How to keep from falling forward: elementary swing leg action for passive dynamic walkers

Abstract

Abstract-Stability control for walking bipeds has been considered a complex task. Even two-dimensional fore-aft stability in dynamic walking appears to be difficult to achieve. In this paper we prove the contrary, starting from the basic belief that in nature stability control must be the sum of a number of very simple rules. We study the global stability of the simplest walking model by determining the basin of attraction of the Poincaré map of this model. This shows that the walker, although stable, can only handle very small disturbances. It mostly falls, either forward or backward. We show that it is impossible for any form of swing leg control to solve backward falling. For the problem of forward falling, we devise a simple but very effective rule for swing leg action: "You will never fall forward if you put your swing leg fast enough in front of your stance leg. In order to prevent falling backward the next step, the swing leg shouldn't be too far in front." The effectiveness of this rule is demonstrated with our prototype "Mike."Index Terms-Legged locomotion, passive dynamic walking, reflex, swing leg control.

Energy efficient walking with central pattern generators: from passive dynamic walking to biologically inspired control

“…In a previous study we showed that there is indeed such a trade-off between energy consumption and robustness (Verdaasdonk et al 2007a) in a similar CPG-controlled bipedal walking model (although that one could not passively walk down a slope, because it had human inertial distribution). The study showed that the robustness against large perturbations is increased with the velocity of the swing leg, which agrees with the statement of Wisse et al (2005) that you will never fall forward if the swing leg is put fast enough in front of the stance leg. There are two methods to increase swing leg velocities and by that the robustness against large perturbations.…”

Optimization of energy efficiency of walking bipedal robots by use of elastic couplings in the form of mechanical springs

“…However, this is not a necessary measure [1]. The idea of adjusting the step frequency by a hip spring was also applied to prevent stumbling by shortening the swing phase of planar passive dynamic walking robots with trunk in simulation [41] and experiment [40].…”

Design of a biped robot actuated by pneumatic artificial muscles

“…It has high compliance and can provide large force with a lightweight mechanism. Wisse, et al built several biped robots with McKibben muscle actuators to walk on a flat floor, namely, Mike [11,12], Max [13], and Denise [14]. Hosoda and his research group also developed a series of pneumatic actuated biped robots [15][16][17][18][19][20][21][22][23].…”