GB2108244A - Weapon triggering system - Google Patents

Abstract

An automatic weapon triggering system, e.g. for a land mine, comprises pyroelectric detection means such that an object in its field of view produces signals representative of an increase over ambient temperature. The triggering system 16 (Figure 2) includes a threshold means 21 to detect local increases in target vehicle temperature at the wheel and axles, a counter 22 to count such local increases and a comparator 27 to compare them with a preset count for a particular vehicle. In a more elaborate arrangement (Figure 3) a linear array of pyroelectric detectors extend perpendicularly to the direction of the vehicle and produce signals representing a 2-dimensional thermal side-view of the vehicle. The signals are digitised and correlated with digital representations of thermal images of acceptable target objects. The triggering system may also be used with submarine mines, mortar guns and rocket launchers. A laser range finder may be included to define the range of the detection zone. <IMAGE>

Description

SPECIFICATION Automatic weapon triggering system This invention relates to weapon triggering systems and in particular to automatic triggering systems in which sensing of a target object initiates operation of the weapon.

In automatically triggered weapons, for example, land mines, the weapon is normally provided with a fuze triggered by one or more magnetic or 'mechanical' influences of the target on the weapon/fuze such as pressure or vibration. However similar such effects may be produced by a variety of objects only some of which represent desirable targets. To provide discrimination between the influences would require a fuze of such sophistication that it would be difficult to provide in the fuzing space available in present weapons while adding prohibitively to the cost of each weapon. Furthermore, where the weapon is not readily accessible, e.g.

buried, the ability to select a particular type of influencing target is offset by any ability to change the influencing target readily.

It is an object of the present invention to provide a method of automatically triggering a weapon and an automatic weapon triggering system which requires only minor modifications to existing weapons while being readily adjustable in respect of influencing targets.

It is a further object of the present invention to provide a weapon system incorporating such a triggering system.

According to a first aspect of the present invention an automatic weapon triggering system comprises pyroelectric detection means operable to detect an object of temperature greater than ambient within the field of view of the detection means and produce a detector signal having a level in accordance with the temperature difference, and processing means operable to compare the detector signal with stored signals representing the detection of one or more particular target objects and responsive to a successful comparison to initiate triggering of the weapon.

According to a second aspect of the present invention a weapon system comprises a weapon and a weapon triggering system as defined in the preceding paragraph. The weapon may comprise a land mine adapted to be buried beneath a roadway and connected to an automatic triggering system adapted to be located to the side of the roadway to detect and respond to vehicles in the vicinity of the mine.

According to a third aspect of the present invention a method of which an object is detected in terms of destinguishing regions of higher temperature than the remainder of the object and comparison achieved by counting the number of such regions and comparing the count total with the obtainable from a known target object.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 7 is a partly sectioned perspective view of a tank vehicle on a roadway mined with a weapon triggered by an automatic triggering system accord ing to the present invention, Figure 2 is a block schematic of a simple triggering system employing a single detector, and Figure 3 is a block schematic of a more complex triggering system employing an array of detectors.

Referring to Figure 1, a roadway 10 has a vehicle, such as a tank 11, travelling thereon and is mined by a buried mine weapon 12, including an armour piercing projectile 13, contained in a covered, con ceased chamber 14. A cable 15, buried within the ground surface extends between the mine 12 and a triggering system 16 iocated,in this example, on the surface at a location laterally of the road and in the vicinity of the mine.

Referring also to Figure 2, which shows in detail the component of the triggering system 16, the system comprises a pyroelectric detector 17 located so as to have a narrow field of view across the roadway adjacent the buried mine as shown by lines 18 and slightly inclined so as to be intersected by vehicles passing along the roadway at about wheel axle height to define, with the boundaries of the road a densing zone for the triggering system. In Figure 2 the field of view is shown define D by a focusing mirror 19 but it will be appreciated that other conventional thermal focussing arrangements may be employed.

The detector 17 preferably is sensitive to radiation in the 1 - 15 micrometre wavelength band so that it is operable without the requirement for cooling, although any suitable form of sensor may be employed.

Signals produced by thermal radiation incident upon the detector 17 is passed by way of amplifier 20 to a threshold detector 21 arranged to pass only detector signals above a predetermined threshold level.

The signals received from detector 17 in the absence of a vehicle represent an ambient thermal emission from the surrounding environment. When a vehicle passes through the beam the signal increases to a higher level and falls when the vehicle has passed.

When the vehicle passes there will in general be a temporary increase in temperature detected due to the passage of the wheels and axles which normally run at a slightly higher temperature than the remainder of the vehicle body (expecting engine and exhaust components). The threshold level of threshold detector 21 is set to pass only the pulselike signals (detector pulses) due to such temporary increases in signal level.

Such detector pulses are applied by threshold detector 21 to a pulse counter 22 and a start input 23 of a timer 24.

The counter 22 has a plurality of outputs 25 representing the instantaneous value of the count which are connected to one set of inputs 26 of a comparator 27. The comparator has a second set of inputs 28 connected to a generator 29 which is settable manually by thumb-wheel switches (not shown) to give outputs representing a pulse count (wheel count) of a vehicle to which the mine is to be sensitive; in the tank example of Figure 1 the number of wheels which will pass through the beam is five.

The comparator 27 has a trigger input 30 connected to the output of timer 24 and two output terminals 31 and 32. The output 31 is connected to reset terminals of counter 22 and timer 24 and output 32 is connected by way of cable 15 to the conventional mine safety and arming arrangement 33 which in turn is connected to a detonator 34.

Considering operation of the circuit thus far described when a vehicle enters the field of view of the detector and a first wheel produces a detector pulse from threshold detector 21, the timer 24 is triggered and the detector pulse and subsequent detector pulses are applied to counter 22. The outputs of counter 22 and generator 29 are applied to the comparator 27 which when triggered by a timer 24 output after a predetermined time (sufficiently long for passage of a vehicle) makes a comparison between the two inputs. If the comparison is unsuccessful, i.e. the correct number of wheels have not passed, an output is provided at 31 and the counter 22 and timer 24 reset until another vehicle is detected.

If the comparison is positive an output is provided at 32 and detonation of the mine initiated, subject to the constraints of safety and arming circuit 33.

Several modifictions to the above described basic triggering system are possible. The duration of the interval of timer 24 may be varied in accordance with a measurement of the interval between two successive detector pulses. The threshold detector 21 may have an output line 35 connected to a bistable latch 36 which in turn enables a gate 37 by way of which clock pulses from a clock 38 are applied to a setting input 39 of the timer 24. The latch 36 responds to the first two detector pulses to open the gate 37 for the interval between them, clock pulses representing the duration of the interval setting the interval of timer 24. The timer duration may be an approximate value or narrowly defined on the basis of the vehicle selected at generator 29.

It will be appreciated that in general a vehicle is not fully identified until it has passed completely through the field of view of the detection means and in order to ensure effective strike by the mine 12, the beam should be offset from the mine in the direction of expected approach of a target vehicle. The system circuit may then contain a delay element 40 set in accordance with a manual input offset device, 41, to which the measured physical displacement or offset between mine and detection region are input, and an output from gate 37 representing the speed of the vehicle. The delay element 40 may also take into account dimensional parameters of a specific target as selected by setting of generator 29.

The system and its modification described above are based upon detection of a single selected target which is defined by the count number to which generator 29 is set manually. It will be understood that as the triggering system is exposed and away from the location of the mine, this function may readily be changed. As a further modification the triggering system may include a reference store 42 of generator settings for detection of different vehicles and able to set generator 29 automatically. The store 42 may be arranged to provide a first setting for generator 29 and thereafter in response to a 'non-compa-rison' output at 31 inhibit the reset of counter 22 while applying a new count value, representative of a different vehicle, to the generator 29 and triggering a fresh comparison.

The stored values may be limited to a chosen group set manually or one or more values may be selected by signals received from a command post by way of a receiver 43 operating on any conventional principle, e.g. radio, optical, acoustic.

It will be appreciated that detection may be interfered with by heating vehicle parts such as engine or exhaust causing a long duration signal, rather than identifiable pulses. This may be avoided if necessary by operating the thresholding detector in an a.c. mode to eliminate the effects of all but short-lived pulses.

The above described system, particularly in its more basic forms, is simple and relatively inexpensive to implement and provides for simple discrimination between say tracked vehicles, multi-axle trucks and (warm legs of) animals. However, it may be desired to produce a more positive identification of a target than can be provided for by the information contained in such local hot-spots.

Referring to Figure 3 this shows a schematic representation, similar to Figure 2, of such a system.

The detection means 50 comprises a linear array of pyroelectric detectors 51 (corresponding to 17 in Figure 2) which array extends upwards, perpendicular to the direction of motion of vehicles with a field of view defined by 'optics' 52.

Each detector receives thermal radiation from a different vertical portion of the field of view of the detection means and provides by way of amplifier 53 signals to a threshold circuit 54. Each threshold detection circuit 54 in adjusted to the ambient thermal signal level due to radiation (preferably automatically), so that the presence of an object in the field of view causing an increased temperature results in a detector signal related to the temperature difference above ambient. Detector signals are fed by each threshold detector to an associated averaging circuit 55 in which the average signal level is provided at output 56 until reset, or cleared, by a post-clock pulse from clock 57.The signals which vary continuously as the vehicle passes are thus digitised, and the digital samples are applied to an input of a shift register storage means 58 (under the control of clock pulse from clock 57) having a plurality of stages through which are shifted the detector signal samples at clock - pulse intervals.

The number of register stages and clock pulse intervals are chosen such that a digitised side-view representation of a complete vehicle which passes through the field of view of the detection means is stored in the register storage means 58.

The outputs of the shift register storage means 58 are connected to one set of inputs 59 of a correlator 60, also operable under the control of clock 57. A second set of correlator inputs 61 are connected to a correlator reference store 62 in which a plurality of storage areas 63, 64, etc. are given to storage of data representing digitised side-views of acceptable targets (and illustrated by representations 65, 66 of a truck and tank respectively).

The correlator reference store 62 has a store selection controller 67 which may be adjusted to select which of the stored vehicle representations are made available in any operation.

An output terminal of the correlator at 68 is connected by way of an option time delay element 69 to the fuze safety and arming arrangement 33, and detonator 34 of the mine 12.

In operation, when the register storage means 58 is full, or the passage of a vehicle is otherwise indicated, the register contents are passed to the correlator which attempt to match the digitised 'side-view' with the reference image representations. The degree of correlation sufficient to be considered a match may be adjustable and if and when a match is obtained signal is provided at an output at 68 to initiate detonation of the mine.

If after correlation with all the reference images identification is not made, the register storage means 58 is cleared in readiness for the next object to be detected.

Variations to this circuit and alternatives to individual elements may be made similarly to those described above to the circuit of Figure 2. In particular the reference store selection controller 67 may be controlled by signals received by a receiver 70 from a remote command station (not shown).

Both ofthe above described embodiments have made reference to a roadway 10 which defines the range of the potential target within the beam. It will be appreciated that if no such range definition is available other means is necessary to establish the position ofthe target.

This may be achieved by incorporating a laser rangefinder (not shown) aimed alongside the field of view of the detection means (but not so close to provide a signal return within it) and triggered by detection of a target object by the triggering means.

It will be appreciated that in both of the embodiments described with reference to Figures 2 and 3 the triggering system may be located other than to give the detection means a side view of the target.

For example the triggering system could be located lined along side or in line with the mine to provide detection means of an underneath view of a target.

Similarly the invention is not limited to use with land mines but may form part of a weapon system employing submarine mines or projectile firing weapons such as rocket launcher or mortar-gun.

Claims (18)

1. An automatic weapon triggering system comprising pyroelectric detection means operable to detect an object of temperature greater than ambient within the field of view of the detection means and produce a detector signal having a level in accordance with the temperature difference, and processing means operable to compare the detector signal with stored signals representing the detection of one or more particular target objects and responsive to a successful comparison to initiate triggering of the weapon.

2. Aweapon triggering system as claimed in claim 1 in which the processing means comprises a thresholding means responsive to passage of a part of the body of higher temperature than the remain derthrough the detector field of view tb generate a detector pulse from the detector signal, a counter of detector pulses produced by the threshoiding means, a presettable generator operable to produce an output in the same form as the counter and representing a reference pulse count number indicative of a suitable target, and comparison means operable t6 compare the counter total with the generator output to produce a weapon triggering initiating signal.

3. A weapon triggering system as claimed in claim 1 or claim 2 in which the processing means includes timing means responsive to a first detector pulse from the thresholding means to set a timing interval for which subsequent detector pulses are counted.

4. Aweapon triggering system as claimed in claim 3 in which the timing means is arranged to set the timing interval as a function of the reference count number and a measured time interval between successive detector pulses.

5. A weapon triggering system as claimed in any one of the preceding claims in which the pyroelectric detection comprises a single detector sensor having a field of view directed to a sensing zone and arranged to intersect said sensing zone at a height above the ground of wheel axles of a potential target-forming vehicle.

6. Aweapon triggering system as claimed in claim 1 in which the detection means comprises a linear array of pyroelectric detector said array extending in a direction perpendicularly to the notion of the target object past the detection means, each of said detectors providing a detector signal to the processing means, and in which the processing means comprises thresholding means operable to pass only detector signals in excess of a predetermined threshold level above ambient, timing means operable to define reception time intervals for the signal from each detector, storage means operable to store the detector signals for each of a plurality of said time intervals as a target object passes the detection means and correlation means operable to correlate the signals received from individual detection for said plurality of time intervals with a stored set of signals representative of the passage of a known target object past the detection means to provide for a satisfactory degree of correlation a trigger initiating signal.

7. A weapon triggering system as claimed in claim 6 in which the correlator stores in a reference store a set of representations for each of a plurality of target objects.

8. Aweapon triggering system as claimed in claim 7 in which the correlator is selectable either to attempt correlation for one target object or to attempt correlation with each of a plurality of target object representations until a satisfactory degree of correlation is achieved.

9. Aweapon triggering system as claimed in any one of claims 6 to 8 in which the timing means comprises a clock started by the first detector signal to exceed said threshold level.

10. Aweapon triggering system as claimed in claim 9 in which the clock frequency is fixed.

11. A weapon triggering system as claimed in any one of the preceding claims including a range finder operable to determine the distance of the target from the sensor.

12. An automatic triggering system substantially as herein described with reference to and as shown in Figure 2 or Figure 3 of the accompanying drawings.

13. Aweapon system comprising a weapon and an automatic weapon triggering system as claimed in any one of the preceding claims.

14. A weapon system as claimed in claim 13 in which the weapon comprises a land mine adapted to be buried beneath a roadway and connected an automatic triggering system adapted to be located to the side of the roadway to detect and respond to vehicles in the vicinity of the mine.

15. A method of triggering a weapon comprising detecting the passage of a target object through the field of view of pyroelectric detection means as a function of the change from ambient temperature it presents, comparing the changes with stored representations of the changes caused by one or more known objects and initiating triggering of the weapon upon a successful comparison.

16. A method as claimed in claim 15 in which an object is detected in terms of destinguishing regions of higher temperature than the remainder of the object and comparison achieved by counting the number of such regions and comparing the count total with the count obtainable from a known target object.

17. A method of triggering a weapon as claimed in claim 15 in which the pyroelectric detection means comprises individual detectors and extends orthogonally to the direction of motion of the object providing, in combination with the object movement, a set of signals representing an image of the object, and the comparison comprises correlating the image representing detector signals with stored signal representations of one or more known objects.

18. A method of triggering a weapon substantially as herein described with reference to and as shown in Figures 2 or 3 of the accompanying drawings.