Effort Generation Capabilites Mapping for Personalized Robotic Assistance of the Elbow

This study explores the use of a robotic aid to improve the mobility of people with neuromuscular or neurodegenerative disorders, who have reduced motor skills. It aims to compare the use of either a musculoskeletal model or a torque-angle joint model in a shared control framework of an upper limb exoskeleton in order to assists elbow flexion/extension movements. The method consists of measuring the effort-generating capacities of the elbow using an isokinetic ergometer. Data were then used to calibrate the two models. Both were integrated into an exoskeleton control law to estimate online user isometric capacities during a mass-holding task performed in various positions. Four experimental conditions were compared: without exoskeleton, with exoskeleton without assistance, with assistance computed from the quadratic model and from the musculoskeletal model. In order to test the method against individual variability, the study was conducted with nine participants. The results show a decrease in muscular activity for the biceps in both assistance conditions. In extrapolating effort-generating capacities outside the ergometer's measured range, the musculoskeletal model is more robust than the torque-angle joint model. Its estimations are more consistent with the literature, while torque-angle joint model errors induces unintended triceps activation. In conclusion, this study highlights the potential of combining a musculoskeletal model with shared control for assisting elbow.