Browsing by Subject "Flexible Manufacturing Systems"

Now showing 1 - 6 of 6

Open Access
An analysis of FMS scheduling problem: a beam search based algorithm and comparison of scheduling schemes
(1994) Karabük, Süleyman
FMS scheduling procedures in the literature can be classified into on-line and off-line schemes according to the number of scheduling decisions made at a point in time. Online scheduling attempts to schedule operations one at a time when it is needed and off-line scheduling refers to scheduling operations of available jobs for the entire scheduling period. In the literature there is no unified argument for or against either of these scheduling schemes. This research has two main objectives: development of a new scheduling scheme called quasi on-line that makes a trade-off between on-line and off-line schemes and comparison of the proposed scheme with others under various experimental conditions. A new algorithm is proposed on which the quasi online scheme is based. The proposed algorithm is a heuristic and utilizes a beam search technique. It considers finite buffer capacity, routing and sequence flexibilities and generates machine and AGV schedules for a given scheduling period. A simulation model is also developed to implement and test scheduling schemes.
Open Access
Analysis of scheduling problems in dynamic and stochastic FMS environment : comparison of rescheduling polices
(2001) Kızılışık, Ö Batuhan
In this thesis, we study the reactive scheduling problems in a dynamic and stochastic flexible manufacturing environment. Specifically, we test different scheduling policies (how-to-schedule and when-to-schedule policies) under process time variations and machine breakdowns in a flexible manufacturing system. These policies are then compared with on-line scheduling schemes. The performance of the system is measured for the mean flowtime criterion. In this study, a beam search based algorithm is used. The algorithm allows us to generate partial or full schedules. The results indicate that on-line scheduling schemes are more robust than the off-line algorithm in dynamic and stochastic environments.
Open Access
Analytical loading models and control strategies in flexible manufacturing systems: a comparative study
(1990) Kırkavak, Nureddin
There are three problem areas in designing and implementing a manufacturing line : the part family selection and grouping, system configuration and toolings and the operational control of manufacturing. The manufacturing process has to be stream-lined by considering resources and products to achieve flow lines operating around product families with acceptable levels of utilization. The stream-lined processes have to be assigned to tandem machines in the manufacturing lines. Then, interactions between production and inventory levels should be controlled at the operational level. Based on this framework, first a system configuration and tooling problem is modeled. The model turns out to be a large mLxed integer linear program, so that some alternative optimal seeking or heuristic techniques are used to solye the model for constructing a flow line structured Flexible Manufacturing System. Push systems of the Material Requirements Planning type or pull systems like the base-stock or Kanban schemes are often seen as alternatives for controlling manufacturing systems. The differentiating features of push, pull and a hybrid strategy are studied by discrete event simulation under different system and environmental characteristics for Flexible Manufacturing Systems. The impact of assignment of operations to machines on the performance of the system is also discussed.
Open Access
Joint lot sizing and tool management in a single CNC environment
(1996) Önen, Siraceddin
111 most of the studies on tool management, lot sizes are taken as pi'edetermined input while deciding on tool allocations and machining |)arameters. In this study, we considered the integration of lot sizing and tool rnaricigement problems for single and multi i:>eriod cases. For the single period case, we proposed a new algorithm. By this algorithm we not only improved the overall solution by exploiting interactions, but also prevented any infeasibility that might occur lor the tool management problem due to the 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 a. traditional approach were infeasible and the proposed joint approach improved the overall solution by 6.8%. For the multi period case, we proposed live new algorithms. Among these algorithms, the most promising one was tlie Look Atiea.d-LUC algorithm, which improved the overall solution on the average by 6.5% compared to the best known algorithm, Wa.gner-Whitin, used in traditional approcich, over a set of randomly generated problems.
Open Access
Multiple part-type scheduling in flexible robotic cells
(Elsevier, 2012-02) Batur, G. D.; Karasan, O. E.; Akturk, M. S.
This paper considers the scheduling problem arising in two-machine manufacturing cells which repeatedly produce a set of multiple part-types, and where transportation of the parts between the machines is performed by a robot. The cycle time of the cell depends on the robot move sequence as well as the processing times of the parts on the machines. For highly flexible CNC machines, the processing times can be adjusted. To this end, this study tries to find the robot move sequence as well as the processing times of the parts on each machine that jointly minimize the cycle time. The problem of determining the best cycle in a 2-machine cell is first modeled as a traveling salesman problem. Then, an efficient 2-stage heuristic algorithm is constructed and compared with the most common heuristic approach of longest processing time (LPT). (C) 2011 Elsevier B.V. All rights reserved.
Open Access
Unidirectional loop newtork layout problem in flexible manufactaring systems
(1999) Bilen, Canan
Unidirectional Loop Networks are the most common architecture in FMSs. This is partly due to lower implementation costs of unidirectional loop networks. But mainly it is the higher flexibility unidirectional loop networks provide that makes then more common. In this thesis we are interested in the arrangement of machines in a unidirectional loop network. Our objective is to determine an assignment of machines yielding the minimum cost defined as the sum of products of the parts moving between machines and the distances moved. We give our formulation of the problem and propose two heuristics; Positional Move Heuristic and Positional Move-Pairwise Interchange Heuristic. The computational effectiveness of these heuristics is compared with other existing heuristics from the literature.