  In this paper, 3D humanoid walking is decoupled into periodic and
transitional motion, each of which is decoupled into planar walking in the
sagittal and lateral plane. Reduced order models (ROMs), i.e. actuated
Spring-loaded Inverted Pendulum (aSLIP) models and Hybrid-Linear Inverted
Pendulum (H-LIP) models, are utilized for motion generation on the desired
center of mass (COM) dynamics for each type of planar motion. The periodic
motion is planned via point foot (underactuated) ROMs for dynamic motion with
minimum ankle actuation, while the transitional motion is planned via
foot-actuated ROMs for fast and smooth transition. Composition of the planar
COM dynamics yields the desired COM dynamics in 3D, which is embedded on the
humanoid via control Lyapunov function based Quadratic programs (CLF-QPs).
Additionally, the ground reaction force profiles of the aSLIP walking are used
as desired references for ground contact forces in the CLF-QPs for smooth
domain transitions. The proposed framework is realized on a lower-limb
exoskeleton in simulation wherein different walking motions are achieved.
