Fixing Device Guide Member Corrects Back Curl
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Solution Overview
Problem
In image forming apparatuses using electrophotography, thermal fixation of toner images leads to temperature differences between the heating member and pressure roller, causing moisture evaporation imbalances that result in back curling of recording sheets, which complicates sheet stacking and leads to wrinkles, especially with two-ply envelopes.
Innovation Solution
A fixing device with a flexible endless fixing member, a heater, a nip forming member, and a pressure member that forms a fixing nip portion with a specific planar and curved design to apply heat and pressure evenly, along with a guide member to correct back curl by bending the sheet opposite to the curl direction, ensuring uniform fixation and preventing wrinkles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thermal fixation is applied using a heating member and pressure roller, then the toner image is fixed onto the recording sheet, but temperature differences cause moisture evaporation imbalances that result in back curling of the recording sheet
Solution Approach 1:
The patent introduces a guide member that applies a counteracting force to the back curl by bending the recording sheet in the opposite direction. This inversion principle directly counterbalances the harmful effect of back curling caused by thermal fixation, allowing the recording sheet to exit the fixing device in a flattened state.
Solution Approach 2:
The guide member acts as an intermediary element between the fixing nip and the sheet ejection system. It provides mechanical support and guidance to the recording sheet during the critical transition phase after fixation, preventing back curl without interfering with the thermal fixation process itself.
2Reliability
If back curl is generated in the fixing nip portion, then image fixation is achieved, but sheet stacking becomes complicated and wrinkles occur
Solution Approach 1:
The guide member applies a counteracting force to the back curl by bending the recording sheet in the opposite direction. This inversion principle directly counterbalances the harmful effect of back curling caused by thermal fixation, allowing the recording sheet to exit the fixing device in a flattened state.
3Reliability
If heat and pressure are applied in the fixing nip portion, then the toner image is fixed, but uneven temperature distribution causes wrinkles especially with two-ply envelopes
Solution Approach 1:
The nip forming member features a curved surface with varying radius of curvature along the feeding direction. The upstream end has a smaller radius while the downstream end has a larger radius, creating localized variations in pressure distribution that compensate for temperature non-uniformity across different regions of the recording sheet.
Solution Approach 2:
The curved surface of the nip forming member replaces a flat surface with a continuously varying curvature. This spherical/geometric form allows for gradual transition of pressure application, improving uniformity of heat and pressure distribution across the recording sheet width and length.
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 reduces back curling and prevents wrinkles, allowing for proper stacking of sheets and maintaining image quality by ensuring uniform heat and pressure distribution across the recording sheet, even with two-ply materials.
Implementation Method 1
a heater to heat the fixing member... applies heat and pressure to fix an image transferred to a recording sheet when the recording sheet passes through the fixing nip portion
Implementation Method 2
a pressure member, disposed opposite the nip forming member via the fixing member, to press against the fixing member to form a fixing nip portion together with the nip forming member
Implementation Method 3
a guide member, disposed downstream of the fixing nip portion in the feeding direction of the recording sheet on the same side as the pressure member relative to a feeding path of the recording sheet, to guide the recording sheet to bend in a direction opposite a direction of a back curl of the recording sheet generated in the fixing nip portion
Data Source
AI summary
A fixing device includes a fixing member; a heater to heat the fixing member; a nip forming member to contact the fixing member; and a pressure member, disposed opposite the nip forming member to press against the fixing member to form a fixing nip portion together with the nip forming member. The fixing device applies heat and pressure to fix an image transferred to a recording sheet when the recording sheet passes through the fixing nip. The nip forming member includes a first and second planar portions disposed at an upstream end and a downstream end, respectively, of the fixing nip portion, and the first planar portion and the second planar portion are continuous with a curved portion of the nip forming member. A guide member guides the recording sheet to bend in a direction opposite a back curl of the recording sheet generated in the fixing nip portion.