Hue-Based Color Calibration for Liquid Electrophotographic Printers
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Solution Overview
Problem
Current liquid electro-photographic (LEP) printing systems face challenges in accurately calibrating ink layer thickness, leading to color errors, especially for high chroma colors, due to the weak dependence of optical density on layer thickness, which results in large hue mismatches and reduced color gamut.
Innovation Solution
A hue-based color calibration process is implemented, iteratively adjusting electrode and developer roller voltages based on calculated hues from reflection spectra to achieve precise ink layer thickness control, using the Kubelka-Munk model for better prediction of ink layer thickness and the L*C*h° color space for accurate color management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If optical density is used to control ink layer thickness, then the control process is simple, but the color accuracy deteriorates due to weak dependence of optical density on layer thickness
Solution Approach 1:
The patent changes the control parameter from optical density to hue value. By measuring the hue of the printed patch and comparing it to a target hue, the system can precisely control ink layer thickness. The hue is calculated from reflection spectra using the Kubelka-Munk model, providing a stronger correlation with layer thickness and enabling accurate color control, especially for high chroma colors.
2Ease of manufacture
If optical density based calibration is used, then the calibration process is straightforward, but color errors increase especially for high chroma colors
Solution Approach 1:
The patent implements a feedback-based calibration process where the hue of printed patches is measured and used to adjust the voltage applied to the developer roller. The system iteratively prints test patches, measures their hue, compares to target hue, and adjusts voltage until the desired color accuracy is achieved. This closed-loop feedback mechanism significantly improves color accuracy for high chroma colors compared to open-loop optical density based methods.
3Manufacturing precision
If iterative voltage adjustment is implemented, then color accuracy improves, but the number of calibration iterations increases
Solution Approach 1:
The patent performs preliminary characterization of the printing system to establish the relationship between developer roller voltage and resulting ink layer properties. This pre-established model allows the iterative calibration process to converge faster, as each iteration can make more informed adjustments based on the known voltage-hue relationship rather than requiring extensive trial and error.
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 approach significantly improves color accuracy, reduces color errors, and enhances the color gamut by directly controlling layer thickness based on hue, resulting in tighter tolerances and fewer calibration iterations, while being less affected by measurement variations.
Implementation Method 1
a spectral measurement device to measure a reflection spectrum from the printed patch
Implementation Method 2
using the Kubelka-Munk model for better prediction of ink layer thickness and the L*C*h° color space for accurate color management
Data Source
AI summary
A method of calibrating a developer unit of a liquid electrophotographic printer, the method comprising: setting a developer roller voltage and iteratively printing a patch on a print medium using different electrode voltages until a hue of a patch printed using one of the electrode voltages is within a tolerance of a target hue; and setting an electrode voltage based on said one of the electrode voltages and iteratively printing a patch on a print medium using different developer roller voltages until a hue of a patch printed using one of the developer roller voltages is within the tolerance of the target hue.