GB1580850A - Closure element - Google Patents

Description

(54) CLOSURE ELEMENT (71) We, WEIGHWRITE LIMITED, a British Company, of 44 Middle Gordon Road, Camberley, Surrey, GU15 2HP, and LEONARD FRANCIS GORMAN, a British Subject, of 3A Highlands Road, Heath End, Farnham, Surrey, 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 closure element provided with a magnetically releasable locking mechanism and particularly, but not exclusively to such a closure element constructed to be used as a manhole cover.

It is desirable, in order to avoid unauthorised removal of, or tampering with the contents of a manhole, and removal of the cover itself, to provide a cover with a concealed locking mechanism and with outward appearance which gives no indication of the location or manner of release of the locking mechanism.

According to the invention there is provided a closure element comprising a slab of non-magnetic material, a locking mechanism including a latch member which is releasable from a locking position in which it can retain the closure element in an aperture closing position with a face of the slab exposed, and a magnetic link within the slab for completing a magnetic circuit between a magnetic key when correctly positioned adjacent said exposed face and the locking mechanism to release the latch member, the link being concealed from the exposed face.

The latch member is preferably spring biased to said locking position, and may comprise a bolt which in the locking position projects laterally outwardly of the slab and which is fixed to a ferromagnetic actuator element displaceable disposed within a cavity in the slab to be magnetically attracted toward corresponding ends of a pair of ferromagnetic arms constituting the magnetic link, when a magnet, constituting the magnetic key, is positioned with its poles adjacent the opposite corresponding ends of said arms, disposed beneath said exposed surface of the slab.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawing, in which: Figure 1 is an exploded, perspective view of the major components forming a manhole cover in accordance with the invention, and Figure 2 is a part sectional, part exploded view of the manhole cover shown in Figure 1.

The illustrated cover 1 comprises a rec tangular slab 2 of a strong non-magnetic material, in this case a sand filled epoxy resin, which is capable of withstanding substantial load of the order of magnitude usually ex perienced by manhole covers set into road surfaces. A surround 3 is open upwardly and downwardly, but encloses the slab 2 on three sides thereof by three relatively fixed side members 4 and on the fourth side by a side plate 5 fixed by means of fixing bolts 6 to top and bottom mounting struts 7 extending between the corresponding ends of two para llel side members 4. The slab 2 is recessed along a portion of this fourth side to define a cavity 8 which houses part of a magnetically releasable locking mechanism.This mechanism comprises a locking bolt 9, constituting a latch member, fixed to and projecting normally from a movable actuator plate 10 located in the cavity 8. The bolt projects outwardly of the cover through a hole 11 provided in the side plate 5, and is, in this embodiment, spring biased outwardly by means of a helical tension spring 12 arranged coaxially on the bolt between the actuator plate 10 and the inside of the side plate 5. The bolt is capable of securing the cover in an aperture defined by a frame provided with some form of cooperating latch engagable by the bolt when in its outwardly biased position.

The actuator plate 10 is made of ferromagnetic material and is arranged to be magnetically attracted inwardly of the cover by a magnetic key 13.

A pair of parallel magnetic circuit arms 14 are set obliquely in the non-magnetic slab 2 and have respective horizontal upper end faces 15 parallel to, but sunk beneath the upper, exposed surface of the slab, and vertical lower end faces 16 within the cavity 8.

The key 13 is a permanent or electro-magnet having poles spaced in correspondence with the spacing of the upper end faces 15, and when it is positioned on the slab with its poles in register over such faces 15, the arms 14 form a magnetic link to complete a magnetic circuit between the key and the actuator plate IO which roves to withdraw the bolt 9 permitting removel of the cover.

It will be appreciated that the concealment of the upper end faces 15 of the arms 14 beneath the slab surface prevents, or at least renders extremely difficult, unlocking of the cover without prior knowledge of the location and spacing of the arms 14 and the required magnetic strength necessary to release the locking mechanism.

It will also be appreciated that the locking mechanism may be actuated to secure the cover by means other than the illustrated spring bias. The mechanism may, for example, be gravity actuated.

Only such persons as have a knowledge of the position and spacing of the arms 14, for each particular cover, defining a key position on that cover at which the key must be placed, and the spacing of the key poles, i.e.

the type of key required to release the cover, will be able to gain access to the contents of the manhole, and in this way the security of such contents is enhanced.

WHAT WE CLAIM IS:- 1. A closure element comprising a slab of non-magnetic material, a locking mechanism including a latch member which is releasable from a locking position in which it can retain the closure element in an aperture closing position with a face of the slab exposed, and a magnetic link within the slab for completing a magnetic circuit between a magnetic key when correctly positioned adjacent said exposed face and the locking mechanism to release the latch member, the link being concealed from the exposed face.

2. A closure element according to claim 1 wherein the locking mechanism includes means for biasing said latch member to said locking position.

3. A closure element according to claim 1 or claim 2 wherein the latch member projects laterally outwardly of the slab in the locking position, and is connected to a displaceable ferromagnetic actuator element at least part of which is disposed to be magnetically attracted toward first corresponding ends of a pair of ferromagnetic arms constituting the magnetic link when a magnet, constituting the magnetic key, is positioned with its poles adjacent the opposite corresponding ends of said arms, disposed beneath said exposed surface of the slab.

4. A closure element according to claims 2 and 3 wherein said latch member comprises a bolt arranged for axial displacement by said biasing means to said locking position, said biasing means comprising a helical compression spring carried on said bolt and bearing on said actuator element and on a part of the slab at its respective ends.

5. A closure element according to claim 3 or claim 4 wherein said actuator element is disposed within a cavity in the slab, and wherein said first corresponding ends of said ferromagnetic arms are physically exposed to the interior of said cavity.

6. A closure element according to any preceding claim wherein said slab comprises sand-filled epoxy resin.

7. A closure element substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

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

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. upper, exposed surface of the slab, and vertical lower end faces 16 within the cavity 8. The key 13 is a permanent or electro-magnet having poles spaced in correspondence with the spacing of the upper end faces 15, and when it is positioned on the slab with its poles in register over such faces 15, the arms 14 form a magnetic link to complete a magnetic circuit between the key and the actuator plate IO which roves to withdraw the bolt 9 permitting removel of the cover. It will be appreciated that the concealment of the upper end faces 15 of the arms 14 beneath the slab surface prevents, or at least renders extremely difficult, unlocking of the cover without prior knowledge of the location and spacing of the arms 14 and the required magnetic strength necessary to release the locking mechanism. It will also be appreciated that the locking mechanism may be actuated to secure the cover by means other than the illustrated spring bias. The mechanism may, for example, be gravity actuated. Only such persons as have a knowledge of the position and spacing of the arms 14, for each particular cover, defining a key position on that cover at which the key must be placed, and the spacing of the key poles, i.e. the type of key required to release the cover, will be able to gain access to the contents of the manhole, and in this way the security of such contents is enhanced. WHAT WE CLAIM IS:-

1. A closure element comprising a slab of non-magnetic material, a locking mechanism including a latch member which is releasable from a locking position in which it can retain the closure element in an aperture closing position with a face of the slab exposed, and a magnetic link within the slab for completing a magnetic circuit between a magnetic key when correctly positioned adjacent said exposed face and the locking mechanism to release the latch member, the link being concealed from the exposed face.

2. A closure element according to claim 1 wherein the locking mechanism includes means for biasing said latch member to said locking position.

3. A closure element according to claim 1 or claim 2 wherein the latch member projects laterally outwardly of the slab in the locking position, and is connected to a displaceable ferromagnetic actuator element at least part of which is disposed to be magnetically attracted toward first corresponding ends of a pair of ferromagnetic arms constituting the magnetic link when a magnet, constituting the magnetic key, is positioned with its poles adjacent the opposite corresponding ends of said arms, disposed beneath said exposed surface of the slab.

4. A closure element according to claims 2 and 3 wherein said latch member comprises a bolt arranged for axial displacement by said biasing means to said locking position, said biasing means comprising a helical compression spring carried on said bolt and bearing on said actuator element and on a part of the slab at its respective ends.

5. A closure element according to claim 3 or claim 4 wherein said actuator element is disposed within a cavity in the slab, and wherein said first corresponding ends of said ferromagnetic arms are physically exposed to the interior of said cavity.

6. A closure element according to any preceding claim wherein said slab comprises sand-filled epoxy resin.

7. A closure element substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.