Abstract :
level of humanoid skill. Autonomy, with respect to the processing of information, is realized to a relatively high
degree. What is mainly lacking in robotics, moving from purely anthropomorphic robots to ‘anthropofunctional’
machines, is energetic autonomy. In a previously published analysis, we showed that closer attention to the
functional morphology of human walking could give robotic engineers the experiences of an at least 6 Myr beta test
period on minimization of power requirements for biped locomotion. From our point of view, there are two main
features that facilitate sustained walking in modern humans. The first main feature is the existence of ‘energetically
optimal velocities’ provided by the systematic use of various resonance mechanisms: (a) suspended pendula (involving
arms as well as legs in the swing phase of the gait cycle) and matching of the pendular length of the upper and lower
limbs; (b) inverted pendula (involving the legs in the stance phase), driven by torsional springs around the ankle joints;
and (c) torsional springs in the trunk. The second main feature is compensation for undesirable torques induced
by the inertial properties of the swinging extremities: (a) mass distribution in the trunk characterized by maximized
mass moments of inertia; (b) lever arms of joint forces at the hip and shoulder, which are inversely proportional to
their amplitude; and (c) twisting of the trunk, especially torsion. Our qualitative conclusions are three-fold. (1) Human
walking is an interplay between masses, gravity and elasticity, which is modulated by musculature. Rigid body
mechanics is insufficient to describe human walking. Thus anthropomorphic robots completely following the
rules of rigid body mechanics cannot be functionally humanoid. (2) Humans are vertebrates. Thus, anthropomorphic
robots that do not use the trunk for purposes of motion are not truly humanoid. (3) The occurrence of a waist,
especially characteristic of humans, implies the existence of rotations between the upper trunk (head, neck, pectoral
girdle and thorax) and the lower trunk (pelvic girdle) via an elastic joint (spine, paravertebral and abdominal
musculature). A torsional twist around longitudinal axes seems to be the most important.
