# A Micro-Coordinate Measurement Machine (CMM) for Large-Scale Dimensional Measurement of Micro-Slits
## 3 Experimental Result and Discussion
### Experiments of On-Line Qualification and Gap Width Measurement  
The micro-slit on the precision slot die for measurement has a nominal gap width of 85 \(\pm\) 5 \(\upmu\)m over a length of 200 mm. To avoid the influence of the chamfered edges of the precision flat parts forming the micro-slit, it is necessary for the probe tip to be arranged inside of the micro-slit for measurement of the gap width. In the developed micro-CMM, the probing position along the \(Z\)-direction is determined by utilizing the measurement capability of the shear-mode micro-probe in both the \(X\)- and \(Z\)-directions [26]. Figure 13 shows the detection strategy and the detection results of the chamfered edges of the two precision flat plates, respectively. It can be seen that the inner surfaces of the micro-slit can be identified from the measurement result shown in Figure 13b. The \(Z\)-directional height of the chamfered edges of the precision flat plates was estimated to be approximately 90 \(\upmu\)m and the probing position along the \(Z\)-direction was selected to be lower than areas of the chamfered edges for the following experiments of on-line qualification and gap width measurement. On-line qualification of the effective diameter of the probe tip ball was then conducted by using the calibrated artifact. As a set of the on-line qualification operation, the probe was moved to the side of \(P_{2}\) by the \(X\)-directional servo motor stage for another 5 times of probing at \(P_{2}\) after 5 times of probing at \(P_{1}\). It took approximately 50 s for the set of the operation. The same set of the operation \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Stage** & **Axis** & **Stroke** & **Tilting Error** \\ \hline \multirow{2}{*}{\(Y\)-linear slide} & Rolling & \multirow{2}{*}{300 mm} & 8.10 mrad \\  & Yawing & & 12.31 mrad \\ \multirow{2}{*}{\(Z\)-servo motor} & Rolling & \multirow{2}{*}{1 mm} & 22.59 mrad \\  & Pitching & & 73.40 mrad \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summary of tilting errors of the positioning stages. was repeated 5 times to evaluate the repeatability of probing at the trigger points. Figure 14 shows the results of the on-line qualification. The \(X\)-directional positions of the trigger points at \(P_{1}\) and \(P_{2}\), which is a contact points between the probe tip ball and the inside surface of the slot die, are shown in Figure 14a,b, respectively. The vertical axes shown in Figure 14a,b show the \(X\)-directional probing positions calculated by the output of the laser interferometer. The mean values of the \(X\)-directional positions of the trigger points at \(P_{1}\) and \(P_{2}\) over the 5 sets of on-line qualification operations were 5.625 \(\upmu\)m and 159.344 \(\upmu\)m, respectively. Due to the thermal drift between the laser interferometer and the reflective mirror mounted on the \(X\)-PZT stage, the mean values at \(P_{1}\) and \(P_{2}\) were changed almost linearly due to the influence of thermal drifts. Figure 14c shows the value of \(L_{12}\) calculated by taking the difference of the corresponding results of Figure 14a,b, in which the thermal drift error components were removed. The mean and the standard deviation of \(L_{12}\) over the 5 sets of on-line qualification were 153.781 \(\upmu\)m and 11.5 nm, respectively. Consequently, the effective diameter of the probe tip ball \(D_{e}\) was estimated to be 53.781 \(\upmu\)m.  
Figure 13: Chamfered edge detection by using the micro-probe: (**a**) Detection strategy of the chamfered edge; (**b**) Measurement result of the slit position. After the on-line qualification, the probing position was located to the inside of the micro-slit by moving the slot die with the \(Y\)-linear slide for the gap width measurement. At each \(Y\)-directional measurement position, after the probing at \(P_{3}\), the probe was moved by the \(X\)-directional PZT stage toward the opposite surface of the micro-slit for the probing at \(P_{4}\). This operation was repeated 5 times.