508 PEEK material is used in design D2. This material is very interesting as it  is relatively stiff, has good  mechanical strength chemical stability , and very good fatigue behavior at the current testing stage. The  fatigue stress to Young’s  modulus ratio,  which indicate s the ability of a material to deform without fatigue  rupture, is  2 to 3 times higher than titanium. A very compact design with large angle is thus achievable,  while maintaining high radial to torsional stiffness ratio. In addition, it is very light.  

Design D3 is a high -end application for large angle application. The total range of rotational angle is   140 degrees ( ± 70 degrees), while maintaining lifetime above 100 million  cycles with applicable safety  margin. The stress and torsional stiffness have  been minimized. Center shift is also kept below 10 microns  on the entire range of motion.  More details on this design can be found in R eference 5. 

Design D4 has been developed for a high- frequency oscillatory application that uses the el astic energy as  storage. In this application, a cog- free motor is exciting the first torsional mode of the flex with synchronized  impulse, which compensates  the material damping loss. At each oscillation, the range of motion is  increased to reach a maximal oscil lation of 90 degrees pea k-to-peak (±90 degrees). As the energy stored  in the movement is proportional to the flexure’s stiffness and to the angular range of motion squared , high  stiffness and large angle shall be targeted. In this application, the total el astic energy is 8.4 J per flexure.  

It is worth noticing from Table 1  that the LAFP design optimization  process is able to achieve very different  design goals. For example,  in design D1, the application required a relatively small rotational angle. The  benefits of the Almaflex design family  are the absence of tribological effects thus no wear nor particle  generation, and a stable, predictable behavior all -along lifetime.  In addition, one unique feature is that the  radial stiffness is kept nearly constant during the full rotation. Only 17% stiffness drop is observed between  the radial stiffness at 0° rotation and 70°. This feature is essential for micro -vibration isolation.  

Micro -Vibration  – A Pointing Disturbance  

One of the applications  of large angle flexible pivot is precision pointing mechanism, such as laser  communication terminal, scanner, and flip mirrors. Pointing from a platform to a 1 m diameter tar get that is  distant of 1000 km (Low Earth Orbit)  requires a pointing accuracy and stability that is at least a fraction of  1 µrad, typically 0.1 µrad. Such stability requirement may apply to Earth observation satellite, and laser  communicat ion between space and ground. For intersatellite laser communication link, the stability  requirement is more stringent  as the distance between satellites is generally larger, and diameters of target  optics are smaller.  

To achieve a pointing stability of 0.1 µrad or smaller, understanding the micro -vibration effect on pointing  stability is essential . There are sources of vibration noise on each platform . These sources are coming from  different  moveable parts such as a shutter, solar array drive, reaction wheels , and cryo -coolers. Each of  these mechanisms  has a micro -vibration signature. Reaction wheel s are one of the noisiest equipment. As  shown in Figure 6 , reaction wheels typically generate low vibration noise at low frequenc ies and high noise  at frequencies above 200 Hz.