Mechanical Engineering - Theses
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ItemMachine scheduling problems with setup times( 1993)In this thesis the problem of scheduling a single stage flowshop with setup times is analysed. All the jobs are assumed to be divided into several mutually exclusive classes and a setup task is required when processing switches from jobs of one class to jobs of another class and the setup time is sequence independent. Chapter 1 gives an introduction to the flowshop scheduling problem and discusses the issue of NP-completeness. The second chapter is a review of the literature in this field. In the third chapter a new heuristic is presented for scheduling a single machine with setup times. Its performance is compared with the other known heuristics. The next chapter extends the analysis to parallel machines and some new heuristics for scheduling parallel machines with setups are compared. This section of the research is driven by a problem found in a printing factory in Melbourne. The final chapter presents the conclusions and explores possible future extensions of this research.
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ItemScheduling of distributed autonomous manufacturing systems( 1995)This thesis addresses the scheduling and control of shop-floor production units that operate in a highly autonomous and distributed environment. The distinct feature of this environment is the heterarchical nature of the control where the scheduling function is quite independently carried out by the units. The units solve only part of the overall problem while resolving conflicts to maintain consistent global schedules. The need for communication and coordination, in such circumstances, introduces many complexities that affects the quality of the schedules produced. These include lapses of open-loop control due to uncertainty of up-to-date status information, asynchronous behaviour, and uncontrollable propagation of conflicts. A behaviour-based approach is introduced to solve these problems. Using this approach, the organisation of the shop-floor is viewed as similar to a colony of ants or an eco-system. The units operate quite independently but continue to adapt their schedules to changes in their environment. While they may not directly negotiate to resolve conflicts, their cooperation is innate or in-built through their local adaptive actions. This individual cooperative action of the units brings about a collective behaviour that produces the desired emergent global schedules. The major focus of this research is in examining the link between the individual and collective behaviours and developing a model that realises the desired scheduling functionality at the shop level. In order to achieve high scheduling performance (both locally and globally) a model of a unit incorporating dynamic problem decomposition, allocation algorithms and adaptation mechanisms is developed. For the latter, a reinforcement learning model is used to adapt the scheduling horizon. In fact, an important contribution if this research is the novel view we take of the problem and the manner of adaptation. In addition, a communication model for simulating the scheduling behaviours is designed using concepts of Holonic and other emerging concepts of manufacturing systems. The model is tested for a number of scheduling problems representing a variety of production situations. Preliminary results indicate an impressive scheduling performance comparable to well-known heuristics. Further examination indicates the types of dynamic behaviour that can be expected of such a model, including the levels of unresolved conflicts, the adaptability in the face of uncertainty, consequence of alternative communication policies and the sensitivities to adaptation. This thesis has also a strong qualitative theme in reviewing and consolidating the concepts underlying the design and operational attributes of autonomous distributed organisations of the shop-floor.