Sheet Curl Correction in Image Forming Apparatus
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Solution Overview
Problem
Image forming apparatuses face issues with sheet curling due to heat and pressure, leading to reduced detection accuracy and increased jamming, as curled sheets fail to enter the delivery rollers smoothly, and minimizing curvature to reduce curling increases the apparatus size.
Innovation Solution
An image forming apparatus with a curl-corrector that reverses the sheet's curl direction and a detection unit in the redelivery path downstream of the curl-corrector, combined with a cooling unit to maintain sheet straightness and improve detection accuracy, while maintaining a compact apparatus size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the curvature of the reversing path is maximized to minimize the width of the image forming apparatus, then the apparatus size is reduced, but the sheet curls more due to heat and pressure from the fixing unit
Solution Approach 1:
The curl-corrector is positioned upstream in the reversing path to straighten the sheet before it undergoes significant curling from the curved guide. By performing the straightening action preliminarily, the sheet is prepared in advance to resist or minimize the harmful curling effect that will occur later in the path.
Solution Approach 2:
The invention accepts that the sheet will curl due to the necessary curved path for compactness, but converts this harmful effect into a benefit by using the curl-corrector to deliberately induce curl in the opposite direction. This counter-curling approach transforms the inevitable curling into a controllable parameter that can be neutralized.
2Shape
If a curl-corrector is provided to straighten the sheet after the fixing unit, then sheet straightness is improved, but the apparatus size increases
Solution Approach 1:
The curl-corrector is merged into the existing reversing path structure rather than being added as a separate downstream component. By integrating the curl-correction function within the curved guide area, the invention avoids increasing the overall apparatus width while still providing the necessary straightening capability.
3Productivity
If the sheet is held still at the curved guide of the reversing path to repeatedly circulate sheets, then productivity is improved, but the sheet curls even more
Solution Approach 1:
The sheet is straightened by the curl-corrector before being held still at the curved guide. This preliminary straightening action ensures that even when the sheet remains stationary in the curved path for multiple circulation cycles, it maintains better straightness and does not undergo excessive curling.
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
Effectively corrects sheet curling, enhances detection accuracy, and prevents jamming by straightening sheets before they reach the delivery rollers, while maintaining a reduced apparatus size and stable image density detection.
Implementation Method 1
the curl-corrector corrects the curling of the sheet by curving the sheet in the direction opposite to the direction in which the curved path curves
Implementation Method 2
a cooling unit to maintain sheet straightness
Data Source
AI summary
An image forming apparatus comprises a fixing unit for fixing toner image onto a sheet on which the toner image is formed, and a redelivery path for delivering the fixed sheet ejected from the fixing unit to the image forming unit again. A curved path receives the fixed sheet ejected from the fixing unit, reverses the sheet, and delivers the sheet to the redelivery path again. The redelivery path includes a horizontal-registration detection sensor for detecting the edge of the sheet in the width direction and a color density sensor for detecting the color density and color of an image formed on the sheet. A curl-corrector is disposed downstream of the curved path to straighten the curled sheet and then send the sheet to the horizontal-registration detection sensor and the density sensor.