Monitoring of complex gear system by synchronous cepstral analysis

This article shows the possibilities offered by the use of energy cepstrum for gear box vibratory diagnosis . A model of the signals generated by an accelerometric sensor will be established on which the theoretical expression of the energy cepstrum is partially calculated . This will make it possible to develop a detection tool which we will nether be affected by the signal amplitude, nor the noise to signal ratio nor the position of the sensor . It is shown that the use of an angular sampled signal enables the cepstrum to preserve its full resolution and allows the realization of synchronous averaging to isolate each gear mesh . Some applications of the monitoring procedure are presented .Dans cet article nous étudions les possibilités offertes par le cepstre d'énergie en diagnostic vibratoire des réducteurs à engrenages. Nous présentons un modèle approché de structure des signaux issus d'un capteur accélérométrique, à partir duquel nous calculons partiellement l'expression théorique du cepstre d'énergie. Cette expression nous permet de définir un révélateur de défauts indépendant de l'amplitude des signaux, du rapport signal à bruit et de la position du capteur. Nous montrons que l'utilisation de signaux acquis sous échantillonnage angulaire permet au cepstre de conserver sa résolution maximale et autorise la réalisation de moyennes synchrones pour isoler chaque engrènement d'un réducteur complexe. Enfin nous présentons quelques applications de notre procédure de surveillance

Diagnostic d'un train d'engrenages par analyse cepstrale synchrone

Nous exposons dans cet article nos résultats concernant l'acquisition et le traitement de signaux vibratoires issus d'accéléromètres placés sur des réducteurs à engrenages. Nous montrons que l'analyse cepstrale pratiquée sur des signaux obtenus sous échantillonnage angulaire peut constituer un outil de diagnostic simple et efficace. Nous avons calculé la contribution au cepstre de la modulation due à plusieurs périodes de rotation. Nous montrons que la somme des premiers pics cepstraux associés à chaque période est constante. Ce fait est confirmé par les résultats expérimentaux

Detecting the existence of gene flow between Spanish and North African goats through a coalescent approach

Human-driven migrations are one of the main processes shaping the genetic diversity and population structure of domestic species. However, their magnitude and direction have been rarely analysed in a statistical framework. We aimed to estimate the impact of migration on the population structure of Spanish and African goats. To achieve this goal, we analysed a dataset of 1,472 individuals typed with 23 microsatellites. Population structure of African and Spanish goats was moderate (mean FST=0.07), with the exception of the Canarian and South African breeds that displayed a significant differentiation when compared to goats from North Africa and Nigeria. Measurement of gene flow with Migrate-n and IMa coalescent genealogy samplers supported the existence of a bidirectional gene flow between African and Spanish goats. Moreover, IMa estimates of the effective number of migrants were remarkably lower than those calculated with Migrate-n and classical approaches. Such discrepancies suggest that recent divergence, rather than extensive gene flow, is the main cause of the weak population structure observed in caprine breeds.

Signal patterns of piston slap of a four-cylinder diesel engine

This paper presents an experimental study on the vibration signal patterns associated with a simulated piston slap test of a four-cylinder diesel engine. It is found that a simulated worn-off piston results in an increase in vibration RMS peak amplitudes associated with the major mechanical events of the corresponding cylinder (i.e., inlet and exhaust valve closing and combustion of Cylinder 1). This then led to an increase of overall vibration amplitude of the time domain statistical features such as RMS, Crest Factor, Skewness and Kurtosis in all loading conditions. The simulated worn-off piston not only increased the impact amplitude of piston slap during the engine combustion, it also produced a distinct impulse response during the air induction stroke of the cylinder attributing to an increase of lateral impact force as a result of piston reciprocating motion and the increased clearance between the worn-off piston and the cylinder. The unique signal patterns of piston slap disclosed in this paper can be utilized to assist in the development of condition monitoring tools for automated diagnosis of similar diesel engine faults in practical applications

Chatter stability prediction for CNC machine tool in operating condition through operational modal analysis

The stability of high-speed machining operations is crucial in machining process and presents a key issue for insuring better surface quality, increasing productivity and protecting both machines and safe workpiece. Stability prediction in milling is based on experimental modal analysis by the estimation of frequency response functions using a tap test. One limitation of accurately estimating the stability using such approach is the change in process and the dynamic characteristics of the machine tool under operation. This paper proposes a signal processing procedure applied to vibrations in machining process in order to obtain spindle’s modal variations in operation. The novelty of the proposed approach consists in removing “virtual modes”, caused by harmonic excitations, from the system response before performing operational modal analysis. Thus, the proposed procedure combines two existing techniques that are the Cepstral Editing Procedure and the Least Square Complex Exponential. The importance of the developed methodology is in adjusting the chatter stability criterion for material removal on a dynamic basis. The main work is given as follows: first of all, the Cepstral Editing Procedure (CEP) algorithm is applied on the acceleration signals for removing deterministic vibrations caused by harmonic excitations. The residue signal is the system response to white noise excitation. The frequency response functions (FRF) are then calculated from these signals at different cutting conditions. The outcome is compared to the result of impact test on the spindle under static condition. Similarities in the form of FRFs obtained in static and operational conditions validate the proposed approach while variations of modal properties under different cutting conditions are successfully captured. Secondly, the Least Square Complex Exponential (LSCE) method in operational modal analysis is invoked to find the natural frequencies and damping ratios of the system at different spindle speeds and cutting depths. Then, the dynamic chatter stability lobes diagrams (SLD) are established which account for spindle’s speed-dependent modal variations. A significant change in the stability border is observed which is interesting in machining fields. It will be shown that some depths of cut that are stable with static stability lobes become unstable with dynamic stability lobes and vice versa

Part I and II Blind separation of combustion noise and piston slap in diesel engine : Separation of combustion noise and piston-slap using blind source separation methods

International audienc

Discrimination des signaux vibratoires de courroies à partir de la jauge de contraintes et de l’accéléromètre triaxial

International audienceI - Usage de la courroie et limites - Un "fusible" très répandu et bon marché... - Qui s’use à cause des fortes contraintes... - Pouvant être limitéesII - Traitements statistiques - Les données - Les indicateursIII - Approche nouvelle - Méthodologie - Résultats à partir des indicateursConclusio

Part I and II : Blind separation of combustion noise and piston slap in diesel engine : Separation of combustion noise and piston-slap in diesel engine by cyclic Wiener filtering

International audienc

Utilisation de la déconvolution aveugle pour la détection et la caractérisation de défauts de roulement et d'engrenage

International audienc