A CNC system based on real-time Ethernet and Windows NT

Abstract

Modern manufacturing industry requires computer numerical control (CNC) systems to be more open, extendable, and networked. Real-time Ethernet is introduced and its use in CNC is discussed in this paper. Compared to traditional fieldbus, a real-time Ethernet which modifies the Ethernet data link layer to achieve fast delivery time and high synchronization accuracy is discussed. The method of synchronizing distributing clocks to reduce cumulative jitter of transmission for a synchronization frame is proposed. Some special considerations of this real-time Ethernet are discussed, e.g., incorporation with Windows NT and making feedback returned faster. A CNC system based on such a real-time Ethernet and Windows NT has been developed and presented. The system involves the service-oriented Windows Communication Foundation as an up-layer interface to the Internet, and a real-time Ethernet for connecting to hardware components of a machine tool. The non-real-time aspect of Windows NT is accounted for; for example, a driver rewriting the interrupt descriptor table is introduced and packets to be sent are buffered. Design and implementation of this system, such as main classes and services in the NC kernel, main modules (e.g., data link layer) in salve nodes, are also discussed. At last, experimental results are presented to illustrate the Windows NT’s performance and the real-time accuracy of the synchronization method.