| With the development of welding technology, MIG welding has been increasingly used in automatic welding of all position. However, during the welding, the distance between the welding torch muzzle and the surface of the work piece has to change because of the confine of welded structure, which will cause instabilities of the welding arc and the welding process. To keep the stability of welding arc is an important task in welding automation field, when the distance between the welding torch muzzle and the surface of the work piece changes.This paper analyzes how welding conditions tamper with welding process and welding quality, and the united control strategy of arc length control, by using changeable wire speed and drop-characteristic welding power source, is presented based on this analysis. The fuzzy control theory is inducted to the control as the control system is a complicated nonlinear one.The fuzzy arc length controller is established with arc voltage as the input and wire speed as the output, based on the MATLAB software. Optimizing of the controller's parameters is proceeded based on simulations, and the results indicate a good response characteristic and high precision. The hardware and software design of the control system is completed, taking the MSP430F149 MCU and TMS320LF2407 DSP as chief controllers.The welding experiments indicate the accuracy of the mathematics model of the designed fuzzy control system and the stable work condition of the digital control system. Even when the distance between the welding torch muzzle and the surface of the work piece changes, this control system will keep the stability of arc length, so as to achieve a stable welding process.
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