Communication And Real-time Schduling Of Equipment In DNA System Unit Based On CAN

In 2010, China has approximately 800,000 units of NC machine tools, among which the ratio of advanced type, universal type, and economical type CNC machine tools remains in 1:3:6. Current status of CNC machine tools in China is that the high-grade, middle-grade and low-grade CNC are coexisted, and their efficacy is not fully released. In order to improve the level of manufacturing, it is needed to fully utilize the existed NC machine tools as we are devoted to developing and producing the high-performance NC machine tools. DNC technique is an important approach to implement networked manufacturing and integrated manufacturing. The implementation of unit-level DNC is the basis of DNC system equipment, networked manufacturing and integrated manufacturing. If the problems existed in utilization of the middle-grade and low-grade CNC machine tools are effectively solved by the development and application of DNC technique, the level of enterprise manufacturing and management will be promoted. Meanwhile, the capacity and efficiency of the existed CNC machine tools will also be improved greatly. This thesis focuses on the following aspects which are unit-level equipment communication and real-time scheduling based on CAN bus.The heterogeneous devices are integrated trough CAN bus in the DNC system of units, in which the functions of DNC at different levels are achieved according to the device status. Through extensively investigating the operation principle of NC program, the effect of program consumption rate(PCR) to communication of DNC systems is revealed. A mathematical model is established to avoid the communication conflict. Also, a parameter design method is proposed based on the analysis of system, which provides a theoretical basis for DNC system design. In allusion to the dynamic features of DNC, the existed scheduling schemes that are based on specific production tasks in current DNC are investigated to carry out the flexible control of DNC and improve its ability to adapt for the different production tasks. Considering the non-uniform loads and dynamic time-variation of current DNC, PCR and its determination method based on the process of production are both proposed. Real-time determination of PCR is realized by simulating production process, in which any production materials need not to be consumed. The determined PCR provides the basis for the design of DNC and its communication scheduling. In order to improve program operating efficiency and transmission rate, NC program is optimized for the two typical working procedure—non-circle curve interpolation and holes processing. Finally, the obtained results are verified by practical tests.From the above work, it is obvious that the speed of CNC machine executing NC program is far lower than that of network transmission in the CAN bus-based DNC system. Thus, as the transmission ratio is given, the nodes number of DNC should be determined according to the PCR. Nodes task scheduling priorities are determined using status and task deadline of nodes scheduling process and triggered by the program event, which improves the adaptability of DNC system to the actual working conditions. In addition, relations between the step of interpolation and the speed of programming is nonlinear. Therefore, actual PCR is greatly different from that calculated according to programming instructions speed and feed path length. On the premise of guaranteeing quality processing, the interpolation step should be as large as possible to reduce the number of one-step NC program and the PCR significantly improves the running efficiency by optimizing the NC program.