Real-time operating environment for networked control systems

This paper presents the development of a novel real-time operating environment for networked control systems (NCSs). An open-loop unstable magnetic-levitation (maglev) test bed was constructed and used to develop an NCS with real-time application interface (RTAI). A client-server architecture on a local-area network was developed with the network communication based on the user datagram protocol. The control loop of our NCS is closed over the network. This NCS structure gives the best flexibility and has significant economical merits. The implementation of an event-driven server and a time-driven client presented in this paper facilitates a simple timing scheme that does not require clock synchronization between the client and the server. A novel prediction scheme with a multiple-step-ahead control-signal generator is used to maintain system stability in the presence of excessive time delays and data-packet losses in the communication network. The performance of this NCS, based on the predictor algorithm, is demonstrated experimentally. The current system can compensate for up to 20% data-packet losses without losing stability with the maglev real-time-control test bed in the communication network. Our real-time operating environment also improved the command-following capability by a factor of 4 in terms of command frequency.