Serially Actuated Locomotion for Soft Robots in Tube-Like Environments

Soft robots are able to complete tasks that traditional robots cannot, thus providing new opportunities for robots to navigate confined spaces. These tasks include pipe inspection and endoluminal surgical applications. The research objective of this letter is to present a design methodology for soft robots capable of traversing a cannula or pipe using only passive elements, a single pressure source, and while avoiding blockage, that is, avoiding full occlusion of the cannula to still allow fluid flow. The robot consists of three segments, each with actuators and valves, and is driven by hydraulics (water). The actuators were built using the FREE method and optimized for the specific task of traversing a cannula with a diameter of 19 mm. An experimental approach was used to create a pressure-volume relationship from the kinematic fiber-reinforced elastomer enclosure (FREE) model. The passive valves were built as flow restrictors and modeled with the nonlinear orifice equation. A simulation and grid search was performed over a range of valve coefficients. An objective function was then maximized to produce orifice coefficients that augmented extension of the robot per input pressure cycle. The physical robot was then constructed and tested in a cannula. This resulted in a robot that was serially actuated, never fully occluded the cannula, and was able to successfully locomote a cannula at a rate of 274 mm per two-second cycle. This experimental result was close to the simulated result of 28 per cycle.