Charging Roller Voltage Control for Photosensitive Member Potential Uniformity
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Solution Overview
Problem
In electrophotographic image forming apparatuses, the DC charging method results in non-uniform surface potentials of the photosensitive member, leading to image defects like fog and carrier adhesion due to the lack of potential leveling, which delays the start of charging processing and increases the first copy time (FCOT).
Innovation Solution
The apparatus employs a charging roller with a direct current voltage that includes a first voltage below the discharge start voltage and a second voltage above it, with a control unit managing the voltage rise to ensure a predetermined temporal change, synchronizing with the pre-exposure and development processes to maintain surface potential uniformity and prevent image defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a pre-exposure member is used to neutralize residual charges, then image quality is improved, but the first copy time increases because charging must wait for pre-exposure completion
Solution Approach 1:
The charging roller applies a first voltage (below discharge start voltage) in advance during the pre-rotation operation, before the pre-exposure member completes its neutralization work. This preliminary charging action prepares the photosensitive member surface potential uniformly, allowing the charging process to start earlier and reducing the first copy time while maintaining image quality
Solution Approach 2:
The charging voltage is dynamically controlled in two stages: first applying a low voltage (below discharge start voltage) during pre-rotation, then switching to a high voltage (above discharge start voltage) after pre-exposure completion. This dynamic voltage adjustment allows the system to achieve both early charging preparation and proper image formation, resolving the time-quality tradeoff
2Loss of time
If DC charging voltage is applied immediately after pre-rotation, then first copy time is reduced, but surface potential uniformity deteriorates causing image defects
Solution Approach 1:
The charging voltage parameter is changed based on the operational phase: during pre-rotation, a first voltage parameter (below discharge start voltage) is applied to achieve uniform potential without excessive charging; after pre-exposure, a second voltage parameter (above discharge start voltage) is applied for proper image formation. This parameter change ensures both time efficiency and surface potential uniformity
Solution Approach 2:
The charging process is segmented into two distinct phases with different voltage levels: Phase 1 (pre-rotation) uses low voltage for uniform potential preparation, Phase 2 (after pre-exposure) uses high voltage for image formation. This segmentation allows each phase to optimize its function, achieving both rapid response and high image quality
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 approach reduces image defects and shortens the first copy time by ensuring proper surface potential uniformity and timely charging, enhancing the productivity and quality of the image forming process.
Implementation Method 1
a charging roller configured to charge the photosensitive member to a predetermined surface potential at a charging position
Implementation Method 2
a pre-exposure member configured to irradiate the photosensitive member with light at a pre-exposure position
Implementation Method 3
an image exposure device configured to form an electrostatic image on the photosensitive member by exposing according to an image signal
Data Source
AI summary
A control unit performs control to satisfy TVa<T TVb, where T is a time from a point when irradiation with light by a pre-exposure member is started to a point when a predetermined portion of the photosensitive member which is located at the pre-exposure position when the irradiation is started reaches a charging position, TVa is a time from the point when the irradiation is started to a point when application of a first voltage is started, and TVb is a time from the point when the irradiation is started to a point when application of the second voltage is started.