Machine planning for manufacturing: dynamic resource allocation and on-line supervisory control

Each level of the hierarchical IC architecture may have several components; for example, the Execution Level has one real-time controller per work-cell agent. A supervisory controller in the Coordination Level may coordinate several agents to sequence the jobs needed for a given task. Each system must sense the current conditions, make decisions, and give commands or status reports to other systems. Our planner functions at the Organization Level of Saridis's hierarchy. We will show that a task plan is equivalent to four matrices; these matrices may be passed to a supervisory controller in the Coordination level which sequences jobs and assigns resources. 2.3 Assembly Trees Assembly trees are used in manufacturing to specify a partial ordering of jobs required to complete a nished product. An assembly tree (Wolter, Chakrabarty & Tsao 1992) has a node for each subassembly, and contains information equivalent to the manufacturing bill of materials (BOM) (Baker 1974). An assembly tree or BOM can be considered as a matrix for which entry i; j has a value of 1 if job j is an immediate prerequisite for job i. Neither assembly trees nor BOMs contain any information about the resources needed for the jobs; they contain only product-speci c job sequencing information. We represent assembly trees graphically, with an edge for each 7 A B C D Assemble Drill Figure 2: Sample Assembly Tree manufacturing operation. Nodes in the graph represent parts or subassemblies; the type of the part changes as operations are performed. Figure 2 shows a sample assembly tree; notice that by drilling part A, we create part B. Parts C and D can be assembled to form the single part D. 3 Machine Planning Background This section introduces machine planning terms and gives a brief summary of machine planning research. 3.