【作者】 王德民；

【导师】 高进强；

【作者基本信息】 山东大学 ， 材料加工工程， 2008， 硕士

【摘要】 随着焊接自动化的发展,对在线质量检测提出更高的要求。而焊接过程中焊接熔池包含较为丰富和直接的焊接质量信息,熔池的形状参数是判断焊缝成形和内在质量的重要依据。利用视觉检测获取熔池的形状参数对于验证焊接热过程数值模拟结果、实现焊接质量在线检测以及焊接熔透控制有重要的理论意义和工程实用价值。本文针对弧光、飞溅以及烟尘等干扰因素较多的短路过渡MAG焊接过程,构建了相应的熔池视觉检测系统。基于电弧光谱分析,选择了复合滤光器,减弱了弧光的干扰。设置CCD摄像机曝光时间,设计了短路过渡信号的获取及CCD摄像机外触发电路,准确地将CCD摄像机的曝光时刻定位于短路过渡阶段,从而克服了不同时刻采集亮度不同、飞溅等干扰较多的问题。提出了正前方小角度和正后方大角度的采集方式,采用普通工业CCD摄像机拍摄到了连续清晰且不失真的熔池图像。通过分析焊接熔池区图像,设计了7×7方形中值滤波算法,利用改进的梯度法设计了边缘增强算法,选择了边缘点的动态搜索算法,从而得到完整的熔池边缘,利用针孔模型对摄像机进行标定,实现对熔池几何参数的提取。对采集到的不同焊接电流、焊接速度以及喷嘴高度情况下的熔池图像进行了熔池长度、熔池宽度以及宽长比等几何参数的提取,分析了熔透情况、熔池几何参数与工艺参数间的变化规律。结合熔池侧面检测的结果,分析熔池正面检测时熔池长度结果存在较大误差的原因,并提取侧面图像中熔池倾斜度对正面检测结果进行修正,最后提出了采用以正面检测为主并综合侧面检测结果的熔池检测方案。更多还原

【Abstract】 With the development of welding process automation, a higher demand is expected on the on-line quality monitoring. Since the weld pool contains explicit and abundant information about the welding quality, the geometry of the weld pool has a great effect on the formation and quality of the welded joint. Detecting the weld pool geometrical parameters from topside of work piece with visual sensor is of great theoretical and practical significance in verifying the numerical simulation results of welding thermal process, realizing the on-line quality monitoring and controlling weld penetration.According to the MAG welding of short-circuiting transfer process in which arc light, spatter, smoke dust and other interference exist, a visual-based sensing system is designed. Through the analysis of the arc spectrum, a composite light-filter is determined to eliminate the disturbance of the arc light. A proper sampling time is selected. A short-circuit detection and CCD camera ex-trigger circuit is developed based on the welding voltage waveform. The exposure time is fixed at the moment of short circuit, which solves the problems caused by the surrounding luminance and spatter interference. Grabbed from the front position with small angle and the rear position with large angle, uninterrupted, clear and undistorted images of weld pool are obtained using the ordinary industrial CCD camera.Based on the analysis of the weld pool images, a series of image processing algorithms are developed to extract the whole weld pool edge, including the 7×7 square median filtering, edge-enhanced algorithm and dynamic searching algorithm. According to the calibration result of the pinhole camera, the geometrical parameters of weld pool are acquired.The weld pool geometrical parameters including the length, the width and the breadth length ratio are acquired under different welding current, welding speed and contact tube-to-workpiece. The regularity with the welding parameters, the weld pool geometry and weld penetration changing respectively is analyzed.Combined with the weld pool images captured from the side direction, the reason that causes error in the weld pool length obtained from the topside sensing is analyzed. The original measurement is modified based on the weld pool gradient. A new method that the topside sensing is combined with the results acquired from the side detection is adopted更多还原