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1. (WO1997018399) IMPROVEMENTS RELATING TO MECHANICAL RELEASE SYSTEMS
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"Improvements relating to Mechanical Release Svstems"
This invention relates to mechanical release systems. There are situations in engineering and other spheres where large forces must be held but be released at will by relatively much smaller forces. An example is the large buoyancy load of a life-raft container being automatically released from its mountings as the mountings sink through 3 metres of water (as when the ship is on its way to the bottom) . The pressure trigger is usually a diaphragm over an airtight chamber producing (at the required depth) a few tens of Newtons, and this is required to release maybe tens of KiloNewtons of load.
According to the present invention there is provided a release mechanism comprising two aligned members coupled together by means whose abutting surfaces are aslant to the direction of alignment in a manner such that a parting force in the direction of alignment will wedge the abutting surfaces free of each other, allowing the members to decouple, an element constrictively encircling the members to resist that wedging action until the encircling element itself is released, and means for holding the encircling element in its constricting mode but disengageable therefrom by a force substantially less than the maximum parting force sustainable by the coupled and constrictively encircled members.
In one version the coupling means are hooks on the adjacent ends of said members, the toes of the hooks being aslant to give non-positive interengagement.

Alternatively, said coupling means includes a bridging member with wedge formations which engage complementary wedge formations on said members and which is also encircled by said element. In such a case there will generally be a plurality of such bridging members, equi-spaced around said members. The wedge formations on said members are conveniently formed by screw threads on cylindrical end portions, and the wedge formations on the bridging member (s) are then formed by complementary threads.
In a further version, the aligned members have an overlap and the overlapping portions are screw threaded to form part of the coupling means, with the threading effectively continuous over the join. A filament laid in the valley of the screw threading then serves as both the other part of the coupling means and the encircling element.
The encircling element will preferably be a filament, usually of wire, coiled around adjacent end portions of said members with one end held by a trip. This end of the filament may have an eye, in which case the trip is simply a pin through the eye. Its withdrawal releases the coil, which loosens and allows the two members to pull apart. Conveniently, the pin is housed mainly in a transverse passage provided by said members, one end projecting to cooperate with said eye and the other end being for connection to a trigger mechanism to pull the pin in a manner to withdraw said one end and release said eye. The other end of said filament can be trapped by turns of the coil in the manner of a common whipping.

For a better understanding of the invention, one embodiment will now be described, by way of example, with reference to the accompanying drawings, in which:
Figure 1 is an exploded perspective view of a release mechanism,
Figure 2 is a side, pre-assembly view of part of an alternative release mechanism,
Figure 3 is a side view of that mechanism when assembled, and
Figure 4 is a side view of another release mechanism.

The system of Figure 1 is centred on a two-part link 1. It comprises two generally cylindrical members 2 with hook formations 3 which overlap and interengage when the two members are brought together and axially aligned. Each hook has a deep shoulder 4 and a toe of lazy Z form in side view, the inclined surface 5 sloping away from the main body of the associated member 2. At the extremity of the toe there is an indent 6 before it terminates in a radial surface 7 that will abut the shoulder 4 of the opposite hook. The arrangement is symmetrical, each hook formation 3 being identical so that only one type of member 2 needs to be constructed.
At the free ends of the members 2 remote from the hooks 3 there are shackles 8 for coupling to further members, but these are only one of several options for attaching the mechanism to whatever it is designed to hold and release.
When the members 2 are assembled together as shown, a wire 9 is coiled tightly about the overlapping hook forma- tions 3 and the turns extend beyond them at both ends for a short distance. The coiling may begin by putting one end of the wire into one of the diametral apertures formed by the indents 6, taking it back towards the associated shackle end, and then commencing the coiling. This will securely trap that first end of the wire like a common whipping. When the turns reach the other end of the overlapping hooks and slightly beyond them, the wire is brought back over them in a short length 10 and twisted into an eye 11. This eye is formed so that it will register with the other diametral aperture formed by the indents 6. A pin 12 passed through this aperture between adjacent turns of the wire 11 can project a short distance through the eye 11 and hold the wire in place. This forms a trip, and very little force will be required to pull it back through the aperture and thus release the eye.
Figure 1 also shows a particular use for this release mechanism, although it will be understood that there could be many other applications.
The link 1 is carried by a drum-like stand 13 whose upper perimeter has diametrically opposed notches 14 providing a cradle for the link. A further cylinder 15 with corresponding notches in its lower perimeter 16 can be coaxially secured over this, thus protecting the wire-wound hooks 3 and release pin 12. The link 1 will in fact be turned through 90° about its axis from the position shown so that the apertures formed by the indents 6 extend vertically, and so that the eye 11 is underneath.

The eyelets 17 shown on the cylinder 15 are for use in tethering life rafts and will be weak, to break off above a certain strain.
Above the body 15 there is fitted a co-axial cylindri-cal chamber 18 whose underside is sealed by a flexible rubber diaphragm 19. There is an internal spring 20 biasing this diaphragm downwards, and the end of the spring couples to the pin 12 which passes through the diaphragm (maintaining the seal) to enter the diametral aperture below which there is the eye 11.
Normally, the pin will remain projecting through that eye. But if the external pressure on the diaphragm 19 rises, as it will when the assembly is submerged, the diaphragm flexes into the chamber 18, compressing the spring 20 and raising the pin 12. The eye 11 is therefore released.
With a substantial parting force on the shackles 8 , the surfaces 5 wedge the members 2 apart transversely to their axis. There will be resistance from the friction of the wire 9 on the surfaces of the members 2, but without the end 10 being held the wire tends to loosen by its natural spring, and it will be forced to uncoil further by the separating members 2, provided the parting force is sufficient. Eventually, the surfaces 5 will clear each other and the link 1 will part.
It will be appreciated that the more turns of the wire there are the greater this parting force has to be or, conversely, the less force there is needed to hold the eye 11. It may be said that there is capstan effect. The angle of the surfaces 5 also has a significant influence on what is required to break the link.
Figures 2 and 3 show an alternative release mechanism which, although it employs more parts, may prove to be simpler and easier to manufacture, while losing nothing in performance.
There are two aligned cylindrical members 21, and the adjacent end portions 22 are screw threaded. The hand of the screw is unimportant, and the cross section of the thread may take various forms, the only provision being that the flank facing away from the end of the associated member should slope. In other words, it must not be a buttress thread with the perpendicular flank on the side away from the adjacent end.
Coupling these members 21 together is a bridging assembly 23 comprising two substantially semi-cylindrical shells 24 internally formed with threading 25 complementary to the screw threads 22. These are brought together to form a jacket around the nearly abutting ends of the members 21, and they are then wound by a wire 26 in the manner of the previous example. It iε convenient to use the gap between the ends of the members 21, which is exposed at diametrically opposite points by the not-quite-meeting shells 24, as a trap for one end of the wire 26 before winding and as the passage for a pin 27 equivalent to the pin 12. This engages in an eye 28 at the other end of the wire 26, as in the previous embodiment.
The shells 24 may be formed from an internally screw threaded tube cut longitudinally down the middle. But to ensure free escape from the members 21 when the wire is released, the arc of each shell should probably be rather less than 180°. It may be preferred, therefore, to have four shells 24 each subtending an arc fractionally less than 90° formed by quartering rather than halving a tube.
It will be understood that this mechanism operates in a similar way to the first one described, in that the light restraint of the pin 27 holds the wire 26 in place, and thereby keeps the hooked engagement secure. In this case it is provided by the inter-engaging screw threads . But once the pin is pulled away to release the wire, that uncoils and the jacket is wedged free, uncoupling the members 21.
Instead of screw threads, there may be one or more annular ribs on the end of each member 21, with sloping flanks facing away from the opposite member, and the jacket shells would be correspondingly ribbed internally.
Another version is shown in Figure 4, where two coaxial cylindrical members 29 have a halved joint. Each semi-cylindrical end portion has screw threading 30 which, when the joint is made, is effectively continuous over it. A wire 31 is coiled in the V-shaped valley of the threading, and one end may be held by insertion in an almost diametrical aperture 32 formed by a transverse rebate in the end of one member 29 while the other end has an eye 33 over a similar aperture at the other end of the joint. This aperture receives a trip pin 34.
If desired the turns of the wire could be taken beyond the joint so that they encircled respective complete portions of the members 29, not necessarily resting in screw threading.
It will be appreciated that, in this embodiment, the wire 31 performs a dual function. Until released, it resists any axial parting force on the members 29, and this will be concentrated into shear forces at the points where the wire crosses the join between the members. However, with a good number of turns these forces are shared out and reduced, and the mechanism can sustain very considerable axial tension before there is risk of the wire being sheared. The other function of the wire is as in the previous embodiments, namely to be a lightly held restraint that can easily be released. When tripped, the flanks of the screw threading wedge the coil radially outwards as the members 29 part.
It will be understood that the overlap between the members 29 can be more complicated than a halved joint. There could be interdigitating quarters, for example. Also, if it is important to maintain the members 29 with the halved joint aligned without relying on the wire 31, those members could be tubular, at least at their adjacent ends, and a plain cylindrical core or plug, slotted at its ends to pass beyond the pin 34 and the trapped end of the wire, could be inserted to bridge the join. This would simply fall away on release.
Although cylindrical members are generally the most convenient shape, and kindest for the wire, there may be circumstances where non-cylindrical configurations are appropriate. The screw threaded versions cannot adapt, of course, but it will be understood that the others described can be modified to different cross-sections.
Also, although wire, conveniently with the characteristic of tending to uncoil when tightly wound, is the preferred choice, it may be possible to use non-metallic filaments to bind the mechanisms.