Photosensitive Drum Non-Transfer Area Potential Control
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Solution Overview
Problem
In image forming apparatuses using the electrophotographic method, the surface potential of the photosensitive member's non-transfer area rises excessively due to the shorter contact area with the transfer roller compared to the charging roller, leading to potential differences and issues like discharge, leakage marks, and reverse fogging, which cause defects such as streaks and end portion stains.
Innovation Solution
An image forming apparatus with a control portion that adjusts the exposure unit to expose the non-transfer area of the photosensitive member, ensuring its surface potential is lower than the transfer area, thereby preventing excessive potential rise and associated defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the transfer roller contact area is made shorter to reduce apparatus size, then the apparatus becomes more compact, but the surface potential of the non-transfer area rises excessively causing discharge and leakage marks
Solution Approach 1:
The exposure unit performs pre-exposure on the non-transfer area before the charging roller charges it. This preliminary action reduces the surface potential in advance, preventing the excessive potential rise that would otherwise occur due to the short transfer roller contact area, thereby avoiding discharge and leakage marks while maintaining the compact apparatus design
Solution Approach 2:
The exposure unit exposes the non-transfer area in advance during the rotation of the photosensitive member, creating a preliminary condition where the surface potential is reduced before charging occurs. This ensures that even with limited transfer roller contact, the potential difference remains controlled and prevents harmful discharge phenomena
2Device complexity
If the transfer roller contact area is made shorter to downsize the apparatus, then the apparatus structure is simplified, but reverse fogging and end portion stains occur due to potential differences
Solution Approach 1:
The exposure unit applies preliminary exposure to the non-transfer area, creating an opposing effect that counteracts the potential difference between transfer and non-transfer areas. This prevents reverse fogging and end portion stains while allowing the use of a shorter transfer roller, thus simplifying the apparatus structure without compromising image quality
Solution Approach 2:
The exposure unit selectively exposes only the non-transfer area with different exposure amounts compared to the transfer area. This local differentiation in exposure ensures that the non-transfer area has reduced surface potential specifically, preventing image defects in that region while maintaining normal operation in the transfer area, thereby achieving good image quality with simplified structure
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 of surface potential in the non-transfer area, reducing the risk of discharge, leakage, and cleaning defects, ensuring stable image formation and preventing end portion stains.
Implementation Method 1
an exposure unit configured to expose the surface of the photosensitive member charged by the charging member
Implementation Method 2
a charging member configured to form a charging portion in contact with the photosensitive member and to charge a surface of the photosensitive member at the charging portion
Implementation Method 3
a transfer member configured to form a transfer portion in contact with the surface of the photosensitive member and to transfer the toner image to a recording material from the surface of the photosensitive member at the transfer portion by application of a voltage
Data Source
AI summary
An image forming apparatus includes a photosensitive drum, a charging member, an exposure unit, a developing member, and a transfer member. In a rotational axis direction of the charging member, a width of a transfer portion of the transfer member is shorter than that of a charging portion of the charging member, and an end of the surface of the photosensitive drum in the axis direction includes a non-transfer area in contact with the charging member and not in contact with the transfer member. The exposure unit exposes the non-transfer area during rotation of the photosensitive drum, and forms a surface potential on the surface downstream of an exposing portion and upstream of the transfer portion with respect to a rotational direction. A controller controls such that an absolute value of the surface potential of the non-transfer area is lower than that of the transfer outside paper passing area.