Open Shop Environment Research Articles

On the complexity of preemptive openshop scheduling problems

We investigate the complexity status of the preemptive openshop scheduling problem. After reviewing recent studies of the shop with various objective functions, we define the concept of preempting job w.r. to a schedule, and state some general results for the preemptive openshop environment. These results are then used to show by reduction from the 3-Partition, that the n job-2 machine mean flow time problem with ready times and job preemption is unary NP-hard.

Printed circuit board family grouping and component allocation for a multimachine, open-shop assembly cell

This article considers a particular printed circuit board (PCB) assembly system employing surface mount technology. Multiple, identical automatic placement machines, a variety of board types, and a large number of component types characterize the environment studied. The problem addressed is that of minimizing the makespan for assembling a batch of boards with a secondary objective of reducing the mean flow time. The approach adopted is that of grouping boards into production families, allocating component types to placement machines for each family, dividing of families into board groups with similar processing times, and the scheduling of groups. A complete setup is incurred only when changing over between board families. For the environment studied, precedence constraints on the order of component placement do not exist, and placement times are independent of feeder location. Heuristic solution procedures are proposed to create board subfamilies (groups) for which the component mounting times are nearly identical within a subfamily. Assignment of the same component type to multiple machines is avoided. The procedures use results from the theory of open-shop scheduling and parallel processor scheduling to sequence boards on machines. Note that we do not impose an open-shop environment but rather model the problem in the context of an open shop, because the order of component mountings is immaterial. Three procedures are proposed for allocating components to machines and subsequently scheduling boards on the machines. The first two procedures assign components to machines to balance total work load. For scheduling purposes, the first method groups boards into subfamilies to adhere to the assumptions of the open-shop model, and the second procedure assumes that each board is a subfamily and these are scheduled in order of shortest total processing time. The third procedure starts by forming board subfamilies based on total component similarity and then assigns components to validate the open-shop model. We compare the performance of the three procedures using estimated daily, two-day, and weekly production requirements by averaging quarterly production data for an actual cell consisting of five decoupled machines. © 1994 John Wiley & Sons, Inc.

Two-machine shop scheduling problems with batch processing

We consider shop scheduling problems with group-technology. Groups of jobs are given to schedule them in a flow shop or open shop environment to minimize makespan. Setups have to be performed whenever two jobs of different groups are processed consecutively on the same machine. We show both problems to be NP-hard even in the two-machine case and give several algorithms for solving special cases of the open shop problem.

Group scheduling using group technology concepts

Abstract Group technology (GT) is a manufacturing concept aimed at alleviating the production problems of a proliferation of products with decreasing life expectancy and improved finality. This approach takes advantage of parts similarities parts can be grouped together based on design or manufacturing properties. One aspect that is currently missing from GT classification is grouping parts according to their behavioural parameters. Even parts that share the same group of machines can have diverse properties that suggest different scheduling and routing techniques. This paper- highlights the need for a different classification approach that categorizes parts according to similarity in control measures, This approach is used to construct group-technology based scheduling. This group-technology based scheduling is demonstrated for the open shop environment, and includes the clustering analysis, scheduling algorithms and results.

Supervisor-Worker Relationship Affects Injury Rate

Two research studies on construction safety are presented in this paper. The primary focus is on how managerial styles and company policies can have a direct impact on safety performances. Results show that safer performances exist in those situations where the supervisor respects and acknowledges the worker's viewpoint in job-related conflicts. Situations where a dogmatic approach to conflict resolution was cited to prevail were associated with higher incidences of injuries. Greater assurance of job security exists, along with better safety performance, when the foremen do not have full authority in the firing of workers. In one study it was shown that managerial practices play a more vital role in reducing injuries in an open shop environment than in a union environment.

Program optimization

Sandia Laboratories has established a consulting service designed to improve the overall efficiency of Fortran production programs in use by the scientific community. Since this service was inaugurated in May, 1971, approximately 40 jobs have been reviewed for optimization with varying degrees of success. In several instances it was not possible to improve the operating efficiency of a given program. However, in most cases it has been possible to achieve worthwhile reductions in the use of critical machine resources (primary attention is directed at use of central processor time and allocation of central memory). Average reduction of CPU usage is approximately 30% with one recorded instance of a 97% reduction.This paper addresses the problems encountered in launching and promoting a program optimization service in an open shop environment among users with widely varying levels of programming to indicate the method used to isolate and correct the sections of code that preempt the vital computer resources.