X90 mobile modules
X90 mobile system User's manual V 1.20 - Translation of the original manual
275
Gear damage
DIN 3979 provides a description of gear errors and defects. The most common errors in individual gearboxes are
described below.
The complexity of the machine dynamics must be taken into consideration in individual applications.
Gear ratio
The speed ratio must always be converted according to the gear ratio. The frequencies on the gearwheels are
always based on the speed of the respective axis.
Manufacturing defects
Oscillations due to manufacturing always occur in a gearbox. Typical manufacturing defects are pitch errors, profile
deviations, concentricity and spacing errors.
Depending on the gearwheel pairing, these individual defects can intensify or become less intense depending
on how the defects affect each other. The interplay of the individual defects is also responsible for the overall
oscillation behavior.
Pitch error is a frequently occurring defect and is used as an example here. Depending on whether the pitch error
is positive or negative, it is intensified or compensated by an existing load. The effects on the oscillation behavior
depend very much on the rigidity of the gearwheel. If there is a pitch error, a shock occurs that can be measured
effectively.
In addition to pitch errors, all form and dimensional gear errors lead to oscillations.
Failure mode
Frequency in raw
signal spectrum
Frequency in en-
velope spectrum
Comment
Meshing frequencies
1 x fz
1 x fz
Gear frequencies depend on the respective geometric ratios of
the wheels but can be precisely calculated in any case.
fz
... Meshing frequency
Defects caused by wear
If form and dimensional deviations occur during operation, observing the trend can lead to an appropriate level of
confidence when performing diagnostics.
Failure mode
Frequency in raw
signal spectrum
Frequency in en-
velope spectrum
Comment
Deterioration
1 x fz
1 x fz ± i x fn
Geometric errors increasingly appear additionally with side-
bands for the tooth meshing frequency.
fz
... Meshing frequency
fn
... Nominal speed
Wobbling
If the toothed belt axis and the rotation axis are not parallel, the phenomenon called wobbling occurs. This causes
2 flank errors per revolution. Depending on the position, there is one transmission on the inner edge and one on
the outer edge of the toothed wheel.
The doubled speed frequency is clearly evident in the frequency spectrum.
Failure mode
Frequency in
raw signal spectrum
Frequency in
envelope spectrum
Comment
Wobbling
1 x fn, 2 x fn
1 x fz, 2 x fz
Wobbling movements manifest as doubled speed frequency and
are usually accompanied by sidebands.
fn
... Nominal speed
fz
... Meshing frequency
