Safety trapped key interlock system

Abstract

A trapped key interlock system is disclosed. A pair of hollow tubular casings located one inside the other and each having a series of elongate slots are used. When the lock is in a locked condition the elongate slots are aligned as inner and outer pairs with engaging members extending through the pairs of slots is preventing rotational movement of the tubular casings relative to each other. The engaging members are biased towards this locked condition. On insertion of the correctly coded key the engaging members are caused to move against the biasing force out of engagement with the slots in the outer tubular casing thereby allowing the inner tubular casing to rotate relative to the outer tubular casing and moving the lock to an unlocked condition.

Claims

1. A trapped key interlock system comprising: a lock comprising: a first hollow casing; a second hollow casing disposed within a hollow portion of the first hollow casing; and a lock portion mounted within the second hollow casing; and a key for moving said lock between a locking condition and an unlocking condition, said key comprising a cylindrical member comprising an outer surface and having a plurality of biasing elements disposed on the outer surface and a shaped member attached to said cylindrical member; wherein the lock portion comprises a plurality of annular elements arranged side by side, each said annular element comprising an engaging member extending radially outwards from a periphery of the annular element, wherein the first hollow casing comprises a plurality of first elongate notches extending substantially along a length of the first hollow casing, each first elongate notch disposed at a predetermined position on a periphery of the first hollow casing, wherein the second hollow casing comprises a plurality of second elongate notches extending substantially along a length of the second hollow casing, each second elongate notch disposed at a predetermined position on a periphery of the second hollow casing such that, when said lock is in said locking condition, each of the first elongate notches substantially overlaps with a corresponding second elongate notch, wherein each said engaging member is biased towards a position whereby said engaging member is disposed within one of said first elongate notches and its corresponding overlapping second elongate notch, defining said locking condition in which rotational movement of said second hollow casing within said first hollow casing is prevented, wherein said lock is movable between said locking condition and said unlocking condition in which at least one said engaging member is disposed within a second elongate notch, but is not engaged with its corresponding overlapping first elongate notch, to allow for rotational movement of said second hollow casing within said first hollow casing, wherein said second hollow casing has a closed end comprising a first slot such that, when the key has been disposed inside the second hollow casing, a portion of the shaped member engages with the first slow of the closed end, so that, when the key is rotated, the second hollow casing also rotates; and a key trapping element comprising a disk disposed adjacent the closed end of the second hollow casing, said disk comprising a second slot which, when said lock is in said locking condition, overlaps with said first slot; and wherein when the second hollow casing is rotated by the key, said disk does not rotate such that when the lock moves from the locking condition to the unlocking condition, the key cannot removed from the lock until the key is rotated back to the locking condition.

2. A trapped key interlock system as claimed in claim 1, wherein each said engaging member is biased towards the locking condition in which said engaging member is disposed within one of said first elongate notches and its corresponding second elongate notch, by means of a leaf spring.

3. A trapped key interlock system as claimed in claim 2, wherein each said leaf spring is attached to said annular element and is disposed between interior of said second hollow casing and said annular element at a position on said annular element diametrically opposite the engaging member of that annular element.

4. A trapped key interlock system as claimed in claim 1, wherein each said engaging member is biased towards the locking condition in which said engaging member is disposed within one of said first elongate notches and its corresponding second elongate notch, by means of a spring.

5. A trapped key interlock system as claimed in claim 4, wherein each said spring is mounted between an interior of said second hollow casing and one of said annular elements, at a position on said annular element diametrically opposite the engaging member of that annular element.

6. A trapped key interlock system as claimed in claim 1, wherein said key is adapted to be inserted into the second hollow casing such that, when said key is inserted into said second hollow casing, said lock moves towards the unlocking condition such that none of said engaging members are engaged with the first elongate notches.

7. A trapped key interlock system as claimed in claim 1, wherein said plurality of biasing elements are disposed on said outer surface of said cylindrical member of said key such that, when said key is disposed in said lock, each said biasing element engages with a corresponding annular element such as to move said engaging member out of engagement with its corresponding first elongate notch.

8. A trapped key interlock system as claimed in claim 1, wherein said plurality of biasing elements are disposed on said outer surface of said cylindrical member of said key such that, when said key is disposed in said lock, each said biasing element is disposed diametrically opposite the engaging member of the annular element with which the biasing element engages.

9. A trapped key interlock system as claimed in claim 1, wherein said key includes a built in weakness, disposed at a position on the key adjacent an end of the cylindrical member that is opposite, the shaped member.

Description

(1) A preferred embodiment of the present invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings in which: FIG. 1 shows an end view of a lock in accordance with an embodiment of the present invention;

(2) FIG. 1A shows an exploded perspective view of the lock of FIG. 1;

(3) FIG. 1B shows a perspective view from one end of the lock of FIG. 1;

(4) FIG. 2 shows a perspective view from one end and the side of the second hollow tubular casing and the annular elements of the lock of FIG. 1;

(5) FIGS. 3 and 3A show a perspective view and an exploded perspective view of a key for use with the lock of FIG. 1;

(6) FIG. 4 shows a perspective view of the first hollow tubular casing of the lock of FIG. 1; and

(7) FIG. 5 shows a perspective view of an annular element forming part of the lock of FIG. 1.

(8) With reference to the Figures, a lock is represented generally by reference numeral 1.

(9) The lock 1 comprises a first hollow tubular casing 3, and a second hollow tubular casing 5, which is disposed inside the hollow portion of the first hollow tubular casing 3. The lock 1 further comprises a lock portion 7 mounted within the second hollow tubular casing 5.

(10) As can be clearly seen from FIGS. 1A and 2 in particular, the lock portion 7 comprises a plurality of annular elements 9 arranged adjacent to each other, side by side. Each annular element 9 comprises an engaging element in the form of an elongate tab 11 extending radially outwards from the periphery of the annular element 9.

(11) Moreover, the first hollow casing 3 comprises a plurality of first elongate notches 13 extending substantially along the length L of the first hollow casing 3. As can be clearly seen from FIG. 4 in particular, each first elongate notch 13 is disposed at a predetermined position on the periphery of the first hollow casing 3.

(12) Turning now to the second hollow casing 5, this comprises a plurality of second elongate notches 15 extending substantially along the length L of the second hollow casing 5, each second elongate notch 15 being disposed at a predetermined position on the periphery of the second hollow casing 5. As can be clearly seen from FIGS. 1, 1A and 1B in particular, each of the first elongate notches 13 overlaps with a corresponding second elongate notch 15.

(13) The lock 1 further comprises a set of leaf springs 17 (see FIG. 5) each of which is mounted between the interior of the second hollow casing 5 and one of the annular elements 9, at a position that is diametrically opposite the elongate tab 11 of the annular element 9 upon which the leaf spring 17 is mounted. The leaf springs 17 are fixed to the annular elements 9 by being held in spring slots 18 which are cut into the annular element (see FIG. 2).

(14) Each leaf spring 17 biases the corresponding elongate tab 11 diametrically opposite to it towards a locking condition in which the elongate tab 11 extends through both a first elongate notch 13 and its corresponding overlapping second elongate notch 15. In view of the fact that the elongate tab 11 extends through both the first elongate notch 13 and the second elongate notch 15, the rotation of the second hollow casing 5 within the first hollow casing 3, is prevented, effectively locking the second hollow casing 5 in position.

(15) In order to move the lock 1 between the locking condition and the unlocking condition, a key 19 is provided. As can be seen from FIG. 3 in particular, the key 19 comprises a cylindrical member in the form of coding portion in the form of a barrel 21 comprising a plurality of raised biasing elements in the form of nubs or protrusions 23 disposed on the outer surface of the barrel 21.

(16) It is to be appreciated that the key 19 is adapted to be inserted into the second hollow casing 5 such that, when the key 19 is inserted, the lock 1 moves towards the unlocking condition such that none of the tabs 11 are engaged with the first elongate notches 13. In particular, when the key 19 is disposed in the lock, each of the nubs 23 engages with a specific corresponding annular element 9, such as to move the elongate tab 11 of the annular element 9 out of engagement with the first elongate notch 13, against the biasing action of the leaf spring 17. This movement results from an engagement of the nub 23 with a cam surface 24 which extends radially inward of the inner circumference of the annular member 9.

(17) It is to be appreciated that in this way, each lock is coded such that the positions of the nubs 23 along the length of the matching key 19 are such that they are diametrically opposite to an elongate tab 11 on a particular annular element 9, when the correct key 19 is fully inserted into the lock 1.

(18) It is also to be appreciated that the coding of the lock can be changed by rotating the annular members 9 such that the elongate tabs 11 engage with different first 13 and second 15 elongate slots, or by moving the position of the annular member 9 longitudinally along the lock 1.

(19) In this way, the more first 13 and hence second 15 elongate notches and hence annular members 9 and their associated elongate tabs 11 there are in a particular lock 1, the more potential codes exist. Moreover, it is to be appreciated that the more first 13 and hence second 15 elongate notches and hence annular members 9 and their associated elongate tabs 11 there are in a particular lock 1, the stronger the lock 1 is, in terms of a higher shear force being required to force the lock 1 into the unlocking condition with an unauthorised key.

(20) It is also to be appreciated that the key 19 is designed such that each nub 23 is disposed on the barrel 21 at a specific predetermined position so that when the key 19 is fully inserted into the lock 1, the nub 23 is at the correct position relative to the periphery of the annular element 9 which it is intended to bias towards the unlocking condition. That is, when the key 19 is fully inserted into the lock 1, each nub 23 is disposed at a position diametrically opposite to the elongate tab 11 on the annular element 9 with which the nub 23 is intended to interact. In this way, the nub 23 acts against the associated leaf spring 17 and pushes against the cam surface 24 thereby moving the annular element 9 out of engagement with the first hollow casing 3, in order to move the lock 1 to the unlocking condition.

(21) As can be seen from FIGS. 3 and 3A in particular, the key 19 further comprises a driving portion in the form of a wedge shaped element 25 at its distal end 19a, which, when the key 19 is disposed inside the lock 1, engages with the closed end 27 of the second hollow casing 5. In particular, when the key 19 is disposed inside the lock 1, the wedge shaped element 25 locates inside a driven portion which is a correspondingly sized and shaped slot 29 in the closed end 27. In this way, when the key 19 is inside the lock, and the key 19 is rotated, the wedge shaped element 25 (the driving portion) causes the rotation of the slot 29 (the driven portion) in turn causing the rotation of the closed end 27 of the second hollow casing 5 which therefore also rotates.

(22) By means of example, it is to be appreciated that the key 19 and hence the second hollow casing 5 has 90 degrees of rotational movement when inside the lock 1.

(23) It is to be appreciated that, as an alternative to the wedge shaped element 25, the key 19 could comprise a T-shaped element, for example.

(24) The lock 1 is adapted such that, in the event that the lock 1 moves from its locking condition to its unlocking condition and the second hollow casing 5 is rotated by means of turning the key 19, the key 19 cannot be removed from the lock 1 until the key 19 and consequently the second hollow casing 5, is rotated back to the locking condition. In this way, the lock 1 operates as a trapped key lock and specifically a trapped key interlock. In order to effect this, the lock 1 comprises a key trapping element in the form of a disk 31 disposed adjacent the closed end 27 of the second hollow casing 5. The disk 31 itself comprises a wedge shaped aperture 33 which, when the lock 1 is in the locking condition, overlaps with the wedge shaped slot 29 of the closed end 27 of the second hollow casing 5.

(25) The disk 31 is substantially fixed in position such that it does not rotate in the event that the second hollow casing 5 is rotated by means of turning the key 19.

(26) In this way, as the key 19 is inserted into the lock 1, the wedge shaped element 25 of the key 19 passes through the aperture 33 of the disk 31 and engages with the wedge shaped slot 29 of the closed end 27 of the second hollow casing 5. When the key 19 is then turned, the second hollow casing 5 rotates within the first hollow casing 3 towards the unlocking condition and the key 19 becomes trapped, with the wedge shaped element 25 effectively becoming trapped in the gap between the closed end 27 of the second hollow casing 5 and the disk 31, since the aperture 33 of the disk 31 is at that stage, no longer overlapping with the slot 29 of the closed end 27 of the second hollow casing 5.

(27) It is to be appreciated that as soon as the key 19 begins to turn, that is, as soon as the aperture 33 of the disk 31 is tilted with respect to the slot 29 of the closed end 27, the key 19 becomes trapped.

(28) As can be clearly seen from FIGS. 1, 1A and 1B, the lock 1 further comprises a front face 41 comprising a key slot 39. The key slot 39 is sized and shaped to facilitate the entry of the key 19 into the lock 1, and in particular, is shaped such that the key 19 can only be inserted into the lock 1 in a particular rotational orientation. This is effected by means of a lead slot 39a having the same size and shape as a corresponding projection 49b on the key 19.

(29) Returning to FIGS. 3 and 3A, the key 19 has a handling portion in the form of a handle 47 for engagement or grasping by an operator. The coding portion or barrel 21 is formed from a series (in this example 5) circular coding members 49a and 49b (and generally referred to as 49). The coding members 49 are substantially identical to each other except that the nub 23 on coding member 49b is wider (that is extending around a greater proportion of the circumference of the circular coding member) than those on the coding members 49a so as to only be able to enter the lock through the lead slot 39a.

(30) The coding members 49 are mounted on a central body member 51 as well as on six coding pins 53 with the central body member 51 and the coding pins 53 extending into apertures in a first end plate 55 which together with a second end plate 57 are attached to the handle 47. The final components of the key 19 are end caps 59 and 61 which are located at either end of the coding portion 21. Each of the coding members 49 as well as the end caps 59 and 61 have a series of apertures corresponding to the coding pins 53 so that these components are combined together by sliding the components onto the pins 53 and locating the central body member 51 down the central aperture. As can be seen in FIG. 3A, on each of the coding members 49 the nub 23 is located adjacent one of the apertures through which a coding pin 53 will extend. Different keys can be produced by rotating each of the coding members 49 such that the nub 23 is located adjacent a different coding pin 53. Furthermore, additional codes can be added by replacing one or more of the coding members 49 with a similar coding member where the nub 23 is not located immediately adjacent an aperture for a coding pin but is, for example, located between two apertures. It should be noted that if these alternative coding members 49 are used corresponding changes, in particular to the positions of the slots will need to be made to the first and second tubular casings 3 and 5.

(31) Furthermore, additional coding variations can be created by varying the shape of the shaped driving element 25. For example, by replacing the wedge shape shown in the figures with an alternative shape, such as a star shape, all of the codes for the wedge shaped keys could be repeated for the star shaped keys since even if a wedge shaped key and a star shaped key had the same arrangement of coding members their respective shaped driving elements 25 would not fit thereby preventing one key from being able to operate another lock.

(32) The central body member 51, which holds the shaped driving element 25, has a point of weakness, indicated at 63, in the form of an annular channel cut into the central body member. This annular channel 53 acts as a shear or weak point which will break under a predetermined excessive turning force being applied to the handle 47. The annular channel 63 is located roughly between the first and second end plates 55 and 57 so that in the event of the key breaking the majority of the key is left in the lock and can be relatively easily reached for complete extraction of the key.

(33) The key 19 is also provided with an elongate aperture 65 which extends through the shaped driving element 25 and into the central body member 51. When the key is inserted into the lock this aperture 65 receives a central pin 67 which extends from the back of the lock on the axis of rotation of the lock and through the slot 29 and aperture 23. This pin 67 adds a further obstacle to anyone attempting to gain access to the driven portion, that is, the shaped slot 29, making it even more difficult to apply a turning force to the driven portion.

(34) It will be appreciated by persons skilled in the art that the above embodiment has been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departing from the scope of the invention as defined by the appended claims. In particular, it should be noted that although the above embodiment has been described specifically for use with trapped key interlocks, the same apparatus can be used to create a standard locking device.