EP1341137A1

EP1341137A1 - A security system, particularly for property surveillance, and a sensor

Info

Publication number: EP1341137A1
Application number: EP03075320A
Authority: EP
Inventors: Giorgio Tonelli; Aldo Tonelli
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-02-18
Filing date: 2003-02-03
Publication date: 2003-09-03
Anticipated expiration: 2023-02-03
Also published as: ITMI20020318A1; ES2240909T3; IL154347A; SI1341137T1; ITMI20020318A0; ATE292834T1; DE60300463T2; DE60300463D1; EP1341137B1

Abstract

A security system particularly for property surveillance, to be associated with a guard structure (1) that may be subjected to bending forces. The system is provided with at least one sensor (6) for detecting deflections of the structure resulting from the forces. The sensor (6) comprises a substantially plate-shaped piezoelectric transducer (10) such as to convert mechanical stresses into electrical signals and a container (40) for the transducer (10), which container (40) can be fixed to the guard structure. The container (40) is such as to deform resiliently as a result of the bending forces and to transmit the deflections of the structure to the transducer (10) so that they give rise to corresponding electrical detection signals.

Description

The present invention relates to security systems, particularly for property surveillance. The present invention also relates to a sensor usable in such security systems.
As is known, for some time there has been a need for surveillance of property boundaries and immediate signalling of any intrusion by a stranger into an area to be protected or, similarly, of an attempt to escape therefrom, by the appropriate issue of warnings.
Security systems known as buried barrier systems are known and are widely used; these systems use sensors of various types which are intended to be located in the ground or under flooring or paving and along the boundary of the property to be protected, in order to detect footsteps due to crossing of the boundary.
Amongst these systems, systems based on pressure or seismic sensors, for example, so-called "buried tube" systems or "microphone-cable" installations are very widespread.
There are also complex and expensive installations which use buried coaxial cables or optical fibres to detect footsteps on the boundary which delimits the area subject to surveillance.
It has been found that security systems based on sensors located in the ground may be subject to interference or rendered inactive by adverse environmental conditions such as, for example, heavy rain, snow, or the presence of ice. In other cases, vibrations of the ground caused by the passing of vehicles in the vicinity of the areas to be protected may cause incorrect activation of these systems, giving rise to inappropriate warnings.
Moreover, the use of buried sensors renders installation, maintenance and repair operations in the event of damage particularly complex and expensive.
Amongst the security systems that are currently in use, there are some which do not use buried sensors but which use microwave or infra-red ray barriers. These systems are not suitable for surveillance in open spaces because they are particularly sensitive to atmospheric phenomena, for example, to fog or to the passing of even small animals.
The object of the present invention is to provide a security system which does not have the disadvantages of the above-described systems of the prior art.
This object is achieved by a security system as described in the first claim. A further subject of the present invention is a sensor usable in security systems, as described in Claim 12.
Further characteristics and the advantages of the invention will be understood better from the following detailed description of preferred embodiments thereof, which is given by way of non-limiting example with reference to the appended drawings, in which:
Figure 1 is a schematic plan view of a property delimited by a boundary guard structure,
Figure 2 shows schematically a particular security system according to the invention,
Figure 3 shows an enlarged detail of the security system of Figure 2,
Figure 4 shows a particular embodiment of a sensor according to the invention schematically and in lateral section, with parts separated, and
Figure 5 shows schematically some stages of the operation of the sensor of Figure 4.
A preferred embodiment of a security system SEC-ST according to the invention is described with reference to Figures 1, 2 and 3. In particular, this system is provided for the surveillance of a guard structure 1 of an area 2 in which a dwelling 3 is disposed.
The guard structure 1 is, for example, a fence in the open, composed of a plurality of grills 4, typically metal grills, supported by posts 5 or by other suitable support or holding elements. The support elements have the function of fixing the fence firmly to masonry structures such as, for example, small walls, or to the ground.
In this connection, it is pointed out that the teachings of the present invention are applicable to guard structures of types other than the particular fence referred to in the present description.
In fact, the security system of the invention may be provided for the surveillance of only one side of a property to be protected, or the guard structure 1 may comprise a suitable wire-netting boundary fence supported by stakes, or protective panels made of suitable material.
In another variant, the guard structure 1 may comprise one or more bars or grills installed in openings in the walls of the dwelling 3, for example in doors or windows.
The security system SEC-ST of the invention is particularly suitable for detecting and signalling intrusions or attempted intrusions into the protected property 2.
In the embodiment described, the security system SEC-ST comprises one or more sensors 6, control and supply lines 7 for the sensors, electronic processing means 8, and warning signalling means, the latter being of conventional type and not shown in the drawings.
As shown in Figure 3, the sensors 6 are fitted on posts 5 of the grilles 4, which posts 5 are fixed firmly to a base B. Each of the sensors 6 comprises a respective plate-shaped piezoelectric transducer and can generate electrical signals which are made available on the lines 7, in order to detect deflections (or, in other words, deformations) of the posts 5 due, according to the embodiment described, to attempted intrusions.
A preferred embodiment of the sensors 6 will be described in greater detail below.
As shown schematically in Figure 2, the particular security system of the embodiment described divides the perimeter of the guard structure 1, from a logic point of view, into one or more sections 9, each including at least one sensor 6.
In the embodiment described, the perimeter of the fence 1 is divided into eight sections 9, each of which defines a region subject to surveillance, with which three sensors 6 are associated.
The sensors 6 within the same section 9 are suitably connected, by means of the lines 7, to the electronic processing means 8 which is formed, for example, by an electronic analysis and control card 8 of conventional type.
The lines 7 are, for example, conventional electrical wires which enable the signals generated by the sensors 6 to be transferred towards the electronic analysis card 8.
The electronic analysis card 8, which is preferably digital, has the purpose of receiving the electrical signals emitted by the sensors 6 and processing them. This card 8 is also provided with suitable stages for amplifying and filtering the signals received. The card 8 is also arranged to activate warning-signalling means. The electronic card 8 may also advantageously perform functions for the control and monitoring of the state of the security system.
Anyone attempting an intrusion into the property 2 by trying to clamber over the fence 1 by climbing it directly or with the aid of a ladder is forced to establish physical contact with the fence.
The posts 5 which support the fence are thus subjected to a bending force (or stress) due to the contact with the intruder and to his weight, which gives rise to oscillations. The deflections (that is, the mechanical deformations) of the fence 1 or, more precisely, of the posts 5, are detected by one or more sensors 6 of one or more sections 9, which transmit one or more electrical detection signals to the analysis card 8.
The card 8 receives these signals and after filtering and amplifying them suitably, establishes, on the basis of their nature, whether an attempted intrusion is in progress, consequently activating the warning means.
These warning means produce a local warning signal (for example, an image which can be displayed on a monitor of a control station, sirens or flashing lights) or send the warning signal to a remote control station, for example, by means of a telephonic dialling device or a radio bridge. The logic division into sections 9 enables the card 8 to locate any region of the fence under surveillance that is affected by the intrusion.
It is pointed out that extreme atmospheric conditions such as, for example, strong wind, may cause oscillations or deflections of the fence structure 1, but the electrical signal generated by the sensors 6 in these situations have different characteristics from those relating to intrusion and can therefore be ignored correctly by the control station. For example, the card 8 may analyze the frequency of the signals received, assessing whether it belongs to a frequency band typical of intrusion (typically up to 20 Hz) or of an attempt to break in.
It should be noted that the sensor 6 can detect oscillations of the elements of the guard structure 1 up to very high frequencies. The card 8 advantageously has the task of filtering the electrical signals generated by the sensors 6 so that only the signals with frequencies typical of intrusion attempts are actually processed/analyzed.
In this connection, the structure of the sensors 6 and the electronic card 8 make the security system SEC-ST of the invention particularly suitable for detecting intrusions, for which the corresponding oscillations of an element of the guard structure 1 such as, for example, the post 5 have frequencies of less than 20 Hz. According to a particularly advantageous embodiment, the security system SEC-ST is suitable for detecting intrusions which cause oscillations at frequencies of less than 10 Hz. In particular, the security system SEC-ST permits the detection of intrusions which cause oscillations at very low frequencies, that is, of less than 5 Hz.
The system according to the present invention can advantageously also detect attempts to force/break the guard structure 1. Even if the use of tools of various types, such as, for example, hacksaws or shears, does not bring about actual deflections of the structure 1, it nevertheless causes vibrations which can be picked up by the sensor 6. These vibrations typically have frequencies of between 500 Hz and 10 kHz. For this reason, in a preferred embodiment, the electronic card 8 analyzes the electrical signals generated by the sensors 6 in a window of frequencies suitable for detecting breaking attempts (500 Hz - 10 kHz) as well as in the band specified for intrusion attempts (frequencies below 20 Hz).
In order to discriminate an intrusion/breaking attempt from other causes of oscillations of the guard structure 1, the electronic card 8 may suitably correlate the electrical signals coming from a sensor or from a section with those coming from adjacent sensors or sections.
A preferred embodiment of a sensor 6 usable in the security system of the type described above will now be described with reference to Figure 4.
The sensor 6 according to the present invention comprises a substantially plate-shaped piezoelectric transducer 10 disposed in a container 40 comprising a base 12 and a cover 11.
The plate-shaped piezoelectric transducer 10 is, for example, in the form of a disc, and comprises a plate 21 of conductive material, for example, brass or copper, covered by a thin piezoelectric ceramic layer 22. In the embodiment of Figure 4, the plate 21 has a larger diameter and a greater thickness than the covering ceramic layer 22.
Respective conductive wires 24, 23 extend from the transducer 10, more precisely, from the plate 21 and from the layer 22, and emerge from the container 40 of the sensor 6. These conductive wires 23 and 24 may be suitably connected to the line 7 of the above-described security system.
By virtue of the piezoelectric properties of the ceramic layer 22, the transducer 10 enables deformations, vibrations, and mechanical stresses to which it is subjected to be converted into detectable electrical signals (for example, pulsed signals) on the wires 23 and 24.
Plate-shaped piezoelectric transducers of the type described above are known and, for example, a transducer of this type is produced and marketed by Murata Manufacturing Co., Ltd.
The container 40 of the sensor 6 can be fixed to the post 5 of the guard structure 1 and is such as to deform resiliently as a result of the bending forces to which the post 5 is subjected in order to transmit the deflections of the post to the transducer 10 so that the deflections can give rise to electrical detection signals.
In particular, the base 12 and the cover 11 that can be fixed thereto are made of suitable plastics material such as, for example, ABS (acrylonitrile butadiene styrene), Teflon, Plexiglas, nylon, or PVC (polyvinyl chloride).
The base 12 comprises a first, upper cavity or chamber 13, for example, a cylindrical chamber for housing the piezoelectric transducer 10. The base 12 also comprises a second, lower cavity or chamber 14, for example, a cylindrical chamber, which opens in the upper chamber 13. In the particular embodiment of Figure 4, the lower chamber 14 is coaxial with the upper chamber 13 but has a smaller diameter.
The upper chamber and the lower chamber 14 define a stepped wall 15 provided with an annular abutment rim 19 for the piezoelectric transducer 10.
In an assembled configuration of the sensor 6, the piezoelectric transducer 10 is intended to bear on the annular rim 19 and, in the absence of bending forces or mechanical stresses, the transducer 10 lies on an imaginary rest surface.
Moreover, the sensor 6 comprises a rigid hollow cylinder 18 provided with an annular rim 19'. The cylinder 18 is interposed between the cover 11 and the base 12. The annular rim 19' is intended to rest and bear on peripheral regions of a face of the piezoelectric transducer 10 that faces the cover 11. According to the embodiment of Figure 4, the cylinder 18 is intended to bear on peripheral regions of the plate 21 of the piezoelectric transducer 10 so as not to touch the ceramic layer 22.
Once the cover 11 has been fixed to the base 12, it clamps the hollow cylinder 18 so that the piezoelectric transducer 10 is fitted firmly and rigidly, around its periphery, between the abutment rim 19 and the annular rim 19' of the cylinder 18. In a different embodiment, the cylinder 18 could be, for example, part of the cover 11.
It should be noted that the cylindrical body 18 and the annular rim 19 constitute only a preferred embodiment of rigid clamping means that can be used to secure the piezoelectric transducer 10 in the upper cavity 13 of the container 40. The rigid clamping means may bear on the entire periphery of the plate-shaped transducer 10 or only on some regions, preferably peripheral regions, of the transducer.
The cylindrical body 18 and the annular rim 19 or other clamping means equivalent thereto advantageously enable the transducer 10 to be fixed to the container 40 in a manner such that the transducer can be deflected in two opposite directions relative to the rest surface. The ability to be deflected in opposite directions relative to the rest surface is particularly advantageous since it enables the transducer 20 to detect bending forces resulting from intrusion and having opposite directions and to generate electrical detection signals as a result of deflections of the post 5 in opposite directions.
Moreover, the sensor 6 is advantageously provided with contact means interposed between the container 40 and the transducer 10 in order to exert a force on at least one region of the transducer 10 during the exertion of bending forces.
These contact means may preferably comprise a first protuberance 17, for example a cylindrical protuberance which extends from a wall of the cover 11 and is intended to contact a first face of the plate-shaped transducer 10. In Figure 4, the first cylindrical protuberance 17 contacts the ceramic layer 22 in a central region thereof, in the assembled configuration of the sensor. The sensor 6 advantageously also comprises a second protuberance 16, for example a cylindrical protuberance which extends from a base wall of the lower chamber 14 and is intended to come into contact with a second face of the plate-shaped transducer 10, remote from the first. In Figure 4, the second cylindrical protuberance 16 contacts the plate 21 in a central region thereof.
According to a particular embodiment, the sensor 6 also comprises a protective material 20 disposed in the upper chamber 13. In particular, this material is a resin 20 which almost completely fills the upper chamber 13. For example, the resin 20 is a two-part epoxy resin of known type. A particular resin usable in the sensor 6 is marketed, for example, by CAFARELLI RESINS Co. S.n.c., Montescudaio, Pisa, Italy.
This resin 20 performs a sealing action, preventing the formation of oxide on a face of the piezoelectric transducer 10 due to possible infiltrations of moisture from the exterior or to internal condensation caused by thermal variations.
The resin 20 advantageously has an additional function which consists of the transmission of the bending forces resulting from the deformation of the container 40 to the transducer 10, without absorbing them.
In the above-described security system SEC-ST, the sensor 6 is advantageously fitted substantially on a region of maximum deformability of the element of the guard structure 1, for example, in the embodiment described, in the vicinity of the base B of the post 5. The sensor 6 can be fixed firmly to the post 5 by fixing means 25 such as, for example, screws.
The operation of the sensor 6 when used in the security system SEC-ST will be described with reference to Figure 5.
Attempts to climb over or dismantle the guard structure, etc., produce bending forces, possibly in opposite directions, indicated by arrows 27 and 28 in Figure 5, such as to cause deflection and/or oscillation of one or more posts 5.
The line of the rest surface 26 (in the specific case, a rest plane) defined by the plate-shaped transducer 10 in the absence of mechanical stresses is shown in Figure 5. This line of the rest plane 26 is parallel to a longitudinal axis V-V' of the post 5 which separates the plane of Figure 5 into a right-hand half-plane R and a left-hand half-plane L.
As result of the deflections of the post 5, the container 40 is also deformed and deflected. The container 40 thus transmits the deflections of the post 5 to the piezoelectric transducer 10 which in turn is deflected.
It is pointed out that, by virtue of the clamping action of the cylinder 18 and of the abutment rim 19 shown in Figure 4, the piezoelectric transducer 10 is deflected relative to the rest plane 26 both under the effect of the force 27 and under the effect of the force 28 in the opposite direction.
Figure 5 shows the piezoelectric transducer 10 schematically in two different deflected or deformed configurations (emphasized for greater clarity) indicated 10-R and 10-L, corresponding to the effects of the forces 27 and 28, respectively.
Under the effect of the force 27 (which causes a deflection of the post 5 towards the half-plane R), the piezoelectric transducer is deflected so as to have a concavity facing towards the right-hand half-plane R (configuration 10-R). Conversely, under the effect of the stress 28 (which causes the post 5 to bend towards the half-plane L), the piezoelectric transducer bends so as to have a concavity facing towards the left-hand half-plane L (configuration 10-L).
Moreover, when the piezoelectric transducer is in the 10-R (10-L) configuration, the second (first) protuberance 16 (17) exerts a force on the central region of the plate (ceramic layer) 21 (22).
This force exerted on the piezoelectric transducer 10 significantly increases the magnitude of the mechanical stress undergone by the transducer in comparison with the deformation purely due to the deflection. Moreover, each protuberance 16 or 17 produces an improved and more even distribution of the external bending forces inside the transducer 10, rendering the deformation of the piezoelectric transducer 10 more uniform.
The deflection and/or the deformation as a whole undergone by the transducer 10 leads, by the piezoelectric effect, to the generation of one or more electrical detection signals which are made available on the conductive wires 23 and 24. In particular, the piezoelectric transducer 10 generates voltage pulses of opposite polarities according to whether the deflection took place in one direction or in the other. For example, the piezoelectric transducer 10 generates electrical voltage pulses no greater than about 500 mV.
It is pointed out that it is not strictly necessary for the piezoelectric transducer 10 to be clamped to the container 40 around its entire periphery but it would in fact suffice to clamp it at at least two points disposed substantially opposite one another with respect to the centre of the plate-shaped transducer 10 and on a diameter substantially parallel to the longitudinal axis V-V' of the post 5.
The invention described permits the production of particularly reliable security systems for detecting and signalling intrusion attempts.
The security system of the invention is almost insensitive to external environmental conditions. In particular, the system has been found to be completely insensitive to hailstorms, which represents a critical aspect of many known boundary protection systems.
Moreover, the fitting of these systems can take place on guard structures which are already installed and does not require sensors or other detection apparatus to be buried. A sensor can therefore also be replaced quickly and readily.
It is pointed out that, as well as detecting climbing of fences, the system of the invention is also effective in signalling breaking, escape, or dismantling attempts performed on guard structures in a more general sense.
Naturally, in order to satisfy contingent and specific requirements, a person skilled in the art may apply to the above-described security system and sensor many modifications and variations all of which, however, are included within the scope of protection of the invention as defined by the appended claims.

Claims

A security system (SEC-ST) particularly for property surveillance, to be associated with at least one element (5) of a guard structure (1) that may be subjected to bending forces, the system comprising:

at least one sensor (6) for detecting deflections of the element (5) resulting from the forces, the sensor comprising:

a substantially plate-shaped piezoelectric transducer (10) such as to convert mechanical stresses into electrical signals,

a container (40) for the transducer (10), which container (40) can be fixed to the element (5) of the guard structure, the container (11, 12) being such as to deform resiliently as a result of the bending forces and to transmit the deflections of the element to the transducer (10) so as to give rise to corresponding electrical detection signals, and

electronic processing means (8) connected to the sensor (6) for receiving and processing the electrical detection signals.
A system (SEC-ST) according to Claim 1 in which, in the absence of bending forces, the transducer (10) lies in a rest plane (26), and in which the sensor (6) further comprises rigid clamping means (18, 19) for fixing the transducer (10) to the container (40) in a manner such that the transducer can be deflected in two opposite directions relative to the rest plane (26).
A system (SEC-ST) according to Claim 2 in which the clamping means (18, 19) are such as to fix the transducer (10) in a cavity (13) inside the container (40).
A system (SEC-ST) according to Claim 1 in which the sensor (6) is intended to be fitted substantially in a region of maximum deformation of the element (5).
A system (SEC-ST) according to Claim 1, comprising a plurality of sensors (6) subdivided into sections (9) each corresponding to a respective region under surveillance.
A system (SEC-ST) according to Claim 1, further comprising warning signalling means connected to the processing means (8), the processing means bringing about activation of the warning signalling means on the basis of the electrical detection signals.
A system (SEC-ST) according to Claim 1 in which the processing means (8) comprise an amplification stage and a filtering stage for the electrical detection signals.
A system (SEC-ST) according to Claim 7 such as to detect oscillations of the element (5) having frequencies of less than 20 Hz.
A system (SEC-ST) according to Claim 8 such as to detect oscillations of the element (5) having frequencies of less than 5 Hz.
A system (SEC-ST) according to Claim 7 such as to detect vibrations of the element (5) having frequencies of between 500 Hz and 10 kHz.
A system (SEC-ST) according to Claim 1 in which the guard structure (1) is at least of a type belonging to the group comprising: a plurality of metal grills, a wire netting supported by support posts, a boundary fence.
A sensor (6) usable in security systems (SEC-ST) to detect deflections of an element (5) of a guard structure (1) that may be subjected to bending forces, the sensor (6) comprising:

a substantially plate-shaped piezoelectric transducer (10) such as to convert mechanical stresses into electrical signals, and

a container (40) for the transducer (10), which container (40) can be fixed to the element (5) of the guard structure, the container (11, 12) being such as to deform resiliently as a result of the bending forces and to transmit the deflections of the element to the transducer (10) so as to give rise to corresponding electrical detection signals.
A sensor (6) according to Claim 12 in which, in the absence of bending forces, the transducer (10) lies in a rest plane (26), the sensor (6) further comprising rigid clamping means (18, 19) for fixing the transducer (10) to the container (40) in a manner such that the transducer can be deflected in two opposite directions relative to the rest plane (26).
A sensor (6) according to Claim 13 in which the rigid clamping means (18, 19) bear on peripheral regions of the transducer (10).
A sensor (6) according to Claim 13 in which the rigid clamping means (18, 19) bear on the entire periphery of the transducer (10).
A sensor (6) according to Claim 12 in which the container (40) comprises a base (12) and a cover (11) that can be fixed to the base.
A sensor (6) according to Claim 16 in which the base (12) comprises a cavity (13) for housing the transducer (10).
A sensor (6) according to Claim 17 in which the base (12) comprises a further cavity (14) which opens in the cavity (13).
A sensor (6) according to Claim 12, further comprising contact means (16; 17) interposed between the container (40) and the transducer (10) in order to exert a force on at least one region of the transducer during the exertion of bending forces.
A sensor (6) according to Claim 19 in which the contact means comprise a first protuberance (17) for contacting a first face of the transducer (10).
A sensor (6) according to Claim 20 in which the contact means comprise a second protuberance (16) for contacting a second face of the transducer (10), remote from the first face.
A sensor (6) according to Claim 12, further comprising a layer of protective material (20) disposed on at least one face of the transducer (10).
A sensor (6) according to Claims 13, 14 and 15, in which the clamping means comprise:

a tubular body (18) interposed between the cover (11) and the base (12) and provided with a rim (19') which bears on peripheral regions of a first face of the transducer (10),

an abutment rim (19) for peripheral regions of a second face of the transducer, remote from the first face, the rim (19) being formed in the base (12).
A sensor (6) according to Claim 12 in which the transducer (10) comprises a metal plate (21), a layer of piezoelectric ceramic material (22), and electrically conductive wires (23, 24) connected to the plate and to the layer, respectively, in order to make available electrical detection signals.