Influence of a Compatible Design on Physical Human-Robot Interaction Force: a Case Study of a Self-Adapting Lower-Limb Exoskeleton Mechanism

In the kinematic design of wearable exoskeletons, the issue of axis misalignments between the human and the exoskeleton joints should be well dealt with. Otherwise, large physical human-robot interaction (p-HRI) forces may occur at the human-robot interfaces, which makes the p-HRI uncomfortable or even unsafe. To cope with this issue, a kinematically compatible design approach of wearable exoskeletons has been investigated by researchers, and great development has been made in recent years. Moreover, the influence of such a design on the exoskeleton's p-HRI performance should be evaluated to determine if the design is feasible. In this paper, a self-adapting lower-limb exoskeleton mechanism for three degrees of freedom gait training is proposed, and the mechanical structure of the exoskeleton mechanism is designed in detail. Then, based on the presented exoskeleton mechanism and the use of suitable force/torque sensors, a p-HRI force measurement system is developed. Subsequently, the p-HRI forces of the human-robot closed chain under the static and motion modes are detected, and the influence of the self-adapting design on the lower-limb exoskeleton mechanism's p-HRI force feature is evaluated. The results indicate that additional human-robot connective joints could reduce the p-HRI force significantly, the compatible design of the exoskeleton mechanism is effective, and is thus applied to human lower-limb gait training.