Recent computer developments have allowed a new dimension to the scientific inventory control. An example is the multi-item inventory model described in Johnston (1980) which represents the departure from the traditional optimization towards decision aid models which the manager can use interactively in the examination of the trade-offs which could improve his current policy. The Johnston model has however limitations. The scope of this thesis is to overcome some of these limitations, namely, the treatment of the non-captive demand, the determination of the reorder frequency and the extension to a two level inventory system, together with a critical examination of the variables involved, in order to improve the decision making. In relation to non-captive demand, the problem can become relevant when more than one order overlaps. Then, service levels and average stocks are normally higher than the predictions from formulas derived for captive demand. The main result now achieved is the introduction of the notional control level which relates to the conventional reorder or top up levels and to the lost demand. The notional level allows the extension of established formulations, including the Johnston model, from non-captive to captive demand. Johnston leaves the reorder frequency to be decided on a practical basis. Here, the same criteria adopted by Johnston have been used to derive consistent expressions for the number of orders. Empirical functions have been incorporated to reach formulas ready for use. The two level system comprises one main warehouse and its satellites. The analysis covers, basically, the rules to decide the allocations, the theoretical prediction of service levels and the extension of the initial Johnston formulation to this system. The allocation rule derived says that quantities should be allocated so as to have the same probability of depletion. For the prediction of service levels, the depletion time distribution rather than the demand distribution has been used in the formulations, because the conventional approach, based on the latter, does not produce the desired results. Implementable formulas are given for situations in which satellites are of the same order of magnitude. The results in the three areas mentioned above are accompianied by considerations about the economic meaning of the variables and a method is suggested to cross-check the consistency of the decisions. They are new contributions for the inventory control and constitute an important complement to the initial Johnston model.

Few significant changes in Programmable Logic Controller (PLC) software design techniques have taken place since PLC's were first introduced in the 1960's. Programs written in the traditional language used in PLC's, ladder logic, are generally thought to be difficult to maintain and modify, and thus ill suited to the support of modem flexible manufacturing processes. This work demonstrates that the choice of PLC software structure used in a project has an impact on process flexibility with an appropriate choice providing significant cost savings in development time. An overview of work on formalised programming tools conducted in academia is provided together with a report on the PLC software structures used in industry. The factors influencing the choice of PLC and software structure are identified. Familiarity was found to be a major factor influencing selection. A method for comparing code structures, which allows the results to be expressed as a time saving (and consequently a cost) has been created. Implementation of this approach was used to show that the formalised programming tool under test provides a 33% increase in "right first time" rate together with an 80% time saving over traditional contact based ladder logic. Among experienced practitioners, performance with step-based ladder logic was found to be a close match to the formalised tool, demonstrating that the commonly perceived limitations are the result of the structure in which the language is used rather than a function of the programming tool itself. Further investigation of participant preferences among skilled PLC users showed a mismatch between their performance with a tool and their preference, with at least 25% selecting a tool based on their prior knowledge rather than performance. This highlights the need for the use of objective measures when conducting evaluations between products and technologies. With the information provided in this work, automation end users are provided with a mechanism for ensuring the selection of automation tools best suited to their business needs, whilst at the same time providing automation vendors with the ability to best demonstrate the strengths of the products.

This research aimed to study real-time shop floor control problem in a manufacturing environment with dual resource (machine and labour), under impact of machine breakdowns. In this study, a multiperspective (order and resource perspectives) control strategy is proposed to improve effectiveness of dispatching procedure for promoting shop floor stability. In this control strategy, both order and resource related factors have been taken into account according to information on direct upstream and succeeding workcentres. A simulated manufacturing environment has been developed as a platform for testing and analysing performances of the proposed control strategy. A series of experiments have been carried out in a variety of system settings and conditions in the simulated manufacturing environment. The experiments have shown that the proposed control strategy outperformed the ODD (Earliest Operation Due Date) rule in hostile environments, which have been described by high level of shop load and/or high intensity of machine breakdowns. In hostile environments, the proposed control strategy has given best performance when overtime was not used, and given promising results in reduction of overtime cost when overtime was used to compensate for capacity loss. Further direction of research is also suggested.

Thesis (doctoral)--Friedrich-Alexander-Universität zu Erlangen.

Thesis (Ph. D.)--University of Pennsylvania, 1919. / Bibliography: p. [82]-95.

Thesis (Ph. D.)--Columbia University, 1936. / Without thesis note.

Thesis (Ph. D.)--University of Hong Kong, 2000. / Includes bibliographical references.

Thesis (M.P.A.)--University of Hong Kong, 2000. / Includes bibliographical references (leaves 106-107).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1971. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 137-148). Available also in a digital version from Dissertation Abstracts.