Charging Member Outer Diameter Profile for Image Density Uniformity
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Solution Overview
Problem
In image forming apparatuses using electrophotographic methods, density unevenness in images is caused by vibrations of the image holding member due to the charging member, leading to changes in the forming position of latent images, particularly when the charging member, image holding member, and exposing device are integrally housed.
Innovation Solution
A charging member with a cylindrical or columnar conductive base material and an elastic portion, where the outer diameter at the axial end portion is greater than the maximum outer diameter at the axial center, and the amplitude values in the periodic regions are controlled to prevent density unevenness, ensuring Re > Rc and Ac/Aa ≤ 1.0, thereby stabilizing the image formation process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the charging member has a uniform outer diameter along the axial direction, then the manufacturing process is simple, but vibrations occur during rotation causing density unevenness in images
Solution Approach 1:
The charging member is designed with non-uniform outer diameter where the outer diameter at the axial end portion (Re) is larger than the maximum outer diameter at the axial center (Rc). This local variation in geometry is specifically engineered to reduce vibrations during rotation, thereby preventing density unevenness in images while maintaining manufacturing feasibility through extrusion processes.
2Productivity
If the charging member rotates at high speed, then productivity is improved, but vibrations increase causing latent image forming position changes
Solution Approach 1:
The outer diameter parameters of the charging member are specifically controlled such that Re (outer diameter at axial end portion) > Rc (maximum outer diameter at axial center). This parameter change is designed to reduce vibrations during high-speed rotation, maintaining latent image forming position stability while enabling high productivity.
3Reliability
If the elastic portion thickness is increased to reduce vibrations, then image quality improves, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
Instead of uniformly increasing the elastic portion thickness throughout the charging member, the invention locally varies the outer diameter such that the axial end portion has a larger diameter (Re) than the axial center (Rc). This localized geometric modification reduces vibrations effectively while avoiding the complexity of uniformly thickening the entire 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
The solution effectively prevents density unevenness in images by stabilizing the charging member's contact with the image holding member, reducing vibrations and maintaining consistent image formation, thus enhancing image quality.
Implementation Method 1
an elastic portion provided on the conductive base material... Re is an outer diameter of a charging member at a position of 5 mm from an axial end portion of the elastic portion
Data Source
AI summary
A charging member includes: a cylindrical or columnar conductive base material; and an elastic portion provided on the conductive base material, in which Re and Rc satisfy Re>Rc, where Re is an outer diameter of a charging member at a position of 5 mm from an axial end portion of an elastic portion, and Rc is the maximum value of an outer diameter of the charging member at an axial center of the elastic portion, and a cylindrical or columnar charging member has a value of Ac/Aa of 1.0 or less, in which Ac is the maximum amplitude value in a periodic region from 1.5 mm to 6 mm in a case of periodically analyzing a surface shape of the charging member in a circumferential direction, and Aa is the maximum amplitude value in a periodic region from 1.5 mm to 6 mm in a case of periodically analyzing a surface shape of the charging member in an axial direction.