Sagittal gait synthesis for a five-link biped robot

This work presents a method for synthesising the gait of a planar five-link biped walking on level ground. Both the single support phase (SSP) and the double support phase (DSP) are considered. The compatible trajectories of the hip and the swing limb are first designed, which has the advantage of decoupling the biped into three subsystems, namely a trunk and two lower limbs and thus, substantially simplifies the problem. The hip and the swing limb trajectories are approximated with time polynomial functions and their coefficients are determined through the constraint equations cast in terms of coherent physical characteristics of gait. Special constraints are developed to eliminate the impact effect in spite of physical impact at the heel strike, which avoids the sudden jump of angular velocities and thus reduces the control difficulty. Other constraints considered in this work include the system stability during the DSP and repeatability of the gait. The effectiveness of the proposed method is confirmed by computer simulations.