Real-time middleware for networked control systems and application to an unstable system

A well-designed software framework is important for the rapid implementation of reliable and evolvable networked control applications and to facilitate the proliferation of networked control by enhancing its ease of deployment. In this brief, we address the problem of developing such a framework for networked control that is both real-time and extensible. We enhance Etherware, a middleware developed at the University of Illinois, so that it is suitable for time-critical networked control applications. We introduce a notion of quality of service (QoS) for the execution of a component. We also propose a realtime scheduling mechanism so that the execution of components can not only be concurrent but also be prioritized based on the specified QoS of each execution. We have implemented this framework in Etherware. We illustrate the applicability of this software framework by deploying it for the control of an unstable system, namely, a networked version of an inverted pendulum control system, and verify the performance of the enhanced Etherware. We also exhibit sophisticated runtime functionalities, such as runtime controller upgrade and migration, to demonstrate the flexible and temporally predictable capabilities of the enhanced Etherware. Overall, Etherware thus facilitates rapid development of control system applications with temporally predictable behavior so that physical properties such as stability are maintained.