In context
In early 2024, lower-limb exoskeletons were advancing for medical rehabilitation and human augmentation, yet most stability criteria, such as ZMP, treated the human-exoskeleton system as a single entity, overlooking the critical human-robot interaction force. This gap limited the reliability of dynamic stability assessment in real walking scenarios.
What was reported
Researchers from Anhui Polytechnic University and Wuhu Yunqing Robotics Technology proposed a stability identification and speed optimization method that explicitly considers human-robot interaction force. They built inverted pendulum models for human walking and human-robot cooperative walking, then indirectly expressed the interaction force by fusing centroid acceleration and plantar pressure data, avoiding direct measurement errors. This led to a CoM-CoP-CoA (center of mass, center of pressure, composition of acceleration) mathematical expression.
Using a regional comparison method, they formulated a matrix-inequality-based stability criterion for exoskeleton walking. Additionally, they introduced a stability margin evaluation function to optimize walking speed. Experiments with human-robot cooperative walking at three different speeds validated the approach, showing it could effectively discriminate stability and determine an optimal speed.
The exoskeleton featured hydraulically driven hip and knee joints with passive ankle joints, and each foot had four plantar pressure sensors placed in key regions to compute the CoP.
Why it mattered
By incorporating human-robot interaction force into stability analysis, this work addressed a known limitation of ZMP-based criteria, potentially improving the safety and comfort of assistive exoskeletons in industrial and rehabilitation settings. The proposed method lays groundwork for fall-prevention control strategies.
“The proposed stability criterion and evaluation function can effectively discriminate the stability of exoskeleton walking and optimize the walking speed.”
Source: 《机器人》期刊 (robot.sia.cn) · Published 2024-02-04 · “下肢外骨骼机器人交互力激励估计与稳定性分析”