End-Coupled Light Pipe LED Illuminator for Uniform Radiance
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Solution Overview
Problem
Conventional LED illumination systems for printers and copiers suffer from insufficiently uniform radiance, which affects the accuracy of specular reflectance measurements and calibration processes.
Innovation Solution
An end-coupled illuminator system with a light pipe and a diffuser is introduced, where LEDs emit light into the light pipe, and extractors deflect portions of the light through a lateral surface to a diffuser, which then diffuses the light uniformly along the illuminator axis, improving radiance uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If discrete LEDs are used as point sources to illuminate linear portions of the image bearing surface, then the expense and spacing between light sources are reduced, but the uniformity of light output (radiance) becomes insufficient
Solution Approach 1:
A light pipe is introduced as an intermediary component between the discrete LED point sources and the image bearing surface. The light pipe collects light from the LEDs and distributes it uniformly across its lateral surface through internal light extraction mechanisms, transforming the non-uniform point source illumination into uniform linear illumination.
Solution Approach 2:
The patent modifies the optical parameters by using a light pipe with specific geometric characteristics (length, diameter, refractive index) and surface properties (extractor distribution, surface roughness) to transform the spatial distribution of light from concentrated point sources to uniform linear distribution along the image bearing surface.
2Device complexity
If an end-coupled illuminator with extractors is used to provide illumination, then the spacing between light sources is reduced, but the radiance uniformity remains insufficient
Solution Approach 1:
The light pipe serves as a mediating optical element that receives light from the end-coupled illuminator with extractors and redistributes it uniformly along its lateral surface. This intermediary component corrects the non-uniform radiance pattern produced by the extractor-based illuminator.
Solution Approach 2:
The light pipe transforms the illumination from a point-source geometry (end-coupled) to a line-source geometry (lateral surface emission). This dimensional transformation allows the illumination to extend uniformly along the linear portion of the image bearing surface, improving radiance uniformity.
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 system achieves a more uniform light distribution, enhancing the accuracy of specular reflectance measurements and reducing non-uniformity in the diffuse-to-specular ratio, thereby improving the calibration and imaging processes in printers and copiers.
Implementation Method 1
a light pipe having two opposing end faces and a lateral surface. Two LEDs (or in some instances only one LED) each end-coupled to shine LED light into a corresponding one of the end faces and through the light pipe
Implementation Method 2
The light pipe includes a plurality of light extractors (also referred to herein as extractors) which cause portions of the LED light projected through the light pipe to exit the light pipe through a lateral surface of the light pipe at selected locations along light pipe
Implementation Method 3
The light pipe includes a plurality of light extractors (also referred to herein as extractors) which cause portions of the LED light projected through the light pipe to exit the light pipe through a lateral surface of the light pipe
Implementation Method 4
a diffuser positioned to receive the portions of the first light and diffuse the portions of the first light in the direction of the illuminator longitudinal axis
Data Source
AI summary
An illumination apparatus for illuminating an image bearing surface, comprising including an end-coupled illuminator comprising a light pipe having a first end face, a lateral surface and an illuminator longitudinal axis, a first light source (e.g., an LED) arranged to emit first light into the light pipe through the first end face, and a plurality of extractors disposed at selected locations along the illuminator longitudinal axis each adapted to deflect a corresponding portion of the first light from the light pipe though the lateral surface. The apparatus also includes a diffuser positioned to receive the portions of the first light and diffuse the portions of the first light in the direction of the illuminator longitudinal axis. The illumination apparatus may be included in a copier or a printer.