Proposal for LIBRA-II: A Quasi-statically Balanced Robot with an Elastic Telescopic Arm

Nuclear power station (NPS) decommissioning is a long and arduous process, with the possibility of significant health risks to the humans involved. Fukushima Daiichi NPS ’s Unit 3 MSIV (main steam isolation valve) room poses additional challenges, as it has high radiation levels due to the past presence of irradiated water, indicating an as of-yet unconfirmed leak in the PCV (primary containment vessel); water had been injected into the PCV to cool it after the 2011 Tohoku earthquake. By combining two robotic manipulator concepts developed at our lab – the elastic telescopic arm (ETA) and LIBRA-I’s quasi-static water-based counterweight – we propose LIBRA-II for surveying the Fukushima Daiichi NPS Unit 3 MSIV room. A prototype is built using an improved ETA and simplified counterweight system. We experimentally validate the compact 3-DoF robot’s ability to extend to over 6 meters in length while generating over 340 Nm of counter-torque.