An Improved Trajectory of a Bipedal Robot Walking along a Step with the Dual Length Linear Inverted Pendulum Method

This paper proposes a new design method for obtaining walking parameters for a 3-D biped robot walking along a step. Many researchers concentrated only on the motion of climbing up or down stairs. However, this study investigates a strategy for realizing walking along a step. In conventional methods, the center of mass (CoM) moves up or down during walking in this situation because the pendulum height is kept at the same length for the left and right legs. Thus, extra work is required in order to bring the CoM up to higher ground. In this study, different pendulum heights are applied for the left and right legs and this method is referred to as the dual length linear inverted pendulum method (DLLIPM). However, when different pendulum heights are applied, it is quite difficult to obtain symmetrical and smooth pendulum motions. Furthermore, synchronization between the sagittal and lateral planes is not confirmed. Therefore, DLLIPM with the Newton-Raphson algorithm is proposed to solve these problems. The walking pattern for both planes is designed systematically, and synchronization between the planes is ensured. Finally, the proposed method is verified by simulation and experimental results.