基于单CCD尺寸检测的摄像机标定方法

为提高机械零件尺寸检测的精度,针对Tsai两步标定法中初始参数不精确的问题,提出了基于直线投影约束的三步标定方法.该方法首先利用直线投影约束条件求解出图像中心点和畸变参数的初始值,然后结合径向排列约束条件求解超定方程组得出全部外部参数和余下内部参数值,最后对全局参数进行非线性优化.为验证提出方法的效果,通过建立基于图像模板的世界坐标系实现,即首先利用图像像素坐标求取摄像机坐标,再将摄像机坐标进行归一化,利用外参数矩阵就可以求解出图像点的世界坐标.结果表明,该方法可以有效提高摄像机标定的精度,像素误差可达0.126 5像素点,单目视觉尺寸检测中任意两点距离误差小于0.41%.

Camera calibration method of size detection based on single CCD

The problem of inaccurate initial parameters perplexed the Tsai two-step calibration method,hence a three-step calibration method based on linear projection constraints is proposed for camera calibration in order to improve the size detection precision of mechanical parts.Firstly,the linear projection constraint conditions were used to solve the initial accurate value of the image center and the distortion parameters.Combined the radial alignment constraint conditions with overdetermined equations,all the external parameters as well as the rest of internal parameters are then solved.Finally,the nonlinear optimization is conducted to all the parameters by constrained conditions.The world coordinate system based on image template is established to verify the effect of the proposed method.Using the image pixel coordinates,the camera coordinates are calculated and then normalized.The world coordinates corresponding to image point are solved using the external parameter matrix.An experiment is carried out with single CCD,and the coordinate results are comparatively analyzed with Tsai method and Zhang method.The experiment results show that this proposed method can effectively improve the accuracy of camera calibration,with pixel error reaching 0.126 5 and distance error of arbitrary two points in monocular visual size detection being less than 0.41%.