Figure 2.

Geometric model the developed soft ankle rehabilitation robot (ARBOT). Define O_f is coordinate of fixed platform and the rotation center of end effector is denoted by O_m, ${\mathit{\text{P}}}_{\mathit{\text{i}}}^{\mathit{\text{f}}}$ and ${\mathit{\text{P}}}_{\mathit{\text{i}}}^{\mathit{\text{m}}}$ are the connection point vectors of the upper fixed platform and the lower moving platform, respectively.