Closure fasteners – Magnetic
Reexamination Certificate
1999-10-26
2003-08-26
Barrett, Suzanne Dino (Department: 3676)
Closure fasteners
Magnetic
C292S092000, C292S144000, C292SDIG006
Reexamination Certificate
active
06609738
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of the present invention relates to electromagnetic emergency exit door lock systems. More particularly, the present invention relates to tamper-resistant time delay emergency exit electromagnetic door lock systems.
2. Description of the Related Art
Electromagnetic locks are commonly used in “delayed exit” systems. The purpose of a delayed exit system is to allow people to exit a building immediately in the event of an emergency, or after a 15 to 30 second delay in a non emergency situation while at the same time providing an acceptable measure of security against unauthorized entry or exit. Typically, a person who wishes to exit in an emergency activates the door by pressing down on a spring biased push bar sometimes called a “panic bar” mounted on the door. Alternately a lever or door knob may be turned. This initiates an audible alarm. If the person maintains the initiate signal by holding the panic bar down for the duration of a “nuisance delay” period which is typically 1 to 3 seconds, the system will then begin a delay known as an irrevocable release or egress delay. At the end of the egress time delay the door will open. The egress time is typically 15 or 30 seconds under most building codes.
The purpose of the nuisance delay is to cope with accidental striking of the door or push bar. When someone inadvertently presses against the push bar, an audible alarm warns the person away from the door. If the initiate signal is maintained for less than the duration of the nuisance delay period, the door will “reset” when the initiate signal stops and will therefore not release at the end of the 15 or 30 seconds. This maintains security and also saves building staff from the necessity of going to the door and re-locking it if it had released. The nuisance delay concept was intended to not only deal with accidental striking of the door, but with casual vandalism as might be expected from young persons who would push the door, hear the alarm, and then run away. On the other hand, if the initiate signal is maintained for longer than the nuisance delay period, release after 15 or 30 seconds becomes irrevocable. Such systems are in broad use, particularly in retail establishments where they greatly reduce theft loss while complying with building codes that require a minimum number of emergency exits.
One of the earliest electromechanical delayed exit systems is disclosed in U.S. Pat. No. 4,257,631 issued to Logan. Logan discloses a switch located within a push bar mounted on the door to sense when somebody attempts to exit the building. There are two significant drawbacks to this design. First, on existing doors a push bar is already present so it must be replaced at relatively high cost with a push bar equipped with a switch. Second, the wires to the switch within the push bar must be routed from the door to the frame which carries the electromagnetic lock. This requires either an electric hinge which is costly to purchase and install, or a “door cord” which is looped between the door and frame. Such door cords invite vandalism as the wiring is exposed.
U.S. Pat. No. 4,609,910 issued to Geringer discloses a delayed exit system in which two bolts which mount the armature plate to the door are allowed slack in their holes. When the door is pushed, the door can move slightly, thereby taking up this slack. The door remains securely held by the electromagnetic lock but the slight motion can be detected by a plunger type switch. The switch initiates the delay without the need to supply a switch equipped push bar or to route wires into the door.
One problem with this system is that it is prone to false initiation. To avoid having to precisely align the door and the door frame, the push bar-activated latch is often allowed a significant amount of slack within its securing recess. Wind or vandals rattling the door can take up the slack provided in the bolts of Geringer, thereby activating the switch and initiating the delay even though a person had not intended to exit. This constitutes a type of “false alarm”.
A further drawback of this design is that it is vulnerable to tampering. The plunger switch can be taped down such that the switch is incapable of recognizing when the door has been pushed away from its fully closed position in an effort to exit the building. This type of tampering may be performed by building guards for example who desire to increase security at the expense of egress safety, or who do not wish to have to check on the door when it is activated, either by someone who has exited or by a false initiation. This creates a hazardous and potentially fatal situation.
A similar design is disclosed in U.S. Pat. No. 4,652,028 issued to Logan et al. As in the Geringer design, slack is created by the use of bolts whose heads fit loosely within the armature plate. This design is prone to similar false initiations. Since the Logan et al. design uses a Hall effect sensor to detect the slight movement of the door provided by the slack in the bolts, the mechanism cannot be overridden by the use of tape. However, the system may still be tampered with by the application of an external magnet, which can disrupt the operation of the Hall effect sensor.
A further design is illustrated in U.S. Pat. No. 4,915,431 issued to Bailey. As in Geringer, Bailey employs a mechanical plunger switch, but the switch is positioned in the center of the armature which makes it relatively immune to tampering. As in Geringer, the slack that allows door movement is created by allowing mounting bolt heads to move slightly within the armature. This design is also vulnerable to false initiation by rattling of the door caused by wind or vandals.
A still further design is illustrated in U.S. Pat. No. 5,065,136 issued to Frolov et al. In this design, the electromagnet body is permitted to pivot slightly in response to pressure on the door. The rotational action of the top of the electromagnet creates a small gap between the electromagnet top and the door header which permits a spring biased switch to change state by its trigger moving into the gap. This design is also prone to tampering. Someone working within the facility can temporarily pivot the electromagnet body down and insert a piece of tape to prevent the switch from moving into the gap. This would prevent the switch from being triggered by movement of the door.
An armature mount assembly is disclosed in U.S. Pat. No. 5,184,856, issued Feb. 9, 1993 to Waltz. The disclosure teaches a mount that allows the armature to be pulled outward from the door a small distance to contact an electromagnet mounted to the door frame. However, there is no teaching of an armature mount that allows the door to be opened outwardly a considerable distance while the armature is held against the electromagnet.
SUMMARY OF THE INVENTION
Accordingly, it is a general object of this invention to provide a delayed exit door control system that can be economically implemented for retrofit applications.
It is a further object of the invention to provide a delayed exit door control system that is resistant to false initiations by rattling caused by wind or vandals.
It is a further object of the invention to provide a delayed exit door control system that is resistant to tampering, either from casual vandals or by personnel within the facility.
It is also an object of the invention to overcome disadvantages of the prior art.
To achieve these and other objects, the present invention includes an electromagnet mounted to a door frame, an electromagnet armature mounted to a door facing the electromagnet, and an armature mount allowing considerable outward movement of the door with respect to the frame while the armature is held against the electromagnet. One way of doing this is by providing an armature mounting bolt (sometimes referred to as a “sex bolt” within the industry) that includes a novel internal spring biased plunger to which the armature is mounted. The spring biased plunger extends out the back of the armature mountin
Cook Robert
Frallicciardi Vincent
Roth Thomas
Wojdan Dennis
Barrett Suzanne Dino
Oppenheimer Wolff & Donnelly LLP
Securitron Magnalock Corp.
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