The Army uses robots that are structurally rigid, making them impractical when performing military operations in highly congested and contested urban environments where covert maneuvering is critical for gaining military superiority. Stealthy maneuvering requires high structural flexibility and distributive control to sneak into confined or restricted spaces, operate for extended periods, and emulate biological morphologies and adaptability.

(a) Schematic of a soft actuator device (left), and exploded view of the device and constituent material layers (right). (b) Schematic of depositing (3D printing) hydrogel on the surface of a silicone layer after surface treatment and under UV light exposure. (c) Printing of the ionic hydrogel on the passive layer after surface treatment (left), final 3D-printed DEA (middle), and microstructure image of the device cross-section (right). (U.S. Army illustration)

Current military robots have two major limitations that restrict them from mimicking the locomotion of biological organisms. First, these robots lack the necessary dynamic flexibility, since they are mostly assembled with rigid mechanical and electronic components. Second, rigid robots require complex mechanisms and electrical circuitries to achieve active actuation and complex modes of motion.

To overcome these limitations, researchers sought inspiration from invertebrates to create soft actuator prototypes using active materials with tunable parameters such as structural flexibility, morphology, and dynamic actuation. The prototype is the first fully 3D-printed dielectric elastomer actuator (DEA) that can perform high bending motion. The 3D-printed DEAs exhibited significantly larger deflections — three times more than other recent examples in scientific literature.

The researchers investigated new methods for emulating the locomotion of invertebrates, which provided fundamental insights into the machineries of their soft distributed actuation circuitries that allow for high bending motions without skeletal support. Understanding the innate mechanisms of the distributive actuation observed in nature helped the team identify the important parameters that can be manipulated to accomplish novel functions such as achieving highly flexible modes of motion.

The team built and tested a prototype similar to actuators found in nature via a custom-built 3D printing platform, and then developed a unified mathematical model to study the sensitivity of each parameter and predict the various optimal actuation mechanisms. These circuitries involving soft, stretchable materials with mechanical properties similar to biological organisms such as cephalopods and worms were 3D-printed.

The research suggests that soft actuators can be prime candidates for autonomous additive manufacturing in the battlefield. Unlike current 3D-printed DEAs, the new fabrication method does not require post-processing steps such as assembly, drying, or annealing. Next steps involve discovering emerging dynamics of living structures and emulating them, fabricating functionally complex structures and devices autonomously, and exploiting new modes of actuation not achievable in conventional robotic and mechanical systems.

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This article first appeared in the September, 2018 issue of Tech Briefs Magazine.

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