According to the normal state and the fault state, the corresponding two groups of data in the experiment are taken for analysis. Firstly, the vibration signal is demodulated based on EEMD and symmetrical differential energy operator, and then Fourier transform is performed. In the normal state, the significant frequency of the frequency spectrum of the vibration signal of the planetary gearbox is the meshing frequency and its multiple frequency. Wear fault will lead to fatigue spalling of tooth surface and produce impact components. The spectrum shows that meshing frequency and its multiple frequency are carrier frequency, and fault characteristic frequency is the side band with interval.

The meshing frequency FM = 147.06hz, planet carrier rotation frequency FPC = 2.37hz, planet gear rotation frequency FPZ = 4.65hz, planet gear failure frequency FP = 7.03hz can be obtained.

The data under normal state is demodulated by symmetrical differential energy based on EEMD, and the spectrum diagram is analyzed, as shown in Fig. 1. It can be seen from Fig. 1 that the amplitude of meshing frequency (147.5hz) and its frequency doubling point are significant in the spectrum of normal state signal, which conforms to the characteristics of wear fault of planetary gearbox vibration signal The meshing frequency and the side band near the double frequency are analyzed. The distribution of the side band of the planetary carrier rotation frequency FPC, planetary gear rotation frequency FPZ and planetary gear fault frequency FP is observed, as shown in Fig. 2.

The data in fault state is demodulated by symmetrical differential energy based on EEMD, and its spectrum is analyzed. It can be seen from Figure 2 that the spectrum of the signal in the fault state is similar to that in the normal state, and there are obvious peaks at the meshing frequency (146.5hz) and the frequency at the frequency doubling. The difference is that with the increase of working time, the amplitude of the meshing frequency and the amplitude at the frequency doubling increase significantly, which is in line with the actual working state. Analyze the sideband near the meshing frequency and its frequency doubling in Figure 2, and observe the distribution of sideband with meshing frequency and frequency doubling interval frequency of planet carrier rotation frequency FPC, planet gear rotation frequency FPZ and planet gear failure frequency FP (154hz, 728.5 Hz, 742 Hz, 888hz and 1182hz are equal to planet gear failure frequency FP) As shown in Figure 3.

It can be seen from Figure 3 that in the normal state, the coupling between the meshing frequency and the sideband near the frequency doubling is mostly coupled with the planet carrier rotation frequency FPC and the planet gear rotation frequency FPZ, but the planet gear failure frequency FP does not participate in the coupling, so it can be judged that in the normal state, the meshing frequency and the sideband near the frequency doubling are not coupled with the planet gear failure frequency FP.

Figure 4 shows that in the case of coupling between the meshing frequency and the sideband near the frequency doubling, the appearance of the planet carrier rotation frequency FPC and the planet gear rotation frequency FPZ does not change greatly compared with the normal state, but the planet gear failure frequency FP appears many times. Therefore, it can be judged that the planet gear failure frequency exists in the sideband near the meshing frequency and the frequency doubling under the fault state FP participates in coupling for many times, so it can be judged that the planetary gear has serious wear fault.