Field Calibration Method of Camera for Measuring the Dimensions of Large Forging

Stereo vision technology has the poetential for measuring the dimensions of hot large forging. However, under the high temperature operation circumstance in forging workshop, it is difficult to calibrate the stereo vision sensor by the traditional calibration method, such as planar patterns method and self-calibration method. In this paper, a field calibration method of binocular stereo vision sensor is presented by virtue of projected patterns from a projector, for improving the dimensional measurement precision of large forging. The intrinsic parameters of CCD camera can be obtained by capturing the projected patterns during orthogonal movements of camera, and recognizing the feature points of patterns, while the extrinsic parameters of CCD camera is measured by detecting the distance between the feature points of patterns with the electronic theodolite. Experiments on the field calibration of camera at forging workshop are conducted. And the experimental results show that the relative error of dimensional measurement reaches 0.363%, which indicates that the proposed calibration method is effective for calibrating the dimensional measurement system of large forging.