The parallel ankle robot developed by Tsoi et al. [16
]: (a) the robot with six DOFs without the leg holder, (b) the robot with three rotational DOFs with the shank attached to the leg holder, and (c) the robot in a tilted position. The blue arrow line refers to the slide direction due to gravity; the blue dots represent the ankle joint. A: the moving platform; B: the fixed platform; C: leg holder; D: spherical joint.