Color Registration Compensation in Electrophotographic Imaging

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Solution Overview

Problem

Conventional color image forming apparatuses using electrophotography face challenges in achieving high-quality full-color images due to shifting color issues caused by inaccuracies in photosensitive body positions and optical system errors, leading to moire patterns and image quality deterioration.

Innovation Solution

An image forming apparatus with a shifting amount of color compensation system that calculates and applies compensation amounts in the sub-scan direction, using a storage unit, calculator, address converter, pixel color density converter, half-tone processing unit, and process determination unit to adjust exposure control signals, ensuring accurate color registration and minimizing moire patterns.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If a plurality of photosensitive bodies are used to improve throughput, then productivity increases, but manufacturing precision deteriorates due to color shifting from position errors

Engineering Contradiction:

ImprovethroughputVSAvoidcolor registration accuracy

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent performs preliminary measurement of the actual positions of multiple photosensitive bodies before image formation. Based on these measurements, compensation amounts are calculated in advance and stored. During actual operation, these pre-calculated compensation values are applied to correct color registration without requiring real-time mechanical adjustment, thus maintaining both high throughput and precision.

Inventive Principle:

Principle #10Preliminary action

2Manufacturing precision

If optical path compensation is performed mechanically to improve manufacturing precision, then color shifting is reduced, but device complexity and cost increase

Engineering Contradiction:

Improveoptical path accuracyVSAvoidcompensation optical system complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent replaces complex mechanical optical path compensation systems with a computational approach. Instead of using movable mirrors, lenses, or other mechanical components to adjust optical paths, the system measures position deviations and calculates compensation amounts that are applied to image data. This substitution of mechanical systems with computational methods reduces device complexity and cost while maintaining precision.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Manufacturing precision

If image write start position is compensated to improve manufacturing precision, then partial color shifting is corrected, but loss of time increases due to additional processing

Engineering Contradiction:

Improveimage write position accuracyVSAvoidcompensation processing time

Core Design Contradiction:

Manufacturing precisionVSLoss of time

Solution Approach 1:

The patent calculates and stores compensation amounts for image write start positions in advance based on measured photosensitive body positions. During actual image formation, these pre-calculated values are simply retrieved and applied without requiring time-consuming real-time calculations or mechanical adjustments, thus minimizing additional processing time while maintaining precision.

Inventive Principle:

Principle #10Preliminary action

4Manufacturing precision

If coordinate conversion is applied to compensate color shifting, then manufacturing precision improves, but object-generated harmful factors increase due to moire patterns

Engineering Contradiction:

Improvecolor registration accuracyVSAvoidmoire patterns

Core Design Contradiction:

Manufacturing precisionVSObject-generated harmful factors

Solution Approach 1:

The patent applies different compensation strategies to different regions and types of image data. Instead of uniformly applying coordinate conversion to all images, the system analyzes image characteristics and applies appropriate compensation methods locally. This selective approach maintains color registration accuracy while minimizing the generation of moire patterns in specific regions where they would be most harmful.

Inventive Principle:

Principle #3Local quality

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 effectively compensates for color shifting errors, reducing moire patterns and maintaining high image quality by precise color registration and adjustment, thereby improving the throughput and quality of full-color image production.

Implementation Method 1

an exposure unit used to expose the image carrier

Methodology Applied

Scientific EffectPhotoconductivity: Photoconductivity

Implementation Method 2

a developing unit used to visualize an electrostatic latent image generated by exposure

Methodology Applied

Scientific EffectElectrostatic attraction: Electrostatics

Data Source

PatentUS7344217B2Image forming apparatus and its control method, and computer program and computer readable storage medium

Publication Date: 2008.03.18 CANON KK

AI summary

A shifting amount of color compensation amount is calculated based on a shifting amount of color obtained from a shifting amount of color storage unit for each image forming unit, and shifting amount of color compensation in the pixel unit is performed by executing address conversion using the calculation result. A feature of an image to be processed is detected, and color density conversion compensation for performing shifting amount of color compensation in less than the pixel unit is performed according to the detected feature. Furthermore, half-tone processing or exceptional processing is selectively executed according to the detected feature.