Quick and efficient light control for conventional automatic optical inspection (AOI) systems

Abstract

This study discusses a method to determine optimal illumination quickly in order to increase the process efficiency of automatic optical inspection (AOI) systems. Optimum searching methods were applied to find optimal illumination of a single color to enhance the quality of a monochrome image and reduce searching time. The problem was defined as optimizing 1D searching between light intensity and image sharpness. The image sharpness is the degree of distinctness of the image and is a non-linear function of the input voltage, which can be used to adjust the light intensity. We considered conventional optimum search methods, such as steepest descent, conjugate gradient, Newton’s method, bisection, and golden section. These derivative methods and direct searches were tested for a sample pattern using single color lights under coaxial illumination. The iteration for the optimal condition was 6.7% of full scanning in average. The optimal illumination was obtained using low input voltages, implying that a fine image could be obtained by applying appropriate electric energy. Additionally, we checked the possibility of applying these search methods to automatic lighting in industrial machine vision.