Abstract:
A method for detecting a number of events having an acceleration profile greater than a predetermined threshold. The method including: detecting a number of events having the acceleration profile greater than the predetermined threshold; counting the number of events detected having the acceleration profile greater than the predetermined threshold; and outputting a mechanical or electrical signal based on whether the counted number of events having the acceleration profile greater than the predetermined threshold is greater than a predetermined number.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of earlier filed U.S. Provisional Application No. 61/637,817, filed on Apr. 24, 2012, the entire contents of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to multi-stage mechanical mechanisms for the initiation of pyrotechnic materials in thermal batteries or the like devices requiring pyrotechnic initiation in munitions, and more particularly for initiation of such pyrotechnic materials in munitions following a predetermined number of deceleration events such as the so-called set-forward acceleration in gun-fired munitions and mortars or target impact events. The means of the said activation may be mechanical by causing certain relevant motion in the system/device to be produced or electrical by causing a circuit to be closed or opened and/or electrical pulses to be generated or cause other detectable events that indicate the impact event and/or the severity of the impact. 
     2. Prior Art 
     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. 
     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 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. 
     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. 
     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. 
     In an activated thermal battery, since the electrolyte is in its molten state, the battery cannot withstand high-G shocks that are caused as the munitions impacts a hard surface such as the intended target. For this reason, when the thermal battery is intended to be used to power certain devices following target impact, then it is highly desirable for the thermal battery to be activated following such shock loadings. In certain applications, the munitions is intended to enter the interior of a building or a bunker through more than a single wall, ceiling, floor or otherwise significant barrier (hereinafter, all such significant barriers are referred to collectively as “significant barriers”, with the aim of including those obstacles that cause shock loading of the munitions above certain predetermined level and excluding minor obstacles that are not used for protection against incoming munitions). In such applications, it is highly desirable for the thermal battery to be initiated following a prescribed number of shock loadings (impacts), each corresponding to shock loading due to impact with a significant barrier. 
     It is appreciated by those skilled in the art that an initiation device that is used to ignited pyrotechnic materials in thermal batteries may also be used to initiate pyrotechnics materials in other devices or initiate explosive charges. 
     SUMMARY OF THE INVENTION 
     A need therefore exists for the development of novel methods and mechanical inertia-based mechanisms for initiation of thermal batteries and other similar devices used in gun fired munitions, mortars, rockets, gravity dropped weapons and other types of munitions after the said munitions has impacted a prescribed number of “significant barriers”. 
     A need also exists for the development of novel methods and mechanical inertia-based mechanisms for initiation of thermal batteries and other similar devices used in gun fired munitions, mortars, rockets, gravity dropped weapons and other types of munitions after the said munitions has impacted a prescribed number of “significant barriers” or has failed to encounter the prescribed number of “significant barriers” after a prescribed amount of time has elapsed. 
     It is noted that in gun-fired munitions and mortars the direction of the setback acceleration is opposite to the direction of the “significant barrier” impact induced acceleration. Therefore the said novel mechanical inertia-based mechanisms for initiation of thermal batteries and other similar devices in such munitions must be capable of withstanding firing setback acceleration and not initiate. 
     It is also noted that in gun-fired munitions and mortars the direction of the set forward acceleration experienced by the munitions is in the same direction as the direction of the “significant barrier” impact induced acceleration. Therefore for the said novel mechanical inertia-based mechanisms for initiation of thermal batteries and other similar devices to correctly detect the number of encountered “significant barriers”, it must be capable of differentiating the set forward acceleration from the “significant barrier” impact induced acceleration. This task is generally not difficult to accomplish as described later in this disclosure, since the set forward acceleration level is usually much lower than the level of “significant barrier” impact induced acceleration. 
     A need therefore also exists for novel mechanical inertia-based mechanisms for initiation of thermal batteries and other similar devices to be used in gun-fired munitions and mortars and the like to be able to differentiate the set forward acceleration from the “significant barrier” impact induced acceleration. 
     In certain applications, the said novel mechanical inertia-based mechanisms for (mechanical or electrical) initiation of thermal batteries and other similar devices are desired to in addition of detecting (“counting”) the number of encountered “significant barriers”, to also determine the corresponding level of each encountered impact force. The level of encountered impact force is usually desirable for the purpose of determining the strength of the encountered significant barrier. In addition, in certain cases it is desired to also know the time history (i.e., the profile) of the encountered impact force, since such a profile give an indication of the strength, type and thickness of the encountered “significant barrier”. 
     A need therefore also exists for novel mechanical inertia-based mechanisms for (mechanical or electrical) initiation of thermal batteries and other similar devices to detect the number of encountered “significant barriers” as well as their resulting impact force levels. 
     A need therefore also exists for novel mechanical inertia-based mechanisms for (mechanical or electrical) initiation of thermal batteries and other similar devices to detect the number of encountered “significant barriers” as well as the time history (time profile) of their resulting impact force levels. 
     In addition, new improved chemistries, manufacturing processes and packaging technologies have been developed in recent years 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. It is, therefore, highly desirable for the developed mechanical inertial-based initiation devices to be small for such small and low power thermal batteries, particularly those that are being developed for use in miniaturized fuzing, future smart munitions, and other similar applications. 
     The innovative inertia based initiation devices would preferably be scalable to thermal batteries and other similar devices of various sizes, in particular to miniaturized initiation devices for small size thermal batteries. 
     Such inertia based initiation devices must in general be safe and in particular they should not initiate if dropped, e.g., from up to 7 feet onto a concrete floor for certain applications; should withstand high firing accelerations, for example up to and in certain cases over 20-50,000 Gs; and should be able to be designed to initiate after a predetermined number of “significant barriers” have been encountered. To ensure safety and reliability, inertial igniters should not initiate during acceleration events which may occur during manufacture, assembly, handling, transport, accidental drops, or other similar accidental events. In addition, such inertia based devices must be capable of differentiating the aforementioned accidental events such as dropping from up to 7 feet or accelerations and decelerations during transportation from shock loading experienced as a result of impact with a “significant barrier”, i.e., the device should not be activated to count such accidental events as “significant barrier” impacts. 
     In certain applications, the pyrotechnic materials in thermal batteries or the like are required to be initiated by electrical initiation elements. In such applications, electrical energy is preferably generated by piezoelectric elements during one or more of encountered high G events such as firing setback or set forward accelerations or impact shock when encountering “significant batteries” or during the munitions fight as a result of vibration and/or oscillatory motions. In such applications, the available electrical power may be used to power appropriate electronics and logics circuitry such that the number of encountered “significant barriers” could be counted and initiation command provided once a prescribed number of “significant barriers” have been encountered. Such electronics and logics circuitry can be provided with timing capability such that if the prescribed number of “significant barriers” are not encountered, a predetermined action(s) is taken. Such action options may include the following:
         Rendering of the munitions disarmed;   Initiating the pyrotechnics materials of the device;   Transmit information to a “fire control center”, including its present location, the number of “significant barrier” impacts encountered; its state (armed or disarmed or the time to detonation, etc.); and/or other sensory information;   Starting to collect sensory data and transmitting the said data to a “fire control center” for decision making purposes;   Transmit homing signal for incoming munitions;   Transmitting information as to the location of the munitions, and if an UXO, whether it is armed or disarmed;   Expulsion of sensory and other devices, sub-munitions; warhead, etc.;   Expulsion of the damage assessment devices and means of transmitting the collected information to a “fire control center” center.       

     A need therefore also exists for the development of novel methods of integrating piezoelectric-based electrical energy generation devices and the proper electronics and logics circuitry for performing one or more of the aforementioned tasks into the aforementioned mechanical inertia-based mechanisms for initiation of thermal batteries and other similar devices used in gun fired munitions, mortars, rockets, gravity dropped weapons and other types of munitions after the said munitions has impacted a prescribed number of “significant barriers”. 
     In certain other applications, the munitions or any other system using the disclosed novel mechanical inertia-based mechanisms have a source of electrical energy and the pyrotechnic materials in thermal batteries or the like are required to be initiated by electrical initiation elements. In such applications, an embodiment of the disclosed novel mechanical inertia-based mechanisms is used as an electrical switch, for the purpose of opening or closing a circuit each time an aforementioned “significant barrier” is encountered. The available electrical power may then be used to power appropriate electronics and logics circuitry such that the number of encountered “significant barriers” could be counted and initiation command provided once a prescribed number of “significant barriers” have been encountered. The said command may be for initiation of a pyrotechnic material or the like or for the initiation of any other predetermined (programmed) actions. 
     In an alternative embodiment, at least one novel mechanical inertia-based mechanism is used that consists of at least one stage mechanism, which once the process of reaction to an impact with a “significant barrier” has ended, it would essentially return to its initial (pre-impact) state. The device also acts as an electrical switch, opening and/or closing once actuated due to the encountered impact with a “significant barrier”. The numbers of “significant barriers” are then counted by the number of times that the device is actuated and returned to its initial state after encountering a “significant barrier”. 
     In a variation of the above embodiment, the at least one novel mechanical inertia-based mechanism consists of several stages, each actuated at a predetermined impact induced acceleration level and each acting as en electrical switch as previously described. Then upon encountering impact with a “significant barrier”, the aforementioned stages of the mechanical inertia-based mechanism would actuate sequentially as the impact induced acceleration level increases, each at different (increasing) acceleration level threshold, thereby allowing both impact occurrence as well as its induced acceleration level be determined (to the discrete threshold levels). 
     Reliability is also of much concern since the most munitions 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 design of inertia based initiation devices must also consider the manufacturing costs and simplicity of the design to make them cost effective for munitions applications. 
     The need to differentiate accidentally induced accelerations such as accelerations due to dropping or during handling and transportation as well as firing setback and set forward accelerations from target impact induced accelerations necessitates the employment of novel inertia-based mechanisms that can safety and reliably make such comparisons. In addition, the said novel inertia-based mechanisms must be able to count the number of impacts with targets that constitute “significant barriers” since the devices that are to be activated by such novel inertia-based mechanisms may be required to be activated following a certain number of “significant barrier” encounters since cases most thermal batteries are not capable of withstanding shock loading due to a “significant barrier” encounter. 
     The novel inertia-based mechanisms described herein provide mechanical mechanisms that respond to accelerations that are induced due to target impact in the direction opposite to the munitions travel and that are above certain threshold. The disclosed inertial based mechanisms differentiate between accelerations in the same direction as the target impact induced accelerations, including the set forward acceleration, since the level of acceleration experienced by munitions during impact with a “significant barrier” is significantly higher than the aforementioned acceleration threshold. 
     The disclosed novel inertia-based mechanisms may have a multi-stage design. All stages of the device are however prevented from actuation (responding to impact with a “significant barrier”) except for the first stage of the device. Then once an impact with a “significant barrier” is encountered, the first stage is actuated, and the next stage is enabled to actuate in response to an impact with the next “significant barrier”. Thus, the different stages of the device sequentially detect impacts with the encountered “significant barriers”. In such inertial-based mechanisms, each stage of the device stays in its actuated state following impact with a “significant barrier”, while enabling the next stage of the device to actuate as a result of impact with the next “significant barrier”. In one embodiment of the present invention, when a predetermined number of “significant barrier” impacts are encountered, the inertia-based mechanism initiates a pyrotechnic charges or the like. In another embodiment of the present invention, each said stage of the device acts as an “electrical switch” to provide an electrical or electronics and/or logics circuitry with a signal indicating the occurrence of such an impact with a “significant barrier”. In another embodiment of the present invention, each said stages of the present novel inertia-based devices are composed of more than one mechanically actuated stage that are sequentially actuated and held in their actuated state when an increasing impact acceleration threshold is reached. As a result, these said devices can be used to detect impact with “significant barriers” as well as the level of the level of impact acceleration that it experiences within a discrete number of impact acceleration thresholds. 
     Alternatively, the novel inertia-based mechanisms may have at least one stage, which after encountering impact with a “significant barrier” and ensuing actuation, it returns to its initial stage. Each encountered actuation event of the inertia-based mechanism stage is then used to generate an electrical or mechanical signal that is used by an appropriate electrical device or electronics and/or logics circuitry, or mechanical mechanism to advance a counter or event detection mechanism, or perform certain sequential electrical, electronic or mechanical action. The action includes initiation of a pyrotechnic charge to initiate a thermal battery or the like or initiate a munitions detonation charge after a predetermined number of “significant barriers” are encountered or a prescribed amount of time has elapsed without such encounters. The initiation of pyrotechnic material may be electrical by an electrical initiator or mechanically by releasing, for example, a spring preloaded striker mass to initiate the pyrotechnic material by impact energy. 
     The actuation of the at least one stage novel inertial-based mechanism may also be used to act as an electrical switch to open or close a circuit to provide the signal indicating detection of an encounter with a “significant barrier”. 
     When electrical power is required to power the electronics and/or logics circuitry of the device and/or for initiating the pyrotechnics materials of the device, the electrical energy is preferably generated by piezoelectric elements during one or more of encountered high G events such as firing setback or set forward accelerations or impact shock when encountering “significant batteries” or during the munitions fight as a result of vibration and/or oscillatory motions. In such applications, the available electrical power may be used to power appropriate electronics and logics circuitry such that the number of encountered “significant barriers” could be counted and initiation command provided once a prescribed number of “significant barriers” have been encountered. Such electronics and logics circuitry would preferably be provided with timing capability such that in the prescribed number of “significant barriers” are not encountered, a predetermined action(s) is taken. Such action options may include one or more of the aforementioned actions, such as disarming the device, transmitting a signal as to its status, etc., as previously described. 
     The ignition of pyrotechnic material 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. 
     Those skilled in the art will appreciate that the basic novel method for the development of inertial igniters that can detect munitions encounter with “significant barriers” disclosed herein may provide one or more of the following advantages over prior art mechanical and/or electrical and/or electronics equipped with accelerometers or the like and related electronics, with and without microprocessor units or the like, in addition to the previously indicated advantages: 
     provide the means to initiate thermal battery or the like pyrotechnics after munitions has encountered a prescribed number of “significant barriers”; 
     provide the means of turning an electrical “switch” on or off to render an electrical circuit open or closed; 
     provide the means to generate an electrical pulse after each “significant barriers” encounter; 
     provide the means to incorporate any possible time delay period that may be required for inertial igniters and other similar applications; 
     provide inertial igniters with mechanical means of detecting and “counting” munitions encounters with “significant barriers” and initiating pyrotechnic materials or performing certain other actions once a specified number of such “significant barriers” have been encountered; 
     provide mechanical means of detecting and “counting” munitions encounters with “significant barriers” as well their levels of impact shock and initiating pyrotechnic materials or performing certain other actions once a specified number of such “significant barriers” have been encountered; 
     provide methods of developing mechanical means of detecting and “counting” munitions encounters with “significant barriers” as well their levels of impact shock and activating and initiating pyrotechnic materials or performing certain other actions once a specified number of such “significant barriers” have been encountered; 
     making it possible to provide the said inertial igniters for thermal batteries and the like in very small packages and without requiring external power sources; and 
     provide inertial igniters that can be sealed in a package to simplify storage and increase their shelf life. 
     In this disclosure, novel and basic methods are presented that are used for compact mechanisms for miniature inertial igniters for initiation of thermal batteries and the like that can detect impacts with “significant barriers”, count the number of such encounters with “significant barriers”, and initiate the thermal battery or the like once a predetermined number of such encounters has occurred and/or provide this information to an electrical or electronics device in the form of switching actions to open or close a circuit or send a pulse by first opening (closing) a circuit and then opening (closing) the circuit or the like. The method is based on the employment of a mechanical mechanism that does not react to firing setback and set-forward accelerations, but sequentially reacts to each munitions impact with a “significant barrier” at/near target location. In this mechanical mechanism, each sequential “significant barrier” encounter causes a sequential actuation of a series of actuation stages of the said mechanical mechanism. In an alternative design, an actuation stage returns to its pre-actuation configuration following an encounter with a “significant barrier”, while in the process causing an electrical, electronic or mechanical “counter” or “switch” or “pulsing” mechanism to be operated. The device may be provided with several actuation devices, each designed to be actuated at different level of impact shock acceleration level, thereby allowing measurement of the level of impact shock within the provided levels that has been experienced by munitions during each encounter with a “significant barrier”. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  illustrates the schematic of one embodiment of a “significant barrier” encounter event detection mechanism. 
         FIG. 2  illustrates the schematic of an alternative embodiment of the “significant barrier” encounter event detection mechanism of  FIG. 1 . 
         FIG. 3  illustrates the schematic of another alternative embodiment of the “significant barrier” encounter event detection mechanism of  FIG. 1 . 
         FIG. 4  illustrates the schematic of another alternative embodiment of the “significant barrier” encounter event detection mechanism of  FIG. 1  which uses a mechanical mechanism to “count” the number of encountered events. 
         FIG. 5  illustrates the schematic of another embodiment of the “significant barrier” encounter event detection device, which is capable of counting the number of such encounters and their impact acceleration (force) levels. 
         FIG. 6  illustrates the schematic of another embodiment of the “significant barrier” encounter event detection device. 
         FIG. 7  illustrates the schematic of yet another embodiment of the “significant barrier” encounter event detection device. 
         FIG. 8  illustrates the schematic of yet another embodiment of the “significant barrier” encounter event detection device. 
         FIG. 9  illustrates the schematic of yet another embodiment of the “significant barrier” encounter event detection device. 
         FIG. 10  illustrates the schematic of another embodiment of the “significant barrier” encounter event detection device. 
         FIG. 11  illustrates the schematic of another embodiment of the present invention for mechanical initiation of a pyrotechnic material after a prescribed number of “significant barriers” have been encountered. 
         FIG. 12  illustrates the schematic of an alternative embodiment of the “significant barrier” encounter event detection mechanism of  FIG. 11 . 
         FIG. 13  illustrates the schematic of an alternative embodiment of the “significant barrier” encounter event detection mechanism of  FIG. 12  for direct initiation of pyrotechnic charges. 
         FIG. 14  illustrates an example of a multiple contact opening or closing configuration that can be used in contact opening/closing embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment  200  of a highly compact mechanisms and method for detecting “significant barrier” encounter events and providing the means to count the number of such encounter events for use in miniature inertial igniters for thermal batteries or other safe and arm devices and the like and their operation is shown in the schematic of  FIG. 1 . The device  200  is designed to close an electrical circuit by causing two contacts that keep the circuit open to come into contact when the device is subjected to an acceleration in the direction of the arrow  201  as a result of encountering a “significant barrier”, i.e., as a result of impact shock caused by the munitions encountering a “significant barrier”. 
     The device  200  mechanism consists of the main moving elements  202  and  203 . The element  202  can slide back and forth (to the right and left as seen in the schematic of  FIG. 1  over the surface  204  of the device structure  205 . The element  203  is provided with a guide  206 , which is preferably provided in the structure  205  of the device  200  or is fixed to the said device structure  205 . The element  202  is biased to its left-most position by the compressive spring  207 , which rests against the stop  208  provided on the device structure  205 . The element  202  is preferably held in its left-most position by the stop  209 . Alternatively, the element  202  may be held in its left-most position by the tip  210  of the element  203 , which is pressed against the inclined surface  211  of the element  202  by the compressive spring  212 . The element  203  may be provided with a protrusion  213  which limits its upward motion by coming against the stop  214  provided on the device structure  205 . 
     The element  203  is provided with certain amount of mass so that when the device  200  is subjected to an acceleration in the direction of the arrow  201 , the force exerted by the tip  210  of the element  203  on the inclined surface  211  of the element  202  is proportionally increased. The spring elements  212  and  207  are also provided with certain amount of compressive preloading such that until certain acceleration level is reached the element  202  would not begin to displace (to the right). The spring rates of the spring elements  212  and  207  are also selected such that as a specified acceleration level corresponding to the aforementioned encounter with a “significant barrier” is reached, the force exerted by the tip  210  due to the acceleration acting on the mass of the element  203  is large enough to displace the element  202  far enough (to the right as seen in the schematic of  FIG. 1 ) to cause the portion  215  of the element  202  to press against the flexible metal (strip) element  217  to bend, thereby bringing the contact elements  216  and  218  into contact. The flexible metal element  217  is fixed to the device structure  205  while being electrically isolated from the device structure by the non-conducting material member  220  (in the schematic of  FIG. 1 , via the stop  208 ). The contact  218  is in turn attached to a conducting element  219 , which is preferably electrically isolated from the device structure  205  (and in the case of the schematic of  FIG. 1 , from the stop member  208 ) by similar non-conducting materials (not shown). The electrical wires  221  and  222  are attached to the flexible metal element  217  and the conducting element  219 , respectively, and provide the means of closing a circuit once the contacts  216  and  218  come into contact as described above due to the device  200  experiencing an acceleration in the direction of the arrow  201  that is at the prescribed level or above that would be experienced by the munitions using the device  200  when it encounters a “significant barrier”. 
     When used to initiate the pyrotechnic materials in a thermal battery or initiate pyrotechnic materials or the like in other devices, an electronic circuitry and logic device or a microprocessor  280 ,  FIG. 1 , hereinafter referred to as the “control unit”, is used for collecting and processing of the device  200  encounters with “significant barriers”. During each “significant barrier” encounter, the control unit  280  registers the encounters and when the prescribed number of “significant barriers” has been encountered, it would initiate the process of igniting the intended pyrotechnic material. In general, the “control unit” is also designed to either initiate the pyrotechnic material ignition or initiate a disarming process if the prescribed number of “significant barrier” is not encountered within a prescribed amount of time, which could indicate that the desired target has not been reached. Here, if an electrical initiation device is being used, the latter process generally involves the passing a high enough current through the electrical initiation filament or the like to heat or produce sparks to ignite the surrounding pyrotechnic material (such as by discharging the energy stored in a provided capacitor). The design and construction of such “control units” and the electrically initiated igniters (filament and other types) are well known in the art and are not discussed in the present disclosure. 
     It is appreciated by those skilled in the art that the device  200  shown in the schematic of  FIG. 1  may be readily modified to open a normally closed circuit. This can, for example, be achieved as shown in  FIG. 2  that illustrates changes to be made to the electrical contact region of the device  200  of  FIG. 1 . In this alternative design, the first (relatively flexible and electrically conductive) contact element  230  with the contact end  231  is attached to the device  200  structure  205  with an isolating non-conducting element  232 . The second (relatively flexible and electrically conductive) contact element  233  with the contact end  234  is also attached to the device  200  structure  205  with an isolating non-conducting element  235 . The contact points  231  and  234  are normally in contact, thereby keeping a circuit connected through the electrically conductive contact element  230  and  233  via wires  236  and  237 , respectively, closed. However, when the device  200  is subjected to acceleration in the direction of the arrow  201  as shown in  FIG. 1  due to the munitions using the device  200  encountering a “significant barrier”, then the element  201  and its end member  215  (also shown partly in  FIG. 2 ) is forced to move rightward as was previously described and shown in dashed lines in  FIG. 2  and in combination enumerated with numeral  238 . The end member  215  (dashed lines) will then force the contact element  233  to bend away from the contact element  230 , thereby causing contact between their contact points  231  and  234  to be lost, thereby causing the aforementioned electrical circuit to be rendered open. 
     It is appreciated by those skilled in the art that since in the embodiments of  FIGS. 1 and 2  the number of “significant barrier” encounters are counted electronically by the “control unit”  280 , the preferred type of initiation device to be used for the ignition of the pyrotechnic material of the thermal battery or other devices would be an electrical initiator. 
     It is noted that in the embodiments shown in  FIGS. 1 and 2 , once the aforementioned encounter with a “significant barrier” has ended, the electrical contacts return to their original state and the closed or opened circuit would also returns to its original state. Such embodiments are preferably used to provide an essentially pulse signal to the system electronics and logics circuitry for “significant barrier” encounter counting and/or decision making purposes. It is appreciated by those skilled in the art that the device  200  shown in the schematic of  FIG. 1  (or the alternative design shown in  FIG. 2 ) may be readily modified to close a normally open circuit (or open a normally closed circuit) and keep the circuit in its closed (opened) state after the aforementioned encounter with a “significant barrier” has ended. 
     As an example, this can be readily achieved for the normally closed circuit embodiment of  FIG. 2  by the following minor modification in the design of the contact element shown in  FIG. 2 . In the modified design, the schematic of which is shown in  FIG. 3 , the first (relatively flexible and electrically conductive) contact element  250  with the contact end  251  is attached to the device  200  structure  205  with an isolating non-conducting element  252 . The second (and flexible and electrically conductive) contact element  253  with the contact end  254  is also attached to the device  200  structure  205  with an isolating non-conducting element  255 . The contact points  251  and  254  are normally in contact, thereby keeping a circuit connected through the electrically conductive contact element  250  and  253  via wires  256  and  257 , respectively, closed. The contact element (flexural beam)  253  is preloaded (in bending) to bring its contact point  254  into contact with the contact point  251 , and in its free state, i.e., without the contact point  251  preventing it from returning to its free state, it would come to rest at its free state shown in dashed line and indicated by the numeral  259 . 
     When the device  200  is subjected to acceleration in the direction of the arrow  201  as shown in  FIG. 1  due to the munitions using the device  200  encountering a “significant barrier”, then the element  202  and its end member  215  (also shown partly in  FIG. 2 ) is forced to move rightward as was previously described and shown in dashed lines in  FIG. 3  and in combination enumerated with numeral  258 . The end member  215  (dashed lines) will then force the contact element  253  to bend towards its free state  259  and pass over the contact point  251 , thereby causing contact between the contact points  251  and  254  to be lost, thereby causing the aforementioned electrical circuit to be rendered open. Then once the acceleration in the direction of the arrow  201  as shown in  FIG. 1  due to the munitions using the device  200  encountering a “significant barrier” has ended, the contact element  253  and its contact point  253  will return to its free state  259 . As a result, the contact between the contact points  251  and  254  and thereby the aforementioned electrical circuit will stay open. 
     It is appreciated by those skilled in the art that the “significant barrier” event detector embodiment of  FIG. 3  can be used for only a single measurement of such an event. This is the case since unlike the embodiments of  FIGS. 1 and 2 , the contact elements do not return to their original positions following a “significant barrier” encounter. 
     In another embodiment, the basic mechanism of the device  200  shown in the schematic of  FIG. 1  is used to respond to a “significant barrier” encounter of the munitions into which the device  200  is installed as previously described. However, instead of using normally open or close electrical contacts, a mechanical means such as a “mechanical counter” is employed and is advanced each time the device  200  experiences an encounter with a “significant barrier”. Many different types of “mechanical counters” that advance upon each full actuation of the mechanism of the device  200  (i.e., each rightward travel of the element  202  towards the stop  208 ) are known in the art and may be used. One such preferred mechanism is a ratchet type mechanism as shown in the schematic of  FIG. 4 . 
     In the schematic of  FIG. 4 , the mechanical event detection mechanism is shown to consist of a linear ratchet member  270 , which is provided with the ratcheting teeth  271 . The ratchet member  270  can slide in a guide  272  provided in the structure of the device  200 . The guide  272  is preferably provided with enough friction or with a spring loaded friction pad (not shown) to require certain amount of force for the ratchet member  270  translate within the guide  272 . A flexible ratchet “pawl”  274  is fixed to the end member  273  of the translating element  202  as shown in  FIG. 4 , such as without the use of a fastener  275 , for example by pressing its fixed end into a cut provided on the member  273 . It is noted that a generally hinged and spring-loaded pawl commonly used in ratchet mechanisms could also be used instead of the flexible element  274 . However, since the device  200  is intended to be as small as possible, the use of the indicated flexible ratchet “pawl”  274  type element would occupy a significantly smaller device volume, particularly since the “pawl”  274  is only required to transmit a relatively small force to overcome the friction between the ratchet member  270  and its guide  272 . 
     When the device  200  is subjected to acceleration in the direction of the arrow  201  as shown in  FIG. 1  due to the munitions using the device  200  encountering a “significant barrier”, then the element  202  (shown partly in  FIG. 4 ) and its end member  273  is forced to move rightward as was previously described and shown in dashed lines in  FIG. 4  and in combination enumerated with numeral  276 . The end member  273  (dashed lines) will then cause the flexible ratchet “pawl”  274  to push the ratchet member  270  rightward and translate it one ratchet step. It is noted that the stop  208  shown in  FIG. 1  ensures controlled (rightward) translation of the ratchet element  270 . Then once the acceleration in the direction of the arrow  201  as shown in  FIG. 1  due to the munitions using the device  200  encountering a “significant barrier” has ended, the element  202  and its end element  273  are returned to its original state by the spring element  207  ( FIG. 1 ) as shown with solid lines in  FIG. 4 . The flexible ratchet “pawl”  274  is then pulled out of its present ratcheting teeth  271 , flexed over the top surface  277  of the ratchet member  270 , and is positioned in the next ratcheting teeth  271  (or on the next top surface section of the ratchet member  270  as shown in  FIG. 4 . The device  200  is now ready to detect the next “significant barrier” encounter and advance the ratchet member  270  another step forward. 
     As a result, the device  200  can indicate the number of encountered “significant barriers”; be used with contact elements shown in the schematics of  FIGS. 1-3  when a prescribed number of such “significant barrier” encounters; actuate a mechanical mechanism such as actuating a mechanical device or releasing a spring loaded element to initiate a pyrotechnic loaded element such as a percussion cap; etc. 
     For example, as is shown in the schematic of  FIG. 4 , the ratchet member  270  may be provided with an end region  281  and a tip  282 . An electrically conductive contact element  283  is attached to the side of the end  281  of the ratchet member by, for example, a fastener  284 . At least one contact (three contacts  285 ,  286  and  287  are shown in the schematic of  FIG. 4 ) is attached to the base structure  205  of the device  200  ( FIG. 1 ). The surfaces of the contact  285 ,  286  and  287  are covered by electrically conducting materials, isolated electrically from the base structure  205  (not shown), and are connected to the electrically conductive wires  288 ,  289  and  290 , respectively. Then as the ratchet member  270  is advanced one notch as the device  200  encounters a “significant barrier”, the contact element is brought into contact with the contact  285 , thereby closing the electrical circuit between the electrically conductive wires  288  and  291  (attached to the electrically conductive ratchet member  270  or directly to the contact element  283 —not shown in  FIG. 4 ). Each consequent encounter with a “significant barrier” will then advance the ratchet member one notch, thereby advancing the contact element  283  to the contact  286 , and next to the contact  287  and so on. The wires  288 ,  289 ,  290  and  291  are in turn connected to the control unit of the device  200 ,  FIG. 1 , which can then determine the number of encountered “significant barriers” and when the prescribed number of “significant barriers” have been encountered would initiate its programmed task, such as initiating pyrotechnic materials of a thermal battery or the like. 
     In addition, as previously indicated, the advancing movement of the ratchet member  270  may be used to initiate mechanical ignition of thermal battery or the like pyrotechnic material when a prescribed number of “significant barriers” has been encountered. In general, the following three basic methods can be used to design such mechanical initiation devices. 
     In the first method, after the prescribed number of “significant barriers” have been encountered, i.e., after the ratchet member  270  has been advanced the prescribed number of notches, a spring preloaded “hammer mass” element  312  is caused to be released and impact the provided pyrotechnic material, thereby causing it to ignite as shown in the schematic of  FIG. 6 . In the schematic of  FIG. 6  only one end of the ratchet member  270  is shown together with the indicated added pyrotechnic material initiation components. In this embodiment, an edge element  311  is fixed to the side of the ratchet member  270 . A “hammer mass” element  312  is provided (which can be provided with a up-down sliding guide—not shown for clarity), which engages the top surface of the edge element  311  as shown in  FIG. 6  and can ride along the top surface of the edge element  311  as the ratchet member  270  is advanced (to the right) as the device  200  encounters “significant barriers”. The “hammer mass” element  312  is provided with a compressively preloaded spring element  313 , which provides a force pressing the “hammer mass” element  312  down against the top surface of the edge element  311 . The “hammer mass” element is preferably provided with a protruding element  314 , which preferably rides in front of the edge element  311  to minimize the chances that it would “dig” into the top surface of the edge element  311  and thereby making it difficult for the ratchet member  270  to advance. The device  200  is also provided with pyrotechnic material  315 , which is positioned as shown in  FIG. 6  over the base structure  205  and in the path of downward motion of the “hammer mass” element  312 . The surface of the base structure  205  covered by the pyrotechnic material  315  can be provided with a protrusion  316 , which would act as an anvil as described below. The surfaces of the protruding elements  314  and  316  are preferably hard enough so that their impact as described below would cause minimal plastic deformation. 
     The “significant barrier” impact detecting device  200  equipped with the embodiment of  FIG. 6  will then operate as follows. As the device  200  encounters “significant barriers”, the ratchet member  270  is advanced one notch for each such encounter as previously described. As the ratchet member  270  advances (to the right as seen in the schematic of  FIG. 6 ), the “hammer mass” element  312  slides (to the left) over the edge element  311 . Then during that prescribed “significant barrier” encounter, as the edge element  311  travels to the right, the edge  317  of the “hammer mass” element  312  moves past the end edge  318  of the edge element  311 , thereby freeing the “hammer mass” element  312  to move downwards towards the pyrotechnic material  315 . At this time, the compressively preloaded spring  313  would force the “hammer mass” element  312  to be accelerated downward towards the pyrotechnic material  315 , and impact it at relatively high speed. The force of such impact would then pinch the pyrotechnic materials  315  between the surfaces of the protruding elements  314  and  316 , causing the pyrotechnic material to be ignited. It is appreciated by those skilled in the art that the amount of impact energy that is required for ignition of the pyrotechnic material  315  is dependent on the type of the pyrotechnic material, which is either known for most commonly used pyrotechnic materials or can be readily determined experimentally. The amount of impact energy imparted by the “hammer mass” element  312  is dependent on the amount of preload and stiffness of the spring  313 , the mass of the “hammer mass” element  312  and the distance  319  ( FIG. 6 ) that the “hammer mass” element  312  travels (is accelerated) before the impact. Therefore, by selecting appropriate values for the parameters, the impact energy required to reliably initiate the pyrotechnic material  315  can be achieved. 
     In a second method, the spring element (element  313  in the embodiment of  FIG. 6 ) that drives “hammer mass” element (element  312  in the embodiment of  FIG. 6 ) is not initially preloaded (in compression in  FIG. 6 ), and the advancement of the ratchet member  270  causes the spring element to be preloaded as the device  200  encounters “significant barriers”. One such embodiment is shown in the schematic of  FIG. 7 . This embodiment is similar to the embodiment of  FIG. 6 , except that the edge element  320  ( 311  in the schematic of  FIG. 6 ) is made with an inclined top surface  321 , over which the “hammer mass” element  322  rides. The “hammer mass” element  322  can be provided with a protruding element  323 , which can ride in front of the edge element  320  to minimize the chances that it would “dig” into the top surface of the edge element  320  and thereby making it difficult for the ratchet member  270  to advance. The spring element  324  ( 313  in the schematic of  FIG. 6 ) is provided to similarly drive the “hammer mass” element towards the pyrotechnic material  315 . The “hammer mass” element  322  is initially at the right-most position (shown in dashed lines) of the ratchet member  270 . Then as the ratchet member  270  is advanced to the right as the device  200  encounters “significant barriers”, the inclined edge element  320  pushes the “hammer mass” element  322  up as can be seem in the schematic of  FIG. 7 , from its initial dashed position towards the solid lined position and then towards the dotted lined position. As can be seen in the schematic of  FIG. 7 , as the “hammer mass” element  322  is moved upwards, the spring element  324  is preloaded in compression. Further advancement of the ratchet member  270  pushes the bottom left edge  325  of the “hammer mass” element  322  past the left-most edge  326  of the edge element  320 , thereby freeing the “hammer mass” element  322  to move downwards towards the pyrotechnic material  315 . At this time, the compressively preloaded spring  324  would force the “hammer mass” element  322  to be accelerated downward towards the pyrotechnic material  315 , and impact it at relatively high speed. The force of such impact would then pinch the pyrotechnic materials  315  between the surfaces of the protruding elements  323  and  316 , causing the pyrotechnic material to be similarly ignited. 
     In a third method, the ratchet member  270  is to actuate a mechanism that would in turn release a “hammer mass” element, which is driven by a preloaded spring to similarly impact the pyrotechnic material and cause it to ignite. An example of such an embodiment is shown in the schematic of  FIG. 8 . In this embodiment, a “hammer mass” element  330  and a compressively preloaded spring  331  similar to those used in the embodiment of  FIGS. 6  ( 312  and  313 , respectively) are also used. The “hammer mass” element  330  is held in its position with the compressively preloaded spring  331  by the tip  332  of the rotating link  333  (solid line). The rotating link  333  is attached to the base structure  205  by a rotary joint  334 . Then as the ratchet member  270  is advanced to the right as the device  200  encounters “significant barriers”, when the prescribed number of “significant barriers” are encountered, the end  335  of the ratchet member  270  reaches the end  336  of the link  333  (solid line) and begin to rotate the link in the counterclockwise direction (shown in dashed lines in the schematic of  FIG. 8 ), thereby releasing the “hammer mass” element  330 , thereby freeing the “hammer mass” element  330  to move downwards towards the pyrotechnic material  337 . At this time and as it was described for the embodiment of  FIG. 6 , the compressively preloaded spring  331  would force the “hammer mass” element  330  to be accelerated downward towards the pyrotechnic material  337 , and impact it at relatively high speed. The force of such impact would then pinch the pyrotechnic materials  315  between the surfaces of the protruding elements  338  and  338  (similar to the protruding elements  314  and  316  in the embodiment of  FIG. 6 ), causing the pyrotechnic material  337  to be ignited. 
     It is appreciated by those skilled in the art that the ratchet type “significant barrier” encounter detection based initiation devices shown in the schematics of  FIGS. 6-8  would only initiate when the prescribed number of impacts are not encountered. These embodiments are particularly suitable in applications in which if the prescribed number of “significant barriers” are not encountered, the thermal battery or other type of devices (e.g., various gun fired munitions, mortars, rockets, missiles or gravity dropped weapons) operating by the initiation of pyrotechnic materials are not desired to operate. 
     In the schematics of  FIGS. 6-8 , the “hammer mass” element driving spring is shown to be a compressively loaded. It is, however, appreciated by those skilled in the art that by attaching the spring to the base structure  205  on the opposite side (below) the ratchet member, one could also construct the mechanisms to operate with springs that are preloaded in tension. Tensile preloading of springs is usually more stable than those preloaded in compression. 
     In the schematic of  FIG. 4 , a linear type of ratchet mechanism is shown to be employed for detecting (“counting”) the number of encountered “significant barriers”. However, it is appreciated by those skilled in the art that a rotary type ratchet mechanism or any other mechanical intermittent motion mechanism may also be used for this purpose as well. 
     In certain applications, in addition of detecting (“counting”) the number of encountered “significant barriers”, it is also desired to determine the corresponding level of each encountered impact force. The level of encountered impact force is usually desirable for the purpose of determining the strength of the encountered significant barrier. In addition, in certain cases it is desired to also know the time history (i.e., the profile) of the encountered impact force, since such a profile can give an indication of the strength, type and thickness of the encountered “significant barrier”. The following embodiments describe inertia-based devices that address such needs. 
     In one embodiment, at least two novel mechanisms  200  of the type shown in the schematic of  FIG. 1 , with the “significant barrier” detecting normally open contacts  216  and  218 , or its alternative normally closed contacts shown schematically in  FIG. 2 , or their combinations, are used. Hereinafter and for the sake of simplicity, the embodiment  200  and its variations shown in  FIGS. 1 and 2  are referred to as simply “barrier detectors”. Now consider the case in which the embodiment  300  shown schematically in  FIG. 5  is constructed with three “barrier detectors” indicated by the numerals  301 ,  302  and  303 . The “significant barrier” encounter detecting (“counting”) device  300  is intended to detect “significant barrier” encounters as well as their corresponding impact force levels. The three “barrier detectors”  301 ,  302  and  303  are identical, except for the spring rates of one or both spring elements  207  and  212  and/or their amounts of preloading, and/or the inertia (mass) of element  202  and/or  203 , and/or the slope of the inclined contact surface  211 ,  FIG. 1 . It is appreciated by those skilled in the art that making any one of the above changes, the contact elements  216  and  218  would come into contact at different device acceleration in the direction of the arrow  201 ,  FIG. 1  (or open the contacts  231  and  234  in the embodiment of  FIG. 2 ). For example, by increasing the spring rate of the spring element  270 ,  FIG. 1 , the level of acceleration in the direction of the arrow  201  at which contacts elements  216  and  218  come into contact (i.e., that the device “register” or a “significant barrier” count, is increased). As another example, a similar effect is achieved by reducing the inertia (mass) of the element  203 . It is appreciated by those skilled in the art that similar effects, i.e., the level at which the device  200  would count a “significant barrier” encounter may be increased or decreased by appropriate changes in the aforementioned changes in the parameters of the device  200 . 
     The inertia-based “significant barrier” counting and corresponding impact level force detecting device  300  operates as follows. As an example, let the three “barrier detectors”  301 ,  302  and  303  be designed to detect (open or close contacts as previously described for the embodiments of  FIGS. 1 and 2 ) a “significant barrier” causing acceleration in the direction of the arrow  304  on the platform  305  (for example a projectile) to which they are attached as shown in  FIG. 5 . Let, for example, the “barrier detector”  301 ,  302  and  303  be designed to detect “significant barrier” induced acceleration levels of 20,000 G, 40,000 G and 60,000 G, respectively, each corresponding to similarly increasing level of encountered impact force (their corresponding impact force levels being dependent on the structural characteristic of the projectile  305 ). Then as the platform (projectile)  305  encounters a “significant barrier” that result in an acceleration level in the direction of the arrow  304  of say 30,000 G, then only the “barrier detector”  301  would detect a “significant barrier” encounter. If the acceleration level is around 50,000 G, then the “barrier detectors”  301  and  302  would detect such a “significant barrier” encounter. If the acceleration level is above 60,000 G, then all three “barrier detectors”  301 ,  302  and  303  would detect the “significant barrier” encounter. 
     In an embodiment, an electronic circuitry and logic device or a microprocessor  306 , hereinafter referred to as the “counter”,  FIG. 5 , is used for collecting and processing of the “barrier detector”  300  encounters with “significant barriers”. During each “significant barrier” encounter, the “counter”  306  registers the encounters detected by each one of the three “barrier detectors”  301 ,  302  and  303 . The number of “significant barrier” encounters and their impact force levels are then determined by each “barrier detector” detection generated signal (contact opening or closing for the case of embodiments of  FIG. 1  or  2 ) and their relative timing as follows. 
     It is appreciated by those skilled in the art that when the platform  305  (for example a projectile or the like) impacts a “significant barrier” that generates acceleration levels in the “barrier detectors”  301 ,  302  and  303  that is in this case above the aforementioned 60,000 G, the “significant barrier” is first detected by the “barrier detector”  301  and then shortly after (depending on the speed of the projectile, which is usually very high and in cases supersonic, and the relatively rigid structure of the projectile, usually in a fraction of a millisecond), the “barrier detector”  302  and then  303  would detect the “significant barrier” encounter. As a result, since the highest detectable acceleration (impact force) level as detected by the “barrier detector”  303  was detected in a very short time (as indicated above usually in a fraction of a millisecond), the “counter”  306  would recognize it as an encounter with essentially a single “significant barrier”. However, if the time elapsed between two consequent “significant barrier” detections is relatively large (as compared, for example, to the aforementioned fraction of a millisecond, such as several or even tens of milliseconds), then the “counter”  306  would recognize the encounter as impacts with as many numbers of “significant barriers” with the impact acceleration (impact force) level as indicated by the detecting “barrier detector”. 
     It is appreciated by those skilled in the art that by providing more “barrier detectors”, the range and the (step-wise) number of acceleration (impact force) level measurements can be readily increased. 
     It is noted that in the element  203  in the embodiments of  FIGS. 1-8 , which actuates the element  202  when its mass is subject to acceleration in the direction of the arrow  201  and the element  202  itself are shown to undergo linear (sliding) motions. It is, however, appreciated by those familiar with the art that one or both elements  202  and  203  may also be designed to undergo rotary motion. For example, the element  203  ( FIG. 1 ) may be replaced with the link  340  as shown in the schematic of  FIG. 9 . The link  340  is attached to the base structure  205  via the rotary joint  341 . The link  340  is also provided with (preferably) rounded shaped tip  342 , which is in contact with the inclined surface  211  of the sliding element  202 . The link  340  is also biased downwards by the compressive spring  343  as shown in  FIG. 9  to keep the tip  342  in contact with the inclined surface  211 . Then as the resulting device  200  ( FIG. 1 ) using the mechanism shown schematically in  FIG. 9  is subjected to acceleration in the direction of the arrow  201  (in this case due to a “significant barrier” encounter), the acceleration acts on the inertial of the link  340 , causing the tip  342  to apply a force to the inclined surface  211 , thereby causing the device  200  to operate as was previously described for the embodiment of  FIG. 1 . 
     It is appreciated by those skilled in the art that the compressively preloaded spring elements  212  and  207  in the embodiment of  FIG. 1 ; and the compressively preloaded spring elements  313 ,  324 ,  331  and  343  in the embodiments of  FIGS. 6 ,  7 ,  8  and  9 , respectively, may also be configured to perform the same functions while preloaded in tension (by positioning them to apply the same forces in the same direction while in a tensile loading state). 
     It is also appreciated by those skilled in the art that the spring elements may be integrated into the structure of the members to which they apply force, for example, the sliding element  203  may be provided with axial flexibility (in the direction of the motion of the element  203 ), thereby eliminating the need for a separate spring element. 
     It is also appreciated by those skilled in the art that the sliding joints of the elements  202  and  203  in the embodiment of  FIG. 1 ; the sliding joint of the element  270  in the embodiment of  FIG. 4 ; sliding joints of the members  312 ,  322  and  330  of the embodiments of  FIGS. 6 ,  7  and  8 , respectively; and the rotary joints of the links  333  and  340  of the embodiments of  FIGS. 8 and 9 , respectively, can be living joints. 
     It is also appreciated by those skilled in the art that the spring elements used in the different embodiments may be integrated into the structure of the corresponding moving members and be provided with integrated living joints (or their equivalent) to provide the required sliding and/or rotary motions. For example, the rotating link  340  together with its rotary joint  341  may be replaced with a flexible beam (with the tip  342 ) that is attached to the base structure  205  (for example, at the location of the rotary joint  341 ). By providing the resulting (cantilever beam—not shown) with the required flexibility that was required of the spring element  343  and the required amount of tip deflection when its inertia is subjected to the acceleration in the direction of the arrow  201 , then the cantilever beam would operate as was described for the link  340  as shown in the schematic of  FIG. 9 . 
     Another embodiment  350  is shown in the schematic of  FIG. 10 . The device  350  is designed to close an electrical circuit by causing two contacts that keep the circuit open to come into contact when the device is subjected to an acceleration in the direction of the arrow  351  as a result of encountering a “significant barrier”, i.e., as a result of impact shock caused by the munitions encountering a “significant barrier”. The device  350  consists of the sliding element  352 , which is provided with a guide  353 , which is provided in the structure  354  of the device  350  or is fixed to the device structure  354 . The spring element  357  is attached to the device structure  354  on one end and to the sliding element  352  on the other end and is preloaded in tension. The element  352  is provided with a protrusion  355  which limits its upward motion by coming against the stop  356  provided on the device structure  354 . The sliding element  352  is provided with certain amount of mass so that when the device  350  is subjected to an acceleration in the direction of the arrow  351 , the resulting dynamic force acting on the sliding element  352  overcomes the tensile force of the spring element  357  and causes it to move downwards as seen in the schematic of  FIG. 10  and actuate the device as described below. 
     The device  350  is also provided with a member  358  which is fixed to the device structure  354 , against which the sliding member  359  can slide in a provided guide  360 . The sliding member  359  is provided with at least one engagement element  361  (three such elements are shown in the schematic of  FIG. 10 ), which are attached to the sliding member  359  by the rotary joints  362  (which is preferably a living joint). The engagement elements  361  are provided with springs (not shown for the sake of clarity—but which can be provided by the flexibility of living joints used in the construction of the rotary joints  362 ), which keeps them in the configuration shown in  FIG. 10 , i.e., essentially in line with the sliding member  359 . Each engagement elements  361  is also provided with a side edge  363 , which would stop against the surface  364  of the member  365 , which is fixed to the device structure  354  in front of the fixed member  358 . The sliding member  359  is provided with an end member  366 , which is used to bias the sliding member  359  leftwards by the compressively preloaded spring  367 , which is positioned between the end member  366  of the sliding member  359  and the member  366 , which is fixed to the device structure  354 . As a result, the sliding member  359  is at all times biased leftwards, stopping the sliding member  359  by engaging a side edge  363  against the surface  364  of the end member  365 . 
     The device  350  is configured to operate as follows. When the device is subjected to acceleration in the direction of the arrow  351  due to a “significant barrier” encounter, the acceleration acts on the inertia of the sliding element  352 , generating a dynamic force that forces the sliding element downwards. The spring element  357  is provided with certain amount of tensile preloading such that until a certain acceleration level is reached the sliding element  352  would not begin to displace downwards. However, when an acceleration level corresponding to the desired “significant barrier” encounter is reached, the dynamic force overcomes the tensile preloading of the spring  357 , and the sliding element begins  352  to translate downwards. At some point, the tip  369  will reach the top surface of the underlying engagement element  361 , and pushes it downward to the configuration  370  (shown in dashed lines in the schematic of  FIG. 10 ), disengaging the side edge  363  from the surface  364  of the end member  365 , thereby allowing the compressively preloaded spring  367  to push the sliding member  359  leftwards. Then when the acceleration due to the “significant barrier” encounter has ended, the sliding element  352  is pulled back against the stop  356  by the tensile spring  357 , and the sliding element will slide leftwards until the next side edge  363  comes to a stop against the surface  364  of the end member  365 . The process is then repeated every time that the device  350  encounters a “significant barrier”. 
     The device  350  may be used to mechanically (via direct impact) initiate a pyrotechnic material or to close (open) an electrical circuit, which can in turn be used to “count” the number of aforementioned “significant barrier” encounters. Both these options are described below. 
     In one embodiment, the device  350  is provided with the means to “count” “significant barrier” encounters as shown in the schematic of  FIG. 10 . In this embodiment, the sliding member  359  is provided with an electrical contact element  371  (which is preferably provided with flexural flexibility), which is attached to the sliding member  359  by a fastener  372 , or other means such as welding or soldering or brazing. The sliding member can be constructed with a conductive material such as a metal (which can be stainless steel or brass), to which a conducting wire  373  is attached to form a direct electrical connection to the electrical contact element  371 . The device  350  is also provided with appropriately spaced (not drawn to scale in the schematic of  FIG. 10  for simplicity) electrical contacts  374 , which are attached to the device structure  354  with an intermediate electrically nonconductive element  375 . An electrically conductive wire  376  is also attached to the electrical contact element  371 . Then as the sliding member  359  is advanced leftwards one step following an encounter with a “significant barrier”, the electrical contact element  371  comes into contact with the first electrical contacts  374 , thereby closing the electrical circuit between the electrical wires  373  and  376 . When the device  350  encounters the next “significant barrier”, the sliding member  359  is advanced leftward one more step, and the electrical contact element  371  comes into contact with the next electrical contact  374 . 
     It is noted that in the schematic of  FIG. 10  the electrical contact element  371  is shown not to be in contact with an electrical contact  374 . It is, however, appreciated by those skilled in the art that the device  350  may alternatively be configured with the two contacts being initially in contact, thereby rendering the circuit (between the wires  373  and  376 ) closed. 
     It is also noted that in the schematic of  FIG. 10 , the embodiment  350  is shown with three sets of electrical contacts  374  (with electrically nonconductive material  375  and electrical wire  376 ). It is, however, appreciated by those skilled in the art that the embodiment  350  may be constructed with any number of such electrical contacts  374  (with the sliding member  359  also constructed with a corresponding number of engagement element  361 ), to make the device  350  capable of “countering” the desired number of “significant barrier” encounters. 
     It is also noted that the embodiment  350  shown in the schematic of  FIG. 10  is configured to open and then close an electrical circuit between the wire  373  and the wire  376  of the contacting electrical contact  374 . It is appreciated by those skilled in the art that the device  350  can be readily configured to cause the electrical circuit to be closed and then opened during each encounter of the device with a “significant barrier”. This is readily accomplished by placing the first electrical contact  374  (together with its electrically nonconductive material  375  and electrical wire  376 ) as shown in the schematic of  FIG. 10  (circuit being initially open), and then positioning the remaining sets of electrical contacts  374  equally spaced thereafter such that during each sliding member  359  advance due to a “significant barrier” encounter, the electrical contact element  371  is first closed and then opened, i.e., that the electrical contact element  371  would first come into contact with an electrical contact  374  and passes it and comes to rest in between two electrical contacts  374 . 
     It is appreciated by those skilled in the art that the device  350  shown schematically in  FIG. 10  may be used to electrically initiate a pyrotechnic material (or provide the counting information to the system processor or electronics or other devices to initiate their prescribed actions) as was previously described after a prescribed number of “significant barrier” encounters have been counted. Alternatively, if the prescribed numbers of “significant barriers” have not been encountered with a prescribed period of time, the system (munitions) could initiate an appropriate (predetermined) action such as initiating the pyrotechnic material or disabling the system initiation for safety reasons or the like. 
     In a modified embodiment  350  shown in the schematic of  FIG. 11 , the device  350  is intended to ignite pyrotechnic material  380  once a prescribed number of “significant barriers” have been encountered. The pyrotechnic material  380  is attached to the device structure  354  and is provided with a protrusion  381 , which would act as an anvil as described below. The modified embodiment  350  will then operate as follows. When the device is subjected to acceleration in the direction of the arrow  351  due to a “significant barrier” encounter, the acceleration acts on the inertia of the sliding element  352  ( FIG. 10 ) as previously described, moving it downwards and disengaging the side edge  363  of the engagement element  361  from the surface  364  of the end member  365 , thereby allowing the compressively preloaded spring  367  to push the sliding member  359  leftwards. Then when the acceleration due to the “significant barrier” encounter has ended, the sliding element  352  is pulled back against the stop  356  by the tensile spring  357 , and the sliding element will slide leftwards until the next side edge  363  comes to a stop against the surface  364  of the end member  365 . The process is then repeated every time that the device  350  encounters a “significant barrier”. Then when the last prescribed “significant barrier” is encountered, the last engagement element  361  is released from its engagement with the surface  364  of the end member  365 , and frees the sliding member  359  to move leftwards towards the pyrotechnic material  380 . At this time the compressively preloaded spring  367  would force the sliding member  359  to be accelerated leftward towards the pyrotechnic material  380 , and impact it at relatively high speed. The force of such impact would then pinch the pyrotechnic materials  380  between the surfaces of the protruding element  381  and the end surface  382  (which can also be provided with a similar protruding element—not shown), causing the pyrotechnic material  380  to be ignited. 
     The mechanism of the embodiments of  FIGS. 10 and 11  are designed to achieve stepwise linear motion of the sliding member  359  following each “significant barrier” encounter. It is, however, appreciated by those skilled in the art that the mechanism may also be designed to achieve stepwise rotary motion of a rotary member following each aforementioned encounter with a “significant barrier”. Such an embodiment  400  operating with the alternative rotary mechanism is shown in the schematic of  FIG. 12 . In the schematic of  FIG. 12 , the top view of the rotary members  401  (replacing the sliding member  359  in the embodiment  350  of  FIGS. 10 and 11 ) and its operating spring  402  (replacing the sliding member  367  in the embodiment  350  of  FIGS. 10 and 11 ) are only shown and the sliding element  352  that reacts to the accelerations due to “significant barrier” encounters as described previously and its related components are not shown for the sake of clarity. 
     In the embodiment  400 , the rotary member  401  is attached to the device  400  structure  403  by the rotary joint  404 . At least one engagement member  405  (three such members are shown in the schematic of  FIG. 12 ) are attached at the base  406  to the rotary member  401  as shown in  FIG. 12 . Each engagement member  405  is provided with an “edge” member  407 , which is fixed to the engagement member  405 . The device  400  is also provided with a stop member  408 , which is fixed to the device structure  403 . The stop member  408  has certain thickness (in the direction perpendicular to the plane of  FIG. 12 ), and can be constructed essentially as a relatively short cantilever beam. A lever  409  is also attached to the rotary member  401  at its end  410 , and is attached to the spring  402  at its other end. The spring  402  is preloaded in tension. The side  411  of the edge member  407 , in normal conditions, is at a level that would engage the side  412  of the stop member  408  when the rotary member  401  is rotated in the clockwise direction by the tension preloaded spring  402 . 
     In an initial configuration, the device  400  can be configured as shown in the schematic of  FIG. 12 . In this initial configuration, the tensile preloaded spring  402  has rotated the “first” engagement member  405  to bring its side  411  of the edge member  407  to stop against the side  412  of the stop member  408  as shown in the schematic of  FIG. 12 . 
     It is noted that a sliding element  352  assembly similar to that of the embodiment  350  of  FIG. 10  is positioned above (above the plane of the view of the device  400  assembly shown in  FIG. 12 , and is intended to operate as previously described for the embodiment  350  of  FIG. 10 , i.e., to slide downwards due to acceleration in the direction of the arrow  351  due to a “significant barrier” encounter,  FIG. 10 . In the case of device  400 , the sliding element  352  is positioned above the engagement member  405  that has come to a stop against the stop member  408 . In the schematic of  FIG. 12 , the position of the sliding member  352  is shown by the cross marking  413 . 
     The device  400  is configured to operate as follows. When the device  400  is subjected to acceleration in the direction of the arrow  351  ( FIG. 10 ) due to a “significant barrier” encounter, the acceleration acts on the inertia of the sliding element  352 , generating a dynamic force that forces the sliding element downwards, overcoming the tensile force of the spring element  357 , allowing the sliding element  352  to begin to displace downwards as was described for the embodiment  350  of  FIG. 10 . The tip  369  ( FIG. 10 ) will then reach the spot  413  on the engagement member  405 , and begin to push the engagement member  405  downwards (in the schematic of  FIG. 12 , the position of the sliding element  352  is shown by the dash lined circle  414 ). The engagement member  405  is constructed essentially as a cantilever beam that is attached to the rotary member  401  and is provided with enough (flexural) flexibility to undergo downward bending upon the application of the downward force by the tip  369  of the sliding member  352 . The flexural flexibility of the engagement member  405  is selected such that with the desired level and duration of the aforementioned acceleration of the device  400  due to an encounter with a “significant barrier”, the engagement member  405  is bent downwards enough for the contact between the surfaces  411  and  412  to be lost. As a result, the corresponding edge member  407  and the engagement member  405  are pushed under the stop member, and the tensile preloaded spring  402  will cause the rotary member  401  to rotate in the clockwise direction and move under the stop member  408 , until the surface  411  of the edge member  407  of the next engagement member  405  comes into contact with the sliding element  352  (not shown). Then after the “significant barrier” encounter has ended, the rotary member  401  will continue to rotate in the clockwise direction until the surface  411  of the edge member  407  of the next engagement member  405  comes to a stop against the surface  412  of the stop member  408 . As a result, the rotary member is advanced “one step” following each one of its encounters with a “significant barrier”. 
     The device  400  may be used to mechanically (via direct impact) initiate a pyrotechnic material or to close (open) an electrical circuit, which can in turn be used to “count” the number of aforementioned “significant barrier” encounters. Both these options are described below. 
     In one embodiment, the device  400  is provided with the means to “count” “significant barrier” encounters by the closing (opening) of an electrical circuit as shown in the schematic of  FIG. 12 . In this embodiment, the engagement member  405  is provided with an electrical contact element  415  (which is preferably provided with flexural flexibility), which is attached to the engagement member  405  by a fastener or other means such as welding or soldering or brazing. The engagement member  405  is preferably constructed with a conductive material such as a metal (which can be stainless steel or brass), which can then conduct electricity from the contact element  415  to the device structure  403 , and from there to the stop member  408  and the electrically conductive wire  416  (the wire  416  may alternatively be attached to the device structure  403  or the engagement member  405 , or other intermediate members). Then as the rotary member  401  advances (rotates) one step due to an encounter with a “significant barrier” as previously described, the contact element  415  comes into contact with the contact element  417 , which is attached to the device structure  403  with an intermediate electrically non-conducting element  418 . As a result, an electrical circuit is established between the electrical wires  416  and the electrical wire  419 , which is attached to the contact element  417 . The device  400  is also provided with an appropriate number of similar electrical contacts  417 , which are spaced to sequentially engage the contact element  415  as the rotary member  401  advances (rotates) each step due to an encounter with consecutive “significant barriers” (three such electrical contacts are shown in the schematic of  FIG. 12 ). 
     In the schematic of  FIG. 12  the said electrical circuit is closed between the conductive wires  416  and  419 , each attached to the indicated members of the device  400 . It is, however, appreciated by those skilled in the art that, for example, the wire  416  may be connected to any other intermediate members such as the base structure  403 . 
     It is noted that in the schematic of  FIG. 12  the electrical contact element  415  is shown not to be in contact with an electrical contact  417 . It is, however, appreciated by those skilled in the art that the device  400  may alternatively be configured with the two contacts being initially in contact, thereby rendering the circuit (between the wires  416  and  419 ) closed. Alternatively, the contact  415  may be positioned such that it is not initially in contact with the electrical contact  417  as shown in the schematic of  FIG. 12 . The electrical contacts  417  can then be positioned such that as an engagement member  405  is advanced one step, the contact  415  comes into contact with an electrical contact  417 , and then loses contact with the electrical contact  417  and comes to a stop between two electrical contacts  417 . As a result, during each engagement member advancement step, the electrical circuit between the wires  416  and  419  is closed and then quickly opened, thereby causing a signal to be provided to the system control circuits indicating an encounter with a “significant barrier”. 
     It is also noted that in the schematic of  FIG. 12 , the embodiment  400  is shown with three sets of electrical contacts  417  (with electrically nonconductive material  418  and electrical wires  419 ). It is, however, appreciated by those skilled in the art that the embodiment  400  may be constructed with any number of such electrical contacts  417  (with the rotary member  401  also constructed with a corresponding number of engagement members  405 ), to make the device  400  capable of “countering” the desired number of “significant barrier” encounters. 
     In another embodiment, the device  400  is used to mechanically (via direct impact) initiate a pyrotechnic material. In this embodiment shown in the schematic of  FIG. 13 , an impact pin  420  with a hard tip  421  is attached to the first engagement member  405 . The device  400  is also provided with the pyrotechnic material  422 , which is attached to the device structure  403  and is provided with a protrusion  423 , which would act as an anvil as described below. Then when the last prescribed “significant barriers” is encountered, the last engagement element  405  is released from its engagement with the stop member  408 , allowing the tensile preloaded spring  402  to accelerate the impact pin  420  towards and impact the pyrotechnic material  422 . As a result, the hard tip  421  will pinch the pyrotechnic materials  422  between the surfaces of the protruding element  423  and the hard tip  421 , causing the pyrotechnic material  422  to be ignited. 
     It is noted that in the schematic of  FIGS. 12 and 13 , a linear helical spring that is preloaded in tension is shown to be used to bias the rotary member  401  in the clockwise direction. It is, however, appreciated by those skilled in the art that a compressively preloaded linear spring or a preloaded torsion spring may be also be employed to provide the same function. In fact, particularly when a limited number of “significant barrier” encounters are intended to be detected, the rotary joint  404  may be constructed as a living joint with appropriate level of elasticity such that by rotating the rotary member  401  in the counterclockwise direction to bring it to its initial pre-target-impact position shown in  FIGS. 12 and 13 , the living joint is preloaded enough in torsion to eliminate the need for added torsion or other preloaded spring elements. 
     In the embodiments of  FIGS. 1-4 ,  9 - 10  and  12 , a single electrical contact are shown to be closed or opened as a result of a “significant barrier” encounter. It is, however, appreciated by those skilled in the art that many other single or multiple contact configurations may also be implemented to achieve the desired multiple circuit opening and/or closing actions. As an example, consider the configuration shown in  FIG. 14 , showing the electrical contacts and operating members of the embodiment of  FIG. 10 . In  FIG. 14 , the frontal portion of the sliding member  450  (member  359  in  FIG. 10 ) is shown, which slides relative to the base structure  451 . The contact element  452  (contact  371  in  FIG. 10 ) is attached to the tip of the sliding member  450  as shown in  FIG. 14 , for example with a fastener  453  or using any other method such as welding or brazing. The contact units  454  consisting of at least two electrical contacts  455  (in the schematic of  FIG. 14  only two such contacts are shown), which are fixed to the device structure  451  with intermediate electrically non-conductive elements  456 , and to each of which an electrically conductive wire  457  is attached. Then as the device encounters a “significant barrier”, the sliding member  450  is advanced one step as was described for the embodiment of  FIG. 10 , moving the sliding member  450  in the direction of the arrow  458  and placing the contact element  452  in contact with the two contacts  455  (the contact element  452  in its latter position is shown by dotted and is indicated by the numeral  459  in  FIG. 14 ). As a result, the circuit between the two contact wires  457  is closed. 
     It is appreciated by those skilled in the art that many different contact opening and closing configurations one or more contact  455  is possible. For example, as was previously described, the contact element  452  may be positioned initially in contact with the two contacts  455  (shown in dotted lines  459 ) and as a result of the device encountering a “significant barrier”, the contact element  452  is moved to the next contact assembly  454 . Alternatively, the contact element  452  may be positioned initially as shown in  FIG. 14  and as a result of the device encountering a “significant barrier”, the contact element  452  is moved forward in the direction of the arrow  458 , comes into contact with the two contacts  455 , thereby closing the circuit between the two wires  457 , and pass the contact assembly  454  and stop between two such contact assembly  454 . As a result, as the device encounters a “significant barrier”, the circuit between the two wires  457  is closed for a very short time, thereby allowing the system control to register such an encounter with a “significant barrier”. 
     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.