ESPI: Dynamic Safety Evaluation Index for Human-Exoskeleton System

Currently there are no specific medications for people with spinal cord injuries (SCI), and lower limb exoskeletons can improve their motor ability significantly to help them back to society. However, the human-exoskeleton system's safety is fragile, and there is no effective safety evaluation index. In this paper, the Enhanced Stability Pyramid Index (ESPI) is proposed to evaluate the system's safety, especially in a dynamic situation. To incorporate dynamic information of the system, this index employs eXtrapolated Center of Mass (XCoM) instead of the center of mass (CoM). Meanwhile, Time-to-Contact (TTC), the urgency of safety, is utilized as an automatic weight assignment factor instead of the traditional manual one. The system's current safety state can also be represented by scalar and vector to provide more information for the exoskeleton and pilot. Finally, the indicator's effectiveness is verified by the human-exoskeleton walking simulation controlled by the linear inverted pendulum in Gazebo.