Fixing Device Charge Application for Offset Prevention
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Solution Overview
Problem
The existing fixing devices in image forming apparatuses face an offset phenomenon where toner transfers to the fixing member due to differences in electric charge between the toner and the fixing member, which is not adequately prevented by applying an electric charge only to the toner on the sheet.
Innovation Solution
A charge application portion is introduced that generates a corona discharge between a discharge electrode and counter electrodes to apply a positive electric charge to the surface of the fixing member, ensuring both the toner and the fixing member have the same polarity, thereby utilizing charge repulsion to restrict toner transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a corotron is provided between transfer portion and fixing portion to apply electric charge to toner on sheet, then offset phenomenon is prevented, but toner still transfers to fixing member due to charge difference between toner and fixing member surface
Solution Approach 1:
The invention applies preliminary action by charging the fixing member surface before the toner reaches it. A charge application portion is provided upstream of the fixing portion to apply electric charge to the fixing member surface in advance, ensuring that when toner contacts the fixing member, both have the same polarity and charge repulsion prevents toner transfer.
Solution Approach 2:
The invention introduces an intermediary charge application portion between the transfer portion and fixing portion. This intermediary component applies electric charge to the fixing member surface, mediating the interaction between toner and fixing member by ensuring charge compatibility and preventing direct harmful transfer.
2Reliability
If electric charge is applied only to toner on sheet, then toner adhesion to sheet is improved, but charge difference between toner and fixing member causes toner transfer
Solution Approach 1:
The invention applies local quality by differentiating the charging treatment: toner on the sheet is charged by the transfer portion, while the fixing member surface is charged separately by the charge application portion. This localized differentiation ensures both have appropriate charges for their respective functions while maintaining charge compatibility to prevent transfer.
Solution Approach 2:
The invention changes the parameter of electric charge distribution by introducing a separate charging mechanism for the fixing member. Instead of uniform charging, the system independently controls the charge state of both toner and fixing member surface, adjusting their charges to match polarities and prevent unwanted transfer.
3Object-generated harmful factors
If fixing member surface is charged to same polarity as toner, then charge repulsion prevents toner transfer, but additional charging mechanism increases device complexity
Solution Approach 1:
The charge application portion is designed with multi-functionality, serving both to charge the fixing member surface and to control the charge distribution. This universal component integrates multiple functions into a single mechanism, reducing overall device complexity while achieving the goal of preventing toner transfer through charge repulsion.
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 effectively restricts the offset phenomenon by maintaining the same polarity between the toner and the fixing member, preventing toner transfer to the fixing member and enhancing the fixation process.
Implementation Method 1
by causing a corona discharge to be generated between a discharge electrode and a counter electrode that are disposed apart from the outer circumferential surface of the first fixing member
Implementation Method 2
a sheet with a toner image formed thereon is passed through a nip portion between a pair of fixing members that are rollers or belts, and the sheet is heated and pressed
Implementation Method 3
an offset phenomenon may occur, wherein in the offset phenomenon, a part of the toner transfers to the surface of the fixing member. There is known an image forming apparatus in which, to prevent the offset phenomenon, a corotron is provided between a transfer portion and the fixing portion such that the corotron applies an electric charge to the toner on the sheet
Data Source
AI summary
A fixing device includes a first fixing member, a second fixing member, and a charge application portion. The first fixing member contacts unfixed toner on a sheet conveyed along a conveyance path. The second fixing member forms a nip portion between itself and the first fixing member such that the sheet passes through the nip portion. The charge application portion applies an electric charge to the unfixed toner on the sheet and to an outer circumferential surface of the first fixing member at a region on an upstream side of the nip portion in a movement direction of the outer circumferential surface, by causing a corona discharge to be generated between a discharge electrode and a counter electrode that are disposed apart from the outer circumferential surface of the first fixing member.