Within manufacturing, increasing interest in being placed in the possibilities of integrated process planning and scheduling. Separating these two related tasks can impose constraints, on the final schedule, which are both undesirable and unnecessary. These constraints arise from premature decisions regarding the allocation of manufacturing resources. By making use of flexible process plans, these decisions can be delayed until the most appropriate time: during scheduling. The decisions can then be made on the basis of objectives common to both tasks (such as the minimisation of manufacturing cost). This thesis outlines an approach to manufacturing planning which is based on a highly general formulation of the problem. This integrated process planning/scheduling problem can be viewed as a generalisation of process plan optimisation, a task which is also considered in detail. A novel approach to plan optimisation is proposed, which in turn forms the basis for integrated planning and scheduling. Some research into integrated planning/scheduling has been reported in the literature. However, researchers differ in the way they formulate the integrated task. This thesis therefore attempts to outline a general framework for the characterisation of integrated process planning and scheduling problems. This considers both the degree and representation of process plan flexibility, and also the level of detail at which the shop floor is modelled. This framework forms a basis for a comparison of solution approaches. Published solution approaches are mostly based on the use of dispatching rules, but attempts have been made to use optimal search. The use of dispatching rules is essentially an ad hoc approach and, although relatively easy to apply in practice, produces solutions of mediocre quality. However, new research using simulated annealing suggests that neighbourhood search may offer a valuable alternative. This observation is supported by ambitious research published on the use of genetic algorithms. Because of the extreme combinatorial complexity of the combined task, optimal search methods are unlikely to be usable in practice. Furthermore, such methods exhibit a severe lack of generality because they make highly specific assumptions about problem formulation. Neighbourhood search techniques have inherent properties which give them a much higher level of generality. Although it is not an optimal search method, simulated annealing has been shown to provide solutions of significantly higher quality than those achieved by dispatching rule techniques. Also, and unlike optimal search techniques, it appears able to handle the immense complexity of the integrated planning/scheduling task. For the above reasons, it is argued that neighbourhood search techniques, such as simulated annealing, provide the best compromise available between solution quality and practical applicability.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:241154 |
| Date | January 1994 |
| Creators | Palmer, Gareth John |
| Publisher | University of Huddersfield |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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