Papers by YAKEU HAPPI KEMAJOU HERBERT
IJETT Journal , 2025
In this paper, an experimental study was conducted on a gear mechanism with eccentricity anomalie... more In this paper, an experimental study was conducted on a gear mechanism with eccentricity anomalies, emphasising advanced time-frequency domain methods to improve the diagnosis. Vibrations captured under various operating conditions were examined using RPM-frequency mapping, Short-Time Fourier transform (STFT), 3D waterfall FFT, and 3D Time-Frequency analysis. These techniques allowed for more accurate detection of eccentricity signs, including its impact on the interaction between gears and transmission performance. The results showed that elaborate phenomena such as intense modulation and nonlinear behaviors complicate accurate fault detection using traditional methods based solely on time and frequency domain. However, the multidimensional method adopted here allows for highlighting localised signal indicators that are directly associated with transmission disturbances due to eccentricity. This work, therefore, highlights the need to apply time-frequency methods to monitor the condition of gears and optimize their maintenance more effectively.
IJETT Journal , 2025
This paper employs a nine-degree-of-freedom dynamic model, considering torsional and lateral moti... more This paper employs a nine-degree-of-freedom dynamic model, considering torsional and lateral motions, to analyse the dynamic characteristics of a two-stage spur gear system. The model incorporates gear eccentricity faults and dynamic transmission errors by establishing a mesh stiffness model. The differential vibration equations for the spur gear system are derived using the Lagrangian method. Numerical simulations are conducted using a combination of the Short-Term Fourier Transform (STFT), 3D Waterfall FFT (Fast Fourier Transform), and RPM-frequency mapping technique under various operating scenarios. Analysing the responses imposed by the system under both regular and chaotic vibrations reveals that gear eccentricity faults significantly impact the system's performance. The frequency content changes over time and 3D plots provide a more detailed frequency-RPM representation, allowing the detection of transient faults in gears compared to the time domain and frequency domain. Theoretical analysis confirms the effectiveness of the STFT and 3D Waterfall FFT-based frequency-RPM transmission error detection approach.
Pitting and Crack Coexistence in a Model-Based Gear Dynamic System (Part I)
The analysis of the coexistence of pitting and cracking in a model-based dynamic gear system is u... more The analysis of the coexistence of pitting and cracking in a model-based dynamic gear system is uncommon. Most studies on the analysis of spur gear faults focus exclusively on a single defect, either pitting or cracking. This paper is focused on extracting and diagnosing the features of a two-stage spur gear's combination of pitting and cracking and determining which of the two has the most effect on the gear vibrations. The governing equations for coupled lateral and torsional vibrations of a two-stage spur gear model are established based on the energy principle. Numerical simulations based on feature extraction and diagnosis of coexistence of pitting and cracking in spur gears are carried out under stochastic perturbations of the initial conditions. Furthermore, Time-Frequency techniques and a Revolution Per Minute-Frequency map are used in various simulation scenarios to identify effective and sensitive signals to reflect high fault features. The results and analysis reveal that the Short-time Fourier transform (STFT) and RPM-Frequency map are appropriate indicators to extract the features and detect and diagnose that the pitting has a stronger influence than the cracking in a gear system with two-stage.
Journal of Vibroengineering
This paper uses a dynamic six-degree-of-freedom model that considers torsional and lateral motion... more This paper uses a dynamic six-degree-of-freedom model that considers torsional and lateral motions to predict the impact of pitting on vibration parameters in a spur gearbox for various operating speeds and torque loads. The study examines the dynamic characteristics of a gearbox with localized pitting damage on a single gear tooth using theoretical and experimental approaches. The research analyzes the forced vibrations of a single-stage spur gear system with pitting damage, which includes variations in mesh stiffness, damping, and gear error excitation, to identify symptoms of default. The equation of motion for the rotary gearbox system is established using the Lagrangian method in tandem with Short-Time Fourier Transform (STFT) and frequency-RPM map fault diagnosis. During real-time vibration monitoring, vibration signals are captured via accelerometers and processed in both the time and frequency domains using the LabVIEW data acquisition signal processing package to extract di...
Vibration, Feb 8, 2023
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
JOURNAL OF VIBROENGINEERING, 2023
This paper uses a dynamic six-degree-of-freedom model that considers torsional and lateral motion... more This paper uses a dynamic six-degree-of-freedom model that considers torsional and lateral motions to predict the impact of pitting on vibration parameters in a spur gearbox for various operating speeds and torque loads. The study examines the dynamic characteristics of a gearbox with localized pitting damage on a single gear tooth using theoretical and experimental approaches. The research analyzes the forced vibrations of a single-stage spur gear system with pitting damage, which includes variations in mesh stiffness, damping, and gear error excitation, to identify symptoms of default. The equation of motion for the rotary gearbox system is established using the Lagrangian method in tandem with Short-Time Fourier Transform (STFT) and frequency-RPM map fault diagnosis. During real-time vibration monitoring, vibration signals are captured via accelerometers and processed in both the time and frequency domains using the LabVIEW data acquisition signal processing package to extract diagnostic information. The experimental findings demonstrate how vibration analysis combined with time-frequency processing can recognize machine conditions even in harsh operational conditions. Moreover, the experimental results indicate a significant similarity with the theoretical analysis and validate the effectiveness of the RPM frequency technique-based pitting detection method, which can be an asset in gear fault monitoring.
Vibration
This work considers forced vibrations in a rotating structure consisting of a two-stage spur gear... more This work considers forced vibrations in a rotating structure consisting of a two-stage spur gear system with coexisting defects, specifically pitting and cracking. Numerical simulations and experimental analysis in various scenarios of the system in operation were conducted using the RPM–Frequency mapping technique. To identify fault characteristics, the analysis performed assumed the gear system had been misadjusted by a combination of pitting and cracking on the gear teeth. The correlation of the system-forced responses under regular and chaotic vibrations revealed that the system is far more sensitive to the crack than to the pitting when there are fluctuating harmonic peaks present at high vibration levels.
Vibration, 2023
This work considers forced vibrations in a rotating structure consisting of a two-stage spur gear... more This work considers forced vibrations in a rotating structure consisting of a two-stage spur gear system with coexisting defects, specifically pitting and cracking. Numerical simulations and experimental analysis in various scenarios of the system in operation were conducted using the RPM-Frequency mapping technique. To identify fault characteristics, the analysis performed assumed the gear system had been misadjusted by a combination of pitting and cracking on the gear teeth. The correlation of the system-forced responses under regular and chaotic vibrations revealed that the system is far more sensitive to the crack than to the pitting when there are fluctuating harmonic peaks present at high vibration levels.
IEEE, 2022
The analysis of the coexistence of pitting and cracking in a model-based dynamic gear system is u... more The analysis of the coexistence of pitting and cracking in a model-based dynamic gear system is uncommon. Most studies on the analysis of spur gear faults focus exclusively on a single defect, either pitting or cracking. This paper is focused on extracting and diagnosing the features of a two-stage spur gear's combination of pitting and cracking and determining which of the two has the most effect on the gear vibrations. The governing equations for coupled lateral and torsional vibrations of a two-stage spur gear model are established based on the energy principle. Numerical simulations based on feature extraction and diagnosis of coexistence of pitting and cracking in spur gears are carried out under stochastic perturbations of the initial conditions. Furthermore, Time-Frequency techniques and a Revolution Per Minute-Frequency map are used in various simulation scenarios to identify effective and sensitive signals to reflect high fault features. The results and analysis reveal that the Short-time Fourier transform (STFT) and RPM-Frequency map are appropriate indicators to extract the features and detect and diagnose that the pitting has a stronger influence than the cracking in a gear system with two-stage.
The dynamic analysis of the influence of pitting and crack coexistence in a two-stage spur gear s... more The dynamic analysis of the influence of pitting and crack coexistence in a two-stage spur gear system is investigated in this experimental study. Gear cracking is one of the main factors causing vibration in gears, and tooth pitting failure is the failure mode of the gear system that can simultaneously occur. An experiment was conducted on a two-stage spur gear test rig to extract and analyse its vibration features. The dynamic responses under variable parameters such as acceleration, frequency, and speed of the gear system behaviour are investigated. Parameter effects revealed a fractional frequency multiplication component and anomalous maximum variation due to the coexistence of pitting and cracking during the experimental test. The Short-Time Fourier Transform (STFT) and Frequency-Revolution Per Minute spectrum provide additional information to understand the influence of the coexistence of pitting and cracking during the engagement of the defective tooth with others. Therefore, the obtained results show the demonstrative power and the sensitivity of the proposed diagnostic technique to detect the gear defects at an operating speed greater than standard Fast Fourier Transform analysis. The STFT and the Frequency-RPM methods have proven effective in extracting and studying the characteristics of pitting and cracking faults in a spur gear system. The analysis results of the experiment showed a qualitative similarity with the obtained numerical results.
The dynamic analysis of the influence of pitting and crack coexistence in a two-stage spur gear s... more The dynamic analysis of the influence of pitting and crack coexistence in a two-stage spur gear system is investigated in this experimental study. Gear cracking is one of the main factors causing vibration in gears, and tooth pitting failure is the failure mode of the gear system that can simultaneously occur. An experiment was conducted on a two-stage spur gear test rig to extract and analyse its vibration features. The dynamic responses under variable parameters such as acceleration, frequency, and speed of the gear system behaviour are investigated. Parameter effects revealed a fractional frequency multiplication component and anomalous maximum variation due to the coexistence of pitting and cracking during the experimental test. The Short-Time Fourier Transform (STFT) and Frequency-Revolution Per Minute spectrum provide additional information to understand the influence of the coexistence of pitting and cracking during the engagement of the defective tooth with others. Therefore, the obtained results show the demonstrative power and the sensitivity of the proposed diagnostic technique to detect the gear defects at an operating speed greater than standard Fast Fourier Transform analysis. The STFT and the Frequency-RPM methods have proven effective in extracting and studying the characteristics of pitting and cracking faults in a spur gear system. The analysis results of the experiment showed a qualitative similarity with the obtained numerical results.
IEEE, 2021
The vibration signal developed by an affected gear pair in the gearbox and its detection is possi... more The vibration signal developed by an affected gear pair in the gearbox and its detection is possible in the vibration signal analyzer through various signal processing techniques. The persistence spectrum (pspectrum) is one of the techniques used to detect the energy in the time-frequency plane by reassigning energy in frequency for a fixed time. However, such an analysis is deficient in fault diagnosis in spur gearbox systems. The results do not give enough information through the time, and frequency components of the signal regarding the cracked tooth cannot. Its modulated signal analysis cannot detect any faults due to the crack. This paper describes an alternative technique to enhance the crack's diagnosis and detection of the crack on a single gear tooth in the gearbox system. The technique is based on the time domain, Fast Fourier Transform (FFT), and the combination of Short-Time Fourier Transform (STFT) and Frequency-RPM map fault diagnosis methodology. The technique enables to detect a crack in a 6 degree of freedom (6-DOF) torsional-lateral coupled model of a spur gear which is not the case of the frequency and time-frequency with the function pspectrum alone. Results and analysis reveal that the proposed technique can detect and diagnose early-stage crack tooth effects in the gearbox.
Experimental Study of the Influence of pitting and Crack Coexistence in Spur Gear System (Part II)
2022 IEEE 13th International Conference on Mechanical and Intelligent Manufacturing Technologies (ICMIMT)
Crack Fault Diagnosis for Spur Gears Using Gear Frequency-RPM spectrum
2021 IEEE 12th International Conference on Mechanical and Intelligent Manufacturing Technologies (ICMIMT)
The vibration signal developed by an affected gear pair in the gearbox and its detection is possi... more The vibration signal developed by an affected gear pair in the gearbox and its detection is possible in the vibration signal analyzer through various signal processing techniques. The persistence spectrum (pspectrum) is one of the techniques used to detect the energy in the time-frequency plane by reassigning energy in frequency for a fixed time. However, such an analysis is deficient in fault diagnosis in spur gearbox systems. The results do not give enough information through the time, and frequency components of the signal regarding the cracked tooth cannot. Its modulated signal analysis cannot detect any faults due to the crack. This paper describes an alternative technique to enhance the crack's diagnosis and detection of the crack on a single gear tooth in the gearbox system. The technique is based on the time domain, Fast Fourier Transform (FFT), and the combination of Short-Time Fourier Transform (STFT) and Frequency-RPM map fault diagnosis methodology. The technique enables to detect a crack in a 6 degree of freedom (6-DOF) torsional-lateral coupled model of a spur gear which is not the case of the frequency and time-frequency with the function pspectrum alone. Results and analysis reveal that the proposed technique can detect and diagnose early-stage crack tooth effects in the gearbox.
Process Biochemistry 42 5 856 862 Stereoselective Synthesis of L Homophenylalanine Using the Carbamoylase Method with in Situ Racemization via N Acylamino Acid Racemase
UK:Elsevier Ltd., 2007
IEEE, 2021
The vibration signal developed by an affected gear pair in the gearbox and its detection is possi... more The vibration signal developed by an affected gear pair in the gearbox and its detection is possible in the vibration signal analyzer through various signal processing techniques. The persistence spectrum (pspectrum) is one of the techniques used to detect the energy in the time-frequency plane by reassigning energy in frequency for a fixed time. However, such an analysis is deficient in fault diagnosis in spur gearbox systems. The results do not give enough information through the time, and frequency components of the signal regarding the cracked tooth cannot. Its modulated signal analysis cannot detect any faults due to the crack. This paper describes an alternative technique to enhance the crack's diagnosis and detection of the crack on a single gear tooth in the gearbox system. The technique is based on the time domain, Fast Fourier Transform (FFT), and the combination of Short-Time Fourier Transform (STFT) and Frequency-RPM map fault diagnosis methodology. The technique enables to detect a crack in a 6 degree of freedom (6-DOF) torsional-lateral coupled model of a spur gear which is not the case of the frequency and time-frequency with the function pspectrum alone. Results and analysis reveal that the proposed technique can detect and diagnose early-stage crack tooth effects in the gearbox.
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Papers by YAKEU HAPPI KEMAJOU HERBERT