CA1147367A - Hit detection and ricochet discrimination in target apparatus - Google Patents

Abstract

ABSTRACT

Disclosed is an apparatus for use in marksmanship training. The apparatus includes means for detecting and indicating a position in a measurement plane in the vicinity of a target through which a projectile passes. In addition, the apparatus includes means for measuring the velocity of the projectile in the vicinity of the target. The measured velocity is compared with a predetermined expected velocity to determine if the projectile passed through the measurement plane in free flight or if it had ricocheted prior to passing through the measurement plane. The apparatus will then afford the marksman both an indication of where the projectile passed relative to the target and an indication of whether the projectile has struck the target on a ricochet.

Description

~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 .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 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 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 _ 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 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.

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 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 , 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 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 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 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, 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~

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 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. ~

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

16 90 lOK~
17 92 820J~

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 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 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:

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 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 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.

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1~L473~7 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 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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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.

~7367 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 .

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~7367 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.

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~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 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):

23 ~1- VTH2 ~ ~8) 33 where VO = voltage of wave form D, Figure 8C, .

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~73~7 01 ~ 32 -02 and 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), 12 tl - TH2 13 ~K (1.1) 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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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.

. ' 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 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 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 ~' ' : ` :

~7~67 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 09 VST = Vs~O ~ (13) 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 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.
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~736~

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.
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~73~7 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.

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73~i7 01 ~ 43 ~

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 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.

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~;~

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".
,~

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 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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, 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 : ~ :

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02 By simple algebra, it is possible to find an 03 expression for distance travelled in a given time, which is:

05 d(t) = Vme~kt 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.
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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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Claims (11)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Apparatus for use in marksmanship training in which a projectile travels along a trajectory from a firing point toward a target member and through a measurement plane comprising:
means for detecting and indicating relative to a target representation a location in said measurement plane through which said trajectory passes, thereby providing at least an approximate indication of where said projectile passes relative to said target member; and means for measuring velocity of the projectile in the vicinity of the target member; comparing said measured velocity with at least one expected projectile velocity value to ascertain if said measured velocity is within an expected projectile velocity range, and providing an indication of the result of said comparison between said measured velocity and said at least one expected velocity value, whereby a marksman is provided with an approximate indication of where the projectile passes relative to the target member, as well as an indication of whether the projectile has passed through said measurement plane in free flight or has ricocheted prior to passing through said measurement plane.

2. Apparatus according to claim 1, wherein said projectile velocity measuring means comprises means for detecting passage of said projectile past two points spaced apart at a known distance along a line substantially parallel to said trajectory, and means responsive to said passage detecting means for calculating at least an approximate value of said projectile velocity in the region of said target member.

3. Apparatus according to claim 2, wherein said projectile is traveling at supersonic velocity and at least one of said passage detecting means comprises a transducer responsive to an airborne shock wave from the projectile.

4. Apparatus according to claim 2, wherein at least one said passage detecting means comprises means for projecting at least one light curtain, and means for detecting light reflected by said projectile as said projectile passes through said light curtain.

5. Apparatus according to claim 2, wherein at least one of said passage detecting means comprises said hit detecting means.

6. Apparatus according to claim 2, wherein one of said passage detecting means comprises means for detecting a time of discharge of said projectile from weapon fired at said target member from said firing point, said calculating means taking into account deceleration of said projectile from said firing point to the region of said target member.

7. Apparatus according to claim 1, wherein said detecting and indicating means comprises:

8. Apparatus according to claim 7, wherein said graphic display means comprises a visual display screen fitted with a graticule bearing said target representation, said visual display screen displaying a visible mark relative to said graticule to indicate said detected location.

9. Apparatus according to claim 8, further comprising means for comparing said detected location with a predetermined range of locations representing a target window in said measurement plane, said graphic display means being further responsive to said comparing means for providing a visual indication of whether said detected location is within said predetermined range of locations.

10. The apparatus according to claim 4, wherein said means for projecting a light curtain comprises:
a laser beam generator for generating a laser beam, an inclined mirror having a mirror coating on one surface for receiving said laser beam and transmitting a portion of said laser beam therethrough;
a lens positioned for receiving said portion of said laser beam and for transmitting a light beam of substantially rectangular cross-section and substantially no divergence whereby a curtain of light is formed.

11. The apparatus of claim 10, wherein the means for detecting light reflected by said projectile comprises:
said lens and mirror which collects and directs the reflected light and produces a beam of reflected light;
a photoelectric cell for receiving said beam of reflected light and producing an electrical signal when a projectile passes through said light curtain.