Study on Glass Defect Inspection Based on Projecting Grating Method

Abstract An inspection method based on transmission-mode projecting grating for glass defects has been proposed and verified by experiments. Sinusoidal fringe on the glass is collected using a linear CCD. The fringe curve can be corrected through the Fourier series fitting method to eliminate the constant non-uniformity of the light intensity of a light-emitting diode. The one-dimensional Fourier transform is applied to the corrected fringe curve; the Gaussian band-reject filter is designed to attenuate the first-order spectrum, and a Gaussian band-pass filter having the opposite characteristic attenuates other frequencies (except those in the first-order spectrum). In this way, the defect image and the phase map are obtained. A double threshold segmentation algorithm is applied to get a ternary-value image of the defects, with judgment of the defects’ size and position based on the connected region. Based on the phase map, a calculation method of diopters is proposed. A method for defect type judgment is raised. The results show that the resolution of the real-time testing can reach 0.1 mm × 0.1 mm.