Study On CNC Fieldbus Technology Based On Ethernet

The pulse or analog interface standard is still used in communication between CNC (Computer Numerical Control) equipment and servos in domestic CNC systems. The behindhand standard has become the bottleneck to the development of high capability CNC system because they cannot meet the requirement of high speed and high precision. To cope with the bottleneck, most of foreign companies use fieldbus for CNC communication among the inner modules. However, these fieldbuses use special hardware equipment, which made them incompatible and high costs. Comparatively, Ethernet technology is mature, low cost and good compatibility. Therefore, the fieldbus for CNC system based on Ethernet technology is one of most important researches for the next generation CNC system. Here, the topic of"Ethernet based CNC fieldbus system"is proposed, and the research is outspread around this topic.Based on the study of the architecture, communication protocol of the foreign popular Ethernet based fieldbus technologies, and the analysis of the merit and demerit of these technologies, a hierarchical real-time communication and time synchronization architecture for the networked CNC system based on Ethernet/Internet is proposed.To cope with the hard real-time communication and precise time synchronization of the field network, an optimized real-time communication and precise time synchronization arithmetic is proposed, which can finish precise time synchronization in an un-prolonged communication cycle.Based on the optimized real-time communication and precise time synchronization arithmetic, a real-time communication and time synchronization protocol for CNC fieldbus system is proposed. The reliability of the protocol is studied and the solution is designed. Because the protocol gives attention to real-time communication and time synchronization synchronously, the real-time communication and time synchronization can be operated harmoniously, and the interfering and network load caused by time synchronization to the real-time communication can be reduced.A dynamic fieldbus scheduling arithmetic is proposed to cope with the multi-type task scheduling of CNC system, which can cope with the dynamic scheduling of the task system including cyclic real-time tasks, acyclic real-time tasks, non-real-time tasks and time slot tasks under multi-processor system. The model of the task system is set, and the model is described via formalization method. The priority is defined according to the level and deadline of task. The relation adding is used to normalize the time slot task to general task. The real-time communication and time synchronization scheduling is used as an example to explain the arithmetic and protocol, and the arithmetic is analyzed in time and space cost.Based on the real-time communication and time synchronization protocol, a CNC fieldbus controller is developed to control the communication and time synchronization operation, and the prototype of CNC system (called HNC-22Me) based on the real-time communication and time synchronization protocol is developed. In the last, the real-time, synchronization, and reliability of the protocol were measured and analyzed via experiments.