Shadow-Free Moire Interferometer with Dual Projection for In-Line Inspection of Light Emitting Diodes

Abstract

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 probleminduced 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.

A Single-Lens Multi-Sensor Imaging System for 3-D Shape Inspection with a Wide Field of View

“…One camera is on the top (right camera), one on the right (left camera), with a beam splitter (BS) in the middle. As shown in Figure 4, to implement the phase profilometry, the multi-directional pattern projectors are equipped to solve the shadow problem, and the related patterns are projected in sequence (Kim and Koh 2007). After the image acquisition with the initial phase variations of the projected patterns, the imaging system sends the images obtained from the tested object to the personal computer with the connected image cable and image grabber.…”

“…The imaging system concept is the same as depicted in Figure 4. For the real world implementation, the projection system was modified to have eight pattern projectors with physically different optical projection axes toward the test objects, which is helpful in solving the shadow problem in the projection-type phase profilometry (Kim and Koh 2007). In addition, for a compact inspection head, reflection optics was chosen to implement the projection section.…”

“…Conventional imaging systems with a limited field of view (FOV) need to obtain their object images through the physical movement of the sensors, objects, or scanning devices in order to cover the entire area of interest (Kim and Koh 2007;Potsaid et al 2005;Hua and Liu 2008;Schechner and Nayar 2002). Through this stepwise imaging technique, it is possible to maintain the image quality with a high resolution during the inspection process.…”