## 3 Result Analysis
### Analysis of 2D Vibration Imaging  
As described earlier, the reasons to employ 2D vibration imaging are as follows. One reason is to create an invariant scenario for different loads and rpms. For each health type (HC, IRF, BF, ORF at center, ORF at orthogonal and ORF at opposite), the 2D imaging exhibits identical patterns across working conditions. Another reason is to provide the CNN with the full advantages of the  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Fs = 12 kHZ**} & \multirow{2}{*}{**Health Type**} & \multirow{2}{*}{**Motor Load**} & \multirow{2}{*}{**Motor Speed**} & \multicolumn{2}{c}{**Crack Size**} \\ \cline{3-5}  & & & & **Diameter (Inches)** \\ \hline \multirow{5}{*}{Working Condition 1} & Healthy Condition (HC) & 0 & 1797 Rounds/min & Nil \\ \cline{2-5}  & Inner Race Fault (IRF) & 0 & 1797 Rounds/ min & 0.007 \\ \cline{2-5}  & Ball Fault (BF) & 0 & 1797 Rounds/min & 0.007 \\ \cline{2-5}  & Outer Race Fault at center & 0 & 1797 Rounds/min & 0.007 \\ \cline{2-5}  & (ORF@12) & 0 & 1797 Rounds/min & 0.007 \\ \cline{2-5}  & Outer Race Fault at orthogonal (ORF@3) & 0 & 1797 Rounds/min & 0.007 \\ \cline{2-5}  & Outer Race Fault at opposite (ORF@6) & 0 & 1797 Rounds/min & 0.007 \\ \hline \multirow{5}{*}{Working Condition 2} & Healthy Condition (HC) & 1 & 1772 Rounds/min & Nil \\ \cline{2-5}  & Inner Race Fault (IRF) & 1 & 1772 Rounds/min & 0.007 \\ \cline{2-5}  & Ball Fault (BF) & 1 & 1772 Rounds/min & 0.007 \\ \cline{2-5}  & Outer Race Fault at center (ORF@12) & 1 & 1772 Rounds/min & 0.007 \\ \cline{2-5}  & Outer Race Fault at opposite (ORF@6) & 1 & 1772 Rounds/min & 0.007 \\ \hline \multirow{5}{*}{Working Condition 3} & Healthy Condition (HC) & 2 & 1750 Rounds/min & Nil \\ \cline{2-5}  & Inner Race Fault (IRF) & 2 & 1750 Rounds/min & 0.007 \\ \cline{2-5}  & Ball Fault (BF) & 2 & 1750 Rounds/min & 0.007 \\ \cline{2-5}  & Outer Race Fault at opposite (ORF@6) & 2 & 1750 Rounds/min & 0.007 \\ \hline \multirow{5}{*}{Working Condition 4} & Healthy Condition (HC) & 3 & 1730 Rounds/min & Nil \\ \cline{2-5}  & Inner Race Fault (IRF) & 3 & 1730 Rounds/min & 0.007 \\ \cline{2-5}  & Ball Fault (BF) & 3 & 1730 Rounds/min & 0.007 \\ \cline{2-5}  & Outer Race Fault at center (ORF@12) & 3 & 1730 Rounds/min & 0.007 \\ \cline{2-5}  & Outer Race Fault at orthogonal (ORF@3) & 3 & 1730 Rounds/min & 0.007 \\ \cline{2-5}  & Outer Race Fault at opposite (ORF@6) & 3 & 1730 Rounds/min & 0.007 \\ \cline{2-5}  & Outer Race Fault at opposite (ORF@6) & 3 & 1730 Rounds/min & 0.007 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Details of the considered working conditions with the same health types.  
2D structure with visibility of identical patterns. A further reason is be able to visually distinguish between the source and target domains to reduce negative transfer learning. Figure 7a-f shows the output of vibration imaging for each health type under different working conditions. Using the S-transform, the frequency domain is divided into several bandwidths, providing micropatterns based on bandwidth. From close observation, the rpm and load do not affect the identical patterns of the signals under different working conditions. Across different rpm and load levels, the pattern for each health condition does not vary, which demonstrates the similarity among all the working conditions for different health types.