Vibration measurement and control of planetary gears

Abstract

Planetary gears are widely used in many applications such as power transmission in automotive vehicles, aircraft, turbines, power screws etc. They are different from parallel shafts gears because of their compactness, better load-carrying capacity etc. These advantages do not restrict them from vibrating during operation. This research work focuses on their mathematical modelling, vibration measurement and control. Mathematical modelling was done in order to predict the free and forced vibration responses of a planetary gear comprising different numbers of up to six planet gears. Two coordinate systems were used namely fixed and rotating frames of reference. It is shown that the same natural frequencies can be obtained using either a fixed or rotating frame of reference, but on the condition that the carrier speed is set to zero when using a rotating frame of reference. Furthermore, the effect of the carrier speed on the natural frequencies were investigated using a rotating frame of reference on a four-planet model. It shows that only the natural frequencies of the translational modes are either increasing or decreasing, the natural frequencies of the rotational and planet modes remain significantly unchanged. Both the predicted and experimental results were compared, there is a certain level of agreement. Spinning vibration experiments were conducted in order to determine the effect of various loads at a constant speed, and various speeds at a constant load on the natural and mesh frequencies of a planetary gear. This was achieved with the use of MEMs accelerometers which were mounted and rotate with the system to measure the vibration of a carrier, sun and planets. A further investigation identified the principal source of vibration in the planetary gear train during operation considering different loads and speeds. A Principal component analysis (PCA) was employed to identify the principal vibration sources. Finally, a method of active vibration control called pole placement was used to shift the poles of the system theoretically in order to mitigate vibration. This was done to prevent resonances which may occur if the frequency of the synchronous vibration or mesh frequency coincides with any of the system natural frequencies. Poles were assigned to the carrier and sun gear for different scenarios and subsequently assigned simultaneously to them. Some of the poles of the translational modes whose vibration can be very severe were shifted, the poles corresponding to the rotational modes remain unchanged.

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ORCID for Neil Ferguson: orcid.org/0000-0001-5955-7477

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