Abstract
Due to the complexity and high degrees of freedom, the detailed assessment of human biomechanics is necessary for the design and optimization of an effective exoskeleton. In this paper, we present full kinematics, dynamics, and biomechanics assessment of unpowered exoskeleton augmentation for human running gait. To do so, the considered case study is the assistive torque profile of I-RUN. Our approach is using some extensive data-driven OpenSim simulation results employing a generic lower limb model with 92-muscles and 29-DOF. In the simulation, it is observed that exoskeleton augmentation leads to 4.62% metabolic rate reduction for the stiffness coefficient of alpha ^*=0.6. Moreover, this optimum stiffness coefficient minimizes the biological hip moment by 26%. The optimum stiffness coefficient (alpha ^*=0.6) also reduces the average force of four major hip muscles, i.e., Psoas, Gluteus Maximus, Rectus Femoris, and Semimembranosus. The effect of assistive torque profile on the muscles’ fatigue is also studied. Interestingly, it is observed that at alpha ^{#}=0.8, both all 92 lower limb muscles’ fatigue and two hip major mono-articular muscles’ fatigue have the maximum reduction. This result re-confirm our hypothesis that ”reducing the forces of two antagonistic mono-articular muscles is sufficient for involved muscles’ total fatigue reduction.” Finally, the relation between the amount of metabolic rate reduction and kinematics of hip joint is examined carefully where for the first time, we present a reliable kinematic index for prediction of the metabolic rate reduction by I-RUN augmentation. This index not only explains individual differences in metabolic rate reduction but also provides a quantitative measure for training the subjects to maximize their benefits from I-RUN.
Highlights
Due to the complexity and high degrees of freedom, the detailed assessment of human biomechanics is necessary for the design and optimization of an effective exoskeleton
The optimal spring coefficient is close to one, which we previously reported in the I-RUN paper
We showed that the best assistive torque profile for reducing the joint biological moment and muscles’ force is the assistive torque profile that minimizes the biological torque without changing its sign
Summary
Due to the complexity and high degrees of freedom, the detailed assessment of human biomechanics is necessary for the design and optimization of an effective exoskeleton. As a result, (1) adaptation of compliant elements (devising a semi-passive exoskeleton)[20,21] as well as (2) modification of subjects’ kinematic by training[4] are two solutions for improving the performance of a full-passive exoskeleton To materialize these two approaches for an assistive device, a low-cost and simple compliance adaptation method and a quantitative straight-forward kinematic measure for subject training are required. Based on simulation results, it is suggested that a shifted exoskeleton torque profile for the hip joint is very effective for reducing the metabolic cost of running[27]; based on that, an active exosuit device was d evised[30] As another example, Jackson et al.[29] explained the exoskeleton effects on the biomechanical parameters by a forward simulation approach
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