1,720,984 research outputs found
Vibration Monitoring: Gearbox identification and faults detection
Full text linkL'abstract è presente nell'allegato / the abstract is in the attachmen
Optimization of irregular-shaped resonant plates for pyroshock testing in the aerospace industry
No full textThe simulation of pyroshock tests through resonant plates is a standard procedure to verify the resistance of space equipment to high-frequency shocks generated by pyrotechnic devices. These shocks lead to significant risks, potentially compromising missions. Space qualification criteria - typically expressed in Shock Response Spectrum (SRS) terms - vary based on launch vehicle characteristics and follow the guidelines provided in international standards such as the NASA-STD-7003A. This study employs a frequency domain-based numerical model and a heuristic optimization algorithm to optimize resonant plate designs, considering irregular quadrilateral shapes. Integrating a CAD modeler, finite element solver, and genetic algorithm optimizer improves SRS prediction accuracy, reduces calibration times, and minimizes trial-and-error repetitions. While adopted decisions may influence specific outcomes, this work outlines a general methodology applicable across diverse requirements and constraints
ANOVA and other statistical tools for bearing damage detection
Full text linkThe aim of the paper is to exhaustively exploit and test some statistical tools, such as ANOVA and Linear Discriminant Analysis, to investigate a massive amounts of data collected over a rig available @DIRG Lab, specifically conceived to test high speed aeronautical bearings; the rig permits the control of rotational speed (6000 - 30000 RPM), radial load (0 to 1800 N) and temperature, and allows monitoring vibrations by means of 4 tri-axial accelerometers. Fifteen different damages have been realised on the bearing but, for simplicity, this papers only treats those cases where simple identification methods have failed or not demonstrated to be fully affordable. The damages have been inferred on rolls or on the internal ring, with different severities, which are reported as a function of their extension, i.e. 150, 250, 450 μm. A total number of 17 combinations of load and speed have been analysed per each damaged bearing. Although ANOVA rigorously applies when some conditions are respected on the probability distribution of the responses, such as Independence of observations, Normality (normal distribution of the residuals) and Homoscedasticity (homogeneity of variances - equal variances), the paper exploits the robustness of the technique even when data do not fully fall into the requisites. Analyses are focused on the best features to be taken into account, trying to seek for the most informative, but also trying to extract a "best choice" for the acceleration direction and the most informative point to be monitored over the simple structure. Wanting to focus on the classification of the single observation, Linear Discriminant Analysis has been tested, demonstrating to be quite effective as the number of misclassification is not very high, (at least considering the widest damages). All these classifications have unfortunately the limit of requiring labelled examples. Acquisitions in un- damaged and damaged conditions are in fact essential to guarantee their applicability, which is quite often impossible for real industrial plants. The target can be anyway reached by adopting distances from un-damaged conditions which, conversely, must be known as a reference. Advantages of the statistical methods are quickness, simplicity and full independence from human interaction
Condition monitoring of an industrial book-cutting machine using a novel mixture of vibration and physics-based features
No full textThis study presents an enhanced approach to machinery diagnostics and prognostics, using artificial intelligence and machine learning to improve vibration monitoring systems for industrial equipment maintenance. Targeting a complex automatic book-cutting machine, the proposed diagnostic system integrates a mixture of diverse feature types, combining accelerometric data with physics-based features to provide a more comprehensive and accurate monitoring solution. A dataset, developed through a full factorial design of experiments, covers a range of operational states, while data processing generates an optimal feature set for maintenance decision-making. This hybrid approach, exploiting the novel combination of features, offers superior identification of machine states of health compared to traditional vibration monitoring, generating benefits such as reduced downtime and costs, as well as enhanced product quality. In the specific application analyzed, the proposed method improved classification accuracy by approximately 7% compared to traditional vibration monitoring techniques. By integrating these advancements, achieved through sensor fusion and multi-channel data, into a Supervisory Control And Data Acquisition (SCADA) system, this research aligns with the goals of Industry 4.0, supporting digital and cyber-physical manufacturing systems with an intelligent, data-driven condition-based maintenance strategy suitable for modern automated environments
Bearing damage detection techniques and their enhancement: comparison over real data
No full textThe Dynamics & Identification Research Group at POLITO has been involved in the challenge of bearing damage identification for aero-engines for more than ten years. The role of gearboxes in future aircraft scenario is well focused by the Horizon 2020 - Green Engine program, where some important issues are addressed. One is surely the future of fan propeller engines, where the entire engine powers is flowing through the gearbox as for the case of helicopters. This is a real challenge for early diagnostic techniques both for gears and bearings. In this frame, the DIRG has developed and tested a huge number of algorithms seeking for the ―best performances‖ on real application; this statement must be interpreted as a trade-off among many factors such as: the limited number of sensors, the missing direct torque measure, the short time allowed for real time analysis, the decisional path compromise, the number of false and missed alarms, and so on. Some of these methods are quite ancient (RMS, Kurtosis, Skewness, Crest, and similar evolutions such as FM0 - NA4 - NA4* - FM4 -M6A - NB4) but still can be used as a reference to check how more recent techniques can improve the results and the sensibility to early damages, as well as the localisation (in spite of longer elaboration time). Among the new methods, EMD / EEMD [1], SK [3], Stochastic Resonance [2] and Principal Component Analysis (PCA) [4] are compared in the paper in terms of detection capability but also location identification, minimum number of sensors, false alarms and so on. In practice, however, it should be borne in mind that most of these methods are usually employed in sequence or parallel, so that a meaningful comparison cannot be done and, in this case, it would generate a huge number of combination sets. The elaboration time is also considered as one of the parameters toward its adoptability along the paper
Numerical Modeling of a Pyroshock Test Plate for Qualification of Space Equipment
Full text linkOver their life, space equipment needs to withstand strong high-frequency shocks, which could cause mission and safety critical damages. In order to verify the compliance with safety standards, pyroshock tests are employed. Based on launch vehicle characteristics, the requirements for the qualification of space equipment are usually established following the NASA-STD-7003A international standards in terms of a Shock Response Spectrum (SRS) representing the damage potential of the shock. Laboratory tests should then match the actual stress conditions reached during a real launch. Historically, this was obtained by means of explosive charges (hence the name “pyroshock”). Nevertheless, to foster repeatability and safety in laboratories, hammers or bullets are commonly used in nowadays shock testing machines.
In this work, a resonant fixture test bench is considered. In this very common layout, a resonant metallic plate is interposed between the impact location and the test component so as to better simulate the shocks. The response of the resonant plate - which determines the required shock response spectrum - is currently empirically tuned by adding masses, damping, stiffness, or by varying the nature of the impact. This study aimed at developing a numerical model able to completely simulate a pyroshock test. Such a model can be used both for designing and for tuning the test bench so as to easily match different SRS requirements for different components under test. This leads to great economical advantages as can cut the calibration times leading to more efficient and effective testing
The Politecnico di Torino rolling bearing test rig: Description and analysis of open access data
Full text linkNowadays, machines-diagnostics via vibration monitoring is rising an always growing interest thanks to the huge and accurate amount of health information which could be extracted by the raw data coming from accelerometers. Damage severity, type and location of a fault are the kind of information which are buried in the time records.
The scope of this paper is double: first, to present the huge amount of data which have been acquired on the rolling bearing test rig of the Dynamic and Identification Research Group (DIRG), in the Department of Mechanical and Aerospace Engineering at Politecnico di Torino and to share them with the scientific community; secondly, to present a statistical approach analysis and its performances as example of a simple technique to be fruitfully adopted for comparison. To this goal, a detailed presentation of the test rig is given, which comprehends different working conditions up to 30,000 rpm, damage types and levels, var- ious sensors positions and directions as well as an endurance test. The related time records can be downloaded from ftp://ftp.polito.it/people/DIRG_BearingData/.
Afterword, tried-and-tested statistical tools are exploited to learn the information about bearing damages from this massive amounts of data. This ‘‘data mining” will be performed using inferential statistical techniques as analysis of variance (ANOVA), applied on usual statistical features, which characterize of the signal. A linear discriminant analysis (LDA) in the configuration proposed by Fisher will be also used to see if the data were classifiable in a multidimensional space with this basic algorithm. Finally, an Outlier Analysis based on Mahalanobis distance will be formulated, so as to distinguish a damage condition from the healthy state (training data), compensating when possible for environmental (temperature) and operational (speed and load) variations
Performance of Envelope Demodulation for Bearing Damage Detection on CWRU Accelerometric Data: Kurtogram and Traditional Indicators vs. Targeted a Posteriori Band Indicators
Full text linkEnvelope demodulation of vibration signals is surely one of the most successful methods of analysis for highlighting diagnostic information of rolling element bearings incipient faults. From a mathematical perspective, the selection of a proper demodulation band can be regarded as an optimization problem involving a utility function to assess the demodulation performance in a particular band and a scheme to move within the search space of all the possible frequency bands {f, Δf} (center frequency and band size) towards the optimal one. In most of cases, kurtosis-based indices are used to select the proper demodulation band. Nevertheless, to overcome the lack of robustness to non-Gaussian noise, different utility functions can be found in the literature. One of these is the kurtosis of the unbiased autocorrelation of the squared envelope of the filtered signal found in the autogram. These heuristics are usually sufficient to highlight the defect spectral lines in the demodulated signal spectrum (i.e., usually the squared envelope spectrum (SES)), enabling bearings diagnostics. Nevertheless, it is not always the case. In this work, then, posteriori band indicators based on SES defect spectral lines are proposed to assess the general envelope demodulation performance and the goodness of traditional indicators. The Case Western Reserve University bearing dataset is used as a test case
Turbomolecular high-vacuum pump bearings diagnostics using temperature and vibration measurements
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