Patent Publication Number: US-8522682-B1

Title: Advanced grenade concept with novel placement of MEMS fuzing technology

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The present invention described herein may be manufactured and used by or for the Government of the United States of America for government purposes without the payment of any royalties thereon or therefore. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to explosive systems and micro-electromechanical systems (MEMS). More particularly, the present invention relates to systems and methods for explosive systems such as grenades with novel MEMS fuze and novel placement of the MEMS fuze providing increased performance, reliability, and safety. 
     BACKGROUND OF THE INVENTION 
     Conventionally, high velocity grenades rely on a mechanical impact fuze located in the front of the grenade. The mechanical impact fuze is a complex device that uses environmental parameters associated with gun launch (e.g., setback and spin) to arm. Upon impact with a target the nose of the mechanical impact fuze is crushed. This action projects a stabber into an explosive charge located at the base of the mechanical impact fuze. A charge detonates and launches a metal projectile towards a main charge, which then detonates upon impact. This action collapses a metal shaped charge liner, which is projected forward through the mechanical impact fuze and into the target. At the same time the main charge fragments the body of the grenade and throws those fragments outward. 
     There are several limitations with conventional systems. The mechanical impact fuze is a complex device that is prone to failure. It has been known to arm and detonate early, posing a hazard to the gunner. These failures have primarily been attributed to errors made during manufacturing. The mechanical impact fuze may also fail to fire if the weapon impacts at an oblique angle or hits soft material such as snow. This situation poses an unexploded ordnance hazard to operators and bystanders. In addition, the presence of the mechanical impact fuze in front of the shaped charge inhibits the ability of the weapon to penetrate armor. Before the shaped charge can penetrate the target it must first go through the steel and aluminum components of the mechanical impact fuze. Further, the rear of the fragmenting grenade body has a tendency to come off as a single piece and fly straight back, which is a hazard to the gunner. Finally the device does not meet Department of Defense (DOD) “Insensitive Munitions” requirements, which are standards designed to reduce of risk of injury to personnel as a result of accidents such as dropped items or a fire. 
     BRIEF SUMMARY OF THE INVENTION 
     In an exemplary embodiment, an explosive system includes a case with an interior with a front portion, a middle portion, and a rear portion; a main explosive charge disposed within the middle portion of the interior of the case; and a micro-electromechanical systems fuze disposed within the rear portion of the interior of the case, wherein the micro-electromechanical systems fuze is configured to detonate the main explosive charge and the micro-electromechanical systems fuze includes a plurality of safety mechanisms. The explosive system may further include a shaped charge liner disposed in the front portion of the interior of the case. The shaped charge liner is configured to penetrate a target upon detonation of the main explosive charge where the penetration is unimpeded by the micro-electromechanical systems fuze. The shaped charge liner is shaped to optimize penetration into the target. The case may include a fragmenting case configured to fragment upon detonation of the main explosive charge. The explosive system may further include electronic circuits disposed in the rear portion and communicatively coupled to the micro-electromechanical systems fuze; and an energy source powering the electronic circuits and the micro-electromechanical systems fuze. The energy source may include a piezoelectric energy harvester. The plurality of safety mechanisms may include a setback lock on the micro-electromechanical systems fuze, a timer in the electronic circuits configured to remove a command lock on the micro-electromechanical systems fuze, and sensors in the electronic circuits detecting impact and spinning of the explosive system. The setback lock is released upon launch of the explosive system, the command lock is removed upon expiration of the timer, and a micro-detonator on the micro-electromechanical systems fuze detonates the main explosive charge based upon the sensors detecting impact or cessation of the spinning. The micro-electromechanical systems fuze may include a spin armed slider; a command lock and a setback lock holding the spin armed slider in place; and an initiator out of line from a micro-detonator cup disposed to the spin arm slider. The explosive system may further include electronic circuits disposed in the rear portion and communicatively coupled to the micro-electromechanical systems fuze; where upon firing, the setback lock is moved out of position. The electronic circuits are configured to: activate a timer upon firing, release the command lock upon expiration of the timer, and detect spinning and impact of the explosive system. Upon release of the command lock and the setback lock, the spin armed slider moves into position such that the micro-detonator cup is in line with the initiator thereby arming the micro-electromechanical systems fuze. 
     In another exemplary embodiment, electronic circuitry for an explosive system includes electronic circuits disposed on a circuit board; a micro-electromechanical systems fuze including plurality of safety mechanisms, where the micro-electromechanical systems fuze is communicatively coupled to the electronic circuits; and an energy source powering the electronic circuits and the micro-electromechanical systems fuze. Each of the circuit board, the micro-electromechanical systems fuze, and the energy source are disposed in a rear portion of the explosive system. The energy source may include a piezoelectric energy harvester. The plurality of safety mechanisms may include a setback lock on the micro-electromechanical systems fuze, a timer in the electronic circuits configured to remove a command lock on the micro-electromechanical systems fuze, and sensors in the electronic circuits detecting impact and spinning of the explosive system. The setback lock is released upon launch of the explosive system, the command lock is removed upon expiration of the timer, and a micro-detonator on the micro-electromechanical systems fuze detonates a main explosive charge in the explosive system based upon the sensors detecting impact or cessation of the spinning. The micro-electromechanical systems fuze may include a spin armed slider; a command lock and a setback lock holding the spin armed slider in place; and an initiator out of line from a micro-detonator cup disposed to the spin arm slider. Upon firing, the setback lock is moved out of position where the electronic circuits are configured to activate a timer upon firing, release the command lock upon expiration of the timer, and detect spinning and impact of the explosive system. Upon release of the command lock and the setback lock, the spin armed slider moves into position such that the micro-detonator cup is in line with the initiator thereby arming the micro-electromechanical systems fuze. 
     In yet another exemplary embodiment, a method includes launching a round, wherein the round includes a micro-electromechanical systems fuze in a rear portion of the round after explosive charges; releasing a setback lock on the micro-electromechanical systems fuze upon launching; initiating a timer upon launching; releasing a command lock on the micro-electromechanical systems fuze based on the timer thereby allowing a micro-detonator on the micro-electromechanical systems fuze to slide into position; and detecting impact and detonating the round through the micro-detonator. The method may further include detecting no impact and detecting the round has stopped spinning and detonating the round through the micro-detonator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated and described herein with reference to the various drawings, in which like reference numbers denote like method steps and/or system components, respectively, and in which: 
         FIG. 1  is a front perspective, cut-out view of an explosive system according to an exemplary embodiment of the present invention; 
         FIG. 2  is a diagonal perspective, cut-out view of the explosive system of  FIG. 1  according to an exemplary embodiment of the present invention; 
         FIG. 3  is a cross-sectional view of the explosive system of  FIG. 1  according to an exemplary embodiment of the present invention; 
         FIG. 4  is a top perspective view of a MEMS fuze for use in the explosive system of  FIG. 1  according to an exemplary embodiment of the present invention; 
         FIG. 5  is a bottom perspective view of a MEMS fuze for use in the explosive system of  FIG. 1  according to an exemplary embodiment of the present invention; and 
         FIG. 6  is a flowchart of an operational method  60  utilizing the explosive system of  FIGS. 1-3  and the MEMS fuze of  FIGS. 4-5 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In various exemplary embodiments, the present invention relates to systems and methods for explosive systems such as grenades with novel MEMS fuze and novel placement of the MEMS fuze providing increased performance, reliability, and safety. The MEMS fuze is disposed towards a rear portion of the explosive system providing superior performance and design flexibility. Further, the explosive system includes electronics configured to implement a launch timer and to sense impact or when the system stops spinning. The present invention includes an operational method improving safety and reliability by preventing detonation until after the launch timer expires, upon impact, or when the explosive system stops spinning. 
     Referring to  FIGS. 1-3 , in an exemplary embodiment, an explosive system  10  is illustrated in a front perspective view ( FIG. 1 ), a diagonal perspective view ( FIG. 2 ) and a cross sectional view ( FIG. 3 ). In an exemplary embodiment, the explosive system  10  may include a high explosive, dual purpose (HEDP), high velocity grenade. For example, HEDP grenades may be intended for use against personnel and lightly armored vehicles. The explosive system  10  includes a fragmenting case  12  designed to fragment upon detonation of a main explosive charge  14  disposed within an interior of the fragmenting case  12 . The explosive system  10  further includes a shaped charge liner  16  disposed in front of the main explosive charge  14  and within the interior of the fragmenting case  12 . The main explosive charge  14  and the shaped charge liner  16  may include various explosive materials and compounds as are known in the art. Upon detonation of the main explosive charge  14 , the shaped charge liner  16  is configured to project forward and to penetrate into a target. In the examples of  FIGS. 1-3 , the shaped charge liner  16  is illustrated extending from a point near the center of the fragmenting case  12  interior with a parabolic, conical shape towards covering the entire front of the fragmenting case  12  interior. The present invention contemplates various geometries and material compositions of the shaped charge liner  16  as required for penetrating different target types and functioning in different weapon environments. The explosive system  10  spins while it flies in order to maintain ballistic stability. The shaped charge liner  16  may include spin compensation in order to counteract associated rotational forces. This compensation comes in the form of geometric changes (called fluting) or material changes. Different weapon systems may have different environmental parameters that the present invention accommodates. 
     In an exemplary embodiment of the present invention, the explosive system  10  includes a MEMS fuze  20  disposed towards a rear portion of the fragmenting case  12  interior. Specifically, the explosive system  10  may include a front portion with the shaped charge liner  16 , a middle portion with the main explosive charge  14 , and a rear portion with the MEMS fuze  20 . Advantageously, placing the MEMS fuze  20  in the rear allows for greater design flexibility and optimization of penetration with the shaped charge liner  16 . MEMS Fuze technology is being developed that requires less space and is more configurable than current technology. Specifically, the MEMS fuze  20  is disposed after the main explosive charge  14  and the shaped charge liner  16  relative to the front of the fragmenting case  12 . Thus, the MEMS fuze  20  does not interfere with the shaped charge liner  16  upon impact. The explosive system  10  further includes circuit boards  22  with various electronic components related to operation of the explosive system  10 . Also, the explosive system  10  includes an energy source  24  that powers the MEMS fuze  20  and the circuit boards  22  in the rear portion of the explosive system  10 . For example, the energy source  24  may include a piezoelectric energy harvester. Note, the MEMS fuze  20 , the circuit boards  22 , and the energy source  24  may each be communicatively coupled for power and data transfer therebetween. The circuit boards  22  may include electronic components  21  configured to control the MEMS fuze  20 , provide a timer, sense spinning of the explosive system  10 , and sense impact of the explosive system  10 . For example, the circuit boards  22  may control various components associated with or on the MEMS fuze  20 , and the energy source  24  may power both the circuit boards  22  and the MEMS fuze  20 . 
     Referring to  FIGS. 4 and 5 , in an exemplary embodiment, the MEMS fuze  20  is illustrated in a top perspective view ( FIG. 4 ) and a bottom perspective view ( FIG. 5 ). The MEMS fuze  20  includes a spin armed slider  30  (shown in  FIG. 4 ) with a micro-detonator cup  32  (shown in  FIG. 5 ). The micro-detonator cup  32  is disposed towards the center of the MEMS fuze  20  chip. The spin armed slider  30  is restrained from moving by a command lock  34  and a setback lock  36 . An initiator  38  stands out of line from the micro-detonator cup  32 . Upon firing, the force of gun launch moves the setback lock  36  out of position. At the same time, a sensor inside electronics on the circuit boards  22  activates a timer. After a prescribed period of time, the timer counts down and the electronics remove the command lock  34 , allowing the spin armed slider  30  to move into position. Centrifugal force from rotation of the explosive system  10  moves the spin armed slider  30  such that the micro-detonator cup  32  is in line with the initiator  38 . The MEMS fuze  20  is now armed. When the explosive system  10  hits a target, the electronics on the circuit boards  22  command the initiator  38  to fire, which detonates energetic material disposed inside the micro-detonator cup  32 . This configuration causes the explosive system  10  to detonate. To reduce the risk of unexploded ordnance, the electronics on the circuit boards  22  may instruct the MEMS fuze  20  to fire once the round stops spinning. This situation occurs if the explosive system  10  fails to impact the target and subsequently lands on the ground. 
     The MEMS fuze  20  may be implemented through various mechanisms. For example, the MEMS fuze  20  may be fabricated on a silicon on insulator (SOD wafer. Here, a silicon substrate (also known as a handle layer) is covered by an insulating or intermediate layer, such as silicon dioxide, over which is bonded or deposited another silicon layer, also known as the device layer, which is the layer from which the MEMS fuze  20  assembly components are fabricated. The MEMS fuze  20  assembly components may be formed by a DRIE (deep reactive ion etching) process that removes unwanted portions of device layer. The DRIE process is a well developed micromachining process used extensively with silicon based MEMS devices. For this reason, silicon is an exemplary material for the MEMS fuze  20  assembly of the present invention, although other materials are possible. In other exemplary embodiments, materials other than silicon may be used as a substrate, including glass, stainless steel, and a plastic material, such as, polycarbonate. 
     Referring to  FIG. 6 , in an exemplary embodiment, a flowchart illustrates an operational method  60  utilizing the explosive system  10  and the MEMS fuze  20 . A round is launched and a setback in the round releases a lock inside the MEMS fuze and initiates a timer (step  62 ). Note, the round may include the explosive system  10 , a grenade, or the like. The timer is set for a prescribed time period, and provides improved safety in preventing the round from detonating immediately upon launch. Based on the timer, a command lock is removed in the MEMS fuze allowing a micro-detonator to slide into position (step  64 ). In the operational method  60 , the round is configured to sense an impact, such as through electronics disposed with the explosive system  10  (step  66 ). Upon impacting a target, the micro-detonator is initiated, detonating the round (step  68 ). As described herein, the explosive system  10  includes the MEMS fuze disposed towards the rear of the explosive system  10 . As such, upon impact, the explosive system  10  provides a shaped charge jet from the front that penetrates the target since the fuze and electronics are not interfering with the front of the explosive system  10 . Further, fragments from a casing associated with the explosive system  10  may serve in an anti-personnel function. If no impact is sensed by the round, a fire command is sent after the round stops spinning (step  70 ). For example, the electronics in the explosive system  10  may include sensors to detect when the round stops spinning. The fire command prevents unexploded ordinances. 
     The present invention provides several advantages over conventional designs, specifically in areas of performance, reliability, and safety. Moving the MEMS fuze to the rear of the round reduces the amount of material the shaped charge has to go through before it reaches the target resulting in better penetration. The fragmenting case is modified such that it will not project the rear of the body to the firer, improving safety. The explosive fill itself is changed to be more compliant with Insensitive Munition standards. The MEMS fuze has fewer moving parts than the current mechanical impact fuzes, and the tolerances are easier to control due to the batch process methods used to fabricate the components. This configuration improves reliability and reduces the likelihood of a premature detonation. Finally, the presence of an electronic fire control system reduces the likelihood of dud rounds. 
     In an exemplary embodiment, the explosive system  10  may include a 40×53 High-Velocity, High-Explosive Dual-Purpose (HEDP) M430 cartridge (subsequently replaced in production by the M430A1) or the like. Thus, the concepts described herein may enhance the safety and reliability of the M430A1 HEDP. It may also be applied to a wide variety of other small and medium caliber weapons. Advantageously, the present invention addresses the need for smaller and smarter weapons. Relocation of the fuze, combined with the MEMS technology, allows for significant optimization and configuration of weapons technology. The M430A1 provides both armor penetration and anti-personnel effects. 
     Although the present invention has been illustrated and described herein with reference to exemplary embodiments and specific examples thereof, it will be readily apparent to those of ordinary skill in the art that other embodiments and examples may perform similar functions and/or achieve like results. All such equivalent embodiments and examples are within the spirit and scope of the present invention and are intended to be covered by the following claims. 
     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.