GB2421275A

GB2421275A - Multiple purpose locking mechanism using active material switching

Info

Publication number: GB2421275A
Application number: GB0507187A
Authority: GB
Inventors: Simon Powell
Original assignee: PBT IP Ltd
Current assignee: PBT IP Ltd
Priority date: 2004-12-20
Filing date: 2005-04-08
Publication date: 2006-06-21
Also published as: WO2006067367A1; GB0427875D0; GB0507187D0

Abstract

A latching mechanism comprising first and second members relatively moveable with respect to each other in a first direction in one plane. The members have a respective inter-engagable projection and recess for locking the members together at a pre-selected position along a path of travel in the first direction and are arranged to permit limited movement in the first direction in the locked position. A release member and an electrically controlled device are provided for moving the release member in to a position whereby a mechanical force applied to one of the members in the first direction causes the release member and resilient portion to contact each other and thus flex the resilient portion to release the first and second member from the locked position. The latching member may be electrically controlled by an active material such as a piezo-ceramic, shape memory, electro-strictive or magneto-strictive. A preferred use is in a door lock.

Description

MULTIPLE PURPOSE LOCKING MECHANISM USING ACTIVE MATERIAL

SWITCHING Background to the invention The use of active materials in locks has already been proposed. Such devices are effective, but limited in their application by virtue of both their size and their mode of operation, which is usually in the form of a plunger being permitted to enter the body of the device or not. Much of the size of such devices arises due to the mechanical components involved in the locking chain, particularly when such components are required to rotate and take compressive strain. Any pivot must have a quantity of material to form it and the section must be sufficient to withstand the loading. Where the loading is transferred to another part of the component, by having an element of sliding within the pivot, the size of the mechanical component must still be relatively substantial. It is a feature of active materials, such as piezo-ceramic benders, that their motion is limited, so all pivots and linkages require careful consideration of their impact on the allowances for engagement and disengagement. Locks and latches are made in a very large range of formats and sizes, but all ultimately want to retain or immobilise a component. It would be beneficial for there to be a very compact fundamental element that combines active material actuation with the single action of immobilising and releasing a part with the necessary accommodation of the changes that occur in such actuators over temperature variations and for such a design to have few or no pivots or other causes of cumulative tolerance build up. Description of the Invention According to the invention there is provided two parts in suitable material that interface with each other such that they have only one plane of relative motion. One part is fixed to a non-moving member and the other part is fixed to a moving member within any suitable latch configuration. A spring blade or wire spring of suitable construction is fixed to one part such that it strikes and is held by a hook, projection or similar feature on the other part and this interference prevents the relative motion. Before the parts are prevented from their motion there is a small amount of permitted motion and the insertion into the path of the spring component of a suitable guide member will cause the spring to deflect by the size of the hook feature and so the spring will fail to engage upon the hook, permitting unrestricted relative motion. It is a particular feature of the invention that the spring component has a high ratio of width to thickness such that the tensile strength of the spring is high, but the part lies flat against the moving parts and is highly compliant perpendicular to the relative motion of the main parts. Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which:- Fig. 1 shows a perspective view of a first part of a latch assembly; Fig.2 shows a perspective view of a second part of the latch assembly and arranged to inter-fit with the first part; Fig. 3 shows a plan view of the first and second parts in operative position and in a first condition; Fig. 4 shows a plan view similar to Fig.3 but with the parts in a second position; Fig 5 shows a plan view similar to Fig. 3 but with the parts influenced by a blocking plate so as to be in a third condition; Fig.6 shows a plan view similar to Fig. 5 but with the parts in a fourth condition; Fig. 7 shows a perspective view of an actuator device for use with the parts shown in Figs 5 and 6.Fig. 8 shows a perspective view of the actuator device of Fig 7 in situ on the latch assembly; Fig. 9 shows a side view of the actuator device and latch assembly shown in Fig. 8; Fig. 10 shows a perspective view from the back of the assembly shown in Fig. 9; Fig. 11 shows a detailed perspective view of part of the assembly shown in Fig. 8; Fig. 12 shows one way of implementing use of the latch assembly; and Fig 13 shows a perspective view of a part of a further embodiment of the present invention. As shown in Figs. 1 and 2, there is provided a locking part 10 upon which is provided a mounting surface for a suitable actuator 20, locking blades 30 and a spline system 40 that interfaces with the travelling part 50 to ensure that the part can only move in one direction and this can be of any suitable form being shown in this case as a cruciform socket. The travelling part 50 has a mating spline array 60 that interfaces with the locking part splines 40 to permit free motion in the direction of the arrow 55. The travelling part 50 carries upon itself a locking spring 70 shown in Figs. 3 and 4 that has at least one locking feature 72. In the illustration and preferably there are two such locking features arranged such that sudden vibration that may force one spring end to move away from the locking feature 30 causes the opposite one to engage more closely. The spring locking feature 72 is constructed such that when no external forces are acting upon it the feature will collide with and be retained by the locking feature 30 as the locking part 10 and travelling part 50 move apart. A small amount of free space exists before this engagement, and Figure 3 shows the assembly fully closed, whilst Figure 4 shows the assembly locked. The width of the locking spring 70 is such that the spring extends beyond the locking blades 30 into a space below the actuator mount 20. The actuator 15 is formed such that it is affixed to the mount 20 and its free end 17 moves towards the spring 70 upon activation. The actuator 15 is fabricated from two blades 13, joined at the end of the first cantilever 12. Each blade 13 comprises a controlled expansion alloy metal substrate and a piezo ceramic plate 14 bonded together with any appropriate process such that the piezo electric contraction of the piezo ceramic plate causes a curvature of the beam. This technology is well known and does not require further explanation for the purposes of this invention. Affixed to the free end of the actuator 17 is a shunt plate 85 that has two symmetrical angles 86 upon its forward facing edges. This angle may be adjusted to take account of travel and friction, but must be such that when the assembly is at its most compressed, the spring locking feature 72 is above the face, and the face must completely cover the locking feature. If the shunt plate 85 is inserted into the space above the locking features 30 where the spring 72 will pass as the mechanism is opened, the locking features 72 will strike the angles 86. Any force exerted in the direction of the arrow 55 will create a vector force according to the tangent of the angle of the shunt plate faces 86, causing the spring 70 to flex outwards to the condition shown in Figure 5 and for the locking features 72 to pass by the locking blades 30. If the locking blades 30 are bypassed there is no restriction on the continued motion of the travelling part 50 and so the mechanism can be considered to be unlocked, as shown in Figure 6. To reset the device, the actuator 15 is discharged and thus to its starting position and the travelling part 50 is urged back to the starting position, typically by means of a spring. As soon as the tips of the spring 70 pass the locking blades 30 the inherent bias in the spring 70 causes the locking features 72 to realign over the locking blades 30 preventing repeated opening until the actuator 15 is once again energised. The position of the actuator 15 is such that the effects of hysteresis across the temperature range of the lock do not permit the shunt plate 85 to remain in the actuating space 21 when the actuator 15 is discharged. This capability is achieved by the careful selection of the initial offset height 4. Turning now to Figs. 10 and 11, in order to facilitate incorporation of the device into latch systems there is provided on the face opposite the actuator an array of mounting features. On each of the main components there is a threaded mounting hole 90, and an aligning hole 91. In applications where the relative motion is linear the parts are mounted using both features, but where the parts describe an arc or other locus, the threaded mounting hole 90 is used in conjunction with a shouldered bolt, permitting the parts to rotate on their mountings in the manner of a trunion. A typical trunion installation is shown in Figure 12, whereby the pivoted jaw 84 is shown closed and open, and the angular change of the system can be understood. By the use of various simple linkages, the device here described can be used to make latches that provide: Push-Pull action, such as on a drawer or cabinet Slam action, such as on a rim latch or mortice latch Dead bolt action, such as on a mortice lock or multiple point lock Sliding action, such as on a sliding door or hand bolt Snap in action, such as on a padlock By using the device herein described in conjunction with arrangements such as cams and springs it is possible to use it to influence the behaviour of much larger mechanisms and thereby greatly increase the force resistance of the latch. Turning now to Fig 12, this shows a further embodiment of the present invention with parts omitted for clarity. In the embodiment shown in Fig 12, the locking mechanism is housed in a container, only the end walls 101 and 102 of which are shown. The remainder of the container is not shown so as to expose the interior. In this embodiment, the travelling part is constituted by a rod 103 which extends through the end walls 101,102. One or more spring members 105 are provided on the rod 103 by having one end 106 of the or each member 105 fixedly attached to the rod 103. Each member 105 is generally flat plate provided with an elongate hole 107 and an inwardly directed finger 108. The end wall 101 is formed with an axially extending portion 110 and a side wall of the portion 110 is provided with a projection 111 which is arranged to be received in the elongate hole 107 in the member 105. The projection 111 and hole 107 are sized and shaped such that there is limited axially movement permitted between the rod 103 with respect to end wall 101. The end wall 101 is also provided with an electrically actuated device 115 which in this embodiment is in the form of a hairpin-shaped piezo-ceramic bender. One end 116 of the bender is attached to the end wall 101 and the other end 117 of the hairpin is moveable depending on whether or not the bender is energized. The end 117 contacts a slider element 120 so as to move the slider element 120 in a slideway towards and away from the rod 103 in the vicinity of the finger 108 of the member 105. In operation, with the bender 115 and the slider 120 in the position shown in Fig 12, the slider 120 is in the path of movement of the finger 108 during limited axial relative movement between the projection 111 and the hole 107 such that the member 105 is bent away from the rod 103 sufficiently to release the member 105 from the projection 111 and permit extended movement of the member 105 and hence the rod 103 to which it is attached. Thus, it will be apparent that any mechanical force applied to the rod will cause the rod 103 to slide through the container. Depending on the type of locking mechanism desired, the bender 105 may be energized so as to be in the condition shown in Fig 12 in which case movement of the rod 103 is only possible when the bender 105 is energized and mechanical force is applied to the rod 103.If no energization of the bender 115 occurs, the bender returns to a relaxed state where the slider 120 is lifted away from the rod 103 and hence out of the path of movement of the finger 108. Consequently, if a mechanical force is applied to the rod 103 in this condition, only limited axial motion is possible, restricted by the projection 111 and hole 107. It will be understood that the reverse operation is possible whereby energization of the bender 115 results in only limited axial movement of the rod 103. Various modifications can be made to the above described embodiment. For example, the rod need not extend completely from the end members 101, 102 as shown. This embodiment, however, is useful if the container is filled with a damping fluid such as a water-excluding high dielectric silicone oil in view of the fact that despite movement of the rod 103, the parts located within the container remain a constant volume. Additionally, although two members 105 are shown, it is possible to utilise only a single member 105 in certain circumstances. All the above embodiments describe the use of a piezo-ceramic device for electrically controlling the latching member, it is possible to use alternative active materials such as shape memory, magnetic shape memory, electro-strictive and magneto-strictive devices.

Claims

CLAIMS:

1. A latching mechanism comprising first and second members relatively moveable with respect to each other in a first direction in one plane and having a respective inter-engageable projection and recess for locking the members together at a preselected position along a path of travel in the first direction, wherein one of the projection and recesses provided on a resilient portion of one of the members and the inter-engaging projection and recess are arranged to permit limited movement in the first direction in the locked position, and wherein a release member and an electrically controlled device are provided for moving the release member in to a position whereby a mechanical force applied to one of the members in the first direction causes the release member and resilient portion to contact each other and thus flex the resilient portion to release the first and second members from the locked position.

2. A latching mechanism according to claim 1 wherein the resilient portion is shaped to engage the release member when moving in the first direction and be deflected by the release member.

3. A latching mechanism according to claim 1 or 2, wherein the release member is shaped whereby relative movement of the first and second members in the first direction causes the resilient portion to flex.

4. A latching mechanism according to any one of the preceding claims wherein the recess is formed in the resilient portion.

5. A latching mechanism according to claim 1, 2 or 3 wherein the projection is formed in the resilient portion.

6. A locking mechanism according to claim 1 wherein the release member is moveable in a direction transverse to said one plane.

7. A locking mechanism according to claim 1 wherein the electrically controlled device has electro or magneto-strictive properties.

8. A locking mechanism according to claim 7, wherein the electrically controlled device is a piezo-ceramic actuator.

9. A locking mechanism according to claim 7 wherein the release member is attached to one end of a hairpin-shaped piezo-ceramic actuator.

10. A locking mechanism according to any one of the preceding claims wherein there are two inter-engageable projections and recesses.

11. A lock device comprising a housing containing a locking mechanism according to any one of the preceding claims.

12. A lock device according to claim 10 wherein the housing is sealed and contains a damping fluid.

13. A lock device according to claim 11 wherein the damping fluid is a waterexcluding high dielectric silicone electric oil.