Marking Underwater Infrastructure: A Crab-Like Robot for Traversing Pipes

Abstract

Underwater infrastructure projects are increasingly seeking robots to inspect, repair, maintain, and salvage in the ocean with minimal human diver time. To perform tasks that would otherwise require human workers, most remotely operated vehicles (ROVs) are designed to operate either while resting on bottom surfaces (which provides stability) or while suspended neutrally buoyant in the water column (which expands workspace, but requires careful thrust control for large forces or precise motion). Here, our hypothesis is that by using the legs to locomote on and grasp infrastructure substrates, stable toolpaths are generated while walking, without relying on localization or thrust actuators. To our knowledge, the robot presented here is the first legged, underwater robot capable of walking along pipes. To show repeatable, consistent toolpaths, we attach a marker that leaves continuous paths on the cylindrical surface of the pipe. Specifically, we demonstrate that our half meter-wide hexapod walks horizontally or climbs vertically on both 25.4 cm and 45.7 cm diameter pipes. Full (360°) circumferences on both pipes are completed in 75 s, and a 3.5 cm × 2.5 cm square is drawn in 3 s. Individually, these demonstrations parallel future application-specific tasks such as cutting a piling into sections for salvage, cleaning patches of pipeline for ultrasonic testing, or dislodging invasive species. Taken together, our work suggests that bio-inspired legs can provide robust robotic solutions to support ambitious undersea construction projects. Future work is expected to demonstrate value of combining closed-loop model-based control; adaptive behaviors for addressing biofouling or other pipe irregularities; underwater thrusters for initial positioning.