GB2425569A

GB2425569A - Electromagnetic door retainer

Info

Publication number: GB2425569A
Application number: GB0508429A
Authority: GB
Inventors: Mark Batt Rawden
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-04-26
Filing date: 2005-04-26
Publication date: 2006-11-01
Also published as: GB0508429D0; WO2006114612A1

Abstract

A door retaining system 1 comprises a movable attractive element 11 mounted in a recess in the bottom surface 13 of a door 2, and a fixed attractive element 7 in the form of a plate fixed to the floor beneath the path of the door. The movable attractive element 11 is in the form of an electromagnet attached to a power supply. The fixed attractive element 7 is formed from a material which may be magnetized in use when it comes into proximity with the electromagnet. In use, the electromagnet 11 is connected to a power supply, and the opposed attractive surfaces 3, 5 defined by the attractive elements 7, 11 brought into face-to-face relation with one another by movement of the door to a selected open position. The electromagnet 11 magnetizes the fixed retaining plate 7 and the electromagnetic attraction generated between the opposed attractive elements 3, 5 retains the door in an open position. The door may be moved into and out of the retained position by moving it to a more open or closed position manually, with the opposed attractive surfaces sliding over one another to allow movement of the door in either direction.

Description

Door Retainer The present invention relates to a door retaining system.

More particularly, the present invention relates to an electromagnetic door retaining system.

Building regulations require that certain doors in buildings close in the event of an emergency e.g. a fire or power failure to try to prevent the e.g. fire spreading quickly through the building. These doors are typically those leading to an emergency exit route, such as a stairwell.

One way to try to meet such regulations is to use a system which maintains the doors permanently closed at all times during normal use while releasing the doors in an emergency to permit escape, e.g. by providing the doors with a release mechanism connected to an emergency detector system, or to fit the doors with devices which automatically return the doors to a closed position whenever they are opened during normal use.

However, it is inconvenient for each door in the building associated with a potential emergency exit route to be fitted with a closing mechanism, which results in the default state of the door being closed. Residents often remove door closing mechanisms after building regulations approval has been obtained, or prop doors open, e.g. using a wedge or fire extinguisher. This may result in buildings insurance being invalidated, and is dangerous in the event that a fire breaks out, as the open doors may allow a fire to spread throughout the building, and into a potential escape route. This is a particular problem in nursing homes, where residents may feel vulnerable if they are unable to open doors themselves.

if doors are retained closed during normal use, or arranged to automatically return to a closed position, this may in itself lead to a problem because fire and smoke alarms are often located in passageways and stairway areas. If a fire breaks out in an area separated from the smoke or fire alarm by the closed door, the smoke or fire alarm may not be triggered until the fire has burnt through the door, by which time it may be difficult to control, and may prevent escape.

Various systems have been proposed to allow doors to be retained in an open position during normal use, while ensuring that they are closed should an emergency situation be detected, e.g. a fire or smoke alarm be activated in the building. The present invention is directed to a door retaining system of this type, which may retain a door in an open position during normal use while allowing the door to close on detection of an emergency situation.

While some door retaining systems of this type are known which operate on a mechanical basis, the present invention is directed to electromagnetic door retaining systems.

Electromagnetic door retaining systems for retaining a door in an open position during normal use while allowing the door to close on detection of an emergency situation generally comprise a pair of opposed attractive elements, e.g. an electromagnet and a retaining plate which may be magnetized by the electromagnet in use when brought into proximity with the energised electromagnet.

The attractive elements are mounted respectively to the door and a wall behind the door. In this way, when the door is opened to bring the attractive elements into contact with one another the door may be retained against the wall by the attraction generated between the elements when the electromagnet is energised in use. The power supply to the electromagnet is connected to a smoke or fire alarm system, so that when the smoke or fire alarm is activated, the power supply to the electromagnet is interrupted, releasing the door.

The applicant has realised that known electromagnetic door retaining systems of this type are not well suited to domestic or residential applications, and are unattractive as they interfere with normal operation of the doors.

For example, the attractive elements may project into the space between the door and the wall when the door is opened, preventing the door from being opened to its fullest extent. This may also result in the system appearing ugly and cumbersome. Known systems do not allow variation in the opening range of the door, with the door either being closed or held in the open position defined by the position in which the attractive elements contact one another.

The Applicant has realized that there is a need for an improved electromagnetic door retaining system, allowing a door to be retained in an open position during normal use, while allowing the door to close on detection of an emergency condition, e.g. a fire, power cut, and permitting a full range of operation during normal use.

In accordance with the present invention there is provided an electromagnetic door retaining system, the system comprising opposed attractive elements which cooperate to retain the door in an open position when the system is energised in use, wherein said attractive elements are located one above the other.

The present invention therefore provides an improved system which may retain a door in an open position during normal use, while allowing the door to close in an emergency situation. The system comprises opposed attractive elements which cooperate to retain the door in an open position in use. As the opposed attractive elements are located one above the other, the present invention may provide a more space-efficient and unobtrusive door retaining system than conventional electromagnetic door retaining systems in which the attractive elements are mounted respectively to the door and wall i.e. side-by-side. Conventional systems may suffer from the disadvantages described above, in that the attractive elements may obstruct the full opening of a door, and may be detrimental to the appearance of the door area.

The opposed attractive elements comprise respectively an electromagnet and a magnetizable retaining element. The attractive elements may cooperate when the electromagnet is energised in use to retain the door in an open position as a result of the attraction generated between the elements, while allowing the door to close on interruption of a power supply to the electromagnet.

One of the attractive elements is mounted to the door. The other element may be mounted to the floor or ceiling. Preferably the other attractive element is mounted to the floor. The system therefore comprises a fixed attractive element and a movable attractive element.

The attractive elements define a pair of opposed attractive surfaces locatable with respect to one another to retain the door in a selected open position when the electromagnet is energized in use. The surfaces are those opposed surfaces of the attractive elements which face one another in use. The attractive surfaces are located one above the other in accordance with the invention. Preferably the entire attractive surface defined by one of said attractive elements is located above the attractive surface of the opposed attractive element.

The present invention extends to a method of retaining a door in a selected open position using a door retaining system in accordance with the invention in any of its aspects and embodiments.

In accordance with a further aspect, the present invention provides a method for retaining a door in a selected open position using an electromagnetic door retaining system comprising opposed attractive elements, the method comprising energising said system whereby the attractive elements cooperate to retain the door in the open position, wherein said attractive elements are located one above the other.

it will be appreciated that the present invention in any of its aspects and embodiments may provide a system in which the attractive elements are slidable with respect to one another on movement of the door i.e. the element mounted to the door is slidable over the opposed element on movement of the door e.g. between an open and a closed position.

In accordance a further aspect of the present invention there is provided an electromagnetic door retaining system, the system comprising opposed attractive elements which cooperate to retain the door in an open position when the system is energised in use, wherein the attractive elements define opposed attractive surfaces which are slidable over one another on movement of the door.

In accordance with a further aspect, the present invention provides a method for retaining a door in a selected open position using an electromagnetic door retaining system comprising opposed attractive elements, the method comprising energising said system whereby the attractive elements cooperate to retain the door in the open position, wherein said attractive elements are slidable over one another on movement of the door.

In accordance with the invention in any of its aspects and embodiments the attractive elements may define opposed attractive surfaces lying in a horizontal plane. Preferably the attractive elements define opposed attractive surfaces which are horizontal, or substantially horizontal. Preferably the opposed attractive surfaces of the opposed attractive elements extend in a plane substantially parallel to the top or bottom surface of the door and the floor or ceiling respectively.

In accordance with a further aspect, the present invention provides an electromagnetic door retaining system, the system comprising opposed attractive elements which cooperate to retain the door in an open position when the system is energised in use, wherein the opposed attractive surfaces defined by said attractive elements are horizontal surfaces.

In accordance with a further aspect, the present invention provides a method for retaining a door in a selected open position using an electromagnetic door retaining system comprising opposed attractive elements, the method comprising energising said system whereby the attractive elements cooperate to retain the door in the open position, wherein said attractive elements define horizontal attractive surfaces for retaining the door.

Preferably the electromagnetic attraction generated between the attractive elements when located in proximity with one another when the electromagnet is energised in use is sufficient to retain the door in a desired open position alone, and without any further retaining means being required. Preferably the retaining means in accordance with the invention is the sole retaining means of the door, and the door does not comprise any further retaining means. Preferably the system comprises a pair of opposed attractive elements. This may provide a particularly simple and effective arrangement, which is easy to install.

However, it will be appreciated that in other arrangements, a plurality of pairs of opposed attractive elements in accordance with the invention might be provided which cooperate to retain the door in a selected open position in use. Each pair may comprise any or all of the features described in relation to "the't opposed attractive elements.

It will be appreciated that the attractive surfaces of the elements will be located in facing relation in use to retain the door in an open position when the electromagnet is energised, i.e. in the "retaining position". Preferably the attractive surfaces of the elements contact one another when located in facing relation. The strength of the electromagnetic field required to provide a given retaining force between the surfaces increases exponentially with distance between the attractive surfaces. The closer the surfaces are to one another when in the retaining position, the weaker the magnetic field required. If the surfaces are arranged to be close to one another, and preferably in contact with one another when in their retaining position, this may provide a simpler and more cost effective arrangement, allowing the door to be more easily manually moved to a closed or more open position without deenergising the electromagnet as described below. The frictional forces arising between the attractive surfaces when in contact may help to contribute to the retaining force, further reducing the strength of electromagnetic field required in these arrangements.

Preferably the attractive surfaces directly contact one another in the retaining position, i.e. with no floor covering or similar extending between the surfaces.

It will be appreciated that the position in which the door is held by the retaining means will depend upon the location of the fixed attractive element, and thus the position at which the door must be located for the movable or door mounted attractive element to be brought into face to face relation with the fixed attractive element, thus allowing the elements to cooperate and retain the door in the selected position when the electromagnet is energised in use.

The selected open position may be a fullest open position of the door.

Typically the fixed attractive element may then be located in a position adjacent the line extending perpendicular from the axis about which the door is mounted, e.g. a wall to which the door is mounted. However, preferably the attractive elements are located such that the door is retainable in a selected open position which is not a fully open position of the door. Preferably the method comprises the step of arranging the attractive elements such that the open position of the door is not a fully open position of the door.

Conventional electromagnetic door retaining systems only allow a door to be moved from a selected open position to a more closed position when the electromagnet is de-energized. For example, systems may comprise a manual override switch allowing a user to interrupt the power supply to the electromagnet thus de-energizing it, and allowing the door to be fully closed. However, the Applicant has realised that a system in accordance with the present invention may allow a door to be moved from a selected open position defined by the position of the attractive surfaces towards a more closed and/or open position without needing to deenergise the electromagnet. This may provide a more flexible system, and reduce the likelihood of a user forgetting to reactivate the system, as it is not necessary to deactivate it each time the door is opened or closed.

The system may therefore easily be used, even by elderly or infirm people.

This is because the force required to retain the door in an open position using attractive elements arranged in accordance with the present invention is generated in a different direction i.e. a vertical direction, to the direction in which force needs to be applied to close/open the door. This latter force may be exerted in a horizontal plane perpendicular to the retaining force i.e. as a shear force. The user therefore does not need to exert a force sufficient to overcome the vertical retaining force of the door in the same direction as the retaining force as in conventional arrangements.

Typically conventional systems use an electromagnet that generates a retaining force of greater than 35 Newtons. The system of the present invention may generate the same retaining force between the attractive elements. If one were to try to pull the attractive elements apart in the direction perpendicular to the attractive surfaces i.e. in the direction of the retaining force, as in a conventional arrangement, one would have to overcome a magnetic field of this magnitude.

However, because the attractive elements are located one above the other, and are slidable past one another on opening/closing of the door in accordance with the present invention, to move the door towards a more open or closed position, only the shear force generated between the attractive surfaces need be overcome. Typically this only requires an additional force of around 1-5 Newtons to overcome the magnetic and frictional shear forces holding the door in place. Where a door closer is fitted, a lesser force is required to move the door to the closed position, as the closer will already exert some shear force urging the door towards a closed position.

The system may preferably be arranged such that any desired shear force may be exerted to close/open the door when the electromagnet is energised, to allow easy opening/closing, but to avoid accidental open/closing of the door.

Preferably the present invention therefore provides a door retaining system in which the door may be manually moved from a selected open position defined by position in which the attractive elements cooperate with one another to retain the door in use towards a more open and/or closed position of the door while the electromagnet is energised in use. Preferably the system allows the door to be at least manually moved towards a more closed position in use while the electromagnet is energised. The door is preferably movable to a more open position. However, as described above, whether this is possible will depend upon the location of the fixed attractive element relative to the wall to which the door is mounted.

Preferably the method of the present invention comprises the step of operating the system such that the attractive elements cooperate with one another to retain the door in a selected open position in use while allowing the door to be moved manually at least towards a more closed position, and preferably towards a more open position, while the electromagnet is energised in use.

As the attractive elements are located one above the other, the door may be moved to a fully open position without interference by the attractive elements, in contrast to conventional arrangements, where the fixed attractive element projects into the path of the door, e.g. a space between the door and a wall. In such arrangements it is not possible to open the door more fully beyond the open position it defines when the vertical attractive elements contact one another in use. In these preferred embodiments, the attractive surfaces of the elements are movable out of engagement with one another manually while the electromagnet is energised.

Preferably the door mounted attractive element is slidable over the full width of the fixed attractive element i.e. of the attractive surface of the fixed attractive element. The width of the fixed attractive element is its dimension in the direction extending parallel to the door opening. Preferably the door mounted attractive element is movable over the fixed attractive element completely past the fixed attractive element towards the most open position of the door on opening of the door i.e. to a position in which the inner edge of the door mounted attractive surface lies outboard of the outer edge of the fixed attractive surface. By the inner edge of the door mounted attractive surface, it is meant the edge closest to the position occupied by the door when closed, while "outboard" or "outer" refer to the position closer to the most open position of the door.

in accordance with a further aspect, the present invention provides an electromagnetic door retaining system having attractive elements for retaining the door in a selected open position when the electromagnet is energised in use, wherein the door is manually movable to a more open or closed position than said selected open position when the electromagnet is energised.

In accordance with a further aspect, the present invention provides a method of operating an electromagnetic door retaining system having attractive elements for retaining the door in a selected open position when the electromagnet is energised in use, the method comprising the step of operating the system such that the door is manually movable to a more open or closed position than said selected open position while the electromagnet is energised. in this way, the door may be retained in a selected open position by the retaining means. If a user wishes to open the door more fully or to close the door, he may simply push or pull the door as appropriate, moving the opposed retaining surfaces out of engagement with one another.

Preferably the method comprises the step of operating the system whereby the attractive surfaces may be moved out of engagement with one another to move the door towards a more open or closed position on application of a shear force in the range of less than 10 Newtons, or preferably from 1 to 5 Newtons.

Preferably the attractive elements may cooperate to hold the door in a selected open position while allowing the door to be moved from the selected open position towards a more open position and/or moved towards a more closed position on manual intervention by the user while the electromagnet is connected to a voltage in the range of from 12 to 36 V DC supply in use, and preferably of 24 V DC.

The attractive element mounted to the door may be mounted to the upper or lower part of a door, depending upon the location of the opposed attractive element with which it is to cooperate. Preferably the door mounted attractive element is mounted to the lower part of the door. Preferably the door mounted attractive element is mounted to a floor or ceiling facing surface of the door. Preferably the door mounted attractive surface forms a part of the floor or ceiling facing surface of the door, and preferably of the floor facing surface.

The door mounted attractive element may be mounted to the door in any suitable manner which allows it to cooperate with the opposed attractive element to retain the door in a selected open position, and being movable past the fixed - 10 - attractive element on movement of the door in use, at least in the direction of closing of the door, and preferably in both the directions of opening and closing of the door.

The door mounted attractive element may be mounted within the door or may be mounted to an external surface of the door.

In some preferred embodiments the door mounted attractive element is mounted within a recess in the door. Preferably the door mounted attractive element is mounted in a recess within the floor facing surface of the door.

In other arrangements the door mounted attractive element is mounted to a vertical surface of the door. The element may be mounted to the inner or outer vertical external surface of the door. The attractive element may then define an attractive surface located adjacent the floor facing surface of the door. In these embodiments, the attractive element is preferably mounted to a surface of the door which faces a wall towards which the door opens in use.

The door mounted attractive element preferably defines an attractive surface extending substantially parallel with a horizontally extending surface of the door.

The attractive surface may be located such that it projects or is recessed relative to the horizontal plane defined by the surface of the door. If the attractive surface is recessed relative to the horizontally extending surface of the door the strength of the electromagnet should be selected appropriately to ensure that sufficient attraction may still be obtained between the opposed attractive elements of the system to retain the door when the electromagnet is energised in use.

Preferably the door mounted attractive element defines an attractive surface which lies flush with a horizontal surface of the door, preferably the bottom surface of the door. In this way, the attraction between the opposed attractive elements may be enhanced, while still allowing the attractive surfaces to easily slide over one another, without impeding movement of the door in use.

Preferably the attractive elements define attractive surfaces having areas of around 500 to 2000 square mm, and preferably in the range of from 500-1200 square mm.

The door mounted attractive element may be mounted to the door at any suitable horizontal distance from the vertical axis about which the door opens. The distance should be selected such that a sufficient retaining force may be generated when the electromagnet is energised in use to retain the door in the open position.

The electromagnetic force required will depend upon the distance from the axis of the door at which the surface is mounted, and thus the shear force to be resisted.

The closer the attractive element is located to the axis of the door, the greater the electromagnetic force required to retain the door open. If the attractive surface is located close to the edge of the door which is joined to the wall, then the distance along which any wires associated with movable attractive element must extend will be reduced. Preferably the door mounted attractive element mounted at least 30% of the width of the door from its axis.

The other attractive element may be fixed to any region of the floor or ceiling which allows it to cooperate with the door mounted attractive element to retain the door in an open position.

Preferably the fixed attractive element does not project vertically more than 2 cm, and preferably 5 mm, from the floor or ceiling. Preferably the fixed attractive element defines an attractive surface which is flush with the floor or ceiling. By this is meant that the attractive surface does not extend substantially in a vertical direction above the highest horizontal plane defined by the surface of the floor (and any floor coverings above which the element is mounted) facing the lower surface of the door in the region over which the lower surface of the door may move, or alternatively the lowest horizontal plane defined by the ceiling facing the upper surface of the door in the region over which the upper surface of the door may move. This will allow the opposed attractive surfaces to more easily move over one another as the door is moved between an open and closed position.

The fixed attractive element may be mounted at any point along the radius defined by the path of the door between its closed and open positions. The element may be located adjacent a line extending perpendicular from the axis about which the door is mounted. However, preferably the fixed element is located in the path of the door in a position to allow the door to be retained in a partially open position. In some embodiments, the fixed attractive element is spaced from a line extending perpendicular from the axis about which the door is mounted. In this way, the door may be pushed back to a fullest open extent beyond the open extent at which it is held by the attractive elements when the electromagnet is in energized in use.

Preferably the fixed attractive element, and preferably the attractive surface defined by the element, is located at a point on the radius defined by path of the door as it opens such that the door is retained at an open position which is at an angle of from degrees to 120 degrees from the closed position in use. The angle is the angle measured between the lines extending respectively along the door from the fixed attractive element to the axis of the door when in a closed position, and along the door to its axis when the door is in its retained open position. In contrast to conventional arrangements, this may allow the door to be easily opened to a fuller extent relative to the open position defined by the retaining means.

One of the attractive elements comprises an electromagnet. The attractive surface of the element may be a surface of the electromagnet. In these arrangements, the attractive element may consist of an electromagnet. This may provide a particularly simple and cost effective arrangement, suitable for installation by a domestic user. In other arrangements, the attractive element may comprise an electromagnet and a housing. In these embodiments the attractive surface may be a surface of the housing associated with the electromagnet. The electromagnet may then act indirectly through the surface of the housing to attract the opposed element in use. The surface of the housing which defines the attractive surface of the attractive element in these embodiments should therefore comprise a magnetizable material.

Preferably the door mounted attractive element comprises an electromagnet.

It has been found that the electromagnet may be more easily mounted to a door by a domestic user. In particular, the electromagnet may be relatively easily mounted in a recess in the lower surface of the door.Preferably the attractive surface of the door mounted attractive element is a surface of an electromagnet. A door is typically made of materials which may more easily hollowed out without the use of special tools, or causing disruption to the surrounding area. However, it will be appreciated that either of the attractive elements may comprise the electromagnet, e.g. depending upon ease of wiring, connection to a power supply and other considerations.

In domestic contexts it is often preferable to mount the electromagnet in the door to avoid needing to cut a recess in the floor or ceiling covering. However, in - 13 - other cases where the door is expected to be moved frequently, it may be desirable to mount the electromagnet to the floor to avoid wear and tear on the wires connecting the electromagnet to a power supply on movement of the door. In domestic situations it has been found that often doors need only be moved from an open position on average once or twice a day, e.g. at night, and in some cases, such as living areas, even less frequently under normal circumstances.

The other attractive element may comprise any material which is magnetizable when the attractive elements are brought into proximity with one another in use to retain the door in a selected open position. Typically the attractive element comprises a soft magnetic material. Any commercially available electromagnet and associated keeper plate may be used to provide the attractive elements.

In use, the electromagnet is connected to a power supply which is operable to energize the electromagnet while allowing the electromagnet to be de-energized when the power supply is interrupted. The electromagnet may be connected to a power supply in any conventional manner, e.g. using wires or cables. Preferably the power supply is a mains power supply. The electromagnet may be directly connected to the mains supply, but is preferably connected via a DC power supply to the mains. Preferably the power supply is a low voltage power supply. This may allow the electromagnet to be simply connected to a power supply e.g. via means of wires or cables. Preferably the power supply is in the range of 12-3 6 V, and preferably a 24 V D.C. supply. it will be appreciated that any references to the operation of the system when the electromagnet is energised in use refer to the operation of the system when the electromagnet is connected to the electrical power supply with which it is intended for use.

The present invention extends to a door retaining system in accordance with the invention in any of its aspects and embodiments in which one of the attractive elements comprises an electromagnet connected to a power supply.

Preferably the system of the present invention is arranged whereby the power supply of the electromagnet is interrupted on detection of an emergency condition, and the method of the present invention in any of its aspects and embodiments - 14 - comprises operating the system such that the power supply of the electromagnet is interrupted on detection of an emergency condition to allow the door to close.

The system may simply be arranged to result in release of a door on interruption of the power supply to the electromagnet e.g. in the event of a power cut. Preferably, the power supply of the electromagnet is interruptible in use on detection of an emergency condition. Preferably the power supply is interruptible in use on activation of a smoke or fire alarm. Systems for electrically connecting door closure systems and fire alarm or other emergency detecting systems so that the power supply to the door closure system is interrupted on activation of the e.g. fire alarm system are known. These may operate using an appropriate arrangement of electrical switches. If regulations require, separate power supplies may be provided to the fire alarms and the electromagnet associated with the door closure system, provided that the system is operable to interrupt the power supply to the door closure system on activation of the smoke or fire alarm. Preferably the electromagnet is connected to the mains via a power supply unit which is connected via a switch to an emergency detecting system e.g. a smoke alarm.

It will be appreciated that the door retaining means should be operable such that the door is released allowing it to close within a relatively short time once a power supply to the electromagnet is interrupted. The materials of the electromagnet, and the attractive elements should be selected to provide release of the door within a desired response time on interruption of the power supply to the electromagnet. The electromagnet, and the attractive surfaces of the attractive elements preferably exhibit little or no residual magnetism. Suitable materials having such properties are known for use in conventional electromagnetic door releasing systems.

The attractive elements may be mounted to the door or ceiling or floor in any suitable manner e.g. using adhesives, or mechanical fasteners. Preferably the attractive elements are mounted using one or more threaded fasteners, e.g. screw fasteners. Preferably at least the attractive element which is not associated with the electromagnet comprises a bore for receiving a fastener. Preferably a or each attractive element comprises a recess for receiving a fastener whereby a fastener for mounting the attractive element may be arranged to be flush or recessed relative to the attractive surface. Preferably the attractive elements are mounted such that no fasteners associated with the respective elements extend into the region between the attractive surfaces when the surfaces are located in face to face relation. In this way, the fasteners may not interfere with movement of the attractive surfaces past one another.

The attractive surfaces of the attractive elements may be of any suitable configuration. The configuration of the surfaces should be chosen appropriately with respect to the weight of the door, dimensions of the door and strength of the electromagnet to allow an electromagnetic field of sufficient strength to be generated between the opposed surfaces in use to retain the door in a desired open position. The configuration of the surfaces may also be selected with regard to the dimensions of the surfaces of the door and floor/ceiling with which they are associated to facilitate installation.

It will be appreciated that the attractive elements may be planar elements, or may be elements having appreciable height. For example, as discussed above, one element may be an electromagnet. If the element has any appreciable depth it may be located in a recess to allow its attractive surface to lie flush with a surface of the door, or of the floor or ceiling. Preferably the attractive element not associated with an electromagnet is in the form of a plate. Preferably the fixed attractive element is in the form of a plate. Preferably at least one of the opposed attractive elements is circular in horizontal cross-section. However, the elements may be e.g. rectangular or of any other shape in horizontal cross section.

Preferably the door is arranged to automatically return to a closed position when the attractive elements are moved out of engagement with one another or the electromagnet is deenergised. For example, the door may be weighted to automatically close when not retained in an open position, and/or may comprise separate door closing means. Door closing means are well known. For example, door closing means may be mechanically and/or electronically operable, and may comprise e.g. an overhead mechanism. For example, the door closing means may comprise a spring operable to return to the door to a closed position.

The door closing means may be operable only on interruption of the power supply to the electromagnet. For example, the closing means may be operable on

I

detection of an emergency situation e.g. by a smoke or fire alarm detected in the same way as the retaining means. In other cases, the door closing means may act on the door at all times to urge it towards a closed position. It will be appreciated that where the door closing means acts on the door at all times to urge it towards a closed position, it should be selected to be of a strength which is not sufficient to overcome the retaining force generated between the attractive elements and holding the door in an open position during normal operation. When the door closing means operates at all times, then if the door is moved to a more fblly open position relative to the selected open position defined by the position in which the attractive elements face one another, the door closing means may urge the door towards the closed position.

As the door moves back towards the closed position, the attractive elements will move over one another. The door may then be held in the selected open position once more, or allowed to close ftilly.

Depending upon the size of the door and the force required to retain it in an open position, a plurality of door retaining systems in accordance with the present invention may be provided associated with the door. For example, one or more sets of opposed attractive elements in accordance with the invention may be provided associated with either or both the top and bottom of the door.

Although the door retaining system has been described in terms of a door which opens by rotating along an angular path between a closed and open position, it is envisaged that the system may also be applied to a slidable door system.

Preferably the door is a mounted along one edge to a vertical axis, and is movable along an angular path between open and closed positions.

Although the door retaining system has been described in terms of pairs of cooperating attractive elements, it will be appreciated that provided the system comprises at least one electromagnet, and one cooperating attractive element, further floor or ceiling mounted attractive elements may be provided cooperating with the same electromagnet for retaining the door in different selected open positions. For example, the system may comprise a door mounted attractive element comprising an electromagnet and a plurality of opposed attractive elements mounted to the floor or ceiling for cooperating with the door mounted attractive element in use to retain the door in a plurality of selected open positions.

A door retaining system in accordance with the present invention may be provided associated with each door which must be closed in an emergency situation.

The door retaining systems associated with each door may then be operable such that the respective door is closed when a power supply to the electromagnet of the door retaining system is interrupted. For example, the door retaining systems of each door may be connected in series with a switch operable on activation of a smoke or fire detector to interrupt the power supply to the respective electromagnets.

The present invention extends to the use of a door retaining system in accordance with the invention in any of its aspects and embodiments to retain a door in an open position while allowing the door to close in an emergency situation.

In accordance with the further aspect, the present invention therefore provides a method for retaining a door in an open position, the method comprising providing opposed attractive elements, mounting one of the elements to the door and the other to the floor or ceiling, one of said elements comprising an electromagnet, connecting the electromagnet to a power supply, locating the attractive elements in proximity with one another and energising the electromagnet to retain the door in an open position as a result of the attraction generated between the opposed attractive elements. Preferably the method further comprises the step of operating the system such that the door is movable towards a more open or closed position than the selected open position defined by the opposed attractive elements on manual intervention of a user while the electromagnet is energised. Preferably the method further comprises operating the system whereby the power supply to the electromagnet is interrupted on detection of an emergency situation.

Some preferred embodiments of the invention will now be described by way of example only, and with reference to the accompanying drawings in which:- Figure 1 is an underside view of a door incorporating an attractive element of a door retaining system in accordance with the present invention; Figure 2 is a view of the fixed opposed attractive element of a door retaining system mountable to a fixed surface in accordance with the invention which may cooperate with the movable attractive element of Figure 1 to hold the door open in use, and showing a fastener for mounting the element; Figure 3 is a view of the fixed attractive element of Figure 2, but with the fastener omitted for clarity; Figure 4 shows the electromagnet which forms the movable attractive element and its associated wiring in more detail; Figure 5 illustrates the location of the respective attractive elements of the retaining system of a door closure system in accordance with the present invention having attractive elements as shown in Figures 1 and 2; Figure 6 is a view from one side of a door having an attractive element mounted adjacent an outer surface of the door in accordance with an alternative embodiment of the present invention; and Figure 7 illustrates the way in which a plurality of door retaining systems in accordance with the present invention associated with different doors may be connected to a power supply and smoke alarm.

A door retaining system I in accordance with the present invention will be described with reference to Figures 1 to 5. Figures 1 to 4 show schematically the movable and fixed attractive elements of the system, while Figure 5 illustrates the location of the elements when mounted to a door and floor respectively.

The door retaining system I comprises a movable attractive element 11 mounted to the bottom surface 13 of a door 2 which faces the floor in use. The movable attractive element 11 which is mounted to the door 2 is shown in more detail in Figures 1 and 4. The attractive element 11 defines one of a pair of opposed attractive surfaces 3, 5 which cooperate to hold the door open in use. The other attractive surface 5 is defined by the fixed attractive element 7 shown in Figure 2.

The door 2 is provided with a cylindrical recess 5 at a distance 1 from the edge of the door which is closest to the wall to which the door is attached. The distance 1 is around 30% of the distance along the door from its axis where it is attached to a wall. The attractive element 11 is an electromagnet which is located in the recess 5, such that a circular end face of the electromagnet lies flush with the lowermost surface of the door 13 to provide the attractive surface 3. A wire 10 extends through a channel 15 provided in the lower surface of the door to connect the electromagnet to an electrical power supply.

The door retaining system I also includes a fixed attractive element 7 which together with the movable attractive element 11 provides the other of the opposed attractive surfaces 3, 5 for retaining the door in an open position in use as described below when power is supplied to the electromagnet 11. The fixed attractive element 7 is shown in more detail in Figure 2 and 3. The fixed attractive element 7 is in the form of a circular plate having a central aperture 17 for receiving a screw fastener 19. One surface 5 of the plate 7 defines the fixed attractive surface.

In use, the fixed attractive element shown in Figures 2 and 3 is screwed into the floor at a position corresponding to that at which it is intended to cooperate with the movable or door mounted attractive element 11 and retain the door in a selected open position. The plate 7 is screwed into the carpet in such a way that the attractive surface 5 defined by the upper surface of the fixed attractive element sits on the surface of the carpet. The screw fastener 19 should not project above the level of attractive element 7. For example, a shouldered screw fastener may be used. The fixed attractive surface contacts the movable attractive surface when the door is located in the open position in use. This may allow frictional forces to contribute to holding the door in an open position, and may allow a lower strength electromagnet to be used. The attractive surfaces 3,5 are of around 35 mm diameter, giving a surface area for each of around 800mm.

In use, the electromagnet 11 is connected to a power supply, and the opposed surfaces 3,5 of the retaining system are brought into engagement with one another, by moving the door in the direction of the arrow in Figure 3, thus bringing the attractive surface 3 of the movable door mounted attractive element 11 into face to face relation with the attractive surface 5 of the fixed attractive element 7, the tretaining positiont. It will be appreciated that as the opposed attractive elements are located in parallel horizontal planes, they may be slidably moved over one another as the door and thus the attractive element 11 is moved. The electromagnet 11 magnetises the fixed retaining plate 7, and the electromagnetic attraction generated between the opposed attractive elements 3,5 retains the door in an open position.

- 20 - It has been found that an electromagnet of 32 mm diameter may exert a holding force of around 35 Newtons between the plates, i.e. in a direction perpendicular to the attractive surfaces.

The power supply to the electromagnet is drawn from a low voltage DC supply unit connected to the mains supply. The power supply to the electromagnet is 24 V D.C. The power supply is connected via a set of contacts to a fire alarm system, such that upon operation of the fire alarm, the contacts open, and electrical power supply to the electromagnet 11 is interrupted. On interruption of the power supply to the electromagnet, or on exertion of a pulling or pushing force to the door of a force sufficient to overcome the force generated between the opposed attractive elements 11, 7 the opposed surfaces 3, 5 of the retaining system are slidable over one another to allow the door to be closed or more fully opened.

it has been found that by adjusting the screw holding the fixed attractive element to the floor, the force required to overcome the retaining force between the elements i.e. the shear force, and move the door towards a closed or open position, may be adjusted. Preferably the shear force required to overcome the retaining force between the elements in use is around 1 to 5 Newtons. Such a force may easily be exerted manually by a user.

Operation of the door retention system will now be described with respect of Figures 1 to 5. The fixed and movable parts of the door retaining system are mounted to the floor and door as shown in Figure 1. The power supply to the electromagnet is turned on, energizing the electromagnet. The door is then opened to the angular position at which the opposed attractive surfaces 3, 5 of the fixed and movable attractive elements of the door retaining system I face one another (schematically shown as position 0 in Figure 5). The fully open position of the door is indicated as B in Figure 5, while the closed position is denoted A. The position 0 is around 90 -120 degrees along the angular path of the door from its closed position. The angular position (0) of the door is defined by the angle the line along the door to its axis at a given open position makes with the line defined by the door in its closed position A. The electromagnet ii then magnetizes the plate 7 defining the fixed attractive element. The magnetic attraction between the electromagnet and the fixed part attractive element retains the door in an open position.

- 21 - in an emergency situation, a fire alarm connected to the door retaining system I operates causing a switch to operate and disconnect the power supply to the electromagnet 11 providing the movable attractive surface 3 of the door retaining means. The magnetic force generated between the opposing surfaces of the fixed and movable parts of the retaining means dissipates, allowing the door to shut.

If it is desired to open the door to a fuller extent, the user may push the door overcoming the attraction between the opposed attractive elements so as to slide the opposed movable attractive element 3 over the fixed attractive element 5 in the direction of the arrow shown in Figure 1 out of engagement with the fixed attractive element 5. The inner edge of the door mounted attractive surface 3 may therefore be moved over the full width of the floor mounted attractive surface such that it is closer to the most fully open position B of the door than the outer edge of the fixed attractive surface 5.

If the door is then released, it will begin to close, with the movable door mounted attractive surface 3 moving back towards the fixed attractive element 7 in the direction opposite to that of the arrow in Figure 1. The door may be allowed to stop in the position where the opposed surfaces of the fixed and movable retaining means 3,5 face one another, thus retaining the door once more in the selected open position 0 once more. if it is desired to close the door, the user may simply pull on the door against the magnetic force developed between the opposed attractive elements 3, 5 sliding the surfaces 3,5 out of engagement with one another, allowing the door to close as the inner edge of the door mounted attractive surface 3 moves past the fixed attractive surface 5.

In this way, the present invention provides a system which allows the door to be located in a selected open position, while not impeding opening of the door to a fuller extent, or closing of the door while the electromagnet even while the electromagnet is still energized.

It will be appreciated that the electromagnetic retaining force generated between the attractive elements in use may be selected appropriately by varying factors such as the electromagnet strength, the surface area of the plates, any vertical spacing between the attractive surfaces and the voltage supplied. The force required to retain the door in an open position may depend upon e.g. the distance the fixed - 22 - attractive element is located from the axis of the door, the weight of the door, whether any door closing mechanism is fitted etc. The door may be fitted with an overhead mechanism or any other conventional mechanism to ensure that it automatically shuts when no longer retained in an open position.

Figure 6 shows an alternative arrangement in which the electromagnet 110 is, rather than being located in a recess in the bottom surface 119 of the door, instead mounted to the inner external surface 112 of the door 108 closest to the wall 114 to which the door is mounted using fasteners, e.g. screw fasteners 116. In this arrangement, as in the arrangement of Figure 1, the surface 118 of the electromagnet provides the movable attractive surface which cooperates with the opposed surface of the fixed part of the retaining means (not shown in Figure 4) to retain the door in an open position when the electromagnet is energised in use. The attractive surface 118 is flush with the plane defined by the bottom surface 119 of the door and is parallel to the surface. The electromagnet shown in Figure 4 may be connected to an electrical power supply using wires as shown in relation to Figure 1.

It will be seen from above that the opposed attractive elements of the retaining system are located one above the other, i.e. to the door and floor respectively. The opposed surfaces of the attractive elements of the retaining means are therefore slidable into and out of engagement with one another in a horizontal plane as in the embodiment of Figures 1 - 5. Operation of the embodiment of Figure 6, and the configuration of the opposed attractive element is identical to that described in respect of Figures 1 to 5.

Figure 7 illustrates a simple circuit in which the power supplies to the electromagnets of a number of different door retaining systems 200, 202, 204 in accordance with the present invention associated with different doors of a building are connected such that they may be interrupted on operation of a smoke alarm. In this arrangement, the electromagnets of each door retaining system are connected in parallel with one another, and all are in series with a switch 208, which is configured to open on operation of a smoke alarm. The electrical supply to the electromagnets of door retaining systems 200, 202, 204 is derived from the mains supply of the building. In use, the switch 208 is closed during normal operation of a system.

- 23 - When a smoke alarm is activated, the switch 208 is opened, interrupting the power supply to the electromagnets of the door retaining systems 200, 202, 204, thus allowing the opposing surfaces of the parts of the door retaining systems to slide over one another, closing the associated doors.

It will be appreciated that in accordance with the present invention, the electromagnet may be provided on the fixed part of the door retaining means, rather than on the movable part as shown in the illustrated embodiments. For example, a cavity may be provided in the floor to house an electromagnet and an engagement plate of the type shown in Figure 2 mounted flush with the lower surface of a door.

It will also be appreciated that in accordance with the invention the door retaining means may be associated with the top of a door, rather than the bottom of the door as shown. More than one door retaining means may be provided associated with each door, i.e. such that the door has a plurality of pairs of opposed attractive elements. The movable or door mounted part of the door retaining means may be located at any distance from the hinges of the door. Rather than being of the shape shown in the drawings, the opposed surfaces may be e.g. circular or square or triangular in shape, and may extend for a greater length or width than shown in the drawings.

Although the system is preferably configured to allow a user to manually open or close a door while the door is held in the open position with the electromagnet energised, it will be appreciated that instead the door may only be movable from the selected open position defined by the retaining means on interruption of the power supply to the electromagnet, e.g. in response to detection of an emergency or on manual intervention.

Claims

- 24 - Claims 1. An electromagnetic door retaining system, the system

comprising opposed attractive elements which cooperate to retain the door in an open position when the system is energised in use, wherein said attractive elements are located one above the other.
2. The electromagnetic door retaining system of claim 1, wherein the opposed attractive elements are respectively an electromagnet and a magnetizable retaining element.
3. The electromagnetic door retaining system of any preceding claim, wherein the door mounted attractive element comprises an electromagnet.
4. The electromagnetic door retaining system of claim 2 or claim 3, wherein the electromagnet is connected to a power supply.
5. The electromagnetic door retaining system of any preceding claim, wherein one of the attractive elements is mounted to the door and the other element to the floor or ceiling.
6. The electromagnetic door retaining system of claim 5, wherein the door mounted attractive element is mounted within a recess in the floor facing surface of the door.
7. An electromagnetic door retaining system, the system comprising opposed attractive elements which cooperate to retain the door in an open position when the system is energised in use, wherein the attractive elements define opposed attractive surfaces which are slidable over one another on movement of the door.

- 25 -
8. The electromagnetic door retaining system of any preceding claim, wherein the attractive elements define opposed attractive surfaces which are substantially horizontal.
9. An electromagnetic door retaining system, the system comprising opposed attractive elements which cooperate to retain the door in an open position when the system is energised in use, wherein the opposed attractive surfaces defined by said attractive elements are horizontal surfaces.
10. The electromagnetic door retaining system of any preceding claim, wherein the attractive surfaces of the attractive elements contact one another when the surfaces are located in facing relation with respect to one another.
11. The electromagnetic door retaining system of any preceding claim, wherein the attractive elements are located such that the door is retainable in a selected open position which is not a frilly open position of the door.
12. The electromagnetic door retaining system of any preceding claim, wherein the door retaining system allows the door to be manually moved from a selected open position defined by a position in which the attractive elements cooperate with one another to retain the door in the selected open position towards a more open and/or closed position of the door while the electromagnet is energised in use.
13. An electromagnetic door retaining system having attractive elements for retaining the door in a selected open position when the electromagnet is energised in use, wherein the door is manually movable to a more open or closed position than said selected open position while the electromagnet is energised.
14. The electromagnetic door retaining system of any preceding claim, wherein the system is arranged whereby a power supply to the electromagnet is interruptible to release the door on detection of an emergency condition.

- 26 -
15. The electromagnetic door retaining system of any preceding claim, wherein a power supply to the electromagnet is interruptible in use to release the door on activation of a smoke or fire alarm.
16. The electromagnetic door retaining system in accordance with any preceding claim, wherein the door is arranged to automatically return to a closed position when the attractive elements are moved out of engagement with one another or when the electromagnet is de-energerised.
17. The use of a door retaining system in accordance with any preceding claim to retain a door in a selected open position while allowing the door to close in an emergency situation.
18. A method of retaining a door in a selected open position using a door retaining system in accordance with any of claims Ito 16.
19. A method for retaining a door in a selected open position using an electromagnetic door retaining system comprising opposed attractive elements, the method comprising energising said system whereby the attractive elements cooperate to retain the door in the open position, wherein said attractive elements are located one above the other.
20. A method for retaining a door in a selected open position using an electromagnetic door retaining system comprising opposed attractive elements, the method comprising energising said system whereby the attractive elements cooperate to retain the door in the open position, wherein said attractive elements are slidable over one another on movement of the door.
21. A method for retaining a door in a selected open position using an electromagnetic door retaining system comprising opposed attractive elements, the method comprising energising said system whereby the attractive elements cooperate to retain the door in the open position, wherein said attractive elements define horizontal attractive surfaces for retaining the door.
22. The method of any one of claims 18 to 21, wherein the method comprises the step of arranging the attractive elements such that the selected open position of the door is not a fully open position of the door.
23. The method of any of claims 18 to 22, further comprising the step of operating the system such that the attractive elements cooperate with one another to retain the door in a selected open position while allowing the door to be moved manually towards a more closed and/or open position, while the electromagnet is energised in use.
24. A method of operating an electromagnetic door retaining system having attractive elements for retaining the door in a selected open position when the electromagnet is energised in use, the method comprising the step of operating the system such that the door is manually movable to a more open or closed position than said selected open position while the electromagnet is energised in use.
25. The method of claim 23 or claim 24, wherein the method comprises the step of operating the system whereby the attractive surfaces may be moved out of engagement with one another to move the door towards a more open or closed position on application of a shear force in the range of less than 10 Newtons, or preferably in the range of from I to 5 Newtons.
26. The method of any of claims 18 to 25, wherein the method comprises operating the system such that a power supply to the electromagnet is interrupted in use on detection of an emergency condition to release the door.
27. An electromagnetic door retaining system substantially as herein described and with reference to any one of the accompanying drawings.

- 28 -
28. A method for retaining a door in a selected open position substantially as herein described with reference to any one of the accompanying drawings.