# Design and Development of Hugging Mechanism for Capturing Chest and Back Auscultatory Sounds
## 3 Results  
For evaluating the accuracy of the hugging mechanism, we measured the positioning error of the articulated arm after pushing the cam mechanism. Incremental encoders (RE2 AR3 ML, Omron, Kyoto, Japan) were implemented into each joint for calculating the positioning error, as shown in Figure 9. With the encoders connected to encoder counters (SKU 8358, Switch Science, Tokyo, Japan), each joint angle was calculated. The pose of the articulated arm could be calculated with each link length and each joint angle. The measured positions were a side plate mounted on the first link of the arm and a back plate mounted on fifth link of the arm. The side plate mounted the acoustic sensors for acquiring the sounds of the middle and lower lobes of the lung and mitral valve, and the back plate mounted the acoustic sensors for acquiring the sounds of the upper and lower lobes of the lung. By comparing the ideal position calculated by the simulator with the actual position measured by the encoder, the angular error of each joint and the position error of the side and back plates when transformed for each body type (obese, standard, and slender) were calculated. The position error was calculated with the Euclidean distance between them. As for the statistical analysis, Student's two-tailed \(t\)-test with a 90% confidence interval was used to determine if there were significant differences in the position error between the side and back plates. Twelve trials were performed in each condition. The results of the angular errors of each arm joint and the position errors of the side and back plates for each body type (obese, standard, and slender) are shown in Figure 10 and Tables 3 and 4. In all conditions, the position errors were less than 15 mm. Also, comparing the left and right arms, the errors were symmetrical in each condition. Comparing the \begin{table}
\begin{tabular}{c c c c} \hline  & **Slender** & **Standard** & **Obese** \\ \hline Width [mm] & 213–251 & 251–288 & 288–333 \\ Thickness [mm] & 152–190 & 190–214 & 214–248 \\ Girth [mm] & 608–736 & 736–864 & 864–992 \\ \hline \end{tabular}
\end{table} 
Table 1: Reference body shape dimensions. \begin{table}
\begin{tabular}{c c c c c c} \hline  & \multicolumn{4}{c}{**Joint Angle**\({}^{\circ}\)} \\ \cline{2-5}  & \(\theta_{1}\) & \(\theta_{2}\) & \(\theta_{3}\) & \(\theta_{4}\) & \(\theta_{5}\) \\ \hline Obese & 40.23 & 29.70 & 42.42 & 27.46 & 40.19 \\ Standard & 41.22 & 12.05 & 73.42 & 15.52 & 37.79 \\ Slender & 41.68 & 0 & 98.28 & 0 & 40.04 \\ \hline \end{tabular}
\end{table} 
Table 2: Theoretical values of joint angles required to generate the intended trajectory. Figure 9: Experimental setup overview. Incremental encoders were implemented into each joint for calculating the positioning error. The measured positions were a side plate mounted on the first link of the arm and a back plate mounted on the fifth link of the arm. position errors of the side and back plates, the back plate was significantly larger than the side plate (\(p<0.05\)). This may be because the side plates were attached to the first link and were not affected by the angular error of each joint, whereas the error in the back plate was due to the cumulative angular error of all the joints because the back plate was attached to the fifth link. Figure 10: The results of the angle error of each joint and the position error of the side and back plates corresponding to (**a**) obese, (**b**) standard, and (**c**) slender. Focusing on the angle error of each link joint, the error trends differed between the obese and standard/slender body types. In the obese body type, the error in the joint at the end of the arm increased. On the other hand, the angular error of the second link switched between positive and negative during the transition from obese to standard. In the standard body type, the angular errors of the second and third links were larger, while the fourth and fifth remained unchanged. In the slender body type, the angular error of any joint was less than in the standard body type.