This paper presents a bio-inspired dynamic leg model with a novel variable stiffness element to create a normal body motion during stance phase. The variable stiffness in the model is implemented through structure-controlled stiffness. It allows to decouple the stiffness from joint motion, which makes the stiffness a independent variable. Sensitivity of leg model to the variable stiffness element is investigated through dynamics analysis. Because of the decoupled structure of dynamics equations, the deflection of ankle joint related to variable stiffness element is planned based on generalized forced vibration motion in order to create the leg’s motion. A detailed study to investigate the dynamic characteristics under different generalized vibration parameters, and the desired variable stiffness function are evaluated. It is found that under the effects of variable stiffness, the ground reaction forces of leg model during stance motion have similar characteristics to those observed for mammals. Furthermore, in order to create a normal motion during stance phase, linear stiffness variation characteristics and small stiffness range are needed for the proposed variable stiffness actuator.

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