Charge and Development Bias Control for Image Density Uniformity

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Solution Overview

Problem

Existing electrophotographic image forming apparatuses face challenges in maintaining uniform image density due to rotational unevenness of photosensitive drums or developing sleeves, which can lead to periodic image density irregularities and risk product quality deterioration from fogging or carrier adhesion issues when correcting these irregularities.

Innovation Solution

An image forming apparatus that includes a photosensitive member, a charging unit, an exposure unit, a developing device, a reading unit, and a controller to generate charge and development correction biases based on test image readings, ensuring these biases' amplitudes are equal to or less than a threshold to suppress periodic density fluctuations without deviating the fog removal potential from an appropriate range.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If the charging bias or developing bias is modulated to correct periodic uneven image density, then image density uniformity is improved, but fog removal potential fluctuates causing fogging or carrier adhesion

Engineering Contradiction:

Improveimage density uniformityVSAvoidproduct quality stability

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent applies parameter changes by dynamically adjusting the charging bias and/or developing bias in a periodic manner synchronized with the rotation of the photosensitive drum. The controller modifies the bias voltage levels at specific rotational positions to compensate for density unevenness caused by rotational irregularities, while ensuring the fog removal potential remains within a safe range to prevent fogging or carrier adhesion

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements feedback control by detecting image density characteristics and using this information to adjust the charging and developing biases. The controller monitors the actual image formation process and modifies the bias parameters based on detected density variations, creating a closed-loop system that maintains both density uniformity and product quality

Inventive Principle:

Principle #23Feedback

2Manufacturing precision

If modulation amplitude of charging bias or developing bias is increased to suppress density fluctuation, then image density uniformity is improved, but fog removal potential deviates from appropriate range causing fogging or carrier adhesion

Engineering Contradiction:

Improvedensity fluctuation suppressionVSAvoidfogging and carrier adhesion risk

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The patent applies partial action by implementing bias modulation with controlled amplitude that is sufficient to suppress density fluctuations but not excessive enough to cause harmful effects. The controller calculates appropriate modulation depths and timing to achieve the minimum necessary correction while maintaining fog removal potential within safe boundaries

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

The patent implements beforehand cushioning by pre-calculating safe modulation parameters and setting appropriate bias levels in advance. The controller is programmed with predetermined modulation patterns that are designed to correct density unevenness while inherently preventing fogging and carrier adhesion by maintaining potential differences within acceptable ranges

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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

Effectively reduces periodic image density unevenness while preventing product quality deterioration from fogging and carrier adhesion, ensuring stable image formation and apparatus operation.

Implementation Method 1

a charging unit configured to charge the photosensitive member based on a charging bias

Methodology Applied

Scientific EffectElectrostatic field: Electric Field

Implementation Method 2

an exposure unit configured to expose the photosensitive member charged by the charging unit with laser light to form an electrostatic latent image

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 3

a developing device configured to develop the electrostatic latent image based on a development bias to form an image on the photosensitive member

Methodology Applied

Scientific EffectElectrophoresis: Electrophoresis

Data Source

PatentUS12044984B2Image forming apparatus with charge and development bias controlling features

Publication Date: 2024.07.23 CANON KK

AI summary

An image forming apparatus includes: an image forming unit comprising: a photosensitive member configured to rotate; a charging unit configured to charge the photosensitive member based on a charging bias; an exposure unit configured to expose the photosensitive member charged by the charging unit with laser light to form an electrostatic latent image on the photosensitive member; and a developing device configured to develop the electrostatic latent image based on a development bias to form an image on the photosensitive member, a reading unit configured to read a test image formed by the image forming unit, and a controller configured to: control the image forming unit to form the test image; control the reading unit to read the test image.