Nip-Area Fixing Assembly with Smaller-Radius Projection for Sheet Separation
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Solution Overview
Problem
Existing fixing apparatuses face issues with sheet separation due to excessive adhesion of toner to the fixing film and curling of sheets under high-temperature and high-humidity conditions, leading to difficulties in stacking.
Innovation Solution
A fixing apparatus with a nip forming member featuring a first and second projection portion, where the second projection portion has a smaller radius of curvature than the fixing film, positioned to reduce the film's radius of curvature and guide sheets away from the curling direction, enhancing separation and stackability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the fixing film has a large radius of curvature, then the sheet can be smoothly conveyed, but the separating ability to separate the sheet from the fixing film deteriorates
Solution Approach 1:
The invention applies local quality by creating a localized region with different curvature characteristics. The nip forming member introduces a local area with small radius of curvature (projection portion) within the overall fixing film structure that has large radius of curvature. This localized curvature change at the specific position where the sheet separates from the fixing film improves separation ability without affecting the smooth conveyance of the sheet through the rest of the fixing apparatus.
Solution Approach 2:
The invention utilizes curvature principles by intentionally creating a projection portion on the nip forming member that has a smaller radius of curvature than the fixing film. This curvature difference creates a mechanical advantage for sheet separation - the sharper curvature of the projection portion helps break the adhesion between the toner image and fixing film, enabling reliable sheet separation while the overall large-radius fixing film maintains smooth sheet conveyance.
2Reliability
If the protrusion significantly protrudes toward the pressure roller, then the separating ability is improved, but the sheet curls into a tubular shape under high-temperature and high-humidity conditions
Solution Approach 1:
The invention applies asymmetry by positioning the projection portion of the nip forming member asymmetrically relative to the fixing film and pressure roller arrangement. The projection portion is located at a specific asymmetric position that optimizes separation ability while minimizing its impact on sheet curling behavior. This asymmetric placement allows the protrusion to effectively interfere with the adhesion zone without creating excessive mechanical leverage that would amplify curling under thermal and humidity stress.
Solution Approach 2:
The invention utilizes parameter changes by carefully controlling the geometric parameters of the projection portion - specifically its radius of curvature, height, and position. By optimizing these parameters, the projection portion achieves sufficient protrusion to improve sheet separation while maintaining sheet shape stability. The radius of curvature of the projection portion is specifically designed to be smaller than that of the fixing film but not so small as to create excessive stress concentration that would induce tubular curling.
3Strength
If the adhesion strength between the fixing-film outer surface and the toner image is excessively high, then the toner image is firmly fixed, but the sheet cannot be separated from the fixing-film outer surface
Solution Approach 1:
The invention applies preliminary action by introducing the projection portion of the nip forming member that acts on the sheet-toner image-fixing film system before the sheet is fully discharged. The projection portion creates a localized mechanical interference that preliminarily disrupts the adhesion bonds between the toner image and fixing film outer surface, reducing the adhesion strength just enough to enable separation while maintaining sufficient fixation. This preliminary mechanical intervention occurs at the optimal moment during the sheet passage through the fixing nip.
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 separates sheets from the fixing film and improves stackability by reducing the film's curvature and guiding sheets in a direction opposite to the curling direction, ensuring reliable discharge and stacking.
Implementation Method 1
a heater held by the nip forming member... configured to heat a toner image, which is borne on a recording material, in the nip area
Data Source
AI summary
A fixing apparatus including: a first rotary member; a second rotary member; a nip forming member; and a heater. The nip forming member includes: a first projection portion inside a nip area; and a second projection portion located outside the nip area. The first and second projection portion abut against the inner circumferential surface of the first rotary member. In a direction orthogonal to a nip tangent, a distance between a tip of the second projection portion and the nip tangent is larger than a distance between a tip of the first projection portion and the nip tangent. The second projection portion extends toward the second rotary member without exceeding the nip tangent. A radius of curvature at a tip portion of the second projection portion is smaller than a radius of an inner circumferential circle of the first rotary member.