Dynamics and control of bipedal locomotion.

The human frame is built for walking. It has both the right kinematics and the right dynamics--so much so, in fact, that our legs are capable of walking without any motor control. Their gait can be sustained simply by interaction of gravity and inertia, in a natural limit cycle which we call passive dynamic walking. This cycle needs motor input only for starting and stopping, for modulation when terrain calls for irregular strides, and for energy supply when the need arises. Analytical study reveals that any of several simple control strategies are effective for these purposes. This helps to explain why dextrous and efficient walking is so easy to a child to master. Moreover, it suggests that rehabilitation and robot design may be less difficult than one might at first imagine.