Charging Roller Axis Stability for Image Forming Apparatus
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Solution Overview
Problem
Conventional non-contact roller type charging devices face challenges in maintaining consistent charge gaps and preventing toner adhesion and charge irregularities due to temperature fluctuations and material properties, leading to reduced durability and ineffective charging performance.
Innovation Solution
A charging roller design featuring a cored bar coated with a conductive discharging member and ring-like abutting members with a diameter larger than the discharging member, fixed to the axis member, which maintains a consistent charge gap and prevents toner adhesion by using a rigid axis member and abutting members with a degree of hardness of at least 44 JIS D, ensuring stable charging performance across varying temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a film member is wound around the conductive rubber to maintain charge gap, then the charge gap is maintained, but the film member embeds in the conductive rubber at high temperatures causing charge gap reduction and toner adhesion
Solution Approach 1:
The patent changes the material parameter of the discharging portion from flexible conductive rubber to rigid conductive plastic, which fundamentally alters the thermal expansion and embedding behavior. This material substitution eliminates the temperature-dependent embedding issue while maintaining charge gap stability and preventing toner adhesion.
Solution Approach 2:
The patent uses a composite structure combining rigid conductive plastic with a heat shrinkable tube material. The conductive plastic provides structural stability and temperature resistance, while the heat shrinkable tube provides the necessary flexibility and embedding compensation. This composite approach resolves the contradiction between rigidity for stability and flexibility for temperature compensation.
2Reliability
If a rigid conductive plastic is used as discharging portion, then toner adhesion is reduced, but the film member falls off due to friction with photoconductor
Solution Approach 1:
The patent uses a heat shrinkable tube as a flexible covering for the rigid conductive plastic discharging portion. This thin film structure provides the necessary flexibility to withstand friction with the photoconductor while the rigid plastic core maintains charge gap stability and prevents toner adhesion. The flexible shell protects the rigid structure from mechanical damage.
3Duration of action of stationary object
If heat shrinkable tube is thermally shrunk to abut onto photoconductor, then durability is improved, but thickness deviation causes charge gap fluctuation
Solution Approach 1:
The patent changes the material parameter of the abutting member from heat shrinkable tube to rigid plastic with controlled hardness (44-63 JIS D). This material substitution eliminates the thickness deviation and charge gap fluctuation issues while maintaining the durability and photoconductor contact stability through the rigid structure.
4Adaptability or versatility
If conductive rubber hardness is reduced at high temperature, then embedding increases, but charge gap reduces causing toner fixation
Solution Approach 1:
The patent changes the material parameter from conductive rubber to rigid conductive plastic, which fundamentally alters the temperature-response characteristic. The rigid plastic maintains its dimensional stability across temperature variations, preventing the embedding and charge gap reduction that occurs with conductive rubber at high temperatures.
Solution Approach 2:
The patent uses a composite structure combining rigid conductive plastic with heat shrinkable tube material. The conductive plastic provides structural stability and temperature resistance, while the heat shrinkable tube provides the necessary flexibility and thermal compensation. This composite approach resolves the contradiction between rigidity for stability and flexibility for temperature compensation.
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 maintains a consistent charge gap and prevents toner adhesion and charge irregularities, enhancing the durability and charging performance of the charging device by stabilizing the charge gap between 15 and 75 μm across a temperature range of 10 to 32°C, reducing fluctuations and ensuring reliable image formation.
Implementation Method 1
a non-contact roller type charging device for subjecting a latent image supporting body to charging evenly through discharge from a discharging portion such as a conductive rubber
Implementation Method 2
keeping a predetermined charge gap between the discharging portion and latent image supporting body in the charging roller
Data Source
AI summary
An image forming apparatus has a latent image supporting body configured by a substrate and a covering layer provided on the substrate; and a charging device which is a rotating body configured by an axis member and a charging member provided on the axis member, and which charges the latent image supporting body facing the charging member. In this image forming apparatus, a value, which is obtained by dividing a capacitance [pF] between the axis member in the rotating body and the substrate in the latent image supporting body by the length [mm] in the direction perpendicular to the direction of the surface migration of the charging member, is set to be at least 0.35 [pF/mm], the capacitance being obtained when, instead of the latent image supporting body, the substrate in the latent image supporting body is caused to face the charging member.