Lola Institut
  • Belgrade, Serbia
Recent publications
Strontium (Sr) and sodium (Na) are the most used modifiers in the aluminum casting industry. Both lose their concentration (fade) during holding in the melting furnace. Three types of chemical reactions in the melt may cause modifier fading: vaporizing, oxidizing, or reacting with some other elements from the melt. Due to Na and Sr’s very low vapor pressure, their vaporization from the aluminum melt was excluded as a reason for the modifiers’ fading. Oxidation looks like the major chemical reaction that causes the fading of Na and Sr from an aluminum melt. The present paper aimed to quantify the fading of Na and Sr in an Al–Si–Cu–Mg alloy. The loss of modifiers (Na and Sr) during melt holding in a furnace can be analytically quantified using equations taken from the literature. The calculated surface reaction rate constant (ks) can estimate the modifier’s loss during melt holding in industrial and laboratory furnaces.
The modification of silicon particles in as-cast aluminum alloys can be done with different modifiers. Sodium is the strongest one not so often used in aluminum casting plants. This is because sodium fading is considerably vigorous compared to other modifiers. This study examined the effect of sodium fading on the modification level of silicon particles in the AlSi7Cu0.5Mg (356) aluminum alloy. The cooling curve analysis has been applied to quantify sodium fading. Approximately 65 ppm of sodium in the tablet form was added to the melt. The sodium was held for 200 minutes in the melt to observe its fading. It was found that sodium does not fade rapidly, as the literature data proposed. Furthermore, it was recognized that modification with sodium produces more dross that can have a negative impact on the quality of cast parts if it is not properly removed from the melt. Besides thermal and chemical analysis, an image analysis technique can be additionally used as a quality control tool to assess the efficiency of modifiers.
In this paper, the methodology for verifying inverse kinematic equations is presented. Analysis of the kinematic structure of the machine is shown, which results in the kinematic equations needed for the configuration of the machine's postprocessor. The machine proposed in this paper is a five-axis machine tool with two rotating axes on the spindle. The machine's configuration is X'OYZBA. The derived equations are used to transform the CL data for a test model into a G code used on a virtual model of the machine tool. A simplified model of the machine is developed using the PTC Creo software, in which the initial testing of the equations was performed. The inverse kinematic equations were implemented in a postprocessing program using the Matlab software. Generated G-code for multi-axis machining process was tested on a virtual machine tool in the Vericut software.
This paper presents a method for the implementation of a robot forward kinematics algorithm that complies with the Denavit-Hartenberg (DH) convention in Robot Operating System (ROS). The integration of the algorithm in ROS is based on the representation of DH parameters in dual quaternion space. The main motivation for the presented research is to make use of ROS powerful visualization tools available in tasks that require robot forward kinematics calculation while keeping the principles of DH robot modeling convention. Implementation of the dual quaternion-based robot forward kinematics algorithm in ROS is demonstrated using a serial 6DoFs robot as an example.
The paper proposes a programming methodology for advanced manufacturing based on STEP-NC, a compliant to multi-axis CNC woodworking machining center. The equivalent virtual machine in the CAD/CAM, STEP-NC environment, is developed as a part of a programming system for considered CNC woodworking machining center. STEP-NC aims to provide a digital thread for CNC manufacturing running in the STEP-NC System world via the Internet that can enable advanced e-Manufacturing. Virtual machine as a digital twin is configured and implemented into the control system based on LinuxCNC, but configured virtual machine as a Web interface based on STEP-NC, also. The developed methodology is validated through machining simulation using the configured digital twin in the control system and machining experiments on the real machine.
Elderberry (Sambucus nigra) pith was modified with polyethyleneimine (PEI) in order to improve the adsorption properties. Characterization of both dried Sambucus nigra pith (DSNP) and amino modification of elderberry pith with branched PEI (PEI/DSNP) was performed by: Fourier-transform infrared spectroscopy (FTIR), optical microscopy, and porosity determination. The amine and ester number, as well as acid value, were determined on DSNP and PEI/DSNP samples using standard volumetric methods. The samples were used as adsorbents for Pb2+ ions from an aqueous solution in a batch system. The obtained results were fitted using suitable equilibrium isotherm and kinetic models. The maximum adsorption capacity for Pb2+ ions on DSNP and aminаted sample, obtained using Langmuir adsorption isotherm at 298 K, are 18.9 and 47.8 mg g-1, respectively. Based on the kinetic studies, the adsorption process follows the pseudo second-order model. Thermodynamic parameters showed that the adsorption process is endothermic and spontaneous. In general, the overall adsorption process was improved by modifying starting material with branched PEI modifier by introducing large numbers of amino functionalities having high affinity to cations.
On the way to building smart factories as the vision of Industry 4.0, the casting process stands out as a specific manufacturing process due to its diversity and complexity. One of the segments of smart foundry design is the application of artificial intelligence in the improvement of the casting process. This paper presents an overview of the conducted research studies, which deal with the application of artificial intelligence in the improvement of the casting process. In the review, 37 studies were analyzed over the last 15 years, with a clear indication of the type of casting process, the field of application of artificial intelligence techniques, and the benefits that artificial intelligence brought. The goals of this paper are to bring to attention the great possibilities of the application of artificial intelligence for the improvement of manufacturing processes in foundries, and to encourage new ideas among researchers and engineers.
The indirect identification of the geometric errors (GEs) in the rotary axis of a machine tool yields six equivalent GEs (EGEs) that are position-dependent; through an analytical proof, this study demonstrates that these errors also represent four position-independent GEs of the axis. Moreover, a novel algorithm using ball bar measurements to calculate the EGEs of a nutating rotary B-axis and a rotary C-axis is presented herein. This paper also presents a new analytical solution for the actual inverse kinematics of a nonorthogonal five-axis machine tool; this solution is used for GE compensation. The presented algorithms are implemented in a self-developed software that alters the nominal numerical control code in order to eliminate GEs. The compensation accuracy and efficiency are tested using a simulation system. The results demonstrate that the proposed compensation algorithm eliminates all identified GEs. Lastly, a cutting test executed on a machine confirms that the proposed algorithms considerably improve machining accuracy.
The parallel 2DOF (Degrees of Freedom) mechanism presented in this paper has been the basis of much research by many authors. There are many significant results for the presented mechanism, and some of them are reported in this paper. The main goal of the research regarding the parallel mechanism is to create a hardware and software system that will be used to configure machine tools with three or more DOFs. The software system consists of two parts. One part is a set of applications intended for machine analysis and defining optimal configuration, and the other part is a control system of the machine adapted to the hardware of the machine, its configuration and purpose. For the presented mechanism, the kinematic model of the mechanism is described first. Based on the kinematic model, equations representing solutions of kinematics problems are derived. The derived equations are in a generalized form, with some variable parameters of the machine, and in such a form they correspond to every possible configuration of the reconfigurable mechanism. The equations are initially used to analyze some basic configurations, and then to analyze some configurations that have not been analyzed and presented so far. Also, equations in this form that are applicable for all possible configurations of the mechanism, are part of both parts of the software system. The final result of the presented procedures is one machine that has optimized parameters in accordance with the appropriate production process and with a configured control system that corresponds to the configuration of the machine.
This paper considers computational fluid dynamics (CFD) analysis and experimental test strength verification of the UAV wing made of composite materials. The CFD calculation and static strength testing results of specific UAV wing are illustrated. Specific attention was given to the definition of aerodynamics loads acting on UAV wing and experimental tests of UAV wing. For a precise definition of aerodynamic loading of UAV in this work the commercial CFD software was used. The work aims to carry out one-way fluid–solid interaction (FSI) for UAV structural design, in which aerodynamics loads obtained from CFD analysis can be applied on the vehicle structure for steady-state static FE analysis. To determine precise aerodynamic loads of UAV in this research, the complete “tail-aft on booms” shaped configuration UAV is modelled and analyzed using CFD numerical simulation.
One of the consequences of the growth of the world industry is the increased need for electricity. It is imperative for developed countries to use renewable sources, both due to the declining reserves of conventional fuels and the reduction of environmental pollution. The unstoppable growth in the use of alternative sources is more than evident in these countries, while less developed countries are trying to keep up with them. This paper analyzes the development of renewable energy sources in the Republic of Serbia and some surrounding countries and the USA, Germany, France, Japan, Australia, and the Netherlands in the previous decade. A comparative analysis of utilization trends in developed countries in the world is also given, as well as a brief overview of the development of devices used in the processes of the utilization of these energy sources.
In the base, working of ventilation system can be analyzed in regular and incidental modes of operation. This paper concerns the specification of the longitudinal ventilation necessary to prevent upstream movement of combustion products in a tunnel fire. In this work the objective of the study is to analyze the road way tunnel ventilation system using CFD software to create comfort ventilation system in the tunnel. The comfort ventilation concept refers to the situation when air quality within the tunnel is reduced due to presence of polluted air in the tunnel. This paper is focused on ventilation system in a road traffic tunnel in moment of accident situation as fire. In this investigation numerical simulation of fire was carried out and determination of a critical air velocity depending on the power of the fire was conducted. The output results of the software developed for this purpose, which is also used in the realization of practical projects, are shown.
This paper presents an approach for developing the programming and offline simulation systems for low-cost industrial robots in the MatLab/Simulink environment. The approach is presented in the example of a virtual model of a 4-axis robot with hybrid kinematics intended for manipulation tasks. The industrial robot with hybrid kinematics consists of the well-known 5R planar parallel mechanism to which two serial axes have been added. The programming system developed in a MatLab environment involves generating G-code programs based on given pick and place points. The virtual model included in the simulation system is configured in the Simulink environment based on the CAD model of the robot and its kinematic structure. The kinematic model and the inverse kinematic problem have to be included in the virtual model to realize the motion of the virtual robot. The system of programming and simulation has been verified through several examples that include object manipulation to perform various tasks.
Due to the great expansion of woodworking, profile tools manufacturing has become current and in demand. In wood industry there are two large groups of tools: rotary and spindle milling cutters that can be profile or flat. The technology of making profile rotary milling cutters requires, apart from cutting, turning, milling, 5-axis grinding operation that is performed on a 5-axis CNC grinding machine with the A'OXYZC configuration.It is a machine of a very complex kinematics and high cost-price. The paper presents a new machine that has been built for 3+2-axis grinding - Profilator 100,used for industrial manufacturing of rotary and spindle profile milling cutters. The accuracy of measures and shapes of the profile cutters built on Profilator 100 is of a high level and in industrial exploitation the difference is not observed between the profile cutters built on 5-axis CNC grinding machines. Regarding technoeconomic cost-effectiveness, production costs of Profilator 100 are lower even by ten times compared to the cost-price of 5-axis CNC grinding machines of renowned world manufacturers such as Schneeberger and Volmer.
The paper shows the configuration of a new educational machine based on hybrid kinematics mechanism. The concept of a three-axis O-X hybrid mechanism is described, consisting of a single serial translational axis and a two-axis parallel mechanism that can operate in two variants, with extended form O and crossed form X-joints of the parallel mechanism. The virtual prototype of the machine was configured in a CAD/CAM environment, where simulations of the mechanism's operation were performed. A programming system for machine has been prepared that also enables program verification. An open architecture control system based on the LinuxCNC platform has been configured for control of the machine. The trial work of the machine was performed in order to verify the realized prototype and control.
Does Alzheimer Disease show a decline in cognitive functions that relate to the awareness of external reality? In this paper, we will propose a perspective that patients with increasing symptoms of AD show a change in the awareness of subjective versus objective representative axis of reality thus consequently move to a more internal like perception of reality. This paradigm shift suggests that new insights into the dynamicity of the conscious representation of reality in the AD brain may give us new clues to the very early signs of memory and self-awareness impairment that originates from, in our view the microtubules. Dialog between Adso and William, in Umberto Eco’s The Name of the Rose, Third Day: Vespers. “But how does it happen,” I said with admiration, “that you were able to solve the mystery of the library looking at it from the outside, and you were unable to solve it when you were inside?” “Thus, God knows the world, because He conceived it in His mind, as if it was from the outside, before it was created, and we do not know its rule, because we live inside it, having found it already made.”
This paper describes configuring the virtual horizontal machining center LOLA HBG80 within the programming and verification system and the open architecture control system. The horizontal machining center LOLA HBG 80 is represented by an equivalent virtual machine in a CAD/CAM environment (PTC Creo and Catia), STEP-NC Machine environment, and the control system. Virtual simulation is essential for machining, and the developed virtual machines are used for program verification and monitoring of the machining process. The virtual machine in the programming system allows the verification of the program before sending it to the real machine and includes verification of the tool path (CLF-Cutter Location File) and G-code. The paper also discusses the possibility of applying a new programming method known as STEP-NC and preparing an adequate environment that includes a virtual machine. The virtual machine in the control system represents the last level for the final program verification and the process monitoring system.
Safe and efficient training using flight simulation training devices (FSTD) is one of the fundamental components of training in the commercial, military, and general aviation. When compared with the live training, the most significant benefits of ground trainers include improved safety and the reduced cost of a pilot training process. Flight simulation is a multidisciplinary subject that relies on several research disciplines which have a tendency to be investigated separately and in parallel with each other. This paper presents a comprehensive overview of the research within the FSTD domain with a motivation to highlight contributions from separate research topics from a general aspect, which is necessary as FSTD is a complex man–machine system. Application areas of FSTD usage are addressed, and the terminology used in the literature is discussed. Identification, classification, and overview of major research fields in the FSTD domain are presented. Specific characteristics of FSTD for fighter aircraft are discussed separately.
This paper presents an application of an open architecture control system implemented on a multi-axis wood computer numerical control milling machining center, as a digital twin control. The development of the digital twin control system was motivated by research and educational requirements, especially in the field of configuring a new control system by "virtual commissioning", enabling the validation of the developed controls, program verification, and analysis of the machining process and monitoring. The considered wood computer numerical control (CNC) machining system is supported by an equivalent virtual machine in a computer-aided design and computer-aided manufacturing (CAD/CAM) environment, as well as in the control system, as a digital twin. The configured virtual machines are used for the verification of the machining program and programming system via machining simulation, which is extremely important in multi-axis machining. Several test wood workpieces were machined to validate the effectiveness of the developed control system based on LinuxCNC.
The thermomechanical buckling and postbuckling behavior of layered composite shell type structure are considered with the finite element method (FEM) under the combination of temperature load and applied mechanical loads. To account for through-thickness shear deformation effects, the thermal elastic, Higher-Order Shear deformation Theory (HOST) is used in this study. The refined higher order theories, that takes into account the effect of transverse normal deformation, is used to develop discrete finite element models for the thermal buckling analysis of composite laminates. Attention in this study is focused on analyzing the temperature effects on buckling and postbuckling behavior of thin shell structural components. Special attention in this paper is focused on studying of values of the hole in curved panel on thermal buckling behavior and consequently to expend and upgrade previously conducted investigation. Using FEM, a broader observation of the critical temperature of loss of stability depending on the size of the hole was conducted. The presented numerical results based on HOST can be used as versatile and accurate method for buckling and postbuckling analyzes of thin-walled laminated plates under thermo-mechanical loads.
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19 members
Zoran Dimic
  • Robotics
Jelena Vidakovic
  • ILR Robotics lab
Radomir Radiša
Pavle Stepanic
  • Computer Controlled Systems
Kneza Viseslava 70a, 11000, Belgrade, Serbia
Head of institution
Srecko Manasijevic, PhD