WO2007049040A1

WO2007049040A1 - Low power lock mechanism

Info

Publication number: WO2007049040A1
Application number: PCT/GB2006/003976
Authority: WO
Inventors: Simon Powell
Original assignee: PBT IP Ltd
Current assignee: PBT IP Ltd
Priority date: 2005-10-26
Filing date: 2006-10-25
Publication date: 2007-05-03
Anticipated expiration: 2008-04-26
Also published as: GB0521847D0

Abstract

The present invention provides a latch assembly comprising an axially moveable member with a splined end and mounted for axial movement in a first plane, a locking interface with matching splines, the axially moveable member being mounted for movement in a direction transverse to the axial direction between a first position where the splined end meshes with the matching splines on the locking interface and a second position where meshing is inhibited, and electrically controllable means for selectively permitting transverse movement of the axially moveable member between the first and second positions. The transverse movement of the axially moveable member is controlled by controlling the balance between two opposed resilient biasing forces acting on the moveable member. This is achieved by using an electrically controlled actuator to allow or inhibit one of the biasing forces to be applied.

Description

LOW POWER LOCK MECHANISM

The present invention relates to electrically controlled mechanical latches.

The development of low power locking requires the ability to move large pieces of material into the path of other pieces in order to resist high attack loads. It is a primary driver for the locking industry to reduce the power consumption of such locks.

A number of patents have been filed by Servocell Ltd relating to the development of low power latch mechanisms, including PCT W02004/077473 and UK 042787.5, which describe the use of a piezo actuator that is deployed to change the behaviour of a mechanism in order to prevent the passage of a plunger part through the mechanism. The inventions described in the preceding patents have relatively small ratings in terms of their resistance to loads, restricting their use to controlling the engagement of a handle or requiring the addition of some auxiliary overload protection. In access control systems, the primary method for locking frequently used doors is the magnetic bolt. These devices work simply through a high magnetic field holding a magnetisable plate against a ground surface.

Magnetic bolts are effective, having very high holding forces and being moderately tolerant of misalignment, but can be defeated by the malicious insertion of an object to prevent the plate closing against the magnet, greatly reducing the holding force. Further this solution is not suitable for bi-directional doors as the magnetic coupling is strongest in tension rather than shear, requiring it to be placed facing the door leaf. The alternative to the standard magnetic bolt is the magnetic shear bolt which pulls a pin into a socket to create a shear-resistant coupling. This modification greatly reduces the tolerance to misalignment, and both systems have very high power requirements, making them unsuitable for use with batteries. Further, the shearbolt type requires a very high initial current to create sufficient magnetic field to draw the bolt into the armature. It would be beneficial for there to be a low cost solution for the securing of doors, such as bi-directional doors that can use low power switching such as an active latch but which can resist the high forces necessary for general passageway doors and attack such as ram-raiding. UK application 0506455.5 describes one potential solution for such a device, but the costs of manufacture can be seen to be very high.

The present invention provides a latch assembly comprising an axially moveable member with a splined end and mounted for axial movement in a first plane, a locking interface with matching splines, the axially moveable member being mounted for movement in a direction transverse to the axial direction between a first position where the splined end meshes with the matching splines on the locking interface and a second position where meshing is inhibited, and electrically controllable means for selectively permitting transverse movement of the axially moveable member between the first and second positions.

Preferably, transverse movement of the axially moveable member is controlled by controlling the balance between two opposed resilient biasing forces acting on the moveable member. This is achieved by using an electrically controlled actuator to allow or inhibit one of the biasing forces to be applied.

The electrically controlled means preferably comprises an electrically controlled actuator assembly having a resiliently biased plunger which engages the axially moveable member, the plunger being arranged to freely move under the action of the resilient bias when the actuator is in one electrical condition and be inhibited from movement when the actuator is in another electrical condition. The electrically controlled means further comprises means for resiliently biasing the axially moveable member into engagement with the plunger with a force greater than the resilient bias applied to the plunger. With this arrangement, the plunger will follow the contours of the axially moveable member as it moves axially when the actuator is in said one electrical condition. Conversely, when the actuator is in said other electrical condition, the plunger will not move and consequently axial movement of the actually moveable member will be translated into transverse movement of the axial member against the action of the further resilient bias applied to the axially moveable member.

Preferably, the transverse movement of the axially moveable member is arcuate movement in the same or a parallel plane to the first plane in which the axially moveable member moves. Alternatively, the transverse movement of the axially moveable member may be rotational movement about the axis of movement of the axially moveable member.

In order that the present invention be more readily understood, embodiments thereof will now be described with reference to their accompanying drawings, in which:-

Fig. 1 shows a diagram to aid understanding of how a ball is retained in a groove;

Fig. 2 shows a perspective view of a first embodiment of the present invention in its rest condition;

Fig. 3 shows a perspective view of the first embodiment of the present invention in its locked condition;

Fig. 4 shows a perspective view of the first embodiment of the present invention in its open condition;

Fig. 5 shows a perspective view of the first embodiment of the present invention in its open condition but with the plunger rotated to show its axial groove;

Fig. 6 shows a perspective view of the first embodiment of the present invention in its open condition but viewed from a different direction to that of Fig. 4;

Fig. 7 shows a perspective view of the locking base designed to interact with the plunger shown in Figs. 2 to 6;

Fig. 8 shows a front view of a second embodiment of the present invention in its rest condition; and

Fig. 9 shows a front view the second embodiment in its locked condition. Description of Invention

According to a first embodiment of the present invention, there is provided an assembly consisting of a main locking ball, an axially movable primary plunger with a splined end, a locking interface with matching splines, two control balls acting in grooves on the primary plunger and an actuating means which is preferably, but not exclusively, an active latch piezo operated controller.

The mechanism's behaviour is determined by the two control balls and the status of the activating means. The activating means can be in the locked or free state, where the term free state means that a plunger of the activating means can be moved along its full travel with little resistance and where the term locked means that this travel is prevented. One control ball is inserted into a helical groove on the surface of the primary plunger, and the other control ball is inserted into an axial groove. Both balls are pushed into their respective grooves by springs with one having the ability to dominate the other. The weaker ball is additionally retained by the activating means, such that its exit from the groove can be prevented thereby changing the system behaviour. The mechanism can be operated by a normally free or a normally locked latch and can be used to switch either control ball to change the system behaviour to suit the application.

In a preferred construction, an active latch is used which is of the type where the plunger is normally blocked when the latch is unenergised and operates upon the ball in the axial groove. In this circumstance, axial pressure on the ball is translated into axial motion of the plunger. The control ball in the helical groove will be pushed from the groove as a result and the motion will be purely axial. In the most likely construction, it is desirable that the mechanism will be locked in this state, so the axial motion will bring the spline features on the primary plunger into contact with similar features in the base of the mechanism, causing the axial motion to be impeded.

Upon actuation of the active latch, when the plunger is depressed, the superior spring force of the control ball in the helical groove will force the active latch backed ball out of the axial groove and cause the primary plunger to rotate. This rotation will cause the spline features on the plunger and base of the mechanism to become misaligned such that they pass each other on further axial motion and so do not impede the progress of the plunger under the axial thrust of the ball.

The preferred embodiment comprises a controlled plunger mechanism arranged to selectively engage with a base provided with interference surfaces to prevent rotation of the plunger. Rotation is controlled by an electrically operated device in the form of a piezo ceramic actuator which is used to control a rod which in turn acts in the plunger to control it.

Referring now to Figs. 2 to 7, a main bearing ball (10) is constrained within a guide tube (20) to move coaxially with the primary plunger (40). The primary plunger (40) is sprung by a reset spring (30) to urge the ball (10) to one end of the tube (20). The primary plunger (40) has a flared and splined end (42) and two control grooves upon the narrower portion. The first control groove is the locking groove (43) and is coaxial with the motion of the plunger. The second control groove is the unlocking groove (44) and describes a helical path for at least the first part of its motion and may then continue as a helix or if sufficient rotation has been achieved for the mechanism purpose the groove may become axial or any combination of the two motions. The flared portion that carries the splines (42) is preferable, but not essential, and serves to increase the circumferential travel of the splines (46) under the influence of the helical track and by this means increase the surface area that can be involved in the locking action.

Features within the casing of the mechanism (35) provide for two control balls to be pressed into a pair of control grooves. As shown in fig. 1, these balls are of such a dimension that they penetrate the control grooves to make a radial contact angle (41) with the groove that is greater than the coefficient of friction between the two materials and that will generate a radial thrust (36) against bias springs that are operating radially to the primary plunger (40). By way of example, if the co-efficient of friction is 0.2 then and angle of 2*atan 0.2 is chosen to give a clear thrust, making the contact angle (41) approximately 22.5 degrees. The mechanism has 4 distinct states, and each is now described.

In the rest state (fig. 2), the main locking ball (10) protrudes from the end of the guide tube (20) and there is a clearance gap (11) between the splines on the primary plunger (46) and matching features in the base (81).

In the resisting state (fig. 3), the main locking ball (10) is forced into the guide tube (20) until the spline features collide and further motion is prevented. In this state the main locking ball (10) is still substantially exposed from the end of the guide tube (20). Before the primary plunger (40) has completed the travel available to it in this state, the unlocking control ball (21) has been ejected from the unlocking groove (44). This ejection is caused by the locking control ball (23) being retained in the locking groove (43) by the combined force of the locking control spring (25) and the active latch (66).

In the unlocking state (fig 4), the active latch (66) is caused to permit its main plunger (68) to travel freely. In this case the force of the locking control spring (25) is overcome by the superior force of the unlocking control spring (28) and thus the locking control ball (23) is ejected from the locking groove (43) under the torque moment created by the helical unlocking groove (44). This state causes the primary plunger (40) to follow a helical path instead of an axial one and the rate of the helix is sufficient for the splines on the primary plunger (46) to miss those in the base of the device (81), permitting the main control ball (10) to move completely into the guide tube (20).

In the reset state, the primary plunger (40) rises under the action of the reset spring (30). As the force acting upon the main locking ball is removed, the reset spring (30) can push the main control ball (10) out of the guide tube (20). If the mechanism had previously been locked then the reset action is axial, driven by the locking control ball (23) and if the mechanism had previously been unlocked then the reset action is helical, driven by the unlock control ball (21). The mechanism as thus described is contained within any suitable assembly and can be mounted onto a door, hatch, gate or turnstile for the purposes of locking. In all cases the primary plunger (40) is set so that its travel is perpendicular to the travel of the part to be locked. Any interface that forms a well from which the main control ball (10) must escape will serve as a locking interface, and any such interface must not permit the ball to exit within the free travel across the gap (11). For a 30mm ball such an interface should provide 9- 12mm of engagement, against 3mm of free travel.

The purpose of this mechanism is to achieve a high resistance to an attack where the ball (10) provides the ability to work from any approach angle. The strength of the system is determined by the compressive strain on the primary plunger (40) and the splines, assuming that the main control ball (10) is made of high strength material such as carbon steel. Assuming 4 contact surfaces by calculation it can be seen that by disposing the splines on a pitch circle of 50 - 60 mm diameter and creating 5-7° of rotation, some 70mm sq. of material is involved in the locking process. If these components are made in steel with a typical compressive strength of 700 MPa the system will resist a load of some 5OkN. Increasing the number of splines to 8 will allow the mechanism to exceed 10OkN of load and this can be raised still higher through the use of advanced materials.

As an alternative to the rotary arrangement described in the first embodiment, it is possible to construct a relatively flat embodiment operating in two directions in effectively the same plane. This embodiment still relies on the use of an axially moveable splined member which can be moved transversally in order to allow the spines to mesh with corresponding splines in a fixed member. Again the transverse movement of the splined axially moveable member is controlled by the balance between two spring forces, one of which is electrically controlled. As before, the electrically controlled resilient bias can take the form of a Servocell Active Latch 1 or Active Latch 2 in view of the fact that these active latches have resiliently biased plungers whose movement can be inhibited by the use of a piezo ceramic bender. Turning now to Fig. 8, this shows a plan view of the second embodiment. This comprises a rectangular housing 80 provided at one end with a fixed splined locking base 81. In this embodiment, the axially moveable member is a composite member in the form of a slider 82 and a control member 83 arranged to reciprocate inside the housing against the action of a return spring 84. The control member 83 is pivotably mounted on the slider 82 at a pivot point which is represented by the reference numeral 86 the control member 83 has its free end engaging a transversely moveable member 88 provided with splines (not shown) which are of a size and shape to mesh with the splined locking base 81 when the control arm is in a suitable pivoted position. One longitudinal edge of the member 83 is profiled and the plunger 91 of an electrically controlled actuator 92 is arranged to contact the profiled edge of the member 83. The plunger 91 is spring biased in a direction towards the member 83 and the other biasing spring acting on the member 83 is located such that the member 83 is held between the two biasing springs.

When the slider 82 is moved towards the splined locking based 81, a shoulder 83a on the profiled edge of the member 83 contacts the plunger 91. In the event that the plunger is free to move under the action of the bias spring within the actuator 92, continued movement of the slider results in the plunger 91 being depressed into the housing of the actuator 92 in view of the fact that the bias spring operating on the other side of the member 83 is of greater spring force than the bias acting on the plunger 91. Thus, the member 83 does not pivot and so the member 88 is not moved transversely of the axial direction of sliding and so the splined end of the member 83 can mesh with the splines in the locking base 81.

However, if the actuator 92 were to be energised so as to inhibit movement of the plunger 91, when the shoulder 83a contacts the plunger 91 during axial sliding of the slider 82, this would result in the member 83 being moved transversely against the action of the other biasing spring which would mean that the splined end of the member 88 would not mesh with the splines in the locking base 81 and further sliding of the slider 82 would be resisted. While the embodiment shows the slider being moved due to rotation of a shaft 100 which carries an actuator disc 101, it will be appreciated that this movement can be occasioned by any suitable mechanism. Equally, the slider itself can be connected to any other member or mechanism such as a deadbolt. Also, the latch shown in embodiment 2 can be used in a normally latched or unlatched condition depending on the desired use and the electrical state of the actuator 92.

Claims

Claims:

1. A latch assembly comprising an axially moveable member having a splined end and being mounted for axial movement in a first plane, a locking interface member with matching splines, the axially moveable member also being mounted for movement in a direction transverse to the axial direction between a first position where the splined end meshes with the matching splines on the locking interface member and a second position where meshing is inhibited, and electrically controllable means for selectively permitting transverse movement of the axially moveable member between the first and second positions.

2. A latch assembly according to claim 1 and comprising means for applying two opposed resilient transverse biasing forces to the moveable member, one of which is changeable by the electrically controlled actuator in order to provide the selective movement.

3. A latch assembly according to claim 1 or 2 wherein the electrically controlled actuator assembly has a resiliently biased plunger which engages the axially moveable member.

4. A latch assembly according to any one of the preceding claims wherein the transverse movement of the axially moveable member is arcuate movement in the same or a parallel plane to the first plane in which the axially moveable member moves.

5. A latch assembly according to any one of the preceding claims wherein the electrically controllable means includes a piezo ceramic actuator.