GB2157814A - Firing range scoring system - Google Patents

Abstract

A scoring system 12 for a live-fire weapon range comprises a generator 13 and weapon mounted electrode 14 for imparting an electrostatic charge to a fired projectile. At the target 10 a detection plane is defined by first and second electrometer means 18, 19 which detect passage of the charge by measurement of the field gradient and derive the angles alpha , beta made between the projectile 29 and the ends of a base line 20 and from which the projectile position with respect to the target can be found by triangulation. The electrometer means 18 (and 19) comprises a pair of electrometers 21, 22, each having a pair of spaced electrodes operable to produce an induced voltage proportional to field direction in relation to a direction of maximum sensitivity, and disposed at right angles to each other to provide by the ratio of their outputs a measure of the projectile angle alpha (and beta for 19). <IMAGE>

Description

SPECIFICATION Firing range scoring system This invention relates to firing ranges in which a projectile is fired from a weapon at a target and in particular to scoring systems for such ranges which determine how close a projectile passes to the target or a predetermined point of the target.

Scoring systems are known which respond to the impact of a projectile on the target both to register a 'hit' and to determine the relationship between the point of impact and a more specific target area. Such systems usually employ physical-impact sensors or the bridging of an electrical circuit by the projectile.

Other systems define a p;anar detection area in (or slightly in front of) the plane of the target by means of a "curtain" of optical or microwave radiation and by means of coordinate detection of radiation reflected by the projectile determine its position in relation to the target. The efficiency of such systems is however limited by the small signal levels to be detected and the effects of atmospheric conditions, in the vicinity of the target, on these.

A somewhat analogous system defines such a planar detection area by means of a linear array of pressure transducers which respond to the shock wave produced by the passage of a projectile through the air at supersonic velocity to define its coordinate position with respect to the area boundaries, and thus the target. The coordinate position is detected by processing the relative arrival times of the shock waves at the spaced transducers. For accurate position determination two or more such arrays are employed to provide a measure of projectile velocity and values for wind velocity and sound velocity (dependent upon atmospheric conditions) have to be determined.The dependence of system accuracy on a complex detector deployment and upon the gathering and monitoring of atmospheric data leads to a system which in practice is complex Furthermore the system is essentially limited to small-arms in which the projectiles travel supersonically and is unsuited to larger calibre weapons which fire sub-sonic projectiles.

It is an object of the present invention to provide a scoring system for a firing range, and a firing range incorporating such a scoring system, which is less complex and not subject to the limitations of known systems.

According to one aspect of the present invention a scoring system for a firing range in which a projectile is fired from a weapon at a target comprises charging means operable to apply an electrostatic charge to a projectile fired at a range target, and measuring means including detection means located in the vicinity of the target, responsive to voltages induced by the passage of a charged projectile to produce signals defining the position of the projectile trajectory with respect to the target.

The detection means of the measuring means may comprise first and second electrometer means operable to define a detection plane including a base line and separated by a known distance along the base line, said first and second electrometer means each being operable to determine passage of a charged projectile through the detection plane as a function of a projectile angle subtended at the electrometer means between the point in the detectionrplane of intersection of the projectile trajectory and the base line, said measuring means including processing means responsive to projectile angles from the first and second electrometer means and said known distance along the base line of electrometer means separation to determine the position within the detection plane of the projectile trajectory intersection therewith.

Each of the first and second electrometer means may comprise (a) two electrometers, each operable to produce a signal voltage proportional to the potential gradient of an electric field extending across a pair of spaced electrodes thereof, disposed so as to be at substantially the same distance from a charged projectile passing through the detection plane with their directions of maximum sensitivity (as herein defined) coplanar and making known angles to each other and to the base line, and (b) combining means comprising peak detection means operable to determine the peak voltages induced in the electrometers by a charged projectile passing through the detection plane and division means operable to determine from the relative magnitudes of the two electrometer peak signals and the relative angles between their directions of maximum sensitivity the projectile angle subtended at the electrometer means between the projectile trajectory and the base line.

According to another aspect of the present invention a firing range in which a projectile is fired from a weapon at a target includes a scoring system as defined by any of the three preceding paragraphs.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a rifle firing range showing a vertical target and illustrating schematically one form of the scoring system of the present invention, Figure 2(a) is a sectional elevation through the detection/target plane of Figure 1 at right angles to the projectile trajectory illustrating the relationship between the electric field of a charged projectile and electometers of the detection means, Figure 2(b) shows the relationship between the voltage signal generated in an electrometer and the distance of the projectile from the detection plane, Figure 3 is a schematic representation of the detection means along the projectile trajectory, illustrating the relationship between the electric field of a charged projectile and the electrometers of the detection means and also of the functional elements of the electrometer signal processing means, Figure 4 is a sectional elevation through one form of charging means mounted on a gun barrel extension, Figure 5(a) is a perspective illustration of an alternative form of electrometer showing adjacent electrometer electrodes disposed so as to be subjected to the same projectile field, Figure 5(b) is a perspective illustration, similar to Figure 5(a) but showing yet another form of electrometer electrode disposition, Figure 6 shows the relationship between the voltage signal generated in the electrometer and distance of the projectile from the electrometer similar to, but at right angles to the direction of Figure 2(b), Figure 7(a) is a perspective view of a rifle firing range, similar to that of Figure 1 and illustrating another form of scoring system according to the present invention, and Figure 7(b) and 7(c) are waveforms of electrometer and reference signal respectively produced in the arrangement of Figure 7(a).

Referring to Figure 1 a firing range of the so-called live fire type includes a target 10, for instance in the form of a frontal outline of a man, at which projectiles in the form of live amunition bullets are fired by a rifle 11. The target 10 is essentially two-dimensional, that is, planar, and stands vertically in what can be considered as the target plane. It may be movable in position and/or hinged to fall if struck.

In order to determine how close a shot is to the target, or a particular point on the target, a scoring system 1 2 is provided which defines a planar projectile detection area, or detection plane, either coplanar with, or immediately in front of or behind, the target plane.

The scoring system 1 2 is in two main parts.

A first part, 1 3 shown adjacent the rifle 11 comprises charging means to apply an electrostatic charge to a bullet as it leaves the barrel.

The charging means is described more fully hereinafter with reference to Figure 4 but may be considered as a conductive charging electrode 14 connected to a source of high electrical potential, say 1 KV, with respect to the rifle by an EHT generator 1 5. The rifle 11 is maintained at earth potential.

A second part of the scoring system comprises measuring means and includes detection means 1 6 located in the vicinity of the target which is responsive to voltages induced by the passage of a charged projectile and processing means 1 7 which produces signals which define the position of the projectile trajectory with respect to the target. The detection means 1 7 comprises first and second electrometer means 18, 1 9 separated by a known distance along a notional base line 20 in (or slightly ahead of) the target plane.The first and second electrometer means are similar and reference to more detailed parts thereof will be exemplified in relation to the means 1 8 only, the means 1 9 having corresponding parts labelled with primed reference numerals. The electrometer means 1 8 comprises two electrometers 21, 22, also identical in construttion. The electrometer 21 comprises a pair of electrodes 23, 24 in the form of conductive rods extending parallel to each other and spaced apart by an air gap, each of the electrodes being connected to one input of a high input impedance amplifier 25 such that an electric field whose potential gradient extends across the gap induces a voltage between the electrodes proportional to the potential gradient at that point and a corresponding output signal voltage is developed by the amplifier.It will be appreciated that each electrometer has a direction of maximum sensitivity which is defined for this specification as extending in the plane containing the electrodes and in their direction of minimum average separation, which for parallel rod electrodes is orthogonal to their direction of extension.

Whilst the polarity of the charge applied to the projectile is immaterial as regards the magnitude of signals produced the polarity is required to be considered and the amplifiers 25 are arranged to produce output signals which depend on the direction of the field gradient of the source with respect to the electrodes. For example, in Figure 1 a positively charged projectile to the left of the electrometer means in region 27 produces an electrometer signal of a particular magnitude and sense from the electrometer 22. A similar projectile at the same distance and angle a, but to the right of the electrometer means, will produce a signal of equal magnitude and sense. The electrometer 21 is subjected to different field directions for such sources to the left and right of the electrometer means and will produce signals of equal magnitude but opposite sense, thereby enabling the electrometer means to determine whether a field source is within the detection region or not.

A negatively charged projectile behaves similarly and so provided the polarity of the charge to be employed remains unchanged the electrometer means may be arranged sim ply to reject signals if an output from either one of the amplifiers 25 is of the wrong polarity. Alternatively, if the charge polarity is known the amplifiers may be fitted with sim ple rectifiers at their outputs permitting both output signals only when the field is in the correct relationship to the electrometer means.

The outputs of electrometer amplifiers 25 are connected to signal combining means 26, the function and component parts of which are described hereinafter.

The electrometer 21 is located with its direction of maximum sensitivity horizontal and along the base line 20. The electrometer 22 is located adjacent thereto with its direction of maximum sensitivity in the same vertical plane as electrometer 21- but extending orthogonally to the base line 20 i.e. vertically.

The common plane of the directions of maximum sensitivity defines a first electrometer means plane.

The electrometers 21' and 22' of electrometer means 1 9 are also adjacently disposed with their directions of maximum sensitivity defining a vertical second electrometer means plane with one extending horizontally along base line 20 and the other vertically and the electrometer output signals are also applied to corresponding signal combining means 26'.

The vertical first and second electrometer means planes are coplanar and define the aforementioned detection plane, indicated at 27. This coincides substantially with the plane of the target and the detection plane may also be considered as the target plane.

The limits of the detection plane to what may be considered as a detection area and schematically illustrated by chain dotted line 27' are, of course, a function of the sensitivity of the electrometer means 1 8 and 1 9 and of the strength of electric field being detected.

The first electrometer means 1 8 is operable to detect the passage of a charged projectile through the detection plane 27 as a function of a projectile angle a, subtended at the electrometer means, between the projectile trajectory and the base line 20.

The value of the projectile angle a is computed by the combining means 26 and the manner in which the angle a and a corresponding projectile angle P, associated with the second electrometer means 19, are computed and thereafter processed in means 1 7 will be understood more readily with reference to Figures 2 and 3.

Referring to Figure 2(a) which is a section through the detection/target plane 27 in the plane of the trajectory 28 of a projectile 29, the charged projectile has a substantially radial electric field illustrated by field lines 30.

The electrometers 21 and 22 are indicated by electrode dispositions with respect to the detection plane 27 and base line 20.

Figure 2(b) shows the relationship between electrometer output signal amplitude and the distance along its trajectory 28 of the projectile 29 from the target plane 27, which amplitude is a function of electric field strength at the electrometer, illustrating a readily discernible peak in the output signal from each electrometer as the projectile passes through the target plane.

The position in the plane at which the trajectory intersects, that is, relative to the detection means 16, and thus the target 10, determines the relative magnitudes of the peak electrometer signals of the electrometer means.

Figure 3 illustrates the target plane 27, through which projectile 29 is passing, and the disposition and circuitry of the electrometer means 1 8, 19, signal combining means 26 and processing means 27.

As stated above, the first and second electrometer means 18, 1 9 are located to define each end of a base line 20 of length L. The electrodes of electrometer 21 are spaced apart horizontally, and the electrodes of electrometer 22 are spaced vertically extending in the electromerer/detection/target plane 27.

The adjacent disposition of the electrometers is such that they are equidistant from the projectile and the portion of the projectile electric field intersecting them is substantially uniform in strength and direction, as illustrated by the field lines 30, and makes angle to the base line 20.

Now the output signal magnitude of each electrometer is a function of the potential gradient of the field between the electrodes and it will be appreciated that if the projectile has a charge Q and is a distance r,8 from the electrometer means 18, then the electrometer 21 will produce an output signal voltage V2, = k.(Q/r218).cos a, where k is a constant of the system, and from electrometer 22, V22 = k.(Q/r2,8).sin a.

Giving similar consideration to electrometer means 19, the field intersects the electrometers thereof at an angle ss with respect to the base line so that the component electrometers produce output voltages V21. = k.(Q/r219).cos ss and V22 = k.(O/r219).sin P.

The electrometer signals from the electrometer means 1 8 are fed to the combining means 26 and those from electrometer means 1 9 to combining means 26'.

The combining means 26 comprises peak detection means 31, to which signals from electrometer 21 and 22 are applied so that subsequent processing is limited to the signals derived from the projectile being in the target plane, and a division circuit 32 where the ratio V22/V2, of the electrometer peak signals is determined. From the above relationships it will be seen that by taking such a ratio the unknown variables 0 and rl8 and system constant K are eliminated giving a field source direction or projectile angle a in the form of function tan a represented by the ratio signal on line 33.

Similarly within the combining means 26' the signals from electrometers 21' and 22' are applied to peak detection means 31' and division circuit 32' giving an output ratio on line 33' of V22,/V21 = tan P.

The two lines 33, 33/ carrying the ratio signals representing functions of the projectile angles are input to processing means 1 7 along with a third input 34 carrying a constant signal representing the length L of the base line 20.

The processing means 1 7 essentially comprises triangulation means 35 containing conventional circuitry and employing conventional techniques, which need not be described in detail, to determine trigonometrically from the two projectile angle representations and the base line length the distance of the projectile trajectory 28 from the electrometer means and/or any point on the base line and with the addition of suitable displacement offsets, the distance of the trajectory from any predetermined point on the target 10.

If the target and detection plane are coplanar as described above then the material of the target must be chosen so that screening or distortion of the electric field by the target is kept to a minimum. This may be obviated by having the detection plane slightly displaced from the target plane adjacent the face of the target.

As stated briefly above, the projectile is charged by passage close to a charging conductor such as the ring 14 in Figure 1. A practicable implementation of projectile charging is shown in Figure 4. The rifle has a barrel 40 to the end of which is attached an extension piece 41 of electrically insulating material, for instance, moulded from plastics material. The bore 42 of the extension piece is of slightly greater diameter than the barrel to -ease alignment and avoid impedance of an emerging projectile. The wall of the extension bore is recessed at 43 and contains a conductive ring 44 which forms the charging electrode.The ring is spaced from the end of the barrel by a distance of the same order of magnitude as the length of a projectile to be fired by the weapon so that when a projectile is fired, with the rear end of the projectile connected to the barrel an electric field is formed between the charging electrode ring 44 and the nose portion of the projectile imparting a charge thereto when the projectile breaks contact with the barrel. The ring 44 is connected by an insulated cable 45 to one output of a high voltage generator 46. The generator has another output 47 connected to earth and to the rifle barrel.

The generator 46 comprises, for example, a conventional battery driven low-power RF oscillator including a high ratio step-up transformer able to produce a d.c. output voltage in the order of 1 KV across the output, that is, between the ring 44 and the barrel. As virtually no power is drawn from the generator it may be made compact and readily carried affixed to, or in addition to, the rifle. Similarly it may take any one of many conventional forms of which the above is just one example.

Furthermore the charging electrode may be constructed other than as a ring as charging is effected by virtue of the proximity of the projectile passage to the electrode.

It will be appreciated that system described above has been limited to those features by which it differs from other such scoring systems and has omitted any common features such as means for counting or otherwise registering the position or positioned accuracy of the fired projectile which do not require further description.

The present invention, as it will be appreciated from the above description, provides a simple foRn of scoring system which is readily portable and the detection means set up merely by placing the electrometer means a measured distance apart to define the base line. The electrometer means and signal combining and processing means are also of simple construction.

In addition to the constructional simplicity of the system it will also be appreciated that the principle of a charged projectile and detection of the charge is not limited to use with specific weapons or projectiles and is equally able to detect the passage of projectiles travelling at sub-sonic, as well as super-sonic, velocities. Whilst in general small arms tend to fire projectiles at super-sonic velocities the scoring systems of the present invention may be employed with larger calibre weapons, for example mortars, which fire projectiles at much lower velocities.

The fact that projectiles fired by some weapons contain explosive material does not preclude use of the scoring system of the present invention as an electrostatic charge will lie only on the outer surface of a conductive body thereof, although it may be preferred to use non-explosive 'dummy' projectiles.

The embodiment described above with reference to Figures 1 to 4 represents only one form which the present invention may take and some of the variations will now be outlined.

The target, detection and electrometer means planes, described above as substantially vertical employ electrometer means disposed along a horizontally extending base line. It will be appreciated that the base line may just as readily be vertically extending, that is, with one electrometer means mounted above the other and both to one side of the target, or with the base line extending in space at any other inclination with respect to the horizontal.

Furthermore, whether the base line extends either horizontally and/or vertically the first and second electrometer means may be disposed with respect to each other other than at opposite sides of the target, so that the target essentially lies on an extension to the base line.

It will be appreciated that while it is pos sible to define the intersection points of the projectile trajectory and detection plane by means of two projectile angles derived from two spaced electrometer means a larger number of such electrometer means may be employed and each contributing a projectile angle, enabling the point of trajectory intersection to be determined with less chance of error.

In the embodiment described above each electrometer means comprises two electrometers disposed with their directions of maximum sensitivity at right angles to each other. it will be appreciated that they may be disposed with these directions other than at right angles. Similarly one of the directions of maximum sensitivity need not be parallel, that is, 0" with respect to the base line but at any other angle which differs from that of the other electrometer. Such departures from the disposition described will, however, render the combining of the electrometer signals to determine the projectile angle, more complex.

In the embodiment described above the simplicity of signal ratio combination to determine the projectile angle depends upon the electrodes of each electrometer being disposed in the projectile field so as to be influenced thereby identically, that is, both the field strength and direction at each are equal.

The field of the charged projectile is radial and where the distance between the projectile and the electrometer means is large in relation to the dimensions of the electrometer electrodes, the electrometers may be assumed in a directionally uniform field, as in Figure 3, when located adjacent each other.

Figures 5(a) and 5(b) show alternative electrode-pair dispositions in which the electrodes are in much closer proximity to each other and effectively are coincident in the field.

In the arrangement of Figure 3 it will be appreciated that with electrometers mounted adjacently as shown therein it may not always be possible to ensure that the projectile passes at sufficient distance for the field directions at each pair of electrodes to be the same.

The combining means 26 may include correction means shown ghosted at 50 in Figure 3 which contains a store in which correction factors are stored for a plurality of projectile source positions relating the offset of field directions at the electrometers from those which would appertain for electrometers located at the nominal electrometer means position on the base line. The correction means applies the correction factors to the electrometer signals which are again divided to give by their ratio an improved approximation of projectile angle. The newly calculated projectile angles of both first and second electrometer means are again employed to determine more accurately the projectile source position in the detection plane and further correction factors applied until successive approximations of the source position cannot improve its accuracy.

With such correction means it will be appreciated that the electrometers of each electrometer means may be intentionally disposed with a greater separation between them in order to facilitate construction although they should still be located so as to be considered at substantially equal distances from the field source projectile.

It will be appreciated that each electrometer is responsive not only to a transient electric field passing orthogonally through the plane containing the two electrodes as shown in Figure 2 but also to a transient electric field passing the electrometer within the plane of the two electrodes giving a response as illustrated by Figure 6. It will be appreciated that as the field source approaches the electrometer the combination of accute angle of intersection between field and electrodes and the distance give a small output signal which rises as a function of lessening distance and lessening of the field angle of intersection to the normal until whilst moving alongside the electrodes the induced voltage and corresponding electrometer output signal is substantially constant before falling off again.The output signal thus takes the form of a voltage pulse having a flattened 'peak' when the projectile, and its field, is adjacent the electrometer.

It will be appreciated that the sharpness of this peak depends upon the length of the electrodes in the direction of field travel and although in general, and in the case of thin rod electrodes in particular, will not be as sharp as extension of the electrodes perpendicular to the projectile trajectory, such an electrode disposition and electrometer signal may prove adequate.

From the above and consideration of Figures 2(b) and 7 it will be appreciated that the direction of maximum sensitivity is defined within a plane containing the two electrodes, in a direction perpendicular to the direction of extension of the electrodes irrespective of the direction of their extension with respect to the direction of travel of the projectile and the electrodes may extend at any angle to the trajectory, albeit that the sharpest response peak is achieved when they are orientated to extend substantially orthogonally to the projectile trajectory as in Figure 2(b).

Although the above description is based on the assumption of rod-like electrodes extending with a parallel disposition and uniform separation it will be appreciated that if desired the electrodes may be disposed with a non uniform separation and/or may take the form of strips or plates having 'width' in a direction at right angles to their length although the capacitance of the electrodes is increased with respect to the input circuit of the amplifier, which increased capacitance may cause limitation of the electrometer response bandwidth.

As will be apparent from the above discussion of signal processing the absolute value of the charge on the projectile at the detection plane is immaterial providing it is adequate to produce an electrometer response. The leakage of charge from the projectile in flight may increase with air moisture and may be compensated for by varying the potential to which the charging electrode is raised.

Furthermore, if the projectile hits an object and ricochets into the detection plane there is a high probability that the charge will be dissipated by contact-with the object and thus not be erroneously detected as a scoring shot.

The signal processing means 26 may be made more sophisticated to avoid erroneous signals due to atmospheric disturbances. For instance the detection means may be 'gated' in time with respect to the instant of weapon firing so that only an electrical impulse due to the projectile is registered. Alternatively, or in addition, the electrometer output signals may be passed by way of high pass filter means whereby slowly changing stray electric fields are rejected but the rapidly peaking pulses due to the projectile passage are preserved.

The signal processing may be performed by functional elements using either analogue or digital techniques.

In the embodiment and variants described above the first and second electrometer means each comprise two or more electrometers disposed with their two or more directions of maximum sensitivity at different angles with respect to the base line in the electrometer plane they define, the projectile angle being determine by the relative magnitudes of the field-induced voltages measured.

An alternative arrangement of electrometer means is shown in a further embodiment of the invention in Figure 7(a). The range and scoring system is similar to that described above with reference to Figure 1 insofar as a weapon 70 is arranged to fire an electrostatically charged projectile at a target 71 in a vertical target plane coincident with a detection plane defined by the electrometer means 72, 73 separated a known distance along a base line 74 in the detection plane.

Each electrometer means has a direction of maximum sensitivity which is rotatable about an axis perpendicular to the detection plane so as to define by its sweep an electrometer means plane. The electrometer means planes are coplanar with the detection and target planes.

The electrometer means 73 is substantially identical with that 72 and only the latter will be described in any detail. The electrometer means 72 comprises a pair of rod-like electrodes 75, 76 disposed parallel to each other in a vertical plane, defining the electrometer means plane. The electrodes are carried, e.g.

printed, on a disc 77 mounted on a shaft 78 for rotation about a horizontal axis, also orthogonal to the detection/electrometer means plane, by a motor 79. The shaft 78, or motor 79, is coupled to position measuring means, such as, a synchro-resolver 80 which produces an a.c. reference cyclic signal as a function of shaft rotation, the peaks or zero crossing points of the reference signal and being arranged to occur in synchronism with the direction of maximum sensitivity of the electrode pair making an angle of 0 to the base line 74.The electrometer is similar to that described earlier in that the electrodes are connected to a high input impedance amplifier 81 but the induced voltage across the electrodes is coupled between the continuously rotating electrodes and the amplifier by an axially rotetable transformer 82. Because of the relatively low levels of induced signals involved it may be preferred to mount the electrometer amplifier also on the rotating disc 77, the amplifier supply voltages and higher amplitude output signals being coupled by slip rings or electromagnetic and/or other forms of coupling.

The output signal of amplifier 81 is connected to a phase comparator 83 along with the reference signal from synchro-resolver 80.

Figures 7(b) and 7(c) show respectively the waveforms of signals expected from the electrometer and synchro-resolver.

The motor 79 of the electrometer means is rotated at such a rate that the electrodes, and thus the direction of the maximum sensitivity, sweeps the detection plane a plurality of times as the charged projectile passes the vicinity of the electrometer means.

Figure 7(b) illustrates the electrometer response as a series of peaks each at an angle of electrode rotation corresponding to the direction of maximum sensitivity being directed at the projectile trajectory. The output of the phase comparator 83 gives an indication of the projectile angle with respect to the base line.

The deduction of projectile position from the projectile angles of both electrometer means is as described hereinbefore.

It will be seen that examination of the phase of the alternating electrometer signal with respect to the reference signal is sufficient to deduce the projectile angle and this can in fact be achieved in advance of the projectile reaching the target in what has been defined as the electrometer plane.

If it is desired to know the instant at which the projectile passes through the detection plane, or if it is desired to limit projectile angle determination to this portion of the detected signal, the electrometer signal may be applied to a demodulator 84 and thence to peak detector 85 to obtain a signal representing the maximum voltage induced, which sig- nal may be employed either to gate operation of the phase comparator 83 or control other measurement functions in accordance with detection of passage of the projectile through the detection/target plane.

The variants as to electrometer disposition, electrode structure and directional disposition discussed hereinbefore are also applicable, in general, to the electrode configuration in this form of electrometer means.

Other embodiments of electrometer means may be devised using known principles, those of Figure 1 and 7 being intended primarily to show that the present invention is not limited to any particular means of detecting the passing electric field of the projectile in terms of a projectile angle and therefrom deducing positional relationship to the target.

As stated hereinbefore the particular polarity of projectile charge is in general immaterial provided it matches the electrometer measuring means. In constructing firing ranges of the type to which the invention relates it is often desired to have several such individual targets and scoring systems as described above, disposed as galleries in side-by-side relationship.

One problem in scoring with such systems is cross-fire protection, that is, avoiding the detection of stray shots from adjacent galleries which have strayed into the detection region.

By arranging the adjacent galleries to employ projectile charges and matched electrometer means of opposite polarity sense, such crossfire protection is substantially improved. Selection means (not shown) may be provided to cohtrol the polarity of the charging electrode with respect to the barrel and the detection sense of the electrometers, either in a plurality of galleries or, if desired, a single gallery.

In the systems described with reference to Figures 1 and 7, the electrometer and detection planes are coplanar with each other and with, or substantially with, the target.

If the range construction is such that the projectile trajectory is almost certain to intersect the target plane substantially orthogonally, then the electrometer planes of electrometer means may be displaced in the direction of the trajectory. Each electrometer means will provide an angle ( or P) as the projectile passes through its plane but such signals are displaced in time.

The above described triangulation technique is still applied to determine the projectile position in a parallel detection plane, which may be notionally defined midway between the two electrometer planes, and the delay between signal peaks is a represenation of the velocity of the projectile at the notional detection plane.

Alternatively both electrometer planes may be coincident to define a detection plane and the measuring means include further detection means, comprising a further pair of electrometer means, disposed in the direction of the trajectory to define a further parallel detection plane. Calculating means (not shown) employs conventional techniques to determine from the time interval between passing through the planes, the projectile velocity and by correlation of the points of intersection of the projectile trajectory and the detection planes its direction of trajectory in the vicinity of the target. Such determination of velocity and direction from two such measurements separated in time and position are well known and require no further description.

While all of the above description has related primarily to vertically defined planes, it will be appreciated that the plane or planes may be other than vertical. For instance, when dealing with projectiles fired at long range in a ballistic trajectory and falling nearly vertically on a target area, a horizontal detection plane (or spaced electrometer planes) may be defined just above ground or target level.

Claims (30)

1. A scoring system for a firing range in which a projectile is fired from a weapon at a target, said system comprising charging means operable to apply an electrostatic charge to a projectile fired at a range target, and measuring means, including detection means located in the vicinity of the target, responsive to voltages induced by the passage of a charged projectile to produce signals defining the position of the projectile trajectory with respect to the target.

2. A scoring system as claimed in claim 1 in which the detection means comprises first and second electrometer means operable to define a detection plane including a base line and separated by a known distance along the base line, said first and second electrometer means each being operable to determine passage of a charged projectile through the detection plane as a function of a projectile angle subtended at the electrometer means, between the point in the detection plane of intersection of the projectile trajectory and the base line, said measuring means including processing means responsive to projectile angles from the first and second electrometer means and said known distance along the base line of electrometer means separation to determine the position within the detection plane of the projectile trajectory intersection thereof.

3. A scoring system as claimed in claim 2 in which each of the first and second electrometer means comprises (a) two electrometers, each operable to produce a signal voltage proportional to the potential gradient of an electric field extending across a pair of spaced electrodes thereof, disposed so as to be at substantially the same distance from a charged projectile passing through the detection plane with their directions of maximum sensitivity (as herein defined) coplanar and making known angles to each other and to the base line, and (b) combining means comprising peak detection means operable to determine the peak voltages induced in the electrometers by a charged projectile passing through the detection plane and division means operable to determine from the relative magnitudes of the two electrometer peak signals and the relative angles between their directions of maximum sensitivity the projectile angle subtended at the electrometer means between the projectile trajectory and the base line.

4. A scoring system as claimed in claim 3 in which the electrodes of each electrometer comprise substantially straight rods disposed parallel to each other and separated by an air gap.

5. A scoring system as claimed in claim 4 in which the rods lie within the electrometer/detection plane.

6. A scoring system as claimed in any one of claims 3 to 5 in which the direction of maximum sensitivity of one of the electrometers of each electrometer means is parallel to the base line.

7. A scoring system as claimed in any one of claims 3 to 6 in which the electrodes of each electrometer means are arranged with their directions of maximum sensitivity at right angles to each other.

8. A scoring system as claimed in any one of claims 3 to 7 in which the electrometers of each electrometer means are disposed with their electrodes adjacent each other so that the projectile field at each electrometer is substantially uniform in direction with respect to the base line.

9. A scoring system as claimed in claim 8 when dependent on claim 7 in which the division means is operable to determine the projectile angle as the ratio of the peak electrometer signal values.

10. A scoring system as claimed in any one of claims 3 to 7 in which the electrometers of each electrometer means are disposed with their electrodes spaced from each other so that they are intersected at different angles with respect to the base line by the radial projectile field.

11. A scoring system as claimed in claim 10 when dependent on claim 7 in which the division means is operable to determine the projectile angle as the ratio of the peak electrometer signal values and includes correction means operable to store for a plurality of projectile source positions within the detection plane correction factors related to the offset of field direction at the electrometers due to their displacement from a nominal electrode means position and responsive to determination of a source position from the projectile angle to apply the appropriate correction factors to the electrometer signals to provide an improved approximation of projectile angle and of projectile position and iteratively applying said projectile angle correction factors with respect to successive approximations of projectile position.

1 2. A scoring system as claimed in any one of claims 3 to 11 in which the first and second electrometer means have the electrometers thereof disposed such that the projectile angle of a projectile trajectory within the vicinity of the target is of the order of 45 .

1 3. A scoring system as claimed in claim 2 in which each of the first and second electrometer means comprises an electrometer operable to produce a signal voltage proportional to the potential gradient of an electric field extendingcrnss a pair of spaced electrodes thereof and having a direction of maximum sensitivity rotatable about an axis orthogonal to the detection plane so as to define with respect to its orientation about the axis the projectile angle with respect to the base line.

14. A scoring system as claimed in claim 1 3 including drive means operable to rotate the direction of maximum sensitivity about the axis at such a speed in relation to that of a projectile that the passage of the projectile through, and in the vicinity of, the detection plane produces an induced voltage in several cycles of rotation peaking in each cycle in a direction of maximum sensitivity orientation with respect to the base line corresponding to the projectile angle, and phase detection means, including reference means operable to produce a reference cyclic signal corresponding to the direction of maximum sensitivity making an angle of 0 to the base line, operable to compare the phases of the signal peaks of the reference and induced signals to determine the orientation with respect to the base line of the projectile angle.

1 5. A scoring system as claimed in any one of claims 2 to 14 in which in each electrometer means the electrometer directions of maximum sensitivity lie in, and define, an electrometer means plane, the electrometer means planes of the first and second electrometer means defining in combination the detection plane.

1 6. A scoring system as claimed in claim 1 5 in which the electrometer means planes of the first and second electrometer means are coplanar and define, by their common plane, the detection plane.

1 7. A scoring system as claimed in claim 1 5 or claim 1 6 in which the target is located in the detection plane.

1 8. A scoring system as claimed in claim 1 6 or claim 1 7 in which the measuring means includes further detection means operable to define a further detection plane displaced in the direction of projectile trajectory and calculating means responsive to detection of passage of a charged projectile through each detection plane to determine the projectile velocity and/or the trajectory direction in the vicinity of the target.

1 9. A scoring system as claimed in claim 1 5 in which the electrometer means planes extend substantially parallel to each other and orthogonally to a known projectile trajectory in the vicinity of the target and are separated in the direction of the trajectory, defining a detection plane extending parallel to them.

20. A scoring system as claimed in claim 1 9 including velocity measuring means responsive to detection of the passage of a charged projectile through each electrometer means plane to determine the projectile velocity.

21. A scoring system as claimed in any one of the preceding claims in which the first and second electrometer means are disposed at opposite sides of the target and the trajectory of a projectile intersecting the target.

22. A scoring system as claimed in any one of the preceding claims in which the charging means comprises a generator of high voltage developed across output terminals thereof having one output terminal connected to earth and to the barrel of the weapon and the other output terminal connected to a charging electrode disposed at a distance from the barrel end of the same order of magnitude as the projectile length such that with one end of the projectile connected to earth by the barrel a field is formed between said other electrode and the projectile whereby the projectile is charged when the projectile breaks contact with the barrel.

23. A scoring system as claimed in claim 22 in which the charging means includes an extension piece for the weapon barrel, said extension piece carrying the charging electrode.

24. A scoring system as claimed in claim 22 or claim 23 in which the charging electrode comprises a ring having a bore greater than that of the weapon barrel and mounted coaxially therewith such that the projectile is ejected from the barrel by way of the ring.

25. A scoring system as claimed in claim 24 in which the extension piece is formed by electrically insulating plastics material.

26. A scoring system as claimed in any one of the preceding claims including selection means operable to select the polarity of the electrostatic charge applied to the projectile and to control the measuring means to respond only to a projectile electrostatic charge of said selected polarity.

27. A scoring system substantially as herein described with reference to and as shown in Figures 1 to 5 or in Figure 7 of the accompanying drawings.

28. A firing range in which a projectile is fired from a weapon at a target and including a scoring system as claimed in any one of the preceding claims.

29. A firing range as claimed in claim 28 when dependent on claim 26 including a plurality of targets and scoring systems adjacent scoring systems being selected to use an opposite projectile charge polarity to that of their neighbours.

30. A firing range substantially as herein described with reference to, and as shown in Figures 1 to 5 or in Figure 7 of the accompanying drawings.