Modeling the Transmission Path in a Planetary Gearbox: A Comparison of Two Methods

When the goal is to reduce the shaft speed with an important ratio between a driving and a driven part, engineers use a planetary gearbox (PG). For this reason, this power transmission system can be found in many mechanical units such as excavators, helicopters, ship propeller, etc. Hence, their condition-based monitoring has been investigated for decades and their diagnostic is still important since their breakdown can cause catastrophes and disasters. So, researchers have been interested in the difference between healthy and damaged cases PG dynamic behaviour. Due to its complex design, the knowledge of its healthy state is still investigated: as known, planet gears have two rotational motions: first one is around itself and the second one is around the gearbox centre. The last motion amplitude modulates the vibration signal acquired by a sensor attached to the housing. Hence, in this work, the variable transmission path in a planetary gearbox is modelled by two mathematical approaches. One of the above methods can be used when the amplitude modulation phenomenon is explicitly modelled from the dynamic model, in other words, when someone thinks to use a windowing function to model amplitude modulation phenomenon in a planetary gearbox. Advantages and drawbacks of each methodology are investigated.