Influence of Motion Restrictions in an Ankle Exoskeleton on Gait Kinematics and Stability in Straight Walking

Exoskeleton devices may impose kinematic constraints on a user’s motion and affect their stability due to added mass and inertia, but also due to the simplified mechanical design. This study explores the impact of kinematic constraints imposed by exoskeletons on user gait, stability, and perceived discomfort. Specifically, it examines how the varying degrees of freedom (DoF) in an ankle exoskeleton influence these factors. The exoskeleton utilized in this study can be configured to allow one, two, or three DoF, thereby simulating different levels of mechanical complexity and kinematic compatibility. A pilot study was conducted with six participants walking on a straight path to evaluate these effects. The findings indicate that increasing DoF of the exoskeleton improves several criteria, including kinematics and stability. In particular, the transition from 1 DoF to 2 DoF yielded a larger improvement than the transition from 2 DoF to 3 DoF, although the 3 DoF configuration produced the best overall results. Higher DoF configurations also resulted in stability values that resemble more closely those of walking without the exoskeleton, despite the added weight. Subjective feedback from participants corroborated these results, indicating the lowest discomfort with the 3 DoF ankle exoskeleton.