Abstract:
A simulated grenade for MILES-type simulations generates a unique RF signal and a unique audio signal. A detector utilizes the time between receipt of the RF signal and the slower-traveling audio signal to determine the distance between the detector and the simulated grenade.

Description:
The United States Government has rights in this invention pursuant to Department of Energy Contract No. DE-AC04-94AL85000 with Sandia Corporation 
    
    
     CROSS REFERENCE TO RELATED APPLICATIONS 
     (Not Applicable) 
     BACKGROUND OF THE INVENTION 
     The military and the police must train for situations that involve deadly force. One widely used training system is the Multiple Integrated Laser Engagement System (MILES) that equips each participant with vest containing a series of laser light detectors and suitable electronics. Participants use weapons that fire a laser beam along with a blank round. If a participant&#39;s detector is illuminated by a weapon&#39;s laser beam, the system provides a signal to the participant and a central command that he has been killed or wounded. MILES permits participants to conduct simulations using real weapons ranging from handguns to heavier weapons without subjecting the participants to the obvious danger of using real ammunition in those weapons. 
     One common military device that has been difficult for MILES to stimulate is the hand grenade. The typical MILES grenade cannot conveniently use a laser to signify a detonation because a grenade detonates in an unpredictable position after being propelled a distance from the user. Furthermore, a grenade is not directional like a bullet or a laser; it can kill or wound multiple people who are unprotected and within a “kill radius” distance of the grenade. Accordingly, the MILES grenade must be able to provide information upon detonation that each participant&#39;s receiver will use to determine if that participant is within the kill radius of a prototype grenade. 
     S. Sampson et. al., U.S. Pat. No. 6,579,097, discloses a MILES grenade that emits encoded infrared signals on detonation. The system tracks the location of each participant and the location of detonation of the grenade, and ‘kills’ participants within the fill radius of a detonating grenade. 
     R. Lynch et al., U.S. Pat. No. 6,569,011, discloses a paintball system where locations are tracked and participants within a predetermined distance of a simulated grenade are designated as ‘killed’. 
     C. Campagnuolo, SIR H1415, discloses a MILES system where the grenade makes a distinct noise and MILES bases damage to a participant on the amplitude of the received noise signal. 
     The U.S. Department of Energy, in an undated specification for MILES equipment, requires a MILES hand grenade to have an effective kill radius of up to 10 meters, an electronic output to interface directly with the MILES equipment, and an output signal that provides an indication to participants that the grenade exploded. An undated specification sheet by Schwartz Electro-optics Inc. shows a grenade simulator designed to those specifications. The Schwartz simulator is understood to generate an RF signal of sufficient strength to be detected only within the kill radius. 
     One difficulty with existing grenade simulators based on noise is that battlefield simulations are noisy environments, and a determination of distance based on amplitude of a received audio or electronic signal is not reliable. A difficulty with simulators using multiple laser outputs is possible eye damage to participants from the high output lasers used in some of these devices. A difficulty with grenades that rely on the intensity of an RF signal is that a hand grenade is activated after being thrown by a user, and it may land in any orientation. The uncertain position of the grenade antenna with respect to the receiver provides an uncertainty in the strength of the received signal. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to provide a grenade simulator that utilizes the time difference between generation and receipt of a sound signal to determine the distance from the grenade to a participant. 
     To achieve the foregoing and other objects, and in accordance with the purpose of the present invention, as embodied and broadly described herein, 
     Additional objects, advantages, and novel features of the invention will become apparent to those skilled in the art upon examination of the following description or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form part of the specification, illustrate an embodiment of the present invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  shows a cut-away view of a grenade simulator according to this invention. 
         FIG. 2  shows details of the grenade of  FIG. 1 . 
         FIG. 3  shows details of a receiver utilized with the grenade of  FIG. 1 . 
         FIG. 4  is a flowchart of the grenade actions. 
         FIG. 5  is a flowchart of the receiver actions. 
         FIG. 6  shows the arrangement of components of a Claymore mine simulator. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIG. 1 , a MILES hand grenade  5  simulates a prototype hand grenade by having a tubular plastic case  10  with a cap  20  for sealing one end  12  and an opposed end  14  having a pivoting handle  26  that rotates around and is connected to case  10  by a slender cylindrical pivot  16 . As is well known in the art, the structure at the connection of handle  26  to case  10  may function in the manner of a hinge. Handle  26  is spring-loaded by a spring  23  ( FIG. 2 ) to move from a stored position (solid lines) parallel to the side of case  10  to a released position (dotted lines) at an angle to case  10 . Handle  26  is held in the stored position by a pin  22  that extends through aligned hole  24  in handle  26  and case  10 . 
     As in a prototype grenade, the user&#39;s throwing hand holds handle  26  against case  10  while pin  22  is pulled. The grenade is then thrown at a target. In the prototype, once the grenade is released by the thrower&#39;s hand, the spring-loaded handle moves to the released position and activates a sort (typically 5 seconds) delay prior to detonation of an explosive contained within the body of the grenade. The explosion propels fragments of the case of the grenade randomly in a 360° radius from the grenade, and has a ‘kill radius’ of about 10 feet. 
     Simulator grenade  5  contains an audio transducer  30  for generating sounds as described hereinafter, a circuit board  32  holding electronics as described in  FIG. 2 , a battery  40 , and a wire antenna  50  that extends from circuit board  32  and may wrap helically around the interior of case  10  for transmitting RF signals. This grenade generates a unique RF signal and a distinguishable audio signal, and relies on a MILES receiver  60  ( FIG. 3 ) to determine the distance from grenade  5  to receiver  60  by measuring the delay between receipt of the RF signal and the audio signal. 
     A schematic representation of a preferred embodiment of the major electronic components of grenade  5  is shown in  FIG. 2 . The actual implementation of the device includes additional biasing and other circuitry that is a matter of routine design to one of ordinary skill in the art. 
       FIG. 2  shows handle  26  in the closed position. Pin  22  has been pulled from hole  24 , so handle  26  will be rotated about pivot  16  to the release position by spring  23  as soon as handle  26  is released by the user. Handle  26  contains a permanent magnet  28  that lies in operational proximity to a magnetically actuated switch  34  embedded at the surface of case  10 . Switch  34  is held closed by magnet  28  when handle  26  is in the closed position (as shown); and switch  34  opens when handle  26  moves magnet  28  away from switch  34 . 
     A standard 9 volt ‘transistor’ battery  40  provides power for grenade  5 . Most of the electronics in the preferred embodiment operates at a lower voltage, so the output of battery  40  is applied through a voltage regulator  42  on circuit board  32  in a conventional manner to obtain a 3.3 volt output. These voltages are a matter of design choice and it is contemplated that other batteries and voltage levels may be used in the practice of the invention. 
     The ‘brain’ of grenade  5  is a microprocessor  36  such as the Atmel® AT90LS4433. A 4 MHz ceramic resonator  38  is connected to provide a reference frequency for microprocessor  36 . A voltage through switch  34  to input  35  provides an interrupt to activate microprocessor  36  when handle  26  is released. One output  37  of microprocessor  36  controls a power MOSFET switch  31  to control the application of +9 volts to audio transducer  30  through a fly-back coil  39 . Other outputs  41  communicate with an RF transmitter  44  such as a 916.5 MHz TR1000 transceiver from RFM®. Previously described antenna  50  connects to the output of transmitter  44 . A connector  33  on circuit board  32  is accessible through end  12  of case  10  and provides for programming microprocessor  36  in a manner well known to those of ordinary skill in the art. Microprocessor  36  also monitors the state of battery  40  through an input from resistive divider  46  so that a low-voltage warning may be generated. 
     Grenade  5  communicates with a receiving unit  60  preferably worn on a MILES vest (not shown). As shown in  FIG. 3 , receiving unit  60  may be carried in a small rugged box  61  that has a microphone  62  extending through one surface for receiving audio signals. In one embodiment, box  61  has a separate compartment  63  for a 9 volt battery  64  that provides circuit power in a manner similar to the grenade power supply. Box  61  may be fastened to the participant by plastic ties, a hook-loop arrangement such as Velcro®, or any other technique. Typically, box  61  would be fastened to a MILES vest worn by the participant. 
     Similar to real battlefields, simulated battlefields can be very noisy. The output of microphone  62  is band-pass filtered by filter  65  to limit the processing to signals in a predetermined frequency range, amplified by amplifier  66 , and limited to two distinct voltage levels (such as the power supply voltage of 3.3 volts and 0 volts) by limiter  67 . This voltage is then applied to an input  69  of microprocessor  68 , which microprocessor may be equivalent to the grenade microprocessor  36 . Receiving unit  60  also has a MOSFET-controlled audio transducer  70 , a MOSFET-controlled light emitting diode (LED)  72 , and an RF receiver  74  that also may be a transceiver equivalent to grenade transceiver  44 . These components are controlled by outputs from microprocessor  68  and are mounted on a circuit board (not shown) within box  61  such that outputs of transducer  70  and LED  72  communicate outside box  61  through openings in the box surface. Transceiver antenna  76  is contained within box  61 . A connector  75  for programming microprocessor  68  may be placed within or at the surface of box  61 . Construction of this device is a routine matter of engineering design for one of ordinary skill in the art. 
     The operation of the aforementioned grenade  5  and receiver  60  is as follows: A simulated explosion consists of the grenade  5  emitting an identifiable audio signal from transducer  30  and transmitting a specially coded radio signal. The area of effect of the simulated grenade explosion is estimated by measuring the distance between the grenade  5  and receiver  60 . The receiver  60  determines distance by measuring the difference in arrival times between the radio signal transmitted by transmitter  44  to antenna  76  at the speed of light and the audio signal transmitted by transducer  30  to microphone  62  at the speed of sound. 
     Sound waves travel approximately one foot per millisecond. Over a distance of a few hundred feet, the transit time for the radio signal is less than one microsecond, which means that the receiver  60  may consider the time of receipt of the radio signal to be identical to the time of transmission. Microprocessor  68  can determine the distance by counting clock pulses between receipt of the radio pulse and receipt of the audio pulse. Any time delay between audio and radio transmissions from grenade  5  is a constant property of that device which is easily factored into the distance calculation by microprocessor  68 . The acoustic and radio signals are preferably transmitted nearly simultaneously, i.e., within a millisecond of each other, to simplify the distance calculations. 
     In a preferred embodiment of the invention, as indicated in  FIG. 4 , once handle  26  is released, grenade microprocessor  36  starts a 5-second delay after which radio  44  transmits 2400 bits per second using AM modulation of a 916.5 MHz RF carrier signal from antenna  50 . The RF signal data identifies the grenade and is preferably encoded using bi-phase-L (Manchester) and consists of a 7-byte preamble, 1 frame byte, 2 data bytes, and a single byte-sum error check. Nearly simultaneously, microprocessor  36  generates an acoustic signal by driving piezoelectric transducer  30  for 12 cycles of a 3200 Hz square wave signal. To increase the likelihood of reception, the radio message and acoustic pulse are repeated four more times at 100 ms intervals. The 100 ms delay between the repeated transmissions ensures the subsequent transmissions do not interfere with earlier transmissions. 
     Following the aforementioned communications, the transducer  30  of grenade  5  transmits a 250 ms pulse at 2600 Hz and 120 dB to simulate the acoustic effects of a detonating grenade. This signal is not part of the distance-determining process discussed above, but it does inform war-game participants that a grenade detonated nearby. The grenade then may enter a diagnostic phase that “chirps” transducer  30  approximately every 10 seconds so personnel can locate the grenade. A double “chirp” is used to signify the battery needs replacing. Closing handle  26  and switch  34  puts microprocessor  36  into “sleep” mode to conserve battery power. 
     After being powered on, the receiver  60  first enters a 5-second diagnostic period that indicates battery health. LED  72  illuminates continuously to indicate that the battery&#39;s charge is adequate. A blinking LED indicates the battery is near exhaustion. The LED extinguishes after the 5-second period and the receiver begins operation. Other such housekeeping chores known in the art may also be accomplished. 
     Radio transceiver  74  ( FIG. 3 ) is tuned to receive a grenade radio signal. After receiver  74  informs microprocessor  68  that a grenade RF signal has been received, microprocessor  68  begins monitoring audio output from microphone  62 . War games typically are very noise environments; therefore, to authenticate the receipt of a signal from a grenade  5 , microprocessor  68  analyzes the amplified, filtered and limited audio output for the presence of five consecutive 3200±100 Hz square-wave signals. Since grenade  5  transmitted 12 consecutive 3200 Hz signals five times, there is a good probability that receiver  60  will authenticate a transmitted grenade signal. But it is extremely unlikely that audio inputs to microphone  62  from other objects will pass this test. 
     Once the received audio signal is authenticated, receiver  60  determines the distance from grenade  5  by measuring the time between receipt of the RF signal by receiver  74  and receipt of the audio signal by microphone  62 . For example, assuming no delay between transmission of the RF and audio signals from grenade  5 , if the audio signal is authenticated by receiver microprocessor  68  within 15 ms after the RF signal was detected, then grenade  5  detonated within 15 feet of receiver  60 . The receiver indicates this distance by generating an audible tone from transducer  70 . The tone pulsates if the grenade is determined to be in a range of between 10 and 15 feet, thereby indicating the participant has been injured by the simulated blast; and the tone is continuous if the distance is less than 10 feet, indicating the participant has been killed by the blast. 
     An output of microprocessor  68  may also communicate with conventional MILES equipment carried by the participant. Information concerning the participant&#39;s status, location, and the identity of the grenade may be transmitted to a central MILES processing station where instructors monitor the flow of action during the simulation. Conventional MILES system already provide for transmitting this information with respect to projectile injuries inflicted on participants during the war-games. 
     The receiver microprocessor  68  may also be programmed to use statistics to determine the extent of injury received by a participant. For example, if 70% of combatants who are within 10 feet of an exploding prototype grenade are killed, 25% are injured, and 5% are unharmed, then the microprocessor can apply these statistics to a determination that a receiver was within 10 feet of the grenade to give the participant a 30% chance of not being designated as killed, thereby mimicking reality. 
     As noted above, a hand grenade is a unidirectional device with a blast pattern corresponding to the radiation patterns of the radio and audio signals transmitted by the simulated grenade  5 . However, the technology utilized in this invention also extends to semi-directional weapons such as the Claymore mine. 
     The prototype M18 Claymore, a directional fragmentation mine, is 8-½ inches long, 1-⅜ inches wide, 3-¼ inches high, and weighs 3-½ pounds. The mine contains 700 steel spheres (10.5 grains) and 1-½ pound layer of composition C-4 explosive. The Claymore is mounted facing the expected position of the enemy and projects from the front of the device a fan-shaped pattern of steel balls in a 60-degree horizontal arc, at a maximum height of 2 meters, and covers a casualty radius of 100 meters. The optimum effective range (the range at which the most desirable balance is achieved between lethality and area coverage) is 50 meters. The forward danger radius for friendly forces is 250 meters. The backblast area is unsafe in unprotected areas 16 meters to the rear and sides of the mine. Friendly personnel within 100 meters to the rear and sides of the mine should be in a covered position to be safe from secondary missiles. 
     To determine the effect of a detonating Claymore simulator in a MILES exercise, both the distance and the location of a participant relative to the front of the mine must be determined. As shown in  FIG. 6 , a simulated Claymore has two spaced acoustic transducers T 1  and T 2 . Transducer T 2  preferably is on a container that replicates the prototype Claymore mine in size and weight. Transducer T 1  is mounted on an arm  92  that extends in front of the container a distance B (which distance could be on the order of one foot). T 1  and T 2  transmit acoustically distinct signals that are each processed by a receiver  80  located a distance C from T 1  and a distance A from T 2 . 
     The receiver  80  determines each of distances C and A in the same manner that the receiver  60  of  FIG. 3  determined distance from grenade  5 . The outputs from the two transducers may be distinguished from each other using either frequency or time separation in a manner well known in the art. 
     The angle α from T 1  to the receiver is α=arccos[(A 2 −B 2 −C 2 )/2BC]. This angle is easily calculated by microprocessor  68  once distances A and C have been determined as set forth above. The combination of range and angle information enables the receiver microprocessor to set an appropriate ‘killed’ or ‘wounded’ alarm based on a comparison of the position of the receiver to the known blast effect of a Claymore mine. 
     It should be apparent that there are many modifications possible with this invention, as long as the concept of using an electrical signal in combination with an audio signal to determine the kill radius of a simulated detonation is followed. For example, the term ‘MILES’ as used herein is describes any system that utilizes participant-carried detectors to simulate receipt of a weapon&#39;s effect on a participant. The Department of Energy&#39;s Engagement Simulation System is another example of such a system. Also, while the system is described for a simulated hand grenade and Claymore mine, the invention is applicable to many applications involving the determination of distance between two devices, including any simulated explosion, such as may be caused by a projected explosive or a stationary mine, among other things. And those of ordinary skill in the art will recognize that many variations of the electronic circuitry in the grenade and receiver will accomplish the desired results. The actuation of the audio and RF signals may be by timer, as for the grenade, or remote signal, as for the Claymore mine. Many variations in programming the microprocessors and coding the acoustic and RF signals may be utilized to transmit the desired information and to minimize reception problems caused by the many other RF and audio signals being transmitted during a MILES exercise. It is intended that the scope of the invention be defined by the appended claims.