Open System Architecture for Real-time Control Using a UML Based Approach Hui-Min Huang, Elena Messina, Harry Scott, James Albus, Frederick Proctor, and William Shackleford National Institute of Standards and Technology Gaithersburg, Maryland 20899 {hui-min.huang, elena.messina, harry.scott, james.albus, frederick.proctor, william.shackleford}@nist.gov Abstract We describe a generic architecture that is applicable to the engineering of many real-time control problems. We further describe how UML is used to apply the architecture to the problems. 1 Introduction Industry desires short lead time for production to enable companies to compete in the global economy [1, 2]. Applying software architectures yields the benefits of interoperability, portability, efficient system integration, etc. [3, 4, 5, 6, 7], which contribute to the industrial objective. Albus [8] proposed a generic, open, reference model architecture called Real-time Control System, (RCS). RCS and its variants, including Intelligent System Architecture for Manufacturing (ISAM), have been applied to various large-scale engineering problems [9, 10, 11, 12, 13, 14]. ISAM/RCS attempts to model the fundamental behaviors of complex systems. The ISAM/RCS model is a hierarchical control structure that is composed of multiple, organized control nodes. High control levels cover system behaviors that are longer in temporal span and wider in spatial span. Low control levels handle tasks that are more detailed, with short time and spatial spans. For example, a shop floor control may handle a production order that takes months to make certain products with multiple workstations. On the other hand, the lowest level may involve the servo control of motors for the machines. We will describe the architecture, together with a method for applying the architecture to engineering problems. Unified Modeling Language (UML) has rapidly emerged as an industrial standard for software engineering. There are many characteristics in ISAM/RCS that make UML a feasible modeling and representation language for the architecture. Since our effort started before UML’s emergence as an industry standard, we will describe how our approach transitions from being C++ language based to being UML-based. We use a manufacturing inspection scenario to illustrate the key concepts. Manufacturing shop operators use inspection systems to measure dimensions of manufactured parts. The systems compare the measurements of the parts with the parts’ models to determine whether the parts are made to the specifications. 2 Reference Model ISAM/RCS provides that nodes in a control system all have the same structure despite their different behaviors. A control node generates behavior through a planning and execution process. The behavior generation process is supported by physical or logical sensory processing functions and real-time knowledge processing functions. These functional aspects of the architecture are shown in Figure 1. This generic-plus-specific structure repeats throughout the entire system. This generic structure gives rise to our software implementation method called generic shell.