Tape-spring deployable device with a non-constant cross section

Abstract

A deployable device includes a tape-spring capable of passing from a wound configuration about a first axis Z to a deployed configuration along a second axis X substantially perpendicular to the first axis Z, the tape-spring having two characteristic dimensions, a first characteristic dimension being the width of the tape-spring along the first axis Z, a second characteristic dimension being the thickness of the tape-spring along a third axis Y substantially perpendicular to the first axis Z and to the second axis X. At least one of the two characteristic dimensions has a non-constant value along the second axis X.

Claims

1. A deployable device of space equipment, the deployable device comprising: a tape-spring capable of passing from a wound configuration about a first axis Z to a deployed configuration along a second axis X substantially perpendicular to the first axis Z, the tape-spring having two characteristic dimensions, a first characteristic dimension being the width of the tape-spring along the first axis Z, a second characteristic dimension being the thickness of the tape-spring along a third axis Y substantially perpendicular to the first axis Z and to the second axis X, wherein at least one of the two characteristic dimensions having a non-constant value along the second axis X, wherein the tape-spring has an embedded end opposite an end of the tape-spring that the tape-spring is wound about the first axis Z in the wound configuration, wherein the first characteristic dimension increases and decreases towards the embedded end over a first portion of the tape-spring and increases towards the embedded end over a second portion of the tape-spring that extends continuously from the first portion to the embedded end, wherein the second characteristic dimension decreases towards the embedded end, wherein the first portion of the tape-spring is between the end of the tape-spring opposite the embedded end and a minimum width of the tape spring, and wherein the second portion of the tape-spring is between the minimum width of the tape-spring and the embedded end of the tape-spring.

2. The deployable device according to claim 1, wherein the tape-spring has a free portion, and wherein the at least one of the two characteristic dimensions decreases towards the free portion.

3. The deployable device according to claim 1, comprising at least one local reinforcement positioned on the tape-spring, extending at least partially along at least one of the first axis Z or the second axis X.

4. The deployable device according to claim 1, wherein a cross section of the tape-spring is a cross section of cylindrical form, of U-shaped form, or of omega form.

5. A satellite comprising the deployable device according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood and further advantages will become apparent upon reading the detailed description of an embodiment given by way of example, the description being illustrated by the attached drawing, in which:

(2) FIG. 1 shows a tape-spring deployable device according to the prior art,

(3) FIG. 2 shows a first embodiment of a deployable device according to the invention,

(4) FIG. 3 shows another view of the first embodiment of the deployable device according to the invention,

(5) FIG. 4 shows a second embodiment of an embedded tape-spring deployable device according to the invention,

(6) FIG. 5 shows another view of the second embodiment of the deployable device according to the invention,

(7) FIG. 6 shows another embodiment of a tape-spring of a deployable device according to the invention,

(8) FIG. 7 shows another embodiment of a tape-spring of a deployable device according to the invention,

(9) FIGS. 8, 9 and 10 show variant cross sections of a tape-spring of a deployable device according to the invention,

(10) FIG. 11 schematically shows a satellite comprising at least one deployable device according to the invention.

(11) For reasons of clarity, the same elements will bear the same references in the various figures.

DETAILED DESCRIPTION

(12) The invention applies to monostable or bistable tape-springs. The employment of monostable tape-springs requires a greater guiding force. Bistable tape-springs are preferred for the uniform nature of their deployment. Furthermore, in the wound configuration, they remain wound, and in the deployed configuration, they remain deployed.

(13) FIG. 1 shows a tape-spring deployable device 1 according to the prior art. The deployable device 1 comprises a tape-spring 2 capable of passing from a wound configuration about a first axis Z to a deployed configuration along a second axis X substantially parallel to the first axis Z. The width 3 of the tape-spring is identical along the entire axis X and equal to the width 3 of the tape-spring at the point of winding about the mandrel 4. This corresponds to the usual deployed configuration of the prior art, and optimum rigidity is obtained by means of a cross section that is as large, as thick, and as closed as possible, optionally associated with embedding of the end of the tape-spring.

(14) FIG. 2 shows a first embodiment of a deployable device 10 according to the invention. The deployable device 10 comprises a tape-spring 11 capable of passing from a wound configuration about a first axis Z to a deployed configuration along a second axis X substantially perpendicular to the first axis Z. The tape-spring 11 has two characteristic dimensions, a first characteristic dimension 13 being the width of the tape-spring 11 along the first axis Z, and a second characteristic dimension 14 being the thickness of the tape-spring 11 along a third axis Y substantially perpendicular to the first axis Z and to the second axis X. According to the invention, at least one of the two characteristic dimensions 13, 14 has a non-constant value along the second axis X. In other words, the width of the tape-spring 11 and/or the thickness of the tape-spring 11 evolves along the second axis X. It may be seen notably in FIG. 2 that the width 13 of the tape-spring towards its free end is less than the width 13 of the tape-spring at the mandrel (the grey-shaded representation of the surface makes it possible visually to compare the widths). This solution allows a considerable saving in terms of mass, of the order of 30%, as compared with a solution in which there is a constant tape-spring cross section, whilst still guaranteeing satisfactory rigidity for the tape-spring. For the purposes of sizing this type of structure, it is sought to optimise the mass/stiffness ratio by attempting to obtain a rate of stress in the material that is as uniform as possible. This type of result may be obtained by virtue of topological optimisation methods that make it possible to identify optimal material distribution in a given volume subject to stresses.

(15) FIG. 3 shows another view of the first embodiment of the deployable device 10 according to the invention, and more precisely a view of the tape-spring 11 deployed along the second axis X. As explained previously, the tape-spring 11 has a free end 16 and the at least one of the two characteristic dimensions (in this case, the width) has a non-constant value along the second axis X. In the example presented, the width decreases towards the free end. It will be seen that for a constant width of a tape-spring the tape-spring 11 would extend as far as the dotted line 17. This results in a saving in terms of mass.

(16) By virtue of this optimisation of the cross section, it is thus possible to implement a smaller-capacity drive device that is lighter in weight and more compact since the cross section is smaller over a long length, implying a lower requirement in terms of winding torque.

(17) Based on the same principle, the thickness 14 of the tape-spring 11 along the third axis Y may also evolve along the second axis X. Preferably, the thickness 14 of the tape-spring 11 is greater at the base of the tape-spring 11, that is to say close to the mandrel, and thinner towards the free end. For example, for a tape-spring 100 mm in diameter, the thickness may be 0.6 mm over 2 or 3 meters of the tape-spring and then evolve to 0.4 mm, ending at 0.3 mm at the end of the tape-spring. The evolving thickness allows a significant gain in terms of mass. The rigidity of the tape-spring is, however, maintained.

(18) It may be noted that the width and/or the thickness increase and/or decrease linearly or non-linearly. Evolving profiles are determined in advance. The cross sections of the foot and of the head of the tape-spring are defined by calculations pertaining to the mechanical strength of the tape-spring, notably using optimisation methods as mentioned previously.

(19) As the tape-spring is made from carbon, glass or other fibres, for the thickness of the tape-spring to evolve fibres are added or removed depending on the required thickness.

(20) In order to obtain an evolving width, the tape-spring is generally machined using numerical control as a function of the stressed or non-stressed zones.

(21) FIG. 4 shows a second embodiment of an embedded tape-spring deployable device 20 according to the invention. The tape-spring 21 has an embedded end 22. The at least one of the two characteristic dimensions (width 13, thickness 14) has a non-constant value along the second axis X, increasing and decreasing over a first portion 23 of the tape-spring 21 and increasing over a second portion 24 of the tape-spring 21 towards the embedded end 22. It may be noted that the axis X is to be understood as the axis along which the tape-spring extends locally in the deployed configuration and which extends locally in a direction substantially perpendicular to the winding axis Z of the tape-spring.

(22) FIG. 5 shows another view of the second embodiment of the deployable device 20 according to the invention, and more precisely a view of the tape-spring 21 deployed along the second axis X. This representation shows the evolving profile of the cross section, in terms of width, of the tape-spring 21. In comparison with the dotted line 25, along which a prior-art tape-spring would extend, the saving in terms of mass is clearly visible.

(23) This results in an optimisation in terms of mass and rigidity of the deployable device. This optimisation may make it possible, frequently in terms of equivalent deployed configuration relative to a prior-art device, to reduce the thickness of the tape-spring and thus to reduce the energy needed to wind the tape-spring.

(24) FIG. 6 shows another embodiment of a tape-spring 31 of a deployable device according to the invention. In this embodiment, the deployable device comprises at least one local reinforcement 32 positioned on the tape-spring 31, extending at least partially along the second axis X. Preferably, the local reinforcement 32 is positioned along the entire length of the tape-spring 31, at the edges thereof and/or at the centre of the tape-spring 31. The reinforcement 32 makes it possible locally to reinforce the tape-spring 31 and thereby to guarantee the required rigidity for the tape-spring 31.

(25) FIG. 7 shows another embodiment of a tape-spring 41 of a deployable device according to the invention. In this embodiment, the deployable device comprises at least one local reinforcement 42 positioned on the tape-spring 41, extending at least partially along the first axis Z. Preferably, the local reinforcement 42 is positioned at the free end of the tape-spring 41, but may be positioned at other locations on the tape-spring 41.

(26) The local reinforcements 32, 42 are generally bands of carbon. They may be in the form of unidirectional fibre or fabric (in the case of longitudinal reinforcements) or fibres woven over a principle cross section or, alternatively, crossing fibres. The fibres are adjusted as a function of the stresses in the tape-spring.

(27) The positioning and the form thereof are connected with the geometry of the tape-spring. They are placed where the stresses are located, the field of stresses being determined beforehand using modelling tools of the tape-spring. Thus, it can be ensured that the cut-out profile does not have an impact on the integrity of the tape-spring, and the rigidity of the tape-spring is guaranteed by the presence, if required, of local reinforcements.

(28) FIGS. 8, 9 and 10 show variant cross sections of a tape-spring of a deployable device according to the invention. FIG. 8 shows a “cylindrical” cross section, like that which has been presented in the preceding figures.

(29) However, the cross section of the tape-spring may be of U-shaped form, as shown in FIG. 9. In the case of a deployable device implementing two tape-springs in one and the same plane, rigidity in this plane is obtained by the presence of two tape-springs. A U-shaped cross section of tape-springs makes it possible to confer enhanced rigidity in the other plane.

(30) Alternatively, it is also possible to consider an “omega” cross section, as shown in FIG. 10. This cross section also makes it possible to limit friction thereon at the entry to the roller.

(31) FIG. 11 schematically shows a satellite 60 comprising at least one deployable device according to the invention.