Journal of Bionic Engineering (2023) 20:57–68  https://doi.org/10.1007/s42235-022-00245-6 

Limb Stifness Improvement of the Robot WAREC-1R for a Faster and Stable New Ladder Climbing Gait 

Xiao Sun1  · Akira Ito2  · Takashi Matsuzawa2  · Atsuo Takanishi2 

1 Department of Mechatronics, University of Yamanashi, Yamanashi 400-8511, Japan
2 Faculty of Science and Engineering, Waseda University, Tokyo 162-8480, Japan

Abstract  Ladder climbing is a relatively new but practical locomotion style for robots. Unfortunately, due to their size and weight, ladder climbing by human-sized robots developed so far is struggling with the speedup of ladder climbing motion itself. Therefore, in this paper, a new ladder climbing gait for the robot WAREC-1R is proposed by the authors, which is both faster than the former ones and stable. However, to realize such a gait, a point that has to be taken into consideration is the deformation caused by the self-weight of the robot. To deal with this issue, extra hardware (sensor) and software (position and force control) systems and extra time for sensing and calculation were required. For a complete solution without any complicated systems and time only for deformation compensation, limb stifness improvement plan by the minimal design change of mechanical parts of the robot is also proposed by the authors, with a thorough study about deformation distribution in the robot. With redesigned parts, ladder climbing experiments by WAREC-1R proved that both the new ladder climbing gait and the limb stifness improvement are successful, and the reduced deformation is very close to the estimated value as well. 

Keywords  Ladder climbing · Legged robot · Bionic robot · Gait · Stifness improvement · Finite element analysis

Fig. 1 Overview and DoF confguration of WAREC-1R