## 2 Materials and Methods  
### Materials  
Dataset  
The experimental setup of the MCC5 gearbox dataset [44] included a 2.2 kW three-phase asynchronous motor as the main power source. The torque on the gearbox input shaft was measured using an S2001 precision torque sensor with an overall accuracy of \(\pm\)0.5% F.S. A two-stage parallel gearbox and a magnetic powder brake were used to simulate realistic operating conditions. Data acquisition was performed using the CMS-ONE-DAQ 16 system, featuring a 24-bit analog-to-digital conversion accuracy. Meanwhile, TES 001 V model three-axis vibration acceleration sensors measured the vibration signals of the motor and the gearbox intermediate shaft at a sampling frequency of 12.8 kHz. The experimental environment temperature was strictly controlled within 20 \({}^{\circ}\)C. The recorded data included the motor output shaft key-phasor signal, input shaft torque signal, and three-axis vibration signals from both the motor and the gearbox, which were used to analyze and diagnose various fault modes of the 36-tooth gear on the intermediate shaft and its adjacent supporting bearings. The detailed specifications of the MCC5 gearbox dataset rolling bearing and gear were as follows: the rolling bearing model was ER16K, with an inner diameter of 1 inch, an outer diameter of 2.0472 inches, a width of 0.749 inches, ball diameter of 0.3125 inches, 9 balls in total, and a pitch diameter of 1.516 inches. The gear parameters included a module of 1.5, a tooth width of 10 mm, and 36 teeth, as shown in Figure 1.  
This dataset contained vibration signals collected from a two-stage parallel gearbox under various working conditions. It included multiple states such as healthy, single-fault, and compound fault scenarios, making it suitable for fault diagnosis research under variable operating conditions. The recorded signals included tri-axial vibration acceleration signals from the motor and the gearbox intermediate shaft bearing seat, torque signals, and motor output shaft key-phase signals, with a sampling frequency of 12.8 kHz. The dataset  
Figure 1: Test rig of MCC5 gearbox dataset. Adapted from [44]. covered 12 operating conditions, encompassing constant and time-varying speed and load scenarios. The rotational speed ranged from 1000 to 3000 rpm, and the load ranged from 10 to 20 Nm. Fault types included single faults such as \"cracks\" and \"tooth fracture,\" as well as compound faults like \"teeth fracture with inner bearing fault\" and \"teeth fracture with outer bearing fault.\" Each fault was further categorized into three severity levels: light, medium, and high. The dataset covered various operating conditions and provided abundant experimental data for different fault types. The experimental setup for the HUST gearbox dataset [45] utilized the Spectra-Quest mechanical fault simulator. The test bench was composed sequentially of a speed controller, motor, accelerometer, gearbox, and data acquisition board. The gearbox model used was the Hub City M2, with a transmission ratio of 1.5:1. Both the gear and pinion were made of forged steel, with pitch angles of 56\({}^{\circ}\)19\({}^{\prime}\) and 33\({}^{\circ}\)41\({}^{\prime}\), a pressure angle of 20\({}^{\circ}\), and backlash tolerance controlled between 0.001 and 0.005 inches. The gear and pinion had 27 and 18 teeth, respectively, with a pinion pitch diameter of 1.125 inches and a gear pitch circle diameter of 1.6875 inches. The bearing configuration included one NSK 6202 deep-groove ball bearing for the pinion and two NSK 6205 deep-groove ball bearings for the gear. The experiment was conducted under 30 different operating conditions, covering 5 load levels (0 to 0.452 Nm) and 6 speed levels (20 to 40 Hz and a time-varying speed from 0 to 40 to 0 Hz). The data sampling frequency was 25.6 kHz, with each sample containing 262,144 data points, corresponding to approximately 10.2 s of vibration signal. The setup and acquisition parameters ensured high precision and reliability of the data.