Mekatronik Mühendisliği Bölümü Yayın Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/255

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Citation - WoS: 9
Citation - Scopus: 9
An integrated scheduling and control model for multi-mode projects
(Springer, 2013) Hazir, Oncu; Schmidt, Klaus Werner; 4168; Mekatronik Mühendisliği
In today's highly competitive uncertain project environments, it is of crucial importance to develop analytical models and algorithms to schedule and control project activities so that the deviations from the project objectives are minimized. This paper addresses the integrated scheduling and control in multi-mode project environments. We propose an optimization model that models the dynamic behavior of projects and integrates optimal control into a practically relevant project scheduling problem. From the scheduling perspective, we address the discrete time/cost trade-off problem, whereas an optimal control formulation is used to capture the effect of project control. Moreover, we develop a solution algorithm for two particular instances of the optimal project control. This algorithm combines a tabu search strategy and nonlinear programming. It is applied to a large scale test bed and its efficiency is tested by means of computational experiments. To the best of our knowledge, this research is the first application of optimal control theory to multi-mode project networks. The models and algorithms developed in this research are targeted as a support tool for project managers in both scheduling and deciding on the timing and quantity of control activities.
Citation - WoS: 9
Citation - Scopus: 10
Computation of supervisors for reconfigurable machine tools
(Springer, 2015) Schmidt, Klaus Werner; 17337; Mekatronik Mühendisliği
The rapid reconfiguration of manufacturing systems is an important issue in today's manufacturing technology in order to adjust the production to varying product demands and types. In this paper, we study the control of reconfigurable machine tools (RMTs) with the aim of fast reconfiguration and an easy controller implementation. We first formulate a particular reconfiguration problem for RMTs in a discrete event system setting, and then provide a necessary and sufficient condition for its solution. Moreover, we propose a polynomial-time algorithm for the construction of a reconfiguration supervisor as the composition of one modular supervisor for each separate RMT configuration. Each modular supervisor operates in three modes. In the first mode, it tracks the plant state if its corresponding configuration is inactive. In the second mode, it performs a configuration change if its corresponding configuration becomes active and in the third mode, it follows the specified behavior of its corresponding configuration if the configuration is active. An important property of the proposed reconfiguration supervisor is that it performs reconfigurations in a bounded number of event occurrences. In addition, the modular realization of our reconfiguration supervisor enables controller modifications such as adding or removing configurations during run-time. All results presented in the paper are illustrated by an RMT example.
Citation - WoS: 26
Citation - Scopus: 30
Effect of powder metallurgy Cu-B4C electrodes on workpiece surface characteristics and machining performance of electric discharge machining
(Sage Publications Ltd, 2016) Cogun, Can; Esen, Ziya; Genc, Asim; Cogun, Ferah; Akturk, Nizami; 3837; 52373; Mekatronik Mühendisliği; Ortak Dersler Bölümü; Makine Mühendisliği
The main aim of this study is to produce new powder metallurgy (PM) Cu-B4C composite electrode (PM/(Cu-B4C)) capable of alloying the recast workpiece surface layer during electric discharge machining process with boron and other hard intermetallic phases, which eventually yield high hardness and abrasive wear resistance. The surface characteristics of the workpiece machined with a PM/(Cu-B4C) electrode consisted of 20 wt% B4C powders were compared with those of solid electrolytic copper (E/Cu) and powder metallurgy pure copper (PM/Cu) electrodes. The workpiece surface hardness, surface abrasive wear resistance, depth of the alloyed surface layer and composition of alloyed layers were used as key parameters in the comparison. The workpiece materials, which were machined with PM/(Cu-B4C) electrodes, exhibited significantly higher hardness and abrasive wear resistance than those of machined with the E/Cu and PM/Cu. The main reason was the presence of hard intermetallic phases, such as FeB, B4C (formed due to the boron in the electrode) and Fe3C in the surface layer. The improvement of the surface hardness achieved for steel workpiece when using PM/(Cu-B4C) electrodes was significantly higher than that reported in the literature. Moreover, the machining performance outputs (workpiece material removal rate, electrode wear rate and workpiece average surface roughness (Ra)) of the electrodes were also considered in this study.
Citation - WoS: 8
Citation - Scopus: 8
Effects of the Information Presentation Format On Project Control
(Taylor & Francis Ltd, 2011) Hazir, O.; Shtub, A.
In this paper, we investigate the relationship between the information presentation format and project control. Furthermore, the effects of some system conditions, namely the number of projects to be controlled and the level of time pressure, on the quality of the project control decisions are analyzed. Information provided by Earned Value Analysis is used to monitor and control projects, and simulation is applied to replicate and model the uncertain project environments. Software is developed to generate random cost figures, to present the data in different visual forms and to collect users' responses. Having performed the experiments, the statistical significance of the results is tested. Journal of the Operational Research Society (2011) 62, 2157-2161. doi: 10.1057/jors.2011.11 Published online 2 March 2011
Citation - WoS: 3
Citation - Scopus: 5
Multi-Objective Trajectory Planning for Slung-Load Quadrotor System
(Ieee-inst Electrical Electronics Engineers inc, 2021) Ergezer, Halit; 293396; Mekatronik Mühendisliği
In this article, multi-objective trajectory planning has been carried out for a quadrotor carrying a slung load. The goal is to obtain non-dominated solutions for path length, mission duration, and dissipated energy cost functions. These costs are optimized by imposing constraints on the slung-load quadrotor system's endpoints, borders, obstacles, and dynamical equations. The dynamic model of a slung-load quadrotor system is used in the Euler-Lagrange formulation. Although the differential flatness feature is mostly used in this system's trajectory planning, a fully dynamic model has been used in our study. A new multi-objective Genetic Algorithm has been developed to solve path planning, aiming to optimize trajectory length, mission time, and energy consumed during the mission. The solution process has a three-phase algorithm: Phase-1 is about randomly generating waypoints, Phase-2 is about constructing the initial non-dominated pool, and the final phase, Phase-3, is obtaining the solution. In addition to conventional genetic operators, simple genetic operators are proposed to improve the trajectories locally. Pareto Fronts have been obtained corresponding to exciting scenarios. The method has been tested, and results have been presented at the end. A comparison of the solutions obtained with MOGA operators and MOPSO over hypervolume values is also presented.
Citation - WoS: 0
Citation - Scopus: 0
New model for liquid-based rapid prototyping with a scanning Lorentz beam
(Elsevier Gmbh, 2021) Arpali, C. Caglar; 20809; Mekatronik Mühendisliği
In this work, a new model is proposed to examine the effect of scanning Lorentz beam on a liquid based rapid prototyping scheme. The interaction of a Lorentz laser beam with a photocurable resin is analysed for different kinds of processing parameters such as beam power, beam size, scan speed, cure depth, width of the cured region and critical radiant exposure. The penetration depth profile of curing is obtained while the beam propagates inside the resin. It is shown that the proposed laser scanning model can be used to estimate the depth profile of the cured region that is treated for a certain amount of critical exposure. The Lorentzian beam generates fine and narrow hatch structures along the scan direction. This distinct ability facilitates the development of a low resolution process for fabricating complex patterns.
Citation - WoS: 6
Citation - Scopus: 6
Thermo-fluid multi-physics modeling and experimental verification of volumetric workpiece material removal by a discharge pulse in electric discharge machining process
(Iop Publishing Ltd, 2020) Erdem, Oguz; Cogun, Can; Uslan, Ibrahim; Erbas, Murat; 3837; Mekatronik Mühendisliği
The volume of material removed from the workpiece by a pulse (V-v) in the electric discharge machining was quantitatively determined using a multi-physics simulation model in ANSYS CFX software. Electrical heating is used in the model to simulate the plasma channel formation by defining the boundary and time-controlled current density initial conditions. Time-dependent physical properties at plasma temperature were used to reflect the actual processing environment. The heat was transferred from the plasma channel to the workpiece by electrical heating from the electrode, and V(v)was calculated by means of the amount of heat transfer. The calculated V(v)values for AISI4140, Ti6Al4V and Inconel 718 workpieces were lower than the experimental results and the difference was observed to change between 38.3% and 46.9%.
Citation - WoS: 3
Citation - Scopus: 5
Two Majority Voting Classifiers Applied to Heart Disease Prediction
(Mdpi, 2023) Karadeniz, Talha; Maras, Hadi Hakan; Tokdemir, Gul; Ergezer, Halit; 34410; 293396; Bilgisayar Mühendisliği; Mekatronik Mühendisliği; Yazılım Mühendisliği
Two novel methods for heart disease prediction, which use the kurtosis of the features and the Maxwell-Boltzmann distribution, are presented. A Majority Voting approach is applied, and two base classifiers are derived through statistical weight calculation. First, exploitation of attribute kurtosis and attribute Kolmogorov-Smirnov test (KS test) result is done by plugging the base categorizer into a Bagging Classifier. Second, fitting Maxwell random variables to the components and summating KS statistics are used for weight assignment. We have compared state-of-the-art methods to the proposed classifiers and reported the results. According to the findings, our Gaussian distribution and kurtosis-based Majority Voting Bagging Classifier (GKMVB) and Maxwell Distribution-based Majority Voting Bagging Classifier (MKMVB) outperform SVM, ANN, and Naive Bayes algorithms. In this context, which also indicates, especially when we consider that the KS test and kurtosis hack is intuitive, that the proposed routine is promising. Following the state-of-the-art, the experiments were conducted on two well-known datasets of Heart Disease Prediction, namely Statlog, and Spectf. A comparison of Optimized Precision is made to prove the effectiveness of the methods: the newly proposed methods attained 85.6 and 81.0 for Statlog and Spectf, respectively (while the state of the heart attained 83.5 and 71.6, respectively). We claim that the Majority Voting family of classifiers is still open to new developments through appropriate weight assignment. This claim is obvious, especially when its simple structure is fused with the Ensemble Methods' generalization ability and success.

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