Manufacturing errors on the tooth working surfaces of a gear can be approximately categorized into three classes:(1)
the manufacturing error component common to all teeth on the gear(2) manufacturing errors with strong correlations over multiple-tooth spans,and(3)manufacturing errors with weak or negligible correlations over multiple-tooth spans.
Manufacturing errors (and intentional tooth modifications)in class(1)provide STE contributions only to the tooth-meshing harmonics; manufacturing errors in class(2)provide STE contributions primarily to the very-low-order rotational harmonics and "sideband" rotational harmonics in the immediate neighborhoods of the tooth-meshing harmonics;
whereas, manufacturing errors in class(3)generally provide weak contributions distributed to the rotational harmonics that are observed in the rotational harmonic spans between the groups of "sideband" harmonics associated with the tooth-meshing harmonics. The typical amplitudes of the geometric manufacturing errors in the class(3) do not differ
significantly from the amplitudes of early tooth damage, or changes in tooth elastic deformations caused by tooth or gear body fatigue cracks. The tooth-working-surface manufacturing errors in class(3)constitute the "interference" that a successful damage-detection algorithm must discriminate against