Coordination of Operations by Relation Extraction for Manufacturing Cell Controllers

A method for generation of the control function for flexible manufacturing cells is presented in this paper. The control function is separated from the rest of the programmable logic control (PLC) program, and partitioned into a high-level part handling the operation sequence and a low-level part defining the execution process of the operations. The program structure enables high-level supervisor synthesis, which alleviates the state-space explosion problem. Information present in earlier steps of the development process is reused and processed, to automatically generate the automata needed for supervisor synthesis. An algorithm for generating automata, from the low-level safety requirements that restrict the high-level behavior, is presented. Algorithms are also presented for extracting the relations between the operations defining the work in the cell, from the synthesized supervisor. These relations give an easy-to-read representation of the control function that makes it interpretable by machine operators and maintenance personnel, an important feature to make the method applicable in an industrial setting. Hence, the control function generated by our method combines the benefits of a traditional supervisor, namely optimality and flexibility, with simplicity and clarity.