Continuum Arm With a Gear-Synchronized Backbone for Repeatable and Load-Bearing Grasp-and-Store Manipulation

This paper presents a continuum arm architecture that enables repeatable and load-bearing manipulation by employing a gear-synchronized backbone. Although conventional continuum arms provide excellent compliance in confined spaces, their inconsistent motion and low stiffness hinder applications requiring robustness and precision. To address these limitations, we propose a modular structure that passively synchronizes joint motion using interlinked gear mechanisms. This internal synchronization ensures uniform angular displacement across all target joints, allowing predictable and mechanically stable arm bending without additional sensors or actuators. The compact actuation system simplifies integration and reduces hardware complexity. The proposed system is validated through a dual-arm grasp-and-store task, which uses two mechanically coordinated arms to sequentially grasp and store an object. Experimental results on the human-scale prototype show high repeatability and structural robustness: the system achieves a maximum positional RMSE of$\text{5.18}\,\text{mm}$across15trials, with the end-effector tracking error consistently within$5.83\%$of the total arm length. The arm also reliably supports payloads up to$\text{1}\,\text{kg}$during dynamic motion, confirming its capability for load-bearing manipulation in semi-structured environments.