在激光电弧(MIG)复合对接焊中，焊缝成形尤其焊缝根部(反面)成形状况的好坏，是衡量复合焊焊接质量及其适应能力的重要指标。为研究视觉信号和焊缝根部成形的关系，建立了由辅助照明光源、可触发拍摄的CCD摄像机、以电弧焊接电流为信号源的触发电路以及图像采集卡组成的视觉传感系统。通过在工件底面拍摄的方法，得到了清晰的熔池背面实时图像。分析了拍摄过程的成像机制，并开发了一套算法实时检测背面熔宽、坡口间隙宽度以及熔池相对坡口的偏移量，结果表明实时检测到的熔宽和实际的焊缝背面宽度有很好的对应关系。

Weld formation, especially root weld formation is an important criterion to evaluate weld quality and adaptability in Laser-MIG hybrid butt joint welding. A vision sensing system consisting of an external illumination source, a CCD camera, a trigger circuit with the input of MIG current signal and video grabber is established to study the relation between vision signal and root weld formation. The backside image of molten pool is obtained clearly in real time by setting the camera under the workpiece, and the imaging mechanism is analyzed. The image processing algorithm to detect backside width of molten pool, gap width and the offset of molten pool is developed and the calculated result shows a good precision comparing with the actual root width of weld.