Abstract:
A mechanism including: a toggle link rotatably connected to a base structure; a stop connected to the base structure for limiting a rotational travel of the toggle link; a biasing element having a first end attached to the base structure and a second end attached to the toggle link such that the toggle link is biased towards the stop when the toggle link is positioned on a first side of a singular position and the toggle link is biased towards an opposite direction from the stop when the toggle link is positioned on a second side of the singular position; and an inertial element movably disposed between the base structure and the toggle link such that that inertial element moves the toggle link from the first side of the singular position to the second side of the singular position when the base structure undergoes an acceleration event greater than a predetermined threshold.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims benefit to U.S. Provisional Application 61/551,405 filed on Oct. 25, 2011, the entire contents of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to linear or rotary acceleration (deceleration) or rotary speed (spin) operated mechanical delay mechanisms, and more particularly for inertial igniters for thermal batteries used in gun-fired munitions and other similar applications or electrical G-switches to open (close) a normally closed (open) circuit upon the device experiencing a prescribed said acceleration or rotary speed profile threshold. 
         [0004]    2. Prior Art 
         [0005]    Thermal batteries represent a class of reserve batteries that operate at high temperatures. Unlike liquid reserve batteries, in thermal batteries the electrolyte is already in the cells and therefore does not require a distribution mechanism such as spinning. The electrolyte is dry, solid and non-conductive, thereby leaving the battery in a non-operational and inert condition. These batteries incorporate pyrotechnic heat sources to melt the electrolyte just prior to use in order to make them electrically conductive and thereby making the battery active. The most common internal pyrotechnic is a blend of Fe and KClO 4 . Thermal batteries utilize a molten salt to serve as the electrolyte upon activation. The electrolytes are usually mixtures of alkali-halide salts and are used with the Li(Si)/FeS 2  or Li(Si)/CoS 2  couples. Some batteries also employ anodes of Li(Al) in place of the Li(Si) anodes. Insulation and internal heat sinks are used to maintain the electrolyte in its molten and conductive condition during the time of use. Reserve batteries are inactive and inert when manufactured and become active and begin to produce power only when they are activated. 
         [0006]    Thermal batteries have long been used in munitions and other similar applications to provide a relatively large amount of power during a relatively short period of time, mainly during the munitions flight. Thermal batteries have high power density and can provide a large amount of power as long as the electrolyte of the thermal battery stays liquid, thereby conductive. The process of manufacturing thermal batteries is highly labor intensive and requires relatively expensive facilities. Fabrication usually involves costly batch processes, including pressing electrodes and electrolytes into rigid wafers, and assembling batteries by hand. The batteries are encased in a hermetically-sealed metal container that is usually cylindrical in shape. Thermal batteries, however, have the advantage of very long shelf life of up to 20 years that is required for munitions applications. 
         [0007]    Thermal batteries generally use some type of igniter to provide a controlled pyrotechnic reaction to produce output gas, flame or hot particles to ignite the heating elements of the thermal battery. There are currently two distinct classes of igniters that are available for use in thermal batteries. The first class of igniter operates based on electrical energy. Such electrical igniters, however, require electrical energy, thereby requiring an onboard battery or other power sources with related shelf life and/or complexity and volume requirements to operate and initiate the thermal battery. The second class of igniters, commonly called “inertial igniters”, operates based on the firing acceleration. The inertial igniters do not require onboard batteries for their operation and are thereby often used in high-G munitions applications such as in gun-fired munitions and mortars. 
         [0008]    In general, the inertial igniters, particularly those that are designed to operate at relatively low impact levels, have to be provided with the means for distinguishing events such as accidental drops or explosions in their vicinity from the firing acceleration levels above which they are designed to be activated. This means that safety in terms of prevention of accidental ignition is one of the main concerns in inertial igniters. 
         [0009]    In general, electrical igniters use some type of sensors and electronics decision making circuitry to perform the aforementioned event detection tasks. Electrical igniters, however, required external electrical power sources for their operation. And considering the fact that thermal batteries (reserve batteries) are generally used in munitions to avoid the use of active batteries with their operational and shelf life limitations, and the aforementioned need for additional sensory and decision making electronics, electrical igniters are not the preferred means of activating thermal batteries and the like, particularly in gun-fired munitions, mortars and the like. 
         [0010]    Currently available technology (U.S. Pat. Nos. 7,437,995; 7,587,979; and 7,587,980; U.S. Application Publication No. 2009/0013891 and U.S. Application Ser. Nos. 61/239,048; 12/079,164; 12/234,698; 12/623,442; 12/774,324; and 12/794,763 the entire contents of each of which are incorporated herein by reference) has provided solution to the requirement of differentiating accidental drops during assembly, transportation and the like (generally for drops from up to 7 feet over concrete floors that can result in impact deceleration levels of up to 2000 G over up to 0.5 milli-seconds). The available technology differentiates the above accidental and initiation (all-fire) events by both the resulting impact induced inertial igniter (essentially the inertial igniter structure) deceleration and its duration with the firing (setback) acceleration level that is experienced by the inertial igniter and its duration, thereby allowing initiation of the inertial igniter only when the initiation (all-fire) setback acceleration level as well as its designed duration (which in gun-fired munitions of interest such as artillery rounds or mortars or the like is significantly longer than drop impact duration) are reached. This mode of differentiating the “combined” effects of accidental drop induced deceleration and all-fire initiation acceleration levels as well as their time durations (both of which would similarly tend to affect the start of the process of initiation by releasing a striker mass that upon impact with certain pyrotechnic material(s) or the like would start the ignition process) is possible since the aforementioned up to 2000 G impact deceleration level is applied over only 0.5 milli-seconds (msec), while the (even lower level) firing (setback) acceleration (generally not much lower than 900 G) is applied over significantly longer durations (generally over at least 8-10 msec). 
         [0011]    The safety mechanisms disclosed in the above referenced patents and patent applications can be thought of as a mechanical delay mechanism, after which a separate initiation system is actuated or released to provide ignition of the device pyrotechnics. Such inertia-based igniters therefore comprise of two components so that together they provide the aforementioned mechanical safety (delay mechanism) and to provide the required striking action to achieve ignition of the pyrotechnic elements. The function of the safety system is to hold the striker in position until a specified acceleration time profile actuates the safety system and releases the striker, allowing it to accelerate toward its target under the influence of the remaining portion of the specified acceleration time profile. The ignition itself may take place as a result of striker impact, or simply contact or “rubbing action” or proximity. For example, the striker may be akin to a firing pin and the target akin to a standard percussion cap primer. Alternately, the striker-target pair may bring together one or more chemical compounds whose combination with or without impact will set off a reaction resulting in the desired ignition. 
         [0012]    In addition, inertial igniters that are used in munitions that are loaded into ships by cranes for transportation are highly desirable to satisfy another no-fire requirement arising from accidental dropping of the munitions from heights reached during ship loading. This requirement generally demands no-fire (no initiation) due to drops from up to 40 feet that can result in impact induced deceleration levels (of the inertial igniter structure) of up to 18,000 Gs acting over up to 1 msec time intervals. Currently, inertial igniters that can satisfy this no-fire requirement when the all-fire (setback) acceleration levels are relatively low (for example, as low as around 900 G and up to around 3000 Gs or above) are not available. In addition, the currently known methods of constructing inertial igniters for satisfying 7 feet drop safety (resulting in up to 2,000 Gs of impact induced deceleration levels for up to 0.5 msec impulse) requirement cannot be used to achieve safety (no-initiation) for very high impact induced decelerations resulting from high-height drops of up to 40 feet (up to 18,000 Gs of impact induced decelerations lasting up to 1 msec). This is the case for several reasons. Firstly, impacts following drops occur at significantly higher impact speeds for drops from higher heights. For example, considering free drops and for the sake of simplicity assuming that no drag to be acting on the object, impact velocities for a drop from a height of 40 feet is approximately 15.4 m/sec as compared to a drop from a height of 7 feet is approximately 6.4 m/sec, or about 2.3 times higher for 40 feet drops). Secondly, the 7 feet drops over concrete floor lasts only up to 0.5 seconds, whereas 40 feet drop induced inertial igniter deceleration levels of up to 18,000 Gs can have durations of up to 1 msec. As a result, the distance travelled by the inertial igniter striker mass releasing element is so much higher for the aforementioned 40 feet drops as compared to 7 feet drops that it has made the development of inertial igniters that are safe (no-initiation occurring) as a result of such 40 feet drops impractical. 
         [0013]    A schematic of a cross-section of a conventional thermal battery and inertial igniter assembly is shown in  FIG. 1 . In thermal battery applications, the inertial igniter  10  (as assembled in a housing) is generally positioned above the thermal battery housing  11  as shown in  FIG. 1 . Upon ignition, the igniter initiates the thermal battery pyrotechnics positioned inside the thermal battery through a provided access  12 . The total volume that the thermal battery assembly  16  occupies within munitions is determined by the diameter  17  of the thermal battery housing  11  (assuming it is cylindrical) and the total height  15  of the thermal battery assembly  16 . The height  14  of the thermal battery for a given battery diameter  17  is generally determined by the amount of energy that it has to produce over the required period of time. For a given thermal battery height  14 , the height  13  of the inertial igniter  10  would therefore determine the total height  15  of the thermal battery assembly  16 . To reduce the total volume that the thermal battery assembly  16  occupies within a munitions housing, it is therefore important to reduce the height of the inertial igniter  10 . This is particularly important for small thermal batteries since in such cases the inertial igniter height with currently available inertial igniters can be almost the same order of magnitude as the thermal battery height. 
         [0014]    A design 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 co-pending patent application Ser. No. 12/835,709, the contents of which are incorporated herein by reference. 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—not shown) to allow the ignited sparks and fire to exit the inertial igniter into the thermal battery positioned under the inertial igniter  200  upon initiation of the inertial igniter pyrotechnics  204 ,  FIG. 2 , or percussion cap primer when used in place of the pyrotechnics as disclosed therein. 
         [0015]    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 . 
         [0016]    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 is preferably 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. 
         [0017]    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 . 
         [0018]    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 is preferably 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 . 
         [0019]    Alternatively, a two-part pyrotechnics compound, e.g., potassium chlorate and red phosphorous, may be used. When using such a two-part pyrotechnics compound, the first part, in this case the potassium chlorate, can be provided on the interior side of the base in a provided recess, and the second part of the pyrotechnics compound, in this case the red phosphorous, is provided on the lower surface of the striker mass surface facing the first part of the pyrotechnics compound. In general, various combinations of pyrotechnic materials may be used for this purpose with an appropriate binder to firmly adhere the materials to the inertial igniter (e.g., metal) surfaces. 
         [0020]    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. 
         [0021]    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. 
         [0022]    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. 
         [0023]    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 aforementioned rectangular cross-section wave springs or the like has the following significant advantages over helical springs that are constructed with wires with circular cross-sections. Firstly and most importantly, as the spring is compressed and nears its “solid” length, the flat surfaces of the rectangular cross-section wires come in contact, 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 also significantly increase the repeatability of the initiation for a specified all-fire condition. The second advantage of the use of the aforementioned wave springs with rectangular cross-section, particularly since the wires can and are usually made thin in thickness and relatively wide, is that the solid length of the resulting wave spring can be made to be significantly less than an equivalent regular helical spring with circular cross-section. As a result, the total height of the resulting inertial igniter can be reduced. Thirdly, since the coil waves are in contact with each other at certain points along their lengths and as the spring is compressed, the length of each wave is slightly increased, therefore during the spring compression the friction forces at these contact points do certain amount of work and thereby absorb certain amount of energy. The presence of this friction force ensures that the firing acceleration and very rapid compression of the spring would to a lesser amount tend to “bounce” the collar  211  back up and thereby increasing the possibility that it would interfere with the exit of the locking balls from the dimples  209  of the striker mass  205  and the release of the striker mass  205 . The above characteristic of the wave springs with rectangular cross-section should therefore also significantly enhance the performance and reliability of the inertial igniter  200  while at the same time allowing its height (and total volume) to be reduced. 
         [0024]    The striker mass  205  and striker tip  216  may be a monolithic design with the striking tip  216  being machined as shown in  FIG. 2  or as a boss protruding from the striker mass, or the striker tip  216  may be a separate piece, possibly fabricated from a material that is significantly harder than the striker mass material, and pressed or otherwise permanently fixed to the striker mass. A two-piece design would be favorable to the need for a striker whose density is different than steel, but whose tip would remain hard and tough by attaching a steel ball, hemisphere, or other shape to the striker mass. A monolithic design, however, would be generally favorable to manufacturing because of the reduction of part quantity and assembly operations. 
         [0025]    In the embodiment  200  of  FIGS. 2 and 3 , following ignition of the pyrotechnics compound  215 , the generated flames and sparks are designed to exit downward through the opening  204  to initiate the thermal battery below. Alternatively, if the thermal battery is positioned above the inertial igniter  200 , the opening  204  can be eliminated and the striker mass could be provided with at least one opening (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. 
         [0026]    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. 
         [0027]    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 is particularly the case for relatively small thermal batteries. In such thermal battery configurations, since the inertial igniter  240  ( 250 ) is inside the hermetically sealed thermal battery  241  ( 251 ), there is no need for a separate housing to be provided for the inertial igniter itself. In this assembly configuration, the thermal battery housing  242  ( 252 ) is provided with a separate compartment  243  ( 253 ) for the inertial igniter. The inertial igniter compartment  243  ( 253 ) is preferably formed by a member  244  ( 254 ) which is fixed to the inner surface of the thermal battery housing  242  ( 253 ), preferably by welding, brazing or very strong adhesives or the like. The separating member  244  ( 254 ) is provided with an opening  245  ( 255 ) to allow the generated flame and sparks following the initiation of the inertial igniter  240  ( 250 ) to enter the thermal battery compartment  246  ( 256 ) to activate the thermal battery  241  ( 251 ). The separating member  244  ( 254 ) and its attachment to the internal surface of the thermal battery housing  242  ( 252 ) must be strong enough to withstand the forces generated by the firing acceleration. 
         [0028]    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. 
         [0029]    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. 
         [0030]    It is appreciated by those skilled in the art that by varying the mass of the striker  205 , the mass of the collar  211 , the spring rate of the setback spring  210 , the distance that the collar  211  has to travel downward to release the locking balls  207  and thereby release the striker mass  205 , and the distance between the tip  216  of the striker mass  205  and the pyrotechnic compound  215  (and the tip of the protrusion  217 ), the designer of the disclosed inertial igniter  200  can try 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. 
         [0031]    Briefly, the safety system parameters, i.e., the mass of the collar  211 , the spring rate of the setback spring  210  and the dwell stroke (the distance that the collar  210  has to travel downward to release the locking balls  207  and thereby release the striker mass  205 ) must be tuned to provide the required actuation performance characteristics. Similarly, to provide the requisite impact energy, the mass of the striker  205  and the aforementioned separation distance between the tip  216  of the striker mass and the pyrotechnic compound  215  (and the tip of the protrusion  217 ) must work together to provide the specified impact energy to initiate the pyrotechnic compound when subjected to the remaining portion of the prescribed initiation acceleration profile after the safety system has been actuated. 
         [0032]    In certain applications, however, the inertial igniter is required to withstand no-fire accelerations that are significantly higher in amplitude and that are relatively long in duration For example, when the firing (setback) acceleration may be in the range of 900-3000 Gs with a duration of over 8-12 msec, while for safety considerations, the inertial igniter may be required to withstand (no-fire) accelerations resulting from drops from heights as high as 40 feet (which can generate inertial igniter impact deceleration levels of up to 18,000 Gs with durations of up to 1 msec). This is readily shown to be the case since for drops from high-heights of the order of 40 feet that result in impact induced inertial igniter deceleration levels of up to 18,000 Gs with durations of up to 1 msec, due to the high velocity of the inertial igniter and its various elements (including the collar  211 ,  FIG. 2 ) at the time of impact and the long duration of the impact induced inertial igniter deceleration, the amount of downward travel of the collar  211  ( FIG. 2 ) relative to the inertial igniter body (element  203 ) will become so long that makes such inertial igniters impractical for munitions applications. This is particularly the case for inertial igniters used in munitions with relatively low all-fire (setback) acceleration levels, since the compressive preload in the striker spring  210  ( FIG. 2 ) needs to be low (since the dynamic force resulting by the firing acceleration acting on the inertia of the collar  211  must be significantly less than the compressive preloading level of the striker spring  210  to allow the release of the striker mass  205  when all-fire acceleration level is reached and thereby cause igniter initiation), thereby the fast downward translation of the collar  211  relative to the inertial igniter body  203  is minimally impeded by the upward force generated by the striker spring  210 . 
         [0033]    Thus, it is shown that it is not possible to use the methods used in the design of currently inertial igniters of the type shown in  FIG. 2  (e.g., see U.S. Pat. Nos. 7,587,979; 7,587,980 and 7,832,335; U.S. Patent application Publication Nos. 2009/0013891 and 2010/0307362 and U.S. patent application Ser. Nos. 13/207,355; 12/079,164; 12/794,763; 12/835,709 and 13/207,280, each of which is incorporated herein by reference) except the ones provided in U.S. patent Application No. 13/180,469 filed on Jul. 11, 2011 (incorporated herein by reference) to provide no-fire safety for accidental drops from height of up to 7 feet to design inertial igniters that provide no-fire safety for the aforementioned drops from heights of up to 40 feet. 
         [0034]    The aforementioned currently available inertial igniters have a number of shortcomings for use in thermal batteries for munitions, particularly for munitions that are launched at relatively low setback accelerations, such as a few hundred or even less G levels. This is particularly the case for inertial igniters that are required to withstand high G accelerations with significant durations caused by accidental drops from the aforementioned high heights of up to around 40 feet. 
         [0035]    In addition, in certain munitions or similar applications, the munitions are subjected to relatively low setback accelerations with relatively short duration. Currently available inertial igniters designs cannot provide both safety and initiation requirements since in such applications the setback acceleration duration is not long enough to allow the safety mechanism actuate or release the striker mass as well as accelerate the striker mass to a high enough velocity to initiate the pyrotechnic material. 
         [0036]    In addition, in recent years, new and improved chemistries and manufacturing processes have been developed that promise the development of lower cost and higher performance thermal batteries that could be produced in various shapes and sizes, including their small and miniaturized versions. Thus, it is important that the developed inertial igniters be relatively small and suitable for small and low power thermal batteries, particularly those that are being developed for use in miniaturized fuzing, future smart munitions, and other similar applications. 
       SUMMARY OF THE INVENTION 
       [0037]    The need to differentiate accidental and initiation accelerations by the resulting impulse level of the event necessitates the employment of a safety system which is capable of allowing initiation of the igniter only during high total impulse levels. The safety mechanisms described herein are novel mechanical rotary and rotary-toggle type mechanism, which respond to linear and/or rotary (spin generating) acceleration applied to the inertial igniter. If the applied acceleration reaches or passes the designed initiation levels and if its duration is long enough, i.e., larger than any expected to be experienced as the result of accidental drops or explosions in their vicinity or other non-firing events, i.e., if the resulting impulse levels are lower than those indicating gun-firing, then the delay mechanism returns to its original pre-acceleration configuration, and a separate initiation system is not actuated or released to provide ignition of the pyrotechnics. Otherwise, the separate initiation system is actuated or released to provide ignition of the pyrotechnics. 
         [0038]    Inertia-based igniters must therefore comprise two components so that together they provide the aforementioned mechanical safety (mechanical delay mechanism) and to provide the required striking action to achieve ignition of the pyrotechnic elements. The function of the safety system is to prevent the striker mechanism to initiate the pyrotechnic, i.e., to delay full actuation or release of the striker mechanism until a specified acceleration time profile has been experienced. The safety system should then fully actuate or release the striker, allowing it to accelerate toward its target under the influence of the remaining portion of the specified acceleration time profile and/or certain spring provided force. The ignition itself may take place as a result of striker impact, or simply contact or proximity or a rubbing action. For example, the striker may be akin to a firing pin and the target akin to a standard percussion cap primer. Alternately, the striker-target pair may bring together one or more chemical compounds whose combination with or without impact or a rubbing will set off a reaction resulting in the desired ignition. 
         [0039]    Herein is described novel rotary and rotary-toggle type mechanism mechanical mechanisms that provide the means to achieve aforementioned required munitions safety due to accidental dropping or the like while providing the means to activate the inertial igniter when subjected to setback acceleration in a very small size and volume packages (as compared to prior art mechanisms). These mechanisms are particularly suitable for inertial igniters, but may also be used in other similar applications, for example as so-called electrical G-switches that open (or close) an electrical circuit only when the device is subjected to a prescribed acceleration profile (impulse) threshold. Also disclosed are a number of inertial igniter embodiments that combine such mechanical delay mechanisms (safety systems) with impact or rubbing or contact based initiation systems. 
         [0040]    A need therefore exists for the development of novel methods and resulting mechanical inertial igniters for thermal batteries used in gun fired munitions, mortars, small rockets and for other similar applications that occupy very small volumes and eliminate the need for external power sources and can initiate at relatively low setback impulse levels (i.e., either relatively low acceleration levels or relatively short setback acceleration duration or both relatively low acceleration levels and relatively short setback acceleration duration). The development of such novel miniature inertial ignition mechanism concepts also requires the identification or design of appropriate pyrotechnics and their initiation mechanisms. 
         [0041]    A need also therefore exists for the development of novel methods and resulting mechanical inertial igniters for thermal batteries used in gun fired munitions, mortars and for other similar applications that occupy very small volumes and eliminate the need for external power sources and can initiate when subjected to high spin rates, such as those in the order of 100 or more cycles per second, or relatively high rotary (spin) accelerate rates. Such inertial igniters must in general be safe and in particular they should not initiate if dropped, e.g., from up to 7 feet onto a concrete floor (generally corresponding to acceleration levels of up to 2,000 G for a duration of up to 0.5 msec) for certain applications, and from up to 40 feet (generally corresponding to acceleration levels of up to 18,000 G for a duration of up to 1 msec). The development of such novel miniature inertial ignition mechanism concepts also requires the identification or design of appropriate pyrotechnics and their initiation mechanisms. 
         [0042]    The innovative inertial igniters would preferably be scalable to thermal batteries of various sizes, in particular to miniaturized igniters for small size thermal batteries. Reliability is also of much concern since the rounds should have a shelf life of up to 20 years and could generally be stored at temperatures of sometimes in the range of −65 to 165 degrees F. This requirement is usually satisfied best if the igniter pyrotechnic is in a sealed compartment. The inertial igniters must also consider the manufacturing costs and simplicity in design to make them cost effective for munitions applications. 
         [0043]    A need also therefore exists for the development of novel methods and resulting mechanical G-switches for use in gun fired munitions, mortars, small rockets or other similar applications that can be used to open (close) a normally closed (open) electrical circuitry or the like upon the device using such G-switch experiencing an acceleration profile corresponding to one of the aforementioned setback acceleration profiles (i.e., either relatively low acceleration levels or relatively short setback acceleration duration or both relatively low acceleration levels and relatively short setback acceleration duration). Such G-switches must occupy relatively small volumes and do not require external power sources for their operation. In many gun fired munitions and mortar and other similar applications, such G-switches must not operate when dropped, e.g., from up to 7 feet onto a concrete floor (generally corresponding to acceleration levels of up to 2,000 G for a duration of up to 0.5 msec) for certain applications, and from up to 40 feet (generally corresponding to acceleration levels of up to 18,000 G for a duration of up to 1 msec). 
         [0044]    A need also exists for the development of novel methods and resulting mechanical G-switches for use in gun fired munitions, mortars, small rockets or other similar applications that can be used to open (close) a normally closed (open) electrical circuitry or the like upon the device using such G-switch experiencing high spin rates, such as those in the order of 100 or more cycles per second, or relatively high rotary (spin) accelerate rates. Such G-switches must occupy relatively small volumes and do not require external power sources for their operation. In many gun fired munitions and mortar and other similar applications, such G-switches must not operate when dropped, e.g., from up to 7 feet onto a concrete floor (generally corresponding to acceleration levels of up to 2,000 G for a duration of up to 0.5 msec) for certain applications, and from up to 40 feet (generally corresponding to acceleration levels of up to 18,000 G for a duration of up to 1 msec). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0045]    These and other features, aspects, and advantages of the apparatus of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
           [0046]      FIG. 1  illustrates a schematic of a cross-section of a thermal battery and inertial igniter assembly. 
           [0047]      FIG. 2  illustrates a schematic of a cross-section of an inertial igniter for thermal battery described in the prior art. 
           [0048]      FIG. 3  illustrates a schematic of the isometric drawing of the inertial igniter for thermal battery of  FIG. 2 . 
           [0049]      FIG. 4   a  illustrates a schematic of a cross-section of a thermal battery 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. 
           [0050]      FIG. 4   b  illustrates a schematic of a cross-section of a thermal battery 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. 
           [0051]      FIG. 5  illustrates a schematic of cross-section of an inertial igniter for thermal battery described in prior art with an outer housing. 
           [0052]      FIG. 6   a  illustrates a schematic of the first embodiment of an inertia igniter configured to initiate pyrotechnic materials when subjected all-fire spin rate. 
           [0053]      FIGS. 6   b - 6   e  illustrate the inertia igniter of  FIG. 6   a  in various stages of spin rates. 
           [0054]      FIG. 7   a  illustrates a schematic of an electrical G-switch configured to close (open) when it is subjected to a prescribed spin rate. 
           [0055]      FIGS. 7   b   1 ,  7   b   2  and  7   c  illustrate the schematic of details of general configuration of the contact elements of a normally open version of the electrical G-switch of  FIG. 7   a.    
           [0056]      FIG. 7   d  illustrates the schematic of the electrical G-switch of  FIG. 7   a  in its activated configuration. 
           [0057]      FIGS. 8   a  and  8   b  illustrate the schematic of details of general configuration of the contact elements of a normally closed version of the electrical G-switch of  FIG. 7   a.    
           [0058]      FIG. 8   c  illustrates the schematic of the electrical G-switch of  FIG. 8   a  in its activated configuration. 
           [0059]      FIG. 9   a  illustrates a schematic of another embodiment of an inertia igniter configured to initiate pyrotechnic materials when subjected all-fire axial (setback) accelerations of relatively low amplitude and/or low duration. 
           [0060]      FIG. 9   b  illustrates the inertia igniter of  FIG. 9   a  in its activated configuration following an all-fire setback acceleration. 
           [0061]      FIGS. 9   c - 9   d  illustrate view “A” of  FIG. 9   a , showing the operation of the striker link release mechanism of the inertia igniter of  FIG. 9   a.    
           [0062]      FIG. 10  illustrates a schematic of another embodiment of an inertia igniter configured to initiate pyrotechnic materials when subjected all-fire spin acceleration for use in so-called spinning rounds, i.e., rounds that are fired by rifled gun to gain high spin rate about their long axis for stability upon gun barrel exit. 
           [0063]      FIG. 11  illustrates an overall isometric view of an inertial igniter of one of the disclosed embodiments packaged in housing with flame exit opening. 
           [0064]      FIG. 12  illustrates the assembly of two or more (in this illustration three) packaged inertial igniters shown in  FIG. 11  on a single platform for assembly inside a thermal battery for providing two or more independent means of thermal battery initiation to achieve very high level of thermal battery initiation reliability. 
           [0065]      FIG. 13  illustrates an overall isometric view of a G-switch of one of the disclosed embodiments packaged in housing. 
           [0066]      FIG. 14  illustrates the assembly of two or more (in this illustration three) packaged G-switches shown in  FIG. 13  on a single platform for providing two or more independent means of detecting all-fire condition to achieve very high level of all-fire condition detection reliability. 
           [0067]      FIG. 15  illustrates an alternative means of releasing the rotary striker of the inertial igniter of the embodiment of  FIG. 10  under all-fire spin acceleration via the controlled breakage of a shear pin. 
           [0068]      FIG. 16  illustrates another alternative means of releasing the rotary striker of the inertial igniter of the embodiment of  FIG. 10  under all-fire spin acceleration via a detent pin. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0069]    One embodiment  100  of the present inertial igniter invention is shown in the schematic of  FIG. 6   a . In this embodiment, the striker component of the inertial igniter  100  is a toggle type of mechanism with the toggle link  101 , which is attached to the structure of the inertial igniter  102 , by a pin joint indicated with numeral  103 . In its rest and normal position shown in  FIG. 6   a , the striker (toggle) link  101  is biased to rest on its right-most position shown in  FIG. 6   a , against the stop  104 , by the spring  105 . The spring  105  is preloaded in tension, and serves as the toggle mechanism spring, and is attached to the structure  102  on the end  107  and to the striker link  101  on the other end  108 , preferably with pin or pin-like joints. The elements  106  and  114 , fixed to the striker link  101  and the inertial igniter structure  102 , respectively, are the two components of the ignition pyrotechnic. Alternatively, a one piece pyrotechnic element may be used, in which case the element  106  is preferably the ignition impact mass or pin and the element  114  is preferably the one piece impact initiated pyrotechnic element. 
         [0070]    The inertial igniter  100  is intended to be used in spinning munitions and is designed to activate by centrifugal forces generated by the spinning of the round about its long axis as described below. In the schematic of  FIG. 6   a , the inertial igniter  100  is being viewed along the long axis of the spinning round with the axis of spinning rotation (center of rotation of the inertial igniter as viewed in the schematic of  FIG. 6   a ) is considered to be at the point  109 . 
         [0071]    The operation of the embodiment  100  is as follows. At rest, the striker link  101  is biased to the right of the line  115  that passes through the pin joint  103  of the striker link  101  and the attachment point  107  of the spring  105 , and leaving the striker link  101  attachment point  108  of the spring  105  to the right of the said line  115 . When the munitions using the inertial igniter  100  is fired and begin to spin, the centripetal acceleration acts on the inertia of the element  110 , generating a centrifugal force that will tend to push the element  110  in the direction of the arrow  111 , against the surface  112  of the inertial igniter structure  102  and the side  113  of the striker link  101 . If the munitions spin rate is high enough, it would generate a large enough centrifugal force on the element  110  in the direction of the arrow  111  to overcome the force exerted by the spring  105  on the striker link  101  to press it against the stop  104  and preventing it from rotating in the counterclockwise direction. As the aforementioned spin rate keeps increasing, the centrifugal force acting on the element  110  increases, thereby beginning to rotate the striker link  101  in the counterclockwise direction as shown in the schematic of  FIG. 6   b , until the attachment point  108  of the spring  105  reaches the line  115  as shown in  FIG. 6   c , i.e., until the toggle mechanism (striker) link  101  reaches its so-called singular position. With any further increase in the spin rate, the striker link  101  is further rotated in the counterclockwise direction and passes the aforementioned singular position, and the tensile force of the spring  105  will accelerate it rotationally in the counterclockwise direction (at least partially aided by further motion of the element  110  in the direction of the arrow  111 ) as shown in  FIG. 6   d . The striker link  101  will keep rotating in the counterclockwise direction with accelerating rate until the pyrotechnic components  114  and  106  impact and cause ignition. The latter state of the striker link  101  is shown in dashed lines in  FIG. 6   e.    
         [0072]    The flames and sparks generated by the ignition of the pyrotechnic material  114  and  106  is then routed out from provided ports, usually through a hole such as the hole  120  to below the base to initiate the thermal material pyrotechnics. In some applications the flames and sparks are required to be routed from the side or from the top (opposite to the direction of exit from the hole  120 ) side of the inertial igniter  100 . 
         [0073]    It is noted that if the center of mass of the striker link  101  is away from the pin joint  103 , then as the device spins, the resulting centripetal acceleration would act on the inertia of the striker link  101 , generating a centrifugal force that would tend to rotate/keep the striker link  101  towards/at the aforementioned singular position shown in  FIG. 6   c . For this reason, the striker link  101  can be constructed such that its center of mass is located at the pin joint  103  or as close to it as possible. 
         [0074]    In general, the tensile preloading of the spring  105  and the inertia (mass) of the element  110  are selected such that if the munitions in which the inertial igniter is installed is accidentally dropped (in the direction of accelerating the element  110  in the direction of the arrow  111 ) or if the said munitions is made to gain spin rates that falls below the all-fire spin, or in case of any specified accidental events, the resulting counterclockwise rotation of the striker link  101  would always be less than required to bring it to (even close) to its aforementioned singular position shown in the schematic of  FIG. 6   c . Then following any one of such accidental events, the preloaded spring  105  would force the striker link to return to its initial inactivated state shown in the schematic of  FIG. 6   a.    
         [0075]    The inertial igniter  100  can be readily modified to operate as a so-called electrical G-switch upon activation by the aforementioned all-fire spin rate would close (open) a normally open (closed) electrical circuit. One embodiment  150  such a G-switch is shown in the schematic of  FIG. 7   a . The construction and operation of the electrical G-switch is identical to those of the inertial igniter  100  of  FIGS. 6   a - 6   d,  except that the pyrotechnic components  106  and  114  of the inertial igniter  100  is replaced by contact and circuit closing (opening) elements described below. 
         [0076]    The schematic of the electrical G-switch  150  is shown in  FIG. 7   a . In this embodiment, the pyrotechnic component  114  of the inertial igniter  100  ( FIG. 6   a ) is replaced with the contact element  151  and its pyrotechnic component (or striker pin) element  106  by the contact bridging element  152 . All other elements of the G-switch  150  are indicated with the same numerals as the inertial igniter  100  of  FIG. 6   a.    
         [0077]    The close-up view “A” of the contact element  151  is shown in the schematic of  FIG. 7   b   1 . The contact element  151  is fixed to the structure  102  of the device and is constructed with at least two contacts  153  and  154 , which are mounted on an electrically non-conductive base  157 . The contact element  151  is also provided with conductive wires  155  and  156 , which are connected to the contacts  153  and  154 , respectively. The electrically conductive wires are passed through the electrically non-conductive base  157  as shown in  FIG. 7   a  to prevent them from making contact. 
         [0078]    It is appreciated by those skilled in the art that if the structure  102  of the G-switch  150  is constructed with electrically conductive material, then the conductive wires  153  and  154  have to be routed out of the electrically non-conductive base  157  (from the side as shown in  FIG. 7   a  or through a hole in the electrically conductive base of the structure  102 —not shown in  FIG. 7   a ). In applications in which the G-switch is attached, for example, to a printed circuit board  161  as shown in  FIG. 7   c , the electrically non-conducting base  157  is preferably mounted over a provided opening  159  in the structure  102  as shown in  FIG. 7   c , preferably in a provided recess  160 , thereby allowing the contact wires  162  and  163  to pass through the provided opening  159  to reach the underlying element (in this case the printed circuit board  161 ). The wires can then be connected to the appropriate circuit provided over or bellow the circuit board  161 —not shown). 
         [0079]    The close-up view “B” of the contact element  152 ,  FIG. 7   a , is also shown schematically in  FIG. 7   b   2 . The contact element  152  consists of an electrically non-conductive base  165 , which is fixed to the surface of the link  166  ( 101  in the inertial igniter  100  of  FIG. 6   a ) as shown in  FIG. 7   a . An electrically conductive contact strip  164  (which can be relatively thin and flexible) is mounted on the surface of the electrically non-conductive base  165 . 
         [0080]    The electrical G-switch  150  operates in a manner similar to the inertial igniter  100  of  FIG. 6   a - 6   e,  i.e., as the aforementioned spin rate is increased and reaches certain predetermined threshold, the link  166  begins to rotate in the counterclockwise direction. As the spin rate is further increased, the link  166  rotates further in the counterclockwise direction, until at a predetermined spin rate, the link  166  reaches its aforementioned singular position (as shown for the striker link  100  in the schematic of  FIG. 6   c ). With further increase in the spin rate, the striker link  166  is further rotated in the counterclockwise direction and passes its aforementioned singular position, and the tensile force of the spring  105  will accelerate it rotationally in the counterclockwise direction (at least partially aided by further motion of the element  110  in the direction of the arrow  111 ) as shown in  FIG. 6   d  for the inertial igniter  100 . The link  166  will then keep rotating in the counterclockwise direction with accelerating rate until the contact strip  164  of the contact element  152  comes into contact with the contacts  153  and  154  of the contact element  151  as shown in the schematic of  FIG. 7   d . As a result, the wires  155  and  156  are connected electrically, and the circuit to which they are connected is closed. 
         [0081]    It is appreciated by those skilled in the art that more than two contacts  153  and  154  may be provided on the contact element  151 , thereby allowing the electrically conductive strip  164  of the contact element  152  to close more than one electrical circuit (when using pairs of contacts  153  and  154  and electrically isolated electrically conductive strips  164  on the contact elements  151  and  152 , respectively) or allowing at least three contacts (similar to contacts  153  and  154 ) on the contact element  151  to form a junction by an electrically conductive strip  164 . 
         [0082]    The electrical G-switch  150  of  FIG. 7   a  is designed for closing an electrical circuit once the G-switch is activated. Alternatively, the electrical G-switch  150  can be designed for opening an already closed electrical circuit by replacing the pair of contact elements  151  and  152  shown in  FIGS. 7   b   1  and  7   b   2 . In such an alternative embodiment of the present invention, the alternative pair of contact elements may be constructed in many different configurations. As an example, the contact elements  151  and  152  may be replaced by alternative contact elements  171  and  172 , respectively, which are shown in the close-up views “C” and “D” in the schematics of  FIGS. 8   a  and  8   b.    
         [0083]    As can be seen in the close-up view “C” of  FIG. 8   a , the contact element  171  is fixed to the structure  102  of the electrical G-switch, and is constructed with at least two electrical contacts  173  and  174 , which are mounted on an electrically non-conductive base  175 . The electrical contacts  173  and  174  are fabricated of electrically conductive material commonly used in electrical contacts, are configured such that they are normally in contact as shown in  FIG. 8   a , and can be relatively flexible so that they could be pushed apart the required amount without causing them to permanently deform, i.e., such that they would return to their contacting configuration after separation of a relatively small amount as described below for their proper operation as a normally closed G-switch. The contact element  171  is also provided with conductive wires  176  and  177 , which are connected to the contacts  173  and  174 , respectively. The electrically conductive wires are passed through the electrically non-conductive base  175  as shown in  FIG. 8   a  to prevent them from making contact. 
         [0084]    It is appreciated by those skilled in the art that as described for the normally open G-switch embodiment  150  of  FIGS. 7   a , if the structure  102  of the G-switch is constructed with electrically conductive material, then the conductive wires  176  and  177  have to be routed out of the electrically non-conductive base  175  (from the side as shown in  FIG. 8   a  or through a hole in the electrically conductive base of the structure  102 —not shown in  FIG. 8   a ). In applications in which the G-switch is attached, for example, to a printed circuit board  161  as shown in  FIG. 7   c  for the contact element, the electrically non-conducting base  175  ( 157  in  FIG. 7   c ) can be mounted over a provided opening (similar to the opening  159  in  FIG. 7   c ) in the structure  102  as shown in  FIG. 7   c , such as in a provided recess  160 , thereby allowing the contact wires  176  and  177  (wires  162  and  163  in  FIG. 7   c ) to pass through the provided opening  159  to reach the underlying element (in this case the printed circuit board  161 ). The wires can then be connected to the appropriate circuit provided over or bellow the circuit board  161 —not shown). 
         [0085]    The close-up view “D” of the contact element  172  is shown schematically in  FIG. 8   b . The contact element  172  consists of an electrically non-conductive base  178 , which is fixed to the surface of the link  166  ( FIG. 7   a ) as shown in  FIG. 8   b . An electrically no-conductive (preferably relatively thin but rigid) plate  179  is mounted on the surface of the electrically non-conductive base  178 . The tip  180  of the electrically non-conductive plate can be relatively sharp to facilitate insertion between the contacts  173  and  174  during the G-switch activation as described below. 
         [0086]    The electrical G-switch  150  with the normally closed contacts  171  and  172  operates in a manner similar to the aforementioned normally open G-switch shown in  FIGS. 7   a  and  7   d , i.e., as the aforementioned spin rate is increased and reaches certain predetermined threshold, the link  166  begins to rotate in the counterclockwise direction. As the spin rate is further increased, the link  166  rotates further in the counterclockwise direction, until at a predetermined spin rate, the link  166  reaches its aforementioned singular position (as shown for the striker link  100  in the schematic of  FIG. 6   c ). With further increase in the spin rate, the striker link  166  is further rotated in the counterclockwise direction and passes its aforementioned singular position, and the tensile force of the spring  105  will accelerate it rotationally in the counterclockwise direction (at least partially aided by further motion of the element  110  in the direction of the arrow  111 ) as shown in  FIG. 6   d  for the inertial igniter  100 . The link  166  will then keep rotating in the counterclockwise direction with accelerating rate until the tip  180  of the electrically non-conductive plate  179  is wedged in the space  181  between the contacts  173  and  174 ; spreads the contacting surfaces of the contacts  173  and  174  apart; and is inserted between the contacts  173  and  174  as shown in the schematic of  FIG. 8   c . As a result, the contact between the contacts  173  and  174  is interrupted, and the circuit connected to the wires  176  and  177  is opened. 
         [0087]    It is appreciated by those skilled in the art that the spin rate that is required to achieve activation of the inertial igniter  100  of  FIG. 6   a - 6   e  and electrical G-switches  150  of  FIGS. 7   a - 7   d  and  8   a - 8   c  can be varied by varying the inertia and geometry of the element  110 , the angles between the surface  112  of the structure  102  of the device and the surface  113  of the link  101  as seen in the schematic of  FIG. 6   a . In addition, the surfaces  112  and  113  as well as the contacting surfaces of the element  110  may be formed as curved to achieve the desired levels of counterclockwise rotation of the link  101  as the element  110  moves in the direction of the arrow  111 . In this manner, the contact force and direction on the contacting surfaces between the element  110  and the surface  113  of the link  101  as well as between the element  110  and the surface  112  of the device structure  102  can be controlled as is done in the design of cam and follower surfaces. 
         [0088]    It is also appreciated by those skilled in the art that the element  110  of the inertial igniter  100  of  FIG. 6   a - 6   e  and electrical G-switches  150  of  FIGS. 7   a - 7   d  and  8   a - 8   c  may be provided with a spring  190  (shown in dashed lines in  FIG. 6   a ) to provide a preloading force on the element  110  for the purpose of assisting the aforementioned centrifugal force that tends to move it in the direction of the arrow  111  as the device spins about the axis  109  (in which case, the spring  190  is preloaded in compression). A preloading of the spring  190  in tension would provide a force that counters the centrifugal force that tends to move it in the direction of the arrow  111  as the device spins about the axis  109 . 
         [0089]    It is also appreciated by those skilled in the art that the stop  104  may be positioned such that any desired angle  191  ( FIG. 6   a ) of the link  101  from its aforementioned singular position (shown in  FIG. 6   c ), i.e., from the line  115 , can result. As a result, the amount of counterclockwise rotation that the link  101  has to undergo before it passes its singular position and activate the device can be controlled. As a result, and particularly by providing the element  110  with a spring  190  that is preloaded in compression, the spin rate at which the device is activated can be reduced. 
         [0090]    It is also appreciated by those skilled in the art that with a compressively preloaded spring  190 , the amount of torque (moment of the force applied by the element  110  to the link  101  about the pin joint  103 ) required to rotate the link counterclockwise to its said singular position ( FIG. 6   c ) is determined by the opposing torques that the springs  105  and  190  apply to the link  101 . As a result, for a given device, by increasing the level of compressive preloading of the spring  190 , the tensile preloading of the spring  105  can be increased for a given device activation spin rate. As a result, the potential energy stored in the spring  105  increased, thereby increasing the kinetic energy of the striker link  101  as the pyrotechnic components  106  and  114  impact. This capability of the inertial igniter embodiment  100  and G-switch embodiment  150  is particularly important in applications in which the spin rate of the munitions using these devices is relatively low. 
         [0091]    It is also appreciated by those familiar with the art that by moving the attachment point  107  of the spring  105  to the device structure  102  to the right or to the left, the amount of counterclockwise rotation of the link  101  that is required to bring it to its new aforementioned singular position is changed. For example, by moving the attachment point  107  to the right, the angle is increased (the line  115  is rotated counterclockwise, thereby increasing the angle  191  of the link  101  to the line  115 , i.e., to its singular position). 
         [0092]    The spin rate that is required to achieve activation of the inertial igniter  100  of  FIG. 6   a - 6   e  and electrical G-switches  150  of  FIGS. 7   a - 7   d  and  8   a - 8   c  can be varied by varying the inertia and geometry of the element  110 , the angles between the surface  112  of the structure  102  of the device and the surface  113  of the link  101  as seen in the schematic of  FIG. 6   a . In addition, the said surfaces  112  and  113  as well as the contacting surfaces of the element  110  may be formed as curved to achieve the desired levels of counterclockwise rotation of the link  101  as the element  110  moves in the direction of the arrow  111 . In this manner, the contact force and direction on the contacting surfaces between the element  110  and the surface  113  of the link  101  as well as between the element  110  and the surface  112  of the device structure  102  can be controlled as is done in the design of cam and follower surfaces. 
         [0093]    With a compressively preloaded spring  190 , the amount of torque required to rotate the link counterclockwise to its said singular position ( FIG. 6   c ) is determined by the opposing torques that the springs  105  and  190  apply to the link  101 . As a result, for a given device, by increasing the level of compressive preloading of the spring  190 , the tensile preloading of the spring  105  can be increased for a given device activation spin rate. As a result, the potential energy stored in the spring  105  increased, thereby increasing the kinetic energy of the striker link  101  as the pyrotechnic components  106  and  114  impact. This capability of the inertial igniter embodiment  100  and G-switch embodiment  150  is particularly important in applications in which the spin rate of the munitions using these devices is relatively low. 
         [0094]    Another embodiment  300  of the present inertia igniter invention is shown in the schematic of  FIG. 9   a . In this embodiment, the striker component of the inertial igniter  300  is the striker link  301 , which is attached to the structure of the inertial igniter  302 , by a pin joint indicated with numeral  303 . A spring  305 , which can be preloaded in tension, is attached to the structure of the inertial igniter  302  on the end  306  and to the striker link  301  on the other end  307 , preferably with pin or pin-like joints. In its pre-activation state shown in  FIG. 9   a , the striker link  301  is pressed (such as near its tip  308 ) against a rotating link  309 , through an intermediate ball  310 . The link  309  is attached to the structure of the inertial igniter  302  via a rotary joint  311 , which allows it to rotate about the axis  312 . The axis  312  is parallel to the plane of view of  FIG. 9   a , thereby allowing the link  309  to rotate up or down relative to the plane of the rotation of striker link  301 . A mass  317  is attached to the tip of the link  309 . The mass  317  may be required to be added if the center of mass of the link  309  is not on the side of the striker link  301  or if it is relatively low to properly operate the inertial igniter as described later in this disclosure. The latter becomes particularly the case when the setback acceleration level is relatively low. The elements  313  and  314 , fixed to the striker link  301  and the inertial igniter structure  302 , respectively, are the two components of the ignition pyrotechnic. Alternatively, a one piece pyrotechnic element may be used, in which case the element  313  can be the ignition impact mass or pin and the element  314  can be the one piece impact initiated pyrotechnic element. 
         [0095]    In general, a relatively shallow “dimple”  315  is provided on the surface of the striker link  301  to seat the ball  310  so that the ball  310  is prevented from sliding out from between the link  309  and the striker link  301 . The tensile force applied to the striker link  301  is seen to generate a torque that tends to rotate the striker link  301  in the counterclockwise direction, thereby pressing the ball  301  against the surface of the link  309 . The link  309  can be provided with a stop  316  under it as shown in  FIG. 9   a  (or above the ball  310  contact side of the link  309 ) to prevent its ball contacting end from significantly moving up and loose contact with the ball  310 . The link  309  is also provided with a biasing compressive spring  331  shown in the side view “A” of  FIG. 9   c , which tends to rotate its ball contacting end up, thereby pressing its opposite end against the stop  316 . In practice, the spring  331  can be a torsion spring. 
         [0096]    The inertial igniter  300  is intended to be initiated by setback acceleration, which is considered to be in the direction perpendicular to the plane of the rotation of the striker link  301  (the plane of the  FIG. 9   a ) and directed upwards (outward from the said plane of the rotation of the striker link  301 ). In particular, the inertial igniter  300  is intended to be initiated by setback accelerations that are either relatively low level or are relatively short in duration or both relatively low level and relatively short duration. In such applications, the setback acceleration is not long enough in duration to actuate a release mechanism, which is required for safety reasons to prevent accidental initiation, as well as accelerate a striker mass long enough to provide it with enough mechanical energy to achieve ignition of pyrotechnic materials of the inertial igniter upon the previously described pyrotechnic impact (between a two part pyrotechnic components, a pin impacting a one-part pyrotechnic material, a pin impacting a percussion cap, or the like). 
         [0097]    The operation of the embodiment  300  is as follows. At rest, the tip  308  of the striker link  301  is pressed against the link  309  through the ball  310  by the tensile force of the preloaded spring  305  acting on the striker link  301  as can be seen in the schematic of  FIG. 9   a . When the munitions using the inertial igniter  300  is fired, the setback acceleration (in the direction of the arrow  330  shown in  FIG. 9   c , which is perpendicular to the plane of the inertial igniter  300 , i.e., the plane of  FIG. 9   a ) will cause the mass  317  to be pushed down. As the tip of the link  309  (with the mass  317 ) moves down, the surface of the link  309  that is in contact with the ball  310  slides pass the ball  310 , and when it has moved down enough and passed the ball  310 , it is designed to have also moved passed the bottom surface of the striker link  301 , thereby clearing the striker link  301  to be released. In  FIG. 9   c , the positions of the link  309  and mass  317  after the application of said setback acceleration and its said downward motion to clear the striker link  301  is shown in dashed lines and indicated by the numeral  332 . The tensile force of the spring  305  will then accelerate the striker link  301  rotationally in the counterclockwise direction until the pyrotechnic components  313  and  314  impact and cause ignition. The latter state of the striker link  301  is shown in  FIG. 9   b . The flames and sparks generated by the ignition of the pyrotechnic material  313  and  314  is then routed out from provided ports, usually through a hole such as the hole  318  to below the base to initiate the thermal material pyrotechnics. In some applications, the generated flames and sparks are required to be routed from the side or from the top (opposite to the direction of exit from the hole  318 ) side of the inertial igniter  300 . 
         [0098]    It is appreciated by those skilled in the art that the inertial igniter  300  can still operate without the use of the intermediate ball  310  being present between the striker link  301  (such as near the tip  308 ) and the rotating link  309 . However, the inertial igniter  300  can be constructed with such an intermediate rolling element to minimize the friction forces between the striker link  310  and the rotating link  309 . In general, it is desired that the friction forces be as small as possible so that the (downward) force that the setback acceleration needs to generate while acting on the inertia (mass  317 ) to rotate the rotating link  309  down to release the striker link  301  is minimized. By minimizing the required downward setback acceleration generated force, the inertia of the required mass  317 , i.e., the size of the required mass  317 , is minimized. 
         [0099]    It is appreciated by those skilled in the art that the aforementioned biasing (torsion) spring of the link  309  is selected such that in the case of accidental drops or other similar accidental (no-fire) events, the link  309  is not rotated downwards enough for the link  309  to clear the ball  310 , i.e., to release the striker link  301 . 
         [0100]    It is also appreciated by those skilled in the art that the spring  305  may be a compressive spring preloaded in compression in the configuration of the inertial igniter shown in the schematic of  FIG. 9   a . Such a compressively preloaded spring  305  needs to be positioned above the striker link  301  as viewed in the schematic of  FIG. 9   a , so that it would apply a preloading counterclockwise torque to the striker link  301  which would allow the inertial igniter  300  to operate as previously described for the tensile spring  305 . Alternatively, the spring  305  may be a torsion spring, which can be positioned at the pin joint  303 , and preloaded in the clockwise direction so that in the configuration shown in the schematic of  FIG. 9   a , it would apply a counterclockwise torque to the striker link  301  which would allow the inertial igniter  300  to operate as previously described for the tensile spring  305 . 
         [0101]    It is also appreciated by those familiar with the art that in an alternative embodiment of the inertial igniter  300 ,  FIG. 9   a , the rotating link  309  may be replaced by a translating element  320 , as shown in the  FIG. 9   d  of the appropriately modified side view “A” of  FIG. 9   a . In this alternative embodiment, the link  309  and its rotary joint  311  are replaced with the translating element  320 , which is designed to translate in the guide  321  (sidewalls of the guide to prevent lateral displacement of the translating element  320  not shown for clarity—the guide may also be provided with friction reducing coated surfaced and/or rolling elements such as balls or rolling needles—not shown), which is in turn attached to the inertial igniter structure  302 . The translating element  320  is also provided with a compressive biasing spring  322 , which at rest would keep the translating element  320  in the configuration shown in solid lines against the stop  323 . As was previously described for the embodiment of  FIG. 9   a , the tensile force applied to the striker link  301  by the spring  305  generates a torque that tends to rotate the striker link  301  in the counterclockwise direction, thereby pressing the ball  301  against the surface of the translating element  320 . In its pre-activation state shown in  FIG. 9   a , the striker link  301  is pressed (preferably near the tip  308 ) against the translating element  320 , through an intermediate ball  310 ,  FIG. 9   d . Depending on the level of setback acceleration, i.e., if it is relatively low, then the mass of the translating element  320  may have to be increased by increasing its size and/or material density. 
         [0102]    The inertial igniter  300  embodiment with the translating element  320  is still intended to be initiated by setback acceleration, which is considered to be in the direction of the arrow  330  shown in  FIG. 9   d . In particular, the inertial igniter is similarly intended to be initiated by setback accelerations that are either relatively low level or are relatively short in duration or both relatively low level and relatively short duration. In such applications, the setback acceleration is not long enough in duration to actuate a release mechanism, which is required for safety reasons to prevent accidental initiation, as well as accelerate a striker mass long enough to provide it with enough mechanical energy to achieve ignition of pyrotechnic materials of the inertial igniter upon the previously described pyrotechnic impact (between a two part pyrotechnic components, a pin impacting a one-part pyrotechnic material, a pin impacting a percussion cap, or the like). 
         [0103]    The operation of the inertial igniter  300  embodiment with the translating element  320  is as follows. At rest, the tip  308  of the striker link  301  is pressed against the translating element  320  through the ball  310  by the tensile force of the preloaded spring  305  acting on the striker link  301  as can be seen in the schematic of  FIG. 9   a . When the munitions using the inertial igniter is fired, the setback acceleration (in the direction of perpendicular to the plane of the inertial igniter  300 , i.e., the plane of  FIG. 9   a ) will act on the inertia of the translating element  320  (and the mass  324 —if present), causing the translating element  320  to travel down. As the translating element  320  moves down, the surface of the translating element that is in contact with the ball  310  slides pass the ball  310 , and when it has moved down enough and passed the ball  310 , it is designed to move passed the bottom surface of the striker link  301 , thereby clearing the striker link  301  to be released. The latter position of the translating element  320  is shown in dashed line in  FIG. 9   d  and with numeral  324 . The tensile force of the spring  305  will then accelerate the striker link  301  rotationally in the counterclockwise direction until the pyrotechnic components  313  and  314  impact and cause ignition,  FIG. 9   a . The latter state of the striker link  301  is as shown in  FIG. 9   b  for the inertial igniter  300  with the rotating release link  309 . The flames and sparks generated by the ignition of the pyrotechnic material  313  and  314  is then routed out from provided ports, usually through a hole such as the hole  318  to below the base to initiate the thermal material pyrotechnics. In some applications, the generated flames and sparks are required to be routed from the side or from the top (opposite to the direction of exit from the hole  318 ) side of the inertial igniter  300 . 
         [0104]    It is appreciated by those skilled in the art that the inertial igniter  300  can also operate without the use of the intermediate ball  310  being present between the striker link  301  (preferably near the tip  308 ) and the translating element  320 . However, the inertial igniter  300  is preferably constructed with such an intermediate rolling element to minimize the friction forces between the striker link  310  and the translating element  320 . In general, it is desired the said friction forces be as small as possible so that the (downward) force that the setback acceleration needs to generate while acting on the inertia of the translating element  320  to translate the translating element  320  down to release the striker link  301  is minimized. By minimizing the said required downward setback acceleration generated force, the inertia of the translating element  320 , i.e., the size of the resulting device is also reduced. 
         [0105]    It is appreciated by those skilled in the art that the aforementioned compressive biasing spring  322  is selected such that in the case of accidental drops or other similar accidental (no-fire) events, the translating element  320  is not translated downwards enough to clear the ball  310 , i.e., to release the striker link  301 . 
         [0106]    The inertial igniter  300  can also be readily modified to operate as a so-called electrical G-switch upon activation by the aforementioned all-fire setback acceleration and thereby close (open) a normally open (closed) electrical circuit. The construction and operation of the electrical G-switch is identical to those of the inertial igniter  300  of  FIGS. 9   a - 9   d,  except that the pyrotechnic components  313  and  314  of the inertial igniter  300  are replaced by contact and circuit closing (opening) elements described below. 
         [0107]    In one embodiment of the resulting electrical G-switch, the pyrotechnic component  314  of the inertial igniter  300  ( FIG. 9   a ) is replaced with the contact element  151  (as shown in  FIG. 7   a  and the close-up view “A” of  FIG. 7   b   1 ) and its pyrotechnic component (or striker pin) element  313  by the contact bridging element  152  (as shown in  FIG. 7   a  and the close-up view “B” of  FIG. 7   b   2 ). All other elements of the resulting G-switch are identical to those of the inertial igniter  300  of  FIG. 9   a.    
         [0108]    The contact element  151 , replacing the pyrotechnic component  314  of the inertial igniter  300  ( FIG. 9   a ) and the close-up view “A” of which is shown in the schematic of  FIG. 7   b   1 , is similarly fixed to the structure  302  of the resulting electrical G-switch. 
         [0109]    The contact element  152 , replacing the pyrotechnic component  313  of the inertial igniter  300  ( FIG. 9   a ) and the close-up view “B” of which is shown in the schematic of  FIG. 7   b   2 , is similarly fixed to the striker link  301  of the resulting electrical G-switch. 
         [0110]    It is also appreciated by those skilled in the art that all alternative features and methods of construction and operation described for the electrical G-switch  150  of  FIG. 7   a  may also be applied to the present electrical G-switch resulting from the inertial igniter  300 . 
         [0111]    The resulting electrical G-switch operates in a manner similar to the inertial igniter  300  of  FIGS. 9   a - 6   b,  i.e., as a result of the all-fire setback acceleration, the tip of link  309  that engages the tip  308  of the link  301  via the intermediate ball  310  is pushed down, thereby releasing the striker link  301  as was previously described for the inertial igniter  300 . The tensile force of the spring  305  will then accelerate the striker link in the counterclockwise direction until the contact strip  164  of the contact element  152  (close-up view “B” of  FIG. 7   b   2 ) comes into contact with the contacts  153  and  154  of the contact element  151  (close-up view “B” of  FIG. 7   b   2 ) as shown in the schematic of  FIG. 7   d  for the G-switch  150 . As a result, the wires  155  and  156  are connected electrically, and the circuit to which they are connected is closed. 
         [0112]    It is appreciated by those skilled in the art that similar to the electrical G-switch  150  of  FIGS. 7   a - 7   d,  more than two contacts  153  and  154  may be provided on the contact element  151 , thereby allowing the electrically conductive strip  164  of the contact element  152  to close more than one electrical circuit (when using pairs of contacts  153  and  154  and electrically isolated electrically conductive strips  164  on the contact elements  151  and  152 , respectively) or allowing at least three contacts (similar to contacts  153  and  154 ) on the contact element  151  to form a junction by an electrically conductive strip  164 . 
         [0113]    It is appreciated by those skilled in the art that as was described for the electrical G-switch  150  of  FIG. 7   a , the electrical G-switch resulting from the inertial igniter  300  may be designed for opening an already closed electrical circuit by replacing the pair of contact elements  151  and  152  shown in  FIGS. 7   b   1  and  7   b   2 , for example by the alternative contact elements  171  and  172 , respectively, which are shown in the close-up views “C” and “D” in the schematics of  FIGS. 8   a  and  8   b . The G-switch will then operate as was described for the  150  of  FIG. 7   a.    
         [0114]    It is also appreciated by those familiar with the art that all alternative designs and variations that were previously described for the G-switch embodiment  150  of  FIG. 7   a  may also be applied to the present G-switch embodiment resulting similarly from the inertial igniter  300  of  FIG. 9   a  and its disclosed variations. 
         [0115]    It is appreciated by those familiar with the art that spinning rounds are fired in rifled barrels so that as the round is accelerated along the length of the barrel to the desired barrel exit velocity, the round is also accelerated rotationally (about its long axis) to the desired barrel exit spin rate. Hereinafter, the rotational acceleration about the long axis of the round (i.e., the spin axis) is referred to as the “spin acceleration”, and the spin acceleration corresponding to the all-fire setback acceleration experienced by the round during firing is referred to as the “all-fire spin acceleration”. 
         [0116]    In another embodiment, a method for constructing inertial igniters that utilizes the aforementioned all-fire spin acceleration to initiate pyrotechnic materials of the igniter is described together with examples of such inertial igniter designs. These all-fire spin acceleration activated inertial igniters are intended to stay inactive, i.e., do not initiate, when subjected to axial acceleration (even the setback acceleration) and rotary accelerations that are not along the long axis of the round. 
         [0117]    Such “all-fire spin acceleration” activated inertial igniters have a very important safety advantage over inertial igniters that are activated by setback acceleration. This safety advantage results from the fact that during acceleration drops, even from relatively high heights, e.g., from the aforementioned heights of 40 feet, that could result in accelerations of up to 18,000 Gs with durations of up to 1 msec, can only induce spin acceleration levels that are a very small fraction of the round all-fire spin acceleration levels. As a result, such inertial igniters are particularly suitable from the safety point of view for the so-called spinning rounds, i.e., those rounds that are fired by rifled barrels to achieve (usually high) spin rates, sometimes of the order of magnitude of several hundred spins per second. 
         [0118]    One representative embodiment  350  of such “all-fire spin acceleration” activated inertial igniter is shown in the schematic of  FIG. 10 . In this embodiment, the striker component of the inertial igniter  350  is the rotary striker  351 , which is attached to the structure of the inertial igniter  352 , by a pin joint indicated with numeral  353 . The tip  354  of a relatively elastic beam element  355  or the like, which is attached to the structure of the inertial igniter  352 , is positioned to engage mating groove  356  of a groove providing portion  357  attached (such as being integral) to the tip  358  of the rotary striker  351 . The elements  359  and  360 , fixed to the rotary striker  301  and the inertial igniter structure  352 , respectively, are the two components of the ignition pyrotechnic. Alternatively, a one piece pyrotechnic element may be used, in which case the element  359  is preferably the ignition impact mass or pin and the element  360  is preferably the one piece impact initiated pyrotechnic element. The inertial igniter  350  is intended to be initiated by the aforementioned firing setback acceleration induced (all-fire) spin acceleration, which is considered to be in the direction by the arrow  361  in  FIG. 10 . 
         [0119]    In general, a stop  362  which is attached to the inertial igniter structure  352  is provided to prevent the clockwise rotation of the rotary striker  351 ,  FIG. 10 . 
         [0120]    The operation of the embodiment  350  is as follows. At rest, and its pre-activation configuration, the tip  354  of the elastic beam  355  engages the groove  356  of the groove providing portion  357  attached to the tip  358  of the rotary striker  351 . As a result, the elastic beam  355  provides resistance to the rotational motion of the rotary striker  351  about the pin joint  353  as shown in the schematic of  FIG. 10 . When the munitions using the inertial igniter  350  is fired by a gun, the setback acceleration and the barrel rifling forces the round to be also accelerated rotationally about the long axis of the round, i.e., causes the round to be subjected to an all-fire spin acceleration, in the direction of the arrow  361 , noting that the direction of the firing acceleration is intended to be perpendicular to the plane of the  FIG. 10  and outward from the plane. 
         [0121]    When the round is fired, as the setback acceleration and thereby the spin acceleration (in the direction of the arrow  361 —i.e., clockwise direction) of the round structure (to which the inertial igniter structure  352  is attached) is increased, the essentially stationary rotary striker  351  begins to be accelerated in the same clockwise direction by the engaging elastic beam  355 . The clockwise acceleration of the rotary striker  351  acts on the moment of inertia of the rotary striker  351 , generating a resisting (dynamic reaction) torque. The resisting torque in turn needs to be generated by a force applied by the engaging elastic beam  355  to the rotary striker  351  tip  358  at the groove  356 . As a result, the elastic beam begins to deflect in bending (downward as seen in the schematic of  FIG. 10 ), until the clockwise acceleration being applied to the rotary striker  351  is large enough to cause enough deflection of the tip  354  of the elastic beam  355  to free the rotary striker  351  from engagement with the elastic beam  355 . From this moment of disengagement of the rotary striker  351  from the elastic beam  355 , the inertial igniter structure  352  continues to spin accelerate in the clockwise direction (direction of the arrow  361 ). As a result, pyrotechnic component  360  is accelerated towards the pyrotechnic component  359 , until they impact and cause ignition. The flames and sparks generated by the ignition of the pyrotechnic material  359  and  360  are then routed out from provided ports, usually through a hole such as the hole  363  in the inertial igniter structure  352  below its base to initiate the thermal material pyrotechnics. In some applications, the generated flames and sparks are required to be routed from the side or from the top (opposite to the direction of exit from the hole  363 ) side of the inertial igniter  350 . 
         [0122]    The length of the engaging tip  354  inside the groove  356  and the stiffness of the elastic beam  355  determine the level of torque that the rotary striker  351  needs to apply to the elastic beam  355  to disengage it from the said elastic beam (following certain amount of—preferably elastic—bending deformation of the elastic beam  355 ), i.e., the level of spin acceleration at which the rotary striker  351  is released. This level is generally desired to be relatively high for safety reasons, i.e., to prevent inertial igniter activation during accidental drops as previously discussed. The level of spin acceleration at which the rotary striker  351  is released is also desired to be relatively high so that to increase the relative speed of the pyrotechnic components  359  and  360  at the time of their impact to ensure ignition reliability. 
         [0123]    It is appreciated by those familiar with the art that a number of elastic element types known in the art may be used instead of the elastic beam  355  to perform the same function, i.e., accelerate the rotary striker  351  in the clockwise direction to certain desired release acceleration level (generally significantly below the all-fire spin acceleration levels) before releasing the rotary striker  351 . Alternative methods of achieving the same goal can also be achieved using a connecting element  381  to connect the tip  358  of the rotary striker  351  to the inertial igniter structure  352  as shown in  FIG. 15 . The connecting element  381 , in this case a shearing pin, is then designed to fail (i.e., break) to shear and release the rotary striker  351  at the desired spin acceleration level. In general, the shear pin  381  can be provided with a notch  382  to concentrate shearing stress in that section of the shear pin  381  to achieve more controlled shearing at the desired spin acceleration level. 
         [0124]    Another alternative method of achieving rotary striker release at the desired spin acceleration level is the use of a detent pin  385  as shown in the schematic of  FIG. 16 . The detent pin  385  is attached to the inertial igniter structure  352  and its locking ball  386 , which is biased forward by the preloaded compressive spring  387 , engages the dimple  388  provided on the tip  358  of the rotary striker  351 . The size of the detent ball and the depth of the dimple and its preloading spring would then determine the level of acceleration at which the rotary striker  351  is released during the firing. 
         [0125]    In addition, the elements (such as the elastic element  355 ) providing the aforementioned resisting torque may be positioned at the rotary joint  353 , and may be of a torsion spring type. 
         [0126]    It is noted that the center of mass of the rotary striker  351 ,  FIG. 10 , can be located along the axis of rotation of the rotary joint  353 . By such positioning of the center of mass of the rotary striker  351 , any accidental acceleration (in the axial or lateral directions or rotational accelerations about axes perpendicular to the spin axis), even very high axial or lateral accelerations caused by drops from aforementioned high heights causing linear accelerations of up to 18,000 Gs with duration of up to 1 msec, would not cause a torque about the spin axis (the axis of the rotary joint  353 ) of the rotary striker  351 , therefore would not cause the inertial igniter  350  to be initiated. 
         [0127]    The inertial igniter  350  can also be readily modified to operate as a so-called electrical G-switch upon activation by the aforementioned all-fire (setback acceleration induced) spin acceleration, and thereby close (open) a normally open (closed) electrical circuit. The construction and operation of the electrical G-switch is identical to those of the inertial igniter  350  of  FIG. 10 , except that the pyrotechnic components  359  and  360  of the inertial igniter  350  are replaced by contact and circuit closing (opening) elements described below. 
         [0128]    In one embodiment of the resulting electrical G-switch, the pyrotechnic component  360  of the inertial igniter  350  ( FIG. 10 ) is replaced with the contact element  151  (as shown in  FIG. 7   a  and the close-up view “A” of  FIG. 7   b   1 ) and its pyrotechnic component (or striker pin) element  359  by the contact bridging element  152  (as shown in  FIG. 7   a  and the close-up view “B” of  FIG. 7   b   2 ). All other elements of the resulting G-switch are identical to those of the inertial igniter  350  of  FIG. 10 . 
         [0129]    The contact element  151 , replacing the pyrotechnic component  360  of the inertial igniter  350  ( FIG. 10 ) and the close-up view “A” of which is shown in the schematic of  FIG. 7   b   1 , is similarly fixed to the structure  352  of the resulting electrical G-switch. 
         [0130]    The contact element  152 , replacing the pyrotechnic component  359  of the inertial igniter  350  ( FIG. 10 ) and the close-up view “B” of which is shown in the schematic of  FIG. 7   b   2 , is similarly fixed to the rotary striker  351  of the resulting electrical G-switch. 
         [0131]    It is also appreciated by those skilled in the art that all alternative features and methods of construction and operation described for the electrical G-switch  150  of  FIG. 7   a  may also be applied to the present electrical G-switch resulting from the inertial igniter  350 . 
         [0132]    The resulting electrical G-switch operates in a manner similar to the inertial igniter  350  of  FIG. 10 , i.e., when the round is fired, as the setback acceleration and thereby the spin acceleration in the direction of the arrow  361  (clockwise direction) of the round structure to which the inertial igniter structure  352  is attached is increased, the essentially stationary rotary striker  351  begins to be accelerated in the same clockwise direction by the engaging elastic beam  355 . The said clockwise acceleration of the rotary striker  351  acts on the moment of inertia of the rotary striker  351 , generating a resisting (dynamic reaction) torque. The said resisting torque in turn needs to be generated by a force applied by the engaging elastic beam  355  to the rotary striker  351  tip  358  at the groove  356 . As a result, the elastic beam begins to deflect in bending (downward as seen in the schematic of  FIG. 10 ), until the said clockwise acceleration being applied to the rotary striker  351  is large enough to cause enough deflection of the tip  354  of the elastic beam  355  to free the rotary striker  351  from engagement with the elastic beam  355 . The inertial igniter structure  352  will then continues to spin accelerate in the clockwise direction (direction of the arrow  361 ). As a result, the contact element  151  is accelerated towards the contact element  152 , until the contact strip  164  of the contact element  152  (close-up view “B” of  FIG. 7   b   2 ) comes into contact with the contacts  153  and  154  of the contact element  151  (close-up view “B” of  FIG. 7   b   2 ) as shown in the schematic of  FIG. 7   d  for the G-switch  150 . As a result, the wires  155  and  156  are connected electrically, and the circuit to which they are connected is closed. The resulting electrical G-switch is preferably provided with a biasing tensile spring  364 , which is attached to the rotary striker  351  on one end and the inertial igniter structure  352  on the other end, preferably by pin joints  365  and  366 , respectively, as shown in the schematic of  FIG. 10 . The presence of the biasing tensile spring  364  ensures that once the contacts  151  and  152  come into contact as is described above, they will stay in contact. 
         [0133]    It is appreciated by those skilled in the art that similar to the electrical G-switch  150  of  FIGS. 7   a - 7   d,  more than two contacts  153  and  154  may be provided on the contact element  151 , thereby allowing the electrically conductive strip  164  of the contact element  152  to close more than one electrical circuit (when using pairs of contacts  153  and  154  and electrically isolated electrically conductive strips  164  on the contact elements  151  and  152 , respectively) or allowing at least three contacts (similar to contacts  153  and  154 ) on the contact element  151  to form a junction by an electrically conductive strip  164 . 
         [0134]    It is also appreciated by those skilled in the art that as was described for the electrical G-switch  150  of  FIG. 7   a , the electrical G-switch resulting from the inertial igniter  350  may be designed for opening an already closed electrical circuit by replacing the pair of contact elements  151  and  152  shown in  FIGS. 7   b   1  and  7   b   2 , for example by the alternative contact elements  171  and  172 , respectively, which are shown in the close-up views “C” and “D” in the schematics of  FIGS. 8   a  and  8   b . The G-switch will then operate as was described for the  150  of  FIG. 7   a.    
         [0135]    It is also appreciated by those familiar with the art that all alternative designs and variations that were previously described for the G-switch embodiment  150  of  FIG. 7   a  may also be applied to the present G-switch embodiment resulting similarly from the inertial igniter  350  of  FIG. 10  and its disclosed variations. 
         [0136]    The inertial igniter embodiments  100 ,  300  and  350  shown in the schematics of  FIGS. 6 ,  9  and  10 , respectively, and all their indicated variations can be packaged in a relatively rigid housing, such as in the cylindrical package  400  shown in the isometric view of  FIG. 11 , which can consist of a top cap  401 , sidewall  402  and base  403 . In general and to make the packaged inertial igniter  400  small, the base  403  (or cap  401 ) and/or sidewall  402  of the housing can be integral to the structure  102 ,  302  and  352  of the inertial igniter embodiment  100 ,  300  and  350  shown in the schematics of  FIGS. 6 ,  9  and  10 , respectively. In the isometric view of  FIG. 11 , the inertial igniter flame exit port  404  is shown to be located on the base  403  of the packaged inertial igniter  400 , to allow the flame  405  to exit and initiate the thermal battery in which the packaged inertial igniter is assembled. 
         [0137]    The inertial igniter  300  is intended to be initiated by setback accelerations that are either relatively low level or are relatively short in duration or both relatively low level and relatively short duration. In such applications, the setback acceleration is not long enough in duration to actuate a release mechanism, which is required for safety reasons to prevent accidental initiation, as well as accelerate a striker mass long enough to provide it with enough mechanical energy to achieve ignition of pyrotechnic materials of the inertial igniter upon the previously described pyrotechnic impact (between a two part pyrotechnic components, a pin impacting a one-part pyrotechnic material, a pin impacting a percussion cap, or the like). 
         [0138]    The inertial igniter  350  is intended to be initiated by setback acceleration induced spin acceleration in spinning rounds (fired by guns with rifled barrels). When center of mass of the rotary striker  351  is located on its axis of rotation (along its rotary joint axis), then no linear (axial or lateral) accelerations or rotational accelerations along axes perpendicular to the spin axis will not initiate the inertial igniter. Therefore the inertial igniter will be safe when dropped from very high heights such as 40 feet that can cause linear accelerations of the order of 18,000 G with up to 1 msec duration. 
         [0139]    It is appreciated by those familiar with the art that the inertial igniter housing may be any shape instead of the cylindrical shape as shown in the isometric view of  FIG. 11 . In addition, the flame exit port may be located almost anywhere on the inertial igniter housing, including the side  402  or the top cap  401 , depending on where the igniter pyrotechnic material is located and how it is guided to exit for proper initiation of the thermal battery pyrotechnics. 
         [0140]    In certain applications, the thermal battery is required to be initiated under all-fire condition with an extremely high level of reliability, for example, a reliability of even better than 99.999% at 95% confidence level. In such situations, even if an inertial igniter is designed and fabricated for very high initiation reliability under all-fire condition, it might not be capable of satisfying such extremely high reliability level requirements. In addition, even if an inertial igniter is expected to be reliable to such extremely high levels, the process of proving such reliability levels requires extensive and extremely costly testing procedures. For these reasons, it is highly desirable to provide such thermal batteries with at least two, independently activated, inertial igniters to make it possible to achieve such extremely high thermal battery initiation reliability using inertial igniters with significantly lower proven reliability levels that can be achieved at significantly lower costs. The isometric view of  FIG. 12  shows such an assembly  420  (indicated by numerals  421 ) of three packaged inertial igniters  400  over a common base  422 . 
         [0141]    It is also appreciated by those familiar with the art that the G-switch embodiment  150 , formed from the inertial igniter embodiment  100  of  FIG. 6 , as well as the G-switches that can be similarly formed as described previously in this disclosure from the inertial igniter embodiments  300  and  350  of  FIGS. 9 and 10 , respectively, including all their indicated variations, can be packaged in a relatively rigid housing as shown in the isometric view of  FIG. 13  and indicated by the numeral  450 . Such a housing  451  may, for example, be cylindrical in shape with the G-switch sealed within the housing to protect its elements from environmental effects. The G-switch housing may also be in any shape instead of the cylindrical shape of  FIG. 13 . The at least two contact wires  452  and  453  may, for example, be brought out from the base of the G-switch packaging  450 . Alternatively, the at least two contact tab elements or pins (not shown) commonly used in electronic components may be used for mounting of the G-switch on circuit boards or the like as is common practice in the electronics industry. 
         [0142]    In general and to make the packaged G-switch  450  small, the housing can be integral to the structure  102 ,  302  and  352  of the inertial igniter embodiment  100 ,  300  and  350  shown in the schematics of  FIGS. 6 ,  9  and  10 , respectively, which are used to construct the indicated G-switches. 
         [0143]    It is appreciated by those familiar with the art that similar to the multiple inertial igniter assembly of at least two inertial igniters shown in  FIG. 12 , two or more G-switches  450  may also be assembled and used to significantly increase the reliability with which the resulting G-switch assembly can detect all-fire condition. An example of an isometric view of such an assembly  470  of three G-switches  471  over a common base  472  is shown in  FIG. 14 . 
         [0144]    In one alternative embodiment of the G-switch assembly  450 , at least one of the G-switches of the assembly may be used to detect accidental drops, particularly accidental drops from very high height, such as drops from heights of up to 40 feet that can result in impact shocks of up to 18,000 Gs with up to 1 msec of duration. Similarly, other at least one G-switches may be used to detect shock loadings due other accidental drops or nearby explosions. As a result, the resulting G-switch assembly can be used to differentiate all-fire conditions from almost all no-fire conditions, even drops from very high heights. 
         [0145]    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.