Abstract
Induction motor-planetary gearbox drivetrains are widely used for industrial productions, including machine tools in manufacturing systems. For fault diagnosis of planetary gearboxes in such electromechanical systems, motor current signal analysis provides an effective alternative approach, because motor current signals have easier accessibility and are free from time-varying transfer path effects. Planetary gearbox faults generate load torque oscillations, leading to both amplitude modulation and frequency modulation (AM-FM) effects on induction motor current signals. To thoroughly understand gear fault features in current signals, an AM-FM current signal model is derived through mechanical–magnetic–electric interaction analysis, explicit equation of Fourier spectrum is derived, and sidebands characteristics are summarized. To avoid an intricate sideband analysis, amplitude and frequency demodulation analyses are proposed, explicit equations of corresponding demodulated spectra are derived, and gear fault features are summarized. The theoretical derivations are validated through lab experiments. Localized fault on the sun, planet, and ring gears are all successfully diagnosed using the proposed method.
Highlights
P LANETARY gearboxes have unique merits of large transmission ratio and high load capacity in a compact package, and, are widely used for power transmission in many electromechanical systems, including machine tools in manufacturing industries [1]–[3]
Feng et al [8], [9] derived explicit equations for gear fault frequency calculation, summarized the spectral characteristics of vibration signals, and proposed amplitude and frequency demodulation analyses methods for planetary gearbox fault diagnosis. All these works focus on vibration signal analysis
Planetary gearboxes feature high vibration complexity because of their intricate structure and involute kinematics, the planet gear revolution around the sun gear and the resultant time-varying gear mesh location relative to vibration sensors. This leads to difficulty in planetary gearbox fault diagnosis via vibration signal analysis
Summary
P LANETARY gearboxes have unique merits of large transmission ratio and high load capacity in a compact package, and, are widely used for power transmission in many electromechanical systems, including machine tools in manufacturing industries [1]–[3]. FENG et al.: INDUCTION MOTOR STATOR CURRENT AM-FM MODEL AND DEMODULATION ANALYSIS FOR PLANETARY GEARBOX FAULT DIAGNOSIS 2387 oscillations, and further lead to changes in electric machine currents because of mechanical–magnetic–electric interactions. Ottewill et al [15] studied epicyclic gearbox fault effects on current signals based on a mathematical model of drive motor-epicyclic gearbox, and detected gear tooth profile errors via a synchronous averaging technique These works explain the interaction between gear faults and electric machine currents, but a thorough understanding of planetary gearbox fault current signals and an explicit summary on gear fault signatures are still in demand. This paper involves signature extraction from a large amount of current signals collected at high sampling frequency, and, closely relates to big data analysis
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