Abstract:
A system for correcting the aim of a weapon which is operative to launch a projectile from a barrel on a ballistic path toward a target. A rear surface of the projectile is coated with a fluorescent dye that re-emits radiation when excited by laser radiation. The system includes a source of laser radiation (strobe) pulses that form a cone of light intersecting the ballistic path of the projectile. The strobe pulses are emitted at predetermined times (T 1,  T 2,  T 3,  . . . Tn) following firing of the projectile (at time T 0 ). An optical detector receives the radiation re-emitted by a the fluorescent dye at the rear of the projectile at times (T 1   z,  T 2   z,  T 3   z,  . . . Tnz) producing measurable location signals allowing the system to measure the vertical and lateral positions of the projectile at said times, where “z” is a re-emission delay and T 1   z,  T 2   z,  T 3   z,  . . . Tnz are the respective times T 1,  T 2 ,  T 3,  . . . Tn each delayed by amount z.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from the U.S. Provisional Application No. 61/803,826 filed Mar. 21, 2013. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to weaponry and fire control. More specifically, it relates to an ammunition projectile and a fire control device for tracing the path of a projectile while in ballistic flight toward a given target, so as to improve precision and accuracy when aiming a subsequent projectile at the same or another target. 
         [0003]    The U.S. Pat. No. 8,074,555 discloses a system for tracking the lateral drift and vertical drop of an ammunition projectile while in flight to provide a precise aim point for firing one or more subsequent projectiles. With this system, a projectile is provided with an optical emitter, in the rear of the projectile housing, which produces optical strobe signals at predetermined times (T 1 , T 2 , T 3  . . . ) following firing of the projectile (at time T 0 ). An optical detector receives the optical signals and an image processor determines the lateral drift (i.e. X 1 , X 2 , X 3  . . . ) and vertical drop (i.e. Y 1 , Y 2 , Y 3  . . . of the projectile at the predetermined times (T 1 , T 2 , T 3  . . . ) following time T 0 . The subject matter of this patent is incorporated herein by reference. 
         [0004]    This system uses the real time data to correct for aiming errors due to gun jump, wind turbulence, altitude-dependant wind conditions, lot-to-lot ammunition irregularities, bore sight misalignment and the like, for use when firing subsequent projectiles. This system is optimized to function with projectiles that have adequate energy to power LED&#39;s to emit strobe light and where the ballistic trajectory angles are significant (e.g., with mortars, artillery and 40 mm systems). 
       SUMMARY OF THE INVENTION 
       [0005]    The principal object of the present indention is to improve the precision and accuracy of weaponry systems by taking into account all the factors that affect the actual ballistic flight of a projectile. 
         [0006]    It is another object of the present invention to improve the fire control device of the type disclosed in the U.S. Pat. No. 8,074,555 to render it more reliable and less expensive. 
         [0007]    It is still another object of this invention to improve the fire control device disclosed is the U.S. Pat. No. 8,074,555 to minimize power consumption of projectile-borne batteries, used for example in projectile fuses, and simplify the sensor array (detactor) that views the projectile. 
         [0008]    These objects, as well as still further objects which will become apparent from the discussion that follows, are achieved, in accordance to the present invention by providing an otherwise conventional ammunition projectile with a coating of fluorescent dye material, on or near its rear surface, whereby the dye re-emits radiation in response to excitation by laser light. 
         [0009]    The fluorescent dye, optimized to luminance in response to laser radiation, exploits a natural phenomenon known as “laser-induced-fluorescence.” The dye is coated on an external rear surface of the projectile. The coating is preferably covered by a transparent shield or coating and, for example, it may be disposed on the inside surface of a transparent window on the rear of the projectile. 
         [0010]    The present invention also provides a system for correcting the aim of a weapon that is operative to launch such a projectile on a ballistic path toward a target. The aim-correcting system preferably includes the following components:
       (1) a source of short (strokes) radiation pulses directed toward the ballistic path of the projectile for excitation of the fluorescent dye material on the projectile, such pulses being emitted at predetermined times (T 1 , T 2 , T 3  . . . ) following firing of the projectile (at time T 0 );   (2) a radiation detector for receiving strobe radiation re-emitted by the fluorescent dye on the projectile allowing for the vertical and lateral measurement of the projectile&#39;s position at times (T 1   z,  T 2   z,  T 3   z  . . . ), where “z” is the time delay of re-emission after excitation;   (3) a signal processor, coupled to the radiation detector, for processing the electronic signals produced by the detector to determine the lateral (X) and vertical (Y) coordinates of the projectile at such times (T 1   z,  T 2   z,  T 3   z  . . . ) during flight;   (4) a computer, coupled to the processor, for calculating a lateral correction and a vertical correction in the aim of the weapon; and   (5) an output device, coupled to the computer, for facilitating an adjustment in the aim of the weapon toward the target, prior to firing the next projectile.       
 
         [0016]    Using this aim-correcting device the aim of the weapon may bo adjusted after the launch of one projectile to compensate for aiming errors prior to the next launch of a projectile. 
         [0017]    By means of this system, either the signal processor or the computer calculates the lateral drift and the vertical drop of the projectile at the predetermined times. 
         [0018]    Preferably the radiation source is laser source adapted to be affixed to the weapon so that the cone of illumination of the laser source intersects with the ballistic path of the projectile and excites the photo-luminescent material. 
         [0019]    Preferably the radiation detector is a digital camera for producing an image of the ballistic path of the projectile. 
         [0020]    Depending upon the type of fluorescent dye material, the frequency of the excitation radiation may be in one of the UV, visual and IR spectral bands. 
         [0021]    Both the laser source and radiation detector may utilize narrow pass filters that provide for stealth in illuminating the projectile and simplified signal processing and optical detector construction as the technique provides for optimized signal to noise ratios. 
         [0022]    The radiation source preferably includes a narrow hand-pass filter for selectively passing a narrow spectrum of laser light to the projectile to excite the fluorescent dye. The radiation detecting device preferably also includes a narrow bend pass filter allowing only the re-emitted light from the fluorescent dye to pass to the detector, thereby minimizing the data processing required of the detector output. 
         [0023]    The output device of the system may be a display for the operator who manually adjusts the aim in the weapon&#39;s bore sight or it may automatically adjust the aim of the weapon, for example by passing the projectile drift and drop data to the fire control device of the weapon. 
         [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 time diagram of laser induced fluorescence showing the delay in response to excitation. 
           [0026]      FIG. 2  is a representational diagram showing an ammunition projectile having a fluorescent dye at its rear surface. 
           [0027]      FIG. 3  is a diagram showing a weapon and the trajectory of a projectile fired from a weapon. 
           [0028]      FIG. 4  is a diagram showing a cone of illumination of strobe light emitted by a laser source that intersects the ballistic flight path of a projectile fired from a weapon. The laser aim is slightly depressed from the bore sight for optimized intersection with the projectile&#39;s trajectory within the dispersion of the light cone. 
           [0029]      FIG. 5  is a diagram showing an optical detector which receives a light emission from a laser-illuminated fluorescent dye on an ammunition projectile. 
           [0030]      FIG. 6  is a perspective view of a weapon having a laser source to illuminate a projectile in flight. 
           [0031]      FIG. 7  is a representational diagram showing an error imparted by a fire control device which uses ballistic tables and metrological sensors to calculate a predicted hit point (gunner aiming point). 
           [0032]      FIG. 8  is a representational diagram showing how the system of the present invention identifies the X and Y location of the detected fluorescent dye strobe signal against the sky or backdrop. 
           [0033]      FIG. 9  is a representational diagram showing how the system of the present invention uses the laser-induced and emitted strobe signal to correct for the actual drift in the azimuth and inaccuracy in the ballistic fall of fired projectile (the view from fire control device at gunner&#39;s position). 
           [0034]      FIG. 10  is a representational diagram showing how the system of the present invention is used, post firing, to shift fields of view. The system measures the angular changes of the platform or camera at the same moment that the tracer&#39;s strobe signal is detected. 
           [0035]      FIG. 11  is a representational diagram showing how the fire control computer calculates a new fire control solution after measuring actual drift and drop of an observed “strobe tracer” projectile. 
           [0036]      FIG. 12  is a block diagram of the system according to the present invention which uses an algorithm that computes a solution for bore sight adjustment and/or automatically adjusts the aim point of subsequently fired projectiles. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0037]    The preferred embodiments of the present invention will now be described with reference to  FIGS. 1-12  of the drawings. Identical elements in the various FIGS. are designated with the same reference numerals. 
         [0038]    The invention provides for a method and arrangement to collect optical location signals emitted by a projectile in flight fired from a weapon while simultaneously recording movement and/or acceleration. These optical signals are transmitted from a projectile in flight in either the visual, ultraviolet and infra-red spectrum. The signals are re-emitted from the projectile at predetermined times T 2   z,  T 3   z,  etc.) following the time of firing (T 0 ). An optical detector incorporated into the weapon launcher or on an associated platform detects the angular geometry (projectile location in the sky) of the radiation re-emitted by the photo-luminescent material on the projectile as well as the duration (time length) of this re-emitted strobe in its field of view. 
         [0039]      FIG. 1  is a time diagram illustrating the time delay of fluorescence in response to excitation by laser light. As may be seen, there is a delay of about 3 milliseconds between excitation and response. This period of delay is designated hereinafter by the letter “z”. 
         [0040]    The operating sequence of the system according to the invention is depicted in Table 1 below. 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Sequence of Measurements 
               
               
                 Sequence of Measurement Methodology 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 T0-a 
                 Fire Control Displays solution based on solution 
               
               
                   
                   
                 derived from algorithm (based on previous 
               
               
                   
                   
                 measurement) 
               
               
                   
                 T0-b 
                 Measurement of (a) radial Azimuth/Elevation Barrel 
               
               
                   
                   
                 Centerline and (b) elevation of barrel/fire control 
               
               
                   
                   
                 if not aligned 
               
               
                   
                 T0-c 
                 Firing Pin Trigger pull (or hammer fall sensor) 
               
               
                   
                   
                 where a, b and c are lengths of time before T0 
               
               
                   
                 T0 
                 Set Back of Cartridge Launch 
               
               
                   
                 T1 
                 Laser emits short pulse 
               
               
                   
                 T1 + z 
                 Response of dye projectile time z later 
               
               
                   
                 T1 + z 
                 Camera image (x1, y1) of strobe response and camera 
               
               
                   
                   
                 position (xx1, yy1) 
               
               
                   
                 T2 
                 Laser emits short pulse 
               
               
                   
                 T2 + z 
                 Response of dye on projectile time z later 
               
               
                   
                 T2 + z 
                 Camera image (x2, y2) of strobe response and camera 
               
               
                   
                   
                 position (xx2, yy2) 
               
               
                   
                 T3 
                 Laser emits short pulse 
               
               
                   
                 T3 + z 
                 Response of dye on projectile time z later 
               
               
                   
                 T3 + z 
                 Camera image (x3, y3) of strobe response and camera 
               
               
                   
                   
                 position (xx3, yy3) 
               
               
                   
                 Tn + z 
                 Camera image (xn, yn) of strobe response and camera 
               
               
                   
                 etc. 
                 position (xxn, yyn) 
               
               
                   
                   
               
             
          
         
       
     
         [0041]      FIG. 2  shows an ammunition projectile  10  having a fluorescent dye  11  applied to its rear surface. The fluorescent dye preferably has a transparent or translucent coating to protect against damage or it is covered by a plastic shield or the like attached to the rear of the projectile. 
         [0042]    The system according to the invention has the capability to detect the laser-induced fluorescence (“LIF”) of a projectile while in flight. The re-emission in response to the LIF occurs the short period of time (z) after transmission of the laser strobe excitation. 
         [0043]    When a phosphor is included with the projectile dye, the system can utilize phosphor thermometry. By measuring this re-emitted light duration (z) the system can use temperature differences observed on projectiles in flight to further differentiate between and among the locations of multiple projectiles when the rate of fire is such that multiple projectiles are in flight at the same time. 
         [0044]    The system of the present invention is shown generally in  FIGS. 3, 4 and 5 ,  FIG. 3  shows a weapon  12  capable of firing projectiles in the direction of a target  14 . The projectiles impact in the region of the target in a dispersion zone  16 .  FIG. 4  shows a laser source  18  mounted on the barrel of the weapon emitting pulses (strobes) of light in a cone of illumination  20  that intersects the projectile  10 .  FIG. 5  shows light  22  re-emitted by the fluorescent dye  11  on the projectile  10 , reaching an optical detector  24  on or near the weapon  12 . This arrangement is illustrated in perspective in  FIG. 6   
         [0045]    The laser strobe emits light at precise time intervals after launch or cartridge setback. The weapon fire control system compares the actual flight position at these precise post-firing intervals to the location that is forecasted by the original solution algorithm. The“delta” positions are recorded (stored/registered) and the fire control provides a gunner with new “corrected” aim points using the registered shots. 
         [0046]    The optical signals emitted by the fluorescent dye material on the projectile are collected by an optical detector, such as an IR camera, co-located with the weapon. The image is digitally processed and X and Y coordinates of the projectile&#39;s strobe signal are identified by collection at the predetermined time intervals. When a gunner subsequently wishes to engage new targets, the computer associated with the system uses an algorithm to identify a precise aim point solution using the observed trajectory of previous shots, thereby re-measuring and re-calibrating the distance and relative target elevation for subsequent firing of the weapon. 
         [0047]    Optical emissions include light in the ultraviolet, infra red and visual wavelengths. The weapon&#39;s fire control unit has the capability to emit a cone of light (modulated to strobe at a set time) that intersects with the ballistic path of the projectile. Normally, the laser emission will be aligned vertically. The laser&#39;s horizontal alignment will drop slightly at an inclination so the top edge of the laser light illumination cone is aligned horizontally with the centerline of the barrel. This geometry allows the laser light cone to cover the entire ballistic drop of the projectile. 
         [0048]    The laser emitter  18  transmits a short, intense light strobe signal at predetermined times after set back during the flight path of the projectile. This occurs at T 1 =(time of emission+z), T 2 =(time of emission+z), T 3  =(time of emission+z), Tn=(time of emission+z) where z is the time delay in milliseconds. Using this technique it is possible to select dye combinations where the laser strobe transmits strobe signals at a given frequency and the dye&#39;s optical response differs in its response frequency. This is used by the optimize system to preclude detection by potential adversaries. It is possible, in fact, to harness the heat of the projectile to change the spectral response of the dye. 
         [0049]    The transmission of electromagnetic (optical) signals differs under certain atmospheric conditions and frequencies. The delay between the laser&#39;s production of a light strobe and the tracer&#39;s fluoresced re-emitted response, as well as the length (duration) of the response signal, are used by the fire-control detection software to eliminate detection of stray reflective light that occurs when the laser beam strobe signal reflects off of objects and to distinguish between multiple projectiles. 
         [0050]    Projectile flight geometry provides for reflection of light rearward to the gunner&#39;s position at pre-set intervals though the entire flight path. The fire control device associated with the weapon optically identifies the position (T 1 =position x 1 , y 1 , T 2 =position x 2 , y 2 , T 3 =position x 3 , y 3 , . . . Tn=position xn, yn) of the projectile at set intervals. 
         [0051]    The invention provides for a system to collect optical location signals from a projectile in flight which are excited by an optical light source (visual, ultraviolet and infra-red). The fire control uses observed time-location and angular observation date to compute an improved ballistic solution. 
         [0052]    The system allows the fire control computers to readily observe and calculate fire control solutions that reduce or eliminate (1) occasion-to-occasion errors, (2) ammunition lot-to-lot errors, and (3) bore sight misalignment. 
         [0053]    Fire control computers can readily adjust aim points using sensors to measure air temperature, pressure, firing geometry and standard muzzle velocities; however, practical considerations still limit the accuracy of calculated solutions. Lot-to-Lot ammunition variations along with occasions-to-occasion errors still result in limitations in the accuracy of fire control solutions. These errors also include those errors that result from varying wind conditions. Hence, measurement of the actual observed projectile drift and drop is necessary to allow fire control systems to provide improved aiming solutions. 
         [0054]    The current generation of fire-control devices use ballistic tables and metrological sensors to calculate a predicted hit point (gunner aiming point). Some fire control systems allow users to input manual drift and elevation offsets, but these manual offsets are generally linear. Hence, the current generation fire control devices continue to provide inaccurate aim points due to the fact that they only calculate a limited number of inputs while many “unsolved” sources of errors are not factored in. Unsolved errors include (a) bore sight misalignment, (b) lot-to-lot errors, (c) occasion-to-occasion errors and (d) limitations in existing wind sensor technology. All unsolved errors degrade the accuracy and precision of weapon fire control solutions, as illustrated in  FIG. 7   
         [0055]    The projectile&#39;s stimulated dye response occurs at discrate intervals (at T 1 + z,  T 2 + z,  T 3 + z,  . . . Tn+z, where z is the response delay) that are observed by fire control devices equipped with optical sensors. The dye&#39;s strobe response to laser illumination identifies the position of the projectile at set time intervals after set-back (time T 0 ). As illustrated in  FIG. 8 , the system according to the invention optically collect the strobe light emissions at predetermined post firing (post set-back or launch) time windows. The projectile&#39;s fluorescent dye emits light strobe pulses that are collected by the optical detector  24  (e.g. a camera) and digitally recorded. At each pre-set time window the device also records changes in the X and Y orientation of dye emission. The system&#39;s image processing software measures or signal processing algorithms calculate the X and Y location of the optical strobe emission at the pre-set time window. 
         [0056]    The system&#39;s signal processor identifies the X, Y location of the detected dye strobe signal against the sky or backdrop, as shown in  FIGS. 9 and 10 , thereby determining the actual drift and drop of the projectile  10  as seen from the gunner&#39;s position. 
         [0057]    The measurement of observed projectile drift and vertical drop are obtained by an image processor to isolate the strobe tracer&#39;s position. Simultaneously, angular changes in the detector are measured. The image processor search and detects the strobe images at pre-set intervals after firing. Alternatively, the signal processor detects the signal at pre-set intervals after firing. 
         [0058]    Post firing resonance can create shifting fields of view. The system measures the angular changes of the platform or optical detector (camera) at the same moment that the projectile&#39;s strobe signal is recorded. 
         [0059]    After detecting the actual observed azimuth drift and drop of a cartridge ( FIG. 9 ), a weapon&#39;s fire control system can utilize two methods to provide improved fire control solutions. The fire control system can (1) reset subsequent fire control solutions to use actual observed drift and drop, or (2) establish a correction factor which modifies the calculated fire control solution. Hence, use of actual observed data provides for a more accurate fire control solution. 
         [0060]    Fire control computer calculates a new fire control solution after measuring actual drift and drop of an observed “strobe tracer” projectile, as illustrated in  FIG. 10 . 
         [0061]    The diagram of  FIG. 11  shows projectile strobe signals from the next subsequently fired projectile as viewed from a gunner&#39;s position with the hit point corresponding to aim point. 
         [0062]    The system and methodology according to the invention allow fire control devices to adjust the aim point (in azimuth and elevation) so that subsequently fired cartridges hit the intended target by using actual observed azimuth drift and vertical drop. With the actual drift observed by the fire control&#39;s optical sensor, the fire control computer calculates improved solutions for new engagements. As subsequent volleys are fired, the fire control may use commonly known mathematical algorithms to further improve the precision of the corrected aim point as it repeatedly measures the actual position of cartridge drift and azimuth with a larger sample size. 
         [0063]    In the system shown in  FIG. 12  an algorithm computes a solution for bore sight adjustment and/or automatically adjusts the aim point of subsequently fired projectiles. The algorithm develops fire control solutions (aim points) using actual, observed azimuth and elevation. 
         [0064]      FIG. 12  shows a system  30  according to the invention for a weapon  12  comprising an emitter  33 , one or more sensors  34 , an optical detector (e.g. camera)  36 , a signal processor  38  and a computer  40  operating with software  42 . 
         [0065]    The sensors  34  are used to identify various parameters of the weapon  12 . Such sensors can be of various types, for example, position sensors, sensors for gun elevation, optical sensors and the like. The emitter  33  is a high-powered laser which is triggered by the computer  40  to produce a strobe of light. 
         [0066]    The optical detector  40  can be any type of image capturing device, for example a video camera, infrared camera or the like. It produces electronic signals representing the images and passes them to a signal processor  42 . The processor  42  determines X, Y location and as well as the time duration of each received response from a projectile in flight. This information is passed to the computer  40  for calculating a lateral correction and a vertical correction in the aim of the weapon  12 . 
         [0067]    The fire control device measures the angular position of the weapon  12  when the weapon fires a projectile aimed at a target. This angular position information includes a radial azimuth/elevation barrel centerline and elevation of barrel/fire control elevation, The angular position is measured by the sensors  34  and this information is also passed to the computer  40 . 
         [0068]    The computer determines the drift and drop of the fired projectile and passes this data to the fire control device for adjusting the aim point of for the next projectile to be fired. 
         [0069]    The time delay (z) of the re-emitted signal allows the computer  36  to disregard reflections received by the detector  40  from stray objects. The time duration of the re-emitted signal allows the computer to distinguish between multiple projectiles in flight which have been rapidly fired successively by the weapon  12 . Closer (and therefore hotter) projectiles will have shorter duration re-emissions that the projectiles that are further away (and therefore cooler). 
         [0070]    There has thus been shown and described a novel apparatus for correcting ballistic errors using laser induced fluorescent (strobe) tracers 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 toy the invention, which is to be limited only by the claims which follow.