An adaptive precision ball screw drive concept is presented in which a self-sufficient actuator is able to adjust the axial preload during the operation. The adjustment is effected by thermal shape memory alloy pucks, which either expand or contract according to the surrounding temperature field of the process. For this purpose, no external energy is needed and so the system is self-supported (energy harvesting). In this case, the extrinsic two-way shape memory effect occurs and the reversible full cycle of shape change is accomplished by a bias force of a flexure. Basing on temperature and force measurements on a double nut ball screw, a thermo-mechanical model is developed. Using the investigated principles adaptive mechanisms, a shape memory-based actuator is designed. Initial tests reveal an unwanted reduction of the preload of up to 800 N with rising temperature. Due to the shape memory actuation device, experiments results show an increase in axial load in approximated 70 % of the reduction.
Shape memory alloys (SMA) like Nickel-Titanium possess a very high mechanical energy density in relation to
conventional drives. Fiber reinforced plastics (FRP) will be increasingly applied to create lightweight structures.
Combining both innovative materials will evolve synergy effects. Due to functional integration of SMA sheets into a
base of FRP it is possible to realize adaptive composites for resource-efficient constructions as for instance flaps or
spoilers on cars. For this purpose the interaction between SMA as an actuator and FRP as a return spring need to be
designed in a suitable way. The computation of such structures is complex because of its non-linear (SMA) and
anisotropic (FRP) mechanical behavior. Therefore, a structural simulation model based on the finite element method was
developed by means of the software ANSYS. Based on that simulation model it is possible to determine proper
geometrical parameters for a composite made of SMA and FRP to perform a certain mechanism. The material properties
of SMA or FRP could also be varied to investigate their influence. For exemplary components it could be shown that the
stress-strain behavior is computable.
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