GB2139596A - Raisable stand - Google Patents

Abstract

A trailer-borne structure for a microwave antenna has four folding sides comprising hinged frames 11 and providing an operational state in which the antenna, supported on a base 12, is raised high above the ground, and a retracted or folded state in which the base is nested away between the hinged frames, and at a lower level than the hinges 16 so as to provide a low centre of gravity suitable for towing the trailer from place to place. <IMAGE>

Description

SPECIFICATION Raisable stand This invention relates to raisable stands and is particularly concerned with structures that incorporate a stand which can be raised to an elevated position and still maintain acceptable torsional regidity. By way of example only, one particular application if the invention is in the provision of a stand for a trailer-borne directional radio antenna. Such equipment is typically required to have a relatively low profile and low centre-of-gravity for moving it about from place to place. Then, when a site has been chosen, it is necessary for the equipment to have a raised position for the antenna, typically about 3 metres above ground level, so as to raise its sightline above the height of commonly occurring obstacles in the vicinity.In this context it is to be noted that if the antenna has a directional sensitivity of about 1 milliradian, the structure supporting the antenna may, in its raised position, typically be required to maintain its azimuthal stability to about 0.1 milliradians in normal wind conditions.

According to the present invention there is provided a structure incorporating a raisable rigid stand supported by three or more side frames, each of which is formed by two hinged together parts and is hinged to the stand and to a rigid base member, wherein the hinging together of the two parts of each frame is parallel with the hinging of that frame both to the stand and to the base member, wherein releasable securing means are provided for rigidly securing together each pair of adjacent side frames, and wherein the configuration of the side frames is such that with the securing means released the structure is able to be articulated between an extended state in which the securing means are operable to provide rigidity with the hinging linking the side frame parts at a level intermediate that of the stand hinging and the base member hinging, and a contracted state in which the securing means are operable to provide rigidity with the stand hinging at a level intermediate that of the base hinging and the hinging linking the frame parts.

Preferably the sides co-operate in a symmet rical arrangement such that in the extended state the angles, in any plane parallel with the stand, between each pair of adjacent sides are all equal. Typically such a structure has four sides. The dimensions of the component parts of the sides can be varied to give them the optimum geometries and angles for any particular application.

The invention further provides a trailerborne microwave antenna mounted on a structure having three or more folding sides providing an operational state for the antenna in which it is raised high above the ground and a retracted folded state in which the antenna is nested between the sides to provide a lower centre of gravity suitable for towing the antenna from place to place.

There follows a description of trailer-borne raisable stands embodying the invention in preferred forms. The description refers to the accompanying drawings in which Figure 1 depicts schematically a perspective view of a trailer-borne raisable stand for a microwave antenna Figures 2, 3 and 4 are diagrams illustrating the folding structure of Figure 1 respectively in its fully erected, partly lowered and fully retracted positions Figure 5 depicts schematically a modified version of the folding structure of Figure 1, and Figure 6 depicts a scrap view of a further modification.

Referring to Figure 1, a trailer 10 supports a folding framework structure 11 with a stand 1 2 carrying a microwave antenna 1 3. The folding framework structure has four sides, each of which is hinged at the top 14 to the stand 1 2 and at the bottom 1 5 to trailer 10, and each of the sides is formed in two parts hinged together at 1 6. For each side the hinge 1 6 is aligned parallel with the hinges 14 and 1 5. Figure 1 shows the framework structure in its raised position, and it is held in this position by securing adjacent sides together in the region of their hinges 1 6.

It is not convenient to move the trailer from site to site with the antenna in this raised position. This is partly because of its overall height and partly because its centre-of-gravity is too high for stability when towing over rough terrain. To lower the antenna to a position for towing the clamps (not shown) that hold the four sides together are released.

This allows the stand to sink vertically down as depicted in Figures 2, 3 and 4.

Figure 2 shows the folding framework in the fully erected state. The four corners of the stand 1 2 are hinged to the tops A,B,C,D of the four sides making up the framework while their bottoms E,F,G,H are hinged to the trailer floor. The side corners I to P of the side frames are at the extremities of the hinges 1 6 linking the upper and lower parts of these side frames. In the fully erected state corner J butts against corner K, while similarly corners L, N and P are butted respectively against corners M, 0 and i.

Figure 3 depicts the structure with the stand partly lowered. The lowering of the stand has caused the four sides to splay out, with the result that corners J and K have moved apart. Similarly corners L and M, N and 0, and P, I have also moved apart.

When the lowering of the stand 1 2 takes it beneath the level of corners I to P, it is found that further lowering begins to bring the pairs of corners together again until the stand reaches it fully retracted position, depicted in Figure 4, in which the pairs of corners are once again butted together. By making fast these pairs of corners the rigid structure is again produced, and the equipment is ready for transport to a different location. There, reerection of the antenna is the reverse of the above-described procedure.

The size of the folding framework structure must be sufficient to give adequate clearance for the antenna in the retracted state, but with certain types of antenna shape it may be possibie to accommodate an antenna whose major dimension exceeds the length of the diagonal from corners J,K to corners N,O provided that in the raising or lowering of the structure the ends of the antenna pass through the level of the corners I to P while they are still separated.

The structure of Figure 5 incorporates a number of modifications of the structure previously described with reference to Figures 1 to 4. One of the modifications concerns providing each side with a pair of spaced apart hinges 54 at the top, and a second pair 55 at the bottom, instead of the single hinges 14 and 1 5 of Figure 1. A single hinge is quite adequate in the fully erected and fully retracted positions of Figures 2 and 4, but it will be seen that in the intermediate positions such as that of Figure 3, any uneven loading of the stand 12 tending twist its plane out of parallelism with that of the trailer floor is directly transmitted to these hinges. The resulting torque is considerably reduced by the spaced apart hinges of the Figure 5 structure.

Optionally, additional bracing (not shown) may be provided for each side to make each of its two parts into a fully triangulated integer.

Another of the modifications concerns dimensioning the sides so that their lower parts are substantially vertical in the fully erected position while their upper halves are inclined at between 30 and 45", preferably at about 37 to the vertical. Reverting attention to the first described structure of Figures 1 to 4 it will be noticed that it is an overconstrained structure. Thus for instance, if the height of the side defined by the corners B,K,F and L is enlarged out of proportion with the heights of the other sides, then when corners N and I meet corners 0 and P respectively (Figure 2), corners K and L will still be at a distance from their corresponding corners d and M.In a practical case, simple trigonometry shows that the separation distance may be over ten times the height discrepancy. This magnification factor is reduced severalfold by arranging for the upper part of the side to be inclined at a significant angle to the lower part, and thus renders the structure more tolerant of in-use distortions resulting for instance from accidental damage or mishandling. The preferred angle is in the region of 37 because at angles of less than about 30 the tolerance improvement becomes significantly reduced, while at angles of greater than about 45 the overall size of the structure to achieve a given lift of the stand between its retracted and extended states rises increasingly strongly, and also the size of the stand becomes too small in relation to the overall structure size.

The inclining of the upper parts of the sides and the use of spaced apart hinges at the top and bottom produces a structure that can be simply raised and lowered by means of single stage hydraulic jacks 57 acting between the platform and cross members 58 on the upper parts of the sides. For many applications two, rather than four jacks, will prove sufficient.

The problem of overconstraint previously referred to may alternatively be tackled by incorporating an extra linkage in the top hinge 14 of one of the sides, or alternatively in one of the bottom hinges 1 5. This linkage is constructed so that it is free to articulate over a certain range, but incorporates a restraining mechanism to lock it up firmly in any particular attitude within that range. An example of such a linkage is depicted in Figure 6. This has a lever 60 hinged at one end 61 to the top of one of the sides 62 of the folding framework, hinged at an intermediate point 63 to the stand 12, and hinged at the other end 64 to a rod 65. The ends of the rod are screw-threaded and carry lock nuts 66, but when these are loosened the rod is able to move up and down in a slot 67 thereby permitting the lever to articulate about its hinge point 63.When the stand is being raised or lowered the nuts 66 are loosened so that the lever is free to articulate over a limited arc and so accommodate any discrepancies in the relative dimensions of the component parts of the framework. Then, when the framework is locked up in the extended or retracted position, the nuts 66 are re-tightened so that the lever is able to become loadbearing again.

The linkage is useful not only in absorbing the manufacturing tolerances of the components of the structure, thereby reducing manufacturing costs, but also, when locked up, can be used to impart a preloading of the structure to give increased stiffness by removal of residual backlash in the hinges.

In the case of a structure which has a pair of spaced apart hinges at the top and bottom of each side, like the structure of Figure 5, the overconstraint problem can be solved in analogous manner with the use of two restrainable linkages, one being fitted for instance at the top left-hand hinge of one side, and its pair being fitted at the top right-hand hinge.

Claims (11)

1. A structure incorporating a raisable rigid stand supported by three or more side frames, each of which is formed by two hinged to gether parts and is hinged to the stand and to a rigid base member, wherein the hinging together of the two parts of each frame is parallel with the hinging of that frame both to the stand and to the base member, wherein releasable securing means are provided for rigidly securing together each pair of adjacent side frames, and wherein the configuration of the side frames is such that with the securing means released the structure is able to be articulated between an extended state in which the securing means are operable to provide rigidity with the hinging linking the side frame parts at a level intermediate that of the stand hinging and the base member hinging, and a contracted state in which the securing means are operable to provide rigidity with the stand hinging at a level intermediate that of the base hinging and the hinging linking the frame parts.

2. A structure as claimed in claim 1, wherein the side frames co-operate in a symmetrical arrangement such that in the extended state the angles, in any plane parallel with the stand, between each pair of adjacent sides are equal.

3. A structure as claimed in claim 1 or 2, wherein the number of the side frames is four.

4. A structure as claimed in claim 1, 2 or 3, wherein each side frame is hinged to the stand with a pair of spaced apart hinges and is hinged to the base member with a further pair of spaced apart hinges.

5. A structure as claimed in claim 1, 2, 3 or 4, wherein in the extended state the angle between the two hinged together parts of each side is between 135 and 150

6. A structure as claimed in claim 1, 2, 3, 4 or 5, wherein one of the side frames is hinged to the stand or to the base by a hinged linkage having a range over which it is free to articulate, and incorporating restraining means operable to lock the linkage in any particular attitude within that range.

7. A structure substantially as hereinbefore described with reference to the accompanying drawings.

8. A microwave transmitter and or receiver station incorporating a structure as claimed in any preceding claim with an antenna mounted on its stand.

9. A station as claimed in claim 8, wherein the structure base is formed by or mounted on the platform of a trailer.

10. Trailer-borne equipment incorporating a structure as claimed in any claim of claims 1 to 7, wherein the structure base is formed by or mounted on the platform of a trailer.

11. A trailer-borne microwave antenna mounted on a structure having three or more folding sides providing an operational state for the antenna in which it is raised high above the ground and a retracted folded state in which the antenna is nested between the sides to provide a lower centre of gravity suitable for towing the antenna from place to place.