Zusammenfassung:
In the last decades, more and more space applications required actively controlling the orientation of certain devices like scanning mirrors, antennas, calibration units mounted on satellites and spacecraft. The benefit of using compliant mechanisms for such applications is multiple. First, frictionless flexible joints present no generation of wear particles and do not require lubrication which allows to use flexures near optical surfaces. Second, lifetime including long time storage can be extended to infinite as material is used below its infinite fatigue limit. Third, micro-vibration can be damped by tuning the stiffness of the flexure to obtain first eigenfrequency of the system far below micro-vibration excitation frequencies. Finally, compliant joints accommodate easily thermo-elastic constraints between the surrounding structure and the supported payload. Flexible pivots are therefore most often the retained choice in the context of long life, clean and precise applications for space applications. The AlmaFlex is a novel flexure design family that has been invented and patented by Almatech SA. The pivot design has been further developed in the frame of the associated Core Technology Program (CTP) which led to the Large Angle Flexible Pivot (LAFP): a flexible pivot capable of ±70° rotations for infinite life in cryogenic conditions while maintaining the centre shift below 10μm and keeping actuation torque in the Newton meter range. To achieve targeted performances, efforts have been set on design optimization, material selection, manufacturing processes and post-treatments. This paper presents the design of the LAFP, its optimization process as well as the accelerated fatigue test results performed on an extensive selection of test samples. The Almaflex design is based on pure bending deformations of blades. The flexure consists in two symmetric identical rings, a rotor and stator mounted on a synchronizing ring. Each stage comprises a set of four blades plus T-bars connecting the ring to its center which is then connected to the synchronizing ring via connecting members also using T-bars. Larger angular ranges can also be obtained by using additional stages. This design allows very good decoupling between each DoF which is particularly useful for stiffness optimization considering in-orbit operations, launch locking, gravity sag adjustments, thermo-elastic aspects...
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