Abstract:
A high precision electro-mechanical fuze mechanism for a munition such as a hand grenade. The fuze mechanism includes an electromagnetic signal generator having an armature, a permanent magnet, a coil and a magnetic impulse generator (MIG) member. The armature is preloaded during assembly through the use of a spring. Releasing an actuating lever of the grenade allows the armature to begin spinning and to dissipate the energy stored by the spring. This causes a current to be electromagnetically generated in the coil, which is transmitted to an electronic control circuit in the fuze mechanism. The electronic control circuit implements two time delays from two separate timers which each must time out before the control circuit can send an electric firing signal to an electric detonator. Movement of the armature also causes a simultaneous movement of a rotor, which moves a stab detonator into a position closely adjacent the electric detonator. Detonation of the electric detonator immediately causes detonation of the stab detonator, which in turn detonates the primary explosive charge of the munition.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates to munitions, and more particularly to a high precision fuze mechanism for electronically generating a firing signal to detonate a hand grenade through the use of a magnetic signal generator incorporated in the fuze mechanism. 
     2. Discussion 
     Present day hand grenades typically incorporate pyrotechnic fuze mechanisms. These fuze mechanisms employ a fuze element that begins burning when the safety pin of the grenade is pulled from the grenade. At the end of a delay period the burning fuze element ignites a pyrotechnic element which in turn detonates the primary explosive compound of the grenade. 
     Such present day fuze mechanisms for grenades suffer from a number of drawbacks. For one, the delay time before detonation cannot be controlled with excellent accuracy and repeatability. Delay times typically fluctuate +/− about one to two seconds. Another drawback is that the performance of the fuze element degrades over time. This can cause further variations in the accuracy of the delay time implemented before the grenade is detonated. 
     It would therefore be advantageous to provide an electronically controlled fuze mechanism which would provide much greater accuracy and reliability in implementing the time delay before detonating the grenade. The difficulty with this has been the lack of electrical power available for powering a suitable electronic control circuit. With other forms of munitions that are launched from sea or air, often environmental elements such as wind are used to assist in generating electrical power for the various electronic components of the fuze mechanism of the munition. With a hand grenade, however, such environmental elements as wind force are not present in sufficient degree to reliably assist in providing power for a manually thrown hand grenade. 
     It would therefore be advantageous to provide a high precision fuze mechanism for a munition, such as a hand grenade, which incorporates a reliable, relatively low cost means for generating electrical power for a brief period of time, to thereby enable an electronic control system to be employed to control more precisely the time delay period prior to detonating the grenade. 
     It would also be advantageous to provide a fuze mechanism for a hand grenade which incorporates an electronic control circuit capable of implementing one or more time delay periods, through the use of small, lightweight electronic components, before the control circuit causes detonation of the grenade. 
     Still further, it would be advantageous to provide a high precision fuze mechanism for a hand grenade which incorporates an electrical impulse generator, which is only activated upon removal of a safety pin of the grenade and releasing of the grenade, and which generates sufficient electrical power to power an electronic control circuit for a short period of time, which may then be used to detonate the grenade. 
     Still further, it would be advantageous to provide a high precision fuze mechanism for a hand grenade which includes an electrical power generator and an electronic control circuit for implementing a precisely controlled time delay before causing detonation of the grenade, and which does not significantly increase the size, weight or overall cost of the hand grenade. 
     Furthermore, it would be advantageous to provide a high precision fuze mechanism for a hand grenade which includes an electrical power generator for powering an electronic control circuit, where the power generator is activated as soon as a safety pin of the grenade is withdrawn and the grenade is released, and which is not affected by the velocity with which the grenade is thrown or the orientation of the grenade through its trajectory or the position in which it lands, or by other environmental elements, before it is detonated. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a high precision electromechanical fuze apparatus and method for arming and detonating a munition such as a grenade. In a preferred embodiment the fuze mechanism of the present invention comprises a magnetic signal generator which is electrically coupled to an electronic control system. The magnetic signal generator is comprised of an armature, a permanent magnet, a coil circumscribing the permanent magnet and an assembly for transmitting the electric current induced in the coil to the electronic control system. The armature is assembled in a “preloaded” state and held immovably by a safety pin. Removal of the safety pin allows the armature to rotate rapidly, thus causing an electric current to be induced in the coil of the magnetic signal generator. This signal is transmitted to the electronic control circuit which includes means for implementing at least one time delay before generating an electrical firing signal. The electrical firing signal is then used to activate an electric detonator which in turn causes detonation of a stab detonator. Detonation of the stab detonator causes detonation of the primary explosive charge of the munition. 
     In a preferred embodiment the armature is preloaded in the unarmed state by a coil spring. The entire assembly of the armature, a permanent magnet and the means for transmitting the electrical pulse signal are all housed within a magnetic impulse generator (MIG) housing. The armature includes a shaft to which is secured a rotor. The rotor carries the stab detonator. The coil spring is coupled to the shaft of the armature and the stored energy of the spring maintains the armature in the preloaded condition when a safety pin is inserted in an interfering relationship with a portion of the armature. Preferably a lever associated with the safety pin is employed, which must be released by the user before the safety pin can be removed. The lever is preferably spring loaded such that it automatically withdraws the safety pin as soon as the grenade is released by the user. 
     When the lever pin is released, thus causing the safety pin to be withdrawn, the energy stored in the spring is immediately dissipated, which causes the armature to be rotated rapidly for several revolutions. This rapid rotational movement causes a current to be electromagnetically induced in the coil. The current is transmitted through a current transmitting assembly to an electronic control system. The electronic control system incorporates at least one timer, and preferably a pair of timers, which are each initiated upon receipt of the electrical signal from the coil. After at least one, and preferably a pair, of predetermined time delays have expired, the control circuit generates an electrical firing signal which is used to detonate an electrical detonator. The stab detonator is also moved into position adjacent the electrical detonator as soon as rotation of the armature starts to occur after the safety pin is withdrawn. Detonation of the electrical detonator causes essentially simultaneous detonation of the stab detonator, which in turn causes detonation of a booster pellet disposed adjacent the primary explosive charge of the munition, and which causes detonation of the primary explosive charge. 
     In a preferred embodiment, the electronic control circuit includes a first timer which is initiated upon an electrical signal being received from the coil. When this timer times out, a first switch is turned on. A second timer is also initiated when the electrical signal from the coil is received. The second timer has a second time delay which is longer than the delay period of the first timer. When the second timer times out, it turns on a second switch. Only when the first and second switches are both closed does the electronic control circuit generate an electrical firing pulse to the electrical detonator to initiate the explosive train that detonates the munition. 
     The fuze mechanism of the present invention thus forms a high precision, lightweight, compact and relatively inexpensive means for arming and detonating a munition such as a hand grenade after a predetermined time has elapsed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The various advantages of the present invention will become apparent to one skilled in the art by reading the following specification and subjoined claims and by referencing the following drawings in which: 
     FIG. 1 is a perspective view of a hand grenade incorporating a high precision, electromechanical fuze mechanism in accordance with a preferred embodiment of the present invention; 
     FIG. 2 is a top view of the grenade of FIG. 1; 
     FIG. 3 is a cross sectional side view of the grenade of FIG. 2 taken in accordance with section line  3 — 3  in FIG. 2; 
     FIG. 4 is an exploded perspective view of the major subassemblies of the fuze mechanism; 
     FIG. 5 is an exploded perspective view of the major components housed within the MIG housing of the fuze mechanism; 
     FIG. 6 is a perspective view of the MIG; 
     FIG. 7 is a bottom view of the MIG of FIG. 6; 
     FIG. 8 is a perspective view of the armature and armature shaft coupled together; 
     FIG. 9 is a perspective view of the safety pin; 
     FIG. 10 is a side view of the safety pin of FIG. 9; 
     FIG. 11 is a perspective view of the MIG housing; 
     FIG. 12 is a top view of the MIG housing; 
     FIG. 13 is a perspective view of the lower housing member; 
     FIG. 14 is a plan view of the lower housing member; 
     FIG. 15 is a bottom view of the lower housing member; 
     FIG. 16 is a cross sectional side view of the lower housing member taken in accordance with section line  16 — 16  in FIG. 14; 
     FIG. 17 is a side view of the lower housing; 
     FIG. 18 is a perspective view of the rotor; 
     FIG. 19 is a side view of the rotor of FIG. 18; 
     FIG. 20 is a top plan view of the rotor; 
     FIG. 21 is a bottom plan view of the rotor; 
     FIG. 22 is a perspective view of the rotor from the opposite orientation of that shown in FIG. 18; 
     FIG. 23 is a bottom plan view of the fuze housing; 
     FIG. 24 is a perspective view of the threaded housing member; 
     FIG. 25 is a top plan view of the threaded housing member; 
     FIG. 26 is a cross sectional side view of the threaded housing member taken in accordance with section line  26 — 26  in FIG. 25; 
     FIG. 27 is a partial assembly view of the rotor and lower housing showing the rotor in the position it is in before the fuze mechanism is armed; 
     FIG. 28 is a partial assembly view showing the rotor in FIG. 26 having been moved approximately 90 degrees into an armed position adjacent the electric detonator; and 
     FIG. 29 is an electrical schematic diagram of the electronic control circuit of the fuze mechanism. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1-3, a grenade  10  incorporating a high precision, electromechanical fuze mechanism  12  in accordance with a preferred embodiment of the present invention is shown. With specific reference to FIG. 1, the fuze mechanism  12  is secured to a body housing  14  within which is contained a high explosive composition. The body housing  14  preferably consists of an aluminum shell, approximately 0.170 inch thick, which is impregnated with a matrix of steel balls. The steel balls have a diameter of preferably about 0.125 inch. 
     The fuze mechanism  12  is threadably secured to a portion of the body housing  14 , as will be explained further in the following paragraphs. The fuze mechanism  12  generally includes a housing  16  having a pivot portion  18  and a rear portion  20 . The pivot portion  18  has a pair of integrally formed pivot members  22  upon which is secured an actuating lever  24 . The actuating lever  24  is pivotably secured at end portions  26  thereof. A key-shaped aperture  28  permits a portion of a safety pin  30  to be staked to the actuating lever  24  so as to be movable with the lever. The lever includes parallel flanges  24   a  (only one being visible in FIG. 1) each having a second aperture  32 , while the rear portion  20  includes a bore  34  (see FIG. 3) through which a manually graspable safety pull pin  36  extends to lock the lever  24  in place to ensure that the fuze mechanism  12  does not become accidentally armed. A shipping clip  38  is also engaged with the actuating lever  24  over a lip  40  of the fuze housing  14  (see FIG. 3) to further ensure that the actuating lever  24  cannot rotate, thereby accidentally arming the fuze mechanism  12 . Accordingly, both the shipping clip  38  and the safety clip  36  must removed before the actuating lever  24  can be rotated to arm the fuze mechanism  12 . 
     Referring now to FIG. 4, the fuze mechanism  12  is shown in greater detail. The mechanism  12  further includes a spring  42  for biasing the actuating lever  24  against the body  14 . A grommet  44  receives the safety pin  30  therethrough and seals an aperture  16   a  in the fuze housing  16  through which the safety pin  30  extends. A magnetic impulse generator (MIG) assembly  46  resides within the fuze housing  16  together with a lower housing  48  and a printed circuit board  50  disposed on the lower housing  48 . A rotor  52  supports a stab detonator  54  within a recess  184  of a threaded housing member  56 . The threaded housing member  56  includes a booster pellet  58  which is disposed in a cavity  60  thereof. The booster pellet preferably comprises a PBXN-5 explosive. 
     Referring now to FIG. 5, the MIG assembly  46  can be seen to include a ferrous armature  62  having an elongated shaft  64  with a pinion gear  66  at an outermost end thereof. An annular, permanent magnet  68  is disposed concentrically within a neck portion  70  of a spool-shaped bobbin member  72 . An annular coil  74  is formed by winding electrically conductive wire over the neck portion  70 . The entire assembly of the bobbin member  72 , coil  74 , permanent magnet  68  and armature  62  resides within a ferromagnetic impulse generator member (MIG)  76 . 
     With further reference to FIG. 5, a spring  77  is disposed concentrically below the MIG  76  and within a MIG housing  78  and wound into the form shown during assembly. As will be explained in the following paragraphs, the spring  77  is coupled to the armature shaft  64  to “preload” or “pretension” the armature  62  during assembly of the fuze mechanism  12 . The printed circuit board  50  is also housed within the MIG housing  78 . A speed clip  80  is used to secure an electric detonator  82  within an aperture  84  in the lower housing  48 . 
     With brief reference to FIG. 8, the armature  62  and its shaft  64  are shown coupled together. The armature  62  includes three lobes  62   a ,  62   b  and  62   c , with lobe  62   c  having a notch  86  formed therein. The notch  86  permits the safety pin  30  to engage the armature  62  when the fuze mechanism  12  is in the unarmed state to hold the armature  62  stationary. The shaft  64  includes a notched portion  88  which engages with an inner terminal end  126   a  (FIG. 5) of the coil spring  77 . In this manner the coil spring  77  is able to exert a preload force on the armature  62  when the MIG assembly  46  is assembled, while the safety pin  30  holds the armature  62  in this preloaded state until it is lifted upwardly out of engagement with the notch  86  by the force of the spring  42  acting on the actuating lever  24 . 
     Referring to FIGS. 9 and 10, the safety pin  30  is shown in greater detail. The safety pin  30  includes a boss portion  30   a  having a tab  30   b  and an integrally formed body  30   c . The body  30   c  has a tapered edge  30   d . The boss  30   a  and tab  30   b  extend outwardly of a base  30   e . The body  30   c  extends through the aperture  16   a  in the housing  16  (FIG. 4) and the boss  30   a  and tab  30   b  extend into the key-shaped aperture  28  in the actuating lever  24  to key the safety pin  30  to the lever  24 . When the safety pin  30  is staked to the actuating lever  24 , the pin  30  can only be moved longitudinally by movement of the actuating lever  24 , and is not able to rotate within the aperture  16   a.    
     Referring again to FIG. 5, the bobbin member  72  includes an arm portion  90  having a pair of apertures  92 . The apertures  92  receive insulated, electrically conductive bobbin pins  94  therethrough which are coupled at one end to the two terminal ends of wire forming the coil  74 . The bobbin pins  94  extend downwardly into apertures  96  in the printed circuit board  50  to transmit current induced in the coil  74  to the electrical components of the electronic control system mounted on the circuit board  50 . 
     Referring now to FIGS. 5-7, it can be seen that the MIG  76  includes a notch  98  into which the arm portion  90  of the bobbin member  72  is inserted during assembly. The MIG  76  further includes a plurality of arm portions  100  protruding from a lower surface  102  (FIG.  7 ). The arm portions  100  fit within arcuate openings  102  (see FIG. 12) of the MIG housing  78  while a bottom wall  104  of the MIG  76  rests on a circumferential internal shoulder  106  of the MIG housing  78 . Opening  108  (FIG. 12) in a bottom wall  110  of the MIG housing  78  permits the arm portion  90  of the bobbin member  72  to extend therethrough. A central aperture  112  permits a portion of the armature shaft  64  to also extend through the bottom wall  110  of the MIG housing  78 . 
     Referring to FIGS. 11 and 12, the MIG housing  78  includes a plurality of notches  114  formed in an annular wall  105  in an upper end thereof. A plurality of notches  116  are also formed at a lower end of the annular wall  105 . 
     With further reference again to FIGS. 5,  6  and  7 , the MIG  76  also includes a peripheral wall  118  having the notch  98  and a boss  120  having a bore  122  for receiving the armature shaft  64  therethrough. Notches  124  serve to ease assembly of the bobbin member  72  into the MIG  76 . A notch  104   a  is present for allowing clearance for the arm portion  90  of the bobbin member  72 . The notches further help to define three equally spaced, raised lobes  125 . Notch  125   a  allows clearance for the safety pin  30  so that the pin  30  can be inserted also into the notch  86  in the armature  62 . 
     With brief reference now to FIGS. 5,  7 , and  12 , the arm portions  100  of the MIG  76  are received within the apertures  102  in the bottom wall  110  of the MIG housing  78  when the fuze mechanism  12  is assembled. The peripheral wall  118  of the MIG  76  also rests on the circumferential internal shoulder  106  of the MIG housing  78 . 
     Referring further to FIGS. 5,  7  and  12 , the spring  77  (FIG. 3) includes an outermost end  126  formed in a U-shape. The outermost end  126  fits around the arm  100   a  that is inserted in opening  102   a  in the bottom wall  110  of the MIG housing  78  (FIG.  12 ). In this manner the spring  77  is captured by the assembly of the MIG  76  and MIG housing  78  such that when the armature shaft  64  is rotated counterclockwise in the drawing of FIG. 4 the spring  77  will not simply rotate within the MIG housing  78 , but will enable the armature  62  to be preloaded prior to completing assembly of the fuze mechanism  12 . 
     Referring now to FIGS.  5  and  13 - 17 , the lower housing  48  is shown in greater detail. The lower housing  48  includes a bottom wall  130  and a peripheral wall  132  extending about a major portion of the periphery of the bottom wall  130 . The peripheral wall  132  includes a plurality of spaced apart, raised projections  134  which are adapted to fit within the notches  116  of the MIG housing  78  (FIG.  11 ). The bottom wall  130  also includes a boss  136  having a bore  138  which receives the armature shaft  64  therethrough. A notch  140  is formed in the bottom wall  130  to provide clearance for the arm portion  90  of the bobbin member  72  such that the arm portion  90  can extend through the bottom wall  130 . A recess  142  in the bottom wall  130  supports the electric detonator  82  (FIG. 5) therein. Standoffs  144  protrude through openings in the printed circuit board  50  and are peened during assembly to secure the printed circuit board  50  thereto. The boss portion  136  also projects into the central aperture  112  in the MIG housing  78  (FIG. 12) to maintain the lower housing  48  coaxially aligned with the MIG housing  78 . With specific reference to FIG. 14, a recess  146  in the bottom wall  130  provides clearance for one electronic component mounted on an undersurface of the printed circuit board  50 . 
     In FIGS. 15-17, the lower housing  48  can also be seen to include a neck portion  148 . The neck portion  148  includes a recess  150  and an extended portion  152  having a tab  154 , the function of which will be explained momentarily. The extended portion  152  allows the recess  142  (FIGS. 13 and 14) to receive the electric detonator  82  (FIG. 5) such that a portion of the detonator  82  extends below the bottom wall  130 . A notch  142   a  is formed in the neck portion  148  so as to open into the recess  142 , thus exposing the electric detonator  82  when the detonator is inserted in the recess  142 . 
     Referring now to FIGS.  4  and  18 - 22 , the rotor  52  can be seen in greater detail. The rotor  52  includes a base portion  160  having a small neck portion  162 . The base portion  160  also includes a raised portion  164  which is integrally formed with an upper neck portion  166 . A leaf spring  168  is also integrally formed with the raised portion  164  to project generally tangentially therefrom. A recess  170  is also formed in the raised portion  164 . Recess  170  houses the stab detonator  54  (FIG. 4) therein. With specific reference to FIGS. 19 and 20, the central portion  166  includes an upper neck portion  172  integrally formed therewith. The upper neck portion  172  seats within the recess  150  (FIG. 15) of the lower housing  48 . The neck portion  162  seats within the threaded housing member  56  (FIG.  4 ), which will be described further in the following paragraphs. In this manner, the rotor  52  is mounted for rotational movement by the neck portions  162  and  172 . 
     Referring further to FIGS. 18,  20 ,  21  and  22 , a spur gear  174  is formed from a plurality of teeth formed on an arcuate portion of the base  160 . The gear  174  engages with the gear  66  formed at the outermost end of the armature shaft  64  (FIG. 5) which enables rotation of the armature shaft  64  to cause simultaneous rotation of the rotor  52 . 
     With further reference to FIGS. 18-20, the raised portion  164  can be seen to include an opening  176  formed so as to open into the recess  170 . When the rotor  52  is rotated by gear  66  (FIG.  5 ), the rotor  52  is moved into position abutting the lower portion  148  of the lower housing  48  with the electric detonator  82  (FIG. 5) disposed closely adjacent the stab detonator  54  within the recess  170  (FIG.  27 ). It will be appreciated then that the rotor  52  can only rotate about a limited arc, preferably about a maximum 90° arc. The gear  174  of the rotor  52  further disengages from the armature gear  66  after the rotor  52  has moved about 75° from its initial position. This is accomplished by forming teeth  174   a  of the gear  174 , as shown in FIG. 20, such that these teeth provide an area of clearance, designated by reference numeral  178 , where the pinion gear  66  can rotate freely without engaging the rotor  52 . Continued rotation of the pinion gear  66  and its armature shaft  64  is important for the continued electromagnetic generation of current in the coil  74 , which powers the components of the printed circuit board  50 . When the rotor  52  rotates into its armed position, the leaf spring  168  will lock the rotor  52  in the armed position by engagement with a portion of the threaded housing member  56 , as will be explained further momentarily. 
     Referring to FIG. 23, the undersurface of the fuze housing  16  can be seen. The undersurface includes three recesses  16   f  formed in a flange portion  16   b  and a hollow area  16   c  for receiving the MIG assembly  46 . An annular recess  16   d  circumscribes an opening  16   e  leading to the hollow area  16   c.    
     Referring now to FIGS.  4  and  24 - 26 , the threaded housing member  56  can be seen in greater detail. The threaded housing member  56  includes a base portion  180  having a plurality of upstanding tabs  182 . The tabs  182  fit within recesses  16   f  formed in the undersurface of the fuze housing  16  (FIG. 23) to affix the threaded housing member  56  to the housing  16 . 
     Referring to FIGS. 25 and 26, the base portion  180  further includes a raised circumferential rim  183  and the recess  184 . The raised circumferential rim  183  engages within the annular recess  16 d of the housing  16  (FIG. 23) when the threaded housing member  56  is attached to the housing  16 , and is secured thereto by ultrasonically welding the two components. Recess  184  includes a secondary recess  186  and a through aperture  188 . The through aperture  188  receives therethrough a portion of the electric detonator  82 . 
     With further reference to FIG. 25, a groove  190  is formed in the recess  184 . The groove  190  receives tab  154  of the lower housing member  48  such that the member  48  is keyed to the threaded housing  56  and is therefore not able to rotate. A second groove  192  receives the leaf spring  168  of the rotor  52  (FIGS. 18-22) such that once the rotor  52  is rotated  900  into the armed position the leaf spring  168  is engaged in the groove  192  and locks the rotor  52  in the armed position. 
     The recess  184  further includes an arcuate groove  194  which provides clearance for the portion of the armature shaft  64  and its pinion gear  66  such that same are able to extend into the recess  184  so that the pinion gear  66  can engage gear  174  of the rotor  52 . Arcuate groove  196  provides clearance for area  155  (FIG. 15) of the lower portion of the lower housing  48 . 
     With further reference to FIGS. 3 and 26, the threaded housing member  56  further includes a threaded neck portion  198  which is adapted to engage with a threaded aperture  199  in the grenade body housing  14  (FIG. 3) of the grenade  10 . The threaded housing member  56  is attached to the grenade body housing  14  simply by screwing the threaded neck portion  198  into the threaded recess  199  in the body  14 . At the lower end of the neck portion  198  is the cavity  60  in which the booster pellet  58  is inserted. 
     With brief reference to FIGS. 3 and 26, an O-ring  195  (FIG. 3) is placed around a boss  197 . The O-ring  195  fits into an annular recess  198 a (FIG. 26) to help seal the threaded housing member  56  to the body housing  14 . 
     Referring now to FIG. 27, the orientation of the rotor  52  relative to the electric detonator  82  shown when the grenade  10  is in the unarmed state. After the shipping clip  38  and the safety pull pin  36  are both removed by the user, and the grenade  10  is released, the spring force provided by the lever spring  42  urges the actuating lever  24  outwardly. This outward movement lifts the safety pin  30  out of the notch  86  in the armature  62  (FIG.  8 ). The armature  62  immediately begins to spin to dissipate the energy stored by the spring  77 . The spinning of the armature  62  causes the armature lobes  62   a ,  62   b  and  62   c  to move in and out of alignment with the lobes  125  of MIG  76 . When in alignment (i.e., “in phase”), the magnetic flux linking the coil  74  is maximized. When the lobes  62   a ,  62   b ,  62   c  are in between the lobes  125 , the flux is minimized. The result is an alternating current which is induced in the coil  74 . This alternating current is transmitted through the electrically conductive bobbin pins  94 , which are electrically coupled to the ends of the wire comprising the coil  74 , and transmitted to the printed circuit board assembly  50 . 
     As explained hereinbefore, as soon as the armature shaft  64  begins to rotate, the pinion gear  66 , which is intermeshed with gear  174  of the rotor  52 , causes immediate rotation of the rotor  52 . This degree of rotation is approximately about 75° before the pinion gear  66  disengages from the rotor gear  174 . The momentum of the rotor carries it approximately an additional 15° (as shown in FIG.  28 ), whereupon the leaf spring  168  of the rotor  52  engages within groove  192  (FIG. 24) of the threaded housing  56 , thereby essentially locking the rotor  52  in the armed position. When the rotor  52  rotates fully approximately 90°, the stab detonator  54  is placed closely adjacent the electric detonator  82 , as shown in FIG.  28 . 
     Referring now to FIG. 29, an electronic control circuit  200  of the grenade  10  is illustrated. Electronic control circuit  200  is formed on the printed circuit board  50  and generally comprises a capacitor  202  for storing the electric energy received from the bobbin pins  94 , a voltage regulator  204 , a comparator  206 , a programmable timer  208 , a first field effect transistor (FET)  210  and a second FET  212 . Associated with the comparator  206  is a resistor  214  and a capacitor  216 , which together form an RC time constant network. The programmable timer  208  makes use of capacitor  218  and resistors  220  and  222 , the values of which determine the frequency of a clock signal applied to the programmable timer  208 . 
     In operation, when the electrical signal is received from the electrically conductive bobbin pins  94 , the entire circuit  200  is immediately powered up and the voltage signal is full wave rectified by a rectifier circuit  224 . Capacitor  202  is charged and the voltage across this capacitor is then divided down and regulated to approximately 4.0 volts DC to provide operating voltage for the two integrated circuits  206  and  208 . 
     The comparator  206  is used to provide safe separation and turns on (i.e., closes), the first FET  210  approximately 4.5 seconds after the application of power to the circuit  200 . This time delay is achieved by charging capacitor  216  through resistor  214  and comparing the voltage across capacitor  216  to the comparator&#39;s internal reference voltage. Once the capacitor  216  reaches the reference voltage, the comparator&#39;s  206  output  226  is used to turn on the FET  210 . 
     The programmable timer  208  turns on FET  212  after an approximately six second (plus/minus 0.25 seconds) time delay from the application of power to the circuit  200 . The programmable timer  208  utilizes the clock signal generated by capacitor  218  and resistors  220  and  222 . Once the timer  208  has counted the  128  clock signal edges at the set frequency, its output  228  turns on the FET  212 . Once FETs  212  and  210  are turned on, the remaining energy stored by capacitor  202  is discharged at output  230  to the electric detonator  82 . Accordingly, it is only when both of the FETs  212  and  210  are turned on that the electric detonator  82  can be fired. 
     It will be appreciated then that the fuze mechanism  12  forms a high precision and reliable means for detonating the grenade  10 . The MIG assembly  46  forms a relatively low cost means for reliably providing power to the electronic control circuit  200 , which in turn precisely controls the delay time before causing detonation of the grenade  10 . The fuze mechanism  12 , once armed, is not affected by the velocity with which the grenade  10  is thrown, by its trajectory or by the orientation in which the grenade  10  lands. The delay time implemented by the electronic control circuit  200  provides a delay time accuracy within about +/− 0.25 seconds over a temperature range of about −40° F. to +140° F. The electronic control provided by the fuze mechanism  12  further provides a longer shelf life for the grenade  10 . 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification and following claims.