Insulating Member Between Pressing Roller and Fixing Frame
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Solution Overview
Problem
In electrophotographic image forming apparatuses, downsizing the fixing device and shortening the distance from the transfer portion to the sheet discharging portion can lead to electrical conduction between the fixing frame and the pressing roller via water droplets, causing transfer current leakage and image defects under high temperature/high humidity conditions.
Innovation Solution
An insulating member is placed between the electroconductive pressing roller and the electroconductive fixing frame to prevent electrical connection, ensuring a stable transfer current and reducing the likelihood of image defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the distance from transfer portion to sheet discharging portion is shortened to downsize the fixing device, then the fixing device size is reduced and first print out time is shortened, but water droplets can bridge the electroconductive pressing roller and fixing frame causing transfer current leakage
Solution Approach 1:
An insulating member is introduced as an intermediary between the electroconductive pressing roller and the electroconductive fixing frame. This insulating member prevents direct electrical conduction while allowing the pressing roller to maintain its electroconductive properties for proper transfer current flow, thus resolving the contradiction between downsizing and maintaining transfer current stability.
2Reliability
If the pressing roller is made electroconductive to control transfer current, then transfer current control is improved, but water droplet conduction to the grounded fixing frame causes current leakage and image defects
Solution Approach 1:
The pressing roller is made electroconductive in specific regions where transfer current control is needed, while the insulating member is positioned at specific locations to prevent water droplet-induced conduction to the fixing frame. This localized application of electroconductive and insulating properties resolves the contradiction between transfer current control and preventing current leakage.
3Reliability
If a grounding resistor is added to the pressing roller to prevent current leakage, then transfer current stability is improved, but the device complexity increases
Solution Approach 1:
The grounding resistor configuration is extracted and replaced by a simpler insulating member positioned between the pressing roller and fixing frame. This insulating member directly prevents water droplet-induced conduction without requiring complex grounding resistor circuits, thus resolving the contradiction between transfer current stability and device complexity.
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 insulating member effectively prevents electrical conduction between the pressing roller and the fixing frame, maintaining a sufficient transfer current and preventing image defects even in high temperature/high humidity environments, thus ensuring proper image transfer.
Implementation Method 1
an insulating member is provided between the opposing surface and the outer surface of the first rotatable member
Implementation Method 2
water contained in the recording material is vaporized by heating, and thus condenses on a peripheral feeding path
Data Source
AI summary
An image forming apparatus for forming a toner image on a recording material. The image forming apparatus includes an image forming portion to form the toner image on the recording material, and a fixing portion to fix, at a nip, the toner image on the recording material by feeding and heating the recording material on which the toner image is formed. The fixing portion includes a roller having an outer surface that has electroconductivity, a rotatable member that forms the nip and is in contact with the roller, and a casing having electroconductivity. An electrical insulating member is positioned (i) nearest to the outer surface of the roller, and (ii) between the inner surface of the casing and the outer surface of the roller. The electrical insulating member does not directly or indirectly contact the outer surface of the roller, and is provided with a water-absorbing member.