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Fig. 8. Typical Baseline Spectrum

Fig. 7. Planetary Gear Example (OH-58C)

When all planets are equally spaced, they system has cyclic symmetry and its natural frequencies and modes have a well-de.ned structure. (Ref. 24)
Planetary sidebands were investigated by Inalpolat and shown to have characteristics unique to the number of plan-ets, planet spacing, and planet phasing. (Ref. 24) At least two groups of sidebands exist for signals from mounted ac-celerometers. One set appear at integer shaft orders and the rest are non-integer shaft orders. The .rst is due planets passing a .xed accelerometer. The signal experiences an increase in amplitude thus, an N planet system, one car-rier rotation yields N lobes. This is like having a(t) of Equation 2 with a frequency of N fg. Therefore, a sideband appears in the accelerometer’s frequency response at ±N from each harmonic component of the shaft order. In this work, .ve planetary transmission categories were created. The OH-58C has un-equally spaced planets and arbitrarily phased gear meshes (non-sequential) thus it is characterized by very rich sideband activity and the sidebands are non-symmetric. (Ref. 24)
Vibration Separation

The FM4 condition indicator has performed well for gear pair con.gurations. However, they have shown to be ineffective on the individual components of a planetary sys-tem. (Ref. 25) TSA has proven to be an effective tool to isolate non-commensurate dynamics. While this may be able to isolate the planetary system from others, it does not isolate the individual components of the planetary system. In 1990, McFadden introduced a method called vibration separation that allows for standard condition indicators to be applied directly to individual components of a planetary gear. Vibration separation is a signal processing technique used on planetary gear systems for the purpose of isolating dynamics associated with a single planet, sun, or ring gear. It involves extracting a subset of a measured acceleration signal at a time when a given planet is aligned with that ring-mounted accelerometer. This extraction is then used to synthesize a new signal, termed the Vibration Separation Vector , that represents the dynamics of the target gear. The underlying assumption is that the extracted signals are dom-inated by the simultaneous meshing of the aligned planet’s teeth with the ring and sun gears and that averaging can be used to expose the sought-after dynamics. The target gear’s tooth engagement schedule is computed and is used to match extracted data with each of the target gear’s teeth.
　
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