Browsing by Subject "Process control"

Now showing 1 - 10 of 10

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
Binary integer formulation for mixed-model assembly line balancing problem
(Pergamon Press, 1998-04-01) Gökçen, H.; Erel, E.
The assembly line balancing problem has been a focus of interest to the academicians of production/operations management for the last 40 years. Although there are numerous studies published on the various aspects of the problem, the number of studies on mixed-model assembly lines are relatively small. In this paper, a binary integer programming model for the mixed-model assembly line balancing problem is developed and some computational properties of the model are given.
Open Access
Economic design of EWMA control charts based on loss function
(Elsevier, 2009) Serel, D. A.
For monitoring the stability of a process, various control charts based on exponentially weighted moving average (EWMA) statistics have been proposed in the literature. We study the economic design of EWMA-based mean and dispersion charts when a linear, quadratic, or exponential loss function is used for computing the costs arising from poor quality. The chart parameters (sample size, sampling interval, control limits and smoothing constant) minimizing the overall cost of the control scheme are determined via computational methods. Using numerical examples, we compare the performances of the EWMA charts with Shewhart over(X, -) and S charts, and investigate the sensitivity of the chart parameters to changes in process parameters and loss functions. Numerical results imply that rather than sample size or control limits, the users need to adjust the sampling interval in response to changes in the cost of poor quality.
Open Access
Generalizing predicates with string arguments
(Springer New York LLC, 2006-06) Cicekli, I.; Cicekli, N. K.
The least general generalization (LGG) of strings may cause an over-generalization in the generalization process of the clauses of predicates with string arguments. We propose a specific generalization (SG) for strings to reduce over-generalization. SGs of strings are used in the generalization of a set of strings representing the arguments of a set of positive examples of a predicate with string arguments. In order to create a SG of two strings, first, a unique match sequence between these strings is found. A unique match sequence of two strings consists of similarities and differences to represent similar parts and differing parts between those strings. The differences in the unique match sequence are replaced to create a SG of those strings. In the generalization process, a coverage algorithm based on SGs of strings or learning heuristics based on match sequences are used. © Springer Science + Business Media, LLC 2006.
Open Access
An integrated process planning approach for CNC machine tools
(Springer-Verlag, 1996) Aktürk, M. S.; Avcı, S.
In view of the high investment and tooling cost of a CNC machining centre, the cutting and idle times should be optimised by considering the tool consumption and the non-machining time cost components. In this paper, we propose a detailed mathematical model for the operation of a CNC machine tool which includes the system characterisation, the cutting conditions and tool life relationship, and related constraints. This new module will be a part of an overall computer-aided process planning system to improve the system effectiveness and to provide consistent process plans. A hierarchical approach is presented for finding tool-operation assignments, machining conditions, appropriate tool magazine organisation and an operations sequence which results in the minimum production cost. © 1996 Springer-Verlag London Limited.
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
Match-up scheduling under a machine breakdown
(Elsevier, 1999) Aktürk, M. S.; Görgülü, E.
When a machine breakdown forces a modified flow shop (MFS) out of the prescribed state, the proposed strategy reschedules part of the initial schedule to match up with the preschedule at some point. The objective is to create a new schedule that is consistent with the other production planning decisions like material flow, tooling and purchasing by utilizing the time critical decision making concept. We propose a new rescheduling strategy and a match-up point determination procedure through a feedback mechanism to increase both the schedule quality and stability. The proposed approach is compared with alternative reactive scheduling methods under different experimental settings. © 1999 Elsevier Science B.V. All rights reserved.
Open Access
Optimal timing of project control points
(Elsevier, 2000) Raz, T.; Erel, E.
The project control cycle consists of measuring the status of the project, comparing to the plan, analysis of the deviations, and implementing any appropriate corrective actions. We present an analytical framework for determining the optimal timing of project control points throughout the life cycle of the project. Our approach is based on maximizing the amount of information generated by the control points, which depends on the intensity of the activities carried out since the last control point and on the time elapsed since their execution. The optimization problem is solved with a dynamic programming approach. We report the results of numerical experimentation with the model involving different types of activity intensity profiles and several levels of information loss. For each combination, we compared the optimal amount of information to the amount of information obtained with two simpler policies: control at equal time intervals, and control at equal activity contents intervals. We also investigated the effect of adding more control points on the amount of information generated.
Open Access
A simulation based learning meachanism for scheduling systems with continuous control and update structure
(IEEE, 2005) Metan, G.; Sabuncuoğlu, İhsan
A simulation based learning mechanism is proposed in this study. The system learns in the manufacturing environment by constructing a learning tree and selects a dispatching rule from the tree for each scheduling period. The system utilizes the process control charts to monitor the performance of the learning tree which is automatically updated whenever necessary. Therefore, the system adapts itself for the changes in the manufacturing environment and works well over time. Extensive simulation experiments are conducted for the system parameters such as monitoring (MPL) and scheduling period lengths (SPL) on a job shop problem with objective of minimizing average tardiness. Simulation results show that the performance of the proposed system is considerably better than the simulation-based single-pass and multi-pass scheduling algorithms available in the literature.