Power plants – Motor operated by expansion and/or contraction of a unit of... – Mass is a solid
Reexamination Certificate
2000-10-27
2001-10-09
Nguyen, Hoang (Department: 3748)
Power plants
Motor operated by expansion and/or contraction of a unit of...
Mass is a solid
C060S528000
Reexamination Certificate
active
06298662
ABSTRACT:
TECHNICAL FIELD
The invention mainly concerns a device designed to control a relative rotation between two elements articulated relative to each other around a given axis.
The invention also concerns a deployable mechanical structure, such as a solar array, a radiator or an antenna on a space vehicle, the deployment of which is controlled by means of one or more devices of this type.
The invention finds a favoured application in the context of the folding mechanism of the different mechanical structures which are fitted to space vehicles (satellites, space probes, etc.). It can however also be used in other fields, since the deployment or folding up of a mechanical structure must be able to be controlled, with high torque and high. amplitude, by means of a compact device built into the structure.
STATE OF THE ART
When a space vehicle is launched, it is necessary to keep a certain number of pieces of equipment such as solar arrays, radiators, antennae or the like, in the folded up position. Indeed, this configuration allows them to withstand the loads induced by the launch and to be compatible with the restricted volume which is allocated to them on the launcher. Devices providing this retention in the folded position are generally called “stacking devices”.
A space vehicle must therefore comprise deployment control devices, which are activated when the vehicle is in orbit, after the stacking devices have been unlocked.
Most current deployment control devices use either pre-stressed springs, or electric motors.
When a spring folding mechanism is used, substantial jarring occurs at the end of deployment, which may damage or disturb the mechanism of the equipment stowed on the space vehicle. To overcome this disadvantage, a control unit is frequently added to spring control devices. However, this reduces the reliability of the mechanism.
When an electric motor is used to control deployment, there are fitting constraints associated with the space requirement of the motor. Moreover, the unit constituted by the motor and by its electronic control system substantially increases the cost of the equipment and, consequently, of the space vehicle.
In document FR-A-2 684 638, a proposal was made to mechanise the deployment of a mechanical structure by means of a torsion spring, an elongation torque plate or arm, made of a bistable shape memory alloy. The change in metallurgical structure is obtained either by heating the motor part locally at one of its ends, or by heating it uniformly, but in a controlled way. A locking device keeps the structure in its final deployed state, when it reaches this configuration.
The use of a motor component made of a shape memory alloy, to control the deployment of a space vehicle mechanical structure, eliminates the disadvantages arising from the use of pre-stressed springs or electric motors. However, the solutions advocated in the document FR-A-2 684 638 have a certain number of disadvantages.
Thus, when a torsion spring is used, it is necessary to resort to a heavy and bulky spring to produce high capacity and to generate a high rotation torque.
When the motor component is in the form of a plate, it is practically impossible to control high deployment angles.
Lastly, the use of a torque arm requires a mechanical gear ratio which is restricting in terms of mass and space occupied.
Furthermore, when the heating of the motor component is carried out uniformly, document FR-A-2 684 638 proposes to guide the heating so as to control the deployment kinematics. This imposes complex and costly control electronics.
Also, in the case where the motor component is heated at one end, the natural heat propagation along this component is expressed by very high temperatures at the level of the heating device, by virtue of the steep temperature gradient between the two ends of the motor component.
Lastly, given that the deployment of the mechanical structure is generally locked at the end of its travel, when the required deployment angle is reached, the torque generated by the motor component is withstood by this same component and may cause it to break, after the stop is reached. This disadvantage can only be eliminated if the locking and heating cut-off are synchronised, which serves to complicate still further the device and its electronic control unit.
DISCLOSURE OF THE INVENTION
The main object of the invention is a device allowing the control of a relative rotation between two elements by means of a motor component made of a bistable shape memory alloy, so as to benefit from the advantages arising from the use of such a component, while allowing a high rotation torque to be generated and a high deployment angle to be attained, for a relatively low space requirement, weight and cost.
In accordance with the invention, this result is obtained by means of a device for controlling a relative rotation between two elements articulated relative to each other around a given axis, the device including a torsion bar made of a bistable shape memory alloy, centred on said axis and connected to each of the elements at points spaced out along said axis, and bar heating means, activation of which generates said relative rotation, under the effect of a change in the metallurgical structure of the alloy, the device being characterised in that the torsion bar is able to generate an angle of relative rotation between said points on the bar, greater than a pre-set relative rotation angle to be controlled between the elements, a stop being provided to restrict the relative rotation angle between the elements to the pre-set angle, and at least one mechanical fuse being provided between the torsion bar and a first of said elements, to absorb excess relative rotation between said points on the bar, beyond said pre-set angle.
The use of a motor component constituted by a bar made of a bistable shape memory alloy, working in torsion, allows a high rotation torque to be generated and a high deployment angle to be attained, for a particularly low space requirement and remaining weight. In the event of the device according to the invention being used in parallel with an resilient deployment system (for example a solar array with several flaps of which several articulation lines are spring mechanised) the bistable shape memory alloy bar can allow surplus in the folding mechanism to be brought to bear to help the deployment of a failing articulation line, thanks to additional transmission elements (for example, pulleys and interlinking cables). Moreover, it is not necessary to resort to a complex electronic control unit, since the heating of the torsion bar is carried out without it being necessary to control it or guide it. Also, a control device designed in this way has great reliability, and is remarkably straightforward to operate and fit.
Moreover, the presence of a mechanical fuse and a stop allows the torque to be absorbed which continues to be generated by the torsion bar when the two elements reach the stop. The integrity of the bar is thus preserved, without it being necessary to synchronise the locking and the cut-off of the heating.
Preferably, the mechanical fuse is constituted by a rod of smaller cross section than the torsion bar, which extends the latter along the articulation axis of the two elements and the ends of which are connected in rotation to one end of the bar and to the first element respectively.
A resilient means such as a spring is then advantageously interposed between the rod and the first element, so as to act upon the latter towards the torsion bar, along the above-mentioned axis.
To ensure operational reliability in orbit, the fuse may possibly be replaced before the launch by a very resistant part in order to avoid premature fracture of said fuse in the event of a friction point being encountered during the last deployment.
In the preferred embodiment of the invention, the heating means include heaters distributed over the whole length of the torsion bar, stuck onto it and individually retained by hooping rings.
Furthermore, a reverse running stop locking mec
Baudasse Yannick
Kerhousse Patrice
Reimbold François
Vezain Gerard
Viale Daniel
Alcatel
Nguyen Hoang
Pearne & Gordon LLP
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