Document Reading Apparatus Filter for Density Reproducibility
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Solution Overview
Problem
The use of a white LED with a blue LED and yellow light-emitting fluorescent material in document reading apparatuses causes issues with density reproducibility due to mismatched spectral characteristics between the monochrome image sensor and standard daylight visibility, leading to incorrect luminance readings for colors.
Innovation Solution
A color filter is arranged on the optical path between the monochrome line sensor and the document to suppress transmission of light at the peak wavelength of the white LED, ensuring the intensity received is lower than that from the fluorescent material, thereby aligning the spectral characteristics with standard visibility under daylight conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If a white LED using a blue LED and yellow light-emitting fluorescent material is used as the light source, then power consumption is reduced and costs are lowered, but the spectral characteristics mismatch causes density reproducibility problems in monochrome image sensing
Solution Approach 1:
A color filter is introduced as an intermediary component between the white LED light source and the monochrome image sensor. The filter has a transmission characteristic that suppresses the blue LED's peak wavelength (around 450 nm) and allows the yellow fluorescent material's peak wavelength (around 560 nm) to pass through, thereby mediating the spectral mismatch between the LED source and the sensor's response to achieve accurate density reproduction while maintaining energy efficiency
Solution Approach 2:
The spectral transmission parameters of the optical system are modified by introducing a color filter with specific transmission characteristics. The filter's transmission curve is designed to reshape the overall spectral characteristics of the light source-sensor system, shifting the effective peak wavelength from the blue LED region to the yellow fluorescent material region, thereby aligning with the monochrome sensor's response characteristics for accurate density measurement
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 solution improves density reproducibility by matching the spectral sensitivity of the monochrome line sensor with standard daylight visibility, ensuring accurate color representation and reduced luminance differences when reading documents.
Implementation Method 1
a white LED including an LED and a fluorescent material and configured to irradiate a document reading position with light
Implementation Method 2
a white LED including an LED and a fluorescent material configured to irradiate a document reading position with light
Implementation Method 3
the filter is configured to suppress transmission of light at a peak wavelength of the LED
Data Source
AI summary
A document reading apparatus includes a white LED including an LED and a fluorescent material and configured to illuminate a document reading position with light, a reading unit having a color line sensor and a monochrome line sensor and configured to read an image of a document illuminated with the light emitted from the white LED, and a filter arranged on an optical path between the monochrome line sensor and the document, and wherein the filter is configured to suppress transmission of light at a peak wavelength of the LED so that, regarding an intensity of light to be received on the monochrome line sensor, the intensity of the light at the peak wavelength of the LED is smaller than the intensity of the light at the peak wavelength of the fluorescent material when the light emitted from the LED is received.