Model-Based Design of Antagonistic Shape Memory Alloy Actuators for Bistable Structures

Space missions benefit greatly from adaptive structures with reversible shape change, enabling optimized instrument performance across various operational stages. However, lightweight, compact, and reliable actuation of these structures remains an open challenge. Antagonistic shape memory alloy (SMA) actuation of bistable structures has seen particular interest for its low-energy actuation potential. However, current literature lacks analytic design frameworks for such systems. In this work, a predictive antagonistic model for determining the equilibrium positions of antagonistic SMA spring actuators is proposed. This approach enables the design of SMA actuators targeted for particular bistable structures without relying on computationally expensive finite element frameworks. The model is parameterized by extracting key metrics from the force-displacement curves of SMA springs and can then predict the stable positions of antagonistic SMA actuators. The proposed antagonistic model, as well as the underlying constitutive model, are validated through experiments and predict the equilibrium positions of antagonistic actuators with an accuracy of 2.1%. To demonstrate a practical application, an SMA-driven iris mechanism for reconfiguring a bistable helical antenna is presented. The insights gained from these models facilitate the design of morphing structures, reconfigurable systems, and articulating mechanisms.