Research On Distributed Control System For Tandem Arc Pulsed MIG High-speed Welding Based On ARM

Tandem arc pulsed MIG high-speed welding technology can not only improve welding speed, deepen the melting pool depth, enhance the weld seam toughness, but also decrease porosity of weld joint. It becomes the research focus in the field of welding because of its efficient and high quality. Double wire welding is not simple combination of two single wire weldings. The traditional direct digital control system and discrete auxiliary equipments can not meet the need of precise coordination control and automation welding of double wire welding.A distributed control system is ideal system architecture for tandem arc pulsed MIG high-speed welding. The design idea is that, every welding equipment, such as welding power source, wire feeder, running gear, water cooling tank, gasholder and manual control box, is a embedded intelligent control unit with the ability of solving the local problems. They share welding process information by fieldbus and closely cooperate with each other to complete double wire welding process. The system architecture can not only solve the problem of coordinated control, but also improve the welding automation level. Welding intelligent control unit is a embedded realtime system. It includes database, control, environmental reaction and communication modules. The paper will research its hardware, software and control algorithm.Digital arc welding inverter and wire feeder with CAN bus are designed using ARM as controller. Digital PWM generator of ARM enhances the static properties and dynamic response ability.μC/OS-Ⅱ, an embedded realtime multi-task operating system, can improve the response ability against various welding signals and software reliability of arc welding inverter and wire feeder. All the contents of the welding process will be divided into different tasks with priority level. The most important task, the higher priority level. To avoid simultaneous-sharing on the shared resources, some semaphores are introduced in to ensure the smooth performance of the arc welding power supply. An important task transfers data processed to other not important task via message boxes to improve the data processing speed.The CAN bus is a communication media via it welding equipment share information. A welding communication protocol for welding equipment information interaction is developed.The local high speed bus between master and slaver arc welding inverter is designed in tandem arc pulsed MIG welding system using full-duplex RS-422 bus. A complete communication protocol is defined.The application of fuzzy logic control technology in double wire welding is researched. Using peak voltage error and error rate as input, pulse valley time as output, fuzzy logic controller controls arc voltage to keep the length of arc stable. Continuous detecting of the wire feeding speed, three parameters of PID controller are adjusted online according to error and erroe rate. The wire feeder has fast response ability and constant wire feeding speed.A distributed control system of tandem arc pulsed MIG high speed welding is designed and a lot of testing are done based on it. The communication between welding equipments can work well and they can closely work together to complete automated welding process. The cooperative control between master and slaver welding power sources works well. The relationship of pulse phases of master and slaver welding currents comply with the design requirements. The arc welding power sources have excellent static and dynamic characteristics. The arc length keeps stable during welding process. The system has high welding speed and high efficiency.