Halftone Processing for Non-Uniform Scan Speed Imaging
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Solution Overview
Problem
Electrophotographic image forming apparatuses face issues with image failure due to variations in exposure amount per unit area caused by non-uniform scan speeds, especially when using optical scanning apparatuses without the fθ characteristic, leading to size constraints and imaging performance limitations.
Innovation Solution
The apparatus includes a photosensitive member, an irradiation unit for scanning with non-uniform speed, a correction unit for tone value adjustment, and a halftone processing unit using dither matrices with submatrices to control exposure regions, ensuring consistent pixel width and exposure amount across the image forming surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a scan lens with fθ characteristic is used to achieve uniform scan speed, then imaging performance is improved, but device size increases
Solution Approach 1:
The patent removes the scan lens with fθ characteristic from the optical scanning apparatus. Instead of using optical means to achieve uniform scan speed, the invention extracts this component and replaces it with a control-based approach that varies the light beam emission frequency according to the instantaneous scan speed, thereby reducing device size while maintaining imaging performance
Solution Approach 2:
The patent changes the parameter of light beam emission frequency dynamically. By varying the emission frequency in accordance with instantaneous scan speed, the system compensates for the non-uniform scan speed caused by removing the fθ lens, achieving both size reduction and maintained imaging performance
2Manufacturing precision
If clock frequency is changed to maintain constant pixel width, then pixel dimensions are controlled, but exposure amount per unit area varies causing image failure
Solution Approach 1:
The patent changes multiple parameters simultaneously: both the emission frequency of the light beam and the exposure duration are adjusted according to instantaneous scan speed. This dual parameter adjustment ensures that both pixel width consistency and exposure amount uniformity are maintained, preventing image failure while preserving pixel dimension control
Solution Approach 2:
The patent implements a feedback control mechanism where the emission frequency and exposure duration are varied in accordance with instantaneous scan speed. This feedback approach allows the system to dynamically adjust to speed variations and maintain both pixel width and exposure amount within acceptable ranges, ensuring image quality
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 solution enables consistent image quality by adjusting tone values and exposure regions, reducing the likelihood of image failures and allowing for a more compact optical scanning apparatus design without compromising imaging performance.
Implementation Method 1
an optical scanning apparatus configured to expose a photosensitive member. The optical scanning apparatus scans/exposes the photosensitive member by emitting a light beam based on image data
Implementation Method 2
reflecting the emitted light beam by a rotating polygonal mirror
Implementation Method 3
transmitting it through a scan lens having a fθ characteristic. Note that the fθ characteristic refers to an optical characteristic that causes a spot by the light beam to move on the surface of the photosensitive member at a uniform velocity
Data Source
AI summary
An image forming apparatus includes: a halftone processing unit configured to perform halftone processing on image data by a dither matrix that includes a plurality of submatrices and decide an exposure region of an image. In at least one of a first dither matrix corresponding to a first section, and a second dither matrix corresponding to a second section adjacent to the first dither matrix in the main scanning direction and corresponding to a second section different from the first section in tone value, at least a size of an exposure region of an image formed by using a first submatrix corresponding to a predetermined tone value in the dither matrix and a size of an exposure region of an image formed by using a second submatrix corresponding to the predetermined tone value are different.