Research On The Real-time Of EtherCAT Network Control System

Real-time performance is an important technical index of the control system,especially for the networked control systems, because of the communication network inthe field control layer, the requirements to real-time is more stringent. At present,comparing to other communication network the industrial Ethernet with lower cost,higher communication speed and better compatibility, has been widely used, andcomparing to other industrial Ethernet EtherCAT Industrial Ethernet is more superior inthe performance. Therefore, the EtherCAT Industrial Ethernet Control System as theobject, studying real-time is necessary. Because of the inter station transmission delay isvery important in the whole network communication delay part and complicated, so thetransmission delay between stations needed to be studied. At the same time, in variouscontrol tasks, the servo synchronous motion control requirement of real-time is thehighest, so real-time is focus on the servo control, the impact of servo axes on thecommunication delay is mainly researched.First of all, various kinds of the requirement of real-time control tasks is analyzed,it is concluded that the requirements of servo motion control for real-time is the highest.The typical industrial Ethernet technology is introduced; the performance of variouskinds of industrial Ethernet is compared; the superiority of EtherCAT Industrial Ethernetis showed; EtherCAT technology is analyzed.Secondly, according to the EtherCAT from the two types of physical layer interface-MII and EBUS, and according to two directions from data frame transmission, eightcategories are divided from the transmission delay between stations, component of thetransmission delay is analyzed, and the theoretical calculation method is derivedThen, analyzing the architecture structure of the servo motion control system, thereal-time requirements are obtained; it is that when centralized structure is used, thewhole network communication delay must be smaller than the cycle of position loop.Analysis of communication delay is composed of four parts which is the data frameforming time, master station receiving and forwarding data frame delay, the station nodedelay and cable delay, each part of the calculation method of the time delay theory isresearched. At the same time, in view of the actual project, the real-time requirements ofthe most configuration of the number of servo axes are estimated.Finally, through the experimental test, the correctness of transmission delay and communication delay theory from the station is verified. A feasibility analysis method isprovided for the construction of network control system, calculating from the interstation transmission delay and estimating the number of the servo axis.