2018 年 53 巻 8 号 p. 605-614
We have proposed a fast stair-climbing robot with a simple hopping mechanism. The robot, which consists of two (upper and lower) bodies connected by springs and wire, travels using wheels mounted on its lower body, and hops to climb stairs by releasing energy stored in the springs. The trajectories of the bodies during hopping depend on the design and control parameters. The former are the two body masses and the spring constant, which cannot be changed after fabrication. The latter are the initial spring contraction and horizontal velocity, which can be changed during locomotion. This mechanism allows the robot to climb stairs quickly and to land softly without complicated feedback control. In our previous research, we analyzed a defined soft landing point, i.e., a no-impact landing point (mathematically, a stationary, inflection, and descending point on the lower-body trajectory), using equations of motion, clarified the conditions, and showed the existence characteristics that the point is created by the friction during the spring contraction phase. On the basis of this result, we fabricated the stair-climbing robot and realized fast stair climbing and soft landing. However, the robot cannot climb any stairs with riser heights other than the predetermined riser value. In this paper, to achieve soft landing for multiple riser heights, we analyze how many soft landing points can be creatable by changing only the control parameters using identical design parameters. It is shown that an infinite number of solution sets creating two soft landing points exist, a unique solution set creating three soft landing points exists, and no solution set creating more than three soft landing points exists. Additionally, a numerical simulation showed that these parameters had values in a practical design range.
