Syed Shaul Hameed The same module must be used by all meshing gears: Each millimeter of pitch circle diameter corresponds to one tooth in a one-module gear. A 0.3 mod gear with 60 teeth, for example, will have a pitch circle diameter of 18 mm (0.3 *60).

When two gears are meshing, their modules must be the same. It is the distance calculated on the pitch circle's circumference from one tooth's point to the tooth's equivalent point.

The teeth' stiffness depends on geometry (contact ratio) and force (torque). Both parameters are sensitive to the operating conditions, and the system must be treated as a nonlinear stiffness configuration. It is common to find a jump effect, meaning that the response depends on the initial conditions. Verify your mesh stiffness; you may have a range of frequencies depending on the function you used to model the force during teeth contact.

Juan Carlos Jauregui

Gear meshing frequency is a kinematic (rotation speed-related) parameter. If you have another maximum in the spectrum under loading conditions, this effect can probably be related to another source (gear coupling or bearing). Of course, if you have reduced rotation speed under load (motor power drop), you will have shifted the frequency of gear meshing.

Your gearmesh frequency looks a bit higher than your calculation. The line at 642 Hz probably results form another source (element bearings?) whose response depends highly on load. This line is amplified by a local resonance between 600 and 650 Hz, which you can better view in log scale. Using a lower resolution FFT (shorter FFT window) would also show better the resonances (modal responses) by the spectrum bottom shape. Other resonances are at 100 Hz, 320 Hz.

Another idea: Sometimes application of the load introduces a fluctuating torqueon the gears, and the frequency of this fluctuation shows up as a modulation frequency of the gearmesh frequency, and sometimes also as a modulation of the shafts rotating frequencies as well.

Here the difference in frequency is 141 Hz. Does this can be related to any torque fluctuation?

Luc Fromaigeat as suggested I did a short window ftt (narrowed frequency range around gear mesh frequency) and found the meshing frequency peak at around 762.6 Hz however the calculated frequency was 768Hz and the side band harmonics of the gear to be= [multiples of gear mesh frequency (+/ -) 8 Hz ]. where 8 Hz was later identified as carrier frequency.

* How do I find the resonance frequency of the entire test setup as a whole?

* What side bands should I observe if there are any defects in the gears?

This shows your gearmesh central frequency with an inaccuracy of -0.7%, which is possible. Then sidebands are at +- 8.03 Hertz, which represents +- 481.7 RPM. This frequency must correspond to something in the kinematics.

Luc Fromaigeat 481.7 rpm is the output speed of the gearbox.

*How do I find the resonance frequency of the gearbox components without individual performing impact test after disassembly?

* What side bands should I observe if there are tooth breakage defect in the gears?

OK,

1) you may examine the base noise on the spectra, and average enough to get a baseline that can be read

2) You may record a cascade plot, or a spectrogram when the machine runs down, or up, and o nthis plot, see where the response is high at constant frequency, versus variable frequency with speed.