Showing papers on "Job shop published in 1984"

ISIS—a knowledge‐based system for factory 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 variety of constraints. Schedules are influenced by such diverse and conflicting factors as due date requirements, cost restrictions, production levels, machine capabilities and substitutability, alternative production processes, order characteristics, 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. We examine both the representation of constraints within ISIS, and the manner in which these constraints are used 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.

Characterization of automatic guided vehicle dispatching rules

Abstract: SUMMARY Hardware failures notwithstanding, the ability of an automated system operating according to promised potential is dependent upon the operational control measures in force. In this paper, some heuristic rules for dispatching Automatic Guided Vehicles (AGVs) in a job shop environment are presented. The rules are useful for assigning priorities to work stations requesting the services of a vehicle for material pickup. The likely effects of these rules on the performance of a job shop are postulated. Simulation results to demonstrate the effects of these rules arc also presented.

Sequencing Rules and Due-Date Assignments in a Job Shop

Abstract: Recent research studies of job shop scheduling have begun to examine the interaction between sequencing priorities and the method of assigning due-dates. This paper surveys the tactical aspects of this interaction, focusing primarily on average tardiness as a measure of scheduling effectiveness. The discussion highlights several factors that can affect the performance of dispatching rules, such as the average flow allowance, the due-date assignment method, and the use of progress milestones. A set of simulation experiments illuminates how these factors interact with the dispatching rule, and the experimental results suggest which combinations are most effective in a scheduling system.

Autonomous Manufacturing: Automating the Job-Shop

Abstract: The term \"factory of the future\" has lost much of its meaning because of excessive publicity heralding each new machine tool, robot, or computer-based controller. It has become increasingly difficult to differentiate between fact and fantasy. Our purpose in writing this article is to examine some of the issues involved in creating an \"autonomous manufacturing environment\" for discrete parts. We restrict the concept of autonomous manufacturing to only the activities performed on the shop floor. In particular, autonomous manufacturing pertains to the complete automation of decision making on the shop floor, whether or not the actual production is performed manually or automatically. While much of computer-aided manufacturing has been concerned with \"flexible automation,\" we are concerned with the decision-making methodologies required for planning and control. The introduction of robotic and other flexible technologies into manufacturing increases the number of ways a product can be produced and decreases the production rate. Unfortunately , flexible technologies increase the complexity of operation and production scheduling and, because of the subsequent decrease in setup times, there is less time for decision making. Today, decisions made manually in the shop are less than satisfactory, demonstrated by high in-process time of orders, low machine utilization, and high overheads. Such manual planning and control methods limit our ability to utilize the flexibility afforded by robotic technology. We investigate the issues involved in constructing software systems for the planning and control of activities in the job-shop. Manufacturing is composed of many activities that can be monitored and controlled at different levels of abstraction. A shop floor can be viewed as a group of work centers, a work center as composed of manufacturing cells, and a manufacturing cell as composed of individual machines, robots, and tools (see Figure 1). Activity planning in such an environment is a complex problem in which activities must be selected and resources must be assigned and scheduled at each level of abstraction to meet production goals. While much of this can be performed before production begins, the dynamics of the manufacturing environment tend to quickly invalidate predictive planning, forcing the shop to adapt to changes. In our discussion, we assume the existence of a shop with the following characteristics: * a set of predefined parts to be produced in small batchese * one or more sequences of manufacturing operations defined for each part; * one or more work centers in which an operation is …

Analysis of group technology scheduling heuristics

Abstract: The need for increased productivity in small batch manufacturing has recently brought focus to the topics and concepts of group technology. The results of a simulation analysis of the use of three job shop simulation scheduling rules which focus on inducing efficiency in the shop is presented. Two of these rules show significant gains in efficiency and, unexpectedly, they also show significant gains in effectiveness. These rules, in effect, induce the efficiency gains expected with group technology implementation.

Input scheduling and load balance control for a job shop

Abstract: This paper deals with a method for scheduling and control of a maching job shop where the average number of operation stages per part is six and the average operation time per stage is about one hour. The method is based on the adjustment of load balance among machines and the limitation of the amount of work input. By simulation with real data, it was found that two variables, the load balance and input amount of work, definitely influence shop performances such as lateness, mean flow time and utilization of machines. If these two variables are well controlled, good results can be obtained no matter what the dispatching priority rules on the shop floor may be.

A comparative study of priority dispatching rules in a hybrid assembly/job shop

Abstract: SUMMARY This paper reports on research conducted on the use of priority dispatching rules in a hybrid assembly/job shop which manufactures both single-component and multiple-component products. A simulation model was constructed and a large stale experiment performed. Statistical analysis of the simulation results indicated significant impact of both the priority rules tested, and the product-mix considered on shop performance. Among the 12 priority rules tested, the SPT (shortest processing time) rule and the ASMF-SPT (assembly jobs first with SPT as tie-breaker) rule performed very well with respect to measures like lateness, flow time, tardiness, staging time, and percent of jobs tardy. These findings lead to further investigation of a combined priority rule, MIXED, which implements the ASMF-SPT rule at all machine centres that process components of assembly jobs, and the SPT rule at the remaining machine centres which process non-component jobs. The additional research results yielded evidence that th...

The design and validation of a digital simulation model for job shop control decision making

Abstract: A previous paper (Browne et al. 1981) identified the decision making problems associated with job shop control and presented an objective function for measuring its performance. Given that definition of job shop control and cost-based objective function, simulation modelling offers the best prospect of a solution of the problem of providing a management tool to aid in the decision making associated with job shop control. This paper provides a detailed analysis of the design of such a model. The model, written in the GASP fV simulation language and running on a CDC 7600 computer, is based on the job shop of a major machine tool manufacturer and has been validated against actual job shop performance.

Optimal policies in stochastic shop scheduling

Abstract: In this paper a survey is presented of some of the recent results in stochastic open shop, flow shop and job shop scheduling. The distributions of the processing times of the jobs are known in advance, but the actual processing times are not known in advance. The jobs may have due dates. Optimal preemptive and nonpreemptive policies are determined for the minimization of various objective functions, such as the expected makespan, the expected flow time and the expected number of late jobs. The effect of various degrees of dependence between the processing times of any given job on the various machines is investigated. Under given conditions bounds are obtained for the expected makespan in the different models.

Improved decision rules in a combined system for minimizing job tardiness

Abstract: SUMMARY In a recent article, Miyazaki described a combined system for setting due dates and sequencing jobs in order to reduce tardiness in a job shop. This paper interprets the major features of that system in the context of current research and suggests improvements in both components of the system.

Inequalities and bounds in stochastic shop scheduling

Abstract: In this paper, stochastic shop models with m machines and n jobs are considered. A job has to be processed on all m machines, while certain constraints are imposed on the order of processing. The effect of the variability of the processing times on the expected completion time of the last job (the makespan) and on the sum of the expected completion times of all jobs (the flow time) is studied. Bounds are obtained for the expected makespan when the processing time distributions are New Better (Worse) than Used in Expectation.

The Phased Release of Batches into a Job Shop

Abstract: Much research has been reported on the possibilities of using various heuristic priority rules to sequence batches through a job shop. The SPT (Shortest Priority Time) heuristic, or modifications to it, has been proved useful in many studies. This paper reports on the results obtained when simulating the work flow through a real machine shop. The simulation model has been used to test the effect on well known priority rules of releasing batches into the shop in order of decreasing expected throughput time. The important effect of this “phased release” of batches was to increase the percentage of batches delivered in finished parts stores on time, particularly in the case where priority rules were in use which might otherwise have resulted in poor delivery. This has important repercussions for management because it implies that by “phased” release of batches in the manner discussed, a large proportion of batches will be delivered on time whatever priority rule is in operation in the shop.

State dependent priority rules for scheduling

Abstract: : The purpose of this thesis is to enhance the priority setting procedures for job shop scheduling systems. The new state dependent priority rules extend the concept of a myopic dispatching heuristic by allowing a wide choice of forecasting and planning horizons and by encompassing indirect or direct load information, even performance feedback, while maintaining the flexibility and robustness of the dispatching approach. Preliminary results are proven in the special case of proportionate flow shops with pre-emption. Many optimal rules for lateness and tardiness problems are extended from the single machine case to flow shops. Appropriate lead time estimation used in setting operation due dates can be shown to guarantee the achievement of a global optimum when applying a myopic rule locally. In more general job shop environments, we study scheduling with due dates when jobs have different tardiness penalties. Advanced slack evaluation methods have been developed for our Apparent Urgency rule and for the modified CoverT rule. First, waiting line analysis furnishes the use of indirect load information, such as the distribution of the jobs' weights and processing times, in assigning static priority-based waiting time estimates for each operation. Second, the waiting time estimation and look-ahead parameters of the rules are further adjusted on the basis of direct, periodically updated state information, such as the anticipated queue lengths in the shop. Third, an iterative scheme is used to revise new lead time estimates based on the jobs' realized waiting times in successive schedules. This lead time iteration provides also feedback from the performance of the rule for the coordination of the priority assignments.

The decision to adopt new technology—Effects on organizational size

Abstract: FMS is new technology with many considerations that differ from those familiarly applied to job shop, flow shop and automated flow shop work configurations. A major obstacle to using FMS is that little is known about how to co-ordinate flexible work and transfer activities to obtain a relatively constant flow of marketable output. In the past year, articles on FMS have appeared with increasing frequency. Their emphasis highlights the reduction in variable production costs that FMS promises. This paper describes a different approach, namely, to uncover the effects of FMS technology on optimal organizational size. To achieve this end, we must consider factors other than variable production cost savings. This enlarges the scope of the decision model required to evaluate FMS configurations. The investigation proceeds along two diverse, but complementary paths. One is based on a theoretical model, using non-linear breakeven analysis. The second employs empirical data obtained from industrial users. The theoretical model indicates that FMS requires a larger total output than the system it replaces. Empirical results tend to confirm this finding. In addition, FMS alters other managerial considerations, including appropriate marketing strategies.

Comparison of dispatch policies for a single server queueing model with limited operational control

Abstract: SUMMARY In this paper we consider a single server queueing model for a single machine dynamic job shop in which shop level scheduling is not permitted. External arrivals of jobs are received in a dispatch area from which their release to the job shop is controlled. To overcome the limitation of operational control, we propose three different dispatch policies and compare their performances to that of a first come first served dispatch policy. The four dispatch policies considered are (1) first come first served, (2) scheduling within generations, (3) scheduling within periodic review, and (4) scheduling within fixed batch sizes.

Group technology — a strategy towards higher quality of working life

Abstract: For the time being, small batch production uses to be organized as job shop manufacturing. There exists, indeed, a completely different way of organizing small batch production by means of group technology. Group technology principles can be implemented in four major stages, i.e. by grouping parts, grouping machinery, grouping personnel, and organizational grouping. Obviously, the idea of group technology denotes a general organizational concept rather than a single technique. Therefore, its strengths and weaknesses are discussed in some detail as compared to job shop manufacturing. Some technical, economic, and social reasons for group technology approaches getting more important recently are considered as well. As a main topic, the opportunities and advantages of group technology for achieving higher quality of working life in manufacturing are then illustrated. This explanation includes such aspects as the reduction of horizontal and vertical division of labour, the enlargement of margins of action, and personality enhancement by better using and developing human skills. In relation with this, the sort of technical assistance and devices needed to implement those work structures without diminishing the level of productivity are discussed as well. For illustration, an existing computer integrated production insula and a flexible manufacturing system are regarded as examples of group technology implementations.

Operational analysis of a job shop

Abstract: We propose and develop a discrete-time, continuous-flow model with linear control for studying the operation of a job shop that sees a stationary input mix of job types. We are not concerned with issues of detailed scheduling, but rather hope to develop a planning tool for a job shop operation. With the model we are able to characterize the operational behavior of each work center in the job shop for a given control policy. The control rule that we assume sets the production rate at a work center as a fixed proportion of its queue level in each time period. This control rule is consistent with the assignment of a planned lead time to each work center. For such control rules the model gives the steady-state distribution of the production levels at each work center, as well as the distribution of queue lengths. We show how to use the model not only to evaluate a specification of the control rules but also to find a good specification of the control rules that results in acceptable shop behavior.

The development of an interactive simulation model for management decision making

Abstract: Simulation has generally been applied in problem areas where the variables and their relationships are understood but where no efficient analytical method solution exists. Batch manufacturing systems design and analysis is such an area. Simulation models of varying complexity may be used either as design tools for plant layout, scheduling systems, batch sizing decisions, capital acquisition decisions etc — or alternately, as an online decision support system to establish the time release of batches and the priority of each batch at each work centre. However, simulation models are complex, often require access to large data banks and involve high CPU times. Further, they tend to be inflexible in that the user is often unable to modify conditions to allow a true “what if” capability. This militates against their use by industrial personnel. This paper describes the development of an interactive simulation model of a job shop and its use as a decision support system to aid management decision making. The interactive model was developed from an existing batch processing model. The interactive nature of the model is demonstrated through its application to situations where certain resources (work centres) are discarded and alternative process routes are simulated. The design of the database of the model is described in detail as it is through interaction with the database — e.g. product structure data, machine routing data, work centre data — that much of the flexibility is achieved. Consideration is given to the further development of the model to allow its integration into a full computerized production system through linkage to an MRP (Materials Requirements Planning) system and a real time Shop Floor Control System,

Design of Hierarchical Control Systems for Automated Job Shops

Abstract: The problem of real-time control system design for an automated or semi-automated job shop is considered. Prototype software tools for this purpose have been developed and used at BBN. In a small-batch environment with considerable part mix, the efficiency of programming and testing the control system itself can be as important as product throughput to the overall acceptance of automation and to shop efficiency