Research And Realization Of FPGA-Based Real-Time Motion Control Networks

With the growing requirements in multi-axis coordinated motion andnetworked manufacturing, as well as the development of Ethernettechnology, networked motion control systems(NMCSs) have become adevelopment trend in industrial automation field. However, dozens or evenhundreds of stations must be able to do coordinated motion in NMCSs,which proposed strict requirements of real-time communication and clocksynchronization for motion control networks(MCNs). The traditionalMCNs finish the processing of data packets in application layer and thetotal delay of one slave station reaches dozens of micro-seconds, which isdifficult to meet the real-time requirements of high-precision motioncontrol. While most of MCNs with outstanding performance in real-timecommunication are implemented on dedicated hardware, they are difficultto be integrated into existing DSP plus FPGA-based motion controlsystems.A field programmable gate array (FPGA) based real-time MCN hasbeen proposed in this paper. It adopts layered communication system. Infield layer, an FPGA-based real-time Ethernet protocol has been developedto realize the real-time communication between master station and slavestations. A hardware data processing strategy is designed and the data linklayer of real-time communication is implemented on FPGA. Moreover, inorder to decrease the forwarding delay, the forwarding of real-timecommunication data is shifted down to data link layer from applicationlayer. Transparent clock mode of IEEE1588protocol is used to implementthe clock synchronization between slave stations and master station.Synchronization precision of sub-microsecond has been achieved. In process monitoring layer, the FPGA-based real-time MCN uses winpcap tolisten and to receive raw data in data link layer. Ethernet is adopted toreplace the traditional computer buses, such as PCI and ISA, to realize theinformation exchanging between process monitoring layer and field layer,so that every layer uses protocols of the same category: Ethernet.Moreover, testing software in process monitoring layer has beendeveloped to test and monitor the field layer. This software is developed inVisual C++6.0. The main functions include initialization of field layer,parameters setting, the performance of real-time communication and clocksynchronization monitoring.Finally, an experimental platform has been set up to test theperformance of the proposed real-time MCN. The real-time performanceand the clock synchronization precision, as well as the Ethernetcommunication between process monitoring layer and field layer havebeen tested. The experimental results show that the total delay of a slavestation is less than2microseconds, and high precision of sub-microsecondin clock synchronization has been achieved. The winpcap-based Ethernetcommunication between process monitoring layer and field layer can meetthe requirements of testing and monitoring.