Research Of Large-scale Stereo Vision Extrinsic Parameters On-line Calibration Technology

With the rapid development of technology, especially the computer science and photoelectricity, a measure method based on modern optics is developed. This method syncretizes computer graphics technology, electronics, information processing, computer vision and etc. Because of these advantages, such as un-touch measurement, high precision,good real time ability, highly automatic, this method has more and more applications in science research, industry application and etc. The large scale 3D machine vision measurement is an important direction of vision measurement methods. It mainly for the increasingly high requirements of processing and assembly of large and complex components dimensional inspection, reverse engineering, deformation detection, and other three-dimensional measurement tasks. Because of simple structure, straightforward measuring process, high precision, stereo vision measurement technology plays an important role in the visual three-dimensional measurement technology.For the camera external parameters calibration directly affecting the precision of stereo vision 3D coordinate measurement, an on-line extrinsic parameters calibration method utilizing optic reference bar is presented. To meet the requirements of 3D measurement of large components, taking the infrared LED which relative coordinates on the bar are pre-calibrated accurately as feature points. This way greatly improved the image quality,simplified the identification and matching methods of feature points. Using the bilinear interpolation of gray squares weighted centroid location algorithm to the exact location of feature points under the on-site complex conditions.For the proposed stereo vision external parameters on-line calibration method based on optical reference bar, we make the optical reference bar imaged along the width and depth direction. The corresponding points can be get during the two cameras. The epipolar restriction equation can be get based on coplanar restriction of vision measurement, and for the traits of on-line calibration, the paper deeply does research for the normalization method of epipolar restriction equation, error criterion and the building method of error equation, and the resolving method of epipolar restriction equation based on M method is proposed,meanwhile the baseline distance and rotation matrix representing the external parameters are got from the solution of resolving result. The corresponding scale factor is determined by the known distance restriction among the optical points in the optical reference bar. The influence on precision of relative azimuth angle of cameras, baseline distance, sampling frequency,orientation of optic reference bar and etc are discussed. Experiment results indicated that this method has high precision and agility in the on-line occasion of stereo vision calibration to meet the requirements of large scale 3D coordinates measurements, and it is practicable.