Showing papers on "Job shop published in 1983"

The Effect of Workload Dependent Due-Dates on Job Shop Performance

Abstract: This study explores the due-date performance of job shop control systems which base job due dates on a time-phased representation of the workload and the machine capacity in the shop. The performance is measured by the mean and the standard deviation of the lateness. Two parameters are used to vary the functioning of the due-date assignment system: a minimum allowance for waiting, denoted by SL, and a maximum fraction of the available capacity allowed for loading, denoted by CLL. The system increases the waiting lime allowance if congestion is observed when loading a new job. The capability of the system to observe congestion is determined by the parameters CLL and SL. Simulation experiments are used to investigate the performance of the assignment system. It is shown that the assignment system performs quite well with respect to reducing the standard deviation of the lateness; the performance is not very sensitive however to the parameter values used; with an expected capacity utilization of 90%, CLL should be set between 0.80 and 1.00 times the mean available capacity and SL should be set between 0.55 and 0.90 times the mean operation waiting time in the shop. The assignment system may also perform well with respect to controlling the mean lateness. If SL is set between 0.55 and 0.75 times the mean expected waiting time in the shop, a constant mean lateness is obtained independent of the utilization of the shop if CLL is set between 0.70 and 0.80 times of the mean available capacity. However, the mean lateness turns out to be quite sensitive to variations in the job-mix of the workload. Finally it is shown that if the values of the assignment parameters are adequate, the mean job lateness is independent of the number of operations in a job. This property can be used to monitor the correctness of the parameter values.

Time completion for various dispatching rules in job shops

Abstract: This study investigates the relative priority of various job shop dispatching rules for various shop utilization levels under both deterministic and stochastic assumptions with regard to processing times The primary criterion for evaluation is that of percentage on time completion The results indicate that an assumption of accurately predetermining actual operation times in most cases is not likely to weaken the analysis and impact of research studies which are performed using such an assumption Also conclusions indicate that the ranking of dispatching rules according to their effectiveness varies significantly with shop utilization levels

ISIS: A Constraint-Directed Reasoning Approach to Job Shop Scheduling.

Abstract: : Analysis of the job shop scheduling domain has indicated that the crux of the scheduling problem is the determination and satisfaction of a large number and variety of constraints. Schedules are influenced by such diverse factors as due date requirements, cost restrictions, production levels, machine capabilities, operation precedences, resource requirements, and resource availability. This paper describes ISIS, a scheduling system capable of incorporating all relevant constraints in the construction of job shop schedules. The authors examine both the representation of constraints within ISIS, and the manner in which these constraints are utilized in conducting a constraint-directed search for an acceptable schedule. The important issues relating to the relaxation of constraints are addressed. Finally, the interactive scheduling facilities provided by ISIS are considered. (Author)

Priority scheduling with cost considerations

Abstract: Although many articles have been published on the general priority scheduling problem, very few have been concerned with directly minimizing costs. The few studies which do consider overall costs do not use these costs in establishing a job's priority in the queue. This paper investigates how the time and cost performance of jobs are affected by the use of a rule which directly considers costs. A simulation model of a hypothetical job shop is used to examine several of these cost rules, as well as some common rules concerned with the timeliness of jobs. Performance measures include both time-oriented and cost-oriented measures. The results indicate that rules which directly consider costs (or profit) may prove practical for a manager where minimization of WTP and maximization of ROT are the primary and secondary objectives of the company

Scheduling for a combination of made-to-stock and made-to-order jobs in a job shop

Abstract: This paper deals with selecting a heuristic rule for concurrent scheduling of mixtures of due-date and non-due-date jobs. The measure of performance for the mixture of jobs is chosen to be mean flowtime subject to the constraint that due dates are satisfied. To handle varying levels of due-date tightness, three types of schedules are introduced. Dispatching rules for two of the three types of schedules were selected by simulation. Decision rules for determining the best schedules in appropriate situations are suggested.

Flow complexity—a data suitability index for flowline systems

Abstract: In layout planning the concept of ‘flow dominance’—the situation in which relatively few paths of flow dominate the overall materials movement problem— has been recognized for many years as a guide to whether line layout may be effective. More recently, so-called upper and lower bounds on flow dominance and a parameter‘problem complexity’ based on these bounds have been proposed as being more informative than flow dominance alone. In this paper it is shown that these so-called upper and lower bounds are only bounding values under certain conditions. A new parameter, ‘flow complexity’, is proposed which more effectively measures the complexity of flow. This parameter has a value which does lie between two bounds, one of which implies a pure flow line situation, the other the pure job shop situation.

Animation of output applied to manufacturing capacity analysis

Abstract: A general purpose technique for animating simulation output is described. The technique can be implemented using inexpensive hardware and is applicable to many types of simulation models. An example which uses the procedure for capacity analysis in a job shop is presented.

Single Queue Management of a Job Shop as Implemented by a Data Flow Architecture

Abstract: We investigated management of an automated job shop having an unpredictable job stream and randomly failing machines. The shop’s stochastic nature precluded a traditional scheduling approach. We devised an artificial intelligence system based on a distributed data flow control architecture. Machine utilizations in a simulated shop based on typical machine and job stream characteristics exceeded 93% for average machine downtimes below 16%. This conference paper briefly describes the architecture and experiment. It considers at length the technology required to implement the control system, and speculates briefly about the effect of this system on machine tool design.

Artificial intelligence techniques for industrial applications in job shop scheduling.

Abstract: : The application of AI (artificial intelligence) techniques to the scheduling of industrial production operations offers a promising new approach to a scheduling problem of great magnitude and complexity. Foremost among these techniques is a powerful knowledge representation language that is capable of modeling the production environment at all levels of detail. The capturing of such complexity in the data base enables the computer to generate feasible schedules from a very large solution space which are highly rated by human experts. An introduction to artificial intelligence is presented that discusses knowledge representation techniques and describes an intelligent scheduling system. The relevance of AI techniques to military industrial production operations is explored by examining the closed job shop in the contest of jet engine repair.

A preliminary review of batch sizes in a job shop using a digital simulation model

Abstract: A previous paper 1described the design of a simulation model. This model, written in GASP IV, allows the management of a large machine shop to try out policies under realistic assump tions without disrupting operations.This paper outlines the results of approximately 30 "runs" on the model, which are designed to provide an insight into the ef fects of modifying the batch sizes used in the machine shop. The results obtained suggest that the major impact of increased batch sizes is on the flow of work through the plant. The overall conclusion is that the current manufacturing system cannot ac commodate larger batch sizes. The presently used batch sizes suit the configuration of work centres and the deployment of labour in the job shop.