SURVEY OF DYNAMIC SCHEDULING IN MANUFACTURING SYSTEMS <s> Dispatching Rules <s> Scheduling of job shops has been extensively researched over the last three decades and it continues to attract the interests of both academic researchers and practitioners. This paper provides a state-of-the-art survey of the simulation-based research on dynamic job shop scheduling with a distinct emphasis on two important aspects. First, job-shop simulation modeling and experimental considerations are discussed with a review of the different approaches taken in the literature. Second, a review of the different studies is provided with a focus on their findings on the job shop performance criteria of interest. This paper is aimed at both practicing managers and researchers in the area of job shop scheduling because of the following considerations: 1. (i) The number of factors that characterize a job shop is very large and there is considerable variation in modeling and experimentation across the vast number of studies reported. Important research findings relevant to these issues reviewed in this paper would facilitate comparison of the currently available research results and their extension or application to other situations.2. (ii) A review of the various studies focusing on some of the more important performance criteria should help practitioners in the selection of scheduling rules to match the criterion particularly relevant to their shops.3. (iii) Recent studies which have modeled job shops as dual-resource constrained systems and assembly shops have been included in this survey for a more comprehensive coverage. A detailed bibliography is included and every effort has been made to make the survey up-to-date. <s> BIB001 </s> SURVEY OF DYNAMIC SCHEDULING IN MANUFACTURING SYSTEMS <s> Dispatching Rules <s> Abstract We present a simulation-based real-time scheduling methodology for a flexible manufacturing system. Developed is a scheduling mechanism in which the job dispatching rule varies dynamically based on information from discrete event simulation that evaluates a set of candidate rules. Major components of the scheduling mechanism are a simulation mechanism and a real-time control system. The simulation mechanism evaluates dispatching rules and selects the best dispatching rule for a given criterion. The real-time control system periodically monitors the shop floor and checks the performance value of the system. The selected dispatching rule is used until the difference between the actual performance value and the value estimated by simulation exceeds a given limit. Then a new simulation is performed with the remaining operations in the simulation mechanism to select a new rule. Results of computational tests show that the scheduling mechanism can be used effectively in real situations because it can fully use the information on the actual state of shop floors. <s> BIB002 </s> SURVEY OF DYNAMIC SCHEDULING IN MANUFACTURING SYSTEMS <s> Dispatching Rules <s> This study examines the effects of scheduling rules on the performance of flexible manufacturing systems (FMSs). Several machine and AGV scheduling rules are tested against the mean flowtime criterion. In general, scheduling rules are widely used in practice ranging from direct applications as a stand-alone scheduling scheme to indirect application as a part of complicated scheduling systems. In this paper, we compare the rules under various experimental conditions by using an FMS simulation model. Our objective is to measure sensitivity of the rules to changes in processing time distributions, various levels of breakdown rates, and types of AGV priority schemes. A comprehensive bibliography is also presented in the paper. <s> BIB003
Dispatching rules have played a significant role within dynamic contexts. Over the years, a variety of simple and complex dispatching rules have been proposed in the literature. It was found that no rule performs well for all for all criteria. Hence many investigations were carried out towards recognising a combination of several dispatching rules to find a range of system states in which the relative performance of each rule is 8 highest. In order to assess the performance of various dispatching rules dynamically under different dynamic and stochastic conditions of the shop floor, simulation was used. Simulation allows the execution of several dispatching rules, and the rule that yields the best performance is selected. A number of authors have used simulation to evaluate the performance of dispatching rules. BIB001 ,  presented excellent state-of-the-art surveys of dispatching rules in dynamic job shops and flow shops. They evaluated the performance of a variety of dispatching rules with respect to some common performance criteria discussed in literature, such as variance of flow time, minimum and maximum flow time, mean tardiness, maximum tardiness and variance of tardiness, etc. They classified these rules into fives categories: rules involving process times, rules involving due dates, simple rules involving neither process times nor due dates, rules involving shop floor conditions, and rules involving two or more of the first four categories. It has been observed that no single rule performs well for all important criteria related to flow time and tardiness of jobs. In general, it has been noted that process time based perform better under tight load conditions, while due date based rules perform better under light load conditions. Holthaus (1999) presented a simulation-based analysis of dispatching rules for scheduling in job shops with machine breakdowns. With respect to flow time and due date based objectives, the relative performance of well known and the new dispatching rules proposed were evaluated for different settings of the model parameters. The results revealed that the relative performance of scheduling rules can be affected by changing the breakdown parameters. BIB003 presented a comprehensive simulation study on scheduling rules for flexible manufacturing systems in the presence of various levels of breakdown rates and changes in processing times. He reported that no single rule is the best under all possible conditions. A comprehensive bibliography is also presented in the paper. Shafaei and Brun (1999a) in their simulation study investigated the performance of a number of scheduling rules for a dynamic job shop. Their performance measure considered is an economic objective, which includes the main costs involved in a scheduling decision.  presented a comprehensive comparative study of more than twenty dispatching rules in a dynamic job shop with weighted tardiness criterion for dynamic job arrivals. BIB002 and proposed a simulation-based scheduling system with two major components: a simulation mechanism and a reactive control mechanism. The simulation mechanism evaluates various rules and selects the best one. The reactive control mechanism monitors the system operation periodically and determines the timing of the new simulation runs. Jeong and Kim (1998) used simulation and dispatching rules for real-time scheduling of a flexible manufacturing system in the presence arrivals of urgent jobs, machine breakdowns, and tool breakage. Simulation evaluates the dispatching rules and the scheduler based on this evaluation selects the best dispatching rule, which satisfies the requested criteria. Kutanoglu and Sabuncuoglu (2001) used simulation to investigate the performance of various schedule repair heuristics based on rerouting the jobs to their alternative machines (no rerouting, queue rerouting, arrival rerouting, and all rerouting) for unexpected machine failures in dynamic job shops. The experimental results showed that the proper selection of a good schedule repair heuristic is based not only on the system characteristics (utilisation, machine down times, and frequency of machine failures) but also on the material handling system in terms of speed and number of material handling system devices. 