Abstract:
An apparatus used in a fuze device, which includes a MEMS micro-rotor. The micro-rotor of the apparatus may move an explosive material, for example, a fuze material, from an out-of-line position to an in-line position. The micro-rotor includes an integral cavity in which the material may be safely loaded and held in the out-of-line position. At an appropriate time, the fuze device of a fully assembled ordnance may be armed. When the apparatus is activated, the micro-rotor carefully moves the explosive material to the in-line position, where the ordnance is armed.

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 any royalties thereon or therefore. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to fuzes and more particularly to a MEMS fuze that utilizes a plurality of thermal V-beam actuators to control a micro-rotor to move an explosive material from an out-of-line position to an in-line position. 
     2. Background 
     MEMS is an initialism for microelectromechanical system, and the abbreviation will be used throughout hereto forth. Fuze systems serve to detonate the main charge (‘secondary’ of military ordinance) of munitions, cartridges, and shells (collectively referred to herein as ordnance) at a desired time or location. The fuze plays an essential safety role in preventing accidental detonation of the ordnance, and it is instrumental in making the ordinance safe to handle. There are a variety of technologies used in fuze systems. For examples, some fuze systems are armed immediately prior to the ordnance being fired, and other systems are timed so that the fuze initiates detonation of the secondary charge of the ordnance at a desired time and/or location. One common approach to a fuse system is to charge a capacitor, and then discharge it at the desired time across a thin wire to create sufficient local heating or a spark to ignite the pinner-edgeary explosive, which subsequently ignites the main charge. On-board electronics or mechanical devices control the timing of the electrical discharge. Fuzes typically incorporate “g-switches” that prevent detonation until the fuze has been exposed to accelerations of a magnitude and time typically only encountered when fired while in a gun barrel. In other systems, a pinner-edgeary explosive such as silver azide is used to ignite the secondary explosive, where there are multiple safe guards to prevent accidental ignition of the secondary explosive even if the pinner-edgeary explosive ignites. An example, bombs and missiles carried by planes are not fitted onto the ordnance until just before the planes take off, thus preventing accidental ignition of the explosive firetrain. A system that utilized a secondary explosive as an igniter where secondary explosive are classified as less sensitive than pinner-edgeary explosives would be an even safer system. An example of a secondary explosive is EDF-11. It has been found that EDF-11 may be deposited as a slurry mix and, after drying, will perform as a secondary explosive. A secondary explosive may be ignited if subjected to a sufficient electrical spark or shock. 
     SUMMARY OF THE INVENTION 
     The disclosed invention is an apparatus for a fuze device where an apparatus has a MEMS micro-rotor, which can move an explosive material, where the explosive material is a fuze material. In operation, the MEMS micro-rotor moves the explosive material from an out-of-line position to an in-line position. The micro-rotor includes an integral cavity in which the material may be safely loaded and held in the out-of-line position indefinitely. At an appropriate time, the fuze device in fully assembled ordnance may be armed without physically adding the fuze device. The micro-rotor of the apparatus is actuated, and it securely and reliably moves the explosive material from the out-of-line position to the in-line position, where the ordnance is armed. 
     As will become apparent, the invented apparatus has a MEMS architecture immune to inertial effects in any direction. It is capable of higher speed translation, and has a smaller footprint. The smaller footprint allows for more fuze devices to be fabricated per wafer run, which is the most direct measure of cost per fuze device. 
     An aspect of the invention is that the micro-rotor is a superior alternative to using a traditional spring-mass system to translate, linearly, the explosive material loaded into the integral cavity to a channel cavity. Further, the explosive material is in-line with the firetrain, in large part, as the apparatus is based on a MEMS architecture, which is broadly a silicon based micro machine. The micro machine has excellent aging characteristics even in a salt water environment. 
     Another aspect of the invention is that the apparatus may largely be fabricated using processing methods that are used to make other MEMS based devices. A starting fabrication material is a multilayer wafer that includes a silicon device layer, a silicon supporting layer and an intervening insulator. The insulator may be etched away without damaging the device layer or the supporting layer. A plurality of the invented apparatus may be replicated utilizing the wafer, and then dicing the replications into multiple identical chips of the apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing invention will become readily apparent by referring to the following detailed description and the appended drawings in which: 
         FIG. 1  is an elevated view of the apparatus wherein the micro-rotor is in the start position, the integral cavity (without any explosive material) is located at three o&#39;clock, and there are four thermal actuators, which by default when there is no current, restrain movement of the micro-rotor; 
         FIG. 2  is an elevated perspective view of the apparatus shown in  FIG. 1 , where the micro-rotor has rotated approximately 90 degrees, and the integral cavity has been moved and it is now located at six o&#39;clock (in-line), where it is aligned with the through-layer channel cavity etched in the silicon supporting layer; 
         FIG. 2 a    is an exploded view illustrating the actuation mechanism that caused the micro-rotor to rotate from three o&#39;clock to six o&#39;clock; and 
         FIG. 3  is a diagrammatic elevated view illustrating an 180 degree arc of rotation from about twelve o&#39;clock to six o&#39;clock; 
         FIG. 4  is a diagrammatic view illustrating the MEMS Fabrication process flow diagram for a wafer for at least one apparatus, where the process employs Deep Reactive-Ion Etching (DRIE). 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invented rotary apparatus is fabricated using MEMS technology, which enables very small machines and electrical circuits to be formed. As an order of magnitude, a starting material is a silicon oxide insulator (SOI) wafer that has a silicon device layer, an insulator layer, and a silicon supporting layer. In the illustrated exemplary embodiment, the silicon device layer is about 100+/−50 microns thick, the insulator layer is about 4+/−3 microns thick, and the silicon supporting layer is about 500+/−200 microns thick. 
     The embodied apparatus  10  is illustrated in  FIG. 1 . The silicon device layer  20 , the insulator layer  30 , and the silicon supporting layer  40  are visible from this elevated perspective view. The apparatus  10  enables small quantities of material, for example an explosive material  100  which has the potential as a fuze material (EDF-11), to be loaded in a micro-rotor  12  having an integral cavity  14 , and moved to an armed position that is in-line with the firetrain. In the illustration, the starting position of the integral cavity  14  is at about three o&#39;clock and the in-line armed position is at about six o&#39;clock, as shown in  FIG. 2 . The about three o&#39;clock position is out-of-line from an underlying through-layer channel cavity  42  located in the silicon supporting layer  40 . At three o&#39;clock, the integral cavity  14  is only 90 degrees from an in-line position. In  FIG. 3 , the starting position is at twelve o&#39;clock, which is 180 degrees from the in-line position. So long as the integral cavity  14  is out-of-line from the underlying through-layer channel cavity  42  of the silicon supporting layer  40 , the fuze is in a safe state, as the explosive cannot move into the through-layer channel cavity  42 . 
     The micro-rotor  12  is a perforated disc  11  including an non-perorated center inner-edge portion  16  with an open center  17 , at least one hub spoke  18 , a perimeter edge  19  and the integral cavity  14 , which is inboard of the perimeter edge  19   
     The integral cavity  14  is sized to be sufficiently large to retain the explosive material  100 , for example EDF-11. The perforations  13 , as shown in  FIG. 2 a   , are a by-product of fabrication to remove the insulator layer  30  from beneath the disc  11 . 
     The apparatus  10  include a stationary element, which is a central axial stator  22  that provides an axle point. The apparatus also includes a spring element  50  connecting the stationary central axial stator  22  to the hub spokes  18  of the micro-rotor  12 . The spring element  50  provides elevational support for the micro-rotor  12 , so that micro-rotor does rub against the silicon supporting layer  30  when rotating. 
     There is a plurality of thermal V-beam actuators  60  in the silicon device layer  20 . As shown in the current embodiment, there are four actuators  60 , where each actuator  60  has a pair of electrical contact pads  62 . The thermal V-beam actuators  60  are equidistantly positioned outboard the perimeter edge  19  of the micro-rotor  12 . They are electrically actuated by a current at a rate that is in-part dependent on a frequency of the current. Actuation produces a frictional force and a tangential force against the perimeter edge  19  of the micro-rotor causing the micro-rotor and the integral cavity  14  carrying the explosive material toward the channel cavity  42 , which is the armed position. The rotation also winds and tensions the spring element  50 , which is a coiled spring. 
     The thermal V-beam actuators  60  shown in the figures produce high force and are highly reliability. As shown in  FIG. 2 a   , when a current is passed through the legs  62  of the actuator  60  there is thermal expansion and consequently a lateral motion of a center shuttle  64  that is attached to a V-beam  66 . The V-beam motion has a tangential vectorial component, and a tip end  68  of the V-beam impinges the perimeter edge of the micro-rotor. The tangential vectorial component is equal or greater than 30 degrees from perpendicular. As the V-beam pushes against the perimeter edge  19 , it causes the micro-rotor to rotate. 
     In addition to the actuators  60 , the micro-rotor  12  may be frictionally held in position by tab tip elements  29 , as shown in  FIG. 2 a   . The tap tip elements  29  are formed in the silicon device layer  20 , which are in close proximity to the perimeter edge  19 . 
     Thermal actuators  60  are based on strain relief of constrained thermal expansion. When a current is passed through the legs  62  of the actuator  60 , the legs closest to the micro-rotor  62   a  do not expand as much as the adjoining parallel legs  62   b . The anisotropic expansion results in the strain relieving motion causing the center shuttle  64  to shift toward the micro-rotor. When the current is lowered, the warmer legs  62   b  cool, and the shuttle moves away from the micro-rotor. Thermal actuators come in multiple variations but all rely on anisotropic expansion. A unique property of the illustrated thermal actuator is that movement of the center shuttle  64  is linear. The iterative action of the thermal actuators  60  cause the micro-rotor to rotate. 
       FIG. 4  diagrammatically illustrates the MEMS Fabrication process flow diagram for a wafer for at least one apparatus. The process employs Deep Reactive-Ion Etching (DRIE). As shown the SIO wafer includes a silicon device layer  20 , a insulator layer  30 , and a silicon supporting (aka handle) layer. In one step the gold (Au) terminal pads  61  for the thermal actuators  60  are deposited on the silicon device layer  20 . The pattern for the micro-rotor  12  and elements of an actuator  60  are etched into the silicon device layer  20 . The channel cavity  42  is etched through the silicon support layer  40 . In step  4 , a portion of the insulator layer  30   a  underlying the perforated disc  11  is etched away using HF (hydrofluoric) vapor release. The pores  13  ( FIG. 2 a   ) improve access and therefore the efficiency of etching. The stator  22  is left attached to the insulating layer  30   b  and the silicone support layer (handle)  40 . The HF etching provides freedom of movement for the V-beam  66  of an actuator. When the process of replicating the apparatus on the wafer, the wafer may be broken into one or more individual MEMS chip(s) of the apparatus. 
     The invented apparatus  10  may be included in a MEMS assemblage. The MEMS architecture is immune to inertial effects in any direction. It is capable of higher speed translation, and has a smaller footprint. The smaller footprint allows for more fuze devices to be fabricated per wafer run, which is the most direct measure of cost per fuze device. 
     Finally, any numerical parameters set forth in the specification and attached claims are approximations (for example, by using the term “about”) that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of significant digits and by applying ordinary rounding.