Reducing Migration of Knee Exoskeletons With Dynamic Waist Strap

Abstract

Downward migration of knee exoskeletons under external forces is one major concern against their normal operations. It may be reduced by increasing the friction between exoskeletons and the human thigh. However, the effectiveness of friction control remains questionable, as the natural invertedcone shape of the human thigh will aggravate downward migration, and the overwhelming strapping intensity will degrade the activation level of muscles. In this paper, we propose a new suspension system called the Dynamic Waist Strap. Theoretical analysis and experimental validations on multiple subjects are conducted to show its advantages over the three mainstream suspension systems commonly used for knee exoskeletons in terms of the reduction of migration, interaction torque, and maximum dip angle. This study highlights the importance of the suspension system when attaching a knee exoskeleton to the human and introduces a new dynamic interaction interface to improve the coupling from a knee exoskeleton to an individual.

A Human Lower Limb Mechanical Phantom for the Testing of Knee Exoskeletons

“…Other mechanical phantoms use alternative materials such as polyurethane gels and polyether foam rubber to simulate soft-tissue deformation and interface friction [47], [48]. Because exoskeleton migration across the lower limb would affect the assistive movement, devices tested on the ballistic gel phantom should measure if there is migration and reduce it accordingly [49]. In the experiments here, we assumed that exoskeleton assistance does not affect the joint kinematics of walking.…”

Mechatronic Design and Control of a Rigid-Soft Hybrid Knee Exoskeleton for Gait Intervention

“…Several studies attempted to address this issue by designing self-alignment joint mechanisms or adding passive DoFs [16], [17], [18], [19], [20], or using curved guide rail [21], but those designs only work on sagittal plane and/or frontal plane and meanwhile add extra weight. In addition, the migration of the exoskeleton along the leg due to its large weight also leads to misalignment [22].…”