Anti-barricade lock

Abstract

A lock comprises a drive mechanism, a bolt moveable between an extended and withdrawn positions by the drive mechanism, and first and second locking inputs configured to operate the drive mechanism. T

Description

BACKGROUND The present disclosure relates to locks, for example for doors, which are operated by multiple locking inputs. For example, a lock may be operable by a key and also by a thumb turn. It may be desirable for a lock to be operable by way of one such input, even when operation of the lock is resisted via another such input. For example, it may be desirable to be able to open the lock from the outside of a room while an occupant of the room attempts to prevent access. This may be the case for example in institutions such as hospitals, in which it may be important to enter a room whilst actively resisted by the occupant, for example to prevent harm to the occupant. There is a desire for locks with improved barricade resistance. SUMMARY According to one aspect of the present disclosure, there is provided a lock comprising a drive mechanism, a bolt moveable between an extended position and a withdrawn position by the drive mechanism, a first locking input configured to operate the drive mechanism and a second locking input configured to operate the drive mechanism. The extended position of the bolt may be considered a locked configuration of the lock, and the retracted position may be considered an unlocked configuration. The first locking input may be operable via a thumb turn, and the second locking input may be operable via a key. In an example, the thumb turn is on an “interior” side of the lock, and the key is operated from an “exterior” side of the lock. For example, the interior side of the lock may correspond to the interior of a room such as a patient’s room in a hospital or similar institution, and the exterior side of the lock may correspond to the exterior of the patient’s room. The drive mechanism is moveable between a first unlocked state wherein the bolt is in the retracted position, a first locked state wherein the bolt is in the extended position, a second unlocked state wherein the bolt is in the retracted position, and a second locked state wherein the bolt is in the extended position. In the first unlocked state, the first locking input is operable to place the drive mechanism into the first locked state, and the second locking input is operable to place the drive mechanism into the second locked state. In the first locked state, the first locking input is operable to place the drive mechanism into the first unlocked state, and the second locking input is operable to place the drive mechanism into the second unlocked state. In the second unlocked state, the first locking input is inhibited from placing the drive mechanism into any of the first unlocked state and the first and second locked states, and the second locking input is operable to place the drive mechanism into the first locked state. In the second locked state, the first locking input is operable to place the drive mechanism into the first locked state, and the second locking input is operable to place the drive mechanism into the first unlocked state. Thus, starting from the first unlocked state, the lock can be locked and unlocked by either of the inputs. Having been locked by the first input (i.e. placed into the first locked state), the lock can be unlocked by the second input i.e. placed into the second unlocked state. However, when the lock is in the second unlocked state, the first input is prevented from locking the lock. This means that a first user who controls the first locking input (for example an occupant of a room locked by the lock, such as a patient) is prevented from barricading the lock: a second user controlling the second locking input (such as a member of staff) can unlock the lock, and the first user cannot re-lock it. This provides a significant advantage over comparative examples in which, even if the second locking input can forcibly open the lock after it has been locked by the first input, the first input is not prevented from re-locking the lock. In such comparative examples, the first user can still barricade the lock by quickly re-locking the lock after the second user has unlocked it. Furthermore, starting again from the first unlocked configuration, the second locking input can transition the lock into the second locked configuration, thereby locking the lock. However, the first locking input can transition the lock from the second locked configuration into the first locked configuration, from which it can transition the lock into the first unlocked configuration. Thus, even after the lock has been locked by the second locking input, it can still be unlocked by the first locking input. Thus, in an example in which the first locking input is operated by an occupant of a room, this prevents the occupant from being accidentally locked in the room. In an example, the drive mechanism comprises an input override element moveable between a first configuration, a second configuration and a third configuration. In the first unlocked state and the first locked state, the input override element has the first configuration. In the second unlocked state, the input override element has the second configuration, in which the input override element inhibits the first locking input from placing the drive mechanism into any of the first unlocked state and the first and second locked states. In the second locked state, the input override element has the third configuration, in which the input override element permits the first locking input to place the drive mechanism into the first locked state. The input override element thus provides an effective way of preventing and allowing motion between the different states as set out above. In one such example, the input override element comprises a plate moveable with the bolt and configured to engage with a peg. The plate comprises a first portion configured to receive the peg in the first configuration, a second portion configured to receive the peg in the second configuration, and a third portion configured to receive the peg in the third configuration. This provides an effective way of implementing the three configurations described above, such that each configuration corresponds to an engagement between the peg and one of the three portions of the input override element. In such an example, the first portion comprises a first recess, the second portion comprises a second recess, and the plate comprises a raised portion between the first recess and the second recess. The raised portion is configured to inhibit motion of the peg between the second recess and the first recess whilst the peg is engaged with either one of the second recess and the first recess. Operation of the second locking input may disengage the plate from the peg. Thus, the peg can only be moved between the first and second recesses by the second locking input. This means that once the lock has been transitioned by the second locking input into the second unlocked state (in which the peg is engaged with the second recess), the first locking input is effectively prevented from transitioning the lock out of this state and into a locked state. The raised portion between the first recess and the second recess may have a first side defining a side of the first recess and a second side defining a side of the second recess, the first and second sides being substantially normal to an axis connecting the first recess and the second recess. The raised portion may thus protrude in such a way as to effectively prevent motion of the peg between the first and second recesses whilst engaged with either of the first and second recesses. In an example, the aforementioned third portion is responsive to input from the first locking input, whilst the peg is engaged with the third portion, to permit motion of the peg from the third portion to the first portion. The first locking input is thus able to transition the lock from the second locked configuration into the first locked configuration (from which the first locking input can then transition the lock into the first unlocked configuration, thereby unlocking the lock). In one such example, the third portion comprises a third recess, wherein the plate comprises a raised portion between the first recess and the third recess. The raised portion is configured to inhibit motion of the peg from the first recess to the third recess whilst the peg is engaged with the first recess, and to permit motion of the peg from the third recess to the first recess whilst the peg is engaged with the third recess. This provides an effective way of allowing the first locking input to move from the third recess to the first recess, whilst still preventing the first locking input from moving the peg out of the first recess as discussed above. This may be achieved by the raised portion between the first recess and the third recess having a first side defining a side of the first recess and a second side defining a side of the third recess, wherein the first side is substantially normal to an axis connecting the first recess and the second recess, and the second side has an obtuse angle relative to said axis. The peg is thus able to slide from the third recess to the first recess whilst engaged i.e. in contact with the plate, by sliding up the second side, over the raised portion and into the first recess. The peg is prevented from sliding from the first recess to the third recess by way of the substantially normal first side. Alternatively to the above, the third portion may comprise a portion adjacent to the first recess and raised relative to the first recess. The behaviour described above may thus be achieved by way of the peg being able to slide from the adjacent portion into the first recess, but being unable to slide from the first recess to the adjacent portion by way of a side wall of the first recess. In an example, the peg described above may be a floating peg coupled to the first locking input such that operation of the first locking input causes the peg to move in a direction parallel to an axis of motion of the bolt. This provides an effective way of implementing the behaviour discussed above. The floating peg may for example be a means by which the first locking input engages with the bolt to extend and retract it. In an example, a control plate is configured to transmit drive from the first locking input to the bolt, to move the bolt between the extended position and the withdrawn position, wherein the control plate comprises the input override element. This provides an effective way of implementing the input override element and connecting its configuration to the allowed motion of the bolt. The control plate may for example comprise a deadlocking element configured to have a first configuration in which the bolt is held in the withdrawn position, and a second configuration in which the bolt is held in the extended position. Operation of the second locking input may cause the deadlocking element to move between the first configuration and the second configuration. This provides an effective way of ensuring that the lock exhibits deadlocking behaviour, i.e. that the bolt can only be extracted or retracted by operation of one of the locking inputs. In one such example, the deadlocking element comprises a first recess configured to engage with a fixed peg in the first configuration, and a second recess configured to engage with the fixed peg in the second configuration. Operation of the second locking input may disengage the deadlocking element from the fixed peg. This provides an effective way of implementing the aforementioned deadlocking behaviour. In alternative examples, the bolt itself may comprise the input override element. This provides an alternative way of implementing the input override element, which may for example be located within a rear portion of the bolt i.e. a portion that remains within a housing of the lock when the bolt is extended. In an example, the first locking input comprises a first rotatable cam configured to engage with the drive mechanism, and the second locking input is configured to be received from a second rotatable cam engaging with the drive mechanism. This provides an effective way of implementing the first and second locking inputs. The lock may be for a closure, wherein the first rotatable cam is operable from a first side of the closure and the second rotatable cam is operable from a second side of the closure. Thus, the behaviour described above, in which the lock is resistant to barricade by a user on the first side and can be opened by a user on the second side, can be achieved. The first rotatable cam may be operable by a thumb turn, for example by the occupant of a room locked by the lock as described above. The second rotatable cam may be comprised within a cylinder lock, for example operable with a key held by a staff member as described above. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1A to 1C depicts a lock according to an example. Figures 2A to 2C depict an example cam component of a lock. Figures 3A and 3B depict an example plate component of a lock. Figures 4A to 4F illustrate operation of a lock according to an example. Figures 5A to 50 depict a lock according to an example. Figures 6A to 6D depict an example cam component of a lock. Figures 7A to 70 depict an example bolt component of a lock. Figures 8A to 8D depict an example plate component of a lock. Figures 9A to 9F illustrate operation of a lock according to an example. Figure 10 illustrates state transitions of locks according to examples. DETAILED DESCRIPTION Figures 1A to 10 depict a lock 100 according to an example. The lock 100 may for example be configured to be mounted in a door, for example a door to a patient’s room in an institution such as a hospital or clinic as described above. Figure 1A depicts a side view of the lock 100, and Figure 1B depicts an isometric elevation of the lock 100 in the same configuration. Figure 1C depicts an exploded view of the lock 100. The lock 100 comprises a bolt 105 which is moveable between a withdrawn, unlocked position (pictured) and an extended, locked position. The bolt is moved by a drive mechanism 110 which comprises several components. In addition to the bolt 105, in some examples the lock 100 comprises a spring-loaded roller bolt 115. When the lock 100 is mounted in a door and the door is in a closed configuration, the roller bolt 115 extends into a recess in the door frame such that the door is held closed even if the bolt 105 is retracted. However, when a user opens the door, the roller bolt 115 engages with the door frame and is pushed into the housing of the lock 100. After the door clears the door frame, the spring extends the roller bolt 115. The same process is performed in reverse when the door is closed. The lock 100 comprises a first locking input 120a and second locking input 120b. Both locking inputs 120a, 120b are configured to operate the drive mechanism 110. The first locking input 120a is a cam configured to be rotated by a follower (not pictured) located in the square orifice 125a within the cam 120a, such that rotation of the cam causes the bolt 105 to retract and / or extend. The follower is operated by a thumb turn on one side of the lock 100 (for example an interior side of the door within which the lock 100 is mounted. The second locking input 120b comprises a riser (visible in the foreground of Figures 1A and 1B) and a sliding member located behind the riser, configured to engage with a cam of a cylinder lock located in the cylinder-lock-shaped orifice 125b such that rotation of the cam causes the bolt 105 to retract and / or extend. The sliding member may for example be a rear portion of the bolt 105. Thus, each of the locking inputs 120a, 120b can independently be operated to lock and unlock the lock 100. Figures 2A to 2C depict the cam 120a. Figure 2A depicts a side view of the cam 120a in a first position, in which a protruding part of the cam is oriented in a direction 1. Figure 2B depicts a side view of the cam in a second position, in which the protruding part is oriented in a direction 2. Rotation of the cam (by rotation of a follower inserted therein) causes the cam 120a to move between the first and second positions. Figure 2C depicts an isometric view of the cam. Returning to Figures 1A and 1B, it can be seen that the cam 120a is depicted in the first position. The drive mechanism comprises a plate 130. As will be seen in subsequent Figures, the plate 130 is moveable with the bolt 105, i.e. it can move in an extension direction with the bolt 105 as the bolt 105 extends, and move in a retraction direction with the bolt 105 as the bolt 105 retracts. Figures 3A and 3B depict a configuration of the plate 130 according to an example. The plate 130 comprises cut-out portions defining features configured to engage with other components of the lock 100. In particular, the plate 130 comprises an input override element 305 and a deadlocking element 310. The input override element 305 is defined by three recesses 1,2,3, separated by raised portions. The raised portion between recesses 1 and 2 has sides which are substantially normal to a direction of motion of the bolt 105. The raised portion between recesses 1 and 3 has one side (facing recess 1) substantially normal to said bolt motion direction, and another side (facing recess 3) and an obtuse angle thereto. The obtuse angle is such as to define a relatively shallow (e.g. less than 45 degree) slope from recess 3 to the crest of the raised portion. The deadlocking element 310 is defined by two recesses 1, 2. These are separated by a raised portion having sides which are substantially normal to the direction of motion of the bolt 105, or have an angle so as to define a relatively steep (e.g. more than 45 degree) slope from either of recess 1 and 2 to the crest of the raised portion. Returning to Figures 1A and 1B, the input override element 305 of the plate 130 is configured to engage with a peg 135, the peg 135 being attached to another component of the lock 100. The peg 135 may for example be a floating peg that can move relative to the housing of the lock 100. For example, it may be attached to a plate located behind the plate 130. The peg 135 is depicted as being in the first recess of the input override element 305 but, as will be seen with reference to subsequent figures, this depends on the configuration of the lock 100. The deadlocking element 310 of the plate 130 is configured to engage with a peg 140. The peg 140 may for example be a fixed peg that is fixed to the housing of the lock 100 and does not move relative thereto. The peg 140 is depicted as being in the second recess of the deadlocking element 310 but, as will be seen with reference to subsequent figures, this depends on the configuration of the lock 100. The deadlocking element serves to ensure deadlock behaviour of the lock, in which the bolt 105 can only be retracted or extended by operation of a locking input and not by direct mechanical manipulation of the bolt itself. The lock 100 may comprise other elements, for example other elements of the drive mechanism 110 which serve to transmit, permit and / or deny motion from one of the locking inputs 120a, 120b to the bolt 105. One skilled in the art will appreciate that the specific details of these can be determined for a particular implementation. However, for the purposes of the present disclosure, the configuration of the lock 100 can be defined by way of three elements: 1. the orientation {1,2} of the cam 120a; 2. the recess {1, 2, 3} of the input override element 305 which is engaged with the peg 135; and 3. the recess {1, 2} of the deadlocking element 310 which is engaged with the peg 140. Transition of the lock 100 between various states, defined in terms of the configuration of these three elements, will now be described with reference to Figures 4A-4F. Figure 4A depicts the lock 100 in a first unlocked state. This is the configuration that is depicted in Figures 1A and 1B. In the first unlocked state: 1. the cam 120a is in orientation 1; 2. the peg 135 is engaged with recess 1 of the input override element 305; and 3. the peg 140 is engaged with recess 1 of the deadlocking element 310. From the first unlocked state, the lock 100 can be locked by operation of the first locking input 120a, i.e. rotation of the cam 120a to orientation 2. This places the lock 100 into a first locked state, which is depicted in Figure 4B. In the first locked state: 1. the cam 120a is in orientation 2; 2. the peg 135 is engaged with recess 1 of the input override element 305; and 3. the peg 140 is engaged with recess 2 of the deadlocking element 310. From the first locked state, the lock 100 can be unlocked by operation of the first locking input 120a, placing the lock 100 back into the first unlocked state. Additionally, the lock 100 can be unlocked by operation of the second locking input 120b, i.e. operation of a cylinder lock located in orifice 125b. This places the lock 100 into a second unlocked state. Figure 4C depicts a midpoint of this transition, in which the cam 120a remains in orientation 2 (because there has been no operation of the cam 120a), the peg 135 has been disengaged from recess 1 of the input override element 305, and the peg 140 has been disengaged from recess 2 of the deadlocking element 310. Figure 4D depicts the lock 100 following completion of the transition to the second unlocked state, in which: 1. the cam 120a is in orientation 2; 2. the peg 135 is engaged with recess 2 of the input override element 305; and 3. the peg 140 is engaged with recess 1 of the deadlocking element 310. The second locking input 120b can thus cause the peg 135 to disengage with recess 1 and engage with recess 2 of the input override element 305, and peg 140 to disengage with recess 2 and engage with recess 1 of the deadlocking element 310, retracting the bolt and unlocking the lock 100. The second locking input 120b (e.g. via a key) can thereby override the first locking input 120a (e.g. a thumb turn), unlocking the lock 100 without motion of the cam 120a. This allows the lock to be unlocked via the second locking input even if actively resisted by a user operating the first locking input. The operator of the first locking input 120a may attempt to reset the lock by manipulating the first locking input 120a, in order to re-lock the lock after it has been overridden and unlocked as described above. When in the second unlocked state (i.e. after having been overridden), operation of the cam 120a causes the lock 100 to enter the state depicted in Figure 4E. In this state: 1. the cam 120a is between orientations 2 and 1, having been prevented from fully rotating back to orientation 1; 2. the peg 135 remains engaged with recess 2 of the input override element 305, being prevented from moving to recess 1 by the raised portion between recesses 1 and 2; and 3. the peg 140 has partially disengaged from recess 1 of the deadlocking element 310 but the plate 130 is prevented from moving the deadlocking element 310 laterally, such that the peg 140 remains aligned with recess 1. Thus, as a consequence of the raised portion between recesses 1 and 2 of the input override element 305, and in particular its sides which are substantially normal (or at least steeply angled, greater than 45 degrees) to the axis of motion of the bolt, the peg 135 is maintained in recess 2 despite the motion of the cam 120a. This effectively prevents the first locking input from transitioning the lock 100 out of the second unlocked state. Only operation of the second locking input 120b can transition the lock 100 out of the second unlocked state (and back into the first locked state). This presents a significant improvement over comparative examples in which operation of the cam 120a can transition the lock 100 from the second unlocked state into the first unlocked state, from which further operation of the cam 120a can transition the lock 100 back into the first locked state, thereby re-locking the lock 100. In the present example, an operator of the first locking input 120a is prevented from re-locking the lock 100 after the first locking input 120a has been overridden and the lock unlocked by way of the second locking input 120b. Finally, starting from the first unlocked state (Figure 4A), the lock can be locked by operation of the second locking input 120b, i.e. turning a key in a cylinder lock in orifice 125b. This places the lock 100 into a second locked state, depicted in Figure 4F. In the second locked state: 1. the cam 120a is in orientation 1; 2. the peg 135 is engaged with recess 3 of the input override element 305; and 3. the peg 140 is engaged with recess 2 of the deadlocking element 310. Further operation of the second locking input 120b can then transition the lock 100 back into the first unlocked state, unlocking the lock. Additionally, in the second locked state, operation of the first locking input 120a causes the plate 130 to move such that peg 135 slides up the gently angled (e.g. less than 45 degrees relative to the axis of motion of the bolt 105) side of the raised portion between recesses 1 and 3 of the input override element. Peg 135 thus slides onto the crest of the raised portion, and into recess 1, thereby transitioning the lock 100 into the first locked state. From this state, further operation of the first locking input 120a can transition the lock 100 into the first unlocked state, unlocking the lock 100. This means that the first locking input 120a can always be used to unlock the lock 100, preventing an operator of the first locking input 120a from being locked in. The four states described above, and the possible transitions therebetween, can thus be summarised in Table 1: Table 1 State: First unlocked First locked Second unlocked Second locked Orientation of cam 120a: 1 2 2 1 Input override element recess engaged with peg 135: 1 1 2 3 Deadlocking element recess engaged with peg 140: 1 2 1 2 Operation of first locking input 120a causes transition to state: First locked First unlocked No transition possible First locked Operation of second locking input causes transition to state: Second locked Second unlocked First locked First unlocked An alternative implementation of the present disclosure will now be described. This implementation achieves the same technical outcome as the lock 100 described above, but via a different mechanical operation. Figures 5A to 5C depict a lock 500 in side, isometric and exploded view, respectively. Differences between the lock 500 and the previously described lock 100 will be described; aspects which are similar are not repeated. The lock 500 comprises a bolt 505, driving mechanism 510 and roller bolt 515. The driving mechanism can be operated by a first locking input 520a and a second locking input 520b. The first locking input 520a is a cam operable by a follower in an orifice 525a, and the second locking input 520b is operable by a cam of a cylinder lock located in an orifice 525b. The second locking input 520b may comprise a riser (visible in the foreground of Figures 5A and 5B, and an engagement element of the bolt 505 (behind the riser). In such a configuration, operation of a cylinder lock causes a cam of the cylinder lock to engage with the second locking input 520b to raise the riser and laterally push the engagement element of the bolt to extend the bolt. Figures 6A to 6D depict the cam 520a. Figure 6A depicts a side view of the cam 520a in a first position, in which a protruding part of the cam is oriented in a direction 1. Figure 6B depicts a side view of the cam in a second position, in which the protruding part is oriented in a direction 2. Rotation of the cam (by rotation of a follower inserted therein) causes the cam 520a to move between the first and second positions. Figure 6C depicts a side view of the cam 520a, and Figure 6D depicts an isometric view of the cam 520a. It can be seen that the cam 520a is depicted in the first orientation. Figures 7A to 7C depict front, back and isometric views of the bolt 505, respectively. The bolt 505 comprises recess elements configured to engage with other components of the lock 500. In particular, the bolt 505 comprises an input override element 705 and a deadlocking element 710. The input override element 705 is defined by two recesses 1, 2, separated by a raised portion, and a further raised portion 3 adjacent to recess 1. The raised portion between recesses 1 and 2 has sides which are substantially normal to a direction of motion of the bolt 505. The raised portion 3 is immediately adjacent to the recess 1 such that an edge of the recess 1 defines an edge of the raised portion 3. The deadlocking element 710 is defined by two recesses 1, 2. These are separated by a raised portion having sides which are substantially normal to the direction of motion of the bolt 505, or have an angle so as to define a relatively steep (e.g. more than 45 degree) slope from either of recess 1 and 2 to the crest of the raised portion. As can be seen in the isometric view 7C, the recess 2 may have only one side (i.e. the side of the raised portion between recesses 1 and 2), and be open on its other side such that it can be considered a space bounded on one side and open on the other. Returning to Figures 5A and 5B, the lock comprises a floating peg 535, which can move relative to the housing of the lock 505. The peg 535 is spring loaded to bias it towards a position of engagement with the input override element 705 of the bolt 505, as described in more detail below. In Figures 5A and 5B, the peg 535 is engaged with recess 1 of the input override element 705. The spring is mounted to a peg holding member behind the riser 520b (not visible in Figures 5A and 5B). The peg 535 additionally engages with the riser 520b such that when the riser is raised (by operation of the second locking input 520b), the peg 535 is disengaged from the input override element 705. The driving mechanism comprises a plate 530 functioning as a tumbler. This plate 530 is illustrated in Figures 8A to 8D, in which Figures 8A and 8B show front and back side views, and Figures 8C and 8C show front and back isometric views. The plate 530 has a protrusion 540. Returning to Figures 5A and 5B, it can be seen that the protrusion 540 engages with the deadlocking element 710 of the bolt 505 to provide a deadlocking behaviour of the lock 500. In Figures 5A and 5B, the protrusion 540 is engaged with recess 1 of the deadlocking element 710. The plate 530 is further configured to engage with the cam 520a such that when the cam is rotated, the plate 530 is lifted, disengaging the protrusion 540 from the deadlocking element 710 and allowing the bolt to be extended or retracted. The plate 530 is further configured to engage with the riser 520b to be lifted when the riser lifts, thereby allowing the second locking input 520b to disengage the protrusion 540 from the deadlocking element 710 and thereby extend or retract the bolt. The lock 500 may comprise other elements, for example other elements of the drive mechanism 510 which serve to transmit, permit and / or deny motion from one of the locking inputs 520a, 520b to the bolt 505. One skilled in the art will appreciate that the specific details of these can be determined for a particular implementation. However, for the purposes of the present disclosure, similarly to the lock 100, the configuration of the lock 500 can be defined by way of three elements: 1. the orientation {1,2} of the cam 520a; 2. the recess {1, 2} or raised portion {3} of the input override element 705 which is engaged with the peg 535; and 3. the recess {1, 2} of the deadlocking element 710 which is engaged with the protrusion 540. Transition of the lock 500 between various states, defined in terms of the configuration of these three elements, will now be described with reference to Figures 9A to 9F. As will be seen, whilst the mechanical means are different, the states and the transitions between them as expressed in terms of these three elements are conceptually the same as for the lock 100 depicted in Figures 4A-4F, such that the summary in Table 1 applies to lock 500 as well as lock 100. Each of Figures 9A to 9F depicts, from left to right, a side view of the lock 500, an isometric view, and a side view with a cutaway of element 520b so that the engagement of peg 535 with input override element 705 can be more clearly seen. Figure 9A depicts the lock 500 in a first unlocked state. This is the configuration that is depicted in Figures 5A and 5B. In the first unlocked state: 1. the cam 520a is in orientation 1; 2. the peg 535 is engaged with recess 1 of the input override element 705; and 3. the protrusion 540 is engaged with recess 1 of the deadlocking element 710. From the first unlocked state, the lock 500 can be locked by operation of the first locking input 520a, i.e. rotation of the cam 520a to orientation 2. This places the lock 500 into a first locked state, which is depicted in Figure 9B. In the first locked state: 1. the cam 520a is in orientation 2; 2. the peg 535 is engaged with recess 1 of the input override element 705; and 3. the protrusion 540 is engaged with recess 2 of the deadlocking element 710. From the first locked state, the lock 500 can be unlocked by operation of the first locking input 520a, placing the lock 500 back into the first unlocked state. Additionally, the lock 500 can be unlocked by operation of the second locking input 520b, i.e. operation of a cylinder lock located in orifice 525b. This places the lock 500 into a second unlocked state. Figure 9C depicts a midpoint of this transition, in which the cam 520a remains in orientation 2 (because there has been no operation of the cam 520a), the peg 535 has been disengaged from recess 1 of the input override element 705, and the protrusion 540 has been disengaged from recess 2 of the deadlocking element 710. Figure 9D depicts the lock 500 following completion of the transition to the second unlocked state, in which: 1. the cam 520a is in orientation 2; 2. the peg 535 is engaged with recess 2 of the input override element 705; and 3. the protrusion 540 is engaged with recess 1 of the deadlocking element 710. Thus, similarly to the transition depicted in Figures 4B-4D, the second locking input 520b can cause the peg 535 to disengage with recess 1 and engage with recess 2 of the input override element 705, and protrusion 540 to disengage with recess 2 and engage with recess 1 of the deadlocking element 710, retracting the bolt 505 and unlocking the lock 500. The second locking input 520b (e.g. via a key) can thereby override the first locking input 520a (e.g. a thumb turn), unlocking the lock 500 without motion of the cam 520a. Similarly to the lock 100, this allows the lock to be unlocked via the second locking input even if actively resisted by a user operating the first locking input. The operator of the first locking input 520a may attempt to reset the lock by manipulating the first locking input 520a, in order to re-lock the lock after it has been overridden and unlocked as described above. When in the second unlocked state (i.e. after having been overridden), operation of the cam 520a causes the lock 500 to enter the state depicted in Figure 9E. In this state: 1. the cam 520a is between orientations 2 and 1, having been prevented from fully rotating back to orientation 1; 2. the peg 535 remains engaged with recess 2 of the input override element 705, being prevented from moving to recess 1 by the raised portion between recesses 1 and 2; and 3. the protrusion 540 has partially disengaged from recess 1 of the deadlocking element 710 but the plate 530 prevents lateral motion of the bolt 505, such that the protrusion 540 remains aligned with recess 1 and the lock 500 remains unlocked. Thus, similarly to the lock 100, the peg 535 is maintained in recess 2 despite the motion of the cam 520a. This effectively prevents the first locking input from transitioning the lock 500 out of the second unlocked state. Only operation of the second locking input 520b can transition the lock 500 out of the second unlocked state (and back into the first locked state). The lock 500 thus exhibits the same advantages of the lock 100, which are discussed above. In particular, the lock 500 effectively prevents an operator of the first locking input 520a from re-locking the lock 500 after the first locking input 520a has been overridden and the lock unlocked by way of the second locking input 520b. Finally, starting from the first unlocked state (Figure 9A), the lock can be locked by operation of the second locking input 520b, i.e. turning a key in a cylinder lock in orifice 525b. This places the lock into a second locked state, depicted in Figure 9F. In the second locked state: 1. the cam 520a is in orientation 1; 2. the peg 535 is engaged with raised portion 3 of the input override element 705; and 3. the protrusion 540 is engaged with recess 2 of the deadlocking element 710. As with lock 100, further operation of the second locking input 520b can then transition the lock 500 back into the first unlocked state, unlocking the lock. Additionally, in the second locked state, operation of the first locking input 520a causes the bolt 505 to move laterally relative to peg 535, such that peg 535 slides off raised portion 3 and into recess 1 of the input override element 705. Lock 500 is thereby transitioned into the first locked state. From this state, further operation of the first locking input 520a can transition the lock 500 into the first unlocked state, unlocking the lock 500. This means that the first locking input 520a can always be used to unlock the lock 500, preventing an operator of the first locking input 520a from being locked in. The four states described above, and the possible transitions therebetween, are thus conceptually the same as those of the previously described lock 100, such that Table 1 describes both lock 100 and lock 500. Figure 10 is a state diagram summarising four states of locks 100 and 500 (first unlocked, first locked, second unlocked, second locked), and the permitted transitions between them as set out in Table 1. Each state is represented as a circle and arrows depict possible transitions. Solid arrows represent the first locking input 120a, 520a, for example a thumb turn in an interior of a room having a door locked by the lock 100, 500. Dashed arrows represent the second locking input 120b, 520b, for example a cylinder 100, 500 lock operated by a key in an exterior of said room. It can be seen that both locking inputs can transition the lock 100, 500 from the first unlocked state into a locked state: the first locked state for the first locking input 120a, 520a, and the second locked state for the second locking input 120b, 520b. The locking inputs 120a, 120b, 520a, 520b can also transition the lock 100, 500 back from these respective locked states into the first unlocked state. It can be seen that the second locking input 120b, 520b can transition the lock 100, 500 from the first locked state into the second unlocked state, thereby overriding the first locking input 120a, 520b. It can further be seen that the first locking input 120a, 520a cannot transition the lock 100, 500 out of the second unlocked state, ensuring that the first locking input 120a, 520a cannot undo the overriding and re-lock the lock 100, 500. Finally, it can be seen that the first locking input 120a, 520a can transition the lock 100, 500 from the second locked state to the first locked state, thereby ensuring that the operator of the first locking input 120a, 520b cannot be locked in the room. Examples have thus been described to illustrate the present concepts, in which barricade resistance of a lock can be significantly improved. In particular, the described locks allow a first locking input to be overridden, unlocking the lock, in such a way that the first locking input cannot undo the overriding and re-lock the lock. It will be appreciated that these specific examples are intended to illustrate some of the ways in which the present disclosure can be implemented, the scope of this being defined by the appended claims.

Claims

:

1. A lock, comprising:a drive mechanism comprising an input override element moveable between a5 first configuration, a second configuration and a third configuration;a bolt, moveable between an extended position and a withdrawn position by the drive mechanism;a first locking input configured to operate the drive mechanism; anda second locking input configured to operate the drive mechanism;10 wherein the drive mechanism is moveable between a first unlocked state whereinthe bolt is in the retracted position, a first locked state wherein the bolt is in the extended position, a second unlocked state wherein the bolt is in the retracted position, and a second locked state wherein the bolt is in the extended position, wherein:in the first unlocked state, the input override element has the first15 configuration, in which:the first locking input is operable to place the drive mechanism into the first locked state; andthe second locking input is operable to place the drive mechanism into the second locked state,20 in the first locked state, the input override element has the firstconfiguration, in which:the first locking input is operable to place the drive mechanism into the first unlocked state; andthe second locking input is operable to place the drive mechanism25 into the second unlocked state,in the second unlocked state, the input override element has the second configuration, in which:the input override element inhibits the first locking input from placing the drive mechanism into any of the first unlocked state and the30 first and second locked states; andthe second locking input is operable to place the drive mechanism into the first locked state, andin the second locked state, the input override element has the third configuration, in which:08 10 25the input override element permits the first locking input to be operable to place the drive mechanism into the first locked state; andthe second locking input is operable to place the drive mechanism into the first unlocked state.

52. A lock according to claim 1, wherein the input override element comprises a plate moveable with the bolt and configured to engage with a peg, and wherein the plate comprises:a first portion configured to receive the peg in the first configuration;10 a second portion configured to receive the peg in the second configuration; anda third portion configured to receive the peg in the third configuration.

3. A lock according to claim 2, wherein:the first portion comprises a first recess;15 the second portion comprises a second recess; andthe plate comprises a raised portion between the first recess and the second recess, the raised portion being configured to inhibit motion of the peg between the second recess and the first recess whilst the peg is engaged with either one of the second recess and the first recess.

204. A lock according to claim 3, wherein the raised portion between the first recess and the second recess has a first side defining a side of the first recess and a second side defining a side of the second recess, the first and second sides being substantially normal to an axis connecting the first recess and the second recess.

255. A lock according to any of claims 3 to 4, wherein the third portion is responsive to input from the first locking input, whilst the peg is engaged with the third portion, to permit motion of the peg from the third portion to the first portion.30 6. A lock according to claim 5, wherein the third portion comprises a third recess,wherein the plate comprises a raised portion between the first recess and the third recess, the raised portion being configured to inhibit motion of the peg from the first recess to the third recess whilst the peg is engaged with the first recess, and to permit motion of the peg from the third recess to the first recess whilst the peg is engaged with35 the third recess.08 10 257. A lock according to claim 6, wherein:the raised portion between the first recess and the third recess has a first side defining a side of the first recess and a second side defining a side of the third recess;5 the first side is substantially normal to an axis connecting the first recess and thesecond recess; andthe second side has an obtuse angle relative to said axis.

8. A lock according to claim 5, wherein the third portion comprises a portion adjacent 10 to the first recess and raised relative to the first recess.

9. A lock according to any of claims 3 to 8, wherein operation of the second locking input disengages the plate from the peg.15 10. A lock according to any of claims 2 to 9, wherein the peg is a floating peg coupledto the first locking input such that operation of the first locking input causes the peg to move in a direction parallel to an axis of motion of the bolt.

11. A lock according to any of claims 1 to 10, comprising a control plate configured 20 to transmit drive from the first locking input to the bolt, to move the bolt between the extended position and the withdrawn position, wherein the control plate comprises the input override element.

12. A lock according to claim 11, wherein:25 the control plate comprises a deadlocking element configured to have a firstconfiguration in which the bolt is held in the withdrawn position, and a second configuration in which the bolt is held in the extended position,operation of the second locking input causes the deadlocking element to move between the first configuration and the second configuration.3013. A lock according to claim 12, wherein the deadlocking element comprises a first recess configured to engage with a fixed peg in the first configuration, and a second recess configured to engage with the fixed peg in the second configuration.08 10 2514. A lock according to claim 13, wherein operation of the second locking input disengages the deadlocking element from the fixed peg.

15. A lock according to any of claims 1 to 10, wherein the bolt comprises the input 5 override element.

16. A lock according to claim 15, wherein the input override element is located within a rear portion of the bolt.10 17. A lock according to any preceding claim, wherein the first locking input comprisesa first rotatable cam configured to engage with the drive mechanism, and the second locking input is configured to be received from a second rotatable cam engaging with the drive mechanism.15 18. A lock according to claim 17, the lock being for a closure, wherein the firstrotatable cam is operable from a first side of the closure and the second rotatable cam is operable from a second side of the closure.

19. A lock according to claim 17 or claim 18, wherein the first rotatable cam is20 operable by a thumb turn and the second rotatable cam is comprised within a cylinder lock.

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