This paper focuses on assessing gait stability by metrics derived from dynamical systems theory to understand the influence of unilateral robot assistance on the human walking pattern. A motorized assistive robot is applied to the right knee joint to provide stance support. The metrics related to global stability (the maximum Floquet multiplier, max FM), local stability ( short-term and long-term divergence exponents, λs and λl), and variability (median absolute deviation, MAD) are considered. These metrics are derived for bilateral hip, knee, and ankle joint angles. Additionally, a biomechanical metric, the minimum margin of stability is assessed. Experiments are conducted on 11 healthy participants with different robot controllers. The max FM and λs yield statistically significant results, showing that the unassisted (left) leg is more stable in right knee assistance conditions when compared to the normal walking condition due to inter-limb coordination. Moreover, MAD and λl show that the variability and chaotic order of walking pattern during assistance are lower than those of normal walking. The proposed control strategy (automatic impedance tuning, AIT) improves local and orbital gait stability compared to existing controllers such as finite-state machine (FSM). The assessment of dynamic gait stability presented in this paper provides insights for further improving control strategies of assistive robots to help a user reach improved gait stability while maintaining appropriate variability.

中文翻译：

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使用下肢辅助装置评估人体动态步态稳定性


本文重点通过动力系统理论导出的指标来评估步态稳定性，以了解单侧机器人辅助对人类行走模式的影响。电动辅助机器人应用于右膝关节以提供站立支撑。考虑与全局稳定性（最大 Floquet 乘数，最大 FM）、局部稳定性（短期和长期散度指数，λs 和 λl）以及变异性（中值绝对偏差，MAD）相关的指标。这些指标是根据双侧髋关节、膝关节和踝关节角度得出的。此外，还通过生物力学指标评估最小稳定性裕度。使用不同的机器人控制器对 11 名健康参与者进行了实验。最大 FM 和 λs 产生统计上显着的结果，表明由于四肢间的协调，与正常行走条件相比，无辅助（左）腿在右膝辅助条件下更加稳定。此外，MAD和λl表明，辅助期间步行模式的变异性和混乱顺序低于正常步行。与有限状态机（FSM）等现有控制器相比，所提出的控制策略（自动阻抗调整，AIT）提高了局部和轨道步态稳定性。本文提出的动态步态稳定性评估为进一步改进辅助机器人的控制策略提供了见解，以帮助用户在保持适当的可变性的同时提高步态稳定性。