Grid Electrode with Openings for Uniform Charging
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Solution Overview
Problem
In electrophotographic image forming apparatuses, corona-based charging devices face challenges in achieving uniform surface potential on photosensitive members due to increased peripheral velocity and electrostatic capacity, leading to non-uniform charging and potential level convergence issues, especially when the charging area extends beyond the preset range.
Innovation Solution
The image forming apparatus incorporates a corona charger with a grid electrode having a portion with openings and a non-opening portion in the charging region, where the downstream peripheral portion intersects a straight line passing through the exposure position and discharging wire, ensuring uniform charging and preventing excessive ion flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the charging device is improved in charging performance to increase peripheral velocity and electrostatic capacity, then the charging speed and capacity are improved, but the surface potential becomes non-uniform and fails to converge to the desired value
Solution Approach 1:
The grid electrode is divided into multiple regions with different opening ratios along the peripheral surface direction of the photosensitive member. The opening ratio is made smaller in regions where the charging area extends beyond the preset range, thereby segmenting the charging control to achieve uniform surface potential distribution across the entire photosensitive member surface.
Solution Approach 2:
Different portions of the grid electrode are assigned different opening ratios according to the local charging requirements. Specifically, the opening ratio is reduced in the downstream region where the charging area extends beyond the preset range, allowing localized control of ion flow to prevent excessive charging in that region and maintain overall uniformity.
2Productivity
If the charging device size is increased to improve charging performance, then the charging capacity is improved, but the distance between the charging device and photosensitive member is reduced, causing the charging area to extend beyond the preset range
Solution Approach 1:
The grid electrode implements spatially varying opening ratios to compensate for the extended charging area caused by reduced distance. By making the opening ratio smaller in the downstream region, the device locally controls ion distribution to prevent over-charging in areas where the charging field naturally extends beyond the preset range.
3Volume of moving object
If the distance between charging device and photosensitive member is reduced to decrease apparatus size, then the compactness is improved, but ions flow to the exposing position through the gap between grid electrode and casing
Solution Approach 1:
The grid electrode structure with varying opening ratios provides localized control over ion flow paths. By reducing the opening ratio in specific regions, the structure naturally limits ion escape through gaps while maintaining the reduced distance configuration, thus preventing harmful ion flow to the exposing position without requiring additional shielding structures.
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 stabilizes the surface potential of the photosensitive member, ensuring uniform charging and preventing potential level deviations, thereby improving image quality and reducing the size of the image forming apparatus.
Implementation Method 1
a corona charger (32) including a discharging wire (32a) and a plate-like grid electrode (32b) and configured to charge a surface of the photosensitive member (1) at a charging position (a2)
Implementation Method 2
said grid electrode (32b) includes a first portion (111) having a plurality of openings and a second portion (115) having only a non-opening portion in a charging region for charging the photosensitive member (1) with respect to a longitudinal direction of the corona charger (32)
Data Source
AI summary
An image forming apparatus includes a corona charger including a discharging wire and a grid electrode for charging a photosensitive drum at a charging position and an exposure device for exposing the drum charged by the charger at an exposure position which is at a downstream side of the charger (in a rotational direction of the drum) at the charging position. The grid electrode includes a first portion having openings and a second portion having only a non-opening portion in a charging region for charging the drum in a longitudinal direction of the charger, and the second portion includes a downstream side peripheral portion at a downstream end of the grid electrode with respect to the rotational direction. In a cross-section orthogonal to the longitudinal direction and including the charging region, the downstream side peripheral portion is intersected by a straight line passing through the exposure position and the wire.