Browsing by Subject "Flexible manufacturing systems"

Now showing 1 - 20 of 21

Open Access
The analytic hierarchy process applied to the justification of advanced manufacturing systems
(1991) Urhan, Kubilay Ediz
In this thesis, a multi-attribute decision model for the justification of advanced manufacturing systems by use of Analytic Hierarchy Process is developed. The model constructed is a general model which can be applied to any advanced manufacturing system justification problem. In the model, cost is directly included in a single hierarchy with tlie benefits, and the final decision is given depending on the priority vector of this single hierarchy. A hypothetical cell replacement decision in a cellular manufacturing system is given to demonstrate the application of the model.
Open Access
Analytical loading models in flexible manufacturing systems
(Elsevier, 1993) Kırkavak, N.; Dinçer, C.
It would be difficult to efficiently implement a manufacturing system without solving its design and operational problems. Based on this framework, a system configuration and tooling problem is modeled. The model turns out to be a large mixed integer linear program, so that some alternative optimal seeking and heuristic techniques are used to solve the model for constructing a flow line structured Flexible Manufacturing System. As a result, it may be possible to construct flexible, efficient, simple and easily controllable manufacturing systems. © 1993.
Open Access
Beam search based algorithm for scheduling machines and AGVs in an FMS
(Institute for Industrial Engineers, 1993) Karabük, S.; Sabuncuoğlu, İhsan
This paper presents a beam search based scheduling algorithm for a random FMS. The proposed algorithm considers finite buffer capacity, routing and sequence flexibilities and generates machine and AGV schedules in varying time windows. The performance of the algorithm is measured using makespan, flow time, and tardiness criteria under various experimental conditions.
Open Access
A beam search-based algorithm and evaluation of scheduling approaches for fexible manufacturing systems
(Taylor & Francis, 1998) Sabuncuoglu İ.; Karabuk, S.
This paper presents a new algorithm for the flexible manufacturing system (FMS) scheduling problem. The proposed algorithm is a heuristic based on filtered beam search. It considers finite buffer capacity, routing and sequence flexibilities and generates machine and automated guided vehicle (AGV) schedules for a given scheduling period. A new deadlock resolution mechanism is also developed as an integral part of the proposed algorithm. The performance of the algorithm is compared with several machine and AGV dispatching rules using mean flow time, mean tardiness and makespan criteria. It is also used to examine the effects of scheduling factors (i.e., machine and AGV load levels, routing and sequence flexibilities, etc.) on the system performance. The results indicate thai the proposed scheduling algorithm yields considerable improvements in system performance over dispatching rules under a wide variety of experimental conditions. © 1998 "IIE".
Open Access
Due date and cost-based FMS loading, scheduling and tool management
(Taylor & Francis, 2007) Turkcan, A.; Akturk, M. S.; Storer, R. H.
In this study, we consider flexible manufacturing system loading, scheduling and tool management problems simultaneously. Our aim is to determine relevant tool management decisions, which are machining conditions selection and tool allocation, and to load and schedule parts on non-identical parallel CNC machines. The dual objectives are minimization of the manufacturing cost and total weighted tardiness. The manufacturing cost is comprised of machining and tooling costs (which are affected by machining conditions) and non-machining cost (which is affected by tool replacement decisions). We used both sequential and simultaneous approaches to solve our problem to show the superiority of the simultaneous approach. The proposed heuristics are used in a problem space genetic algorithm in order to generate a series of approximately efficient solutions.
Open Access
Dynamic lot sizing and tool management in automated manufacturing systems
(Elsevier, 2002) Aktürk, M. S.; Önen, S.
The overall aim of this study is to show that there is a critical interface between the lot sizing and tool management decisions, and these two problems cannot be viewed in isolation. We propose "ve alternative algorithms to solve lot sizing, tool allocation and machining conditions optimization problems simultaneously. The "rst algorithm is an exact algorithm which "nds the global optimum solution, and the others are heuristics equipped with a look-ahead mechanism to guarantee at least local optimality. The computational results indicate that the amount of improvement is statistically signi"cant for a set of randomly generated problems. The magnitude of cost savings is dependent on the system parameters.
Open Access
Essays on scheduling with controllable processing times in flexible manufacturing systems
(2003) Türkcan, Ayten
In this study, we consider FMS loading, scheduling and tool management problems simultaneously. Our aim is to determine the machining conditions, to load and schedule parts on the nonidentical parallel CNC machines and to determine tool allocation and replacement decisions. We consider due date and cost based objectives. The due date related objectives are minimization of weighted tardiness, and weighted earliness/tardiness. The cost related objective is the minimization of the manufacturing cost, which is the sum of machining, tooling and nonmachining costs. An important issue in flexible manufacturing systems is that the processing times can be controlled by changing the machining conditions. In this study, we consider controllable processing times because of the flexibility they provide for finding alternative solutions in predictive and reactive scheduling.
Open Access
An evaluative study of operation grouping policies in an FMS
(Kluwer Academic Publishers, 2003) Sabuncuoǧlu, İ.; Lahmar, M.
The increased use of flexible manufacturing systems to provide customers with diversified products efficiently has created a significant set of operational challenges for managers. This technology poses a number of decision problems that need to be solved by researchers and practitioners. In the literature, there have been a number of attempts to solve design and operational problems. Special attention has been given to machine loading problems, which involve the assignment of job operations and allocation of tools and resources to optimize specific measures of productivity. Most existing studies focus on modeling the problem and developing heuristics in order to optimize certain performance metrics rather than on understanding the problem and the interaction between the different factors in the system. The objective of this paper is to study the machine loading problem. More specifically, we compare operation aggregation and disaggregation policies in a random flexible manufacturing system (FMS) and analyze its interaction with other factors such as routing flexibility, sequencing flexibility, machine load, buffer capacity, and alternative processing-time ratio. For this purpose, a simulation study is conducted and the results are analyzed by statistical methods. The analysis of results highlights the important factors and their levels that could yield near-optimal system performance.
Open Access
Experimental investigation of FMS machine and AGV scheduling rules against the mean flow-time criterion
(Taylor & Francis, 1992) Sabuncuoglu, Ihsan; Hommertzheim, D. L.
Although a significant amount of research has been carried out in the scheduling of flexible manufacturing systems (FMSs), it has generally been focused on developing intelligent scheduling systems. Most of these systems use simple scheduling rules as a part of their decision process. While these scheduling rules have been investigated extensively for a job shop environment, there is little guidance in the literature as to their performance in an FMS environment. This paper attempts to investigate the performances of machine and AGV scheduling rules against the mean flow-time criterion. The scheduling rules are tested under a variety of experimental conditions by using an FMS simulation model.
Open Access
Integrated lot sizing and tool management in automated manufacturing systems
(IIE, 1997) Aktürk, Mehmet Selim; Önen, Siraceddin
We propose a new algorithm to solve lot sizing, tool allocation and machining conditions optimization problems simultaneously to minimize total production cost in a CNC environment. Most of the existing lot sizing and tool management methods solve these problems independently using a two-level optimization approach. Thus, we not only improve the overall solution by exploiting the interactions, but also prevent any infeasibility that might occur for the tool management problem due to decisions made at the lot sizing level. We showed that in a set of randomly generated problems 22.5% of solutions found by the two-level approach were infeasible and we improved the solution on the average by 6.79% for the remaining cases with an average computation time of 63.4 seconds.
Open Access
Integrated scheduling and tool management in flexible manufacturing systems
(Taylor & Francis, 2001) Aktürk, M. S.; Özkan, S.
A multistage algorithm is proposed that will solve the scheduling problem in a flexible manufacturing system by considering the interrelated subproblems of processing time control, tool allocation and machining conditions optimization. The main objective of the proposed algorithm is to minimize total production cost consisting of tooling, operational and tardiness costs. The proposed integrated approach recognizes an important trade-off in automated manufacturing systems that has been largely unrecognized, and which is believed can be effectively exploited to improve production efficiency and lead to substantial cost reductions.
Open Access
Joint lot sizing and tool management in a CNC environment
(Elsevier, 1999) Aktuük, M. S.; Önen, S.
We propose a new algorithm to solve lot sizing, tool allocation and machining conditions optimization problems simultaneously to minimize total production cost in a CNC environment. Most of the existing lot sizing and tool management methods solve these problems independently using a two-level optimization approach. Thus, we not only improve the overall solution by exploiting the interactions among these decision making problems, but also prevent any infeasibility that might occur for the tool management problem due to decisions made at the lot sizing level. The computational experiments showed that in a set of randomly generated problems 22.5% of solutions found by the two-level approach were infeasible and the proposed joint approach improved the solution on the average by 6.79% for the remaining cases.
Open Access
Non-identical parallel CNC machine scheduling
(Taylor & Francis, 2003) Türkcan, A.; Selim Aktürk, M.; Storer, R. H.
In this study, we solve the non-identical parallel CNC machine scheduling problem. We have two objectives: minimizing the manufacturing cost (comprising machining, non-machining and tooling costs) and minimizing the total weighted tardiness. The tooling constraints affect the non-machining times as well as the machining conditions, such as cutting speed and feed rate, which in turn specify the machining times and tool lives. We propose a two-stage algorithm to find optimal machining conditions and to determine machine allocation, tool allocation and part scheduling decisions. The proposed algorithm generates different schedules according to the relative importance of the objectives.
Open Access
Optimal hybrid control of a two-stage manufacturing system
(IEEE, 2006) Gökbayrak, Kağan; Selvi, Ömer
We consider a two-stage serial hybrid system for which the arrival times are known and the service times are controllable. We derive some optimal sample path characteristics, in particular, we show that no buffering is observed between stages. The original non-smooth optimal control problem is first transformed into a convex optimization problem which is then simplified by the no buffer property. Further simplifications are possible for the bulk arrival case.
Open Access
Part-machine grouping using a multi-objective cluster analysis
(1996) Akturk, M.S.; Balkose H.O.
In the existing literature, the part-family formation problem is handled either by the coding systems or the cluster analysis. In this study, we propose a new method that will consider both design and manufacturing attributes and operation sequences simultaneously, in conjunction with the related performance measures such as the machine investment, the amount of workload deviations within and between the cells, and the number of skippings. Finally, the proposed method is compared with the similarity coefficient method under different experimental settings and its robustness is checked against the varying system parameters.
Open Access
A problem space genetic algorithm in multiobjective optimization
(Springer New York LLC, 2003) Türkcan, A.; Aktürk, M. S.
In this study, a problem space genetic algorithm (PSGA) is used to solve bicriteria tool management and scheduling problems simultaneously in flexible manufacturing systems. The PSGA is used to generate approximately efficient solutions minimizing both the manufacturing cost and total weighted tardiness. This is the first implementation of PSGA to solve a multiobjective optimization problem (MOP). In multiobjective search, the key issues are guiding the search towards the global Pareto-optimal set and maintaining diversity. A new fitness assignment method, which is used in PSGA, is proposed to find a well-diversified, uniformly distributed set of solutions that are close to the global Pareto set. The proposed fitness assignment method is a combination of a nondominated sorting based method which is most commonly used in multiobjective optimization literature and aggregation of objectives method which is popular in the operations research literature. The quality of the Pareto-optimal set is evaluated by using the performance measures developed for multiobjective optimization problems.
Open Access
Pure cycles in flexible robotic cells
(Elsevier, 2009) Gultekin, H.; Karasan O. E.; Akturk, M. S.
In this study, an m-machine flexible robotic manufacturing cell consisting of CNC machines is considered. The flexibility of the machines leads to a new class of robot move cycles called the pure cycles. We first model the problem of determining the best pure cycle in an m-machine cell as a special travelling salesman problem in which the distance matrix consists of decision variables as well as parameters. We focus on two specific cycles among the huge class of pure cycles. We prove that, in most of the regions, either one of these two cycles is optimal. For the remaining regions we derive worst case performances of these cycles. We also prove that the set of pure cycles dominates the flowshop-type robot move cycles considered in the literature. As a design problem, we consider the number of machines in a cell as a decision variable. We determine the optimal number of machines that minimizes the cycle time for given cell parameters such as the processing times, robot travel times and the loading/unloading times of the machines.
Open Access
Reactive scheduling in a dynamic and stochastic FMS environment
(Taylor & Francis, 2003) Sabuncuoğlu, İ.; Kızılışık, Ö. B.
In this paper, we study the reactive scheduling problems in a dynamic and stochastic manufacturing environment. Specifically, we develop a simulationbased scheduling system for flexible manufacturing systems. We also propose several reactive scheduling policies (i.e. when-to-schedule and how-to-schedule policies) and test their performances under various experimental conditions, processing time variations, and machine breakdowns. Moreover, we compare offline and online scheduling schemes in a dynamic manufacturing environment. The results of extensive simulation experiments indicate that the variable-timeresponse is better than the fixed-time-response. The full scheduling scheme generally performs better than the partial scheduling. Finally, the online scheduling is more robust to uncertainty and variations in processing times than the optimumseeking offline scheduling. A comprehensive bibliography is also provided in the paper.
Open Access
Scheduling in a three-machine flexible robotic cell
(IFAC, 2006) Gültekin, Hakan; Aktürk, M. Selim; Karasan, Oya Ekin
In this study, a three-machine flexible robotic manufacturing cell in which the CNC machines are used is considered. These machines are highly flexible and are capable of performing several different operations. Each machine is assumed to be capable of performing all of the required operations of each part. As a consequence of this assumption, a new class of cycles is defined and three simple and widely used cycles among this class is proposed. The regions of optimality for these cycles as well as the worst case performances are derived.
Open Access
Tool allocation and machining conditions optimization for CNC machines
(Elsevier, 1996) Aktürk, M. S.; Avcı, S.
In the literature, there exist many variations of machining economics problem in terms of modelling approaches and solution methodologies. However most of the existing studies focus on the single machining operation which is seldom in practice. On the other hand, tool management approaches at the system level fail to relate the tooling issues to the machining conditions, and ignore the tool availability and tool wear restrictions. A new solution methodology is developed to determine the optimum machining conditions and tool allocation simultaneously to minimize the production cost of a multiple operation case where there can be alternative tools for each operation. As a result, we can both improve the solution by exploiting the interaction between these two decisions, and also prevent any infeasibility that might occur for the tool allocation problem due to tool contention among the operations for a limited number of tool types by considering the tool availability and tool life limitations.