Design of a Lattice-Reinforced Shape Memory Alloy Actuator for Underwater Soft Robots.

Throughout the development of soft robots, shape memory alloy (SMA) actuators have received considerable attention due to their inherent advantages, such as high power-to-weight ratio, low driving voltage, and high response speed. This study presents a lattice-reinforced SMA actuator with improved response speed and increased deformation range. The SMA wires are used to drive the actuator to achieve bending, while the high elastic wire's elasticity is used to achieve recovery. The actuator is cast into a lattice structure with five connection nodes, named Lattice-N5. Lattice-N5's fast response properties are validated through finite element analysis and experiments. Compared with the actuator without lattice structure (nonlattice), lattice-N5's bending deformation increases by up to 390.59% and 204.4% under optimal (voltage of 20 V, duty ratio of 30%, and frequency of 4 Hz) and practical (voltage of 20 V, duty ratio of 20% and frequency of 1 Hz) conditions, respectively, while reaching a stable state more rapidly under a periodic actuation. Therefore, the lattice-reinforced actuator exhibits robust actuation capabilities and improved response frequencies and thus can be employed in a biomimetic jellyfish robot for underwater monitoring and detection by combining a flexible pressure sensor. Moreover, the jellyfish robot with Lattice-N5 actuators exhibits a speed improvement of 111% under the optimal condition (duty ratio of 20% and frequency of 4 Hz) and 55% under the practical condition (voltage of 20 V, duty ratio of 20% and frequency of 1 Hz) compared with the robot with the nonlattice. This study provides a simple and effective design scheme for improving the performance of SMA actuators and prompting the development of underwater soft robots.