GB1605023A

GB1605023A - Contact sensor devices

Info

Publication number: GB1605023A
Application number: GB4135176A
Authority: GB
Original assignee: Dynamit Nobel AG
Current assignee: Dynamit Nobel AG
Priority date: 1977-02-05
Filing date: 1977-02-05
Publication date: 1981-12-16

Description

(54) IMPROVEMENTS IN OR RELATING TO CONTACT SENSOR DEVICES (71) We, DYNAMIT NOBEL AKTIENGESELLSCHAFT, a Germany company, of 521 Troisdorf, Near Cologne, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a contact sensor device, more particularly a sensor device for monitoring terrain for the presence of objects having certain specified properties, which comprise an elongate sensor member to be laid on the terrain to be monitored.

With one type of metallic sensor which is known, the sensor reacts to the proximity of a metallic or non-metallic object and accordingly emits electric signals, without making physical contact with the object. A disadvantage of such sensors is that they also usually react to metallic objects travelling past them laterally, and in this case it is not certain that an explosive charge to be fired on receipt of the electric signals will be reliably actuated, because this charge is only intended to be effective with certainty when covered by the target.

Anti-tank weapons may comprise contact sensors in the form of so-called "buckle fuses". These fuses are activated when run-over by an armoured vehicle, the wheels, tracks or other parts of which buckle a particular switching portion and cause a switching operation to take place. In addition, compression fuses are known, which are activated only by the pressure of the wheels or tracks of the target running directly over them and hence closure of an electric circuit whereby detonation of an explosive charge occurs takes place only when the fuse is suitably aligned with the wheels or tracks of a vehicle running thereover.

According to the present invention, there is provided a contact sensor device for monitoring the presence of objects travelling over terrain, the device comprising an elongate sensor member which is either straight or includes a curved portion and which is suitable to be laid on the ground and an electric response circuit including a vibration-receiving or oscillation producing member in contact with said sensor member or contactable by said sensor member when the sensor member is contacted by a said object, which vibration-receiving or oscillation producing member is adapted respectively to produce electrical oscillations in said circuit in response to vibrations received, in use, from said sensor member, said sensor member being responsive to vibrations set up therein by a said object travelling thereover, but not to ground vibrations or to produce continuously an electric oscillation of substantially unform amplitude which is altered when said sensor member is contacted by a said object, whereby, in use, when the sensor member is contacted by a said object, electrical signals are set up in the response circuit to produce a predetermined response in actuable means operatively associated with the contact sensor device in use thereof.

Although the sensor member will usually be in the form of a wire, it is not essential that it should be formed of metal. Only in certain sensors embodying this invention and to be described hereinafter, is it essential for the sensor member to be formed of metal.

Thus the material of the sensor member is not critical when the sensor member is, according to one embodiment of the invention, adapted to transmit, in use, mechanical vibrations to oscillation-producing means for reproducing the vibrations in the form of an electric current supplied to the response circuit. The sensor member need not necessarily be a metal wire, and may be any kind of member which is capable of taking up and transmitting mechanical oscillations such as those exerted, for example, by a rolling tracked or wheeled vehicle on contact therewith. However, a sensor wire is to be preferred because it can be so fine that it is difficult to perceive.

If such a sensor wire is run over by a tank or other armoured vehicle, a continuous scraping contact is set up, which is transmitted in the form of mechanical vibrations to the transducer. These oscillations are further processed by the electric response circuit connected on to the output side of the transducer so as to produce a firing signal.

The sensor device may comprise a piezoelectric transducer, in which case the piezo-element to which a sensor wire is connected is preferably in the form of a disc, a flexural oscillator, or a thin pipe or tube through which passes the sensor member in contact with the inner surface thereof. The electrodes of the piezo-element are then connected to the electric response circuit.

The type of piezo-element to be employed in each instance will depend essentially upon the mode of vibration set up in the sensor wire. The choice will therefore be made in accordance with the practical requirements in each instance. The use of a piezo-element generally has the advantage of a simple construction and small dimensions. In addition, it is unnecessary for a source of energy to be provided for the sensor wire or the transducer.

When the device embodying this invention is actuated by mechanical vibrations the electric response circuit preferably comprises a frequency filter which is attuned to the mechanical vibration frequency of the sensor member.

With a second general class of contact sensor device embodying this invention, the sensor member is made of metal and is a component part of the inductance or of the capacitance of an oscillator the oscillation frequency and/or damping of which is variable on contact of the sensor member with a metal object. The parts of the oscillator other than the sensor member preferably possess a monolithic construction.

In this case, the sensor member may be constructed as a closed induction wire loop, or it can be connected at one end to a winding which is connected by means of an electric conductor to the remaining component parts of the oscillator to which the other end of the sensor member is connected.

This latter type of contact sensor device may alternatively be constructed as an oscillator-capacitor whose capacitance varies on contacting thereof of a metal object.

The variations of inductance and capacitance with the latter type of sensor device result in each instance in a variation of the oscillation frequency and/or the damping, which is detected in the subsequent evaluating circuit and where necessary results in the initiation of an ignition operation, as with an anti-tank mine or of a switching operation with an arrangement for which monitoring by the contact device has been effected.

Various types of contact sensor devices embodying the invention can be combined with one another if it is desired to detect a number of properties of a target or to ensure that ignition of an explosive charge for example, takes place. Thus, for example, a piezo-element may be connected to a sensor wire, which is a component part of an electric oscillator. The piezo-element reacts to mechanical oscillations and indicates a continuous scraping contact, while detuning of the oscillator indicates the presence of a metal object. Both criteria can be evaluated in an AND circuit whose output signal indicates that the prequisites for the initiation of the igniting action are satisfied. The contact device would then be safe against the stepping thereon of personnel, but could be used in the destruction of tanks.On the other hand, it is also possible to combine the outputs of a number of such contact sensors in an OR gate in order to bring about the ignition when at least one of a number of criteria is satisfied.

For a better understanding of the invention, and to show how the same can be carried into effect reference will now be made, by way of example only, to the accompanying drawings, in which: Figures 1 to 3 each show in cross-section the construction of different types of a piezo-electric contact sensor embodying the present invention Figure 4 diagrammatically illustrates an inductive contact sensor comprising an inductance concentrated at the end of a sensor wire; Figure 5 illustrates an inductive contact sensor in which the sensor wire is constructed as an induction loop; and Figure 6 illustrates a combination of the contact sensors of Figures 3 and 5.

Referring to Figures 1 to 3 of the drawings, the piezo-electric contact sensors shown therein comprise, in each instance, a thin sensor wire 10. one end of which terminates freely, while its other end is connected to a piezo-electric transducer 11.

12, 13 in Figures 1, 2 and 3 respectively.

Two signal conductors 14 extend in each instance from the piezo-electric transducer to a sequentially connected electric response circuit (not shown), which is acted on by the oscillations produced by the piezo-electric transducer which last for a predetermined time and causes firing of an explosive charge when a predetermined amplitude value is exceeded.

In the form of construction shown in Figure 1, the contact sensor 10 is connected to an oscillating diaphragm 15 which forms a closure for a housing 16 containing a piezoelement 17 embedded in a sealing composition 18, for example an epoxy resin. The electrical terminal connecting members are constituted by the conductors 14.

When longitudinal vibrators of oscillations are set up in the sensor wire 10, they are transmitted through the diaphragm 15 to the piezo-element 17 and converted into electrical oscillations. The latter are passed on to the response circuit through the signal conductors 14.

With the piezoelectric oscillator illustrated in Figure 2, flexural oscillations are produced in the sensor wire 10 by the scraping thereover of a vehicle. The piezoelement 12 is attached to one end of the sensor wire and extends in the longitudinal direction thereof. The piezo-element converts the oscillations into voltage signals and passes them on through the signal conductors 14. One of the signal conductors 14 is here directly connected to the sensor wire 10.

With the constructional form of piezoelectric contact sensor illustrated in Figure 3, the piezoelectric transducer 13 consists of a narrow pipe or tube which is pushed over one end othe sensor wire 10.

Here again, a fixed mechanical contact exists between the pipe or tube and the sensor wire, so that the vibrations set up in the sensor wire are converted into electrical oscillations and passed on through the conductors 14.

Referring next to Figure 4, there is shown an inductive contact sensor which comprises an insulated or non-metal insulated sensor wire 20, one end of which is connected to an oscillator circuit 21, while the other end of which is connected to an inductance in the form of a coil 22. The sensor wire 20 is connected to one end of the coil 22, the other end of which is connected to the oscillator circuit 21 through an insulated conductor 23.

The oscillator circuit 21 is tuned to a particular frequency at which the oscillator oscillates in the inoperative state. When the sensor wire 20 connected to the inductance 22 comes into contact with a metal object, the oscillator is damped or detuned as a whole, so that the oscillation frequency varies. The frequency change or the amplitude change of the oscillation of the oscillator is detected in an evaluating circuit connected to oscillator conductors 24 connected to the oscillator circuit 21 and a signal is emitted for performing a switching action or for firing a mine.

Again in the constructional form of contact sensor shown in Figure 5, the contact of the sensor wire with a metal object is inductively detected. The sensor wire 25 is here laid in the form of an elongate loop having its loop arms relatively close together and possessing a known inductance. The two ends of the loop are connected to an oscillator 26. When a metal object touches the sensor wire 25, the frequency and/or the amplitude of the oscillator 26 is again varied. The variation is transmitted through conductors 27 to an evaluating circuit, which reacts in the manner already explained with reference to Figure 4.

The above-described types of sensor arrangement may be combined to form multi-component sensors with AND or OR action for particular tasks. One such type of combination is illustrated in Figure 6 to which reference is finally made. In Figure 6 there is shown a sensor wire 25 which is laid in the form of a loop in manner shown in Figure 5 and which is connected to an oscillator circuit 26. The output conductors 27 from the oscillator circuit 26 lead to one input of an AND gate 28.

Attached to one arm of the loop of the sensor wire 25 is a piezo-electric transducer 13 in the form of a pipe or tube as shown in Figure 3 and which responds to continuous scraping contact of the sensor wire 25 and whose output conductors 14 are led to the second input of the AND gate 28.

A firing signal is set up at the output 29 of the AND gate only when 1) a metallic object touches the sensor wire 25, and 2) a continuous scraping contact of the metallic object on the sensor wire takes place.

Only when these two criteria are satisfied is the firing initiated.

Whilst military applications have been referred to above for the sensor devices, such applications are merely illustrative and civil applications are possible, for example in monitoring or in alarm systems in buildings.

The circuits shown in Figures 4 to 6 can be varied by providing for variation of the capacitance of an oscillator due to contact with the induction loop 25 to be varied and hence provide the required switching or firing action.

Reference is made to United Kingdom Patent Specification No. 634,804 which describes an arrangement for indicating the passage of an aircraft or vehicle along a road comprising vibration responsive means in the form of, for example, a crystal microphone in vibration transferring contact with the road. The response of such a microphone is subsequently used. The signals to the microphone may be transmitted along a rod which may be on the surface of the road and be clamped thereto. Such a rod will transmit both vibrations resulting from the contacting thereof by a vehicle and vibrations of vehicles in the proximity thereof.

Moreover, reference is made to United Kingdom Patent Specification No.

1,387,523 wherein there is described an airoperafed piezo-electric generator for use in the nose part of a projectile, the generator comprising a housing having a cavity therein, an air inlet to the cavity and an air outlet therefrom and a flexible tongue member in the cavity to be vibrated by air passing therethrough and connected to a piezoelectric element which receives its vibrations.

WHAT WE CLAIM IS: 1. A contact sensor device for monitoring the presence of objects travelling over terrain, the device comprising an elongate sensor member which is either straight or includes a curved portion and which is suitable to be laid on the ground and an electric response circuit including a vibration-receiving or oscillation producing member in contact with said sensor member or contactable by said sensor member when the sensor member is contacted by a said object, which vibration-receiving or oscillation producing member is adapted respectively to produce electrical oscillations in said circuit in response to vibrations received, in use, from said sensor member, said sensor member being responsive to vibrations set up therein by a said object travelling thereover but not to ground vibrations or to produce continuously an electric oscillation of substantially uniform amplitude which is altered when said sensor member is contacted by a said object, whereby, in use, when the sensor member is contacted by a said object, electrical signals are set up in the response circuit to produce a predetermined response in actuable means operatively associated with the contact sensor device in use thereof.

2. A device as claimed in claim 1, wherein the sensor member is a sensor wire.

3. A device as claimed in claim 1 or 2, wherein the sensor member is adapted to transmit, in use, mechanical vibrations and said oscillation-producing means is a piezoelectric transducer for reproducing the mechanical vibrations from the sensor member in the form of an electric current supplied, in use, to said response circuit.

4. A device as claimed in claim 3, wherein the piezoelectric transducer is in the form of a disc.

5. A device as claimed in claim 3, wherein the piezoelectric transducer is in the form of a flexural oscillator comprising a member adapted to flex in accordance with mechanical vibrations in the sensor member, and act on a piezo-element to produce said electric oscillations therein.

6. A device as claimed in claim 3, wherein the piezoelectric transducer is in the form of a pipe or tube through which passes the sensor member in contact with the inner surface thereof.

7. A device as claimed in any one of claims 3 to 6, in which the electric response circuit comprises a frequency filter which is attuned to the mechanical vibration frequency of the sensor member.

8. A device as claimed in claim 2 or any one of claims 2 to 7 when appended to claim 2, in which the sensor member is metal and is a component part of the inductance or of the capacitance of an oscillator the oscillation frequency and/or dampping of which is variable on contact of the sensor member with a metal object.

9. A device as claimed in claim 8, in which the parts of the oscillator other than the sensor member possess a monolithic construction.

10. A device as claimed in claim 8 or 9, in which the sensor element is in the form of a closed wire loop.

11. A device as claimed in claim 8 or 9, in which the sensor member is connected at one end to a winding which is connected through an electric conductor to the remaining component parts of the oscillator to which the other end of the sensor member is connected.

12. A device as claimed in claim 8 or 9, in which the sensor member is constructed as an oscillator-capacitor whose capacitance is variable on the contacting thereof of a metal object.

13. A device as claimed in any one of claims 8 to 12, wherein the sensor member is metal, adapted to transmit, in use, mechanical vibrations and connected to a piezoelectric transducer for reproducing mechanical vibrations from the sensor member in the form of an electric current supplied, in use, to said response circuit, while forming part of the inductance or of the capacitance of an oscillator the oscillation frequency and/or damping of which is variable on contact of the sensor member with a metal object.

14. A device as claimed in claim 13, in which the outputs of the piezoelectric transducer and of the oscillator are connected to inputs to an AND circuit or an OR gate having an output connected to a said electric response circuit.

15. A contact sensor device as claimed in claim 1, substantially as hereinbefore described with reference to any figure of the acompanying drawings.

16. An anti-tank mine which comprises a contact sensor device as claimed in any one of the preceding claims.

17. A method of monitoring the pre

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the road and be clamped thereto. Such a rod will transmit both vibrations resulting from the contacting thereof by a vehicle and vibrations of vehicles in the proximity thereof. Moreover, reference is made to United Kingdom Patent Specification No. 1,387,523 wherein there is described an airoperafed piezo-electric generator for use in the nose part of a projectile, the generator comprising a housing having a cavity therein, an air inlet to the cavity and an air outlet therefrom and a flexible tongue member in the cavity to be vibrated by air passing therethrough and connected to a piezoelectric element which receives its vibrations. WHAT WE CLAIM IS:

1. A contact sensor device for monitoring the presence of objects travelling over terrain, the device comprising an elongate sensor member which is either straight or includes a curved portion and which is suitable to be laid on the ground and an electric response circuit including a vibration-receiving or oscillation producing member in contact with said sensor member or contactable by said sensor member when the sensor member is contacted by a said object, which vibration-receiving or oscillation producing member is adapted respectively to produce electrical oscillations in said circuit in response to vibrations received, in use, from said sensor member, said sensor member being responsive to vibrations set up therein by a said object travelling thereover but not to ground vibrations or to produce continuously an electric oscillation of substantially uniform amplitude which is altered when said sensor member is contacted by a said object, whereby, in use, when the sensor member is contacted by a said object, electrical signals are set up in the response circuit to produce a predetermined response in actuable means operatively associated with the contact sensor device in use thereof.

2. A device as claimed in claim 1, wherein the sensor member is a sensor wire.

17. A method of monitoring the pre

sence of objects travelling over terrain, which comprises employing for said monitoring a contact sensor device as claimed in any one of claims 1 to 15 with the sensor member disposed on the terrain.