Intelligent Manufacturing System Control: Reference Model and Initial Implementation

This paper describes the concept of a task within a control architecture called Intelligent Systems Architecture for Manufacturing (ISAM). The paper also describes the approach for modeling and developing the tasks and the controllers for ISAM based applications. 1 . Architectural Overview An architecture for intelligent manufacturing systems describes the structure of such systems, including the components that comprise the systems, the functionality of the components, and the relationships and interactions among the components. A reference-model architecture further emphasizes that the architectural model needs to be generic and applicable to multiple types of problems. An open system allows components, possibly developed by different people, to be easily integrated and function harmoniously. Major efforts in this area include the U.S. Air Force Next Generation Controller (NGC) program [1], which developed a specification for an open architecture standard. The European Open System Architecture for Controls within Automation Systems project (OSACA) [2] and the Japanese Open System Environment for Controller (OSEC) project [3] address the open architecture issues related to the cell, individual machine, or subsystem controllers. Researchers in the Manufacturing Engineering Laboratory of the National Institute of Standards and Technology are developing an open system referencemodel architecture called the Intelligent Systems Architecture for Manufacturing (ISAM). ISAM is intended to facilitate the organization, interconnection, and intelligent control of manufacturing systems. ISAM is based on concepts from the NIST Real-time Control System (RCS) architecture [4, 5, 6, 7] and is a hierarchical control architecture. ISAM prescribes a canonical form that is capable of modeling application systems to any level of control authority. Each level has a pre-defined level of authority. Each level can have multiple controller nodes. Figure 1 illustrates ISAM hierarchy. The level names indicate a smooth transition from the broader to the narrower scopes of authority from the higher to the lower levels. All the controller nodes have a generic functionality, but employ different algorithms that are consistent with the node’s assigned boundary of authority. 2 . Task and Task Decomposition A manufacturing system performs assigned tasks. Tasks and the decomposition of tasks within the architecture are part of the key concepts in ISAM. Manufacturing system goals, described in terms of tasks, are entered from the highest level of the system’s ISAM controller. In Figure 1, the highest level controller, known as the facility controller, facility (application scope)