Image Density Correction Using Test Image Phase Detection

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Solution Overview

Problem

Density unevenness occurs in image forming apparatuses due to slip between rotating members, leading to inaccurate correction of exposure amounts and reduced measurement accuracy of density unevenness.

Innovation Solution

An image forming apparatus that forms images on a sheet using a photosensitive member, an intermediate transfer member, and a sensor to detect a test image, with a controller determining a reference output signal to generate correction data based on the timing of the test image reaching a detection position, thereby reducing density unevenness by correcting control parameters such as exposure amount.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If sampling of the optical sensor output signal is started after a predetermined time from the home position sensor output signal, then the measurement process is simplified and synchronized, but measurement accuracy deteriorates when slip occurs between the photosensitive drum and intermediate transfer belt

Engineering Contradiction:

Improvesynchronization of sampling processVSAvoiddensity unevenness measurement accuracy

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The system uses the output signal from the optical sensor as feedback to detect the actual timing when the test image reaches the detection position. This feedback mechanism allows the system to adjust for timing deviations caused by slip between the photosensitive drum and intermediate transfer belt, thereby maintaining measurement accuracy while preserving the simplified synchronization approach.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system forms a test image in advance on the photosensitive drum, transfers it to the intermediate transfer belt, and conveys it to the detection position before actual image formation. This preliminary action allows the system to measure density unevenness under actual operating conditions, including any slip that may occur, thereby improving measurement accuracy.

Inventive Principle:

Principle #10Preliminary action

2Device complexity

If a constant conveyance time is assumed for the test image, then the control system is simplified, but the relationship between measurement phase and rotational phase shifts when slip occurs

Engineering Contradiction:

Improvecontrol system complexityVSAvoidphase alignment accuracy

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The system replaces the mechanical assumption of constant conveyance time with an optical detection method. The optical sensor detects the actual timing when the test image reaches the detection position, substituting the mechanical timing model with an optical feedback mechanism that automatically compensates for variations in conveyance time due to slip.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Productivity

If correction data is generated from density unevenness data with phase shift, then exposure amount correction is applied, but the density unevenness is not accurately corrected due to rotational phase mismatch

Engineering Contradiction:

Improvecorrection process efficiencyVSAvoidcorrection accuracy

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The system uses the output signal from the optical sensor as feedback to determine the actual timing when the test image reaches the detection position. This feedback allows the system to generate correction data that is accurately aligned with the rotational phase of the photosensitive drum, ensuring reliable correction of density unevenness while maintaining efficient correction processing.

Inventive Principle:

Principle #23Feedback

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

Accurately corrects density unevenness by aligning the phase of profile data with the rotational phase of the photosensitive member, improving measurement accuracy and reducing phase shifts caused by slip and positional tolerances.

Implementation Method 1

a sensor configured to receive reflected light from a test image on the intermediate transfer member passing through a detection position and output an output signal based on a reception result of the reflected light

Methodology Applied

Scientific EffectPhotoelectric Effect: Photoelectric Effect

Data Source

PatentUS12596320B2Correcting density unevenness in image forming apparatus

Publication Date: 2026.04.07 CANON KK

AI summary

A test image is formed by an image forming unit. A sensor receives light reflected from a test image on an intermediate transfer member passing through a detection position and outputs an output signal based on a reception result of the reflected light. A controller reduces density unevenness of images to be formed in a rotation direction of a photosensitive member based on a correction data, determines a reference output signal used to generate the correction data among output signals output from the sensor in time series based on a timing at which the test image reaches the detection position.