Abstract: This paper proposes a system for stable ladder climbing of the human-sized four-limbed robot “WAREC-1”, including the following 3 components: (a) Whole-body motion planning; (b) Rung recognition system and (c) Reaction force adjustment. These 3 components guarantee appropriate ladder climbing motion, successful rung grub and proper reaction force distribution at contact points throughout the climbing motion, respectively. With this system, (1) Stable ladder climbing in 2-point contact gait by a human-sized robot and (2) Successful and stable climbing of an irregular ladder (with a higher or inclined rung) in both 3-point and 2-point contact gait with the capability of recognizing the target rung and the corresponding motion planning are realized, which have rarely been realized by former studies. Finally, experiment results and data of the robot ladder climbing are also presented to evaluate the proposed system. 

Key words: legged robot, ladder climbing, stability, proximity sensor feedback, force control