Graduate Thesis Or Dissertation
 

Structure and Actuation of Cephalopod-Inspired Soft Robots

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  • Cephalopod-inspired soft robot arms have been studied as a new type of manipulator. These arms have been proposed for reach and grab tasks, underwater locomotion via swimming and walking, and robotic surgery. However, the capabilities of existing soft arms are limited to simple motions and light loads. Arm design has been conducted through iterative prototypes, and studies have not rigorously investigated soft arm mechanics. Arm capabilities and limitations, and their relation to the structure of the arm, are not well understood. Existing arms are most commonly modeled for control, and rely on physical parameters, e.g., stiffness, that are determined by testing constructed arms. These arm-specific models cannot be used to investigate the relationship between arm structure and function. This dissertation develops and validates a reduced-order model of soft arm bending that generalizes across designs, and uses it to analyze overactuated arms, i.e., more actuators are pressurized than are necessary to achieve a given bend direction. The model is generalizable because it uses actuator force characterizations determined from samples tested outside of an arm. The actuators were characterized in deformation states beyond actuation, including unpressurized strains, pressurized compression and pressurized extension. The bending arm model extends Euler-Bernoulli beam theory, and considers large deformations and a shifting neutral axis location. The model was validated for load-free and loaded soft arms. Model results demonstrated that arm force diminishes rapidly as the tip moves outward toward the workspace edge. Wider arms have higher peak forces, but narrower workspaces, and their load capacity is not higher at all points. Model results also indicated that load capacity was directional, and that motions that pull from the workspace edge to toward the center have higher capacities. Overactuated arm architectures were also evaluated using the model, and their performance was validated experimentally. These arms have many actuators around the cross section perimeter, and bend direction can be controlled by applying a single pressure signal to selected actuators, rather than balancing the ratio of two pressure signals. These arm architectures are shown to achieve equivalent curvature and improve load capacity compared to exactly actuated arms. This dissertation can be used to improve soft arms by allowing rapid design analysis in simulation. Designs can be examined rigorously, because the model can be used to identify the design features that improve or limit capabilities. The primary contributions are: 1. A method of characterizing soft actuators independently from a soft arm or other robot. The actuator force functions can be used to develop generalizable models. Deformation states beyond actuation, such as pressurized compression, are considered. 2. A model of soft arm bending that generalizes across designs, which can analyze designs prior to manufacturing. This model is the first validated generalizable model of fluid-driven soft bending arms. 3. Development and analysis of an overactuated soft arm architecture. Overactuated arms can be controlled more intuitively, maintain curvature compared to exactly actuated arms and improve on their load capacity.
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  • This work was supported by the National Science Foundation, under award IIS-1734627, and the Office of Naval Research, under award N00014-16-1-2529.
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  • Pending Publication
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  • 2020-06-12 to 2021-07-13

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