Charging Roller Contact Width Variation for Photosensitive Drum Wear
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Solution Overview
Problem
In image forming apparatuses, uneven wear occurs on photosensitive drums due to uneven pressure distribution from cleaning brushes and increased discharge at the ends, leading to premature wear at the end portions compared to the central portion.
Innovation Solution
A charger with a roller-shaped charging member and a contact width varying device that adjusts the contact width with the image holding member to reduce uneven wear by varying the contact width along the axial direction, using coil springs and eccentric cams to control the contact pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed applied voltage is used on the charging roller, then the charging function is maintained, but uneven wear occurs at the end portions due to increased discharge amount
Solution Approach 1:
The charging roller is designed with varying contact width along its axial direction, creating different local contact characteristics. The contact width is larger at end portions and smaller at the central portion, allowing each region to have optimized discharge characteristics that prevent uneven wear while maintaining overall charging function.
Solution Approach 2:
The contact width parameter of the charging roller is changed along the axial direction to control the divided voltage and discharge amount. By making the contact width variable rather than uniform, the patent adjusts the electrical parameters locally to reduce harmful discharge effects at the end portions.
2Device complexity
If uniform contact width is maintained across the charging roller, then the structure is simple, but uneven wear occurs due to pressure distribution from cleaning brushes
Solution Approach 1:
Instead of uniform contact width, the charging roller implements local quality variation by having different contact widths at different axial positions. This allows the end portions to have larger contact width that compensates for the higher pressure from cleaning brushes, while the central portion has smaller contact width appropriate for its lower pressure region.
3Object-affected harmful factors
If the charging roller contact width is increased at end portions, then uneven wear is reduced, but the overall device complexity increases
Solution Approach 1:
The charging roller incorporates a contact width varying device that makes the contact width dynamic rather than static. The device allows the contact width to be adjusted along the axial direction, creating a gradient distribution that optimizes wear characteristics while managing the added complexity through a focused mechanical solution.
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 reduces uneven wear by increasing contact width at the end portions and decreasing it at the central portion, resulting in a more uniform wear rate across the photosensitive drum, thereby extending its lifespan and maintaining image quality.
Implementation Method 1
both end portions of the charging roller are pressed, from rear surface sides toward front surface sides, against a photosensitive drum by coil springs
Implementation Method 2
contact width varying devices that vary contact widths... using coil springs and eccentric cams to control the contact pressure
Implementation Method 3
a charging roller is in contact with a surface of a photosensitive drum so as to charge the surface of the photosensitive drum
Implementation Method 4
the discharge amount increases in end portions compared to a central portion where the film thickness of the photosensitive member is relatively large. This promotes wear at the end portions due to stress caused by discharge
Data Source
AI summary
A charger includes a roller-shaped charging member and a contact width varying device. The charging member is in contact with a surface of an image holding member so as to charge the surface of the image holding member. The contact width varying device varies in an axial direction of the image holding member a contact width of the charging member with the image holding member so as to decrease uneven wear occurring in the axial direction of the image holding member.