Research And Application Of Real-time Ethernet Motion Control Bus And Its Reliability

With the development and improvement of fieldbus, the fieldbus is adopted gradually by motion control system using as the hardware platform. But the demands of the automation equipment on real-time, multi-axis synchronization, precision are increasing. The fieldbus can’t meet these demands because it is subject to restrictions in terms of the communication rate, real-time response, etc. Therefore, the real-time Ethernet for motion control has become the development direction of the CNC system. In this paper, an in-depth study about real-time Ethernet EtherMAC is conducted. The topology and function of EtherMAC is extended and improved. At the same time, a variety of measures on reliability and safety are proposed to ensure the stable operation of the system. The real-time and reliability of EtherMAC are verified through the application project.The paper begins with a review of the development process of motion control system and fieldbus, and pointes out the advantages and problems of real-time Ethernet applying on the motion control platform. The characteristics and advantages of EtherMAC are stated by analyzing the technical characteristics and development status of other famous real-time Ethernet buses at home and abroad.The communication and synchronization mechanism of EtherMAC are detailed in this paper. Based on the linear network and ring network, a binary tree network is proposed and achieved. The subsystem of short-cycle tree network can achieve high-speed and high-precision interpolation operation. Based on synchronization of linear network, the synchronization scheme of tree network has a smaller forwarding latency and synchronization jitter. Meanwhile, meeting the demands for different applications, the common I/O module and encoder module are designed and implemented, and the function of single-axis module is expanded. These modules improve the node types of EtherMAC. A gateway approach is used in EtherMAC in order to be compatible with Modbus, RTEX, CANopen and other common buses, which makes the equipment such as inverters, sensors, bus motors can be connected to EtherMAC motion control system seamlessly. It expands the applied ranges of EtherMAC.For failures of EtherMAC that may occur in the industrial field, the reliability of real-time Ethernet is researched and analyzed. By optimizing the hardware and program of the slave node, the stability and anti-interference capability of the system is improved. The retransmission mechanism based on the Cyclic Redundancy Check in the master node is designed and implemented to correct errors during transmission. Meanwhile, combining the IEC61508standard, the safety mechanism is designed, in order to ensure that the system will not cause harm to the people, environment or equipment when a fault occurs.Finally, the theories and functions above mentioned are used in the practical projects. The control system of spray paint production line based on EtherMAC can control13motors and many Ⅰ/O points, and mix the radio of paint by Modbus. The system can achieve to paint and dry the doors and windows, and achieves the database management for materials. The system is stable and reliable. The motion control platform of PCI+EMAC not only retains PCI kernel driver and functions in motion control library, but also adds the flexible and open characteristics of Ethernet. This approach can achieve a shorter communication cycle and high-speed multi-axis interpolation operation. By debugging and analyzing the practical projects in the industrial field, the real-time and reliability are verified.