Design and Experimental Verification of a Hip Exoskeleton Based on Human-Machine Dynamics for Walking Assistance

High motion compatibility with the human body is essential for lower limb exoskeletons. However, in most exoskeletons, internal/external rotational degrees of freedom are not provided, which makes accurate alignment between the biological and mechanical joints difficult to achieve. To solve this problem, a novel hip exoskeleton with a parallel structure is developed in this article. The unique parallel structure eliminates the misalignment problem and enables walking free of restrictions. On the other hand, this requires a coordinated control among actuations within the parallel exoskeleton structure. In this light, a model-based controller is proposed in this article. The controller is based on a human-machine integrated dynamic model and can generate coordinated force control references that could increase the closed-loop system's sensitivity to its wearer's movements. The controller requires only kinematic information from the wearer, but not interaction force data that most existing exoskeletons require in their control design, which saves spaces and makes the system compact for use. Experiments were conducted to demonstrate the kinematic compatibility and assistive performance of the proposed hip exoskeleton.