Research On Critical Method Of Large Objects Three-dimensional Measurement Based On Structured Light

The 3D measurement have been widely used in modern industrial manufacturing, include size detection, quality control, reverse engineering, robot vision, face recognition, 3D printing and other industrial production. As structured light fringe projection profilometry offers the advantages of non-contact operation, full-field acquisition, and easy information processing, it is explored and researched by many relevant scholars, and has an important significance in the three-dimensional shape measurement.With the development of science and technology, the measurement and detection of large size surface has gradually become the key issues and trends in product manufacturing industry, and become a new hotspot in 3D measurement. Such as aircraft and engine blades in the aerospace, car and ships in the transportation, they all have large measurement size, complex surface, and need high measurement precision. So the traditional 3D measurement method is difficult to meet the measurement requirements. The large object 3D measurement method based on structured light is of great significance in their full 3D information acquisition.When measuring the large objects’ 3D shape with intersecting axis measurement system, the following problems usually appears. First, as the measurement conditions of long-distance, large field of view, and large complex surface, the cycle of the grating fringe on the reference surface is broadening. Also, the non-linear distortion of CCD camera will affect the measurement accuracy. Second, as the measurement range is limited by the size of large objects, its full 3D information can not be got once. This paper will do the relevant study and research in the following questions.As the existence of non-linear distortion of CCD camera, this paper proposes an effective lens distortion correction method. Based on CCD camera calibration, this paper builds the lens distortion correction model with Newton iteration. Also, this paper presents a flexible, simple method to calibrate the projector with calibrated camera.According to the phase unwrapping of large object and the transform rule of projected fringe cycle on the reference plane, the theoretical model of temporal phase unwrapping method based on the fringe cycle correction is proposed. And the high accuracy of the single surface 3D shape measurement can be obtained. Using monocular vision 3D registration method, the mark points’ coordinate conversion registration method based on global coordinates system and LM optimization algorithm is proposed. As well as the 3D registration method of large objects base on cylindrical coordinates. With these registration methods, the integrated information of large object can be obtained, and the limitation of single surface measurement can be overcome.Experiment results show that, the proposed CCD lens distortion correction method is of good result to the non-linear distortion. The method of temporal phase unwrapping method based on the fringe cycle correction can not only correct the cycle of the projected fringe, but also obtain the measurement shape exactly, finally improve the measurement accuracy. With structured light monocular vision 3D measurement system, the proposed 3D registration measurement method, i.e. the mark points’ coordinate conversion registration method based on global coordinates system and LM optimization algorithm, and the 3D registration method of large objects base on cylindrical coordinates, can complete the 3D registration measurement well. The overall registration measurement accuracy is 0.20 mm. The measurement error is within the allowable range, and the proposed method in this paper can complete the 3D registration measurement of large objects with high precision.