# MOIRA-UNIMORE Bearing Data Set for Independent Cart Systems
## 4 Fault Injection Methodology  
Fault injection was performed using two methods: non-disassembled and fully dismantled bearings. Initially, faults were introduced using a Lab-available drill mill without dismantling the bearings. However, the limited maneuverability of the drill mill head, the proximity of the bearing races, and the inherent rigidity of the stainless steel material made it difficult to create significant faults. As a result, the faults were of an incipient nature and did not fully encompass the grooves. To overcome this limitation, a picosecond laser (EKSPLA Atlantic 50) was used to create controlled faults without dismantling. The EKSPLA Atlantic 50 generated a Gaussian beam profile at an infrared (IR) wavelength of 1064 nm (see Figure 3). This laser source produces ultrashort pulses in the picosecond range, enabling the precise ablation of both the inner and outer races by creating accurately shaped grooves. Notably, this process is not limited by the hardness of the material being processed. The diameter of the laser beam at the focal point is set at \(\phi\approx 10\) um, measured at the \(1/e^{2}\) intensity level. A dedicated optical path for the IR wavelength ensures that the laser beam is efficiently delivered from the source to the scanning head. The system employs a Raylase SuperScan IV galvanometric scanner coupled with an 80 mm F-theta lens, providing a square working area with a side length of 39 mm. Movements outside this scanning area are facilitated by the translation of a stage in the \(X\) and \(Y\) directions, on which the bearings to be processed are mounted. Additionally, the \(Z\)-axis translation ensures that the bearings are processed at the correct focal height. The entire setup, located in the BrightLab laboratory of the DISMI Department, is illustrated in Figure 4. Preliminary tests were conducted to assess the material's response to infrared radiation. These tests were crucial for identifying and defining the optimal process parameters to achieve damage with specific geometry, dimensions, and prescribed depth. The laser parameters used in the process are summarized in Table 4. Although effective, this method presented challenges, particularly in damaging the inner and outer races. The first challenge stemmed from the \begin{table}
\begin{tabular}{c p{142.3 pt} p{142.3 pt} p{142.3 pt}} \hline \hline
**Phase** & **Description** & **Issues** & **Improvements** \\  & & **En encountered** & **Implemented** \\ \hline \multirow{3}{*}{**Initial Experiments**} & Faults injected manually; data collected with acquisition system & Poor fault injection; low-resolution data; low sampling frequency & Baseline experiments with initial setup \\ \hline \multirow{3}{*}{**Refined Experiments**} & Different cart numbers and loading mechanisms tested & Variability in results due to inconsistent loads and cart configurations & Standardized mechanisms \\ \hline \multirow{3}{*}{**Data Acquisition Upgrade**} & Upgraded to 24-bit resolution with 50 kHz sampling & Improved resolution, but inconsistent fault injection & Laser Fault Injection \\ \hline \multirow{3}{*}{**Laser Fault Injection**} & Laser fault injection without dismantling the bearings & Result variability due to partial fault coverage from inner-outer race proximity & Bearings were disassembled \\ \hline \multirow{3}{*}{**Final Experiments**} & Laser-based fault injection with bearing disassembly & None & Final data set used for analysis \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Experimental timeline and improvements over different phases. To address these limitations and ensure consistent damage results across various bearing components--comparable to those achieved in preliminary planar tests--an assessment of the allowable depth of focus was necessary.