This invention relates to linkages for rotatably joining two parts of a structure together, and specifically provides for two members to be joined together in a first attitude until, on deployment for example, they are released and automatically take up a second, rigid attitude.

Such linkages are known and used, for example, for folding rod or tubular members of a structure intersected by nodes. The object in this arrangement is for tne structure to be folded into a minimum volume for transportation, and for it to open automatically into a specific, fixed relationship when required. A particular requirement for this is the deployment of skeletal structures used as space platforms: tnese have to be stowed as compactly as possible in the launch vehicle and need to be erected reliably and as automatically as possible. The types of joint used hitherto for such purposes have usually Deen buliy, nave required additional components to restrain the initial impulsion rate, and have contained separate locking elements.

According to this invention, a linkage comprises a rod member; a sleeve slideable over a bifurcated, cylindrical end portion of the rod member; a link member pivoted within the ends of the said end portion and having two parallel sides profiled to provide a sliding fit within the sleeve, an angled side portion against which the end of the sleeve is urged when the linkage is in a partly open position and a rounded, profiled end portion to provide clearance for the sleeve when

the linkage is opening; means for limiting the sliding movement of the sleeve on the end portion; and a coil spring located around the end portion and between one end or the sleeve ana a step on the rod member to provide a torque for opening the linkage when released from the closed position.

The rod member may comprise a rod or tube into which a snaft having a bifurcated end is rigidly secured, the shaft constituting the end portion of the rod member and providing a seat along which the sleeve is slideable and for the coil spring which extends from the end of the tube to the sleeve. The link member may be an appendage to a base unit, for example, or a multiple joint may include a plurality of similar link members, but in an alternative and preferred form the lin member may be symmetrical in form and be pivotally attached in similar fashion to two similar rod members and the invention may provide a linkage for interconnecting two rod members by the said link member.

Whilst the link member as described need nave an angled side portion at one or both ends of only one of its two parallel sides, a more adaptable linkage may result if a similar angled side portion is provided at one or both ends of the otner parallel side. The linkage may readily be released from the locked, open position by withdrawing the sleeve from the link memDer against the action of the spring, and if the link member is in the latter form then the rod member may be rotated in either direction into the closed position.

The angled side portions are preferably formed at an angle in the range 5° to 15° to the parallel sides of the link member, an angle of 10° being found particularly suitable in one form of construction, but the extent of the angled side portion must not be too great to cause the length of the parallel sides to be insufficient to provide rigidity when engaged in the open position inside the sleeve.

By way of example, embodiments of the invention will now be described with reference to the drawings, of which

Figure 1 is a side elevation of a linkage in the closed position,

Figure 2 is an enlarged section on the mid-plane of tne link member of the linkage illustrated in Figure 1, Figure 3 is a partly cut-away perspective view of the linkage in a partly open position,

Figure 4 is a side elevation of the linκage in the locked, open position,

Figure 5 is a perspective view of an alternative arrangement, in the open position, to that shown in Figures 1 to , and

Figure 6 is a side elevation of the alternative arrangement in the closed position.

With reference to Figure 1, two hollow rods 1 and 2 are inter-connected by a link member, the link member being rotatably mounted on pivots formed by two axles 4 and 5 passing through the bifurcated ends of shafts 6 and 7 secured within the ends of the rods 1 and 2 respectively. Sleeves 8 and 9 are slideably retained on the shafts 6 and 7 respectively, and are urged against the link member 3 by coil springs 10 and 11 mounted around the shafts 6 and 7 and bearing against the ends of the rods 1 and 2 which function as a step on the snaϊts. The extent of sliding movement of the sleeves is limited by the provision of spigots 12 and 13 on the snafts which extend into respective slots 14 and 15 in the sleeves.

The axles 4 and 5 may be secured either to the link member 3 or to one or both of the bifurcated ends of each shaft; care has to be taken that the axles do not protrude from the shaft and hence foul the end of the respective sleeve when the linkage is opened.

The link member 3 is in the form of a flat plate wnose thickness enables it to rotate within the bifurcated ends of the shafts 6 and 7 (see Figure 3). As shown in Figure 2, the link member has two parallel long sides which are profiled to enable it to slide with a close fit within the inside walls of

the sleeves, and rounded ends which are likewise shaped and profiled to slide into and within the sleeves.

At each end of both of the long sides of the link member there is provided a fiat portion 16 inclined at an angle of 10° to the long sides. The inclined portions are not profiled and provide a bearing surface against which the ends of the sleeves a and 9 are urged when the linkage is in a partly open position, as shown in Figure 3.

In use, an assembly of members interconnected by one or more of such linkages may be stored within a larger tube or other container; in this position the springs 10 and 11 are in a compressed state urging the sleeves and 9 against the link member 3. When the linkage is released, for example by removal from its container, the torque created by the force of the sleeves against the link member causes the rods 1 and 2 to separate, an intermediate position being shown in Figure 3. As the rods continue to separate, the reaction between the sleeves and the inclined portions 16 tends to keep the torque at a constant value, and tne sleeves continue to move along the shafts under the force of the springs so tnat the link member commences to enter the sleeves.

Finally, the fully open (straight) position is reached, illustrated in Figure 4, in which the link member 3 is fully witnin the sleeves which are tnemselves in contact witn one another.

By correct profiling of the periphery of tne link member a rigid, substantially play-free fit of the link member within the sleeves can be obtained and by the limitation of the sleeve movement imposed by the spigot and slot arrangement correct positioning of the sleeve ends over the mid-line of the link member can be achieved. The maximum packing density of rods in a storage container is made possible by providing for the separation of the pivots to be substantially equal to the diameter of the hollow rods 1 and 2, for the sleeves to have

the same diameter as the rods and for the springs to be contained within said diameter.

In the embodiment described, a linkage between two similar members has been provided by an essentially symmetrical arrangement. The invention may however take tne form of an arrangement in which a single rod carrying a spring-loaded sleeve is rotatable on release of the link member just described. Such an arrangement may provide, for example, a pivotal connection between more than two rods , eacn rod being separately pivotable on a common platform, or one rod to a fixed member such as a base unit.

In these cases, the sliding movement of eacn sleeve on its shaft may be limited either by the spigot and slot arrangement just described, or by a physical step on the common or fixed member. Alternatively, just one of the shafts carries a sleeve, as in the embodiment illustrated in Figures 5 and 6.

In this embodiment two shafts 17 and 18 both having bifurcated ends are as before connected by a link member 19. One of the shafts 17 carries a sleeve 20 which is urged towards tne link member by a coil spring 21 which in order to prevent rotation of the sleeve on the shaft is positively located in a slot 22 in tne sleeve and a recess 23 in the snaft.

The sleeve 20 is provided with an axially extending nib portion 24 which in the open position bears against the link member but which when the joint closes after release engages against a spigot 25 provided on the other shaft 18, as illustrated in Figure 6. In this embodiment, the sleeve 20 is sufficiently long to cover, in the closed position, the entire hinged portion of the joint including the link member. This arrangement, particularly when coupled with a spigot/slot guide means in the sleeve, provides an additional torsional rigidity to the joint and hence to any structure of which the joint forms an integral part.

By combining different linkage arrangements, quite complex structures may be assembled in a form which can be stored compactly prior to erection at a remote location, for example, honeycomb or other skeletal support structures intended for deployment in space.

In all cases, the linkage can be made quite rigid against bending stresses and yet may be closed very readily simply by manually sliding the sleeve or sleeves away from the link member against the action of the spring. Those skilled in the art will appreciate that there are many variations in design, other than the embodiments just described, within the scope of the invention. The materials used for the linkage may be metallic, but particularly where weight considerations are important carbon fibre resin composites may be used.

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