# Design of Shape Memory Alloy-Based Soft Wearable Robot for Assisting Wrist Motion
## 3 Design of Soft Wrist Assist (SWA)
### User Test  
Wearability and ROM are also the important factors that have to be considered, as the SWA is focused on patients who have difficulties in manipulating the wrist. To observe the performances in these factors, several experiments were conducted. In all experiments, five healthy subjects (all male), with no impairment in the upper arm, were tested. Tests were conducted after obtaining informed consent from the participants. The average ages of the subjects are 24.2 years.  
The ROM in the four directions were measured by the use of image capture, similar to the motion capture measurement [64]. The markers were attached to the wrist joint, hand, and forearm respectively, and the ROM was measured by calculating the angles formed by these three markers after the device was maximally rotated. In the experiment, the subjects were instructed to relax their wrist. Therefore, the wrist motion was made passively only by the robot. Figure 10a shows the average ROMs for the four wrist motions. The average ROMs of five subjects were 33.8, 30.4, 21.4, and 15.4 degrees for flexion, extension, radial deviation, and ulnar deviation respectively. The greatest ROM was measured in flexion motion, while the smallest ROM was measured in ulnar deviation motion. The standard deviations of the ROM of flexion and extension motion are around 13, which is the directions that have large ROM. The lowest standard deviation is observed in ulnar deviation, around 3.  
The ROM produced by the robot showed variation depending on the person wearing it since the size of the wrist, arm and hand of each person is different from the rest. Additionally, the difference due to the passive stiffness of the wrist of each individual can be another factor that accounts for the dissimilarity. Therefore, when designed according to the size of the hand and wrist of each user, the SWA can generate a large amount of ROMs that are adequate for the wrist  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Wrist Motion** & **Flexion** & **Extension** & **Radial Deviation** & **Ular Deviation** \\ \hline Maximum Torque (Nm) & 0.61 & 1.32 & 0.90 & 0.62 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Maximum torque of the robot in the direction of various wrist motions.  
Figure 10: User test of the proposed robot for five subjects, (**a**) range of motion, (**b**) wearing time.  
the SWA is designed by simply attaching multiple SMA-based actuators at desired locations, the torque and ROM can be easily increased by attaching additional actuators to the robot.  
The wearability is assessed by measuring the time spent wearing the robot. The experiments were conducted in consideration of the fact that the robot is designed to be used by patients who have difficulties in manipulating lower arm. Two scenarios were provided for the experiments; self and assistive wearing. The self-wearing experiment was conducted to observe how easily the patients could wear the robot on their own. Therefore, the subjects wore the robot on the passive hand, by using only one hand in this experiment. In the assistive wearing experiment, the time that it takes to attach the robot to the patients by an assistant was measured.  
Figure 10b shows the measured average wearing times of two experiments. The average time spent on self-wearing was measured as 87 s. The average assistive wearing time was measured at 75 s. The step that consumed the most time was inserting fingers into the glove in both experiments. The fact that it takes less than 2 min to wear the robot indicates that the proposed robot system can be worn easily. In particular, the experimental result of the self-wearing implies that the proposed robot can be worn solely by the patient with only one hand in about 80 to 90 s. Therefore, the patients facing motor impairments in their wrist can also wear the robot without the need for external assistance.