A three-dimensional vision system using dual projection for shadow problem

Currently, backlighting units have been studied widely for the uniform light source of flat panel in LCD display industry. Due to size, uniformity and efficiency of illumination source, traditional backlighting units composed of fluorescent lamps have been replaced with LED backlighting units gradually. In small display markets of cell-phone, PMP, PDA, etc., small-size LEDs are generally used for backlight units' illumination part. For their uniform light-emitting, the volumetric size control of each one's pocket is crucial in LED manufacturing process, because the pocket fills with the transparent molding material for protecting led die and bonding wire in final manufacturing stage. Here, we present a three-dimensional vision system for volumetric inspection of LED pocket. Because of the high ratio of outside wall's height to inside base's width, conventional measurement techniques easily produce noisy results due to the shadow problem. For preventing this effect, the proposed sensor system utilizes dual projection system. By using two measurement results acquired from projection with different incident angles, the shadow-free results can be acquired finally. In this paper, we will describe the sensor system's principle and the sensor fusion algorithm combining two measurement results. After a series of experiments, the measurements results are discussed in depth.