Photosensitive Member Charging Width Control for Fog Prevention
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Solution Overview
Problem
Conventional electrophotographic image forming apparatuses face issues with fog occurrence at the end portions of photosensitive members and defective image generation due to faulty charging, particularly caused by dielectric breakdown and uneven potential distribution during the direct current charging method.
Innovation Solution
The image forming apparatus incorporates a charging unit, an image exposure unit, and a weak exposure unit to control the potential of the photosensitive member, ensuring a relationship where the weak exposure area is wider than the developing width and charging width, thereby preventing fog and defective images by maintaining appropriate potential differences and reducing the risk of dielectric breakdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a direct current charging method is used to charge the photosensitive member, then the photosensitive member can be charged to a high potential, but fog occurs at the end portions and defective images are generated due to dielectric breakdown and uneven potential distribution
Solution Approach 1:
The charging process is segmented into multiple stages with different charging potentials. The photosensitive member is charged in steps rather than directly to the final high potential, allowing controlled charge distribution that prevents dielectric breakdown and fog at end portions while achieving the required charging potential for image formation.
Solution Approach 2:
A preliminary charging step is performed at a lower potential before the main charging process. This preliminary action establishes a baseline charge distribution that prevents subsequent dielectric breakdown when higher potentials are applied, thereby preventing fog and defective images while enabling high potential charging.
2Power
If the photosensitive member is overcharged to ensure sufficient potential for image formation, then the charging potential is adequate, but fog occurs at the end portions due to excessive potential
Solution Approach 1:
The charging potential is made dynamic rather than static, varying during the charging process and across different regions of the photosensitive member. The potential is adjusted based on the charging stage and position, applying lower potentials to end portions prone to fog while maintaining sufficient potential in image formation areas.
Solution Approach 2:
Different charging potentials are applied to different regions of the photosensitive member. End portions that are prone to fog generation receive controlled, lower charging potentials, while the central image formation area receives sufficient high potential, creating local quality variations that prevent fog while ensuring adequate charging for image formation.
3Device complexity
If a conventional charging width is used, then the charging process is simple, but the weak exposure area is not wide enough to prevent fog at the end portions
Solution Approach 1:
The solution extends the weak exposure area beyond the conventional charging width by adding a margin in the width direction. This dimensional extension ensures that the weak exposure covers not only the charging area but also the end portions where fog occurs, providing comprehensive fog prevention without significantly complicating the charging process.
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 effectively suppresses fog occurrence and defective image generation by ensuring appropriate potential control and reducing the risk of dielectric breakdown, leading to improved image quality and apparatus reliability.
Implementation Method 1
A charging unit 2, an image exposure unit 30, and a weak exposure unit 32 are disposed on the rotational axis side of the photosensitive drum 1
Implementation Method 2
an image exposure unit configured to form image portion potential by exposing the photosensitive member to light after the photosensitive member is charged by the charging unit
Implementation Method 3
a weak exposure unit configured to form non-image portion potential by exposing the photosensitive member to weak light having a lower exposure amount than the light for forming the image portion potential after the photosensitive member is charged by the charging unit
Data Source
AI summary
An image forming apparatus includes a photosensitive member, a charging unit, an image exposure unit configured to form image portion potential by exposing the photosensitive member to light, a weak exposure unit configured to form non-image portion potential by exposing the photosensitive member to weak light having a lower exposure amount than the light for forming the image portion potential, and a developer bearing member configured to carry developer, wherein a relationship of Ldev<Lvd<Lbg is satisfied, where the photosensitive member exposed to the weak light by the weak exposure unit has a weak exposure area having a length of Lbg in a photosensitive member longitudinal direction, a length of the developer carried by the developer bearing member in the photosensitive member longitudinal direction is Ldev, and the photosensitive member charged by the charging unit has a charging area having a length of Lvd.