GB2114812A - A mechanism for extending and hauling in a folding structure such as a solar cell panel array - Google Patents

Abstract

The invention is particularly applicable to solar cell booms on satellites. Mounted on central body 1 is a folding structure 2 consisting of several structural elements 3, 4, 5, for instance solar cell panels, which are connected hingedly to one another, adjacent structural elements being swingable in opposite directions about common swivel axes 9, 9', 9''. Cables 7, 8 running over cable pulleys 10, 11 can be drawn in from the central body 1. The cable pulleys 10, 11 are mounted so as to be freely rotatable about the swivel axes 9. These cables 7, 8 change from one side to the other of the pulley from one cable pulley to the next and are, in each case, fastened to the structural element 3 arranged furthest outwards from the central body 1. A closed loop cable 20 and pulleys 18, 19, act as a traction gear and cable tension can be adjusted by means of a strainer 21. <IMAGE>

Description

SPECIFICATION A mechanism for extending and hauling in a folding structure This invention relates to a mechanism for extending and hauling in a folding structure which is mounted on a central body and which consists of several structural elements hingedly connected to one another, in which respect adjacent structural elements are in each case swingable in opposite directions about common swivel axes.

Such a mechanism is already known from German Patent No. 20 21 580 which describes foldabie solar cell booms for a satellite. These booms each consist of several panels ranged side by side with, in each case, adjacent panels swingable about a common axis of rotation (in each case in opposite directions relative to the associated axis of rotation). Such a solar cell boom thus forms a folding structure which is mounted on the satellite as a central body, in which respect the individual panels represent structural elements which are hingedly connected to one another. The panels are swingable about the longitudinal axes of respective torsion bars which are rigidly connected in each case at their one end to the one, and at their other end to the other, of the two associated panels.The arrangement is so designed that the torsion bars are not under tension in the extended state of the structure, but upon the hauling in of the folding structure are twisted increasingly about their respective longitudinal axes. Accordingly, prior to extension, the entire folded-together stack of panels stands under a certain initial tension or bias, which can be utilised for the unfolding procedure. Additionally, in order to make the unfolding procedure uniform or smooth, a series of connection of traction means gears is provided. Each of these gears consists of two rigid circular discs as well as a closed cable or rope securely connected to the circular discs. The circular discs are, on the one hand, fastened rigidly to the upper ends of the torsion bars and, on the other hand, fastened rigidly to the lower corners of the panels.As a whole the mode of operation of these traction means gears is such that, upon the pivoting of any particular panel, the pivoted motion is transmitted to all the other panels so that a concertina-like or zig-zag folding or unfolding of the folding structure results.

With respect to the unfolding and folding procedure, i.e. the extending and hauling in of the folding structure the known mechanism not symmetrical in design. The extension is, from the very start, fostered by the torsion bars which are under tension in the folded state. Moreover, the torsion bars are exposed to considerable material loading. Whilst the extension of the structure is effected mainly by way of the torsion bars, the presence of a motor is essential to carry out the hauling in or folding procedure with the aid of the traction means gears. In this respect, of course, the resistance of the elastic torsion bars has to be overcome.

An object of the invention is to provide a mechanism, of the kind mentioned at the beginning hereof, which in a simple and reliable way allows extension and hauling in of the folding structure by equally balanced operations and in which the movement procedures are to controllable at any time relative to speed and position. In particular, the use of torsion bars of the known kind is to be avoided.

This object is achieved in accordance with the invention in that cables are provided which can be drawn in from the central body, which cables run over cable pulleys mounted so as to be freely rotatable about the swivel axes and change from one side of the pulley to the other from one cable pulley to the next cable pulley and are, in each case, fastened to the structural element arranged furthest outwards from the central body.

When applied to the above-described known solar cell booms this means that cable pulleys are provided at least at the upper edge, but advantageously also at the lower edge, of the panels which are ranged side by side and which form the structural elements. In place of the elastic torsion bars of the known mechanism these are rigid swivel axes, about which he panels are, in each case, swingable and on which the freely-rotatable cable pulleys are mounted. These serve for the guidance of the cables, at least one of which, in each case, is associated with the function of extension and at least one of which is associated with the function of hauling in the structure.As a result of the freely-rotatable, quasiidle cable pulleys, as well as the fact that the cables act, in each case, on the structural element which is situated furthest outwards from the central body, a satisfactory and very direct transfer of force is guaranteed. The cable pulleys can be actuated jointly by a motor which is fastened to the central body.

In order to guide the cables satisfactorily and to keep them under tension at all times, it is proposed firstly that the cables should, in each case, run around the cable pulleys once, so that they cannot lose contact with said pulleys and secondly that the cables should run over cable strainers which are fastened to the central body.

The invention thus provides a mechanism which allows repeated, satisfactory and reliable extension and hauling in again of the folding structure. The number of structural elements to be ranged side by side is not, in principle, limited. The movement procedures can be controlled according to speed and position of the structural elements and stoppage is possible at any time. In this respect, the same extension and hauling-in moments occur at all the swivel axes.

Furthermore, it is particlarly advantageous that thermal expansion of the various component parts have no effect on the precision of the movement procedures.

The mode of construction of the proposed foldable assembly is, as a whole, uncomplicated as only a small number of relatively simple component parts are needed. Also the power necessary for performing the movement procedures is comparatively slight. Moreover, the power required can be considerably reduced by selecting a long extension time and neither power peaks nor engagement shock occur.

The mechanism is envisaged as being particularly useful for solar cell booms for satellites. Its applicability is, however, in no way restricted thereto. Thus, the structural elements forming the folding structure may also be carriers for planar radiator elements of an antenna. The applicability of the mechanism in no way depends on what functional elements the structural elements are intended to carry. The invention will be appliable to various folding structures which are folded in the manner of a concertina or zig-zag and in which, consequently, no torque, or only a very slight torque, is transmitted to the central body.

The invention will be described further, by way of example, with reference to the accompanying drawing in which the single figure is a perspective view of one practical embodiment of the mechanism of the invention.

The drawing shows in a schematic manner a folding structure 2 which comprises three platelike structural elements 3, 4, 5. Mounted on these structural elements are planar solar cells (not shown). The folding structure 2 is mounted swingably on a central body 1. The structural elements 3 and 4 as well as 4 and 5 are, in each case, swingable about common swivel axes 9, 9', in each case in opposite directions. In other words, in the depicted position the structural element 3 is swingable in an anticlockwise direction whilst the structural element 4 is swingable in a clockwise direction about the swivel axis 9, and the structural element 4 is swingable in a clockwise direction whilst the structural element 5 is swingable in an anticlockwise direction, about the swivel axis 9'. The folding structure 2 is mounted by way of a swivel axis 9" on the central body 1.

Mounted on the swivel axes 9, 9' and 9" are respective pairs of cable pulleys 1 0, 11 as well as 10', 11' and 10", 11" which are freely rotatable independently of one another. Acting on a fastening element 6 mounted on the structural element 3 which is the element situated furthest outwards from the body 1 are two cables 7, 8, the first of which is associated with the function of extension or unfolding of the structure 2 and the second of which is associated with the function of hauling in or folding the structure 2. The first cable 7 runs in peripheral guide grooves of the cable pulleys 10, 10' and 10" in such a way that it runs around each of these cable pulleys once. In the same way the second cable 8 is associated with the cable pulleys 11, 1 1' and 1 1".Two similar cable pulleys extend at the lower edge of the folding structure 2.

A motor 14 is mounted in the interior of the central body 1 and two cable drums 16, 17 are superimposed, one behind the other, on a shaft 1 5 of the motor 14. The two cables 7,8 pass over respective cable structures 13, 12 (also mounted in the central body 1) to the respective cable drums 17, 16. The cables 7, 8 are wound onto the respective cable drums 17, 1 6 in opposite directions to each other and are fastened thereto.

Upon rotation of the shaft 1 5, for example in the anticlockwise direction, the cable 8 is tightened whilst the cable 7 is loosened to a corresponding degree. The shortening of the cable 8 causes the folding structure 2 to become bent or kinked in a concertina-like manner by swinging of the structural elements 3, 4, 5 about the associated swivel axes 9, 9', 9". The magnitude of the torques occurring in this respect are determined only by the tensile force and the radii of the cable pulleys. The diameters of the cable drums 16, 17 as well as the length and strength of the spring elements of the cable strainers 1 2, 13 are so coordinated with one another that the two cables 7, 8 are always tautly tensioned, although rotation of the shaft 1 5 of the motor 14 always one of the two cables is tightened and the other is loosened.

The same holds true of the two cable pulleys at the lower edge of the folding structure 2.

Two traction means gears, as mentioned at the beginning hereof during discussion of the prior art, are also shown in the drawing. These consist in each case of two circular discs, which are connected to one another by way of a closed or endless loop cable fastened to them. At the upper edge of the folding structure 2 this traction means gear consists of the two circular discs 1 8 and 1 9 as well as the closed or endless loop cable 20 (shown in dot-dash manner). The closed cable 20 can be placed, and held, under tension with the aid of a tensioning device 21. A corresponding traction means gear is indicated at the lower edge of the folding structure 2 underneath the structural element 4. The traction means gears are intended to guarantee the angular uniformity of the extension and hauling in movements.

If the folding structure 2 is completely extended, the equal moment produced by the cable pull with respect to each swivel axis is available as holding moment. The cable is so severely tensioned that the stiffness of the entire extended folding structure is not disadvantageously affected. The uniform distribution of cable tension over the entire cable length which occurs by virtue of the freelyrotatable cable pulleys is particularly advantageous. Changes in length in the cable or in individual cable portions which are caused by temperature, can be compensated for by the associated cable strainer. The power required and the stress occurring during the extension and hauling-in performance is distributed very uniformly over the individual structural elements.

With the aid of the cable strainers it is theoretically possible to actuate a switch which switches the motor 14 on and off in a temperature-dependent manner. In order to prevent the cable from running or slipping back when the motor is switched off it is necessary to provide a brake or a self-locking gear. The extension or hauling-in speed of the cable and the structure is given by the rotary speed of the motor 14 and is adaptable within a large range to requirements.

Claims (7)

1. A mechanism for extending and hauling in a folding structure which is mounted on a central body and which consists of several structural elements connected hingedly to one another, in which respect adjacent structural elements are in each case swingable in opposite directions about common swivel axes, characterised in that cables are provided which can be drawn in from the central body, which cables run over cable pulleys mounted so as to be freely rotatable about the swivel axes and change from one side of the pulley to the other from one cable pulley to the next cable pulley and are, in each case, fastened to the structural element arranged furthest outwards from the central body.

2. A mechanism as claimed in claim 1, characterised in that two cable pulleys are mounted so as to be freely rotatable on each swivel axis one of said pulleys guiding the cable intended for extension of the structure and the other guiding the cable which is intended for hauling the folding structure in again.

3. A mechanism as claimed in claim 1 or 2, characterised in that each cable runs once around the respective cable pulley.

4. A mechanism as claimed in claim 1, 2 or 3, characterised in that the cables run over cable strainers which are fastened to the central body.

5. A mechanism as claimed in any preceding claim, characterised in that a motor is mounted in or on the central body and has a shaft which carries two axially offset cable drums, the cable or cables intended for extending the structure being wound in one direction of rotation onto the one cable drum and the cable or cables intended for hauling in the structure being wound in the other direction of rotation onto the other cable drum.

6. A mechanism as claimed in any preceding claim wherein the structural elements are planar solar cell carriers.

7. A mechanism for extending and hauling in a folding structure substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.