Figure 2.

Schematic diagram of (a) the shoulder and (b) the elbow modules. In the diagram, local frames, $\left\{O_0\right\}$, $\left\{O_1\right\}$, and $\left\{O_2\right\}$ are located on the center of the shoulder joint, the center of the elbow joint, and the attachment point between the forearm cuff and human forearm, respectively; the global frame $\left\{O_G\right\}$ is located at the center point of base cuff.