Kinematic Modeling of a Soft Everting Robot from Inflated Beam Theory

The compliant nature of vine robots, or everted tubes, makes them very useful for passively navigating sensitive and cluttered environments. Like many soft robots, their compliance makes kinematic modeling difficult. This work seeks to validate the assumption that everted tubes can be modeled as an inflated cantilever beam. The tip deflection and curvature of tubes constructed from Low Density Polyethylene (LDPE) and commercially available silicone coated nylon, two commonly used materials for everted tube robots, were measured under several different loading conditions in both everted and non-everted configurations. Our data show that everted tubes constructed from LDPE can be modeled with Comer's model for inflated isotropic beams, which has been assumed in recent literature. In contrast, this model did not fit the silicone coated nylon beams' behavior. This is because of the anisotropic properties of fabric the current model does not consider. Results also showed that everted tubes collapsed before the modeled maximum loading condition at a constant tip displacement, whereas uneverted tubes collapsed slightly after the modeled maximum load. From the inflated beam model, we present an iterative approach to computing the forward kinematics of an everted tube in contact with an obstacle within an environment. This allows for estimating contact forces and determining the static pose of an everted tube.