EKT AOI system performs inspection mainly based on optical principle and comprehensive use of principles color operation, color extraction, gray scale operation, image contrast.

1. Optical principle

AOI’s light source is composed of red, green and blue LED lamps. The three primary colors are combined into different colors. Combined with the specular reflection, diffuse reflection and oblique reflection in the optical principle, the welding of the patch elements on the PCB is displayed. As shown in the following figure:

2. Color operation principle

Through rasterization of a BMP picture, the imaging details, such as the position coordinates of the color distribution of each pixel and the color transition relationship between imaging grids, are analyzed and several functional formulas are listed. Then, data extracted from several similar pictures with the same area size is analyzed and calculated. The calculation results are restored according to the weight relationship set by software and the pixel colors and coordinates of the original BMP image to a virtual and weighted digital image. The main digital information covers the image’s graphic outline, color distribution, weight relationships allowing changes, etc.

3. Principle of image contrast

During inspection, the equipment captures the images of the inspected circuit board through the CCD camera system, transfers the images into the computer through digital processing, calculates and compares the images with the standard images (the comparison items include the size, angle, offset brightness, color and position of the components, etc.) and outputs the images with the comparison results exceeding the rated error threshold through the display, and displays the specific positions of the images on the circuit board.

4. Principle of color extraction

Any color can be mixed with red, green and blue in a certain proportion. A three-dimensional color cube is formed with red, green and blue. Color extraction is to cut a small color cube that we need from a set of color cubes. In other words, the color range is selected according to needs. Then, whether the ratio of the color in the inspected image that meets the color in the cube to the total number of colors in the image meets the setting range required. Under the red, green and blue light, this method is most suitable for the inspection of soldering tin such as resistance and capacitance.

5. Principle of gray scale operation

The target image is converted into gray scale image according to certain method. Then, a certain brightness threshold is selected for image processing. The image below the threshold is directly turned into black, and the image above the threshold is directly turned into white. In this way, the concerned areas, such as characters and IC short circuits, are directly separated from the original image.