Fig. 4
Definition of frames, angles and floating base states variables of the exoskeleton. The thick black lines represent the link of one leg of the exoskeleton viewed from the side (sagittal plane). The joints (hip, knee and ankle are indicated by black circles. The lever arms of the actuated joints are indicated by purple bars. The frame of each link is shown in a different color with all z-axes pointing outward of the paper. The link angles ϕi and the lever arm angles θi are defined starting from the previous link (=reference link) and according to the right hand rule. The knee joint and lever arm angle are thus negative in this configuration. px and py represent the position of the center of mass of the floating base link, the pelvis link. The angle ψ is the angle of the floating base with respect to the world frame