Autonomous robotic refueling of an unmanned surface vehicle in varying sea states

In an effort to improve sailor safety during underway replenishment on the open sea, a robotic refueling system has been developed to autonomously refuel unmanned surface vehicles (USVs). The Rapid Autonomous Fuel Transfer (RAFT) project has demonstrated a methodology that could be used on the open water to autonomously refuel Navy vessels at significant sea states. The prototype refueling system is made up of two robotic arms: a rigid and precise industrial robotic manipulator to pinpoint the location of the target fuel tank and a novel soft pneumatic arm (Octarm) to provide compliant and safe contact with the USV. At the end of the Octarm, a magnetic end effector was designed (patent pending) to transfer a refueling “puck” from the robotic system to the target fuel tank. Acting under manual control or autonomously through visual tracking techniques, the robotic refueling system was shown to effectively transfer fuel to the target US Navy Sea Fox vessel under sea state 3.25 conditions at the US Army Aberdeen Test Center. The results demonstrate the feasibility of using a robotic solution to allow autonomous shore-to-ship or ship-to-USV refueling. It also illustrates the benefits and challenges of future robotic ship-to-USV refueling operations. This represents the first demonstrated use of a robotic system for fluid transfer to vessels in active sea states. This paper describes the design, development, and demonstration of the prototype autonomous refueling system.