GB2083177A - Improvements in or relating to position determining apparatus - Google Patents

Abstract

In an apparatus for determining the position of the trajectory of a supersonic projectile in which a plurality of transducers detect the sonic shock wave generated by the projectile, and the position of the trajectory is calculated from the time delays between the instants of reception of the shock wave by the transducers, separate means are provided to measure directly the speed of the projectile, to improve the accuracy of the apparatus.

Description

SPECIFICATION Improvements in or relating to position determining apparatus The present invention relates to an apparatus for determining information concerning the trajectory of a supersonic projectile passing through a predetermined area, said apparatus comprising transducers to be located adjacent said predetermined area and means to calculate, from the signals generated by the transducers, information concerning the trajectory of a passing projectile.

When a projectile travels through the atmosphere with a speed faster than the speed of sound, namely at a supersonic speed, the projectile generates a conically expanding pressure or shock wave, the projectile being at the apex of the shock wave, and the shock wave subsequently expanding conically away from the trajectory of the projectile.

It has been proposed to provide apparatus to determine the position of the trajectory of a projectile with an apparatus in which transducers or the like are utilised to detect such a shock wave generated by a supersonic bullet or projectile. One such proposal is described in the U.S.A. Patent Specification 3,778,059 (Rohrbaugh) and in the apparatus disclosed in this Specification two metal rods are located respectively adjacent the base and one side edge of the target, there being acoustic transducers attached to the ends of the rods. When a bullet is fired at the target the shock wave generated by the bullet will impinge on the rods, and a resultant acoustic wave or vibration generated within the rods will be transmitted to the transducers at the ends of the rods which subsequently produce electric signals.The resultant signals are fed to a timing and calculating device which calculates the position of the trajectory of the bullet and permits the position at which the bullet hits the target to be displayed on a device such as a visual display unit or cathode ray tube.

One disadvantage of this proposal is that the rod adjacent the side edge of the target is exposed, and can be damaged if accidentally hit by a shot fired atthetarget.

Afurther prior proposal is disclosed in U.S.A. Patent Specification No. 2,925,582 (Mattei) and this Specification discloses the use of four transducers placed around the periphery of a target area, signals derived by the four transducers when a bullet is fired at the target being fed to an appropriate calculating and display device adapted to calculate and display the position of the bullet. The calculating device initially determines the duration of the shock wave detected by each transducer, since the duration of the shock wave increases with increasing distance from the origin of the shock wave. Signals representative of the durations of the shock wave control the beam scanning circuit of a display device. This prior proposed arrangement suffers from the disadvantage that at least three of the transducers are exposed to fire from the marksman and are thus susceptible to damage.Furthermore, the levels of accuracy obtainable with the system described in this U.S.A. Patent Specification are not very high.

It will be appreciated that the prior art discussed above discloses the general use of transducers to detect airborne shock waves generated by a projectile such as a bullet, but all the prior proposed arrangements suffer from either the disadvantage that the arrangement does not provide an accurate indication of the precise position of the bullet or the disadvantage that the transducers are in a position in which they may be damaged by bullets hitting the transducers.

The present invention seeks to provide an improved target range in which the above described disadvantages are obviated or reduced.

According to the broadest aspect of this invention there is provided an apparatus for determining the position of the trajectory of a supersonic projectile passing through a predetermined area relative to a predetermined target, said apparatus comprising a plurality of transducers to be located adjacent the predtermined area, means to determine the instants of reception by the transducers of the shock or pressure wave generated by the projectile and means to calculate, from the determined information, the position of the trajectory relative to the target, said apparatus comprising an array or row of at least three transducers located adjacent one edge of said area of spaced positions, the transducers being exposed to airborne pressure or shock waves generated by supersonic projectiles fired at said target, said transducers each being adapted to provide an output signal in response to detection of such a shock or pressure wave, means to measure the time delays between the output signals generated by each of the transducers and separate means for measuring directly the velocity of the projectile relative to the target in the region of the target, and means adapted to calculate, from the time delays and from the measured bullet velocity the position of the trajectory relative to the target.

Preferably the apparatus further comprises means for 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 further provided with an indication of whether a detected hit on said target has resulted from a free flight projectile hitting said target or from a projectile which has ricocheted prior to hitting said target.

However, it is to be appreciated that by determining the velocity of the projectile the calculation that has to be performed by the calculating means to calculate the position of the trajectory of the projectile from the measured time delays is simplified.

Advantageously said apparatus is associated with means resonsive to the output of said apparatus for providing a visual representation of said target and for graphically displaying said determined position relative to said target representation. Said graphic display means may comprise 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.

Said apparatus may further comprise means for comparing said determined position with a predetermined range of positions 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 positions.

Preferably 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.

Conveniently, at least one of said passage detecting means comprises a transducer responsive to an airborne shock wave from the projectile.

At least one said passage detecting means comprise 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.

Conveniently, 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.

In one embodiment of the invention the means for measuring the bullet velocity comprise one of the tansducers of the said transducer row, together with a further transducer, the further transducer being substantially aligned with said one transducer so that the further transducer and said one transducer are substantially aligned with the anticipated trajectory of a bullet fired at the target from a firing position associated with the target.

Alternatively other means may be provided for detecting bullet velocity, such as two transducers, entirely separate from said row of transducers, said two transducers being substantially aligned with the anticipated trajectory of a bullet fired at the target from a firing position associated with the target. Alternatively again means may be provided for generating two light curtains at spaced positions in front of the target, the light curtains being substantially parallel with the plane of the target, means being provided for detecting radiation reflected by a bullet passing through each of said light curtains and means being provided for measuring the instants at which such reflections from a bullet or other projectile are detected and means for calculating the speed of the bullet or other projectile.

Alternatively again means may be provided for generating one light curtain at a position spaced from said transducer row, means being provided for detecting radiation by a bullet passing through the light curtain, and means for measuring the instant at which the reflection is detected, and for determining the time delay between that instant and the instant at which the pressure or shock wave generated by the projectile is detected by one of said transducers.

Alternatively again means may be provided for determining the instant at which the projectile is fired, and for determining the time delay between that instant and the instant at which the pressure or shock wave generated by the projectile is detected by one of said transducers.

Where the means for determining the velocity of the bullet comprise a further transducer aligned with one of the tranducers of the transducer row, preferably the transducers form a "T" or "L" configuration. The single further transducer may be on the target side of the row or on the firing point side of the row of transducers.

Preferably the transducers are located adjacent the lower side edge of the target and are shielded from the firing point by means which the projectiles cannot penetrate, such as an earthwork.

Preferably means are provided for measuring either the speed of sound in air in the region of the target or one or more parameters which determine the speed of sound in air in the region of the target, output signals from said measuring means being supplied to said calculating means.

In one embodiment of the invention, means are provided for measuring the temperature of the air in the region of the target, since this parameter is the parameter which largely determines the speed of sound in air. Other parameters only have a very minor influence on the speed of sound in air.

The calculating means may be adapted to calculate, from the measured velocity of the projectile, and from the known relationship between the velocity of a projectile and the deceleration of the projectile, the effective deceleration of the projectile. Information concerning the relationship between velocity and deceleration for any particular type of projectile can be readily ascertained, but it is to be noted that in utilising such an embodiment of the invention it would be necessary to programme the calculating means with regard to the types of projectiles to be utilised.

Preferably said array or row of transducers comprises four or more transducers. Whilst results of reasonable accuracy can be obtained with three tranducers it is to be understood that if a higher number of transducers is utilised, a greater degree of "redundancy" can be achieved, and consequently results of higher accuracy can be obtained.

Preferably each transducer comprises a disc-shaped member of piezo-electric material having a diameter of five mm or less.

Preferably each transducer comprises a member of rigid material for transmitting said airborne shock or pressure wave to a piezo-electric member in firm contact with the base of the member, the member of rigid material having a convex surface exposed to a shock wave. Preferably said convex suface is hemispherical.

Preferably each transducer comprises a member of insulating material having a recess to accommodate a disc of piezo-electric material having conductive coatings on two opposed faces thereof and channels accommodating conductive wires connected to said coatings, the base of said hemispherical member being secured to the piezo-electric disc. Conveniently, each transducer is mounted in such a way as to be acoustically de-coupled from the member or members supporting the transducer.

Preferably means are provided for amplifying the signal produced by each transducer, said amplifying means comprising an initial amplifying means and a threshold comparator which only passes signals having a predetermied minimum value.

A range utilising an apparatus in accordance with the invention as described above may be utilised in combination with a weapon, means being provided on the weapon for detecting the pressure applied to predetermined parts of the weapon by a person holding the weapon, there being means for recording or displaying the pressure applied to the weapon.

The weapon may be a gun or rifle, and the means for detecting the applied pressure may comprise transducers or the like. In such an embodiment of the invention preferably a visual display unit is provided to display the pressures applied to the weapon, comprising means to display a representation of the weapon and means for causing part of the representation to have colours representative of the pressure applied to the corresponding parts of the actual weapon.

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 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 trandsducers; 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 4; 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 timer interface 64 of Figure 4; Figures 8A and 88 show a suitable circuit arrangement for the air temperature sensing unit 78 of Figure 4; Figure 8Cshows a timing digram for the circuits of Figures 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 Figure 9; Figures 11 and 12 show one possible form of construction for airborne shock wave-sensing transducers; Figure 13 shows an acoustically decoupled mounting for the airborne shock wave transducers; Figures 14A and 14B are flow charts for computer subroutine CALL(3); Figures 15A - 15C show flow charts for computer subroutine CALL(4); Figures 16 - 18 show alternate transducer arrangements in plan view;; Figure 19 shows apparatus for generating a light curtain and detecting the passage of a projectile 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 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 Figure 4.

Figure 1 shows in perspective view a marksmanship training range employing concepts of the present invention. The range has a plurality of firing points 10 from which 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 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 froom 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 Figure 1) are in this embodiment also 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 the target represenation, 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 marksmen 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 Figure 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 Figure 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 Figure 2, or any other suitable apparatus. Various 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 Australasian 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 Figure 2, transducers S1-S1 are mounted on a rigid support member 40, which is in turn mounted on the target mechanism 36. Although the transducer arrays 18 may be supported separately from the target mechanism beneath targets 14 (as in Figure 1), affixing the transducer array to the target mechanism as in Figure 2 assure correct alignment of the measurement plane relative to target member 35.

Transducers S1-S4 (Figure 2) preferably each comprise a disk-shaped piezoelectric element of 5 mm diameter mounted to a hemishperical aluminum dome, the hemispherical surface of the dome being exposed for receiving the shock wave from the bullet. The airborne 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.

Figure 3 shows a three-dimensional coordinate system in which the positions of the four transducers S1-S4 are related to a reference point (0,0,0). The transducer array illustrated is similar to that shown in Figure 2, with a row of three transducers S2, 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 inersecting the origin of the Z axis of the coordinate system shown in Figure 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 Figure 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 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 All times of arrival are measured with respect to an arbitrary time origin. Us is defined as the propagation velocity of the shock wave front in air in a direction normal to the wave front, while Va is defined as the velocity of the supersonic projectile along its trajectory.

The velocity V5 of the bullet in a direction normal to the measurement plane is 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:

Then the propagation velocity of the shock wave front in a direction normal to the projectile velocity may be defined as:

The differences between the times of arrival of the shock wave may be defined as: ti = T3 - T1 (3) t2 = T4 - T1 (4) The X-axis coordinate of the intersection point of the projectile trajectory with the measurement plane is::

The distance in the measurement plane from sensor S1 to the point of intersection of the projectile trajectory with the measurement plane is:

The Y-axis coordinate of the intersection point of the bullet trajectory with the measurement plane is: Y = 1 - x2 (7) It is possible to construct a mathematical solution for the above-described tranducer 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 arithmetic, and in general can only be solved by iterative techniques.

It can be seen that the transducer arrangements shown in Figures 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 Z-axis of Figure 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 Figure 4, a plan view of the transducers S1-S4 in a "T" configuration is illustrated schematically. Each transducer is coupled by an appropriate shielded cable to a respective one 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 provides 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, including 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 airtemprature 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 Figures 8A-8C.

Figure 4 also shows schematically the target mechanism 36 and the inertia switch 38 of Figure 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 Figure 2.The output of isolator module 66 is supplied to two remaining inputs of timer interface unit 64, indicated in Figure 4 as channels 7 and "S.S." Minicomputer 70 of Figure 4 may be of type LSI-2/20G, available from Computer Automation Inc. of Irvine, California, Part No. 10560-16. The basic LSI-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 flopy 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 LSI-2 minicomputer.Other peripheral units which are not necessary for operation of the system in accordance with the invention, but which may be 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 represenation 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 LSI-2 minicomputer.

Also shown in Figure 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, availble 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 Figure 4, the 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.

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

Suitable components for isolator module 66 are: 82,84 1N914 86 471of 88 BC177 90 : 10KQ 92 820Q 94 5082-4360 96 470Q 98 6-8KQ 100 1OCLF 102 74LS 221N Monostable Multivibratorwith Schmitt-trigger inputs 104 DS8830N Differential line driver 106 0-221lF 108 47Q Figure 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 filter 110 to one input of a differential amplifier 112 which serves as a threshold detector. The remaining input of differential amplifier 112 is provided with a preset threshold voltage of up to, for example, 500 millivolts.The output of threshold detector 112 is supplied to a lamp driver circuit 114, to one input of a NAND gate 116 and to the trigger input of a monostable multivibrator 118 which provides an output pulse of approximately 50 millisecond duration. A shaped output pulse is therefore provided from NAND gate 116 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 (described below), the resulting projectile trajectory data is displayed on the visual display unit 72 and/or units 72', 72" of Figure 4.

Figures 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. Figure 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 Ch0-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 signals to each of timer interface inputs Ch0-Ch7 comprise logic signals which are first buffered and then supplied to the clock input CK of respective latches FF0-FF7. The latch outputs LCH0+ through LCH7+ are provided, as shown, to exclusive OR gates EOR1-EOR7, which in turn provide counter enabling signals ENA1- through ENA7-. Latches FF0-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 1-8 thus has 16 binary outputs, each output coupled to a respective one of terminals TBOp- through TB15- via a controllable gate circuit (indicated for channel 1 as "GATES 1") on receipt of a command signal (indicated for channel 1 as "IN0-"). 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 oveflow 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 2-7 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 lN7-for passing the counter contents to terminals TBO- through TB15-.Figure 7A also shows a gate NAND 1 which receives the latch outputs LCH0+ through LCH7+ and provides an output signal SEN7+, the purpose of which is explained below.

Figure 7B shows a circuit for providing clear signal CLR, which resets input latches FF0-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 CLR in the form of a logic pulse to clear up/down counters 1-7 and input latches FF-FF7 of Figure 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 Ch.

Figure 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 Figures 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 ABO3-ABO7 (Figure 7D) and a "function code" on lines ABOp-ABO2 (Figure 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.

Figure 7D shows exclusive OR gates EOR1 1-EOR15 which decode the "device address." A "device address" can also be selected manually by means of swiches SW1-SW5. The address signal AD- from gate NAND3 is then further gates 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.

Figure 7F shows a latch 2A which holds the function code of lines ABOp-ABO2 when either the IN or OUT signal is produced. The input/output function signals from latch 2A are labeled IOFPlthrough 1 OF2.

If the computer executes an IN instruction to receive data from the timer interface, the combination of IOF through IOF2 and ADIN- (Figure 7D) produce one of signals lN through IN7- at BCD/decimal decoder 5A of Figure 7E. Each of signals INlb- through lN7- enables data from one of up/down counters 1-8 to be placed on data bus terminals TBO- through TB15-.

If the computer is executing a "select" instruction for the timer interface, the combination of signals IOF IOF2 and ADEXP- (Figure 7D) produce one of select signals SEL- through SEL7- at BCD/ decimal decoder 5B of Figure 7E.The select signal functions employed in the presently described invention are: SEL1- enables triggering of latch FF9 (Figure 7C) SEL2- resets up/down counter 8 (Figure 7A) SEL4- resets latch FF8 (Figure 7C) and triggers monostable element 328 via NAND2 (Figure 7B) If the computer is executing a sense instruction from the timer interface, the combination of signals IOF,0 IOF2 (Figure 7F) and AD- (Figure 7D) allow one of sense signals SEN0+ through SEN7+ to be placed on the SER- line (Figure 7F). This allows the computer examine the state of one of these sense signals. The only sense signal employed in the presently-described embodiment is SEN7+, 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 FFp - FF7, producing a respective one of signals LCH,0+ through LCH7+. Signals LCH1 + through LCH7+ each control the up/down line of one of counters 1-7 and are also provided to OR gates EOR1 through EOR7 to produce a respective counter enabling signal ENA1-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 Chp 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 8 with signal SEL2- and then causes a general reset with signal SEL4-. Signal SEL4- causes gate NAND2 (Figure 7B) to trigger monostable element 328, producing clear signal CLR, which resets latches FF - FF7 and up/down counters 1-7 (Figure 7A). Reset signal SEL4also clears latch FF8 (Figure 7C). Latch FF9 (Figure 7C) is preset by the computer with signal SEL 1-, 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 FFp - 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 through Ch7 or the "S.S." channel 8 has been triggered. Since channel Ch has not yet triggered, signal LCH0+ is low. The remaining input of gate EOR is permanently high, so the output of gate EORp is high. Since sinals 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 Figure 4. Channel 3 of Figure 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 Chjb and channel Chi then trigger simultaneously. Signal LCH0+ goes high, so the output of gate EOR 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 NAND1 in Figure 7A gos 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 ABOp-ABO7 and the IN signal which cause BCD-to-decimal decoder 5A (Figure 7E) to issue signals IN1-through IN7- in sequence so that the computer will sequentially "read" the state of each counter (on output lines TBO,0- t through TB1 5-).

The computer has thus received counts representing times as follows: T1 zero count from counter 1 (transducer 51) 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 module as explained below with reference to Figure 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- (Figure 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 Figure 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 overlows, causing a ripple carry signal (RC1 - through RC7-).

All of the ripple carry signals are supplied to gate NAND2 (Figure 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.

Figures 8A and 8B show in detail a suitable circuit arrangement for the air temperature sensing unit 78 of Figure 4. Figure 8C shows wave forms of various points in the circuit of Figures 8A and 8B. The effect of the air temperature sensing unit is to generate a pulse at a time t1 following the time to at which channel Chi of comparator unit 62 is triggered (allowing of course for propagation delays in connecting cables).

Referring to Figure 8B, a temperature sensor IC1 mounted in a sensor assembly, assumes a temperature substantially equal to that of ambient air in the vicinity of the transducer array. Temperature sensor IC1 may be, for example, Model AD590M, available for Analog Devices Inc., P.O. Box 280, Norwood MA 02062, U.S.A.

Temperature sensor IC1 permits a current 11N to flow through it, current 11N being substantially proportional to the absolute temperature (in degrees Kelvin) of the semiconductor chip which forms the active element of temperature sensor IC1.

Referring again to Figure 8A, when transducer S1 detects a shock wave generated by the bullet a wave form similar to that shown at A in Figure 8C is produced at the output of its associated amplifier 54 (Figure 4).

Integrated circuit chip IC3B of Figure 8A forms a threshold detector, the threshold being set equal to that set in channel Chi of comparator unit 62 of Figure 6.

Integrated circuit chip IC3 may be of type LM 319, available from National Semiconductor Corporation, Box 2900, Santa Clara, California 95051. When wave A of Figure 8C exceeds the preset threshold, wave form D is generated at the output of circuit chip The leading edge (first transition) of wave form B triggers the monostable multivibratorformed by half of integrated circuit chip IC4 of Figure 8B and the associated timing components R8 and C3. Circuit chip IC4 may be of type 74LS221 N, 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 semiconductor Q2, the wave form at this point being depicted as C in Figure 8C.

Transistor Q1 may be of type BC107, available from Mullard Ltd., Mullard House, Torrington Place, London, U.K., and semiconductor Q2 may be of type VN 40AF, available 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 IC1 (proportional to its absolute temperature), the voltage at the output of integrated circuit chip IC2 starts to rise, as shown at D in Figure 8C.The rate of rise in volts per second of wave form D is substantially proportional to the current flowing through temperature sensor IC1 and thus is proportional to the absolute temperature of temperature sensor IC1. Integrated circuit chip IC2 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 presettheshold 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 of half of integrated circuit IC4 and timing components C4 and R9. The outputs 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 Figures 8A and 8B may be mathematically described as follows (assuming that the ramp at wave form D of Figure 8C is linear and ignoring offset voltages in the circuit, which will be small):

where V0 = voltage of wave form D, Figure 8C, and dV IN (9) dt C1 where 1IN = current through IC1 IIN = COK (10) where C is a constant of proportionality and 0K is the absolute temperature of IC1 combining (8), (9) and (10),

Timer interface unit 64 can then measure time t1 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 S1. Counter 5 will stop counting upon receipt of the pulse wave form G from the air temperature sensing unit at time t1. Thus, the count on counter 5 of the timer interface unit will be directly proportional to the reciprocal of the absolute temperature of sensor IC1.

Each of transducers S1-S4 may be a flat disk 530 of piezoelectric material (Figure 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 Figure 10. It is desired to masure the time T illustrated in Figure 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 533, 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 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 contact 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 constanttiming errorthereby introduced will cancel out during calculation of the bullet trajectory location.

The hemispherical dome prevents or minimizes generation of positive-going pip 542 so the output of s 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 tranducer must have a fast response.

It is advantageous to utilize a piezoelectric disk having a diameter of about 5 mm, which provides 7 response time and a relatively high amplitude output signal.

Referring now to Figures 11 and 12 of the drawings, one possible form of transducer for use in -i3-r.ne.:::t.

with the present invention comprises a transducer element consisting of a disk 550 of piezoelectric mt,tel such as, for example, lead zirconium titanate. The disk 550 is about 1 mm thick and 2-5 mm in diameter, c d may be part No. My1043, available from Mullard Ltd., Torrington Place, London, U.K. The opposed pianc,- faces of disk 550 are provided with a coating of conductive material 552, which may be vacuurn-depos.ta silver.

Two electrically conductive wires 554, 556 of, for example, copper or gold are connected to the cel 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 mm and a diameter adapted to the transducer disk diameter, and being aligned with an axial bore 562 extending through member 558 to accomodate 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 accomodat: wire 556 and terminating in an open recess 566 adjacent the main recess 560.Member 558 may be forms 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 aluminum case 568 and subsequently being machined. If the latter construction is employed, aluminum 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 cyano-acrylic 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 aluminum 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 Figure 12 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 amplifier 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 Xylonite, 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 Figure 13 and forming a recess 582 within the block of material for accomodating the transducer assembly of Figure 12. 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 summarize 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 times 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 shockwave 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: - Determine the speed of sound in ambient air in the vicinity of the transducer array (to a reasonable approximation) buy a known formula

where Vsiis the speed of sound in air at the given temperature T, and Vs0o c is the speed of sound at zero degrees Celsius.

- Determine 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 ortarget hits from stones kicked up by the bullets 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 automatially 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 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 presently described arrangement may utiiise three possible techniques for processing the information from the timer inerface 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 could 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 Figure 2. By suppressing all targetimpacts 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 LSI 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 be recognised 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 discrimination. 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 algorithm 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 calulated 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 readies the circuitry for use. This subroutine is assigned the Assembly Language label RESET.

CALL(4, Z0, 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.

Figures 14A and 14B 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 tests that CALL(3) has only one parameter. Another subroutine labeled RST (line 31) is then called which contains the instructions to reset the timer interface unit circuits.

Subroutine RESET ends by returning to BASIC.

Figures 15A, 15B and 1 5C 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 Figures 2 and 4 may be modified within the spirit and scope of the present invention. For example, Figures 16-18 show alternate embodiments of arrays in which the transducers may be positioned. In each case two transducers are aligned with the anticipated trajectory of the projectile to enable the speed or velocity of the projectile to be determined directly.

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. Figure 2 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 suface thereof, relative to beam 602, such that a portion of beam 602 is transmitted therethrough to form beam 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 610 will be approximately 50% of beam 609. Beam 610 passes through an optical band pass filter 612 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 614focuses beam 613 onto the center of a photoelectric cell 615, which emits an electrical signal 617. Signal 617 thus indicates the time at which the projectile passed through the light curtain.

Figure 20 shows schematially 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. Atarget 596 is mounted on a target mechanism 598 (which may be as shown in Figure 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 Figure 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 Figure 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 618 of photoelectric cell 615 and the output of transducer S2 of Figure 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 descried in U.K. Patent Application No.7900148 (Serial No.2013844) (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 rifle 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 said U.K. PatentApplication No. 7900148 and the comparator output signals then 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 descried in U.K.Patent Application Serial No. 7900148 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 Figure 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 and represenations thereon of the location at which each bullet has struck or passed by the target.Such an arrangement provides the trainee 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 said U. K. Patent Application Serial No. 7900148, 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 togehter 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 an inertia switch to detect a "hit" of the projectile on a target member. Other apparatus may also be employed for this purpose, if desired. For example, Figures 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 assembly 702 is provided though 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 Figures 11-12) mounted in a block of acoustic isolating material 708 (such as described above with reference to Fgure 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 through 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 Figure 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 Fiures 23, 24 and 25A-5B. Figure 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 Figures 11-13) is located behind the rigid target member 720 and preferably within the arc of curvature thereof. The output of tranducer 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 Figure 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 Figures 25A and 25B respectively.

The signal processing circuit 726 of Figure 24 operates to distinguish the signals of Figures 25A and 25B by the use of integrating capacitor C and bleed-off resistor R2. Only multiple peaks as in Figure 25A will trigger the second threshold detector of Figure 28.

The technique for distinguishing "hit" from "miss" described above with reference to Figure 24 applies in principle to any combination of rigid target and sensor, but has particular benefit when used with a 3-dimensjional type target such as that shown in Figure 23 or such as a target which completely encircles the transducer (such as a conically-shaped target member). By virtue of the shape of the 3-dimensional targets, existing mechanical hit registrations 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 provies 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 Figure 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 insulating 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 Figure 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 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 Counter 748 is supplied with pulses from a clock generator 750 and counts the clock pulses until a signal is received from transducer 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 Vt is: Vt = V" ,d-k where Vt = prDjectile velocity at point in question - Vm = ncminal velocity of projectile at weapon or known origin d = distance from muzzle (or know 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) = Vm e-kt where t is the inependent 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 Figure 31 operates to determine a notional 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 Vt 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.

Figure 28 shows a graticule overlay used on the visual display screen 72" of Figure 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 along 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 R0=1/R 1020 DATA 0.0, 0.5, 0.0, 0.29, -0.5,0.0.5, -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 INPUTVO 1045 K=0001 1100 CALL(3) 1120 CALL (4,20, A2, T7, T6, T5, T4, T3, T2, T1) 1125 Ti=Ti*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 GOT01450 1160 V1=(C(1.3)-C(2.3))/(T2-T1) 1165 N1=0 1170 IFV1 > V0 GOTO 1180 1175 N1-N1+2 1180 IFA2= GOTO 1210 1135 IFN1 < 2 GOTO 1200 1190 IFT7=T1 < 0002GOTO 1400 1195 IF T7-Ti < -00005 GOTO 1400 1200 N1=N1+1 1210 IF Nl > 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 Gi=G*(T9-Ti) 1305 G2=2*G1 1310 G4=0(K.1)C(1.1 1315 G3=2*G4 1320 G1=G1*(T9+T1)-G4*(C(K.1)+0*1.1)) 1325 H1=G*(T1T8) 1330 H2=2*H1 1335 H4=C(1.1)-C(J.1) 1340 H3=2*H4 1345 H1=H1+(T1 +T8)-H4X(C(1.1 )+C(J.1)) 1350 Xi=(H2*Gi-Hi*G2)/(H3*G2-H2*G3) 1355 B3=(G1+G3*X1)/G2 1360 Yi=Ti-B3 1365 Y1-G*Y1*Y1 1370 G4=X1-C(1.1) 1375 Yi =Y1 -G4*G4 1380 Y1 =SQR(Y1) +C(1.2) 1385 GOTO 1110 1400 X1=0 1405 Y1=O 1410 PRINT"X="; X1; "Y"; Y1; "SHOT STATUS NO="; N1 1420 PRINT"N1=0 FOR MISS" 1425 PRINT"Nl=i FOR HIT" 1430 PRIN7N1 =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 * 8 OFF 16 BIT WORDS WILL BE INPUT TO MEMORY 0008 * FOR EVERY HIT 0009 * 0010 * 0011 001A NAM RESET, IN:HIT, OP:BIN 0022 005A 0012 0000 REL 0 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 000A BCC2 REF 0024 000B PTT: REF 0025 000C EVL: REF 0026 000D FIX:REF 0027 000E FLAG RES 1 0028 000F 0000 COUNT RES 1.0 0029 0018 M1 EQU 24 0030 0010 58C0 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 COUNTERS 1 to 8 0036 0016 44C1 SEA M1.1 ARM TIMER 0037 0017 58C7 INA M1.7 0038 0018 OA00 EIN 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 0OiE FEOD 0011 JST RST 0045 001F 0110 ZAR CLEAR TO SHOOT 0046 0020 9E12 OOOE STA FLAG 0047 0021 F71E 0003 JMP *POP: 0048 0022 0800 IN:HIT ENT 0049 0023 FF23 0000 CALL *PSH:SAVE RETURN 0050 0024 C60A LAP 10 0051 0025 FF20 0005 CALL *VAC: CHECK COUNT 0052 0026 5801 HOLD ISA I/P CONSOLE SENSE REG 0053 0027 C00E CAI 14 CHECK FOR "E" 0054 0028 F203 002C JMP ESCAPE GET OUT IF IT IS 0055 0029 49C7 SEN M1.7 MODULE READY? 0056 002A F215 0040 JMP P:NEXT DATAVAVAILABLE 0057 002B F605 0026 JMP HOLD NO.GO ROUND AGAIN 0058 002C C707 ESCAPE LAM 8 0059 002D 9E1E 000F STA COUNT 0060 002E 0110 ZAR 0061 002F FA1E 004E JST PASSV 0û62 0030 DE21 000F IMS COUNT 0063 0031 F603 002E JMP $-3 0064 0032 B624 000E END LDA FLAG 0065 0033 FAIA 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 OOOF STA COUNT 0072 0037 B627 0010 LDA INA 0073 0038 9A00 0039 STA HERE 0074 0039 HERE RES 1 0075 003A AA2E 0069 XOR MASK1 0076 003B FA12 004E JST PASSV 0077 003C DE03 0039 IMS HERE 0078 003D DE2E 000F 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 MASK1 0086 0042 314D 0035 JAN PASS 0087 0043 58C2 INA M1.2 0088 0044 AA24 0069 XOR MASK1 0089 0045 3150 0035 JAN PASS 0090 0046 58C3 INA M1.3 0091 0047 AA21 0069 XOR MASK1 0092 0048 3153 0035 JAN PASS 0093 0049 58C4 INA M1.4 0094 004A AA1E 0069 XOR MASK1 0095 004B 3156 0035 JAN PASS 0096 004C 58C7 INA Mi.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 000C CALL *EVL: 0103 0053 B74A 0009 LDR *BCC1 0104 0054 9C00 0000 STA &commat;0 0105 0055 B74B 000A LDA *BCC2 0106 0056 9C01 0001 STA &commat;1 0107 0057 F709 004E RTN PASSV 0108 0058 FF52 0006 ER CALL *ERR: 0109 0059 C6D7 DATA FW û11Q 005A 0800 OP:BIN ENT 0111 005B FF5B 0000 CALL *PSH: 0112 005C C602 LAP 2 0113 005D FF58 0005 CALL *VAC 0114 005E FF53 0008 CALL *PTT: 0115 005F 3108 0068 JAN ERROR 0116 0060 FF54 000C CALL *EVL: 0117 0061 FF54 000D CALL *FIX: 0118 0062 B75B 0007 LDA *ACT1 0119 0063 493B SEN 7.3 0120 0064 F601 0063 JMP 5-1 0121 0065 6C38 OTA 7.0 0122 0066 493B SEN 7.3 0123 0067 F601 0066 JMP $-1 0124 0068 F765 0003 ERROR JMP *POP: 0125 0069 7FFF MASKI DATA :7FFF INVERT 15 BITS 0126 END 0000 ERRORS 0000 WARNING Reference is made to co-pending Application No. 8000447 (Serial No. 2042696) from which the pesent application is divided and which relates to an arrangement in which an array of transducers, and an associated timing means, are used to calculate the position of the trajectory of the projectile, and separate means are provided to give a positive confirmation of a target "hit".

Claims (28)

1. An apparatus for determining the position of the trajectory of a supersonic projectile passing through a predetermined area relative to a predetermined target, said apparatus comprising a plurality of transducers to be located adjacent the predetermined area, means to determine the instants of reception by the transducers of the shock or pressure wave generated by the projectile and means to calculate, from the determined information, the position of the trajectory relative to the target, said apparatus comprising an array or row of at least three transducers located adjacent one edge or said area at spaced positions, the transducers being exposed to airborne pressure or shock waves generated by supersonic projectiles fired at said target, said transducers each being adapted to provide an output signal in response to detection of such a shock or pressure wave, means to measure the time delays between the output signals generated by each of the transducers and separate means for measuring directly the velocity of the projectile relative to the target in the region of the target, and means adapted to calculate, from the time delays and from the measured bullet velocity the position of the trajectory relative to the target.

2. An apparatus according to claim 1 wherein the apparatus further comprises means for: 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 further provided with an indication of whether a detected hit on said target has resulted from a free flight projectile hitting said target or from a projectile which has ricocheted prior to hitting said target.

3. An apparatus according to claim 1 or claim 2, wherein said apparatus is associated with means responsive to the output of said apparatus for providing a visual representation of said target and for graphically displaying said determined position relative to said target representation.

4. An apparatus according to any one of the preceding claims wherein said apparatus further comprises means for comparing said determined position with a predetermined range of positions 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 positions.

5. An apparatus according to any one of the preceding claims wherein said projectile velocity measuring means comprise 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.

6. An apparatus according to claim 5 wherein at least one of said passage detecting means comprises a transducer responsive to an airborne shock wave from the projectile.

7. An apparatus according to claim 5 wherein at least one said passage detecting means comprise 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.

8. An apparatus according to claim 5 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.

9. An apparatus according to claim 6 wherein the means for measuring the bullet velocity comprise one of the transducers of the said transducer row, together with a further transducer, the further transducer being substantially aligned with said one transducer so that the further transducer and said one transducer are substantially aligned with the anticipated trajcectory of a bullet fired at the target from a firing position associated with the target.

10. An apparatus according to claim 6 wherein the means provided for detecting bullet velocity comprise two transducers, entirely separate from said row of transducers, said two ransducers being substantially aligned with the anticipated trajectory of a bullet fired at the target from a firing position associated with the target.

11. An apparatus according to claim 7 wherein means are provided for generating two light curtains at spaced positions in front of the target, the light curtains being substantially parallel with the plane of the target, means being provided for detecting radiation reflected by a bullet passing through each of said light curtains and means being provided for measuring the instants at which such reflections from a bullet or other projectile are detected and means for calculating the speed of the bullet or other projectile.

12. An apparatus according to claims 6 and 7 wherein means are provided for generating a light curtain at a position spaced from said transducer row, means being provided for detecting radiation reflected by a bullet passing through the light curtain, and means for measuring the instant at which the reflection is detected, and for determining the time delay between that instant and the instant at which the pressure or shock wave generated by the projectile is detected by one of said transducers.

13. An apparatus according to claim 6 and claim 8 wherein means are provided for determining the instant at which the projectile is fired, and for determing the time delay between that intant and the instant at which the pressure or shock wave generated by the projectile is detected by one of said transducers.

14. An apparatus according to claim 9 wherein said further transducer is aligned with one of the transducers of the transducer row.

15. An apparatus according to any one of the preceding claims wherein the transducers are located adjacent the lower side edge of the target and are shielded from the firing point by means which the projectiles cannot penetrate.

16. An apparatus according to any one of the preceding claims wherein means are provided for measuring either the speed of sound in air in the region of the target or one or more parameters which determine the speed of sound in air in the region of the target, output signals from said measuring means being supplied to said calculating means.

17. An apparatus according to claim 16 wherein means are provided for measuring the temperature of the air in the region of the target.

18. An apparatus according to any one of the preceding claims wherein the calculating means are adapted to calculate, from the measured velocity of the projectile, and from the known relationship between the velocity of a projectile and the deceleration of the projectile, the effective deceleration of the projectile.

19. kn apparatus according to any one of the preceding claims wherein said array or row of transducers comprises four or more transducers.

20. An apparatus according to any one of the preceding claims wherein each said transducer comprises a disc shaped member of piezo-eectric material having a diameter of five mm or less.

21. An apparatus according to any one of the preceding claims wherein each said transducer comprises a member of rigid material for transmitting said airborne shock or pressure wave to a piezo-electric member in form contact with the base of the member, the member of rigid material having a convex surface exposed to a shock wave.

22. An apparatus according to claim 21 whrein said convex surface is hemispherical.

23. An apparatus according to claim 22 wherein each said transducer comprises a member of insulating material having a recess to accommodate a disc of piezo-electric material having conductive coatings on two opposed faces thereof and channels accommodating conductive wires connected to said coatings, the base of said hemispherical member being secured to the piezo-electric disc.

24. An apparatus according to any one of the preceding claims wherein each said transducer is mounted in such a way as to be acoustically de-coupled from the member or members supporting the transducer.

25. An apparatus according to any one of the preceding claims wherein respective means are provided for amplifying the signal produced by each said transducer, said amplifying means comprising an initial amplifying means and a threshold comparator which only passes signals having a predetermined value.

26. A range utilising an apparatus in accordance with any one or more of the preceding claims in combination with a weapon, means being provided on the weapon for detecting the pressure applied to predetermined parts of the weapon by a person holding the weapon, there being means for recording or displaying the pressure applied to the weapon.

27. A range according to claim 26 wherein the weapon is a gun or rifle, and the means for detecting the applied pressure comprise transducers.

28. A range according to claim 26 or 27 wherein a visual display unit is provided to display the pressures applied to the weapon, comprising means to display a representation of the weapon and means for causing part of the represenation to have colours representative of the pressure applied to the corresponding parts of the actual weapon.