Modeling and analysis of restart, transport, and resource allocation in manufacturing systems using sequences of operations

Licentiate thesis, 2012

Highly automated and flexible manufacturing systems have gained industrial popularity for their ability to combine high product volumes with high product quality. However, the process planning, the process to design and plan the tasks and actions, the operations, that constitute the manufacturing process, is a complex and time consuming process. The process planning struggles with continuously changed requirements from the products to be produced and demands and capabilities of the manufacturing system itself. The high cost of investment of a manufacturing system in combination with many interlaced manufacturing systems in a factory, requires that the manufacturing process is running smoothly with high utilization of the resources and that stoppages are avoided. To reach a high resource utilization, multiple products may be concurrently produced in a manufacturing system. In systems where several product routes are possible, the design of operations that combine concurrent manufacturing and high utilization is a difficult task. One major reason for stoppages is the occurrence of unforeseen errors that cause the manufacturing system to halt. The succeeding error recovery is often a complex and thereby time consuming process that typically requires manual involvement. To plan for restart after errors already during the process planning would therefore shorten the time the system is halted. To accomplish a useful process plan that faces the presented problems and is adaptive to (late) requirement changes, it is favorable to base the analyses and activities during the process planning on mathematically well defined methods, formal methods, well-suited for computerized calculations but heavily depended on precise models to calculate useful results. To support the process planning, this thesis presents how to use formal methods to analyze transport, resource allocation for concurrent manufacturing, and restart in manufacturing systems. To overcome the modeling issue, the required formal models are automatically generated from the operations that model the manufacturing processes and the result of the methods are given as additional operations and extensions to existing operations.