Sheet Surface Height Measurement for Image Quality Adjustment
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Solution Overview
Problem
The accuracy of image quality adjustment in electrophotographic image forming apparatuses is compromised due to sheet curl, waving, and fluttering, which cause fluctuations in the sheet's surface height, leading to inaccurate read values and reduced image quality, especially when using conventional line sensors that cannot detect surface height positions effectively.
Innovation Solution
An image forming apparatus that includes a measuring section to determine the sheet's surface height position, a control section to identify a planar region with minimal height fluctuations, and an image forming section that forms and reads reference images within this region, allowing for precise image quality adjustment using read values obtained from the reading section.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a guide plate is provided below the sheet to make the gap narrower at the reading position, then the sheet surface height fluctuation is suppressed, but the sheet conveyance resistance increases and conveyance performance deteriorates
Solution Approach 1:
The sheet conveyance path is divided into two functional zones: a narrow gap region at the reading position for height stabilization and a wider gap region elsewhere for smooth conveyance. This segmentation allows the system to achieve both accurate reading and good conveyance performance by applying different gap widths in different spatial locations.
Solution Approach 2:
The gap width is made non-uniform along the conveyance direction, with a locally narrow gap at the reading position and wider gaps in other regions. This local quality variation optimizes the system by providing height stabilization only where needed (at the reading position) while maintaining easy conveyance in other areas.
2Measurement precision
If the sheet is made to contact with the reading surface of the line sensor, then the sheet surface height is stabilized, but the reading surface is easily soiled and anti-smudge coating may detach
Solution Approach 1:
A light-receiving lens is introduced as an intermediary optical element between the line sensor and the sheet. The lens focuses light onto the sheet surface without requiring direct contact between the sensor and sheet, thereby maintaining reading accuracy while preventing soiling and coating detachment that would occur with direct contact.
Solution Approach 2:
The direct mechanical contact between the line sensor and sheet is replaced with an optical system using a light-receiving lens. This substitution eliminates the mechanical friction and contact pressure that cause soiling and coating detachment, while still achieving the goal of stabilizing sheet height for accurate reading through optical focusing.
3Measurement precision
If a special sensor is used to detect the height position of the sheet surface, then the reading accuracy is improved, but the device complexity increases
Solution Approach 1:
The line sensor is made multi-functional by equipping it with a light-receiving lens. The same sensor system that reads reference images is also used to detect sheet height position through optical focusing. This eliminates the need for separate height detection sensors and reduces device complexity while maintaining measurement precision.
Solution Approach 2:
The functions of reference image reading and sheet height detection are merged into a single integrated system using the line sensor with light-receiving lens. By combining these two measurement functions into one sensor assembly, the patent avoids the complexity of using separate special sensors for height detection while achieving both measurement goals simultaneously.
Data Source
AI summary
An image forming apparatus includes: a measuring section which measures a height position of a surface of a sheet at a reading position at which a reference image for image quality adjustment is read; a control section which determines a planar region of the sheet according to the height position, and determines a forming position of the reference image within the planar region; an image forming section which forms the reference image at a position of a sheet corresponding to the forming position, the sheet being newly fed after determination of the forming position; and a reading section which reads the reference image at the reading position, wherein the control section adjusts image quality by using a read value obtained from the reference image by the reading section.