Patent Publication Number: US-2023140161-A1

Title: Compact inertial igniters and impulse switches with accidental activation prevention for munitions and the like

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of priority to U.S. Provisional Application No. 63/274,561, filed on Nov. 2, 2021, the entire contents of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field 
     The present disclosure relates generally to mechanical inertial igniters and electrical impulse switches, and more particularly to compact, reliable and easy to manufacture mechanical inertial igniters for reserve batteries such as thermal batteries and initiation trains and the like with preset no-fire protection that are activated by shock loadings such as by gun firing setback acceleration with a prescribed level and duration or the like. 
     2. Prior Art 
     Reserve batteries of the electrochemical type are well known in the art for a variety of uses where storage time before use is extremely long. Reserve batteries are in use in applications such as batteries for gun-fired munitions including guided and smart, mortars, fusing mines, missiles, and many other military and commercial applications. The electrochemical reserve-type batteries can in general be divided into two different basic types. 
     The first type includes the so-called thermal batteries, which operate at high temperatures. Unlike liquid reserve batteries, in thermal batteries the electrolyte is already in the cells and therefore does not require a release and 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. 
     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. 
     The second type includes the so-called liquid reserve batteries in which the electrodes are fully assembled for cooperation, but the liquid electrolyte is held in reserve in a separate container until the batteries are desired to be activated. In these types of batteries, by keeping the electrolyte separated from the battery cell, the shelf life of the batteries is essentially unlimited. The battery is activated by transferring the electrolyte from its container to the battery electrode compartment (hereinafter referred to as the “battery cell”). 
     A typical liquid reserve battery is kept inert during storage by keeping the aqueous electrolyte separate in a glass or metal ampoule or in a separate compartment inside the battery case. The electrolyte compartment may also be separated from the electrode compartment by a membrane or the like. Prior to use, the battery is activated by breaking the ampoule or puncturing the membrane allowing the electrolyte to flood the electrodes. The breaking of the ampoule or the puncturing of the membrane is achieved either mechanically using certain mechanisms usually activated by the firing setback acceleration or by the initiation of certain pyrotechnic material. In these batteries, the projectile spin or a wicking action is generally used to transport the electrolyte into the battery cells. 
     Reserve batteries are inactive and inert when manufactured and become active and begin to produce power only when they are activated. Reserve batteries have the advantage of very long shelf life of up to 20 years that is required for munitions applications. 
     Thermal batteries generally use some type of initiation device (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,” operate based on the firing acceleration. The inertial igniters do not require onboard batteries for their operation and are thereby often used in munitions applications such as in gun-fired munitions and mortars. 
     Inertial igniters are also used to activate liquid reserve batteries through the rupture of the electrolyte storage container or membrane separating it from the battery core. The inertial igniter mechanisms may also be used to directly rupture the electrolyte storage container or membrane. 
     Inertial igniters used in munitions must be capable of activating only when subjected to the prescribed setback acceleration levels and durations and not when subjected to any of the so-called no-fire conditions such as accidental drops or transportation vibration or the like. This means that safety in terms of prevention of accidental ignition is one of the main concerns in inertial igniters. 
     In recent years, new improved chemistries and manufacturing processes have been developed that promise the development of lower cost and higher performance thermal and liquid reserve batteries that could be produced in various shapes and sizes, including their small and miniaturized versions. 
     Mechanical inertial igniters have been developed for many munitions applications in which the munitions are subjected to relatively high firing setback accelerations of generally over 1,000 Gs with long enough duration that provides enough time for the inertial igniter to activate the igniter pyrotechnic material, which may consist of a primer or an appropriate pyrotechnic material that is directly applied to the inertial igniter as described in previous art (for example, U.S. Pat. Nos. 9,160,009, 8,550,001, 8,931,413, 7,832,335 and 7,437,995, the contents of which are hereby considered included by reference). 
     Inertia-based igniters must provide two basic functions. The first function is to provide the capability to differentiate the aforementioned accidental events such as drops over hard surfaces or transportation vibration or the like, i.e., all no-fire events, from the prescribed firing setback acceleration (all-fire) event. In inertial igniters, this function is usually performed by either keeping the device striker fixed to the device structure during all aforementioned no-fire events until the prescribed firing setback acceleration event is detected or allowing for a limited motion of the device striker, within which it does not strike the igniter percussion primer of other provided pyrotechnic material. The second function of an inertia-based igniter is to provide the means of accelerating the device striker to the kinetic energy level that is needed to initiate the device percussion primer or other pyrotechnic material as it (hammer element) strikes an “anvil” over which the pyrotechnic material is provided. In general, the striker is provided with a relatively sharp point which strikes the percussion primer or pyrotechnic material covering a raised surface over the anvil, thereby allowing a relatively thin pyrotechnic layer to be pinched to achieve a reliable ignition mechanism. In many applications, percussion primers can be used due to the cost considerations. In all such inertial igniters, exit holes are provided on the inertial igniter to allow the reserve battery activating flames and sparks to exit. 
     Two basic methods are currently available for accelerating the device striker to the needed velocity (kinetic energy) level for percussion primer or provided pyrotechnic material described above. The first method is based on allowing the setback acceleration to accelerate the striker mass following its release. This method requires the setback acceleration to have long enough duration to allow for the time that it takes for the striker mass to be released and for the striker mass to be accelerated to the required velocity before pyrotechnic impact. As a result, this method is applicable to larger caliber and mortar munitions in which the setback acceleration duration is relatively long and in the order of several milliseconds, sometimes even longer than 10-15 milliseconds. This method is also suitable for impact induced initiations in which the impact induced decelerations have relatively long duration. 
     The second method relies on potential energy stored in a spring (elastic) element, which is then released upon the detection of the prescribed all-fire conditions. This method is suitable for use in munitions that are subjected to very short setback accelerations, such as those of the order of 1-2 milliseconds or when the setback acceleration level is low and space constraints does now allow the use of relatively large striker mass or where the height limitations of the available space for the inertial igniter does not provide enough travel distance for the inertial igniter striker to gain the required velocity and thereby kinetic energy to initiate the pyrotechnic material. 
     Inertia-based igniters must therefore comprise two components so that together they provide the described mechanical safety, the capability to differentiate the prescribed all-fire condition from all no-fire conditions, and to provide the required striking action to achieve ignition of the percussion primer or other provided pyrotechnic material. The function of the safety system is to keep the striker element in a relatively fixed position until the prescribed all-fire condition (or the prescribed impact induced deceleration event) is detected, at which time the striker element is to be released, allowing it to accelerate toward its target under the influence of the remaining portion of the setback acceleration or the potential energy stored in its spring (elastic) element of the device. 
     The ignition itself may also be configured with ignition material that provide ignition by contact or proximity. For example, 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. 
     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 (in the direction of the acceleration) 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 must 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 space that the thermal battery assembly  16  occupies within a munitions housing (usually determined by the total height  15  of the thermal battery), it is therefore important to reduce the height of the inertial igniter  10 . This can be important for small thermal batteries since in such cases and with currently available inertial igniter, the height of the inertial igniter portion  13  is a significant portion of the thermal battery height  15 . 
     A configuration of an inertial igniter for satisfying the safety (no initiation) requirement when dropped from heights of up to 7 feet (up to 2,000 G impact deceleration with a duration of up to 0.5 msec) is described below using one such embodiment disclosed in the aforementioned patents. An isometric cross-sectional view of this embodiment  200  of the inertia igniter is shown in  FIG.  2   . The full isometric view of the inertial igniter  200  is shown in FIG.  3 . 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 integral but may 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 of the housing  202  is also provided with at least one opening  204  (with a corresponding opening in the thermal battery  12  in  FIG.  1   ) to allow the ignited sparks and fire to exit the inertial igniter into the thermal battery core under the inertial igniter  200  upon initiation of the inertial igniter pyrotechnics  215 ,  FIG.  2   , or percussion cap primer when used in place of the pyrotechnics  215  as disclosed therein. 
     In addition, in certain applications, while the firing setback acceleration levels are relatively very low, sometimes in the order of several hundred or even lower Gs, the inertial igniter is required to provide protection against initiation when dropped from 5-7 feet or higher on hard surfaces, usually acceleration shocks with peaks that may reach well over 2,000 Gs, sometimes up to 10,000-18,000 G with 0.5 msec or longer durations. In addition, the inertial igniters are routinely required to be small and occupy as little volume as possible. 
     A striker mass  205  is shown in its locked position in  FIG.  2   . The striker mass  205  is provided with vertical surfaces  206  that are used to engage the corresponding (inner) surfaces of the posts  203  and serve as guides to allow the striker mass  205  to ride down along the length of the posts  203  without rotation with an essentially pure up and down translational motion. The vertical surfaces  206  may be recessed to engage the inner three surfaces of the properly shaped posts  203 . 
     In its illustrated position in  FIGS.  2  and  3   , 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.  2   . A setback spring  210 , which can be in compression, is also provided around but close to the posts  203  as shown in  FIGS.  2  and  3   . In the configuration shown in  FIG.  2   , the locking balls  207  are prevented from moving away from their aforementioned locking position by the collar  211 . The collar  211  can be provided with partial guide  212  (“pocket”), which are open on the top as indicated by numeral  213 . The guides  213  may be provided only at the locations of the locking balls  207  as shown in  FIGS.  2  and  3    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 would result 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 would 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. 
     The collar  211  can ride up and down the posts  203  as can be seen in  FIGS.  2  and  3    but is biased to stay in its upper most position as shown in  FIGS.  2  and  3    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.  2  and  3   , the setback spring  210  which is biased (preloaded) to push the collar  211  upward away from the igniter base  201 , would hold the collar  211  in its uppermost position against the locking balls  207 . As a result, the assembled inertial igniter  200  stays in its assembled state and would not require a top cap to prevent the collar  211  from being pushed up and allowing the locking balls  207  from moving out and releasing the striker mass  205 . 
     In this embodiment, a one-part pyrotechnics compound  215  (such as lead styphnate or some other similar compounds) is used as shown in  FIG.  2   . The surfaces to which the pyrotechnic compound  215  is attached can be roughened and/or provided with surface cuts, recesses, 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, impact occurs mostly between the surfaces of the tips  216  and  217 , thereby pinching the pyrotechnics compound  215 , thereby providing the means to obtain a reliable initiation of the pyrotechnics compound  215 . 
     Alternatively, instead of using the pyrotechnics compound  215 ,  FIG.  2   , a percussion cap primer can be used. An appropriately shaped striker tip can be provided at the tip  216  of the striker mass  205  (not shown) to facilitate initiation upon impact. 
     The basic operation of the embodiment  200  of the inertial igniter of  FIGS.  2  and  3    is now described. In case of 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 the acceleration is applied over long enough time in the axial direction  218 , the collar  211  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 event acceleration and its time duration is not sufficient to provide this motion (i.e., if the acceleration level and its duration are less than the predetermined threshold), the collar  211  will return to its start (top) position under the force of the setback spring  210  once the event has ceased. 
     Assuming that the acceleration time profile was at or above the specified “all-fire” profile, the collar  211  will have translated down past the locking balls  207 , allowing the striker mass  205  to accelerate down towards the base  202 . In such a situation, since the locking balls  207  are no longer constrained by the collar  211 , the downward force that the striker mass  205  has been exerting on the locking balls  207  will force the locking balls  207  to move outward in the radial direction. Once the locking balls  207  are out of the way of the dimples  209 , the downward motion of the striker mass  205  is no longer impeded. As a result, the striker mass  205  accelerates 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. 
     In the embodiment  200  of the inertial igniter shown in  FIGS.  2  and  3   , the setback spring  210  is of 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 other available inertial igniters. The use of the 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, thereby generating 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.  2  and  3   ), 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 wave springs with rectangular cross-section would therefore significantly increase the reliability of the inertial igniter and significantly increase the repeatability of the initiation for a specified all-fire condition. 
     In the embodiment  200  of  FIGS.  2  and  3   , following ignition of the pyrotechnics compound  215 , the generated flames and sparks are configured 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 (not shown) 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. 
     Alternatively, side ports 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. Other alternatives known in the art may also be used. 
     In  FIGS.  2  and  3   , the inertial igniter embodiment  200  is shown without any outside housing. In many applications, as shown in the schematics of  FIG.  4   a    ( 4   b ), the inertial igniter  240  ( 250 ) is placed securely inside the thermal battery  241  ( 251 ), either on the top ( FIG.  4   a   ) or bottom ( FIG.  4   b   ) of the thermal battery housing  242  ( 252 ). This can be 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 ) can be formed by a member  244  ( 254 ) which is fixed to the inner surface of the thermal battery housing  242  ( 253 ), for example, 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. 
     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. 
     The inertial igniter  200 ,  FIGS.  2  and  3   , may also be provided with a housing  260  as shown in  FIG.  5   . The housing  260  can be one piece and fixed to the base  202  of the inertial igniter structure  201 , such as 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  at its open end  261 , in which case the base  202  can be 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. 
     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 disclosed inertial igniter  200  can be configured to 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. 
     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  211  must 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. 
     The significant shortcomings of the prior art inertial igniters are related firstly to the need to be significantly redesigned and make major changes in the inertial igniter geometry and its components to satisfy a new set of (all-fire and no-fire) requirements for each new application. This means that a major engineering effort is generally needed for each new application, which would also require new sets of performance and reliability testing, which together translates to a significant cost. Secondly, the basic design of the prior art inertial igniters shown in  FIGS.  1 - 4   , such as the geometry of the base  202  and its posts  203 , the presence of the collar  211  and its specialized setback spring  210 , make the design and its manufacture relatively complex and thereby costly. Thirdly, the basic design of the prior art inertial igniters shown in  FIGS.  1 - 4   , such as due to the presence of the setback spring  210  and the collar  211  and the need for its free movement outside the posts  203  demand a certain amount of open space around the inertial igniter as it is assembled inside a battery housing. As a result, the actual volume occupied by the inertial igniter becomes larger than the inertial igniter itself and the battery manufacturer must make sure that the volume around the inertial igniter stays clear, which usually means that the inertial igniter has to be either assembled in a separate compartment as shown in  FIGS.  1  and  4    or be provided with its own housing as shown in  FIG.  5   . Fourthly, due to the above reasons, the prior art inertial igniters shown in  FIGS.  1 - 4    cannot be designed in very compact form with no additional volume and/or compartment or housing requirement for their assembly inside batteries. 
     It is also appreciated by those skilled in the art that currently available G-switches of different type that are used for opening or closing an electrical circuit are designed to perform this function when they are subjected to a prescribed acceleration level without accounting for the duration of the acceleration level. As such, they suffer from the shortcoming of being activated accidentally, e.g., when the object in which they are used is subjected to short duration shock loading such as could be experienced when dropped on a hard surface as was previously described for the case of inertial igniter used in munitions. 
     When used in applications such as in munitions, it is highly desirable for G-switches to be capable to differentiate the previously indicated accidental and short duration shock (acceleration) events such as those experienced by dropping on hard surfaces, i.e., all no-fire conditions, from relatively longer duration firing setback (shock) accelerations, i.e., all-fire condition. Such G-switches should activate when firing setback (all-fire) acceleration and its duration results in an impulse level threshold corresponding to the all-fire event has been reached, i.e., they must operate as an “impulse switch”. This requirement necessitates the employment of safety mechanisms like those used in the inertial igniter embodiments, which can allow the switch activation only when the firing setback acceleration level and duration thresholds have been reached. The safety mechanism can be thought of as a mechanical delay mechanism, after which a separate electrical switch mechanism is actuated or released to provide the means of opening or closing at least one electrical circuit. 
     Such impulse switches with the aforementioned integrated safety mechanisms are highly desirable to be very small in size so that they could be readily used on electronic circuit boards of different products such as munitions or the like. 
     SUMMARY 
     A need therefore exists for compact mechanical inertial igniters that occupy minimal volume when integrated into thermal reserve or other reserve batteries and the like for initiation when subjected to a prescribed minimum acceleration for a minimum of duration, and that the inertial igniter is highly reliable, for example, have better than 99.9 percent reliability with 95 percent confidence level. 
     A need also exists for mechanical inertial igniters that can satisfy the safety requirement of munitions, i.e., the no-fire conditions, such as accidental drops and transportation vibration and other similar events. 
     A need also exists for compact mechanical inertial igniters that can be readily modified to satisfy other all-fire and no-fire requirements without requiring significant overall and component modifications. 
     A need therefore exists for miniature mechanical inertial igniters for thermal reserve and other reserve batteries in gun-fired munitions, mortars, rockets, and the like, such as for small thermal batteries that could be used in fuzing and other similar applications, that are safe (i.e., satisfy the munitions no-fire conditions), are compact and occupy minimal volume inside the thermal battery. 
     Such innovative inertial igniters are can be scalable to thermal reserve and other reserve batteries of various sizes, such as to miniaturized inertial igniters for small size thermal batteries. Such inertial igniters are generally also required not to initiate if dropped from heights of up to 5-7 feet onto a concrete floor, which can result in impact induced inertial igniter accelerations of up to 2000 G magnitude that may last up to 0.5 msec. In certain applications, the inertial igniter may be subjected to significantly higher accidental (no-fire) accelerations of 10,000-18,000 G magnitude that may last up to 1 msec. The inertial igniters are also generally required to withstand high firing accelerations, for example up to 20-50,000 Gs (i.e., not to damage the thermal battery); and configured to ignite at prescribed minimum acceleration threshold when subjected to such accelerations for a prescribed amount of time, determined from the munition firing acceleration profile. 
     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 intended firing of ordinance from a gun, the device should initiate with high reliability. It is also conceivable that the igniter will experience incidental low but long-duration accelerations, whether accidental or as part of normal handling, such as during transportation, which must be guarded against initiation. Again, the impulse given to the inertial igniter will have a great disparity with that given by the prescribed munition initiation acceleration profile because the magnitude of the incidental long-duration acceleration will be quite low. 
     In addition, the inertial igniters used in munitions are generally required to have a shelf life of better than 20 years and could generally be stored at temperatures of sometimes in the range of −65 to 165 degrees F. The inertial igniter configuration must also consider the manufacturing costs and simplicity in the configurations to make them cost effective for munitions applications. 
     Accordingly, fully mechanical compact inertial igniters are provided that can satisfy a wide range of munition prescribed all-fire and no-fire requirements. Such inertial igniter do not rely on stored potential energy. Such inertial igniters can be suitable for use in a wide range of gun-fired munitions, mortars and rockets and the like. 
     The mechanical compact inertial igniters for initiation of thermal or other reserve batteries can be activated upon target impact. 
     The mechanical compact inertial igniters can be activated by certain linear or rotary actuation device upon firing, or after a prescribed delay following firing, or upon target impact. 
     Also provided are fully mechanical compact igniters that can satisfy a wide range of munition prescribed all-fire and no-fire requirements. Such inertial igniters can be suitable for relatively small reserve batteries used in munitions. 
     Also provided are fully mechanical compact igniters that can be initiated upon target impact. 
     Also provided are fully mechanical compact inertial igniters for activating certain linear or rotary actuation devices upon firing, or after a prescribed delay following firing, or upon target impact. 
     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: 
     provide inertial igniters that are compact, safe and can differentiate no-fire conditions from all-fire conditions based on the prescribed all-fire setback acceleration level (target impact acceleration level when used for target impact activation) and its prescribed duration; 
     provide compact inertial igniters that do not require additional volume around them when integrated into thermal reserve or other reserve batteries or in initiation trains; 
     provide compact inertial igniters that allow the use of standard off-the-shelf percussion cap primers or commonly used one part or two-part pyrotechnic components; 
     provide inertial igniters that can be sealed to simplify storage and to increase shelf life. 
     Accordingly, a compact inertial igniter is provided. The inertial igniter comprising: a striker mass movable towards one of a percussion cap or pyrotechnic material; and a striker mass release mechanism for releasing the striker mass to strike the percussion primer or pyrotechnic material upon experiencing a prescribed acceleration magnitude and its duration thresholds. 
     The striker mass release mechanism further comprises biasing members, such as helical springs, for biasing the striker mass to demand a prescribed all-fire release acceleration level. 
     The compact inertial igniter striker mass and the release mechanism are readily tuned to modify all-fire and no-fire acceleration and duration thresholds. 
     The striker mass release mechanism is returnable from the path of releasing the striker mass when the acceleration duration and magnitude (all-fire condition) threshold is not reached. 
     Also provided is a method for initiating a thermal battery. The method comprising: releasing a striker mass upon an acceleration magnitude and duration greater than a prescribed threshold; and accelerating the striker mass by the applied acceleration to gain enough kinetic energy to strike and initiate the provided percussion cap or pyrotechnic material. 
     The method can further comprise returning the striker mass release mechanism to its original (zero acceleration condition) position when the acceleration duration and magnitude (all-fire condition) threshold is not reached. 
     It is appreciated by those skilled in the art that the disclosed compact inertial igniter mechanisms may also be used to construct electrical impulse switches, which are activated like the so-called electrical G switches but with the added time delays to account for the activation shock level duration requirement, i.e., similar to the disclosed compact inertial igniters to activate when a prescribed shock loading (acceleration) level is experienced for a prescribed length of time (duration). The electrical “impulse switches” may be configured as normally open or closed and with or without latching mechanisms. Such impulse switch embodiments that combine such safety mechanisms with electrical switching mechanisms are described herein together with alternative methods of their construction. 
     A need therefore exists for miniature impulse switches for use in munitions or the like that can differentiate accidental short duration shock loading (so-called no-fire events for munitions) from generally high but longer duration, i.e., high impulse threshold levels, that correspond to all-fire conditions in gun fired munitions or the like. Such impulse switches must be very small in size and volume to make them suitable for being integrated into electronic circuit boards or the like. They must also be readily scalable to different all-fire and no-fire conditions for different munitions or other similar applications. Such impulse switches must be safe and should be able to be configured to activate at prescribed 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 or other similar events which last over very short periods of time, for example accelerations of the order of 500 Gs when applied for 10 msec as experienced in a gun as compared to 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 most munitions are required to 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 device is in a sealed compartment. The impulse switch must also consider the manufacturing costs and simplicity of configuration to make it cost effective for munitions applications. 
     Those skilled in the art will appreciate that the compact impulse-based mechanical impulse switches disclosed herein may provide one or more of the following advantages over prior art mechanical G-switches: 
     provide impulse-based G-switches that are small in both height and volume, thereby making them suitable for mounting directly on electronic circuit boards and the like; 
     provide impulse-based switches that differentiate all-fire conditions from all no-fire conditions, even those no-fire conditions that result in higher levels of shock but short duration, thereby eliminating the possibility of accidental activation; 
     provide impulse switches that are modular in configuration and can therefore be readily customized to different no-fire and all-fire requirements; 
     provide impulse switches that may be normally open or normally closed and that are modular in configuration and can be readily customized for opening or closing or their combination of at least one electric circuit. 
     Accordingly, impulse-based impulse switches with modular configuration for use in electrical or electronic circuitry are provided that activate upon a prescribed acceleration profile threshold. In most munition applications, the acceleration profile is usually defined in terms of firing setback acceleration and its duration. 
     A need therefore exists for miniature mechanical inertial igniters for reserve batteries, such as thermal or liquid reserve batteries used in gun-fired munitions, mortars, rockets, and the like, such as for small reserve batteries that could be used in fuzing and other similar applications, that are safe, i.e., satisfy the munitions no-fire conditions, and that can be used in applications in which the setback acceleration level is relatively low. 
     Such compact inertial igniters can also be scalable to reserve batteries of various sizes, such as to miniaturized inertial igniters for small size reserve batteries. The inertial igniters are also generally required to withstand high firing accelerations, for example up to 20-50,000 Gs, i.e., not to damage the battery; and should be able to be configured to ignite at specified acceleration levels when subjected to such accelerations for a specified amount of time to match the firing acceleration. 
     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 intended firing, i.e., a prescribed firing acceleration level and its duration threshold, the device should initiate with high reliability. 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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the apparatus will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
         FIG.  1    illustrates a schematic of a cross-section of a thermal battery and inertial igniter assembly of the prior art. 
         FIG.  2    illustrates a schematic of a cross-section of an inertial igniter for thermal battery of the prior art. 
         FIG.  3    illustrates a schematic of the isometric drawing of the inertial igniter for thermal battery of  FIG.  2   . 
         FIG.  4   a    illustrates a schematic of a cross-section of a thermal battery of the prior art with an inertial igniter positioned on the top portion of the thermal battery and in which the ignition generated flame to be directed downwards into the thermal battery compartment. 
         FIG.  4   b    illustrates a schematic of a cross-section of a thermal battery of the prior art with an inertial igniter positioned on the bottom portion of the thermal battery and in which the ignition generated flame to be directed upwards into the thermal battery compartment. 
         FIG.  5    illustrates a schematic of cross-section of an inertial igniter for thermal battery of the prior art with an outer housing. 
         FIG.  6    illustrates the schematic of the cross-sectional view of the first embodiment compact inertial igniter. 
         FIG.  7    illustrates the isometric view of the compact inertial igniter embodiment of  FIG.  6   . 
         FIG.  8 A  illustrates the blow-up view “A” of  FIG.  6    for describing the forces acting on the various components of the inertial igniter at rest or as it is being subjected to axial acceleration. 
         FIG.  8 B  illustrates the free-body-diagram of the inertial igniter locking ball for force analysis while the inertial igniter is at rest. 
         FIG.  9 A  illustrates the blow-up view “A” of  FIG.  6    for describing the forces acting on the various components of the inertial igniter after being subjected to axial acceleration that causes the igniter locking balls impacting the bottom surface of the provided groove. 
         FIG.  9 B  illustrates the free-body-diagram of the inertial igniter locking ball for dynamic analysis. 
         FIG.  10    illustrates the schematic of the cross-sectional view of the first embodiment compact inertial igniter of  FIG.  6    as it is being subjected to axial acceleration. 
         FIG.  11    illustrates the schematic of the cross-sectional view of a modified compact inertial igniter embodiment of  FIG.  6    that is configured to prevent spinning of the inertial igniter striker mass in it housing. 
         FIG.  12    illustrates the top view of the modified compact inertial igniter embodiment of  FIG.  11   . 
         FIG.  13    illustrates the schematic of the cross-sectional view of the modified compact inertial igniter embodiment of  FIG.  11    with a curved groove pocket to prevent spinning of the inertial igniter striker mass in it housing and increase initiation time delay. 
         FIG.  14    illustrates the schematic of the cross-sectional view of the compact inertial igniter embodiment configured for ignition flame and spark exiting from the striker mass side of the inertial igniter. 
         FIG.  15    illustrates the isometric view of the compact inertial igniter embodiment of  FIG.  14   . 
         FIG.  16 A  illustrates the cross-sectional view of a striker mass of the different compact inertial igniter embodiments with ball pockets oriented upward from the direction of perpendicular to the direction of striker mass displacement. 
         FIG.  16 B  illustrates the cross-sectional view of a striker mass of the different compact inertial igniter embodiments with ball pockets oriented downward from the direction of perpendicular to the direction of striker mass displacement. 
         FIG.  17    illustrates the cross-sectional view of a modified compact inertial igniter embodiment of  FIG.  6    that is provided with two identical groove pockets. 
         FIG.  18    illustrates the schematic of the cross-sectional view of the compact inertial igniter embodiment of  FIG.  14    with added compressive spring to resist striker mass downward motion. 
         FIG.  19    illustrates a schematic of the cross-sectional view of the normally open non-latching impulse switch embodiment for closing electrical circuits when subjected to a prescribed all-fire or the like acceleration event in its non-activated state. 
         FIG.  20    illustrates the schematic of the cross-sectional view of the modified normally open non-latching impulse switch embodiment of  FIG.  19    to convert it to a normally open and latching impulse switch in its non-activated state. 
         FIG.  21    illustrates the schematic of the cross-sectional view of the normally closed non-latching impulse switch embodiment for opening electrical circuits when subjected to a prescribed all-fire or the like acceleration event in its non-activated state. 
         FIG.  22    illustrates the schematic of the cross-sectional view of the modified normally closed and latching impulse switch embodiment of  FIG.  21    in its pre-activation configuration. 
         FIG.  23    illustrates the schematic of the cross-sectional view of the modified normally open latching impulse switch embodiment of  FIG.  22    in its pre activation configuration. 
         FIG.  24    illustrates the schematic of the cross-sectional view of the normally open latching impulse switch embodiment of  FIG.  23    in its post activation configuration 
     
    
    
     DETAILED DESCRIPTION 
     The compact inertial igniters are herein described through the following examples of their application. 
     The schematic of the cross-sectional view of the first embodiment compact inertial igniter  300  is shown in  FIG.  6   . The isometric view of the compact inertial igniter  300  is shown in  FIG.  7   . 
     The compact inertial igniter  300  is constructed with a cylindrical igniter body  301  with the bottom  302 , leaving a cylindrical space  303  inside the body of the compact inertial igniter. Around the inside wall  304  of the compact inertial igniter body  301  is provided a continuous groove  305 , which consists of a “top” surface  306 , a “sidewall”  307  and a “bottom” surface  308  as can be seen in  FIG.  6   . The bottom surface  308  has a linear cross-section as can be seen in  FIG.  6   , which is inclined relative to a plane normal to the central axis of the cylindrical body  301 , with which it makes the angle θ. 
     The compact inertial igniter  300  is also provided with the striker mass  309 , which can be cylindrical and is provided with a relatively small clearance with the wall  304 , so that it could slide up and down freely inside the cylindrical space  303  within the igniter body  301 , unless it is prevented from free up or down translation by the at least one “locking” balls  310 . 
     The striker mass  309  is provided with at least one cylindrical pocket  311 , within each a ball  310  and a preloaded compressive spring  312  is provided. In general, at least three such pockets can be provided symmetrically in a plane perpendicular to the axis of symmetry of the striker mass  309 . 
     It is appreciated that in the schematic of  FIG.  6    the compact inertial igniter  300  is shown in its pre-activation state. In this state of the compact inertial igniter  300 , the preloaded compressive springs  312  can be seen to have forced the balls  310  against the outwardly shaped surface  307 ,  FIG.  6   , thereby displacing the striker mass upward to the point at which the balls  310  rest against the top surface  306  of the groove  305 . 
     As can be seen in the schematic of  FIG.  6   , the body  301  of the compact inertial igniter  300  is also provided with a pocket  313  on the bottom surface  317  inside the space  303 , within which a percussion primer  314  is properly assembled. The bottom surface  302  of the compact inertial igniter  300  is also provided with a small hole  315  (usually around 2 mm in diameter) to allow the flame and sparks generated by the initiation of the percussion primer  314  to exit. The striker mass  309  is provided with a properly sized sharp tip  316 , which is positioned to strike and initiate the percussion primer with the required velocity. 
     An operation of the embodiment  300  of the inertial igniter of  FIGS.  6  and  7    is now described. In case of any relatively low magnitude acceleration in the axial direction, i.e., in the direction of the arrow  319 , which would overcome the resisting force of the preloaded compressive springs  312 , it would initiate a relatively small downward motion of the striker mass. Here, relatively low magnitude acceleration is intended to mean acceleration levels that the preloaded compressive springs  312  would support and only allow for downward motion of the striker mass  309  until the balls  310  reach the bottom surface  308  of the groove  305  and can be calculated as follows. 
     It is appreciated by those skilled in the art that when the compact inertial igniter  300  is at rest, the pressure of the balls  310  over the surface  307  of the groove  305  due to the force preloaded compressive spring force F S  would result in an upward component on an F u  from the reaction force at the contact point between the wall and the surface  307  of the groove  305  due to the initial inclination angle α between the surface  307  and vertical direction as seen in  FIG.  6   , the region of which is redrawn in the blow-up view of  FIG.  8 A . 
     The free-body-diagram of the ball  310  is provided in  FIG.  8 B  (the striker mass  309  is not shown in the free-body-diagram for clarity) to show the forces acting on the ball while the compact inertial igniter  300  is at rest. As can be seen in  FIG.  8 B , the presence of the preloaded compressive spring force F S  results in a reaction normal force F N  at the contact surface between the ball  310  and the surface  307  of the groove  305 . The normal reaction force F N  is readily seen as dependent on the angle α and given as 
     
       
         
           
             
               
                 
                   
                     F 
                     N 
                   
                   = 
                   
                     
                       F 
                       S 
                     
                     
                       Cos 
                       ⁢ 
                         
                       α 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     The reaction force F u  is then seen to become 
     
       
         
           
             
               
                 
                   
                     F 
                     u 
                   
                   = 
                   
                     
                       
                         F 
                         N 
                       
                       ⁢ 
                       Sin 
                       ⁢ 
                         
                       α 
                     
                     = 
                     
                       
                         
                           
                             F 
                             S 
                           
                           ⁢ 
                           Sin 
                           ⁢ 
                           α 
                         
                         
                           Cos 
                           ⁢ 
                           α 
                         
                       
                       = 
                       
                         
                           F 
                           S 
                         
                         ⁢ 
                         tan 
                         ⁢ 
                         α 
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     Now when the compact inertial igniter  300  begins to be subjected to an increasing acceleration in the direction of the arrow  319 ,  FIG.  6   , the acceleration acts on the effective assembled mass of the striker mass  309 , which includes the mass contribution of the springs  312  and the balls  310 , thereby exerting a dynamic force F D  (in opposite direction to the force F u ,  FIG.  8 B ) as 
         F   D   =ma   (3)
 
     where m is the effective mass of the striker mass  309  assembly with the springs  312  and balls  310  and a is the acceleration of the compact inertial igniter  300  in the direction of the arrow  319 . 
     Then as the level of the acceleration a in the direction of the arrow  319  is increased, then at an acceleration level a min  given by equation (4), the reaction force F u  is reduced to zero and with any further increase in the acceleration a, the striker mass  309  assembly would begin to slide down as view in  FIG.  6   . 
     
       
         
           
             
               
                 
                   
                     a 
                     min 
                   
                   = 
                   
                     
                       F 
                       u 
                     
                     m 
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     With increasing level of acceleration beyond the level a min , equation (4), the striker mass  309  assembly begins to displace down with increasing velocity, during which time the balls  310  would be rolling/sliding over the surface  307  of the groove  305  as the spring force F S  and therefore the normal reaction force F N  increase due to further compression of the springs  312  due to the inclination angle α. 
     It is appreciated that while the striker mass  309  is displacing down and before the balls  310  strike the bottom surface  308  of the groove  305 , the forces acting on the balls  310 ,  FIG.  9 B  (the striker mass  309  is not shown in the free-body-diagram for clarity), and the downward acceleration of the balls  310  relative to the inertial igniter housing  301 , thereby the downward acceleration of the striker mass relative to the inertial igniter housing  301 , are calculated as follow. 
     Assuming pure rolling of the balls  310  over the surface  307  of the groove  305 , the normal force F N  is given by equation (1) and the dynamic force F D  is given by equation (3), therefore from the balance of the sum of all forces in the vertical direction, i.e., in the direction of the inertial igniter acceleration,  FIG.  9 B , we get 
         F   D   −F   N  Sin α= ma   B/I   (5)
 
     where a B/I  is the acceleration of the balls  310  and therefore the striker mass  309  assembly relative to the compact inertial igniter housing  301 , i.e., relative to the device to which the inertial igniter is rigidly attached. By substituting F N  and F D  from equations (1) and (3) into equation (5), the acceleration a B/I  of the balls  310  and therefore the striker mass  309  assembly relative to the compact inertial igniter housing  301  becomes 
     
       
         
           
             
               
                 
                   
                     a 
                     
                       B 
                       / 
                       I 
                     
                   
                   = 
                   
                     a 
                     - 
                     
                       
                         
                           F 
                           S 
                         
                         ⁢ 
                         tan 
                         ⁢ 
                         α 
                       
                       m 
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     It is appreciated by those skilled in the art that if during downward displacement of the striker mass  309  the balls  310  do not undergo pure rolling over the surface  307  of the groove  305  and is thereby also sliding over the surface  307  and that there are other frictional forces acting on the balls  310  against their points of contact with the surfaces of the pockets  311  and their contacts with the preloaded compressive springs  312 , then they would also have an effect that is the same as the effect of the spring force F S  in reducing the acceleration am of the acceleration of the balls  310  and therefore the striker mass  309  assembly relative to the compact inertial igniter housing  301 . For example, by only considering only the sliding friction force F f ,  FIG.  9 B , of the balls  310  over the surface  307  of the groove  305  and neglecting the usually negligible other indicated friction forces, then the acceleration am is reduced by the amount F f /m to 
     
       
         
           
             
               
                 
                   
                     a 
                     
                       B 
                       / 
                       I 
                     
                   
                   = 
                   
                     a 
                     - 
                     
                       
                         
                           
                             F 
                             S 
                           
                           ⁢ 
                           tan 
                           ⁢ 
                           α 
                         
                         + 
                         
                           F 
                           f 
                         
                       
                       m 
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
     Now if the acceleration in the direction of the arrow  319 ,  FIG.  6   , is relatively short duration even if it is relatively high in magnitude, before the balls  310  reach the bottom surface  308  of the groove  305 ,  FIGS.  6  and  9 A , the striker mass  309  comes to a stop and displaced back to its rest position of  FIG.  6    by the upward component of the preloaded compressive spring force −F u  (opposite direction to the reaction force F u ), equation (2). The compact inertial igniter  300  can therefore be configured to accommodate, i.e., not activate, when subjected to relatively low magnitude accelerations, such as those experienced during transportation, and short duration and higher accelerations such as accidental drops from relatively low heights. 
     However, if the acceleration in the direction of the arrow  319  has high enough magnitude and long enough duration, the striker mass  309  would be accelerated downward and gain speed until the balls  310  impact the surface  308  as shown in  FIGS.  9 A and  10   . The impact of the balls  310  with the inclines surface  308  (with the angles θ as indicated in  FIGS.  6 ,  9 A and  10   ) would cause the balls  310  to “bounce” back in the direction normal to the surface  308 , i.e., initially in the direction of the arrows  320 ,  321  as shown in  FIG.  10   . As a result, the striker mass  309  assembly would “bounce” back upwards in the direction of the arrow  319 , i.e., the applied acceleration. 
     It is appreciated that due to the first such impact, the striker mass  309  assembly (which includes the balls  310  and the springs  312 ) would begin to move upwards as viewed in  FIG.  10    essentially at the projection of the impact rebounding velocity in the direction of the arrow  320 ,  321 . It is appreciated by those skilled in the art that the impact rebounding velocity is dependent on the mass of the striker mass  309  assembly and the coefficient of restitution characteristics of the striker body  301  at the impact surface  308 . It is also appreciated by those skilled in the art that the component of the velocity of the balls  310  in the direction of further compressing the compressive springs  312  and related kinetic energy transferred to the springs as potential energy and friction losses between the balls and the surface of the cylindrical pockets  311  housing the springs  312  must be considered in determining the profile of the speed with which the striker mass  309  is going to displace upwards. 
     Now if the acceleration in the direction of the arrow  319  ceases shortly after the above described balls  310  impact with the (inclined) surface  308 , if the resulting rebounding velocity of the striker mass  309  assembly is high enough, then the striker mass assembly would travel upward until the balls  310  impact the upper surface  306  of the groove  305 ,  FIGS.  9 A and  10   , and bounce downward with a certain velocity that is again determined by the total mass of the striker mass  309  assembly and the coefficient of restitution between the two impacting objects, i.e., the striker mass with its impacting balls  310  and the surface  306  of the compact inertial igniter body  301 . Otherwise, the striker mass  309  assembly move up and the spring force F S  would eventually bring it to a stop with the balls  310  resting against the surface  306 , i.e., in the compact inertial igniter rest position shown in  FIG.  6   . 
     Now if the above acceleration in the direction of the arrow  319  persists and is high enough, i.e., is higher than the prescribed minimum all-fire acceleration level and duration (when used in munitions), the balls  310  will impact the top surface  306  of the groove  305 , rebound downwards and depending on its rebounding speed, may impact the surface  308  a second time and eventually after one or more up and down rebounding against the surfaces  308  and  306  of the groove  305  it would essentially “settle” over the surface  308  and is pushed inside the spring pockets  311  while being sliding down the surface  308  due to the dynamic force F D ,  FIG.  9 B , which tends to push the balls  310  inside the pockets  311 , i.e., outside the groove  305  space, and thereby freeing the slider mass  309  assembly from engagement with the groove  305  of the housing  301  and to begin to be accelerated downwards. The striker mass  309  is then accelerated downward and gain further velocity, thereby kinetic energy. The striker mass  309  sharp tip  316  would then strike the percussion primer  314  and initiates it if the striker mass  309  has gained the requisite kinetic energy. 
     In the embodiment  300  of  FIG.  6   , following initiation of the percussion primer  314  (or the provided pyrotechnics compound), the generated flames and sparks are configured to exit downward through the opening  315  to initiate the thermal (or liquid) reserve battery below or initiate an initiation train and the like. Alternatively, side ports may be provided to allow the flame to exit from the side of the compact inertial igniter to initiate the pyrotechnic materials (or the like) of a thermal reserve battery or the like that is positioned around the body of the inertial igniter. Other alternatives known in the art may also be used. 
     It is appreciated by those skilled in the art that by varying the mass of the striker  309 ; the spring rate and preload level of the springs  312 ; the height and angles α and θ of the groove  305 ; and the distance between the tip  316  of the striker mass  309  and the percussion primer  314 , the disclosed compact inertial igniter  300  can match the prescribed all-fire minimum acceleration magnitude and duration and the no-fire requirements for various applications and safety protection, such as against accidental dropping of the compact inertial igniter and/or the munitions or the like within which it is assembled. It is appreciated that to provide the requisite impact energy, the striker mass  309  assembly the separation distance between the tip  316  of the striker mass and the percussion primer  314  must work together to provide the specified impact energy to initiate the percussion primer when subjected to the remaining portion of the prescribed initiation acceleration profile after the balls  310  have cleared the groove  305 . 
     It is appreciated by those skilled in the art that the compact inertial igniter embodiment  300  of  FIG.  6    is intended to be assembled and held firmly in reserve batteries or any other component of a munition or the like. It is, therefore, appreciated that if the munition in which the compact inertial igniter is assembled undergoes spinning during the firing, then since the groove  305  in the inertial igniter housing  301  is provided around the entire inner surface of the inertial igniter housing, then the balls  310  provide minimal resistance to the striker mass  309  from spinning (rotating) relative to the compact inertial ignite housing  301 . In many applications, such as when the munition spin acceleration in the barrel is very high, such high spin acceleration of the striker mass  309  relative to the inertial igniter housing  301  is not desirable since it could cause damage to the groove  305  and the striker mass and interfere with the proper operation of the inertial igniter as was previously described. The cross-sectional view of a modified compact inertial igniter embodiment  300  the prevents spinning of its striker mass relative to the inertial igniter housing is shown in  FIG.  11    and is indicated as the compact inertial igniter embodiment  325 . 
     It is noted that all components and features of the compact inertial igniter embodiment  325  of  FIG.  11    are identical to those of the embodiment  300  of  FIG.  6    except those related to the groove  305 , and the identical components and features are identified by the same numerals. The inertial igniter embodiment  300  housing with the modified groove is still indicated by the same numeral  301 . 
     In the modified compact inertial igniter embodiment  325 , unlike the embodiment  300  of  FIG.  6    in which the cavity  305  is provided over the entire inner surface  304  of the inertial igniter housing  301 , they are provided with separate “groove pockets”  322  of the same central cross-sectional areas as the groove  305  of embodiment  300  but limited in width to accommodate each a single ball  310  as shown in  FIG.  11    and its top view of  FIG.  12   , in which top views of four groove pockets are shown with dashed lines. 
     In the schematics of  FIGS.  11  and  12   , the compact inertial igniter embodiment  325  are assumed to have four symmetrically positioned groove pockets to accommodate engaging balls as described for the compact inertial igniter embodiment  300  of  FIG.  6   . However, it is appreciated by those skilled in the art that depending on the size of the striker mass  309  and the housing  301  and the balls  310 , the inertial igniter can be provided with more or even fewer number of such groove pockets as long as there is room to accommodate them. It is, however, appreciated that for the sake of stability of striker mass movement, at least three symmetrically positioned groove pockets with proper engaging balls are generally desired to be provided. 
     It is appreciated that the cross-sectional view of an assembled modified compact inertial igniter embodiment  325  of  FIG.  11    with four symmetrically provided groove pockets  322  looks exactly like the cross-sectional view of the compact inertial igniter embodiment  300  of  FIG.  6   . The compact inertial igniter embodiment  325  also operates as was described previously for the embodiment  300  when subjected to acceleration in the direction of the arrow  323  ( 319  in  FIG.  6   ) corresponding to prescribed minimum acceleration magnitude and duration (all-fire condition in munitions) and other accidental accelerations (no-fire conditions in munitions). The only difference between the two embodiments  325  and  300  being that in the inertial embodiment  325 , the balls  310  can only travel up and down in the groove pockets  322  as they are constrained by the walls  324  of the groove pockets from displacing in the lateral directions. Thereby the striker mass  309  is prevented from rotating (spinning) relative to the inertial igniter housing  301  while the balls  310  are inside the groove  305  when the inertial igniter is subjected to spinning acceleration, which is not the case for the compact inertial igniter embodiment  300  of  FIG.  6   . 
     It is appreciated that in the compact inertial igniter embodiment  325 ,  FIG.  11   , once the balls  310  have cleared the grove pockets  322  under acceleration in the direction of the arrow  323 , the striker mass  309  is free to rotate (spin) relative to the inertial igniter housing  301  as it travels down towards the percussion primer. In certain application, however, it might be desirable to prevent such rotational motion of the striker mass  309 . This is ready accomplished by extending one or more of the groove pockets  322  further down (as shown with dashed lines in  FIG.  11    and indicated by the numeral  327 ) to or past the point at which the engaging ball(s)  310  would be after the tip  316  of the striker mass  309  has impacted the percussion primer  314 . 
     As can be seen in the view of  FIG.  11   , the groove pocket  322  is vertical to allow the balls  310  and thereby the striker mass  309  to travel down without rotation relative to the inertial igniter housing  301  when the inertial igniter  325  is subjected to acceleration in the direction of the arrow  323  and as long as the balls  310  are still in the groove pockets  322 . To increase the time that it takes for the balls  310  to clear the groove pockets  322  and thereby allow for free downward motion of the striker mass  309  to striker and initiate the percussion primer  314 , the groove pockets  322  may have different curves shapes as extended downward from their top surface  326  ( 306  in  FIG.  6   ), such as a helical shape  328  as shown in  FIG.  13   . 
     The schematic of the cross-sectional view of another compact inertial igniter  330  is shown in  FIG.  14   . This embodiment is similar in the configuration to the embodiment  300  of  FIG.  6   , except that it is configured for the ignition flame and sparks to exit from the striker mass side of the inertial igniter as described below. The isometric view of the compact inertial igniter  330  showing the flame and spark exit hole  331  (usually around 2 mm in diameter) is shown in  FIG.  15   . 
     The compact inertial igniter  330  is constructed with a cylindrical igniter body  332  that is identical to the inertial igniter body  301  of inertial igniter embodiment  300  of  FIG.  6   , except the it is not provided with the pocket  313  and its contained percussion primer and exit hole  315  on its bottom side  317  and instead, on its inside bottom surface  333 , it is provided with a relatively sharp tip  334  that is suitable for initiating a percussion primer upon impact with the required amount of kinetic energy. 
     Around the inside wall  336  ( 304  in  FIG.  6   ) of the compact inertial igniter body  336  ( 304  in  FIG.  6   ) is provided an identical continuous groove  335  ( 305  in  FIG.  6   ), with identical “top” surface  306 , a “sidewall”  307  and a “bottom” surface  308  as can also be seen in  FIG.  6   . 
     The compact inertial igniter embodiment  330  is provided with a striker mass  337 , which is provided with identical pockets  339  ( 311  in  FIG.  6   ), balls  338  ( 310  in  FIG.  6   ) and preloaded compressive springs  340  ( 312  in  FIG.  6   ) as was the striker mass  309  of the inertial igniter embodiment  300  of  FIG.  6   . The striker mass  337  is, however, provided with a pocket  341 , within which a percussion primer  342  is firmly assembled. The striker mass  337  is also provided with an exit hole  331  as shown in  FIGS.  14  and  15   , through which the flames and sparks generated by the initiation of the percussion primer  342  could exit. 
     In general, like the compact inertial igniter  300  of  FIG.  6   , at least three pockets  339  are provided in the striker mass  337 , which can be provided symmetrically in a plane perpendicular to the axis of symmetry of the striker mass  337 . 
     Like the striker mass  309  of the compact inertial igniter  300  of  FIG.  6   , the striker mass  337  can also be cylindrical and is provided with a relatively small clearance with the wall  336 , so that it could slide up and down freely inside the cylindrical space  343  within the igniter body  332 , unless it is prevented from free up or down translation by the at least one “locking” balls  338 . 
     It is appreciated that in the schematic of  FIG.  14   , the compact inertial igniter  330  is shown in its pre-activation state. In this state of the compact inertial igniter  330 , the preloaded compressive springs  340  can be seen to have forced the balls  338  against the sidewalls of the groove  335 , thereby displacing the striker mass upward to the point at which the balls  338  rest against the top surface of the groove  335  as was also described for the compact inertial igniter  300  of  FIG.  6   . 
     An operation of the compact inertial igniter embodiment  330  of  FIGS.  14  and  15    is similar to that of the compact inertial igniter embodiment  300  of  FIG.  6   , except for the percussion primer location and the direction of the ignition flame and spark exit. In case of any relatively low magnitude acceleration in the axial direction, i.e., in the direction of the arrow  345 , which would overcome the resisting force of the preloaded compressive springs  340 , it would initiate a relatively small downward motion of the striker mass  337 . Here, relatively low magnitude acceleration is intended to mean acceleration levels that the preloaded compressive springs  340  would support and only allow for downward motion of the striker mass  337  until the balls  338  reach the bottom surface of the groove  335  and that can be calculated as was described previously for the compact inertial igniter embodiment  300  of  FIG.  6   . 
     Now when the compact inertial igniter  330  begins to be subjected to an increasing acceleration in the direction of the arrow  345 ,  FIG.  14   , the acceleration act on the effective assembled mass of the striker mass  337 , which includes the mass contribution of the springs  340  and the balls  338 , thereby exerting a dynamic force F D , equation (3). Then, as was described for the compact inertial igniter embodiment  300 , as the level of the acceleration in the direction of the arrow  345  is increased beyond the level a min , equation (4), the striker mass  337  assembly begins to displace down with increasing velocity, during which time the balls  338  would be rolling/sliding over the surface of the groove  335  as the spring force F S  and therefore the normal reaction force F N  increase due to further compression of the springs  340  due to the inclination angle α,  FIG.  6   . 
     Now as it was previously described for the compact inertial igniter embodiment  300  of  FIG.  6   , if the acceleration in the direction of the arrow  345 ,  FIG.  14   , is relatively short duration and even if it is relatively high in magnitude, before the balls  310  reach the bottom surface of the groove  335  (as shown in  FIG.  9 A ), the striker mass  337  comes to a stop and is displaced back to its rest position of  FIG.  14    by the upward component of the preloaded compressive spring force. The compact inertial igniter  330  can therefore be configured to accommodate, i.e., not activate, when subjected to relatively low magnitude accelerations, such as those experienced during transportation, and short duration and higher accelerations such as accidental drops from relatively low heights. 
     However, as it was previously described for the compact inertial igniter embodiment  300  of  FIG.  6   , if the acceleration in the direction of the arrow  345  has high enough magnitude and long enough duration, the striker mass  337  would be accelerated downward and gain speed until the balls  338  impact the bottom surface of the groove  335 . The impact of the balls  338  with the inclines bottom surface of the groove (surface  308  with the angles θ as indicated in  FIGS.  6 ,  9 A and  10   ) would cause the balls  338  to “bounce” back in the direction normal to the bottom surface  308 . As a result, the striker mass  337  assembly would “bounce” back upwards in the direction of the arrow  345 , i.e., the applied acceleration. 
     It is appreciated that due to the first such impact, the striker mass  337  assembly (which includes the balls  338  and the springs  340 ) would begin to move upwards as viewed in  FIG.  14    as was previously described for the embodiment  300  of  FIG.  6   . It is appreciated by those skilled in the art that the said impact rebounding velocity is dependent on the mass of the striker mass  337  assembly and the coefficient of restitution characteristics of the striker body  332  at the impact surface. It is also appreciated by those skilled in the art that the component of the velocity of the balls  338  in the direction of further compressing the compressive springs  340  and related kinetic energy transferred to the springs as potential energy and friction losses between the balls and the surface of the cylindrical pockets  339  housing the springs  340  must be considered in determining the profile of the speed with which the striker mass  337  is going to displace upwards. 
     Now if the acceleration in the direction of the arrow  345  ceases shortly after the above described balls  338  impact with the bottom (inclined) surface of the groove  335 , if the resulting rebounding velocity of the striker mass  337  assembly is high enough, then the striker mass assembly would travel upward until the balls  338  impact the upper surface of the groove  335 , and bounce downward with a certain velocity that is again determined by the total mass of the striker mass  337  assembly and the coefficient of restitution between the two impacting objects as was previously described for the compact inertial igniter embodiment  300  of  FIG.  6   . Otherwise, the striker mass  337  assembly move up and the spring force F S  would eventually bring it to a stop with the balls  338  resting against the surface of the groove  335 , i.e., in the compact inertial igniter rest position shown in  FIG.  14   . 
     However, if the above acceleration in the direction of the arrow  345  persists and is high enough, i.e., is higher than the prescribed minimum all-fire acceleration level and duration (when used in munitions), as was previously described for the compact inertial igniter embodiment  300  of  FIG.  6   , the balls  338  will impact the top surface of the groove  335 , rebound downwards and depending on its rebounding speed, may impact the bottom surface of the groove  335  a second time and eventually after one or more up and down rebounding against the top and bottom surfaces of the groove  335  it would essentially “settle” over the surface and is pushed inside the spring pockets  339  while being sliding down the surface  336  due to the dynamic force F D  ( FIG.  9 B ), which tends to push the balls  338  inside the pockets  339 , i.e., outside the groove  335  space, and thereby freeing the slider mass  337  assembly from engagement with the groove  335  of the housing  332  and to begin to be accelerated downwards. 
     The striker mass  337  is then accelerated downward and gain further velocity, thereby kinetic energy. The percussion primer  342 , which is firmly embedded in the pocket  341  of the striker mass  337 , would then strike the sharp tip  334  at the bottom surface  333  of the compact inertial igniter body  332 ,  FIG.  14   , and is initiated if the striker mass  337  assembly has gained the requisite kinetic energy. 
     In the embodiment  330  of  FIG.  14   , following initiation of the percussion primer  342  (or the provided pyrotechnics compound), the generated flames and sparks are configured to exit upward through the opening  331  to initiate the thermal (or liquid) reserve battery above or initiate an initiation train and the like. Alternatively, side ports may be provided to allow the flame to exit from the side of the compact inertial igniter to initiate the pyrotechnic materials (or the like) of a thermal reserve battery or the like that is positioned around the body of the inertial igniter. Other alternatives known in the art may also be used. 
     It is appreciated by those skilled in the art that by varying the mass of the striker  337 ; the spring rate and preload level of the springs  340 ; the height and angles α and θ of the groove  335  (see  FIG.  6   ); and the distance between the sharp tip  334  of the inertial igniter body  332  and the percussion primer  342 , the compact inertial igniter  330  can be configured to match the prescribed all-fire minimum acceleration magnitude and duration and the no-fire requirements for various applications and safety protection, such as against accidental dropping of the compact inertial igniter and/or the munitions or the like within which it is assembled. 
     It is appreciated that to provide the requisite impact energy, the striker mass  337  assembly the separation distance between the sharp tip  334  of the inertial igniter body  332  and the percussion primer  342  must work together to provide the specified impact energy to initiate the percussion primer when subjected to the remaining portion of the prescribed initiation acceleration profile after the balls  338  have cleared the groove  335 . 
     It is appreciated by those skilled in the art that the compact inertial igniter embodiment  330  of  FIG.  14    is intended to be assembled and held firmly in reserve batteries or any other component of a munition or the like that is subjected to indicated accelerations for initiation. It is, therefore, appreciated that if the munition in which the compact inertial igniter is assembled undergoes spinning during the firing, then since the groove  335  in the inertial igniter housing  332  is provided around the entire inner surface of the inertial igniter housing, then the balls  338  provide minimal resistance to the striker mass  337  from spinning (rotating) relative to the compact inertial ignite housing  332 . In many applications, such as when the munition spin acceleration in the barrel is very high, such high spin acceleration of the striker mass  337  relative to the inertial igniter housing  332  is not desirable since it could cause damage to the groove  335  and the striker mass and interfere with the proper operation of the inertial igniter as was previously described. For such cases, the compact inertial igniter embodiment  330  may be modified as was previously described for the compact inertial igniter embodiment  300  of  FIG.  6    and shown in the compact inertial igniter embodiment  325  of  FIG.  11    to prevent spinning of its striker mass relative to the inertial igniter housing. 
     It is noted that all components and features of such a modified version of the compact inertial igniter embodiment  330  stays the same as those of the embodiment  330  of  FIG.  14   , except that the groove  335  is replaced by the grooves  322  shown in the schematic of  FIG.  11    (or alternatively grooves  328  of  FIG.  13   ). 
     It is appreciated that as was described for the modified compact inertial igniter embodiment  325  of  FIG.  11   , the modified “no-spin” version of the compact inertial igniter embodiment  330  is provided with separate “groove pockets” ( 322  in  FIG.  11   ) of the same central cross-sectional areas as the groove  335  of embodiment  330  but limited in width to accommodate each a single ball  338  as shown in  FIG.  11    for the embodiment  323  and its top view of  FIG.  12   , in which top views of four groove pockets are shown with dashed lines. 
     It is noted that in the schematics of  FIGS.  11  and  12   , the compact inertial igniter embodiment  325  are assumed to have four symmetrically positioned groove pockets  322  to accommodate engaging balls as described for the compact inertial igniter embodiment  330  of  FIG.  14   . However, it is appreciated by those skilled in the art that depending on the size of the striker mass  337  and the housing  332  and the balls  338 , the inertial igniter can be provided with more or even fewer number of such groove pockets as long as there is room to accommodate them. It is, however, appreciated that for the sake of stability of striker mass movement, at least three symmetrically positioned groove pockets with proper engaging balls are generally desired to be provided. 
     It is appreciated that the aforementioned modified version of the compact inertial igniter embodiment  330  of  FIG.  14    with four symmetrically provided groove pockets ( 322  in  FIG.  11   ) looks exactly like the cross-sectional view of the compact inertial igniter embodiment  330  of  FIG.  14   . The modified version of the compact inertial igniter embodiment  330  also operates as was described previously for the embodiment  330  when subjected to acceleration in the direction of the arrow  345  ( 323  in  FIG.  11   ) corresponding to prescribed minimum acceleration magnitude and duration (all-fire condition in munitions) and other accidental accelerations (no-fire conditions in munitions). The only difference between the embodiments  330  and its modified version is that in the inertial embodiment  330 , the balls  338  can only travel up and down in the groove pockets ( 322  in  FIG.  11   ) as they are constrained by the walls  324  of the groove pockets,  FIG.  11   , from displacing in the lateral directions. Thereby the striker mass  337  assembly is prevented from rotating (spinning) relative to the inertial igniter housing  332  while the balls  338  are inside the groove pockets ( 322  in  FIG.  11   ) when the inertial igniter is subjected to spinning acceleration, which is not the case for the compact inertial igniter embodiment  330  of  FIG.  14   . 
     It is appreciated that like the compact inertial igniter  325  of  FIG.  11   , in the compact inertial igniter embodiment  330 ,  FIG.  14   , once the balls  338  have cleared the grove pockets  322  ( FIG.  11   ) under acceleration in the direction of the arrow  345 , the striker mass  337  is free to rotate (spin) relative to the inertial igniter housing  332  as it travels down towards the sharp tip member  334 . In certain application, however, it might be desirable to prevent such rotational motion of the striker mass  337 . This is ready accomplished by extending one or more of the groove pockets  322  further down (as shown with dashed lines in  FIG.  11    and indicated by the numeral  327 ) to or passed the point at which the engaging ball(s)  338  would be after the percussion primer  342  of the striker mass  337  has impacted the sharp tip  334  in the inertial igniter bottom surface  333 . 
     In addition, as it was described for the compact inertial igniter  325  of  FIG.  11   , the groove pocket  322  is vertical as viewed in  FIG.  11    to allow the balls  310  ( 337  in  FIG.  14   ) and thereby the striker mass  309  ( 337  in  FIG.  14   ) to travel down without rotation relative to the inertial igniter housing  301  ( 332  in  FIG.  14   ) when the inertial igniter  325  ( 330  in  FIG.  14   ) is subjected to acceleration in the direction of the arrow  323  ( 345  in  FIG.  14   ) and as long as the balls  310  ( 337  in  FIG.  14   ) are still in the groove pockets  322 . To increase the time that it takes for the balls  338  to clear the groove pocket  335  and thereby allow for free downward motion of the striker mass  337  assembly and the percussion primer  342  to strike the sharp tip  334  and be initiated, the groove pockets  322  ( FIG.  11   ) may have different curves shapes as extended downward as shown in  FIG.  13    as was previously described for the comp. act inertial igniter  325  of  FIG.  11   . 
     In the compact inertia igniters embodiments  300 ,  325  and  330  of  FIGS.  6 ,  11  and  14   , respectively, the striker mass elements ( 309  and  337  in  FIGS.  6  and  14   , respectively) are seen to be provided with ball pockets ( 311  and  339  in  FIGS.  6  and  14   , respectively) that are perpendicular to the interior surface of the inertial igniter body ( 304  and  336  in  FIGS.  6  and  14   , respectively), i.e., normal to the direction of the striker mass displacement. 
     It is, however appreciated that the ball pockets may also be directed upward ( FIG.  16 A ) or downward ( FIG.  16 B ) from their aforementioned normal direction to the direction of the striker mass displacement. 
     It is appreciated by those skilled in the art that if the ball  346  pocket  348  in the striker mass  344  is directed upward an angle φ u  as shown in  FIG.  16 A , then the lateral force F s  of the preloaded compressive spring  347  as shown in  FIG.  8 B  would be also make an angle φ u  with the horizontal centerline as shown with the dashed line arrow  349 . As a result, the forces F N  and Fu given by equations (1) and (2) are readily shown to be derived from the force balance equations (8) and (9) below. 
         F   S  Sin φ u   +F   N  Sin α= F   u   (8)
 
         F   N  Cos α= F   S  Cos φ u   (9)
 
     Now solving equations (8) and (9) for F u , we obtain 
     
       
         
           
             
               F 
               u 
             
             = 
             
               
                 
                   F 
                   S 
                 
                 ⁢ 
                 Sin 
                 ⁢ 
                 
                   φ 
                   u 
                 
               
               + 
               
                 
                   
                     F 
                     S 
                   
                   ⁢ 
                   Cos 
                   ⁢ 
                   
                     φ 
                     u 
                   
                   ⁢ 
                   Sin 
                   ⁢ 
                   α 
                 
                 
                   Cos 
                   ⁢ 
                   α 
                 
               
             
           
         
       
     
     Which can be simplified to 
     
       
         
           
             
               
                 
                   
                     F 
                     u 
                   
                   = 
                   
                     
                       F 
                       S 
                     
                     ( 
                     
                       
                         Sin 
                         ⁢ 
                         
                           φ 
                           u 
                         
                       
                       + 
                       
                         Cos 
                         ⁢ 
                         
                           φ 
                           u 
                         
                         ⁢ 
                         tan 
                         ⁢ 
                         α 
                       
                     
                     ) 
                   
                     
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
           
         
       
     
     From equation (10) it can be seen that the effect of upward direction of the ball pocket  348  by an angle φ u  as shown in  FIG.  16 A  would be to increase the effective force F u  that resists downward motion of the striker mass when the compact inertial igniter  300 ,  325  and  330  of  FIGS.  6 ,  11  and  14   , respectively, are subjected to acceleration in the direction of the arrows  319 ,  323  and  345 , respectively. Which means that the minimum acceleration a min , equation (4), in the direction of the arrows  319 ,  323  and  345  of  FIGS.  6 ,  11  and  14   , respectively, that the striker mass members  309  (embodiments of  FIGS.  6  and  11   ) and  337  (embodiment of  FIG.  14   ) is increased. 
     Similarly, it is appreciated by those skilled in the art that if the ball  353  pocket  351  in the striker mass  354  is directed downward an angle φ d  as shown in  FIG.  16 B , then the lateral force F S  of the preloaded compressive spring  352  as shown in  FIG.  8 B  would be also make an angle φ d  with the horizontal centerline as shown with the dashed line arrow  350 . As a result, the forces F N  and Fu given by equations (1) and (2) are readily shown to be derived from the force balance equations (11) and (12) below. 
         F   N  Sin α− F   S  Sin φ d   =F   u   (11)
 
         F   N  Cos α= F   S  Cos φ d   (12)
 
     Now solving equations (11) and (12) for F u , we obtain 
     
       
         
           
             
               F 
               u 
             
             = 
             
               
                 
                   - 
                   
                     F 
                     S 
                   
                 
                 ⁢ 
                 Sin 
                 ⁢ 
                 
                   φ 
                   d 
                 
               
               + 
               
                 
                   
                     F 
                     S 
                   
                   ⁢ 
                   Cos 
                   ⁢ 
                   
                     φ 
                     d 
                   
                   ⁢ 
                   Sin 
                   ⁢ 
                     
                   α 
                 
                 
                   Cos 
                   ⁢ 
                   α 
                 
               
             
           
         
       
     
     Which can be simplified to 
         F   u   =F   S (Cos φ d  tan α−Sin φ d )  (13)
 
     From equation (13) it can be seen that the effect of downward direction of the ball pocket  351  by an angle φ d  as shown in  FIG.  16 B  would be to decrease the effective force F u  that resists downward motion of the striker mass when the compact inertial igniter  300 ,  325  and  330  of  FIGS.  6 ,  11  and  14   , respectively, are subjected to acceleration in the direction of the arrows  319 ,  323  and  345 , respectively. Which means that the minimum acceleration a min , equation (4), in the direction of the arrows  319 ,  323  and  345  of  FIGS.  6 ,  11  and  14   , respectively, that the striker mass members  309  (embodiments of  FIGS.  6  and  11   ) and  337  (embodiment of  FIG.  14   ) is decreased. 
     It is appreciated that as can be seen in the cross-sectional view of  FIGS.  6  and  14    of the compact inertial igniter embodiments  300  and  330  and their isometric views of  FIGS.  7  and  15   , respectively, the top surfaces of their striker mass members  309  and  337  are slightly below the top surfaces  355  and  356  of the inertial igniter housings  301  and  332 , respectively. This is configured to be the case so that the compact inertial igniters can be assembled in the reserve battery or other provided housings while being supported on both top and bottom surfaces, and when needed laterally. 
     In the compact inertial igniter embodiments  300  and  330  of  FIGS.  6  and  14   , respectively, the inertial igniter housing  301  and  332  are shown to be provided with only one grooves pocket  305  and  335 , respectively, along the length (vertical direction as viewed in  FIGS.  11  and  14   ) of the compact inertial igniter housings. The compact inertial igniters may, however, be provided with multiple such groove pockets as shown in the schematic of  FIG.  17    with two such groove pockets and indicated as the embodiment  360 . In  FIG.  17   , the cross-sectional view of a modified compact inertial igniter embodiment  300  of  FIG.  6    is shown that is provided with two identical groove pockets. 
     In the compact inertial igniter embodiment  360  of  FIG.  17   , all components of the inertial igniter are identical to those of the embodiment  300  of  FIG.  6    except that the height of its housing  355  is increased to accommodate a second identical groove pocket  356 . 
     Then when the compact inertial igniter  360  is subjected to acceleration in the direction of the arrow  357 , as was previously described for the embodiment  300  of  FIG.  6   , if the acceleration in the direction of the arrow  357  persists and is high enough, i.e., is higher than the prescribed minimum all-fire acceleration level and duration (when used in munitions), the balls  359  will impact the bottom surface  364  of the groove pocket  358 , rebound and depending on its rebounding speed, may impact the top surface of the groove pocket  358  and eventually after one or more up and down rebounding against the top and bottom surfaces of the groove pocket  358  it would essentially “settle” over the bottom surface  364  and is pushed inside the spring pockets  365  while being sliding down the surface  367  due to the dynamic force F D ,  FIG.  9 B , which tends to push the balls  359  inside the pockets  365 , i.e., outside the groove pocket  358  space, and thereby freeing the slider mass  368  assembly from engagement with the groove pocket  358  of the housing  355  and allowing it to begin to move down until the balls  359  engage the second groove pocket  356  and are pushed inside the groove pocket space by the preloaded compressive spring  366 . 
     The same process of the balls  359  impacting the top and bottom surfaces of the groove pocket  356  would then follow and eventually, the balls  359  would similarly “settle” over the bottom surface of the groove pocket  356  and is pushed inside the spring pockets  365  while being sliding down the surface  367  due to the dynamic force F D ,  FIG.  9 B , which tends to push the balls  359  inside the pockets  365 , i.e., outside the groove pocket  356  space, and thereby freeing the slider mass  368  assembly from engagement with the groove pocket  356  of the housing  355  and allowing it to begin to be accelerated downwards. The striker mass  309  is then accelerated downward and gain further velocity, thereby kinetic energy. The striker mass  368  sharp tip  361  would then strike the percussion primer  362  and initiates it if the striker mass  368  has gained the requisite kinetic energy. 
     Then following initiation of the percussion primer  362  (or the provided pyrotechnics compound), the generated flames and sparks are configured to exit downward through the opening  363  to initiate the thermal (or liquid) reserve battery below or initiate an initiation train and the like. Alternatively, side ports may be provided to allow the flame to exit from the side of the compact inertial igniter to initiate the pyrotechnic materials (or the like) of a thermal reserve battery or the like that is positioned around the body of the inertial igniter. Other alternatives known in the art may also be used. 
     It is appreciated by those skilled in the art that by providing the second grove pocket  356  to the compact inertial igniter  360 , the delay time from the start of the prescribed acceleration in the direction of the arrow  357  to the time of initiation of the percussion prier  362  is increased—even almost doubled—as compared to the amount of the time that it would take compact inertial igniter  300  of  FIG.  6    for the same prescribed acceleration event. It is appreciated that more than two such groove pockets may be provided in a similar compact inertial igniter to further increase its initiation delay, but at the cost of further increasing the height of the compact inertial igniter. It is also appreciated that once the balls  359  have entered the groove pocket  356 , if the acceleration in the direction of the arrow  357  would cease, the balls  359  would still be trapped inside the groove pocket  356  and therefore the striker mass  368  assembly would not return to its initial engagement with the groove pocket  358  as shown in the cross-sectional view of  FIG.  17   . 
     It is appreciated that in the above disclosed compact inertial igniters, the ball springs ( 312 ,  340 ,  347 ,  352  and  366  in  FIGS.  6 ,  14 ,  16 A,  16 B and  17   , respectively) are biasing the corresponding striker masses ( 309 ,  337 ,  344 ,  354  and  368  in  FIGS.  6 ,  14 ,  16 A,  16 B and  17   , respectively) towards their uppermost position, shown for example in  FIGS.  6 ,  14  and  17   . However, if needed, added upward biasing force can be provided by the addition of a compressive spring between the striker mass and the compact inertial igniter housing. As an example, the compact inertial igniter embodiment  300  is shown with the added compressive spring  375  in the cross-sectional view of  FIG.  18   . All other above compact inertial igniter embodiments may similarly be provided with additional compressive springs. 
     In the compact inertial igniter embodiment  370  of  FIG.  18   , a compressive spring  375  is shown to be positioned inside  376  the inertial igniter body, between the bottom surface  372  of the striker mass  371  and the bottom surface  373  inside the inertial igniter body  374 . As a result, when the inertial igniter begins to be subjected to an increasing acceleration event in the direction of the arrow  377 , then as was previously described for the compact inertial igniter embodiment  330  of  FIG.  14   , the preloaded compressive spring and ball  379  assemblies would resist part of the dynamic force F D , equation (3), until the acceleration level reaches the level of a min , equation (4). Then if the compressive spring  375  has a spring constant k and is preloaded a distance d (providing a preloading force F p =kd), then the minimum acceleration level a min  at which the striker mass  371  assembly would begin to move down would be increased to 
     
       
         
           
             
               
                 
                   
                     a 
                     min 
                   
                   = 
                   
                     
                       
                         F 
                         u 
                       
                       + 
                       
                         F 
                         p 
                       
                     
                     m 
                   
                 
               
               
                 
                   ( 
                   14 
                   ) 
                 
               
             
           
         
       
     
     As can therefore be seen in equation (14), by preloading the compressive spring  375  to provide the force F p , the minimum acceleration a min  at which the striker mass  371  would begin to displace and accelerated downward is increased. It is appreciated that the compressive spring  375  would provide added resistive force as it is deformed. For example, once the compressive spring  375  is deformed (i.e., displaced downward as viewed in  FIG.  18   ) a distance δ, then the force applied by the compressive spring  375  to the striker mass  371  is increased by the amount δ, bringing to a total applied force of 
         F   p   =k ( d +δ)  (15)
 
     And the a min , equation (14), is also similarly increased by the increase in the resisting compressive spring force, equation (15), at each compressive spring deformation level  6 . 
     It is appreciated by those skilled in the art that the addition of the preloaded compressive spring  375  to any of the disclosed compact inertial igniters provides the means of providing a desired no activation acceleration level (no-fire condition for munitions) to the compact inertial igniter. 
     It is also appreciated by those skilled in the art that similar to the compact inertial igniter embodiment  360  of  FIG.  17   , which is provided with more than one groove pockets  358  and  356 , the compact inertial igniter embodiment  325  of  FIG.  11    may also be provided with more than one groove pocket  322  along the length of the inertial igniter body  301 . Each additional groove pocket must obviously be positioned below the groove pocket above it. In addition, at least one of the groove pockets must extend down the entire length of the inertial igniter inside surface (as shown by the dashed line  327  in  FIG.  11   ), i.e., as far down as needed for the balls  310  would travel down for the tip  316  of the striker mass  309 ,  FIG.  6   , to strike and initiate the percussion primer  314 . 
     The compact inertial igniter embodiments  300 ,  325 ,  330 ,  360  and  370  of  FIGS.  6 ,  11 ,  14 ,  17  and  18   , respectively, are configured to initiate a percussion primer when subjected to a previously described prescribed all-fire condition or other similar events. An operating mechanism of these embodiments may also be used to construct normally open (closed) electrical switches that close (open) a circuit when subjected to similar prescribed minimum acceleration shock loading levels and durations as described below for inertial igniter embodiment  300  and  330  of  FIGS.  6  and  14   , but it is readily seen that all other embodiments can be similarly converted to the indicated electrical impulse switched. 
     In all the above disclosed compact inertial igniter embodiments, in response to a prescribed minimum acceleration level and duration in the activation direction, for example in the direction of the arrow  319  in  FIG.  6    for the inertial igniter embodiment  300 , the striker mass ( 309  in  FIG.  9   ) of the inertial igniter is accelerated downward to impact the provided percussion primer or pyrotechnics materials causing them to ignite. The same mechanism used for the release of the striker mechanism due to a prescribed acceleration event (a prescribed minimum acceleration level with a prescribed minimum duration, i.e., a prescribed impulse threshold) can be used to provide the means of opening or closing or both of at least one electrical circuit, i.e., act as a so-called “Impulse Switch”, that is actuated only if it is subjected to the above prescribed minimum acceleration level as well as its minimum duration (all-fire condition in munitions), while staying inactive during all impulse conditions, even if the acceleration level is higher than the prescribed minimum acceleration level but its duration is significantly shorter than the prescribed duration threshold. 
     Such “impulse switches” also have numerous non-munitions applications. For example, such impulse switches can be used to detect events such as impacts, falls, structural failure, explosions, etc., and open or close electrical circuits to initiate prescribed actions. 
     Such “impulse switch” embodiments for opening/closing electrical circuits, with and without latching features, are described herein together with alternative methods of their configuration, such as modular configurations that can be readily assembled into the customer device or circuit. 
     The disclosed “impulse switches” function like the disclosed compact inertia igniter embodiments. The “impulse switches” would similarly respond to applied acceleration in the direction of their activation, and when the applied acceleration has a prescribed minimum level and duration, then their “striker mass” (for example,  309  in the embodiment  300  of  FIG.  6   ) is released and is accelerated downwards as was described for the disclosed compact inertial igniters. The difference between the disclosed compact inertial igniters and the “impulse switches” to be disclosed below is that instead of the striker mass initiating a percussion primer, it would be used to open or close an electrical switching mechanism as described below. 
     The impulse switching mechanism may be held in its activated state, i.e., may be provided with a so-called latching mechanism, or may move back to its pre-activation state after opening or closing the circuit. 
     A configuration of such impulse switches using the configuration and functionalities of the above disclosed compact inertial igniter embodiments is herein described using the compact inertial igniter embodiment  300  of  FIG.  6   . However, it is appreciated by those skilled in the art that other disclosed compact inertial igniter embodiments may also be similarly modified to function as impulse switches as will be described below for the embodiment  300  of  FIG.  6   . 
     The schematic of such an impulse switch embodiment  380  is shown in  FIG.  19   . A configuration of the impulse switch  380  is like the compact inertial igniter embodiment of  FIG.  6   , except that its percussion primer  314  and the sharp tip  316  of the striker mass are removed and its assembly pocket  313  and the exit hole  315  region are modified to assemble the electrical switching contacts and related elements described below to convert the compact inertial igniter into impulse switches for opening or closing electrical circuits. 
     In the impulse switch embodiment  380  of  FIG.  19   , an element  381 , which is constructed of an electrically non-conductive material is fixed to the impulse switch base  382  as shown in  FIG.  19   . The electrically non-conductive element  381  may be attached to the base  382  by fitting it through the provided, such as a stepped hole  383  in the impulse switch base  382  to resist being pressured out of the assembled position shown in  FIG.  19   . The element  383  is provided with two electrically conductive elements  384  and  385  with contact ends  386  and  387 , respectively. The electrically conductive elements  384  and  385  may be provided with the extended ends to form contact “pins” as shown in  FIG.  19    for direct insertion into provided holes in a circuit board or may alternatively be provided with wires  388  and  389 , respectively, for connection to appropriate circuit junctions, in which case, the wires  388  and  389  may be desired to exit from the sides of the impulse switch  380  (not shown). 
     Previously described inertial mass  390  (striker mass in the compact inertial igniter  300  of  FIG.  6   ) is provided with a flexible strip of electrically conductive material  391 , which is fixed to the surface of the inertial mass  390  as shown in  FIG.  19   , for example, with fasteners  392  or by soldering or other methods known in the art, such as by being integrally formed with the mass  390 . 
     An operation of the impulse switch  380  of  FIG.  19    is very similar to that of the compact inertial igniter  300  of  FIG.  6   . Here again and as was described for the compact inertial igniter  300 , when the impulse switch  380  is accelerated in the direction of the arrow  394 ,  FIG.  19   , as the prescribed minimum acceleration level and duration thresholds are reached, the inertial mass  390  is released as was described for the compact inertial igniter  300  of  FIG.  6   . The inertial mass  390  is then accelerated downward until the strip of electrically conductive material  391  comes into contact with the contact ends  386  and  387 , thereby closing the circuit to which the impulse switch  380  is connected (through the extended ends  384  and  385  or wires  388  and  389 ). 
     It is appreciated by those skilled in the art that once the strip of electrically conductive material  391  comes into contact with the contact ends  386  and  387 , thereby closing the circuit to which the impulse switch  380  is connected, the inertial mass  390  would usually bounce back due to its acquired kinetic energy, thereby ending the indicated closing of the circuit. The impulse switch  380  is thereby suitable for use in circuits in which only a “pulsed” closure of a circuit needs to be detected as a result of the prescribed minimum acceleration level and duration thresholds are detected. The impulse switch embodiment  380  of  FIG.  19    is thereby classified as a normally open and non-latching impulse switch. In addition, to ensure that the circuit is not closed and opened multiple times due to the bouncing back and forth of the inertial mass  390 , a relatively soft spring  395  (shown in dashed lines in  FIG.  19   ) may be provided to ensure that the inertial mass  390  and its strip of electrically conductive material  391  stay apart from the contacts  386  and  387  following the first closing of the circuit as described above. 
     If the impulse switch is desired to stay closed following activation, i.e., if the impulse switch  380  is desired to be a normally open and latching impulse switch, then it can be modified as shown in the cross-sectional view of  FIG.  20   . 
     The normally open and latching impulse switch embodiment  400  of  FIG.  20    has all its components identical to those of the impulse switch embodiment  380  of  FIG.  19   , except the following modifications. 
     In the “normally open and latching impulse switch” embodiment  400  of  FIG.  20   , the groove pocket  396  ( 405  in the embodiment  380  of  FIG.  19   ) is positioned closer to the bottom surface  407  of the interior volume of the impulse switch body  397 , thereby positioning the inertial mass  399  also closer to the bottom surface  407  as can be seen in  FIG.  20   . This opens the space  406  above the top surface  403  of the inertial mass  399  inside the impulse switch body  397 . The impulse switch body  397  is also provided with a cap member  401 , which is fixedly attached to the wall of the impulse switch body  397 , for example by fasteners or other means known in the art. Within the space  406  is then provided a preloaded compressive spring  402  between the top cap  401  and the top surface  403  of the inertial mass  399 . 
     The aforementioned configuration parameters of the of the impulse switch embodiment  400  and the characteristics of the compressive spring  402  and its preload level are selected such that when the device to which the “normally open and latching impulse switch” is attached is subjected to acceleration in the direction of the arrow  404  that has the prescribed minimum level and duration, then the inertial mass  399  is released as was previously described for the compact inertial igniter embodiment  300  of  FIG.  6   . The inertial mass  399  is then accelerated downward until the strip of electrically conductive material  391  comes into contact with the contact ends  386  and  387 , thereby closing the circuit to which the impulse switch  400  is connected (through the extended ends  384  and  385  or wires  388  and  389 ). At this point, the preloaded compressive spring  402  is configured to keep the strip of electrically conductive material  391  in contact with the contact ends  386  and  387  and keep the circuit to which the impulse switch is attached in its closed configuration. 
     The normally open and non-latching impulse switch embodiment  380  of  FIG.  19    and the normally open and latching impulse switch embodiment  400  of  FIG.  20    may also be modified to function as normally closed and non-latching and normally closed and latching impulse switches. The schematic of such a normally closed and non-latching impulse switch embodiment  410  is shown in  FIG.  21   . A configuration and operation of the impulse switch  410  is identical to that of the normally open non-latching impulse switch embodiment  380  of  FIG.  19   , except for its electrical switching contacts and related elements described below to convert it from a normally open to a normally closed impulse switch. 
     In the normally closed and non-latching impulse switch embodiment  410  of  FIG.  21   , like the normally open and non-latching impulse switch  380  of  FIG.  19   , an element  408 , which is constructed of an electrically non-conductive material is fixed to the impulse switch base  382 . The electrically non-conductive element  408  may be attached to the base  382  by fitting it through the provided stepped hole  452  as shown in  FIG.  21   . The element  408  is provided with two electrically conductive elements  411  and  412  with flexible contact ends  413  and  414 , respectively. The flexible electrically conductive contact ends  413  and  414  are biased to press against each other as seen in the schematic of  FIG.  21   . As a result, a circuit connected to the electrically conductive elements  411  and  412  is normally closed in the pre-activation state of the impulse switch  410  as shown in the configuration of  FIG.  21   . 
     The electrically conductive elements  411  and  412  are shown in  FIG.  21    to be provided with the extended ends to form contact “pins” for direct insertion into provided holes in a circuit board or may alternatively be provided with wires  415  and  416  for connection to appropriate circuit junctions, in which case, the wires  415  and  416  may be desired to exit from the sides of the impulse switch  410  (not shown). 
     The previously described inertial mass  390  is then provided with an electrically nonconductive wedge element  409 , which is fixed to the bottom surface of the inertial mass  390  as shown in  FIG.  21   , for example, by an adhesive or using other methods known in the art. 
     An operation of the normally closed and non-latching impulse switch  410  of  FIG.  21    is very similar to that of the normally open and non-latching impulse switch  380  of  FIG.  19   . Here again and as was described for the normally open and non-latching impulse switch  380 , when the impulse switch  410  is accelerated in the direction of the arrow  417 ,  FIG.  21   , as the prescribed minimum acceleration level and duration thresholds are reached, the inertial mass  390  is released as was described for the compact inertial igniter  300  of  FIG.  6   . The inertial mass  390  is then accelerated downward until the electrically nonconductive wedge element  409  is inserted between the contacting surfaces of the flexible electrically conductive contact ends  413  and  414 , thereby opening the circuit to which the impulse switch  410  is connected (through the extended ends  411  and  412  or wires  415  and  416 ). In addition, to ensure that the circuit is not closed and opened multiple times due to the bouncing back and forth of the inertial mass  390 , a relatively soft spring  395  (shown in dashed lines in  FIG.  21   ) may be provided to ensure that the inertial mass  390  and its electrically nonconductive wedge element  409  stay apart from the contacts  413  and  414  following the first opening of the circuit as described above. 
     Like the normally open and non-latching impulse switch embodiment  380  of  FIG.  19   , the normally closed and non-latching impulse switch embodiment  410  of  FIG.  21    may be modified to obtain a normally closed and latching impulse switch as shown in the cross-sectional view of  FIG.  22    and indicated as the embodiment  420 . 
     The normally closed and latching impulse switch embodiment  420  of  FIG.  22    has all its components identical to those of the impulse switch embodiment  410  of  FIG.  21   , except the following modifications. 
     In the “normally closed and latching impulse switch” embodiment  420  of  FIG.  22   , the groove pocket  418  ( 405  in the embodiment  405  of  FIG.  21   ) is positioned closer to the bottom surface  419  of the interior volume of the impulse switch body  421 , thereby positioning the inertial mass  422  closer to the bottom surface  419  as can be seen in  FIG.  22   . This opens the space  423  above the top surface  424  of the inertial mass  422  inside the impulse switch body  421 . The impulse switch body  421  is also provided with a cap member  425 , which is fixedly attached to the wall of the impulse switch body  421 , for example by fasteners or other means known in the art. Within the space  423  is then provided a preloaded compressive spring  426  between the top cap  425  and the top surface  424  of the inertial mass  422 . 
     The aforementioned configuration parameters of the of the impulse switch embodiment  420  and the characteristics of the compressive spring  426  and its preload level are selected such that when the device to which the “normally closed and latching impulse switch” embodiment  420  is attached is subjected to acceleration in the direction of the arrow  427  that has the prescribed minimum level and duration, then the inertial mass  422  is released as was previously described for the compact inertial igniter embodiment  300  of  FIG.  6   . The inertial mass  422  is then accelerated downward until the nonconductive wedge element  428  ( 409  in  FIG.  21   ) is inserted between the contacting surfaces of the flexible electrically conductive contact ends  429  and  430  ( 413  and  414  in  FIG.  21   ), thereby opening the circuit to which the impulse switch  420  is connected (through the extended ends  432  and  433  or wires  434  and  435 ), which are provided in the electrically non-conductive element  431  as was described for the identical element  408  of the embodiment of  FIG.  21   . In addition, to ensure that the circuit is not subsequently opened, a relatively soft spring  426  may be provided to ensure that the inertial mass  422  and its electrically nonconductive wedge element  428  stay inserted between the contacting surfaces of the flexible electrically conductive contact ends  429  and  430  and keep the circuit to which the impulse switch is attached in its closed configuration. 
     It is appreciated that the normally open and latching impulse switch embodiment  400  of  FIG.  20    has longer height to accommodate the preloaded compressive spring  402 . In addition, due to the preloading of the compressive spring  402 , to prevent activation at certain level of accidental accelerations in the direction of the arrow  404 , either the preloading levels of the compressive springs  312  or the angle α of the grove pocket  305 ,  FIG.  6   , must be increased. To avoid these changes and to significantly reduce the height of the normally open and latching impulse switch, the normally open and latching impulse switch embodiment  400  of  FIG.  20    can be modified to as shown in the cross-sectional view of  FIG.  23   , which is hereinafter referred to as the “compact normally open and latching impulse switch” embodiment  440 . 
     The “compact normally open and latching impulse switch” embodiment  440  of  FIG.  23    uses an inertial mass assembly  436 , which is identical to the inertial assembly  399  of the impulse switch embodiment  400  of  FIG.  20   , i.e., the inertial mass and its assembled balls and preloaded springs, members  309 ,  310  and  312  as shown in  FIG.  6   , and the strip of electrically conductive material  391 ,  FIG.  20   . The compact normally open and latching impulse switch embodiment  440  also uses a body  437 , which is similar to the body  397 , with the difference being its smaller height and the addition of a second grove pocket  438  in addition of the groove pocket  439  ( 396  in  FIG.  20   ). 
     The added groove pocket  438 , however, has an inverted cross-sectional profile (inverted with respect to a line perpendicular to the long axis, i.e., vertical direction as viewed in the plane of  FIG.  23   ) as seen in the cross-sectional view of the compact normally open and latching impulse switch embodiment  440  of  FIG.  23   . In the cross-sectional profile of the groove pocket  438 , the angles α and θ may, however, be different than those of the groove pocket  439  (usually larger angle α and smaller angle θ as described later). 
     Then similar to the normally open and latching impulse switch embodiment  400  of  FIG.  20   , when the device to which the “compact normally open and latching impulse switch” embodiment  440  of  FIG.  23    is attached is subjected to acceleration in the direction of the arrow  441  that has the prescribed minimum level and duration, then the inertial mass  436  is released as was previously described for the compact inertial igniter embodiment  300  of  FIG.  6   . The inertial mass  436  is then accelerated downward until the strip of electrically conductive material  442  ( 391  in  FIG.  20   ) comes into contact with the contact ends  444  and  445  ( 386  and  387  in  FIG.  20   ), thereby closing the circuit to which the impulse switch  440  is connected (through the extended ends  446  and  447  or wires  448  and  449 ). At around this time, the balls  450  in the pockets  451  of the inertial mass  436  are pushed into the groove pocket  438  and due to the angle α, they are forced down against the bottom surface  453  of the groove pocket  438 . In general, the angle α is made larger than those in the groove pocket  439  so that the downward force acting on the inertial mass  436  due to the forces exerted by the preloaded compressive springs  452  on the balls  450  are increased and thereby the inertial mass is pressed downward, thereby the strip of electrically conductive material  442  is pressed against the contact ends  444  and  445 . The angle θ on the other hand is decreased so that the inertial mass  436  would settle in its final position shown in  FIG.  24    quickly. The strip of electrically conductive material  442  is also provided with enough flexibility so that as the inertial mass  436  settles in its final positioning shown in  FIG.  24   , its contact with the contact ends  444  and  445  is not lost. The compact impulse switch embodiment  440  of  FIG.  23    would therefore function as a compact normally open and latching impulse switch. 
     In the impulse switch embodiments of  FIGS.  19 - 23   , the electrical contacts and members to open or close the circuits and latch or not to latch them after circuit opening and closing following the detection of the prescribed minimum acceleration level and its duration were accomplished by the specifically configured members and mechanisms for each impulse switch type. However, miniature normally open or closed and latching and non-latching electrical switches are mass produced and relatively low cost and can be used in place of the above switch components. An example, a “Nano-miniature model KMT2” tactile switch, which is 2×2.6 mm in size and 0.65 mm in height and manufactured by C&amp;K Switches of Waltham, Mass. may be used in the normally open and non-latching impulse switch embodiment  380  of  FIG.  19    in place of the conductive strip  391  and the assembly  383  and its conducting members. Similar miniature switches (normally open or closed and latching and non-latching may also be used in this or other impulse switch embodiments. 
     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.