Cross four-bar linkage for the knees of a planar bipedal robot

Usually the bipedal robots use knee joints with only one degree of freedom. Several biomechanical researches have proved that the human knee joint is a complex joint with more than one degree of freedom. In the sagittal plane the human knee joint allows a rolling and a sliding of the thigh on the shin. In the case of a bipedal robot we propose a closed structure, called cross four-bar knee, which gives an additional degree of freedom in translation for the knee joint in the sagittal plane. Two different planar bipedal robots equipped of revolute knee joints and cross four-bar knees respectively are compared. For both bipedal robots we present the calculation of the dynamic model. A parametric optimization method is used to calculate the reference cyclic trajectories in order to compare the energy consumption of the two bipedal robots.