Modulation characteristics
Modulation characteristics exist widely in gear vibration and noise. When there are local defects in the gear, or scars, pits and other defects on the gear teeth, a amplitude modulation caused by periodic pulse excitation will be given on the spectrum diagram, and numerous low-frequency sideband will appear. The increase of vibration energy caused by faults and defects is mostly reflected in the sideband component. If the defect extends closer to the collar teeth, it will cause a larger, denser side band centered on the mesh frequency
Frequency modulation is the modulation of the central frequency at the meshing frequency by a pure single-frequency excitation, which will produce a side band family with equal time interval (a frequency in the frequency domain). If the vibration form is described in the form of simple harmonic period, where: is the meshing vibration frequency, which can be used as the carrier frequency; And are the modulation frequencies. There are amplitude modulation and frequency modulation due to the modulation characteristics.
Amplitude modulation (am)
Is the modulation factor, whose size depends on the state of defects. Amplitude modulation Y (t) is the modulation of shaft frequency to gear meshing frequency in FIG. 3, where A is amplitude vector; Is the modulation frequency; Is the carrier frequency; Is the initial phase.
The above modulation action can be expressed as adding two pairs of amplitudes and to the original meshing frequency component, and the corresponding frequency is and. It is the extra frequency component due to modulation, equivalent to the ξ NC frequency, known as the "sideband cluster". After amplitude modulation, the total energy of the modulated signal increases the sum of and, which can reflect the state characteristics of gear defects.