为实现大空间复杂工件的准确测量,精确标定立体视觉系统变得越来越重要。为了克服传统立体摄像机标定过程繁复、户外实现困难的弱点,提出了一种基于光学参考棒的灵活、有效的立体视觉测量系统标定技术。参考棒水平和深度方向各有三个距离已知的红外LED作为特征点。通过在测量范围内的不同位置和方位移动光学参考棒,两像机同时捕获参考棒上特征点的图像。基于匹配的特征像点以及对极线约束,利用线性算法和Levenberg-Marquardt(LM)迭代算法快速地标定立体视觉测量系统。两像机之间平移量的比例因子由参考棒上特征点间的已知距离确定。参量标定过程中,自动地控制光强,优化曝光时间,使不同位置处光点图像的强度均一致,可以获得高的信噪比,提高标定精度。实验结果表明,该方法灵活、有效,在线标定能达到很高的精度,将现场标定过程应用到实际的大空间三维测量系统中,测量最大误差为0.18 mm。

To carry out the precise measurement of large-scale complex workpieces, accurately calibration of the stereo vision coordinate system has becoming more and more important. This paper presents a flexible and valid method for calibrating stereo vision coordinate system, which overcomes the complexity and difficulty of the traditional calibration methods. By moving the optical reference bar over the measurement volume, there are three horizontal infrared LEDs and three vertical infrared LEDs with known length which are as feature points, the two cameras capture the images of the feature points. Then, the relative orientation and position of two cameras can be quickly determined with epipolar constraint of the stereo camera through linear algorithm and Levenberg-Marquardt (LM) iteration method. The scale factor of the translation between the two cameras can be calculated by the distance between the two extremity feature points of the optical reference bar. By automatically controlling the light intensity and optimizing the exposure time, the feature points can get uniform intensity and obtain higher signal-to-noise ratio at different position, so the calibration accuracy is improved. The experimental results prove that the proposed calibration method is flexible, valid, and can obtain high calibration accuracy. The maximum error of the large-scale three-dimensional measurement system is 0.18 mm.