A Novel and Effective Surface Flaw Inspection Instrument for Large-Aperture Optical Elements

Surface defects on precision optical elements must be carefully inspected since they impact the normal operation of an optical system. It is a challenge to inspect defects of large-aperture optical elements using an imaging system because of efficiency and accuracy. This paper designs a novel and effective inspection instrument with two imaging systems for large-aperture optical elements. They are the dark-field imaging system (DFIS) with a line scan camera in 10-μm resolution and the bright-field (BF) imaging system with a microscopic camera in a 0.85-μm resolution. To keep the clarity of the DFIS in large-scope quickly scanning, an adaptive scan path planning method is proposed. A set of novel algorithms is proposed to process a large number of dark-field images. Due to the limitations of the DFIS in scattering effect, the corresponding BF images are obtained according to the dark-field images. The classification of flaws and their sizes measurement based on BF images are also presented. The experiments show that the instrument can scan an optical element with the size of 810 mm × 460 mm in less than 6 min and the inspection precision can reach 3 μm.