Closure fasteners – Magnetic
Patent
1996-05-24
1998-01-20
Lindsey, Rodney M.
Closure fasteners
Magnetic
292254, 292DIG72, E05C 1916
Patent
active
057094217
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to electromagnetic locking devices of the kind used, for example, in connection with security doors and fire doors to hold such doors closed under normal circumstances whilst allowing them to be released quickly in an emergency.
Basically there are two types of electromagnetic locking device used for such purposes, each including an electromagnet, which is normally mounted on a door frame, and a co-operating armature, which is normally mounted on the door itself, so that energisation of the electromagnet establishes a high attractive holding force on the armature which resists opening movement of the door relative to the door frame.
In the first type the armature is arranged in face-to-face relationship with the electromagnet so that the attractive force acts directly opposite to the direction in which the door moves away from the door frame when it is opened. In other words, the door is held closed purely by the electromagnetic force acting on the armature. Despite the fact that one or more electromagnetic locking devices of this kind can exert very high forces on the door, in the order of 350 kgf, such locking force can nevertheless be overcome by a shock load, as for example by kicking or a sledgehammer blow.
The other type overcomes this disadvantage by arranging the armature in an edge face of the door in such a manner that as a result of the attractive force generated by the facing electromagnet in the door frame, the armature is drawn towards the electromagnet so as to engage behind an abutment, usually in the form of a shear plate, which is associated with the electromagnet. When the electromagnet is energised the armature is retained behind the shear plate so that the door is mechanically locked. When the electromagnet is de-energised, the armature is free to retract under the force of an associated spring, thereby clearing the shear plate and allowing the door to be opened.
This second type of electromagnetic locking device therefore offers much greater security than the first type.
However, there is a potential problem with this type of electromagnetic locking device in that if a high static load is imposed on the door, in the direction required to open the door, as may happen for example in a panic situation where people are pressing against the door, the armature will tend to be frictionally held by the shear plate due to the force exerted on the armature which holds it against the shear plate.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide such an electromagnetic locking device in which this disadvantage is overcome.
In accordance with the present invention we provide an electromagnetic locking device of the kind comprising an actuating assembly which includes an electromagnet having an operative face and at at least one side thereof an abutment which extends in a direction substantially perpendicular to said operative face and projects beyond said operative face, and a co-operative assembly which includes an armature mourned for movement towards and away from said operative face in a direction substantially perpendicular thereto when the electromagnet and armature are aligned and arranged so as to engage behind said abutment when the electromagnet is energised, characterised in that the armature is mounted so as to allow the armature pivotally to move progressively onto and off the electromagnet across the width thereof; and said actuating assembly includes at least one member adjacent to one side of the electromagnet and which is mounted for movement substantially perpendicularly to said operative face between a retracted position and an extended position relative to said operative face, and means for driving the member into its extended position out of contact with said armature to displace said armature out of contact with said electromagnet progressively across said operative face when said electromagnet ceases to be energised.
Thus, in accordance with the invention, when the electromagnet is de-energise
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Lindsey Rodney M.
Newman Tonks Group P.L.C.
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