Research Of High-Precision Clock Synchronization In Distributed CANbus System

With the rapid growth of modem industry and manufacture scale, the demand of integration of manufacture automation as well as other information is increasing. Due to its highly dependability, distributed control system has become the best solution. Some critical systems need high-stability and high-efficiency to accomplish the key work and task. Thus the requirement for consistency of clocks in distributed system is extremely strict. Therefore, how to synchronize all clocks of distributed system precisely is a quite important issue.The key problems of the clock synchronization of distributed system are the measurement and compensation of the packet transmission delay. PTP is a high-precision time synchronization protocol in industrial control system. Using special hardware device, it generates a high-precision time stamp at physical layer, therefore the network delay can be measured accurately. Considering the real-time characteristics of CANbus and the idea of PTP algorithm, a novel scheme of high-precision clock synchronization system is proposed in this thesis. The scheme includes a clock node, which is composed by two CAN controllers, and it can generate high-precision time stamps. The precision of synchronization is about 10 us.In this thesis, Several popular clock synchronization protocols are discussed. Particularly, the synchronization mechanisms of NTP and PTP are analyzed. And PTP is chosen as basic synchronization algorithm. The technical specification of CANbus is introduced in detail, and the uncertainties of network transmission delay on CANbus are analyzed. Consequently, a scheme is proposed to restrain the network transmission delay. A synchronization clock node, which can monitor packet transmission,is designed based on dual CAN controllers. And a clock synchronization system is built according to this scheme. High-precision short time-interval measurement technique is introduced, and the synchronization precision measuring method of the clock synchronization system is put forward. Because of the limitation of time, the scheme has not yet been realized. At last the thesis sums up and prospects the research simply.