An Investigation on the Usefulness of Employing a Two-Segment Foot for Traversing Stairs

In this paper, effects of employing toe-off and heel-contact gait phases on the performance of bipedal robots traversing stairs are examined. The main goal is to demonstrate the hypothesis that employing toes and heels during walking up and down stairs improves the gait performance in terms of actuating joint torques and energy consumption. For this purpose, a comprehensive dynamics model for a 3D biped robot is developed and the inverse dynamics solutions during various walking phases are presented. To realize walking up and down stairs, a zero moment point (ZMP)-based pattern generation routine in the task space is proposed. In this routine, first, trajectories for the feet and the pelvis in the task space are designed to realize the desired task and preserve the feasibility constraints. Then, consistent with the topology of walking, suitable trajectory for the toe joint is generated. To examine the effects of heel-contact and toe-off gait phases, three walking topologies for walking up stairs and four walking topologies for walking down stairs, depending on the use of toe-off and heel-contact motions, are considered. For these topologies, the optimization procedure is conducted to yield the optimal patterns. Finally, the obtained patterns are compared in terms of energy consumption and joint torques, while obtained results show a significant improvement in the gait performance in terms of considered cost functions.