## 3 Results  
Our measurement results for wear on the contact strip are shown in Figure 15. In particular, the result obtained by processing the first fitted line is shown in Figure 15a, while that obtained by processing the second fitted line is shown in Figure 15b. It is clear that the deformation results for the contact strip are more accurate (by one additional point) in Figure 15b than in Figure 15a. By applying the fitted line result of the bottom laser line to the results shown in Figure 15b, the detected deformations increased, as indicated via blue boxes in Figure 15c. It is found that the blue box has not accurately measured the size of wear without the blob process.  
Figure 14: Post-processing for measurements of the contact strip: (**a**) overlay of laser line and base line, (**b**) extraction of the wear size between the base line and laser line, and (**c**) size determination via blob processing.  
Figure 15: Wear measurement results for the contact strip using the (**a**) first top fitted line, (**b**) second top fitted line, and (**c**) bottom fitted line.  
The wear results shown in Figure 15b are compared with the physical measurement values shown in Figure 4 in order to verify the accuracy of the target image by the proposed algorithm. The total thickness of the wear of the target image that is measured via visual inspection in the laboratory is 20 mm. As shown in Figure 14, W is the width and H is the thickness of the wear at different locations on the contact strip. As shown in Table 3, the results of the comparison with the physical measurement value show that the width at P1 has a maximum error of 9.04 mm and a minimum of 1.04 mm at P6. In terms of thickness, a maximum error of 6.01 mm was observed at P3, while a minimum error of 0.01 mm is realized at P4 and P2. The average error of the wear shape excluding P1 is 1.52 mm width, and 3.58 mm height.  
Furthermore, Figure 16 shows the wear detection results obtained by analyzing the target image of the contact strip in normal wear condition. The total thickness of the wear is 108 mm and a width of 10 mm is machined off from the center of the contact strip. The wear measurement results indicated an error of 9 mm and 4 mm in terms of width and thickness, respectively, compared with the physical values.  
The correlation formula is extracted based on the results in Figure 15b to check the change in the image measurement values according to the physical measurement values. The correlation formula between the physical measurement value and the image measurement value is shown by a trend line (orange line) as shown in Figure 17. The P1 in Figure 17 is excluded because the shape of wear is different. The trend line shows the formula in the linear distribution to derive the correlation by checking the coefficient that determines the accuracy. The image values (\(y\)-axis intercept) obtained by substituting for 180 mm width and 10 mm height of the physical values (\(x\)-axis intercept) of the contact strip in Figure 16 via the correlation formula is 104 mm width and 9 mm height (thickness). The result of the comparison of the derived image values of the correlation formula and the image values of Figure 15 is shown, with a difference of 2 mm in width and 3 mm in height. In the future, the correlation formula generated from the type of wear is expected to reduce the difference between the image value and the physical value.  
Figure 16: Result of wear measurement in normal contact strip.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Item** & **P1** & **P2** & **P3** & **P4** & **P5** & **P6** & **P7** \\ \hline Width & 9.04 mm & 1.45 mm & 2.01 mm & 1.99 mm & 2.11 mm & 1.03 mm & 2.02 mm \\ Height & 4.01 mm & 2.01 mm & 6.01 mm & 2.00 mm & 4.99 mm & 5.02 mm & 5.02 mm \\ \hline \hline \end{tabular}
\end{table}
Table 3: Error result of the physical value and the detection value of the simulation contact strip.