Fixing Device Curved Nip Forming Member for Stiff Sheet Conveyance
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Solution Overview
Problem
The existing fixing devices face issues with a small contact area between the cylindrical pressuring member and the planar fixing belt, leading to short nip width, difficulty in separating sheets, and potential image deviation due to insufficient pressure and depressurization, especially with stiff sheets like cardboard.
Innovation Solution
A fixing device with a nip forming member inside the fixing belt, featuring a first curved face arching towards the upstream side and a second curved face arching towards the downstream side, both connected at an inflection point near the pressuring member's rotation center, extending the nip width and ensuring consistent pressure distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the pressing face of the nip forming member is formed in parallel to the conveyance direction of the sheet (planar fixing face), then the sheet can be conveyed smoothly, but the contact area with the cylindrical pressuring member becomes small and the nip width becomes short
Solution Approach 1:
The pressing face of the nip forming member is formed with a curved surface (circular arc shape) that matches the cylindrical shape of the pressuring member. This curvature allows the pressing face to maintain contact along the curved surface of the pressuring member, thereby increasing the contact area and nip width compared to a planar fixing face.
2Shape
If the nip forming member is formed in a circular arc shape of a single curved line, then the fixing belt is formed in a circular arc shape, but stiff sheets like cardboard are hardly deformed along the fixing belt and sufficient nip pressure is not obtained at certain positions
Solution Approach 1:
The circular arc shape of the fixing belt is segmented into multiple sections with different curvature radii. Specifically, the upstream side has a larger curvature radius while the downstream side has a smaller curvature radius. This segmentation allows different regions of the fixing belt to adapt to different requirements: the upstream side with larger radius helps deform stiff sheets, while the downstream side with smaller radius maintains pressure for toner fixation.
Solution Approach 2:
Different sections of the fixing belt are given different local properties through varying curvature radii. The upstream section has a larger curvature radius to facilitate sheet deformation, while the downstream section has a smaller curvature radius to maintain pressure. This local differentiation optimizes the fixing performance for different regions of the sheet.
3Shape
If an inflection point of the curved face is recessed from the periphery, then the curved face is formed, but pressuring force insufficiently reaches the inflection point and depressurization of the fixing nip is caused
Solution Approach 1:
The curved face is designed with asymmetric curvature where the upstream side has a larger curvature radius and the downstream side has a smaller curvature radius. This asymmetric design ensures that the inflection point does not create a recessed region that would cause depressurization. Instead, the gradual transition of curvature radii maintains continuous pressuring force across the entire fixing nip area.
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 enhances sheet separability, reduces depressurization, and maintains image quality by providing a wider nip area and consistent pressure application, even with stiff sheets.
Implementation Method 1
The fixing belt is heated by a heat source, such as an IH unit
Implementation Method 2
The pressuring member is pressured to the fixing belt to pressure the sheet passing between the pressuring member and the fixing belt
Data Source
AI summary
The fixing device (13) includes the fixing belt (20), the pressuring roller (21) and the pad (24). The pad (24) sandwiches the belt (20) with the roller (21) to form the fixing nip. The pad (24) is extended in the nip width direction, and the pressing face (40) has the first and second curved faces (41) and (42) at upstream and downstream sides in the sheet conveyance direction. The first and second curved faces (41) and (42) are formed arch-like curved to the roller (21) toward upstream and downstream sides. The first and second curved faces (41) and (42) continue at the inflection point (B) near the intersection point of the extending line (A) parallel to the pressuring direction and through the rotation center of the roller (21) on the pressing face (40). The first curved face (41) has the curvature radius (Ra) larger than the second curved face (42).