Charging Roller Additive Coating to Prevent Drum Scratches
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Solution Overview
Problem
In cleanerless type and contact charging image forming apparatuses, foreign substances transferred to the charging roller can scratch the photosensitive drum, leading to image defects due to uneven charging and potential differences.
Innovation Solution
An external additive coating operation is performed to transfer an external additive with opposite polarity to the toner onto the photosensitive drum, followed by transferring it to the charging roller, with specific voltage control to prevent discharge and ensure uniform coating, and a cleaning operation to remove any remaining toner.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If foreign substance is transferred to the charging roller through recording material, then the charging roller surface is contaminated, but this causes scratches on the photosensitive drum and image defects
Solution Approach 1:
The patent applies preliminary action by performing an external additive coating operation before normal image forming operations. This coating transfers external additive particles to the charging roller surface in advance, creating a protective layer that prevents foreign substances from directly contacting and scratching the photosensitive drum. The controller executes this coating operation by controlling the developing unit to supply toner and the transfer unit to transfer it to the photosensitive drum, where the external additive is then transferred to the charging roller.
Solution Approach 2:
The patent uses external additive particles as an intermediary substance between the charging roller and the photosensitive drum. These particles form a intermediate layer that prevents direct contact between foreign substances on the charging roller and the photosensitive drum surface. The external additive acts as a mediator that protects the photosensitive drum while still allowing the charging function to operate effectively.
2Productivity
If voltage is increased to improve transfer efficiency, then more toner is transferred to recording material, but discharge may occur between transfer unit and photosensitive drum
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the transfer voltage based on the operational state. During the external additive coating operation, the transfer voltage is set to a first value that enables effective transfer of external additive particles. During normal image forming operations, the transfer voltage is set to a second value optimized for toner transfer efficiency. This dynamic parameter adjustment prevents discharge while maintaining high productivity during normal operation.
Solution Approach 2:
The patent implements dynamics by making the transfer voltage adjustable and state-dependent rather than fixed. The controller switches between different voltage levels based on whether the system is in coating mode or normal operation mode. This dynamic voltage control allows the system to optimize transfer efficiency during normal operation while preventing discharge conditions during the coating operation.
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
Prevents foreign substance adhesion to the charging roller, reducing the occurrence of black spot images by maintaining consistent charging and preventing scratches on the photosensitive drum.
Implementation Method 1
a charging unit that rotates in contact with the photosensitive drum, and charges a surface of the photosensitive drum
Implementation Method 2
a developing unit that supplies toner containing an external additive which has a charging polarity that is an opposite polarity of a charging polarity of the toner to the surface of the photosensitive drum
Implementation Method 3
a transfer unit that transfers the toner, which has been supplied to the photosensitive drum by the developing unit, to a recording material
Implementation Method 4
V1>V2 represents a potential relationship in which an electrostatic force, directed from a position of a potential V1 to a position of a potential V2, acts on particles having a same charging polarity as a charging polarity of the external additive
Data Source
AI summary
An additive coating is executed, where an additive is transferred, from a developing roller to a photosensitive drum by setting a surface potential of the drum to be lower than a developing voltage, and from the drum to a charging roller by setting a charging voltage to be lower than the surface potential. By setting a potential difference Vback between the surface potential and a developing voltage in a developing portion to be larger in the external additive coating than that in the image forming, a development amount of the additive is increased. Further, by setting a transfer voltage to be higher than the surface potential, transfer of the additive is suppressed. By setting the potential difference between the surface potential and the transfer voltage to be smaller than a discharge threshold between the transfer roller and the drum, the additive is suppressed from having a strong positive polarity.