145 research outputs found

    Project scheduling under undertainty – survey and research potentials.

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    The vast majority of the research efforts in project scheduling assume complete information about the scheduling problem to be solved and a static deterministic environment within which the pre-computed baseline schedule will be executed. However, in the real world, project activities are subject to considerable uncertainty, that is gradually resolved during project execution. In this survey we review the fundamental approaches for scheduling under uncertainty: reactive scheduling, stochastic project scheduling, stochastic GERT network scheduling, fuzzy project scheduling, robust (proactive) scheduling and sensitivity analysis. We discuss the potentials of these approaches for scheduling projects under uncertainty.Management; Project management; Robustness; Scheduling; Stability;

    Scheduling of nonconforming devices: the case of a company in the automotive sector

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    This article presents a project developed in a company’s quality department aiming at scheduling the nonconforming devices analysis’ process. The company faced a problem of low compliance with pre-established time requests, resulting in large fines paid to its customers of the automotive sector. In order to overcome this problem, scheduling tools were developed and tested, with the goal of minimizing the number of tardy tasks in identical parallel machines. The simulation of different scheduling rules allowed confirmation that the current prioritization rule is not the most effective one. Preliminary simulations were carried out using Lekin software [18], showing that other criteria promote better results. The use of a newly developed algorithm, combining two different criteria, resulted in a reduction of tardy tasks, thus decreasing tardiness fines paid to customers. Despite the preliminary status of present results, it is possible to foresee some improvements in the analysis process performance, by using decision making support tools based on scheduling algorithms. This way, a significant improvement on the number of analysis which fulfills the defined pre-requirements will be achieved.This work has been supported by COMPETE: POCI-01-0145-FEDER-007043 and FCT – Fundação para a Ciência e Tecnologia within the Project Scope: UID/CEC/00319/2013.info:eu-repo/semantics/publishedVersio

    A survey of scheduling problems with setup times or costs

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    Author name used in this publication: C. T. NgAuthor name used in this publication: T. C. E. Cheng2007-2008 > Academic research: refereed > Publication in refereed journalAccepted ManuscriptPublishe

    Heuristic Algorithms to Minimize Total Weighted Tardiness on the Single Machine and Identical Parallel Machines with Sequence Dependent Setup and Future Ready Time

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    This study generates heuristic algorithms to minimize the total weighted tardiness on the single machine and identical parallel machines with sequence dependent setup and future ready time. Due to the complexity of the considered problem, we propose two new Apparent Tardiness Cost based (ATC-based) rules. The performances of these two rules are evaluated on the single machine and identical parallel machines. Besides of these two rules, we also propose a look-ahead identical parallel machines heuristic (LAIPM). When a machine becomes idle, it selects a job to process from available jobs and near future jobs. The proposed method, LAIPM, is evaluated with other look-ahead methods on the identical parallel machines

    Dynamic scheduling of maintenance activities under uncertainties.

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    International audienceCompetencies management in the industry is one of the most important keys in order to obtain good performance with production means. Especially in maintenance services field where the dierent practical knowledges or skills are their working tools. We address, in this paper, the both assignment and scheduling problem that can be found in a maintenance service. Each task that has to be performed is characterized by a competence level required. Then, the decision problem of assignment and scheduling lead to find the good resource and the good time to do the task. For human resources, all competence levels are dierent, they are considered as unrelated parallel machines. Our aim is to assign dynamically new tasks to the adequate resources by giving to the maintenance expert a choice between the robustest possibilities

    Energy aware hybrid flow shop scheduling

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    Only if humanity acts quickly and resolutely can we limit global warming' conclude more than 25,000 academics with the statement of SCIENTISTS FOR FUTURE. The concern about global warming and the extinction of species has steadily increased in recent years

    Efficient Heuristics for Scheduling Tasks on a Flo Shop Environment to Optimize Makespan

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    In modern manufacturing the trend is the development of Computer Integrated Manufacturing, CIM technologies which is a computerized integration of manufacturing activities (Design, Planning, Scheduling and Control) produces right products at right time to react quickly to the global competitive market demands. The productivity of CIM is highly depending upon the scheduling of Flexible Manufacturing System (FMS). Shorting the make span leads to decreasing machines idle time which results improvement in CIM productivity. Conventional methods of solving scheduling problems based on priority rules still result schedules, sometimes, with significant idle times. To optimize these, this paper model the problem of a flow shop scheduling with the objective of minimizing the makes pan. The work proposed here deal with the production planning problem of a flexible manufacturing system. This paper model the problem of a flow shop scheduling with the objective of minimizing the makes pan. The objective is to minimize the make span of batch-processing machines in a flow shop. The processing times and the sizes of the jobs are known and non-identical. The machines can process a batch as long as its capacity is not exceeded. The processing time of a batch is the longest processing time among all the jobs in that batch. The problem under study is NP-hard for makespan objective. Consequently, comparison based on Gupta’s heuristics, RA heuristic’s, Palmer’s heuristics, CDS heuristics are proposed in this work. Gantt chart was generated to verify the effectiveness of the proposed approaches

    System performance evaluation through preventive maintenance scenarios using simulation technique

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    Equipment is one of the major contributors to the performance and profitability of manufacturing systems and its importance is rather increasing in the growing advanced manufacturing technology application stages (Kutucuoglu et al., 2001). The equipment is subject to deteriorations and failures as the consequence of usage, aging, fatigue, environmental conditions or other extreme events. Such system deterioration may lead to higher production cost, lower product quality and increase probability of breakdown (Mobley, 2002). Unexpected breakdowns not only increase the operating cost of the productive machines but in fact, the cost of lost production is inevitable for operation interruptions. Scheduled downtime is to control when the system will be down in favour of production. According to Ali et al. (2008), downtime will be more predictable if preventive maintenance is employed. The area of asset maintenance is becoming increasingly important as greater asset availability is demanded. Effective maintenance management is essential and critical as a way to reduce the adverse effect of equipment failures and to maximize equipment availability (Muhammad et al., 2010). The ultimate goal of maintenance is to provide optimal reliability and availability of production equipment, and maintain its operability to meet the business needs of the company

    Just-in-time preemptive single machine problem with costs of earliness/tardiness, interruption and work-in-process

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    This paper considers preemption and idle time are allowed in a single machine scheduling problem with just-in-time (JIT) approach. It incorporates Earliness/Tardiness (E/T) penalties, interruption penalties and holding cost of jobs which are waiting to be processed as work-in-process (WIP). Generally in non-preemptive problems, E/T penalties are a function of the completion time of the jobs. Then, we introduce a non-linear preemptive scheduling model where the earliness penalty depends on the starting time of a job. The model is liberalized by an elaborately–designed procedure to reach the optimum solution. To validate and verify the performance of proposed model, computational results are presented by solving a number of numerical examples
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