Computer simulation is a well-established decision support tool in manufacturing industry. However, factors such as wrong conceptualisation, inefficient input data modelling, inadequate verification and validation, poorly planned experimentation and lengthy model documentation inhibit the rapid development and deployment of simulation models. A serious limitation among the above factors is inefficient data modelling. Typically, more than one third of project time is spent on identification, collection, validation and analysis of input data. This study investigated potential problems which influence inefficient data modelling. On the basis of a detailed analysis of data modelling problems, the study recommends a methodology to address many of these difficulties. The proposed methodology, discussed in this thesis, is called MMOD (Methodology for Modelling Of input Data). An activity module library and a reference data model, both developed using the IDEF family of constructs, are the core elements of the methodology. The methodology provides guidance on the best way of implementation and provide a tool kit to accelerate the data modelling exercise. It assists the modeller to generate a customised data model (entity model), according to the knowledge gained from the conceptualisation phase of the simulation project. The resulting customised data model can then be converted into a relational database which shows how the entities and relationships will be transformed into an actual database implementation. The application of the MMOD through simulation life cycle also enables the modeller to deal with important phases in the simulation project, such as system investigation, problems and objective definitions and the level of detail definitions. A sample production cell with different level of detail has been used to illustrate the use of the methodology. In addition, a number of useful methods of data collection and the benefits of using a MMOD approach to support these methods and data rationalisation which accelerates the data collection exercise are also covered. The aim of data rationalisation is to reduce the volume of input data needed by simulation models. This work develops two useful data rationalisation methods which accelerate the data collection exercise and reduce the model complexity. This work produced a novel approach to support input data modelling in simulation of manufacturing system. This method is particularly useful when the complex systems are modelled.

Analysis of flexible manufacturing cells (FMCs) shows their requirement for flexible, correct, reliable, safe and distributed control. A comparison of the state of the art in software engineering for parallel systems, and an examination of safety related systems, reveal a need for formal and rigorous techniques at all stages in the software life cycle. However, parallel software, safety related software and formal techniques are complex. It is better to avoid faults rather than eliminate or tolerate them, and although less flexible, avoidance is often simpler to implement. There is a need for a tool which overcomes many of these complexities, and this thesis discusses and defines such a tool in the form of a methodology. The novelty of the work is in the combination of the core goals to manage these issues, and how the strategies guide the user to a solution which will not deadlock and which is comprehensible. Place-transition Petri nets are an ideal representation for designing and modelling the interaction of concurrent (and distributed) processes. Occam is a high level real time parallel language designed to execute on one or a network of transputers. Transputers are processing, memory and communication building blocks, and, together with occam, are shown to be suitable for controlling and communicating the control as the DCS in FMCs. The methodology developed in this thesis adopts the mathematically based tools of Petri nets, occam and transputers, and, by exploiting their structural similarities, incorporates them in a steps and tasks to improve the development of correct, reliable and hence safe occam code. The four steps: identify concurrent and sequential operations, produce Petri net graphs for all controllers, combine controller Petri net graphs and translate Petri net graphs into occam; are structured around three core goals: Petri net/occam equivalence, comprehensibility and pro-activity; which are manifest in four strategies: output-work-backwards, concurrent and sequential actions, structuralise and modularise, and deadlock avoidance. The methodology assists in all stages of the software development life cycle, and is applicable to small DCSs such as an FMC. The methodology begins by assisting in the creation of DCS requirements from the manufacturing requirements of the FMC, and guides the user to the production of dependable occam code. Petri nets allow the requirements to be specified as they are created, and the methodology's imposed restrictions enable the final Petri net design to be translated directly into occam. Thus the mathematics behind the formal tools is hidden from the user, which should be attractive to industry. The methodology is successfully applied to the example FMC, and occam code to simulate the FMC is produced. Due to the novelty of the research, many suggestions for further work are given.

The work reported in this thesis describes research carried out into the detailed design and operation of Flexible Machining Cells (FMC) incorporating automated work and tool flow, dual flow. Three modes of cell management are considered for dual flow cells, where the author examines both their operational and economic performance. A framework is defined for investigating these dual flow cells, and a structured approach providing a novel and detailed modelling capability is described. The question of how this approach compares to single flow modelling and the additional or alternative requirements for dual flow modelling is examined via the following key areas; the specification of material handling requirements, tool transportation and issue and finally, the control required to examine the interaction between the two flows operating concurrently. The framework is tested for its industrial applicability via an industrial case study. A major aim of this study is to examine the view that a hybrid cell management strategy, competitive management, could outperform the other strategies examined. The aim of this methodology is to provide a solution for the control of FMCs. Emphasis is placed on the ease of control and how the loading and control rules selection can maximise economic enhancement of a cells performance.

The author has investigated software support tools to enable concurrent design for injection moulding, and the view is taken that the kernel for a manufacturing system can be defined as the source of product and manufacturing information which must be available for each application. The Product model provides a consistent source of product information as the design evolves, and the Manufacturing model captures information related to manufacturing resources and processes to support product realisation.

The study relates to manufacturing conditions in a particular company. Flow synthesis and cell formation analysis have been conducted. A modification of methodology proposed by other researchers has assisted analysis. The main investigation is concerned with modelling, simulation and evaluation of seven alternative FMS configurations conceived for the machining cell manufacturing prismatic parts. The alternative systems encompass 6 CNC machines with (i) manual transport of materials and tools, (ii) with two and four station automated pallet changers, (iii) conveyor system, (iv) stacker crane, (v) rail guided shuttle, and (vi) AGV transport.

Thesis (M.Sc.Eng.) / Consistent with the automotive industry, other highly technological industries have discovered the value of implementing lean manufacturing operations. In today’s economy, companies are realizing that controlling and minimizing manufacturing cost is a requirement for a successful business. Businesses are hiring the help of consulting companies to implement better manufacturing techniques. However, more often than not, these businesses struggle with the actual implementation due to the underlying disturbances in the current production floor. These disturbances range from demand balance issues to the more complex quality defects. The goal of this study is to provide a theoretical framework, analysis and simulation of the disturbances in a mixed-model manufacturing production system. Mixed-model production systems employ a single set of resources to manufacture multiple product lines, giving room to a complex set of production issues which are often hard to visualize. This thesis simulates the production floor of a company with a single mixed-model production system that assembles three highly technological, complex engineering, multi-configuration products such as automotive engines. A discrete event simulation model was used to manipulate the disruptions on the production system. The real manufacturing performance was used to verify and validate the model. Individual modification of the disturbances revealed their effect on production efficiency. Optimization policies like rework strategies and Kanban sizing are presented to minimize the effect of said disturbances.

Thesis (Ed.M.)--Boston University

Thesis (M.B.A.)--Boston University

Thesis (Ed.D.)--Boston University.

Thesis (M.B.A.)--Boston University