Ezey M. Dar-El

Job shop scheduling—A systematic approach

Abstract A systematic analysis of shop performance versus different scheduling rules is presented in this paper using a computer simulation model of a conventional job shop as a basis. The simulation model is used to identify dependent parameters such as shop load and service distribution for a set of scheduling rules. These conditions should represent different existing shop conditions. Six different scheduling rules and two different performance measures were used in the analysis. A complete statistical analysis and categorization of the simulation results were performed which produced some interesting anticipated as well as unanticipated results.

Assembly line sequencing for model mix

SUMMARY This paper describes a model sequencing algorithm for model-mix assembly lines. A new formulation of the sequencing problem is proposed, the objective function of which is to minimize the overall assembly line-length for no operator interference. Lower bounds for the overall line-length are developed. Two types of work station interfaces are considered; ‘closed’, where boundaries cannot be violated, and ‘open’ where defined boundaries do not exist—adjacent operators being allowed to enter each others apparent work areas without causing any interference. A complete factorial experiment was made on five factors to determine their influence on the overall assembly line length. These are, the number of models, the model cycle time deviation, the production demand deviation for each model, the operator time deviation, and the number of stations in the assembly line. The main conclusions of this experiment are discussed and recommendations made for the selection of parameters used in the design of model...

A comparative analysis of the COVERT job sequencing rule using various shop performance measures

The COVERT job shop dispatching rule was tested extensively twenty years ago with impressive results, however, since then it has been included in only one comparative analysis with other sequencing rules, and, reported instances of its application have been infrequent. In this paper, the COVERT rule is examined in detail relative to its applicability, its sensitivity to various operating parameters and performance measures, and its performance compared to several other sequencing rules including truncated SPT rules, dynamic slack rules and modified duedate rules. The performance of COVERT is examined for a variety of tardiness measures. The examination is conducted within the context of a simulation model of a machine-constrained job shop with serial jobs and random routings. The results indicate that COVERT performs well as a sequencing rule and in most instances was superior to the other sequencing rules tested both directly and across varying degrees of due-date tightness.

MALB—A Heuristic Technique for Balancing Large Single-Model Assembly Lines

Abstract This paper is concerned with the development of a heuristic algorithm (MALB) for the general solution of large single-model assembly line balancing problems. It is based on the optimum-seeking backtracking method proposed by Mansoor (1964). Excellent results were obtained from tests taken over a wide range of large ALB problems. Over a third of the tests yielded a 100% line efficiency and the overall computation time was 22 sec on an IBM 7040/7044.

A methodology for solving single-model, stochastic assembly line balancing problem

In this paper, a methodology is developed to solve the single-model, stochastic assembly line balancing problem for the objective of minimizing the total labor cost and the expected incompletion cost arising from tasks not completed within the prescribed cycle time. The methodology is based on determining an initial DP based solution and its improvement using a branch-and-bound procedure which uses an approximate solution instead of a lower bound for fathoming nodes. Detailed experimentation shows the superiority of this method over the most promising one from the literature.

Group set-up for printed circuit board assembly

The current practice in the assembly of electronic components on printed circuit boards (PCBs) is serial production, a process characterized by very long set-up times. However, with the advent of efficient on-line process information, new production control methods are now possible. This paper proposes a different production method, called the group set-up (GSU) method, which can significantly reduce set-up times. The traditional and the GSU production methods are compared, and it is shown that the GSU always performs better than the traditional method in terms of total production flow (throughput) and labour time. However, the traditional method performs better than the GSU in terms of work in process (WIP) inventory; and in some cases, in terms of makespan (lead time). A detailed analysis for a small number of PCBs is presented.

A dual-phase model for the individual learning process in industrial tasks

A new dual-phase model for learning industrial tasks is presented, based on the combined effects of cognitive and motor processes. The model proposes that cognitive elements dominate learning during the early cycles, whereas motor elements dominate the learning process as the number of repetitions becomes large. The implication is that the observed learning slope is a variable whose value gradually increases as experience is gained. Experimental studies are described whose results support the behavior of the dual-phase learning model.

Solving Large Single-Model Assembly Line Balancing Problems—A Comparative Study

Abstract A comparative study is made between three methods for balancing single-model assembly lines. These include: 10-SP, which selects the best of ten single-pass solutions; ARCUS—a random multi-pass method, and MALB, an iterative backtracking method. The assembly tasks contain up to 140 work elements with widely differing precedence structures. Measurements of the Balance Delay are used for comparing the solution efficiencies and computation times are also compared. The experiments show significant differences between the three line balancing methods and that these differences are accentuated for certain conditions of task size, precedence structure and the imposed balancing requirements. It is shown that 10-SP is yet another simple but effective technique for balancing single-model assembly lines.

A methodology for the selection of assembly systems

The design of an assembly system for a particular product is a complex engineering effort involving many interrelated decisions. The wide range of alternative system configurations makes a detailed design of each alternative too expensive and time-consuming. In this work a methodology is developed which helps the decision maker by ranking possible alternatives according to ‘subjective’ cost/ benefit criteria.

Mixed-model assembly line sequencing problems

The paper develops a comprehensive classification of mixed-model assembly lines from which four categories of model sequencing are derived. Each category aims at satisfying one or both of two objective criteria, the one minimizing the overall line length, and the other minimizing the thruput time. Approaches for solving the sequencing problem in each category are presented. The paper suggests a design strategy that can be followed by designers of mixed-model assembly lines. Specific topics requiring further research are also defined.