Thermo-mechanical self-adaptive ball screw drive using thermal shape memory effect

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.