This study presents a differential elastic joint for use in multi-linked pipeline inspection robots. Active joints to stretch against the pipe wall are essential for adapting robots to use in vertical pipes and slippery inner surfaces where a large traction force is required. Series elastic actuators with a high reduction system have typically been used to sense force/torque in such applications. However, compactness, power, and bi-directional series elasticity are required to conduct in-pipe inspections. In this study, we propose an active joint using a differential elastic actuator with a rubber spring for decreasing the size and increasing the stiffness of the joint. After describing the configuration of the differential elastic actuator that is suitable for our robot and the design theory of the rubber spring cross-section, we conducted experiments to verify its torque property.
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