薄板激光拼焊视觉检测系统标定方法研究

The Calibration Method of the Vision Measurement System Used in Laser Welding

激光焊接是一种高质量、高速度、低变形的焊接方法,广泛应用于机械制造、航空航天、汽车生产、微电子等领域。为在进行薄板拼焊前获取焊缝轨迹,利用视觉系统焊接轨迹进行规划。使用了数控焊接机床,激光焊接头安装在数控机床的Z轴上,视觉检测系统安装在激光焊接头上。主要对焊缝检测系统中,CCD相机内参数和低功率激光器投影光平面标定方法进行了研究。相机内参数的标定使用了张氏标定法。投影光平面标定时,靶标放置在数控机床的X-Y平台上,低功率激光器投射结构光条纹在靶标上,视觉系统随Z轴移动并在三个位置拍摄靶标图像。在三个位置分别提取靶标上特征点及投影光条中心,应用交比不变性得到投影光条的空间坐标,拟合后可得到结构光平面。

Because of the advantage of high quality, high speed and low deformation, laser welding had been widely used in the area of machinery, aerospace, automobile and microelectronics. Machine vision could be used to acquire the seam tracking. In order to improve the seam tracking precision, CNC machine tool was used in this work. The fiber laser welding head and the vision system were fixed on the Z axis of the CNC machine tool. The inner parameter of the CCD camera and the structure light plane radiated by the low power laser were calculated. The inner parameter of the CCD camera was calibrated using the Zhang＇s method. The low power laser projected structured light on the model plane which was located on the X-Y plane of CNC tool. The vision system moved with the Z axis of the CNC tool, and stayed at three different positions. Then, the vision system shot the images of model plane at the three different positions. After acquired the center line of the structured light, the world coordinate of the feature points were calculated using the cross-ratio invariance. Then, the structured light plane was calculated by least-squares fitting.