# Patent

## Title
Adapted torque motorisation system for deployable spatial structures

## Abstract

A motorization device comprises two substantially parallel winding cylinders, and at least one longitudinal linking element able to maintain a predetermined distance between the winding cylinders and wound around winding tracks, the linking element consequently having a crossing point located between the winding cylinders. The motorization device includes two flexible tracks, fixed on each of the winding cylinders and arranged to face and to touch eachother at the contact point, a pre-stressing force being applied to the contact point under the effect of said linking element. The flexible tracks are spiral shaped and arranged such that the contact point between the two spiral-shaped flexible tracks, located between the winding cylinders, is offset relative to the crossing point of the linking element, such that a torque dependent on the distance between the contact point and the crossing point is applied to the contact point, causing reciprocal rotation of the flexible tracks.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority to foreign French patent application No. FR 1004765, filed on Dec. 7, 2010, the disclosure of which is incorporated by reference in its entirety.
FIELD OF THE INVENTION
The present invention relates to the field of mechanisms for deploying spatial appendices, such as antennas or solar generators.
These mechanisms comprise hinge lines generally using torsion-spring, spiral-spring or Carpentier-joint motorization components, making it possible to counteract resistive torque and ensure the margins required in terms of torque generated to ensure the full deployment of the appendices.
BACKGROUND
In this context, known motorization components provide scalable or variable motorization torque, which causes over-motorization and impacts on full deployment.
These impacts may be significant and cause damage to the spatial appendices on full deployment, as well as parasitic torque harmful to the piloting of the spacecraft. To mitigate this problem, deployable structures are dimensioned and reinforced to make them resistant to end-of-travel impacts caused during deployment thereof, but this solution is unsatisfactory and notably increases the overall weight of the structure.
Specific advancements have resulted in the development of deployment mechanisms having near-zero resistive torque. Such mechanisms, such as the hinge line described in patent application FR 2635077, have the advantage of requiring limited motorization power and minimising end-of-travel impacts. Other mechanisms have been developed by improving the aforementioned mechanism, notably in terms of mass and volume. Such a deployment mechanism is disclosed in patent application FR 0605653.
These hinge mechanisms, for the deployment of spatial appendices, nonetheless have different drawbacks that have not been addressed in the prior art.
First of all, the known mechanisms, such as those described in patent applications FR 2635077 and FR 0605653, have a maximum angular deployment capacity of 180°. Furthermore, the overall kinetics thereof generate very irregular motorization torque, on account of the structure thereof. Finally, the deployment speed of known deployment mechanisms, as already mentioned, involves an end-of-travel energy release, and therefore an impact, because said deployment speed is not regulated.
SUMMARY OF THE INVENTION
The invention notably mitigates the aforementioned drawbacks. Thus, to enable deployments at more than 180° using a motorization mechanism that is not over-dimensioned and causes only very minimal end-of-deployment impacts, the present invention provides a motorization system based on the use of two spiral-shaped flexible tracks that are rotatable in relation to one another and arranged such as to generate a torque applied at a contact point between the two flexible tracks.
More specifically, the invention concerns a motorization device comprising two substantially parallel winding cylinders, at least one longitudinal linking element, said linking element being able to maintain a predetermined distance between said winding cylinders, and being wound around said winding cylinders, said linking element consequently having a crossing point located between said winding cylinders, the motorization device also comprising at least two flexible tracks, one flexible track being fixed on each winding cylinder, said flexible tracks being arranged to face one another and having a contact point, a pre-stressing force being applied to said contact point of the flexible tracks under the effect of said linking element; the motorization device according to the invention is characterised in that said flexible tracks are spiral shaped, said spiral shape being arranged such that the contact point between the two spiral-shaped flexible tracks is offset relative to said crossing point of the linking element, said contact point and said crossing point not being aligned on a single axis parallel to the axes of rotation of the winding cylinders, such that a torque dependent on the distance between the contact point and the crossing point is applied to said contact point, said torque being able to cause the reciprocal rotation of the flexible tracks.
Advantageously, the spiral shape is arranged such that the distance between the contact point between the flexible tracks and the crossing point of the linking element is equal to a predetermined value and the elasticity and rigidity of the flexible tracks are configured such as to control said torque exerted on said contact point between the flexible tracks.
In a specific embodiment, said torque is constant.
In another embodiment, said torque is variable.
Advantageously, the linking element may be formed by two flexible winding strips.
Advantageously, the linking element may alternatively be formed by a set of cables.
Advantageously, the motorization device according to the invention may include an end-of-travel stop.
Advantageously, the motorization device according to the invention may include a non-return stop.
Advantageously, the flexible tracks may have a variable cross section.



BRIEF DESCRIPTION OF THE DRAWINGS
Other features and advantages of the invention are disclosed in the description provided below in relation to the drawings attached, which show:
FIG. 1a: a known Carpentier-joint deployment mechanism, in stowed position;
FIG. 1b: a known Carpentier joint deployment mechanism, in deployed position;
FIGS. 2a and 2b: diagrams of the motorization system according to the invention, in the stowed and deployed positions;
FIGS. 3a and 3b: examples of spiral shapes for the flexible tracks of the motorization system according to the invention;
FIGS. 3c and 3d: two diagrams showing a flexible track of the motorization system according to the invention, subjected to different pre-stressing forces;
FIG. 4: a motorization system according to the invention, fitted with an end-of-travel stop;
FIGS. 5a and 5b: two diagrams showing an exemplary implementation of the device according to the invention with variable-profile winding tracks.



DETAILED DESCRIPTION
FIG. 1 is a diagram of an example of a known Carpentier-joint motorization system, built into a deployment mechanism corresponding to the teaching of patent application FR 0605653. The winding cylinders 1a, 1b are substantially parallel and held in position by the winding strips 3, or by any other suitable elements, such as cables, wound in a figure of eight around said winding cylinders 1a, 1b. The partially circular flexible tracks 2a, 2b are respectively connected to each of the winding cylinders 1a, 1b and arranged such as to surround each of the cylinders 1a, 1b. The flexible tracks 2a, 2b are arranged to face and touch one another. The winding strips 3 induce a pre-stressing force applied to the contact point between the flexible tracks 2a, 2b. On account of the circular geometry of the winding cylinders 1a, 1b and the winding tracks 2a, 2b, the contact point between said flexible tracks and the crossing point of said winding strips 3 are aligned on a parallel equidistant longitudinal axis of the axes of revolution of the two winding cylinders 1a, 1b. Appendices, such as solar generators GS, are attached to each winding cylinder/flexible track unit 1a-2a/1b-2b. 
As is well known, a Carpentier joint 10 is a thin metal strip having a curved cross section that is used as a motorization spring. Furthermore, a Carpentier joint 10 provides the advantage of maintaining a certain degree of rigidity when open. In FIG. 1a, the Carpentier joint 10 is closed and the device is in a stowed position. In FIG. 1b, the Carpentier joint 10 is open and the device is in a deployed position.
As mentioned above and shown in FIG. 1b, a major drawback of this type of Carpentier-joint motorization is that there is an angular limit to deployment, which cannot exceed 180° on account of the arrangement of said Carpentier joint 10 on the hinge.
FIGS. 2a and 2b illustrate the principle of the invention. The architecture of the hinge is similar to that shown in FIGS. 1a-1b. The flexible tracks 20a, 20b are respectively connected to each of the winding cylinders 1a, 1b. The innovative concept of the motorization system for a deployment mechanism according to the invention is based on the flexible tracks 20a, 20b, which consist of spiral-shaped flexible tracks. In relation to the flexible tracks 2a, 2b shown in FIGS. 1a, 1b, the present flexible tracks 20a, 20b have this specific spiral shape which makes it possible to offset the contact point P between the flexible tracks 20a, 20b in relation to the crossing point C of the winding strips 3. The contact point P and the crossing point C are not on the same axis parallel to the axes of rotation of the winding cylinders 1a, 1b. This offsetting by a distance D of the contact point P in relation to the crossing point C offsets the pre-stressing force induced by the winding strips 3 applied to the contact point P. Consequently, a torque R is generated between the contact point P and the crossing point C, inducing the rotation of the flexible tracks 20a, 20b. The reciprocal rotation of the flexible tracks 20a, 20b, attributable to the spiral shape thereof, causes a variation in the centre-to-centre distance of the winding cylinders, which changes from E in closed position C to E′ in open position O.
This torque R is configurable as a function of choices made concerning the shape of the spiral and the physical characteristics of the flexible tracks 20a, 20b, in particular the elasticity and rigidity thereof. To increase the torque R exerted on the flexible tracks, it is possible to increase the offset of the contact point P from the crossing point C by creating a spiral with a large opening angle, as shown in FIG. 3a, or to increase the force exerted on the contact point P by creating a stiffer flexible track, as shown in FIG. 3b. To increase the force exerted at contact point C, it is also possible to increase the bowing of the flexible tracks 20a-20b. FIGS. 3c-3d show the flexible track 20a subjected to a pre-stressing force F, flexible track 20a′ corresponding to flexible track 20a not subject to any pre-stressing force. The bowing of the flexible track 20a in FIG. 3c is greater than in FIG. 3d, such that the force applied to the contact point C is greater in the arrangement in FIG. 3c. 
To generate a constant torque R during the deployment phase, an Archimedean spiral is preferable.
The invention also provides for the possibility of adapting the motorization torque R to compensate for certain variable friction torques introduced by elements outside the hinge. These are typically the strands of electrical cables carrying electricity between two solar generator panels GS. This enables a near-constant motorization margin throughout deployment. Motorisation requirements are then adjusted to what is strictly necessary.
According to an embodiment of the invention, the system comprises an end-of-travel stop B, shown in FIG. 4, that is able to arrest the opening of the system in a suitable position.
Notably, said opening may be greater than 180°.
According to a specific embodiment shown in FIGS. 5a and 5b, a specific system may be provided to compensate for variations in the offset D occurring during opening of the motorization system. Such a compensation system is intended to limit the bowing of the flexible tracks 20a-20b. Indeed, the winding strips 3 are very rigid along the axis thereof. The use of scalable winding tracks 1a and 1b enables the flexible tracks 20a and 20b to be brought closer together during opening of the hinge. The profile of these winding tracks 1a and 1b is determined as a function of the profile of the spiral shape of the flexible tracks 20a-20b in order to guarantee the bowing of said flexible tracks 20a-20b, as well as the torque generated. The winding strips 3 are thus wound onto the small-diameter winding tracks 1a and 1b in the stowed position, shown as radius r in FIGS. 5a and 5b, then on to the large-diameter winding tracks 1a and 1b in the deployed position, shown as radius R in FIGS. 5a and 5b. This layout makes it possible to reduce the centre-to-centred distance, which changes from E to E′, between the two winding tracks 1a and 1b and the flexible tracks 20a and 20b. 
FIGS. 5a and 5b thus shows an example of a winding track 1a and 1b enabling a constant torque to be achieved.
In short, the principal advantage of the invention is proposing an automatic motorization system solution for a deployment mechanism for spatial appendices. The motorization system according to the invention provides an angular capacity that can exceed 180°. Furthermore, the invention makes it possible to control the torque generated in order to open the deployment mechanism. Said generated torque may also be adapted to the motorization strictly required as a function of the resistive torques opposing it. One sample application could be a constant motorization torque.
The system according to the invention also has the advantage of mechanical simplicity, as it comprises few parts, ensuring a certain simplicity of assembly. Finally, the arrangement of the flexible tracks in a spiral shape results in a small contact surface, and therefore minimal friction, which means that the motorization system need not be over-dimensioned and that the risk of end-of-travel impact is reduced.

## Claims

1. A motorization device, comprising:
two substantially parallel winding cylinders,
at least one linking element, the linking element being wound around said winding cylinders in a figure-of-eight shape such that the linking element has a figure-of-eight configuration defining a crossing point located between said winding cylinders, and
two spiral-shaped flexible tracks, each one of the two spiral-shaped flexible tracks being fixed on and encircling a respective one of the two substantially parallel winding cylinders, the two spiral-shaped flexible tracks being arranged to face and touch one another at a contact point, a pre-stressing force being applied to the contact point of the flexible tracks under the effect of the linking element,
the two spiral-shaped flexible tracks being arranged such that the contact point between the two spiral-shaped flexible tracks forms an axis parallel to axes of rotation of the winding cylinders, the axis of the contact point being offset relative to the crossing point of the linking element such that a torque generated by the pre-stressing force and a distance between the contact point and the crossing point is applied to the contact point, said torque being able to cause rotation of the flexible tracks.

2. The device according to claim 1, wherein the spiral shape is arranged such that the distance between the contact point between the flexible tracks and the crossing point of the linking element is equal to a predetermined value and wherein the elasticity and rigidity of the flexible tracks are configured such as to control said torque exerted on the contact point between the flexible tracks.

3. The device according to claim 1, wherein the two spiral-shaped flexible tracks are configured such that said torque generated is constant.

4. The device according to claim 1, wherein the two spiral-shaped flexible tracks are operable to change a distance between said winding cylinders to vary the torque generated by the pre-stressing force.

5. The device according to claim 1, wherein the linking element comprises two flexible winding strips.

6. The device according to claim 1, wherein the linking element comprises a set of cables.

7. The device according to claim 1, further comprising an end-of-travel stop.

8. The device according to claim 1, wherein the two spiral-shaped flexible tracks each have a variable radius.

9. The device according to claim 3, wherein the two spiral-shaped flexible tracks each include an Archimedean spiral.

10. The device according to claim 1, wherein each one of the two spiral-shaped flexible tracks encircling the respective one of the two substantially parallel winding cylinders revolves at least 360° around the respective one of the two substantially parallel winding cylinders thereof.

11. The device according to claim 1, wherein an angular limit of deployment of the two substantially parallel winding cylinders is greater than 180°.