Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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SELECTION OF AN ALGORITHM FOR THE PREDICTION OF STOPPAGES AND/OR FAILURE OF EXCAVATION UNITS USING SUPERVISED MACHINE LEARNING
No full textThe paper presents research into the possibility of applying machine learning algorithms in the prediction of stoppages and/or failure of excavator units. Regression trees, Random Forest and Support Vector Machine (SVM) algorithms were tested with different hyperparameter variations on the collected set of data on the causes and downtime of stoppages of the observed excavator units. The result indicates that the trained SVM algorithm with sufficient accuracy (MSE 0.106) can predict the stoppages of the observed excavator units. Further research is aimed at expanding the database and further improving the possibility of predicting the level of danger for various causes of stoppages and/or failure of the observed excavator units
Мобилни уређаји за гашење пожара у моторним возилима
Get PDFУ првом делу разматрања је изложена класификација мобилних уређаја за
гашење пожара, као и преглед законске регулативе која прописује обавезу држања мобилних
уређаја за гашење пожара у моторним возилима. У другом делу се разматра
учестаност различитих узрока пожара на моторним возилима, на основу које су дати
предлози за избор мобилних уређаја за гашење пожара намењених за употребу у моторним
возилима
EXCAVATOR DOWNTIME’S DIFFERENCES BETWEEN TYPES AND COMPARISON WITH OTHER MINING EQUIPMENT
Get PDFMining equipment working time is critical for ensuring output and fulfilling mining project deadlines. In order to find trends and possible downtime minimization measures, this article analyses numerous types of excavators, dump trucks, loaders, backhoe loaders, bucket wheel excavators, and surface-top hammer drill rigs in Serbian mining sites. The study collects data on mechanical, electrical, technological, organizational, abuse and meteorological downtimes types with the aim to highlight efficient ways for minimizing non-operational periods, hence improving the overall productivity and safety of mining operations in the industry. Special emphasis is put on excavators whose role in the mining industry is pivotal, directly impacting project timelines and financial outcomes. The methodology includes analysing the duration and implications of different downtime categories. Collected data showed non-parametric features, according to the descriptive statistics. To compare the data, the non-parametric Mann-Whitney U-test is implemented. The results of the research showed that, in most cases, there is a difference in the duration of downtimes between different categories of excavators` downtimes. However, a comparison between excavator downtimes and other machinery downtimes has not shown any statistically significant differences. This analysis aims to contribute to the optimisation of mining equipment usage, offering valuable insights for mining industry stakeholders
Calibration of a Hybrid Machine Tool from the Point of View of Positioning Accuracy
No full textThe development of machine tools in the last twenty years includes, among other things,
the application of mechanisms with a non-linear kinematic structure as the mechanical basis of
machines. This results in significant improvements in kinematic characteristics and problems related to non-linear dependencies of the accuracy of the drive elements and the realization of movement in the machine’s external coordinates. The paper presents an approach to machine tool calibration based on the original O-X glide mechanism based on the ISO 230-4 standard with the mono- and bi-directional compensation of systematic errors and adaptation to the specifics of the mechanism’s kinematics. A machine tool prototype was designed and built for the research presented in the paper. The obtained results indicate the possibility of applying the existing recommendations and standards for testing the accuracy of machine tools with the need to correct the methodology by using linear and non-linear kinematic structures in machine tools
Geometrical design of gears using motion analysis in cad software
No full textThe utilization of tools provided by CAD software has become an essential component of any design process in modern mechanical design. These tools provide a simplified design methodology that does not require expert knowledge for the design of complex mechanical parts. Gears, as one of the most used mechanical components, have precisely defined and well-understood several types of tooth geometry. However, different shapes of tooth profiles cannot be easily analyzed and designed without knowledge of mathematics and analytical geometry. With modern design tools, especially CAD software, that knowledge is not necessarily required in the design process. Engineers can simply define the relative motion of one component to produce all necessary parameters that define the shape and geometry of another component
From Innovation to Standardization—A Century of Rolling Bearing Life Formula
Get PDFThis review paper is an homage to Arvid Palmgren’s pioneering paper on rolling bearing service life to highlight its relevance a century later. It follows the evolution of bearing service life theory from Palmgren’s fundamental research to the contemporary international standard ISO 281. Palmgren’s theory, based on the previously published papers of Stribeck and Hertz, laid the basis for the later development of bearing service life assessment methodology. Based on the Weibull theory of probability of damage, Lundberg and Palmgren introduced stochastic elements to explain the effect of reliability on bearing service life prediction. Harris and Ioannides, who made a significant contribution to the revision of the international standard on rolling bearing load rating and rating life are mentioned as well. Zaretsky’s critical analysis also was not neglected in this review, due to a different approach respecting the original influence of material properties and bearing performances. Despite standardization, ongoing research by leading advanced bearing industries and academic institutions continues to refine methodologies for service life assessment. Through a comprehensive review and analysis, this paper offers insight into the current state of bearing service life theory, highlighting the collaborative efforts bringing progress in this field
Investigation of occupants’ characteristics impact on thermal comfort assessment using a novel neural network PMVo calculation model
No full textThe main aim of this study is the analysis of the impact that occupants’ characteristics have on thermal comfort assessment, through establishing a novel PMVo model using an approximation method, based on the experimental data. The parameters which are chosen as model’s inputs are the air temperature, mean radiant temperature, relative humidity, basic clothing insulation, air velocity and occupants characteristics – gender, age, height, and body mass, while the output is the PMVo, a novel thermal comfort index. Since existing standards concerning thermal comfort do not consider these occupants’ characteristics, the main novelty of the introduced model is the inclusion of occupants’ characteristics in the thermal comfort assessment. To ensure enhanced precision, the model is established using both linear regression and by training neural network. These two approximation methods are compared to determine which one is more applicable in the context of data approximation. Study shows that regardless of dataset based on which models are established and regardless of testing input values, neural network (R2 in the range of 99.87% to 99.96%) is a superior mathematical approximation algorithm compared to the linear regression (R2 in the range of 95.3% to 97.5%). Novel neural network based thermal comfort assessment model is used for investigation of occupants’ characteristics impact on thermal comfort assessment. Analysis of the results showed that gender, age, height and body mass may significantly impact thermal comfort indices calculation, which implies the necessity of their inclusion in thermal comfort prediction and evaluation. Thus, the presented PMVo model may be highly beneficial to implement within existing thermal comfort standards, ensuring well-being and satisfaction with conditions of indoor environment for wider range of the occupants
Numerical investigation of fatigue behavior in Ti-6Al-4V orthopedic hip implants subjected to different environments
No full textIn this paper, hip implants made of Ti-6Al-4V titanium alloy are analyzed numerically using Extended Finite Element Method XFEM. The combined effect of corrosion and fatigue was considered here since this is a common cause of failure of hip implants. Experimental testing of Ti-6Al-4V alloy was performed to determine its mechanical properties under different working environments, including normal, salty, and humid conditions. The integrity and life of the hip implant were assessed using the Linear Elastic Fracture Mechanics (LEFM) approach. For this purpose, the conditional fracture toughness Kq using CT specimens from all three groups (normal, humid, salty conditions) were determined. This provided insight into how different aggressive environments affect the behavior of Ti-6Al-4V alloy; i.e., how much its resistance to crack growth would degrade depending on conditions corresponding to the real exploitation of hip implants. Next, analytical and XFEM analyses of fatigue behavior in terms of the number of cycles were performed for all three groups, and the obtained results showed good agreement, confirming the validity of the integrity assessment approach shown in this work, which also represented a novel approach since fatigue and corrosion effects were investigated simultaneously
KIBERNETSKO-FIZIČKI METROLOŠKI MODEL ZA INDUSTRIJU 4.0: DIGITALNI BLIZANAC I INTEROPERABILNOST
No full textU svrhu kreiranja kibernetsko-fizičkog modela (KFM) za proces planiranja inspekcije (PPI) na numerički upravljanoj mernoj mašini (NUMM), konfigurisan je merni sistem sa mernim predmetom, NUMM-om i steznim priborom. KFM sadrži dva skupa komponenti: virtuelne i fizičke. Virtuelna komponenta je virtuelni merni sistem kreiran u CAD (Computer Aided Design) okruženju. Dalje, u poglavlju se prikazuje modeliranje i simulacija virtuelnog mernog sistema baziranog na stvarnoj NUMM-i korišćenjem PTC Creo softvera. Simulacija uključuje programiranje merne putanje i generisanje DMIS (Dimensional Measuring Interface Standard) - (*.ncl) datoteke, za standardne tipove tolerancija (pravost, ravnost, itd.). Takođe, modelovane su komponente NUMM-e i definisan je celokupan sklop mašine sa kinematičkim vezama. Simulacija i generisanje izlazne DMIS datoteke u PTC Creo-u se vrši korišćenjem virtuelne NUMM-e. Koristeći generisanu DMIS datoteku, stvarna NUMM-a je programirana i korišćena je za realno merenje. Nakon toga, generisan je izveštaj o merenju. Glavni rezultat ovog poglavlja jeste modeliranje kibernetsko-fizičkog sistema baziranog na digitalnom mernom blizancu (DMB) i DMIS datoteci kao protokolu komunikacije. DMB predstavlja integraciju virtuelnog i stvarnog okruženja i stvara se u svrhu optimizacije, simulacije, komunikacije, praćenja i verifikacije procesa merenja. Ovo istraživanje prezentuje novi pristup programiranju NUMM-e u tzv. off-line režimu. S druge strane, u svrhu interoperabilnosti i komunikacije sistema, porede se i analiziraju DMIS kodovi koji potiču iz različitih softverskih aplikacija
HYBRID KINEMATIC MACHINE TOOLS
No full textZnačajan pravac za inovacije i razvoj novih mašina alatki je razvoj mašina alatki sa hibridnom kinematikom (MHK) koja ima odgovarajuće prednosti serijskog i paralelnog mehanizma. Ovaj rad razmatra i daje pregled razvijenih domaćih konfiguracija mašina sa hibridnom kinematikom. U radu su prikazane originalne konfiguracije mašina na Mašinskom fakultetu Univerziteta u Beogradu i Fakultetu tehničkih nauka Univerziteta u Novom Sadu.Significant direction for the innovation and development of new machine tool is a developing a hybrid kinematic machine (HKM) which have the respective advantages of serial and parallel mechanism. This paper considers the developed domestic configurations of HKM. The paper presents the developed original HKM configurations in University of Belgrade Faculty of Mechanical Engineering and Faculty of Technical Science University of Novi Sad