Browsing by Subject "Job shops."

Now showing 1 - 7 of 7

Open Access
An analysis of order review
(1995) Karapınar, H Yavuz
Order Review/Release (ORR) activities have mostly been ignored in past job shop research. In the majority of these studies, arriving jobs are immediately released to the shop floor without considering any information about the job and the system status. In practice, however, jobs arriving at the shop are first collected in a pool and then released periodically according to some release criterion. Although practitioners use ORR mechanisms to improve shop floor performance, researchers have found limited supports for the use of these input regulation policies. In this thesis, we reexamine the problem in a capacitated system. Specifically, we compare the performances of the ORR policies in a job shop with finite buffer capacities and material handling considerations. A new ORR mechanism is also proposed and compared with other methods.
Open Access
Analysis of reactive scheduling problems in manufacturing systems
(1997) Bayız, Murat
In this study we develop a new scheduling algorithm for the job shop problem. The proposed algorithm is a heuristic method based on the filtered beam search. After extensive analyses on the evaluation functions and search parameters of the beam search, we measure the performance of the algorithm in terms of quality of solutions and CPU times for both the makespan and mean tardiness criteria. In the second half of the research, we study the reactive scheduling problem. Specifically, we analyze several reactive methods such as no response, periodic response and continuous response under various experimental conditions. The beam search based partial scheduling is also studied in this thesis. The method is analyzed for both deterministic and stochastic environments under several job shop configurations.
Open Access
Flowtime estimation in dynamic job shops
(1996) Çömlekçi, Abdullah
In the scheduling literature, estimation of job flowtimes has always been an important issue since the late sixties. The previous studies focus on the problem in the context of due date assignment and develop methods using aggregate information in the estimation process. In this study, we propose a new method which utilizes the job, shop and route information on an operational basis. The performance of the proposed method is measured using a simulation model. It is also compared with the existing methods for a wide variety of performance measures under various experimental conditions.
Open Access
Job shop scheduling under dynamic and stochastic manufacturing environment
(1995) Kutanoğlu, Erhan
In practice, manufacturing systems operate under dynamic and stochastic environment where unexpected events (or interruptions) occur continuously in the shop. Most of the scheduling literature deals with the schedule generation problem which is only one aspect of the scheduling decisions. The reactive scheduling and control aspect has scarcely been addressed. This study investigates the effects of the stochastic events on the s\'stem performance and develops alternative reactive scheduling methods. In this thesis, we also study the single-pass and multi-pass scheduling heuristics in dynamic and stochastic job shop scheduling environment. We propose a simulation-based scheduling system for the multi-pass heuristics. Finally, we analyze the interactions among the operational strategies (i.e, lookahead window, scheduling period, method used for scheduling), the system conditions, and the unexpected events such as machine breakdowns and processing time variations.
Open Access
Lot streaming in flow shops
(1994) Topaloğlu, Engin
Lot streaming is permitting partial transfer of processed portions of a job to downstream machines, thus allowing ovelapping operations. The primary motivation is to improve the measures of performance by the quick movement of work in the shop. In this thesis, we study various forms of the lot streaming problem in flow shops to derive the characteristics of optimal solutions. We first analyze single job lot streaming problems, then extend the results to multi-job problems. When there is a single job, the lot streaming problem is to find the best transfer batch sizes that optimizes the given criterion. We consider three different measures of performance, job, sublot and item completion time criteria. We derive a closed form solution for a special case of job completion time criterion. Under sublot completion time criterion, when the first machine has the largest processing time, we show that partial transfers of equal size are optimal. We propose two polynomial time algorithms for the problem in which only two transfer batches are permitted between each consecutive machines for sublot and item completion time criteria. In multi-job lot streaming problems, the sequencing and lot streaming decisions must be considered simultaneously. For multi-job problems we investigate the hierarchical application of lot streaming and sequencing decisions.
Open Access
Lot streaming in multi stage shops
(1994) Şen, Alper
In this thesis, a number of lot streaming problems in flow, open and job shops are investigated. Lot streaming is the process of splitting a job to allow for overlapping of its operations on various machines resulting in shorter completion times. When there is a single job, the problem is to find the size of the transfer batches (“sublots”) which minimizes a given performance measure (e.g., makespan, mean flow time). Multi-job problems are harder, since sequencing and sizing decisions must be made simultaneously. Most of the current research in lot streaming is concerned with minimum makespan problems in flow shops. In this study, other performance measures and shop structures are also analyzed. Optimal sublot sizes are derived for the single job two machine flow shop mean flow time problem. Solution methods are proposed for the minimum makespan problem in open shops both for multiple job and single job cases.
Open Access
A re-examination of the effectiveness of priority rules in a dynamic job shop environment
(1997) Lejmi, Tahar
III dyiiaiuic job .shop .sdiccliiliiig li(cra(urc, an cxicnsivc research clioil lias been spent to study the performance of priority rules, wliich play an important role to manage scheduling tasks in real life manufacturing systems. This study extends the previous research on priority rules by investigating the effect of due date, processing time, and load variation on the pei (drmance of some well used priority rules in a Job shop environment. Furthermore, tliis study will analyze the performance of the rules under the due window approach. The performance of the rules will be measured in terms of two regular criteria: mean flow time and mean tardiness. In addition, with the incieasing emphasis on using non regular measures, we further study the performance of the rules with respect to the mean absolute deviation (MAD) criterion. Finally, we propose two new rules that perform quiet effectively for the MAD criterion.