Contribution of actuated head and trunk to passive walkers stabilization

Passivity-based walkers represent a model for human walking and a solution for low-energy locomotion for humanoid robots. The presence of an upper-body and even a head in this kind of systems is necessary as a better model for humans and to improve their usability. The benefits of these additions have never been studied, and no work experimented the addition of a head limb to a passivity-based walker. So, we aim, in this paper, to study the effects of the addition of these modifications on walkers with fully passive lower limbs. By comparing three systems (a passive compass, an upper-body stabilizing walker and a head stabilizing walker) simulations show that: (ii) upper-body stabilization improves the stability of the walking limit cycle; (ii) in return, the stabilization of the upper body requires a noticeable amount of the kinetic energy of the walker, and a significant energy supply (steeper slopes for the passive case) is necessary to guarantee the stability of the gait, especially for the case of head stabilization; and (iii) in a dynamical context, such as steep slopes, the upper-body and head stabilization have close performances for absorbing perturbations and smoothing the impacts, but with a slight advantage for the latter.