Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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Research of the draw hook failures on rail vehicles in Serbia
No full textDraw hook failures present significant problems for railway safety and operational efficiency. Although failures on the draw gear are not frequent, they can induce serious problems on the vehicles and infrastructure when some elements break. This paper presents comprehensive research on the potential causes of these failures, aiming to provide insights for prevention measures related to materials, production process, geometry and manipulation practices during train operation. The draw hook, as one of the vital components in connections of wagons and locomotives, ensures the safety and reliability of trains during operation. By analyzing the historical failure data and relevant literature, this study identifies several key factors contributing to coupler failures. Material degradation emerges as a prominent concern, with factors such as fatigue, wear, and corrosion compromising the structural integrity of the coupler hook and other components over time. Overloading during starting, impacts, or improper coupling procedures further increase the risk of failures. Mechanical and physical characteristics of used material, as well as geometric inconsistencies, may also induce failure under operational conditions. Environmental factors, such as extreme temperatures, moisture ingress, and chemical exposure, pose additional challenges by accelerating material degradation and corrosion processes. Understanding the complex interaction of these factors is crucial for developing effective preventive maintenance strategies and for addressing and improving observed imperfections in draw gear elements. Implementing the results from this research can help railway operators and manufacturers of subjected elements mitigate the risk of failures, thereby ensuring the continued reliability and safety of rail transportation systems
DEGRADATION OF THE SURFACE OF SINTERED SAMPLES BASED ON CORDIERITE AND TALC UNDER THE EFFECT OF CAVITATION
No full textIn the paper, the cavitation resistance of refractory cordierite samples with the addition of 10%, 15% and 20% talc, sintered at 1200⁰ C, was investigated. The quality control method of the obtained sintered samples was investigated using the ultrasonic vibration method with stationary sample according to the ASTM G 32 standard. The formation and development of damage to the surface of the samples was monitored using a scanning electron microscope and the level of damage to the surface of the samples was quantified using image analysis. The change in the mass of the samples as a function of the cavitation time was monitored and the cavitation rate was determined. By measuring the mass loss and morphological analysis of the pits formed on the surface of the sintered samples of the mixture of cordierite and talc, the mechanism of degradation and resistance to the effect of cavitation was monitored. The obtained results were compared with the results of earlier tests of cavitation resistance of sintered cordierite samples. It was shown that the addition of talc in the mixture with cordierite significantly improved the properties of the sintered material compared to sintered pure cordierite. Small mass losses, small surface damage of samples of sintered cordierite with the addition of talc, indicate the possibility of obtaining a refractory materials with imroved properties of resistance to the effect of cavitation. The tests were done primarily to see the potential application of this material in hydrodynamic conditions, and especially because of the strong corrosion resistance of these refractory materials. Tests have shown that the application of the ultrasonic vibration method is suitable for a quick assessment of the quality of sintered samples and a forecast of resistance and stability during exploitation under cavitation conditions
FLEKSIBILNI ROBOTSKI HVATAČI U INDUSTRIJSKOM OKRUŽENJU– PREGLED POSTOJEĆIH MEHANIČKIH STRUKTURA
No full textHvatanje i manipulacija objektima spadaju u klasu osnovnih zadataka robotskih sistema. Robotski hvatači omogućavaju da se ovi zadaci realizuju i služe kao jedinstveni mehanički interfejs između robotskog sistema i okruženja, odnosno objekata manipulacije. Razvoj robotskih hvatača uslovljen je različitim zahtevima, među kojima se mogu izdvojiti stabilnost hvatanja, izbegavanje
proklizavanja, izbegavanje oštećenja objekta manipulacije i hvatanje objekata različitih oblika,
dimenzija i materijala. U uslovima velike varijantnosti objekata kojima se manipuliše javlja se potreba za razvojem hvatača sa ugrađnim visokim stepenom fleksibilnosti koji umnogome imitiraju sposobnosti ljudske šake. U ovom radu će biti izvršen pregled različitih mehaničkih struktura koje se koriste prilikom projektovanja podaktuiranih fleksibilnih robotskih hvatača i robotskih šaka
ARTIFICIAL NEURAL NETWORKS IN THE ANALYSIS OF SAFETY AND ERGONOMIC ASPECTS OF CABS OF MINING MACHINES
No full textPrethodna istraživanja su ukazala na značaj uticaja ergonomskih i ponašajnih faktora na bezbednost i zdravlje na radu rukovalaca rudarskim mašinama. U ovom istraživanju analiziraju se bezbednosni aspekti rada koristeći podatke o fizičkim karakteristikama rukovaoca i ergonomskim uslovima rada u rudarskoj industriji, tačnije u kabinama šest različitih tipova rudarskih mašina (buldozer, bager, damper, kombinirka, bušilica i utovarivač). Analiza je sprovedena nad podacima prikupljenim anketiranjem 61 rukovaoca rudarskim mašinama o ergonomskim faktorima, koji utiču na mogućnost povreda na radu. Primenom veštačkih neuronskih mreža, izvršeno je predviđanje pojave povreda. Rezultati pokazuju visok stepen tačnosti modela, što sugeriše mogućnosti unapređenja bezbednosti i zdravlja na radu kroz ergonomske intervencije i daje preporuku za dalju primenu veštačke inteligencije u rudarskoj industriji
SMARTMINER PROJECT AS A ROADMAP TO SMART, GREEN AND SUSTAINABLE MINING MACHINERY WORKPLACES
No full textRecent publications have acknowledged the many difficulties, concerns, and
problems facing the mining industry, as one of the oldest industries, still
encountered today, all of which require immediate attention. Through the
SmartMiner project, we are driven to suggest a variety of green digital
transformation strategies and solutions. By aligning advanced operator 14.0&5.0
and society S5.0 standards, project proposes novel concept which contains smart
solutions for raising the level of enviromnental quality in complex interactions
between physical, behavioral, and organizational processes field. It also proposes a
paradigm shift from pure technology to a Human and Data-Centric Engineering,
which can be easily transferred to other industries. Namely, mining machinery
operator and his enviromnent represent a set of complex interactions between
physical, psychosocial, and organizational factors and processes, which, if
mastered could lead to sustainable company performance and people-centric
smarter society. SmartMiner approach points out to operator's workplace micro
and macro enviromnent. Operator's MICRO enviromnent is represented by his
physical enviromnent - noise, human vibration, lighting, temperature, air quality,
workplace layout etc. Job stressors load, if sustained over time, produces adverse
effects such as health and safety problems and lack of performance. Operator's
MACRO enviromnent is determined by organizational contextual factors - safety
awareness, competence and communication on operational and managerial level,
organizational enviromnent dimensions, management support, risk judgment and
management reaction, safety precautions, accident prevention. Micro and micro
levels as physical processes layers are to be connected and balanced by real time
analytics - digital processes layers to fit high sustainability performance indicators
( economic, social, environmental etc.). After data collection on operators ( 460)
and managers (160) in surface mines, the structural equational modelling and
multicriteria decision aid methodologies are applied. Continuous monitoring and data acquisition on noise, whole body vibrations,
thermal stress, humidity, emission of gaseous and particulate pollutants from
internal combustion engines, and indoor air quality (gases, particulate pollutants)
at operator's workplace through sensors, is also done. Finally, using the machine
learning tools and algorithms, the predictive optimization models will be
developed in aim to predict the level of each workplace pollution and safety
parameters and productivity assessment, in line with innovative context-specific
multi-sensorial mining machinery operator aid system, based on sensorial model
and sustained with the soft/management parameters measurement scales, in aim to
enable improvement and optimization of techno-economic, environmental and
societal aspects of a workplace, while maintaining the highest standards of safety
CHATTER DETECTION USING SUPPORT VECTOR MACHINE
No full textThe paper presents a methodology for chatter detection based on machine
learning. The machining of an internal cone was performed on a CNC lathe, with
several different steps varied during the process. Concurrently with the machining,
acceleration was measured using an accelerometer in the direction of the penetration
force. The acceleration signal showed a sudden change in the form of an increase in
amplitude at the point of chatter occurrence. Using a Support Vector Machine-based
machine learning system, an algorithm was trained to detect chatter based on the
accelerometer signal. The goal of the algorithm is to identify three different states of
the system (stable, unstable – chatter, and transitional regime) on existing signals.
Four signals were used for training the algorithm, while two signals were utilized for
model validation
Integrity and Life in Emerging Architecture - Positioning the Architect in Continual Digital Design
No full textGuided by questions of contemporaries, leading to the question of integrity and durability of architecture, and by conclusions from recent conferences which advance architecture through digital approaches to designing and guiding architecture towards Artificial Intelligence (AI), we need to get back to the question on how to design in the future under multi-layered complex conditions and sustainability requirements of emerging architecture. Based on this, we conclude that the topic - Integrity of Architectural Objects is yet highly relevant, and this paper represents a continuation of research/ consideration of architectural spatiality as an activity of creativity and structural durability. The sense of careful and complex structural design as an example of a continual digital approach, e.g. a multi-layered network - joint effect of design and realisation of architecture is highlighted.
As digital design in architecture has proven to be elusive and occasionally uncontrollable without the meaningful participation of the architect, this paper highlights positioning of the architect as an important factor in solving integrity and durability challenges of emerging architecture.
Digital approaches in architecture are constantly developed and improved, and structural integrity and durability issues are becoming increasingly complex and serious, especially in relation to geometry/space design and sustainability, so architect’s knowledge involvement is inevitable and necessary in future data-driven design processes.
Positioning of the architect is based on expertise - activities and features, crucial in the process with identical characteristics, as the continuous development and improvement of knowledge, linking and anticipating all needs of the architectural process, the integrity and durability of architecture.
Additionally, knowledge will be meaningfully placed and integrated by positioning of the architect in society, in a critical attitude towards new technological achievements and re-examination of integrity and life of the structure in terms of sustainability and resilience of functional and spatial features of architecture.
The aim of the work is to show that knowledge as the main characteristic of the architect’s positioning in future design and realisation, is also the foundation for integrity and life in emerging architecture
POSITION CONTROL OF ROBOT MANIPULATOR USING OPTIMAL PID CONTROLLER
No full textDue to increasing demands of productivity and accuracy in today’s robotic applications, scientific community is under constant pressure to deliver more and more efficient control strategies. This is a challenging task considering the nonlinear nature of robotic structure, which is often accompanied with some degree of uncertainty of model parameters. Most of robots work in industrial surrounding and again, most of them are controlled through standard
proportional-integral-derivative (PID) algorithms. The reason for this lies in the relatively
simple structure of PID controller which can be easily implemented in practice, and the fact it
can achieve desired position without steady-state error. However, tuning control gains of the regulator in order to guarantee transient performance is not an easy task, and deserves further research.
In our case, a robotic manipulator is actuated by electric motors with reduction gears of high ratios. The presence of gears tends to linearize system dynamics and nonlinear coupling effects between the joints can be neglected. This way, each robotic joint can be controlled independently by using a linear model of DC motor. In this paper we are revisiting the PID control of robot manipulators in the light of modern control theory, which assumes an inevitable trade-off between the performance and robustness of the closed loop system.
Efficient load disturbance response is of primary concern when designing a control system. Also, system should be robust with respect to model uncertainties, i.e. it should possess a certain degree of relative stability when it comes to modeling errors. It is also important to have a good response to set point changes. More specifically, in this paper we are interested in achieving a set point response without overshoot, so that robot manipulator can approach the manipulated object without damaging it. Last but not least, the closed loop system should be able to cope with negative effects of measurement noise, and this is accomplished by incorporating derivative filter in the control design procedure. All the above specifications are necessary to be captured in an appropriate mathematical form. For example, the efficiency of load disturbance rejection can be expressed in terms of the integrated absolute error (IAE) due to a unit step at the process (motor) input. Sensitivity to modeling errors can be evaluated by the largest value of the sensitivity function. A good set
point response without overshoot can be achieved by placing dominant poles of the closed loop system in predetermined positions on the negative real axis of the complex s plane. Finally, noise attenuation can be adequately addressed by limiting the largest value of the sensitivity to measurement noise. So, having in mind everything stated above, the design specifications can
be formulated as the following optimization problem: find controller parameters that maximize proportional gain subject to the constraints on robustness and sensitivity to measurement noise. In order to successfully cope with the given problem, it is required to solve four nonlinear algebraic equations. Some preliminary results of position control of a robot manipulator with
three degrees of freedom are given in the figure below. Controller gains are determined based on the well-defined constrained optimization problem. Time response of every joint due to the unit step change of the set point value is shown. It can be seen that a zero overshoot set point response is obtained, which under a given robustness and performance constraints provides
optimal load disturbance rejection
ULTIMATE STRENGTH OF CORRODED HULL
No full textDuring the preliminary design of ships, almost all structural assessments are based on prescribed rule-based formulas and occasional direct calculations such as longitudinal strength, buckling and finite element analysis. Consequently, the maximum stress of the structure resulting from the critical loading is evaluated with respect to rule-prescribed allowable stress, which is lower than the yield stress of the material. This means that the strength of the ship is assessed only considering its predicted loading scenarios, original (as-built) scantlings and within its elastic response. However, the strength of the ship with respect to excessive (unpredicted) loadings, such as vertical bending moment and corroded scantlings is generally neglected. Fortunately, IACS has been developing ultimate strength procedures in its Common Structural Rules for Bulk Carriers and Oil Tankers (CSR BC & OT) based on progressive-collapse analysis (PCA) and nonlinear finite element method (NLFEM). Therefore, this work aims to present the ultimate strength assessments for a bulk carrier, in intact condition (no corrosion) and in corroded conditions of various severities and types. Moreover, an actual levels of ultimate strength reductions of the hull due to ageing of structural elements are delivered, proving that it has an important effect on structural integrity of the ship
The influence of welding parameters on the geometric characteristics of surface weld metal obtained by handheld laser welding
No full textThe handheld laser welding process is the latest innovation in welding technology with an increasingly broad range of applications primarily due to the simplicity of the welder's training, the minimal influence of the welder on joint quality, the low heat input, the high welding speed, and lower equipment costs. In this paper, the influence of selected welding parameters (wire feed rate and laser oscillation width) on the geometric characteristics of surface welds on low-carbon steel P235 is presented. Additionally, based on the selected optimal parameters, a butt joint was performed by welding plates made of the same base material. The dependence of these parameters on the weld metal width and the weld metal reinforcement was determined. Furthermore, it was concluded that the use of a device with higher power would most likely result in complete root penetration during butt welding