The invention concerns a sensing device for detecting the penetration of high-speed metallic objects, especially bullets, which device is capable of fulfilling the role of a target primarily in weapon firing practice exercises. In addition, the invention concerns apparatus containing the sensing device suitable for the automatic indication of the penetration of high-speed metallic objects, especially bullets, i.e. for the display of the number of "hits". The automatic detection of hits on target bodies to be disposed in the target area of shooting practice ranges, the transmission of the number of hits to the shooting positions and the display of the result at the shooting positions is a problem which has not yet been reliably solved. Attempts have been made to sense automatically the penetration of the bullet by detecting a large variety of physical phenomena (primarily displacement) arising

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from the interaction of the bullet and the target body.

In Volume 13 of "Internationale Wehr-Revue" an article entitled "Gunner training systems" describes a hit indicating apparatus wherein the target body is made of polyethylene and a complicated electronic apparatus monitors its mechanical displacement (accel¬ eration). The electronic displacement measuring apparatus or accelerometer is so constructed that it records or indicates a hit only within predetermined ranges of acceleration magnitudes or values. Quite apart from the complicated nature of this apparatus, it is a problem that a false indication may arise,in spite of all the effort taken, under the effect of a sudden wind shock or mechani al impulse, whereby to falsify the result. It is a further problem with this apparatus that the regenerative capacity of the poly¬ ethylene target body is relatively low and is suitable for taking up at most about two thousand hits.

British patent specification No.1,394,850 describes a target board containing two sensing units placed behind eath other each of which contains two electrically conductive plates which are short-circuited by the penetrating bullet. The conductive plates or sheets are fixed to a rigid and solid supporting plate and a space is formed between the conductive members . In this construction the regenerative ability of the sensors is minimal because a hit permanently deforms the rigid supporting plate and tears through

the thinner conductive layer or plate which is adhesively bonded to the support plate. Thus on multiply repeated hits the sensing or detection is no longer guaranteed. An aim of the present invention is to provide a sensing device of novel type or construction which is reliably capable of detecting the penetration of high-speed metallic objects and which is suitable for detecting a number of hits which in practice is unlimited. The invention is based on the discovery that a plate made from a natural rubber-based material of the appropriate composition and mechanical characteristi has a resilience which is satisfactory for accommodating any desired number of penetrations and the sensing can be achieved electrically by making electric contact via the metallic object by providing the rubber plate or body in the form of a plurality of layers of varying electrical conductivity. The metallic object causes a short-circuit (low resistance) between the outer conductive layers separated from each other by inter¬ mediate insulating layers and this electrical phenomenon is readily and simply detectable.

The invention provides a sensing device for detecting the penetration of high speed metallic objects, especially bullets, which is characterised in that it is in the form of a multi-layer plate comprising interconnected resilient and flexible rubber-based layers which are connected to each other and which have

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the same or closely similar mechanical properties, wherein there are electrically conducting layers separated from each other by insulating layer(s).

Preferably, the conductive layers have a specific volume resistivity at least six (decimal) orders of magnitude smaller than that of the insulating layers .

In this case, the short-circuit caused by the penetrating metallic object electrically connecting the conductive layers is unambiguously detectable. The specific volume resistivity of the conductive layers is in a preferred embodiment chosen to be less than 10 ohm-centimetre.

The advantageous and desirable mechanical and electrical properties of the conductive and insulating layers may be assured by a suitable choice of appropriate additive material. Electrical conductivity is assured by adding carbon black, for example, to the rubber material, which has a large secondary structure, i.e. has a structure forming long and branching agglomerates, As a carbon black additive, acetylene black is preferred. The amount of the carbon black additive is expediently between 5-40% by weight. The electrical conductivity is improved when advantageously the rubber contains, in addition to the carbon black, at most 20%-by weight of graphite. In the interest of improving the mechanical properties, the rubber material may also contain at most 10% by weight of a softener or plastici^er.

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The basic material of the insulating layer may be formed from natural rubber types of high specific volume resistivity; These properties may be improved by the utilisation of about 5-20% by weight of a mineral filler. The appropriate and desired insulating properties may be assured by the use of inactive, or semi-active silicate type filler, e.g. kaolin or talc, in an amount expediently between 10-40% by weight. Advantageously, at most 20% by weight of plasticizer may also additionally be used. The thus formed structure Is suitably resilient, flexible, and on penetration of the metallic object, expediently a bullet, the latter comes into good contact with the layers surrounding it under the effect of the resilient biassing force of the layers. After the passage of the metallic object through the plate structure, the rubber layers resiliently pull together and the place of the penetration can in practice scarcely be seen at all, This assures that the life-time of the sensing device according to the invention is in practice unlimited.

Although the invention is suitable particularly for detecting the penetration of bullets, it may also be used for indicating the penetration of other metallic objects.

In utilising the detecting device according to the invention an apparatus has also been created in the invention for detecting the penetration of

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metallic objects especially bullets, which has a detecting device separately and physically remotely arranged from a controlling and indicating unit, between which a two-way communication link or connection is formed, and according Lo the invention the detecting device contains at least one laminated detector(s) made from a plurality of rubbers of differing electrical conductivity, the conductive layers of the or each detector being separated from each other by insulating layers and being connected to a store the output of which is connected to one terminal of the communication link or connection, ^" the controlling and display unit having numerical displays associated with the Individual detectors the inputs of which are connected to the outputs of a decoding and storing unit connected to the other terminal of the communication link or connection.

The apparatus according to the invention is very favourably utilisable as a 'hit ¹ indicating device in target shooting ranges, and is capable of storing the hits of several volleys or series of shots and for indicating the result at he: shooting position. In the embodiment where the communication link or connection is formed by a radio transmitter-receiver, then the apparatus is readily erectable on site and/or postable.

The invention is described purely by way of example with reference to the accompanying schematic drawings, wherein;

Figure 1 is a diagrammatic view of the detecting device according to the invention;

Figure 2 is a general block diagram of a hit indicating apparatus constructed from a plurality of detecting devices according to the invention;

Figure 3 is a detailed block diagram of the detecting units of the apparatus shown in Figure 2; and

Figure 4 is a detailed block diagram of the controlling and display units of the apparatus shown in Figure 2. Figure 1 diagrammatically illustrates the structure of the penetration or through-passage indicating device according to the invention. The detector shown in Figure 1 consists of three linearly connected special rubber layers. The two outer layers 1 and 3 have been rendered electrically conductive by means of a suitable filler material. The electrical conductivity is assured by adding carbon black to the basic rubber material, which has a large secondary structure, i.e. a structure forming long and branching agglomerates. As a carbon black additive, especially acetylene black is advantageous. Un er the effect of the carbon additive, conductive chains are formed in the rubber mixture and

these greatly reduce the specific volume resistivity of the rubber. The specific volume resistivity may be further decreased by the addition of graphite flakes. The conductive mixture may contain 5-40% by weight of carbon and 0-20% by weight of graphite.

As a function of the amount of the filler materials, the mixture may also contain 0-10% by weight of a softener.

Apart from the above stipulations, the production of the conductive layers 1, 3 can be effected by conventional rubber industry technology. The magnitude and duration of the shear stress arising in the mixing device during production has to be limited because otherwise the conductive carbon agglomerates may break up and the conductive chains may be interrupted. The specific volume resistivity of the conductive layers 1, 3 should preferably be maintained at a low value.

3 4 This value is expediently In the range of 10 -10 ohm- centimetre or less. The two examples set out below illustrate preferred compositions for the conductive layers 1, 3. Example 1

The composition of the conductive layer was as follows: Constituent Quantity in parts by weight

Butadiene-styreae rubber 50

Polychloroprene rubber 50

Acetylene black ^* 40

MgO 2

ZnO 5

Stearic acid 2

Extracted oil 5

N-isopropyl-N-phenyl-p-phenylene- . diamine

Sulphur 1 2-rnercapto-imidazoline 0.3

N-oxy(diethylene)-2-benzthiazole- sulphenamide 1

157.3

Example 2

Anoth r preferred composition of the conductive layer;

Constituent Quantity expressed in parts by weight

Polychloroprene rubber 100

Acetylene black 40

ZnO 5 Stearic acid 2

Extracted oil 5

N-isopropyl-N-phenyl-p-phenylene- diamine

2-mercapLo-imidazolinc 0.4

2,2'-dibenzothiozildisulphide 0.2 MgO 4

157.0 The two conductive layers 1 and 3 sandwich an insulating layer 2 which may al- _^ o be produced by conventional rubber technology processes. The basic material of the insulating layer may Le from rubber types

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of high specific volume resistivity. Such rubbers or elastomers are, for Instance, the ethylene-propylene- terpolyiners, ethylene-propylene-copolymers, butyl rubber, natural rubber or a butadiene-styrene elastomer, or a mixture of these. The favourable technical properties, i.e. the rupture strength and the dynamic properties are assured by adding a high-activity filler material in an amount of about 5-20% by weight. The use of carbon black, especially those of high secondary structure should not be used. The desired insulating characteristics can be assured by adding inactive or semi-active silicate- type fillers, expediently kaolin or talc. These fillers may amount to 10 to 40% by weight. In dependence uponthe amount of filler material the workability of the rubber mixture can be improved, by the addition of 0-20% by weight of a softener. Preferably the specific volume resistivity of the Insulating layer 2 should beadjusted to a value exceeding 10 ohm-centimetre..

The two examples given below set out preferred compositions for the Insulating layer 2.

Exampl 3

A composition of the insulating layer:

_r Cons_, _* t-i-_tuen xt. Q^uantity ex,presse,d in parts by we eht Ethyl ei e-propyleiie terpolymer lϋO

HAF (high abrasive furnac<- ) carbon black 5 kaolin 50

Hydrated silica 20

ZnO 5

Stearic a cid 1

Extracted oil 30

Sulphur 9

N-oxy(diethylene)-2-benzthiazole- sulphene-amide 2

Tetramethyl- hiuram-monosulphide 2

Octylated diphenyl-amine 1.5

248.5

Example 4

Another example for the composition of the insulating layer: Constituent Quantity expressed in parts by weight

Butyl rubber 100

ZnO 5 Stearic acid 1

Hydrated silica 20

HAF carbon black 5

Kaolin 40

Talc 20 Extracted oi 5

Sulphur 2

Tetramethyl-thiuram ^' -disulphide 0. 5

2-mercapto-benzthiazole 1

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The mechanism illustrated in Figure 1 has been produced by conventional rubber technology methods by producing the individual layers. The ready mixtures forming the individual layers can be taken off in the form of sheets of appropriate thickness from a cylinder frame (roller frame) or may be removed after calendering. The fitting together of the individual layers can in.- carried with conventional rubber technology methods, including manual adhesive bonding or continuous doublering carried out on a calender. The vulcanisation may be carried out in a press in an air or steam furnace or in a continuous vulcanisation system.

Between the adjacent layers of the thus produced detecting mechanism, the specific volume resistivity difference is at least of the order of magnitude of

10 ohm-centimetre. The structure has suitable flexibility and resilience and is resistant to repeated penetrations. According to our experiences the hole remaining after penetration of a hand-gun bullet does not attain a size of 1 milliiaetre and Indeed, in most cases, cannot even by seen with the naked eye.

Referring again to Figure 1, it may be seen that the conductive layers 1, 3 project beyond the insulating layer 2 and are connected to a respective terminal 4 and 5 which in turn are connected with the inputs of an electronic unit b. The output of the electronic unit 6 is connected to an indicating or display unit 7 which is capable of indicating or displaying in a pre¬ determined manner when a penetrating metallic object interconnects the normally separated conductive layers 1 and 3

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The detecting mechanism according to the invention is primarily destined far indicating hits in firing or shooting practice, but to a man skilled in the art it will be obvious that the device is capable of indicating the penetration or through- passage of any pointed or sharp metallic object. When the detecting device is formed not from three but from more layers and the area of distribution of the individual layers is suitably designed, then the individual leads from the conductive layers may not only enable the detection of the fact of penetration but also the position or band of the penetration . For instance a target board may be formed from regular concentric circles which is capable of establishing the point or numerical value of the hit.

The three-layered structure illustrated in Figure 1 is about 5-10 millimetres thick, and has a suitable rigidity and is weather-resistant. According to practical experience a construction of normal target dimensions preserved its original properties even after about 40,000 hits or impacts, i.e. the lifetime of the structure is in practice unlimited.

Figure 2 is a diagrammatic illustration of the arrangement of a shooting range target hit indicating device according to the invention provided with detecting or sensing devices according to the invention.

The hit indicating apparatus comprises two main parts, namely a sensing or detecting device 100 disposed in the target area and a controlling and display unit 200 disposed in the vicinity of the shooting position. The signal communication between the two parts Is ensured by respective radio transmitter-receivers (transceivers) 101 and 201.

The detecting device 100 contains m juxtaposed target figures arranged in n depths, and each target figure is formed by a detecting device constructed accord¬ ing° to Fig°ure 1. Each of the individual detectors Enm is co-ordinated with a respective transducer or signal shaping unit JE connected via a line v to a respective

^ ° nrn nm ^r register or store T. Each line or depth is associated with a respective register or store T.. In the example shown in Figure 2, the number of lines or depths is n=3 and in each line the number of targets is m=5. The registers or stores T are connected to a radio

° n transceiver 101. A display pand 202 is arranged in the vicinity of the shooting ^to p ¹ ositions L1, , L2„ Lm in the controlling ^& and indicating unit 200; the panel or board containing numerical displays J _ associated with the target figures ^ι _" and arranged in n rows and m columns. The indicator board or display panel 202 contains m keys B,, B^...^ controlling the display of the data of the individual lines or depths and switch S for switching the apparatus on or off.

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In Figures 3 and 4 examples are given for the construction of the detecting apparatus 100 and the controlling and display unit 200, respectively.

Referring to Figure 3, of the m sensors or detectors belonging to the first line or depth, the first detector E., , and the last detector E, are shown.

11 lm

Each of these is connected to a signal shaping unit JE, which in the preferred embodiment illustrated here consists of an amplifier and a monostable multivibrator. If a bullet passes through the detector, then its outer conductive layers 1 and 3 are interconnected for a short time. This electrical connection closes the input circuit of the amplifier connected thereto, the amplifier having a gain of about 60 dB and an amplified pulse signal appears on the output. The monostable multivibrator is triggered by the amplified signal and a standardised pulse appears at its output.

It can be seen from Figure 3 that the first register T, consists of m individual registers T, , .... T, each of which is connected to the appropriate output of the signal shaping amplifiers JE -...JE. . The output pulse of the monostable multivibrator that arises on detecting a hit is written into the associated store. The store or register stores the sum of the successively arriving pulses„

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At each depth or line a similar apparatus is to be found. The outputs of the registers belonging to the individual lines are multiplexed together, as can be seen in Figure 3. Thus each register is multiplexed with a number of stores equal to the number n of the lines. From the n combined stores ^* or registers a group is formed corresponding to the m juxtaposed target bodies and these are connected to the m inputs of a multiplexer unit 102.

The output 103 of the receiver of the radio transceiver 101 is connected to the input of a control stage 104 wherein there are n selective circuits. The outputs of the selective circuits are connected to the

Inputs of the individual registers T. which permit or enable reading out and which ^" are designated Ee. , Ee_...Ee .

1 2 n If, for instance, the input Ee enabling reading-out of the first register receives a command, then, of the multi¬ plexed registers behind each other, only the contents of the registers belonging to the first register T, can be passed to the unified output line, i.e. to the appropriate input of the multiplexer unit 102.

The control stage 104 is so constructed that when one of its selective circuits recognises or detects a command then the appropriate output is activated to a steady state and at the same time the output 105 is also activated while the output 106 receives a starting signal. The output 105 is connected to the transmission control input of the radio transceiver 101 and is connected to the control input of the switch S. In the activated state of

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the output, the radio transceiver 101 is switched to transmitting mode and its modulating input 107 is connected via the switch S to the output of an oscillator unit 108. The output 106 of the control stage 104 is connecte with the input of a clock generator 109 which generates clock pulses of frequency f . and 4f ..

The output of the clock generator 109 belonging to the clock pulses of frequency f , Is connected to the input of counter 110 which has states and the outputs of which control the setting inputs of the multiplexer unit 102_ The location of the counter with the highest mathematical place-value is connected via a line 111 to the input of the control stage 104 and to the reference input of the clock generator 109.

The output of the clock generator 109 with frequency 4f . is connected to the clock input of a parallel-serial converter 112. The input of the latter is connected with the output of the multiplexing unit 102 while its output is connected with the first input of the oscillator 10S. The other input of the oscillator unit 108 is controlled by the output of the clock genera¬ tor 109 of frequency f .

On receiving a command from the radio channel, the apparatus illustrated in Figure 3 reads out and trans¬ mits the numerical data relating to hits stored and associated with the selected line. Let it be assumed that by broadcasting the selective tone of the first line through the ratio channel command arrives for transmission of the data of the first line. Then the control stage 104

enables the read-enable input Ee of the register T. of the first line while at the same time the transceiver 101 is set into its transmission mode, the switch S is switched off and the clock generator 109 is actuated. In its basic position, the multiplexing unit 102 is connected with the combined outputs of the first registers T.......T ,. Of these, only the register T., is enabled for reading out, hence the parallel input of the parallel-serial converter 112 is controlled by the coded value of the number of hits detected by the first detector or sensor E. , *. The parallel-serial converter 112 reads or inputs this coded numerical value as serial information to the first input of the oscillator unit 108 in four successive clock cycles of frequency 4f .. During the duration of the pulses passed to the first input of the oscillator unit 108 the latter commands the modulating input 107 with a signal of frequency f of about 3000 Hz a which information passes to the radio channel as a modulat¬ ing signal. By end of the fourth cycle the serial conversion or transformation and signal transmission have terminated and the counter 110 counts the first pulse of frequency f just starting and the multiplexing unit 102 connects its second input with the output. The now succeeding parallel- serial conversion takes place In a similar manner except that the Information reflects the contents of the register T _? . It can be seen that in every case or condition of the multiplexing unit 102 the associated store is read out and the data is transmitted.

In order that the individual pulse series should be separated on the receiving side, during the duration of the clock pulse of requency f , (while the multiplexing unit 102 switches to the next input) the second input of the oscillator unit 108 receives a command under the effect of which a characteristic frequency f, (significantly lower than the frequency f ) is passed to the radio channel.

After reading the contents of the last mth register, i.e. the register T _η , the counter 110 overflows and so it lm erases itself and resets the control stage 104 and stops the clock generator 109. This at the same time also means the reading of a store or register T..

When the data of next line are requested from the radio channel, then everything is repeated in accordance with the above-described operation but now the registers of the store unit T„ of the second line receive an enabling signal on their enable inputs Ee„ _β According to the above, in n steps all the data can be read out. Referring now to Figure 4, there is shown a construction of a controlling and display unit 200. The receiving output 203 of the radio-transceiver 201 is connected to the inputs of filters 204 and 205. The filter 204 is tuned to a frequency f„ and the filter 205 is tuned to a frequency f . The output of the filter 204 is passed via a signal or pulse shaper 206 to the input of a demultiplexing unit 207. The filter 205 is connected via a pulse shaper 208 to the control input of a demultiplexing unit 207„ The demultiplexing unit 207 has m outputs which are connected with the individual compartment

or locations of a decoding and storing unit 209 having m compartments or locations. The decoding and storing unit 209 has m outputs, in the present case five outputs and each output has an output point required for causing a decimal number to be displayed. The outputs are connected to an output bus 210 which. is oonnected to an indicating unit 221 containing m groups of numerical display units having m numerical display units per group.

The enabling Inputs of the individual groups D,, D ₂ . ••D are connected to the respective outputs of an operating unit 212 and these outputs are also connected to the control input of the selective call tone generator G, ,

G _n ...G . n

The inputs of the operating unit 212 are connected with the line selecting keys B. , B _? ...B , while its triggering or starting output Is connected with the input of a transmission controller 213. The other inputs of the transmission controller 213 are connected with the output of the individual generators G^ _a . _U G . Under the effect of the starting signal the transmission controller 213 controls the modulating input 214 of the radio trans¬ ceiver 202 at the frequency of the appropriate generator. The operation of the controlling and display unit 200 illustrated in Figure 4 is as follows. Let It be assumed that after termination of a volley or sequence of shots the operator wishes to interrogate the detecting unit 100 as regards the hits associated with the target in the first line or depth and to display then.

This is started by depressing the key B whereupon the operating unit 212 actuates the generator G. , the

frequency signal f, passes via the transmission controller 213 to the modulating input of the radio transceiver 202 and from there to the radio channel.

The detecting device 100 receives this signal and in accordance with the data therein the data stored in the first line or depth associated with the detectors E, ..„E are transmitted on the radio channel. The data of frequency f serially transmitted via the filter 204 and

3. the pulse shaper 206 are passed to the first output of the demultiplexing unit 207. The data are received in the first compartment or location of the decoding and storing unit 209 where the serially transmitted data is converted in parallel and stored in a decoded form.

After the arrival of the first data series, a signal of frequency f, arrives from the detecting and sensing device 100 which is passed via filter 205 and pulse shaper 208 to the control input of the demultiplexing unit 207 and causes the latter to be shifted by one. The next series of data then passes via the demultiplexing unit 207 and is written into the second compartment or location of the decoding and storing unit 209. This proces continues until the arrival of the last series of data while the decoding and storing unit 209 contains in its individual compartments or locations the number of hits collected in the target belonging to the first line or depth. The operating unit 212 now gives an enabling signal to the group D. , hence the data available on the output bus 210 actuates only the display units of the group D. on which then a number of hits detected by the associated sensors is displayed in order _*

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The reading out of the next line or depth takes place in a similar manner but is started by depressing the key B ₂ . The frequency signal of the generator G* _j actuates the reading-out of the store or register unit of the second line via the radio channel. The process is repeated but now the data of the output bus 210 can be seen on the display indicators of the second group D„ because the group D„ receives an enabling signal.

From the above example it can be seen that the apparatus according to the invention has a simple electroni construction, can collect and indicate the number of hits for each target figure and for all this it requires only one radio or other transmission channel. From this it follows that the erection on site of the apparatus accordin to the invention is extremely simple.

It may be seen that in addition to the specific embodiments described above by way of example, a man skilled in the art could produce numerous other similarly operating variants and hence the invention is not restric- ted to any one of the described or illustrated preferred embodiment .