Research On Real-time Ethernet Clock Synchronization System Based On Improved Kalman Filter Algorithm

With the rapid development of real-time Ethernet technology,it has gradually replaced the common industrial bus in the field of motion control.As an important problem in the field of motion control,synchronous motion control has two difficulties: clock synchronization and synchronous control strategy.The traditional clock synchronization system based on software timestamp has many problems,such as simple synchronization process,low cost,low synchronization precision and severe noise during measurement.Based on real-time Ethernet,this paper analyzes and studies the IEEE1588 clock synchronization principle.The main research work of this paper is as follows:Firstly,PTP synchronization message is described based on IEEE1588 clock synchronization principle.Based on the principle of clock synchronization,the main factors affecting the accuracy of clock synchronization are discussed,such as clock frequency drift,timestamp acquisition position,network link asymmetry,synchronization interval,etc.Then the improvement scheme of clock synchronization is put forward based on the main factors affecting the accuracy of clock synchronization.A frequency compensation scheme is proposed,which can make the frequency difference between master and slave clocks within one point and reduce the synchronization error caused by frequency drift.A software timestamp compensation scheme is proposed to make the software timestamp closer to the hardware timestamp and reduce the synchronization error caused by the low precision of the software timestamp.The scheme of correcting clock deviation and transmission delay is proposed to reduce delay jitter caused by link asymmetry and synchronization error caused by link asymmetry.Finally,the improved Kalman filtering algorithm is introduced to filter clock deviation and frequency drift,so that the clock deviation measurement process is more accurate and stable,and the clock synchronization accuracy is further improved.Then for the clock synchronization system,the design includes two parts: hardware and software.The hardware of the system is designed,including the selection of hardware controller and the transplantation of the system.The software is mainly the algorithm and implementation process of the clock synchronization system,including UDP communication process,optimal main clock algorithm process,local clock synchronization algorithm and Kalman filtering algorithm process.Finally,experiments are carried out to verify the main factors affecting clock synchronization accuracy and the feasibility of the improved algorithm.The experiments before and after software timestamp compensation verify that the closer the timestamp accuracy is to the underlying clock synchronization accuracy,the higher the accuracy is and the feasibility of the compensation software timestamp algorithm is verified.Repeated experiments were conducted by adjusting the synchronization time interval to verify the influence of the synchronization period and clock frequency drift on the synchronization accuracy,and the optimal synchronization time interval was 1s.By connecting different intermediate devices between master and slave clocks,the paper verifies the influence of link asymmetry on clock synchronization accuracy,and analyzes the reasons for the different clock accuracy among different devices.Through the measurement of clock deviation before and after the introduction of Kalman filter,the advantages of Kalman filter are verified,which can make the measurement process converge rapidly,reduce the clock deviation significantly,and greatly improve the synchronization accuracy,the synchronization accuracy up to 14?s;Finally,by measuring the clock deviation between the clocks before and after filtering,it is proved that the proposed system and algorithm can improve the clock synchronization accuracy of the multi-axis synchronous control system up to 20?s.