Characterization and Modeling of the System Behavior of High Load SMA Actuators

Actuators are key elements in almost every production plant and machine. Thermal shape memory alloys (SMA) have an enormous energy density and can be used as a structural component of the machine. The technology therefore represents an interesting alternative to conventional actuator technologies. Wire-based SMA actuators are already established in industrial applications but are limited to low forces (N-range) at small strokes (mm-range). However, there are also applications and demands for compact SMA actuators with higher forces (kN-range). They require more massive geometries and new integration concepts of the shape memory components. This can significantly change the thermal system behavior, knowledge of which is required for design and optimization, as well as for dynamic control of the actuators. This paper describes the thermal system characterization and simulation methods for bulk actuators based on SMA. First, a technology demonstrator is presented, which is the basis for the measurements and models discussed. Next, two connected models for the thermal system behavior are presented: A thermal FE model and a lumped-parameter model with significantly reduced complexity to simulate dynamic behavior in real time and for optimization. Both models are validated with measurement data. In the end, the benefits and limitations of both models are discussed.