Showing papers on "Job shop published in 1990"

Dynamic job shop scheduling: A survey of simulation research

Abstract: 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.

Models for Determining Estimated Start Times and Case Orderings In Hospital Operating Rooms

Abstract: In this paper, we address a number of scheduling problems that are often faced in a hospital's operating room (OR). The operating room can be modeled as a one machine job shop where the surgical procedures are thought of as the jobs and the operating room itself is the machine. The procedure (job) times are stochastic and the operating room scheduler exerts control over the schedule of jobs. The situation can also be thought of as a D/GI/1 queueing system, where the arrival times of the customers are a decision variable. Initially we address the problem where the scheduler is given the sequence of jobs and must determine the estimated starting times of the procedures in order that the surgeons may plan their personal schedules with respect to hospital rounds and office visits. The costs that must be balanced are (1) the idle time costs if the estimated starting time is later than the actual available start time, and (2) the surgeon's waiting time if the estimated starting time is before the actua...

Job shop scheduling with alternative machines

Abstract: SUMMARY In this paper we investigate the problem of minimizing the mean flow time in a general job shop type machining system with alternative machine tool routeings. An analytical formulation of the problem as a mixed integer programming is developed. An efficient algorithm based on this formulation is developed to solve the problem by decomposing it into subproblems that are easier to solve. The algorithm solves large problems in relatively short time. A second algorithm based on the SPT rule is developed and its performance is compared with the first algorithm. A greedy procedure is also developed for the case when a penalty cost is associated with adding alternative machines. Numerical examples are given to demonstrate the use of the above algorithms.

Two new rules to minimize tardiness in a job shop

Abstract: SUMMARY In this paper we present two new dispatching rules for minimizing tardiness in a job shop. Both rules are closely related to the modified operation due date (MOD) rule. The first is a combination of the shortest processing time (SPT) rule and the critical ratio (CR) rule, and the second is a combination of the SPT rule and the slack per remaining work (S/RPT) rule. The two new rules are simple to implement and can easily be adapted to minimize weighted tardiness. Moreover they do not require any parameter estimation for their implementation, which is a notable disadvantage of some earlier rules such as COVERT. Simulation results show that the performance of the two new rules is better than that of other rules that have been developed to minimize total weighted and unweighted tardiness. This holds true across a range of shop conditions. Furthermore, the rules are effective in minimizing the number of tardy jobs.

Job sequencing with fuzzy processing times

Abstract: In practice, processing times can be more accurately represented as intervals with the most probable completion time somewhere near the middle of the interval. A fuzzy number which is essentially a generalized interval can represent this processing time interval exactly and naturally. In this work, triangular and trapezoidal fuzzy numbers are used to represent those vague job processing times in job shop production systems. The job sequencing algorithms of Johnson and Ignall and Schrage are modified to accept fuzzy job processing times. Fuzzy makespans and fuzzy mean flow times are then calculated for greater decision-making information. Numerous examples are used to illustrate the approach.

An investigation of dynamic group scheduling heuristics in a job shop manufacturing cell

Abstract: SUMMARY The objective of this study is to develop dynamic scheduling heuristics for cellular manufacturing environments (group scheduling or family heuristics) and compare them with existing family heuristics under various shop floor conditions. The proposed family heuristics stress good due date performance while reducing overall set-up time. Computer simulation is used to test three queue selection rules in conjunction with three dispatching rules under eight experimental conditions in a job shop cell. The results indicate that several of the proposed heuristics substantially improve the performance of the cell over the best previously suggested family heuristic under all experimental conditions.

Minimizing the Flow-time Variance in Single-machine Systems

Abstract: In this paper we deal with an n-job, single-machine scheduling problem. All jobs are available from the start, and the objective is to minimize the variance of job flow-times. A heuristic procedure which is based on the complementary pair-exchange principle is proposed. It has been concluded that this heuristic procedure provides improved results (in terms of objective-function value) when compared with other heuristics. Our heuristic procedure has the complexity of O(n log n).

Schedule generation in a dynamic job shop

Abstract: SUMMARY An extension of Giffler and Thompson's algorithm (1960)is developed to create all active schedules in a dynamic job shop. A partitioning scheme is also developed that works extremely well in reducing the number of active schedules created. This reduced enumeration method is much more efficient than the full generation scheme and, based upon the results of test problems, it appears to be nearly as effective.

Manufacturing systems with forbidden early shipment: implications for choice of scheduling rules

Abstract: SUMMARY Recent progress in manufacturing systems research has identified the feature of forbidding early shipment (FES) of orders as a prevalent characteristic of real systems. This report examines the implications of this feature on the choice of scheduling rules within a job shop. Simulation results of a simplified job shop reconfirm the superiority of the modified due date approach when the criterion is mean job tardiness. However, when the criterion is system inventory, the slack time per remaining operation ratio approach performs slightly better than modified due date. The shortest operation processing time yields very poor results in job shops that include the FES assumption.

An investigation of the applicability of expert systems to job shop scheduling

Abstract: Although the job shop scheduling (JSS) problem is of eminent practical importance and has received considerable attention by both industry and academia, because of its complexity, it still remains an enigma. Artificial Intelligence holds the potential for providing solutions to complex problems, such as the JSS problem. However, due to the magnitude of the JSS problem, search techniques are not computationally feasible. Expert Systems, though, have been successfully applied to problems of this type. The development of an expert system, however, implies the availability of an expert. Regrettably, such experts are not readily available in the JSS environment. The approach presented in this paper involves the use of computer simulation models of a job shop to train subjects so that they are capable of effective scheduling, and then extracting the knowledge of these “experts” to develop an expert system.

Optimal nondelay job shop schedules

Abstract: The heuristic job shop scheduling algorithm evaluated in this paper was based on finding optimal nondelay schedules (an approach that had been overlooked by past researchers). The makespan was the ...

Equipment Investment Decision Analysis in Cellular Manufacturing

Abstract: Cellular manufacturing is the organisation of manufacturing equipment based on the requirements of the product or component. Transition to cellular manufacturing generally requires reorganisation of existing equipment. It is likely that the existing equipment alone is not suitable for a cellular layout. During the cell planning and design phase equipment investment analysis is important to identify equipment needs. Transition from job shop production to cellular production is detailed. Cell formation and cell evaluation techniques are provided to assist in equipment procurement decisions. In particular, a structured procedure and analytical tools are given to evaluate fully the cellular system to identify appropriate equipment and methods. A case example is provided to explain the procedure.

Analysis of material flow in a job shop with assembly operations

Abstract: SUMMARY Facing competitive pressure from both domestic and foreign sources, today's manufacturers must strive to keep delivery promises and reduce inventory. This depends largely on a manufacturer's ability to predict job flowtimes reliably, hence allowing the assignment of accurate and attainable due-dates. An approximation method is presented to estimate the mean and standard deviation of job flowtimes in a dynamic job shop with assembly operations. The accuracy of the method for predicting the flowtimes of jobs with varying structural complexities is assessed through computer simulation. While in general it is more accurate for jobs with simpler structure, the simulation results indicate that, over a range of test conditions, the approximation method is both simple and effective for estimating job flowtimes in assembly shops.

The robustness of selected job-shop dispatching rules with respect to load balance and work-flow structure

Abstract: Most of the published job-shop research has focused primarily on the identification of dispatching rules which perform well under a variety of shop conditions. Most of the research has assumed that the job shop was an open shop in the sense that a virtually unlimited number of job routeings was possible, as compared to a closed shop, which has much more standardized routeings. Also, most research has further assumed that the capacities at all machines are relatively even, and thus no permanent bottleneck exists. In this research, some of the best-known dispatching rules are studied to determine whether the rules are robust with respect to capacity balance and work-flow structure. In order to be useful in all types of job shop, a rule should perform well regardless of the balance of capacity and work-flow structure in the shop. Results indicate that most of the rules studied are not affected by either of the above factors.

Common due-date assignment and scheduling for a single processor to minimize the number of tardy jobs

Abstract: This paper considers the problem of assigning a common due-date to a set of simultaneously available jobs and sequencing them on a single production facility. The objective is to determine the optimal common due-date value and job sequence that jointly minimize a cost function based on the assigned due-date and the number of tardy jobs. It is shown that the optimal due-date coincides with one of the job completion times and ordering jobs in non-decreasing processing times yields an optimal sequence which in general is not unique. An efficient (polynomial-bound) algorithm to find the optimal solution is presented and an illustrative example is provided.

Factory Model and Test Data Descriptions: OPIS Experiments

Abstract: : The goal of this report is to define a factory model and a set of experiments that can be used to compare alternative scheduling methods. The model was originally created to provide a comparative analysis of the OPIS and ISIS constraint directed scheduling systems and the COVERT dispatch rule. The model is a simplification of the model used originally to test ISIS. This report defines a Job Shop in terms of: (1) Parts, including physical characteristics; (2) Process plans composed of operations, precedence relations, and resource requirements; (3) Resource descriptions, including labor machine ratios; and (4) Constraints covering due dates, work in process, machine restrictions, etc. Twenty-two experiments are defined each containing orders composed of release dates, due dates, parts, quantity, and priority. Orders were statistically generated based on the parameters described in the latter sections.

On the Simulation Run Length: A Step towards Real Time Control in an FMS

Abstract: In any real time control system, its scheduling and control policy should be reassessed every time the state of the system changes. In large and complex systems, this could be a self‐defeating goal. Implementing real time control in such systems would require an enormous amount of computation time. Determination of discrete time interval (simulation window length) is the main objective of this study. To implement and demonstrate this methodology, we selected a Flexible Manufacturing System (FMS) which approximates a dynamic job shop. The Expert Control System (ECS) developed in this study integrated programmes for different functions and employed multi‐pass simulation to determine the best scheduling strategy in the system. The simulation output is then subjected to Analysis of Variance (ANOVA) and Newman‐Keuls′ range tests to obtain a “good” simulation window length for different performance criteria of optimisation.

Job shop configuration optimization at Tinker Air Force Base

Abstract: This paper discusses a large simulation model that was developed to aid the reconstruc tion efforts after a disastrous fire at Tinker Air Force Base. The model, developed in SLAM, facilitated the analysis and efficient design of the functional layout that replaced the previous machine-based layout in the appropriate number of machines to place within a modular repair center (MRC), stacker capacity for in-process inventory, location of elevators for sending parts to the conveyor, and the optimal design and routing scheme for overhead conveyor system. The new layout, as predicted by the simulation model, has proven to be quite effective compared with the pre fire layout. Improvements that have been achieved include a 50 to 80% decrease in material handling, substantive decrease in flow times, better manage ment control of part transfers, $4.3 million savings from the elimination of excess capacity, and $1.8 million savings resulting from higher direct labor efficiency.

A study of labor assignment rules with bottlenecks

Abstract: Although labor flexibility has been recognized as an effective managerial tool to handle bottleneck problems, most of the past research in labor assignments rules has been done in an evenly loaded job shop. In this study, five new labor assignment rules, which incorporate bottleneck information, are developed and tested with the traditional rules in a bottleneck job shop. Four dispatching rules are used to determine the sequence of jobs at the work center. Three levels of mean labor transfer time were tested. One-way Analysis of Variance was used to examine the significance of the labor assignment rules for each dispatching rule and performance criteria. For the statistically significance variables, Tukey test was used to examine the relative performance of labor assignment rules. The results were different from the past research in an evenly loaded job shop in that the labor assignment rules had a significant effect on the shop performance.

One-machine scheduling for minimizing total flow time with release dates

Abstract: The one-machine scheduling problem of minimizing total flow time with different release dates is addressed. This problem is equivalent to the problems of minimizing total completion time, total job lateness, and mean number of jobs in the shop, and it is NP-hard. A necessary and sufficient condition is proved for local optimality and can be considered as a priority rule. Based on this condition, a subset containing all the optimal schedules is defined. Any schedule in this subset verifies some dominance properties proved by other researchers. The author also proposes some efficient heuristic algorithms using the proven condition to build a schedule belonging to this subset. The algorithm performances are provided. >

Multiple Performance Measures in the Selection of a Sequencing Rule

Abstract: While it is well known that managers make scheduling decisions based on multiple objectives, the majority of sequencing research is directed towards single criterion assessments of scheduling performance. A preference value decision model approach for the selection of job shop sequencing rules using multiple performance criteria is presented. The model is general in nature and may be applied to any of a number of sequencing rules and performance measures. A case example is provided to illustrate the procedure.

CIM implementation for job-shop environments

Abstract: Abstract. The small to medium-sized job-shop manufacturing industry can benefit most from the implementation of computer integrated manufacturing (CIM) technology, to meet the increasing demand for high-quality and economically priced products. The injection mould making industry is a typical representative for this group, where a manufacturer would generally produce moulds which consist of parts that are standard to every mould type or very similar. Thus, manufacturing techniques, such as group technology (GT), and production planning and control (information) management systems could make significant contributions in improving the efficiency of design and production operations. The objective of the project, presented in this paper, was the development of a GT-based classification and coding (C/C) system for injection mould parts especially for the design and process planning phases, and the development of a production planning and shop-floor control (SFC) information management system. An exten...

The quasi-simultaneous finishing of work orders on a flexible automated manufacturing cell in a job shop

Abstract: SUMMARY The introduction of flexible automated machine tools changes some of the characteristics of the production system in component manufacturing shops. Not only are machines made more universal by the use of flexible production automation, but it also is becoming more and more possible to change the set up of a machine without loss of productive hours. However, because of a limitation in the number of (often expensive) fixtures available per type of fixture, work orders are often finished more or less simultaneously, rather than in a sequential manner. This paper considers the logistic implications of these changes. In particular, the consequences of the quasi-simultaneous finishing of work orders for the throughput time will be analyzed. The paper shows that the work order lot size is a major factor in the determination of the throughput time per work order.

Toward a blackboard framework for opportunistic planning and dynamic scheduling in a modular job shop scheduling system

Abstract: This paper addresses a proposed scheduling system architecture for developing job shop production schedules in a modular fashion. The blackboard architecture forms a base framework to which application-specific plug-in modules can be applied in a toolkit manner. The issues relating to the implementation of such a flexible architecture and the current status of the HORIZON Project are discussed.