Gait Generation of 6-DOF Biped Robot on Inclined Deformable Terrain Using Nonlinear Inverted Pendulum

Abstract

In this paper, a 6-DOF biped’s gait is generated based on the motion of the center of mass and the contact point of a nonlinear inverted pendulum (NIP). For walking on deformable terrain, the foot-terrain interaction is modeled using terrain stiffness and damping. The impact dynamics of the NIP model is used to obtain the curve of capture to stop the motion and the curve of equal local energy for walking with equal minimum velocity. The step length obtained from the intersection of the energy curve of the NIP and the terrain is used for the swing leg ankle trajectory. The center of mass and contact point trajectories of the NIP are used in the trajectory generation of the hip-link and the stance leg’s ankle, and the joint angles of the biped are obtained from the inverse kinematics. The floating-base dynamics is used to compare the actual and desired center of mass trajectories of the biped robot. The energy analysis of the biped validates the footstep planning on deformable terrain. The joint torques of the actuated joints are obtained from the inverse dynamics, and the actuation energy is shown to be negligible for energy-efficient walking. The dynamic stability of the biped’s gait is also analyzed based on the rotation of the foot on the deformable terrain.