This report mentions some of the difficulties faced by labor estimators when predicting the labor necessary to produce complex weapon systems. Specific attention is focused on estimating the durations and frequencies of testing, troubleshooting, and retesting activities. Emphasis is placed on estimating in a logical manner while using factors based on subjective judgment.

M. S.

In a Flexible Manufacturing System (FMS) jobs are moved between work-centers by an Automated Guided Vehicle System (AGVS). The operation of the AGVS is governed by two kinds of AGV dispatching rules: Workcenter Initiated Rules (WI), and Vehicle Initiated Rules (VI). At work-centers. jobs are prioritized for processing by Job Dispatching (JD) Rules. The objective of the study is to characterize system behavior when dispatching rules from each of the three categories are used concurrently -- an issue which has received very little attention in published research. In addition to common measures of system performance such as job flowtime and shop throughput, measures specifically directed at AGVS effectiveness such as waiting times and queue lengths for AGVs, and empty AGV travel are used. Combinations of rules from the three categories are studied under conditions of high and low AGV utilization. The simulation model of the FMS was developed using SLAM II - Material Handling Extension. The hypothetical FMS consists of four non-identical workcenters which process multiple part types. A fleet of four AGVs move the jobs between workcenters. Results indicate that for the system analyzed, WI rules (for vehicle selection) do not play a significant role in determining system performance even when the AGV fleet is under-utilized. For the system analyzed, V1 rules (for selecting jobs to picked up by AGVs) were found to have a significant effect on all measures of performance, only under conditions of constrained AGV fleet size. Good results were obtained with the Shortest Travel Distance rule. The relative performance of VI rules was found to be independent of job dispatching rules. However, some combinations of these rules interacted to produce inexplicable results. A notable observation of this research was that job dispatching rules have a significant effect on measures of AGVS performance. The effectiveness of AGV dispatching rules appears to be dependent on the system being analyzed. / Master of Science

This thesis considers a Flexible Manufacturing System (FMS) comprised of programmable machine tools which are capable of performing multiple operations and which are interconnected by computer-controlled automated material handling equipment. The specific problem addressed is a job-shop type of situation in which at least a given number of each type of job needs to be performed on a given set of machines. The flexibility in the system arises in the form that each job can be performed in a variety of ways with each possible manner of performing it, called an Alternate Routing Combination (ARC), being defined by specifying the number of operations needed and the associated machine sequence. The problem is to select a set of jobs and their associated ARCs to be performed, and schedule their operations on the machines so as to optimize various objectives such as minimizing makespan or maximizing machine utilization, or minimizing total flowtime. This problem is mathematically modeled, and heuristic algorithms are presented along with computational results for the case of minimizing the makespan. / M.S.

M. S.

This research addressed two very fundamental issues in cellular manufacturing. These two issues were organizational feasibility for the implementation of cellular manufacturing and the choice of method approach for part-family/machine grouping if feasibility was adjudged, given organizational and manufacturing characteristics. The approach to part-family/machine grouping may follow one of the following options—a design-oriented approach, a production-oriented approach, or a combination of both. An examination of published literature, in English, on cellular manufacturing indicated the need for this research. A methodology was developed to address the above issues. A Conceptual Flow Model (CFM) was first developed to structure and rationalize the research problem. The concept of the CFM originated from the basic input-output production model in literature. This model helped the formulation of the research problem by rationalizing that a new manufacturing approach, cellular manufacturing, was feasible for an organization if certain performance measures were weak and if certain criteria regarding the products, available resources, procedures used, and organizational characteristics were met. On the other hand, the model proposed that an organization could remain functionally arranged and improve its existing procedures for better performance if these criteria were not met. This work, however, did not include this latter part of the model as a research issue. Once feasibility for the implementation of cellular manufacturing was adjudged, the model hypothesized that a part-family/machine grouping approach was necessary for the initial design of the cells. This approach was to be selected from the design-oriented approach, the production-oriented approach, or a combination of both. This model formulation enabled the identification of important attributes pertinent to the research problem. The attributes were identified through a comprehensive review of applicable literature in cellular manufacturing. The attributes for the feasibility issue were clustered into four categories. These were the products and processes category, the resources category, the procedures category, and the organizational characteristics category. The attributes pertinent to the choice of method issue were clustered into the product category, the resources category, and the objectives category. The identification of the attributes was followed by an explanation of their relevance. A set of propositions was developed next to relate the level of an attribute to the feasibility for the implementation of cellular manufacturing and the choice of method issues. The propositions further strengthened the theoretical background of this research through the use of past research and enabled the construction of the rules necessary for resolving the choice of method issue. A complete set of definitions and specifications was then developed for each of the attributes for both issues. The purpose of the specifications was to enable the measurement of the attribute levels through developed measures of each attribute. All the attributes were weighted according to their perceived importance. A scoring model was developed to determine a score for feasibility for cellular implementation. This score represented a calculated measure of an organization’s feasibility for the implementation of cellular manufacturing. A rule-based procedure was developed to determine the choice of method for part-machine grouping. To verify the relevance of the attributes, their measures and weights, and (indirectly) the propositions, companies engaged in cellular manufacturing were visited and data pertinent to the feasibility analysis and choice of method procedures were collected. Valuable information was gained from these visits, and it was found that some attribute measures will require possible refinement in future research. This field research also indicated the possibility of refinement of the feasibility matrix constructed from the feasibility analysis procedure. Certain attributes pertinent to the choice of method procedure also may require refinement in future research. For comparison purposes, data were also collected from a company with a functional layout and used with the scoring model. In summary, the objective of developing a framework for determining organizational feasibility for the implementation of cellular manufacturing and the choice of method approach for part-family/machine grouping if feasibility was adjudged, given organizational and manufacturing characteristics, was undertaken. The framework was developed and its components verified through field work. / Ph. D.

A simulation model is developed for use in programmable controller ladder diagram testing. The developed model represent a physical flexible manufacturing system that can be controlled by different ladder logic diagrams. The model is capable of detecting initial ladder errors, displaying state changes in the ladder, and logging an operations history. As a result of the simulation development, insight into a generalized system descriptive language is obtained. This includes the language structure, specific data requirements, and an interface control method. The model also allows the user to locate optimal ladder solutions by comparing the results produced by different ladder diagrams. This thesis contains a literature review that establishes a history of programmable controller ladder testing and simulation modeling. The literature review provides impetus to the research by conveying the need for alternative methods of ladder diagram development, debugging, and testing. / M.S.

No description available.

A systems approach for manufacturing system design calls for the division of a system design into sub-designs, and their specification over multiple levels of detail. Through an iterative design and evaluation process, a system design progresses from an abstraction to an implemental specification. To facilitate the evaluation process, models of sub-designs must be applicable to modular assembly, even if the sub-designs are heterogeneously specified. Computer simulation modeling is currently the most flexible method of manufacturing system analysis. When used in the multi-level design process, two forms of simulation models are encountered, uni-level and multi-level. A simulation model of a manufacturing system is considered uni-level if objects of equivalent type within the system are modeled at the same level of detail. On the other hand, a model is considered multi-level if objects of equivalent type are not modeled at the same level of detail. Unfortunately, current simulation frameworks do not integrate modular construction with the various discrete event and continuous simulation techniques needed to support multi-level modeling. This dissertation describes GIBSS (Generalized Interaction Based Simulation Specification), a simulation framework which supports the modular construction of uni-level and multi-level simulation models. Under GIBSS, the mechanisms and attributes of a manufacturing system simulation are distributed among various classes of independent sub-models. These classes are passive, internal interaction, external interaction, and master simulation. GIBSS describes the mechanics of each of these classes, as well as their method of synchronization. Using GIBSS, sub-models are created, executed, and validated independently, and then brought together to execute in parallel or near parallel fashion. As a result, uni-level and multi-level system simulation models are assembled from multiple sub-models. GIBSS eliminates a barrier to the rapid evaluation of manufacturing system designs. It facilitates the multi-level design process, and is the basis of a research effort, dedicated to the development of a new generation of computer-aided manufacturing system design environments. / Ph. D.

Manufacturing techniques are based on the principles of Flexible Manufacturing and Dedicated Manufacturing for mass production. Reconfigurable Manufacturing Systems (RMS) is a manufacturing system that can provide for Agile Manufacturing (AM). This has lead to research on the concept, design and equipment implementation for RMS. RMS requires three key capabilities: rapid changeover between products, rapid introduction to new products and unattended operation. The relationship between these manufacturing techniques has been investigated. Research has been focused on the research and design of a Reconfigurable Modular Machine (RMM) for RMS. The research has addressed the design of subsystems for RMM by using the generic modular mechatronics control. This approach included modular machine controller hardware, software, mechanical design and generic "plug-and-play" capability, These designs of subsystems allowed for rapid reconfiguration of RMS that increased system efficiency and significantly minimized manufacturing change over downtime. / Manufacturing techniques are based on the principles of Flexible Manufacturing and / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2006. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2006.