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Title:
FIRE DOOR RELEASE MECHANISM
Document Type and Number:
WIPO Patent Application WO/2023/031630
Kind Code:
A1
Abstract:
There is described a releasable door locking device which incorporates a solenoid, The releasable door locking device may be incorporated in a slave unit which wirelessly communicates with a master unit to send a trigger signal to release the door lock. The releasable door locking device comprises a housing which is mountable to a door; a locking mechanism comprising a locking arm which is moveable between a locked position in which a foot of the locking arm protrudes from the housing and an unlocked position in which the foot is substantially located within the housing; and a solenoid release mechanism located within the housing. The solenoid release mechanism comprise a lever which is rotatable from a rest position to a release position to release the locking arm from the locked position; a solenoid which is configured to be activated by a trigger signal and which when activated engages with the lever to rotate the lever between the rest and release positions; and a resilient member which is configured to return the lever from the release position to the rest position after the locking arm is released; and a receiver for receiving the trigger signal.

Inventors:
DREWNICKI ALEXANDER (GB)
DREWNICKI LEIGH (GB)
DREWNICKI RICHARD (GB)
Application Number:
PCT/GB2022/052264
Publication Date:
March 09, 2023
Filing Date:
September 06, 2022
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
DREWNICKI ALEXANDER (GB)
DREWNICKI LEIGH (GB)
DREWNICKI RICHARD (GB)
International Classes:
E05C1/04; E05B15/00; E05B15/10; E05B47/00; E05B47/06; E05B53/00; E05C17/44; E05F1/00; G08B17/00
Domestic Patent References:
WO2007057672A22007-05-24
WO2017191449A12017-11-09
Foreign References:
GB2359335A2001-08-22
JPH0714059U1995-03-10
US1772604A1930-08-12
DE2351042A11975-04-30
DE2443444A11976-03-25
KR20190041244A2019-04-22
CN201125585Y2008-10-01
Attorney, Agent or Firm:
APPLEYARD LEES IP LLP (GB)
Download PDF:
Claims:
CLAIMS

1 . A releasable locking device for a door, the locking device comprising a housing which is mountable to a door; a locking mechanism comprising a locking arm which is moveable between a locked position in which a foot of the locking arm protrudes from the housing and an unlocked position in which the foot is substantially located within the housing; a solenoid release mechanism located within the housing, the solenoid release mechanism comprising a lever which is rotatable from a rest position to a release position to release the locking arm from the locked position; a solenoid which is configured to be activated by a trigger signal and which when activated engages with the lever to rotate the lever between the rest and release positions; and a resilient member which is configured to return the lever from the release position to the rest position after the locking arm is released; and a receiver for receiving the trigger signal from a master unit, wherein the trigger signal is a long range radio wireless signal.

2. The releasable locking device of claim 1 , wherein the solenoid comprises a wire coil wrapped around a pin which is moveable between a rest position in which the pin is spaced from the lever and an activated position in which the pin engages the lever.

3. The releasable locking device of claim 2, wherein the wire coil has low resistance.

4. The releasable locking device of any one of the preceding claims, wherein the solenoid engages the lever at a first end and the lever is rotatable about a hinge point at an opposed end of the lever to the first end.

5. The releasable locking device of any one of the preceding claims, wherein the lever comprises first and second portions which are set at an angle to each other.

6. The releasable locking device of any one of the preceding claims, wherein the resilient member is in the form of a spring which is compressed as the lever moves from the rest position to the release position to generate a compression force which returns the lever from the release position to the rest position. 7. The releasable locking device of claim 6, wherein the parameters of the spring are selected to provide a compression force of approximately 100N.

8. The releasable locking device of any one of the preceding claims, further comprising a locating mechanism for retaining the locking arm in the locked position, wherein the lever is connected to the locating mechanism so that as the lever rotates from the rest position to the release position, the locating mechanism is released to release the locking arm.

9. The releasable locking device of claim 8, wherein the locating mechanism comprises a friction plate which is moveable between an engaged position in which the friction plate frictionally engages with the locking arm to prevent movement of the locking arm relative to the friction plate and a free position in which the locking arm moves freely relative to the friction plate.

10. The releasable locking device of claim 9, wherein the lever is connected to the friction plate via a connecting arm, whereby movement of the lever moves the friction plate and vice versa.

11. The releasable locking device of claim 9 or claim 10, wherein the resilient member is configured to move the friction plate from the free to the engaged position.

12. The releasable locking device of any one of claims 9 to 11 , further comprising at least one release insert on the friction plate which cooperates with a corresponding release abutment to release the locking arm as a mechanical failsafe mechanism.

13. The releasable locking device of any one of the preceding claims, further comprising at least one battery for powering the releasable locking device.

14. A system comprising at least one slave unit comprising the releasable locking device as set out in any one of claims 1 to 13; and a master unit which is connected to the at least one slave unit via a one-way long range wireless communication network whereby the master unit is able to wirelessly send the trigger signal to the at least one slave unit.

15. The system according to claim 14, wherein the master unit is configured to transmit messages at regular intervals and the at least one slave unit is configured to open a receive window at a time in which a message is expected.

16. The system according to claim 15, wherein the at least one slave unit is configured to switch to a failsafe mode in response to a message not being received in the receive window. 17. The system according to any one of claims 14 to 16, wherein there are a plurality of slave units and the master unit is configured to transmit a trigger signal simultaneously to each slave unit.

18. The system according to any one of claims 14 to 17, wherein the master unit comprises a master control unit for detecting a fire alarm and for triggering the trigger signal in response to detecting a fire alarm and a master communication unit for receiving the trigger signal from the master control unit and relaying the trigger signal to the at least one slave unit.

19. The system according to claim 18, wherein the master control unit comprises at least one microphone and a processor which is configured to detect a fire alarm by receiving at least one sample which is derived from a sound signal detected by the at least one microphone; comparing the at least one received sample with a reference pattern using fuzzy logic to determine whether an alarm is sounding and when it is determined that an alarm is sounding, generating the trigger signal.

Description:
FIRE DOOR RELEASE MECHANISM

FIELD

[01] The invention is a release mechanism for releasing a locking member, in particular on a fire door when an alarm is detected, and a system incorporating such a release mechanism.

BACKGROUND

[02] Various mechanisms for achieving automatic opening of locking members on fire doors are known in the art and a commonly used design incorporates a foot plunger as the releasable locking member. An example of a device incorporating such a releasable foot plunger is shown in WO2017/191449 and depicted in Figures 1a and 1b.

[03] Figures 1a and 1b show the device 110 comprises a housing 112 which is mounted to a lower part of a door 114. The device comprises a foot plunger moveable between a deactivated position (shown in Figure 1a) and an activated position (shown in Figure 1b). The foot plunger comprises a foot actuator 124 which when activated causes a foot 126 to move between an inactivated position in which it is substantially located within the housing of the device (shown in Figure 1a) and an activated position (shown in Figure 1b). In the activated position, the foot 126 is received in an aperture in a foot plate 122 which is fixed to the floor adjacent the door 114. Thus, when plunger is activated by a user by pressing down in the direction of the arrow shown in Figure 1b on the foot actuator 124, the device locks the door. Thus, the foot actuator, foot and foot plate form a locking mechanism with the foot plunger acting as a locking arm which is moveable between a locking position and an unlocking position. The device can return to the deactivated state on detection of a fire so that the door is unlocked.

[04] There are various mechanisms which are known for controlling the foot plunger, including for example actuators, magnets or cams to lift the foot plunger (and to release the door). These release mechanisms are normally driven by a continuous low torque electric motor which is unable to provide sufficient force to activate the release mechanism directly. Additional gearing mechanisms are typically used to increase the torque and the motor is typically run for a number of seconds to enable the gearing mechanism to develop sufficient force to positively release the foot plunger. Once the motor is turned on, the continuous nature of the motor means that there is nothing to stop the motor unless the power is removed and/or a switch is activated to turn the motor off. Accordingly, all designs using a continuous electric motor require this additional gearing to maintain the low torque requirements of the continuous electric motors. Low torque continuous electric motors and their associated gearing mechanisms also require additional positional sensor switches to provide positional feedback for components within the release mechanism, e.g. to detect the end-points. Additional firmware is also needed to monitor and provide feedback information with regard to the position of the release mechanism, and the positional monitoring of the end points detected by the switches. An example of a cam release design is shown in Figure 1c. A screw actuator design typically has more components than the cam release design.

[05] Figure 1c shows a foot actuator 224 which moves the foot plunger and hence the foot 226 from a deactivated to activated state by a user. In the activated state, the foot 226 is held in the extended position by a friction plate 234 which friction ally engages with the foot plunger. A release mechanism incorporating a continuous electric motor 220 is used to move the foot 226 from the activated state to the deactivated state when a fire is detected. The continuous electric motor 220 requires an additional gearing mechanism (not shown) to provide sufficient torque to move the foot 226. The release mechanism comprises a cam 230 which is driven by the motor 220. The cam 230 pulls on a connecting arm 232 which in turn changes the angle of the friction plate 234 relative to the foot plunger to remove the friction engagement and hence release the foot plunger. As the connecting arm pulls down the friction plate 234, the friction plate also compresses a spring 236 so that when the cam is in the deactivated position, the motor is switched off, and the friction plate 234 is returned to its original position by the decompression of the spring. The movement of the friction plate 234 in turn moves the cam 230 back to its starting position. As explained above, the motor is a geared motor to increase the torque available and to allow for sufficient force to pull the lever arm 232. The addition of the gearing mechanism increases the time needed to activate the release mechanism due to the required motion of the gearing mechanism.

[06] Figure 1c also shows that there is a plurality of switches which monitor the positional information of the cam and motor to provide feedback which allows the correct start and end points of the cam to be determined. In this example, there is a release switch 250, a motor switch 252, a foot switch 254 and a battery switch 256. The switches provide a feedback loop which allows the start and stop points for the motor to be determined and ensures that the motor is either started or stopped as required. The feedback from the switches is monitored by the firmware/software in the device.

[07] It will be appreciated that considerable power is needed in a device such as that shown in Figure 1c. The design described below aims to reduce the power consumption as well as improving other aspects such as speed of release without compromising safety.

SUMMARY

[08] According to the present invention there is provided an apparatus and method as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows.

[09] We describe a releasable locking device for a door, the releasable locking device comprising a housing which is mountable to a door; a locking mechanism comprising a locking arm which is moveable between a locked position in which a part of the locking arm protrudes from the housing and an unlocked position in which the part of the locking arm is substantially located within the housing; and a solenoid release mechanism located within the housing. The solenoid release mechanism comprises a lever which is rotatable from a rest position to a release position to release the locking arm from the locked position; a solenoid which is configured to be activated by a trigger signal and which when activated engages with the lever to rotate the lever between the rest and release positions; and a resilient member which is configured to return the lever from the release position to the rest position after the locking arm is released. The releasable locking system also comprise a receiver for receiving the trigger signal. As explained in more detail below, the trigger signal is generated by a master unit.

[10] The solenoid may comprise a wire coil wrapped around a pin. The pin may be moveable between a rest position in which the pin is spaced from the lever and an activated position in which the pin engages the lever. Activation of the solenoid by the trigger signal triggers the movement of the pin. The solenoid may further comprise a return mechanism (e.g. a resilient element) to movement the pin to its original position once the trigger signal ceases. The wire coil may have low resistance, e.g. up to 50% lower resistance than a standard 3V solenoid. The wire coil may be made from a low resistance material and/or have a reduced gauge. In this way, the solenoid has reduced power consumption when compared to a standard solenoid.

[11] When activated, the solenoid may engage the lever at a first end. The lever may be rotatable about a hinge point at an opposed end of the lever to the first end. This maximises the lever force provided by the activation of the solenoid. The first end of the lever may comprise a contacting portion for the pin of the solenoid. The lever may comprise a first and second portion which are set an angle to each other. In this way, the lever may have a sufficient length to provide the lever force required to release the locking mechanism and still fit compactly into the device without contacting other components when rotating.

[12] The resilient member may be a spring which is compressed as the lever moves from the rest position to the release position to generate a compression force which returns the lever from the release position to the rest position. The parameters of the spring (e.g. diameter of the wire, length of the spring and spring strength) may be selected to provide a compression force which is sufficient to reset the solenoid release mechanism, e.g. approximately 100g.

[13] The device may comprise a locating mechanism for retaining the locking arm in the locked position, wherein the lever is connected to the locating mechanism so that as the lever rotates from the rest position to the release position, the locating mechanism is released to release the locking arm. The locating mechanism may comprise a friction plate which is moveable between an engaged position in which the friction plate frictionally engages with the locking arm to prevent movement of the locking arm relative to the friction plate and a free position in which the locking arm moves freely relative to the friction plate.

[14] The lever is connected to the friction plate via a connecting arm whereby movement of the lever moves the friction plate and similarly movement of the friction plate moves the lever. For example, as the lever rotates from the rest position to the release position, in response to activation of the solenoid, the connecting arm moves the friction plate from the engaged position to the free position. After the solenoid is deactivated, there may be no engagement between the solenoid and the lever and thus the lever is free to rotate back to its rest position. The resilient member may be configured to move the friction plate from the free position to the engaged position. This movement of the friction plate returns the lever from the release position to the rest position. In other words, the solenoid release mechanism is automatically reset once the trigger signal ceases.

[15] The locking mechanism may further comprise a locking plate having an aperture which receives and engages with the locking arm in the locking position. In the locking position, the art of the locking arm which extends from the housing may engage with a foot plate.

[16] As explained above, the device is designed to be low power, e.g. by appropriate design of the solenoid release mechanism, the lever and other components. Accordingly, the device is suitable to be battery powered and thus the device further comprises at least one battery. The device comprises a receiver for receiving the trigger signal. The trigger signal may be received from an external master unit, for example when the master unit has detected a fire, e.g. by detecting a fire alarm. By restricting the master unit to one-way communication with the device, e.g. so that the master unit only sends signals to the device and no signals are transmitted to the master unit by the device, further power saving is achieved.

[17] Thus, the releasable locking device described above may be incorporated in a system comprising a master unit.

[18] We also describe a system comprising at least one of the releasable locking systems describe above as a slave unit and a master unit which is connected via one-way long range wireless (e.g. LoRa™) communication network to the at least one slave unit whereby the master unit is able to send the trigger signal to the at least one slave unit. Long range means that the communication network can cover an entire building, e.g. at least up to 500m. The system may comprise a plurality of slave units connected to the master unit. A suitable communication network may use long range radio wireless signals at 868 MHz or 915MHz for example. There may be a plurality of slave units and the master unit may be configured to simultaneously transmit the trigger signal to each of the slave units, thereby releasing a plurality of release mechanisms to close a plurality of doors. The master unit may comprise a master control unit for detecting a fire alarm and for triggering the trigger signal in response to detecting a fire alarm and may comprise a master communication unit for transmitting the trigger signal. As described below, the master control unit may comprise at least one microphone to detect a fire alarm (or other sound) using acoustic sensing.

[19] The master unit may be configured to transmit messages at regular intervals and the at least one slave unit may be configured to open a receive window at a time in which a message is expected. By keeping the receive window to a short period, e.g. 2 to 5 milliseconds, the power drain is reduced. The at least one slave unit may be configured to switch to a failsafe mode in response to a message not being received in the receive window. The at least one slave unit may further comprise at least one sensor selected from a vibration sensor and a battery sensor and the at least one slave unit is configured to switch to a failsafe mode in response to a signal being received from the at least one sensor. By introducing this failsafe mode, it is not essential to include a battery back-up system for the master unit because if a message is not received during the receive window, the at least one slave unit will switch to the failsafe mode so that the locking mechanism is released. The regularly transmitted message may be a synchronisation message to keep the master unit synchronised in time with each slave unit.

[20] As an alternative or in addition to the electrical failsafe modes described above, the releasable locking device may comprise a mechanical failsafe mechanism which is activated by a user to release the locking arm. The mechanism failsafe mechanism may be operated or activated by a user applying a force to a door to which the releasable locking device is attached. The mechanism failsafe mechanism may comprise at least one release insert on the friction plate which cooperates with a corresponding release abutment to release the locking arm. Any forced movement of the door, which may be in the partially open or closed position, may be automatically and mechanically detected. The detection may result in the immediate mechanical release of the locking arm. This release maintains fire safety compliance at all times and free access to potential through traffic as well as preventing damage to the internal door mechanism itself from unwanted force and mechanical wear. A mechanical failsafe is not reliant on vibration sensing, sensing battery voltages or other electrical methods for a successful activation. When combined with the electrical failsafe, the mechanical failsafe may be considered to provide a dual failsafe mechanism.

[21] The master unit may comprise a master control unit for detecting a fire alarm and for triggering the trigger signal in response to detecting a fire alarm. The master unit may comprise a master communication unit for receiving the trigger signal from the master control unit and relaying the trigger signal to the at least one slave unit. The master control unit may be configured to detect a fire alarm by any suitable method. The master control unit may comprise at least one microphone and a processor for detecting the fire alarm. The processor may be configured to receive at least one sample which is derived from a sound signal detected by one or more microphones; compare the at least one received sample with a reference pattern using fuzzy logic to determine whether an alarm is sounding and if the processor determines that an alarm is sounding, generate the trigger signal. Fuzzy logic is a known form of logic in which the truth value of variables may be any real number between 0 and 1 .

[22] The alarm may be a fire alarm. Alternatively, the alarm may be a doorbell or other similar alarm. The alarm is preferably of the continuous type, be that single tone, multi tone, or swooping tone. Any pattern is acceptable so long as the sound doesn't stop. It will be appreciated that the master control unit may be configured to detect any type of sound, not just a fire alarm.

[23] The master control unit may be configured to learn the reference pattern. The reference pattern may comprise a series of reference frequencies with each reference frequency being the frequency of the maximal sound level for each of a plurality of samples of a sound signal. The master control unit may be configured to receive a plurality of samples. The master control unit may be configured to determine whether the number of received samples is greater than a sample pre-set threshold before carrying out the compare step. The master control unit may be configured to compare a frequency of each of the received samples with each of the series of reference frequencies and determine whether an alarm is sounding by determining whether a match between the compared frequencies is greater than a match pre-set threshold.

[24] The master control unit may further comprise a fast Fourier transform (FFT) component which determines the frequency of a maximal sound within a sound signal detected by the microphone and the at least one sample is the determined frequency. The master control unit may be configured to determine whether the sound signal detected by the microphone(s) has a loudness which is greater than a loudness pre-set threshold. The master control unit may be configured to receive the at least one sample after the sound signal has a loudness greater than the loudness pre-set threshold.

[25] Although a few preferred embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

[26] For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example only, to the accompanying diagrammatic drawings in which:

[27] Figures 1a and 1b are perspective views of a prior art locking system mounted on a door with Figure 1a showing an unlocked state and Figure 1b showing a locked state;

[28] Figure 1c is an example of a cam release mechanism which may be incorporated in the system of Figures 1a and 1b;

[29] Figures 2a and 2b are perspective views of a new design of releasable locking system mounted on a door with Figure 2a showing an unlocked state and Figure 2b showing a locked state;

[30] Figures 3a and 3c are perspective images of a solenoid release mechanism which can be incorporated into the releasable locking system of Figure 2a in a rest and release position;

[31] Figures 3b and 3d are views of a detail of the release mechanism of Figures 3a and 3c respectively;

[32] Figures 4a to 4d are internal views of the device showing the interaction between the release mechanism of Figure 3a and a locking mechanism;

[33] Figure 5a is a schematic block diagram of a system incorporating the alternative release mechanism of Figure 3a;

[34] Figure 5b is a front view of a master unit which can be incorporated in the system of Figure 5a;

[35] Figure 6 is a flow chart showing the operation of the system, and

[36] Figure 7a is a perspective image of a variant of the solenoid release mechanism shown in Figure 3a;

[37] Figure 7b is a detail of the release mechanism of Figure 7a; [38] Figures 7c and 7d are side views of the release mechanism of Figure 7a in the un locked and locked positions respectively; and

[39] Figure 7e shows internal detail of the arrangement shown in Figure 7d.

DESCRIPTION OF DRAWINGS

[40] The description below describes a releasable door locking device which incorporates a solenoid to reduce the number of components required and the power consumption relative to the prior art designs. As explained in more detail below, the solenoid is incorporated in a release mechanism together with a lever and a resilient member which cooperate to provide the necessary force to release the locking mechanism and to provide a mechanical return or reset function. The use of a solenoid allows a trigger pulse to activate the release mechanism and release the locking mechanism. The locking mechanism may be released in typically just milliseconds rather than the seconds required in a continuous motor design which needs additional gearing to generate the required force. The same level of control as the continuous motor designs is provided without the need for a continuous motor and a control unit to control the motor.

[41] The trigger pulse may be generated in a separate master unit which is located at a different location to the releasable door locking device. One master unit can be used to control multiple releasable door locking devices (or slave units). With the centralised control, a controller (or processor) which detects a fire is not required in each slave unit. As detailed below, other components can also be omitted from each slave unit and there are thus significant component and cost savings, as well as improvements to the battery life. Further improvement to battery life can be achieved by the use of failsafe modes and message windows as described below.

[42] Figures 2a and 2b show a releasable locking device 10 which comprises a housing 16 which is mounted to a lower part of a door 14. The device 10 comprises a locking mechanism which is at least partially located within the housing 16. In this arrangement, the locking mechanism comprises a foot actuator 24 which is offset centrally relative to the housing 16 although it will be appreciated that other arrangements such as a central arrangement are also possible. The foot actuator 24 is connected to a foot 26 by a rod 28 and the components together may be termed a foot plunger. Actuation of the foot actuator 24 causes the foot 26 to move between a deactivated position in which it is substantially located within the housing 16 of the device as shown in Figure 2a and an activated position in which the foot 26 extends beyond the housing 16 as shown in Figure 2b. This movement compresses a spring (not shown) within the foot plunger and the compressive force of the spring is used to return the foot 26 from the activated position to the deactivated position when the locking mechanism is released. The foot plunger may be considered to act as a locking arm which is moveable between a locked position and an unlocked position (and vice versa). [43] As shown in Figure 2b, in the activated or iocked position, the foot 26 may be received in an aperture in a foot piate 22 (which may also be termed a floor piate or a locking plate) which for example is fixed to the floor adjacent the door 14. The engagement of the foot 26 in the foot plate 22 retains the door in position (either open or closed). For example, for a fire alarm, the housing may be configured to be mounted to a door in use wherein when the locking arm is in the locking position, the door is held open (e.g. at 65 degrees). Typically fire doors and exit doors are weighted or otherwise controlled to close unless they are being held open. The foot plunger is held in the activated position by any suitable locating mechanism which can be released by a subsequent actuation of the foot actuator 24 by a user or a solenoid release mechanism which is automatically activated by a trigger signal which is received wirelessly, for example when a fire is detected. In other words, the solenoid release mechanism can be considered to be both automatically and wirelessly activated. The foot plunger may also be held in the deactivated (or unlocked) position by the locating mechanism which is typically released by actuation of the foot actuator. Thus, when the foot plunger is actuated by a user by pressing down in the direction of the arrows shown in Figures 2a and 2b on the foot actuator 24, the locking mechanism 10 is activated or deactivated. As explained below, there are fewer components than in the prior art arrangements and thus the overall size of the device may be reduced compared to that shown in Figures 1a and 1b.

[44] The device is battery powered and there is a visual indicator provided to a user to indicate when the battery is running low. For example, as shown an LED 15 may be visible on the outside of the housing and the LED may flash to indicate a low battery.

[45] Figures 3a to 3d show details of the components within the housing. As described above, the device comprises a locking mechanism in the form of a foot plunger which comprises a foot actuator 24 connected to a foot 26 by a rod 28. Optionally, the rod 28 comprises a slot 92 near the foot 26. An end stop 90 engages with the slot 92 to help stabilise movement of the foot plunger and also define the position of the foot relative to the housing when in the locked or unlocked position. The various fixing holes for securing the device to the door and for securing the housing are also shown in Figures 3a and 3c. Any suitable fixing mechanisms, e.g. screws, may be used.

[46] The device also comprises a solenoid release mechanism (which may also be termed a lever release mechanism) which is housed in the housing for releasing the locking mechanism. Figures 3a and 3b show the solenoid release mechanism in a rest position, i.e. awaiting activation. Figures 3c and 3d show the solenoid release mechanism in a release position, i.e. just after activation and when the locking mechanism is released. The activation of the solenoid release mechanism is automatic and in response to a signal received wirelessly from a master unit as described below. The signal is received by a receiver 82 which is mounted to a control board 84 (PCB). The device is designed to be energy efficient so that the device may be battery powered, for example by two cells with relatively limited power (perhaps 6000mah at 3V). The battery housing 80 is located adjacent the locking mechanism. Energy efficiency is in part due to the communication between the device and the master unit being one way only and also by appropriate design of the internal components as explained in more detail below.

[47] The foot plunger is held in the locked or unlocked position by any suitable locating mechanism. Further detail of the locating mechanism is shown in Figures 3b and 3d. In this example, the locating mechanism comprises a plate 34 which is mounted around the rod 28. When the plate 34 is at an angle to the horizontal position as shown in Figure 3b, the plate 34 is frictionally engaged with the plate to prevent movement of the rod 28 (i.e. the locking arm) regardless of which position the foot plunger is currently in. For example, a suitable angle for achieving the frictional engagement may be around 3 degrees from the horizontal (e.g, around 87 degrees between the plate and rod). The plate 34 may be termed a friction plate. When the plate 34 is in a horizontal position (i.e. perpendicular to the rod 28) as shown in Figure 3d, the rod 28 moves freely relative to the plate 34 and thus the foot plunger may move between the activated and deactivated positions.

[48] The friction plate 34 may be made from stainless steel, other metals or similarly strong plastics such as Delrin™, Nylon™ or similar. The friction plate 34 comprises a pair of flanges 38 which are either side of the rod 28 and which are set at an upturned angle to the friction plate 34. A connecting arm 32 is connected to the friction plate 34 via a hook 33 which in this arrangement is located in the plate 34 between the flanges 38. The hook 33 may be used to move the friction plate between the angled (or locating) position shown in Figure 3b and the horizontal (or free movement) position shown in Figure 3d.

[49] Figures 3b and 3d also show the detail of a locating chamber 70 which helps stabilise and control the movement of the friction plate 34. The chamber 70 comprises a pair of side walls 72 which are either side of the rod 28 and which support a pair of planar upper portions 74. The chamber 70 also comprises a base 76 which supports a resilient member in the form of a spring 36 which returns the friction plate 34 to its angled position and hence returns the solenoid release mechanism to its rest position as explained below. As shown in Figure 3d, the spring 36 is compressed when the friction plate 34 is in the horizontal position. The vertical movement of the friction plate 34 is constrained between the base 76 and the planar upper portions 74 with the flanges 38 contacting the planar upper portions 74 when the friction plate 34 is in the position shown in Figure 3b. The side walls 72 act as a guide to maintain the position of the friction plate 34.

[50] Returning to Figures 3a and 3c, the detail of the solenoid release mechanism is shown. The solenoid release mechanism comprises a lever 60, a solenoid 50 which is configured to move the lever 60 to release the locking mechanism, the connecting arm 32 which connects the lever 60 to the locating mechanism of the locking mechanism, and the spring 36 which is configured to reset the solenoid release mechanism. The lever 60 is moveable between a first (or rest) position shown in Figure 3a and a second (or release) position shown in Figure 3c in which the locking mechanism is released. When moving from the rest position to the release position, movement of the lever 60 by the solenoid 50 moves the connecting arm 32 which in turn moves the friction plate 34. After releasing the locking mechanism, the lever 60 is returned to its rest position by the release of compression forces in the spring 36. The spring 36 may be a coil of steel wire or other suitable material.

[51] Figures 4a to 4d illustrate the interaction between the lever 60, solenoid 50, connecting arm 32 and spring 36 within the solenoid release mechanism. The solenoid 50 comprises a housing 58 and a coil wound around a pin 52. The pin 52 has a first end 54 which engages a contacting portion at a first end 62 of the lever 60 and a second end 56 which is at the opposed end of the pin 52 and which protrudes from the housing 58 of the solenoid. In Figure 4a, the foot 24 extends beyond the housing and thus the locking mechanism has been activated, for example by the user actuating the foot actuator 26. When the solenoid is activated, e.g. in response to the trigger signal, the pin 52 of the solenoid 50 moves towards the first end 62 of the lever 60 as shown by the direction of the arrow. In other words, the pin 52 moves from a rest position in which it is spaced from the lever to a second or activated position in which it engages the lever 60, more specifically the contacting portion of the lever 60.

[52] Figure 4b shows that the movement of the first end 54 of the solenoid pin 52 pushes the first end 62 of the lever 60 towards the foot plunger as shown by the arrow A. A second end (at an opposed end to the first end 62) of the lever 60 is fixed to form a pivot point 64 about which the lever 60 rotates. The second end also comprises a connector portion 66 to which the connecting arm 32 is connected. As the lever 60 rotates due to the movement of the solenoid pin, the connector portion 66 also rotates which draws the connecting arm 32 towards the foot 24 as illustrated by arrow B. The movement of the connecting arm 32 draws the friction plate 34 towards the foot (i.e. downwards) and into a horizontal position to release the frictional engagement with the rod 28. As the friction plate 34 is drawn downwards, the spring 36 is compressed.

[53] Figure 4c shows that once the friction plate 34 is released, the foot plunger is able to return to its inactivated state, i.e. with the foot 24 generally located within the housing of the device. In other words, the foot plunger moves upwards as shown by the direction of the arrow. The upward movement of the foot plunger may be generated by a spring (not shown) within the rod 28. The spring 36 returns to its normal state and the release of the compressive force moves the friction plate 34 upwards and back to its angled position so that the frictional engagement with the rod 28 is restored. The movement of the friction plate 34 also moves the connecting arm 32 upwards which in turn moves the lever 60. The movement of the lever 60 is a rotation about the pivot point 64 in an opposite direction to that caused by the solenoid 50.

[54] Figure 4d shows the outcome after the full decompression of the spring 36. The friction plate 34 once again engages the rod 28 and thus the foot plunger is locked in place until actuation by the user by pressing on the foot actuator 26. The first end 62 of the lever 60 has also moved to its original position shown in Figure 4a. The solenoid 50 has also returned to its original position so that its second end 56 protrudes from the housing 58. In other words, the pin has moved in the direction shown by the arrow. The return of the solenoid may be controlled by any suitable mechanism, e.g. an internal spring (not shown) which is compressed when the solenoid is activated (e.g. by the trigger signal). When the trigger signal stops, the compression forces of the internal spring automatically move the solenoid pin to its original position. In other words, no electrical resetting or firmware intervention is required to reset the solenoid back to its original position. Thus, the solenoid release mechanism has automatically reverted and reset back to its original position. By contrast, the continuous electrical motor design described in the background section requires further electrical, mechanical and firmware interventions to perform this reset function.

[55] The device is typically battery powered and thus low power consumption is preferable. By contrast to previous continuous electrical motor designs, the design features described above, in particular the use of a solenoid, mean there is no requirement for a motor and no need to monitor the relative position of the components controlled by the motor. As explained above, no feedback switches and associated software/hardware are required in the solenoid release mechanism to control or reset its operation. It will be appreciated that the design thus achieves a significant decrease in component count and has a greatly simplified design. The design thus has reduced power requirements and there is a significant increase in the battery life relative, of the order of days and even months, to prior art designs,

[56] In addition to the removal of the feedback switches and associated software and hardware, the solenoid release mechanism has been further designed to reduce power consumption. In particular, the solenoid has been designed to be a low power device, for example the solenoid may comprise a wire coil which has a lower gauge than normal to reduce resistance and minimise the operating current through the coil. For example, the wire gauge may be reduced by 50% when compared to a standard 3V solenoid. The wire used for the solenoid may be a low resistance wire, e.g. silver plated wire or similar, to further reduce the wire resistance and lower the current draw during operation.

[57] The lever 60 (which may also be termed a lever arm) has been designed to provide sufficient leverage to release the friction plate taking into account the amount of force delivered by the solenoid. The lever 60 may be made from any sufficiently robust and lightweig ht material, e.g. steel, other metals or suitable structural plastics. The lever 60 may be formed with a contacting surface to provide a good contact with the solenoid pin. The contacting surface may protrude generally at right angles at the first end 62 of the lever 60. The design of the solenoid release mechanism is also preferably compact and thus the lever 60 may be non-linear, e.g. comprising first and second portions set an angle to each other. The angle may be set to ensure that the overall length of the lever is sufficient to provide the required force and that the first portion avoids contacting the locating chamber 70.

[58] Similarly, the spring 36 has been designed to minimize power consumption but still provide a sufficient compression force to automatically reset the solenoid release mechanism. The design of the spring may comprise selecting appropriate values for the parameters, including for example diameter of the wire, length of the spring and spring strength. For example, the diameter of the wire may be reduced from 1 mm to 0.6mm and/or the spring strength may be reduced from 200g of force required to activate to under 100g.

[59] As explained above, in the prior art designs using a continuous electric motor, gearing mechanisms are typically required because the torque provided by these motors is insufficient to release the locking mechanisms. Such gearing mechanisms are subject to wear due to friction. By eliminating the motor and its associated gearing, friction within the design has been reduced. Bearings, bushings, washers and other friction eliminating components may also be further incorporated into the locking mechanism and/or the solenoid release mechanism to further reduce friction and thus minimise the required release force.

[60] The solenoid release mechanism 536 may be incorporated into a system 500 such as that shown in Figure 5a, The system 500 comprises a master unit 510 and at least one slave unit 530 comprising the solenoid release mechanism 536. It will be appreciated that three slave units 530 is merely an indicative number and that any number of slave units may be used as long as they are in range depending on the communication method. For example, there may be three, five or over ten slave units for each master unit, in this arrangement, the master unit 510 comprises a master control unit 512 for detecting a fire as described below and a master communication unit 514 which is triggered by the master control unit 512 to send signals to each slave unit 530. Each of the master control unit 512 and the master communication unit 514 comprise a suitable processing unit 518, 528 (also termed a control unit or module) which control operation of these units.

[61] Each slave unit 530 comprises the solenoid release mechanism 536 described above and a module 532 which triggers the solenoid release mechanism 536 when receiving the trigger signal from the master communication unit 512. The use of solenoid release mechanism 536 having a lower powered solenoid has been particularly chosen to allow the system to operate as a one way communication system. In other words, the slave unit receives the trigger signal from the master unit but there is no need for the slave unit to transmit to the master unit. Accordingly, the transmit window from the slave unit may be essentially eliminated as described below. This results in a significant improvement in battery life.

[62] Each slave unit 530 also comprises a sensor 538 which can trigger a failsafe mode as described in more detail below. Although only one sensor 538 is shown in the Figure for simplicity, it will be appreciated that there may be more than one sensor. The sensor may be a vibration sensor which is preferably a passive vibration sensor to reduce the power drain on the battery. Alternatively, or additionally, there may be a battery sensor which detects when the battery compartment of the slave unit 530 is opened. The battery sensor may be any suitable mechanism for making or breaking an electrical contact so that opening of the battery compartment is detectable, e.g. a leaf spring, a screen-printed contact, an insert, a metallic injection moulding or over moulding technique or a battery closure means such as a screw.

[63] The system 500 is a radio frequency (RF) wireless system and thus each of the master communication unit 514 and the slave unit(s) 530 comprise a suitable antenna 524, 534. There is only one way communication and thus the antenna 524 at the master communication unit 514 is a transmitter (not a receiver or transceiver) and the antenna 534 at the siave unit 530 is only being operated as a receiver (not a transmitter or transceiver). Each master communication unit 514 may communicate with a plurality of slave units 530 on the same channel number and the same frequency which allows multiple slave units to be integrated into one system. The signals are interference free long range radio wireless signals (e.g. LoRa ™ at 868 MHz) and may have a range that covers an entire building (e.g. up to 500m). A new slave unit may be added to an existing system by appropriate pairing or programming of the slave unit, e.g. to program the channel number and frequency. The pairing or programming may be completed using a pairing mode button or via any suitable connection, e.g. USB connectors on the slave unit,

[64] As an alternative to having one system cover an entire building, different zones within a building may be created. Each zone has a separate system with a master communication unit and associated slave units. Each separate system may operate interference free from each other separate system even when the separate systems are operating in close proximity to each other (e.g. within the same building). Each separate system may have its own unique identification number (ID) and will communicate on a different channel to avoid trigger events in one system inadvertently triggering an unrelated zone.

[65] It will be appreciated that the functionality of the master control unit 512 and the master communication unit 514 may be separated into two (or more) devices. It will also be appreciated that the master control unit 512 may incorporate the locking mechanism and solenoid release mechanism of each slave unit and may also be used to hold a door open. Alternatively, the master control unit 512 may be a scaled down version with the microphone, processor and communication module to output the trigger signal. The master control unit 512 could be mains powered (using appropriate adapters) and mounted at any appropriate location (e.g. near an alarm source). There may be a batery back up in the event of mains power failure. The battery back-up for the master unit may not be necessary if each slave unit is configured with failsafe protection and can independently enter the failsafe mode in which the solenoid release mechanism is triggered as explained below.

[66] In this arrangement, the master control unit 512 is configured to detect a fire by detecting a fire alarm sounding, for example as described in WO2017/191449. It will be appreciated that any other suitable method for detecting a fire may be used. When the detecting of a fire alarm is used, the master control unit 512 comprises a microphone (MIC) which may sample the sound level at regular intervals, for example approximately every 4 seconds. The sampled sound includes all of the ambient sounds including a possible alarm sound. When a loud sound is detected, for example by determining that the loudness of the sample is higher than a loudness pre-set threshold level, the sampling frequency may increase (e.g. to 3 per second). The system begins to count up or down, depending on whether the sound continues or not. When the loud sound is persistent, the sample is analysed, e.g. using a Fast Fourier Transform component, to determine the frequency and magnitude of the maximal sound. When enough samples of loud sounds have been collected, there is an analysis of the sound pattern. This analysis may comprise using Fuzzy logic to compare the samples with reference samples, for example, reference samples learned from an alarm. If there is a match, an alarm is deemed to be detected. A warning may be provided to the user, e g. on a display screen 516 of the master control unit 510 or by a flashing LED.

[67] The master communication unit 514 may simply comprise the necessary hardware to receive and relay the trigger signal. The master communication unit 514 could be mains powered (using appropriate adapters) and mounted at any appropriate location (e.g. near an alarm source). The master communication unit 514 could also run on batteries, possible with a low power battery backup, utilized as a failsafe to trigger a failsafe output to all the slave units. The battery backup may be avoided by incorporating a failsafe protection mechanism, e.g, the vibration sensor and/or battery sensor into the slave units themselves. The master communication unit 514 may be programmable to set the channel and frequency as explained above. An example working frequency is 868mHz with LoRa demodulation and an output power of 20dbm.

[68] Figure 5b shows an example of a suitable master control unit 514. The master control unit 514 comprises a housing 540 having an external display 542 for displaying information to a user. For example, the display may indicate when the alarm is sounding.

[69] There are also menu programming buttons which in this arrangement comprise five butons 550, 552, 554 but it will be appreciated that other arrangements of buttons can be used. The menu programming buttons are used to program the master control unit 514 for example as described in WO2017/191449. For example, the top and bottom programming buttons 550 may be used to scroll between the different menu items. The right and left programming buttons 552 may be used to select items that are side by side on the display and to select delete function Y/N. The middle button 554 has the "enter" function and is used to either enter a sub-menu or to select an item for editing. Pressing the middle button again may exit editing. The menu options can be viewed on the display and can be controlled using the menu programming buttons. As an example, the menu options include any suitable options, e.g. status, fault, log, date, time, night, closing, opening, sounder, test, learn new alarm, calibrate ambient level, battery, version and restore.

[70] The options of being able to learn a new alarm and/or calibrate ambient level are useful to better set-up the device. For example, if the environment is noisy, the system will make sure that it sets an appropriate level above that for sensing the alarm, in other words the loudness pre-set threshold may be different for different environments and may be set at a specific value above the ambient noise level for the particular environment. The learn new alarm function allows the device to learn the unique acoustic properties of the fire alarm as a reference to trigger the door release. Alternatively, a unit may automatically self-calibrate upon power-up, with the auto-learn version of the firmware installed, requiring no additional set-up.

[71] Figure 6 is a flowchart showing a method of operating the system of Figure 5a. The first phase of Figure 6 (steps S600 to S612) shows a fail-safe phase between the master communication unit and each of the slave units. The master communication unit transmits a regular message as shown at step S600. One type of regular message which may be used is a "live" message and this may be transmitted at regular intervals, e.g. every 15 to 20 seconds up to every hour. The timing of the regular message is known to the slave unit and thus to save battery life, the slave unit may only be open to receive such messages within a specified receive window as shown by step S602. The receive window may be a few seconds or even milliseconds around when the regular message is expected. The slave unit checks whether it has received a live message as shown at step S604. The slave unit may be considered to be in sleep mode when a receive window is not open.

[72] In the event that a regular live message is not received within the expected time window, the slave unit may switch to a failsafe mode and the solenoid release mechanism is released by triggering the necessary output signal for the solenoid at step S612. Additionally or alternatively, the slave unit may switch to a failsafe mode when no regular live message is received after a predetermined amount of time, e.g. one hour. The slave unit may not receive the regular message due to a fault, e.g. power failure or loss of signal, at the master communication unit or due to a fault at the slave unit, e.g. low battery or loss of signal. When low battery is detected at the slave unit, there may also be a visual indicator to a user, e.g. a flashing LED signal. Low battery may be below a threshold voltage, e.g. 2.2V. In addition, the solenoid release mechanism has been designed to operate down to a low 2.0V voltage.

[73] As another failsafe, when a fault is detected at the master unit (either within the master control unit or the master communication unit) which means that the master communication unit is unable to transmit its regular message (step S608), the master communication unit transmits the trigger signal S610. The solenoid release mechanism is thus released at step S612. Such a fault may include a power failure at the master communication unit.

[74] When a transceiver is in standby mode and either transmitting or receiving, there is considerable power consumption (average 12.6 mah for the LoRa communication described above). By using shortened receive windows, and eliminating the need for the slave unit to transmit, there is reduced power consumption at the slave unit. Using fewer regular open windows also helps to reduce the power consumption by reducing the amount of time that the receiver needs to be in receiving mode. It will be appreciated that there is a balance between the reduction in the power consumption and reaction speed of the slave unit. A device with a receive window (also termed listen window) which opened every 15 seconds consumes more power than a device with a listen window opened every 30 seconds. For a maximum reduction in power consumption, the time between the receive windows (i.e. the sleep mode) would be as long as possible (e.g. more than 30 seconds). However, a longer sleep mode may have a detrimental effect on the reaction speed of the slave unit because the slave unit may take longer to react to a trigger signal from the master unit. This is due to the longer timing between each open window. As a balance, each receive window may be approximately 40ms in length and the timing between receive windows is between 15 to 20 seconds. [75] When such shortened or reduced receive windows are used for "live" message and "acknowledgement" responses, it is also important to maintain synchronisation between the master communication unit and each of the slave units. Accordingly, another type of regular message may also be used, namely a synchronisation message. Such a synchronisation message may be transmitted more frequently than the live message, e.g. every 30 minutes, and is used to ensure that the units keep synchronised in time.

[76] As another failsafe, each slave unit may comprise one or more sensors to detect when the failsafe mode may be triggered. In summary, a reading is received from one of the sensors at step S614 and the control module within the slave unit determines at step S616 that failsafe mode should be entered based on the received sensor reading. As shown, the slave unit then loops to step S612 to release the locking mechanism.

[77] For example, the sensor reading may be received from the vibration sensor. In other words, the vibration sensor has detected vibration of the slave unit which may have been caused by opening the battery compartment. A delay phase may be incorporated when determining whether to enter the failsafe model based on the reading from the vibration sensor. For example, the delay may be at least a fixed number of minutes (e.g. 10) after the slave unit has been enabled and made active. In other words, the module will only trigger a release of the locking mechanism when a signal from the vibration sensor after more than a predetermined time has passed from initialisation of the slave unit. This is to avoid falsely triggering failsafe during the set-up of the slave unit, including installation of batteries. Indeed, falsely triggering failsafe during set-up may prevent the set-up because the release mechanism is not armed and the door locked. As an alternative or in addition to a delay phase, the module may only trigger failsafe based on a reading from the vibration sensor when the module enters a sleep or low power mode.

[78] When using the battery sensor, the module may determine whether the slave unit is in a normal operation mode (which may be denoted by N/C) or an error or non-operational model (which may be denoted by N/O). When operating normally, the battery compartment is closed and an electrical contact is established by the battery sensor to confirm that the battery compartment is closed. As explained previously, there may be a visual indicator provided to a user to indicate when the battery is running low (for example the battery is providing less than 2V). When the slave unit is in such a low power mode, it is necessary to change the batteries. Thus, the error mode will normally occur when batteries are being replaced because this necessitates opening the battery compartment which breaks the electrical contact established by the battery sensor. Hence a signal is sent to the module and the door release mechanism will be released during battery replacement. The error mode may also occur when the batteries are producing sufficient voltage (e.g. around 2V to 2.2V) but another error has occurred, e.g. the battery compartment has been inadvertently opened. A warning signal to the user may also be provided to distinguish such an error from the low power error, e.g. by appropriate use of the LEDs or other visual indicator. The release mechanism can only be armed when the slave unit is operating in the normal operation mode and not in the error mode. [79] The next phase of Figure 6 (steps S620 to S628) shows a detection phase. At step S620, the master control unit detects a fire, for example by detecting a fire alarm sounding as described above. In response to the detection, the master control unit outputs a trigger signal which is transmitted to the master communication unit at step S622. On receipt of the trigger signal at step S624, the master communication unit then simultaneously transmits a trigger signal to each slave unit at step S626. The trigger signal is received at the slave unit and the solenoid release mechanism is released at step S628.

[80] In both the failsafe mode and detection phase, the transmission of the trigger signal and receive window is time limited to improve battery life at the slave unit. For example, the transmission of the trigger signal and the corresponding receive window may be for between 0.1 to 0.5 seconds. The time must be sufficient to activate the solenoid, move the lever and other connected parts to release the locking mechanism but kept to a minimum to conserve power.

[81] The embodiments above illustrate a system in which the components in each slave unit are reduced when compared to the master unit. For example, each slave unit does not require the following components which relate to the detection of a fire: smart listening system firmware and associated operating system, smart listening master control unit (MCU) and firmware controller, fire alarm detecting and monitoring via acoustic means, including microphones. The redesign of the locking mechanism within each slave unit also means that the following components which are typically present in such locking mechanisms can be omitted: an electric motor and its associated multipoint control unit (MCU) controller and firmware, torque correction gearing for the electric motor, friction reducing lubrication or other means for reducing wear in the electric motor gearing, and motor position detection system, e.g. microswitches and associated pull up resistors,. Each slave unit thus has a reduced number of components which results in several improvements, including for example improved battery life, reduced production time and costs and reduced point of failure (e.g. by eliminating the gearing). Moreover, the redesign results in an improved performance, for example a reduced activation time of the locking mechanism after receiving the trigger signal.

[82] It is appreciated that the slave unit still requires a control module but it is significantly scaled down and simplified when compared to the MCU in the master unit and a control unit in a motor powered device. This is because the control module in the slave unit has a reduced number of inputs and outputs when compared to these MCUs. The reduction is due to the removal of all microswitches which are not necessary for a solenoid driven release mechanism and the removal of the need to monitor and react to the acoustic environment because this is done by the master unit. This simplifies the product design and save PCB costs for example.

[83] At least some of the example embodiments described herein may be constructed, partially or wholly, using dedicated special-purpose hardware. Terms such as 'component', 'module' or 'unit' used herein may include, but are not limited to, a hardware device, such as circuitry in the form of discrete or integrated components, a Field Programmable Gate Array (FPGA) or Application Specific Integrated Circuit (ASIC), which performs certain tasks or provides the associated functionality. In some embodiments, the described elements may be configured to reside on a tangible, persistent, addressable storage medium and may be configured to execute on one or more processors. These functional elements may in some embodiments include, by way of example, components, such as software components, object-oriented software components, class components and task components, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. Although the example embodiments have been described with reference to the components, modules and units discussed herein, such functional elements may be combined into fewer elements or separated into additional elements. Various combinations of optional features have been described herein, and it will be appreciated that described features may be combined in any suitable combination. In particular, the features of any one example embodiment may be combined with features of any other embodiment, as appropriate, except where such combinations are mutually exclusive. Throughout this specification, the term "comprising" or "comprises" means including the component(s) specified but not to the exclusion of the presence of others. As an alternative or in addition to the electrical failsafe modes described above, the releasable locking device may comprise a mechanical failsafe mechanism which is activated by a user to release the locking arm. An example of such a mechanical failsafe mechanism is shown in Figures 7a to 7e. Such a mechanical failsafe mechanism may be considered to be similar to mechanical kick plate release mechanisms. Figure 7a shows the components of the whole device and Figure 7b shows the detail of the locating mechanism which holds the locking arm in the locked or unlocked position. Figure 7c shows the releasable locking device in its default state, i.e. unlocked and ready to be locked to hold a door in an open position. Figures 7d and 7e shows the release locking device when it is locked and holding a door in an open position and illustrate movement of the door from open to closed.

[84] Most of the features of the variant shown in Figure 7a to 7e are the same as the release locking mechanism described above and shown for example in Figure 3a. The common features have the same reference numbers and to avoid duplication not all features are described again. The device comprises a locking mechanism in the form of a foot plunger which comprises a foot actuator 24 connected to a foot 26 by a rod 28. The foot plunger is held in the locked or unlocked position by any suitable locating mechanism and comprises a friction plate 34 connected to a connecting arm 32 via a hook 33 which is located in the plate 34 between the flanges 38. The device also comprises a solenoid release mechanism with a lever 60, a solenoid 50 which is configured to move the lever 60 to release the locking mechanism. The connecting arm 32 connects the lever 60 to the locating mechanism of the locking mechanism, and there is a spring 36 which is configured to reset the solenoid release mechanism.

[85] As explained above, when there is a change of angle on the friction plate 34, the foot plunger is released from the locked to the unlocked position. Unlocking of the plunger may be accidentally triggered if there is movement of the foot plunger relative to the friction plate. The foot plunger should ideally be maintained in a central position relative to the friction plate 34 to ensure the correct engagement. As shown in more detail in Figure 7e, the mechanical release mechanism comprises a balance mechanism 720 which protrudes from either side of the rod 22. The balance mechanism 720 is positioned between the foot 26 and the friction plate 34. Within the balance mechanism 720 are a pair of springs 722 which are set at right angles to the rod 22 of the plunger (i.e. at right angles to the locking arm). One end of each spring engages a balancing member 732 within the rod 22 and each spring provides an opposing force to maintain the balance of the rod 22 in relation to the friction plate 34. It will be appreciated that the coil springs may be replaced by other equivalent features, e.g. leaf springs, such that the arrangement provides the necessary compensation with regards to the range of different forces that are seen at the boundary between the rod and the friction plate 34.

[86] Figure 7c shows the releasable locking mechanism is in its default state and as shown the pair of springs 722 are not compressed. When the foot plunger 24 is depressed to lock the locking mechanism, the springs 722 within the balance mechanism 720 are compressed as shown in Figures 7d and 7e to create the balancing forces. There is also a spring 730 which is centrally located with the rod 22 and this spring is also compressed when locking the locking mechanism.

[87] Figures 7d and 7e shows the foot plunger in the locked position but in Figure 7d, the angle of the foot plunger is not aligned centrally and the foot 26 is angled relatively to the door as illustrated by the dashed lines. In other words, a user has pushed the door and thus the mechanical release mechanism needs to be triggered. The mechanical release mechanism thus also comprises a pair of release flanges 724 which are an angled portions extending from the friction plate 34. As shown in Figure 7e, each release flange 724 extends in the opposite direction to the corresponding flange on the friction plate (i.e. down and from the under side of the friction plate). When the door is forced and the foot plunger is displaced from a vertical position, each release flange 724 engages with a corresponding flange abutment 726 on the device and releases the balance mechanism thus releasing the foot plunger.

[88] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

[89] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[90] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.