GB2172931A - Thermally-responsive door-locking mechanisms - Google Patents

Abstract

The locking mechanism for the door of a thief-resistant or fire-resistant safe has a thermal "relocker" comprising a shape memory effect (SME) element adapted to activate an additional locking point in the event of a thermal attack or exposure to fire. For example the SME element may be in the form of a coil 14 which expands when heated through its transformation temperature range to place a plunger 17 in the retraction path of an abutment 20 carried with the main bolts of the exclosure. <IMAGE>

Description

SPECIFICATION Thermally-responsive door-locking mechanisms The present invention relates to thermally-responsive door-locking mechanisms. In this specification the term "door" is intended also to embrace drawers and the like container closures where the context so permits. In particular the invention is concerned with locking mechanisms for the doors of security enclosures, such as safes and strongrooms which are designed to resist burglarious attacks using thermal tools, as well as heat-resistant cabinets, files and the like storage equipment which are designed to protect paper, microfilm, magnetic data media etc from the effects of fire whether or not also specifically designed to provide security against burglary.

The invention provides a door-locking mechanism which includes a thermal transducer sensitive to temperature within a region of the door and arranged to activate locking means for the door in response to the detection of a predetermined temperature, the said transducer comprising an element of shape memory effect material.

A shape memory effect (SME) material is one which undergoes a transformation in its crystallographic structure when heated or cooled through a particular temperature range with this transformation being accompanied by a significant change in elastic modulus. By appropriate thermal and mechanical treatment of an element made from such a material, the element can be arranged to exhibit a first stable shape at temperatures below the corresponding transformation range and a different stable shape at temperatures above that range, the element being capable of changing reversibly between its low and high temperature shape conditions when heated or cooled through the transformation temperature range. In other words the element behaves in a manner indicative of retaining a "memory" for either shape.Usually, the SME material is an alloy which on change of temperature in the relevant range exhibits a martensitic transformation, the metallurgical structure changing from martensite to austenite with increase of temperature and vice versa with fall of temperature. A number of such alloys are known, including certain nickel-titanium and copper-zincaluminium (brass) alloys.

In the application of the present invention to the doors of safes and strongrooms for example, the aforesaid thermal transducer may be arranged to activate automatic locking means provided in addition to the primary key or combination locks of the door, if the transducer detects and increase of temperature within a region of the door resulting from an attack eg with melting or flame-cutting tools.

Automatic locking devices which increase the security of the enclosure in this way are known in the art as "relockers". Previously used thermal relockers have employed bimetallic members or fusible alloys as the temperature-responsive element.

However the SME transducer of the present invention can offer considerable advantages over these prior devices.

For example, bimetallic materials are able to produce movements by change of shape when subjected to a temperature variation, but produce gradual and continuing movements over a wide temperature range. In contrast, the change of shape of an SME element can produce relatively large movement which are, however, restricted to a closely-defined temperature range with the element remaining shape-stable outside that range.

Positive activation of the additional locking means at a specified temperature can thus be more reliably achieved with an SME transducer, and the stability of the element below the transformation temperature range minimises the risks of unwanted locking due eg to normal changes in ambient temperature; premature activation can be a problem with bimetallic elements owing to their gradual and extended temperatureldisplacement characteristic.

Fusible alloy detectors have the disadvantage that they are "once only" devices, which cannot be operated again once melted, or tested in use. Also, thermal activation devices based upon these cannot act directly to provide the required locking and are not at all conveniently applied to some functions, for instance the "live" relocking referred to below. In contrast, SME elements can act directly to move locking obstructions and have greater flexibility in terms of the types of application in which they can be used. Another advantage of SME elements as compared with fusible alloys is that they can be tested by cycling through the transformation temperature range and to ensure that the correct function is performed.

By careful selection of the alloy composition the transformation temperature range of an SME element can be matched to the requirements of the application. In the case of thermal relockers provided for the purpose indicated above the lower limit of the transformation temperature range (referred to herein as "T,") should be sufficiently low to provide early detection of a thermal attack, but sufficiently high to avoid unwanted activation by changes in ambient temperature, and therefore may be 50 to 100"C. A transformation temperature range of about 60"C, for example T = 50"C, Tf (ie the upper limit of the transformation range) = 110 C, may be suitable for most relocker applications.

Turning to the application of the present invention to fire-resisting (though not necessarily thiefresisting) storage equipment, a special problem with this type of equipment is the difficulty in predicting the amount of thermal distortion which the container may suffer under different fire conditions. Such containers likewise can be exposed to considerable mechanical distortion eg if located in a building which collapses due to fire. To minimise the chances of distortion causing gaps between the door and body of the container, through which heat might reach the interior of the container and thus damage its contents, it may be desirable to have more bolts or latches etc extending between the door and body under fire conditions than are needed for normal use.To provide the extra locking points by conventional means they all would need to be linked to a common operating handle; this would involve a substantial increase in the volume of metal in the boltwork with the likelihood that this would conduct more heat to the interior.

Automatic activation of the additional locking means by SME transducers in accordance with the invention can provide a solution to this problem.

The form of the SME elements used in transducers according to the invention is open to considerable variation. One form is a tube of SME material one end of which, when heated through the temperature transformation range, twists relative to its other end, so that this rotary movement can be used to move a locking member. Another, and more versatile form is a helical coil of SME wire. Passing through the transformation temperature range will cause the overall length of the coil to increase or decrease as the stiffness of the material changes. Quite large movements can be obtained with such a coil, 100% expansion or contraction being quite feasible.

Various possible embodiments of locking mechanisms according to the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows the boltwork of a safe or strongroom door equipped with thermally-activated relockers; Figure 2A shows elevation and plan views of one of the relockers of Figure 1 in its low temperature condition and Figure 2B shows similar views of the relocker in its high temperature condition; Figure 3A is an elevation, partly in section, of the other of the relockers of Figure 1 in its low temperature condition and Figure 3B is a similar view of the relocker in its high temperature condition; Figure 4A is an elevation of another type of thermally-activated relocker and Figure 4B is a section on the line B-B of Figure 4A; Figure 5 shows the boltwork of Figure 1 equipped with additional relocking functions;; Figure 6A is a sectional view of a "live" thermally-activated relocker in its low temperature condition and Figure 6B is a plan view of the relocker in its high temperature condition; and Figure 7 shows the boltwork of a fire protection cabinet door equipped with thermally-activated bolts.

Figure 1 shows a very elementary boltwork for the door of a safe or strongroom. Four relatively massive door bolts 1 are attached to a common bolt-strap 2 which itself is attached to a cross-arm 3. Rotation of the bolt-throwing spindle 4 moves the cross-arm horizontally and thus moves the door bolts into or out of engagement with a corresponding body or frame (not shown). When the door bolts have been moved into engagement, withdrawl can be prevented by throwing the bolt 5A of a key or combination lock 5, which moves downwards into a recess in the cross-arm 3.In addition to the security provided by the primary lock 5, SME relockers such as are indicated at 6A and 6B can be provided to place additional obstructions in the path of withdrawing movement of the boltwork, automatically in response to the detection of a predetermined temperature such as would result from a thermal attack on the door.

Figure 2 shows one simple type of relocker 6A which acts directly to prevent the door bolt withdrawl. It is shown situated at the end of the crossarm 3 and comprises a robust rectangular block 9 carried at one end of a torque tube 7 made from SME material. In its normal position (Figure 2A), ie at temperatures less than T,, the width of the block 9 is aligned transversely to the cross-arm 3 and in this position the relocker does not prevent withdrawing movement of the cross-arm. However, if the temperature rises through the transformation temperature range of the SME material the torque tube 7 twists and, its lower end being retained by a collar 8, the block 9 is moved through 90" to a position preventing withdrawal of the cross-arm 3, as shown in Figure 2B.Since this function is only of great significance if the primary lock 5 has been prejudiced it must be assumed that considerable force might be applied to the cross-arm 3 in an attempt to overcome the relocker obstruction. For this reason a fixed obstruction block 10 is shown which provides support for the block 9 against end pressure on the cross-arm 3.

In the simple form shown in Figure 2, the relocking action would be lost if the torque tube 7 cooled back through the transformation temperature range and was allowed to return to its Figure 2A position. It is therefore necessary to fit some further detent mechanism (ratchet and pawl for instance) to prevent reverse rotation from the obstructing position.

An alternative type of direct acting thermal relocker 6B is shown in Figure 3. In this case a coil form SME element 11 is used to activate an axiallymovable bolt 12. Provided the temperature remains below To the relocker bolt 12 remains clear of the tail 3A which moves together with the door bolts (Flgure 3A). However heating through the transformation temperature range of the SME material causes the coil 11 to expand axially, raising the relocker bolt 12 into an obstructing position in which it enters a recess in the tail 3A (Figure 3B).

When the bolt 12 has reached its obstructing position it is prevented from disengaging when cooled by the spring loaded detent balls 13. Note that in the initial, (below T,) position the SME coil 11 is not acting as a spring ie. it does not exert a force acting to move the relocker bolt 12 upwards.

Figure 4 shows another type of thermal relocker using a coil form SME element 14. This element is mounted in the longitudinal bore 15 of a housing 16 with a bolt 17 slidable in the housing above the element 14. The housing 16 is preferably made of a metal of high thermal conductivity and is ventilated by slots 18 in the vicinity of the SME element to provide good heat flow to the element from the surrounding region of the door. A transverse bore 19 intersects the bore 16 at the top of the housing 15 and receives a rod 20 fixed on the back of a movable bolt strap 21. Figure 4A shows the posi tion of the relocker below To and with the boltwork of the door thrown. Withdrawing movement of the strap 21 is leftwards as viewed in Figure 4A, so that the rod 20 must pass through bore 19 and across bore 16 in the course of such movement.

Heating of the SME element 14 above To causes it to expand axially thereby raising the bolt 17 to a position in which it intersects bore 19 and obstructs withdrawing movement of the rod 20. In this position a spring-biased plunger 22 (Figure 4B) snaps into a groove 23 provided in the bolt 17 to detain the bolt in its obstructing position irrespective of subsequent cooling of the element 14.

SME elements can also be combined with other types of relocker sensor. For instance a common type of relocker which acts when non-thermal attacks are detected employs a spring loaded bolt normally held out of its obstructing position by a cord attached to a glass plate or the like frangible member. If thieves use explosives or other means of applying gross force to the door, or drill in the vicinity of the fragile member, the latter will fracture, release the cord, and thereby allow the spring to push the relocker bolt into its obstructing position.

By incorporating an SME element into the cordrun of this type of relocker actuation by heat can also be obtained. That is, the same relocker will then be triggered by drilling, explosive, gross force or thermal attack methods. Such an arrangement is shown in Figure 5 as applied to the simple type of boltwork already described.

The relocker bolt 24 is held by the cord 25 away from the cut out in the tail 3A which must move if the door bolts 1 are to be withdrawn. Acting to push the relocker upwards into an obstructing position is a spring in housing 27. One end of the cord 25 is attached to a glass plate 28. If the plate 28 is broken the cord 25 is unable to prevent the relocker bolt 24 being moved by its spring. A thermal attack would not necessarily fracture the plate 28. However, under the thermal attack one or both of two SME sensors 29 incorporated in the cord run will expand when the temperature rises through the corresponding transformation range, so as to relieve the tension in the cord 25 sufficiently to allow the bolt 24 to engage whether or not the plate 28 is broken.For this application also, means should be provided to prevent retraction of the relocker bolt 24 after it has moved to detain the tail 3A.

The use of SME sensors for thermally activated locking in so-called "live" relockers presents a special case. In"live" relocking the secondary locking member moves into an obstructing position each time a primary lock bolt is thrown. Thus in Figure 5 if the cord 25 were attached to the primary lock bolt 5A instead of to the frangible plate 28, and the cord run modified appropriately, it would form a "live" relocking system. The throw of the primary lock bolt 5A is insufficient to withdraw the relocker bolt 24 from the engagement with the tail 3A if the SME elements 29 are expanded by heating through the transformation range. Thus even if an attack achieved compromise of the lock 5 the boltwork would remain locked by the relocker if thermal tools had been used in the attack.

For a "live" relocker the relocker bolt must normally retract each time the primary lock is unlocked and a non-retraction detent arrangement of the type shown in Figure 3 or Figure 4 cannot be used on it. A more secure arrangement is therefore to use the SME sensor to introduce a non-retraction function. Figure 6 shows one means by which this may be accomplished.

In this arrangement a detent bar 30 is carried by an SME torque tube 31 within the spring-biased relocker bolt 24 and normally, at temperatures below T,, adopts the rotational position indicated in broken line in Figure 6B in which it lines up with a slot 32 in the relocker housing 27. In this condition the bar 30 can move with the bolt 24 when the latter is raised under the action of its spring 35 to detain the tail 3A when the primary lock bolt is thrown, and can likewise move with the bolt 24 when the latter is pulled down by the cord 25 to free the tail 3A when the primary lock bolt is withdrawn. However, in the event of a thermal attack which raises the temperature of the torque tube 31 through the transformation range, the tube twists to place the bar 30 in the rotational position indicated in full line in Figure 6B.In this condition the bar 30 is no longer lined up with the slot 32, rather it will bear against the upper surface of housing 27 to prevent the bolt 24 being withdrawn.

The use of SME elements in accordance with the invention is not confined to the actuation of relockers which act upon portions of the main boltwork of a safe or strongroom door as described above.

These thermally-activated elements can also be used to move securing bolts from the door into engagement with the surrounding frame or body. For instance, referring to the simple boltwork of Figure 1, SME elements could be used to cause additional bolts 1 to engage in the top, bottom or hinge side of the door. Such devices could act in the manner of previous examples or could act through bell cranks etc. to translate and/or amplify the motion.

Naturally for thief-resisting applications these devices would again need suitable non-retraction features.

Figure 7 shows a fire protection cabinet door boltwork supplemented by heat-activated bolts. In this illustration the door is normally secured by the cross-arm/bolt 37 which in turn is locked by the lock 36. However the heat from a fire is caused to engage additional bolts. At the top of the door one type of device 38 is shown which is turned by a pivoted SME temperature transducer causing two additional securing points 40 and 41 to engage.

Along the bottom edge are shown other types of SME-actuated locking elements 42 and 43. One of these 42 shoots a bolt 44 when an SME coil contracts on passing through the transformation temperature range while the second 43 is of the previously described expansion coil type, shooting a bolt 45. These devices shown on the bottom edge are of particular importance because the SME elements are located against the door rim and will quickly sense the temperature rise and initiate the additional locking.

Devices of the type shown will act to hold the door, (or a drawer), in position if the body is subjected to heat distortion and/or mechanical force.

Both situations occur when fire causes a building to collapse with debris falling onto the fire protection product or if the product itself falls (for instance if the floor collapses). In such cases the devices will act to prevent file drawers or cabinet doors opening.

Claims (10)

1. A door-locking mechanism including a thermal transducer sensitive to temperature within a region of the door and arranged to activate locking means for the door in response to the detection of a predetermined temperature, the said transducer comprising an element of shape memory effect material.

2. A mechanism according to claim 1 wherein the shape memory effect element is adapted to move a blocking member to extend from the door into an adjacent frame or other fixed structure when heated to a predetermined temperature.

3. A mechanism according to claim 1 including primary locking means for retaining the door closed under the control of a key- or code-responsive lock, and wherein said shape memory effect element is effective to prevent movement of said primary locking means away from its locking position when said element is heated to a predetermined temperature, irrespective of unlocking of said lock.

4. A mechanism according to claim 3 wherein the shape memory effect element is adapted to move a blocking member to a position in which it prevents movement of said primary locking means away from its locking position when said element is heated to a predetermined temperature.

5 A mechanism according to claim 3 comprising means for detection of a mechanical attack upon said lock, a secondary locking member biased towards a locking position for preventing movement of said primary locking means away from its locking position, and a linkage connecting said secondary locking member to said attack-detection means so as normally to hold the secondary locking member away from its locking position unless said attack-detection means is activated; wherein said shape memory effect element is incorporated in said linkage so as to permit the secondary locking member to move to its locking position when said element is heated to a predetermined temperature, irrespective of non-actuation of said attack-detection means.

6. A mechanism according to claim 3 comprising a secondary locking member biased towards a locking position for preventing movement of said primary locking means away from its locking position, and a linkage connecting said secondary locking member to a bolt of said lock so that normally the secondary locking member is moved between its unlocking and locking positions whenever said bolt is moved between its unlocking and locking positions; wherein said shape memory effect element is incorporated in said linkage so as to permit the secondary locking member to remain in its locking position when said element is heated to a predetermined temperature, irrespective of movement of said lock bolt to its unlocking position.

7. A mechanism according to claim 3 comprising a secondary locking member biased towards a locking position for preventing movement of said primary locking means away from its locking position, and a linkage connecting said secondary locking member to a bolt of said lock so that normally the secondary locking member is moved between its unlocking and locking positions whenever said bolt is moved between its unlocking and locking positions; wherein said shape memory effect element is associated with said secondary locking member so as to block that member from movement from its locking to its unlocking position when said element is heated to a predetermined temperature.

8. A mechanism according to any preceding claim wherein said shape memory effect element is in the form of a tube one end of which twists relative to the other when the element is heated through its transformation range.

9. A mechanism according to any one of claims 1 to 7 wherein said shape memory effect element is in the form of a coil the axial length of which changes when the element is heated through its transformation range.

10. A door-locking mechanism according to claim 1 and substantially as hereinbefore described with reference to Figure 1, Figure 2, Figure 3, Figure 4, Figure 5, Figure 6 or Figure 7 of the accompanying drawings.