A Practical Micro Fringe Projection Profilometry for 3-D Automated Optical Inspection

As an important defect detection technology, automated optical inspection (AOI) is widely used in the quality control of printed circuit board assembly (PCBA) and precision electronic manufacturing. To meet the requirement of 3-D AOI with large measurable volume, high speed, and high precision, a practical structured light imaging system based on the micro fringe projection profilometry is proposed. To be compatible with the traditional 2-D AOI system, an optical configuration with an axial bitelecentric lens camera and a lateral Scheimpflug projector is adopted, which helps to achieve a large depth of field (DOF). Adapting to the constraint of limited space for calibration target movement, a simplified and precise telecentric camera calibration method is proposed, which requires no auxiliary device such as micropositioning stage. Then, an improved bundle-adjustment method is introduced to globally optimize the calibration parameters. To accelerate the 3-D reconstruction, we further propose a ray backtracking algorithm after the corresponding point matching by using a modified telecentric camera model. It is demonstrated in experiments using real PCBA and microstructure components that the system DOF is 8 mm with a field of view of 32 mm \times28 mm. The reconstruction time is shortened to 40% of the traditional method.