Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SYSTEM FOR MEASURING THE YAW, SPIN AND MUZZLE VELOCITY OF AN
AMMUNITION PROJECTILE
BACKGROUND OF THE INVENTION
[0001] While fire control systems have improved as sensor
fidelity, electronic miniaturization and improvements in
computational capabilities came of age, the inability to measure
projectile yaw in operational weapons remains an unsolved
problem that stands in the way of improvements in the precision
aiming of firearms and weapons.
[0002] Specialized high-speed imaging and laboratory
methodologies and equipment which are presently used to
determine and measure yaw cannot be readily incorporated into
firearms and weapons used in the field.
[0003] As a projectile exits a barrel it enters a "dirty"
environment that obscures simple detection due to the wash of
gases from the propellant (smoke, powder residue, un-burnt
powder and bright illumination from the propellant burn). This
situation adds to the difficulty of measuring projectile yaw
and/or determining projectile motion parameters such as velocity
and spin.
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[0004] As a consequence, no practical or effective solution
is presently available for firearms and weapons (hereinafter
collectively referred to as "weapons") to measure initial flight
parameters where projectiles are fired from weapons. The
measurement of initial flight parameters allows fire control
systems to record repeatable bias errors which include yaw and
muzzle velocity. Ballistic algorithms can use recorded
measurements in lot performance to improve predictive algorithms
thus improving the precision of aim points and shooting.
[0005] Numerous methods of chronographic measurement of
muzzle velocity are known in the art. The rate of change of
velocity (acceleration/de-acceleration) is not normally
measured, however, because it must be based upon multiple
measurements of projectile velocity.
[0006] Variations in projectile spin create some variation in
shot-to-shot precision but the magnitude of spin variation, as
compared to the effect of yaw, does not significantly affect the
flight ballistics in a way that can be translated into aiming
improvements. Therefore, spin has also rarely been measured,
even in the laboratory.
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SUMMARY OF THE INVENTION
[0007] A principal objective of the present invention,
therefore, is to provide a flight parameter measurement system,
for use in the field with an operational weapon, that can
determine projectile muzzle velocity, spin and yaw at a
plurality of points during projectile's initial flight after
barrel exit through a measurement device housed in a flash
suppressor or muzzle break.
[0008] It is a further objective of the present invention to
provide a flight parameter measurement system for use with an
operational weapon that can determine the rate of change of
muzzle velocity, spin and yaw.
[0009] 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 plurality of
marks arranged in at least one circular row around the
projectile body, with the row of marks extending perpendicular
to the longitudinal axis of the projectile and being of such
character as to be seen by an optical detector while exiting the
barrel.
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[00010] Preferably at least some of the marks have distinctive
patterns such that the optical detector can discriminate between
marks with different patterns.
[00011] Alternatively or in addition, at least some of the
marks have distinctive colors such that the optical detector can
discriminate between marks with different colors.
[00012] Alternatively or in addition, at least some of the
marks are luminescent.
[00013] All of the marks may have the same shape, or some of
the marks may have a different shape than others. For example,
at least some of the marks may be in the shape of a cross.
[00014] Based on the use of such an ammunition projectile, the
present invention provides a projectile flight parameter
measurement system which is usable with a weapon to accomplish
the objectives described above. This system preferably includes
the following components:
(a) a tubular housing which is configured to be attached to the
weapon with its longitudinal axis aligned with the central
longitudinal axis of the gun barrel, so as to receive launched
projectiles as they leave the muzzle end of the barrel;
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(b) at least one light beam emitter arranged in the housing for
illuminating the projectiles as they pass through the housing;
(c) at least one electronic imager arranged in the housing for
viewing the projectile markings that are illuminated by the
emitter, and for producing electronic signals representing
digital images of the projectiles; and
(d) an electronic computational logic device, coupled to the
electronic imager(s), for processing the electronic signals to
determine one or more initial flight parameters of a projectile
that has passed through the housing. According to the invention,
these projectile flight parameters comprise one or more of the
following:
(1) projectile muzzle velocity;
(2) projectile spin;
(3) projectile yaw;
(4) projectile rate of change of muzzle velocity;
(5) projectile rate of change of spin; and
(6) projectile rate of change of yaw.
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[00015] The present invention makes it possible to measure the
asymmetrical gas expansion forces on the base of a projectile
that is exiting a barrel. When utilizing induced fluorescence,
laser or LED light can be used to detect the relative movement
and position of the projectile with respect to the centerline of
the barrel so as to measure the asymmetric expansion (leakage)
of gases as it exits the barrel.
[00016] The beam emitter provides strobe illumination and the
electronic imager captures images of the projectiles as they are
illuminated by the emitter. In particular, the emitter strobes
the illumination and the imager captures stop-action images at
the instants of illumination.
[00017] Preferably, imagers capture two or more successive
views of the projectiles as they pass through the housing. For
example, the imager may capture views at different angles around
a circumference of the projectiles as they pass through the
housing or they may capture images at the same angle at
successive points along the flight path.
[00018] According to a preferred embodiment of the invention,
the system emits a radiation beam or a beam of ions. The
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radiation beam may be in one of the UV, visual and/or IR
spectral bands, for example.
[00019] According to another preferred embodiment of the
invention, the weapon includes an aiming device for the gun
barrel, and the logic device is coupled with the aiming device
for adjusting the aim of the barrel in dependence upon the
flight parameters.
[00020] The apparatus according to the invention thus utilizes
short-duration strobe illumination of a projectile that has
special marks on its surface. As the strobe illuminates the
projectile, the relative position and attitude of the projectile
is observed.
[00021] Advantageously, the projectile markings are imprinted
with specialized dyes that are visible when exposed to
illumination (strobes) at certain wavelengths. This facilitates
optical tracking of the index marks on the projectiles exiting
the barrel and traveling through a flash suppressor or muzzle
break.
[00022] It is desirable to use laser or LED light and "induced
fluorescence" obtained from different colored fluorescent dyes
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used for the markings imprinted on the projectile, denoting the
indexed rotation position of the projectile, to increase the
visibility of the markings. This technique provides for a high
signal-to-noise ratio which is very useful when using electronic
and signal processing equipment to detect movements of the
projectile in a "dirty" environment. As previously noted, the
environment for observation is "washed" with smoke, un-burnt
powder residue, burnt powder residue and burning propellant so
that it is difficult, if not impossible, to determine the
position and attitude of the projectile by viewing only its
outline.
[00023] When utilizing induced fluorescence, laser or LED
light can be used to detect the relative movement and position
of the projectile with respect to the centerline of the barrel
so as to measure the asymmetric expansion (leakage) of gases
when a projectile exits a barrel.
[00024] Generally speaking, projectiles do not undergo a
complete rotation in a distance less than 250-300 millimeters.
If a yaw and muzzle velocity device was devised to observe a
complete rotation, it would probably become too long and bulky
for rifleman. Accordingly, multiple viewing points and
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differentiated indexing points on a projectile allow for a
precise measurement of yaw and muzzle velocity over a short
distance, allowing the device to have an optimum compact nature.
[00025] The following Table illustrates the relationship of
the muzzle velocity and spin to measurement distance for three
different weapon systems.
TABLE
.338 Data (Rifle System)
2890 rotation/second 3.66 rotations/meter
790 meters/second 273 mm 1 rotation 360 degrees
Measurement Length 91 mm 1/3 rotation 120
degrees
.50 Cal Data (12.7mm)(Machine Gun)
2707 rotation/ second 3.18 rotations meter
850 meters/second 314 mm 1 rotation 360 degrees
Measurement Length 105 mm 1/3 rotation 120
degrees
40mm x 53 Data (I117)Automatic Grenade Launcher)
200 rotations second 0.83 rotations meter
240 meters/second 1200 mm 1 rotation 360 degrees
Measurement Length 200 mm 116 rotation 60 degrees
[00026] To measure
the motion parameters (muzzle velocity,
spin and axis rotation (yaw) as well as acceleration/de-
acceleration of the projectile, the projectile is illuminated
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two or more times as it exits the barrel thru the muzzle of the
weapon. After each illumination and image capture, the positions
of the projectile's indexing marks are determined and stored.
The illumination sequence is repeated at known elapsed times
following barrel exit. As a result, this process allows for
accurate determination of the yaw, spin and muzzle velocity, as
well as any acceleration/de-acceleration of the projectile in a
compact device.
[00027] Recorded projectile measurements are then transmitted
to a fire control system (internal or external to the flash
suppressor or muzzle break). This allows the fire control
computer to classify the projectile's performance in the
particular individual weapon system. This can be done as part of
a registration methodology or for improved prediction of aiming
points. Since ammunition muzzle velocity, spin and yaw vary from
ammunition lot-to-lot and from gun-to-gun, the detection of
changes in rotational axis, yaw and muzzle velocity for each
individual weapon provided with the system of the present
invention result in continuous improvements in aiming precision.
[00028] In summary, the system makes it possible to measure
the precise muzzle exit velocity, spin and yaw of the projectile
while at two or more positions while still transiting a flash
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suppressor or muzzle break. The system can also provide the
individual weapon with a sensor input leading to better
precision and ballistic prediction when the measurements are
incorporated into fire control computations.
[00029] 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
[00030] Fig. 1 is a Cartesian coordinate diagram showing
various angles of yaw.
[00031] Fig. 2 is a time sequence diagram showing a
projectile, provided with markings according to the invention,
leaving the barrel of a weapon.
[00032] Fig. 3 is a top and side view of the projectile of
Fig. 2 showing rotational axis changes.
[00033] Fig. 4 is a side view of the projectile of Fig. 2
showing successive angles of yaw.
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[00034] Figs. 5 and 6 are front and side views of a flash
suppressor for RWS and 40mm AGLs incorporating an emitter (Fig.
5) and an optical detector (Fig. 6) according to the invention.
[00035] Fig. 7 is a block diagram of the system according to
the invention incorporated into a flash suppressor for a 40mm
AGL.
[00036] Fig. 8 is a schematic view of a flash suppresser
showing gas wash, powder burn and debris that obscures
observation of the fired projectile.
[00037] Fig. 9 is a schematic view of a flash suppresser
showing the flash illumination of a projectile in first
position.
[00038] Fig. 10 is a schematic view of the flash suppresser of
Fig. 11 showing the image capture of markings on the projectile
in the first position.
[00039] Fig. 11 is a schematic view of a flash suppresser
showing the flash illumination of a projectile in a second
position.
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[00040] Fig. 12 is a schematic view of the flash suppresser of
Fig. 13 showing the image capture of markings on the projectile
in the second position.
[00041] Fig. 13 is a schematic view of a flash suppresser
showing the flash illumination of a projectile in a third
position.
[00042] Fig. 14 is a schematic view of a flash suppresser of
Fig. 15 showing the image capture of markings on the projectile
in the third position.
[00043] Figs. 15a, 15b, 15c and 15d are cutaway views of a
flash suppressor at successive instants of time as a projectile
is launched and imaged as it passes through the device.
[00044] Figs. 16a and 16b constitute a flow chart showing the
operation of the system according to the present invention.
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DESCRIPTION OF THE PREFERRED EMBODIMENTS
[00045] The preferred embodiments of the invention will now
be described with reference to Figs. 1-16 of the drawings.
Identical elements in the various figures have been designated
with the same reference numerals.
[00046] The system according to the invention utilizes the
following components:
[00047] Projectiles provided with high contrast markings (e.g.
color dyed) which may include luminescent characteristics.
[00048] Strobe illumination of the projectiles as they exit
the barrel of a gun and pass through a flash suppressor or
muzzle break.
[00049] Imagers that capture positions of the projectile
markings. Three measurement points are desired so that the rates
of change of the parameters can be measured.
[00050] Optical measurements are captured and recorded,
preferably from multiple angles to confirm the rotation axis.
[00051] A computer with a signal processor, coupled to the
imagers, determines the locations of the projectile markings at
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successive instants of time and computes and records the yaw,
spin and muzzle velocity and the rates of change in these
parameters.
[00052] Generally, for integration into a weapon system it is
advantageous to incorporate the illumination and image detection
into flash suppressor or muzzle break. By incorporation of
these elements into a robust housing, additional spill-light is
not transmitted. The illumination of the projectile coincides
with the light resulting from propellant burn, commonly known as
"muzzle flash". By incorporating the illuminators and
electronic imagers into a common robust housing it is possible
to utilize the flow of un-burnt powder in a manner that
optimizes recording of the projectile yaw, spin and muzzle
velocity. Integration of the system into a flash suppressor or
muzzle break provides for simple upgrading or retrofitting of
operational weapons.
[00053] Fig. 1 shows two Cartesian coordinate systems, x,y,z
and X,Y,Z, arranged along the barrel axis N of a weapon. The two
systems have are angularly displaced with respect to each other
by angles a, p and y. The figure demonstrates the many degrees
of freedom of a projectile in space which result in variations
in ballistic flight.
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[00054] Fig, 2 shows a projectile 10 provided with markings 12
according to the present invention. The projectile is shown
leaving the barrel 14 of a weapon and progressing along the path
of the barrel axis 16 where it is viewed at three successive
moments in time.
[00055] The marks 12 on the projectile are arranged in a
circular row around projectile body transverse to the projectile
axis. In this case, the marks are cross-shaped, making
identification easier by character (patterns recognition. The
marks can also have other various distinctive patterns and
shapes so that the system can discriminate between the different
marks.
[00056] In the projectile of Fig. 2 some of the marks have
distinctive colors such that an optical detector can
discriminate between the marks of different color.
[00057] For better visibility amid the muzzle flash, the marks
may be imprinted with a dye that is luminescent when illuminated
by radiation of a particular frequency.
[00058] As may be seen in the diagram, three measurements are
made by viewing the projectile at successive instants of time.
By viewing angular positions of the colored markings it is
possible to determine the projectile spin. By determining the
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successive distances from the barrel it is possible to determine
the muzzle velocity.
[00059] Fig. 3 is a diagram, similar to Fig. 2, which shows
the projectile from two vantage points that are angularly spaced
by 900; that is, a top view and a side view. By means of this
additional point of view it is possible to more completely
determine the projectile yaw at the successive instants of time.
[00060] By determining the yaw, spin and muzzle velocity at
successive instants of time it is possible to determine the rate
of change of these parameters.
[00061] Fig. 4 is still another diagram showing the projectile
with markings 12 viewed in three successive instants of time.
The spin of the projectile may be seen by observing the marks 12
which rotate, as indicated by the dashed line 18, which
intersects a common mark in the three images, and 20 which
intersects another. In addition, the yaw may be observed by
comparing the positions of a line intersecting all the marks on
each projectile with a line transverse to the central axis 16.
In Fig. 4, the angle of yaw is seen to be increasing from the
first image (no angle of yaw), to the second (small angle 22)
and to the third (larger angle 24).
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[00062] A system for measuring the three projectile parameters
-- yaw, spin and muzzle velocity -- as well as the rates of
change of these parameters, is represented in Figs. 5-7.
[00063] Figs. 5 and 6 are representational diagrams of a flash
suppressor 26 for a 40mm automatic grenade launcher Wa4
showing both front and side views in cross-section.
[00064] In Fig. 5 an emitter 28 emits a momentary flash
illumination 30 as the projectile passes through, electronically
triggered by the firing mechanism of the weapon. The emitter
repeats the flash illumination one or more times (preferably
resulting in three flashes altogether) thus "freezing" the
projectile at successive instants of time.
[00065] In Fig. 6 one or more optical detectors 32 capture an
image of the projectile at the successive instants of time. The
optical detector is preferably a CCD camera which is triggered
to view the projectile during successive windows of time that
overlap with the instants of flash illumination. Advantageously,
three separate cameras may be aligned in spaced positions along
the central axis to capture images as shown in Fig. 2, but a
single camera may suffice to capture all three images.
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[00066] Advantageously one or more additional cameras 32 may
be aligned along the central axis to view the projectile from a
different vantage point and capture images of a different side
of the projectile as shown in Fig. 3.
[00067] Fig. 7 illustrates a complete system comprising a
flash suppressor 26 incorporating one or more emitters 28 and
one or more optical detectors 32, coupled via a cable connector
34 to a computer 36 with an associated memory 38. By way of
example, positions of the emitters 28 and detectors 32 are shown
by arrows 40 in both the front view and side view of the
suppressor.
[00068] In operation, signals representing the digital images
captured by the detectors 32 are passed to the computer for
processing. The computer performs character recognition on the
markings of each projectile and calculates the yaw, spin and
muzzle velocity of the projectile. The results are recorded in
the memory 38 for use by the fire control system which then
calculates the expected ballistic path of the next projectile to
be launched.
[00069] The operation of the system according to the invention
will now be described with reference to Figs. 8-14. These
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figures are all representative diagrams of a flash suppressor at
different stages while a projectile passes through.
[00070] Fig. 8 shows a flash suppressor 26 attached to the
barrel 14 of a gun at the moment a projectile 10 emerges from
the muzzle. When this occurs, gas wash, burned powder and other
debris emerge with it, obscuring visibility in the suppressor
chamber.
[00071] Figs. 9 and 10 illustrate capturing an image of the
projectile using the stop-action flash photography. The image
capture occurs a short time after the initial launch,
illustrated in Fig. 9, when the blast of debris has passed by
the projectile 10, leaving the projectile visible to an
electronic imager 32 when illuminated by an emitter 28.
[00072] Figs. 11 and 12 illustrate the capture of a second
image of the projectile at a second, successive instant of time.
Similarly, Figs. 13 and 14 illustrate the capture of a third
image at a third successive instant of time. The markings on the
projectile are recognized and their positions from one instant
to the next are compared in the computer to determine the
projectile's yaw, spin and muzzle velocity.
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[00073] Figs. 15a through 15d show the flash suppressor 26
incorporating the system of the present invention at successive
instants of time as a projectile 10 passes through it along a
central axis 40. In Fig. 15a the projectile is seen leaving the
barrel 14 of the gun and being imaged in a first strobe flash.
The positions of markings 41 and 42 near the front and the rear,
respectively, of the projectile are captured and identified as
indicated by the arrow 43. In Fig. 15b markings 44 and 45 are
identified as indicated by arrow 46 and in Fig. 15c markings 47
and 48 are identified as indicated by arrow 49. Fig. 15d shows
the projectile 10 with a slight yaw as it leaves the flash
suppressor 26.
[00074] The computer 36, controlled by software, operates
according to an algorithm as represented by the flow chart of
Figs. 16a and 16b. The program starts at block 50 upon receipt
of a trigger signal that fires the projectile 10 at time TO.
Three successive images of the projectile are captured by flash
photography and stored in the memory 38 at times Ti, T2 and T3,
respectively (block 52). The computer processes the signals
defining each image in turn (blocks 54, 56 and 58) to recognize
the markings on the projectile and determine and store the
coordinates of these markings as they appeared at times Ti, T2
and T3. Once the locations of the markings are available, the
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computer calculates and stores the projectile's yaw, spin and
muzzle velocity (MV), respectively, by determining changes in
the marking locations, first between times Ti and T2 and then
between times T2 and T3 (blocks 60-70). Once all these
parameters are available (outputs A, B, C, D, E and F) the
computer calculates the changes in yaw, spin and MV and
determines their respective rates of change (block 72).
[00075] There
has thus been shown and described a novel system
for measuring the yaw, spin and muzzle velocity of an ammunition
projectile 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.
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