124 Figure 10(b) shows an overview of the second design of Arquimea Pin Puller, named Pin Puller V.2. This  design has been conceived in order to obtain a flat model structure. The device external diameter is   100.0 mm, the length is 50.9 mm with the pin retracted, and its estimated weight is 250 g. The Pin Puller  V.2 presents a mechanism similar to the Pin Puller V.1 . Nevertheless, the V.2 pin is supported by rigid  bars that keep it deployed during the un-actuated position. When a crown rotates by a SMA operation, the bars move, allowing the pin stroke by means of a compression spring. Pin Puller V.2  has also been  conceived in order to have a low weight structure, no complex features, and a suitable stiffness. The reset  is also planned to be done by pulling a M4 threaded tool located in the pin tip. The components alignment is also ensured in this Pin Puller, as result of the accurate design process, by using an internal ring that  also ensures the design compactness, locating the supporting spheres. Note that Pin Puller V.2 has been  designed to avoid any rotation of the pin.    Mechanical and Thermal Analyses   The 3D-CAD models of both versions of the Arquimea Pin Puller have been used to develop finite element analyses (FEA) of the structures. The goal of this analysis was to check the feasibility of the design as well as the components and assembly resistance. Two cases have been studied during the FEA, axial load condition and shear load condition. In particular, the axial load condition has been assumed as 180 N applied on the pin tip plus 1264 N applied by the stroke spring. The shear load condition has been assumed as 1000 N applied along a transversal axis of the pin. A factor of safety (FOS) of 1.25 has been suitably assumed both for incrementing the applied forces and for the numerical results in order to obtain a conservative design.   

                                             (a)                                                                        (b)  Figure 10. CAD models of Arquimea Pin Pullers: (a) V.1; (b) V.2.   Figure 11(a) shows the results of the Von Misses stress from the FEA of Pin Puller V.1  structure for the  second case of study (shear load). 450  N/mm2 has been computed as the maximum value (lower than the  yield limit of the selected aluminum alloy). Figure 11(b) shows the stress results of the Pin Puller V.2  FEA.  The maximum stress result has been computed as 290 N/mm2 (lower than the yield limit of the selected  aluminum alloy too) during the second case of study (shear load). Successful results have also been obtained during the vibration analysis of both Pin Puller structures. The same set-ups used for the above-mentioned FEAs have been used for computing the limits of resonance, obtaining 2128.6 Hz for version 1 and 2350.4 Hz for version 2. These limits are above the expected operating frequency for both devices.   Since mechanisms present difficulties during vacuum and extreme temperature conditions, tribology and thermal assessments have been done for both Pin Puller operations. Critical contact zones have been recognized in order to avoid high friction and adhesion. Certain solutions are proposed to resolve the problems, such as application of solid lubricant coating (MoS 2) on moving parts and designing the  mechanical parts assuming specific features that reduce contact among components up to contact lines