Note: Descriptions are shown in the official language in which they were submitted.
z~
Ihis application is a ~;~Tision of Can~cTi~r~ ,pplicatic~i Serial
No. 343,273 filed J~uary ~th, 1980,
3ACRGROUND O~ TEE INVEN~IO~
_
1. ~ield of 'he Invention
The present invention relates *o an apparatus
for determining in o-m~tion concerning the point
in which a trajectory of the supersonic projectile
passes through a predetermined measurement plane,
2. The prior Art
W~en a projectile travels through the atmos-
phere with ~ supersonic velocity, a conically-
expanding pressure or shoc~ wave is generated, with
the projectile being at the apex of the shock wave.
It has been proposed to provide apparatus
for determining the position at which the trajectorv
of ~he projectile passes throug~. a plane, emplo~ing
transd~cers or ,he like to detect such a shock wa~e
generated by a supersonic. projectile. One such
?roposal is descri~ed in ~.5. Patent ~o. 3,778~05C
(~ohrDaugh~.
Other target svstems are disclo~ec` i,. C~;iss
Patent Specification Ch-PS 5~9,835, granted ~ay 15,
1977, to Walti, and Germ~n ~tilit Model Dr-GM
77 2~ 275 of Walti, laid o?en i~arch 1~, 197~.
O her prior art systems are known, as well, bu. r.on~
provides comp-eher.sive ~rzining in prope~ marks-
manship. The prior ar. target arrangemer.ts ~rovi2e
or,l~y partial informat-~on to the trainee marksman aDoUt
the progress of his shooting, For example, the afore-
mentioned prior art re~rences provide s~stems whichdetermine a location at which a projectile fired
at a target p2sses relati~e to the target,
3-
'~.S. Patent No. 3,233,904 of~ers an autornatic
target apparatus h2ving 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.
S'J~RY OF ThE INV~NTION
~ he present invention provides a considerab-
ly more versatile and sophisticated system f~r
1~ training in maxksmanship than has heretofore been
pro~,c,sed. In order to more effectively instruct
trainees in marksmanship training, it is advantageous
~o provide positive and negative reinforcement of
shooting techniques im~ediately after each shot is
fired. Such reinforcement may take a number of
forms, but preferably comprises a plurality of in-
dications concerning each shot fired. For example,
it is desira'ble to provide the trainee marXsman with
an at least approximate ~ndication of where a pro-
~0 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 projectile has ricochete~ prior to
reaching the zone of the targe.. It is also ad-
2~ vantageous to provide, in co-nbination with one of
the foregoing indications, information concerning
whether the trainee marksman is correctly gripping
~he weapon being fire~. The marksmanship training
system is particularly effective for besinning marks-
3Q mt-n who ma~ no~ be hol~ing the weapon correctly
and who may not even be shooting sufficiently near
the target to score a "hit." Such a marksman is
-4-
thus apprised o~ the ~anner in which he should
change his ~echni~ue to imprc,ve his shooting~ ~he
s~stem is, however, also effective for more advancec
shooters, wh~ may wish to not or.ly have an indication
th~t the target has been hit by a prcjectile, but
whether the projectile has struck a particular
region of the target.
A ~irst form of the invention comprises
apparat~s for use in marksmanship trainins in which
a projectile travels along a trajectorv Lrom a firing
point toward a target member and through a measurement
plane. The apparatus detects and indicates relative
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 t~e projectile passes relative to the target
member. The apparatus further detects an~ provides
a positive indicatio of a projectile "~.it" 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 2 positive
indication of whether the projectile has hi~ the
target, the indications making it a sim?le matter fGr
the .rainee marksman to aistinguish hits at the
2~ edge of the target from misses near t:~e edge of
tne target.
In another form of the invention, the apparatus
detects an~ indicates relative to a target represent-
ation a location ir the measurement plane through
which the trajector~ passes, therebv provi~ing at
least an approximate in~ication of where the projectile
passes relative to the target The apparatus also
measures the velocitv of the projec~ile in the vicinity
-5- ~
~f ~e target me~ber, comparing the measured
velocity with at least one expected projectile
velocity ~alue to ascert~in if the me2sured velocit~
is within an expected projectile velocit5~ range.
An indication of thP result of this comparison
is provided, so th trainee marksmzn is apprise~
of where the projectile passes relative to the
target member as well as whether the projectile
has passes through the measurement plane in free
flight ~i.e., without ricocheting) or has ricocheted
prior to passing through the measurement plane.
A third form of the invention provides
the trainee marksman with at least an approximate
indication of where the projectile passes relative
to the target 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 hitting the ta~rget or from a projectile
which has ricocheted prior to hi~ing the target,
Such a system, particulzrl~ for besinnins trainees
who ma~ not even realize that shots are beinq firec
slightly below the target and ricocheting up intc
the region o the target. Absent some means of
de'en~ining ~ositivelv ~:~ether the projectile
has ricochete~, a "ricochet hit" on the target
may b~ indicated as simply a "hit" on the tar~et,
providing the trainee marksman erroneouslv ~ith
positive reinforcement of incorrect shooting techni~ueO
~Q According to one particularly advantageous
form of the inv2ntion, the appaxatus for detecting
a hit on the target com?rises a device, such as a
transducer, spaced ap~rt ~rom, and not physically
connected to the ta ge. me~er for detecting and
-6~
selPctively providing a hit indication onl~ in
response to disturbance of the target mem~er
caused by a projectile hitting the target member.
This particular apparatus for hit cetection is in-
tended to overcome problems with some prior art
syste~s 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 kic~ed-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 flight path of the projectile and shielded
1~ in such a manner as to detect air pressure disturbances
caused by the projectile hittin~ or passing through
t~e target, but not disturbances caused ~ the
airborne shock wave of the supersonic projectile.
Alternately the t~ucer is.loca ~ b~ a 3~ ~sional
~Q target and at least partially shielded from the
airborne shock wa~e of 2 supersonic projec~ile
by the tar~et member itsel,
~ ne particularly advantageous zrrangement
for indicating the location in a measuremen. pi2ne
throuah which the trajectory Ot- a su?ersor,ic projectile
passes is also provided. The arrangement includes
an array of at leas~ three transducers responsive
to an airborne shoc~ wave from the su?ersonic pro-
jectile and located at ~espective predetermined
positions spaced along a line substantially parallel
to the measurement plane. Apparatus is provided for
32~D
, ~
01 ~ 7 ~
02
03 measuring velocity o-f the supersonic projectile, and for
04 measuring velocity of propagation of sound in air in the vicinity
05 of the array of transducers. Computing apparatus is responsive
06 to the transducer array and the projectile velocity and
07 propagation velocit~ 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 invention is
12 some form of graphic display for provi.ding 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 w~ich 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 indication 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.
01 - 8 -
02
03 More particularly, the invention is apparatus or
04 indicating the location in a measurement plane throuyh which the
05 trajectory of a projectile passes, the projectile travelling from
06 a firing point toward a target zone and through the measurement
07 plane, comprising a target member located on the target zone, an
08 array of at least three transducers responsive to an airborne
09 pressure wave from the projectile and located at respective
predetermined positions spaced along a line substantially
11 parallel to the measurement plane, apparat~s for measuring
12 velocity of the projectile, apparatus for measuring velocity of
13 propagation of sound in air in the vicinity of the array of
14 transducers, and computing apparatus responsive to the array of
transducers, the projectile velocity measuring apparatus, and the
16 propagation velocity measuring apparatus comprising apparatus or
17 determining the location in the plane through which the
18 trajectory of the projectile passes, and apparatus for providing
19 an output indicating the determined location.
It will be seen from the description which follows with
21 reference to the drawing figures and computer program appendices
22 that the present invention provides a comprehensive marksmanship
23 training system which is both versatile and sophisticated, and
24 which provides a level of training that has heretofore been
unknown in the field.
9--
2vC~
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 shows in perspective view a marks-
manship trainin~ range employing concepts of the
present invention;
~IGU æ 2 shows in perspective view a target
mechanism equipped with a target member, a hit sensor,
and transducers for detecting an airborne shock wave;
FIGURE 3 shows a coordinate system relating
the positions of shock wave-sensing transducers;
FIGU æ 4 shows a schematic block dia~ram of
an overall system in accordance with the invention;
FIGURE 5 shows an isolator module circuit
for block 66 of Fi~ure 4;
FIGURE 6 shows in block schematic form one
channel of comparator 62 of Figure 4;
FIGURES 7A - 7~ show in detail one possible
form of timer interface 64 of Figure 4;
FIGURES 8A and 8B show a suitable circuit
arrangement for the air temperature sensing unit 78
of Figure 4;
FIGURE 8C shows a timing diagram for the
circuits of Figures 8A and 8B;
FIGURE 9 shows airborne shock waves impinging
on a piezoelectric disc transducer;
FIGURE 10shows an outpu~ waveform for
the transducer of Figure 9;
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);
--10--
~L~2~
FIGUP~S 15~ - 15C show flow charts for
computer subroutine CALL(4);
FIGURF,S 16- 18 show alternate transducer
arrangements in plan view;
FIGUR 19 shows apparatus for generating a
light curtain and detecting the passage of a projec-
tile therethrough;
FIGURE 20 shows an arrangement emploving
- two such constructions as shown in Figure 19, in
combination with an array of txansducers for detecting
an airborne shock wave;
FIGURES 21 and 22 show an arrangement for
sensing impact of a projectile on a target me~ber;
FIGURES 23 and 24 show an alternate arrange-
ment for detecting a projectile hit on a ~arget member;
FIG~RES 25A and 25B show typical transduceroutput signals for "hits" and "misses" of a projectile
passing relative to the target member, respectively;
FIG~RE 26 shows a target member construction
for detecting passa~e of a projectile therethrough;
FIGURE 27 shows an alternative arrangement
for determinina projectile velocity; and
FIGURE 28 shows a ~raticule overlay used on
the visual display screen of Figure 4.
æ~j~
Dr TAILEO D~:SCRIPT101~ OF PR:~ERR--~D EMB3DIl~S
_
Figure 1 shows in perspective view a marks-
manship trainins ranye employing concepts of
the present invention. The range has a plurality
5 . o. firing points 10 from which trainee marksmen 12
shoot at targets 14. Located in front of ~he targets 14
is, for example, an earthen embankment which does not
obstruct the marksman's view of targets 14 rrom the
firing points, but which permits the positioning of
transducer arrays 18 just below the lower edge of
the target and out of the line ol fire, The transducer
.arrays ~ill 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 data processor
or computer (not shown) located near the ~ransducer
array, which is in turn coupled to the visual display
uni~s. As will be explained below, each transducer
2G arra~ de~ects the shock wave generated by a superson~c
projectile, such as a bullet, fire~ at the respective
Izrset, and the computer 22 is operative to de,ermine,
the location in a measurement ?lane in front o_ the
target thlough which the bullet trajector~ ?asses. ~eans
2; ~not shown in Figure 1) are p ovi~ed at each target for
detectins when the target h2s been "hit" b~ a p~ojec.ile.
Co~puter 22 is coupled to suitable visu21 displa~ units 26,
28, 30, located respec_ivelv in the control room 24,
at each firing point 10, and at one or more other
locations 30. Provided on the visual display units may be,
for exam~le,an aFproximate indication, relative to a target
representation, of where the projectile hzs passed
through the measurement plane, and an indlcation of whether
the target has been "hit" by ~he projectile,
01 - 12 -
02 Spectators 32 may observe the progress of shooting of
03 one or more of the trainee marksmen on visual display
0~ unit 30. The computer may be coupled with a suitable
05 printer or paper punching device 34 to generate a
06 permanent record of the bullet trajectory location
07 determined by the computer.
08 Although the targets 14 shown in Figure 1
09 have marked thereon representations of the
conventional bull's-eye type target, the target may be
11 of any suitable configuration, such as a rigid or
12 semi-rigid target member 35 as shown in Figure 2 on
13 which may be provided the outline of a soldier or the
14 like. Means are provided for detecting when a
projectible fired at the target member has "hit" the
16 target member, and the target member may be mounted on
17 a traget mechanism 36 which is operative to lower the
18 target out of sight of the trainee when a "hit" is
19 detected. The "hit" detecting means may be an inertia
switch 38 as shown in Figure 2, or any other suitable
21 apparatus. Alternative "hit" detecting arrangements
22 will be described below. The automated target
23 mechanism may be of the type described in U.S. Patent
24 No. 3,233,904 to GILLIAM et al (the content of which
is incorporated herein by reEerence~. Target
26 mechanisms of this type are available commercially
27 from Australasian Training Aids ~Pty) Ltd., Albury,
28 N.S.W. 2640, Australia, Catalog No. 106535. Inertia
29 switches are commercially available from Australasian
Training Aids (Pty) Ltd., Catalog No. 101805.
31 In the arrangement of Figure 2,
32 transducers Sl-S4 are mounted on a rigid support
33 member 40, which is in turn mounted on the target
34 mechanism 36. ~lthough the transducer arrays 18 may
be supported separately from the target mechanism
36 beneath targets 14 (as in Figure 1), affixing the
37 transducer array to the target mechanism as in Figure
38 2 assure correct alignment of the measuremen~ plane
39 relative to target member 35. Transducers Sl-S4
01 - 13 -
02 (Figure 2) preferably each comprise a disk-shaped
03 piezoelectric element oE 5 mm diameter mounted to a
04 hemispherical aluminum dome, the hemispherical surface
05 of the dome being exposed for receiving the shock wave
06 from the bullet. The airborne shock wave generated by
07 the bullet is represented by the series of expanding
08 rings 42, the bullet trajectory by a line 44, and the
09 acoustic vibrations induced in the target member 35 on
impact of the bullet by arc segments 46
11 Figure 3 shows a three-dimensional
12 coordinate system in which the positions of the four
13 transducers Sl-S4 are related to a reference point ~0,
14 0, 0). The transducer array illustrated is similar to
that shown in Figure 2, with a row of three
16 transducers Sl, S3, 54 situated at spaced locations
17 along the X-axis and with a fourth transducer S2
18 situated at a spaced location behind transducer Sl
19 along the Z-axis. A portion of target member 35 is
also shown for reference purposes, as is an arrow 44
21 representing the bullet trajectory. The distance
22 along the X-a~is from transducer Sl to transducers S3
23 and S4, respectively, is represented by distance d.
24 The distance along the Z-axis between transducers S1
and S2 is represented by d'.
26 The X-~ plane intersecting the origin of
27 the Z-axis of the coordinate system shown in Figure 3
28 is considered to be the measurement plane in which the
29 location of the trajectory is to be determined.
Transducers Sl-S4 provide output signals
31 in response to detection of the shock wave of the
32 bullet, from which the location in the measurement
33 plane through which the p~ojectile trajectory passes
34 can be determined. A mathematical analysis is
provided below for a relatively simple case in which
36 it is assumed that:
37 1) The transducer array is as shown in
38 Figure 3;
3 2~
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 i5 normal to the
05 measurement plane;
06 4) The projectile travels with constant velocity;
07 5) Air through which the shock wave propagates to
08 strike the transducers is
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 accep~able,
17 since the resulting error in calculated location in the
18 measurement plane through which the projectile 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 VB is defined as the velocity of the supersonic
26 projectile along its trajectory.
27 The velocity VB of the bullet in a direction
28 normal to the measurement plane can be determined from the
29 times of arrival Tl, T2 of the shock wave at
-15-
tr~nsducers Sl and S2 an~ ~rom the distance 2' bet~een
tra~sducers Sl and S2:
d` (1)
-- T2 -- Tl
Then the propagation velocit~ o' the shock wave
front in a direction normal to the projectile velocity
may be defined as.
V = V
1 ~ Vs 2 (2)
The differences between the times oL arri~7al
of the shock wave may be defined as:
1 T3 ~1 (3)
t2 = T4 Tl
The X-axis c~o~dinate of the i~.ersecticn
point of the projectile trajectorv w-,h _he measure-
ment plane is:
(tl-t2) (V~2 tlt2 ~ ~2
X
2~ (~1 + t2)
The distance in the measurement plane 'rom
sensor Sl to the point o_ intersection o_ the projectile
trajector~ with the measuremen. plane is:
_ ~2 (tl2 + t~ ) ~
(6)
2V~; ~tl + t2)
The Y-axis coordinate of the intersection
point of the bullet trajectory with the measurement
plane is:
y = 1 2 _ x2 (7)
01 - 16 -
02 It is possible to construct a mathematical solution
03 for the above-described transducer system which incorporates
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 e~pected 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 Sl-S4 in a " T" configuration 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,
01 - 17 -
02 each channel OL which provides an output when the input signal
03 of that channel exceeds a predetermined threshold level. Thus,
04 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.
The output of channel 1 of comparator unit 62 is
16 coupled to the inputs of channels 0 to 1 of timer interface unit
17 64, the output of channel 2 of the comparator uni-t is couple~ to
18 the input of channel 2 of the timer interface unit, the output
19 of channel 3 of the comparator unit is coupled to the inputs of
channels 3 and 43 of the timer interface unit, and the output of
21 channel 6 of the comparator unit is coupled to the input of
22 channel 6 of the timer interface unit. The channel 5 input of
23 the timer interface unit is coupled via comparator unit channel
24 5 to an air temperature sensing unit 78 which has a
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 described below with
28 reference to Figures 8A-8C.
32~
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 swi-tch 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 projectile on the rigid target member
35 of Figure 2. The output of isolator module 66 is supplied to
11 two remaining inputs of timer interface 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 disk drive available
from Compu~er Automation, 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 minicomputer.
01 - 19 -
02 Other peripheral uni-ts 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' for 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 P~rimetric Service and Supplies, 242-2~8 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 equipped 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.
Zq>~
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 92 820~
18 94 50~2~4360
lg 96 ~70
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
2~ 106 0.22uF
29 108 47~
2~
01 - 21 -
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 provicled through a high pass filter 110 to one input of
05 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. ~ 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 value.
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 display unit 72
31 and/or units 72', 72" of Figure 4O
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 ~o. _ Receives Signals initiating from
~ Transducer Sl
16 1 " Sl
17 2 " 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 "UP/DOWN COUNTER 1" ~ .
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 "~ATES 1")
07 on receipt 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 signal CLR and provide clear signals CLB to
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-~ 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
107. 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 ~riggers a monostahle
34 element which then provides clear signal CLR in the form of a
logic pulse to clear up/down counters 1-7 and input latches
36 FF~-FF7 of Figure 7A~
01 - 24 -
02
03
04
05
06
07
08
09 Up/down counters 1-7 are reset by signal SEL4- from
the computer before each shot is fired by a trainee marksman.
11 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 Figures 78E and 7F in response to computer
19 commands. Timer interface input "S.S." receives "hit"
indication signal VEL- from the inertia switch isolator module
21 66, and provides a counter enable signal ENA8- for up/down
22 counter 8.
01 - 25 -
02 The computer communicates with the -timer interface unit b~
03 placing a "device address" on lines AB03- AB07 (Figure 7D) and a
04 "function code" on lines ABO~- 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 in~erface from responding to memory addresses
14 which also appear on the address bus.
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 input/output function signals from latch 2A are
18 labeled IOF0 through I~F2.
13 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.
If the computer is executing a "select" instruction
26 for the timer interface, the combination of signals IOF~ - IOF2
27 and ADEXP- (Figure 7D) produce one of select signals SEL~-
28 through SEL7- at BCD/ decimal decoder 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 7C3 and triggers
34 monostable element 328 via NAND 2 (Figure 7B)
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 Eor 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 E`F~ - FF7,
14 producing a respective one of signals LCH~+ through LCH7+.
Signals LCH1 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 EOR7 to produce a respective counter enabling signal ENA1-
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 associated LCH+ lines are low while the counters
29 are enabled.
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- causes gate NAND 2 (Figure 7B) to trigger
05 monostable element 328, producing clear signal CLR, which resets
06 latches FF~ - FF7 and up/down counters 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 FF~. Latch FF9 is thus clocked set when a
signal VEL- is received at the ''S.SO'' 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 reset, 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 GAT~
19 EO ~ is permanently high, so the output of gate EOR~ is high.
Since signals LCHl+ through LCH7+ are all low, signals ENAl-
21 through ENA7- are all high, disabling all of up~down counters
22 1-7. 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
array shown in Figure 4. Channel 3 of Eigure 7A triggers first,
26 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 highl so the output of gate EO~ 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
01 - 2~ -
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
0~ 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 (Figure 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
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 unit and the output of transducer
S4 triggers counter 5)
31 T6 positive count from counter 6 (transducer S4)
32 T7 positive count rom 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. I~ad the bullet struck the target, a non-zero count
01 - 29 -
02 would be recorded 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 received
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 ~-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
lS signals are supplied to gate NAND 2 (Figure 7B), which fires the
1~ 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
cables).
27 Referring to Figure 8B, a temperature sensor ICl
~8 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.OO
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 ac~ive
36 element of temperature sensor ICl.
01 _ 30 _
02 ReEerring again to Figure 8A, when transducer Sl
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 orm 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., and semiconductor Q2 may be of
24 type VN 40AF, available from Siliconix Inc., 2201 Laurelwood
Road, Santa Clara, California, 95054.
~z~
01 - 31 -
02 When wave form C, which is normally high, goes low, metal o~ide
03 semiconductor ~2 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 IC1
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 rise 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 ~C is linear
26 and ignoring offset voltages in the circuit, which will be
27 small):
28
29 tl_ TH2 (8)
d Vo
31 dt
32
33 where VO = voltage of wave form D, Figure 8C,
01 - 32 -
02 and
03
04 dt VO ~ ~ (9)
05
06 where IIN = current through ICl
07 IIN = C eK (10)
08 where C is a constant of proportionality and
09 4K is the absolute temperature of ICl
combining (8), (9) and (10),
11
12 tl _ V~I2 Cl (11)
13 ceK
14
or
16 ~ _ V~12 Cl (12)
17 K Ct
18
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
2~ 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
piezoelectric material (Figure 9)O 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 to detect this accurately since the amplitude of the
01 ~ 33
02 "pip" 542 depends upon the position of the bullet relative to
03 the transducer, is difficult to distinguish from background
04 noise and can even be absent under some circums-tances.
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.
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, 53~ 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
the diskD 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
01 - 34 -
02 contact with the transducer disk and being suitable
03 for transmitting shock waves from the atmosphere to
04 the transducer disk. Shock waves generated by
05 projectiles fired at the target will always s-trike the
06 hemispherical dome tangentially, and shock waves will
07 be transmitted radially through the dome dlrectly to
08 the center of the transducer. The constant timing
09 error thereby introduced will cancel out during
calculation of the bullet trajectory location.
11 The hemispherical dome prevents or
12 minimizes generation of posi~ive-going pip 542 so the
13 output of the transducer more closely resembles a
14 sinusoidal wave form. The instant oE commencement of
this sinusoidal wave form must be measured with great
16 accuracy, so the transducer must have a fast response.
17 It is advantageous to utilize a
18 piezoelectric disk having a diameter of about 5 mm,
19 which provides a fast response time and a relatively
high amplitude output signal.
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
04 present invention comprises a transducer elemen-t 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 surace of the disk, respectively, by soldering or by ultrasonic
bonding. Disk 550 is then firmly mounted in a housing which
16 comprises a cylindrical member 558 having recess 56n 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 adjacent 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 this 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
aluminum case 568 and subsequently being machined. If the
01 - 36 -
02 latter construc-tion 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 pro~rude 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 550. The dome 57~ may be machined from aluminum or cast
1~ from a setting resin material such as that sold under the trade
mark Araldite. The dome 574 preferably has an outer diameter oE
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 which 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,
if the transducers are mounted on a rigid horizontal frame work,
31 it is important that the transducers be acoustically decoupled
32 from 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.
f -
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 5~80 of
08 acoustic decoupling medium as shown in Figure 13 and forming a
09 recess 582 within the block of material for accommodating the
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.
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.
- 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
24 detecting actual impact of the bullet with the target.
- 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 is fed fro~ the timer
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 programmed to:
05 - 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 = VSeo ~ + 0.09 (13)
1~ C 273
11
12 where VsT is ~he speed of sound in air at the given
13 temperature T, and Vs~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~ ~n
28 the embodiment employing timer interface unit 64, spurious
29 inertia switch triggering will cause 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
3~
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 or the purpose of providing rocochet and stone
hit discrimination.
11 a) Electronic target 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
18 calculated projectile trajectory location is outside the
19 "window", then the "hit" reported by the inertia switch or other
hit registration device canno-t be valid 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
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
01 _ 40 _
02 threshold limit, then the associated mechanical hit registra-tion
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 registration 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 Eor 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 of 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
2~ 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.
2~
01 - 41 -
02 Appendix A attached hereto is a suitable program
03 written in "BASIC" programming language which may be directly
04 used with the Computer Automation LSI 2/206 minicomputer. The
05 program is used for performing -the position calculations
06 indicated above, generating required reset signals ~or the timer
07 interface unit, calculating the speed o~ sound and bullet
08 velocity, performing threshold checks for bullet velocity,
0~ determining whether the inertia switch has cletected a "hit",
determining a ricochet hit and providing appropriate output
ll signals for the printer and displa~ 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
l9 algorithm defining the boundaries of the target outlined in the
measurement plane may be included in the program and compared
21 with the X, Y 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"
may be defined in the program as XA<Xl<XB, YA<Yl<YB, where XA
26 and XB represent the left and right edges of the target "window"
27 and YA and YB represent the lower and upper edges of the targe-t
28 "window", respectively.
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 circuitry for use. This
06 subroutine is assigned the Assembly Lanugage label RESET.
07 CALL(4 Z~, A2, T7, T6, T5, T4, T3, T2, Tl):
08 Execution of this BASIC 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 ~ESET starts on line 40 of the
listing o~ Appendix B. It saves the return address to BASIC and
16 then tests that CAL~(3) 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 tht 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.
01 _ 43 _
02
03
04
05
06 Still further modiflcations 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 cur~ains may
09 be generated for detecting passage of the bullet through an area
in space, for the purpose of determining the velocity of the
ll 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 reerence. 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
h~
01 _ 44 _
02 of a circle cut from a sheet of matrial sold under the trade
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-out portion 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 transverse divergence.
09 Lens 605 comprises a generally triangular slab of
light transmitting ma~erial 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
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 beam will be
24 reflected thereby, and a portion of that reflection will return
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 6:L0.
28 The coating of mirror 603 is such that beam 610 will be
29 approximately 50% of beam 609. Beam 610 passes through an
optical band pass filter 612 which prevents light of frequency
31 substantially different to that of laser 601 from passing,
z~
01 _ ~5 _
02 so as to reduce errors which may arise from stray ligh-t such as
03 sunlight. Beam 610 emerges as beam 613, which then passes
04 through lens 61~. Lens 614 focuses beam 613 onto the center of
05 a photoelectric cell 615, which emits an electrical signal 617.
06 Signal 617 thus indicates the time at which the projectile
07 passed through the light curtain.
08 Figure 20 shows schematically a system according to
09 the invention which may be employed for determining the velocity
of the bullet in a direction normal 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 Eront of
16 target 596 to generate respective light curtains 608, 608' and
17 produce output signals 618, 618' indicating the ti~e 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.
01 ~ 46 ~
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 recognize that, for example, light curtain 608'
06 may he deleted and the velocity of the bullet may be determined
07 from the output 618 of photoelectric cell 615 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 ri~le equipped
12 with pressure sensors at critical points as described in U.S.
13 Patent Application No. 835~431, filed September 21r 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 riEle 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. The 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
2 ~ ~
01 _ 47 _
02 and indication thereon of the pressure applied by the trainee
03 marksman to the rifle. This graphic display may be in addition
04 to a graphic display of the target being fired upon and
05 representations thereon of the location at which each bullet has
06 struck or passed by the target. Such an arrangement provides
07 the trainee marksman 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
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 iring the ri1e. The display may be maintained on the
16 display unit for a predetermined period of time and then erased
17 so the trainee may proceed with firing a further round.
13 The 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 ricoche~ 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 relation to the target, but why the projectile passed through
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
2~ rapid learning of correct skills.
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 purpose. For example,
05 Figures 21-22 show an arrangement for 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
702 includes a transducer mounted within a shrouded housing
11 which prevents any airborne shock wave of 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 r which provides a "hit"
16 output indication. Signal processing circuit 706 may comprise
17 essentially a thre.shold 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
700 when sensor assembly 702 is 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 understood that the
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 Erom
05 signal processing circuit 706 only when the amplitude of the
06 detected disturbance is sufficiently great to indicate that the
07 disturbance of the target was caused by a projec-tile 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 member 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".
32~6~
01 _ 50 _
02 Typical "hit" and "missl' wave forms are shown in
03 Figures ~5A and 25s, respectively~ The signal processing
04 circuit 726 of Figure 24 operates to distinguish the signals of
05 Figures 25A and 25s by the use of integratin~ capacitor C and
06 bleed-off resistor R2. Only multiple pea]cs as in Figure 25A
07 will trigger the second threshold detector of Figure 28.
08 The technique for distinguishing llhitl' from "miss"
09 described above with reference to Figure 24 applied in principle
to any combina-tion 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 ~arget which
13 completely encircles the transducer (such as a conically-shaped
14 target member). By virtue of the shape of the 3-dimensional
targets, 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 relatively poor. Secondly, the curved shape of the target
19 provides very effective screening of the sensor from the
airborne shock wave produced by near-missed supersonic
21 projectiles. ~he curvature of the target can be increased to
22 the point where it forms a complete shell with the sensor
23 positioned inside it thus enabling hit detection from any
24 direction of fire.
01 - 51 -
02
03
04
05
06 Still another apparatus for detecting a projectile
07 "hit" (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
01 - 52 -
02 from ~5 volts to 0 volts, thereby indicating passage of the
03 bullet through the target "sandwich".
04 Still other apparatus is possible for determining the
05 velocity of the projectile, such as shown in Figure 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 7~8 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
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. At any point along its
23 trajectory, the projectile velocity Vt is:
24 Vt = Vm ~ d-k
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 "deceleration" constant
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 accuracy. Thus r 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,
lS permits Vt in the vicinity of the transducer array to be
16 calculated. Detector 746 may be an optical detector sensing the
17 weapon discharge muzzle flash, or an acoustic device responding
18 to the muzzle blast and/or supersonic projectile shock wave.
-
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 seore column for each shot. If the positive hit
08 indication (inertia switeh) is not aetuated, a "0" score is
09 indicated, o-therwise a non-zero point score is displayed. The
positive hit indieation is partieularly advantageous for
ll borderline eases, as for example, shot No. 6. In such cases, it
12 may not be clear from the position display alone whether a "hit"
13 oeeurred. Shot No. 1 is shown as a elear 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 point values.
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