GB2189288A - Security chain door lock - Google Patents

Abstract

A security chain door lock comprises a lock mechanism (6) hingedly (9) attachable to a door frame (2) and having a latch (12) adapted for coupling by a key (5) to one end of a security chain (4) attached at its other end to the inward side of a door (1). The latch mechanism (6) is biased by a spring (17) to a blocking position in which the latch (12) projects beyond the edge of the door on its inward side. The latch (12) is displaceable away from that position either by door contact in a door opening movement when the security chain (4) is incoupled or by manipulation of the security chain (4) when it is coupled by the key (5) to the latch (12). Further the latch (12) is manually movable to a retracted position in order to allow closure of the door (1) from the outward side. <IMAGE>

Description

SPECIFICATION Security chain door lock This invention relates to a security chain door lock and has been devised with the object of providing a door locking arrangement which ensures that a door cannot be closed from the inside unless a security chain has been re-engaged between the door and the doorframe, the underlying purpose of the security chain being to permit opening ofthe door to only a limited extentforthe purpose of checking the identity of visitors.

A security chain door lock in accordance with the present invention comprises a latch mechanism hingedlyattachabletoa doorframeand having a latch adapted for coupling to one end of a security chain attached at its other end to the inward side of a door, the latch mechanism being spring biased to a blocking position in which the latch projects beyond the edge of the door on its inward side, the latch being displaceable away from that position either by door contact in a door opening movement when the security chain is uncoupled or by manipulation ofthe security chain when it is coupled to the latch, the latch being manually movable to a retracted position in orderto allow closure ofthe door bya person on its outward side.

If desired there may be fitted to the lock a visible or audible warning device for indicating that the latch is in a blocking position from which it can only be withdrawn by attachment and manipulation of the safety chain.

A particular and at present preferred embodiment ofthe invention is illustrated somewhat schematically in the accompanying drawings in which: Figure lisa fragmentary perspective view of the inward side of a door, doorframe and locking mechanism with safety chain coupled thereto; Figure 2 is a horizontal section through the components in the position shown in Figure 1; Figure 3 similarto Figure 2 shows a preliminary door opening procedure; Figure 4 similar to Figures 2 and 3, shows a door blocking and alarm position; Figure 5is a vertical section through the locking mechanism; and Figure 60n an enlarged scale, illustrates a latch retaining means.

Referring now to Figure 1 of the drawings there is shown part of a hinged door 1 which is mounted within a frame 2. The door has a handle 3 to enable it to be opened from the inside and a security chain 4 permanently connected at one end to the door 1.

Attached to the other end ofthe security chain 4 is a key 5 formed at its free end with a reduced diameter shank portion 5a and an enlarged tip b (Figure 2).

This key 5 is insertable into a keyhole slot 1 2a in a latch 12which is rotatableabouta horizontal pin 13 and forms part of a mechanism 6 contained ion a housing 7 fixed to the door frame and shown most clearly in Figures 2 to 5.

This mechanism comprises a base plate 8which is attached to the door frame 2 bya hinge 9forlimited angular movement about an axiswhich is parallel to the door hinge axis. To perm it this hinging movement of the latch mechanism, the part 7a of the housing which faces the door is suitably cut away.

The mechanism is biased towards a position against the door by a coil spring 17. When it is required to prevent this hinging movement, e.g. at night, there is inserted through a hole in the top ofthe housing an elongated bo!t 24 which projects downwardly past the latch 12.

The mechanism further comprises a spring bolt 10, of conventional type, which co-operates with a pressure pad 11 mounted on the door and is outwardly biased by a spring 18. The already mentioned latch 12 is angularly movable about its pivot pin 13 between a first position (Figures 1,2 and 4) in which it projects horizontally from the housing and an upwardly retracted position (Figure 5). The latch 12 (Figure 6) is retained in the first ofthese positions by a pivoted arm 14 which is biased in a clockwise direction by a spring 15 to a position in which it engages a lug 1 2b projecting from the side of the latch 12. When the arm 14 is turned out of engagementwiththe lug 12bthe latch 12 can be turned manually into the retracted upright position shown in Figure 5.The latch 12 is restorableto it's horizontal projected position by means of a rod 16 which is fixed to the spring bolt 10. When the spring bolt 10 is pressed inwards by engagement with the pressure pad 1 1,the rod 16 engages and swings the latch 12 to the position shown in chain-dashed outline, whereafter by gravity action, it resumes it's previous horizontal blocking position. Buffer plates (not shown) may be fitted in fixed positions one on each side of the latch 12 to damp vibration of the latch during opening and closing ofthe door.

Optionally, there is attached to the inward side of the door a low voltage battery connected to an audible warning circuit 19 incorporating a buzzer 21 and a pair of closely adjacent contacts 22 on the outward side of the door which, when bridged by the latch 12, cause the buzzerto sound.

The mode of operation is as follows.

When the door has been closed from the inside, the key 5 of the safety chain 4 is engaged with the key hole slot 12a in the latch 12. To enable an arriving visitor to be identified the doorwill be opened from the inside to the limited extent permitted by the length of the security chain 4. If the visitor is to be admitted, the key 5 is removed from the latch 12 and the door is opened fully. This full opening of the door is possible after a striker plate 23 on the door has applied pressure to the side of the latch 12 because of the hinged mounting of the mechanism which thereupon by action of the spring 17 returns to its initial position against the door frame.

The onlyway in which the door can now be re-closed is by engaging the key 5 of the security chain with the key-hole slot 12a in the latch 12 and pulling the latter until the mechanism swings sufficiently about the hinge 9 to allowthe doorto clearthelatch 12 (Figure 3). The door cannot otherwise be closed and if an attempt is madeto close the door without engaging the security chain pin in the latch 12 and hinging the mechanism as aforesaid the latch 12 bridges the contacts 22 and causes the buzzerto sound (Figure 4). This reminds the userthatthe key 5 must be re-engaged with the latch 12 and used to swing the mechanism to the position shown in Figure 3to allow the doorto be closed from the inside.

When it is required to leave the premises and close the doorfrom the outside it is necessaryfirstto move the 14 manually upwards to release itfrom the lug 12b on latch 12 and allowthe latterto be swung in an upward direction to thefull line position shown in Figure 5. The action of thereafter closing the door however causes the spring bolt 10 to slide momentarily inwards and the rod 16 to restore the latch 12 to its original horizontally projecting position. In a subsequent re-entry from the outside, after a main lock has been released pressure applied to the outside of the door and thence to the outward face ofthe latch 12 allows the mechanism to swing aboutthe axis of hinge 9 to a sufficient extent to permit full opening ofthe door as previously explained.

Claims (7)

1. Asecuritychain doorlockcomprising a latch mechanism hingedly attachable to a doorframe and having a latch adapted for coupling to one end of a security chain attached at its other end to the inward side of a door, the latch mechanism being spring biased to a blocking position in which the latch projects beyond the edge ofthe door on its inward side, the latch being displaceable away from that position either by door contact in a door opening movement when the security chain is uncoupled or by manipulation of the security chain when it is coupled to the latch, the latch being manually movable to a retracted position in order to allow closure ofthe door from the outward side.

2. A security chain door lock as claimed in claim 1 and further comprising a spring boltwhich co-operates with the door and means which operates from the spring boltwhen the door is closed from the outward side to restore the latch to its blocking position.

3. A security chain door lock as claimed in claim 1 orclaim2andfurthercomprising alarm meansfor indicating that when the door is being closed from the inward side the latch has not been displaced after attachment ofthe security chainthereto.

4. A security chain door lock as claimed in any of claims 1 to 3 in which the latch has a keyhole slot for accommodating a key by which the safety chain can be coupled to the latch.

5. A security chain door lock as claimed in any of claims 1 to 4 in which the latch is pivotally mounted and releasably retained in its blocking position by a pivoted arm engaging a lug on the latch.

6. A security chain door lock as claimed in claim 3 in which the alarm means comprises an open electric circuit with a pair of spaced contacts situated on the door at a position such as to be bridged by the latch when the latter has not been retracted by the security chain to actuate an alarm signal.

7. A security chain door lock constructed and adapted to operate substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.