Shadow-free moire interferometer with dual projection for in-line inspection of light emitting diodes

In small-sized liquid crystal display markets, small light-emitting diodes (LEDs) are generally used for the illumination part of backlight units. For their uniform light-emitting, the volumetric size control of each pocket is crucial to the LED manufacturing process because the pocket fills with the transparent encapsulating material which plays a role in focusing the emitted light ray from the LED chip and protecting the LED wafer chip and wire-bonding. A special three-dimensional vision system is presented for volumetric inspection of the LED pocket with concave shape. Conventional measurement techniques of measuring the LED pocket easily produce noisy results due to the shadow problem-induced geometric configuration of the imaging part and pattern projecting part. In order to prevent this effect, the proposed sensor system utilizes a dual projection system. By using two measurement results acquired from pattern projections switching with different incident angles, shadow-free results can be acquired. In this article, we will describe the sensor system's principle and the sensor fusion algorithm combining two measurement results efficiently. A series of experiments is conducted to verify the performance of this proposed system. The measurements results show very satisfactory inspection performance and they are discussed in depth.