Research On Variable Structure Control Systems Of Inverter CO₂Welder Based On ARM_Linux Embedded System

Digital control has many characteristics, such as stable, flexible, reliable and highintegration, which provide necessary conditions to guarantee process stability and reducespattering during short-circuit transfer CO₂welding process. Empolying advanced digitalcontrol technologies, researchers have realized the optimization and management of weldingpower supply, thus its welding quality was highly improved and welding spattering wasobvious reduced. However, too much attention was focused on the power’s performance,fewer has done to investigate the remote network monitoring, touch screen ofhuman-computer interface and the overall co-ordination of the welding power supply.In this paper, circuit structure and control principle of inverter CO₂welding machinewas first analyzed, then a double close-loop control method of variable structure waveformcontrol system was presented to settle the problem of waveform singleness andnon-adjustable when using analog circuit controlling welding machine. In this way, weldingcurrent of inverter CO₂welding process can realize "dual slope" rising in short-circuitperiod and slowly descending first and then keeping steady aroud a lower value in arcperiod. The welding power’s control system employed “ARM_Linux”framwork andembedded chip S3C2440companied with software programme to realize double close-loopcontrol and incremental PI control.Hardware circuit and software system were designed based on ARM Linux frameworkembedded control system. In hardware system, S3C2440was used as the kernel processorchip, periphery circuit、welding control analog circuit, drive circuit and wire circuit weredesigned following the rule of digital and analog separating. Software control system isconstructed based on embedded Linux system, the main tasks contained cutting andmodifying Linux2.6.32.2kernel, making file system and so on. In application layer ofcontrol system, four child processes were derived from the main program, includingwelding task controlling, Qt human-computer interaction, website communication andsystem parameter setting process. Among them, LCD touch screen to input and displaywelding parameters can be realized by Qt human-computer interaction process. Controllingof arc period and short-circuit period to guarantee normal and stable droplet transfer was incharge of welding task controlling process. Website communication process was responsiblefor receiving set welding parameters by remote client and sending vedio of welding site to the users again, it’s convenient for the experts to guide and supervise the site of welding.Named-pipe（FIFO） communication technology was employed among four child processesto ensure more accuracy and faster commnication of data packets.Experiments were done to verify the designed control system, the results of somerelevant datas including waveforms and pictures sending from the site show that, thewelding machine can meet the functional and performance requirements as designed.