Research Of Time Characteristics And Synchronization Mechanism On Hybrid Network In NCS Scenario

The industrial bus as the wired backbone network, the wireless network as complement and extension to the wired network, the hybrid network can be constructed.The hybrid network architecture is considered to be reliable and feasible. However, the collaborative work of the hybrid network in NCS scenario need to further research in theory, algorithm and technical solution, to ensure that it can meet the requirement of control precision and stability of NCS.To study the time characteristics and synchronization mechanism of the wired/wireless hybrid network, can be a useful supplement to the theoretical research of NCS, and help to solve difficulty of the traditional industrial bus in NCS scenario.Firstly, the model of NCS is analyzed, and summarizes basic features of NCS in the communications domain and control domain. In the control domain, time delay characteristics of the detection unit, control unit and execution unit of typical control system are analyzed, and the corresponding delay structure is proposed. In the communication domain, three kinds of hybrid network topology that can be applied in NCS scenario are defined.Secondly, based on the theory of real-time communication, three different time parameters and timing models in hybrid network are analyzed, including:idle time, slot time and turnaround time. For the reason of the presence of queue delay in hybrid network, data transmission may be affected by network congestion, and a correction method is proposed based on the time parameters. For the problem for real-time data exchange in NCS scenario, two different types of data exchange modes are discussed, namely:periodic data exchange and non periodic data exchange. The relationship between the data exchange time and packet error rate of link in hybrid network is study.Thirdly, CAN bus is selected as wired segment in hybrid network, and WSN based on IEEE802.15.4 protocol is selected as wireless segment in hybrid network. The timing models of periodic data exchange and non periodic data exchange are proposed, and these two timing models are applicable to NCS scenario. According to the timing model in hybrid network,the real-time performance of data exchange is researched in single master configuration and multi-master configuration. The calculation method of polling time is given respectively about sequential polling scheme and cross polling scheme.Fourthly, time synchronization in application layer is regarded as a special case of periodic data exchange. According to the requirement of time synchronization in NCS scenario, clock models and synchronization process based on PTP mechanism are analyzed.The technical solution that PTP synchronization is used in hybrid network is proposed. The application layer model about time synchronization is designed in IS node of hybrid network.Finally, the cluster control system of flat knitting machine is selected as a case. The mode of real-time data exchange and the scheme of time synchronization are verified. These solutions can realize efficient cluster control and orderly management for flat knitting machine production.