## 6 Results and Discussion  
Table 3 shows the results obtained by experimental measurement of the bending angle of the 3D-printed finger using computer vision, manual measurement with an electronic protractor, and numerical results obtained by FEA. Figure 8: Object detection using image processing. (**left**) Original image of the 3D-printed finger. (**middle**) Segmented object region represented with white pixels in the segmented binary image. (**right**) Detected object bounded with an extracted minimal rectangle (blue-colored rectangle). Figure 9: Example of different joint positions: (**a**) unloaded and (**b**) loaded. Original images (left column) of the 3D-printed finger. Segmented object regions represented with white pixels in the segmented binary images (middle column). Detected object bounded with an extracted minimal rectangle represented by blue-colored rectangle (right column). As can be noticed, FEA results show a large error with respect to experimentally measured values in cases where small loads were applied, while in cases of maximum loading, this error is reduced. FEA shows that both compliant fingers have very similar results in output angles but still provide better results for a curved flexure hinge with a 90-degree bend. On the other hand, the experiment shows that a 21-degree bend curved flexure hinge provides better results. The reason for that can be contained in the assumption that the information provided by the material manufacturer is different for the filament used for 3D-printed prototypes of fingers. In order to prove this assumption, a tensile test was performed to determine the material properties of 3D-printed test specimens (Figure 10). The tensile test was performed according to the international standard ISO 527-2, which determines the tensile properties of molding and extrusion plastics. In Figure 10a, the test specimen at the beginning of the tensile test (without a load) can be seen, and in Figure 10b, the test specimen during the load stage is shown. As a result of the tensile test for the 3D-printed Taulman Nylon 230 material, the stress-strain curve shown in Figure 11 was obtained. The orange line illustrates the hypothetical straight line that the material would follow if it were constantly in the area of elasticity (in the region where [PERSON]'s law applies), whereas the blue line depicts the actual behavior of this material when it is stretched. The slope of the straight-line portion of the stress-strain curve can be utilized to define the modulus of elasticity (Young's modulus). Special attention should be paid to the instant of the stress point where the material enters the non-linear deformation region (i.e., when the blue and the orange lines diverge), as this is the region where the compliant fingers material is when the large angular deformations take place. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Flexure Hinge Type**} & \multirow{2}{*}{**Method**} & \multicolumn{4}{c}{**Force (N)**} \\ \cline{3-6}  & & \(\approx\)**0.1** & \(\approx\)**0.2** & \(\approx\)**0.3** & \(\approx\)**0.4** \\ \hline \multirow{4}{*}{**Flexure Hinge Type**} & Computer Vision & 31.9\({}^{\circ}\) & 69\({}^{\circ}\) & 94.1\({}^{\circ}\) & 124.2\({}^{\circ}\) \\  & Protractor Measurement & 32.7\({}^{\circ}\) & 68.7\({}^{\circ}\) & 93\({}^{\circ}\) & 126.9\({}^{\circ}\) \\  & FEA & 70.854\({}^{\circ}\) & 110.98\({}^{\circ}\) & 126.57\({}^{\circ}\) & 134.96\({}^{\circ}\) \\ \hline \multirow{4}{*}{**Flexure Hinge Type**} & Computer Vision & 34.9\({}^{\circ}\) & 68.5\({}^{\circ}\) & 92.8\({}^{\circ}\) & 123.3\({}^{\circ}\) \\  & Protractor Measurement & 33.5\({}^{\circ}\) & 68.1\({}^{\circ}\) & 92.1\({}^{\circ}\) & 121.7\({}^{\circ}\) \\ \cline{1-1}  & FEA & 79.54\({}^{\circ}\) & 115.09\({}^{\circ}\) & 129.14\({}^{\circ}\) & 135.93\({}^{\circ}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results for the bending angle \(\theta\) measured at the endpoint of compliant finger.