Real-time operational control of flexible manufacturing systems

This paper provides a real-time operational control detailed scheme for flexible manufacturing systems. The control is organized in a hierarchical structure according to the various decisions that take place at the different time scales at which each level operates, from a few days to miliseconds. At each level down the hierarchy, the details of the decisions and the communication rate increase. Feedback laws are developed to optimally take into account the real-time status of the system at each level. The highest real-time level accepts short-term management production requirements and the lowest level issues commands to the direct machine controllers. The control actions range from determining the changing product mix and input flow rate, through in-process parts movement decisions, to resource allocation in order to perform these moves in an efficient, conflict-free manner. Each level issues target commands to the level below and receives performance feedback. The overall control aims to optimize FMS performance while meeting the production requirements. Models for each level and the interaction among the levels are presented and demonstrated via a case study. A previous version of the controller is currently used to control and run some experimental and industrial systems.