3d visual measurement system for featured structures based on phase-shifting fringe structured light

The measurement of small features on workpieces (such as locating holes, waist grooves, etc.) directly affects their assembly accuracy, service life, and safety. When using line lasers for scanning measurement of workpieces (especially in large-scale scenarios), due to the high relative scanning speed and the limitation of camera frame rate, the number of laser lines captured by the camera on small features is too small. This leads to issues such as point cloud missing and poor dimensional fitting accuracy in feature reconstruction, making it difficult to meet the requirements of submillimeter- level localization and dimensional fitting accuracy. To address this limitation, we introduced digital grating phase-shifting fringe structured light projection. Compared with line lasers, planar structured light features high stability, high measurement efficiency, and high resolution. Based on the phase shift principle, we developed an innovative automated feature localization and measurement prototype system. The system uses a DLP projector to project monochromatic phase-shifting fringes, which are captured by a high-resolution CCD grayscale camera. Combined with advanced optical algorithms and point cloud fitting algorithms, it achieves accurate 3D feature reconstruction. Technically, we project three-frequency four-step phase-shifting fringes, adopt the multi-frequency heterodyne method for phase unwrapping, and perform high-precision calibration of the system using the inverse camera model. Meanwhile, the perception of 3D spatial coordinates is completed based on the binocular stereo imaging model. On this basis, we have added more processing steps to improve the system's performance in terms of accuracy and speed, including projector distortion correction, phase-3D lookup table acceleration, feature localization and local reconstruction, etc., forming a complete and mature processing workflow and algorithm framework from 2D images to high-precision 3D point clouds. The system has undergone accuracy verification in accordance with international standards for accuracy testing of structured light measurement systems, and has realized high-precision and high-speed identification, localization, fitting, and measurement of feature structures on metal workpieces with diffuse reflective surfaces, achieving an accuracy of 0.03mm and a speed of 300ms, which significantly improves measurement accuracy and detection efficiency.