Systematic Evaluation of Hip Exoskeleton Assistance Parameters for Enhancing Gait Stability During Ground Slip Perturbations

2026-01-21

AI Summary

This study addresses the limitations of existing lower-limb exoskeleton controllers, which predominantly prioritize energy efficiency while neglecting reactive stability under slip-like perturbations. Focusing on a bilateral hip exoskeleton, the work systematically modulates assistance magnitude and duration, employing whole-body angular momentum (WBAM) as a quantitative metric for gait stability. It reveals, for the first time, the critical influence of assistance duration on stability, arguing that stability optimization should extend beyond conventional energy-based criteria and incorporate personalized parameter tuning. Experimental results demonstrate that stability-optimized control parameters reduce WBAM fluctuations by an average of 25.7% compared to energy-optimal settings, with substantial inter-subject variability in optimal parameters, thereby validating the efficacy of individualized control strategies.

Technology Category

• Intelligent Robots: Behavior Learning & Control
• Constraint Satisfaction and Optimization: Constraint Optimization
• Humans and AI: Human-Aware Planning and Behavior Prediction

Application Category

• User Modeling, Personalization and Recommendation: Studies of user behavior, including longitudinal effects of personalized systems
• Responsible Web: Machine-in-the-loop, human agency and autonomy
• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments

Abstract

Falls are the leading cause of injury related hospitalization and mortality among older adults. Consequently, mitigating age-related declines in gait stability and reducing fall risk during walking is a critical goal for assistive devices. Lower-limb exoskeletons have the potential to support users in maintaining stability during walking. However, most exoskeleton controllers are optimized to reduce the energetic cost of walking rather than to improve stability. While some studies report stability benefits with assistance, the effects of specific parameters, such as assistance magnitude and duration, remain unexplored. To address this gap, we systematically modulated the magnitude and duration of torque provided by a bilateral hip exoskeleton during slip perturbations in eight healthy adults, quantifying stability using whole-body angular momentum (WBAM). WBAM responses were governed by a significant interaction between assistance magnitude and duration, with duration determining whether exoskeleton assistance was stabilizing or destabilizing relative to not wearing the exoskeleton device. Compared to an existing energy-optimized controller, experimentally identified stability-optimal parameters reduced WBAM range by 25.7% on average. Notably, substantial inter-subject variability was observed in the parameter combinations that minimized WBAM during perturbations. We found that optimizing exoskeleton assistance for energetic outcomes alone is insufficient for improving reactive stability during gait perturbations. Stability-focused exoskeleton control should prioritize temporal assistance parameters and include user-specific personalization. This study represents an important step toward personalized, stability-focused exoskeleton control, with direct implications for improving stability and reducing fall risk in older adults.

Problem

• gait stability
• slip perturbations
• hip exoskeleton
• fall risk
• reactive stability

Innovation

• hip exoskeleton
• gait stability
• slip perturbation
• whole-body angular momentum
• personalized control