A Cable-Driven Parallel Hip Exoskeleton for High-Performance Walking Assistance

Misalignment between human and exoskeleton joints is a common issue in exoskeletons of rigid structure, as it can lead to discomfort or even injuries. Cable-driven exoskeletons, by using human skeletal joints, remove misalignment as a potential issue. However, large parasitic forces due to cable pulling endure as a shortcoming of cable-driven exoskeletons. To address the problem, this article proposes a novel cable-driven hip exoskeleton of parallel structures for assisted walking with eliminated parasitic force. The parasitic force potentially caused by either the misalignment or direct pulling can be removed mechanically. The new exoskeleton, conceptually different compared to existing anthropomorphic exoskeletons or soft exoskeletons, can conjugate flexibility and kinematic redundancy in flexion/extension and ab/adduction for self-alignment with anatomical joints. The unique design enables internal/external rotation for versatile walking gaits. In the work, the misalignment between the mechanical and biological hip joints is quantified both theoretically and experimentally. Moreover, an adaptive robust controller is designed to provide desired force during assisted walking. Experimental results demonstrate the performance of the proposed cable-driven exoskeleton system and improved wearing comfort with parasitic forces eliminated.