Photosensitive Drum Pre-Exposure for Potential Uniformity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In image forming apparatuses using the electrophotographic method, the surface potential of the photosensitive member's non-transfer area rises excessively when the contact area with the transfer roller is shorter than with the charging roller, leading to issues like reverse fogging, cleaning defects, and potential differences that cause streaks and damage.
Innovation Solution
An image forming apparatus with a control system that applies a normal polarity voltage to the transfer member when no recording material is present and performs a secondary exposure with a reduced exposure amount on the non-transfer area after it has passed through the transfer portion, reducing the potential difference between the transfer and non-transfer areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the contact area of the photosensitive member with the transfer roller is made shorter than with the charging roller, then the apparatus can be downsized and cost reduced, but the surface potential of the non-transfer area rises excessively causing reverse fogging and cleaning defects
Solution Approach 1:
The invention applies a preliminary action (pre-exposure) to the non-transfer area before the charging process to prevent the excessive rise in surface potential that would otherwise occur. By exposing this area in advance, the photosensitive material's sensitivity is reduced, preventing excessive charge accumulation during the charging roller contact, thereby counteracting the potential reliability issue before it arises.
Solution Approach 2:
The pre-exposure unit performs a preliminary action on the non-transfer area by irradiating it with light before the charging process. This preliminary exposure reduces the photosensitivity of the non-transfer area, preventing excessive charge accumulation when the charging roller contacts this area, thus maintaining surface potential uniformity while allowing the transfer roller contact area to be shortened.
2Device complexity
If the contact area of the photosensitive member with the transfer roller is made shorter than with the charging roller, then the apparatus structure is simplified, but potential differences cause streaks and damage to the photosensitive member
Solution Approach 1:
The pre-exposure unit applies a preliminary anti-action to the non-transfer area by reducing its photosensitivity before charging. This prevents excessive potential differences from developing between the transfer and non-transfer areas, thereby preventing the harmful effects of streaks and damage to the photosensitive member that would result from such potential differences.
Solution Approach 2:
The invention converts the potentially harmful effect of the non-transfer area (which would normally accumulate excessive charge and cause streaks) into a beneficial outcome. By applying pre-exposure, the non-transfer area's photosensitivity is reduced, transforming it from a source of potential damage into a controlled region that maintains uniform surface potential and prevents streak formation.
3Device complexity
If DC charging method is used without pre-exposure means, then the apparatus size and cost are reduced, but the surface potential control in the non-transfer area becomes problematic
Solution Approach 1:
The invention applies preliminary anti-action by using the pre-exposure unit to reduce photosensitivity in the non-transfer area before the DC charging process. This prevents excessive charge accumulation in the non-transfer area, maintaining surface potential uniformity while allowing the use of the simpler DC charging method without AC power supply requirements.
Solution Approach 2:
The pre-exposure unit performs a preliminary action on the non-transfer area by irradiating it with light at a reduced exposure amount. This preliminary exposure modifies the photosensitive material's properties in advance, enabling the use of DC charging method while maintaining control over surface potential uniformity that would otherwise be problematic without pre-exposure means.
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 solution effectively suppresses the excessive rise in surface potential of the photosensitive member's end portion, preventing defects like end portion stains and charging issues, thereby improving image quality and reducing maintenance needs.
Implementation Method 1
a surface of a photosensitive member is charged substantially uniformly by a charging means to form a dark portion potential on the surface of the photosensitive member
Implementation Method 2
The surface of the photosensitive member after the charging process is then exposed by an exposure means to form a light portion potential on the surface of the photosensitive member, and an electrostatic latent image is formed
Implementation Method 3
a transfer voltage having an opposite polarity to a normal charging polarity of the toner (normal polarity) is applied to the transfer roller, and the toner image on the photosensitive member is electrostatically transferred onto the recording material
Data Source
AI summary
An image forming apparatus includes a photosensitive drum and an exposure unit for exposing a surface of the photosensitive drum to form an image by a first exposure amount. In a rotational axis direction of a charging portion, a width of a transfer portion is shorter than that of a developing portion, a width of the transfer portion is shorter than that of the charging portion and an end portion of the surface includes a non-transfer area in contact with the charging portion and not in contact with the transfer portion. The voltage having the normal polarity is applied to the transfer portion when no recording material exists at the transfer portion, and the exposure unit exposes an area, including the non-transfer area of the surface that has passed through the transfer portion during application of the voltage, by a second exposure amount less than the first exposure amount.