Document Lighting Device Uniform Illumination via LED Array and Lens
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Solution Overview
Problem
Document lighting devices for image readers face challenges with non-uniform illumination in the main scanning direction due to insufficient brightness of LED elements and inefficient light distribution, leading to wasted light and reduced effectiveness.
Innovation Solution
A document lighting device is designed with a light source unit comprising multiple LEDs arranged in the main scanning direction and a long-sized lens that converges light at an angle in the sub-scanning direction, ensuring higher convergence and reducing light diffusion losses, while maintaining uniformity across the scanning area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If multiple LED elements are arranged in an array to increase brightness, then illumination intensity is improved, but light diffuses wider and requires more power, reducing effectiveness
Solution Approach 1:
A light guide is introduced as an intermediary component between the LED array and the original document. The light guide collects light from the LED elements and redirects it to illuminate the original uniformly, preventing direct light diffusion while maintaining illumination intensity without requiring excessive power
Solution Approach 2:
The patent changes the optical parameters by using a light guide with specific refractive index and geometric shape to control light propagation. By adjusting the light guide's physical parameters, the system achieves efficient light redirection that reduces energy loss while maintaining high illumination intensity
2Volume of moving object
If LED elements are used to reduce device size, then compactness is improved, but brightness is insufficient compared to traditional lamps
Solution Approach 1:
The patent merges multiple LED elements into a unified lighting system combined with a light guide. By combining the compact LED array with the light-guiding function, the system achieves both small device size and sufficient brightness, as the light guide amplifies the effective illumination area without increasing the physical footprint
Solution Approach 2:
The light guide extends the illumination in the vertical dimension by redirecting light downward onto the original document. This dimensional transformation allows the compact LED array to provide adequate brightness over a larger area without increasing the horizontal device size
3Illumination intensity
If light is concentrated on the cross-section in the sub-scanning direction, then light convergence is improved, but non-uniformity occurs in the main scanning direction
Solution Approach 1:
The light guide is designed with spatially varying optical properties - different regions of the light guide have different refractive indices or geometric characteristics to control light distribution. This local differentiation allows the system to achieve high convergence in the sub-scanning direction while maintaining uniformity in the main scanning direction through localized optical adjustment
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
This configuration enhances light utilization in the main scanning direction, reduces non-uniformity, and achieves higher illumination efficiency with fewer LEDs, improving the reading quality and reducing power consumption.
Implementation Method 1
a long-sized lens that converges light at an angle in the sub-scanning direction
Implementation Method 2
a long-sized lens which is not converged in a cross section in the sub-scanning direction
Data Source
AI summary
In a document lighting device, each of the plurality of the light emitting elements arrayed in a light source unit is arranged in a vicinity of a focal point on a cross section in a sub-scanning direction of a long-sized lens, and a convergent point is placed at a location departing a predetermined distance in the main scanning direction from a location on the surface to be illuminated included in the sub-scanning cross section.