GB2194371A - Security grille - Google Patents

Abstract

The grille has a number of hollow bars 13 secured by frangible means 24 to upper and lower lid members 12. Fibre optic cables 17 pass through the bars and extent into the lid members through passages adapted to ensure that relative movement between the bar and either lid member will result in shearing of the cable. The cables are connected in an optical circuit including a light transmitter and receiver, the latter being connected to a warning device which is activated if the receiver ceases to receive light. <IMAGE>

Description

SPECIFICATION Alarmed window grille The present invention relates to alarmed grilles, particularly window grilles, for use in warning of attempts at unauthorised exit from prisons and at unauthorised entry to private premises.

Typically a grille of this type is intended to physically prevent passage therethrough, consists of a number of bars secured directly into a wall or onto a frame which is fixed in a wall, and has a warning system incorporated therein which includes electrical wiring connected to a system which detects breaks in the wiring. Electrical alarm systems have in the past proved to be susceptible to circumvention (for example by the use of by-pass circuitry) and to be liable to give false alarms.

The false alarms arise usually because of damage to the wiring system caused, for example by the access of water to the system, or, when a system has been incorporated as part of a building system, due to settling of the building with age. Consequently the use of fibre optic cable to conduct light is increasingly being used as a substitute for electrical warning systems.

Examples of warning systems using fibre optics are EP-A0073927 in which a fibre optic wire is carried within a helically wound tube weakened by means of notches or grooves and fitted with barbed wire cutting members, and UK-A2098770 in which optic cable is passed through hollow lattice members in a rectangular hollow frame. These prior art systems are responsive to deformation of the optic fibres which is sufficient to cause a change in the light passing from a transmitter to a receiver. However, optic cables can be deformed to a considerable extent without significantly affecting the amount of light passed therethrough, so that systems to detect changes of light other than a complete cessation of transmission are inevitably complicated and expensive.The systems of both these prior art documents are such that a considerable degree of deformation might be expected before fracture of an optical cable can be relied on.

It is an object of the present invention to provide an alarmed security grille which can be installed as an original fitting or as a replacement for existing unalarmed or electrically alarmed systems, and which will give an early warning of attempts to break through the grille, using conventional components of a simple, and cheap nature.

According to the present invention a security grille includes a plurality of hollow bars secured between an upper and a lower lid member, at least one bar having at least one fibre optic cable passing therethrough and extending into the upper and lower lid members through passages adapted to ensure that relative movement between the bar and either lid member will result in shearing of the cable, the bars being secured to the lid members by frangible means.

In a preferred embodiment the bars and lid members are secured together by soft aluminium rivets.

Preferably, every bar will have at least one, and preferably two rod members passing therethrough, to assist in positioning the fibre optic cables. There will preferably be one or two continuous circuits throughout the security grille. In use the grille will be installed over a window or other possible access point and the fibre optic cable will be connected to a light transmitter at one end and a light receiver at the other end, with the light receiver adapted to set off a warning when it is no longer receiving light. The grille will normally be used in conjunction with a grille designed to prevent passage therethrough.

It will be appreciated that with an arrangement such as this only a comparatively slight amount of deformation of a hollow bar will cause the frangible means to fail, resulting in relative movement of the bar and one or both lid members, resulting in the shearing of a fibre optic cable therein causing a warning to be given. Preferably, the light receiver at least will be remotely situated from the grille. The grille will then be preferably secured to its attachment points in such a way that removal therefrom will result in fracture of the fibre optic cable or cables leading away from the grille to the light receiver and warning devices.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, of which: Figure 1 is an elevation of a grille according to the invention, Figure 2 is an end view, in section along line ll-ll of a member of the grille, Figure 3 is an enlarged elevation, in Section, of another member of the grille shown in Fig.

1, Figure 4 is a plan view, in section along line lV-lV of the member shown in Section in Fig.

3, and Figure 5 is an elevation, in Section and enlarged, of a detail of the grille.

A security grille, shown in general at 10 in Fig. 1, has upper 11 and lower 12 lid members, and a plurality of bars such as those shown at 13 extending there-between. Each lid member 11, 12 is in the form of a hollow rectangle (Fig. 2) formed from two L-shaped channel members 14, 15 which are secured together in the assembled grill by welding, blind rivetting, or any other suitable means.

Each bar member 13 (Figs. 3, 4, 5) is also of hollow rectangular shape and is closed at each end by an end piece 20 secured to the bar member 13 by a weld 21. Each end piece 20 has therein two holes 22 for the passage of fibre optic cables and two holes 23 for the passage of rivets.

Running through each bar member 13 are two rod members 16, each associated with a hole 22 in each of the end pieces 20.

The bars 13 are secured to the lid members 11, 12 (Fig. 5) by means of blind soft aluminium rivets 24 which pass through holes 23 in the end pieces 20 and associated holes 25 in the lid members 11, 12.

Fibre optic cables 17 are passed through the rods 16 (Fig. 5) to extend into the lid members 11, 12, through holes 22 in the end pieces 20 and associated holes 26 in the lid members 11, 12. It will be realised that during the construction process the L-shaped channel members 14, 15 will not be connected together until the fibres 17 are in position.

In use the grille 10 is installed in a aperture, such a window, through which access is to be prevented, and the optical cables 17 connected to one or more light transmitters and one or more light receivers to provide one or more optical circuits. The light receivers are connected to a warning system. The light transmitters and light receivers may be adjacent to the grille 10 but are preferably at a remote site. When the transmitter and receiver are remotely situated the position where the fibre optic cables 17 are routed away from the grille 10 is preferably such that distortion of the grille 10 relative to its mounting will cause fracture of the fibre optic cables thus causing a warning to be given.Distortion of a bar 13 will very quickly result in fracturing of the soft aluminium rivets 24 with consequent relative movement of the bar 13 and lid members 11, 12 and shearing of the fibre optic cable 17, triggering the associated warning system.

Methods of joining fibre optic cables such as those shown at 1 7 are well known and are routine for those skilled in the art, form no part of the invention, and will therefore not be described here. Likewise optical transmission and receiving systems, and warning devices, are well known and the use thereof is routine to those skilled in the art and hence will not be described here.

The welds 21 are preferably such that the grille 10 gives the appearance that bars 13 are welded to the lid members 11, 12.

It will be realised that grille 10 as described above will provide only limited opposition to attempts to pass therethrough, and should be used in conjunction with a conventional security grille. Grille 10 can, of course be adapted to offer more physical resistance to passage therethrough by, for example, limiting relative movement of bars 13 and lid members 11, 12, by situating the ends of bars 13 in depressions in lid members 11, 12.

Claims (9)

1. A security grille including a plurality of hollow bars secured between an upper and a lower lid member, at least one bar having at least one fibre optic cable passing therethrough and extending into the upper and lower lid members through passages adapted to ensure that relative movement between the bar and either lid member will result in shearing of the cable, the bars being secured to the lid members by frangible means.

2. A security grille as claimed in claim 1 wherein the frangible means include one or more frangible rivets.

3. A security grille as claimed in Claim 2 wherein the rivets are formed from soft aluminium.

4. A security grille as claimed in any one of Claims 1 to 3 wherein each bar has at least one fibre optic cable passing therethrough.

5. A security grille as claimed in Claim 4 wherein each bar has two fibre optic cables passing therethrough.

6. A security grille as claimed in any one of Claims 1 to 5 wherein each fibre optic cable passes through a rod in each bar.

7. A security grille substantially as herein described with reference to Figs. 1 to 5 of the accompanying drawings.

8. A security grille as claimed in any one of Claims 1 to 7 having at least one fibre optic cable in an optical circuit including a light transmitter and a light receiver.

9. A security grille as claimed in Claim 8 wherein the light receiver is connected to a warning device such that the warning device is activated when the receiver ceases to receive light.