Showing papers on "Job shop published in 1978"

Multiple Resource–Constrained Scheduling Using Branch and Bound

Abstract: This paper focuses upon the problem of assigning feasible start times to a set of activities making up a project, static job shop, or static flowship type schedules under two constraint sets: (1) no activity may be started until all activities technologically established as its predecessor set have been completed, and (2) the total resource requirements of all activities in process at any time in the schedule must not exceed the level of availability for each of the multiple resource classes. The solution procedure used for these problems is branch and bound, and the resulting complete schedules are optimized with an objective of minimizing the completion time of the entire set of activities. Computational results on tests conducted on a number of randomly generated problem sets with up to 60 activities and six resource classes are presented.

An instructable production system: basic design issues1

Abstract: The full advantages of the incremental properties of production systems have yet to be exploited on a large scale. A promising vehicle for this is the task of instructing a system to solve problems in a complex domain. For this, it is important to express the instruction in a language similar to natural language and without detailed knowledge of the inner structure of the system. Instruction and close interaction with the system as it behaves are preferred over a longer feedback loop with more independent learning by the system. The domain is initially an abstract job shop. The beginning system has capabilities for solving problems, processing language, building productions, and interacting with the task environment. All parts of the system are subject to instruction. The main problem-solving strategy, which permeates all four system components, is based on means-ends analysis and goal-subgoal search. This is coupled with an explicit representation of control knowledge. The system's behavior so far is restricted to simple environmental manipulations, a number of which must be taught before more complex tasks can be done.

Steady state waiting time in a multicenter job shop

Abstract: This paper analyzes the waiting-time distribution of a specific job as it moves through a job-shop with multiple centers and exponential service times. The movement of the job through the shop is governed by a Markovian transition matrix and ends with the job's exit from the shop.

Performance analysis of multiprocessor systems containing functionally dedicated processors

Abstract: General models of multiprocessor systems in which processors are functionally dedicated are described In these models, processors are divided into different types A task can be assigned only to a processor of certain types Clearly, the model of multiprocessor systems with identical processors is a special case of our models These models also include the job shop problem in which there is exactly one processor of each type Worst case performance bounds of priority-driven schedules are obtained

The Presentation of Information to the Job-Shop Scheduler

Abstract: Three graphic methods of presenting scheduling information were compared with each other and with a conventional, numerical presentation. The graphic methods were based on the Gantt chart, and all three proved more effective than the numerical presentation in helping the subjects produce efficient schedules. One method in particular which used a machines-by-time organization and identified machines by color code proved superior to the others. This is explained in terms of the perceptual nature of problem solution using these methods. It is suggested that this organization of information be adopted when the primary criterion for schedule evaluation is machine utilization and there are limitations on the display space and color-coding available.

Practice of Management Science---Orderbook Balancing Using a Combination of Linear Programming and Heuristic Techniques

Abstract: In complex manufacturing situations, when product demand exceeds the manufacturing capacity by a very wide margin, both the production planning and scheduling functions become extremely difficult and time-consuming to handle---even with modern computers and sophisticated analytical techniques. Our studies had shown that in such cases the tasks of production scheduling and detailed planning could be made easier if the orderbook were first balanced in an aggregate manner such that monthly or other periodic demands were approximately in line with the manufacturing capabilities. We applied this basic approach in the development of an improved planning tool for Bethlehem Steel's roll manufacturing operations, where approximately 4,000--6,000 cast rolls of 300 different types, each requiring an average of ten operations, are machined in a large m/n job shop each year. This planning tool, which is a hybrid computer package combining linear programming and heuristic methods, is being routinely used to balance the roll orderbook. The quick estimate of shop capacity and due-date performance provided by this package gives shop management an improved ability to negotiate roll delivery and resolve order-distribution problems with the plants. Due dates are changed and/or orders are dropped during one or more rounds of negotiations with each plant, and a balanced, or feasible, orderbook for the plants as a whole is obtained. Accurate production schedules and long-term plans are then generated by elaborate simulation models.

Overtime usage in a job shop environment

Abstract: Problems are encountered in a job shop which has a fixed capacity if the total work content of the jobs passing through the shop increases sufficiently. Even the use of effective priority dispatching rules and/or expediting does not adequately shorten the queues which develop if the total work content continually exceeds shop capacity. To avoid losing job orders because the orders are unduly delayed, the job shop might resort to overtime usage. This study examines the efficient and economic use of overtime to relieve the backlog problem and uses overtime as the basic criterion for evaluation of overtime usage. The study employs GPSS V programming language to simulate a hypothetical job shop. The shop is loaded to various proportions of its normal capacity and various levels of overtime are tested. Findings show that overtime should not be assigned indiscriminately but rather should be based on a shop's unique conditions of overtime cost, the priority rule being employed, and the level of capacity utilization. Marginal benefit-cost ratio curves are developed to determine whether overtime usage is economically reasonable. These curves may also be used to determine the maximum or limiting amount of overtime to use under specific shop conditions.

Seqential approach in job shop scheduling

Abstract: This study investigats a new approach‐the sequential approach‐ in job shop scheduling. The objective is to minimize the total of lateness cost and set‐up cost in job shops. Whenever a scheduling decision has to be made as to which job should receive the next processing, this approach considers each cost sequentially. One of the two costs is considered first, and every time all waiting jobs must be examined in terms of this cost, and only those jobs qualified would the second cost apply to and from which a job would be selected for processing. This investigation was carried out by using GASP IV simulation under a variety of job shop situations. The effectiveness of this approach and job selection mechanism constitute the main theme of this study.

A large scale job-shop simulation based on actual operating data

Abstract: This paper describes a simulation study of a large job-shop based on actual operating data and procedures. The simulation model is used to investigate and solve problems of shop floor congestion and poor lead times. Statistically design experiments are used to evaluate the effect of material handling support and job input rates on various common measures of shop performance. A predictive model for mean job flow time is also developed using multiple regression. This analysis provides the basis for several layout changes which reduce material handling and shop floor congestion. The results of the study also show the need for formalized work center loading and scheduling procedures based on the finite capacity of the work centers.

Laser Job Shopping Using Today's Laser Technology

Abstract: The high capital investment necessary to investigate the use of laser technology provides the laser job shop with a role not common to job shops in other industries. It may act as a transfer agent of the new technology into the manufacturing world by laser processing parts on the contract basis, by training the staffs of companies who purchased their own equipment, and by becoming a "second source" to those companies. Two case histories, complete with technical details, are used as examples. Precision hole drilling in metals and alumina substrates was investigated and refined in just a few days, resulting in considerable gain both technically and economically for the companies involved. A checklist is also provided as a guide to help an engineer determine if job shopping is applicable to his particular situation.

“pass”: an interactive online simulator for predictive production control

Abstract: An interactive online simulator PASS (Predictive Adaptive Simulation System) has been developed as a packaged tool for predictive production control systems. PASS is a man-machine system to enhance the following functions: prediction of process status and evaluation of alternative precautionary measures. In this paper, the present version (a job shop model) is described in terms of the prediction and evaluation functions, the simulation model, and the software structure.