inertial igniters should not initiate during acceleration events which may occur during manufacture, assembly, handling, transport, accidental drops, or other similar accidental events. 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. 
         [0025]    Those skilled in the art will appreciate that the basic novel method for the development of multi-stage mechanical time delay mechanisms, the resulting mechanical time delay mechanisms, and the resulting inertial igniters disclosed herein may provide one or more of the following advantages over prior art mechanical time delay mechanisms and resulting inertial igniters in addition to the previously indicated advantages: 
         [0026]    provide mechanical time delay mechanisms that are significantly shorter and occupy significantly less volume than currently available one stage mechanical time delay mechanisms; 
         [0027]    provide mechanical time delay mechanisms with almost any possible time delay period that may be required for inertial igniters and other similar applications; 
         [0028]    provide inertial igniters that are significantly shorter than currently available inertial igniters for thermal batteries or the like, particularly for relatively small thermal batteries to be used in munitions without occupying very large volumes; 
         [0029]    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 for the inertial igniter assembly; 
         [0030]    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; and 
         [0031]    provide inertial igniters that can be sealed to simplify storage and increase their shelf life. 
         [0032]    In this disclosure, a novel and basic method is presented that can be used to develop highly compact and long delay time mechanisms for miniature inertial igniters for thermal batteries and the like. The method is based on a “domino” type of sequential displacement or rotation of inertial elements to achieve very large total displacements in a compact space. In this process, one inertial element must complete its motion due to the imparted impulse before the next element is released to start its motion. As a result, the maximum speed that is reached by each element is controlled, thereby allowing the system to achieve maximum delay times. This process is particularly effective in reducing the required length (angle) of travel of the aforementioned inertial elements due to the aforementioned quadratic nature of time and the distance traveled by an inertial element under an applied acceleration. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    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: 
           [0034]      FIG. 1  illustrates a schematic of a thermal battery and inertial igniter assembly of the prior art. 
           [0035]      FIG. 2  illustrates a schematic of a cross-section of an inertial igniter of the prior art 
           [0036]      FIG. 3  illustrates a partial schematic of the thermal battery and inertial igniter assembly of the prior art with the inertial igniter of  FIG. 2  disposed therein. 
           [0037]      FIG. 4  illustrates a schematic of a cross-section of an embodiment of an inertia igniter. 
           [0038]      FIG. 5   a  illustrates an isometric view of an embodiment of a multi-stage mechanical delay mechanism. 
           [0039]      FIGS. 5   b - 5   d  illustrate the multi-stage mechanical delay mechanism of  FIG. 5   a  in various stages of acceleration. 
           [0040]      FIG. 6  illustrates an expansion constrained mass-spring model for evaluating delay time as a function of total vertical distance that the inertial (mass) element(s) of the various mechanical delay mechanisms have to travel due to the vertical travel distance of the inertial elements of the igniter. 
           [0041]      FIG. 7  illustrates a plot of the expansion constrained mass-spring model of  FIG. 6  where a 2000 G pulse is applied to the base for 0.5 millisecond duration. 
           [0042]      FIGS. 8   a  and  8   b  illustrate an isometric view of another embodiment of a multi-stage mechanical delay mechanism with  FIG. 8   b  being illustrated without its housing. 
           [0043]      FIGS. 8   c - 8   f  illustrate the multi-stage mechanical delay mechanism of  FIGS. 8 and 8   a  in various stages of acceleration. 
           [0044]      FIG. 9   a  illustrates an isometric view of an embodiment of an inertia igniter including the multi-stage mechanical delay mechanism striker of  FIG. 5   a  configured to initiate pyrotechnic materials. 
           [0045]      FIGS. 9   b - 9   e  illustrate the inertia igniter of  FIG. 9   a  in various stages of acceleration. 
           [0046]      FIGS. 10   a  and  10   b  illustrate isometric views of another embodiment of an inertia igniter configured to initiate pyrotechnic materials, where  FIG. 10   a  illustrates the inertia igniter without a top cover and  FIG. 10   b  is a cut-away illustration to clearly show its internal components. 
           [0047]      FIGS. 10   c - 10   e  illustrate the inertia igniter of  FIG. 10   a  in various stages of acceleration. 
           [0048]      FIG. 11   a  illustrates an isometric view of yet another embodiment of an inertia igniter configured to initiate pyrotechnic materials. 
           [0049]      FIG. 11   b  illustrates a sectional view of  FIG. 11   a  as taken along line A-A in  FIG. 11   a.    
           [0050]      FIGS. 11   c - 11   d  illustrate the inertia igniter of  FIG. 11   a  in various stages of acceleration. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0051]    A schematic of an embodiment of an inertial igniter design which reduces the height of the inertial igniter component  13  ( FIG. 1 ) is shown in  FIG. 4 . In such embodiment, the height  13  is reduced by over 45% as compared to the height required for the currently available igniters shown in  FIG. 2  (see U.S. patent application Ser. No. 11/599,878, filed on Nov. 15, 2006, the contents of which is incorporated herein by its reference). In  FIG. 4 , the schematic of a cross-section of an embodiment  30  of the inertia igniter is shown, which is referred to generally with reference numeral  30 . The inertial igniter  30  is constructed with an igniter body  31  and a housing wall  32 . In the schematic of  FIG. 4 , the igniter body  31  and the housing wall  32  are joined together at one end; however, the two components may be integrated as one piece. In addition, the base of the housing  31  may be extended to form the cap  33  of the thermal battery  34 , the top portion of which is shown with dashed lines in  FIG. 4 . The base of the housing  31  is provided with a recess  35  to receive the percussion cap primer  37  (two component pyrotechnic compounds may be used instead). The base of the housing  31  is also provided with the opening  36  within the recess  35  to allow the ignited sparks and fire to exit the primer  37  into the thermal battery  34  upon initiation of the percussion cap primer  37 . The internal components of the inertial igniter  30  are sealed by a cap  42  which can be fastened by any means known in the art or adhered by brazing or welding at seam  42   a  or applied with a suitable adhesive. 
         [0052]    Integral to the igniter housing  31  is a cylindrical part  38  (or bodies with other cross-sectional shapes) having a wall defining a cavity, within which a striker mass  39  can travel up and down. The striker mass  39  is however biased to stay in its upper most position as shown in  FIG. 4  by a striker spring  41 . In its illustrated position, the striker mass  39  is locked in its axial position to the cylindrical part  38  of the housing  31  of the inertial igniter  30  by at least one locking ball  43 . The setback locking ball  43  locks the striker mass  39  to the cylindrical part  38  of the housing  31  through the holes  45  provided on the cylindrical part  38  of the housing  31  and a concave portion such as a groove (or dimple)  44  on the striker mass  39  as shown in  FIG. 4 . In the configuration shown in  FIG. 4 , the locking balls  43  are prevented from moving away from their aforementioned locking position by the cylindrical setback collar  46 . The cylindrical setback collar  46  can ride on the outer surface of the cylindrical part  38  of the housing  31 , but is biased to stay in its upper most position as shown in the schematic of  FIG. 4  by the setback spring  48 . The cylindrical setback collar  46  has a concave portion such as an upper enlarged shoulder portion  47 , within which the locking balls  43  loosely fit and are kept in their aforementioned position locking the striker mass  39  to the cylindrical part  38  of the housing  31 . The striker mass  39  has a tip  40 , which upon release of the striker mass and appropriate level of acceleration for the striker mass  39  to overcome the resisting force of the striker spring  41  and strike the percussion cap primer  37  with enough momentum, would initiate the percussion cap primer  37 . 
         [0053]    The basic operation of the disclosed inertial igniter  30  is as follows. Any non-trivial acceleration in the axial direction  49  which can cause the cylindrical setback collar  46  to overcome the resisting force of the setback spring  48  will initiate and sustain some downward motion of only the setback collar  46 . The force due to the acceleration on the striker mass  39  is supported by the locking balls  43  which are constrained by the shoulder  47  of the setback collar  46  to engage the striker mass. 
         [0054]    If an acceleration time in the axial direction  49  imparts a sufficient impulse to the setback collar  46  (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  43  are no longer constrained to engage the striker mass  39  to the cylindrical part  38  of the housing  31 . If the acceleration event is not sufficient to provide this motion (i.e., the acceleration time profile is less than the predetermined threshold), the setback collar will return to its start position under the force of the setback spring. 
         [0055]    Assuming that the acceleration time profile was at or above the specified “all-fire” profile, the setback collar  46  will have translated down full-stroke, allowing the striker mass  39  to accelerate down towards the percussion cap primer  37 . In such a situation, since the locking balls  43  are no longer constrained by the shoulder  42  of the setback collar  46 , the downward force that the striker mass  39  has been exerting on the locking balls  43  will force the locking balls  43  to move in the radial direction toward the housing wall  32 . Once the locking balls  43  are tangent to the outermost surface of the striker mass  39 , the downward motion of the striker mass  39  is impeded only by the elastic force of the striker spring  41 , which is easily overcome by the impulse provided to the striker mass  39 . As a result, the striker mass  39  moves downward, causing the tip  40  of the striker mass  39  to strike the target percussion cap primer  37  with the requisite energy to initiate ignition. 
         [0056]    As previously described, the safety mechanisms can be thought of as a time delay mechanism, after which a separate initiation system is actuated or released to provide ignition of the igniter pyrotechnics. In the designs of  FIGS. 2 and 4 , purely mechanical safety delay mechanism are used that operate based on the total length of travel of certain inertial elements (inertial element  66  in the device of  FIG. 2  and the inertial element  46  in the device of  FIG. 4 ), and the corresponding total amount of travel time of the said inertial elements that operate or release the ignition mechanism. To base a delay mechanism on the travel (translational, rotational or their combination) of a single inertial element is tantamount to limiting the axial compactness achievable because of the necessary and significant stroke length required to achieve the requisite delay timing. 
         [0057]    The novel method to achieve highly compact and long delay time mechanisms for miniature inertial igniters for thermal batteries and the like may be best described by the following “finger-driven wedge design,” which is a multi-stage mechanical delay mechanism embodiment and its basic operation. The schematic of such a three-stage embodiment  80  is shown in  FIG. 5   a . The device  80  can obviously be designed with as many fingers (stages) as is required to accommodate any delay time requirement and no-fire specifications commonly seen in gun-fired munitions or the like. The mechanism generally has three fingers (stages)  81 ,  82  and  83 , each of which provides a specified amount of delay when subjected to a certain amount of acceleration (in the vertical direction of the arrow  89  as viewed in  FIG. 5   a ). The fingers are fixed to the mechanism base  84  on one end. Each finger is provided with certain amount of mass and deflection resisting elasticity (in this case in bending). Certain amount of upward preloading may also be provided to delay finger deflection until a desired acceleration level is reached. When at rest, only the first finger  81  is resting on the sloped surface  87  of the delay wedge  85 . The delay wedge  85  is preferably provided with a resisting spring  88  to bring the system back to its rest position, if the applied acceleration profile is within the no-fire regime of the inertial igniter and to offer more programmability for the device. The delay wedge  85  is positioned in a guide  86  which restricts the delay wedge&#39;s  85  motion along the guide  86 . 
         [0058]    The operation of the device  80  is as follows. At rest, the delay wedge  85  is biased to the right by the delay wedge spring  88 , and the three fingers  81 ,  82  and  83  are biased upwards with some pre-load. The ratio of pre-load to effective finger mass will determine the acceleration threshold below which there will be no relative movement between components. The positions of the three fingers  81 ,  82  and  83  are such that finger  81  is above the sloped surface  87  of the delay wedge  85  and fingers  82  and  83  are supported by the top surface  90  of the delay wedge  85 , and are prevented from moving until the delay wedge  85  has advanced the prescribed distance. This is illustrated in  FIG. 5   a.    
         [0059]    If the device  80  experiences an acceleration in the direction  89  above the threshold determined by the ratio of initial resistances (elastic pre-loads) to effective component masses, the primary finger  81  will act against the sloped surface  87  of the delay wedge  85 , advancing the delay wedge  85  to the left. 
         [0060]      FIG. 5   b  shows the first finger  81  fully actuated and the delay wedge  85  advanced one-third of its total finger-actuated travel distance. At this instant, the second finger  82  is no longer supported by the top surface  90  of the delay wedge  85  and is free to move downwards provided that the acceleration is still sufficiently high to overcome the preload for the second finger  82  and the delay wedge spring  88  force at the aforementioned one-third travel distance. 
         [0061]    If the acceleration continues at an all-fire profile, the second finger  85  will drive the delay wedge to two-thirds of its total finger-actuated travel distance, allowing the third finger  83  to act on the top surface  90  of the delay wedge  85 . This is shown in  FIG. 5   c.    
         [0062]    If the acceleration terminates or falls below the all-fire requirements, the mechanism will reverse until balance is achieved between the acceleration reaction forces and the elastic resistances. This may be a partial or complete reset from which the mechanism may be re-advanced if an all-fire profile is applied or resumed. 
         [0063]    Full actuation of the mechanism will occur once all three fingers  81 ,  82  and  83  have driven the delay wedge  85  to its full travel in succession. This non-linear progression will be carried out as a continuation of the partial actuations described above. The full actuation of such a mechanism is shown in  FIG. 5   d.    
         [0064]    Obviously, the amount of preloading and/or resistance to bending of the fingers  81 ,  82 ,  83  vary such that the first finger  81  bends under a certain acceleration profile, finger  82  bends under a larger acceleration profile than the first finger  81  and the third finger  83  bends under the largest acceleration profile. Furthermore, the delay wedge  85  can be configured to provide the ignition of the thermal battery upon full activation. 
         [0065]    The above multi-stage mechanical delay mechanism  80  may obviously be configured in a wide variety of configurations with the common characteristics of providing the means for sequential travel of two or more inertial elements under an applied acceleration. This novel method of providing a mechanical time delay mechanism via sequential travel of inertial elements provides devices that occupy very short heights while achieving very long time delays. The significance of the multi-stage design in reducing the height of the mechanical time delay mechanisms, thereby the size (particularly the height) of inertial igniters can be described as follows. 
         [0066]    The mathematical model that can be used to evaluate the delay time as a function of the total vertical distance that the inertial (mass) element(s) of the various mechanical delay mechanisms have to travel due to the vertical travel distance of the inertial elements of the igniter, i.e., the minimum height of the device and thereby the resulting inertial igniter, is based on an expansion constrained mass-spring model as shown in  FIG. 6 , consisting of a mass (inertia) element  101  and spring element  102 . The spring element  102  is attached to the base  103 , which in turn is fixed to the accelerating platform  105 . The spring element  102  is preloaded in compression, and is constrained to expand from its preloaded position shown in  FIG. 6  by the stop  107 , which is fixed to the accelerating platform  105 . 
         [0067]    When the base is accelerated upwards in the direction of the arrow  106 , the mass  101  will experience a reaction force downward. Since the spring  102  is preloaded in compression, a threshold will exist below which the reaction force on the mass will not be high enough to deflect the spring from its preloaded position. Beyond this acceleration threshold, the mass  101  will move downward. For relatively high preloads and relatively small spring  102  deflections (such as those employed in the described miniature inertia igniters) the spring  102  force can be assumed to be constant throughout the deflection. The net force on the mass is then equal to the difference between the reaction force from the acceleration and the constant spring force. 
         [0068]    To generate a generic model applicable to a system without a predetermined mass or spring rate, the preload force may be expressed in terms of a force equivalent to the supported mass under some acceleration 
         [0000]    
       
      
       F 
       p 
       =m A 
       p  
       g  
      
     
         [0000]    where F p  is the preload force, A p  is the equivalent preload acceleration magnitude in G&#39;s, and g is the gravitational acceleration constant. This acceleration, A p , may now be subtracted from the acceleration which is producing the reaction force on the mass  101 . In other words, we specify the preload not in terms of force, but in terms of the threshold of acceleration below which there will be no spring  102  deflection. If the net equivalent acceleration on the mass  101  in G&#39;s is A, the displacement of the mass  101 , i.e., the deflection of the spring  102 , y, as a function of time t, can be expressed as 
         [0000]        y= ½ A g t   2   (1)
 
         [0069]    Now, from the equation (1) we can compare the necessary axial displacement of the inertial elements (mass  101  in the model of  FIG. 6 ) in a single stage mechanical delay mechanism with the axial displacement of the inertial elements (mass  101  in the model of  FIG. 6 ) in a multi-stage mechanical delay mechanism. In the plot of  FIG. 7 , a 2000 G pulse is considered to be applied to the base  103  in the direction of the arrow  106  for 0.5 millisecond duration. The mass elements  101  in both mechanical delay mechanisms are supported by constant-force springs  102  with preload forces equivalent to a movement threshold of 700 G. The vertical displacement of the mass (inertial) elements  101  have been scaled such that the displacement of the mass  101  in the single-stage mechanical delay mechanism (indicated by the curve  110  in the plot of  FIG. 7 ) at the end of the aforementioned acceleration pulse has a magnitude of one. Considering a three-stage mechanical delay mechanism, the vertical displacement of the first, second and third mass elements  101  of the first, second and third stages are shown in  FIG. 7  by the curves  111 ,  112  and  113 , respectively. The total vertical displacement required for the three stages (in fact for any number of stages) of a multi-stage mechanical delay mechanism is seen to be limited to the displacement of one of its stages alone. From the plot, the advantage of the three-stage design is clear: the total vertical displacement of a three-stage design nearly 90% smaller than that of the single-stage (currently available) designs. 
         [0070]    It is noted that the reason behind a significant advantage of the disclosed multi-stage inertial mechanical delay mechanisms is the fact that for a single mass subjected to an acceleration, the resulting displacement is a quadratic function of the time of travel, equation (1) above. A quadratic function, curve  110  in  FIG. 7 , is more or less flat at the beginning, i.e., during the first relatively small intervals of time the displacement is small since the inertial element  101  has not gained a considerable amount of velocity. The present multi-stage inertial igniters take advantage of this characteristic of the aforementioned quadratic delay time vs. displacement relationship, equation (1), by limiting the total (vertical) displacement of the inertial elements  101  of each individual stage, thereby achieving very small vertical height requirement. 
         [0071]    The mechanical delay mechanisms, such as the one shown schematically in  FIG. 5 , provide a high degree of design flexibility and programmability with the following parameters that can be used to tune the device for performance to meet requirements in a broad range of applications: 
         [0072]    Delay wedge interface angle 
         [0073]    Delay wedge resistance spring rate 
         [0074]    Delay wedge pre-load force 
         [0075]    Delay wedge mass 
         [0076]    The effective mass of each finger may be prescribed individually. 
         [0077]    The spring rate of each finger may be prescribed individually. 
         [0078]    The pre-load force of each finger may be prescribed individually. 
         [0079]    The number of drive fingers (stages) in the design. 
         [0080]    The distance through which fingers displace to advance the delay wedge. 
         [0081]    The mechanical delay mechanisms developed based on the disclosed novel method may be applied in a variety of embodiments to a large number of initiation systems such as to inertial igniters through a plurality of locking mechanisms. Several of such embodiments and their combinations are described herein. 
         [0082]    It is noted that the present method and the resulting mechanical delay mechanisms do not rely on dry friction or viscous or any other type of damping elements to achieve time delay. This is a significant advantage of the present novel method and the resulting mechanical delay mechanisms since friction and damping forces, particularly friction forces, are highly unpredictable or require velocity gain (large displacements) for effectiveness. In addition, the characteristics of friction and damping elements generally change with time, thereby resulting in relatively short shelf life for such devices. 
         [0083]    However, if shelf life and/or performance precision are not an issue, friction and/or viscous damping element(s) of some kind may be used together with the spring elements (preferably in parallel with the spring elements  102 ,  FIG. 6 , not shown) in one or more stages of the mechanical delay mechanism to slow down the motion of one inertial elements. The dry friction elements (such as braking elements) are well known in the art. Viscous damping elements operating based on fluid or gaseous flow through orifices of some kind or a number of other designs using the fluid or gas viscosity, or the use of viscoelastic (elastomers and polymers of various kind and designs) are also well known in the art. 
         [0084]    However, the use of any of the aforementioned viscous damping elements has several practical problems for use in inertial igniters for thermal batteries that are to be used in munitions. Firstly, to generate a significant amount of damping force to oppose the acceleration generated forces, the inertial element must have gained a significant amount of velocity since damping force is proportional to the attained velocity of the inertial element. This means that the element must have traveled long enough time and distance to attain a high enough velocity, thereby resulting in too long igniters. Secondly, fluid or gaseous based damping elements and viscoelastic elements that could be used to provide enough damping to achieve a significant amount of delay time cannot usually provide the desired shelf life of up to 20 years as required for most munitions. 
         [0085]    The schematic of another embodiment  120  of the present invention is shown in  FIG. 8   a . In  FIG. 8   b , the housing  130  of the mechanical delay mechanism  120  is removed to show its internal components. In this embodiment, a closed-profile carriage element  121  is used instead of an open profile delay wedge  85  of the embodiment of  FIG. 5 . The closed-profile carriage element  121  is constrained to longitudinal translation between the guides  127  and the bottom wall  129  and top wall  131  of the housing  130  of the mechanical delay mechanism  120 . The closed-profile carriage element  121  provides an anti-back-drive multi-stage mechanical delay mechanism that operates in a manner similar to the embodiment of  FIG. 5 . With the provision of the closed-profile carriage element  121 , the engaging fingers (stages),  123  and  124  and  125  and  126  in  FIG. 8   b , prevent the closed-profile carriage element  121  to translate along its longitudinal guides  127  if subjected to acceleration in the said direction. This characteristic of this mechanical delay mechanism allows it to withstand high centripetal accelerations experienced by spin-stabilized projectiles, and not to activate by not allowing the closed-profile carriage element  121  to displace under such longitudinal accelerations. 
         [0086]    The fingers  123 ,  124 ,  125  and  126  are fixed on one end to the wall  128  of the housing  130 . A spring element  122  (shown as a bending beam type of spring), attached on one end to the wall  128  of the housing  130  and on the other end to the closed-profile carriage element  121 , which is preferably preloaded, is used to bias the closed-profile carriage element  121  against the last finger  123  to the right. 
         [0087]    When subjected to acceleration in the direction of the arrow  132 , the mechanical delay mechanism  120  will operate as follows: At rest, the mechanical delay mechanism  120  is configured as shown in  FIG. 8   b , with all four delay fingers  123 ,  124 ,  125  and  126  pre-loaded upwards inside the closed-profile carriage element  121 . The lateral stiffness of the delay fingers prevents the bending drive spring  122  from displacing the closed-profile carriage element  121 . Upon experiencing an acceleration great enough to overcome the preload of the first bending finger  126 , this first finger will begin to move downwards out of the closed-profile carriage element  121 . All other fingers  125 ,  123  and  123  are prevented from displacing vertically by the closed-profile carriage element  121  floor  133 . Once the first (stage) finger  126  has exited the carriage  121 , the bending drive spring  122  will advance the carriage  121  until the second (stage) bending finger  125  contacts the carriage  122  face  134 . The carriage  121  will now come to rest. The result of this first-stage actuation is shown in  FIG. 8   c.    
         [0088]    Now that the second finger  125  is no longer supported by the carriage floor  133 , if the acceleration is great enough to overcome the preload of the second finger  125 , this finger will begin to move down in a manner similar to the finger  126  in the first stage. The result of this and subsequent stages are shown in  FIGS. 8   d - f.    
         [0089]    As can be observed, the mechanical delay mechanism  120  makes use of multiple stages and lateral displacement of the carriage  121  to control the delay characteristics (this leads to great vertical compactness), but is not sensitive to lateral forces which may back-drive the carriage  121 . 
         [0090]    As previously stated, any one of the multi-stage mechanical delay mechanisms developed using the present novel method, such as those of the embodiments shown in  FIGS. 5 and 8 , can be readily mated with an appropriate striker mechanism to initiate the pyrotechnic materials of the resulting inertial igniter. The schematic of one embodiment  140  of such an inertial igniter is shown in  FIG. 9   a . In this embodiment  140 , the mechanical delay mechanism  80  illustrated in  FIGS. 5   a - 5   d  is indicated as segment  141  of the inertial igniter  140 , is used with an attached striker portion, indicated as  142 . The multi-stage mechanical delay mechanism shown has three stages with three fingers  143 ,  144  and  145 , a delay wedge  146  and resisting spring  147 , all mounted on the base structure  148  and operating as described for the embodiment of  FIG. 5 . The striker portion  142  consists of an extension  149  of the base structure  148  of the mechanical delay mechanism; and a striker mass  152 , which when free could traverse the guide  155 , and is normally attached to the sides of the guide  155  with an appropriately sized shear pin  153 . In the schematic of  FIG. 9   a , two part pyrotechnic components  151  and  150  are shown to be attached to the striker mass  152  and the end piece  154  of the base structure  149 . If a one piece pyrotechnic element or a percussion primer is used, they are preferably attached to the end piece  154  with the initiation pin (if necessary) attached to the striker mass  152 . 
         [0091]    The operation of the mechanical delay portion  141  is identical to that of the embodiment of  FIG. 5 . In this embodiment, however, the spring element  147 , which resists the progression of the delay wedge  146 , serves also as the spring for the striker mass  152 . In FIG.  9   a  the inertial igniter  140  is shown at rest. The direction of the acceleration that the inertial igniter is subjected to during the munitions firing is shown by the arrow  156 . The operation of the striker system is described as follows. In the event of an all-fire acceleration profile, the delay wedge  146  is driven to the left first by the first stage finger  143 , then by the second stage finger  144  and then by the third stage finger  145 , while potential energy is being stored in the spring element  147  due to its compression as shown sequentially in  FIGS. 9   b - d . The device can be designed such that the shear pin  153  (or other anchoring element which is securing the striker mass  152  to the structure  149 ) will fail when the force developed in the spring element  147  is indicative of full actuation of the delay wedge  146 . The fingers  143 ,  144  and  145 , still under the influence of the all-fire acceleration profile, will keep the delay wedge  146  in place while the spring element  147  accelerates the striker mass  152  towards its target, causing the component  151  of the two component pyrotechnic to impact its second component  150 , thereby initiating the pyrotechnic ignition. This initiation is shown in the  FIG. 9   e.    
         [0092]    In an alterative embodiment of the present invention, instead of the pin  153 , a stop mechanism such as a lever mechanism or a sliding stop mechanism (not shown) is used to prevent the striker mass  152  from moving to the right. Then as the third stage finger  145  is depressed and moves the delay wedge  146  towards its leftmost position, the delay wedge  146  actuates the aforementioned stop mechanism, thereby freeing the striker mass  152  to accelerate to the left and affect the initiation of the pyrotechnic element(s). Alternatively, the aforementioned stop mechanism is actuated by the last stage finger  145 . Such mechanical stops that are actuated by the movement of a secondary element are well known in the art and are therefore not described in more detail herein. 
         [0093]    One of the advantages of the above embodiment of the inertia igniter of  FIG. 9   a  is its high degree of initiation safety in the sense that the spring element  147  that actuates the striker mass  152  is not preloaded while the device is at rest; therefore there is no possibility of accidental ignition. In addition, the device does not use dry friction or damping elements which are highly unpredictable or require velocity gain (large displacements) for effectiveness. The above advantages are in addition to the previously stated advantage of multi-stage mechanical delay mechanisms in significantly reducing the required size, particularly height, and volume of the resulting inertial ignited. 
         [0094]    Another embodiment  160  is shown schematically in  FIGS. 10   a - 10   e.  The inertial igniter  160  without a top cap is shown in  FIG. 10   a . Cutaway drawings of this device are used in the drawings  10   b - 10   e  to clearly show its internal components and its operation. The mechanical delay mechanism of the embodiment of  FIG. 10   a  is a two-stage finger design, similar to the embodiment shown in  FIG. 5 , with a difference being that fingers  161  and  162  operate in a plane parallel to the direction of advancement of the delay wedge  163  during its motion. The fingers  161  and  162  are preferably flexural members to achieve a compact design. In this embodiment, a ball release mechanism is used to couple the mechanical delay mechanism component  164  to an adjacent pre-loaded striker system and its pyrotechnic component  165  as shown in  FIG. 10   b . The operation of this inertial igniter embodiment can be described as follows. At rest, the fingers  161  and  162  are preloaded upwards and the delay wedge  163  preloaded to the left by the spring  166 . These preload forces and the effective mass of the fingers  161  and  162  and associated components establish an acceleration magnitude threshold below which no relative motion of these components may occur. The device at rest is shown in  FIGS. 10   a  and  10   b . Upon having a sufficient impulse imparted on the housing of the device in the direction of the arrow  167 , the finger  161  will act against the sloped surface  168  ( FIG. 10   c ) of the delay wedge  163  with a force caused by reaction to the acceleration of the projectile in the direction of the arrow  167 . This resultant force will drive the delay wedge  163  to the right. If the acceleration profile is sufficient to fully depress the first finger  161 , the delay wedge  163  will be driven half its full stroke, allowing the finger  162  to engage the sloped surface  168  of the delay wedge  163  rather than being supported by the top surface  169  of the delay wedge  163  as was previously the case. This is shown in  FIG. 10   c . In the case of an all-fire acceleration profile, the second finger  162  will also be driven fully downwards, fully advancing the delay wedge  163 . This is shown in  FIG. 10   d . At this point, the ball  170  is pushed into a recess  171  provided on the side of the delay wedge  163 , thereby releasing the striker  172 , allowing the preloaded striker spring  173  to accelerate the striker  172  towards the element  174 , causing their impact. By providing pyrotechnic materials (one or two part pyrotechnic elements) on either or both impacting surfaces (with pressure concentrating pins if necessary—not shown), the pyrotechnic material(s) is ignited. This is shown in  FIG. 10   e . In the case of partial actuation of the mechanical delay mechanism  164 , the mechanism will fully reverse and reset, ready for future operation. 
         [0095]    It is noted that a difference between the embodiments shown in  FIGS. 5 and 10  is that in the embodiment of  FIG. 5 , the spring  147  which actuates the striker  152  is not preloaded. In contrast, in the embodiment of  FIG. 10 , the spring  173  that actuates the striker  172  is preloaded. This means that in general, the embodiment of  FIG. 5  provides for more safety since accidental ignition due to the release of the striker (i.e.,  172  in the embodiment of the  FIG. 10 ) cannot occur in the embodiment of  FIG. 5 . 
         [0096]    In yet another embodiment  180 , the mechanical delay mechanism portion  181  is combined with a striker and pyrotechnic part (the remaining components of the inertial igniter embodiment  180 ). The mechanical delay mechanism component  181  is a four-stage finger design with fingers  182 ,  183 ,  184  and  185 , similar to the multi-stage fingers of the embodiments of  FIGS. 5 ,  9  and  10 . The four-stage fingers  182 ,  183 ,  184  and  185  are fixed at one end to the inertial igniter structure  186  as shown in  FIG. 11   a  and the section A-A illustrated at  FIG. 11   b . The free end of the fingers  182 ,  183 ,  184  and  185  are provided with a preferably rounded extension  195 . 
         [0097]    The striker component of the inertial igniter  180  is a toggle type of mechanism with the toggle link  187 , which is attached to the structure of the inertial igniter  180 , by a pin joint indicated with numeral  188 . In its rest and normal position, the striker (toggle) link  187  is biased to rest on its right-most position shown in  FIG. 11   a , against the stop  196 , by the spring  189 . The spring  189  is preloaded in tension, and serves as the toggle mechanism spring, and is attached to the structure  186  on one end and to the striker link  187  on the other end, preferably with pin or pin-like joints. The surface of the striker link  187  that faces the multi-stage mechanical delay mechanism  181  is provided with a sloped section  192 , shown in  FIG. 11   a  and in the cross-section A-A in  FIG. 11   b . The elements  190  and  191 , fixed to the striker link  187  and the inertial igniter structure  186 , respectively, are the two components of the ignition pyrotechnic. Alternatively, a one piece pyrotechnic element may be used, in which case the element  190  is preferably the ignition impact mass or pin and the element  191  is preferably the one piece impact initiated pyrotechnic element. 
         [0098]    Each finger  182 ,  183 ,  184  and  185  is provided with certain amount of mass and deflection resisting elasticity (in this case in bending). Certain amount of upward preloading may also be provided to delay finger deflection until a desired acceleration level is reached. When at rest, only the extension  195  of the first finger  182  is resting on the sloped surface  192  of the striker link  187 . The extensions  195  of the other fingers  183 ,  184  and  185  rests on the top (flat) surface  193  of the striker link  187 . 
         [0099]    The operation of the device is as follows. At rest, the striker link  187  is biased to the right by the spring  189 , and the four fingers  182 ,  183 ,  184  and  185  are biased upwards with some pre-load. The ratio of pre-load to effective finger mass will determine the acceleration threshold below which there will be no relative movement between components. The positions of the four fingers  182 ,  183 ,  184  and  185  are such that the extension  195  of the finger  182  is over the sloped surface  192  of the striker link  187  as shown in  FIGS. 11   a  and  11   b , and extensions  195  of the fingers  183 ,  184  and  185  are supported by the top surface  193  of the striker link  187 , and are prevented from moving until the striker link  187  has rotated a prescribed angle to the left (counterclockwise), allowing the next extension  195  of the next finger (finger  183 ) to move over the sloped surface  192 . This is illustrated in  FIG. 11   a . If the device  180  experiences an acceleration in the direction  194 ,  FIG. 11   b , above the threshold determined by the ratio of initial resistances (elastic preloads) to effective component masses, the first stage finger  182  will act against the sloped surface  192  of the striker link  187 , rotating it one step counterclockwise. 
         [0100]      FIG. 11   c  shows the first finger  182  fully actuated and the striker link  187  advanced in rotation one step in the counterclockwise direction. At this instant, the second stage finger  183  is no longer supported by the top surface  193  of the striker link  187 , and is moved over the sloped surface  192 , and is therefore free to move downwards provided that the acceleration is still sufficiently high to overcome the preload for the second stage finger  183  and the striker link spring  189  force. If the acceleration continues at an all-fire profile, the second stage finger  183  will move down and rotate the striker link  187  further counterclockwise, allowing the extension  195  of the third stage finger  184  to move over the sloped surface  192 . This is shown in  FIG. 11   d . If the acceleration continues at an all-fire profile, the third stage finger  184  and then the fourth stage finger  185  will sequentially move down and rotate the striker link  187  further counterclockwise. This is shown in  FIG. 11   e.    
         [0101]    If the acceleration terminates or falls below the all-fire requirements any time before the last (fourth) stage finger  185  has actuated downward, the mechanical delay mechanism  181  will reverse until balance is achieved between the acceleration reaction forces and the elastic resistances. This may be a partial or complete reset from which the mechanism may be re-advanced if an all-fire profile is applied or resumed. If the fourth stage finger  185  is actuated downward as shown in  FIG. 11   e , the striker link  187  (the toggle mechanism) passes its spring  189  stabilized position on the right hand side of the inertial igniter  180 , and is accelerated in the counterclockwise direction, until the pyrotechnic components  190  and  191  impact and cause ignition. The latter state of the striker link  187  is shown in dashed lines in  FIG. 11   e.    
         [0102]    Besides use in munitions, as described above, the novel inertial igniters disclosed above have widespread commercial use and can be utilized in any application where a safe power supply having a very long shelf life is desired. Examples of such devices are emergency consumer devices, such as flashlights and communication devices, such as radios, cell phones and laptops. The inertial igniters disclosed above could provide such a power supply upon a required acceleration, such as striking the device upon a hard surface/ground. 
         [0103]    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.