# Designing a User-Centered Inspection Device's Handle for the Aircraft Manufacturing Industry
## 4 Discussion  
### Global Results  
The main contribution of the current study is to provide a user-centered design of a handle for a novel inspection device with ergonomic requirements obtained from a thorough scientific study, including qualitative and quantitative data for a comprehensive assessment of the handle prototypes. Primarily, the results of the subjective comfort assessment point out that \"handle 3\" is the least comfortable. Regarding \"handle 1\", the participants reported a positive global comfort, mainly after its use. This methodological approach is based on psychophysical assessment being relevant and frequent in similar ergonomic studies (as adopted by [14]). Therefore, we consider that the results collected with this questionnaire are relevant to support the final handle design. However, to complement this assessment, as previously mentioned, several objective data were collected, namely partial times to capture an image, stability metrics, joint angles, and EMG data. In this domain, the results demonstrate that the level of stability achieved by any handle can be considered acceptable, e.g., the oscillations of the device position are in the order of tenths of a millimeter. Furthermore, initial observations of the mean values of some stability metrics (velocity and oscillations of the position, velocity, and acceleration) seemed to indicate differences between handles. In fact, one could expect \"handle 3\" to perform better in terms of stability since it includes physical support. However, the observed differences were found statistically insignificant, and thus, the use of \"handle 3\" can be considered similar to the other handles. This is positive because it means that no additional accessory is required to improve stability other than an appropriate design of the handle itself. Regarding efficiency, in terms of partial times to capture an image, the participants completed the tasks relatively fast, with average times shorter than 4 s and maximum times shorter than 6 s. This evidence was observed throughout the different handles tested. In addition, one should note that the task duration is intimately related to the ability of the subject to keep the device stable because the focus and blur of the resulting image depend on it. Globally, it is reasonable that both partial times and stability metrics lead to the same conclusion, that no significant differences are verified between the mean values along the three handles tested. Therefore, these metrics do not distinguish the handles in terms of their potential to improve the device's stability and, consequently, its efficiency. \begin{table}
\begin{tabular}{l c c c} \hline
**Variable** & **Handle 1/Handle 2** & **Handle 1/Handle 3** & **Handle 2/Handle 3** \\ \hline Partial time & 0.581 & 0.991 & 0.555 \\
3D acceleration & 0.971 & 0.971 & 0.999 \\
3D velocity & 0.402 & 0.144 & 0.301 \\ Oscillations of the acceleration & 0.649 & 0.260 & 0.593 \\ Oscillations of the velocity & 0.306 & 0.131 & 0.235 \\ Oscillations of the position & 0.695 & 0.523 & 0.396 \\ Traveled distance & 0.370 & 0.854 & 0.580 \\ Shoulder flexion/extension & 0.606 & 0.065 & 0.023 \({}^{\star}\) \\ Elbow flexion/extension & 0.651 & 0.077 & 0.057 \\ \multicolumn{4}{l}{Wrist flexion/extension} & 0.328 & 0.555 & 0.756 \\ \multicolumn{4}{l}{Wrist ulmar/radial} & 0.054 & 0.122 & 0.785 \\ deviation & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} \\ EMG—DA & 0.011 \({}^{\star}\) & 0.512 & 0.044 \({}^{\star}\) \\ EMG—FCR & 0.157 & 0.020 \({}^{\star}\) & 0.255 \\ EMG—ECU & 0.110 & 0.045 \({}^{\star}\) & 0.854 \\ \hline \end{tabular}
\end{table} 
Table 1: Results (\(p\)-value) of the mean differences tests (paired \(t\)-test). \({}^{\star}\) statistical significance at \(p<0.05\). Relative to the kinematics analysis, a higher deviation from the neutral position of the joint (joint angle \(\sim\)0\({}^{\circ}\)) occurs with \"handle 3\".