This paper presents a comparative study on the performance of dispatching rules in the following sets of dynamic manufacturing systems: flowshops and jobshops, and flowshops with missing operations and jobshops. Three new dispatching rules are proposed. We consider a total of 13 dispatching rules for the analysis of the relative performance with respect to the objectives of minimizing mean flowtime, maximum flowtime, variance of flowtime, proportion of tardy jobs, mean tardiness, maximum tardiness and variance of tardiness. First, we carry out the simulation study in flowshops with jobs undergoing processing on all machines sequentially and in jobshops with random routeing of jobs. The results of the study reveal some interesting observations on the relative on the performance of the dispatching rules in these two types of manufacturing systems. Next, we consider flowshops with missing operations on jobs and jobshops with random routeing of jobs. We observe some interesting results in the sense that the performance of dispatching rules is being influenced by the routeing of jobs and shopfloor configurations.

Chandrasekharan Rajendran

Department of Management Studies

Computer simulation

FLEXIBLE MANUFACTURING SYSTEMS

Machinery

Optimization

performance

productivity

DISPATCHING RULES

FLOWSHOP

JOBSHOP

scheduling

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IIT Madras

A comparative study of dispatching rules in dynamic flowshops and jobshops

European Journal of Operational Research

This paper addresses the problem of dispatching in flowshops with bottleneck machines. The presence of bottleneck machines results in the restricted throughput in flowshops. The objective is to develop dispatching rules for scheduling by taking into account the presence of bottleneck machines. The measures of performance are the minimization of total flowtime of jobs, the minimization of the sum of earliness and tardiness of jobs, and the minimization of total tardiness of jobs, considered separately. Many existing conventional dispatching rules and the proposed dispatching rules have been extensively investigated for their performance by generating a large number of problems of various sizes and bottleneck conditions. The results of the experimental investigation show that the proposed dispatching rules emerge to be superior to the conventional dispatching rules. © 2006 Elsevier Ltd. All rights reserved.

Computers and Industrial Engineering

Dispatching in flowshops with bottleneck machines

Most dispatching rules for job shop scheduling assume that the cost of holding per unit time is the same for all jobs. Likewise, it is assumed that the cost of tardiness per unit time is the same for all jobs. In other words, it is implied that the holding cost of a job is directly proportional to its flowtime, and the tardiness cost of a job is directly proportional to its positive lateness. These assumptions may not hold good in all situations. Some attempts were made to overcome this deficiency, and a couple of dispatching rules were proposed by considering different weights or penalties for different jobs. However, these dispatching rules assume that the holding and tardiness costs per unit time of a given job are the same, even though these costs may differ from job to job in practice. In this study, we propose dispatching rules by explicitly considering different weights or penalties for flowtime and tardiness of a job. Many measures of performance related to weighted flowtime and weighted tardiness of jobs are considered, and the results of simulation are presented. © 2003 Elsevier B.V. All rights reserved.

Development and analysis of cost-based dispatching rules for job shop scheduling

Most studies on scheduling in manufacturing systems using dispatching rules deal with jobshops, while there are only few reports dealing with dynamic flowshops. It is known that the performance of many dispatching rules in dynamic jobshops is different from that in dynamic flowshops. Moreover, many research reports assume that there are no buffer constraints in the shop, and even those reports dealing with buffer-constrained shops present the evaluation of existing dispatching rules for unconstrained shops in the context of buffer constraints with the consideration of a limited number of objectives of scheduling. In this study, we deal with the problem of scheduling in dynamic flowshops with buffer constraints. With respect to different time-based objectives, the best dispatching rules for scheduling in unconstrained shops have been identified from the existing literature. In addition, two new dispatching rules specially designed for flowshops with buffer constraints are proposed. All dispatching rules under consideration are evaluated in dynamic flowshops with buffer constraints on the basis of an extensive simulation study covering different levels of buffer constraints, shop load or utilization, and missing operations in flowshops. The proposed rules are found to perform better than the existing dispatching rules in buffer-constrained flowshops with respect to many measures of performance.

International Journal of Production Research

A study on the performance of scheduling rules in buffer-constrained dynamic flowshops

This paper provides a set of new dispatching rules for the minimization of various performance measures such as mean, maximum and variance of flow time and tardiness in dynamic shops. A static rule which minimizes the number of tardy jobs is also proposed. To evaluate these proposed rules, their relative performance is analysed in open job shops and reported in comparison with the standard benchmark rules such as the SPT (shortest process time) and EDD (earliest due-date), popular rules like ATC (apparent tardiness cost) and MOD (modified operational due-date), and the best performing rules in current literature such as RR, PT + WINQ, PT + WINQ + SL and AT-RPT. Thereafter, a comparative analysis of the relative performance of these rules is carried out in job shops (with no machine revisitation of jobs) and flow shops (with missing operations on jobs) in dynamic environments. Based on the simulation study and analysis of results in different manufacturing environments viz. job shops and flow shops, observations and conclusions are made, highlighting some interesting aspects about the effect of routeing on the individual performance of rules.

New dispatching rules for shop scheduling: A step forward

Many dispatching rules for scheduling in dynamic jobshops have been proposed over many years. The research issues in jobshop scheduling seem to be still open in the sense that no single rule has been found to be the best under all shopfloor conditions even with respect to one single measure of performance. Added to this problem, there are several meas ures of performance, e.g. the minimizations of mean, maximum and variance of flowtime, percentage of tardy jobs, and mean, maximum and variance of tardiness of jobs. Recent studies have reported the development of more efficient dispatching rules than the popular rules, e.g. SPT, COVERT, MOD and ATC. This study is an attempt to improve some of the recently reported dispatching rules. An extensive simulation study reveals that the improved rules developed in the present study appear to be quite effective in minimizing mean flowtime, and maximum tardiness and variance of tardiness of jobs. © 2000, Taylor & Francis Group, LLC. All rights reserved.

Production Planning and Control

Efficient jobshop dispatching rules: Further developments

We consider in this article the development of new and efficient dispatching rules with respect to the objectives of minimizing mean flowtime, maximum flowtime, variance of flowtime, proportion of tardy jobs, mean tardiness, maximum tardiness and variance of tardiness. We present five new dispatching rules for scheduling in a job shop. Some of these rules make use of the process time and work-content in the queue of the next operation on a job, by following a simple additive approach, in addition to the arrival time and dynamic slack of a job. An extensive and rigorous simulation study has been carried out to evaluate the performance of the proposed dispatching rules against those rules such as the SPT, WINQ, FIFO and COVERT, and the best existing rule. It has been observed that the proposed rules are not only simple in structure, but also quite efficient in minimizing several measures of performance. The important aspects of the results of experimental investigation are also discussed in detail.

International Journal of Production Economics

Efficient dispatching rules for scheduling in a job shop

In this paper we present a new dispatching rule which is dynamic and global in its structure. The rule adapts itself to the variation in the shop floor utilization level and assigns appropriate weights to the process time and due date information accordingly. Another important feature of the proposed rule is that the weights to the two components, viz. the process time and the due date components, differ from machine to machine. The results of a simulation study are presented to demonstrate the effectiveness of the rule with respect to the rules most commonly used in industry and the proven rules reported in the literature. The proposed rule is found to perform quite well with respect to mean flow time, mean tardiness and variation in tardiness. © 1993.

Journal	Data powered by TypesetEuropean Journal of Operational Research
Publisher	Data powered by TypesetElsevier Science B.V., Amsterdam
ISSN	03772217
Open Access	No