## 4 Feasibility Validation of the QCES System  
In order to analyze the reliability of the QCES system designed in this study in recognizing the limb angles of working postures, a comparison was first made between the QCES system and the OptiTrack motion capture system in terms of the mean, standard deviation, and \(t\)-test of limb angles of working postures, as shown in Table 2. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Limb Parts**} & \multicolumn{2}{c}{**Mean (SD)**} & \multirow{2}{*}{**Significance**} \\ \cline{2-3} \cline{5-4}  & **QCES System** & & **OptiTrack Motion Capture** \\ \hline Neck & 14.56 (12.37) & 17.13 (16.19) & No Significance \\ Waist & 0.67 (10.12) & 3.00 (8.81) & No Significance \\ Left Leg & 163.41 (9.37) & 163.33 (11.83) & No Significance \\ Left upper arm & 64.48 (32.09) & 69.46 (37.01) & No Significance \\ Left forearm & 88.24 (27.20) & 91.18 (29.47) & No Significance \\ Left wrist & 19.74 (9.33) & 21.85 (9.66) & No Significance \\ Right Leg & 155.2 (14.07) & 157.46 (12.10) & No Significance \\ Right upper arm & 79.2 (35.40) & 81.48 (38.10) & No Significance \\ Right forearm & 103.7 (29.54) & 108.07 (31.93) & No Significance \\ Right wrist & 17.72 (8.81) & 16.82 (8.46) & No Significance \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Results of \(t\)-tests between the OptiTrack motion capture system and the QCES system. From the table, it can be seen that the mean (standard deviation) of the QCES system in limb positions such as the neck, right leg, left upper arm, right upper arm, right upper arm, right forearm, left wrist, and right wrist are relatively close to the corresponding data of the motion capture system. The two systems have certain similarities in recognizing the limb angles of working postures. Moreover, there is no significant difference in the angle values of all limb positions. These results to some extent prove that the QCES system can replace the OptiTrack motion capture system as a tool for recognizing the limb angles of workers' working postures. Secondly, in terms of arm angle capture, there is a certain difference between the QCES system (64.48 \(\pm\) 32.09) and the OptiTrack motion capture system (69.46 \(\pm\) 37.01) in the left upper arm, as well as in the limb angle of the right forearm, where the QCES system (79.2 \(\pm\) 35.40) and the OptiTrack motion capture system (108.07 \(\pm\) 31.93) also differ slightly. However, the differences between the two are not significant. Therefore, this study analyzed the captured limb angles of each posture in more detail. To conduct a more detailed analysis of the differences between the QCES system and the OptiTrack motion capture, this study expanded on the limb angles recognized by both methods, as shown in Table 3. The table lists the RMSEs and \(\rho\) correlations calculated by the QCES system and the OptiTrack motion capture for all limb angles. These results indicate that the RMSE errors of different limb angles in various working postures are relatively small, with an average RMSE error of 5.64 for 18 movements. Among them, the capture situation of the working posture labeled as W2-60 is the best, with an average RMSE value of 3.16 (where 9 out of 10 limb angles have error values less than 5), while M1-60 exhibits a poorer performance with an average error value of 8.93 (where only 4 out of 10 limb angles have error values less than 5). Furthermore, this study conducted a more detailed analysis of the correlation between the QCES system and the OptiTrack motion capture in limb angles across 18 different postures. The average [PERSON]'s rank coefficient of correlation for 10 limb angles is 0.87, with the Neck, left upper arm, Left forearm, Left wrist, right upper arm, and Right forearm all exceeding 0.85. These results clearly demonstrate the validity of hypothesis H1. The QCES system designed in this study maintains consistency with the OptiTrack motion capture in the recognition of limb angles.