The knee of biped robots has usually one degree of freedom which one is a revolute joint. This work focuses on the study of rolling contact knee. The knee is composed of a cylinder in the extremity of the femur, rolling on another cylindrical surface which is the tibia. Studies have shown that this structure allows to reduce the torque during the gait. Energetic optimization series were made with this structure and for different cylinder radii. The angular trajectories describing the gait are generated by cubic splines functions. The gait is composed of single support phase followed by an impact. The minimization of energetic criterion is realized using the Simplex algorithm of Nelder-Mead. The results show that higher radii of the tibia permit to reduce energy consumption during the gait. The study of new contact surfaces is a way to decrease the energy consumption.
