Design of a controllable shape-memory-actuator with mechanical lock function

Machine tools for small work pieces are characterized by an extensive disproportion between workspace and cross section. This is mainly caused by limitations in the miniaturization of drives and guidance elements. Due to their high specific workloads and relatively small spatial requirements, Shape-Memory-Alloys (SMA) possess an outstanding potential to serve as miniaturized positioning devices in small machines. However, a disadvantage of known actuator configurations, such as an SMA wire working against a mechanical spring, is that energy is steadily consumed to hold defined positions. In this paper we present a novel SMA actuator design, which, due to an antagonistic arrangement of two SMA elements does not require energy whilst holding position. The two SMA actuators are applied in a differential setup and were designed regarding material, geometrical parameters, applied load, and control aspects. Furthermore, closed loop control concepts for positioning applications are implemented. These not only cover approaches using sensors, but also sensor-Iess concepts which utilize the distinctive length - resistance - correlation of SMAs for position controlling. Furthermore, a model/sam pie actuator has been used to demonstrate the designs capabilities to serve as miniaturized positioning device in small machines.