Simulation of spring uses in an ankle exoskeleton during human gait

Abstract: Background:Approximately 15% of the world’s population are affected bysome kind of disability where over 150 conditions may affect the human gaitpattern. The ability to ambulate with ease is important for overall well-being.Various assistive devices have been developed to improve mobility of theirusers. A lot of research is currently focused on ankle exoskeletons, showingpromising results in providing important assistance during stance phase of gait. Objective:To investigate how different combinations of active and passiveelements in an ankle exoskeleton affects the metabolic cost of walking. Methods:Musculoskeletal simulations were carried out in OpenSim Moco.Different assistive configurations were tested over one gait cycle using a pas-sive element, an active element, and a parallel connection of the both. Parame-ter values were modified to find the most optimal setup for reducing metaboliccost. Results:All assistive configurations were found successful in reducing bothwhole-body metabolic cost and the metabolic cost of the plantarflexors whencompared to the unassisted gait. Most whole-body metabolic cost reductionwas found when using a passive spring with resting length of 0.28 m and stiff-ness of 6 kN/m in parallel with an active motor capable of providing forceequal to 150% of body weight. The most reduction in metabolic cost of theplantarflexors was also found for a parallel connection of elements, but herewith a 100% body weight motor and spring with rest length of 0.19 m andstiffness of 10 kN/m. With higher assistance, more reduction in ankle mo-ment generated by the muscles was observed. Conclusion:Powered ankle exoskeletons are promising in terms of minimiz-ing metabolic cost during walking due to assistance during late stance phaseof gait for ambulators requiring plantarflexor assistance. Keywords:Simulation, exoskeleton, ankle, moco.