LAUSR

Microscopic profilometry based on fringe projection is notable for its noncontact and robust nature and is widely used in industrial electronics. However, its ability to observe electronic packages is limited by the depth of field (DOF) of the lens. This article proposes a novel reconstruction scheme based on telecentric 3-D profilometry to overcome this limitation. The advantage of profilometry based on phase-shifting fringe projection is utilized through defocus detection to achieve high-precision contour measurement with a single DOF. After completing such local reconstruction, a complete 3-D model is registered from partial fragments in different DOFs, making it simple for the microscope system to measure the geometric structure of objects whose thickness exceeds three times the DOF. To accommodate occlusion in local reconstruction, a specific detection algorithm is designed based on intensity variance. Beyond that, we present a novel projection system calibration scheme to improve the calibration robustness and accuracy. Instead of directly using the detected phase to calculate the coordinates of the corners, we first model the relationship between the phase and pixel coordinates and then leverage the estimated parameters to recover the phase. Our proposed method reduces the influence of calibration board spraying errors on the calibration results. Experiments show the effectiveness of this new approach.