Experimental Detection of Spur Gear Eccentricity Severity Through Denoised FFT and STFT Analysis

Vaal University of Technology, Vanderbijlpark, Department of Industrial Engineering, Operations Management and Mechanical Engineering, South Africa.

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Published online: 14 January 2026

Abstract

Eccentricity in spur gears commonly results from manufacturing tolerances and assembly errors, generating periodic geometric deviations that affect gear-mesh dynamics and vibration signatures. An experimental study is undertaken to assess eccentricity severity using denoised Fast Fourier Transform (FFT) and Short-Time Fourier Transform (STFT) analyses. The experimental setup consists of a two-stage spur gearbox test rig fitted with radial accelerometers on the bearing housings of both the input and output shafts. Fault severity was systematically varied by attaching eccentric masses of 200 g, 400 g, and 890 g to the driven gear while maintaining constant operating conditions. Prior to frequency analysis, vibration signals were processed with a causal IIR filter to reduce background noise. FFT results showed a clear amplification of sidebands around the gear-mesh frequency and its harmonics as eccentricity increased. STFT representations further highlighted persistent and evenly spaced time–frequency components aligned with the mesh frequency, particularly at higher eccentricity levels.