Elastic Telescopic Arm Extension/Contraction Mechanism using a Helically Grooved Flexible Conduit

Thin and long-reach arms are effective for the decommissioning of the Fukushima Daiichi Nuclear Power Plant, particularly for measuring in-vessel structures and removing fuel debris. Currently, there is a need for an arm that can investigate the bottom of the reactor pressure vessel by attaching a vertically extending arm equipped with investigation equipment to the tip of a horizontally extending long-reach arm. Telescopic arms are expected to provide a high extension-to-contraction ratio, reduce the installation space of the arm, and enable entry into narrow spaces and wide-area observation. In this paper, we propose an extension/contraction mechanism that uses a helically grooved flexible conduit as a feed screw. Using the proposed mechanism, the conduit is fed into an elastically bendable arm, and a prototype that can extend/contract up to 8.6 m is developed. The fundamental performance of the elastic telescopic arm was evaluated through experiments in which the arm was extended/contracted horizontally (0 deg), tilted (45 deg), and upward (90 deg), payload experiments, and an external environment interference experiment.