GB2272245A - Door lock alarm - Google Patents

Abstract

A lock mechanism comprising a lock bolt 6 and sensor (20, 24, 26, 30) for detecting a shear force of a predetermined magnitude applied to the lock bolt 6. The sensor output is connected to an alarm circuit which may either be connected to an external alarm system via a terminal 46, or to an alarm circuit for producing an alarm tone through a loudspeaker. The mechanism may be used in conjunction with a lock keep 48 having a pivoting member 50. When the bolt is partially extended recess 56 at the end of the bolt lies in slot 64 and the pivoting of member 50 allows limited opening. <IMAGE>

Description

ALARM LOCK This invention relates to a lock incorporating an alarm.

Battery powered alarm systems are available that comprise a unit for fitting to a door frame and a second unit incorporating a proximity sensor, for fitting to a door.

Such systems may raise an alarm when the door is opened.

This is only of limited use since once the door is open an intruder has free access to the room that was protected by the alarm. Furthermore, such systems cannot be used in conjunction with a door-chain type device.

It is an object of the present invention to provide an alarm for a door which overcomes at least some of the disadvantages of prior door alarms.

According to a first aspect of the present invention, there is provided a lock for a door comprising at least one sensor for detecting an attempt to force the door, and an alarm signal generator coupled to an output of the or each sensor, the signal generator being operable to generate an alarm signal when a predetermined output signal is received from the sensor.

The lock may comprise at least one lock bolt for preventing the door from opening when in a shut position. A sensor may be provided that can provide an output indicative of a shear force on the bolt or bolts. By arranging for such a force to be detected, the action of the door being forced may be sensed.

The sensor is preferably a pressure transducer comprising a combination of a switch and a resilient element adjacent one side of the bolt which is compressed when a force normal to the side, is exerted on the bolt. The resilient element may be an elastomeric block. Since the block will try to maintain a substantially constant volume, the compression in one direction will result in an expansion in another. This expansion may be used to activate the switch (which may be a microswitch) either directly or via at least one lever.

A bearing plate having a low friction bearing surface may be placed between the block and the bolt to permit the bolt to slide freely over the sensor when it is extended or retracted in order to lock and unlock the door to which the lock is fitted. The plate may be a polished or anti-friction coated plate of metal or any other similar low friction material. The sensor may be located in the lock or in an associated lock keep.

The signal generator is preferably an electronic tone generator the output of which may be coupled to a loudspeaker mounted in the housing of the lock. The loudspeaker may be of the piezo-electric type. In addition or alternatively, an output from the signal generator may be provided which is suitable for connection to an external alarm system such as a domestic burglar alarm, thereby allowing the alarm in the lock mechanism to be integrated with a larger system. Thus when an alarm is raised, a triggering signal can be coupled to the larger system.

The lock may advantageously be powered by battery. Since this means that access must be provided for replacement of the battery, there is a possibility that the alarm could be disabled by disconnecting the battery. This may be avoided by fitting a switch to the flap permitting access to the batteries, this switch being coupled to the alarm signal generator such that the alarm is triggered when the flap is opened.

It may be desirable to be able to arm and disarm the alarm and preferably this is achieved by relating the arm/disarm state to the position of the lock bolt or bolts. By arming the alarm whenever the bolt is not fully retracted, the alarm may be automatically armed whenever the door is locked. Alternatively this may be achieved by providing and arming switch or keyswitch.

A further security feature may be incorporated in the lock.

Thus, according to a second aspect of the invention, there is provided a lock for a door comprising at least one lock bolt and a lock keep wherein a slot member, having a slot for engagement with the lock bolt, is pivotally fixed to the keep. The slot member may be arranged to pivot in a plane substantially perpendicular to a major face of the door. By arranging for the lock bolt to have a step near, but spaced from the end which extends from the housing, the bolt may be engaged in a slot provided on the slot member, the step serving to prevent the bolt being forced or falling out of engagement with the slot. This feature permits the door to be opened slightly but provides a restriction to full opening of the door.The slot may be formed in a plate which is pivotally mounted on the keep and which allows the slot to move in a plane substantially parallel to the plane of movement of the edge of the door adjacent the lock mechanism. By including this feature on a lock and keep assembly which also has the pressure transducer feature mentioned above, an alarm can be raised when the door is forced even when it is only prevented from opening by the slot and step arrangement.

The invention will now be described by way of example, with reference to the drawings in which: Figure 1 is a cross-section through a lock in accordance with the invention; Figure 2 is a cross section on a line X-X of figure 1; Figure 3 is a partial cross-section on a line Y-Y of figure 1; and Figure 4 is a plan view of a lock keep in accordance with the invention.

In a preferred embodiment of the invention, a lock mechanism for a door comprises two sliding lock bolts operated by a lock barrel in a conventional manner, a power source, an alarm circuit, a loudspeaker, and at least one pressure sensor associated with the bolts. This pressure sensor is arranged to detect a side force imposed on either.bolt as a result of, for instance, the door being forced.

With reference to Figure 1, the lock mechanism is housed in a steel casing 2. This surrounds the lock mechanism in the manner of the outer sleeve of a matchbox, in that two faces of the mechanism are left uncovered. This permits the mechanism to be inserted from one end during manufacture and located using a screw 4 which passes through the casing into the mechanism within.

Since in operation, the lock is not subjected to large forces that would dislodge the mechanism from the casing, a strong fixing between the mechanism and case, need not be provided However additional security is provided by passing a lock barrel mechanism (not shown) through an opening in the casing. The lock barrel mechanism cooperates with the lock mechanism to cause lock bolts 6 to be extended or retracted by rotating a key in the barrel. The barrel mechanism is rigidly fixed in a tamper-proof manner to a cover 8 which encloses it except for an opening provided for insertion of the key. The barrel mechanism itself is fixed to the opening in the casing. Since the mechanism cannot be removed from the casing with the barrel mechanism in place, and since the barrel mechanism cannot be removed with the cover 8 in place, the mechanism is effectively secured in the casing.

The mechanism comprises a carrier 10 which carries the components necessary for operation of the alarm, and the lock bolts 6 which, when in a locking position, extend from one of the ends of the carrier not covered by the casing.

The carrier is made of a plastics material and, with reference to Figure 2, has a battery compartment 12 and a recess 14 for accepting a PCB which carries an alarm circuit. The circuit comprises an electronic tone generator, an audio amplifier and timing and latch circuitry to control the operation of the alarm. The output of the amplifier is connected to a piezo-electric loudspeaker housed in a hinged flap 16. This flap permits access to the battery compartment for battery replacement.

Connected to the alarm circuit via wires routed through channels in the carrier are two microswitches 18, 20 which are mounted in recesses in the carrier.

The first microswitch 18 is fixed to the carrier at a position opposite the internal end of one of the bolts 6, the bolt moving substantially in the direction indicated "A" in Figure 1 as it is retracted and extended, and the microswitch 18 is arranged to detect when the bolt is fully retracted. This switch is connected to the alarm circuit, which is arranged such that the alarm is put in a disarmed state only when the bolt is fully retracted i.e. when the door is unlocked. By arming and disarming the alarm in this way, it is unnecessary to use a separate switch or key to arm the alarm since it will automatically be armed every time the door is locked.

The second microswitch 20 is mounted in the carrier close to the end from which the bolts project. Resting against a switch pin 22 of the microswitch 20 is a cranked lever 24 pivotally housed in the carrier 10. The lever is flat in the plane of Figure 2 but is largely 'L' shape in plan view.

The two ends of the lever are also cranked to form a small pad area at each end. One pad rests against the switch pin and the other pad 25 rests against a resilient block 26.

With reference to Figures 1 and 3, The resilient block is fixed in a recess 28 in the carrier by friction and/or adhesive. The recess is formed adjacent the lock bolt and has an opening facing the bolt. Sandwiched between the block 26 and the bolt 6 and covering the opening, is a metal bearing plate 30. This plate 30 allows the bolt 6 to slide freely in the direction "A", yet transmits any side force on the bolt 6 in the direction "B" to the block 26. A second opening is provided in the recess 28 adjacent the pad 25, and it is through this that the pad 25 is able to rest against the block 26.Since the recess 28 is of identical dimensions to that of the block 26 and since the block 26 is almost completely enclosed by the walls of the recess and the plate 30, when a side force is imposed on the bolt 6, and the block 26 is compressed by the bearing plate 30, the block 26 expands out of the recess adjacent the pad 25.

Since the pad 25 rests against the block 26, this is caused to move away from the recess 28, which causes the lever 24 to pivot about a fulcrum point 32 which is formed in the channel in the carrier in which it rests, and thereby to depress the switch pin 22. The closing of the switch contacts triggers the alarm. The force required to trigger the alarm depends on the resiliency of the block 26, the dimensions of the block 26 and recess 28, the angles of the cranked lever 24 and the amount of depression of the switch pin 22 that is required before the switch contacts close.

Since these factors are under control of the lock designer, the trigger point of the alarm in relation to the magnitude of the side force, can be tailored for different applications.

It will be appreciated by those skilled in the art, that a different type of sensor could be used in this application e.g. a strain gauge, a piezo sensor or a conventional pressure transducer.

With reference to Figure 2, access holes 34 and 36 are provided in the carrier to permit access to fixing bolts (not shown) for fixing the case to the door. The fixing bolt heads rest in countersunk recesses 38 formed in the case. In the case of holes 36, the lock bolts 6 obscure the fixing bolt heads except when the lock bolts are fully retracted. In this position, a hole 40 through each lock bolt, is brought into line with the hole 36 and recess 38 and this permits a screwdriver or the like, to be inserted through holes 26 and 40 to gain access to the fixing bolts.

Thus the lock case 2 can only be removed from the door when the lock bolts are fully retracted, i.e. when the lock is unlocked. Thus it is not possible to open the door when it is locked, by attempting to remove the lock from the door.

The holes 36 are covered by caps 42 when not in use. The holes 34 are covered by a single cap which lies outside the case and extends between the holes. This cap has a cantilever with a pin extending from the unsupported end of the cantilever, the pin being directed down into the carrier through a hole in the case. The pin enters the carrier adjacent the pad 44 of the cranked lever 24 and on the opposite side of the pad from the switch pin 22. When the unsupported end of the cantilever is pressed, it is caused to pivot about its supported end which in turn, causes the pin to press against the pad and to depress the switch pin, thereby triggering the alarm. Thus the cantilever part of the cap forms a 'panic' button which can be used to trigger the alarm manually.

An electrical socket 46 is connected to the alarm circuit and provides a trigger output for a domestic alarm system.

With reference to Figure 4, the lock includes a lock keep 48 with a slot member 50 pivotally mounted to the keep by a bolt 52 with a plastic bearing 54. One of the lock bolts 6 is recessed to produce a stepped portion 56 at the end which first emerges from the mechanism as the bolt is extended.

In a first extension position of the bolt 6 as shown in Figures 1 and 2, the stepped portion of the bolt 6 is sufficiently extended from the mechanism to engage with the slot member 50 but not to engage with bolt-receiving apertures 58 of the lock keep 48. In use, the slot member 50 hangs substantially vertically and a stop pin 60 engages in a cutout 62 to ensure that a slot 64 of the slot member 50 is aligned with the apertures 58.

If an attempt is made to open the door with the bolt 6 in the first position, the door will start to open since the bolt is not engaged in the apertures. Since the bolt is however engaged in the slot 64, the slot member 50 is caused to pivot generally as shown in Figure 4. The stepped portion 56 gradually slides along the slot 64 until the portion 56 is at an end of the slot 64 and the slot member 50 is approximately normal to the longest side of the keep 48. In this position, the door is prevented from opening further and any additional force on the door increases the load on the pressure sensor comprising the resilient block 26 and microswitch 18. Thus if the door is forced, the alarm may be set off. To summarise, when the door is shut and the bolt 6 is in a first, partially extended position, the slot member 50 is automatically engaged by the bolt 6 and the door may only be opened partially. If the bolt 6 is extended further, it engages in the aperture 58 and the door is prevented from opening at all. In both cases, the alarm may be triggered by an attempt to force the door.

With reference to Figure 1, the alarm mechanism is strengthened by steel inserts 66 inserted in the carrier near the end of the casing 2 where the bolts 6 exit. This strengthens the carrier to prevent it being crushed by side loads imposed on the bolts 6 and the pressure sensor. On the opposite side of the bolts, the case has indents 68 which space the bolts from the case and provide a series of bearing points for smooth running of the bolt 6.

Claims (13)

1. A lock for a door comprising at least one sensor for detecting an attempt to force the door, and an integral alarm circuit including an alarm signal generator coupled to an output of the or each sensor, the signal generator being operable to generate an alarm signal when a predetermined output signal is received from the sensor.

2. A lock according to claim 1, including at least one lock bolt wherein at least one sensor is operable to sense a shear force applied to the bolt.

3. A lock according to claim 2, wherein the sensor is a strain gauge, or a piezo-electric sensor.

4. A lock according to claim 2, wherein the sensor comprises a resilient element adjacent a side of the bolt arranged to be compressed by the bolt when a force normal to the side is applied to the bolt and further comprising a microswitch arranged to be switched by movement of the resilient element when the applied force reaches a predetermined level.

5. A lock according to claim 4, wherein the microswitch is switched via at least one lever.

6. A lock according to any of claims 2 to 5, wherein a bearing plate is located between the bolt and the sensor which is operable to permit the bolt to slide freely over the sensor during extension and retraction of the bolt.

7. A lock according to any preceding claim, wherein the alarm circuit comprises a loudspeaker and an electronic tone generator coupled to the loudspeaker and wherein the alarm signal is an alarm tone played through the loudspeaker.

8. A lock according to any preceding claim, comprising an output terminal for connecting the alarm signal to an external alarm system.

9. A lock according to any preceding claim, wherein the alarm circuit is battery powered.

10. A lock according to any preceding claim, wherein the alarm circuit is armed when the lock is locked an disarmed when the lock is unlocked.

11. A lock according to any preceding claim, comprising at least one lock bolt and a lock keep wherein a slot member, having a slot for engagement with the lock bolt, is pivotally fixed to the keep.

12. A lock according to claim 11, wherein the slot member is arranged to pivot in a plane substantially perpendicular to the major faces of the door.

13. A lock constructed and arranged substantially as described herein with reference to the drawings.