Function Research And Development Of Embedded Canopen Master Station And I/O Slave Station

The fieldbus complied with the needs of the development of control technology,which is one of the key technologies for the development of industrial automationcontrol field. CAN-bus is a kind of serial communication network for solving theproblem of distributed real-time control. CANopen is a high-level communicationprotocol specification based on CAN-bus. CAN-bus and CANopen have themainstream position in the industrial control field in Europe and the United States.They have been widely used almost in every indusrial control field.As an importantkind of field bus, the development of CANopen is relatively backward in domestic, itneeds to strong research and development, promotion and application.Design embedded CANopen network of master station and slave station whichhas the function of digital/analog I/O. Choose embedded structure as the hardwarestructure of CANopen master station and slave station. Design hardware circuit basedon STM32F103VET6which is a32-bit MCU of ARM Cortex-M3. Hardware includesCAN drive interface circuit, serial debugging circuit of USART, isolated input andoutput circuit of digital I/O, isolated power circuit, etc. Design schematic diagram ofcircuit and multilayer PCB board in the EDA software Altium Designer.CANopen software of master station and slave station is mainly composed offour parts: the STM32underlying driver, operating system FreeRTOS, CanFestivalprotocol stack and application program. The underlying driver uses the STM32firmware library functions to write. Transplant the FreeRTOS real-time operatingsystem which is used for management and scheduling tasks. CanFestival protocolstack code used to implement the CANopen communication protocol. Applicationprogram create different tasks for different application objects.The CANopen master station and slave station have carried on the systemperformance test. Use the CAN message analysis software CANalyst to test SDO,PDO, NMT, Heartbeat message of network communication object. Monitor the bootprocess of CANopen network node. Test the CANopen master-slave structure systemresponse delay, establish the relationship curve between baud rate and response timedelay. Using the oscilloscope to carry on the preliminary analysis of CANopennetwork time delay, it shows that CANopen master-slave structure has real-timeperformance of a few milliseconds. CANopen network based on master-slave control structure is verified in theactual welding process control test. Slave station collect the pulse welding currentsignal and sent it to master station. Master station process signal and controlelectromagnetic valve’s action which is controlled by I/O port of another slave station.This action decides pulse switch of shielding gas composition. The comparison resultbetween the waveform of welding electric parameter and the control signal shows thatthe structure of embedded CANopen master station and slave station has goodreal-time performance and reliability in practical applications.