Note: Descriptions are shown in the official language in which they were submitted.
~7367
_
Thi~ a~plication is a division o. Carlac~ A?plicatir~rl Se~ial
~o. 343,273 fil~ J~ua1v 8'~, 1980.
BACRGROU~ O~ TEE INVENTION
1. ~ield of the Invention
The present invention relates *o an apparatus
for determining inform~tion concernina the point
in which a tr~jectory of the supersonic projectile
passes through a predetermined measurement plane.
2. The prior Art
~hen a projectile travels through the atmos-
phere with a supersonic velocity, a conically-
expan~ing pressure or shock wave is generated, with
the projectile being at the apex OL the shock wave.
It has been proposed to provide apparatus
for determining the position at which the tr2~ectorv
o~ th.e projectile passes through a plane, emplo~ing
transducers or the like to detect such a shocX wa~e
generatea by a supersonic projectile. One such
proposal is described in b,s. Patent No -3,778,C;q
(~ohrDaugh).
Other target svstems are disclo~ed in Ct~iss
Paten~ Specification Ch-PS 5~9,835, granted May 15,
1977, to Walti, a~d Germ n Utllity Model DE-GM
77 2~ 275 of Walti, laid o?en l~arch 1~, 1978.
-~ O.her prior art systems are known, as well, but r.one
provi~es comp_eher.sive tr2inin~ in proper maxks-
manship. The prior ar. target arranqemer.ts provide
onlv partial in~ormatLon to the trainee m2rksman CDOUt
the progress o his shooting, ~or example, the afore-
mentioned prior art ref~rences provide systems which
determine a location at which a projectile fired
at a target p2sses relative to the target
3t;7
- --3
.S. Patent No. 3,233,904 offers an automatic
target apparatus having an impulse switch for de-
tecting projectile hits on a target and initiating
operation of a target mechanism which drops the
target from a fully raised to a fully lowered
position.
SU~RY OF THE INVENTION
The present invention provides a considerab-
ly more ~ersatile and sophisticated system for
training in marksmanship than has heretofore been
proposed. In order to more effectively instruct
trainees in marksmanship training, it is advantageous
to provide positive and negative reinforcement of
shsoting techniques immediately after each shot is
fired. Such :reinforcement may take a number of
f~rms, but preferably comprises a plurality of in-
dications concerning each shot fired. For example,
it is ~esirable to provide the txainee marksman with
an at ]east approximate ~ndication of where a pro-
jectile fired at a target has passed relative to thetarget and/or a positive indication of whether the
projectile has actually hit the target and/or
whether the projectiIe has ricocheted prior to
r4aching the zone of the target. It is also ad-
vantageous to provide, in combination with one ofthe foregoing indications, information concerning
whether the trainee marksman is correctIy gri~ping
~he weapon being fired. The marksmanship training
system is particularly effective for beginning mar~s-
~en ~ho ma~ no. be holdi~g the weapon correctlyand who may not even be shooting sufficiently near
the target to score a "hit." Such a marksman is
7~;7
thus apprised of the manner in which he should
; c~ange his Lechni~ue to improve his shooting. The
s~stem is, hcwever, also ef~ective for more advanced
shooters, who may wish to not only have an indication
that the target has been hit by a projectile, ~ut
whether the projectile has struck a particular
region of the target.
A first form of the invention comprises
apparatus for use in marksmanship trainins i~ which
a projectile travels along a trajectory from a firing
point toward a target member and through a measurement
plane. The apparatus detects and indicates r~lative
to a target representation a location in the measure-
ment plane through which the trajectory passes,
thereby providing at least an approximate indication
of where the projectile passes relative to the ta~get
mem~er. The apparatus further detects and provides
a positive indication of a projectile "hit" on
the target member, In this way, a trainee marksman
is provided with at least an approximate indicaticn
; of where the projectile passes as well as a positive
indication of whether the projectile has h'~ the
target, the indications making it a sim~le matter fGr
the trainee marksman to distinguish hits at the
edge of the target from misses near the edge of
the target.
In another form of the invention, the apparatus
detects an~ indicates relative to a target represent-
ation a location in the measurement plane through
which the trajectory passes, thereby providing at
least an approximate indication of where the projectile
passes relative to the target, The apparatus also
measures the velocity of the projectile in the vicinity
--5
of the target member, c~m?aring the measured
velocity with at least one expected projectile
velocity value to ascer-,ain if the mezsured velocity
is within an expected projectile velocity range.
5 An indication of the result of this comparison
is provided, so the trainee marksman is apprised
of where the projectile passes relative to the
target member as well as whether the projectile
has passes through the measurement plane in free
fligh~ (i.e., without ricocheting) or has ricocheted
prior to passing through the measurement plane.
A third form of the investion provides
the trainee marksman with at least an approximate
indication of where the pro~ectile passes relative
to the targ~t member, a positive indication of a
projectile hit on the target member, and an in-
dication of whether a detected hit on the target
has resulted from a free flight (i.e., non-ricocheting)
projectile hitti~g the target or from a projectile
which has ricocheted prior to hit~ing the ~arget.
Such a system, particularly for beginning trainees
~ who ma~ not even realize that shots are bei~q fired
;~ slightly below the target and ricocheting up int.o
~; the region of the target. Absent so~e means of
2~ de.ermining positivelv whether the projectile
. has ricocheted, a "ricochet hit" on the target
may be indicated as sim~ly a "hit" on the target,
providing ~he trainee marksman erroneously ~ith
positive reinforcement of incorrect shoo'ing techni~ue.
According to one particularly advantageous
form of the invention, the appar~tus for detecting
a hit on the target com?rises a device, such as a
transducer, spaced apart ~rom and no~ ph~sically
connected to the ta se~ me~er for detecting and
;:~
3~;7
--6--
selectively providing a hit indication onl~ in
response to disturbance of the tzrget mem~er
caused by a projectile hittins the target member.
This particular apparatus for hit detection is in-
S tended to overc~me problems with some prior artsystems in which stones kicked up by,bullets
ricocheting off the ground in front of the target
sometimes erroneously provide a "hit" indication,
such as when kicked-up stones hit the target but
the ricocheting projectile does not, When used
with supersonic projectiles, it is intended that
this hit detection arrangement comprise.
a transducer located in front of the target relative
to the ~light path of the projectile and shielded
in such a manner as to detect air pressure disturbances
caused by the projectile hitting or passing through
the targ~t, ~ut not disturbances caused by the
airborne shock wave of the supersonic projectile,
Alt~tely the t~u~er is.located b~ 2 3-d~sional
2Q target and at least partially shielded from the '
airborne shock wave of a supersonic projectile
by the taryet member itself.
One particularly advantageous zrrangement
for indicating the loca,ion in a measuremen. plane
throuqh which the trajectory of a supersonic projec.ile
passes is also provided. The arrangement incluàes
an array of at leas~ three~ transducers responsive
to an airborne shock wave ~rom the supersonic pro-
jectile and locate~ at -espective predetermined
positions spaced along a line substantially parallel
to the measurement plane. Apparatus is provided for
~7~7
01 _ 7 _
02
03 measuring velocity oE the supersonic projectile, and for
04 measuring velocity of propagation of sound in air in the vicinity
05 of the array o transducers. Computing apparatus is responsive
06 to the transducer array and the projectile velocity and
07 propagation velocity measuring apparatus, and determines the
08 location in the plane through which the trajectory of the
09 supersonic projectile passes, and provides an output indicating
the determined location.
11 Also contemplated within the scope of the inven-tion is
12 some form o graphic display for providing the desired positive
13 and negative reinforcement to each trainee marksman for each shot
14 fired. For example, a visual display screen may be provided with
a representation of the target fired upon, relative to which is
16 displayed an indication of where the projectile has passed by or
17 struck the target. Since it may at times be difficult to
18 distinguish between hits at the edge of the target and near
19 misses at the edge of the taret, it is desired to provide
supplemental positive indication of whether a hit has been
21 detected. It is also contemplated to provide an indica-tion of
22 the region of a target which has been hit, as well as to provide
23 a positive indication of whether the projectile has ricocheted.
;~ 24 Useful for competitive shooting situations is a graphic display
of the trainee marksman's score for each shot fired and total
26 score for a grouping of shots fired.
:; :
3~i7
01 - 8 -
02
03 More particularly, the invention is apparatus for use
04 in marksmanship training in which a projectile travels along a
05 trajectory rom a firing point toward a target member and through
06 a measurement plane comprising apparatus for detecting and
07 indicating relative to a target representation a location in the
0~ measurement plane through which the trajectory passes, thereby
09 providing at least an approximate indication of where the
projectile passes relative to the target member, and apparatus
11 for measuring velocity of the projectile in the vicinity of the
12 target member, comparing the measured velocity with at least one
13 expected projectile velocity value to ascertain if the measured
14 velocity is within an expected projectile velocity range, and
providing an indication of the result of the comparison between
16 the measured velocity and the at least one expected velocity
17 value, whereby a marksman is provided with an approximate
18 indication of where the projectile passes relative to the target
19 member, as well as an indication of whether the projectile has
passed through the measurement plane in free flight or has
21 ricocheted prior to passing through the measurement plane.
22 It will be seen from the description which follows with
23 reference to the drawing figures and computer program appendices
24 that the present invention provides a comprehensive marksmanship
training system which is both versatile and sophisticated, and
26 which provides a level of training that has heretofore been
27 unXnown in the ield.
367
BRIEF DESCRIPTION OF THE DR~I~INGS
FIGUR~ 1 shows in perspective view a marks-
manship training range employing concepts of the
present invention;
FIGURE 2 shows in perspective view a target
mechanism equipped with a target member, a hit sensor,.
and transducers for detecting an airborne shock wave;
FIGVRE 3 shows a coordinate system relating
the positions of shock wave-sensing transducers;
FIGURE 4 shows a schematic block diagram of
an overall system in accordance with the invention;
FIGURE 5 shows an isolator module circuit
for block 66 of Figure ~;
FIGURE 6 shows in block schematic form one
channel of comparator 62 of Figure 4;
FIGURES 7A - 7F show in detail one possible
form of timex interface 64 of Fiyure 4;
FIGURES 8A and 8B show a suitable circuit
arrangement for the air temperature sensing unit 78
of Figure 4;
FIGURE 8C shows a tîming diagram for the
circuits of Figures 8A and 8B;
FIGURE 9 shows aixborne shock waves impinging
~ on a piezoelectric disc transducer;
: 25 FIGURE lOshows an out~ut waveform or
the transducer of Figure 97
FIGURES 11 and 12 show one possible form of
construction for airborne shock wave-sensing transducers;
FIGURE 13 shows an acoustically decoupled
mounting for the airborne shock wave transducers;
FIGURES 14A and 14B are flow charts for
computer subroutine CALL(3);
. ; .
.~LL~t7367
--10--
FIGUP~S 15A ~ 15C show flow charts for
computer subroutine CALL(4);
FIGURF.S 16 - 18 show alternate transducer
arrangements in plan view;
FIGURE 19 shows apparatus for generating a
light curtain and detecting the passage of a projec~
tile therethrough;
FIGURE 20 shows an arrangement employing
two such constructions as shown in Figure 19, in
combination with an array of transducers for detecting
an airborne shock wave;
FIGURES 21 and 22 show an arrangement for
sensing impact of a projectile on a target member;
FIGURES 23 and 24 show an alternate arrange-
ment for detecting a projectile hit on a target member;
FIGURES 25A and 25B show typical transduceroutput signals for "hits" and "misses" of a projectile
passing relative to the target member, respectively;
FIGURE 26 shows a target member construction
for detecting passa~e of a projectile therethrough;
FIGURE 27 shows an alternative arrangement
for determining projeciile velocity; and
FIGURE 28 shows a graticule overlay used on
the visual display screen of Figure 4.
.
~73~7
DF~TAILED DESCRIPTION C)P PREF':ERR~D E!~BODIME~'TS
~ igure 1 shows in perspective ~iew a marks-
manship training ranye employing concepts of
the present invention. The range has a plurality
of firing points 10 from which trainee marksmen 12
shoot at targets 14. Located in front of the targets 14
is, for example, an earthen embankment which does not
obstruct the marksman's view of targets 14 from the
firing points, but which permits the positioning of
transducer arrays 18 just below the lower edge of
the targét and out of the line of fire, The transducer
-arrays will be described in more detail below, but
it will be understood that they may be connected by
suitable cables to a computer 22 situated in a control
room 24 located behind the firing points, as shown,
or may alternatively be connected to a dat2 processor
or computer (not shown) located near the _ransducer
array, which is in turn coupled to the visual display
units. As will be explained below, each transducer
2G arra~ detects the shock wave generated b~ a supersonic
projectile, such as a bullet, .ire2 at the respective
~arget, and the computer 22 is operative ~o determine
the location in a measurement plane in .ron~ o~ the
target through which the bullet trajector~ passes. ~eanC
(not shown in Figure 1) are proviaed at each target for
detecting when the target has been "hit" b~ a p-ojec_ile.
Computer 22 is coupled to suitable visual dlsplat units 26,
28, 30, located respec'ivel~ in the control room 24,
2'_ each firing point lQ, and at one or ~ore other
locations 33. Provided on the visual display units ma~ be,
for ex~m~le,an a~proximate indication, relative to a target
representation, of where the projec,ile has passed
through the measurement plane, and an indication of whether
the target has been "hit" by 'he projectile,
1~7~7
-12-
,
Spectators 32 may observe the progress of shootins
of one or more of the trainee marksmen on ~isual
display unit 30. The co.',puter may be coupled with 2
suitable printer or paper punching device 34 to
generate a permanent record of the bullet trajecto~
location determined by the computer, .
Although the targets 14 shown in Figure 1
have marked thereon representations of the conventional
bull's-eye type ta~get, the target may be of any suitable
configuration, such as a rigid or semi-rigid target
member 35 as shown in Figure 2 on which may be provided
the outline of a soldier or the like, ~eans are pro-
vided for detecting when a pr~jectile fired at the target
member has "hit" the target member, and the target
member may be mounted on a target mechanism 36 which
is operative to lower the target out of sight of the
trainee when a "hit" is detected. The "hit" detecting
means may be an inertia switch 38 as shown in Figure 2,
or any other suitable apparatus ~ Alternative "hit"
detecting arrangements ~ill be described belo~. The
automated target mechanism may be of the tv?e descri~e~
in U.S. Patent No. 3,233,904 to GILLIh~l et al (the
content of which is incor~orated here n b~ re'erence).
Target mechanisms o~ this ty?e are~avail2ble commercially
from Australasian Training Aids Pty, Lt~., Al~ury,
.S.W. 264Q, Australia, Catalog No. 10653;. Inertia
switches are commerciall~ available rom ~ustralasian
~raining Aids Pty. Lta., Catalog No. 101805.
In the arrangement of Figu-e 2, transd-~cers
Sl-S~ are mounted on a~rigid support member 40, which ~s
in turn mounted on the target mechanism 35, Although
the transducer arrays l& may be supported separztely
from the target mechanism beneath targets 14 (as in
Figure 1~, affixing the transducer array to the taraet
mecnanism as in Figure 2 assure correc' alignment
of the measurement plane relative to tzr~et member 35.
Transducers Sl-S4 (Figure 2) ?refera~ly e~ch comprise
67
-13-
a disk-shaped piezoelectric element of 5 ~m ~iametez
mounted to a hemishperical ~luminum dome, ~he hemi-
spherical surface of the dome beinc exposed 'or receivinc
the shock wave from the bullet. The ai~borne shock wave
generated by the bullet is represented b~ the series
of expanding rings 42, the bullet trajectorv by a line 4~,
and the acoustlc vibrations induced in the taIget memDex 35
on impact of the bullet by arc sesments 46
Figure 3 shows 2 three-dimensional coordinate
system in which the positions of the ~our'~ar~ducers Sl-S~
are related to a reference point ro, 0~ ?~ The trans-
ducer array illustrated is similar to that shown in
Figure 2, with a row of three transducers Sl, 53, S9
situated at spaced locations along the X axis and with
lS a fourth transducer S2 situated at a spaced location
behind transducer Sl along the Z-axis, A portion of
target member 35 is also shown for reference purposes,
as is an arro~ 44 representinq the bulle. trajectory~
The distance along the X-axis from transducer Sl to
transducers S3 and S4, res~ectively, is re?resente~
by ~istance d. The distance along the Z-axis be.ween
transducers S1 and S2 is represented by d',
The X-Y plane intersecting the o_igin of
the Z axis of the coordina~e s~rstem shown in Fisure 3
. . .
is considered to be the measurement plane ln which the
location of the trajectory is to be determine~.
Transducers Sl-S9 provi~e output s~gn~s in
response to detection of the shock wave o- the bullet,
from which the location in the measuremenl plane thloush
which the projectile tra~ector~r passes can be determlned.
A m2thematical analysis is provided below Eor a
relativel~r simple case in which it is assumed that:
1) The transducer arra~ is as shown in
Fisure 3;
73Çi7
01 - 14 -
02 2) The measurement plane has its X-axis parallel to
03 the straight line joining transducers Sl, S3, S4;
04 3) The projectile trajectory is normal to the
05 measurement plane;
06 4) The projectile travels with constant velocity;
07 5) Air through which the shock wave propagates to
OB strike the transducers i5
09 a) of uniform and isotropic shock wave propagation
velocity, and
11 b) has no velocity (i.e., wind) relative to the
12 transducer array; and
13 6) The shock wave propagation velocity and projectile
14 velocity are separately measured or otherwise known or assumed.
It is noted that small departures from the
16 above-stated conditions have in practice been found acceptable,
17 since the resulting error in calculated location in the
18 measurement plane through which the projec~ile passes is
19 tolerably small for most applications.
The respective times of arrival of the shock wave at
21 transducers Sl, S2, S3, S4 are defined as Tl, T2, T3, and T4.
22 All times of arrival are measured with respect to an arbitrary
23 time origin. Vs is defined as the propagation velocity of the
24 shock wave front in air in a direction normal to the wave front,
while Vg is defined as the velocity of the supersonic
26 projectile along its trajectory.
27 The velocity Vg of the bullet in a direction
28 normal to the measurement plane can be determined from the
29 times of arrival Tl, T2 f the shock wave at
.. . .
.
~7367
transducers 51 and S2 and from the c s.2~ce d' be_ween
transducers Sl and S2:
B T2 Tl (1)
Then the propagation velocit~ of the shock waye
front in a direction normal to the projectile velocity
may be defined as: vs
V
N V
: 1 - Vs 2 ~2)
The differences between the times o~ arrival
of the shock wave may be defined as:
tl = T3 T
t2 = T4 Tl
The X-axis coo~dinate of the intersection
point of the projectil~ trajecto~v ~i,h the measure-
ment plane is:
(tl-t2) (VN2 ~1t2 + ~2~ (51
l; X
2~ (tl t t2)
The distance in the measurement plane _rom
sensor Sl to ~he poin~ o, intersection Ot- the projec-ile
trajector~ with the measurement plane is;
2d2 ~ 2 ~12 ~ ~t22) ]
1 = (6)
~ 2V~ (tl ~ t2)
The Y-axis coordinate of the interse~tion
point o~ the bullet trzjector~7 ~ith the measurement
plane is:
y - 1 2 _ y2 (7)
.
~73~7
01 - 16 -
02 It is possible to construct a mathematical solution
03 for the above-described t~ansducer system which inco~porates
04 such effects as:
05 1~ Wind;
06 2) Non-equally spaced transducers along the X-axis;
07 3) Non-colinear arrays;
08 4) Decelerating projectiles; and
09 5) Non-normal trajectories.
However, most of these corrections require more
11 complex arithmetic, and in general can only be solved by
12 iterative techniques.
13 - It can be seen that the transducer arrangements shown
14 in Figures 1-3 form, when viewed in plan, a "T" configuration
with at least three transducers on the crossbar of the "T" and
16 one transducer at the base of the "T". The stem of the "T" is
17 substantially aligned with the expected bullet trajectory. The
18 error created if the stem of the "T" is not precisely aligned
19 with the anticipated projectile trajectory is relatively minor
and thus the alignment of the "T" can be considered
~21 substantially insensitive to error. However, when the stem of
22 the "T" ~that is, the Z-axis of Figure 3) is aligned parallel to
23 the expected projectile trajectory, the effect is to cancel
~24 substantially any shock wave-arrival-angle dependent time delays
~ in the transducer outputs.
26~ ~ Referring now to Figure 4, a plan view of the trans-
27 ducers S1-S4 in a " T" configuratlon is illustrated schemati-
28 cally. Each transducer is coupled by an appropriate shielded
29 cable to a respective one of amplifiers 54-60. The outputs of
~ amplifiers 54-60 are provided through coupling capacitors to
31 respective inputs of a multi-channel comparator unit 62,
7367
01 - 17 -
02 each channel of which provides an output when the input signal
03 of that channel exceeds a predetermined threshold level. Thus,
09 a pulse is provided at the output of each of channels 1, 2, 3,
05 and 6 of comparator unit 62 at respective times indicating the
06 instants of reception of the shock wave of each of the
07 transducers Sl-S4. In the previously-described form of the
08 invention, channel 4 of the six-channel comparator unit is
09 unused. The outputs of channels 1-3 and 6 of comparator unit 62
are provided to inputs of a timer interface unit 64. Timer
11 interface unit 64 serves a number of functions, including
12 conversion of pulses from comparator unit 62 into digital values
13 representing respective times of shock wave detection which are
14 conveyed via a cable 68 to a minicomputer 70.
~15 The output of channel 1 of comparator unit 62 is
16 coupled to the inputs of channels 0 and 1 of timer interface
~17 unit 64, the output of channel 2 of the comparator unit is
18 coupled to the input of channel 2 of the timer interface unit,
~19 the output of channel 3 of the comparator unit is coupled to the
~20 inputs of channels 3 and 4 of the timer interface unit, and the
21 output of channel 6 of the comparator unit is coupled to the
22 input of channel 6 of the timer interface unit. The channel 5
23 input of the timer interface unit is coupled via comparator unit
~24 channel 5 to an air temperature sensing unit 78 which has a
~25 temperature-sensitive device 80 for measuring the ambient air
26 temperature. The output of amplifier 54 is also provided to air
~27 temperature sensing unit 78, for purposes descri~ed below with
28 reference to Figures BA-8~.
.
36~
01 - 18 -
02 Figure 4 also shows schematically the target mechanism
03 36 and the inertia switch 38 of Figure 2, which are
04 interconnected as shown for the units available from
05 Australasian Training Aids Pty., Ltd. Coupled to terminals A,
06 B, C of the target mechanism/inertia switch interconnection is
07 an isolator module 66 which provides a pulse similar in form to
08 the output pulses of comparator unit 62 when inertia switch 38
09 is actuated by impact of a pro~ectile on the rigid target member
35 of Figure 2. The output of isolator module 66 is supplied to
11 two remaining inputs of timer interrace unit 64, indicated in
12 Figure 4 as channels 7 and "S.S."
13 Minicomputer 70 of Figure 4 may be of type LSI-2/20G,
14 available from Computer Automation Inc. of Irvine, California,
Part No. 10560-16. The basic LSI-2/20G unit is preferably
16 equipped with an additional memory board available from Computer
17 Automation, Part No. 11673-16, which expands the computer memory
18 to allow for a larger "BASIC" program. Minicomputer 70 is
19 preferably also equipped with a dual floppy aisk drive available
from Computer Automationj Part No. 22566-22, and a floppy disk
21 controller available from Computer Automation, Part No.
22 14696-01. Minicomputer 70 is coupled to a terminal 72 having a
23 visual display screen and a key board, such as model "CONSUL
24 520" available fom Applied Digital Data Systems Inc. of 100
Marcus Boulevard, Hauppauge, New York, 11787, U.S.A. The CONSUL
26 520 terminal is plug-compatible with the LSI-2 minicomput~r.
:
,
~7~67
01 - 19 -
02 Other peripheral units which are not necessary for
03 operation of the system in accordance with the invention, but
04 which may be employed to provide greater flexibility in
05 marksmanship training, include a line printer 72' ~or generating
06 permanent output records, and a graphics generator/visual
07 display unit combination 72" which permits the coordinates of
08 the intersection point of the projectile trajectory with the
09 measurement plane to be displayed relative to a representation
of the target, as well as an indication of whether the target
11 has been "hit" and a tally of the trainee marksman's "score".
12 Graphics generator/visual display unit 72" may be, for example,
13 Model MRD "450", available from Applied Digital Data Systems,
14 Inc., which is plug-compatible with the LSI-2 minicomputer.
Also shown in Figure 4 is a thermometer 76, which
16 preferably is a remote-reading digital thermometer such as the
17 Pye-Ether series 60 digital panel meter Serial No. 60-4561-CM,
18 available from Pyrimetric Service and Supplies, 242-248 Lennox
19 St., Richmond, Victoria, 3221, Australia, equipped with an
outdoor air temperature sensor assembly (Reference Job No.
21 Z9846). The remote-reading digital thermometer may have its
22 sensor ~not shown) placed in the region of the transducer array
23 and, if the system is not e~uipped with the air temperature
24 sensing unit 78 shown in Figure 4, the operator of terminal 72
may read the remote-reading digital thermometer 76, and input a
26 value for the air temperature. ~
367
01 - 20 -
02 An approximate value for the speed of the shock-wave
03 front propagation in ambient air can be readily calculated from
04 the air temperature using a known formula as described below.
05 Figure 5 shows a circuit diagram of the inertia
06 switch isolator- module 66 of Figure 4, having inputs A, B, C
07 coupled as in Figure 4 to the commercially-available inertia
08 switch. The isolator module provides DC isolation for the
09 inertia switch output signal and presents the signal to timer
interface unit 64 of Figure 4 in a format comparable to the
11 output signals from comparator unit 62.
12 Suitable components for isolator module 66 are:
13 82, 84 lN914
14 86 47uF
88 BC177
16 90 lOK~
17 92 820J~
18 94 5082-4360
19 96 470JQ
98 6.8K
21 100 lOuF
22 102 74LS 221N Monostable Multi-
23 vibrator with
24 Schmitt-trigger
inputs
26 104 DS8830N Differential line
27 driver
28 106 0.22uF:
~29 108 47~ ;
~:
~7367
0 1
02 Figure 6 shows a block diagram of one channel of
03 comparator unit 62. The output signal from one of amplifiers
04 54-60 is provided through a high pass filter 110 to one input of
0S a differential amplifier 112 which serves as a threshold
06 detector. The remaining input of differential amplifier 112 is
07 provided with a preset threshold voltage of up to, for example,
08 500 millivolts. The output of threshold detector 112 is
09 supplied to a lamp driver circuit 114, to one input of a NAND
gate 116 and to the trigger input of a monostable multivibrator
11 118 which provides an output pulse of approximately 50
12 millisecond duration. A shaped output pulse is therefore
13 provided from NAND gate 116 in response to detection of the
14 air-borne shock wave by one of transducers Sl-S4. Lamp driver
circuit 114 may optionally be provided for driving a lamp which
16 indicates that the associated transducer has detected a shock
17 wave and produced an output signal which, when amplified and
18 supplied to threshold detector 112, exceeds the preset threshold
19 valueO
The logic output signals of comparator unit 62 cause
21 ~ counters in timer interface unit 64 to count numbers of
22 precision crystal-controlled clock pulses corresponding to the
23 differences in times of arrival of the logic output signals,
24 which in turn correspond to the times of arrival of the shock
waves at the transducers. Once this counting process is
26 complete and all channels of the timer interface unit have
~,
27 received signals, the counter data is transferred on command
28 into the computer main memory. Following`execution of a
-29 suitable program (described below), the resulting projectile
trajectory data is displayed on the visual displa~ unit 72
31 and/or units 72', 72" of Figure 4.
~ ~7367
01 - 22 -
02 Figures 7A-7F show in detail one possible form of a
03 timer interface unit 64, which converts time differences between
04 the fast logic edge pulses initiated by the transducers into
05 binary numbers suitable for processing by minicomputer 70.
06 Figure 7A shows the input and counting circuit portions of the
07 timer interface unit, which accept timing edges from respective
08 comparator unit channels and generate time difference counts in
09 respective counters. The timer interface unit has eight channel
inputs labeled Ch~-Ch7 and one input labeled "S.S.", receiving
11 signals as follows:
12
13- Timer Interface
14 Input Channel No. Receives Signals initiating from
~ Transducer Sl
16 1 " Sl
17 ~ " S2
18 3 " S3
19 4 " S3
Air Temperature Sensing Unit 78,
21 if equipped; otherwise transducer S4
~22 6 Transducer S4
23 7 Inertia Switch Isolator Module 66
24 S.S.
The input signals to each of timer interface inputs
26 ~ Ch~-Ch7 comprise logic signals which are first buffered and then
27 supplied to the clock input CK of respective latches FF~-FF7.
28 The latch outputs LCH~+ through LCH7~ are provided, as shown/ to
29 exclusive OR gates EORl-EOR7, which in turn provide counter
enabling signals ENAl- through ENA7-. Latches FF~-FF9 are
31 cleared upon receipt of clear signal CLR. The input and counting
32 circuits also include a respective up/down counter for each of
33 eight channels (indicated for channel 1 as "UPjDoWN COUNTER 1").
~7367
01 - 23 -
02 Each up/down counter comprises, for example, four series-
03 connected integrated circuits of type 74191. Each of up/down
04 counters 1-8 thus has 16 binary outputs, each output coupled to
05 a respective one of terminals TB0~- through TB15- via a
06 controllable gate circuit (indicated for channel 1 as "GATES 1")
07 on ~eceipt of a command signal (indicated for channel 1 as
08 "IN~-"). Up/down counter 1 is connected to receive latch signal
09 LCHl~, enable signal ENAl- a clock signal CLK, and a clear
signal CLR, and to provide a ripple carry output signal RCl-
11 when an overflow occurs. Up~down counters 2-8 each receive a
12 respective one of enable signals ENA2- through ENA8-. Counter 2
" 13 receives its clear signal CLB from counter l; counters 3 and 5
14 receive clear siynal CLR and provide clear signals CLB to
~15 counters 4 and 6, respectively; counter 7 receives clear signal
16 CLR; and counter 8 receives clear signal SEL2-. The up/down
17 inputs of counters 2-7 receive latch signals LCH2~ through
18 LCH7+, respectively, while the up/down input of counter 8 is
19 permanently connected to a +5 volt source. Counters 2-8 each
receive clock signal CLK, while each of counters 2-7 provide a
21 ripple carry signal (RC2- through RC7-, respectively) when the
22 respective counter overflows. Gates 2-8 are coupled to receive
~23 respective command signals INl- through IN7- for passing the
24 counter contents to terminals TB0~- through TB15-. Figure 7A
also shows a gate NAND 1 which receives the latch outputs LCH~-
~26 through LCH7+ and provides an output signal SEN7~, the purpose
27 of which is explained below.
28 Figure 7B shows a circuit for providing clear signal
29 CLR, which resets input latches FF~-FF7 and up/down counters
L--7. When one of ripple carry outputs RCl- through RC7- of
31 up/down counters-1-7 goes to a logic low level, indicating that
~32 a counter has overflowed, or when a reset signal SEL4- is
33 provided from the computer, gate NAND 2 triggers a monostable
34 element which then provides clear signal CLR in the form of a
~35 logic pulse to clear up/down counters 1-7 and input latches
36 FF~-FF7 of Figure 7A.
~7367
01 - 24 --
02
03
04
05
06
07
08
09 Up/down counters 1-7 are reset by siynal SEL4- from
the computer before each shot is fired by a trainee marksman.
ll When a shot is fired, each~counter will count down or up
~12 depending on whether its associated channel triggers before or
13 ~ after a reference channel, which in this case is input channel
14 Ch~.
` Figure 7C shows the input circuitry for input "S.S."
16 of the timer interface. Latch FF8 is coupled to receive reset
17 signal SEL4- and preset signal SELl- from the interface
~18~ ~ controller of ~igures 7E and 7F in response to computer
~l9 commands. Timer interface input~"S.S." receives "hi~" ~
~;~ 20~ ~ indicatlon signal VEL- from the inertia switch isolator module
21 ~ 66, and-proYides a counter en~able~signal ENA8- for up/down
~22~ ~ counter 8.
, :
:
;~.
':
-; ~..
1~L473~7
01 - 25 -
02 The computer communicates with the timer interface unit by
03 placing a "device address" on lines AB03- AB07 (Figure 7D) and a
04 "function code" on lines AB0~- AB02 (Figure 7F). If the
05 computer is outputting data to the timer interface, signal OUT
06 is produced; if the computer is inputting data, signal IN is
07 produced.
08 Figure 7D shows exclusive OR gates EORll-EOR15 which
09 decode the "device address." A "device address" can also be
selected manually by means of switches SWl-SW5. The address
11 signal AD- from gate NAND 3 is then further gated as indicated
12 with computer-initiated signals IN, OUT, EXEC, and PLSE, to
~13 prevent the timer interface from responding to memory addresses
14 which also appear on the address bus.
~;15 Figure 7F shows a latch 2A which holds the function
16 code of lines AB0~-AB02 when either the IN or OUT signal is
`17~ produced. The inputjoutput function signals from latch 2A are
~18 labeled IOF~ through IOF2.
19 If the computer executes an IN instruction to receive
data from the timer interface, the combination of IOF~ through
21 IOF2 and ADIN- (Figure 7D) produce one of~ signals IN~- through
22 IN7- at BCD/decimal decoder 5A of Figure 7E. Each of signals
23 ~ IN~- through IN7- enables data from one of up/down counters 1-8
24 to be placed on data bus terminals TB0~- through TB15~
25 ~ If the computer is executing a "select" instruction
26 for the timer interface, the combination of signals IOF~ - IOF2
27 and ADEXP- (Figure jD) produce one of select signals SEL~-
28 through SEL7- at BCDj decimal decod~er 5B of Figure 7E. The
29 select signal functions employed~ in the presently-described
invention are~
; 31 SELl- enables triggering of latch FF9 (Figure 7C)
~-32 SEL2- resets up/down counter 8 (Figure 7A)
~33 SEL4- resets latch FF8 (Figure 7C) and triggers
34 monostable element 328 via NAND 2 (Figure 7B)
~ '
~7367
01 - 26 -
02 If the computer is executing a sense instruction from
03 the timer interface, the combination of signals IOF~ - IOF2
04 (Figure 7B) and AD- (Figure 7D) allow one of sense signals SEN~+
05 through SEN7+ to be placed on the SER-line (Figure 7F). This
06 allows the computer to examine the state of one of these sense
07 signals. The only sense signal employed in the
08 presently-described embodiment is SEN7-~, which indicates that
09 the timer interface has a complete set of time data for a single
shot fired at the target as explained more fully below.
11 The theory of operation of timer interface unit 64 is
12 as follows. Channel Ch~ is the reference channel. Each channel
13 triggering will clock a respective one of latches FF~ - FF7,
lg producing a respective one of signals LCH~+ through LCH7+.
Signals LCHl through LCH7+ each control the up/down line of one
16 of counters 1-7 and are also provided to OR gates EORl through
17 EO~7 to produce a respective counter enabling signal ENAl-
18 through ENA7-.
19 Exclusive OR gates EORl through EOR7 each achieve two
functions. First the counters of any channel that triggers
~21 before reference channel Ch~ will be enabled until reference
22 channel Ch~ triggers. This has the effect of causing the
23 counters to count down because the associated LCH+ input line is
24 high. Second, the counters of any channels that have not
triggered by the time reference channel Ch~ triggers are all
26 enabled by the reference channel until each individual channel
27 triggers. This has the effect of causing the counters to count
28 up, since the àssociated LCH~ lines are low while the counters
29 are enabled.
' :
.
.`~ ,
:~
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.
367
01 - 27 -
02 Initially, the computer resets up/down counter 8 with
03 signal SEL2- and then causes a general reset with signal SEL4-.
04 Signal SEL4- ca~ses gate NAND 2 (Figure 7B) to trigger
05 monostable element 328, producing clear signal CLR, which ~esets
06 latches F ~ - FF7 and up/down co~nters 1-7 (Figure 7A). Reset
07 signal SEL4- also clears latch FF8 (Figure 7C). Latch FF9
08 (Figure 7C) is preset by the computer with signal SEL 1-, which
09 puts set steering onto FF9. Latch FF9 is thus clocked set when a
signal VEL- is received at the "S.S." input from inertia switch
11 isolator module 66, indicating that the target has been "hit".
;12 Thus, prior to a shot being fired, counters 1-8 are
13 reset, input latches FF~ - FF7 are resetl and latch FF9 is
14 "armed". All resets occur when the computer executes controller
BASIC statement CALL (3), described further below.
16 At this stage, none of channels Ch~ through Ch7 or the
17 "S.S." channel 8 has been triggered. Since channel Ch~ has not
18 yet triggered, signal LCH~ is low. The remaining input of GATE
19 EOR~ is permanently high, so the output of gate EO ~ is high.
Since signals LCH1+ through LCH7~ are all low, signa~s ENAl-
21 through ENA7- are all high, disabling all of up/down counters
22 1-70 Signal ENA8- is also high, disabling up/down counter 8.
23 Assume now that a shot is fired to the left of the
24 target, missing the target, and to the left of the transducer
?5 ~ array shown in Figure 4. Channel 3 of Figure 7A triggers first,
2~ so that signal LCH3+ goes high, causing signal ENA3- to go low
27 and thereby causing up/down counter 3 to begin counting down.
28 Reference channel Ch~ and channel~Chl then trigger simultane-
29 ously. Signal LCH~+ goes high, so the output of gate EOR~ goes
low. This makes signal ENA3- go high, while signals ENA2- and
31 ~ENA4- through ENA7- go low. Signals ENAl- and ENA8- remain high.
32
~7367
01 - 28 -
02 Counter 3 will thus stop counting, counter 1 remains disabled
03 and has no count, and counters 2, and 5-7 will start counting
04 up.
05 As each successive channel triggers, its respective
06 LCH+ signal will go high, removing the associated ENA- signal
07 and stopping the associated counter. When all LCH+ signals are
08 high (indicating that all counters have been disabled), signal
09 SEN7+ at the output of gate NAND 1 in Figure 7A goes from high
to low. The computer monitors signal SEN7+ to wait for all
11 timing edge counts to be completed.
12 When the computer senses signal SEN7+, indicating that
13 a complete set of counts is present in counters 1 through 7, it
14 generates address signals~ AB0~-AB07 and the IN signal which
cause BCD-to-decimal decoder 5A tFigure 7E) to issue sigals INl-
16 through IN7- in sequence so that the computer will sequentially
17 "read" the state of each counter (on output lines TB0~- through
18 TB15-).
19 The computer has thus received counts representing
20 : times as follows:
21 Tl zero count from counter 1 (transducer Sl~
22 T2 positive count from counter 2 (transducer S2)
23 T3 negative count from counter 3 (transducer S3)
24 ~ T4 negative count from counter 4 (transducer S3)
T5 positive count from counter 5 (air temperature
26 sensing module as explained below with reference
27 to Figure 10, or, if none, the output of channel 6
28 amplifier 60 goes to input channel Ch5 of the
29 ~ timer interface unlt and the output of transducer
S4 triggers counter 5)
31: T6 positive count from counter 6 (transducer S4)
32 T7 positive count from counter 7 (inertia switch)
33 A2 zero count from counter 8 (inertia switch)
34 The zero count in A2 indicates that the inertia switch
was not operated, thus showing that the shot fired has missed
36 the target. Had the bullet struck the target, a non-zero count
.
.
~7367
01 - 29 -
02 would be r-ecorded in A2 because signal ENA8- would have gone low
03 upon receipt of signal VEL- (Figure 7C).
04 The computer is programmed to operate on the ~eceived
05 "time" signal Tl through T7 and A2 in a manner which will be
06 described below, such that the coordinates of the bullet
07 trajectory in the X-Y measurement plane of Figure 3 are
08 determined.
09 If any channel of the timer interface unit triggers
spuriously (i.e. the inertia switch may be triggered by a stone
11 shower, one of the transducers may detect noise from other
12 target lanes or other sources, etc.), the associated counter
13 will continue counting until it overflows, causing a ripple
14 carry signal (RCl- through RC7-1). All of the ripple carry
signals are supplied to gate NAND 2 (Figure 7B), which fires the
16 associated monostable element 328, causing generation of clear
17 signal CLR which resets latches FF~ - FF7 and up/down counters
18 1-7.
19 Figures 8A and 8B show in detail a suitable circuit
arrangement for the air temperature sensing unit 78 of Figure
21 4. Figure 8C shows wave forms of various points in the circuit
22 of Figure 8A and 8B. The effect of the air temperature sensing
23 unit is to generate a pulse at a time tl following the time to
24 at which channel Chl of comparator unit 62 is triggered
(allowing of course for propagation delays~in connecting
26 cables).
27 Referrin~ to Figure 8B, a temperature sensor ICl
28 mounted in a sensor assembly, assumes~a temperature
;~; 29 substantially equal to that of ambient air in the vicinity of
the transducer array. Temperature sensor ICl may be, for
31 example, Model AD590M, available from Analog Devices Inc., P.O.
32 Box 280, Norwood, MA. 02062~ Temperature sensor ICl permits a
33 current IIN to flow through it, current IIN being
34 -~ substantially proportional to the absolute temperature (in
degrees Kelvin) of the semiconductor chip which forms the active
36 element of temperature sensor ICl.
~:
, :
~47367
01 ~ 30 -
02 Referring again to Figure 8A, when transducer S1
03 detects a shock wave generated by the bullet, a wave form
04 similar to that shown at A in Figure 8C is produced at the
05 output of its associated amplifier 54 (Figure 4). Integrated
06 circuit chip IC3B of Figure 8A forms a threshold detector, the
07 threshold being set equal to that set in channel Chl of
08 comparator unit 62 of Figure 6.
09 Integrated circuit chip IC3 may be of type LM 319,
available from National Semiconductor Corporation, Box 2900,
11 Santa Clara, California, 95051. When wave form A of Figure 8C
12 exceeds the preset threshold, wave form D is generated at the
13 output of circuit chip IC3B. The leading edge (first
14 transition) of wave form B triggers the monostable multivibrator
formed by half of integrated circuit chip IC4 of Figure 8B and
16 the associated timing components R8 and C3. Circuit chip IC4
17 may be of type 74LS221N, available from Texas Instruments, Inc.,
18 P.O. Box 5012, Dallas, Texas, 75222. The output of this
19 monostable multivibrator is fed via buffer transistor Ql to the
gate of metal oxide semi conductor Q2, the wave form at this
21 point being depicted as C in Figure 8C. Transistor Ql may be of
22 type BC107, available from Mullard Ltd., Mullard House,
23 Torrington Place, London, U.K.j and semiconductor Q2 may be of
24 type VN 40AF, available from Siliconix Inc., 2201 Laurelwood
Road, Santa Clara, California, 95054.
1~73~7
01 - 31 -
02 When wave form C, which is normally high, goes low, metal oxide
03 semiconductor Q2 changes from a substantially low resistance
04 between its source S and drain D to a very high resistance. As
05 a result of the current flowing through temperature sensor ICl
06 (proportional to its absolute temperature), the voltage at the
07 output of integrated circuit chip IC2 starts to rise, as shown
08 at D in Figure 8C. The rate of ri.se in volts per second of wave
09 form D is substantially proportional to the current flowing
through temperature sensor ICl and thus is proportional to the
11 absolute temperature of temperaure sensor ICl. Integrated
12 circuit chip IC2 may be of type CA3040, available from RCA Solid
13 State, Box 3200, Summerville, New Jersey 08876. When the
14 voltage of wave form D, which is supplied to the inverting input
of comparator IC3A, rises to the preset threshold voltage VTH2
16 at the non-inverting input of comparator IC3A, the output of
17 comparator IC3A changes state as indicated in wave form E at
18 time tl. This triggers a second monostable multivibrator formed
19 of half of integrated circuit IC4 and timing components C4 and
R9. The output of this second monostable multivibrator is sent
21 via a line driver circuit chip IC5 to a coaxial cable which
22 connects to the channel 5 input of the comparator unit 62.
23 The operation of the air temperature sensing unit 78
24 of Figures 8A and 8B may be mathematically described as follows
(assuming that the ramp at wave form D of Figure 8C is linear
~26 and ignoring offset voltages in the circuitj which will be
:27 small):
28
23 ~1- VTH2 ~ ~8)
31
32
33 where VO = voltage of wave form D, Figure 8C,
.
:
~73~7
01 ~ 32 -
02 and
03
04 d V0 IIN
05 dt C (9)
06 where IIN = current through ICl
07 IIN = C ~K (10)
08 where C is a constant of proportionality and
09 ~K is the absolute temperature of ICl
combining (8), (9) and (10),
11
12 tl - TH2
13 ~K (1.1)
14
or
16 ~K VTH2Cl (12)
18 Ctl
19 Timer interface unit 64 can then measure time tl by
the same procedure that is employed for measuring the time
21 differences between transducers Sl-S4. It will be recalled that
22 time interface unit 64 will start counter 5 counting up upon
23 receipt of a pulse on channel CH0, which is responsive to shock
24 wave detection by transducer Sl. Counter 5 will stop counting
upon receipt of the pulse of wave form G from the air
26 temperature sensing unit at time tl. Thus, the count on counter
27 5 of the timer interface unit will be directly proportional to
28 the reciprocal of the absolute temperature of sensor ICl.
29 Each of transducers Sl-S4 may be a flat disk 530 of
: pieæoelectric material (Figure 9). If a bullet 532 is fired to
`~31 the right of the transducer 530, the shock wave 532 will impinge
32 on the corner 534 of transducer 530, and the transducer output
; ~33 will have a wave form as illustrated in Figure 10. It is
34 desired to measure the time T illustrated in Figure 12 but it is
difficult eo detect~this accurately s~nce the amplitu~e of the
~,
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~73Çi~
01 - 33 -
Q2 "pip" 542 depends upon the position of the bullet ~elative to
03 the transducer, is difficult to distinguish fLom background
04 noise and can even be absent under some circumstances.
05 The minicomputer is provided in advance with the
06 position of each transducer; all calculations assume that the
07 transducer is located at point 536 and that the transducer
08 output signal indicates the instant at which the shock wave
09 arrives at point 536.
; 10 However, the distance between the transducer surface
11 and each of the trajectories of bullets 532, 538 is equal to a
12 distance L. Since the transducer provides an output as soon as
~13 the shock wave impinges on its surface, the times between the
~14 bullet passing and the output signal being generated are equal.
Therefore, the output of the transducer would suggest that the
16 trajectories of the bullets 532, 538 are equispaced from point
17 536, which is not correct.
18 This disadvantage can be overcome by disposing the
~19 transducers in a vertical orientation so that the transducers
are in the form of vertical disks with the planar faces of the
~21 disks directed toward the trainee marksman. As a bullet passes
22 over the disks and the resulting shock wave is generated, the
~23 shock wave will impinge on the periphery of each disk and the
24 point of impingemenet will be an equal distance from the center of
~he disk. A constant timing error will thus be introduced, but
26 since only time differences are used as a basis for calculation of
27 the bullet trajectory location, this error will cancel out.
~28 However, orienting the disks vertically will not obviate
;~29 the problem of the positive pip 542 at the beginning of the output
signal 540. It is, therefore, preferred to provide each trans-
31 ducer with a dome of a solid material having a convex surface
; 32 exposed to the shock wave, the planar base of the dome being in
3~7
-3~- -
con_act with the transducer c sk arld be_ng s_i~a3'o
ror transmi~ting shoc~; waves from the a-m~sphere tc ho
transZucer disk. Shoc); waves c,~enera~ed by projectiles
fireci at the target will always strike the hem s-~he~ica'
dome tanaen ially, and shock waves will be ,ransmi-Lec
radially throu~h the dome directly to the cen.er of ~he
transducer. The constant timing error the eby intro-
ducec will cancel out during calculatior. of the ~ul'e.
~rajectory location.
The hemispherical dome prevents or minimizes
qeneration of positive-goins pip 542 so the output of
the transducer more closely resembles a sinusoiZal wave
form. The instant of commencement of this sinusoidal
wave form must be measured with great accuracy, so the
1~ transducer must have a fast response.
It is advantageous to utilize a piezoelectric
disk having a diameter of about ~ mm, which provides a
fast response time and a relatively high am?litude
output signal.
. '
7367
01 - 35 -
02 Referring now to Figures 11 and 12 of the drawings,
03 one possible form of transducer for use in connection with the
0~ present invention comprises a transducer element consisting of a
05 disk 550 of piezoelectric material such as, for example, lead
06 zirconium titanate. The disk 550 is about 1 mm thick and 2-5 mm
07 in diameter, and may be part No. MB1043, available from Mullard
08 Ltd., Torrington Place, London, U.K. The opposed planar faces
09 of disk 550 are provided with a coating of conductive material
552, which may be vacuum-deposited silver.
11 Two electrically conductive wires 554, 556 of, for
12 example, copper or gold, are connected to the center of the
13 lower surface of the disk and to the periphery of the upper
14 surface of the disk, respectively, by soldering or by ultrasonic
bonding. ~isk 550 is then firmly mounted in a housing which
16 comprises a cylindrical member 558 having recess 560 in one end
~ 17 thereof, the recess 560 having a depth of about 1.5 mm and a
`~ 18 diameter adapted to the transducer disk diameter, and being
; 19 aligned with an axial bore 562 extending through member 558 to
accommodate wire 554 provided on the lower surface of the
21 piezoelectric member. A second bore 554, parallel to bore 562,
22 is formed in the periphery of member 558, bore 562 accommodating
23 wire 556 and terminating in an open recess 566 ad~acent the main
~24 recess 560. Member 558 may be formed of Tufnol, which is a
phenolic resin bonded fabric, this material being readily
26 obtainable in cylindrical form. The housing may be machined
~27 from th1s material, although the housing may be alternately
28 formed of a two-part phenolic resin such as that sold under the
29 trade mark Araldite, the resin being retained in a cylindrical
~30 aluminum case 568 and subsequently being machined. If the
. ~
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:
~7367
01 - 36 -
02 latter construction is employed, aluminum case 568 may be
03 grounded to provide a Faraday cage to minimize noises. The
04 piezoelectric material and wires are bonded into member 560 with
05 an adhesive such as Araldite or a cyano-acrylic impact
06 adhesive. Two small bores 570, 572 are provided in the lower
07 surface of member 558 and electrically conducting pins are
08 mounted on the bores. Wires 554, 556 protr-ude from the lower
09 ends of bores 562, 564 and are soldered to the pins in bores
570, 572, respectively. An adhesive or other suitable setting
11 material is employed to retain all the elements in position and
12 to secure a solid hemispherical dome 574 to the transducer
13 element 55Q. The dome 574 may be machined from aluminum or cast
14 from a setting resin material such as that sold under the trade
1~ mark Araldite. The dome 574 preferably has an outer diameter of
16 about 8 mm, which is equal to the diameter of the housing 568.
17 A centrally-disposed projection 576 on the base of the dome
18 member 574 contacts and has the same diameter as the the
19 pieoelectric disk 550. Alternatively, dome 574 and member 558
may be cast as a single integral unit, surrounding the
21 transducer disk.
22 The assembled transducer with housing as shown in
23 Figure 12 is mounted, as discussed elsewhere herein, in front of
24 the target. It is important that both the housing and a coaxial
cable coupling the transducer assembly to the associated
26 amplifier be acoustically decoupled from any support or other
27 rigid structure w~ich could possibly receive the shock wave
28 detected by the transducer before the shock wave is received by
29 the hemispherical dome provided on top of the transducer. Thus,
~30 if the transducers are mounted on a rigid horizontal frame ~ork,
31 it is important that the transducers be acoustically decoupled
32 frGm such framework. The transducers may be mounted on a block
33 of any suitable acoustic decoupling medium, such as an expanded
34 polymer foam, or a combination of polymer foam and metal plate.
~7367
01 - 37 -
02 A preferred material is closed-cell foam polyethylene, this
03 material being sold under the trade mark Plastizote by Bakelite
04 Xylonite, Ltd., U.K. Other suitable acoustic decoupling
05 materials may be used, as well, such as glass fiber cloth, or
06 mineral wool.
07 The transducer may be mounted by taking a block 580 of
08 acoustic decoupling medium as shown in Figur-e 13 and forming a
03 recess 582 within the block of material for accommodating the
`10 transducer assembly of Figure 12. The entire block may be
11 clamped in any convenient way, such as by clamps 584, to a
12 suitable framework or support member 586, these items being
13 illustrated schematically. Other suitable mounting arrangements
14 for the transducer assembly will be described later below.
~15 To summarize briefly, the system described above
16 includes:
17 - Transducers Sl, S3, S4 for detecting shock wave
18 arrival times along a line parallel to the measurement plane,
19 which is in turn substantially parallel to the target.
~` 20 - Transducers Sl, S2 for detecting shock wave arrival
21 times along a line perpendicular to the measurement plane and
22 substantially parallel to the bullet trajectory.
~23 - An inertia switch mounted on the target for
~4 detecting actual impact of the bullet with the target.
` 25 - A unit for detecting the ambient air~temperature in
26 the region of the~transducer array.
27 The outputs of the transducers, inertia switch, and
,~
28 air temperature sensing unit are fed through circuitry as
29~ described above to the timer interface unit, which gives counts
representing times of shock wave arrival at the transducers,
~- 31 representing the inertia switch trigger time, and representing
32 ~ the air temperature. This information lS fed from the timer
~'
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~7~67
01 - 38 -
02 interface unit to the minicomputer. Provided that the
03 minicomputer is supplied with the locations of the transducers
04 relative to the measurement plane, it may be prog~ammed to:
OS - Determine the speed of sound in ambient air in the
06 vicinity of the transducer array (to a reasonable approximation)
07 by a known formula
08
09 VST = Vs~O ~ (13)
C 273
11
12 where VsT is the speed of sound in air at the given
~13 temperature T, and V~oc is the speed of sound at zero
14 degrees Celsius.
- Determine the velocity of the bullet in the
16 direction perpendicular to the measurement plane and
17 substantially parallel to the bullet trajectory, and
18 - Determine the location of the trajectory in the
~19 measurement plane.
However, the information provided from the timer
21 interface unit permits still further and very advantageous
22 features to be provided in the system for marksmanship
23 training. The system can be made to discriminate between direct
24 (free flight) target hits by the bullet, on the one hand, and
target hits from ricochets or target hits from stones kicked up
-~ 26 by the bullets striking the ground or spurious inertia switch
27 triggering due to wind or other factors, on the other hand. In
23 the embodiment employing timer interface unit 64, spurious
29 inertia switch triggering will cau~se counter 7 to count until
ripple carry signal RC7- is produced, thereby causing the system
31 to automatically reset. The system can be further made to
32 discriminate between ricochet hits on the target and ricochet
,
33 misses. These features further enhance the usefulness in
367
01 - 39 -
02 training as the trainee can be apprised, immediately after a
03 shot is fired, of the location of the shot relative the target
04 in the measurement plane, whether the target was actually hit by
05 the bullet, whether the shot ricocheted, and even of a "score"
06 for the shot.
07 The present invention contemplates three possible
08 techniques for processing the information from the timer
09 interface unit for the purpose of providing rocochet and stone
hit discrimination.
11 a) Electronic tar-get window. For a hit to be genuine,
~12 the hit position determination system should have recognized a
13 projectile as having passed through a target "window" in the
14 measurement plane approximately corresponding to the outline of
the actual target being fired upon. The target outline is
16 stored in the computer and is compared with the location of the
17 projectile as determined from the transducer outputs. If the
lB calculated projectile trajectory location is outside the
~19 "window", then the "hit" reported by the inertia switch or other
hit registration device cannot be ~alid and it can be assumed
21 that no actual impact of the bullet on the target has occurred.
~22 b) Projectile velocity. It has been found
23 experimentally that, although there is a variation in velocity
24 of bullets from round to round, any given type of ammunition
~25 ~ yields projectile velocities which lie~within a relatively
26 ~ narrow band, typically + or - 5%. It has also been found that
~27 when a projectile ricochets, its apparent velocity component as
28 measured by two in-line sensors along its original line of
29 flight is substantially reduced typically by 40% or more. It is
therefore possible to distinguish a genuine direct hit from a
31 ricochet by comparing the measured velocity component with a
32 preset lower limit representing;an expected projectile velocity
33 (which will generally be different for different ammunitions and
34 ranges). If the detected projectile velocity does not exceed
~7367
01 ~ 40 -
02 threshold limit, then the associated mechanical hit r-egistration
03 (inertia switch) cannot be valid and can be ignored. The
04 computer may be supplied with a minimum valid threshold velocity
05 for the type of ammunition being used, and the appropriate
06 comparison made. It is to be noted that this technique does not
07 require a capability to measure position, but only projectile
08 velocity, and can be implemented using only an impact detector
09 in combination with two sensors positioned relative to the
target for detecting the airborne shock wave generated by the
11 projectile at two spaced locations on its trajectory.
12 c) Hit registr-ation time. For a "hit" detected by the
13 inertia switch to be genuine, it must have occurred within a
14 short time period relative to the time at which the projectile
position determining system detected the projectile. It has
16 been found from theory and practice that this period is very
17 short, not more than ~ or - 3.5 milliseconds for a commonly-used
18 "standing man" target as illustrated in Figure 2. By
19 suppressing all target impacts detected by the inertia switch
outside of this time, many otherwise false target impact
21 detections are eliminated. The position in time and the
22 duration o the period varies with different targets, with
23 position of hit positions sensors (i.e. airborne shock wave
24 responsive transducers) relative to the target, with nominal
projectile velocity and velocity of sound in air, and, to a
26 small extent, with various target materials. All these factors
27 ~are, however, known in advance and it is therefore possible to
28 provide the system with predetermined limits for the time
29 period. It is to be noted that this last technique does not
- require a capability to~measure position or even projectile
31 velocity, and can be implemented using only an impact detector
32 in combination with a single sensor positioned relative to the
33 target for detecting the airborne shock wave generated by the
34 projectile.
.
~736~
01 - 41 -
02 Appendix A attached hereto is a suitable program
03 written in "BASIC" p~ogramming language which may be directly
04 used with the Computer Automation LSI 2/206 minicomputer. The
05 program is used for perfoLming the position calculations
06 indicated above, generating required reset signals for the timer
07 interface unit, calc~lating the speed of sound and bullet
08 velocity, performing threshold checks for bullet velocity,
0~ determining whether the inertia switch has detected a "hit",
determining a ricochet hit and providing appropr-iate output
11 signals for the printer and display units.
12 It will be recognized from the foregoing that the
13 computer programs of Appendix A employ the "projectile velocity"
14 and "hit registration time period" technique for ricochet and
stone hit discrimination. Those skilled in the art will readily
16 recognize the manner in which the programs of Appendix A may be
17 modified to employ the "electronic target window" technique for
18 ricochet and stone hit discrimination. That is, a mathematical
19 algorithm defining the boundaries of the target outlined in the
measurement plane may be included in the program and compared
21 with the X, ~ coordinates of the calculated bullet trajectory
22 location in the measurement plane to determine whether the
23 calculated location lies within the target "window". Assuming
24 for example that the target is a simple rectangle, the "window"
~25 may be defined in the program as XA<Xl<XB, YA<Yl<~B, where XA
~26 and XB represent the left and right edges of the target "window"
27 and YA and Y~ represent the lower and upper edges of the target
28 "window", respectively.
~. ~
:~
~73~7
01 - 42 -
02 Two Assembly Language subroutine facilities are
03 provided in the programming described above. They are:
04 CALL¦3): Execution of this BASIC statement resets the
05 timer interface unit 64 and readies the ciLcuitry for use. This
06 subroutine is assigned the Assembly Lanugage label RESET.
07 CALL~4 Z~, A2, T7, T6, T5, T4, T3, T2, T1):
08 Execution of this BRSIC statement transfer the binary numbers of
09 counters 1-8 of the timer interface unit to BASIC in sequence.
This subroutine is assigned the assembly language label IN: HIT
11 in the Controller BASIC Event Handler Subroutine Module.
12 Figures 14A and 14B show flow chart sections for the
13 subroutine RESET. Appendix B provides a program listing for
14 this subroutine. The subroutine RESET starts on line 40 of the
listing of Appendix B. It saves the return address to BASIC and
16 then tests that CALLl3) has only one parameter. Another
17 subroutine labeled RST ~line 31) is then called which contains
18 the instructions to reset the timer interface unit circuits.
19 Subroutine RESET ends by returning to BASIC.
Figures 15A, 15B and 15C provide a flow chart for the
21 subroutine IN:HIT, while Appendix B contains a program listing
22 for this subroutine~
23 Those skilled in the art will recognize that the
24 configuration of the transducer array in Figures 2 and 4 may be
modified within the spirit and scope of the present invention.
26 For example, Figures 16-18 show alternate embodiments of arrays
27 in which the transducers may be positioned.
~' .
,~
73~i7
01 ~ 43 ~
02
03
04
05
06 Still further modifications may be made in accordance
07 with the present invention, as will be recognized by those
08 skilled in the art. For example, one or more light curtains may
09 be generated for detecting passage of the bullet through an area
~10 in space, for the purpose of determining the velocity of the
11 bullet. Such apparatus may be of the type disclosed in U.S.
12 Patent No. 3,788,748 to KNIGHT et al., the content of which is
13 incorporated herein by reference. Figure 2 shows an apparatus
14 for generating a light curtain and detecting the passage of the
bullet therethrough. A continuous wave helium-neon laser 600
16 generates a beam 602 which is directed onto an inclined quartz
17 mirror 603 having a mirror coating on the second surface
18 thereof, relative to beam 602, such that a portion of beam 602
19 is transmitted therethrough to form beam 604. Beam 604 is
passed into a lens 605. Lens 605 is shaped as a segment
-~ :
3~i7
01 ~ 44 ~
02 of a circle cut from a sheet of matr-ial sold under the t~ade
03 name Perspex. Beam 604 is directed to bisect the angle of the
04 segment and passes centrally thereinto at a circular cut-out
05 portion 606. Cut-o-lt po~tion 606 causes beam 604 to project as
06 beam 608, which is of substantially rectangular cross-section
07 shown by the dotted lines and which has no substantial
08 tr-ansverse divergence.
09 Lens 605 comprises a generally triangular slab of
light transmitting material having two substantially straight
11 edges which converge, and having a part in the form of a part
12 cylindrical notch 606 adjacent to the apex confined by the
13 converging edges, which is adapted to diverge light entering the
14 lens at the apex. The two straight edges of the lens, not being
the edge opposite the apex at which light is to enter the lens,
16 are reflective to light within the lens. For example, the edges
17 may be mirrored. Such a lens is adapted to produce a fan-shaped
18 beam of light (a light curtain) having an angle which is equal
19 to the angle included by the edges of the slab adjacent the apex
~20 at which light is to enter the slab.
21 If a projectile such as a bullet should pass through
22 beam 608, it will be incided by beam 608. Since the projectile
23 cannot be a perfect black body, a portion of the heam will be
24 reflected thereby, and a portion of that reflection will return
~25 to lens 605 where it will be collected and directed at mirror
~26 603 as beam 609. Beam 609 is reflected by mirror 603, which is
~27 first-surface coated, with respect to beam 609, as beam 610.
28 The coating of mirror 603 is such that ~eam 610 will be
29 approximately 50% of beam 609. Beam 610 passes through an
~-30 optical band pass filter 612 which prevents light of frequency
31 substantially different to that of laser 601 from passing,
: -
~ ~7367
01 - 45 -
02 so as to reduce errors which may arise from stray light s~ch as
03 sunlight. Beam 610 emerges as beam 613, which then passes
04 th~ough lens 614. Lens 614 focuses beam 613 onto the cente~ of
05 a photoelectric cell 615, which emits an electrical signal 617.
06 Signal 617 thus indicates the time at which the plojectile
07 passed thro~gh the light curtain.
08 Figure 20 shows schematically a system according to
09 the invention which may be ernployed for determining the velocity
of the bullet in a direction noxmal to the measurement plane and
11 the location in the measurement plane. A target 596 is mounted
12 on a target mechanism 598 (which may be as shown in Figure 2).
13 An array of, for example, three transducers Sl, S2, S3 is
14 provided in front of and below the edge of target 596. Two
arrangements as shown in Figure 19 are located in front of
16 target 596 to generate respective light curtains 608, 608' and
17 produce output signals 618, 618' indicating the time at which
18 the bullet passes through the respective light curtains. Since
19 the spacing between the light curtains 608, 608' is known in
advance, the time difference may be employed to determine the
21 velocity of the bullet in a direction normal to the measurement
22 plane. The calculated velocity and the speed of sound in air
23 (as separately measured or determined) may be employed with the
24 output signals from transducers Sl-S3 to determine the location
at which the bullet trajectory passes through the measurement
26 plane. An inertia switch or other target impact detector may be
27 used, as described above, for registering an actual hit on the
28 target.
:
~73~;7
01 - ~6 -
02 Those skilled in the art will readily recognize the
03 manner in which the BASIC programs of Appendix A may be modified
04 for use with an arrangement as shown in Figure 20. The skilled
05 artisan will also recoynize that, for example, light c~rtain 608'
06 may be deleted and the velocity of the bullet may be determined
07 from the output 618 of photoelectric cell ~15 and the output of
08 transducer S2 of Figure 20.
09 Those skilled in the art will also recognize that
marksmanship training may be further enhanced by combining the
11 use of the arrangements described herein with a rifle equipped
12 with pressure sensors at critical points as described in U.S.
13 Patent Application No. 835,431, filed September 21, 1977 (the
14 content of which is incorporated herein by reference). For
example, the rifle used by the trainee may be equipped with
16 pressure sensitive transducers located at the parts of the rifle
17 that are contacted by the trainee marksman when the rifle is
18 being fired. Thus, a transducer is located at the butt of the
19 rifle to indicate the pressure applied by the shoulder of the
trainee marksman, a transducer is provided at the cheek of the
21 rifle to indicate the pressure applied by the cheek of the
22 trainee marksman, and transducers are provided at the main hand
23 grip and the forehand grip of the rifle. ~he outputs of the
24 transducers are coupled to suitable comparator circuits as
described in U.S. Patent Application No. 835,431 and the
26 comparator output signals then indicate whether the pressure
27 applied by the trainee marksman at each critical point on the
28 rifle is less than, greater than, or within a predetermined
29 desired range. While a display as described in U.S. Patent
Application Serial No. 835,431 may be employed for indicating
31 whether the pressure applied by the trainee marksman to the
32 rifle at each point is correct, it will be understood that the
33 comparator output signals may alternatively be provided to mini-
34 computer 70 in a suitable format so that the visual display unit
72 of Figure 4 will display a graphic representation of the rifle
~73~:i7
01 _ 47 _
02 and indication the~eon of the pressure applied by the trainee
03 marksman to the rifle. This graphic display may be in addition
Oq to a graphic display of the target being fired upon and
05 representations thereon of the location at which each bullet has
06 str~ck or passed by the ta~get, Such an arrangement provides
07 the trainee ma~ksman with an almost instantaneous indication of
08 the manner in which he is holding the rifle and of his shooting
09 accuracy, and permits rapid diagnosis of any difficulties he may
10 ' be having with his shooting. If a switch is mounted on the
11 rifle for actuation when the trigger is pulled as described in
12 U.S. Patent Application Serial No. 835,431, the visual display
13 unit 72" may be made to indicate the pressure applied to the
14 various pressure transducers on the rifle at the precise instant
of firing the rifle. The display may be maintained on the
16 display unit for a pr-edetermined period of time and then erased
17 so the trainee may proceed with firing a further round.
18 ?he addition of the pressure sensitive system enables
19 the simultaneous display of pressure indications together with
the projectile position and for positive target hit indication
21 and/or ricochet indication. Such a simultaneous display has
22 unique advantage in providing the trainee immediately not only
23 with an indication of where the projectile has passed in
24 relatiqn to the target, but why the projectile passed through
~25 its displayed position. This information provides immediate
26 positive and negative reinforcement of marksmanship techniques
27 with respect to the correct grip and aim of the weapon to permit
28 rapid learning of correct skills.
367
01 - 48 -
02 It is not necessary to employ an inertia switch to
03 detect a "hit" of the projectile on a target member. Other
04 apparatus may also be employed for this pu~pose. For example,
05 Figures 21-22 show an arrangement fo~ sensing impact of a
06 projectile on a target member 700 employing a sensor assembly
07 702 positioned in front of the rigid target member 700. The
08 rigid target member 700 may be of any desired shape and may be
09 constructed, for example, of plywood or ABS material. Sensor
7Q2 includes a transducer mounted within a shrouded housing
11 which prevents any airborne shock wave Gf a supersonic
12 projectile from being detected. The output of the shrouded
13 sensor assembly 702 is provided through an amplifier 704.
14 The output of amplifier 704 is provided through a
suitable signal processing circuit 706, which provides a "hit"
16 output indication. Signal processing circuit 706 may comprise
17 essentially a threshold detector. Shrouded sensor assembly 702
18~ may comprise a transducer 709 (as described above with reference
19 to Figures 11-12) mounted in a block of acoustic isolating
material 708 (such as described above with reference to Figure
21 13). The block of acoustic isolating material is, in turn,
22 mounted in a housing or shroud 710, with the transducer 709
23 recessed to provide a restricted arc of sensitivity of the
24 transducer which is appropriate to just-"see'~ the face of target
~25 700 when sensor assembly 702 i9 appropriately positioned
26 relative to the target member 700. A coaxial cable from
27 transducer 709 passes through an opening~in shroud 710 and
28 may be isolated from vibration by a silicone rubber~ring
29 712, or the like. It will be unders~ood that the
~, .
~73~;~
01 - 49 -
02 threshold level of detector 707 in Figure 21 is to be
03 appropriately set so that disturbances of the target detected by
04 transducer 709 will produce a "hit" output indication from
05 signal processing circuit 706 only when the amplitude of the
06 detected distur~ance is sufficiently great to indicate that the
07 distu~bance of the target was caused by a projectile impacting
08 on or passing through target member 700.
09 A further arrangement for determining projectile
"hits" on a rigid target member will now be described with
11 reference to Figures 23, 24, and 25A-25B. Figure 23 shows a
12 rigid target me~ber 720 which has substantial curvature in
13 horizontal cross-section. A sensor 722 (which may be a
14 transducer mounted in an acoustic isolating block as described
above with reference to Figures 11-13) is located behind the
16 rigid target member 720 and preferably within the arc of
17 curvature thereof. The output of transducer 722 is supplied to
18 an amplifier 724, the output of which is in turn provided to a
19 signal processing circuit 726 for providing a "hit" output
indication.
21 One possible arrangement for the signal processing
22 circuit 726 is shown in Figure 24. It has been found that
23 genuine "hits" on the target by a projectile result in
24 electrical signals from the transducer 722 consisting of a
number (typically greater than 10) of large amplitude pulses
26 closely spaced, while misses or hits by stones, debris, etc.,
27 either cause low amplitude signals or low amplitude signals with
28 only occasional high amplitude "peaks".
,~
67
01 - 50 -
02 Typical "hit" and "miss" wave forms are shown in
03 Fig~res 25A and 25B, respectively. The signal processing
04 circuit 726 of Figure 24 operates to distinguish the signals of
05 Figures 25A and 25B by the use of integrating capacitor- C and
06 bleed-off resistor R2. Only multiple peaks as in Figure 25A
07 will trigger the second threshold detector of Figure 28.
08 The technique for distinguishing "hit" from "miss"
09 described above with reference to Figure 24 applied in principle
to any combination of rigid target and sensor, but has
11 particular benefit when used with a 3-dimensional type target
12 such as that shown in Figure 23 or such as a target which
13 completely encircles the transducer (such as a conically-shaped
14 target member). By virtue of the shape of the 3-dimensional
talgets, existing mechanical hit registrations systems, such as
16 inertia switches, often cannot be sued to detect hits on the
17 target because vibration transmission within the target may be
18 telatively poor. Secondly, the curved shape of the target
19 provides very effective screening of the sensor from ~he
airborne shock wave produced by neat-missed supersonic
21 ~ projectiles. The curvature of the target can be increased to
22 the point where it forms a complete shell wi~h the sensor
23 positioned inside it thus enabling hit detection from any
24 d~rection of fire.
-
3~7
01 - 51 -
02
03
04
05
06 Still another apparatus for detecting a projectile
07 'Ihit" (i.e. passage through a target member) is illustrated in
08 Figure 26. In this embodiment, the target member comprises a
09 sheet of suitable electrically insulating spacer material 730
which may be of any desired size. Metal meshes 732, 734 are
~11 cemented to the insulating spacer sheet 730. As a bullet passes
12 through the "sandwich" target comprising bonded-together members
13 730-734, electrical contact between metal meshes 732, 734 is
14 ~ established, so that the voltage at point 736 drops momentarily
:: ~
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:~ : : :
~: : : ~ ; : ~:
,
:
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.
.
,
7367
01 - 52 -
02 from +5 volts to 0 volts, thereby indicating passage of tne
03 bullet through the target "sandwich".
04 Still other appalatus is possible for dete~mining the
05 velocity of the projectile, such as shown in ~igure 27. A
06 projectile fired from a weapon 740 travels along a trajectory
07 742 toward a target member or target zone 744. An array of
08 transducers Sl, S2, S3 is located below one edge of the target
09 member or zone 744. For determining the velocity of the
projectile, a detector 746 is positioned to sense the time of
11 discharge of the projectile from a weapon and provide a signal
12 which starts a counter 748. Counter 748 is supplied with pulses
`13 from a clock generator 750 and counts the clock pulses until a
` 14 signal is received from transducer S2 through an amplifier 752
~15 for stopping the counter.
16 It is known that projectiles, such as bullets,
17 decelerate in a well-defined and consistent manner. This
18 deceleration can be expressed in terms of loss of velocity per
` 19 unit distance travelled along the trajectory, the deceleration
being substantially constant from sample to sample of high
~21 quality ammunition ~such as most military ammunition) and being
22 substantially independent of velocity. ~t any point along its
23 trajectory, the projectile velocity Vt is:
; 24 Vt = Vm ~ d-k
~25 where Vt = projectile velocity at point in question
26 Vm = nominal velocity of projectile at weapon or
27 known origin
28 d = distance from muzzle (or known origin) to
;29 point in question
k = above-mentioned "decelelation" constant
: ~ :
~,
;~ :
~.~
7367
01 - 53 -
02 By simple algebra, it is possible to find an
03 expression for distance travelled in a given time, which is:
04
05 d(t) = Vme~kt
06
07 where t is the independent variable of time. For good quality
08 ammunition the constant "k" is well controlled, and can be
09 predetermined with good accu~acy. Thus, the only "unknown" is
Vm/ which will vary from round to round.
11 , The arrangement according to Figure 31 operates to
12 determine a notional value for Vm by measuring the time of
13 flight of the projectile from the weapon to the array. The
14 preceding equation permits Vm to be computed and, once obtained,
permits Vt in the vicinity of the transducer array to be
16 calculated. Detector 746 may be an optical detector sensing the
I7 weapon discharge muzzle flash, or an acoustic device responding
18 to the muzzle blast and/or supersonic projectile shock wave.
:
'
.
:'
~: :
-
,
`, ~ :
7367
01 ~ 54 ~
02
03
04
05 Figure 28 shows a graticule overlay used on the visual
06 display screen 72" of Figure 4. A target T is provided as well
07 as a separate score column for each shot. If the positive hit
08 indication (inertia switch) is not actuated, a "0" score is
09 indicated, otherwise a non-zero point score is displayed. The
positive hit indication is particularly advantageous for
11 borderline cases, as for example, shot No. 6. In such cases, it
` 12 may not be clear from the position display alone whether a "hit"
13 occur-red. Shot No. 1 is shown as a clear miss; shot No. 2 as a
14 ~ ricochet hit, shot No. 5 as a ricochet miss and shot numbers 3,
4 and 7 as hits having different polnt values.
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