Photoconductor Charge Generation Layer Thickness Variation for Uniform Exposure

Solution Overview

Problem

Electrophotographic image forming apparatuses face challenges in reducing size and cost while maintaining image quality, as scanning lenses with fθ characteristics are large, and alternatives without constant scan speed lead to uneven exposure due to varying scan rates.

Innovation Solution

The apparatus employs a photoconductor with a charge generation layer of varying thickness and an exposure unit that scans at non-constant rates, ensuring a larger exposure amount per unit length in one region compared to another, to maintain uniform image formation without fθ scanning lens characteristics.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a scanning lens with fθ characteristics is used to maintain constant scan speed, then image uniformity is improved, but device size increases

Engineering Contradiction:

Improveimage uniformityVSAvoiddevice size

Core Design Contradiction:

Manufacturing precisionVSVolume of moving object

Solution Approach 1:

The photoconductor drum surface is designed with non-uniform charge generation layer thickness, creating different photoconductive properties in different regions. The first region (lower exposure amount) has a thinner charge generation layer while the second region (higher exposure amount) has a thicker layer, allowing each region to receive appropriate exposure despite varying scan rates

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The scanning system intentionally uses non-constant scan rate instead of constant scan rate, allowing the scan speed to vary across different regions of the photoconductor drum. This dynamic scanning approach is compensated by the corresponding variations in charge generation layer thickness, achieving uniform image formation without requiring an fθ lens

Inventive Principle:

Principle #15Dynamics

2Volume of moving object

If no scanning lens or scanning lens without fθ characteristics is used to reduce size, then device size is reduced, but exposure amount varies due to non-constant scan rate

Engineering Contradiction:

Improvedevice sizeVSAvoidexposure uniformity

Core Design Contradiction:

Volume of moving objectVSManufacturing precision

Solution Approach 1:

The photoconductor drum surface is designed with non-uniform charge generation layer thickness, creating different photoconductive properties in different regions. The first region (lower exposure amount) has a thinner charge generation layer while the second region (higher exposure amount) has a thicker layer, allowing each region to receive appropriate exposure despite varying scan rates

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The physical parameter of charge generation layer thickness is varied across different regions of the photoconductor drum to compensate for the non-uniform exposure amounts caused by non-constant scan rate. This parameter change enables uniform image formation without requiring an fθ lens

Inventive Principle:

Principle #35Parameter changes

3Volume of moving object

If scan rate is varied to reduce device size, then device size is reduced, but image density becomes uneven

Engineering Contradiction:

Improvedevice sizeVSAvoidimage density uniformity

Core Design Contradiction:

Volume of moving objectVSManufacturing precision

Solution Approach 1:

The photoconductor drum surface is designed with non-uniform charge generation layer thickness, creating different photoconductive properties in different regions. The first region (lower exposure amount) has a thinner charge generation layer while the second region (higher exposure amount) has a thicker layer, allowing each region to receive appropriate exposure despite varying scan rates

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The non-constant scan rate, which initially causes uneven exposure, is converted into a beneficial feature by designing the charge generation layer thickness to correspond with the exposure distribution. The varying scan rate is used to create distinct functional regions rather than being corrected uniformly

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 configuration allows for a compact image forming apparatus with improved image uniformity by adjusting scan rates and layer thickness, reducing ghosting and uneven density issues, especially in high-temperature and high-humidity environments.

Implementation Method 1

a photoconductor (4) having a charge generation layer (4c) and a charge transport layer (4d)

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS11036159B2Image forming apparatus for controlling an exposure amount on a surface of a photoconductor

Publication Date: 2021.06.15 CANON KK

AI summary

An image forming apparatus includes a photoconductor including a charge generation layer; a charging member to charge a surface of the photoconductor; and an exposure unit to expose the surface of the photoconductor to form a toner image on the surface of the photoconductor charged. The exposure unit exposes the surface of the photoconductor by scanning a laser beam in a main scanning direction at a non-constant scan rate, and exposure amount per unit length of the surface of the photoconductor in the main scanning direction is larger in a first region than in a second region. The first region is in the surface of the photoconductor exposed at a first scan rate. The second region is in the surface of the photoconductor exposed at a second scan rate higher than the first scan rate. The charge generation layer is thinner in the first region than in the second region.