High efficient illumination system utilizing light-guide and white light LED for document scanner application

摘要

Design and evaluation of new illumination system utilizing white light emitting diode (LED) and plastic light-guide for letter-size (216mm width) document scanner and copier have been performed. We investigated the best condition for illumination on document plane through the optical analysis of scanner imaging system. To compensate the relative illumination fall-off caused by imaging lens, illumination on main-direction was designed to edge enhanced distribution. The illumination on sub-direction was designed to flat-top shape for stable performance against mechanical displacement of optics. The light-guide was designed dual-angled sidewalls for the decrease of light leakage and the increase of the degree of freedom for illumination shaping. The rear area of a light-guide is formed with crossed micro-prism patterns to axial direction to induce scattering of guided light, and the front area is formed with lens-shape for efficient lighting. Total 12 parameters were used for the optimization of design, and the various relationships between parameters and performances were also investigated. The optical characteristics of the proposed illumination system utilizing a white LED and light-guide, fabricated by mold process, were also experimentally evaluated in terms of illumination distribution against main- and sub-direction on image plane. They showed excellent agreement with simulated result and showed good performance of uniformity above 91%, and 89% in sub-direction and main-direction, respectively.