Abstract
An apparatus actuatable under a rotary acceleration having a predetermined duration and magnitude. The apparatus including: a body having a first channel and a second channel, the second channel being disposed radially offset from the first channel; a mass disposed in the first channel, the mass having an arm disposed at a first end of the mass and the arm being rotatable from a first position in which the arm cannot move within the second channel to a second position in which the arm can move inside the second channel; a first biasing spring member having a first end connected to the body and a second end connected to the arm such that when the arm is subjected to the rotary acceleration greater than the predetermined duration and magnitude, the arm is biased to rotate from the first position to the second position; wherein the mass is connected to the arm such that the mass moves in the first channel and the arm moves in the second channel when the arm is biased into the second position.
Claims
1. An apparatus actuatable under a rotary acceleration having a predetermined duration and magnitude, the apparatus comprising: a body having a first channel and a second channel, the second channel being disposed radially offset from the first channel; a mass disposed in the first channel, the mass having an arm disposed at a first end of the mass and the arm being rotatable from a first position in which the arm cannot move within the second channel to a second position in which the arm can move inside the second channel; and a first biasing spring member having a first end connected to the body and a second end connected to the arm such that when the arm is subjected to the rotary acceleration greater than the predetermined duration and magnitude, the arm is biased to rotate from the first position to the second position; wherein the mass is connected to the arm such that the mass moves in the first channel and the arm moves in the second channel when the arm is biased into the second position.
2. The apparatus of claim 1, further comprising: a first projection disposed at a second end of the mass; a second projection disposed at a bottom of the first channel; a flame means disposed on one or more of the first and second projections for producing a flame when the first projection impacts the second projection; and one or more through holes disposed in the body; wherein the first projection impacts the second projection to produce the flame, which travels through the one or more through holes, when the mass moves in the first channel and the arm moves in the second channel.
3. The apparatus of claim 1, further comprising: an insulated first contact disposed at a second end of the mass; an insulated pair of second contacts disposed at a bottom of the first channel in a direction away from the arm, the pair of second contacts forming an open circuit; and wherein the first contact contacts the pair of second contacts to close the open circuit when the mass moves in the first channel and the arm moves in the second channel.
4. The apparatus of claim 1, wherein the arm comprises two arms and the second channel comprises two channels, each of the two arms moves in a respective one of the two channels.
5. The apparatus of claim 1, further comprising one or more stops positioned on the body for limiting a rotation of the arm relative to the body.
6. The apparatus of claim 1, further comprising a second biasing spring member disposed in the first channel for biasing the mass away from a bottom of the first channel.
7. The apparatus of claim 1, further comprising a second biasing spring member disposed in the second channel for biasing the arm away from a bottom of the second channel.
8. The apparatus of claim 1, wherein the arm further having an extension extending in a direction of the second channel such that the extension extends outside the body when the arm moves in the second channel.
9. The apparatus of claim 1, further comprising a second biasing spring member for biasing the mass towards a bottom of the second channel when the arm is rotated to the second position.
10. The apparatus of claim 1, further comprising ball bearings disposed between an inner periphery of the first channel and an outer periphery of the mass.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0065] These and other features, aspects, and advantages of the apparatus of the present invention will become better understood with regards to the following description, appended claims, and accompanying drawings where:
[0066] FIG. 1 illustrates a schematic of a thermal battery and inertial igniter assembly of the prior art.
[0067] FIG. 2 illustrates a schematic of a cross-section of an inertial igniter for thermal battery described in the prior art.
[0068] FIG. 3 illustrates a schematic of the isometric drawing of the inertial igniter for thermal battery of FIG. 2.
[0069] FIG. 4 illustrates a schematic of cross-section of an inertial igniter for thermal battery described in the prior art with an outer housing.
[0070] FIG. 5 illustrates a schematic cross-section of the first inertial igniter embodiment with firing setback spin acceleration arming (enabling) and linear acceleration initiation.
[0071] FIG. 6 illustrates the top view of the inertial igniter embodiment of FIG. 5.
[0072] FIG. 7A illustrates a schematic cross-section of a modified construction of the first inertial igniter embodiment with firing setback spin acceleration arming (enabling) and linear acceleration initiation of FIGS. 5 and 6.
[0073] FIG. 7B illustrates a schematic cross-section of a modified construction of the inertial igniter embodiment of FIG. 7A.
[0074] FIG. 8 illustrates a schematic cross-section of the second inertial igniter embodiment with firing setback spin acceleration arming (enabling) and linear acceleration initiation.
[0075] FIG. 9 illustrates a schematic of an electrical G-switch constructed based on the inertial igniter embodiment of FIG. 5 and configured to close an open circuit when it is similarly armed by a prescribed spin acceleration and actuated by a linear acceleration.
[0076] FIGS. 10A and 10B illustrates the schematic of the G-switch embodiment of FIG. 9.
[0077] FIG. 11 illustrates a schematic of an alternative embodiment of the electrical G-switch of the embodiment of FIG. 9 for the construction of a latching normally open electrical G-switch.
[0078] FIG. 12 illustrates a schematic of the inertial igniter and G-switch embodiments provided with rows of balls provided to reduce linear as well as rotary friction between the device body and the striker mass.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0079] A schematic of a cross-sectional view of a first embodiment 300 of an inertial igniter is shown in FIG. 5. The top view of the inertial igniter 300 as observed in the direction of the arrow 301 is shown in FIG. 6. The inertial igniter 300 can be cylindrical in shape since most thermal batteries are constructed in cylindrical shapes, but may be constructed in any other appropriate geometry to fit the intended application at hand. The inertial igniter 300 consists of a base element 302, which in a thermal battery construction shown in FIG. 1 would be positioned in the housing 18 with the base element 302 positioned on the top of the thermal battery cap 19.
[0080] In the embodiment 300, the inertial igniter body 303, which can be integral to the base element 302, is provided with a cylindrical open compartment 308, which can have a circular cross-section, and which extends to or close to the base element 302, the bottom surface of the open compartment 308 is indicated by numeral 309 in FIG. 5. In FIGS. 5 and 6, the surface of the cylindrical open compartment 308 is indicated by the numeral 310. The cylindrical open compartment 308 is provided with at least one guide 304 that runs down towards the base 302 a certain distance down the body 303 as shown in FIG. 5. In an embodiment 300, two opposing guides 304 are provided in the inertial igniter body 303 for the sake of symmetry and to minimize lateral rotations of the striker mass 305 following inertial igniter arming (enabling) as described below.
[0081] The striker mass 305 has a main cylindrical body with a top portion 306 with at least one end 307, which are shaped to ride in the guides 304 of the inertial igniter structure body 303 as shown in FIGS. 5 and 6. In an embodiment 300, two opposing guides 304 are provided in the inertial igniter body 303 to accommodate two ends 307 of the top portion 306 of the striker mass 305 as shown in FIGS. 5 and 6 for the sake of symmetry and to minimize lateral rotations of the striker mass 305 following inertial igniter arming (enabling) as described later in this disclosure.
[0082] In addition, in FIGS. 5 and 6 the guides 304 in the inertial igniter body 303 and the mating ends 307 of the top portion 306 of the striker mass 305 are shown to be square with sharp ends. It will be, however, appreciated by those skilled in the art that in practice, the guides 304 can take other shapes, such as semi-circular in cross-section or have semi-circular ends for ease of manufacturing. The mating ends 307 of the top portion 306 of the striker mass 305 can be semi-circular to eliminate sharp corners and mate well with the guides 304. In general, the mating surfaces are provided with minimal clearances to minimize rocking action of the striker mass 305 as it travels downwards towards the inertial igniter base 302.
[0083] The striker mass 305 can be provided with a relatively sharp tip 311 and the cylindrical open compartment 308 bottom surface 309 can be provided with a protruding tip 312, which is covered with a pyrotechnics compound 313, such that as the striker mass 305 is released during an all-fire event and is accelerated down, impact occurs mostly between the surfaces of the tips 311 and 312, thereby pinching the pyrotechnics compound 313, thereby providing the means to obtain a reliable initiation of the pyrotechnics compound 313.
[0084] Alternatively, a two-part pyrotechnics compound, e.g., potassium chlorate and red phosphorous, may be used. When using such a two-part pyrotechnics compound, the first part, in this case the potassium chlorate, can be provided on the interior side of the base in a provided recess, and the second part of the pyrotechnics compound, in this case the red phosphorous, can be provided on the lower surface of the striker mass surface facing the first part of the pyrotechnics compound. In general, various combinations of pyrotechnic materials may be used for this purpose and with an appropriate binder to firmly adhere the materials to the inertial igniter (metal) surfaces.
[0085] Alternatively, instead of using the pyrotechnics compound 313, FIG. 5, a percussion cap primer can be used. An appropriately shaped striker tip can be provided at the tip 311 of the striker mass 305 (not shown) to facilitate initiation upon impact.
[0086] Alternatively, the percussion primer or the directly loaded pyrotechnic material may be applied to the striker element 305 and the bottom surface 309 can be provided with the appropriately shaped tip to initiate ignition as previously described.
[0087] On a top surface 314 of the inertial igniter body 303, a support element 315 is provided and to which one end of a tensile spring (elastic) element 316 is attached. The other end of said tensile spring 316 is attached to a U-shaped holding member 318 inside which one end 307 of the top portion 306 of the striker mass 305 is held as shown in FIG. 6. A stop 317 is also provided on the top surface 314 of the inertial igniter body 303 (not shown in FIG. 5 for the sake of clarity), against which the other end 307 of the top portion 306 of the striker mass 305 rests to limit the rotation of the striker mass 305 in the counterclockwise direction.
[0088] The tensile spring 316 may be preloaded in tension so that it would resist a prescribed level of toque applied to the striker mass 305 in the direction perpendicular to the plane of FIG. 6 which would tend to rotate the striker mass in the clockwise direction.
[0089] In the schematic of FIG. 6 and for purpose of demonstrating the basic design and operation of the inertial igniter embodiment 300, only one tensile spring 316 is shown to provide the means of biasing the striker mass 305 rotation in the counterclockwise direction. Similarly, only one stop 317 is provided to limit counterclockwise rotation of the striker mass 305. It is, however, appreciated by those skilled in the art that in practice, counteracting tensile springs can be used to generate a pure couple on the striker mass 305 in the direction of its long axis (perpendicular to the plane of the FIG. 6), for example by either using two opposing tensile springs on either side of the striker mass or by using a torsion type spring. Thus, as a result, the lateral forces acting on the striker mass 305 are minimized and the striker mass motion relative to the inertial igniter body 303 as described below can be expected to become smoother.
[0090] It will be appreciated by those skilled in the art that instead of the tensile spring 316 shown in FIG. 6, compressive or leaf type or in fact any other elastic element, that applies similar biasing rotational torque to the striker mass about the direction perpendicular to the plane of FIG. 6 may also be used.
[0091] It will be appreciated that the inertial igniter 300 is usually packaged in the thermal battery or any other device within a space which provides a rigid stop 319, FIG. 5, to prevent the striker mass 305 from moving out of the inertial igniter body 303. When such a space is not provided, then a separate rigid stop element 319 is fixedly attached to the inertial igniter body 303 to prevent the same effect.
[0092] The basic operation of the inertial igniter embodiment 300 of FIGS. 5 and 6 is now described. In case of any non-trivial linear acceleration in the axial direction indicated by the arrow 320 in FIG. 5 (which corresponds to the direction of munitions firing, i.e., the direction of firing setback acceleration), the stop 319 prevents upward motion and the upper surface 314 of the inertial igniter body, being in contact with the ends 307 of the top portion 306, prevent downward motion of the striker mass 305 relative to the inertial igniter body 303. It is noted that the arrow 320 is intended to indicate the direction of the firing setback acceleration to munitions to which the base 302 and/or the body 303 of the inertial igniter 300 is fixedly attached.
[0093] In addition, if the inertial igniter is subjected to a spin acceleration in the clockwise direction about its long axis (perpendicular to the plane of the FIG. 6 and as indicated by the arrow 321 in FIG. 5 and arrow 322 in FIG. 6), then the stop 317 would prevent the striker mass from rotation about the axis relative to the inertial igniter body 303.
[0094] However, if the inertial igniter is subjected to a spin acceleration in the counterclockwise direction about its long axis, assuming no friction between the surfaces of the striker mass 305 and the inertial igniter body 303, in the absence of the spring 316 (FIG. 6), the device body 303 would begin to rotate in the counterclockwise direction while the striker mass 305 would stay stationary. However, in the presence of the preloaded tensile spring 316, as the inertial igniter body 303 begins to rotate in the counterclockwise direction, the preloaded tensile spring 316 tends to extend and reduce its tensile preloading force if the (inertial) resistance of the striker mass 305 to the applied counterclockwise acceleration is larger than resisting torque applied to the striker mass by the preloaded tensile spring 316. Noting that the inertial resistance of the striker mass is due to its moment of inertial about its long axis (axis of its rotation relative to the inertial igniter body 303). Otherwise the end 307 of the top portion 306 striker mass 305 is forced by the preloaded tensile spring to stay in contact with the stop 317, FIG. 6, and the striker mass 305 does not undergo any rotation relative to the inertial igniter body 303 and is accelerated together with the inertial igniter body 303.
[0095] However, if the spin acceleration applied to the inertial igniter body in the counterclockwise direction is high enough for the resulting resisting inertial torque of the striker mass 305 to overcome the tensile preloading force of the spring 316, then the tensile spring 316 will begin to extend, thereby allowing the striker mass 305 to rotate in the clockwise direction relative to the inertial igniter body 303. If the spin acceleration magnitude is at or above the prescribed threshold and continues for its prescribed duration threshold, then the tensile spring 316 would be extended long enough to allow counterclockwise rotation of the striker mass 305 relative to the inertial igniter body 303 to position the tips 307 of the striker mass 305 over the guides 304 of the inertial igniter body 303. As can be seen in the top view of FIG. 6, a stop 323 that is fixedly attached to the top surface 314 of the inertial igniter body 303 is also provided to prevent rotation of the tips 307 past the guides 304.
[0096] It will be appreciated by those skilled in the art that once the tips 307 of the striker mass 305 are positioned over the guides 304 of the inertial igniter body 303, then the striker mass 305 is free to move down the cylindrical open compartment 308 of the inertial igniter body 303 towards the base 302. The inertial igniter 300 is therefore considered to be armed (enabled) to respond to the linear setback acceleration and ignite the pyrotechnic material 313 as previously described.
[0097] Once the inertial igniter 300 is armed (enabled) by the applied spin acceleration of magnitude and duration corresponding to the prescribed all-fire setback induced spin acceleration profile threshold, the setback linear acceleration would accelerate the striker mass 305 downward and cause the tip 311 of the striker mass to impact the pyrotechnic covered protruding tip 312 of the bottom surface 309 of the cylindrical open compartment 308, thereby pinching the pyrotechnics compound 313, thereby initiating the pyrotechnics compound 313. Following ignition of the pyrotechnics compound 313, the generated flames and sparks are designed to exit downward through the opening 324 to initiate the pyrotechnic materials of the thermal battery or any other pyrotechnic or similar material below.
[0098] It will be appreciated by those skilled in the art that once the inertial igniter 300 is armed by the spin acceleration of magnitude and duration corresponding to the prescribed all-fire setback induced spin acceleration profile threshold, the magnitude of the linear (setback) acceleration (in the direction of the arrow 320) must be high enough so that as the striker mass 305 is accelerated down towards the base 302 of the inertial igniter it would gain enough speed and thereby kinetic energy to ignite the pyrotechnic compound 313 as the striker mass tip 311 impacts the pyrotechnic compound covering the protruding tip 312 of the bottom surface 309.
[0099] It will be appreciated by those skilled in the art that the aforementioned spin acceleration threshold required to arm (enable) the inertial igniter 300 of FIGS. 5 and 6 and the parameters and preloading level of the tension spring 316 must be selected such that considering the munitions firing spin acceleration magnitude and duration profile has enough duration to rotate the striker mass 305 clockwise relative to the inertial igniter body to its arming (enabling) position and allow the striker mass 305 to be accelerated downward to the required velocity to reliably initiate the pyrotechnic compound 313. However, if the firing setback profile threshold does not provide the required duration for the indicated arming and striker mass acceleration to the required pyrotechnic initiation velocity, then the striker mass 305 of the inertial igniter 300 of FIGS. 5 and 6 will stay in the cylindrical open compartment 308 of the inertial igniter body 303, and could possibly initiate the pyrotechnic compound 313 at certain time, for example due to flight vibration, impact, accidental drops, or other similar events. To avoid such conditions, compressive spring (elastic) elements may be provided to push back the striker mass 305 away from the base 302 of the inertial igniter body. Two possible embodiments of the inertial igniter 300 of FIGS. 5 and 6 are shown in the schematic of FIG. 7A. It is appreciated by those skilled in the art that and numerous other return spring designs and configurations are also possible and those illustrated in the schematic of FIG. 7A should be considered only as two of such design examples.
[0100] In one modified inertial igniter embodiment 300 of FIGS. 5 and 6 shown in FIG. 7A, at least one spring (elastic) element 325 is provided inside the guides 304 of the inertial igniter body 303. The spring 325 is at its free length and can be provided with a solid member 326 to provide a relatively flat top surface. Then when the inertial igniter 300 is armed and the tips 307 of the top side 306 of the striker mass 305 begin to move down the guides 304, FIG. 5, the tips 307 come first into contact with the solid member 326 and begin to deform the spring 325 in compression. Then if the magnitude of the linear (setback) acceleration is high enough (i.e., at or above the prescribed threshold) to allow the striker mass 305, FIG. 5, to be accelerated down towards the base 302 of the inertial igniter with the required kinetic energy, the striker mass tip 311 would impact the pyrotechnic compound 313 covering the protruding tip 312 of the bottom surface 309 and initiate it as was previously described. Otherwise if the linear acceleration is below the prescribed all-fire threshold, the springs 325 are compressed certain amount but not enough to allow the striker mass tip 311 to reach the pyrotechnic compound 313 and the inertial igniter 300 is not initiated.
[0101] In an alternative modification of the inertial igniter embodiment 300 of FIGS. 5 and 6 shown in FIG. 7A, a spring (elastic) element 327 is provided inside the cylindrical open compartment 308 of the inertial igniter body 303 between its bottom surface 309 and the striker mass 305 as shown in FIG. 7A. The spring 327 would then perform the same function as the springs 325.
[0102] It will be appreciated by those skilled in the art that the springs 325 and 327 shown in FIG. 7A for the above two modifications of the inertial igniter embodiment of FIGS. 5 and 6 must generally have relatively low stiffness (spring rate) so that they would not demand excessive linear (setback) acceleration for inertial igniter initiation.
[0103] It will also be appreciated by those skilled in the art that as can be seen in the schematic of FIG. 6, once the striker mass 305 is armed and begins to move down towards the base 302, the U-shaped holding member 318 inside which one end 307 of the top portion 306 of the striker mass 305 is held is released. Thus, in the aforementioned case in which the armed inertial igniter does not ignite the pyrotechnic material 313 and that the striker mass 305 is pushed up by the springs 325 and/or 327, the end 307 of the top portion 306 of the striker mass cannot re-engage the U-shaped holding member 318 and be pulled back by a preloaded tensile spring 316 to it prior-arming (disarmed) position shown in FIG. 6. The inertial igniter embodiments of FIG. 7A can, however, be readily modified to allow the striker mass 305 to be returned to its prior-arming (disarmed) position shown in FIG. 6 by extending the portion of the end 307 that engages the U-shaped holding member 318 as shown in the schematic of FIG. 7B. The extension, indicated by the numeral 333 in FIG. 7A, will then stay engaged with the U-shaped holding member 318 at all times before and after inertial igniter arming as the striker mass 305 moves down towards the inertial igniter base 302. Then as the striker mass 305 is pushed up by the springs 325 and/or 327, extension 333 rides back in the U-shaped holding member 318 until the preloaded tensile spring 316 can rotate the striker mass to it prior-arming (disarmed) position shown in FIG. 6.
[0104] In the inertial igniter embodiment 300 of FIGS. 5 and 6, the spin acceleration threshold required to arm (enable) the inertial igniter and the parameters and preloading level of the tension spring 316 are selected such that considering the munitions firing spin acceleration magnitude and duration profile, following previously described arming action, the linear setback acceleration persists long enough at or beyond the prescribed threshold so that the striker mass 305 can be accelerated downward towards the base 302 of the inertial igniter to the required velocity (kinetic energy) for reliably initiating the pyrotechnic compound 313 as the striker mass tip 311 impacts the pyrotechnic compound 313 covering the protruding tip 312 of the bottom surface 309 of the compartment 308, FIG. 5. However, if the firing setback profile threshold does not provide the required duration for the indicated arming of the inertial igniter and striker mass acceleration to the required velocity for reliable initiation of the pyrotechnic compound 313, then the striker mass 305 of the inertial igniter 300 of FIGS. 5 and 6 will be released and may gain a fraction of the required velocity but may or may not be able to initiate the pyrotechnic compound. Such relatively short duration firing setback acceleration profiles are common in many munitions, particularly in many medium caliber or the like munitions. The next disclosed embodiment is intended to provide the means of addressing this issue for short duration firing setback acceleration applications.
[0105] The schematic of the cross-sectional view of a second embodiment 330 of the inertial igniter which is designed for reliable inertial igniter initiations for munitions with short duration firing setback acceleration profiles is shown in FIG. 8. The inertial igniter embodiment 330 is identical to the embodiment 300 of FIGS. 5 and 6, except for the following. Firstly, the inertial igniter body 303 is extended beyond its top surface 314 as indicated by the numeral 332, such as in a shape of a cylindrical shell with a thickness which is radially slightly past the guides 304 openings to allow for their ease of machining. A top cover 328 is also fixedly attached to the top of the provided extension 322. Secondly, a preloaded compressive spring (elastic member) 329 is provided between the top cover 328 and the top side 306 of the striker mass 305 as shown in FIG. 8. A low friction member 331 is also provided between the preloaded compressive spring 329 and the contacting surface of the top side 306 of the striker mass 305 as shown in FIG. 8 to minimize friction generated torque as the striker mass 305 rotates along its long axis during the aforementioned process of inertial igniter arming (enabling).
[0106] If a spin acceleration is applied to the inertial igniter body 303 in the counterclockwise direction (as indicated by the direction of the arrows 321 and 322 in FIGS. 5 and 6, respectively) and its magnitude is equal or larger than the prescribed all-fire magnitude threshold, then the striker mass 305 rotates in the clockwise direction relative to the inertial igniter body 303 until the tips 307 of the striker mass 305 are positioned over the guides 304 of the inertial igniter body 303 as was previously described. The striker mass 305 is then free to move down the cylindrical open compartment 308 of the inertial igniter body 303 towards the base 302, FIGS. 5 and 8, and the inertial igniter 300 is armed (enabled). At this point, the force exerted by the preloaded compressive spring 329 begins to accelerate the striker mass 305 towards the inertial igniter base 302. With a properly designed and preloaded compressive spring 329, the striker mass 305 is accelerated downward towards the base of the inertial igniter to the required velocity (kinetic energy) for reliably initiating the pyrotechnic compound 313 as the striker mass tip 311 impacts the pyrotechnic compound 313 covering the protruding tip 312 of the bottom surface 309 of the compartment 308, FIG. 5, and the generated flames and sparks exit downward through the opening 324 to initiate the pyrotechnic materials of the thermal battery or any other pyrotechnic or similar material below.
[0107] It will be appreciated by those skilled in the art that in cases in which the setback acceleration duration is long enough such that after the inertial igniter embodiment 330 of FIG. 8 is armed as was previously described the setback acceleration continues, then its linear acceleration would assist the preloaded compressive spring 329 in accelerating the striker mass 305 towards the base of the inertial igniter to gain the required velocity (kinetic energy) to reliably initiate the pyrotechnic compound 313. It will be appreciated that the need for a preloaded compressive spring 329 arises only in cases in which either the (linear) setback acceleration magnitude is not high enough to accelerate the striker mass 305 to the required velocity (kinetic energy) or that its duration is not long enough so that following the inertial igniter arming (enabling), the setback linear acceleration could accelerate the striker mass the required velocity (kinetic energy).
[0108] The inertial igniter embodiment 300 of FIGS. 5, 6 and 7A and 330 of FIG. 8 are configured to be armed (enabled) with the applied setback acceleration induced counterclockwise spin acceleration. It is, however, appreciated by those skilled in the art that that such igniters can also be configured to be similarly armed if the direction of the setback induced spin acceleration is in the clockwise direction. This is done simply by changing the circumferential positioning of the spring 316 and its support element 315 and the stops 317 and 323 symmetrically about the guides 304.
[0109] In the above embodiments, following ignition of the pyrotechnics compound 313, FIG. 5, the generated flames and sparks are configured to exit downward through the opening 324 to initiate the thermal battery below. Alternatively, if the thermal battery is positioned above the inertial igniters, the opening 324 can be eliminated and the striker mass could be provided with at least one opening (not shown) to guide the ignition flame and sparks up through the striker mass 305 to allow the pyrotechnic materials (or the like) of a thermal battery (or the like) positioned above the inertial igniter (not shown) to be initiated.
[0110] Alternatively, side ports may be provided in the inertial igniter body 303 instead of the opening 324, FIG. 5, to allow the flame to exit from the side of the igniter to initiate the pyrotechnic materials (or the like) of a thermal battery or the like that is positioned around the body of the inertial igniter. Other alternatives known in the art may also be used.
[0111] The inertial igniter embodiments of FIGS. 5, 7A, 7B and 8 can be readily modified to operate as a so-called electrical G-switch, i.e., to arm (enable) when a setback acceleration induced spin acceleration threshold is applied to the device, and then undergo the switching action either due to the enduring setback (linear) acceleration or by the action of a preloaded spring element such as the preloaded compressive spring 329 in the embodiment of FIG. 8. Here, the switching action refers to the closing (opening) a normally open (closed) electrical circuit. It is also appreciated by those skilled in the art that the resulting spin acceleration armed (enabled) and linear acceleration actuated electrical switches do not function as pure G-switches, but more accurately as impulse switches with spin acceleration arming capability. This is the case since these inertially activated switches operate when subjected to accelerations with certain prescribed magnitude as well as duration.
[0112] The construction and operation of the resulting electrical G-switches is identical to those of the inertial igniter embodiments of FIGS. 5, 7A, 7B and 8, except that the pyrotechnic compound 313 and the protruding tip 312 of the base 302 on one side and the sharp tip 311 of the striker mass 305 on the other side are replaced by contact and circuit closing (opening) elements described below.
[0113] The schematic of one G-switch embodiment 340 constructed based on the design of the inertial igniter embodiment 300 of FIG. 5 is shown in FIG. 9. In this embodiment, the pyrotechnic compound 313, the protruding tip 312 of the base 302, the sharp tip 311, and the opening 324 are eliminated from the inertial igniter embodiment of FIG. 5. Instead, the device is provided with the contact element 334 on the surface 309 inside the device body 303 and by the contact bridging element 335 on the bottom surface of the formerly striker mass 305 as shown in FIG. 9. An opening 336 is also provided on the side of the device body 303 (or alternatively on the base 302) to pass the switching wires through. All other elements of the G-switch 340 are indicated with the same numerals as the inertial igniter 300 of FIG. 5.
[0114] The close-up view of the contact element 334 is shown in the schematic of FIG. 10A. The contact element 334 is fixed to the surface 309 inside the device body 303 and is constructed with at least two contacts 337 and 338, which are mounted on an electrically non-conductive base 339. The contact element 334 is also provided with electrically conductive wires 341 and 342, which are connected to the contacts 338 and 337, respectively. The electrically conductive wires are passed through the electrically non-conductive base 339 as shown in FIG. 10A to prevent them from making contact. The wires passed through the electrically non-conductive base 339 are provided with electrically insulating casing 343 (not shown in FIG. 9).
[0115] In applications in which the G-switch 340 is attached, for example, to a printed circuit board, the electrically non-conducting base 339 can be mounted over a provided opening (similar to the opening 324, FIG. 5) in the base 302 of the device body, such as in a provided recess (not shown), thereby allowing the contact wires 341 and 342 to pass through the provided opening to reach the underlying element (in this case the printed circuit board or the like). The wires can then be connected to the appropriately provided circuit.
[0116] The close-up view of the contact element 335 is shown in the schematic of FIG. 10B. The contact element 335 consists of an electrically non-conductive base 344, which is fixed to the bottom surface of the member 305 (striker mass in the inertial igniter embodiments of FIG. 5, 7A, 7B and 8) as shown in FIGS. 9 and 10B. An electrically conductive contact strip 345 (which can be relatively thin and flexible) is mounted on the surface of the electrically non-conductive base 344.
[0117] The electrical G-switch 340 operates in a manner like the inertial igniter 300 of FIGS. 5 and 6. That is in case of any non-trivial linear acceleration in the axial direction indicated by the arrow 320 in FIG. 5 (which corresponds to the direction of munitions firing, i.e., the direction of firing setback acceleration), the stop 319 prevents upward motion and the upper surface 314 of the inertial igniter body, being in contact with the ends 307 of the top portion 306, prevent downward motion of the striker mass 305 relative to the inertial igniter body (G-switch device body) 303. It is noted that the arrow 320 is intended to indicate the direction of the firing setback acceleration to munitions to which the base 302 and/or the body 303 of the inertial igniter 300 (G-switch body for the embodiment of FIG. 9) is fixedly attached.
[0118] In addition, if the G-switch embodiment 340 (inertial igniter in FIG. 5) is subjected to a spin acceleration in the clockwise direction about its long axis (perpendicular to the plane of the FIG. 6 and as indicated by the arrow 321 in FIG. 5 and arrow 322 in FIG. 6), then the stop 317 would prevent the striker mass 305 from rotation about the axis relative to the G-switch (inertial igniter in FIGS. 5 and 6) body 303.
[0119] However, if the G-switch is subjected to a spin acceleration in the counterclockwise direction about its long axis, assuming no friction between the surfaces of the striker mass 305 and the inertial igniter body 303, in the absence of the spring 316 (FIG. 6), the device body 303 would begin to rotate in the counterclockwise direction while the striker mass 305 would stay stationary. However, in the presence of the preloaded tensile spring 316, as the G-switch body 303 begins to rotate in the counterclockwise direction, the preloaded tensile spring 316 tends to extend and reduce its tensile preloading force if the (inertial) resistance of the striker mass 305 to the applied counterclockwise acceleration is larger than resisting torque applied to the striker mass by the preloaded tensile spring 316. Noting that the inertial resistance of the striker mass is due to its moment of inertial about its long axis (axis of its rotation relative to the inertial ignite body 303). Otherwise the end 307 of the top portion 306 striker mass 305 is forced by the preloaded tensile spring to stay in contact with the stop 317, FIG. 6, and the striker mass 305 does not undergo any rotation relative to the inertial igniter body 303 and is accelerated together with the inertial igniter body 303.
[0120] However, if the spin acceleration applied to the inertial igniter body in the counterclockwise is high enough for the resulting resisting inertial torque of the striker mass 305 to overcome the tensile preloading force of the spring 316, then the tensile spring 316 will begin to extend, thereby allowing the striker mass 305 to rotate in the clockwise direction relative to the G-switch (inertial igniter) body 303. If the spin acceleration magnitude is at or above the prescribed threshold and continues for its prescribed duration threshold, then the tensile spring 316 would be extended long enough to allow counterclockwise rotation of the striker mass 305 relative to the G-switch (inertial igniter) body 303 to position the tips 307 of the striker mass 305 over the guides 304 of the inertial igniter body 303. As can be seen in the top view of FIG. 6, a stop 323 which is fixedly attached to the top surface 314 of the G-switch (inertial igniter) body 303 would prevent rotation of the tips 307 passed the guides 304.
[0121] It will be appreciated by those skilled in the art that once the tips 307 of the striker mass 305 are positioned over the guides 304 of the G-switch (inertial igniter) body 303, then the striker mass 305 is free to move down the cylindrical open compartment 308 of the G-switch body 303 towards the base 302. The G-switch 340 is therefore considered to be armed (enabled) to respond to the linear setback acceleration.
[0122] Once the G-switch 340 is armed (enabled) by the applied spin acceleration of magnitude and duration corresponding to the prescribed all-fire setback induced spin acceleration profile threshold, the setback linear acceleration would accelerate the striker mass 305 downward and cause the electrically conductive contact strip 345 of contact element 335 to come into contact with the at least two contacts 337 and 338 of the contact element 334, FIGS. 10A and 10B, thereby closing the open circuit to which the G-switch 340 is connected.
[0123] It will be appreciated by those skilled in the art that in the G-switch embodiment 340 of FIG. 9, once the aforementioned setback acceleration event that induced G-switch arming and electrical switching action to close the normally open circuit has ceased, the contact between the electrically conductive contact strip 345 of contact element 335 and the at least two contacts 337 and 338 of the contact element 334, FIGS. 10A and 10B, may be lost. Such G-switches are appropriate for circuits that only require a single and short duration circuit closing event (pulse) for their proper operation. However, if the contact is to be maintained, particularly when a contact maintaining force is also desired to be present, then the G-switch may be configured as was described for the inertial igniter 330 of FIG. 8, in which a preloaded compressive spring 329 is used to keep pressing the striker mass 305 against the protruding tip 312 of the base 302 following its arming and downward travel of the striker mass.
[0124] The schematic of the resulting latching normally open G-switch (in its open state), indicated as the embodiment 350, is shown in FIG. 11. All components of the G-switch embodiment 350 are the same as those of the embodiment 330 of FIG. 8, except for the aforementioned changes to the embodiment for the embodiment 300 to obtain the G-switch embodiment 340 of FIG. 9, i.e., the provision of the contact element 334 on the surface 309 inside the device body 303 and by the contact bridging element 335 on the striker mass 305. An opening 336, FIG. 9, is similarly provided on the side of the device body 303 (or alternatively on the base 302) to pass the switching wires through. The G-switch embodiment 350 operates as described for the G-switch embodiment 340 of FIG. 9, except that once the device body 303 is released following the device arming and circuit closing action of the G-switch as was previously described, the compressively preloaded spring 329 acts as a latching mechanism and ensure that contact between the electrically conductive contact strip 345 of contact element 335 and the at least two contacts 337 and 338 of the contact element 334, FIGS. 9, 10A and 10B, is maintained and that the compressively preloaded spring 329 keeps the contact under a prescribed level of pressure.
[0125] It will be appreciated by those skilled in the art that the level of preloading of the compressive spring 329 must be high enough so that during the firing set-forward and when the munitions or the like is subjected to incidental acceleration and deceleration levels such as due to transportation vibration, contact between the electrically conductive contact strip 345 of contact element 335 and the at least two contacts 337 and 338 of the contact element 334, FIGS. 9, 10A and 10B, is maintained and that the compressively preloaded spring 329 keeps the contact under a prescribed minimum level of pressure.
[0126] It is also appreciated by those skilled in the art that the aforementioned spin acceleration threshold required to arm (enable) the G-switch 340 and 350 of FIGS. 9 and 11, respectively, and the parameters and preloading level of the tension spring 316, FIG. 6, must be selected such that considering the munitions firing spin acceleration magnitude and duration profile has enough duration to rotate the striker mass 305 clockwise relative to the inertial igniter body to its said arming (enabling) position, and allow the striker mass 305 to be accelerated downward to achieve the described contact between the electrically conductive contact strip 345 of contact element 335 and the at least two contacts 337 and 338 of the contact element 334, FIGS. 9, 10A and 10B, for the case of the G-switch embodiment 340 of FIG. 9.
[0127] For the case of the G-switch embodiment 350 of FIG. 11, the compressively preloaded spring 329 drives the striker mass downward with or without the continuing setback linear acceleration and also acts as a latching mechanism and ensure that contact between the electrically conductive contact strip 345 of contact element 335 and the at least two contacts 337 and 338 of the contact element 334, FIGS. 9, 10A and 10B, is maintained and that the compressively preloaded spring 329 keeps the contact under a prescribed level of pressure.
[0128] The For the case of the G-switch embodiment 340 of FIG. 9 may also be configured as a non-latching normally open G-switch by providing return springs 326 and/or 327 as is shown for the inertial igniter embodiment of FIG. 7A. By providing the return springs 326 and/or 327, the chances of getting multiple circuit open and closing actions is also eliminated.
[0129] It will also be appreciated by those skilled in the art that numerous other return spring designs and configurations are also possible and those illustrated in the schematic of FIG. 7A should be considered only as two of such design examples.
[0130] It will also be appreciated by those skilled in the art that as can be seen in the schematic of FIG. 6, once the striker mass 305 is armed and begins to move down towards the base 302, the U-shaped holding member 318 inside which one end 307 of the top portion 306 of the striker mass 305 is held is released. Thus, in the case of the alternative embodiment of the G-switch embodiment 340 of FIG. 9 with the springs 325 and/or 327, FIG. 7A, following arming of the striker mass 305, the provided springs 325 and/or 327 push the striker mass up away from the G-switch base 302. In this configuration, however, the end 307 of the top portion 306 of the striker mass 305 cannot re-engage the U-shaped holding member 318 to be pulled back by a preloaded tensile spring 316 to it prior-arming (disarmed) position shown in FIG. 6. The alternative G-switch embodiment 340 with the springs 325 and/or 327, FIG. 7A, may be readily modified to allow the striker mass 305 to be returned to its prior-arming (disarmed) position shown in FIG. 6 by extending the portion of the end 307 that engages the U-shaped holding member 318 as shown in the schematic of FIG. 7B. The extension, indicated by the numeral 333 in FIG. 7B, will then stays engaged with the U-shaped holding member 318, i.e., before and after the G-switch arming as the striker mass 305 moves down towards the G-switch base 302. Then as the striker mass 305 is pushed up by the springs 325 and/or 327, the extension 333 rides back in the U-shaped holding member 318 until the preloaded tensile spring 316 can rotate the striker mass to it prior-arming (disarmed) position shown in FIG. 6.
[0131] The G-switch embodiments 340 and 350 of FIGS. 9 and 11, respectively, the G-switches are configured to be armed (enabled) with the applied setback acceleration induced counterclockwise spin acceleration. It is, however, appreciated by those skilled in the art that the G-switches can also be configured to be similarly armed if the direction of the setback induced spin acceleration is in the clockwise direction. This is done simply by changing the circumferential positioning of the spring 316 and its support element 315 and the stops 317 and 323 symmetrically about the guides 304.
[0132] It will be appreciated by those skilled in the art that in the above inertial igniter and G-switch embodiments of the present invention the spin acceleration is considered to be applied about or close to the axis of symmetry of the device (effectively the longitudinal axis of rotation of the striker mass 305 relative to the device body 303). This would obviously occur only when the device axis of symmetry is coincident or close to the spin axis of the munitions. Otherwise the inertial igniter and G-switch will also be subjected to centrifugal force due to centripetal acceleration. The main effect of centrifugal force on the inertial igniter and G-switch embodiments of the present invention would be to press the surface of the striker mass 305 against the surface 310 of the cylindrical open compartment 308, FIG. 5, thereby increasing resistance to translation and rotation of the striker mass 305 relative to the device body 303 due to the resulting friction forces between the two contacting surfaces. In such cases, the device designer must consider the effect of the generated resisting torque to the rotation of the striker mass relative to the device body 303 in determining the required spin acceleration magnitude threshold for arming the device and the generated resisting friction force to linear translation of the striker mass 305 downward towards the device base 302 following device arming.
[0133] In general, there are three basic methods that can be used to reduce the level of generated resisting torque. Firstly, the contacting surfaces may be coated or provided by a layer of low friction material such as Teflon or other such materials or lubricants such as graphite. This method can also be used to reduce friction between the top surface 314 of the device body 303, FIG. 5, and the top portion 306 of the striker mass 305. The second method is to reduce the diameter of the rotating portion of the striker mass 305 so that the moment arm of the generated friction forces becomes small and therefore the resistance torque level is also reduced. The third method consists of providing rolling elements around the rotating portion of the striker mass, for example by providing at least two rows of (at least three) balls in provided dimples in the device body 303 at the surface of the cylindrical open compartment 308, as shown in the schematic of FIG. 12, against which the rotating portion of the striker mass 305 would rotate and translate relative the device body.
[0134] In the modifications to the above inertial igniter and electrical G-switch embodiments shown in the cross-sectional view of FIG. 12 (the cross-sectional view through the section of the device body that does not include the guides 304), rows of balls 346 are provided which are positioned in dimples 347 in the device body 303 as shown in FIG. 12. Then the striker mass 305 would rotate and translate relative to the device body 303 while mostly in contact with the rolling balls 346 with significantly reduced friction and if properly designed and lubricated with negligible friction.
[0135] 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.
