A sequencing algorithm for makespan minimization in FMS

Job sequencing is an important stage in any hierarchical production control model, especially when a real-time dispatching rule is not employed. The problems become complicated when constraints, such as different parts requiring different operation processes at different machines and with different production priorities, are taken into consideration in the development of sequencing models. This paper first describes a mathematical programming model developed for small flexible manufacturing systems (FMS) makespan minimization sequencing problems. For large problems, a heuristic decomposition-based algorithm is proposed. The algorithm is based on the proposed concept of track generation and track identification. Each part type may require a different number of operation processes at different machines. A numerical example is used to illustrate the use of the algorithm.published_or_final_versio

Sex hormones and apoptosis and immunoglobulin production in systemic lupus erythematosus

BACKGROUND: SLE is an autoimmune disease that affects predominantly female of reproductive age. Previous studies have suggested an immunomodulatory role of sex hormones in the pathogenesis of SLE. Objectives: To examine the effects of various sex hormones on apoptosis and immunoglobulin production by peripheral blood mononuclear cells (PBMCs) in SLE patients …published_or_final_versio

Analysis of road network pattern considering population distribution and central business district.

This paper proposes a road network growing model with the consideration of population distribution and central business district (CBD) attraction. In the model, the relative neighborhood graph (RNG) is introduced as the connection mechanism to capture the haracteristics of road network topology. The simulation experiment is set up to illustrate the effects of population distribution and CBD attraction on the characteristics of road network. Moreover, several topological attributes of road network is evaluated by using coverage, circuitness, treeness and total length in the experiment. Finally, the suggested model is verified in the simulation of China and Beijing Highway networks

Investigation of an additional part to optimal schedule

The pair-wise comparison technique has been applied to many algorithms for solving complicated scheduling problems. The optimality gap between the pair-wise comparison technique and mathematical programming model is mainly due to deterioration in performance when optimal pairs of different sub-schedules are linked together to form a complete schedule. This paper investigates the effect of adding a part prior to the part-pair in a 2-part-2-machine optimal sub-schedule. The conditions in which interchange of part-pair sequence is required in order to minimise or maintain the makespan when a part is added are analysed mathematically, and the results are reported.link_to_subscribed_fulltex

A heuristic approach to machine loading problem in non-preemptive flexible manufacturing systems

This paper first reviews the classification of FMS decision problems. In the operational level concerned, heuristic procedures are developed for FMS loading problem with a bi-objective of minimizing workload unbalance and maximizing system throughput. Decisions are made on the assignment of operations of part types and the associated cutting tools to machines. Solution to the problems hinges on the criteria of rejection factor and virtual total processing time. The proposed algorithm is exactly the reverse of the traditional add-on approach method. Part types are selected by deleting or rejecting other part types instead of picking from the job pool. A numerical example is used to illustrate the use of the loading algorithm. Results are compared with solutions obtained by applying other heuristics for the same problems.link_to_subscribed_fulltex

Operational decisions for minimization of penalty cost in non-pre-emptive FMS

Minimizing penalty cost is one of the major objectives in FMS decision making when job-due dates cannot be met. The study focuses on minimization of penalty cost when neither increase in system capacity nor diversification of jobs to other plants or production lines is possible. A mathematical programming model combining both part type selection and scheduling decision making is proposed for small problems. For large problems, a simple control parameter is identified. Seven despatching rules are applied in conjunction with the control parameter and their differences in performance are reported. Not only proves that performance can be improved by a filtration process applied before despatching rules are applied, but also finds that there is no significant difference in performance between different despatching rules after the appropriate filtration process is applied. The effectiveness of the proposed control parameter is further illustrated by comparing the results with a continuous flow model.link_to_subscribed_fulltex

A sequence algorithm for minimising makespan in multi-part and multi-machine flowshop cases

Minimising makespan aims to achieve high utilisation of equipment and resources by getting all jobs out quickly. This is an important scheduling criterion, especially for automated systems, because of the high investment cost. The problem, however, becomes complex when many parts and machines are involved. This is because different parts may require different numbers of operations, and there are many possible schedules. For small problems, a mathematical programming model for minimising makespan is formulated. For large problems, a sequencing algorithm based on decomposition and pairwise comparison is proposed. The idea of "total overlapping time" in the sequencing algorithm is introduced to determine the solution of each sub-schedule. It maximises the number of jobs working at different machines at the same time, while satisfying the parts' operation precedence and machine constraints. The differences between this method and the traditional graphical method are discussed. The sequencing algorithm significantly reduces the number of schedules for consideration and hence, the computational power required. © MCB University Press.link_to_subscribed_fulltex