“…In our recent work (Kim et al, 2009b), second-derivatives of the six joint coordinates in the lower body under actuation of the three-type joints have been derived like the following: 2 1 2 12 2 1 2 12 2 1 2 12 , , , , , , such that the swaying foot should land on the desired position, the tip of swaying foot should be always higher than the ground, all the joint motors should rotate within their rotation angle limits, and ZMP should be located inside the convex hull of supporting foot area as much as possible while walking. This work updates the previous ones by recalculating kinematics suited to the three-dimensional model and by elaborating the cost function for walking with variable speed.…”