Kinematic Interactions between a Human Musculoskeletal Model and a Lower Limb Exoskeleton

Abstract The requirement and applicability of exoskeletons for rehabilitation has been indicated by the amount of efforts invested in research across the world in the past decades. However, commercial exoskeletons are still expensive and limited by the need for adjusting the structure to the individual user. In this study, the human-exoskeleton interactions are explored by designing a lower limb exoskeleton with ten degrees of freedom: six actuated and four passive. Finite element analysis (FEA) of the structure is carried out to observe that the structural design is able to withstand the operating loads. Furthermore, the model is imported to Opensim software and connected with the human musculoskeletal model at the locations where both bodies would be connected in a real scenario, using braces and straps. The connections between the human and exoskele-ton models are modelled as six degrees of freedom joints with limits. Data of two subjects from an openly available gait data-set is used to carry out kinematic simulations. Comparison of five cases: human without an exoskeleton, human-exoskeleton combined, human-exoskeleton combined with locked hip adduction, human-exoskeleton combined with locked hip rotation, and human-exoskeleton combined with locked hip adduction and rotation, proved that the absence of degrees of freedom from the exoskeleton affects and restricts the motion of joints while trying to execute the same walking movement. The amount of movement at the interfaces is estimated by the simulation results. Therefore, a new approach for simulating humanex-oskeleton combined model is presented here.