A method for analyzing wearing uncertainties and enhancing motion transmission smoothness in exoskeletons and its applications for a novel passive knee exoskeleton

Abstract

It is suggested that exoskeletons may present challenges in terms of wearability due to unexpected human-machine interaction forces, usually caused by wearing uncertainties such as wearing slips, geometric differences in individual knees, and variable-axis knee movements. Additionally, the forces caused by drastic changes in velocity during exoskeleton locomotion may also be a contributing factor. To address these issues, this paper introduces a new passive knee exoskeleton and its human-machine wearing parallel (HMWP) research prototype to compensate and accommodate these uncertainties. Subsequently, a response interval analysis method based on Chebyshev functions is proposed to investigate the effect of uncertainties on the HMWP system's kinematic performance. In order to enhance the motion transmission smoothness, a new kinematic performance evaluation indicator is proposed, which considers solely the exoskeleton-configuration parameters. The response interval analysis method and new indicator are applied together in kinematic dimensional synthesis, resulting in significant improvements in the exoskeleton's kinematic performance. Furthermore, a parameter sensitivity analysis is conducted to facilitate more effective improvements to the exoskeleton's comfort. This research can also be used to improve the wearability of other wearable devices.