Image Density Correction Using Asymmetric Test Patterns
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Solution Overview
Problem
Conventional image forming apparatuses using the electrophotographic method face challenges in accurately correcting density unevenness in the main scanning direction due to variations in charging, exposure, and development processes, leading to inconsistent image density, especially when density unevenness occurs periodically in the sub-scanning direction.
Innovation Solution
An image forming apparatus that forms multiple test images at different intervals in the sub-scanning direction, which are not integral multiples of the photosensitive member or developing sleeve circumferential lengths, allowing for precise density adjustment in the main scanning direction by analyzing and correcting density variations across these images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single pattern image is used for density correction, then the correction process is simple, but the correction accuracy is insufficient when periodic density unevenness occurs in the sub-scanning direction
Solution Approach 1:
The test pattern is divided into multiple pattern images (first, second, and third pattern images) arranged at different intervals in the sub-scanning direction. This segmentation allows measurement of density at multiple positions, enabling accurate detection and correction of periodic density unevenness that would be missed by a single pattern image.
Solution Approach 2:
The invention extends the correction approach from a single position to multiple positions along the sub-scanning direction by arranging pattern images at different intervals. This multi-dimensional measurement strategy captures periodic variations in density that occur as the photosensitive drum rotates, resolving the limitation of single-point measurement.
2Measurement precision
If pattern images are arranged at regular intervals in the sub-scanning direction, then the layout is simple, but the correction fails when the interval matches the periodicity of density unevenness
Solution Approach 1:
The pattern images are arranged at asymmetric, non-uniform intervals in the sub-scanning direction rather than at regular intervals. Specifically, the interval between the first and second pattern images differs from the interval between the second and third pattern images. This asymmetric arrangement ensures that at least one pattern image will fall at a position where density unevenness can be accurately measured, avoiding the pitfall of all patterns falling at incorrect positions due to periodic mismatches.
3Measurement precision
If multiple pattern images are used to improve correction accuracy, then density correction precision improves, but the processing time and complexity increase
Solution Approach 1:
Multiple pattern images are formed in advance on a single sheet during normal operation, and their densities are measured simultaneously. This preliminary arrangement of multiple measurement points allows the system to capture periodic density variations in one go, avoiding the need for multiple separate measurements and reducing overall processing time while maintaining high correction accuracy.
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 approach enables accurate and precise correction of density unevenness in the main scanning direction, preventing overcorrection and ensuring consistent image density, even when density variations occur periodically in the sub-scanning direction.
Implementation Method 1
an exposure unit configured to expose the photosensitive member to form an electrostatic latent image on the photosensitive member
Implementation Method 2
a developing unit having a developing sleeve carrying toner and rotating, and configured to develop the electrostatic latent image on the photosensitive member with the toner on the developing sleeve
Data Source
AI summary
An image forming apparatus includes an image forming unit having a photosensitive member, an exposure unit, and a developing unit having a developing sleeve; and a controller configured to acquire read data relating to a first test image, a second test image, and a third test image formed on a same sheet by the image forming unit, and adjust a density in a main scanning direction of an image to be formed by the image forming unit based on the read data. A first interval between the first test image and the second test image is different from a second interval between the second test image and the third test image. Each of the first interval and the second interval is different from an integral multiple of a circumferential length of the photosensitive member, and is different from an integral multiple of a circumferential length of the developing sleeve.