Design Of Real-time Communication And Synchronous Control Of SERCOS In CNC System

Modern CNC machine tools and machining centers proposed much higher requirementsto the high-speed transmission of real-time data and synchronized motion control. With thedevelopment of open CNC, digital servo and filed bus technology，how to achieve high-speeddata transmission between the motion control unit and the AC servo devices has become a keyproblem in the field of motion control. Digital signal transmission technology，instead oftraditional analog and pulse signal transmission technology，will be a important direction ofnumerical control system.In this paper, after a brief commentary of the development trend of open CNC systemand the application of field bus technology in numerical control system, because of thelimitations of analog and pulse CNC system and the development trend of CNC system, aserial real-time communication structure of CNC system based on SERCOS was proposed:the motion controller as the master station and feed servo drive for slave station for themaster-slave ring network, and coordinate multi-CPU structure with the benchmark of thecommunication cycle. The motion controller sent command data to the servo slave stationthrough the fiber loop, achieving the synchronous control of the three loop servo motor; servoslave station fed back the state date to the SERCOS synchronous controller periodically.Make a profound analysis of the SERCOS bus protocol and features of thecommunication interface device-SERCON816. Then design the communication interfacecircuit of master station basis on DSP6713as the main control chip and program its software.On the basis of the original laboratory pulse CNC system, design the servo drive based onSERCOS bus interface with DSP and FPGA controller，then design the communicationinterface circuit and the software of the servo drive.Because the structure of the CNC system is multi-CPU, that makes the main controllerand servo driver work separately without unified clock reference and servo driver does notexecute the data synchronously, causes processing error. This paper analyzes the synchronousprinciple of SERCOS and proposes a synchronous control method of current loop amongservo feed drivers. This approach allows each axis servo drive current command to1ussynchronized precision, thus ensuring the machine tool axis motion consistency. Finally, this system is used for digital controlling in XKHL650vertical machining centerproduced by lokshun, then debug and test the CNC system, introduces the process and theresult of experiments.Experimental and processing operation suggests that the CNC system based on SERCOSbus communication system meeting the high real-time CNC precision machiningrequirements.