Investigation of the Gear Mesh Vibrations of Planetary Gearboxes Considering Phase Modulation and Internal Measurements

Condition monitoring enables the system manager to have an improved understanding
of a machine’s condition under changing operational conditions. It can
minimize the time and costs that are spent in maintenance activities, especially in
applications where system performance and reliability are important.
The objective of this thesis is to improve the knowledge of forced gear mesh
vibrations of planetary gearboxes and therefore contribute to enhancing condition
monitoring. This is accomplished by proposing two hypotheses.
First, all publications on the subject assume that the effect of the time varying
signal propagation delay between the main vibration source - the gear mesh point
- and the (usually fixed) transducer can be ignored for condition monitoring purposes.
Therefore the effect of the propagation delay is modelled as a phase modulation
of the gear mesh vibration. The results can prove for the first time that the
amplitude of the sidebands from the phase modulation is negligible and would
not interfere with condition assessment based on analysis of the modulation of the
gear mesh frequency, and thus the propagation delay can be neglected for practical
purposes.
A second hypothesis is also formulated and investigated in this work: internal
vibration measurements can detect gear mesh faults that cannot be detected with
external measurements. This is done by placing the vibration transducer on the
rotating parts inside the planetary gearbox. The results of the internal measurement
set-up shows an improved sensitivity for fault detection of planetary gearboxes by
allowing the transducer to rotate on the planet carrier.