GB2120760A - Marksmanship training apparatus - Google Patents

Abstract

To detect when a rigid target 700, used for marksmanship training, has been hit, a sensor 702 is spaced from the target but arranged to respond only to disturbance of the target (or a resulting disturbance of the adjacent air) caused by a hit. The sensor 702 may comprise a transducer shrouded in a housing so that airbourne shock waves from supersonic projectiles cannot reach it. If the target is hollow, the sensor may be mounted inside it. <IMAGE>

Description

SPECIFICATION Improvements in or relating to marksmanship training apparatus The present invention relates to marksmanship training apparatus.

The present invention seeks to provide apparatus that can be utilised to form a considerably more versatile 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 shooting techniques immediately after each shot is fired. Such reinforcement may take a number of forms, but preferably comprises a plurality of indications concerning each shot fired. For example, it is desirable to provide the trainee marksman with an at least approximate indication of where a projectile fired at a target has passed relative to the target and/or positive indication of whether the projectile has actually hit the target and/or whether the projectile has ricocheted prior to reaching the zone of the target.It is also advantageous to provide, in combination with one of the foregoing indications, information concerning whether the trainee marksman is correctly gripping the weapon being fired. An ideal marksmanship training system will be particularly effective for beginning marksman who may not be holding the weapon correctly and who may not even be shooting sufficiently near the target to score a "hit". Such a marksman will thus be apprised of the manner in which he should change his technique to improve his shooting. The ideal system is, however, also effective for more advanced shooters, who may wish to not only have an indication that the target has been hit by a projectile, but whether the projectile has struck a particular region of the target.

According to this invention there is provided marksmanship training apparatus for indicating when a target member has been hit by a projectile fired at said target member, comprising: a target member; and means spaced apart from and not physically connected to said target member for detecting and selectively providing a hit indication only in response to disturbance of said target member or a disturbance of the air adjacent the target member caused by said projectile hitting or passing through said target member.

Preferably said means spaced apart from said target member comprise at least one transducer, the transducer being spaced apart from and not physically connected to said target member, for detecting and providing an output in response to disturbances caused by an object hitting or passing through said target member, and a circuit responsive to said transducer output for providing said hit indication only in response to disturbance of said target member, or a disturbance of the air adjacent the target member caused by said projectile hitting or passing through said target member.

Conveniently said transducer output varies in amplitude in dependence on the magnitude of the said disturbance, and said circuit is operative to provide said hit indication only when said transducer output amplitude exceeds a predetermined level.

Preferably said circuit is further operative to provide said hit indication only when said transducer output includes amplitude peaks which exceed said predetermined level at a rate exceeding a predetermined rate.

Preferably said transducer is responsive to air pressure disturbances caused by objects hitting or passing through said target member.

Conveniently said transducer is located in front of said target member relative to a point from which said projectile is fired at said target member, the apparatus further comprising means for shielding said transducer such that said transducer is responsive only to air pressure disturbances which propagate from the region of said target member toward said transducer.

Alternatively said transducer is located behind a front surface of said target member relative to a point from which said projectile is fired at said target member and then preferably said target member is 3-dimensioned and at least partially surrounds said transducer, whereby said transducer is shielded by said target member so as to be substantially non-responsive to air pressure disturbances caused by projectiles passing by but not hitting said target member. In such a case said target member may surround said transducer.

Conveniently said projectile travels along a trajectory from a firing point toward said target member and through a measurement plane, the apparatus further 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, whereby a trainee marksman is provided with at least an approximate indication of where the projectile passes relative to the target member, as well as a positive indication of whether the projectile has hit the target member, thereby rendering hits at the edge of the target member distinguishable from misses near the edge of the target member.

Preferably said location detecting and indicating means comprises: an array of at least three transducers responsive to an airborne shock wave from the supersonic projectile and located at respective predetermined portions spaced along a line substantially parallel to said measurement plane; means for measuring velocity of the supersonic projectile; means for measuring velocity of propagation of sound in air in the vicinity of the array of transducers; and computing means responsive to said array of transducers, said projectile velocity measuring means, and said propagation velocity measuring means, and operative for: determining the location in said plane through which the trajectory of the supersonic projectile passes, and providing an output indicating said determined location relative to a target representation.

The apparatus may further comprise means for: measuring a velocity of the projectile in the vicinity of the target member, comprising 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 trainee marksman is further provided with an indication of whether a detected hit on said target has resulted from a free flight projectile hitting said target member or from a projectile which has ricocheted prior to hitting said target member.

Preferably the apparatus may further comprise means responsive to said detecting and indicating means for providing a visual representation of said target member for graphically displaying said detected location relative to said target member representation.

Conveniently 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.

Preferably said graphic display means is further responsive to said hit detecting means for displaying a positive visual indication of whether said projectile has hit said target member.

In order that the invention may be more readily understood and so that further features thereof may be appreciated the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows in perspective view a marksmanship 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; Figure 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 Fig. 4; Figure 6 shows in block schematic form one channel of comparator 62 of Fig. 4;; Figure 7A-7Fshow in detail one possible form of timer interface 64 of Fig. 4; Figures 8A and 8B show a suitable circuit arrangement for the air temperature sensing unit 78 of Fig. 4; Figure 8C shows a timing diagram for the circuits of Figs. 8A and 8B; Figure 9 shows airborne shock waves impinging on a piezoelectric disc transducer; Figure 10 shows an output waveform for the transducer of Fig. 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 trans d ucers; Figures 14A and 24B are flow charts for computer subroutine CALL (3); Figures 15A-1 5C show flow charts for computer subroutine CALL (4);; Figure 16-18 show atlernate transducer arrangements in plan view; Figure 19 shows apparatus for generaing a light curtain and detecting the passage of a projectile therethrough; Figure 20 shows an arrangement employing two such constructions as shown in Fig. 19, in combination with an array of transducers for detecting an airborne shock wave; Figures 21 and 22 shown an arrangement for sensing impact of a projectile on a target member; Figures 23 and 24 shows an alternate arrangement for detecting a projectile hit on a target member; Figures 25A and 25B show typical transducer output signals for "hits" and "misses" of a projectile passing relative to the target member, respectively; Figure 26 shows a target member construction for detecting passage of a projectile therethrough; Figure 27 shows an alternative arrangement for determining projectile velocity; and Figure 28 shows a graticule overlay used on the visual display screen of Fig. 4.

Fig. 1 shows in perspective view a marksmanship training range employing concepts of tha present invention. The range has a plurality of firing points 10 from which trainee marksmen 1 2 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 1 8 just below the lower edge of the target 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 data processor or computer (not shown) located near the transducer array, which is in turn coupled to the visual display units. As will be explained below, each transducer array detects the shock wave generated by a supersonic projectile, such as a bullet, fired at the respective target, and the computer 22 is operative to determine the location in a measurement plane in front of the target through which the bullet trajectory passes. Means (not shown in Fig. 1) are provided at each target for detecting when the target has been "hit" by a projectile.Computer 22 is coupled to suitable visual display units 26, 28, 30, located respectively 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 example, an approximate indication, relative to a target representation, of where the projectile has passed through the measurement plane, and an indication of whether the target has been "hit" by the projectile. Spectators 32 may observe the progress of shooting of one or more of the trainee marksman on visual display unit 30. The computer may be coupled with a suitable printer or paper punching device 34 to generate a permanent record of the bullet trajectory location determined by the computer.

Although the targets 14 shown in Fig. 1 have marked thereon representations of the conventional bull's-eye type target, the target may be of any suitable configuration, such as a rigid or semi-rigid target member 35 as shown in Fig. 2 on which may be provided the outline of a soldier or the like. Means are provided for detecting when a projectile 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 Fig. 2, or any other suitable apparatus. Alternative "hit" detecting arrangements will be described below. The automated target mechanism may be of the type described in U.S.Patent No. 3,233,904 to GILLIAM et al (the content of which is incorporated herein by reference). Target mechanisms of this type are available commercially from Australian Training Aids Pty Ltd., Albury, N.S.W.

2640, Australia, Catalog No. 106535. Inertia switches are commercially available from Australasian Training Aids Pty. Ltd., Catalog No. 101805.

In the arrangement of Fig. 2, transducers S1-S4 are mounted on a rigid support member 40, which is in turn mounted on the target mechanism 36. Although the transducer arrays 1 8 may be supported separately from the target mechanism beneath targets 14 (as in Fig. 1), affixing the transducer array to the target mechanism as in Fig. 2 assure correct alignment of the measurement plane relative to target member 35. Transducers S1-S4 (Fig. 2) preferably each comprise a disk-shaped piezoelectric element of 5 mm diameter mounted to a hemispherical aluminium dome, the hemispherical surface of the dome being exposed for receiving the shock wave from the bullet.The airbone shock wave generated by the bullet is represented by the series of expanding rings 42, the bullet trajectory by a line 44, and the acoustic vibrations induced in the target member 35 on impact of the bullet by arc segments 46.

Fig. 3 shows a three-dimensional coordinate system in which the positions of the four transducers S1-S4 are related to a reference point (0, 0, O). The transducer array illustrated is similar to that shown in Fig. 2, with a row of three transducers S1, S3, S4 situated at spaced locations along the X axis and with a fourth transducer S2 situated at a spaced location behind transducer S1 along the Z-axis. A portion of target member 35 is also shown for reference purposes, as is an arrow 44 representing the bullet trajectory. The distance along the X-axis from transducer S1 to transducers S3 and S4, respectively, is represented by distance d. The distance along the Z-axis between transducers S1 and S2 is represented by d'.

The X-Y plane intersecting the origin of the Z axis of the coordinate system shown in Fig. 3 is considered to be the measurement plane in which the location of the trajectory is to be determined.

Transducers S1-S4 provide output signals in response to detection of the shock wave of the bullet, from which the location in the measurement plane through which the projectile trajectory passes can be determined. A mathematical analysis is provided below for a relatively simple case in which it is assumed that: (1) The transducer array is as shown in Fig. 3; (2) The measurement plane has its X-axis parallel to the straight line joining transducers S1, S3, S4; (3) The projectile trajectory is normal to the measurement plane; (4) The projectile travels with constant velocity; (5) Air through which the shock wave propagates to strike the transducers is (a) of uniform and isotropic shock wave propagation velocity, and (b) has no velocity (i.e., wind) relative to the transducer array; and (6) The shock wave propagation velocity and projectile velocity are separately measured or otherwise known or assumed.

It is to be noted that small departures from the above-stated conditions have in practice been found acceptable, since the resulting error in calculated location in the measurement plane through which the projectile passes is tolerably small for most applications.

The respective times of arrival of the shock wave at transducers S1, S2, S3, S4 are defined as T1, T2, T3, and T4. All times of arrival are measured with respect to an arbitrary time origin.

Vs is defined as the propagation velocity of the shcok wave front in air in a direction normal to the wave front, while VB is defined as the velocity of the supersonic projectile along its trajectory.

The velocity VB of the bullet in a direction normal to the measurement plane can be determined from the times of arrival T1, T2 of the shock wave at transducers S1 and S2 and from the distance d' between transducers S1 and S2: d' VB = - (1) T2-Tl Then the propagation velocity of the shock wave front in a direction normal to the projectile velocity may be defined as: V5 VN = - (2) Vs 1- 2 V8 The differences between the times of arrival of the shock wave may be defined as: t1 = T3-T1 (3) t2=T4-T1 (4) The X-axis coordinate of the intersection point of the projectile trajectory with the measurement plane is: (t1-t2) (VN t1t2 + d2) x = (5) 2d (t1 +t2) The distance in the measurement plane from sensor S1 to the point of intersection of the projectile trajectory with the measurement plane is: (2d2VN2 (t12 + t22)) lo = (6) 2VN (t1 + t2) The Y-axis coordinate of the intersection point of the bullet trajectory with the measurement plane is: y = l02-x2 (7) It is possible to construct a mathematical solution for the above-described transducer system which incorporates such effects as: : (1) Wind; (2) Non-equally spaced transducers along the X-axis; (3) Non-colinear arrays; (4) Decelerating projectiles; and (5) Non-normal trajectories.

However, most of these corrections require more complex arithemtic, and in general can only be solved by iterative techniques.

It can be seen that the transducer arrangements shown in Figs. 1-3 form, when viewed in plan, a "T" configuration with at least three transducers on the crossbar of the "T" and one transducer at the base of the "T". The stem of the "T" is substantially aligned with the expected bullet trajectory. The error created if the stem of the "T" is not precisely aligned with the anticipated projectile trajectory is relatively minor and thus the alignment of the "T" can be considered substantially insensitive to error. However, when the stem of the "T" (that is, the Zaxis of Fig. 3) is aligned parallel to the expected projectile trajectory, the effect is to cancel substantially any shock wave-arrival-angle dependent time delays in the transducer outputs.

Referring now to Fig. 4, a plan view of the transducers S1-S4 in a "T" configuration is illustrated schernatically. Each transducer is coupled by an appropriate shielded cable to a respective ante of amplifiers 54-60. The outputs of amplifiers 54-60 are provided through coupling capacitors to respective inputs of a multi-channel comparator unit 62, each channel of which provided an output when the input signal of that channel exceeds a predetermined threshold level. Thus, a pulse is provided at the output of each of channels 1, 2, 3, and 6 of comparator unit 62 at respective times indicating the instants of reception of the shock wave at each of the transducers S1-S4. In the presently-described form of the invention, channel 4 of the six-channel comparator unit is unused.The outputs of channels 1-3 and 6 of comparator unit 62 are provided to inputs of a timer interface unit 64. Timer interface unit 64 serves a number of functions, includng conversion of pulses from comparator unit 62 into digital values representing respective times of shock wave detection which are conveyed via a cable 68 to a minicomputer 70.

The output of channel 1 of comparator unit 62 is coupled to the inputs of channels 0 and 1 of timer interface unit 64, the output of channel 2 of the comparator unit is coupled to the input of channel 2 of the timer interface unit, the output of channel 3 of the comparator unit is coupled to the inputs of channels 3 and 4 of the timer interface unit, and the output of channel 6 of the comparator unit is coupled to the input of channel 6 of the timer interface unit. The channel 5 input of the timer interface unit is coupled via comparator unit channel 5 to an air temperature sensing unit 78 which has a temperature-sensitive device 80 for measuring the ambient air temperature. The output of amplifier 54 is also provided to air temperature sensing unit 78, for purposes described below with reference to Figs. 8A-8C.

Fig. 4 also shows schematically the target mechanism 36 and the inertia switch 38 of Fig. 2, which are interconnected as shown for the units available from Australasian Training Aids Pty., Ltd. Coupled to terminals A, B, C of the target mechanism/inertia switch interconnection is an isolator module 66 which provides a pulse similar in form to the output pulses of comparator unit 62 when inertia switch 38 is actuated by impact of a projectile on the rigid target member 35 of Fig. 2.The output of isolator module 66 is supplied to two remaining inputs of timer interface unit 64, indicated in Fig. 4 as channel 7 and "S.S." Minicomputer 7Q of Fig. 4 may be of type LSI-2/20G, available from Computer Automation Inc. of Irvine, California, Part No. 10560 16. The basic LS1-2/20G unit is preferably equipped with an additional memory board available from Computer Automation, Part No.

11673-16, which expands the computer memory to allow for a larger "BASIC" program.

Minicomputer 70 is preferably also equipped with a dual floppy disk drive available from Computer Automation, Part No. 22566-22, and a floppy disk controller available from Computer Automation, Part No. 14696-01. Minicomputer 70 is coupled to a terminal 72 having a visual display screen and a keyboard, such as model "CONSUL 520" available from Applied Digital Data Systems Inc. of 100 Marcus Boulevard, Hauppauge, New York 11787, U.S.A. The CONSUL 520 terminal is plug-compatible with the LS1 -2 minicomputer.

Other peripheral units which are not necessary for operation of the system in accordance with the invention, but which may employed to provide greater flexibility in marksmanship training, include a line printer 72' for generating permanent output records, and a graphics generator/visual display unit combination 72" which permits the coordinates of the intersection point of the projectile trajectory with the measurement plane to be displayed relative to a representation of the target, as well as an indication of whether the target has been "hit" and a tally of the trainee marksman's "score." Graphics generator/visual display unit 72" may be, for example, Model MRD "450", available from Applied Digital Data Systems, Inc., which is plug-compatible with the LS1-2 minicomputer.

Also shown in Fig. 4 is a thermometer 76 which preferably a remote-reading digital thermometer such as the Pye-Ether series 60 digital panel meter Serial No. 60-4561-CM, available from Pyrimetric Service and Supplies, 242-248 Lennox St., Richmond, Victoria 3221, Australia, equipped with an outdoor air temperature sensor assembly (Reference Job No.

Z9846). The remote-reading digital thermometer may have its sensor (not shown) placed in the region of the transducer array and, if the system is not equipped with the air temperature sensing unit 78 shown in Fig. 4, hte operator of terminal 72 may read the remote-reading digital thermometer 76, and input a value for the air temperature. An approximate value for the speed of the shock-wave front propagation in ambient air can be readily calculated from the air temperature using a known formula as described below.

Fig. 5 shows a circuit diagram of the inertia switch isolator module 66 of Fig. 4, having inputs A, B, C coupled as in Fig. 4 to the comruPercially-availabie inertia switch. The isolator module provides DC isolation for the inertia switch output signal and presents the signal to timer interface unit 64 of Fig. 4 in a format comparable to the output signals from comparator unit 62.

Suitable components for isolator module 66 are: 82,84 IN914 86 47,uF 88 BC177 90 1 OKS2 92 820so 94 5082-4360 96 47051 98 6.8K 100 10yF 102 74LS 221N Monostable Multivibrator with Schmitt-trigger inputs 104 DS8830N Differential line driver 106 0.22yF 108 47Q Fig. 6 shows a block diagram of one channel of comparator unit 62. The output signal from one of amplifiers 54-60 is provided through a high pass filer 110 to one input of a differential amplifier 11 2 which serves as a threshold detector.The remaining input of differential amplifier 11 2 is provided with a preset threshold voltage of up to, for example, 500 millivolts. The output of threshold detector 11 2 is supplied to a lamp driver circuit 114, to one input of a NAND gate 11 6 and to the trigger input of a monostable multivibrator 11 8 which provides an output pulse of approximately 50 millisecond duration. A shaped output pulse is therefore provided from NAND gate 11 6 in response to detection of the airborne shock wave by one of transducers S1-S4.Lamp driver circuit 114 may optionally be provided for driving a lamp which indicates that the associated transducer has detected a shock wave and produced an output signal which, when amplified and supplied to threshold detector 112, exceeds the preset threshold value.

The logic output signals of comparator unit 62 cause counters in timer interface unit 64 to count numbers of precision crystal-controlled clock pulses corresponding to the differences in times of arrival of the logic output signals, which in turn correspond to the times of arrival of the shock waves at the transducers. Once this counting process is complete and all channels of the timer interface unit have received signals, the counter data is transferred on command into the computer main memory. Following execution of a suitable program (descrivbed below), the resulting projectile trajectory data is displayed on the visual display unit 72 and/or units 72', --72" of Fig. 4.

Figs. 7A-7F show in detail one possible form of a timer interface unit 64, which converts time differences between the fast logic edge pulses initiated by the transducers into binary numbers suitable for processing by minicomputer 70. Fig. 7A shows the input and counting circuit portions of the timer interface unit, which accept timing edges from respective comparator unit channels and generate time difference counts in respective counters. The timer interface unit has eight channel inputs labeled Ch Ch7 and one input labeled "S.S", receiving signals as follows: Timer Interface Input Channel No. Receives Signals initiating from Transducer S1 1 Transducer S1 2 Transducer S2 3 Transducer S3 4 Transducer S3 5 Air Temperature Sensing Unit 78, if equipped, otherwise Transducer S4 6 Transducer S4 7 Inertia Switch Isolator Module 66 S.S. Inertia Switch Isolator Module 66 The input singals to each of timer interface inputs Ch-Ch7 comprise logic signals which are first buffered and then supplied to the clock input CK of respective latches FF-FF7. The latch outputs LHQ + through LCH7 + are provided, as shown, to exclusive OR gates EOR1-EOR7, which in turn provide counter enabling signals ENA1- through ENA7-. Latches FFO/FF9 are cleared upon receipt of clear signal CLR.The input and counting circuits also include a respective up/down counter for each of eight channels (indicated for channel 1 as "UP/DOWN COUNTER 1"). Each up/down counter comprises, for example, four series connected integrated circuits of type 74191. Each of up/down counters 108 thus has 16 binary outputs, each output coupled to a respective one of terminals TBO- through TB1 5- via a controllable gate circuit (indicated for channel 1 as "GATES 1") on receipt of a command signal (indicated for channel 1 as "IN-"). Up/down counter 1 is connected to receive latch signal LCH1 +, enable signal ENA1 - a clock signal CLK, and a clear signal CLR, and to provide a ripple carry output signal RC1- when an overflow occurs. Up/down counters 2-8 each receive a respective one of enable signals ENA2- through ENA8-.Counter 2 receives its clear signal CLB from counter 1; counters 3 and 5 receive clear signal CLR and provide clear signals CLB to counters 4 and 6, respectively; counter 7 receives clear signal CLR; and counter 8 receives clear signal SEL2-. The up/down inputs of counters 207 receive latch signals LCH2 + through LCH7 +, respectively, while the up/down input of counter 8 is permanently connected to a + 5 volt source. Counters 2-8 each receive clock signal CLK, while each of counters 2-7 provide a ripple carry signal (RC2- through RC7-, respectively) when the respective counter overflows.

Gates 2-8 are coupled to receive respective command signals IN1- through IN7- for passing the counter contents to terminals TBO- through TB15-. Fig 7A also shows a gate NAND 1 which receives the latch outputs LCH + through LCH7 + and provides an output signal SEN7 +, the purpose of which is explained below.

Fig. 7B shows a circuit for providing clear signal CLR, which resets input latches FF-FF7 and up/down counters 1-7. When one of ripple carry outputs RC1 - through RC7 - of up/down counters 1-7 goes to a logic low level, indicating that a counter has overflowed, or when a reset signal SEL4 - is provided from the computer, gate NAND 2 triggers a monostable element which then provides clear signal CLA in the form of a logic pulse to clear up/down counters 1-7 and input latches FF-FF7 of Fig. 7A.

Up/down counters 1-7 are reset by signal SEL4 - from the computer before each shot is fired by a trainee marksman. When a shot is fired, each counter will count down or up depending on whether its associated channel triggers before or after a reference channel, which in this case is input channel Ch0.

Fig. 7C shows the input circuitry for input "S.S." of the timer interface. Latch FF8 is coupled to receive reset signal SEL4 - and preset signal SEL1 - from the interface controller of Figs.

7E and 7F in response to computer commands. Timer interface input "S.S." receives "hit" indication signal VEL - from the inertia switch isolator module 66, and provides a counter enable signal ENA8 - for up/down counter 8.

The computer communicates with the timer interface unit by placing a "device address" on lines AB03-AB07 (Fig. 7D) and a "function code" on lines AB00-AB02 (Fig. 7F). If the computer is outputting data to the timer interface, signal OUT is produced; if the computer is inputting data, signal IN is produced.

Fig. 7D shows exclusive OR gates EOR11 -EOR15 which decode the "device address." A "device address" can also be selected manually by means of switches SW1 -SW5. The address signal AD - from gate NAND 3 is then further gated as indicated with computer-initiated signals IN, OUT, EXEC, and PLSE, to prevent the timer interface from responding to memory addresses which also appear on the address bus.

Fig. 7F shows a latch 2A which holds the function code of lines ABO-ABO2 when either the IN or OUT signal is produced. The input/output function signals from latch 2A are labeled IOF through IOF2.

If the computer executes an IN instruction to receive data from the timer interface, the combination of IOF through IOF2 and ADIN - (Fig. 7D) produce one of signals INld through IN7 - at BCD/decimal decoder 5A of Fig. 7E. Each of signals lN - through IN7 enables data from one of up/down counters 1-8 to be placed on data bus terminals TBO - through TB1 5-.

If the computer is executing a "select" instruction for the timer interface, the combination of signals IOFld-IOF2 and ADEXP - (Fig. 7D) produce one of select signals SELld - through SEL7 - at BCD/ decimal decoder 5B of Fig. 7E. The select signal functions employed in the presently-described invention are: SEL1- enables triggering of latch FF9 (Fig. 7C) SEL2- resets up/down counter 8 (Fig. 7A) SEL4- resets latch FF8 (Fig. 7C) and triggers monostable element 328 via NAND 2 (Fig. 7B) If the computer is executing a sense instruction from the timer interface, the combination of signals IOF-IOF2 (Fig. 7F) and AD- (Fig. 7D) allow one of sense signals SEN + through SEN7 + to be placed on the SER-line (Fig. 7F).This allows the computer to examine the state of one of these sense signals. The only sense signal employed in the presently-described embodiment is SEN + 7, which indicates that the timer interface has a complete set of time data for a single shot fired at the target as explained more fully below.

The theory of operation of timer interface unit 64 is as follows. Channel Ch is the reference channel. Each channel triggering will clock a respective one of latches FF-FF7, producing a respective one of signals LCH + through LCE7 +. Signals LCH1 + through LCH7 + each control the up/down Ine of one counters 1-7 and are also provided to OR gates EOR1 through EOR7 to produce a respective counter enabling signal ENAl-through ENA7 -.

Exclusive OR gates EOR1 through EOR7 each achieve two functions. First, the counters of any channel that triggers before reference channel Ch will be enabled until reference channel Ch triggers. This has the effect of causing the counters to count down because the associated LCH + input line is high. Second, the counters of any channels that have not triggered by the time reference channel Ch triggers are all enabled by the reference channel until each individual channel triggers. This has the effect of causing the counters to count up, since the associated LCH + lines are low while the counters are enabled.

Initially, the computer resets up/down counter B with signal SEL2 - and then causes a general reset with signal SEL4 -. Signal SEL4 - causes gate NAND 2 (Fig. 7B) to trigger monostable element 328, producing clear signal CLR, which resets latches FF-FF7 and up/down counters 1-7 (Fig. 7A). Reset signal SEL4 - also clears latch FF8 (Fig. 7C). Latch FF9 (Fig. 7C) is preset by the computer with signal SELl -' which 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 isolator module 66, indicating that the target has been "hit".

Thus, prior to a shot being fired, counters 1-8 are reset, input latches FF-FF7 are reset, and latch FF9 is "armed". All resets occur when the computer executes controller BASIC statement CALL (3), described further below.

At this stage, none of channels Ch has been triggered. Since channel Ch has not yet triggered, signal LCH + is low. The remaining input of gate EORIZI is permanently high, so the output of gate EOR is high. Since signals LCH1 + through LCH7 + are all low, signals ENA1 - through ENA7 - are all high, disabling all of up/down counters 1-7. Signal ENA8 is also high, disabling up/down counter 8.

Assume now that a shot is fired to the left of the target, missing the target, and to the left of the transducer array shown in Fig. 4. Channel 3 of Fig. 7A triggers first, so that signal LCH3 + goes high, causing signal ENA3 - to go low and thereby causing up/down counter 3 to begin counting down. Reference channel Ch and channel Ch1 then trigger simultaneously. Signal LCH + goes high, so the output of gate EORZI goes low. This makes signal ENA3 - go high, while signals ENA2 - and ENA4 - through ENA7 - go low. Signals ENA1 - and ENA8 remain high.

Counter 3 will thus stop counting, counter 1 remains disabled and has no count, and counters 2, and 5-7 will start counting up.

As each successive channel triggers, its respective LCH + signal will go high, removing the associated ENA - signal and stopping the associated counter. When all LCH + signals are high (indicating that all counters have been disabled), signal SEN7 + at the output of gate NAND 1 in Fig. 7A goes from high to low. The computer monitors signal SEN7 + to wait for all timing edge counts to be completed.

When the computer senses signal SEN7 +, indicating that a complete set of counts is present in counters 1 through 7, it generates address signals ABOIZI-AB07 and the IN signal which cause BCD-to-decimal decoder 5A (Fig. 7E) to issue signals lN1 - through IN7 - in sequence so that the computer will sequentially "read" the state of each counter (on output lines TBOld through TB - ).

The computer has thus received counts representing times as follows: T1 zero count from counter (transducer S1) T2 positive count from counter 2 (transducer S2) T3 negative count from counter 3 (transducer S3) T4 negative count from counter 4 (transducer S3) T5 positive count from counter 5 (air temperature sensing as explained below with reference to Fig. 10, or, if none, the output of channel 6 amplifier 60 goes to input channel Ch5 of the timer interface unit and the output of transducer S4 triggers counter 5) T6 positive count from counter 6 (transducer S4) T7 positive count from counter 7 (inertia switch) A2 zero count from counter 8 (inertia switch) The zero count in A2 indicates that the inertia switch was not operated, thus showing that the shot fired has missed the target. Had the bullet struck the target, a non-zero count would be recorded in A2 because signal ENA8 - would have gone low upon receipt of signal VEL - (Fig.

7C).

The computer is programmed to operate on the received "time" signals T1 through T7 and A2 in a manner which will be described below, such that the coordinates of the bullet trajectory in the X-Y measurement plane of Fig. 3 are determined.

If any channel of the timer interface unit triggers spuriously (i.e. the inertia switch may be triggered by a stone shower, one of the transducers may detect noise from other target lanes or other sources, etc.), the associated counter will continue counting until it overflows, causing a ripple carry signal (RC1 - through RC7 -). All of the ripple carry signals are supplied to gate NAND 2 (Fig. 7B), which fires the associated monostable element 328, causing generation of clear signal CLR which resets latches FF-FF7 and up/down counters 1-7.

Figs 8A and 8B show in detail a suitable circuit arrangement for the air temperature sensing unit 78 of Fig. 4. Fig. 8C shows wave forms of various points in the circuit of Figs. 8A and 8B.

The effect of the air temperature sensing unit is to generate a pulse at a time t, following the time to at which channel Ch1 of comparator unit 62 is triggered (allowing of course for propagation delays in connecting cables).

Referring to Fig. 8B, a temperature sensor ICI mounted in a sensor assembly, assumes a temperature substantially equal to that of ambient air in the vicinity of the transducer array.

Temperature sensor ICI may be, for example, Model AD590M, available from Analog Devices Inc., P.O. Box 280, Norwood, MA 02062. Temperature sensors ICI permits a current 1,N to flow through it, current 1 IN being substantially proportional to the absolute temperature (in degrees Kelvin) of the semiconductor chip which forms the active element of temperature sensor ICI.

Referring again to Fig. 8A, when transducer S1 detects a shock wave generated by the bullet, a wave form similar to that shown at A in Fig. 8C is produced at the output of its associated amplifier 54 (Fig. 4). Integrated circuit chip IC3B of Fig. 8A forms a threshold detector, the threshold being set equal to that set in channel Chi of comparator unit 62 of Fig. 6.

Integrated circuit chip IC3 may be of type LM 319, available from National Semiconductor Corporation, Box 2900, Santa Clara, California 95051. When wave form A of Fig. 8C exceeds the preset threshold, wave form D is generated at the output of circuit chip IC3B. The leading edge (first transition) of wave form B triggers the monostable multivibrator formed by half of integrated circuit chip IC4 of Fig. 8B and the associated timing components R8 and C3. Circuit chip IC4 may be of type 74LS221N, available from Texas Instruments, Inc., P.O. Box 5012, Dallas, Texas 75222. The output of this monostable multivibrator is fed via buffer transistor Q1 to the gate of metal oxide semi-conductor Q2, the wave form at this point being depicted as C in Fig. 8C.Transistor Q1 may be of type By107, available from Mullard Ltd., Mullard House, Torrington Place, London, U.K., and semiconductor 02 may be of type VN 40AF, available from Siliconix Inc., 2201 Laurelwood Road, Santa Clara, California 95054.

When wave form C, which is normally high, goes low, metal oxide semiconductor Q2 changes from a substantially low resistance between its source S and drain D to a very high resistance.

As a result of the current flowing through temperature sensor ICI (proportional to its absolute temperature), the voltage at the output of integrated circuit chip IC2 starts to rise, as shown at D in Fig. 8C. The rate of rise in volts per second of wave form D is substantially proportional to the current flowing through temperature sensor ICI and thus is proportional to the absolute temperature of temperature sensor ICI. Integrated circuit chip lC2 may be of type CA3040, available from RCA Solid State, Box 3200, Summerville, New Jersey 08876. When the voltage of wave form D, which is supplied to the inverting input of comparator IC3A, rises to the preset threshold voltage VTH2 at the non-inverting input of comparator IC3A, the output of comparator IC3A changes state as indicated in wave form E at time t1.This triggers a second monostable multivibrator formed on half of integrated circuit lC4 and timing components C4 and R9. The output of this second monostable multivibrator is sent via a line driver circuit chip IC5 to a coaxial cable which connects to the channel 5 input of the comparator unit 62.

The operation of the air temperature sensing unit 78 of Figs. 8A and 8B may be mathematically described as follows (assuming that the ramp at wave form D of Fig. 8C is linear and ignoring offset voltages in the circuit, which will be small): VTH2 ti d - V0 (8) dt where V0 = voltage of wave from D, Fig. 8C, and d 1IN -V0 = --- (9) dt C, where 11N = current through ICI lIN=COK (10) where C is a constant of proportionality and 0K is the absolute temperature of ICI combining (8), (9) and (10), VTH2CI ti = ----- (11) COK or VTH2CI AK= (12) Ct, Timer interface unit 64 can then measure time t by the same procedure that is employed for measuring the time differences between transducers S1-S4.It will be recalled that timer interface unit 64 will start counter 5 counting up upon receipt of a pulse on channel ChO, which is responsive to shock wave detection by transducer SI. Counter 5 will stop counting upon receipt of the pulse of wave form G from the air temperature sensing unit at time t,. Thus, the count on counter 5 of the timer interface unit will be directly proportional to the reciprocal of the absolute temperature of sensor ICI.

Each of transducers S1-S4 may be a flat disk 530 of piezoelectric material (Fig. 9). If a bullet 532 is fired to the right of the transducer 530, the shock wave 532 will impinge on the corner 534 of transducer 530, and the transducer output will have a wave form as illustrated in Fig.

10. It is desired to measure the timer T illustrated in Fig. 12 but it is difficult to detect this accurately since the amplitude of the "pip" 542 depends upon the position of the bullet relative to the transducer, is difficult to distinguish from background noise and can even be absent under some circumstances.

The minicomputer is provided in advance with the position of each transducer; all calculations assume that the transducer is located at point 536 and that the transducer output signal indicates the instant at which the shock wave arrives at point 536.

However, the distance between the transducer surface and each of the trajectories of bullets 532, 538 is equal to a distance L. Since the transducer provides an output as soon as the shock wave impinges on its surface, the times between the bullet passing and the output signal being generated are equal. Therefore, the output of the transducer would suggest that the trajectories of the bullets 532, 538 are equispaced from point 536, which is not correct.

This disadvantage can be overcome by disposing the transducers in a vertical orientation so that the transducers are in the form of vertical disks with the planar faces of the disks directed toward the trainee marksman. As a bullet passes over the disks and the resulting shock wave is generated, the shock wave will impinge on the periphery of each disk and the point of impingement will be an equal distance from the center of the disk. A constant timing error will thus be introduced, but since only time differences are used as a basis for calculation of the bullet trajectory location, this error will cancel out.

However, orienting the disks vertically will not obviate the problem of the positive pip 542 at the beginning of output signal 540. It is, therefore, preferred to provide each transducer with a dome of a solid material having a convex surface exposed to the shock wave, the planar base of the dome being in cotact with the transducer disk and being suitable for transmitting shock waves from the atmosphere to the transducer disk. Shock waves generated by projectiles fired at the target will always strike the hemispherical dome tangentially, and shock waves will be transmitted radially through the dome directly to the center of the transducer. The constant timing error thereby introduced will cancel out during calculation of the bullet trajectory location.

The hemispherical dome prevents or minimizes generation of positive-going pipe 542 so the output of the transducer more closely resembles a sinusoidal wave form. The instant of commencement of this sinusoidal wave form must be measured with great accuracy, so the transducer must have a fast response.

It is advantageous to utilize a piezoelectric disk having a diameter of about 5mm, which provides a fast response time and a relatively high amplitude output signal.

Referring now to Figs. 11 and 1 2 of the drawings, one possible form of transducer for use in connection with the present invention comprises a transducer element consisting of a disk 550 of piezoelectric material such as, for example, lead zirconium titanate. The disk 550 is about lmm thick and 2-5 mm in diameter, and many be part No. MB1043, available from Mullard Ltd., Torrington Place, London, U.K. The opposed planar faces of disk 550 are provided with a coating of conductive material 552, which may be vacuum-deposited silver.

Two electrically conductive wires 554, 556 of, for example, copper or gold, are connected to the center of the lower surface of the disk and to the periphery of the upper surface of the disk, respectively, by soldering or by ultrasonic bonding. Disk 550 is then firmly mounted in a housing which comprises a cylindrical member 558 having recess 560 in one end thereof, the recess 560 having a depth of about 1.5 mm and a diameter adpated to the transducer disk diameter, and being aligned with an axial bore 562 extending through member 558 to accommodate wire 554 provided on the lower surface of the piezoelectric member. A second bore 554, parallel to bore 562, is formed in the periphery of member 558, bore 562 accommodating wire 556 and terminating in an open recess 556 adjacent the main recess 560.

Member 558 may be formed of Tufnol, which is a phenolic resin bonded fabric, this material being readily obtainable in cylindrical form. The housing may be machined from this material, although the housing may be alternately formed of a two-part phenolic resin such as that sold under the trademark Araldite, the resin being retained in a cylindrical aluminium case 568 and subsequently being machined. If the latter construction is employed, aluminium case 568 may be grounded to provide a Faraday cage to minimize noise. The piezoelectric material and wires are bonded into member 560 with an adhesive such as Araldite or a cyanoacrylic impact adhesive. Two small bores 570, 572 are provided in the lower surface of member 558 and electrically conducting pins are mounted in the bores.Wires 554, 556 protrude from the lower ends of bores 562, 564 and are soldered to the pins in bores 570, 572, respectively. An adhesive or other suitable setting material is employed to retain all the elements in position and to secure a solid hemispherical dome 574 to the transducer element 550. The dome 574 may be machined from aluminium or cast from a setting resin material such as that sold under the trademark Araldite. The dome 574 preferably has an outer diameter of about 8 mm, which is equal to the diameter of the housing 568. A centrally-disposed projection 576 on the base of the dome member 574 contacts and has the same diameter as the piezoelectric disk 550.

Alternatively, dome 574 and member 558 may be cast as a single integral unit, surrounding the transducer disk.

The assembled transducer with housing as shown in Fig. 1 2 is mounted, as discussed elsewhere herein, in front of the target. It is important that both the housing and a coaxial cable coupling the transducer assembly to the associated amplifer be acoustically decoupled from any support or other rigid structure which could possibly receive the shock wave detected by the transducer before the shock wave is received by the hemispherical dome provided on top of the transducer. Thus, if the transducers are mounted on a rigid horizontal framework, it is important that the transducers be acoustically decoupled from such framework. The transducers may be mounted on a block of any suitable acoustic decoupling medium, such as an expanded polymer foam, or a combination of polymer foam and metal plate.A preferred material is closed-cell foam polyethylene, this material being sold under the trademark Plastizote by Bakelite Xynolite, Ltd., U.K. Other suitable acoustic decoupling materials may be used, as well, such as glass fiber cloth, or mineral wool.

The transducer may be mounted by taking a block 580 of acoustic decoupling medium as shown in Fig. 1 3 and forming a recess 582 within the block of material for accommodating the transducer assembly of Fig. 1 2. The entire block may be clamped in any convenient way, such as by clamps 584, to a suitable framework or support member 586, these items being illustrated schematically. Other suitable mounting arrangements for the transducer assembly will be described later below.

To summarise briefly, the system described above includes: -Transducers S1, S3, S4 for detecting shock wave arrival times along a line parallel to the measurement plane, which is in turn substantially parallel to the target.

-Transducers S1, S2 for detecting shock wave arrival time along a line perpendicular to the measurement plane and substantially parallel to the bullet trajectory.

-An inertia switch mounted on the target for detecting actual impact of the bullet with the target.

-A unit for detecting the ambient air temperature in the region of the transducer array.

The outputs of the transducers, inertia, switch, and air temperature sensing unit are fed through circuitry as described above to the timer interface unit, which gives counts representing times of shock wave arrival at the transducers, representing the inertia switch trigger time, and representing the air temperature. This information is fed from the timer interface unit to the minicomputer. Provided that the minicomputer is supplied with the locations of the transducers relative to the measurement plane, it may be programmed to: -Determined the speed of sound in ambient air in the vicinity of the transducer array (to a reasonable approximation) by a known formula

where Vsr is the speed of sound in air at the given temperature T, and Vsrc is the speed of sound at zero degrees Celsius.

-Determined the velocity of the bullet in the direction perpendicular to the measurement plane and substantially parallel to the bullet trajectory, and determine the location of the trajectory in the measurement plane.

However, the information provided from the timer interface unit permits still further and very advantageous features to be provided in the system for marksmanship training. The system can be made to discriminate between direct (free flight) target hits by the bullet, on the one hand, and target hits from ricochets or target hits from stones kicked up by the bullet striking the ground or spurious inertia switch triggering due to wind or other factors, on the other hand. In the embodiment employing timer interface unit 64, spurious inertia switch triggering will cause counter 7 to count until ripple carry signal RC7 is produced, thereby causing the system to automatically reset. The system can be further made to discriminate between ricochet hits on the target and ricochet misses.These features further enhance the usefulness in training as the trainee can be apprised, immediately after a shot is fired, of the location of the shot relative the target in the measurement plane, whether the target was actually hit by the bullet, whether the shot ricocheted, and even of a "score" for the shot.

The present invention contemplates three possible techniques for processing the information from the timer interface unit for the purpose of providing ricochet and stone hit discrimination.

(a) Electronic target window. For a hit to be genuine, the hit position determination system should have recognized a projectile as having passed through a target "window" in the measurement plane approximately corresponding to the outline of the actual target being fired upon. The target outline is stored in the computer and is compared with the location of the projectile as determined from the transducer outputs. If the calculated projectile trajectory location is outside the "window," then the "hit" reported by the inertia switch or other hit registration device cannot be valid and it can be assumed that no actual impact of the bullet on the target has occurred.

(b) Projectile velocity. It has been found experimentally that, although there is a variation in velocity of bullets from round to round, any given type of ammunition yields projectile velocities which lie within a relatively narrow band, typically + or - 5%. It has also been found that when a projectile ricochets, its apparent velocity component as measured by two in-line sensors along its original line of flight is substantially reduced, typically by 40% or more. It is therefore possible to distinguish a genuine direct hit from a ricochet by comparing the measured velocity component with a preset lower limit representing an expected projectile velocity (which will generally be different for different ammunitions and ranges).If the detected projectile velocity does not exceed this threshold limit, then the associated mechanical hit registration (inertia switch) cannot be valid and can be ignored. The computer may be supplied with a minimum valid threshold velocity for the type of ammunition being used, and the appropriate comparison made. It is to be noted that this technique does not require a capability to measure position, but only projectile velocity, and can be implemented using only an impact detector in combination with two sensors positioned relative to the target for detecting the airborne shock wave generated by the projectile at two spaced locations on its trajectory.

(c) Hit registration time. For a "hit" detected by the inertia switch to be genuine, it must have occurred within a short time period relative to the time at which the projectile position determining system detected the projectile. It has been found from theory and practice that this period is very short, not more than + or - 3.5 milliseconds for a commonly used "standing man" target as illustrated in Fig. 2. By suppressing all target impacts detected by the inertia switch outside of this time, many otherwise false target impact detections are eliminated. The position in time and the duration of the period varies with different targets, with position of hit positions sensors (i.e. airborne shock wave responsive transducers) relative to the target, with nominal projectile velocity and velocity of sound in air, and, to a small extent, with various target materials. All these factors are, however, known in advance and it is therefore possible to provide the system with predetermined limits for the time period. It is to be noted that this last technique does not require a capability to measure position or even projectile velocity, and can be implemented using only an impact detector in combination with a single sensor positioned relative to the target for detecting the airborne shock wave generated by the projectile.

Appendix A attached hereto is a suitable program written in "BASIC" programming language which may be directly used with the Computer Automation LS1 2/206 minicomputer. The program is used for performing the position calculations indicated above, generating required reset signals for the timer interface unit, calculating the speed of sound and bullet velocity, performing threshold checks for bullet velocity, determining whether the inertia switch has detected a "hit", determining a ricochet hit and providing appropriate output signals for the printer and display units.

It will recognized from the foregoing that the computer programs of Appendix A employ the "projectile velocity" and "hit registration time period" techniques for ricochet and stone hit discriminaton. Those skilled in the art will readily recognize the manner in which the programs of Appendix A may be modified to employ the "electronic target window" technique for ricochet and stone hit discrimination. That is, a mathematical alogrithm defining the boundaries of the target outline in the measurement plane may be included in the program and compared with the X, Y coordinates of the calculated bullet trajectory location in the measurement plane to determine whether the calculated location lies within the target "window".Assuming for example that the target is a simple rectangle, the "window" may be defined in the program as XA < X1 < XB, YA < Y1 < YB, where XA and XB represent the left and right edges of the target "window" and YA and YB represent the lower and upper edges of the target "window", respectively.

Two Assembly Language subroutine facilities are provided in the programming described above. They are: CALL (3): Execution of this BASIC statement resets the timer interface unit 64 and reads the circuitry for use. This subroutine is assigned the Assembly Language Label RESET.

CALL (4 2, A2, T7, T6, T5, T4, T3, T2, T1): Execution of this basic statement transfers the binary numbers of counters 1-8 of the timer interface unit to BASIC in sequence. This subroutine is assigned the assembly language label IN: Hit in the Controller BASIC Event Handler Subroutine Module.

Figs. 1 4A and 1 4B show flow chart sections for the subroutine RESET. Appendix B provides a- program listing for this subroutine. The subroutine RESET starts on line 40 of the listing of Appendix B. It saves the return address to BASIC and then rests that CALL (3) has only one parameter. Another subroutine labelled RST (line 31) is then called which contains the instructions to reset the timer interface unit circuits. Subroutine RESET ends by returning to BASIC.

Figs. 15A, 15B and 15C provide a flow chart for the subroutine IN: HIT, while Appendix B contains a program listing for this subroutine.

Those skilled in the art will recognize that the configuration of the transducer array in Figs. 2 and 4 may be modified within the spirit and scope of the present invention. For example, Figs.

16-18 show alternate embodiments of arrays in which the transducers may be positioned.

Still further modifications may be made in accordance with the present invention, as will be recognized by those skilled in the art. For example, one or more light curtains may be generated for detecting passage of the bullet through an area in space, for the purpose of determining the velocity of the bullet. Such apparatus may be of the type disclosed in U.S. Patent No.

3,788,748 to KNIGHT et al., the content of which is incorporated herein by reference. Fig. 1 9 shows an apparatus for generating a light curtain and detecting the passage of the bullet therethrough. A continuous wave helium-neon laser 600 generates a beam 602 which is directed onto an inclined quartz mirror 603 having a mirror coating on the second surface thereof, relative to beam 602, such that a portion of beam 602 is transmitted therethrough to form beam 604. Beam 604 is passed into a lens 605. Lens 605 is shaped as a segment of a circle cut from a sheet of material sold under the trade name Perspex. Beam 604 is directed to bisect the angle of the segment and passes centrally thereinto at a circular cut-out portion 606.

Cut-out portion 606 causes beam 604 to project as beam 608, which is of substantially rectangular cross-section shown by the dotted lines and which has no substantial transverse divergence.

Lens 605 comprises a generally triangular slab of light transmitting material having two substantially straight edges which converge, and having a part in the form of a part cylindrical notch 606 adjacent to the apex confined by the converging edges, which is adapted to diverge light entering the 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, are reflective to light within the lens. For example, the edges may be mirrored. Such a lens is adapted to produce a fan-shaped beam of light (a light curtain) having an angle which is equal to the angle included by the edges of the slab adjacent the apex at which light is to enter the slab.

If a projectile such as a bullet should pass through beam 608, it will be incided by beam 608. Since the projectile cannot be a perfect black body, a portion of the beam will be reflected thereby, and a portion of that reflection will return to lens 605 where it will be collected and directed at mirror 603 as beam 609. Beam 609 is reflected by mirror 603, which is first-surface coated, with respect to beam 609, as beam 610. The coating of mirror 603 is such that beam 601 will be approximately 50% of beam 609. Beam 610 passes through an optical band pass filter 61 2 which prevents light of frequency substantially different to that of laser 601 from passing, so as to reduce errors which may arise from stray light such as sunlight. Beam 610 emerges as beam 613, which then passes through lens 614.Lens 614 focusses beam 61 3 onto to the centre a photelectric cell 615, which emits an electrical signal 617. Signal 617 thus indicates the time at which the projectile passed through the light curtain.

Fig. 20 shows schematically a system according to the invention which may be employed for determining the velocity of the bullet in a direction normal to the measurement plane and the location in the measurement plane. A target 596 is mounted on a target mechanism 598 (which may be as shown in Fig. 2). An array of, for example, three transducers S1, S2, S3 is provided in front of and below the edge of target 596. Two arrangements as shown in Fig. 19 are located in front of target 596 to generate respective light curtains 608, 608' and produce output signals 618, 618' indicating the time at which the bullet passes through the respective light curtains. Since the spacing between the light curtains 608, 608' is known in advance, the time difference may be employed to determine the velocity of the bullet in a direction normal to the measurement plane.The calculated velocity and the speed of sound in air (as separately measured or determined) may be employed with the output signals from transducers S1-S3 to determine the location at which the bullet trajectory passes through the measurement plane. An inertia switch or other target impact detector may be used, as described above, for registering an actual hit on the target.

Those skilled in the art will readily recognize the manner in which the BASIC programs of Appendix A may be modified for use with an arrangement as shown in Fig. 20. The skilled artisan will also recognize that, for example, light curtain 608' may be deleted and the velocity of the bullet may be determined from the output 61 8 of photoelectric cell 61 5 and the output of transducer S2 of Fig. 20.

Those skilled in the art will also recognize that marksmanship training may be further enhanced by combining the use of the arrangements described herein with a rifle equipped with pressure sensors at critical points as described in U.S. Patent Application No. 835,431, filed September 21, 1977 (the content of which is incorporated herein by reference). For example, the rifle used by the trainee may be equipped with pressure sensitive transducers located at the parts of the rifle that are contacted by the trainee marksman when the rifile is being fired.Thus, a transducer is located at the butt of the rifle to indicate the pressure applied by the shoulder of the trainee marksman, a transducer is provided at the cheek of the rifle to indicate the pressure applied by the cheek of the trainee marksman, and transducers are provided at the main hand grip and the forehand grip of the rifle. The outputs of the transducers are coupled to suitable comparator circuits as described in U.S. Patent Application No. 835,431 and the comparator output signals than indicate whether the pressure applied by the trainee marksman at each critical point on the rifle is less than, greater than, or within a predetermined desired range.

While a display as described in U.S. Patent Application Serial No. 835,431 may be employed for indicating whether the pressure applied by the trainee marksman to the rifle at each point is correct, it will be understood that the comparator output signals may alternatively be provided to minicomputer 70 in a suitable format so that the visual display unit 72 of Fig. 4 will display a graphic representation of the rifle and indication thereon of the pressure applied by the trainee marksman to the rifle. This graphic display may be in addition to a graphic display of the target being fired upon the representations thereon of the location at which each bullet has struck or passed by the target.Such an arrangement provides the trainne marksman with an almost instantaneous indication of the manner in which he is holding the rifle and of his shooting accuracy, and permits rapid diagnosis of any difficulties he may be having with his shooting. If a switch is mounted on the rifle for actuation when the trigger is pulled as described in U.S.

Patent Application Serial No. 835,431, the visual display unit 72" may be made to indicate the pressure applied to the various pressure transducers on the rifle at the precise instant of firing the rifle. The display may be maintained on the display unit for a predetermined period of time and then erased so the trainee may proceed with firing a further round.

The addition of the pressure sensitive system enables the simultaneous display of pressure indications together with the projectile position and for positive target hit indication and/or ricochet indication. Such a simultaneous display has unique advantage in providing the trainee immediately not only with an indication of where the projectile has passed in relation to the target, but why the projectile passed through its displayed position. This information provides immediate positive and negative reinforcement of marksmanship techniques with respect to the correct grip and aim of the weapon to permit rapid learning of correct skills.

It is not necessary to employ on inertia switch to detect a "hit" of the projectile on a target member. Other apparatus may also be employed for this purpose. For example, Figs. 21-22 show an arrangement for sensing impact of a projectile on a target member 700 employing a sensor assembly 702 positioned in front of the rigid target member 700. The rigid target member 700 may be of any desired shape and may be constructed, for example, of plywood or ABS material. Sensor 702 includes a transducer mounted within a shrouded housing which prevents any airborne shock wave of a supersonic projectile from being detected. The output of the shrouded sensor assemblv 702 is Provided through an amplifier 704.

The output of amplifier 704 is provided through a suitable signal processing circuit 706, which provides a "hit" output indication. Signal processing circuit 706 may comprise essentially a threshold detector. Shrouded sensor assembly 702 may comprise a transducer 709 (as described above with reference to Figs. 11-12) mounted in a block of acoustic isolating material 708 (such as described above with reference to Fig. 13). The block of acoustic isolating material is, in turn, mounted in a housing or shroud 710, with the transducer 709 recessed to provide a restricted arc of sensitivity of the transducer which is appropriate to just "see" the face of target 700 when sensor assembly 702 is appropriately positioned relative to the target member 700.A coaxial cable from transducer 709 passes though an opening in shroud 710 and may be isolated from vibration by a silicone rubber ring 712, or the like. It will be understood that the threshold level of detector 707 in Fig. 21 is to be appropriately set so that disturbances of the target detected by transducer 709 will produce a "hit" output indication from signal processing circuit 706 only when the amplitude of the detected disturbance is sufficiently great to indicate that the disturbance of the target was caused by a projectile impacting on or passing through target member 700.

A further arrangement for determining projectile "hits" on a rigid target member will now be described with reference to Figs. 23, 24 and 25A-25B. Fig. 23 shows a rigid target member 720 which has substantial curvature in horizontal cross-section. A sensor 722 (which may be a transducer mounted in an acoustic isolating block as described above with reference to Figs.

11-13) is located behind the rigid target member 720 and preferably within the arc of curvature thereof. The output of transducer 722 is supplied to an amplifier 724, the output of which is in turn provided to a signal processing circuit 726 for providing a "hit" output indication.

One possible arrangement for the signal processing circuit 726 is shown in Fig. 24. It has been found that genuine "hits" on the target by a projectile result in electrical signals from the transducer 722 consisting of a number (typically greater than 10) of large amplitude pulses closely spaced, while misses or hits by stones, debris, etc., either cause low amplitude signals or low amplitude signals with only occasional high amplitude "peaks".

Typical "hit" and "miss" wave forms are shown in Figs. 25A and 25B, respectively. The signal processing circuit 726 of Fig. 24 operates to distinguish the signals of Figs. 25A and 25B by the use of integrating capacitor C and bleed-off resistor R2. Only multiple peaks as in Fig. 25A will trigger the second threshold detector of Fig. 28.

The technique for distinguishing "hit" from "miss" described above with reference to Fig. 24 applies in principle to any combination of rigid target and sensor, but has particular benefit when used with a 3-dimensional type target such as that shown in Fig. 23 or such as a target which completely encircles the transducer (such as conically-shaped target member). By virtue of the shape of the 3-dimensional targets, existing mechanical hit registraitons systems, such as inertia switches, often cannot be sued to detect hits on the target because vibration transmission within the target may be relatively poor. Secondly, the curved shape of the target provides very effective screening of the sensor from the airborne shock wave produced by near-missed supersonic projectiles.The curvature of the target can be increased to the point where it forms a complete shell with the sensor positioned inside it thus enabling hit detection from any direction of fire.

Still another apparatus for detecting a projectile "hit" (i.e. passage through a target member) is illustrated in Fig. 26. In this embodiment, the target member comprises a sheet of suitable electrically insulating spacer material 730 which may be of any desired size. Metal meshes 732, 734 are cemented to the insulation spacer sheet 730. As a bullet passes through the "sandwich" target comprising bonded-together members 730-734, electrical contact between metal meshes 732, 734 is established, so that the voltage at point 736 drops momentarily from + 5 volts to 0 volts, thereby indicating passage of the bullet through the target 'sandwich." Still other apparatus is possible for determining the velocity of the projectile, such as shown in Fig. 27. A projectile fired from a weapon 740 travels along a trajectory 742 toward a target member or target zone 744.An array of transducers S1, S2, S3 is located below one edge of the target member or zone 744. For determining the velocity of the projectile, a detector 746 is positioned to sense the time of discharge of the projectile from the weapon and provide a signal which starts a counter 748. Counter 748 is supplied with pulses from a clock generator 750 and counts the clock pulses unitl a signal is received from transducers S2 through an amplifier 752 for stopping the counter.

It is known that projectiles, such as bullets, decelerate in a well-defined and consistent manner. This deceleration can be expressed in terms of loss of velocity per unit distance travelled along the trajectory, the deceleration being substantially constant from sample to sample of high quality ammunition (such as most military ammunition) and being substantially independent of velocity.At any point along its trajectory, the projectile velocity V, is: Vet = Vmd .k where Vet = projectile velocity at point in question Vm = nominal velocity of projectile at weapon or known origin d = distance from muzzle (or known origin) to point in question k = above-mentioned "deceleration" constant By simple algebra, it is possible to find an expression for distance travelled in a given time, which is: d(t) = where t is the independent variable of time. For good quality ammunition the constant "k" is well controlled, and can be predetermined with good accuracy. Thus, the only "unknown" is Vrn, which will vary from round to round.

The arrangement according to Fig. 31 operates to determine a national value for Vm by measuring the time of flight of the projectile from the weapon to the array. The preceding equation permits Vm to be computed and, once obtained, permits V, in the vicinity of the transducer array to be calculated. Detector 746 may be an optical detector sensing the weapon discharge muzzle flash, or an acoustic device responding to the muzzle blast and/or supersonic projectile shock wave.

Fig. 28 shows a graticule overlay used on the visual display screen 72" of Fig. 4. A target T is provided as well as a separate score column for each shot. If the positive hit indication (inertia switch) is not actuated, a "0" score is indicated, otherwise a non-zero point score is displayed.

The positive hit indication is particularly advantageous for borderline cases, as for example, shot No. 6. In such cases, it may not be clear from the position display alone whether a "hit" occurred. Shot No. 1 is shown as a clear miss; shot No. 2 as a ricochet hit, shot No. 5 as a ricochet miss and shot numbers 3, 4 and 7 as hits having different point values.

APPENDIX A 2 REM INTERMEDIATE RANGE PROJECTILE POSITION CALCULATION PROGRAM 7 REM INCLUDING INTEGRATED VELOCITY OF SOUND IN AIR ESTIMATION 1010 R=4998000 1015 RO= 1/R 1020 DATA 0.0, 0.5, 0.0, 0.29, - 0.5, 0.5, - 0.5, 0.0.5, 0.5, 0.0.5, 0.5, 0.0.5 1025 DIM C (6.3) 1030 MAT READ C 1035 MAT PRINT C 1037 PRINT "MINIMUM BULLET VELOCITY, METRES/SEC.?" 1040 INPUT VO 1045 K=0 001 1100 CALL (3) 1120 CALL (4, 20, A2, T7, T6, T5, T4, T3, T2, T1) 1125 T1 = T1*RO 1130 T2 = T2*RO 1135 T3 = T3*RO 1140 T4 = T4*RO 1145 T5 = T5*RO 1150 T6 = T6*RO 1155 T7 = T7*RO 1157 GOTO 1450 1160 V1 =(C(1.3)-C(2.3))/(T2-Tl) 1165 N1 = 0 1170 1F V1 gt;VO GOTO 1180 1175 N1 - N1 + 2 1180 1F A2 = GOTO 1210 1185 1F N1 < 2 GOTO 1200 1190 1F T7 = T1 > 0 002 GOTO 1400 1195 1F T7 = T1 < 0 0005 GOTO 1400 1200 N1 = N1 + 1 1210 1F N1 1 GOTO 1400 1250 BI=BO 1255 B2=BO 1260 J = 3 1265 K=6 1270 T8=T3 1275 T9 = T6 1300 G = BO*BO 1301 G = G/ (1-G/(V1*V1)) 1302 G1 = G* (T9-T1) 1305 G2=2*G1 1310 G4 = O(K.1)-C(1.1) 1315 G3=2*G4 1320 G1 = G1* (T9+T1)-G4*(C(K.1) + 0*1.1)) 1325 H1 = G*(T1-T8) 1330 H2 = 2*H1 1335 H4 = C(1.1)-C(J.1) 1340 H3=2*H4 1345 H1 = H1*(T1+T8) -H4* (C(1.1)+C(J.1)) 1350 X1 = (H2*G1-H1 * G2) / (H3*G2-H2*G3) 1355 B3 = (G1 + G3*X1) / G2 1360 Y1 = T1-B3 1365 Y1 = G*Y1*Y1 1370 G4=X1-C(1.1) 1375 Y1=Yl-G4*G4 1380 Y1 = SQR (Y1) +C(1.2) 1385 GOTO 1110 1400 X1 = 0 1405 Y1 = 0 1410 PRINT "X = "; X1; "Y = "; Y1; "SHOT STATUS NO = ";N1 1420 PRINT "N1 =0 FOR MISS" 1425PRINT "N1 = 1 FOR HIT" 1430 PRINT "N1 = 2 FOR RICOCHET MISS" 1435 PRINT "N1-3 FOR RICOCHET HIT" 1440 GOTO 1500 1450 K1 = K/(T5-T1) 1455 BO = 331.45*SQR (K1/273) + 0.09 1460 GOTO 1160 1500 END APPENDIX "B" 0003 * RESET = RESET SYSTEM 0004 * IN:HIT = SHIFT HIT DATA FROM MEMORY TO BASIC 0005 OP:BIN = OUTPUT HIT/MISS FROM BASIC TO V.D.U.

0006 * 0007 * OFF 16 BIT WORDS WILL BE INPUT 0008 * TO MEMORY FOR EVERY HIT 0009 * 0010 * 0011 001A * NAM RESET, IN:Hit, OP:BIN 0022 005A 0012 0000 REL O 0013 0000 PSH: REF 0014 0001 FLT: REF 0015 0002 OPDEND REF 0016 0003 POP: REF 0017 0004 STR: REF 0018 0005 VAC: REF 0019 0006 ERR: REF 0020 0007 ACC1 REF 0021 0008 ACC2 REF 0022 0009 BCC1 REF 0023 OOOA BCC2 REF 0024 OOOB PTT: REF 0025 OOOC EVL: REF 0026 OOOD FIX:REF 0027 OOOE FLAG RES 1 0028 OOOF 0000 COUNT RES 1.0 0029 0018 M1 EQU 24 0030 0010 58CO INA INA M1.0 0031 0011 0800 RST ENT -0032 0012 0000 NOP 0033 0013 44C7 SEA M1.7 RESET INTERRUPTS 1 to 8 0034 0014 44C2 SEA M1.2 RESET TIMER 1 to 8 0035 0015 44C4 SEA M1.4 CLEAR COUNTRIES 1 to 8 0036 0016 44C1 SEA M1.1 ARM TIMER 0037 0017 58C7 INA M1.7 0038 0018 OAOO ElN 0039 0019 F708 0011 RTN RST 0040 001A 0800 RESET ENT 0041 001B FF1B 0000 CALL *PSH: SAVE RETURN 0042 001C C601 LAP 1 0043 001D FF18 0005 CALL *VAC: CHECK PARAMETER COUNT 0044 001E FEOD 0011 JST RST 0045 001F 0110 ZAR CLEAR TO SHOOT 0046 0020 9E12 OOOE STA FLAG 0047 0021 F7iE 0003 MP *POP: 0048 0022 0800 IN:HIT ENT 0049 0023 FF23 0000 CALL *PSH:SAVE RETURN 0050 0024 C6OA LAP 10 0051 0025 FF20 0005 CALL *VAC: CHECK COUNT 0052 0026 5801 HOLD ISA I/P CONSOLE SENSE REG 0053 0027 COOE CA1 14 CHECK FOR "E" 0054 0028 F203 002C JMP ESCAPE GET OUT IF IS 0055 0029 49C7 SEN M1.7 MODULE READY? 0056 002A F215 0040 JMP P:NEXT DATA AVAILABLE 0057 002B F605 0026 JMP HOLD NO.GO ROUND AGAIN 0058 002C C707 ESCAPE LAM 8 0059 002D 9E1E OOOF STA COUNT 0060 002E 0110 ZAR 0061 002F FA1E 004E 0062 0030 DE21 000F IMS COUNT 0063 0031 F603 002E JMP S-3 0064 0032 B624 000E END LDA FLAG 0065 0033 FA1A 004E JST PASSV 0066 0034 F731 0003 JMP *POP:BACK TO BASIC 0067 * 0068 *PASS 9 VALUES TO BASIC 0069 * 0070 0035 C708 PASS LAM 8 0071 0036 9E27 000F STA COUNT 0072 0037 B627 0010 LDA INA 0073 0038 9A00 0039 STA HERE 0074 0039 HERE RES 1 0075 003A AA2E 0069 XOR MASK 1 0076 003B FA12 004E JST PASSV 0077 003C DE03 0039 IMS HERE 0078 003D DE2E OOOF IMS COUNT 0079 003E F605 0039 JMP HERE 0080 003F F60D 0032 JMP END 0081 * 0082 *P:NEXT DETECTS IF COUNTERS FITTED 0083 0084 0040 58C1 P::NEXT INA M1.1 0085 0041 AA27 0069 XOR MASK 1 0086 0042 3140 0035 JAN PASS 0087 0043 58C2 INA M1.2 0088 0044 AA24 0069 XOR MASK 1 0089 0045 3150 0035 JAN PASS 0090 0046 58C3 INA M1.3 0091 0047 AA2l 0069 XOR MASKI 0092 0048 3153 0035 JAN PASS 0093 0049 58C4 INA M1.4 0094 004A AA1E 0069 XOR MASK 1 0095 004B 3156 0035 JAN PASS 0096 004C 58C7 INA M1.7 0097 004D F627 0026 JMP HOLD 0098 004E 0800 PASSY ENT 0099 004F FF4E 0001 CALL *FLT: 0100 0050 FF45 0008 CALL *PTT: 0101 0051 3106 0058 JAN ER 0102 0052 FF46 OOOC CALL *EVL: 0103 0053 B74A 0009 LDR *BCCl 0104 0054 9C00 0000 STA &commat;O 0105 0055 B74B 000A LDA *BCC2 -0106 0056 9C01 0001 STA 0107 0057 F709 004E RTN PASSV 0108 0058 FF52 0006 CALL *ERR: 0109 0059 C6D7 DATA FW 0110 005A 0800 OP:BIN ENT 0111 005B FF5B 0000 CALL *PSH: 0112 005C C602 LAP 2 0113 0050 FF58 0005 CALL VAC 0114 005E FF53 0008 CALL *PTT: 0115 005F 3108 0068 JAN ERROR 0116 0060 FF54 OOOC CALL *EVL: 0117 0061 FF54 OOOD CALL *FIX: 0018 0062 B75B 0007 LDA *ACC1 0119 0063 493B SEN 7.3 0120 0064 F601 0063 JMP S-1 0121 0065 6C38 OTA 7.0 0122 0066 493B SEN 7.3 0123 0067 F601 0066 JMP S-1 0124 0068 F765 0033 ERROR JMP *POP: 0125 0069 7FFF MASK 1 DATA :7FFF INVERT 15 BITS 0126 END 0000 ERRORS OQQO WARNING

Claims (9)

1. Marksmanship training apparatus for indicating when a target member has been hit by a projectile fired at said target member, comprising: a target member; and means spaced apart from and not physically connected to said target member for detecting and selectively providing a hit indication only in response to disturbance of said target member or a disturbance of the air adjacent the target member caused by said projectile hitting or passing through said target member.

2. Apparatus according to claim 1 wherein said means spaced apart from said target member comprise: at least one transducer, the transducer being spaced apart from and not physically connected to said target member, for detecting and providing an output in response to disturbances caused by an object hitting or passing through said target member, and a circuit responsive to said transducer output for providing said hit indication only in response to disturbance of said target member or a disturbance of the air adjacent the target member caused by said projectile hitting or passing through said target member.

3. Apparatus according to claim 2, wherein said transducer output varies in amplitude in dependence on the magnitude of said disturbance, and said circuit is operative to provide said hit indication only when said transducer output amplitude exceeds a predetermined level.

4. Apparatus according to claim 3, wherein said circuit is further operative to provide said hit indication only when said transducer output includes amplitude peaks which exceeds said predetermined level at a rate exceeding a predetermined rate.

5. Apparatus according to claim 2, 3 or 4 wherein said transducer is responsive to air pressure disturbances caused by objects hitting or passing through said target member.

6. Apparatus according to claim 5, wherein said transducer is located in front of said target member relative to a point from which said projectile is fired at said target member, further comprising means for shielding said transducer such that said transducer is responsive only to air pressure disturbances which propagate from the region of said target member toward said transducer.

7. Apparatus according to claim 5, wherein said transducer is located behind a front surface of said target member relative to a point from which said projectile is fired at said target member.

8. Apparatus according to claim 7, wherein said target member is 3-dimensional and at least partially surrounds said transducer, whereby said transducer is shielded by said target member so as to be substantially non-responsive to air pressure disturbances caused by projectiles passing by but not hitting said target member.

9. Apparatus according to claim 8, wherein said target member completely surrounds said transducer.

9. Apparatus according to claim 8, wherein said target member surrounds said transducer.

10. Apparatus according to claim 8 or 9, wherein the transducer is adjacent the base of the target member.

11. Apparatus according to any one of claims 1 to 10, wherein said projectile travels along a trajectory from a firing point toward said target member and through a measurement plane, further comprising: means for detecting and indicating relative to a target representing 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, whereby a marksman is provided with at least an approximate indication of where the projectile passes relative to the target member, as well as a positive indication of whether the projectile has hit the target member, thereby rendering hits at the edge of the target member distinguishable from misses near the edge of the target member.

12. Apparatus according to claim 11, wherein said location detecting and indicating means comprises: an array of at least three transducers responsive to an airborne shock wave from the supersonic projectile and located at respective predetermined positions spaced along a line substantially parallel to said measurement plane; means for measuring the velocity of the supersonic projectile; means for measuring the velocity of propagation of sound in air in the vicinity of the array of transducers; and computing means responsive to the output of said array of transducers, said projectile velocity measuring means, and said propagation velocity measuring means, and operative for: determining the location in said plane through which the trajectory of the supersonic projectile passes, and providing an output indicating said determined location relative to a target representation.

1 3. Apparatus according to any one of claims 1 to 12, further comprising means for: measuring the 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 trainee marksman is further provided with an indication of whether a detected hit on said target has resulted from a free flight projectile hitting said target member or from a projectile which has ricocheted prior to hitting said target member.

14. Apparatus according to claim 13, further comprising means responsive to said detecting and indicating means for providing a visual representation of said target member for graphically displaying said detected location relative to said target member representation.

1 5. Apparatus according to claim 14, 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.

1 6. Apparatus according to claim 15, wherein said graphic display means is further responsive to said hit detecting means for displaying a positive visual indication of whether said projectile has hit said target member.

CLAIMS (6Jul1983)

1. Marksmanship training apparatus comprising a rigid target member and means for indicating when the target member has been hit by a projectile fired at said target member, said indicating means comprising detecting means spaced apart from and not acoustically directly connected to said target member for detecting and providing a hit indication only in response to disturbance of said target member, or a disturbance of the air adjacent the target member resulting from said disturbance of the target member, caused by said projectile hitting or passing through said target member.

2. Apparatus according to claim 1 wherein said means spaced apart from said target member comprise: at least one transducer, the transducer being spaced apart from and not acoustically directly connected to said target member, for detecting and providing an output in response to disturbances caused by an object hitting or passing through said target member, and a circuit responsive to said transducer output for providing said hit indication only in response to disturbance of said target member or a resultant disturbance of the air adjacent the target member caused by said projectile hitting or passing through said target member.