Improved biped walking performance around the kinematic singularities of biomimetic four-bar knees

This paper studies the effects of replacing pin-joint knees in passive dynamic bipedal walkers with biomimetic four-bar knees. The kinetic model of the four-bar knees is presented in detail, and an analytical model of the passive walking dynamics is derived. The resulting four-bar kneed biped is compared with a pin-joint kneed walker, for their passive walking performance. The geometry of the four-bar knees used in the study is based on human anatomical data. It is found that the biomimetic four-bar knee configuration works to the advantage of the biped, especially around the extended-knee singular position. The four-bar knees are found to overperform the pin-joint ones, resulting in significant reduction of peak impact loads and energetic expenditure.