Network Monitoring System Of Spot Welding Parameters In Welding Workshop

The stability of welding parameters is one of the main factors that affect the quality ofspot welding. After long-time researches and tests, the parameters of common materials arefixed in manufacturers, and welding machines can work reliably after debugged. Netvoltage fluctuation, various interference and the working condition of components in spotwelding machines affects the stability of parameters directly, so they become the keyfactors which affect the quality of welding. Besides, welding cable is used to transportcurrent, which is easy to be damaged, but not easy to be found until it is completelywrecked. Nonetheless, the quality of welding products in this period is mostly decreased.Based on not changing the original spot welding controller, a practical monitoringsystem of welding parameters is added. It can monitor parameters such as current, voltage,welding time and electrode pressure in real time, figure out the effective values of currentand voltage via point by point integration method and work out the resistance value ofwelding cable to judge whether the cable is wrecked or not. If the parameters are not stableor the cable is damaged seriously, the system will sound the alarm and transmits parametersto computer. The system uses Ethernet to transmit parameters.In order to achieve the target of monitoring, this paper designed the hardware circuit,used Protel DXP to draw the schematic and PCB diagram, made the circuit board, fixed allthe components and debugged the board. The system used ATmega128as the maincontroller chip, designed a smallest single-chip system circuit and an external storageexpansion circuit. In the acquisition and conditioning circuit of the current signal, thesystem used a Rogowski coil as the sensor, designed an integral circuit, a ratio circuit, afilter circuit and a precision rectifier circuit, then transmitted the current signal to A/Dconverter in ATmega128. In the conditioning circuit of the voltage signal, the systemdesigned an isolation module circuit, a filter circuit and a precision rectifier circuit, thentransmitted the signal to A/D converter. In the conditioning circuit of the electrode pressure signal, the system designed an amplifier circuit. Besides, the paper designed a power supplycircuit, a warning circuit, a zero-crossing detection circuit and a serial port communicationcircuit. In order to transmit the parameters of defective welding spots to the computer, thepaper designed an Ethernet control circuit with ENC28J60chip and a network interfacecircuit with HR911105A, that realized the communication of the monitoring system andcomputer. What’s more, the system can use one computer to monitor welding parameters ofmany spot-welders at the same time.Based on the hardware circuit, the paper designed the software program in theICCAVR and GCCAVR development environment. The software system includes aninitialization subroutine, a judging welding beginning subroutine, a sampling subroutineand a subroutine to count the effective values. In order to transmit data with the TCP/IPprotocol, the system transplanted an uIP protocol(a micro TCP/IP protocol), set the IPaddress and MAC address of lower computer, packaged the data as IP format andtransmitted it to PC using TCP protocol.After debugging the hardware and software system, the monitoring system is tested inSan You Co., Ltd in Changchun. The system can collect and save5000data of current andvoltage，figure out the effective values of current and voltage, welding time, electrodepressure and figure out the resistance value of welding cable. The current error is lowerthan2%.