Special Issue on Legged Locomotion

Walking is a form of locomotion that is gentle to the environment, and by means of this action, it is possible to move through a variety of environments. In other words, the system of locomotion called walking allows a mover to go through almost any environment while choosing landing points for providing better supporting points, without hurting the environment. On the other hand, the smooth locomotion by wheel is possible only when a road is created by giving a human touch to the natural environment. Moreover, the crawler system using caterpillars creates problems such as the floors and stairs being hurt or the pipes laid on the floors being crushed, although it does have huge locomotive capacity. In addition, a robot capable of working on the bottom of the sea is now desired. However, the use of a screw as a system of locomotion for the robot would create the problem of stirring up various deposits on the bottom and thereby losing its field of vision. Against this background, a large number of walking robots have been developed in recent years for work inside nuclear power plants, the exploration of planets, work on the sea bottom, and work inside forests. In particular, a six-legged robot by Ohio State University, a 6-legged robot for the exploration of Mars by Carnegie Mellon University, and a bi-armed quadruped robot for extreme work created in Japan have all been developed under large walking robot development projects. Because of these large-scale projects, the studies on walking robots have shown remarkable progress in recent years. On the other hand, the investigation from the points of view of control engineering and robotics of how walking controls are performed by the humans and animals presents a very interesting subject, and accordingly a great many studies are being conducted. The normal walking that the humans and animals do forms stable locomotion as a whole by repeating unstable locomotion. In other words, the walking with its static stability constantly maintained is hardly done except in the case of very slow walking. Studies on such dynamic walking have been started relatively recently, and the elucidation of this type of walking has been very fragmentary. In addition, studies for realizing such walking (or running) by robots have been started only very recently, and are therefore at an initial stage as yet. The studies concerning walking by the humans and animals have been carried out, on one hand, from the point of view of dynamics and, on the other hand, from the point of view of trying to make clear how the nervous systems and control circuits which support walking are composed and what operational mechanisms they have. From the latter point of view, studies concerning the pattern generator of walking motion and studies on walk controls using neural networks have increased sharply in recent years. Thus, to have made plans for a special issue on walking robots at this point in time is considered most opportune. Deep appreciation is expressed to those researchers who have contributed their papers to this special issue, and it is hoped, moreover, that the special issue will provide contributions to future studies on walking robots.