Tension reduction method for a modular cable-driven robotic arm with co-shared cables

This paper focuses on the tension reduction method for a Modular Cable-Driven Robotic Arm (MCDRA) that consists of a number of 2-degree-of-freedom (2-DOF) cable-driven joint modules. The MCDRA has implemented a cable routing scheme in which every two adjacent modules co-share one driving cable in order to reduce the number of cables to the minimum required. To investigate the tension distribution of the cables, a new tension analysis algorithm is proposed, in which the cable tension is decomposed into the load-carrying tension and the internal tension. It is revealed that the MCDRA with alternatively co-shared driving cables has inevitable internal tensions, which results in tension magnification. To reduce the cable tensions, the MCDRA is modified by adding two revolute joints with one connected to the base and the other one placed at its distal end. By rotating the base-mounted revolute joint and controlling each of the joints as well as the revolute joint on the distal end accordingly, the modified MCDRA can rotate like a universal joint chain and keep the end-effector pose unchanged. A global optimization algorithm based on interval analysis is proposed to find the optimal rotation angle of the base-mounted revolute joint that produces the lowest cable tensions. The effectiveness of the cable tension reduction method is validated through both simulation and experimental studies.