## 4 Experiments
### Grasp Motion Verification Experiment  
The purpose of this experiment was to test the hand motion performance. That is, to verify whether the hand could achieve the 13 grasp motions as expected. A prototype hand was developed. It was fixed using a vise to perform grasp tasks through a motor controller. The objects used are presented in Table 2. Moreover, Table 3 summarizes the experimental results corresponding to each grasp motion.  
The experimental results demonstrate that the prosthetic hand can realize 13 grasps, as expected. As indicated in Table 3, from top to bottom.  
The easiest grasp is the platform push (grasp 15), as the four fingers simply extend owing to the elastic tendons. Furthermore, the metacarpals of the ring finger, little finger, and thumb form a plane to support the object.  
The lateral Pinch (grasp 16) is a type of lateral grasp, which requires position adjustment of the thumb. The prosthetic hand includes an independent motor to drive thumb adduction or abduction. Thus, it can also adjust the thumb position in different lateral grasps. Although the metacarpals of the ring finger and little finger flex to form an arch along with the thumb, they will not obstruct the lateral grasp, as they are not in the same contact area.  
In the circular grasps, the disk (grasp 10) power grasp is not achievable for the prosthetic hand, because the stable flexion transmission of the four fingers cannot drive the PIP and DIP joints independently, and the MP joints are ignored. However, the remaining grasps of sphere (grasp 11), disk (grasp 12), sphere (grasp 13), and tripod (grasp 14) are easy to realize, owing to the adaptive flexion of the thumb, stable flexion of the four fingers, and arch function.  
In the prismatic grasps, only thumb-4 finger (grasp 6) and thumb-3 finger (grasp 7) cannot be realized, because the metacarpals form an arch along with the thumb adduction movement, in which the ring and little fingertips cannot remain in one straight line (as in grasp 6). Furthermore, as the metacarpals of the ring and little fingers always move together as a unit, it is impossible to obtain a posture of three fingertips in one line (as in grasp 7). Although thumb-2 finger (grasp 8) and thumb-index finger (grasp 9) also require the fingertips to contact the object, only two fingers and one finger are necessary, respectively. Hence, the thumb with the adaptive function can adjust the contact position in grasping. Furthermore, the medium wrap (grasp 3), adducted thumb (grasp 4),  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Object** & **Weight [g]** & **Shape** & **Size [mm]** \\ \hline Card & 4.0 & Thin plate & 54.0 \(\times\) 85.7 \(\times\) 0.6 \\ Wood block & 34.5 & Cylinder & \(\varnothing\)29.4 \(\times\) 119.6 \\ Sponge ball & 24.8 & Sphere & \(\varnothing\)65.6 \\ Foam balls (small) & 0.7 & Ellipsoid & \(\varnothing\)137.0 \(\varnothing\)230.0 \\ Foam balls (big) & 1.7 & Sphere & \(\varnothing\)249.4 \\ PET bottle & 16.6 & Cylinder & \(\varnothing\)66.4 \(\times\) 162.5 \\ Mark pen (big size) & 8.3 & Cylinder & \(\varnothing\)10.5 \(\times\) 141.0 \\ Mark pen (small size) & 12.1 & Cylinder & \(\varnothing\)17.0 \(\times\) 118.0 \\ \hline \hline \end{tabular}
\end{table}
Table 2: List of experimental objects.  
and light tool (grasp 5) are very similar, in which the four fingers are completely flexed to surround the object, but with a slightly different thumb position. Thus, these are easy to realize, owing to the stable function of the four fingers and adaptive function of the thumb.  
Finally, large diameter (grasp 1) and small diameter (grasp 2) are similar to medium wrap (grasp 3). Thus, they can be realized in a similar manner.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & & & \\  & & & \\  & & & \\  & & & \\  & & & \\  & & & \\ \end{tabular}
\end{table}
Table 3: Achievable motion types.