## 6 Applications  
The double-span rotor experimental platform is shown in Figure 7a. The rotor test bed is 134 mm long, 51 mm wide, and 120 mm high, with a total mass of about 50 kg. The test rotor has a shaft size of \(\phi\) 10 mm \(\times\) 810 mm, on which three lumped mass disks are installed. The rotor is supported by four cylindrical bearings and separated into a double-span structure. For the convenience of description, the rotor span close to the motor is named the forward span and the rotor span far away from the motor is named the backward span. The rotor system is driven by a direct current (DC) motor whose power is about 1.1 KW. A flexible connection mode of nylon rope is adopted between the motor output shaft and the front span rotor, and between the front span rotor and the rear span rotor. The DC motor is controlled by a pulse width modulator. The experiments show that the first critical speed of the rotor system is about 2000 r/min, the unstable speed is close to 5000 r/min, and 3000 r/min is the best stable operating point in the flexible working area of the rotor system. The vibration displacement signal acquisition program is implemented on the LabVIEW platform. In order to effectively simulate the rotor imbalance, rotor misalignment, rotor dynamic, and static rub impact fault experiment, the rotor experimental platform is equipped with a counterweight screw, rub impact screw, gasket, and other experimental auxiliary devices. \begin{table}
\begin{tabular}{l l l l l l} \hline
**Algorithm** & \(s_{i}\) & \(\rho_{i}\) & **RCTE/dB** & **PI** & **t/s** \\ \hline JADE & \(s_{1}\) & 0.412 & \(-\)2.131 & & \\  & \(s_{2}\) & 0.589 & \(-\)4.316 & 3.459 & 0.315 \\  & \(s_{2}\) & 0.612 & \(-\)12.315 & & \\ SOBI & \(s_{1}\) & 0.713 & \(-\)12.142 & & \\  & \(s_{2}\) & 0.785 & \(-\)11.311 & 1.213 & 0.082 \\  & \(s_{2}\) & 0.812 & \(-\)17.913 & & \\ MF-SOBI & \(s_{1}\) & 0.991 & \(-\)23.613 & & \\  & \(s_{2}\) & 0.992 & \(-\)21.221 & 0.101 & 0.010 \\  & \(s_{2}\) & 0.983 & \(-\)23.421 & & \\ \hline \end{tabular}
\end{table} 
Table 1: Evaluation indexes’ comparison of blind source separation. Figure 7: The two-span rotor-bearing rig. In order to simulate the rotor dynamic and static rub impact fault on the test bench, a threaded hole is reserved above the test bench bracket, as shown in Figure 7c, and a long white plastic screw is reserved. The long screw is screwed into the threaded hole to make contact with the mass disk, but it cannot make full contact, mainly because, due to the speed increase, the amplitude of the rotor is increasing under the action of unbalanced force. When the amplitude reaches the critical distance, there will be friction between the mass disk and the plastic screw. At the same time, the rub impact fault under different working conditions can be simulated by changing the distance and speed. In this experiment, the dynamic and static rub impact experiments were completed at the speed of 2800 r/min. The sampling frequency was 5000 Hz and the number of sampling points was 1024. The eddy current sensor probe is composed of two vertical probes. The probes are installed near the journal and around the disk. The vibration is obvious and the signal is easy to obtain. The sensor's installation position is shown in Figure 7b. A single sensor at the end of the rotor is used to measure the real-time speed of the rotor. In order to ensure that the number of sensors in blind source separation is greater than or equal to the number of source signals, four sensors are used in the experiment. The four measured sensor signals are shown in Figure 8. The signals separated by the SOBI algorithm are shown in Figure 9. The signals separated by the MF-SOBI algorithm are shown in Figure 10.  
Figure 10: The signals separated by the MF-SOBI algorithm. Figure 9: The signals separated by the SOBI algorithm. Due to the interference of strong impulse noise, the fault characteristics of the rotor system cannot be identified from the time domain waveform of the source signal in Figure 8a.