The gait assistance in both lateral and sagittal plane is provided
under nine states, defining the movements of left and right legs
separately and coordinately. The state transitions are triggered
in two types: stop–start walking and step-to-step transitions are
triggered by the user command, while transitions from stance
to swing to double stance are automatic. During stance/double
stance phases, the joints trajectories are predefined to keep the
user-exoskeleton system in a equilibrium posture. In sagittal
plane, during swing phase, the hip and knee joints trajectories
are predefined by recording the gait patterns of a healthy people
walking with MINDWALKER in zero assistance mode. In lateral
plane, before toe off, the hip a/a joints shift the Center of Mass
(CoM) to the stance side, and move back to their zero positions
before heel strike. To prevent the user falling sideways, the hip a/a
is also adjustable online by using an XCoM algorithm (extrapolated
CoM, suggesting a simple form to enable balance walk) [35].