GB2434851A

GB2434851A - A vibration resistant release mechanism

Info

Publication number: GB2434851A
Application number: GB0602257A
Authority: GB
Inventors: Simon Powell
Original assignee: PBT IP Ltd
Current assignee: PBT IP Ltd
Priority date: 2006-02-03
Filing date: 2006-02-03
Publication date: 2007-08-08
Also published as: GB0602257D0; WO2007088365A1

Abstract

A vibration resistant release mechanism comprises a spring-energised crank assembly 20, 30, 35, 80 with gimbal pivots 18 and oppositely disposed high stiffness piezo-electric beam actuators 60. All components relating to the spring-energised crank assembly are balanced around the gimbal pivot 18 to resist vibration forces and the piezo-electric actuators 60 are mounted to respond to vibration modes in opposition to each other. The release mechanism may be applied to releasing a spring ejection system for drawers or doors; operating the sear of a firearms trigger; causing a retaining plunger to be retracted or inserted; releasing or closing a suitably dimensioned valve; closing or opening electrical contacts; and operating a visible flag.

Description

PIEZO ELECTRIC RELEASE MECHANISM WITH VIBRATION RESISTANT

FEATURES

Background of the Invention

The use of piezo electric actuators as a release medium is known and has been disclosed in application such as a circuit breakers.

It is a feature of piezo electric actuators that in the stack form they have very high force measurable in kilonewtons (kN) but extremely small movement measurable only in microns (j..un). The use of piezo materials to form benders is well known but such devices have significantly reduced output forces so movement of approximately 1mm results in an output force below iN.

We have previously disclosed the use of a bender mechanism to release a spring loaded contact through the use of a sliding surface and levers but all such mechanisms are prone to vibration sensitivity and the greater the ratio of output to trigger forces the It is desirable to employ the low power behaviour of piezo actuators to release spring loaded devices such as drawers, circuit breakers and firearms but to do so in a manner which is resistant to vibration from every direction. It is further desirable that such a release mechanism have a significant mechanical advantage to provide a useful physical output of several Newtons.

A simple mechanism for reducing the holding force of a system is the toggle clamp, which is well known. As the assembly of two pivoted linkages nears a vertical alignment, the lateral force required to hold the assembly in position is low, being a function of the tangent of the angle between the two legs of the linkage assembly. A similar behaviour can be obtained through the use of a rotating arm and spring assembly in a crank relationship, where one end of a spring is fixed to a pin that is radially disposed from the axis of the cam and the other end of the spring is fixed to a point on a suitable mounting plate. As the pin rotates around the centre to the position where the spring crosses over the axle of the rotating arm, the torque generated by the spring falls to zero.

In over-centre mechanisms where the locking angle is small, it is important that the line of action between the spring and the action point does not cross into the area occupied by the pivot as under such conditions the variability in the true pivot may result in the mechanism's release becoming unpredictable. The smaller the pivot the less the angle that can be reliably maintained. In the case of a simple pin pivot, the smaller the pivot the lower the strength of the mechanism in shear loading.

It would be useful to combine the geometry of a crank or toggle with a high stiffness piezo release and for this assembly to further be constructed to be resistant to vibration.

Description of The Invention

According to the present invention there is provided a release mechanism that comprises a spring energised crank assembly with gimbal pivots and oppositely disposed high stiffness piezo electric beam actuators. All components within the spring energised crank assembly are balanced around the gimbal pivot to resist vibration forces and the piezo releases are mounted to respond to vibration modes in opposition to each other.

In order that the present invention be more readily understood, an embodiment thereof will now be described by way of example with reference to the accompanying drawings, in which:-Fig. 1 shows a top plan view of a part of a mechanism according to the present invention; Fig. 2 shows a perspective view of a further part of the mechanism according to the present invention; Fig. 3 shows a perspective view of a mechanism according to the present invention; and Figs. 4 to 6 show plan views of the mechanisms in various stages of operation.

There is provided a balance wheel (10) that comprises two outer discs (20) separated by two radially disposed spring locating pins (30) that are diametrically opposed on the same radius from the centre of the discs (20). At an angle of between 75 and 9 0 to the spring locating pin (30) there is provided an arresting means (40) on the periphery of the discs (20). The balance wheel assembly (10) is mounted into a frame (50) and to this frame is mounted a spring fixing point (35). The force required to hold the assembly stationary at the arresting means (40) is at a minimum when a line drawn between the two spring mounting features crosses the axis of rotation of the balance wheel (10). This line is tenned the reaction line (80). The features to locate a spring onto the balance wheel and to secure the same spring to the frame (50) are duplicated and rotated through 180 degrees around the axis of the balance wheel (10).

The purpose of such replication is to provide resistance to vibration, because any increase in the force on one spring will be mirrored by an equal decrease on the other.

For resistance to more complicated harmonic motions it is also possible for the springs to have non-axial alignment in other planes and for more springs to be deployed at other positions. This additional complexity may be desirable where the mechanism is working under orbital vibration, for example.

Concentric with the balance wheel (10) and radiating out from the outer surface of the plates are two axle shafts (15). Each axle shaft (15) is terminated with a tapered and rounded tip to form one half of a gimbal pivot (18). The use of tapered gimbal pivots is well established as a means of providing the low friction well centred but strong pivot. Such assemblies are common in jewelled watches, gyroscopes and balances.

The frame (50) provides locating features for gimbal cups (55) that capture the gimbal pivots (18) such that they may freely rotate but are backlash free. Further features of the frame (50) provide the means to locate two piezo electric beam actuators (60), having at their tip features that interact with the arresting means (40) on the discs (20).

The beam actuators (60) are substantially planar and are disposed such that their surface is tangential to the periphery of the discs (20). In addition to being planar the actuators (60) are mounted such that their end (61) is axial with the axis of rotation for the balance wheel (10).

The actuators (60) are mounted on opposite sides of the frame (50) such that the force exerted by the springs upon the balance wheel (10) places the actuators (60) in tension, via their interference with the arresting means (40).

Consider now the operation of this assembly, which has a ready and a triggered state.

In the ready state the arresting means (40) of the balance wheel (10) are engaged by the piezo actuators (60) and the resulting strain prevents rotation of the balance wheel (10) under the influence of the acting springs.

The state of the assembly is changed by the application of a charge to the actuators (60). Charging the actuators causes them to curve away from the axis of the balance wheel (10) in such a manner that they no longer interfere with the arresting means (40). Freed from the reaction of the actuators (60) the torque generated by the springs causes the balance wheel to rotate and for the crank angle (80) to increase. If the springs have a substantial preload and a low spring rate, the rate of decline of force will be less than the gain in mechanical advantage that arises from the change of crank angle, so the torque within the system will increase.

Radial to the axle of the balance wheel (10) there is provided an output pin (22). In the rest state the output pin (22) has a starting position (24). The torque output of the output pin is zero whilst the system is at rest due to the restraining action of the actuators (60). Upon the release of the arresting means (40) by the actuators (60) the output pin (22) will rotate to an end position (26).

The torque generated upon the output pin (22) as it moves from its start position (24) to its end position (26) may be used as the driving means for any suitable mechanism.

Potential applications include but not exclusively: Releasing a spring ejection system for drawers or doors; Operating the sear of a firearms trigger; Causing a retaining plunger to be retracted or inserted; Releasing or closing a suitably dimensioned valve; Closing or opening electrical contacts; Operating a visible flag.

While the above embodiment discloses the use of two spaced discs (20), it will be apparent that a single disc (20) could be used but this might require the spring locating pins (30) to project from both major surfaces with the springs extending over both major surfaces in order to maintain a balanced condition.

Claims

CLAIMS: 1. A release mechanism comprising a rotatably mounted member

for rotation about an axis, resilient biasing means for biasing the member to rotate from a first position to a second position, and a plurality of piezo electric actuators coupled to the rotatable member for releasably holding the member in the first position against the force of the resilient biasing means.

2. A release mechanism according to claim 1, where there are a pair of oppositely disposed actuators.

3. A release mechanism according to claim 1 and 2, wherein the actuators are arranged to engage the periphery of the rotatably mounted member.

4. A release mechanism according to claim 1, 2 or 3 wherein the rotatably mounted member comprises two spaced apart discs.

5. A release mechanism according to any one of the preceding claims and comprising an output member.

6. A release mechanism according to claim 5, wherein the output member extends in a direction parallel to the axis of rotation of the member.

7. A release mechanism according to claim 5 or 6, wherein the output member is spaced from the axis of rotation of the member.

8. A release mechanism according to any one of the preceding claims, wherein the actuators are beam actuators.