Multi-functional shape-memory-actuator with guidance function

Actuators for small machine tools usually need separate guidance elements since they cannot carry transversal loads. Hence, cross section and mass as well as the complexity of the actuator system increase. In this paper a new actuator approach, which does not need additional guidance elements is presented. The principle is based on the telescoping of several concentrically arranged tube-shaped elements. These are interconnected by SMA-wires, to obtain a cumulative relative movement of the stages caused by contraction of the single wires. An increasing number of stages lead to an increasing actuator stroke without affecting its length. Due to the angular orientation of the wires the force is split into longitudinal and transversal components. Thus, no further guidance elements are needed. To investigate the actuating principle theoretically a multi-domain-model is developed. It enables to derive correlations between design- and specified parameters. Furthermore a new control approach for antagonistically arranged SMA actuators is presented. It is based on the combination of the metrological and model-based detection of the gradient of the composition-temperature characteristics. With the adaption of the control parameters a deviation-independent dynamic behavior should be realized.