A compact and cost-effective illumination platform was developed for a versatile optical inspection system to improve the detection accuracy of defects in glass substrates. The illumination device was developed in two phases, initially to demonstrate its feasibility for surface defect inspection in glass based on dark field images, and subsequently to optimize the design so it can provide multi-directional lighting and increase light scattering from defects on the substrate. Three LED arrays were installed above the substrate carrier and projected at an angle onto the glass substrate for the phase-I illumination device. Surface defects on the glass substrate were successfully reconstructed from images acquired by a line scanned CCD camera, but non-uniformity of defects intensity distribution on images was revealed. To optimize the illumination, two sets of tightly arrayed 3-watt LEDs were symmetrically installed at the entrance slit of the lens-camera module for phase-II illumination device. The inspection data were able to show clearer images of surface defects. The design issues such as poor contrast and sharpness of acquired images due to low scattering efficiency and non-uniform illumination were addressed as well. PCBs for the installation of the LED arrays and their power supply were also optimized. These were manufactured on aluminum substrate to help regulate heating of the inspection platform. This feature makes the system more compact, operable at low power, and easy for modification.
The mechanical and thermal stress on lens will cause the glass refractive index different, the refractive index of light
parallel and light perpendicular to the direction of stress. The refraction index changes will introduce Optical Path
Difference (OPD). This study is applying Finite Element Method (FEM) and optical ray tracing; calculate off axis ray
stress OPD. The optical system stress distribution result is calculated from finite element simulation, and the stress
coordinate need to rotate to optical path direction. Meanwhile, weighting stress to each optical ray path and sum the ray
path OPD. The Z-direction stress OPD can be fitted by Zernike polynomial, the separated to sag difference, and rigid
body motion. The fitting results can be used to evaluate the stress effect on optical component.
In this study, multivariate data analysis, especially partial least squares regression (PLSR), is applied to analyze the near infrared absorbance spectra of fruit samples in order to acquire the inner qualities without destroying the samples. The calibration models have been established for the samples with raw data, first order derivative and second order derivative treatments, respectively. In the meantime, the models have been verified by using cross validation method. As anticipated, a model with higher correlation coefficient (r) and lower root mean square error of calibration (RMSEC) is preferred for both calibration and cross validation. The results reveal that the calibration models with second order derivative treatments have higher correlation coefficient, coefficient of determination, as well as lower RMSEC. Furthermore, the calibration models have been optimized by selecting partial wavelengths as new variables based on absorbance spectra and regression coefficient. The reasons why the calibration models are improved might be suitably cutting off partial wavelengths causing noises in the model.