MEMS emergetic actuator with integrated safety and arming system for a slapper/EFI detonator

[0003] 1. Field of the Invention

[0004] The present invention pertains to a slapper/EFI(Explosive Foil Initiator) detonator, and more particularly to a slapper/EFI detonator having a safety and arming slider barrier for a barrel integrated with a MEMS (microelectromechanical system) energetic actuator.

[0005] 2. Background Art

[0006] Microelectromechanical devices (also called micromechanical devices or micromachines) are small (micron scale) machines that promise to miniaturize instrumentation in the same way microelectronics have miniaturized circuits. Microelectromechanical(MEM) devices have configurations analogous to conventional macroscale machinery.

[0007] The exploding foil initiator (EFI), also known as the slapper detonator was developed by the DOE National Laboratories (Sandia, Los Alamos, Lawrence Livermore) in the mid 1970's for unconventional weapon applications. A detonator is the heart of a system to set off explosive devices such as warheads, torpedoes and other devices, such as air bag inflators. Traditionally, a blasting cap or a hot bridge wire in contact with a relatively easily detonated primary explosive material is used to set off the ultimate secondary explosive material. These devices have minimum safety, since rather low level, spurious electrical currents can activate the blasting cap or bridge wire. U.S. Pat. No. 4,592,280 to Marvin W. Shores and entitled Filter/Shield For Electro-Explosive Devicesdescribes an explosive device called a squib which utilizes such a bridge wire. See also U.S. Pat. No. 5,621,183 to Todd R. Bailey entitled Initiator For an Air Bag Inflator.

[0008] To overcome the above safety problem, the exploding bridge wire system was developed in which a large current is applied to a bridge wire, rapidly heating it and causing it to explode. In a further development, the exploding bridge wire was replaced with a slapper detonator which includes an exploding foil which forms part of a laminated printed circuit board type structure. When a large electrical current is passed through the foil, it rapidly explodes, or vaporizes, causing a flyer to be sheared from a plastic layer (disk) by a barrel positioned between the plastic layer and an explosive, and the flyer is directed through the barrel towards the explosive. When the flyer “slaps” against the explosive, the explosive is detonated. Slapper detonators are exemplified by U.S. Pat. No. 5,370,053 to Matthew R. Williams et al. entitled Slapper Detonator, U.S. Pat. No. 5,531,104 to James Barker entitled Exploding Fail Initiator Using A Thermally Stable Secondary Explosive; U.S. Statutory Invention Registration No. H1366 to Robert W. Bickes, Jr. et al. entitled SCB Initiator; and U.S. Pat. No. 4,862,803 to Eldon Nerheim et al. entitled Integrated Silicon Secondary Explosive Detonator. In order to avoid premature detonation of the explosive by the flyer U.S. Pat. No. 5,088,413 to Klaus B Huber et al. entitled Method and Apparatus For Safe Transport Handling Arming And firing Of Performing Guns Using A Bubble Activated Detonatorcontemplates utilizing a safety barrier apparatus, for use with a prior art EFI detonator, the safety barrier being disposed in the barrel of the EFI detonator and providing a barrier whereby the flyer impacts the barrier in the barrel when a safe-arm feature is needed to preclude premature detonation of the explosive.

[0009] A problem with the above mentioned safety barrier is that it must be manually inserted into the barrel to engage the safety mode and manually removed for arming. Accordingly, the detonator is subject to premature detonation at any time after the safety barrier is removed.

[0010] accordingly, it is a primary object of the present invention to provide an alternative EFI or slapper detonator which inherently includes all the advantages associated with EFI or slapper detonators, but which overcomes the disadvantages of known EFI or slapper detonators.

[0011] It is another object of the present invention to provide an EFI or slapper detonator having an integrated safety and arming system for closing or opening a barrel of the EFI or slapper detonator.

[0012] It is also an object of the present invention to provide an EFI or slapper detonator integrated with a MEMS energetic actuator to provide a safety and arming feature for closing or opening a barrel of the EFI or slapper detonator.

[0013] It is an additional object of the present invention to provide an EFI or slapper detonator integrated with a slider barrier which closes or opens a barrel of the EFI or slapper detonator to provide a safety and arming feature for the EFI or slapper detonator.

[0014] It is a further object of the present invention to provide an EFI or slapper detonator integrated with a MEMS energetic actuator for controlling a slider barrier which closes or opens a barrel of the EFI or slapper detonator to provide a safety and arming feature for the EFI or slapper detonator.

[0015] These and other objects of the invention are accomplished by designing and providing an EFI or slapper detonator, including a explodable foil (or bridge), a flyer plate and a barrel, with a movable barrier to close the barrel in a safety mode and for opening the barrel in an arming mode, wherein the movable barrier slides from a closed (safety) position to an open (armed) position under the control of a MEMS energetic actuator. The slidable barrier is maintained in the closed position by one or more locking devices of the MEMS energetic actuator until predetermined conditions are met to cause the locking device(s) to release the slidable barrier, thereby arming the EFI or slapper detonator.

[0016] A more complete appreciation of the present invention, any many of the attendant advantages thereof, will become readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein:

[0017] FIGS. 1A and 1B illustrates exploded views of an EFI or slapper detonator having a barrel plate with a slidable barrier for closing and opening a barrel of the barrel plate in a safety mode and an armed mode, respectively, in accordance with a first embodiment of the present invention;

[0018] FIG. 2A is a top view of the EFI or slapper detonator integrated with a MEMS energetic actuator to provide a safety and arming feature for closing or opening a barrel of the EFI or slapper detonator, in accordance with a second embodiment of the present invention;

[0019] FIG. 2B and 2C are close-up views of portions of FIG. 2A; and

[0020] FIG. 3A and 3B are exemplary side views of the EFI or slapper detonator integrated with a MEMS energetic actuator illustrating the closing or opening a barrel of the EFI or slapper detonator.

[0021] FIGS. 1A and 1B depict an EFI or slapper detonator (referred to hereafter as slapper detonator) modified, according to the present invention, to have a safety and arming barrel plate 30. In FIGS. 1A and 1B the slapper detonator includes a bridge, or explodable foil, 10, a flyer plate 20, the safety and arming barrel plate 30 and a high explosive pellet 40. Barrel plate 30 includes a slidable barrier 32 which is shown in FIG. 1A to be in the safety position to close a barrel plate 30. In FIG. 1B the slidable barrier 32 is shown in the arming position to open barrel 34.

[0022] Referring to FIG. 1B, foil 10 is comprised of a low impedance copper strip that has an area of reduced width over barrel 34. When a high voltage, greater than 500 volts DC (direct current) is suddenly (<1 sec) is applied to foil 10, current density at the narrow area of the copper strip increases and heat is generated. At this time a hot high pressure gas (plasma) is generated pushing flyer plate 20 against barrel pate 30. A portion, i.e. a flyer or slapper, of flyer plate 20 is sheared off by barrel 34 of barrel plate 30, passes through barrel 34 and strikes high pellet 40 with enough kinetic energy (½ m^v) to detonate high explosive pellet 40.

[0023] Referring to FIG. 2A, the slapper detonator integrated with a MEMS energetic actuator to provide a safety and arming feature for closing or opening a barrel of the EFI or slapper detonator, is shown. The slapper detonator includes an explodable foil 10, a flyer plate 20 and the safety and arming barrel plate 30. Also, slapper detonator includes a slidable barrier 32 having the barrel 34 integrated therein. Slider barrier 32 is moved from the safety position (FIG. 3A) to the arming position (FIG. 3B) by the MEMS energetic actuators including a pull 36a, engaging unit 38a, Lock #1, Lock #2, pawls 40aand 40band an optical system.

[0024] Pull 36ahas an pull arm 36b, which is preferably a thermal actuator, that is engaged (see FIG. 2B) with slider barrier 32 by engaging unit 38aand engagement arm 38b, which also is preferably a thermal actuator, in response to predetermine condition, such as a circuit controlled by a predetermined stimulus, such as a detected ambient pressure or a predetermined timing operation. Thermal actuators are well known. Lock #1 is responsive to hydrostatic pressure to release slider barrier 32, thereby permitting pull 36ato move slider barrier 32 in order to slide barrel 34 into the fully armed position below foil 10 and flyer plate 20. Since pull arm 36buses a thermal actuator, then the distance of the pull is short. Accordingly, pull 36aand engaging unit 38aare cyclically controlled to slide slider barrier 32 in incremental steps to the fully armed position. FIG. 2B shows a plurality of teeth on pull arm 36bwhich will engage, under the control of engagement arm 38b, a plurality of teeth on slidable barrier 32.

[0025] Lock #1 may be made as described in U.S. Pat. No. 5,824,910 to Howard R. Last et al. and entitled Miniature Hydrostat Fabricated Using Multiple Microelectromechanical Processes, incorporated herein by reference. Briefly, Lock #1 uses a pivotal beam 22 to lock slider barrier 32 in the safe position. There is an ambient fluid in a chamber (not shown) beneath a diaphragm 24 which causes diaphragm 24 to rise due to increased pressure. Alternatively, the fluid could be a thermally expandable fluid which expands in response to an applied an electrical current, or other heating source, which is controlled by a predetermined stimulus, e.g., timing, velocity detection, altitude, depth, etc. The stimulus can be as varied as there are numerous uses for the slapper detonator.

[0026] The MEMS energetic actuator is capable of producing movement, for example, in the range of 100 μm (100×10⁻⁶). This is sufficient movement to fully open a closed barrel. Thus when the MEMS device has produced a mechanical movement in the order of 100 μm, the slapper detonator can be armed and activated. Referring to FIG. 3A, when the barrel 34 is in the closed position (Safe Mode), the explosive pellet 40 will not detonate even if the firing voltage is applied to foil 10. With regard to FIG. 3B, when the barrel 34 is open (Armed Mode) the device will operate as a normal slapper detonator. The slider barrier 32 is made of metal (nickel) capable of absorbing the impact of a flyer to prevent premature detonation of the slapper detonator.

[0027] An optical system, such as a laser, is provided to determine the position of the slider barrier 32 and barrel 34. By collecting light using, for example, fiber optics, the light is focused on a mirror attached to the slider barrier 32. Receiving fiber optics is positioned to capture the reflected light when the slider barrier is in one of the closed or open positions to detect whether the slider barrier is in one of the safety mode or armed mode. Thus, by observing the output of the fiber optics the position of the slider barrier can be determined and the safe mode or armed mode indicated. To this end, a Lock #2 is responsive to a predetermined stimulus, e.g., a timing condition or an environmental condition, identified in FIG. 2A as the flow sensor input to Lock #2, which may be the same stimulus as the stimulus for Lock #1, but is preferably a different stimulus for added safety. The timing or environmental condition can be as varied as there are numerous uses for the slapper detonator. For example, the timing condition may be set to indicate when a launched warhead is a safe distance from the launch pad. An example of an environmental condition may be based on an obtained velocity.

[0028] Referring further to FIGS. 2A and 2C, when Lock #2 is activated by the flow sensor signal in response to a preset condition, rachet pawls 40aand 40bare activated to disengage locking bars 48aand 48bfrom catches 49aand 49bin light deflector arm 50 attached to slider barrier 32. In the position as shown in FIG. 2A, one end of light deflector arm 50 reflects light from laser 42, via optical fiber 52, into optical fiber 44 thereby causing indicator 44 to provide an indication that the slapper detonator is in the safety mode. When Lock #2 is activated and when Lock #1 is activated, slider barrier 32 is pulled into the arming position by pull 36a. At this time, the one end, i.e., distal end, of light deflector arm 50 is no longer in position to deflect the light from laser 42, thus the light is then passed through optical fiber 56 causing indicator 46 to provide an indication that the slapper detonator is in the armed mode. Note that a mirror 58 may be positioned at an angle of 45 degrees on the distal end of light deflector arm 50 to deflect the light into optical fiber 54.

[0029] It will thus be seen that the objects set forth above, among those elucidated in, or made apparent from, the preceding description, are efficiently attained and, since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown on the accompanying drawing figures shall be interpreted as illustrative only and not in a limiting sense. While the foregoing has been directed to the preferred embodiment, there are variations and changes in the embodiments of the present disclosure which will be readily apparent to those of ordinary skill in the art. The aim and thrust of the appended claims is to cover variations that fall within the true spirit and scope of the disclosed invention, and the claims thus set forth the present invention.