Abstract:
A safety device for a front-loading weapon of the type comprising a mortar barrel having a closed breech end and an opposite open end for launching a mortar projectile. The device includes at least one sensor, configured for mounting adjacent the mortar barrel, for sensing a mortar projectile upon its insertion in the barrel and an electronic circuit, coupled to said sensor, for detecting movement of the mortar projectile past said sensor, thereby to detect the presence of the projectile in the barrel.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from the U.S. Provisional Application No. 61/924,749 filed Jan. 8, 2014. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention concerns a safety device for a front-loading weapon, commonly called a “mortar,” which launches projectiles in a high trajectory. The mortar comprises a relatively short barrel having a closed breech end, attached to a breech block forming a base, and an opposite open end, aimed upward, for ejecting the projectile. The mortar is loaded by inserting self-propelled projectiles into the open end of the barrel. Each round is inserted, front end forward, and falls backward inside the barrel. At the breech end of the barrel the projectile is automatically ignited by a firing pin and propelled forward by the propulsive gases ea itted from its tail end. 
         [0003]    While such an weapon is relatively simple and easy to use, it has been the source of frequent and serious accidents resulting in the loss of life and limb to the attending soldiers, called “mortar men.” Such accidents arise from a dangerous combination of circumstances, such as misfires, hang-fires (failure to fire right away) and double loading of the mortar rounds, that lead to inadvertent detonation of this ammunition. 
         [0004]    Modern mortars are capable of high rates of fire (up to 30 rounds for the first one or two minutes of fire). Mortar men are trained to detect hang fires, but in the frenzy of firing, hang fires and misfires can go undetected with catastrophic results. 
         [0005]    The chart below is a short list of known accidents associated with a mortar crew inadvertently double loading a mortar. This situation can easily occur when (1) the mortar has a “low order” event, (2) the mortar crew is rushed and does not observe proper firing, and/or (3) the mortar suffers a hang-fire and the crew is unaware that a mortar round did not fire and exit the barrel before a new round was inserted. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
             
           
               
                   
               
               
                 Unit/ 
                 Mortar 
                 Casualties 
                 Probable 
               
             
          
           
               
                 Location 
                 Year 
                 Type 
                 Killed 
                 Wounded 
                 Cause 
               
               
                   
               
             
          
           
               
                 US Marines 
                 2013 
                 60 mm 
                 7 
                 8 
                 Double 
               
               
                 (Nevada) 
                   
                   
                   
                   
                 loading and 
               
               
                   
                   
                   
                   
                   
                 Hang Fire 
               
               
                 Romanian 
                 2010 
                 Unspeci- 
                 3 
                 3 
                 Double 
               
               
                 Army 
                   
                 fied 
                   
                   
                 loading 
               
               
                 British 
                 1982 
                 81 mm 
                 3 
                 2 
                 Double 
               
               
                 Army 
                   
                   
                   
                   
                 loading 
               
               
                 US Army 
                 2006 
                 81 mm 
                 1 
                 4 
                 Double 
               
               
                 (Hawaii) 
                   
                   
                   
                   
                 loading 
               
               
                 Ukrainian 
                 2008 
                 120 mm  
                 1 
                 3 
                 Double 
               
               
                 Army 
                   
                   
                   
                   
                 loading 
               
               
                 Finnish 
                 2005 
                 120 mm  
                 1 
                 5 
                 Double 
               
               
                 Army 
                   
                   
                   
                   
                 loading 
               
             
          
           
               
                 Total 
                 16 
                 40 
                 56 Casualties 
               
               
                   
               
             
          
         
       
     
         [0006]    Some attempts have been made to address this situation by providing ways to prevent double loading in mortars. One important reference is the U.S. Pat. No. 5,965,835 to Karl Gartz entitled “Apparatus for Monitoring the Loaded or Unloaded Condition of a Front Loading Weapon.” This patent discloses a mortar safety device that employs an array of acoustic sensors located inside the barrel and in the breech block. The sensors are piezoelectric devices tuned to measure characteristic vibrations of the round impacting the firing pin, in particular the reaction of the base plate as well as oscillations of the barrel. A filter is used to collect only those signals from such sensors that are compatible with the impact of the round on the firing pin. After processing these signals, information provided by the electronic controller is used to turn on an alert lamp and/or a mechanical device in the muzzle that prevents further loading. 
         [0007]    The fact that the sensors are located inside the barrel is a serious drawback of this system because it is not easy retrofit this equipment to existing mortars. The patent fails to teach how the sensors are to be installed, nor does it describe in detail how the tuning is realized. 
         [0008]    The U.S. Pat. No. 3,698,282 of Zigmund Albatys, issued Oct. 17, 1972, and entitled “Mortar Safety Device for Preventing Double Loading” describes a purely mechanical device that prevents loading of a mortar round if the barrel has not been cleared by firing a previously loaded projectile. A mechanism located in the muzzle uses a series of arms and locking devices to block the loading of a fresh round until the prior round is fired. This mechanical device returns to its initial position once the barrel is cleared so that a new round can be loaded into the weapon. 
       SUMMARY OF THE INVENTION 
       [0009]    A principal objective of the present invention, therefore, is to provide a warning device for mortar men to prevent an accidental and dangerous combination of circumstances that can lead to inadvertent detonation of ammunition and the loss of life and limb. 
         [0010]    This objective, as well as other objectives which will become apparent from the discussion that follows, are achieved, in accordance with the present invention, by providing a safety device for a front-loading weapon that comprises: 
         [0000]    (a) at least one sensor, configured for mounting adjacent the mortar barrel, for sensing a mortar projectile in the barrel; and
 
(b) an electronic circuit, coupled to the sensor, for detecting the mortar projectile as it moves past the sensor, thereby to detect the presence of the projectile in the barrel.
 
         [0011]    Advantageously, the safety device also comprises a warning device coupled to the electronic circuit, for indicating by a sound and/or a light the presence of the mortar projectile in the barrel. 
         [0012]    Advantageously also, the electronic circuit is operative to detect a movement of the projectile past the sensor both when entering the barrel and when exiting the barrel. 
         [0013]    Preferably the sensor is configured for mounting on the mortar barrel adjacent the open end of the barrel. Alternatively or in addition, the sensor can also be configured for mounting at the breech end of the mortar barrel or at a point between the breech end and the open end of the barrel. 
         [0014]    The preferred embodiments of the invention incorporate various types of sensors, and their associated electronic circuits, for sensing the cartridge or jacket of the projectile. In one preferred embodiment the sensor includes a metal detector, such as a magnetic induction coil, and the electronic circuit is operative to detect changes in an electric current in the coil caused by a movement of the projectile past the coil. The magnetic coil can be arranged on one side of the barrel but it preferably forms a toroid surrounding the barrel. 
         [0015]    In another preferred embodiment the sensor includes a primary coil and a secondary coil, and the electronic circuit is operative (1) to pass an electric current through the primary coil, and (2) to detect changes in an electric current induced in the secondary coil caused by a movement of the projectile past the secondary coil. 
         [0016]    In another preferred embodiment the sensor includes a permanent magnet and an adjacent coil of wire windings surrounding the barrel. The electronic circuit is operative to detect when a metal projectile passes through the barrel at the location of the wire windings, the resulting fluctuations in the magnetic flux and the associated current indicating that a metal projectile has transited the barrel. 
         [0017]    In still another embodiment the sensor includes a thermal sensor and the electronic circuit is operative to detect changes in temperature or the thermal radiation produced by hot propulsive gases emitted by the projectile as it is launched from the barrel. In this case the thermal sensor is preferably configured for mounting on the mortar barrel adjacent to its open upper end. 
         [0018]    In yet another embodiment the sensor includes a visible or ultraviolet light sensor and the electronic circuit is operative to detect the light of the pyrotechnic propulsive emissions from the tail of the projectile as it is launched from the barrel. In this case also, the light sensor is preferably configured for mounting on the mortar barrel adjacent its open upper end. 
         [0019]    In another embodiment the sensor includes a radiation emitter and a radiation sensor disposed on opposite sides of the barrel and the electronic circuit is operative to detect changes in radiation received by the radiation sensor caused by the passage of the projectile between the emitter and the sensor. In this case too, the emitter and the sensor are configured for mounting on the mortar barrel adjacent the open end of the barrel. 
         [0020]    The radiation employed with this system is preferably either visible light or ultraviolet light and the emitter is preferably a laser. 
         [0021]    Finally, the safety device according to the invention advantageously comprises also a lineal accelerometer configured for mounting on the mortar barrel, and a second electronic circuit, coupled to the accelerometer, for detecting the launch of the projectile from the barrel, thereby to determine the instant of launch. Coupled with the projectile sensor at the open end of the barrel, this enables the system to determine the exit velocity of the projectile from the barrel. 
         [0022]    In summary, the mortar safety device according to the invention first detects a projectile entering the barrel of a mortar and thereafter the same projectile exiting the barrel, provides an audible and/or visual warning when the projectile has not timely exited the barrel. The safety device preferably provides (1) a mid-barrel sensing of the change in magnetic flux (field) when a projectile passes within a barrel using an outer coil or magnetometer, and/or (2) sensing of the projectile (either visually or by the light or temperature of the propulsive gases) at the open end of the barrel when projectile is loaded and when it exits the barrel. By using one of these forms of sensing and with the option to couple a shock detector to determine the instant that each projectile fires, the device can identify a dangerous condition (that a projectile has entered the barrel but has not yet fired and exited the barrel) and thus warn the operator not to load a new round. 
         [0023]    The various forms of projectile sensing according to the invention are summarized in the following table. The table indicates those sensors that are preferably mounted adjacent the open muzzle end of the mortar barrel. The magnetic sensors can be mounted at any point along the barrel. 
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
           
               
                   
               
               
                 Methods for Sensing Projectile entering and departing barrel. 
               
             
          
           
               
                   
                   
                 Ease of Retrofit to 
               
               
                 Approach 
                 Concept 
                 USMC Mortars 
               
               
                   
               
             
          
           
               
                   
                   
                 Magnetic 
                 Variation (flux) of 
                 Ease to retrofit in 
               
               
                   
                   
                 Induction 
                 the magnetic field 
                 USMC mortar External 
               
               
                   
                   
                   
                 due to change in the 
                 coils and power supply 
               
               
                   
                   
                   
                 metallic mass of the 
                 Electronic controller 
               
               
                   
                   
                   
                 mortar-round system 
                   
               
               
                   
                   
                 Magnetic 
                 Magnetometers 
                 Possible limitation due 
               
               
                   
                   
                   
                 located outside the 
                 to external metallic 
               
               
                   
                   
                   
                 barrel detect the 
                 sources no related to 
               
               
                   
                   
                   
                 flux as a mortar 
                 the mortar-round system 
               
               
                   
                   
                   
                 projectile passes 
                   
               
               
                   
                   
                   
                 thru the mortar. 
                   
               
               
                   
                 Muzzle 
                 Thermal 
                 Thermal (IR) sensor 
                 This system will detect 
               
               
                   
                 Sensor 
                   
                 located at the 
                 the flash and hot gases 
               
               
                   
                   
                   
                 muzzle 
                 from the muzzle blast. 
               
               
                   
                   
                   
                   
                 Not easy to retrofit 
               
               
                   
                   
                 Laser/ 
                 Laser/light emitters 
                 Possible to combine with 
               
               
                   
                   
                 Light 
                 in the muzzle with 
                 velocity measurement. 
               
               
                   
                   
                   
                 sensors to detect the 
                 Not easy to retrofit, the 
               
               
                   
                   
                   
                 loading and firing of 
                 detection system shall be 
               
               
                   
                   
                   
                 the round 
                 installed in the muzzle. 
               
               
                   
                   
                   
                   
                 Possible improvement for 
               
               
                   
                   
                   
                   
                 a complete redesign of 
               
               
                   
                   
                   
                   
                 the mortar system 
               
             
          
           
               
                 Shock 
                 Acceler- 
                 Lineal 
                 This possible system 
               
               
                   
                 ometers 
                 accelerometers 
                 only will sense if the 
               
               
                   
                   
                 sensors located 
                 round has been fired. 
               
               
                   
                   
                 outside the barrel 
                 Easy to retrofit 
               
               
                   
               
             
          
         
       
     
         [0024]    For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiments of the invention as illustrated in the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  is a representational diagram of a mortar illustrating the double-loading hazard addressed by the present invention. 
           [0026]      FIGS. 2   a  and  2   b  are perspective views of a mortar showing an externally mounted/retrofitted metal detector type device at two different locations on the mortar barrel. 
           [0027]      FIGS. 3   a  and  3   b  are perspective views of a mortar showing a radiation sensor type device ( FIG. 3   b ) located at an upper, open end of the barrel. 
           [0028]      FIG. 4   a  shows two schematic diagrams of a dual-coil magnetic detector type device with an adjacent projectile in different positions;  FIG. 4   b  illustrates a frequency change due to passage of the projectile. 
           [0029]      FIG. 5  is a representational diagram showing the magnetic field lines associated with metal body mortars with a dual-array magnetic detector device. 
           [0030]      FIG. 6  is a representational diagram showing a mortar projectile passing through a mortar barrel with a magnet and coil winding configuration. 
           [0031]      FIG. 7  is a detailed representational diagram of a metal detector type device with a permanent magnet and a coil winding. 
           [0032]      FIG. 8  is a cut-away view of a mortar barrel and a projectile, illustrating how magnetic fields fluctuate when the projectile moves from one to the next of three successive positions. 
           [0033]      FIG. 9  is a representational diagram showing a projectile in a mortar barrel with an adjacent permanent magnet and a coil winding configuration of the type shown in  FIG. 7 . 
           [0034]      FIG. 10  is an FEM Mesh diagram of a mortar barrel with the magnet and coil configuration shown in  FIGS. 7 and 9 , illustrating the magnetic flux/field strength surrounding the projectile as it passes the magnet and coil. 
           [0035]      FIGS. 11   a ,  11   b ,  12   a ,  12   b ,  13   a ,  13   b ,  14   a ,  14   b  and  15  are representational diagrams illustrating the magnetic flux/field strength surrounding the projectile in a mortar barrel as it passes the magnet and coil configuration of  FIG. 9  at successive points in time. 
           [0036]      FIG. 16  is a perspective view of a projectile detector device according to the invention, mounted on the mortar with an audible and visual warning alarm. 
           [0037]      FIGS. 17   a  and  17   b  are close-up and distant perspective views, respectively, illustrating a projectile detector device according to the invention, mounted on the muzzle break with an audible and visual alarm. 
           [0038]      FIG. 18  is a voltage/time diagram illustrating the voltage induced in the winding coil of the magnet/coil configuration of  FIG. 9 , with a projectile falling in the mortar tube (pre-setback) with a velocity of 3.13 m/sec. 
           [0039]      FIG. 19  is a magnetic flux/time diagram illustrating the flux induced in the winding coil of the magnet/coil configuration of  FIG. 9  by traverse of a projectile in the mortar barrel. 
           [0040]      FIG. 20  is a voltage/time diagram illustrating the voltage induced in the winding coil of the magnet/coil configuration of  FIG. 9 , with a projectile under launch conditions traversing the mortar barrel at a velocity of 220 m/sec. 
           [0041]      FIG. 21  shows the mortar safety device according to the present invention comprising a metal sensor, an associated electronic circuit and an audible and/or visual warning device. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0042]    The preferred embodiments of the present invention will now be described with reference to  FIGS. 1-21  of the drawings. Identical elements in the various figures are designated with the same reference numerals. 
         [0043]      FIG. 1  illustrates the problem to which the present invention is addressed. This diagram shows how a mortar is subject to a “double projectile feed” creating a detonation hazard. When a projectile is inserted in a mortar at the upper, open end of the barrel, drops down to the lower, breech end where it is ignited, either right away by its contact with a firing pin at the breech end or on demand in response to a trigger pull. If, due to a hang-fire or due to confusion during firing, a second projectile is inserted before the first projectile is launched, the first projectile will collide with the second, causing an explosive hazard that can result in injury or death of the attendant mortar men. 
         [0044]      FIG. 2   a  illustrates an externally mounted/retrofitted metal detector mounted on a mortar barrel approximately midway between the open, upper end and the lower, breech end mounted on the breech block.  FIG. 2   b  shows two metal detector devices mounted on the mortar barrel near each end. The metal detectors include a sensor for sensing the metal jacket of a mortar projectile upon its insertion in the barrel and an electronic circuit, coupled to the sensor, for detecting movement of the mortar projectile past the sensor, thereby to detect the presence of the projectile in the barrel. 
         [0045]      FIG. 3   a  depicts a radiation sensor-type device on the muzzle of a mortar barrel (with a sensor not shown inside the muzzle break). The radiation sensor detects radiation (visible light, heat or ultraviolet) emanating from the base of the projectile as it is launched by the pyrotechnic propellant.  FIG. 3   b  shows a radiation emitter and sensor located at the upper end of the barrel with a second metal detector positioned lower down on the barrel. Radiation produced by the emitter, which is preferably a laser, is continuously sensed by the radiation sensor unless and until it is interrupted or blocked by the passage of a projectile between the emitter and sensor. 
         [0046]      FIG. 4   a  illustrates a projectile passing through two wiring coils resulting in both a voltage and a frequency change that is sensed by an electronic circuit (not shown). One wiring coil has a voltage applied, creating a magnetic field, and the second coil encounters a fluctuation in frequency when the projectile passes between the coils, as is illustrated in  FIG. 4   b.    
         [0047]      FIG. 5  shows a dual-sensor design with the sensors located near the upper and lower ends of a mortar barrel. The diagram illustrates magnetic field lines associated with a metal jacket mortar projectile. 
         [0048]      FIG. 6  depicts a projectile entering and exiting a mortar barrel with a toroidal permanent magnet and a coil wiring. 
         [0049]      FIG. 7  is a representational diagram of a sensor device with a permanent magnet and coil winding surrounding a mortar barrel. 
         [0050]      FIG. 8  shows the sensor device of  FIG. 7 , illustrating how the magnetic field fluctuates when a projectile moves past the sensor inside the mortar barrel. 
         [0051]      FIG. 9  shows a mortar projectile, a permanent magnet and a coil winding surrounding a mortar barrel, forming the sensing device of  FIG. 7 . This configuration is used in the FEM Mesh illustration of  FIG. 10  and the illustrations of field strength (field fluctuations) depicted in  FIGS. 11-15 . 
         [0052]      FIG. 10  shows an electromagnetic analysis FEM Mesh with a projectile in a mortar barrel shown in cross section. 
         [0053]      FIGS. 11-15  depict the magnetic flux adjacent one side of a mortar barrel produced by the sensor device of  FIG. 7  having a permanent magnet and coil winding surrounding the barrel. These figures show the changes in magnetic flux at successive points in time as a projectile moves through the barrel past the magnet and coil. 
         [0054]      FIG. 16  shows a mortar safety device with an audible and visual warning according to the present invention. 
         [0055]      FIGS. 17   a  and  17   b  show a muzzle mounted safety device according to the present invention. 
         [0056]      FIG. 18  is a voltage/time diagram of the signal produced by the mortar safety device of  FIG. 7  as a projectile is dropped down a mortar barrel (pre-setback) and passes the magnet and coil sensor with a velocity of 3.13 meters per second. 
         [0057]      FIG. 9  shows the flux linkage (W) produced by the mortar safety device of  FIG. 7  versus projectile position (mm) as a projectile traverses the mortar barrel. 
         [0058]      FIG. 20  is a voltage/time diagram of the signal produced by the mortar safety device of  FIG. 7  as the projectile passes the magnet and coil surrounding the barrel at 220 meters per second prior to exiting the mortar barrel. 
         [0059]      FIG. 21  shows the mortar safety device according to the invention comprising a metal sensor  16 , an associated electronic circuit  7  and an audible and/or visual warning device  15 . The metal sensor shown in this case comprises a single coil winding  8 . Alternatively, the metal sensor may include both a primary coil and secondary coil as shown in  FIG. 4   a.    
         [0060]    The mortar barrel  1  is provided with a breechblock  2  carrying a firing pin  3  to ignite the propellant in the projectile  5 . When the projectile  5  is dropped into the open, upper end of the barrel  1  and its igniter contacts the firing pin  3  and, upon firing, ignites the propellant. 
         [0061]    A driver  12  in the electronic circuit  7  passes current through the coil winding  8  and senses fluctuations in the signal caused by the passage of the projectile as it leaves the barrel. A microprocessor  14  keeps track of the entry and exit of projectiles to and from the mortar barrel and causes the warning device  15  to sound the alarm if a projectile remains in the barrel longer than expected. 
         [0062]    An acceleration sensor  4  is provided to determine the moment of launch of each projectile. This sensor is also connected to the electronic circuit  7  through a conductor  6 . The circuit  7  includes an input amplifier  9 , an analog-to-digital converter  10  and a digital frequency filter  11 , in turn connected to the microprocessor  14 . 
         [0063]    The frequency range of the digital filter  11  is selected such that only those frequency portions of the measuring signal are passed which are characteristic of the launch of a projectile. The digital signal values obtained at the output of the frequency filter  11  are thereafter passed to the microprocessor  14  which measures the time between the launch of the projectile and its exit from the mortar barrel (as sensed by the metal detector  15 ) and computes the exit velocity of the projectile. 
         [0064]    There has thus been shown and described a novel mortar safety device which fulfills all the objects and advantages sought therefor. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification and the accompanying drawings which disclose the preferred embodiments thereof. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention, which is to be limited only by the claims which follow.