Gradient-Index Rod Lens Array for Low-Distortion Equal-Magnification Imaging
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Solution Overview
Problem
Conventional rod lens arrays in contact image sensors lack the ability to accurately form erect equal-magnification images, especially for applications requiring high measurement accuracy such as image dimension measuring devices, leading to issues like color bleeding and distortion in printed matter due to insufficient image recognition and reference position feedback.
Innovation Solution
A rod lens array with gradient index lenses arranged in the main scanning direction, ensuring a specific range of optical axis differences and inter-lens distances, along with a refractive index distribution and aperture angles, to achieve an erect equal-magnification image with high accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional rod lens arrays are used in contact image sensors, then the device structure is simple and easy to manufacture, but the image formation accuracy is insufficient leading to color bleeding and distortion
Solution Approach 1:
The patent applies parameter changes by precisely controlling the refractive index distribution parameter (gradient value g) within the range 0.03 to 0.07, and controlling the aperture angle θ within 5 to 15 degrees. These parameter optimizations enable the rod lens array to form erect equal-magnification images with high accuracy (0.1mm or less), resolving the contradiction between manufacturing simplicity and image formation accuracy.
Solution Approach 2:
The patent implements local quality by creating a specific gradient index distribution within each rod lens where the refractive index decreases from the center toward the periphery according to the formula n(r)² = n₀²{1 - (gr)²}. This localized refractive index variation within each lens element enables precise optical path control and high-accuracy image formation without requiring complex overall system design.
2Measurement precision
If rod lens array parameters are optimized for high measurement accuracy, then measurement precision improves to 0.1 mm or less, but manufacturing tolerances become more stringent
Solution Approach 1:
The patent defines specific parameter ranges that balance measurement precision with manufacturing feasibility: gradient value g between 0.03 and 0.07, aperture angle θ between 5 and 15 degrees, and inter-lens distance ΔW between 0.01 and 0.1 mm. These parameter specifications enable high measurement accuracy (0.1mm or less) while providing clear manufacturing targets that can be achieved with standard precision manufacturing processes.
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 measurement accuracy of 0.1 mm or less, allowing precise image formation and correction of aberrations, suitable for high-precision image inspection and measurement devices.
Implementation Method 1
A rod lens is a cylindrical lens having an axisymmetric refractive index distribution in which a refractive index decreases from a center toward a peripheral portion
Data Source
AI summary
A rod lens array in which a plurality of gradient index rod lenses are arranged in a main scanning direction such that optical axes thereof are substantially parallel satisfies 0.01 [mm]≤ΔW≤0.1 [mm] when a substantially erect equal-magnification image of an object surface is formed on an image surface (Note that ΔW is an absolute value of a difference between a length Wob of the object in the main scanning direction and a length Wim of the image in the main scanning direction).