New Multi-color Illumination System for Automatic Optical Inspection

In automatic optical inspection (AOI), the illumination system affects the quality of input images and the result of image processing in the AOI. This paper developed a new multi-color illumination system specially used in the printed circuit board (PCB) inspection to detect a variety of defects in automated optical inspection system. The new illumination system consists of four kinds of colors of light emitting diode (LED) arrays composed of high-density LED surface light source. In order to detect a variety of defects, the radiation angle of the each LED array is different. The system uses a micro-controller to control the four sets of LED arrays, after acquisition of the image, which can self-adjust the light intensity of the illumination system based on the reference and comparison of histogram of the image in real time and can control different color LED array respectively according to the quality of the tested image. This paper analyzed the structural model of the illumination system and designed the control system. The experimental results show that the new illumination system has important performances such as uniform illumination, adjustable light intensity, fast response, lower heat and etc. The system can provide highly stable illumination for the AOI to obtain high-quality images effectively for detect the defects of PCB, and improve the defect detection rate and reduce the defects of the false alarm rate of AOI.