Research On Optimization Of Fieldbus Slave Controller Of CNC Machine Tools

CNC machine tools are the foundation of manufacturing,which directly reflects the industrial level of the country.In terms of high-grade CNC machine tool,there is still a significant gap between China and the advanced level of foreign countries.Fieldbus technology used to realize communication between CNC device and related equipment(programmable logic controllers,sensors,servo drives,etc.)is obviously backward.The performace gap of the slave controller is one of the key factors leading to the backwardness of the bus technology.Taking NCUC-bus slave controller as an example,the lack of distributed clock synchronization technology leads to a synchronization jitter error;the lack of network redundancy strategy leads to communication interruption during line switching.In this dissertation,the research work is focused on the shortcomings of the slave controller in clock synchronization,network redundancy and data communication.By studying the characteristics of hardware signals,the effects of transmission delay and timestamp on clock synchronization performance are analyzed.It is found that the asymmetry of transmission delay is the main factor that leads to the deterioration of clock synchronization accuracy with the increase of the number of slave stations.To solve this problem,a delay compensation algorithm based on the real-time measurement of the data transmission delay of the slave station is proposed,which can eliminate the asymmetry and jitter of the data transmission delay of the slave station ffectively.Drift and offset model of clock is established.Based on this model,a periodic drift and offset compensation algorithm is proposed to compensate the clock rate and offset,respectively,to achieve high-precision clock synchronization between slave stations.The experimental results verify that when the number of slave stations increases,the newly added slave stations can still maintain the original synchronization performance.The fault recovery time of the exsiting ring topology redundancy technology of NC system is longer than its communication cycle,which leads to the loss of communication data.In this dissertation,a fault detection method based on timing mechanism is proposed,and a complete ring topology network redundancy strategy including fault detection,communication recovery and topology reconstruction is designed based on the fault detection mechanism.The strategy can realize the wake-up of redundant network in a communication cycle,and ensure the reliability of real-time data communication.The simulation results show that the network recovery time of this strategy is related to the Ethernet data frame length,the number of network nodes and the communication cycle.Aiming at the data communication problems caused by unreliable network ports,a real-time data channel management mechanism based on sliding window technology is proposed to avoid data pollution,data loss and data duplication during high-speed real-time data interaction.For service data,real-time process data and real-time big data,the functions of free end of writing,real-time data cache and two-way simultaneous reading and writing are designed to ensure the reliability of different data communications.Based on this channel,a channel mapping mechanism is designed to improve the communication efficiency of industrial Ethernet.The calculation shows that in the system with hundreds of communication objects(slave stations),the communication efficiency can reach97.8% when the Ethernet data frame is full.The application test of CNC machine tools shows that the slave controller optimized in this dissertation has the ability to be applied in high-grade CNC systems,surpasses NCUC-bus in clock synchronization,network redundancy and data communication,and reaches the technical level of international first-class bus EtherCAT.