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Simplified LCA of a short belt conveyor
No full textThis paper outlines a simplified Life Cycle Assessment (LCA) of a short-flight belt conveyor, focusing on environmental and energy efficiency improvements. Results inform a model for a formal LCA using SimaPro8 software, aiming to provide detailed insight and quantify environmental impacts. The final LCA, presented as a methodology, offers instructions and recommendations for analysing any short-flight belt conveyor
Modeling of shaped charge jet penetration depth: Analytical and numerical approach
No full textShaped charge is the most effective armor-piercing mechanism, harnessing explosive charge detonation energy to form and accelerate a hypervelocity metal penetrator known as a jet. The process entails intricate dynamics including detonation wave propagation, its interaction with the metal liner, and subsequent liner collapse leading to jet formation. While both analytical and numerical models offer insight into this complex process, each approach presents distinct challenges. Analytical models, while conceptually straightforward, often rely on simplifications that compromise accuracy. Conversely, uncertainty or even unavailability of relevant material properties and high computational cost are the most important drawbacks of numerical models. Notably, the jet penetration phase imposes significantly greater computational demands compared to preceding processes of jet formation. This research aims at providing a deeper understanding of the jet interaction with target, as well as on determining its influence on penetration depth. We revisit an analytical model based on the virtual origin concept and complement it with numerical simulations using Abaqus/Explicit in a pure Eulerian domain. Through comprehensive analysis, we explore various jet parameters – such as kinetic energy, diameter, length, velocity gradient, and effective standoff distance – and their impact on penetration depth. The insights derived from this study hold practical significance for the preliminary evaluation of the shaped charge’s effectiveness and consequent refinement of the design of shaped charge projectiles or warheads
UREĐAJ ZA TERMIČKU PRIPREMU MIKROBIOLOŠKIH KULTURA POD DEJSTVOM TEMPERATURNOG GRADIJENTA DEVICE FOR THERMAL CONDITIONING OF MICROBIOLOGICAL SAMPLES BY TEMPERATURE GRADIENT
No full textУређај којим се врши термичка припрема микробиолошких култура тако што се
на радној плочи која је у контакту са микротитер плочом ствара и одржава
температурни градијент. Уређај се састоји од металног носача (1), вентилатора (2), (3),
хладњака (4), (5), термоелектричних Пелтијеових елемената (6), (7), алуминијумске
радне плоче (8), електричног кола (9) за мерење температуре, електричног кола (10) за
контролу температуре, мини-рачунара (11), електричног напајања (12), бежичне
тастатуре (13), компјутерског миша (14), компјутерског дисплеја (15), HDMI кабла (16),
micro USB кабла (17). Основни принцип рада уређаја је пренос топлоте кондукцијом са
алуминијумске радне плоче на микротитер плочу. Уређај омогућава in vitro испитивање
утицаја температуре на бактериолошке културе. Уређај остварује контролу температуре
у распону који је користан у већини биолошких испитивања (20–55 °C), преносив је,
може се лако серијски произвести јер се састоји од широко распрострањених
електронских компоненти и омогућава унапређење кроз развој програма за
мини-рачунар који је саставни део уређаја
Comparative Mechanical Analysis of PLA and ABS Materials in Filament and Resin Form
No full textAdditive manufacturing (AM), also known as 3D printing, represent technologies where the production of physical models with complex shapes is performed in a layer-by-layer manner, directly from the CAD model. With these processes, there is no need for additional tools or fixtures, and there is no excess material. There are seven different AM technologies, all utilizing different materials depending on the needed final part properties. Recent years were particularly significant for the development and advancement of polymer materials in AM. Among available technologies where polymer materials are used, this research covers extrusion-based Fused Deposition Modeling (FDM) and liquid resin photopolymerization technology called Digital Light Processing (DLP). Concerning the fact that these technologies processmaterials from different forms, the filament and resin form, the goal of this research was to compare the mechanical properties
of two of the most widespread materials in AM, Acrylonitrile Butadiene Styrene (ABS) and PolyLactic Acid (PLA), in filament and resin form. Specimen geometry and test protocols followed the dedicated standards. For a comprehensive analysis tensile, compression, and (three-point) bending tests were utilized here, along with surface fracture 2D optical microscopy and Shore A hardness test
DIRECT AND INVERSE KINEMATICS FOR 6DOF ROBOT BASED ON SCREW THEORY
No full textIn the modern age, robotics is gaining an ever-increasing role in shaping modern life, hence
why innovations are increasingly more directed towards this interdisciplinary scientific field.
The structure of a robot is complex and with a plethora of different ways to construct and
control it, here we provide an elegant geometric approach for achieving the desired task by
using screw theory [1]. As proved by the Chasles-Mozzi theorem, all motion can be obtained by a rotation around
a fixed screw axis and a translation along the same which lends itself naturally to the
representation of motion by screws. This is attained by an exponential coordinate
representation where given a screw axis and an angle we may find a matrix defining our motion
from a given coordinate frame. But why stop there? Not only motion, spatial velocities and
forces are defined within screw theory as twists and wrenches that act on inertial coordinate
frames attached that are instantaneously coincident to a fixed or even possibly moving frame.
However, unlike other ways of describing a robot's motion such as the Denavit-Hartenberg
method which has an excessive amount of coordinate frames, or the use of Euler angles (in
combination with position vectors) which have singularities at points, screw theory uses a less
cumbersome mathematical apparatus and uses implicit representations thereby avoiding
singularities. The mathematical foundation of screw theory lies on the foundation of the SO(3)
and SE(3) Lie groups and their algebras so(3) and se(3) which represent rigid body rotations
and motions in three-dimensional space respectively.
By far, the largest part of screw theory is rooted in linear algebra which ties in nicely to
implementation in practice. Everything described in this paper will be implemented using
Python and the Robot Operating System (ROS) on a six-degree-of-freedom robot manipulator
Niryo One. In Fig. 1(a) we have the basic geometric description of the Niryo One robot where
we have the position of each joint and its direction of rotation. Next, we define a fixed space
frame at the bottom of the robot and a moving body frame at the end-effector. Putting this all
together we have a kinematic diagram.
In robot kinematics, we use the Product of Exponentials to determine the forward kinematics
of a robot-given a set of joint angles, find the representation of the end-effector. While this is
straightforward, a more interesting problem which has garnered a lot of interest and is being
actively researched is the inverse kinematics-given a representation of the end-effector, find
the joint angles that correspond to it. There are two main ways of solving this problem,
analytically and numerically, both of which have their advantages and drawbacks. The Paden-
Kahan subproblems [2] seek to break apart the inverse kinematics into subproblems that have
a known analytical solution. On the other hand, fundamental to numerical nonlinear rootfinding
is the Newton-Raphson method which can find approximate solutions within a given
tolerance. But analytical solutions, if they exist, may not always have a closed-form solution
or their computation may be quite involved. The numerical approach, while usually efficient
and precise to a practically arbitrary degree, may not always converge with a given initial value.
Here we suggest a synergetic approach for robots that do not yield to Paden-Kahan
subproblems by a slight amount. It involves finding an approximate analytical solution using
the Paden-Kahan subproblems and using that as an initial value for the Newton-Raphson
method
COMPARATIVE ANALYSIS OF STATISTICAL FEATURES OF SIGNALS IN THE TIME DOMAIN IN INTERNAL TURNING OPERATIONS
No full textThis paper presents the results of research on the use of statistical features of the processed signal, recorded
during the machining process, on the occurrence of chatter. The change in the value of the selected features is also
their ability to indicate the occurrence of chatter during machining. The signals recorded during the internal turning
of a stepped surface at certain processing modes were compared. The idea is that by changing the depth of cutting
during internal turning, the values of the measured signals change. On that occasion, the stepped inner surface was
machined, in such a way that the tool keeps the same diameter during processing. During machining, two signals
were measured, force and acceleration along the Y direction. The obtained results show that the analyzed statistical
features in stable and unstable processing modes show significantly different values and that they can be useful as
indicators for the detection of chatter during the machining process
THE EFFECT OF MOISTURE CONTENT ON THE HARDGROVE GRINDABILITY INDEX OF COAL FROM THE KOLUBARA BASIN
No full textIn order to obtain data on the effect of moisture content on the grindability of coals, experimental research was conducted. The experiment included six samples of coal from the Kolubara basin. The samples were selected based on experimentally obtained values of their Hardgrove grindability index (HGI), in order to cover the entire range of experimental HGI values. In addition to determining the HGI, proximate, and petrographic analyses were performed on all samples.
Lignites are naturally tough, soft, and greasy when in a moist state. By reducing the moisture content, lignites become more brittle. For this reason, HGI values have different values depending on the moisture content at which they are determined.
The Hardgrove grindability index of coal (HGI) has a nonlinear dependence on the moisture content of the coal. All curves have two inflection points, one minimum and one maximum value of HGI in the tested range. The minimum values of HGI are in the range of 15 – 22 [%] of the mass fraction of total moisture in coal, while the maximum values of HGI are for a total moisture content of 5 – 13 [%].
In the case of high moisture content in coal, the obtained high values of HGI may not reflect the true grindability of the coal. These values could be misleading and not necessarily indicative of the coal's inherent characteristics. Instead, they could be a result of the imperfections in the Hardgrove method used to determine the grindability index of coal with high moisture content
DEEP CRYOGENIC TREATMETN OF ROLLING BEARINGS - INITIAL EXPERIMENTAL RESULTS
No full textRolling bearings are among the most commonly used standardized machine elements today. They have largely replaced sliding bearings in the majority of mechanical systems where precise rotational motion is required. This is the main reason why rolling bearings remain a focal point of scientific research, with the world's leading bearing manufacturers investing significant financial and material resources to improve their characteristics, aiming to increase their reliability and energy efficiency by enhancing dynamic load capacity, wear resistance, and reducing friction in rolling bearings. All these characteristics can be positively influenced by appropriate Deep Cryogenic Treatment (DCT). This process involves one or more cycles of cooling the bearing assembly parts (or the entire bearing) to a temperature significantly below zero degrees Celsius, maintaining that temperature for a predefined time period, and then gradually returning them to room temperature. Although a large number of relevant scientific studies have been conducted worldwide, the precise parameters of DCT that would ensure optimal bearing characteristics have not yet been defined. The problem lies in the complexity of the phenomena occurring in the bearing materials during DCT. Considering that, two teams from the Faculty of Mechanical Engineering at the University of Belgrade and the Fraunhofer – Institute for Machine Tools and Forming Technology (IWU), Chemnitz, Germany, have joined forces and designed a series of experiments to define the appropriate parameters of DCT for bearings. As objects of preliminary research, balls (rolling elements) of bearing types 6306, 6308, and 6310 were selected, as they are the most commonly used in conveyor idlers and the spherical shape particularly exhibits residual stresses that DCT positively affects. The balls were made of 100Cr6 steel, previously quenched and tempered, which limited the possibility of applying DCT between previous thermal treatment phases. Based on previous experience and available literature, parameters for three DCT cycles have been defined: two dynamic and one static, with dimensions, Rockwell C hardness, and surface roughness measured on all ball samples before and after the DCT. The results showed that static DCT is the most optimal for application, as it positively affects all measured characteristics, requiring only one DCT cycle. In the next phase of experimental testing, this DCT will be applied to the most important parts of the rolling bearing assembly, as well as to the bearing as a whole. The idea is to test four groups of samples: rolling bearings with cryogenically treated balls, rolling bearings with cryogenically treated rings, rolling bearings with both the rings and balls cryogenically treated, and rolling bearings without any DCT. During testing, the bearings' vibrations and temperatures will be measured, and, if feasible, the time to failure will also be recorded. The bearings with the best characteristics will then be installed in conveyor idlers, potentially leading to significant energy and financial savings in both surface and underground mining operations, as well as in other idler applications
