Investigating the Mechanics of Human-Centered Soft Robotic Actuators with Finite Element Analysis

Increasing attention has been focused in recent years on the development and analysis of “soft” robots. Such tools can perform a variety of simple tasks in and around humans with minimal risk of injury to people and the environments in which people typically live and work. Some studies have developed computational models, such as finite element models, to compare to experimental analysis. While these models generally show strong agreement with experiments, there has been little use of models to investigate modeling assumptions, buckling behavior, or design spaces. This paper seeks to address these opportunities and challenges through finite element analysis (FEA) of a particular type of soft actuators known as Fiber Reinforced Elastomeric Enclosures (FREEs), both individually and in modules. The FREEs studied in this work are fabricated from thin-walled latex tubes with helically wound cotton fibers at particular angles relative to the tube. Our results suggest that elastomer material behavior can be better described with an Ogden rather than neo-Hookean material model at large deformations and by modeling fibers with 1D truss elements. Additionally, the material properties of the elastomer were found to greatly influence FREE extension, expansion, and rotation (with strains in excess of 25%), while changes to fiber stiffness resulted in negligible differences in deformation. The implications of these results are that in the design and manufacturing of FREEs, substantial attention must be given to accurately measuring, modeling, and understanding elastomer and adhesive properties, and that these may be used for design tuning. Additional results showed that modules made up of multiple FREEs can be effectively studied using FEA to determine range of motion, buckling, and workspace.