Light Guide Prism Angles for Image Reading Illumination
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Solution Overview
Problem
Existing light guides for illuminating devices in image reading apparatuses suffer from inefficient use of light, as light reflected by the reflecting surface is not effectively total-reflected to the reading position, leading to light leakage and reduced utilization.
Innovation Solution
A light guide with a first guide portion and a turn-back member, where the prisms at the second end have angled total-reflecting surfaces designed to redirect light back towards the first end, ensuring efficient total-reflection of light to the reading position, and additional guide portions with prisms on both sides to enhance light distribution and reduce leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-prism configuration is used at the second end of the light guide, then the structure is simple, but light reflected by the reflecting surface is not efficiently total-reflected to the reading position
Solution Approach 1:
The single prism is divided into multiple prisms (first prism and second prism) with different inclination angles. The first prism has a smaller inclination angle to total-reflect light from the light source, while the second prism has a larger inclination angle to total-reflect light from the reflecting surface back to the reading position. This segmentation allows each prism to handle specific light paths efficiently.
Solution Approach 2:
Different regions of the light guide have different prism configurations. The first prism is positioned to handle light from the light source, while the second prism is positioned to handle light from the reflecting surface. Each prism has locally optimized inclination angles suited to its specific function in the light path.
2Use of energy by moving object
If the prism inclination angle is optimized for light from the light source, then light from the source is efficiently directed to the reading position, but light from the reflecting surface is not effectively total-reflected
Solution Approach 1:
The prism function is segmented into two distinct prisms with different inclination angles. The first prism (smaller angle) optimizes light direction from the light source, while the second prism (larger angle) optimizes light reflection from the reflecting surface. This segmentation resolves the conflict between optimizing for one light source versus the other.
Solution Approach 2:
The light guide incorporates local quality variations through prisms with different inclination angles positioned at specific locations. The first prism has a smaller inclination angle located to receive light from the light source, while the second prism has a larger inclination angle located to receive light from the reflecting surface, providing locally optimized performance for each light path.
3Device complexity
If light is allowed to leak from the second end of the light guide, then the structure is simpler, but illumination quality and image reading performance deteriorate
Solution Approach 1:
The light guide structure is segmented into multiple functional sections with different prism configurations. The first section handles light from the light source, the second section handles light from the reflecting surface, and the third section prevents light leakage. This segmentation allows each section to be optimized for its specific function without compromising overall performance.
Solution Approach 2:
The potential harmful light leakage at the second end is converted into a beneficial feature by introducing the second prism. This prism captures light that would otherwise leak and redirects it back to the reading position, transforming a loss into a useful illumination contribution.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables more efficient use of light by ensuring that light is effectively total-reflected to the reading position, reducing leakage and enhancing the illumination quality, thereby improving the image reading process.
Implementation Method 1
a plurality of first prisms provided on a first bottom surface of the first guide portion to be arranged in the first direction, the first bottom surface extending in the first direction, and configured to total-reflect light traveling in the first guide portion to the reading position
Implementation Method 2
a turn-back member configured to turn light coming to a second end of the first guide portion back in the first direction toward the first end
Data Source
AI summary
A light guide has a guide portion extending in a first direction. Light entering the guide portion through a first end is guided to a reading position. The guide portion has prisms provided on a bottom surface to be arranged in the first direction, and a turn-back member configured to turn light coming to a second end of the guide portion back toward the first end. Each of the prisms includes a first total-reflecting surface facing to the first end and a second total-reflecting surface facing to the second end. With respect to at least one of the prisms located within an area extending parallel to the first direction from the second end toward the first end by a predetermined distance, the angle of the first total-reflecting surface to the bottom surface is greater than the angle of the second total-reflecting surface to the bottom surface.