Abstract:
An EFI (exploding foil initiator) or slapper detonator, including a explodable foil (or bridge), a flyer plate and a barrel plate having a movable barrier to close a 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 (microelectromechanical system) energetic actuator. The slidable barrier is maintained in the closed position by one or more locking devices of the MEMS energetic actuator until predetermined stimuli are detected to cause the locking device(s) to release the slidable barrier, thereby arming the EFI or slapper detonator.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of royalties thereon or therefor. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     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. 
     2. Background Art 
     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. 
     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&#39;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 Devices  describes 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.    
     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 Detonator  contemplates 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. 
     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. 
     SUMMARY OF THE INVENTION 
     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. 
     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. 
     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. 
     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. 
     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. 
     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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
     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; 
     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; 
     FIG. 2B and 2C are close-up views of portions of FIG. 2A; and 
     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. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     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 . 
     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 (&lt;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     2   ) to detonate high explosive pellet  40 . 
     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  36   a , engaging unit  38   a , Lock # 1 , Lock # 2 , pawls  40   a  and  40   b  and an optical system. 
     Pull  36   a  has an pull arm  36   b , which is preferably a thermal actuator, that is engaged (see FIG. 2B) with slider barrier  32  by engaging unit  38   a  and engagement arm  38   b , 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  36   a  to 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  36   b  uses a thermal actuator, then the distance of the pull is short. Accordingly, pull  36   a  and engaging unit  38   a  are 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  36   b  which will engage, under the control of engagement arm  38   b , a plurality of teeth on slidable barrier  32 . 
     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. 
     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. 
     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. 
     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  40   a  and  40   b  are activated to disengage locking bars  48   a  and  48   b  from catches  49   a  and  49   b  in 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  36   a . 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 . 
     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.