GB2065408A - Improvements in or relating to projectile detecting means - Google Patents

Abstract

Two detectors, 1 2 each comprising a vidicon tube and associated scanning coils are directed towards a volume of space in front of a target 3 and detect shells fired towards the target. A control device 4 controls the scanning of the vidicons, generating digital numbers to control the scanning the numbers being indicative of the angle of inclination of the trajectory of a shell to each detector when the shell is detected. A monitor 5 displays an image of the target and indicates where each shell impinges on the target. <IMAGE>

Description

SPECIFICATION Improvements in or relating to projectile detecting means This invention relates to projectile detecting means, and more particularly to apparatus which can provide information concerning the trajectory of a detected projectile.

There is a need for an apparatus which can accurately detect the position at which projectiles, such as shells impinge upon a target. At the present time when training artillery men or tank gun men who are to fire shells, the personnel are instructed to file shells at a target, and the position at which each shell impinges the target is noted by visually observing the hole that is formed in the target by the shell. This is inconvenient where firing is taking place over a great distance and also necessitates the frequent repair or replacement of targets.

It is to be noted that some devices have been provided previously which detect shock waves or vibrations generated in a rigid target by a projectile impinging upon the target to provide a hit-miss indicating facility. In a more sophisticated version of such an apparatus means are provided for calculating the position at which a bullet impinges upon a target by measuring the precise instants at which shock waves or vibrations generated in the target reach certain points on the target, but such apparatus again suffers from the disadvantage that the target must frequently be replaced since, if a large number of apertures are formed in the target, as a result of a large number of bullets or shells impinging upon the target, the shock waves or vibrations are no longer transmitted uniformly through the target.

The present invention seeks to provide an apparatus for determining information concerning the trajectory of a projectile, such as a bullet or shell, in which the above described disadvantages of prior proposed systems are reduced or obviated.

British Patent Specification No. 1,220,071 discloses an arrangement for the automatic plotting of the path of a missile, and the specification is specifically related to the plotting of the path of a missile such as a missile carrying a nuclear war head. Thus the specification primarily relates to the detection of very large missiles and does not specifically relate to the detection of missiles as small as bullets or shells. In the arrangement disclosed in British Patent Specification No. 1,220,071 two television cameras or like scanning apparatus face towards an area which is to be examined that is to say an area from which a missile is expected to come.Each camera is provided with a time base apparatus adapted to cause the image formed on the target of the camera to be scanned, the time base apparatus including ramp signal generator circuits which each generate a linearly increasing scanning voltage. The time base apparatus also includes generators which produce signals representative of the bearing and elevation relative to the camera of the point of the image that is focussed onto the target that is being scanned at any particular instant. The camera produces a video output signal which is fed to a comparator which receives a reference signal from a generator. If the video signal is correlated with the reference signal then the comparator provides an dutput pulse.

The reference signal is such that an output pulse will be provided whenever a missile, such as a missile carrying a nuclear war head is detected. Memories record the signals representative of the elevation and bearing being generator at the instant that a control pulse is generated by the comparator and thus the memories, in successive scans of the television camera, store information concerning the elevation and bearing of successive points on the trajectory of the missile relative to the camera. The information derived from the two cameras is combined and a computer performs a relatively complex calculation to determine information regarding the trajectory of the detected projectile, and in particular, provides an estimate of the terminal point of the trajectory of the projectile.

The disclosure of British Patent Specification No. 1,220,071 relates, as mentioned above, to the detection of large missiles and also suffers from several disadvantages. Since each camera has an independent time base, the cameras will not scan simultaneously, and thus if accurate results are to be obtained steps must be taken to ensure that the precise instant in time at which each position on the trajectory is determined is recorded. Also it is to be noted that the computer must perform a relatively complex calculation in order to determine information concerning the trajectory of the projectile, particularly since the computer is intended to calculate not only the terminal point of the trajectory but also to estimate the point of origin of the trajectory.

The present invention seeks to provide an apparatus which is designed so that the calculation to be prformed by a computer is more straight forward than the calculation to be performed in the arrangement described in Specification No. 1,220,071 and also it is to be noted that the present invention seeks to provide an apparatus that will merely determine the point at which a projectile impinges upon a target.

According to this invention there is provided an apparatus for determining information concerning the trajectory of a projectile passing through a substantially planar volume of space said apparatus comprising two detectors, the detectors being located at spaced positions within the plane of said volume of space to have different images of the volume of spaces focussed on to an element thereof so that an image of the projectile is focussed onto said element as the projectile passes through said volume of space, said detectors having optical axes which intersect in said plane each detector being provided with means to provide a digital signal indicative of the inclination of a detected projectile relative to a respective predetermined axis, the apparatus further comprising means to calculate, from the output signals of the detectors, information concerning the trajectory of the detected projectile.

Preferably said detectors are adapted to detect a projectile in each of a plurality of adjacent substantially notional planes within said volume of space and to provide an output signal representative of each such detection of the projectile.

Conveniently said element is scanned or accessed by means which include a digital signal generator, the digital signal generated when an area of the element on which an image of the projectile is, or has been, focussed being used as digital signal indicative of the inclination of the projectile.

Each detector may comprise a scanning cathode ray tube which includes a target upon which a visual image is focussed constituting said element, the visual image resulting in the formation of a corresponding electric charge image or resulting in a target having an image defined in terms of the conductivity of the target, there being means including said digital signal generator to scan the target with an electron beam to provide signals representative of the image on the target. Alternatively the detector may comprise a photo-diode or phototransistor array that is accessed by means which include said digital signal generator. Where a scanning cathode ray tube is used it is preferred that, in each detector the electron beam is scanned so that successive lines of scan traverse regions of the target which correspond to said notional planes.

Preferably the regions of said elements of both detectors corresponding to each respective notional plane are scanned or accessed simultaneously, so that the notional planes are effectively scanned synchronously by the two detectors.

A monitor may be pivoted to display a representation of a target and to indicate the point at which a projectile impinges on the target.

It is to be appreciated that apparatus in accordance with the present invention may be incorporated in to a training rifle range having a plurality of lanes and a plurality of banks of targets, each target having detectors associated with it. Each firing point may have a visual display unit for displaying a representation of the respective target and indications of where projectiles have impinged on the target.

Where the invention is to be utilised in a range having a plurality of targets the detectors may all be connected to a single computer which controls all the detectors and performs all the calculations.

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 is a diagrammatic representation of one embodiment of the invention: Figure 2 is a diagram illustrating the scanning of two detectors constituting part of the embodiment illustrated in Figure 1; Figure 3 is a block circuit diagram of an arrangement in accordance with the invention; and Figure 4 is a more detailed circuit diagram of part of the circuit shown in Figure 3.

Referring now to the drawings Fig. 1 illustrates two detectors 1, 2. Each detector comprises a one inch silicone diode vidison tube such as a TH 9828 as sold by Thompson CSF, together with appropriate scanning coils, such as scanning coils as sold under the designation BU 200 1 K1 by Gerhard-Bauelmente of 601 Reichelsheim of Germany. Each detector 1, 2 is positioned to view a predetermined volume of space from a different aspect, this volume of space, in the described embodiment, comprising a thin vertical volume of space that can be considered to comprise a "plate" of space lying immediately in front of a target 3. Thus this predetermined volume of space viewed by the detectors will include a portion of the trajectory of a projectile fired at the target, such as a shell or the like.In the particularly described embodiment the detectors 1 and 2 are each located adjacent a lower corner of the target, the detectors being inclined so that the axes of the fields of vision of the detectors intersect substantially at the centre of the target. Typically the detectors may be 6 metres apart and may be 70 cms below the bottom edge of the target.

Each detector 1, 2 is provided with a focussing system, the focussing systems being such that a volume of space contained within an ore of 60 in a vertical plane is focussed onto the target of each detector, the lower edge of this 60 ore being at 12" to the horizontal and the upper edge thus being at 72". This can be seen from Fig. 2. The detectors are located so that the axes of the fields of view of the detectors intersect substantially perpendicularly in a plane which is parallel to the plane of the target 3. Thus the field of view of each detector has a predetermined angular width in the vertical plane. The volume of space viewed by the detectors has a predetermined depth i.e. thickness in a direction perpendicular to said plane.The focussing system associated with each detector is such that any projectile passing through the predetermined volume of space on a trajectory towards the centre of the target 3 is clearly in focus whereas projectiles or other items that are not within the immediate zone of the target are not in focus. Thus the focussing system is such that there is a field of relatively clearly focus in the zone of the target 3, but items outside this field are not clearly in focus.

The detectors are connected to a control system 4, which will be described in greater detail hereinafter, the control system 4 being connected to a monitor 5 which may be any standard television monitor.

It is envisaged that the detectors may detect radiation having a wavelength between the infrared wave length range and the visible wave length range, and the focussing system of each detector may include appropriate filters selective of particular wave length of light. Also it is envisaged that the volume in space which is viewed by the detectors may be illuminated for example with alight curtain of infrared light.

As mentioned above, each detector includes vidicon type tube, and such a tube includes a target on which a visual image is focussed, this resulting in the formation of a corresponding charge image. The charge image remains on the target, under normal circumstances, until the charge image is "read" by a scanning electron beam, this reading of the charge image erasing the charge image. If a visual image is still focussed on to the target a fresh charge image will be created before the target is again "read" by the scanning electron beams. Thus, whenever a shell passes through the "plate" of space a change image will be recorded on the target, and this change image will remain until it is subsequently "read" by the scanning electron beam.Thus, if the system is intended to operate at infrared wavelengths, with the use of a "light curtain" and appropriate filters a change image representative of the shell may be created. However, if the system is intended to operate under ambient lighting conditions, a high change may be created on the target where no shell is detected, the areas of the target on which the image of the shell is focussed being a lower change.

In the described embodiment of the present invention the scanning coils of the detectors are controlled by the control arrangement 4 and thus each electron beam within each detector is caused to scan the target sequentially with a predetermined scanning raster, the scanning raster comprising 8 substantially vertical parallel lines of scan. This is, of course, very different from the conventional television scanning raster which involves the use of inter-leaved fields of so-called "horizontal" scan, in which each line is substantially horizontal, but in fact is inclined downwardly due to the effect of the field scanning coil.The control device 4 of the presently described embodiment of the invention may cause the 8 lines of scan all to be scanned in the same direction e.g. from the top of the target within the tube to the bottom of the target or, alternatively the control device 4 may cause the lines to be scanned in alternate directions, the first line thus being scanned downwardly and the second line being scanned upwardly.

The latter arrangement minimises fly back time and also permits the location of the top side and the bottom side of a shell to be detected accurately permitting any error resultant from the diameter of the shell to be obviated. The control device 4 also controls the scanning (or samples the output of the detector) in such a way that for each line scan there are 511 discrete steps of scan. Thus each individual step of scan will correspond with a predetermined angle of inclination from the respective detector relative to a predetermined base line which is, in this embodiment, line inclined 12". Thus each step of scan corresponds to an angular increment of 0.117 degrees.

Thus, the scanning raster of each of the detectors comprises 8 lines each line being divided into 511 discrete steps. The control arrangement 4 causes the two detectors to scan perfectly simultaneously and thus the detectors scan in absolute synchronism.

Fig. 2 pictorially represents a single scan of the two detectors, the detectors being arranged so that, at the commencement of each scan i.e. at point 0 the region of the bottom of the ore of scan of the respective detector is focussed on the part of the target that is being scanned. Each of the line 511 discrete steps of the scan of each detector correspond to an angle of inclination, and with respect to the detectors 1 and 2 the angles of inclinations representative of steps 256 and 511 are shown and identified.

The detectors are so arranged that they both initially synchronously scan the area of the target on which is focussed a vertical "slice" of the "plate" of space that is located furthest from the target. Subsequently the area of the target is scanned on which is focussed a second "slice" of space, parallel with the first "slice". This is repeated until eight "slices" have been scanned. The precise volumes of space scanned by each detector resemble the pages of a book that is held slightly open, and this the volumes are not precisely parallel. However, this does not introduce any significant errors, and effectively eight substantially parallel "slices" of space are scanned.

Assuming that a shell 6 having a negligible diameter passes through the target just above the centre of the target on the central axis of the target, it can be appreciated that the shell will be detected by each of the detectors 1 and 2 during step 256 of each of the scans.

Thus the two detectors will detect the shell precisely simultaneously. However, in the case of a shell 7 on a trajectory which passes through the top right hand side of the target 3 the detector 1 will detect the shell during step 280 of the scan, whereas the detector 2 will detect the shell 7 during step 450 of the scan. Thus the two detectors will not detect the shell precisely simultaneously but will, nevertheless detect the shell during the same scan.

It is to be appreciated that the detectors scan rapidly, each scan having a duration of approximately 40.96 microseconds. There is a fly back time of 4.04 microseconds. The 8 scans of a complete scanning pattern can be completed in 45 microseconds. As eight lines are scanned, and allowing for a frame return time of 5 microseconds, a complete scanning cycle can be completed in 365 microseconds.

If the depth of the volume of space that is viewed, (i.e. the thickness of the "plate") is 30 cms, for a projectile that is 30 cms long and moving at 1 200 metres per second it will take 500 microseconds from the start of the projectile entering the "plate" of space until the end of the projectile leaves the "plate" of space, and thus detection of the projectile is guaranteed.

At the end of each single scan of the two detectors, (which, as mentioned above, scan in synchronism) a pair of numbers is fed to a memory of the control 4. Each of the detectors provides one of the numbers. If the detectors has detected the shell during the scan the number fed to the memory is the number of step of the scan during which the shell was first detected. If the detector did not detect the shell the number fed to the memory is a "zero". At the end of a complete cycle eight pairs of numbers have been fed to eight predetermined memory locations, there being one pair of numbers for each line of SCE 1 of the scanning cycle.

Any pairs of numbers which include at least one "zero" are disregarded, since the shell was not detected by at least one of the detectors during the scan that gave rise to that pair of numbers in the memory. Of course, if all the stored pairs of numbers comprise pairs of zeros no shell at all was detected during the scanning and thus the memories can merely be cleared for the next scanning cycle. The pairs of numbers stored when a shell is detected during a scanning cycle are utilised to calculate the position of the shell at various points on its trajectory, thus defining the trajectory and determining the position at which the shell impinged on the target to be calculated and displayed.

In order to facilitate the detection of a projectile it is envisaged that the output of each director 1, 2 after being suitably amplified 8, 9 (See Fig. 3) will be supplied to a circuit 1 0, 11 where a portion of the output signal is smoothed and delayed or integrated to provide a relatively slowly moving signal which follows the general trend of movement of the output signal but which does not rapidly respond to rapid changes in the output signal of the detector.This signal is compared in comparators 12, 1 3 with another portion of the output signal of the detector which has merely been delayed in a delay line 14, 1 5 for a short period of time and thus, when sudden change in the output of a detector occurs, for example when a shell is detected, the portion of the signal bearing the rapid change is compared with the delayed and smoothed portion which does not bear the rapid change and under these circumstances an output signal is generated. Thus, effectively, the background is subtracted from the output signal and only rapid changes are detected.

As can be seen from Fig. 4, in which detailed circuitry is illustrated for the various items identified by boxes 9, 11, 1 3 and 1 5 in Fig. 3, the smoothing and integrating circuit 11 is provided with a switching element DG 1 91 which is provided to connect the input of the delay and integrating device 11 directly to the output of the amplifier 9 during a period of scan, but to connect the input of the device to a reference voltage during each fly back period, the voltage being set to be typical of the likely input voltage. This prevents the output of the circuit 11 from falling to a very low level during fly back periods, but ensures that the output signal of the circuit 11 is maintained at a substantially constant level during such fly back periods.

It is to be noted that the delay device of circuit 1 5 comprises a delay line designated with the designation D10. This particular delay line is manufactured by Fulmer Research Institute Limited of Stoke Poges, Slough, Bucks, England, but any corresponding adjustable delay line may be utilised.

The outputs of the comparators 1 2 and 1 3 are connected to a processor 1 6 the processor comprising a processor device designated LSI 410 as sold by Computer Automation Limited mounted in a chassis having a power supply as sold under designation 1030500 by Computer Automation Limited, the processor device being provided with an ROM as sold by Intel under designation 2308, plugged into the appropriate socket on the device, although any other equivalent ROM may be utilised. A program is blown into the ROM. The processor is connected to a page memory 1 7 and to a monitor 1 8 which can be any convenient monitor such as monitors utilised in television studios, and it is to be noted that the processor is also connected to the detectors 1 and 2.

The page memory 1 7 comprises ROMs with character generator information stored therein and special graphics information stored therein, and the page memory facilitates the display of information on the monitor, particularly information regarding special graphics to indicate the position of bullets which do not actually hit the target but which are near misses.

The processor 16, as can be seen from Fig.

3, controls the scanning of the detectors, and the processor includes two digital number generators which generate, successively, digital numbers from 0 to 511, and the digital number generators may comprise a clock and shift register. However, both the number generators operate in synchronism. The digital numbers are converted to analog voltages and the analog voltages control the angle of deflection of the electron beams scanning the targets of the respective detectors 1 and 2.

The detector control unit also includes two further digital number generators, again comprising clocks and shift registers, which sequentially generate numbers from 1 to 8, the outputs of these digital number generators again being converted to analog voltage further to control the scanning of the detectors, these voltages controlling the scanning of respective lines of scan.

As described above when a projectile is detected by each detector 1, 2 during a single scan, then the processor stores in a predetermined location in a memory a pair of numbers indicative of the respective steps of the scans of the two detectors 1, 2 at which the projectile is detected. Thus, if the shell 6 is detected a pair of numbers comprising numbers 256 and 256 are stored. If the shell is detected during every line of scan 8 pairs of numbers other than 300 will be stored, but these numbers will differ slightly since the shell will probably not be travelling in a horizontal linear line but will be following a downwardly curved trajectory. If the shell is not detected on any scan by either detector the respective pair of numbers will include at least one zero.

The processor then selects the pairs of numbers where each number is other than zero and calculates the position at which the shell will impinge upon the target 3 and this information is displayed on the monitor 1 8.

Typically the monitor 1 8 will display a pictorial representation of the target at which shells are fired and a portion of the target, corresponding to the region of the target hit by the shell will be indicated. The monitor 1 8 may also indicate a score to be allotted to each round fired at the target and may indicate the total score obtained in the firing of, for example, ten rounds at the target.

Claims (9)

1. An apparatus for determining information concerning the trajectory of a projectile passing through a substantially planar volume of space said apparatus comprising two detectors, the detectors being located at spaced positions within the plane of said volume of space to have different images of the volume of space focussed on to an element thereof so that an image of the projectile is focussed onto said element as the projectile passes through said volume of space, said detectors having optical axes which intersect in said plane relative to a respective predetermined axis, the apparatus further comprising means to calculate, from the output signal of the detectors, information concerning the trajectory of the detected projectile.

2. An apparatus according to claim 1, wherein said detectors are adapted to detect a projectile in each of a plurality of adjacent substantially notional planes within said volume of space and to provide an output signal representative of each said detection of the projectile.

3. An apparatus according to claim 1 or 2 wherein said element is scanned or accessed by means which include a digital signal generator, the digital signal generator when an area of the element on which an image of the projectile is, or has been, focussed being used as said digital signal indicative of the inclination of the projectile.

4. An apparatus according to claim 3 wherein each detector comprises a scanning cathode ray tube which includes a target upon which a visual image is focussed constituting said element, the visual image resulting in the formation of a corresponding electric charge image or resulting in a target having an image defined in terms of the conductivity of the target, there being means including said digital signal generator to scan the target with an electron beam to provide signals representative of the image on the target.

5. An apparatus according to claim 4, as dependent upon claim 2, wherein in each detector the electron beam is scanned so that successive lines of scan traverse regions of the target which correspond to said notional planes.

6. An apparatus according to claim 3, 4 or 5 as dependent upon claim 2 wherein the regions of said elements of both detectors corresponding to each respective notional plane are scanned or accessed simultaneously, so that the notional places are effectively scanned synchronously by the two detectors.

7. An apparatus according to any one of the preceding claims in combination with a monitor to display a representation of a target and to indicate the point at which a projectile impinges on the target.

8. An apparatus for determining information concerning the trajectory of a projectile substantially as herein described with reference to and as shown in the accompanying drawings.

9. Any novel feature or combination of features disclosed herein.