33 research outputs found
Sequencing CONWIP flow-shops: Analysis and heuristics
In this paper, we address the backlog sequencing problem in a flow-shop controlled by a CON\VIP production control system with the objective to minimise the make span We characterise the problem and analyse its similarities and differences with the permutation flow-shop problem A comparison of same well-known flow-shop heuristics is carried out and a simple and fast dispatching rule is proposed. Regarding the more simple and faster heuristics, the proposed dispatching rule outperforms those commonly used for the permutation flow-shop problem. --Scheduling,Sequencing,Flow-Shop,Constant Work in Process (CONWIP),Heuristics,Dispatching Rules
A computational evaluation of constructive and improvement heuristics for the blocking flow shop to minimize total flowtime
This paper focuses on the blocking flow shop scheduling problem with the objective of total flowtime minimisation. This problem assumes that there are no buffers between machines and, due to its application to many manufacturing sectors, it is receiving a growing attention by researchers during the last years. Since the problem is NP-hard, a large number of heuristics have been proposed to provide good solutions with reasonable computational times. In this paper, we conduct a comprehensive evaluation of the available heuristics for the problem and for related problems, resulting in the implementation and testing of a total of 35 heuristics. Furthermore, we propose an efficient constructive heuristic which successfully combines a pool of partial sequences in parallel, using a beam-search-based approach. The computational experiments show the excellent performance of the proposed heuristic as compared to the best-so-far algorithms for the problem, both in terms of quality of the solutions and of computational requirements. In fact, despite being a relative fast constructive heuristic, new best upper bounds have been found for more than 27% of Taillard’s instances.Ministerio de Ciencia e Innovación DPI2013-44461-P/DP
Available-to-promise (ATP) systems: a classification and framework for analysis
Available-to-promise (ATP) systems deal with a number of managerial decisions related to order capture activities in a company, including order acceptance/rejection, due date setting, and resource scheduling. These different but interrelated decisions have often been studied in an isolated manner, and, to the best of our knowledge, no framework has been presented to integrate them into the broader perspective of order capture. This paper attempts to provide a general framework for ATP-related decisions. By doing so, we: (1) identify the different decision problems to be addressed; (2) present the different literature-based models supporting related decisions into a coherent framework; and (3) review the main contributions in the literature for each one of these. We first describe different approaches for order capture available in the literature, depending on two parameters related to the application context of ATP systems, namely the inclusion of explicit information about due dates in the decision model, and the level of integration among decisions. According to these parameters, up to six approaches for ATP-related decisions are identified. Secondly, we show the subsequent decision problems derived from the different approaches, and describe the main issues and key references involving each one of these decision problems. Finally, a number of conclusions and future research lines are discussed.Ministerio de Ciencia e Innovación DPI2007-6134
Linking Scheduling Criteria to Shop Floor Performance in Permutation Flowshops
The goal of manufacturing scheduling is to allocate a set of jobs to the machines in the
shop so these jobs are processed according to a given criterion (or set of criteria). Such criteria are
based on properties of the jobs to be scheduled (e.g., their completion times, due dates); so it is not
clear how these (short-term) criteria impact on (long-term) shop floor performance measures. In this
paper, we analyse the connection between the usual scheduling criteria employed as objectives
in flowshop scheduling (e.g., makespan or idle time), and customary shop floor performance
measures (e.g., work-in-process and throughput). Two of these linkages can be theoretically predicted
(i.e., makespan and throughput as well as completion time and average cycle time), and the other
such relationships should be discovered on a numerical/empirical basis. In order to do so, we
set up an experimental analysis consisting in finding optimal (or good) schedules under several
scheduling criteria, and then computing how these schedules perform in terms of the different shop
floor performance measures for several instance sizes and for different structures of processing
times. Results indicate that makespan only performs well with respect to throughput, and that one
formulation of idle times obtains nearly as good results as makespan, while outperforming it in terms
of average cycle time and work in process. Similarly, minimisation of completion time seems to be
quite balanced in terms of shop floor performance, although it does not aim exactly at work-in-process
minimisation, as some literature suggests. Finally, the experiments show that some of the existing
scheduling criteria are poorly related to the shop floor performance measures under consideration.
These results may help to better understand the impact of scheduling on flowshop performance,
so scheduling research may be more geared towards shop floor performance, which is sometimes
suggested as a cause for the lack of applicability of some scheduling models in manufacturing
Comparison of heuristics for flowtime minimisation in permutation flowshops
In this paper, we address the problem of sequencing jobs in a permutation flow shop with the objective of minimising the sum of completion times or flowtime. This objective is considered to be relevant and meaningful for today's dynamic production environment, and therefore it has attracted the attention of researchers during the last years. As a result, a number of different types of heuristics have recently been developed, each one claiming to be the best for the problem. However, some of these heuristics have been independently developed and only partial comparisons among them exist. Consequently, there are no conclusive results on their relative performance. Besides, some of these types of heuristics are of a different nature and could be combined in order to obtain composite heuristics. In this paper, we first classify and conduct an extensive comparison among the existing heuristics. Secondly, based on the results of the experiments, we suggest two new composite heuristics for the problem. The subsequent computational experience shows these two heuristics to be efficient for the problem under consideration
A review and classification of heuristics for permutation flow-shop scheduling with makespan objective
Makespan minimization in permutation flow-shop scheduling is an operations research topic that has been intensively addressed during the last 40 years. Since the problem is known to be NP-hard for more than two machines, most of the research effort has been devoted to the development of heuristic procedures in order to provide good approximate solutions to the problem. However, little attention has been devoted to establish a common framework for these heuristics so that they can be effectively combined or extended. In this paper, we review and classify the main contributions regarding this topic and discuss future research issues.Ministerio de Ciencia y TecnologÃa DPI-2001-311
Management of leg and pressure ulcer in hospitalized patients: direct costs are lower than expected
Background: In Germany, cost calculations on the financial burden of wound treatment are scarce. Studies for attributable costs in hospitalized patients estimate for pressure ulcer additional costs of € 6,135.50 per patient, a calculation based on the assumption that pressure ulcers will lead to prolonged hospitalization averaging 2 months. The scant data available in this field prompted us to conduct a prospective economical study assessing the direct costs of treatment of chronic ulcers in hospitalized patients
Flowshop sequencing problems with limited buffer storage
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