# Gearbox Fault Diagnosis Based on Multi-Sensor and Multi-Channel Decision-Level Fusion Based on SDP
## 3 Fitting Fault Identification Based on SDP Technology
### Experimental Data Acquisition  
The present study was conducted for the health diagnosis of three different degrees of pitting in the individual gear teeth of an active gear, namely normal, single pitting, and double pitting, where the gear pitting condition usually occurs first on the root surface of the tooth near the pitch line. A schematic diagram of the three types of pitting in the gear is shown in Figure 3.  
Figures 3 and 4 are integrated, with Figure 3 representing a pitting schematic where a single gear gradually changes from a normal condition to a double pitting condition, while Figure 4 represents the real situation of gear pitting. In Figure 3, \(n=1\sim m\), where \(m\) is the number of all of the teeth on the gear and \(n\) indicates a gear tooth with pitting failure on the gear. The arrows in Figure 4 are used to highlight the location of the pitting on the gear teeth. The experimental bench was built on a modified gearbox test bench, which already existed in the project team. The three three-direction sensors were installed in three different planes of the gearbox near to the vibration source, and the structure design diagram, for the sake of comprehensively monitoring the gearbox gear teeth health status, was produced as shown in Figure 5. The installation of the structure design was completed according to the set up that is shown in Figure 6, and the physical construction of the experimental bench was also conducted. The oil was injected at the bottom of the lower box of the gearbox at a height of 10 mm, and the oil immersion lubrication was used in order to reduce the occurrence of the gear wear state and to ensure the normal operation of the gears. As required by the partner, the gear working conditions were as follows: The rotation speed was at 900 r/min and 1000 r/min, low loads were applied, and the operation of the gears was also monitored. The load increased from 0 N\(\cdot\)m to 30 N\(\cdot\)m in steps of 5 N\(\cdot\)m. After several sets of experiments, it was verified that, when the working conditions were at 1000 r/min and the load was 30 N\(\cdot\)m, the pitting of the gears under the different conditions was obvious and could, therefore, help to prevent the appearance of pitting effectively. The experimental working conditions are shown in Table 1.  
Figure 4: Fitting damage levels of the gears: (**a**) Normal condition, (**b**) Single pitting condition, and (**c**) Double pitting condition. Figure 3: The pitting damage levels from normal to twvc (**a**) Normal, (**b**) Single pitting, and (**c**) Double pitting. Figure 5: Structural design of the experimental gear. Figure 6: Experimental setup. 1–7: Active motor; 2–5: Coupling; 3–6: Torque speed sensor; 4: Gearbox; 4.1: drive gear; 4.2: driven gear; 4.3, 4.4, and 4.5: Three-direction acceleration sensor. The data acquisition method was to first install the BK sensor in the three planes of the gearbox body near to the source of the gearbox vibration. Since the test frequency of gearbox gear teeth was 5 kHz\(-\)10 kHz, the test frequency was set to 12.8 kHz in the pulse acquisition system that was used with the BK sensor. For the motor control, the gear working condition was set under the Yblsoft specialized software, and the partner required the speed to be 900 r/min and 1000 r/min, and the load to be increased from 0 N\(\cdot\)m to 30 N\(\cdot\)m in steps of 5 N\(\cdot\)m. Finally, the gear health status was analyzed 30 times from normal, single pitting, and double pitting, and the final result was that the gear was tested at a speed of 1000 r/min and 30 N\(\cdot\)m load. Therefore, it was determined that the working condition of the gear in this study was 1000 r/min, 30 N\(\cdot\)m load, and 12.8 kHz test frequency. In addition, the data acquisition card that was used was the Type 3053-B-120 manufactured by BK. After the completion of the data acquisition, one of the more obvious channels of each sensor signal was selected separately as the data input in order to evaluate the gear's health status.