## 5 Results  
All the measurement data have been processed and interpolated to provide a curve fitting of the motion of the comb-drive depending on the voltage supply; in Figure 11 the two curves related to the two measurement setups are shown, while the detailed results are reported in Tables 4. For low values of the voltage, the observations reveal that the microgripper mobile parts face a certain resistance while attempting to move, showing a certain instability. In fact, the torque-voltage function presents an increasing rate of change. This phenomenon is one of the main source of a high dispersion of the results at low values of voltage, while this problem does not occur for higher values (>4 V). In Table 5 the results of the comparison between the OPS and LTM systems are shown. As already observed in Ref. [44], for the optical profilometer, even if we consider the image acquisition system of the light microscope, it is possible to observe a concordant behavior with the results reported in Refs. [35; 37]. Second order polynomial regression curves have been determined by a least squares fitting method to describe the outcome from the OPS and the LTM systems: the fitting capacity is confirmed by the high value \(R^{2}\) coefficients [51], equal to 0.999 for both the OPS and LTM systems. The Equations (3) and (4) have been used to calculate the type B uncertainty \(\delta_{B}\). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Supply** & **Angular Displ.** & **Angular Displ.** & **Total** & **Total** & **Total Relative** & **Total Relative** \\
**Voltage (V)** & **Mean Value (\({}^{\circ}\))** & **Mean Value (\({}^{\circ}\))** & **Uncertainty** & **Uncertainty** & **Uncertainty** & **Uncertainty** \\
12 & 0.227 & 0.237 & 0.011 & 0.028 & 4.8\% & 11.8\% \\
14 & 0.319 & 0.321 & 0.011 & 0.025 & 3.5\% & 7.9\% \\
16 & 0.427 & 0.414 & 0.017 & 0.030 & 4.0\% & 7.2\% \\
18 & 0.543 & 0.533 & 0.013 & 0.034 & 2.3\% & 6.4\% \\
20 & 0.696 & 0.642 & 0.016 & 0.024 & 2.2\% & 3.7\% \\
22 & 0.810 & 0.787 & 0.017 & 0.019 & 2.1\% & 2.5\% \\
24 & 0.952 & 0.926 & 0.021 & 0.030 & 2.2\% & 3.2\% \\
26 & 1.122 & & 0.023 & & 2.0\% & \\
28 & 1.308 & & 0.021 & & 1.6\% & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Angular rotation, Total Uncertainty, expressed as standard deviation, and Total Relative Uncertainty of comb-drive depending on the applied voltage. Table 4 shows that above 16 V the total relative uncertainty of the optical profilometer is less than 4.0%, while for the microscope it is less than 7.2%. Since the same software for digital image processing has been used, these results may be mainly related to the two different setups. The greatest contribution in the calculation of uncertainty is given by the \(\delta_{\alpha_{t}}\) uncertainty, composed by the angle measurement uncertainty due to the OPS and LTM, \(\left(\frac{\delta_{\alpha_{p}}}{\alpha}\cdot\alpha\right)\), and the angle measurement uncertainty due to the template-matching algorithm of the image processing software \(\delta_{\alpha_{s}}\), that correspond to 0.02\({}^{\circ}\) both for OPS and LTM systems. As mentioned above, the OPS and the LTM generally have different typical values of SNR and this fact is also affecting uncertainty in the two measurement systems. A second evaluation of the two experimental setups has been conducted; indeed, it has been necessary to evaluate whether the different results relative to the mean values of the angular displacement of the comb drive for the two experimental setups are comparable or not, to properly establish if the two measurement systems produce the same results, based on the verification that the differences between the measured mean values are smaller or comparable with the sum of the original uncertainties. Table 5 shows that, for each applied voltage value, there is no significant difference between the results obtained by the two methods.