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.