GB2240384A - Fuzing systems. - Google Patents

Description

IMPROVEMENTS RELATING TO FUZING SYSTEMS This invention relates to fuzing systems, and especially although not exclusively, to fuzing systems used in mines.

In known forms of fuzing system a warhead, deployed on the ground as a scattermine, for example, may be equipped with a target sensing device capable of initiating detonation of a warhead when the target, e.g. a tank, comes within firing range.

Many different forms of sensing device are known, each responsive to a different stimuf-us-generated by a t-arget*-and hitherto it has been common for an enemy to employ an appropriate countermeasure device designed to simulate a target and so initiate premature firing of the warhead. In order to reduce the effectiveness of such countermeasure devices it has been common to provide different mines, in a mine field, with different forms of target sensing device. Each target then needs a highly complex countermeasure system if the mine field is to be successfully penetrated. However, mine fields of this kind, including mines each equipped with one of a number of different forms of sensor, tend to be both time consuming and costly to lay.

It is an object ot the present invention to provide a fuzing system in which the above-described problems are alleviated.

According to the invention there is provided a fuzing system capable of generating a trigger signal suitable to initiate fuzing of a warhead comprising, first and second sensors capable of responding to different characteristic stimulii caused by a target to generate respective first and second output signals, a ranging device capable of generating a third output signal indicative of target range, and an electrical circuit responsive to said first, and second and third output signals and capable of generating the trigger signal provided criteria, to which the circuit is arranged to respond, are satisfied by the three output signals.

In a preferred embodiment, the system is capable of genetzTtzssg-Ghe- trigge signal -provided the first and second output signals have been received by the circuit and the third output signal indicates that the target is located within preset range limits.

The first sensor may be responsive to acoustic signals generated by the target, the second sensor may be responsive to magnetic anomalies created by the target, and the ranging device may be an ultrasonic proximity sensor.

In order that the invention may be more readily understood and carried into effect a specific embodiment thereof is now described, by way of example only, by reference to the accompanying drawings of which Figure 1 illustrates in schematic form, different stages in operation of the fuzing system, and Figures 2 and 3 illustrate different reversionary modes used in operation of the fuzing system.

In a preferred embodiment of the present invention, described in greater detail hereinaf er, the fuzing system includes two passive sensors, namely a magnetic sensor, typically in the form of a fluxgate magnetometer, responsive to a distortion of the earths magnetic field caused by ferromagnetic components of a target (e.g. a tank) and an acoustic sensor e.g. a piezoelectric microphone responsive to noise produced by the target. The fuze also includes a ranging device in the form of a range-gated ultrasonic sensor capable of generating an output signal indicative of target range and, in particular, capable of indicating whether or not a target lies within preset range limits.An ultrasonic sensor of this kind includes an ultrasonic transmi:tter and the microphone, provided in the acoustic sensor, described hereinbefore, can be used as the receiver.

Electrical signals produced by the sensors and ranging device are applied to a common logic circuit, conveniently, though not necessarily, in the form of a microprocessor. As will be described in greater detail hereinafter the logic circuit is conditioned to evaluate received signals, produced by the three forms of sensor, to generate a trigger signal suitable for firing a warhead, providing criteria relating to the nature and position of the target are satisfied.The use of three independent sensing devices (passive magnetic and acoustic sensors and an active ranging device) in conjunction with a logic circuit arranged to evaluate output signals generated thereby constitutes an effec i-re -resistance to a number of possible counterrleasures which could be used in an attempt to initiate premature or late firing of a warhead.

Figures 1 to 3 of the drawings illustrate, in the form of a nunber of flow diagrams, operation of one embod:nt of the present invention, the diamond shaped elements in each Figure representing different evaluations performed by the logic circuit on output signals produced by the sensors and ranging device.

Referring initially to Figure 1, the warhead is represented at W and a target, in the form of a tank in this example, is represented at T in four different positions relative to the warhead. The sensors and ranging device (not shown in the Figurest are mounted to the warhead together with an attitude sensing switch and an anti-handling device. Operation of the fuze is initiated by switching on the power and performing a system check to ensure that the electronic circuits aee functioning correctly.

In an initial interrogation stage, represented at (a) in Figure 1, the logic circuit checks the position of the attitude-sensing switch to establish whether or not the warhead is facing upwards. This may be especially important in the case of a single-ended warhead designed to fire in one direction only. If it is found bhat the warhead is facing downwards, towards the ground, as can sometimes occur for example, when deployed from an aircraft as a scattermine, then the logic circuit enters a first reversionary mode (indicated at (1) in Figure 1) whereby the warhead is prevented from firing and its attitude is checked periodically at intervals (of 5 seconds in this example) defined by a dye at circuit 10.

If the correct attitude is sensed, however, the logic circuit enters a second interrogation stage, shown at (b), by monitoring output signals generated by the acoustic sensor. If a target T is detected the circuit enters a third stage, (c), in which the ultrasonic proximity sensor is used to check that the region immediately above the warhead is clear of obstruction i.e. that no object is detected within the upper range limit of the sensor. If no obstruction is detected the logic circuit enters a fourth interrogation stage (d) in which the magnetic sensor is switched on and output signals generated thereby are monitored.If the magnetic sensor does not indicate, within a preset time interval T (typically 3 sec for a tank) that the target, initially detected by the acoustic sensor, has moved within range of the warhead it is assumed that the target has either stopped short of, or moved away from the warhead. In these circumstances the logic circuit is reset and the interrogation stages (a) to (c) are repeated. This is achieved using an elapsed time loop represented generally at 15 in Figure 1 and including a timing circuit 16 which is triggered simultaneously when the magnetic sensor is turned on. After the time interva < the timing circuit generates a d.c. output level which is applied to one input terminal of an AND gate 17. The other input terminal is held high for as long as:the target remains beyond range of the magnetic sensor. If the target remains out of range for the time intervalJrethe AlD gate 17 generates an output signal which is used to reset the logic circuit. If, on the other hand, a target is detected within the time interval the proximity sensor is again used, in a fifth stage (e), to check its range accurately and will only initiate firing of the warhead if the measured range is found to lie within preset range limits, typically 150 mm and 750 mm in this example.

An ultrasonic proximity sensor, used in this manner, provides valuable confirmation of the existence of a target, and in the case of targets, such as tanks, can be used to prevent firing unless the warhead is located between the line of the tracks, thereby ensuring that the full force of warhead is directed-tdwards the underbelly of the tank. Furthermore, in circumstances where the warhead is located outside the line of the tracks, firing is prevented even though the magnetic sensor may respond to field anomalies caused by the tracks by generating an electrical signal indicating a target.

As described hereinbefore, the ultrasonic proximity sensor is used in a third interrogation stage (c) to check that the warhead is clear of any obstruction. If an obstruction, such as snow or mud, is detected, the proximity sensor cannot then be used, in the fifth interrogation stage (e) to determine target range. In these circumstances the logic circuit assumes a second reversionary mode involving the use of the magnetic sensor only, as illustrated generally at (2) in Figure 1. The logic circuit again monitors output signals generated by the magnetic sensor but initiates firing of the warhead, immediately if a target is detected.An elapsed time loop 25, identical to 15 described hereinbefore, is again used to reset the logic circuit if a target is not detected within a time interval This arrangement conserves power supplied to the logic circuit.

If the proximity sensor proves not to be obstructed it may still indicate, in the fifth interrogation stage (e) that the target range is too low or too high i.e. outside the range 150 mm to 750 mm in this example. If the range is too great, namely beyond the upper range limit of the proximity sensor, it is assumed that the fuze is being attacked by a projected magnetic field countermeasure system designed to simulate a target, by creating a magnetic field anomaly ahead of the genuin2-target. In these circumstances the logic circuit enters a third reversionary mode, illustrated at (3) in Figure 2, in which the acoustic sensor is used again to indicate whether the target has moved within firing range of the warhead.This is achieved by time averaging true RMS acoustic signals, over selected parts of the acoustic frequency band, and using an alogarithm to identify when the derived signals are characteristic of a target prevailing within the firing range.

If the acoustic sensor does indicate the presence of a target its range is again checked using the ultrasonic proximity sensor and if the range is within the preset limits causes the warhead to fire. Again an elapsed time loop 35, identical to those shown at 15 and 25, is used to reset the logic circuit unless the acoustic sensor detects a target within the preset time interval < . If, after the third reversionary mode has come into operation, the ultrasonic proximity sensor still shows that the target is located outside the specified range limits (150 mm - 750 mm in this example) it is assumed that the fuze is also being attacked by an acoustic generator counter measure system, whereby acoustic signals are generated so as to simulate a target ahead of the genuine target and so confuse the acoustic sensor.In this case the logic circuit enters a fourth reversionary mode, shown at (4) in Figure 2, in which the proximity sensor is periodically pulsed, at intervals of t (g second in this example) determined by delay circuit 41 until the target comes within range (i.e. within the specified range limits) when an attack delay circuit 42 is triggered. After the delay, imposed by circuit 42, the range is again checked by the proximity sensor and if the target is still within the specified range limit causes the warhead to fire.A time elapsed loop 45, identical to circuits 35, 25 and 15, is again used to reset the logic circuit unless a target is detected within the range limits within the time interval If during the fifth interrogation stage, shown at (e) in Figure 1, the ultrasonic proximity sensor shows that the range is less the lower range limit (150 mm in this example) the logic circuit assumes that the fuze is being attacked by a tank fitted with a fuil width roller, or similar countermeasure to initiate premature firing of the warhead. In these circumstances the magnetic sensor is switched off and the ultrasonic proximity sensor is pulsed periodically at time intervals t' ( second in this case) defined by a delay circuit 51, until the target range is greater than the upper range limit of the sensor (750 mm in this example).The system then assumes that the warhead is located within the gap between the roller and target and the magnetic sensor is again switched on, and the interrogation stages (d) and (e) described hereinbefore, repeated so as to monitor the tank itself. When the magnetic sensor indicates that the target has entered within range of the warhead the ultrasonic sensor again checks the range and initiates firing of the warhead if the range is within the specified limits.Again an elapsed time loop 55 is used to reset the logic circuit if the roller has not passed the warhead within the preset time interval K The system described hereinbefore by way of - example, involves use of five reversionary modes and is capable of overcoming three different forms of countermeasure designed to respectively confuse the magnetic, acoustic and proximity sensors.

In addition to the above-described safeguards the anti-disturbance sensor, provided in this example, is randomly switched into the fuzing system so that at any particular instant a rninefield including many scattered mines would contain a mixture of mines with and without active anti-disturbance sensors. The distribution of this mixture could moreover, be varied with time.

If a double-ended warhead is used then the above system described in relation to a single-ended warhead would be modified in minor respects. In particular, the attitude sensor used in interrogation stage (a) can be dispensed with thereby eliminating the first reversionary mode (1). Instead the attitude sensor is used to select the correct detonator (i.e.

the one closer to the ground) immediately prior to firing the warhead to ensure maximum warhead effectiveness into the target.

A further modification is to provide two acoustic sensors, one mounted to each end of the warhead, the uppermost sensor being used always to provide input signals to the logic circuit. Only one ultrasonic transmitter need be provided, however, since this can be used as a single source feeding both ends of the warhead.

Both the fluxgate magnetometer used as the magnetic sensor and the microprocessor used to analyse received signals can be --eonstPued in-the---form-of--intearaGed-cireuits.- Moreover, since both the ultrasonic transducer used as the transmitter in the proximity sensor and the piezo electric microphone, used as both the receiver and the passive acoustic sensor, are available in compact form the entire system can be readily mounted into the relatively small space available in the body of a mine.

It will be appreciated that although the above-described example has been described in relation to a programmed microprocessor a hard-wired circuit including logic circuit components could alternatively be used. Moreover, it is also envisaged that the system need not be limited to the particular combination of sensors described, for example the passive acoustic sensor could be replaced by a seismic sensor designed to detect vibrational disturbances caused by target movement.

A seismic sensor may not be particularly desirable, however, when the munition is deployed as a scatter mine, since effective ground coupling is desirable and this may require that the munition be buried in the ground. The ultrasonic sensor could be replaced by an active radio frequency sensor, a small radar for example, which may be designed to operate in any one of several frequency bands. Furthermore, it is possible that optical or infra-red sensors could be used in the fuzing system in either a passive or active role, although these sensors tend to have a relatively short working life especially in a battle field environment where they may become covered with debris.

Claims (6)

1. A fuzing system capable of generating a trigger signal suitable for initiating fuzing of a warhead comprising, first and second sensors responsive to different respective characteristic stimuli, produced by a target, to generate respective output signals, ranging means capable of generating a further output signal related to target range, and processing means responsive to said output signals and capable of generating a trigger signal provided criteria to which the processing means is arranged to respond are satisfied jointly and/or severally by the respective output signals.

2. A fuzing system according to Claim 1 wherein one of said sensors is an acoustic sensor.

3. A fuzing system according to Claim 1 wherein one of said sensors is a magnetic sensor responsive to a magnetic anomaly produced by the target.

4. A fuzing system according to any one of Claims 1 to 3 wherein the ranging means is an ultrasonic proximity sensor.

5. A fuzing system according to any one of Claims 1 to 4 wherein the processing means is arranged to generate said trigger signal provided said first and second sensors generate respective output signals and said further output signal, generated by the ranging means, represents a target range within a preset upper range limit and a preset lower range limit.

6. A fuzing system substantially as hereinbefore described by reference to the accompanying drawings.

6. A fuzing system according to Claim 5 wherein said first and second sensors are an acoustic sensor and a magnetic sensor, responsive to a magnetic anomoly produced by the target, and the processing means includes means arranged to inhibit generation of said further output signal, by said ranging means, unless the magnetic sensor generates a respective output signal within a preset time interval after generation of a respective output signal by the acoustic sensor.

7. A fuzing system according to Claim 5 or Claim 6 including means responsive to a said further output signal, representing a target range exceeding said preset upper limit, to evaluate output signals generated by said acoustic sensor and, in dependence on the evaluation, to generate an indication when the target is within said upper and lower range limits and wherein the processing means is arranged to generate said trigger signal provided the ranging means also generates an output signal, indicative of a target within said upper and lower limits, after generation of the indication, dependent on said evaluation.

8. A fuzing system according to Claim 7 wherein the output signal of the ranging means is sampled, after generation of the indication, at discrete time intervals.

9. A fuzing system according to Claim 5 or Claim 6 wherein the processing means is arranged to respond to a said further output signal, representing a target range less than said lower range limit by sampling periodically said further output signal generated by the ranging means until said further output signal represents a target range exceeding said preset upper limit and then initiate generation of said trigger signal when next both the magnetic sensor has generated an output signal, and the ranging means has produced a said further output signal indicative of a target range within said upper and lower range limits.

10. A fuzing system substantially as herein described by reference to and as illustrated in the accompanying drawings.

Amendments to the claims have been filed as follows 1. A fuzing system capable of generating a trigger signal suitable for initiating fuzing of a warhead comprising, an acoustic sensor or a seismic sensor for generating-a first output signal in response respectively to an acoustic signal or seismic signal produced by a target, a magnetic sensor for generating a second output signal in response to a magnetic anomaly produced by the target, ranging means capable of generating a third output signal provided the target is within a range interval extending from a preset upper range limit to a preset lower range limit, and processing means arranged to generate said trigger signal in dependence on said third output signal being generated and to inhibit generation of said third output signal unless the magnetic sensor generates a said second output signal within a preset time interval of said acoustic sensor or said seismic sensor generating a said first output signal.

2. A fuzing system according to Claim 1 wherein said ranging means is an ultrasonic proximity sensor.

3. A fuzing system according to Claim 1 or Claim 2 wherein the processing means includes evaluation means, responsive to a further output signal produced by said ranging means and representing a target range exceeding said preset upper range limit, to evaluate first output signals generated by said acoustic sensor or said seismic sensor and, in dependence on the evaluation, to generate an indication when the target is within said range interval; and further means to generate said trigger signal provided said ranging means also generates a said third output signal after generation of said indication.

h. A fuzing system according to Claim 3 wherein the ranging means is sampled, after said evaluation, at discrete time intervals.

5. A fuzing system according to Claim 1 or Claim 2 wherein the processing means includes means arranged to respond to a further output signal, produced by said ranging means and representing a target range less than said preset lower range limit, by sampling periodically further output signals generated by the ranging means until a said further output signal represents a target range exceeding said preset upper range limit and then initiating generation of said trigger;signal when next both the magnetic sensor has generated a said second output signal and the ranging means has produced a said third output signal.