Abstract:
A device including: an impact mass movably restrained relative to a base; and a release mechanism configured to be movable between a restrained position for preventing movement of the impact mass and a released position for permitting movement of the impact mass when the release mechanism is subjected to an acceleration greater than a predetermined magnitude and duration; wherein the release mechanism having a release mass movable when subjected to the acceleration, the movement of the release mass not being influenced by movement of the impact mass.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/152,578, filed on Apr. 24, 2015, the entire contents of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to mechanical inertial igniters and G-switches, and more particularly to compact, low-volume, reliable and easy to manufacture mechanical inertial igniters, ignition systems for thermal batteries and for G-switches used in munitions for initiation and the like as a result of setback acceleration (shock) or the like. 
         [0004]    2. Prior Art 
         [0005]    Thermal batteries represent a class of reserve batteries that operate at high temperature. Unlike liquid reserve batteries, in thermal batteries the electrolyte is already in the cells and therefore does not require a distribution mechanism such as spinning. The electrolyte is dry, solid and non-conductive, thereby leaving the battery in a non-operational and inert condition. These batteries incorporate pyrotechnic heat sources to melt the electrolyte just prior to use in order to make them electrically conductive and thereby making the battery active. The most common internal pyrotechnic is a blend of Fe and KClO 4 . Thermal batteries utilize a molten salt to serve as the electrolyte upon activation. The electrolytes are usually mixtures of alkali-halide salts and are used with the Li(Si)/FeS 2  or Li(Si)/CoS 2  couples. Some batteries also employ anodes of Li(Al) in place of the Li(Si) anodes. Insulation and internal heat sinks are used to maintain the electrolyte in its molten and conductive condition during the time of use. Reserve batteries are inactive and inert when manufactured and become active and begin to produce power only when they are activated. 
         [0006]    Thermal batteries have long been used in munitions and other similar applications to provide a relatively large amount of power during a relatively short period of time, mainly during the munitions flight. Thermal batteries have high power density and can provide a large amount of power as long as the electrolyte of the thermal battery stays liquid, thereby conductive. The process of manufacturing thermal batteries is highly labor intensive and requires relatively expensive facilities. Fabrication usually involves costly batch processes, including pressing electrodes and electrolytes into rigid wafers, and assembling batteries by hand or semi-automatically. Other manufacturing processes have also been recently developed that are more amenable to automation. 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 firing setback or the like acceleration (shock) 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]    The need to differentiate accidental and other so-called no-fire events from the so-called all-fire event, i.e., the firing setback acceleration (shock) event necessitates the employment of a safety system which is capable of allowing initiation of the inertial igniter only when the inertial igniter is subjected to the impulse level threshold corresponding to or above the minimum all-fire impulse levels. The safety mechanism is preferably provided with a mechanism that provides for a preset (safety) impulse level threshold, which must be reached before the safety mechanism is activated. The safety mechanism can be thought of as a mechanical delay mechanism, which is usually and preferably provided with certain acceleration threshold detection mechanisms, such that after the safety acceleration threshold has been reached and after a certain amount of time delay, a separate initiation system is actuated or released to provide ignition of the inertial igniter pyrotechnics. The inertial igniter pyrotechnic material may have been directly loaded into the ignition mechanism or may be a separately installed percussion primer. An inertial igniter that combines such a safety system with an impact based initiation system and its alternative embodiments are described herein. 
         [0010]    Inertia-based igniters must therefore comprise two components so that together they provide the aforementioned mechanical safety (delay mechanism that is activated after a prescribed acceleration threshold has been reached) and to provide the required striking (percussion) action to achieve ignition of the pyrotechnic element(s) of the inertial igniter. The function of the safety system (mechanism) is to hold the striker element fixed to the igniter structure until the inertial igniter is subjected to a high enough acceleration level above the aforementioned acceleration threshold level and with long enough duration, i.e., to a prescribed impulse level threshold after the aforementioned safety acceleration threshold has been reached, corresponding to the firing setback acceleration event. The prescribed safety acceleration threshold provides a minimum acceleration level to ensure that the inertial igniter is safe, i.e., the striker element stays fixed to the inertial igniter structure, when subjected to acceleration levels below the safety acceleration threshold even for long duration. Once the all-fire event, i.e., the minimum (safety threshold) acceleration level and the prescribed impulse level threshold has been reached, the safety system (mechanism) releases the striker element, allowing it to accelerate toward its target. The ignition itself may take place as a result of striker impact, or simply contact or proximity. For example, the striker may be akin to a firing pin and the target akin to a standard percussion cap primer. Alternately, the striker-target pair may bring together one or more chemical compounds whose combination with or without impact will set off a reaction resulting in the desired ignition. 
         [0011]    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. 
         [0012]    The isometric cross-sectional view of a currently available inertia igniter is shown in  FIG. 2 , referred to generally with reference numeral  200 . 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 integrally formed as a single piece but may also be constructed as separate pieces and joined together, for example by welding or press fitting or other methods commonly used in the art. The base  202  of the housing can also be provided with at least one opening  204  (with a corresponding opening(s) in the thermal battery—not shown) to allow ignited sparks and fire to exit the inertial igniter and enter into the thermal battery positioned under the inertial igniter  200  upon initiation of the inertial igniter pyrotechnics  215 , or percussion cap primer when used in place of the pyrotechnics  215  (not shown). Although illustrated with the opening  204  in the base, the opening (or openings) can alternatively be formed in a side wall or in the striker mass as described in U.S. Pat. No. 8,550,001, the entire contents thereof is incorporated herein by reference. 
         [0013]    A striker mass  205  is shown in its locked position in  FIG. 2 . The striker mass  205  is provided with guides for the posts  203 , such as vertical surfaces  206 , that are used to engage the corresponding (inner) surfaces of the posts  203  and serve as guides to allow the striker mass  205  to ride down along the length of the posts  203  without rotation with an essentially pure up and down translational motion. 
         [0014]    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 setback spring  210  is preferably a wave spring with rectangular cross-section. The collar  211  is usually provided with partial guide  212  (“pocket”), which are open on the top as indicated by the numeral  213 . The guide  212  may be provided only at the location of the locking balls  207  as shown in  FIGS. 2 and 3 , or may be provided as an internal surface over the entire inner surface of the collar  211  (not shown). 
         [0015]    The collar  211  rides up and down on 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 “lock” the collar  211  in its uppermost position against the locking balls  207 . As a result, the assembled inertial igniter  200  stays in its assembled state and would not require a top cap to prevent the collar  211  from being pushed up and allowing the locking balls  207  from moving out and releasing the striker mass  205 . 
         [0016]    In the inertial igniters of the type shown in  FIGS. 2 and 3 , a one part pyrotechnics compound  215  (such as lead styphnate or other similar compound) is used as shown in  FIG. 2 . The striker mass  205  is usually 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  205  is released during an all-fire event and is accelerated down (opposite to the arrow  218  illustrated in  FIG. 2 ), impact occurs mostly between the surfaces of the tips  216  and  217 , thereby pinching the pyrotechnics compound  215 , thereby providing the means to obtain a reliable initiation of the pyrotechnics compound  215 . Alternatively, a two-part pyrotechnics compound consisting, for example, one being based on potassium chlorate used in place of the pyrotechnics  215  and the other based on red phosphorous which is positions over a (generally larger) tip  216  of the striker mass  206 , may be used. In another alternative design, instead of using the pyrotechnics compound  215 ,  FIG. 2 , a percussion cap primer or the like (not shown) is used. In such inertial igniters, the tip  216  of the striker mass  205  is appropriately sized for initiating the percussion cap primer being used. 
         [0017]    The basic operation of the inertial igniter  200  shown in  FIGS. 2  and is as follows. Any non-trivial acceleration in the axial direction  218  which can cause the collar  211  to overcome the resisting force of the setback spring  210  will initiate and sustain some downward motion of the collar  211 . The force due to the acceleration on the striker mass  205  is supported at the dimples  209  by the locking balls  207  which are constrained inside the holes  208  in the posts  203 . If an acceleration time in the axial direction  218  imparts a sufficient impulse to the collar  211  (i.e., if an acceleration time profile—above the resisting force of the setback spring  210 —is greater than a predetermined threshold), it will translate down along the axis of the assembly until the setback locking balls  205  are no longer constrained to engage the striker mass  205  to the posts  203 . If the acceleration event is not sufficient to provide this motion (i.e., the acceleration time profile provides less impulse than the aforementioned predetermined threshold), the collar  211  will return to its start (top) position under the force of the setback spring  210 . 
         [0018]    Assuming that the acceleration time profile was at or above the specified “all-fire” profile, the collar  211  will have translated down past the locking balls  207 , allowing the striker mass  205  to accelerate down towards the base  202 . In such a situation, since the locking balls  207  are no longer constrained by the collar  211 , the downward force that the striker mass  205  has been exerting on the locking balls  207  will force the locking balls  207  to move outward in the radial direction. Once the locking balls  207  are out of the way of the dimples  209 , the downward motion of the striker mass  205  is no longer impeded. As a result, the striker mass  205  moves downward, causing the tip  216  of the striker mass  205  to strike the pyrotechnic compound  215  on the surface of the protrusion  217  with the requisite energy to initiate ignition. 
         [0019]    In the inertial igniter  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 hole (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  to be initiated. 
         [0020]    In the inertial igniter  200  of  FIGS. 2 and 3 , by varying the mass of the striker  205 , the mass of the collar  211 , the spring rate of the setback spring  210 , the distance that the collar  211  has to travel downward to release the locking balls  207  and thereby release the striker mass  205 , and the distance between the tip  216  of the striker mass  205  and the pyrotechnic compound  215  (and the tip of the protrusion  217 ), the designer of the disclosed inertial igniter  200  can match the all-fire and no-fire impulse level requirements for various applications as well as the safety (delay or dwell action) protection against accidental dropping of the inertial igniter and/or the munitions or the like within which it is assembled. 
         [0021]    Briefly, the safety system parameters, i.e., the mass of the collar  211 , the spring rate of the setback spring  210  and the dwell stroke (the distance that the collar  210  has to travel downward to release the locking balls  207  and thereby release the striker mass  205 ) must be tuned to provide the required actuation performance characteristics. Similarly, to provide the requisite impact energy, the mass of the striker  205  and the aforementioned separation distance between the tip  216  of the striker mass and the pyrotechnic compound  215  (and the tip of the protrusion  217 ) must work together to provide the specified impact energy to initiate the pyrotechnic compound when subjected to the remaining portion of the prescribed initiation acceleration profile after the safety system has been actuated. 
         [0022]    In general, the required aforementioned acceleration time profile threshold for inertial igniter initiation, i.e., the so-called all-fire condition, is described in terms of an acceleration pulse of certain amplitude and duration. For example, the all-fire acceleration pulse may be given as being 1000 G for 15 milliseconds. The no-fire (no-initiation) condition may be indicated similarly with certain acceleration pulse (or half-sine) amplitude and duration. For example, the no-fire condition may be indicated as being an acceleration pulse of 2000 G for 0.5 milliseconds. Other no-fire conditions may include transportation induced vibration, usually around 10 G with a range of frequencies. 
         [0023]    It is appreciated by those skilled in the art that when the inertial igniter  200  of  FIGS. 2 and 3  is subjected to the aforementioned all-fire acceleration profile threshold, the collar  211  is first caused to be displaced downward under the force caused by the acceleration in the direction of the arrow  218  acting on the inertia (mass) of the collar  211 , until the striker mass  205  is released as was described above and accelerated downward to towards the base  202  of the inertial igniter until the tip  216  of the striker mass  205  strikes the pyrotechnic material  215  over the protruding tip  217  and causing it to ignite. It is also appreciated by those skilled in the art that the process of downward travel of the collar  211  takes a certain amount of time, hereinafter indicated as Δt 1 , the amount of which is dependent on the mass of the collar  211  and the aforementioned preloading level of the compressive spring  210  and the distance that it has to travel downward before the balls  207  and thereby the striker mass  205  is released. Similarly, once the striker mass  205  is released, the process of downward travel of the striker mass  205  until its tip  216  strikes the pyrotechnic material  215  over the protruding tip  217  takes a certain amount of time for, hereinafter indicates as Δt 2 , the amount of which is dependent on the level of acceleration in the direction of the arrow  218 . 
         [0024]    In addition, in recent years new improved chemistries and manufacturing processes have been developed that promise the development of lower cost and higher performance thermal batteries that could be produced in various shapes and sizes, including their small and miniaturized versions. However, inertial igniters are relatively large and not suitable for small and low power thermal batteries, particularly those that are being developed for use in miniaturized fuzing, future smart munitions, and other similar applications. This is in general the case for munitions with relatively low firing setback acceleration, particularly those in which the firing setback acceleration pulse (shock) has relatively short duration. 
         [0025]    It is therefore appreciated by those skilled in the art that the duration of the all fire acceleration must at least be the sum of the above two time periods Δt 1  and Δt 2 , hereinafter indicated as Δt=Δt 1 +Δt 2 . For example, for the aforementioned case of all-fire (setback) acceleration being 1000 G for 15 milliseconds, the total time Δt must be less than the indicated acceleration duration of 15 milliseconds. 
         [0026]    In certain cases, due to the small size or geometry of the thermal battery or the like, the height of the inertial igniter that can be used is so small that the striker mass  205  upon its release does not have enough distance to travel downward to gain enough velocity (i.e., enough kinetic energy) before its tip  216  strikes the pyrotechnic material  215  over the protruding tip  217  in order to be able to cause the pyrotechnic material  215  to be reliably ignited. 
         [0027]    Inertial igniter all-fire and no-fire requirements generally vary significantly from one application to the other. Therefore it is highly desirable to develop inertial igniters which are provided with the means of independently varying the aforementioned safety acceleration threshold level that has been to be reached and the amount of time delay before which the inertial igniter striker element is released. 
         [0028]    It is also highly desirable to provide inertial igniter mechanisms and designs which would minimize the effects of friction and stiction between the parts, which would increase initiation reliability, which would reduce the range of acceleration within which initiation is certain to occur. 
         [0029]    It is also highly desirable that the inertial igniter mechanisms and designs would result in devices that can be fabricated inexpensively. 
         [0030]    In certain applications, the aforementioned firing setback acceleration duration is very short thereby the said acceleration cannot be relied upon to both actuate the aforementioned safety mechanism and then accelerate the inertial igniter striker element to the required speed (energy) to achieve pyrotechnic initiation. 
       SUMMARY OF THE INVENTION 
       [0031]    A need therefore exists for inertial igniters that can be used to initiate thermal batteries or the like in munitions or the like when the height available in munitions is too small as is described above for inertial igniters of the type shown in  FIGS. 2 and 3  to be used. 
         [0032]    A need also exists for inertial igniter mechanisms that would provide the means of independently varying the safety acceleration threshold level of the inertial igniter that has to be reached and the amount of time delay before which the inertial igniter striker element is released to ignite the device pyrotechnics. 
         [0033]    A need also exists for inertial igniter mechanisms and designs which would minimize the effects of friction and stiction between the parts. 
         [0034]    A need also exists for inertial igniter mechanisms and designs that would significantly increase operational reliability of the inertial igniter. 
         [0035]    A need also exists for inertial igniter mechanisms and designs that would reduce the range of setback or the like acceleration level within which initiation certainty may occur. 
         [0036]    A need also exists for inertial igniter mechanisms and designs that would make the inertial igniter manufactured at lower cost by reducing the number of parts and/or by reducing the complexity and manufacturing cost of the inertial igniter parts and their quality control and assembly costs. 
         [0037]    A need also exists for inertial igniters that can be used in applications in which the setback acceleration level is relatively low and/or the setback acceleration duration is relatively short. 
         [0038]    Such inertial igniters must be safe and do not initiate when subjected no-fire conditions. In general, such inertial igniters are also required to withstand the harsh firing environment, while being able to be designed to ignite at specified acceleration levels when subjected to such accelerations for a specified amount of time to match the firing acceleration experienced. Very high reliability is also of much concern. The inertial igniters must also usually 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. 
         [0039]    To ensure safety and reliability, inertial igniters should not initiate during acceleration events which may occur during manufacture, assembly, handling, transport, accidental drops, etc. Additionally, once under the influence of an acceleration profile particular to the firing of ordinance from a gun, the device should initiate with high reliability. It is also conceivable that the igniter will experience incidental low but long-duration accelerations, whether accidental or as part of normal handling, which must be guarded against initiation. 
         [0040]    Those skilled in the art will appreciate that the inertial igniters disclosed herein may provide one or more of the following advantages over prior art inertial igniters:
       provide small height inertial igniters that can be initiated when subjected to short duration firing setback acceleration (shock);   can be designed to provide small inertial igniters that can be initiated when subjected to relatively low firing setback acceleration (shock);   can be designed with independently adjustable all-fire (safety) and no-fire acceleration profiles;   can be designed such that its moving parts operate with minimal friction and stiction so that the initiation can be achieved reliably within a relatively small range of acceleration range;   provide inertial igniters that are significantly shorter than currently available inertial igniters for thermal batteries or the like;   provide inertia igniters that could be constructed to guide the pyrotechnic flame essentially downward (in the direction opposite to the direction of the firing acceleration—usually for mounting on the top of the thermal battery as shown in  FIG. 1 ), or essentially upward (in the direction opposite of the firing acceleration—usually for mounting at the bottom of the thermal battery);       
 
         [0047]    In view of such objects, inertial igniters and ignition systems for use with thermal batteries or the like upon subjection to firing setback acceleration, in particular low friction and stiction with independently adjustable no-fire (safety) acceleration threshold and all-fire acceleration activation levels and those that can be fabricated at relatively low cost are provided. Provided are also inertial igniters that are very low height for small thermal batteries. Still yet provided are G-switches based on the disclosed inertial igniters. 
         [0048]    Accordingly, a device is provided. The device comprising: an impact mass movably restrained relative to a base; and a release mechanism configured to be movable between a restrained position for preventing movement of the impact mass and a released position for permitting movement of the impact mass when the release mechanism is subjected to an acceleration greater than a predetermined magnitude and duration; wherein the release mechanism having a release mass movable when subjected to the acceleration, the movement of the release mass not being influenced by movement of the impact mass. 
         [0049]    The release mass can be separated from the impact mass in a lateral direction relative to a direction of the acceleration. 
         [0050]    The impact mass can be rotatably movable relative to the base. 
         [0051]    The device can further comprise a flame producing means for outputting a flame upon movement of the impact mass. The flame producing means can comprise: a first protrusion provided to protrude from a surface of the impact mass; a second protrusion provided to protrude from the base, the second protrusion being positioned such that movement of the impact mass causes contact between the first and second protrusions; a pyrotechnic provided proximate to one of the first and second protrusions such that the contact between the first and second protrusions ignites the pyrotechnic; and an opening in the base for outputting the flame from the base. 
         [0052]    The impact means can include a biasing member for biasing the impact mass in a direction opposite to the direction of the acceleration. 
         [0053]    The device can further comprise a circuit means for one of opening or closing an electrical circuit upon movement of the impact mass. The circuit means can comprise: an electrically conductive member provided to a surface of the impact mass; and first and second electrical contacts, electrically isolated from each other, provided to the base, the first and second electrical contacts being positioned such that movement of the impact mass causes the electrically conductive member to contact and close the electrical circuit between the first and second electrical contacts. The circuit means can comprise: an electrically non-conductive member provided to protrude from a surface of the impact mass; and first and second electrical contacts, electrically connected to each other, provided to the base, the first and second electrical contacts being biased in an electrically closed position and movable to an electrically open position, the first and second electrical contacts being positioned such that movement of the impact mass causes the electrically non-conductive member to move the first and second electrical contacts to the electrically open position. 
         [0054]    The release mechanism can comprise: a shaft having one end engaged with a portion of the impact mass and an other end engaged with the release mass, the shaft being movable to the released position upon movement of the release mass when the release mass is subjected to the acceleration; and a shaft biasing element for biasing the shaft into the released position when the release mass moves and is no longer engaged with the other end of the shaft. The device can further comprise a release mass biasing element for biasing the release mass into a position of engagement with the other end of the shaft. The release mass can move in translation. The release mass can move in rotation. The device can further comprise a housing including the base. 
         [0055]    Also provided is a method for moving an impact mass upon the impact mass experiencing an acceleration greater than a predetermined magnitude and duration. The method comprising: movably restraining the impact mass relative to a base; moving a release mechanism between a restrained position for preventing movement of the impact mass and a released position for permitting movement of the impact mass when the release mechanism is subjected to the acceleration; and configuring the release mechanism to have a release mass movable when subjected to the acceleration, wherein the movement of the release mass is not influenced by movement of the impact mass. 
         [0056]    The method can further comprise separating the release mass from the impact mass in a lateral direction relative to a direction of the acceleration. 
         [0057]    The method can further comprise outputting a flame upon movement of the impact mass. 
         [0058]    The method can further comprise one of opening or closing an electrical circuit upon movement of the impact mass. 
         [0059]    The release mass can move in translation. 
         [0060]    The release mass can move in rotation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0061]    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: 
           [0062]      FIG. 1  illustrates a schematic of a cross-section of a thermal battery and inertial igniter assembly of the prior art. 
           [0063]      FIG. 2  illustrates an isometric cut away view of an inertial igniter assembly of the prior art. 
           [0064]      FIG. 3  illustrates a full isometric view of the prior art inertial igniter of  FIG. 2 . 
           [0065]      FIG. 4  illustrates a schematic of a cross-section of the first inertial igniter embodiment of the present invention. 
           [0066]      FIG. 5  illustrates a schematic of a cross-section of the second inertial igniter embodiment of the present invention. 
           [0067]      FIG. 6A  illustrates a schematic of a cross-section of the third inertial igniter embodiment of the present invention. 
           [0068]      FIG. 6B  illustrates the view “A” of the release mechanism of the embodiment of  FIG. 6A . 
           [0069]      FIG. 7  illustrates a schematic of a cross section of a normally open g-switch embodiment corresponding to the first inertial igniter embodiment of  FIG. 4 . 
           [0070]      FIG. 8  illustrates a schematic of a cross section of a normally open g-switch embodiment corresponding to the second inertial igniter embodiment of  FIG. 5 . 
           [0071]      FIG. 9  illustrates a schematic of a cross section of a normally open g-switch embodiment corresponding to the third inertial igniter embodiment of  FIG. 6A . 
           [0072]      FIG. 10  illustrates a schematic of a cross section of a normally closed g-switch embodiment corresponding to the first inertial igniter embodiment of  FIG. 4 . 
           [0073]      FIG. 11  illustrates a schematic of a cross section of a normally closed g-switch embodiment corresponding to the second inertial igniter embodiment of  FIG. 5 . 
           [0074]      FIG. 12  illustrates a schematic of a cross section of a normally closed g-switch embodiment corresponding to the third inertial igniter embodiment of  FIG. 6A . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0075]    A schematic of a cross-sectional view of a first embodiment  50  of an inertia igniter is shown in  FIG. 4 . The inertial igniter  50  consists of a base element  51 , which in a thermal battery construction shown in  FIG. 1  can be positioned in a housing ( 10  in  FIG. 1 ) with the base element  51  positioned on the top of the thermal battery cap ( 19  in  FIG. 1 ). However, the base element  51  can also be a portion of the housing. A striker mass  52  (alternatively referred to as a impact mass) of the inertial igniter  50  is attached to the base element  51  via a rotary joint  53 . Although shown as being rotatable, the striker mass  52  can also be movable in translation, such as in the direction opposite to the direction of arrow  63 . In such configuration, the striker mass can be on one or more rails for constraining the translation along a direction of the one or more rails and the one or more rails can include bearings or other low friction means, such as treated low friction surfaces between the one or more rails and corresponding bores in the striker mass  52 . 
         [0076]    A post  54 , which is fixed to the base element  51  is provided with a hole  55 . A shaft  57  is positioned in the hole  55  and is movable within the hole from a position engaging the striker mass  52  to a position not engaging the striker mass  52 . Attached to the shaft  57  is the head  59  which in the pre-initiation configuration shown in  FIG. 4  rests against a sliding member  58  (alternatively referred to as a release mass). A compressively preloaded compressive spring  72  is also provided between the head  59  of the shaft  57  and a surface  73  of the post  54  to keep the head  59  in contact with the sliding member  58 . 
         [0077]    In the configuration of  FIG. 4 , the (up-down) sliding member  58  is shown to block the movement of the shaft  57  and head  59  member away from engagement with the striker mass  52  (the release mechanism is engaged with the mass  52  in a restrained position). Thereby in the configuration of  FIG. 4 , an end  60  of the shaft  57  is positioned below a tip  61  of the striker mass  52 , preventing the striker mass  52  from rotating clockwise in the direction of the arrow  62  as shown in  FIG. 4 . 
         [0078]    The sliding member  58  is free to slide down against a member  68 , if necessary via rolling elements  69 . However, sliding contact between the member  68  and sliding member  58  may also be utilized, particularly if the contacting surfaces are low friction surfaces. However, it will be appreciated by those skilled in the art that the rolling elements  69  would provide a means of reducing sliding friction between the sliding member  58  and the member  68  and minimize the possibility of stiction between the moving surfaces. As a result, a level of force needed to move the sliding member down become highly predictable, which in turn makes the level of acceleration needed to release the inertial ignite striker mass  52  more predictable as is described later. Similar roller elements (not shown) may also be positioned between the contacting surfaces of the sliding member  58  and the head  59  of the shaft  57 . The rolling elements  69  can be housed in retaining cavities (not shown) in the sliding member  58  or similarly held onto the sliding member  58  via a commonly used cage element (not shown). 
         [0079]    The member  68  is fixed to the base element  51 . A spring element  70  resists downward motion of the sliding member  58 , and can be preloaded in compression so that if a downward force that is less than the compressive preload is applied to the sliding member  58 , the applied force would not cause the sliding element  58  to move downwards. A stop  71  fixed to the member  68 , is provided to allow the spring element  70  to be preloaded in compression by preventing the sliding member  58  from moving further up (in the direction of arrow  68 ) from the configuration shown in  FIG. 4 . 
         [0080]    During the firing, the inertial igniter  50  is considered to be subjected to setback acceleration in the direction of the arrow  63 . The acceleration in the direction of the arrow  63  acts on the inertia of the sliding element  58  and generates a downward force that tends to slide the sliding element  58  downwards (opposite to the direction of acceleration). The compression preloading of the spring element  70  is generally selected such that with the no-fire acceleration levels, the inertia force acting on the sliding element  58  would not overcome (or at most be equal to) the preloading force of the spring element  70 . As a result, the inertial igniter  50  is ensured to satisfy its prescribed no-fire requirement. Alternatively, and particularly when the peak no-fire acceleration level is higher than the peak all-fire (setback) acceleration levels but is very short duration as compared to the duration of the all-fire acceleration, then the time that it takes for the sliding element  58  to move down enough to clear the head  59  of the shaft  57  is designed to be less than the duration of the no-fire acceleration events. 
         [0081]    Now if the acceleration level in the direction of the arrow  63  is high enough, then the aforementioned inertia force acting on the sliding element  58  will overcome the preloading force of the spring element  70 , and will begin to travel downward. If the acceleration level is applied over a long enough period of time (duration) as well, i.e., if the all-fire condition is satisfied and the sliding element  58  will have enough time to travel down far enough and clears the head  59  of the shaft  57 , then the compressively preloaded spring  72  would push the head  59  and the shaft  57  away from the striker mass  52 , thereby disengaging the tip  60  of the shaft  57  from the tip  61  of the striker mass  52 . As a result, the striker mass  52  is released and is allowed to be accelerated in the clockwise rotation as indicated by the arrow  62  (the release mechanism takes a release portion where it is no longer engaged with the mass  52 ). As a result, for a properly designed inertial igniter  50  (i.e., by selecting a proper mass and moment of inertial for the striker mass  52  and the range of clockwise rotation for the striker mass  52  so that it would gain enough energy), the striker mass  52  will gain enough kinetic energy to initiate the pyrotechnic material  64  between the pinching points provided by the protrusions  65  and  66  on the base element  51  and the bottom surface of the striker mass  52 , respectively, as shown in  FIG. 4 . The ignition flame and sparks can then travel down through the opening  67  provided in the base element  51 . When assembled in a thermal battery similar to the thermal battery  16  of  FIG. 1 , the inertial igniter is mounted in the housing  10  such that the opening  67  is lined up with the opening  12  into the thermal battery  11  to activate the battery by igniting its heat pallets. 
         [0082]    It will be appreciated by those skilled in the art that the duration of the all-fire acceleration level can also be important for the operation of the inertial igniter  50  by ensuring that the all-fire acceleration level is available long enough to accelerate the striker mass  52  towards the base element  51  to gain enough energy to initiate the pyrotechnic material  64  as described above by the pinching action between the protruding elements  65  and  66 . 
         [0083]    It will be appreciated by those skilled in the art that when the inertial igniter  50  ( FIG. 4 ) is assembled inside the housing  10  of the thermal battery assembly  16  of  FIG. 1 , a cap  18  (or a separate internal cap—not shown) is commonly used to secure the inertial igniter  50  inside the housing  10 . In such assemblies, the stop element  71  is no longer functionally necessary since the sliding element  58  can be prevented from being pushed upward by the force of the spring element  70  and releasing the striker mass  52  by an internal surface/component of the cap. It will be, however, appreciated by those skilled in the art that by providing the stop element  71 , particularly if it is extended to at least partially over the top surface of the striker mass  52 , then the storage of the inertial igniter  50  and the process of assembling it into the housing  10  is significantly simplified since one does not have to provide secondary means to keep the spring element  70  from pushing the sliding element  58  further up and thereby clearing the head  59  of the shaft  57  and releasing the striker mass  52 . 
         [0084]    It will be appreciated by those skilled in the art that in the inertial igniter embodiment  50  of  FIG. 4 , and in contrast to the prior art of  FIGS. 2 and 3 , the downward force due to the acceleration in the direction of the arrow  63  acting on the mass (inertia) of the striker mass  52  does not increase the level of force that is required for the slider element  58  to be moved downward to release the striker mass as was previously described. It will also be appreciated by those skilled in the art that in the inertial igniter of the prior art shown in  FIGS. 2 and 3 , as the inertial igniter  200  is accelerated similarly in the direction of the arrow  218 , the generated force due to the mass of the striker element  205  would cause the locking balls  207  to be forced outward against the surfaces of the pockets  212  of the collar  211 , thereby increasing the resistance of the collar to downward motion, thereby to the release of the striker element  205 . This very important feature of the inertial igniter embodiment  50  of  FIG. 4  ensures the consistency with which the igniter striker mass  52  can be released within a very narrow range of acceleration in the direction of the arrow  63 , i.e., for the case of munitions, within a narrow range of firing setback or the like acceleration event. 
         [0085]    It will also be appreciated by those skilled in the art that by providing a preloaded compressive force level in the spring  72  that is greater than the maximum friction and stiction forces between the tip  61  of the striker mass  52  and the tip  60  of the shaft  57  as well as between the shaft  57  and the hole  55  in the post  54 , then once the sliding element  58  has cleared the head  59  of the shaft  57 , then the tip  60  of the shaft  57  is ensured to be pulled away from the top  61  of the striker mass  52  to initiate its accelerated clockwise rotation in the direction of the arrow  62 , thereby initiating the pyrotechnic material  64  as was previously described. 
         [0086]    In the embodiment of  FIG. 4 , the sliding element  58  and the spring element  70  of the release mechanism of the inertial igniter  50  may be configured in numerous ways, e.g., the sliding element  58  may be replaced with a rotating member (which may further reduce friction and stiction in the release mechanism) and the spring member  70  may be integral with the resulting rotating member, i.e., as a flexible beam element with living joints with the inertia of the beam acting as the mass element of the resulting slider element. 
         [0087]    It will be appreciated by those skilled in the art that the hole  55  and the cross-section of the mating shaft  57  do not have to be circular. For example, the designer may choose to use non-circular shapes instead to provide the means of preventing and/or minimizing the rotation of the shaft  57  about its long axis. For example, the designer may choose a trapezoidal mating shape or a shape close to or similar to a trapezoidal shape so that during assembly the two parts could be mated only in the correct orientation and thereby eliminate assembly mistakes and the need for post assembly inspection. 
         [0088]    In certain applications, the all-fire setback acceleration level is either not high enough to impart enough kinetic energy to the striker mass  52  or its duration is not long enough to allow the striker mass be released by the downward motion of the sliding element  58  and the clockwise rotation of the striker mass in the direction of the arrow  62 . As a result, the striker mass  52  is released as a result of setback firing acceleration or other prescribed acceleration events, but the striker mass is not capable to reliably ignite the pyrotechnic material  64  by the resulting impact (pinching) between the protruding elements  65  and  66 . In such applications, additional kinetic energy may be provided by the potential energy stored in appropriately positioned preloaded spring element(s). An example of such an inertial igniter is shown in the schematic of the cross-sectional view of the inertial igniter embodiment  80  of  FIG. 5 . 
         [0089]    All components of the inertial igniter embodiment  80  of  FIG. 5  are identical to those of the embodiment  50  of  FIG. 4 , except for the following added components. The same components illustrated in  FIGS. 4 and 5  are similarly numbered, however, such reference numerals are omitted in  FIG. 5  for the sake of clarity. In the embodiment  80 , the embodiment  50  of  FIG. 4  is provided to add sides  74  and  75  and a top cover  76  to the base element  51  to form a housing. A compressively preloaded spring  77  is also positioned between the top cover  76  and the top surface  78  of the striker mass  52 . Then, as the inertial igniter  80  is subjected to the firing setback acceleration or the like in the direction of the arrow  63 , and if the aforementioned prescribed all-fire conditions have been satisfied, then following the release of the striker mass  52  as was previously described for the embodiment  50  of  FIG. 4 , the continuing acceleration in the direction of the arrow  63  and/or the force exerted by the compressively preloaded spring  77  will rotationally accelerate the striker mass  52  in the clockwise direction as shown by the arrow  62  in  FIG. 4 , imparting enough kinetic energy to the striker mass  52  so that as the resulting impact (pinching) between the protruding elements  65  and  66  would cause the pyrotechnic material  64  to ignite. 
         [0090]    A third embodiment  90  of the inertial igniter of the present invention is shown in the cross-sectional view of  FIG. 6A . All components of the inertial igniter embodiment  90  of  FIG. 6A  are identical to those of the embodiment  50  of  FIG. 4 , except for the slider element  58  based striker mass release mechanism. In the embodiment  90  of  FIG. 6A , the sliding element  58  is replaced by a rotating mechanism to reduce device complexity and the sliding friction forces. In the embodiment  90 , the motion of the head  59  of the shaft  57  away from the striker mass engagement,  FIGS. 4 and 6A , is prevented by the surface  81 , the opposite side of the end  85  of the link  82  shown in the view “A” of  FIG. 6B . The link  82  is attached to the inertial igniter base  51  via the rotary joint composed of the supports  83  and the rotary joint pin  84  as shown in  FIG. 6A  and the view “A” shown in  FIG. 6B . The link  82  is also provided with a preloaded spring  86  which is biased to keep the link  82  against the stop (for example stop  87 , which is fixed to the post  54 ,  FIG. 6A , or the stop  88 , which is fixed to the rotary joint support  83 ,  FIG. 6B ). The link stop (elements  87  or  88 ) is positioned such that in pre-initiation configuration, the biasing preloaded spring  86  would position the end  85  of the link  82  against the head  59  of the shaft  57 . 
         [0091]    Then when the inertial igniter is accelerated in the direction of the arrow  63 , the force resulting by the action of the acceleration on the mass of the link  82  and its end  85  will tend to rotate the link  82  in the clockwise direction as seen in the view “A” of  FIG. 6B . If the level of acceleration in the direction of the arrow  63  is high enough to overcome the preloaded force of the spring  86 , then the link  82  will begin to rotate in the clockwise direction as seen in  FIG. 6B . If the duration of the above acceleration is long enough, then the link  82  will rotate in the clockwise direction enough for the surface  81  of the end  85  of the link  82  to clear the head  59  of the shaft  57 , thereby allowing the shaft  57  to move away from engagement with the striker mass  52 , thereby allowing the striker mass to accelerate downward as was described for the embodiment of  FIG. 4  and cause the pyrotechnic material  64  of the inertial igniter to be ignited. 
         [0092]    It will be appreciated by those skilled in the art that the link  82  may be fixedly attached to the base plate  51  and be provided with a rotary (flexural) living joint to serve the same purposed as is described above for the link  82  and its end  85 . In such an arrangement, the flexibility of the said flexural living joint may be used to serve the purpose of the spring  86 . In which case the aforementioned preloading of the spring  86  may also be achieved by designing the flexural element such that in normal conditions the link  82  positions the end  85  passed the head  59  of the shaft  57 . Then the prescribed preloading level is achieved by rotating the link in the clockwise direction and bringing it to stop against the provided stop element (elements  87  or  88  in  FIG. 6A ). 
         [0093]    In the embodiments  50 ,  80  and  90  of  FIGS. 4 , Sand  6 A, respectively, pyrotechnic materials  64  are shown to be used for ignition upon inertial igniter initiation through the impact (pinching) between the protruding elements  65  and  66 . It is, however, appreciated by those skilled in the art that instead of the pyrotechnic material  64 , which has to be applied individually to the inertial igniter  50  base  51  over the protruding element  65 , one may instead install commonly used percussion caps such as those commonly used in gun bullets or the like in a provided cavity (not shown but usually specified by the percussion cap manufacturer) in the base  51  (to be initiated by the impact of the appropriately shaped protruding element  66 ). The advantage of using the pyrotechnic material  64  is that they can be designed to initiate at impact energies that are significantly lower than that of percussion primers, however at significantly higher per unit cost. Percussion primers are however mass produced at high volumes and are therefore significantly lower in cost and easy to install. For purposes of this disclosure and the appended claims, “pyrotechnic material” will include the use of the pyrotechnic materials as discussed above with regard to  FIGS. 4, 5 and 6A  as well as the alternative percussion caps discussed immediately above. 
         [0094]    In the above embodiments, the disclosed devices are intended to actuate, i.e., release their striker mass  52  in response to an all-fire acceleration level to accelerate downwards to impact the provided pyrotechnics materials causing them to ignite. The same mechanisms used for the release of the striker mass due to an all-fire acceleration can be used to provide the means of opening or closing an electrical circuit, i.e., act as a so-called G-switch, that is actuated only if it is subjected to an all-fire acceleration profile, while staying inactive during all no-fire conditions, even if the acceleration level is higher than the all-fire acceleration level but significantly shorter in duration. As a result, this novel G-switch device would satisfy all no-fire (safety) requirements of the device in which it is used while activating in the prescribed all-fire condition. 
         [0095]    Schematics of such G-switches are shown in  FIGS. 7-12 , where  FIGS. 7-9  illustrate a normally open G-switch corresponding to the inertial igniter configurations of FIGS.  4 ,  5  and  6 A, respectively, and  FIGS. 10-12  illustrate a normally closed G-switch corresponding to the inertial igniter configurations of  FIGS. 4, 5 and 6A , respectively. 
         [0096]    Turning first to the G-switch  100  of  FIG. 7 , which is similar to the inertial igniter illustrated in  FIG. 4 , except that its pyrotechnic material and initiation elements (elements  64 ,  65  and  66  in  FIG. 4 ) are removed. An element  106 , which is constructed of an electrically non-conductive material is fixed to the base  51  of the device as shown in  FIG. 7 . The element  106  is provided with two electrically conductive elements  104 ,  107  with contact ends  103  and  109 , respectively. Electrical wires  105  and  108  are in turn attached to the electrically conductive elements  104  and  107 , respectively. As it was described for the embodiment  50  of  FIG. 4 , when the device is subjected to an all-fire acceleration in the direction of arrow  63 , the striker mass  52  is release and rotated about the pivot  53  in the direction of arrow  62 . The striker mass  52  is provided with a flexible strip of electrically conductive material  101  which is fixed to the bottom surface of the striker mass  52  (such as by being soldered or attached with fasteners  102 ). Therefore, as the striker mass  52  rotates towards the base  51  of the device, it would cause the flexible electrically conductive strip  101  to come into contact with the contact ends  103 ,  109 , thereby causing the circuit through the wires  105  and  108  to close. 
         [0097]    As discussed above with regard to  FIG. 5 , the g-switch of  FIG. 7  can be provided with a biasing spring  77  to ensure that the flexible electrically conductive strip  101  stays in contact with the contact ends  103  and  109 . Such an embodiment is shown in the g-switch  110  of  FIG. 8 . 
         [0098]    As also discussed above with regard to  FIGS. 6A and 6B , the sliding element  58  can be replaced by a rotating mechanism to reduce device complexity and the sliding friction forces. Such an embodiment is shown in the g-switch  120  of  FIG. 9 . 
         [0099]    The G-switch  100  of  FIG. 7  can also be readily modified to provide a “normally close” switching configuration. As an example, the contact components of the G-switch  130  may be modified to that shown in the schematic of  FIG. 10 . This embodiment  130  of the G-switch has all its other components being the same as those of the embodiment  100  of  FIG. 10 . The “normally closed” G-switch  130  is provided with two flexible contact elements  133  and  135 , which are fixed to the electrically non-conductive member  134 , which is fixed to the base  51  of the device  130 . The flexible contact elements  133  and  135  are provided with contact points  131  and  137 , which are normally in contact (such as by being biased towards each other), thereby causing the wires  132  and  136  that are attached to the contact elements  133  and  135  to close the electrical circuit to which they are connected. The striker mass  52  is provided with a non-conductive member  138  as shown in  FIG. 10 . 
         [0100]    As was described for the embodiment  100  of  FIG. 7 , when the device is subjected to an all-fire acceleration in the direction of arrow  63 , the striker mass  52  is release and rotated about the pivot  53  in the direction of arrow  62 . As the non-conductive member  138  reaches the contact points  131  and  137 , the force of the acceleration acting on the inertia of the striker mass  52  causes the member  138  to be inserted between the contact points  131  and  137 , thereby rendering their contacts open and opening the aforementioned electrical circuit to which the wires  132  and  136  are connected. 
         [0101]    As discussed above with regard to  FIG. 5 , the g-switch of  FIG. 10  can be provided with a biasing spring  77  to ensure that the member  138  stays inserted between the contact points  131  and  137 . Such an embodiment is shown in the g-switch  140  of  FIG. 11 . 
         [0102]    As also discussed above with regard to  FIGS. 6A and 6B , the sliding element  58  can be replaced by a rotating mechanism to reduce device complexity and the sliding friction forces. Such an embodiment is shown in the g-switch  150  of  FIG. 12 . 
         [0103]    While there has been shown and described what is considered to be preferred embodiments of the invention, it will, of course, be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention be not limited to the exact forms described and illustrated, but should be constructed to cover all modifications that may fall within the scope of the appended claims.