GB2228288A

GB2228288A - Safety lock for remote actuation

Info

Publication number: GB2228288A
Application number: GB8928218A
Authority: GB
Inventors: Norman Brian Griffiths
Original assignee: ELECTRONIC SURVEILLANCE PRODUC
Current assignee: ELECTRONIC SURVEILLANCE PRODUC
Priority date: 1988-12-22
Filing date: 1989-12-13
Publication date: 1990-08-22
Anticipated expiration: 2009-12-13
Also published as: GB8928218D0; GB2228288B; GB8829961D0

Abstract

A lock mechanism 10, for instance for security doors, has a bolt 12 which can be withdrawn by upward movement of a member 18 which is inaccessible from outside the housing. A second member 70 is normally pulled upwardly by an electromagnet 16, but can drop under gravity when the current is removed. Once the member 70 has dropped, a push pad 72 outside the housing can be used to swing a hook 74 to engage an aperture 76, and lift the hook 74 and member 70, thereby lifting the member 18 and unlocking the lock. A second actuator 20 returns the bolt to the extended position. The lock cannot be unlocked while current flows in the actuator 16. In the case of emergency the supply to the actuator 16 can be discontinued to allow the lock to be opened. If an emergency breaks the supply to the actuator 16, the lock will remain locked but can be opened manually to allow escape. <IMAGE>

Description

Lock Mechanisms The present invention relates to lock mechanisms and to detectors for use therewith.

In large premises, such as factories and warehouses, lock mechanisms may be fitted to doors or gates and be provided with facilities to allow them to be controlled remotely, for convenience. In one proposal, a central control panel can be operated to lock or unlock all of the gates on a system. A visual indication is provided to the operator to indicate whether the locks are activated or deactivated. Thus, emergency exit gates can be kept normally locked, but released by the control panel operator in the event of an emergency. After the emergency, or in the event of a false alarm, the locks can be reactivated.

A difficulty with this proposal arises because the system merely provides an indication as to whether the locks are activated or not, but not whether the gates are closed. The locks may therefore be activated without being effective.

The present invention seeks to obviate or mitigate these and other difficulties associated with the prior art.

According to the invention, there is provided a lock mechanism comprising a retractable bolt, first actuator means operable to control movement of the bolt from a first to a second position, releasable latching means operable to retain the bolt in the second position, and second actuator means operable to cause the bolt to return to the first position.

If the second position is chosen as the unlocked position, this arrangement ensures that the lock mechanism remains unlocked until the second actuator has been activated, and if, as is prefered, the second actuator is operated locally, rather than remotely, the operator can be sure that the door, for instance, is closed before the lock is locked.

Preferably the mechanism further comprises bolt moving means operable to move the bolt from the first to the second position, the first actuator means being operable to enable or disable the bolt moving means.

The mechanism may further comprise coupling means between the bolt and the bolt moving means, the first actuator means being operable to couple or decouple the coupling means. The coupling means may comprise first and second movable members having first and second positions, and a coupling member mounted on the first movable member, the coupling member being operable to engage the second movable member when the first member is in its second position and the second member is in its first position, and the coupling member being unable to engage the second member when the first and second members are in their first positions. The actuator means may be operable to hold the first member in the first position to prevent the first member moving to the second position to engage the second member.The actuator is preferably operable to release the first member to allow the first member to move to the second position and engage the second member.

Preferably the first member is allowed to move to the second position under the influence of gravity. The coupling member may be a hook member moveably mounted on the first member to move into engagement with the second member as aforesaid. The hook member is preferably rotatably mounted on the first member to swing into engagement with the second member as the first member moves to the second position. The hook member is preferably weighted to swing out of engagement with the second member, and is swung into engagement by the bolt moving means bearing on the hook member.

The bolt moving means is preferably operable to move the first member from the second to the first position, thereby moving the second member from the first to the second position. The bolt moving means is preferably manually movable and has a surface which bears on the hook member to swing the hook member to the position at which the second member is engaged when the first member is in the second position, and thereafter to cause the first member to move back to the first position.

The latching means is preferably operable to retain the second member in the second position, and the actuator means is operable to allow the first member to move from the first to the second position while the second member is in the second position, thereby allowing the coupling means to decouple.

The first actuator means preferably comprises an electromagnet operable to hold the first member in the first position.

Alternatively, the first actuator means may be operable to cause the bolt to move from a first to a second position.

Preferably, the second actuator means is operable to release the latching means, thereby allowing the bolt to return to the first position. The second actuator may be operable to cause the bolt to move away from the second position until the latching means is released.

In this arrangement, the first actuator means may comprise a movable member which bears on the bolt during movement, to cause the bolt to move. The latching means may comprise a first surface on the second member or the movable member, respectively, and a second surface on the bolt, the first and second surfaces moving into engagement at the second position of the bolt and being so formed as to latch the bolt in the second position. One of the surfaces of the latching means is preferably provided by an elongate member, the other surface being a concavity into which the elongate member is received. The elongate member is preferably a pin mounted on the second member or the movable member, respectively.

The second member or the movable member, respectively, is preferably linearly movable. The second member or the movable member, respectively, may engage the bolt to cause the said second surface to move transversely to the direction of movement of the second member or the movable member, respectively, and into engagement with the said first surface. Preferably the first or second surface has a notch formation into which the other surface moves when the bolt is in the second position and the first actuator is deactivated, the notch formation being so formed as to cause the other surface to be retained therein. The said other surface is preferably retained in the notch formation by gravitational force.

Preferably the second actuator comprises a release member movable to separate the first and second surfaces of the latching means and thereby release the latching means. The release member preferably bears on the bolt to move the bolt away from the second position until the latching means is released.

The first actuator preferably comprises an electro magnet, and the second actuator is preferably mechanical.

The invention also provides a detector for use with a locking mechanism of the type defined above, the detector comprising a magnetic member and a sensor having first and second relative positions corresponding to the first and second positions of the bolt, the detector being operable in dependence on the output of the sensor to provide an indication of the condition of the locking mechanism.

Preferably the detector is operable further in dependence on the activated or deactivated condition of the first actuator, to provide an indication which distinguishes between conditions in which the bolt is in the first or second position and the first actuator is activated or deactivated.

Preferably the sensor comprises a switch having two conditions which are selected according to the proximity of the magnetic member. The switch preferably has two terminals connected across an indicator element, the terminals being connected and disconnected according to the said proximity, thereby preventing the element from providing an indication or allowing the element to provide an indication.

The or each said element may be a light-emitting element. The or each light-emitting element is preferably a light-emitting diode. Preferably the indicator element comprises first and second elements which provide distinguishable indications and are connected to a common supply and operable in response to respective polarities of the supply. The indicator element preferably comprises two light-emitting diodes of respective colour connected in parallel and with opposite polarities to a common supply.

The first actuator is preferably connected in parallel with the indicator element and in series with a diode, whereby the distinguishable indications indicate the condition of the first actuator while the said two terminals are disconnected. Preferably the said two terminals are connected while the bolt is in the second position.

Preferably the switch is a three terminal, two position switch, the common terminal being one of the said two terminals. The detector may take account of the voltage at the third terminal to determine the position of the bolt.

The invention further provides a lock mechanism as defined above and comprising a detector according to any of the previous definitions.

Embodiments of lock mechanisms according to the present invention and detectors for use therewith will now be described in more detail, by-way of example only, and with reference to the accompanying drawings in which: Figs. 1 and 2 are side and front elevations of a lock mechanism according to the invention; rig. 3 is a schematic partial circuit diagram of a detector for use therewith; Figs. 4 and 5 are side and front elevations of an alternative lock mechanism according to the invention; and Fig. 6 is a schematic partial circuit diagram of a detector for use therewith.

Referring to Figs. 1 and 2, there is shown a lock mechanism 10 comprising a retractable bolt 12. The bolt is retractable into a housing 14. A first actuator 16 is operable to control movement of the bolt 12 from a first extended position shown, to a second, retracted position, as will be described. Releasable latching means 18 are operable to retain the bolt 12 in the retracted position.

A second actuator 20 is operable to cause the bolt 12 to return to the extended position.

In more detail, the bolt 12 has a generally flat front face 22 and a generally arcuate lower edge 24 centred at point 26 about which the bolt 12 is pivcted.

When the lock is released, the bolt 12 swings into the housing 14 until the face 22 is vertical. The rear face of the bolt 12 carries a concavity 28 forming part of the latch 18.

A vertically movable bar or strip 30 carries a horizontal pin 32 which can bear on the upper surface 33 of a small concavity 34 in the bolt 12. Thus, as the strip 30 moves up and down, it can pull the bolt 12 into the housing or allow it to move out of the housing, as the bolt 12 swings about the point 26.

The strip 30 also carries a second horizontal pin 36 forming part of the latch 18. The concavity 28 is shaped and positioned to allow the lip 38 below the concavity to swing across beneath the pin 36 as the strip 30 moves up, until a position is reached at which the lower back corner 40 of the concavity 28 has swung under the pin 36. At this position, the surfaces of the pin 36 and the concavity 28 abut to prevent the bolt 12 moving any further into the housing 14, and this in turn stops upward movement of the strip 30.

The corner 40 forms a small notch. If the strip 30 is fully raised so that the bolt 12 is fully withdrawn, and the strip 30 is then allowed to drop slightly, the pin 36 drops into the notch at the corner 40, thereby lightly holding the bolt 12 against further movement, and latching the bolt 12 in the withdrawn position.

The second actuator 20 comprises a finger 42 pivotally mounted at 44 so that it may swing to engage part of the rear face of the bolt 12. If sufficient force is applied by the finger 42, the bolt 12 can be moved against the action of the latch 18 in order to pull the pin 36 out of the notch at 40, and push the bolt 12 to its extended position.

The finger 42 is carried by a rod 46 which extends through the housing 14 to allow the finger 42 to be moved mechanically by hand.

The lower end of the strip 30 carries a magnet 48.

Mounted near the bottom of the strip 30 is a magnetic proximity switch 50 having two conditions whose choice depends on the proximity of the magnet 48, which in turn depends on the height of the strip 30. Thus, when the strip 30 is at its lowest position, the magnet 48 will be in closest proximity with the switch 50. If the strip 30 rises, the magnet 48 moves away from the proximity switch 50 which changes to its second condition.

The first actuator 16 is an electromagnet located towards the top of the housing 14. A bar 70 projects down from the actuator 16 and is acted upon by it so that when the actuator is energised, the bar 70 is drawn upwardly (to the position shown), and when the actuator 16 is de-energised, the bar 70 can fall under the influence of gravity.

The bar 70 and the strip 30 form first and second members of a coupling between the bolt 12 and a push pad 72 for manually moving the bolt in the way to be described. The coupling further comprises a hook member 74 pivotally mounted on the bar 70, and an aperture 76 near the top of the strip 30.

The hooked member 74 is weighted or sprung to rest in the position shown in Fig. 2 in relation to the bar 70, in the absence of any other influences. The pivotal mounting with the bar 70 is part way along the hook 74 which has a hooked end 78 and a rear, weighted end 80 carrying a pin 82.

The push pad 72 is pivotally mounted about a horizontal axis at 84. Two fingers 86 (not shown in Fig. 1) extend back from the push pad 72 to either side of the bar 70 and hook 74, and underneath the pin 80. The top edge of the fingers 86 is relieved at 88 to provide clearance for a pivot pin 90 connecting the hook 74 and bar 70. The push pad 72 is sprung to the position indicated in the drawings.

The housing completely encapsulates the workings of the lock mechanism, apart from the bolt 12 and push pad 72. The lock mechanism is therefore protected from weathering and can be used out of doors. Non-ferrous metals are preferred for the housing and mechanism.

Electrical circuitry associated with the switch 50 is shown in Fig. 3. The switch 50 is a three terminal, two position switch having three terminals labelled RED, BLUE and WHITE, for convenience. The RED and WHITE terminals are connected across (in parallel with) a light-emitting element 52. The third (BLUE) terminal is connected to a control circuit 54 which also incorporates a power supply applied with reversible polarity to lines 56a, 56b. The supply over the lines 56 is applied to the element 52 through identical resistors 58 connected to either side of the element 52 to form a current limiting voltage divider circuit. The RED and WHITE terminals are connected between the terminals of the element 52 and the corresponding resistors 58. Thus, when the RED and WHITE terminals are connected by the switch 50, the element 52 is shorted and cannot emit light.When the switch 50 changes to connect the BLUE and WHITE contacts, the voltage at the BLUE contact switches to the voltage determined by the voltage divider resistors 58, and the element 52 ceases to be shorted and can emit light.

The element 52 consists of RED and GREEN light emitting diodes connected with opposite polarity. Thus, when the element 52 is not shorted by the switch 50, the colour of light emitted will depend solely on the polarity of the lines 56.

The lines 56 also provide the supply to the coil of the first actuator 16, which is connected across the lines 56 in series with a diode 60. The diode 60 allows the actuator 16 to be activated by one polarity of the lines 56, but prevents activation by the opposite polarity. A small additional diode 62 across the coil 16 absorbs any back EMF generated by the coil 16 when the polarity of the lines 56 is reversed.

The element 52 is mounted to be visible at the lock 10.

The control circuit 54 comprises additional RED and GREEN indicators 64.

Operation of the lock mechanism and detector occurs in the following way. In the normal situation, the door controlled by the lock 10 is closed and the bolt 12 is advanced, so that the door is locked. The line 56a is negative, and the line 56b is positive, so that current is passing through the coil 16. The actuator 16 will be activated to hold the bar 70 raised, so that the hook cannot swing into the aperture 76 to engage the strip 30.

The switch 50 will be in the condition shown in Fig. 3, and the element 52 will be shorted an,d off. The BLUE terminal of the switch 50 is disconnected and this condition is detected by the control circuit 54. The combination of polarity on the lines 56a, 56b, and voltage at the BLUE terminal is unique to the locked condition of the mechanism and this condition can therefore be detected by the detector. Both indicators 64 will be off.

When it is desired to allow the door to be unlocked, a command is given to the control circuit 54 to reverse the polarity of the lines 56, so that line 56a becomes positive. The diode 60 causes current to stop flowing through the coil 16, thereby deactivating the actuator 16.

The bar 70 can now drop but as it does so, the pin 82 bears on the fingers 86 so that as the bar 70 moves down, the hook 74 swings into a position in which the hooked end 78 has entered the aperture 76. At rest, the pivot pin 90 will be located in the reliefs 88.

In this condition, the switch 50 continues to short the element 52 which will be off.

When it is required to release the lock (which must be done manually) the push pad 72 is pushed to pivot about the axis 84 and raise the fingers 86. This causes the hooked end 78 to be held in engagement with the strip 30, and also causes the bar 70 to move up, thereby pulling the strip 30 with it. As the strip 30 is drawn up, the pin 32 engages the surface 33 and swings the bolt 12 back into the housing 14, thereby unlocking the door. When the bolt 12 has been fully withdrawn into the housing 14, the push pad 72 can be released. It will spring back to its orginal position, thereby allowing the bar 70 to fall.

The strip 30 is, however, held at its uppermost position by the latching provided by the pin 36 and notch 40.

In this position, the magnet 48 is away from the switch 50, which accordingly moves to connect the WHITE and BLUE terminals. The element 52 is no longer shorted and the GREEN LED component becomes illuminated to indicate at the lock that the lock has been released. The voltage at the BLUE terminal goes to a centre tap voltage determined by the values of the resistors 58. The combination of the presence of this voltage and the polarity of the lines 56 is unique and allows the control circuit 54 to determine that the lock has been released, and to illuminate the GREEN indicator 64 on the control panel to indicate this.

If it is now desired to allow the lock 10 to be re-locked, a command is given to the control circuit 54 to reverse the polarity of the lines 56. Line 56a now becomes negative and current flows through the actuator 16 to pull the bar 70 up. As it does so, the weighting or spring bias on the hook swings it out of engagement with the strip 30. The strip 30 remains latched in its raised position. The magnet 48 remains away from the switch 50 and the voltage at the BLUE terminal therefore remains at the centre tap voltage. The combination of polarity of the lines 56 and the voltage at the BLUE terminal is again unique and allows the control panel to determine that the lock is lockable (in a manner to be described) but not locked, and to illuminate the RED indicator 64 to indicate this. The reversal of polarity on the lines 56 also causes the GREEN LED at 52 to be extinguished, and the RED LED to be illuminated, to indicate at the lock that the lock can be re-locked (but is not locked).

An operator may now close the gate controlled by the lock, and turn the second actuator 20 to use the finger 42 to push the bolt 12, thereby releasing the latch 18 and pushing the bolt 12 to the locked position. As this is done, the operator can ensure that the gate is correctly positioned for the lock to engage and be effective. Until the bolt 12 has been advanced fully, the pin 36 will not clear the lip 38, and therefore the strip 30 cannot fall.

Once the strip 30 does fall, the magnet switches the switch 50 to extinguish the indicator 52 at the lock. The voltage at the BLUE terminal is no longer set by the resistors 58, and this in combination with the polarity of the lines 56 is again unique, allowing the control panel 54 to determine that the gate has been locked, and to extinguish the RED indicator 64. While current remains in the actuator 16, the door cannot be opened, because the strip 30 is disconnected from any external influence. The door can only be unlocked by de-energising the actuator 16, either deliberately by means of the controls 54, or as a result of an emergency such as a fire which breaks the power supply to the lock. Thus, the system is "fail-safe", because in the absence of power due to an emergency, the lock can be opened normally, preventing personnel being trapped.

Referring to Figs. 4 and 5, there is shown an alternative form of lock mechanism 110 comprising a retractable bolt 112. The bolt is retractable into a housing 114. A first actuator 116 is operable to cause the bolt 112 to move from a first position shown in broken lines, to a second position shown in full lines, as will be described. Releasable latching means 118 are operable to retain the bolt 112 in the second position. A second actuator 120 is operable to cause the bolt 112 to return to the first position.

In more detail, the bolt 112 has a flat front face 122 which is substantially vertical in the second position, and an arcuate lower edge 124 centred at point 126 about which the bolt 112 is pivoted. The rear face of the bolt 112 carries a concavity 128 forming part of the latch 118.

A vertically movable bar or strip 130 carries a horizontal pin 132 which locates in a small aperture 134 through the bolt 112. Thus, as the strip 130 moves up and down, it will pull the bolt 112 into and out of the housing, as the bolt 112 swings about the point 126.

Upward movement of the strip 130 is provided by the actuator 116, which comprises an electro-magnet mounted towards the top of the housing 114. When activated, the electro-magnet 116 pulls the strip 130 upwardly, to retract the bolt 112 into the housing.

The strip 130 also carries a second horizontal pin 136 forming part of the latch 118. The concavity 128 is shaped and positioned to allow the lip 138 below the concavity to swing across beneath the pin 136 as the strip 130 moves up, until a position is reached in which the pin 136 is located at the lower back corner 140 of the concavity 128. At this position, the surfaces of the pin 136 and the concavity 128 abut to prevent the bolt 112 moving any further into the housing 114, and this in turn stops upward movement of the strip 130.

The corner 140 provides a small notch. If the actuator 116 is deactivated when the strip 130 is fully raised and the bolt 112 is fully withdrawn, the strip 130 will drop slightly until the pin 136 is in the notch at the corner 140, thereby lightly holding the bolt 112 against further movement, and latching the bolt 112 in the second (unlocked) position.

The second actuator 120 comprises a finger 142 pivotally mounted at 144 so that it may swing to engage part of the rear face of the bolt 112. If sufficient force is applied by the finger 142, the bolt 112 can be moved against the action of the latch 118 in order to pull the pin 136 out of the notch at 140, anc push the bolt 112 to its first, locked position.

The finger 142 is carried by a rod 146 which extends through the housing 114 to allow the finger 142 to be moved mechanically by hand.

The lower end of the strip 130 carries a magnet 148.

Mounted below the strip 130 is a proximity switch 150 having two conditions whose choice depends on the proximity of the magnet 148, which in turn depends on the height of the strip 130. Thus, when the bolt 112 is in the locked position and the actuator 116 is deactivated, the strip 130 will be at its lowest position and the magnet 148 will in closest proximity with the switch 150 causing it to take a first condition. If the actuator 116 is activated, the strip 130 rises to take the magnet 148 away from the proximity switch 150 which changes to its second condition.

The housing completely encapsulates the workings of the lock mechanism, apart from the opening for the bolt 112. The lock mechanism is therefore protected from weathering and can be used out of doors. Non-ferrous metals are preferred for the housing and mechanism.

Additional circuitry associated with the switch 150 is shown in Fig. 6. The switch 150 is a three terminal, two position switch having three terminals labelled RED, BLUE and WHITE, for convenience. The RED and WHITE terminals are connected across (in parallel with) a light-emitting element 152. The third (BLUE) terminal is connected to a control circuit 154 which also incorporates a power supply applied with reversible polarity to lines 156a, 156b. The supply over the lines 156 is applied to the element 152 through identical resistors 158 connected to either side of the element 152 to form a current limiting voltage divider circuit. The RED and WHITE terminals are connected between the terminals of the element 152 and the corresponding resistors 158. Thus, when the RED and WHITE terminals are connected by the switch 150, the element 152 is shorted and cannot emit light.When the switch 150 changes to connect the BLUE and WHITE contacts, the voltage at the BLUE contact switches to the voltage determined by the voltage divider resistors 158, and the element 152 ceases to be shorted and can emit light.

The element 152 consists of a RED and a GREEN light emitting diode connected with opposite polarity. Thus, when the element 152 is not shorted by the switch 150, the colour of light emitted will depend solely on the polarity of the lines 156.

The lines 156 also provide the supply to the coil or the first actuator 116, which is connected across the lines 156 in series with a diode 160. The diode 160 allows the actuator 116 to be activated by one polarity of the lines 156, but prevents activation by the opposite polarity. A small additional diode 162 across the coil 116 allows current to be passed to absorb any back EMF generated by the coil 116 when the polarity of the lines 156 is reversed.

The element 152 is mounted to be visible at the lock 110.

The control circuit 154 comprises additional RED and GREEN indicators 164.

Operation of the lock mechanism and detector of Figs. 4, 5 and 6 occurs in the following way. In the normal situation, the door locked by the lock 110 is closed and the bolt 112 is advanced, so that the door is locked. The actuator 116 will be deactivated. The switch 150 will be in the condition shown in Fig. 6, and the element 152 will be shorted and off. The BLUE terminal of the switch 150 is disconnected and this condition is detected by the control circuit 154. The line 156a is negative, and the line 156b is positive, so that current is prevented from passing through the coil 116 by the diode 160. This combination of polarity on the lines 156a, 156b, and voltage at the BLUE terminal is unique to the locked condition of the mechanism and this condition can therefore be detected by the detector. Both indicators 164 will be off.

When it is desired to unlock the door, a command is given to the control circuit 154 which reverses the polarity of the lines 156, so that line 156a becomes positive. This causes current to commence flowing through the coil 116, thereby activating the actuator 116.

The strip 130 is drawn up so that the pin 132 engages the aperture 134 and swings the bolt 112 back into the housing 114, thereby unlocking the door. The actuator 116 is continuously activated while-ever the lock is to be held unlocked. Thus the strip 130 is held at its uppermost position and the bolt 112 is held at its fully retracted position.

In this position, the magnet 148 is away from the switch 150, which accordingly moves to connect the WHITE and BLUE terminals. The element 152 is no longer shorted and the GREEN component LED becomes illuminated to indicate at the lock that the lock is released. The voltage at the BLUE terminal goes to a centre tap voltage determined by the values of the resistors 158. The combination of the presence of this voltage and the polarity of the lines 156 is unique and allows the control circuit 154 to determine that the lock is released, and to illuminate the GREEN indicator 164 on the control panel to indicate this.

If it is now desired to re-lock the lock 110, a second command is given to the control circuit 154, which again reverses the polarity of the lines 156. Line 156a now becomes negative and no further current can flow through the actuator 116. The strip 130 is therefore allowed to fall, but can only fall a little way until the pin 136 drops into the notch at 140, thereby latching the bolt 112 in its retracted position. The magnet 148 remains away from the switch 150 and the voltage at the BLUE terminal therefore remains at the centre tap voltage. The combination of polarity of the lines 156 and the voltage at the BLUE terminal is again unique and allows the control panel to determine that the lock is lockable (in a manner to be described) but not locked, and to illuminate the RED indicator 164 to indicate this.The reverse of polarity on the lines 156 also causes the GREEN LED at 152 to be extinguished, and the RED LED to be illuminated, to indicate at the lock that the lock can be re-locked.

An operator may now close the gate controlled by the lock, and turn the second actuator 120 to use the finger 142 to push the bolt 112, thereby releasing the latch 118 and pushing the bolt 112 to the locked position. As this is done, the operator can ensure that the gate is correctly positioned for the lock to engage and be effective. Until the bolt 112 has been advanced fully, the pin 136 will not clear the lip 138, and therefore the strip 130 cannot fall. Once the strip 130 does fall, the magnet switches the switch 150 to extinguish the indicator 152 at the lock. The voltage at the BLUE terminal is no longer set by the resistors 158, and this in combination with the polarity of the lines 156 is again unique, allowing the control panel 154 to determine that the gate has been locked, and to extinguish the RED indicator 164.

Further refinements can be added to the control circuitry 54, 154. A battery back-up may be desirable so that in the event of failure of the mains power supply, the system continues to function. The battery back up may be automatically switched in if the mains fuse blows, and may incorporate an independent, fuse forming a short across an alarm indicator. If the battery fuse also blows, this indicates a fault, such as tampering with the system, so that the buzzer begins to sound.

A voltmeter to indicate the state of the battery backup is preferably provided. An LED or other indication that mains supply is satisfactory can be incorporated, and a separate indicator, such as a flashing red LED, can be used to indicate that the battery is in use.

A key switch is preferably provided for instructing the circuit 54, 154 to unlock or allow manual locking.

The apparatus has been described above in conjunction with a single lock, but it is apparent from the above that the system can be extended to control more than one lock in the same fashion. Thus, a single instruction to change the polarity of the lines 56, 156 will immediately allow all locks on the system to be unlocked (manually), or unlock them. Each lock will have an independent line back to the control panel 54, 154 from the BLUE terminal of the corresponding switch 50, 150, so that the control panel 54, 154 can determine the condition of the locks. Preferably, the control circuitry 54, 154 incorporates logic which functions to light a single green indicator 64 when the locks are able to be disengaged or are disengaged. The logic would also act to keep the red indicator 64, 164 illuminated once the locks have been allowed to be re-locked, until all locks have been re-locked.Thus, if any lock has not been re-locked, the red indicator 64, 164 will be illuminated. In that case, the red LED 52 at the corresponding lock will be also illuminated, so that it becomes a simple matter to identify the lock concerned.

The lock mechanism described above was designed to be reliable during long periods of use out of doors. The mechanical action of the mechanism relies mainly by the magnetic effect of the actuator, and the pull of gravity.

The lock mechanism is envisaged for use, for example, on gates of garden centres and on secure compounds around factories, warehouses or stores of toxic or dangerous materials and articles. Such doors are normally kept locked, but are to be opened or allowed to open if required, or in an emergency.

It will be apparent that various modifications and variations can be made to the apparatus and circuitry described above without departing from the spirit and scope of the present invention.

Claims

1. A lock mechanism comprising a retractable bolt, first actuator means operable to control movement of the bolt from a first to a second position, releasable latching means operable to retain the bolt in the second position, and second actuator means operable to cause the bolt to return to the first position.

2. Apparatus according to claim 1, wherein the mechanism further comprises bolt moving means operable to move the bolt from the first to the second position, the first actuator means being operable to enable or disable the bolt moving means.

3. Apparatus according to claim 2, wherein the mechanism further comprises coupling means between the bolt and the bolt moving means, the first actuator means being operable to couple or decouple the coupling means.

4. Apparatus according to claim 3, wherein the coupling means comprise first and second movable members having first and second positions, and a coupling member mounted on the first movable member, the coupling member being operable to engage the second movable member when the first member is in its second position and the second member is in its first position, and the coupling member being unable to engage the second member when the first and second members are in their first positions.

5. Apparatus according to claim 4, wherein the actuator means is operable to hold the first member in the first position to prevent the first member moving to the second position to engage the second member.

6. Apparatus according to claim 5, wherein the actuator is operable to release the first member to allow the first member to move to the second position and engage the second member.

7. Apparatus according to claim 6, wherein the first member is allowed to move to the second position under the influence of gravity.

8. Apparatus according to any of claims 4 to 7, wherein the coupling member is a hook member movably mounted on the first member to move into engagement with the second member as aforesaid.

9. Apparatus according to claim 8, wherein the hook member is rotatably mounted on the first member to swing into engagement with the second member as the first member moves to the second position.

10. Apparatus according to claim 8 or 9, wherein the hook member is weighted to swing out of engagement with the second member, and is swung into engagement by the bolt moving means bearing on the hook member.

11. Apparatus according to any of claims 4 to 10, wherein the bolt moving means is operable to move the first member from the second to the first position, whereby the second member may be moved from the first to the second position.

12. Apparatus according to claim 11 and any of claims 8 to 10, wherein the bolt moving means is manually movable and has a surface which bears on the hook member to swing the hook member to the position at which the second member is engaged when the first member is in the second position, and thereafter to cause the first member to move back to the first position.

13. Apparatus according to any of claims 4 to 12, wherein the latching means is operable to retain the second member in the second position, and the actuator means is operable to allow the first member to move from the first to the second position while the second member is in the second position, thereby allowing the coupling means to decouple.

14. Apparatus according to any of claims 4 to 13, wherein the first actuator means comprises an electromagnet operable to hold the first member in the first position.

15. Apparatus according to any preceding claim, wherein the second actuator means is operable to release the latching means, thereby allowing the bolt to return to the first position.

16. Appatatus according to claim 15, wherein the second actuator means is operable to cause the bolt to move away from the second position until the latching means is released.

17. Apparatus according to claim 1, wherein the first actuator means is operable to cause the bolt to move from a first to a second position.

18. Apparatus according to claim 17, wherein the first actuator means comprises a movable member which bears on the bolt during movement, to cause the bolt to move.

19. Apparatus according to claim 18 or any of claims 4 to 16, wherein the latching means comprise a first surface on the second member or the movable member, respectively, and a second surface on the bolt, the first and second surfaces moving into engagement at the second position of the bolt and being so formed as to latch the bolt in the second position.

20. Apparatus according to claim 19, wherein one of the surfaces of the latching means is provided by an elongate member, the other surface being a concavity into which the elongate member is received.

21. Apparatus according to claim 20, wherein the elongate member is a pin mounted on the second member or the movable member, respectively.

22. Apparatus according to any of claims 19 to 21, wherein the second member or the movable member, respectively, is linearly movable.

23. Apparatus according to claim 22, wherein the second member or the movable member, respectively, engages the bolt to cause the said second surface to move transversely to the direction of movement of the second member or the moveable member, respectively, and into engagement with the said first surface.

24. Apparatus according to any of claims 19 to 23, wherein the first or second surface has a notch formation into which the other surface moves when the bolt is in the second position and the first actuator is deactivated, the notch formation being so formed as to cause the other surface to be retained therein.

25. Apparatus according to claim 24, wherein the said other surface is retained in the notch formation by gravitational force.

26. Apparatus according to claims 19 to 25, wherein the second actuator comprises a release member movable to separate the first and second surfaces of the latching means and thereby release the latching means.

27. Apparatus according to claim 26, wherein the release member bears on the bolt to move the bolt away from the second position until the latching means is released.

28. Apparatus according to any preceding claim, wherein the first actuator comprises an electromagnet.

29. Apparatus according to any preceding claim, wherein the second actuator is mechanical.

30. A lock mechanism substantially as described above with reference to the accompanying drawings.

31. A detector for use with a locking mechanism according to any preceding claim, the detector comprising a magnetic member and a sensor having first and second relative positions corresponding to the first and second positions of the bolt, the detector being operable in dependence on the output of the sensor to provide an indication of the condition of the locking mechanism.

32. Apparatus according to claim 31, wherein the detector is operable further in dependence on the activated or deactivated condition of the first actuator, to provide an indication which distinguishes between conditions in which the bolt is in the first or second position and the first actuator is activated or deactivated.

33. Apparatus according to claim 31 or 32, wherein the sensor comprises a switch having two conditions which are selected according to the proximity of the magnetic member.

34. Apparatus according to claim 34, wherein the switch has two terminals connected across an indicator element, the terminals being connected and disconnected according to the said proximity, thereby preventing the element from providing an indication or allowing the element to provide an indication.

35. Apparatus according to claim 34, wherein the or each element is a light-emitting element.

36. Apparatus according to claim 35, wherein the or each light-emitting element is a light-emitting diode.

37. Apparatus according to claims 35 or 36 wherein the indicator element comprises first and second elements which provide distinguishable indications and are connected to a common supply and operable in response to respective polarities of the supply.

38. Apparatus according to claim 37, wherein the indicator element comprises two light-emitting diodes of respective colour connected in parallel and with opposite polarities to a common supply.

39. Apparatus according to claim 37 or 38, wherein the first actuator is connected in parallel with the indicator element and in series with a diode, whereby the distinguishable indications indicate the condition of the first actuator while the said two terminals are disconnected.

40. Apparatus according to claim 39, wherein the said two terminals are connected while the bolt is in the second position.

41. Apparatus according to any of claims 33 to 40, wherein the switch is a three terminal, two position switch, the common terminal being one of the said two terminals.

42. Apparatus according to claim 41, wherein the detector takes account of the voltage at the third terminal to determine the position of the bolt.

43. A detector substantially as described above, with reference to the accompanying drawings.

44. A lock mechanism according to any of claims 1 to 30 and comprising a detector according to any of claims 31 to 43.

45. Any novel subject matter or combination including novel subject matter disclosed, whether or not within the scope of or relating to the same invention as any of the preceding claims.