## 4 Results and Discussion
### Study B: Reverse Stroke Analysis through Segmentation Technique  
Study B focused on evaluating the reverse stroke at the three different health states by applying the proposed signal segmentation technique. The vibration signal was segmented into 8 segments and used the 10% and 20% limits. When evaluating the RMS and standard deviation features in the reverse stroke direction, similar to the forward direction study, their percentage error is less than 5%, as depicted in Figure 7, while the other features, peak-to-peak and kurtosis, both exhibited percentage errors above the 20% limit, as demonstrated in Figure 14.  
Figure 14: Full reverse stroke healthy vs. faulty comparison of time domain features. (**a**) Peak-to-Peak, (**b**) Kurtosis. Figure 13: Forward stroke repair signal segmentation analysis. (**a**) Peak-to-Peak, (**b**) Kurtosis. Similar to study A, both RMS and the standard deviation features were further evaluated under the applied signal segmentation technique. The results for both features, also illustrated in Figure 15, were as follows:  
* Both features in the half stroke analysis showed an increase in the first segment. However, unlike the results from study A, the feature magnitudes do not exceed the 10% limit. Nevertheless, when segmented at the quarter stroke level, immediately a major shift of the percentage error can be observed from 7% at the half stroke level to 26%. * When the signal is segmented once more to the eighth stroke level, the feature's magnitude increases once again reaching a percentage error of 46% when compared to the baseline state. Despite this major shift, another change can also be observed in the eighth segment that exceeds the 10% limit, deeming it a suspect area. To localize the area of the misalignment, the evaluated segments like in study A were also related to the position of the linear axis. In contrast to the previous study, the segments that showed a major shift to the features are the initial segments rather than the last. Since the system starts at a misaligned state this shift on the features is higher at the beginning. This demonstrates how the reverse stroke is a mirror image to the forward stroke signal. Additionally, it can be observed that the misalignment had the most effect on the vibration signal in the first quarter stroke segment, which equates to the first 175 mm of travel in the reverse direction. However, when the signal is segmented once more to the eighth stroke level, the first segment that relates to the initial 87.5 mm of travel had the highest change to the vibration signal. Similar to the forward stroke study, the kurtosis and peak-to-peak features had above 20% error when compared to the baseline at the full stroke level analysis. However, when subjected to the proposed segmentation technique, also demonstrated in Figure 16, the following results occur:  
Figure 15: Reverse stroke faulty signal segmentation analysis. (a) RMS, (b) Standard Deviation. * The peak-to-peak feature consistently shows an above 20% error in the first segment at the half, quarter, and eighth stroke levels where the misalignment was most acute. In comparison, all other segments stay below the 10% error limit. Thus, demonstrating peak-to-peak is a useful feature when looking at the misalignment fault. * Kurtosis showed quite a difference at the different segment levels. Firstly, at the half stroke level, the first segment where the misalignment was introduced showed approximately 30% error when compared to its baseline counterpart. However, the second segment exceeded the 10% limit as well, showing that the system underwent a change in the other half of the stroke. When segmented once more to the quarter level, the last segment exceeded the 20% limit while the first decreased to 16%. Finally, when segmented once more to the eighth stroke level, all segments decreased to baseline state values similar to study A, except the last two segments which exceeded the 10% established limit. Study B was also concluded by evaluating the repair state condition of the linear axis.