Dither Matrix Pattern Design for Gear-Driven Drum Interference
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Solution Overview
Problem
In image forming apparatuses, uneven rotation of the photoconductor drum due to gear engagement leads to interference fringes in the printing medium, causing variable density issues in the image.
Innovation Solution
The apparatus employs a dither matrix with sub-matrices arranged in a specific rule, where each sub-matrix has threshold values allowing dots to grow from an original point, and the gear pitch (a) and line pitch (b) relationship is optimized to satisfy a≥0.08 mm and b/a<0.80 or a1.27, reducing interference fringes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If gear transmission is used to drive the photoconductor drum, then the drum can be rotated at controlled speed, but uneven rotation occurs due to gear engagement causing interference fringes
Solution Approach 1:
The patent applies preliminary action by pre-calculating and pre-compensating for the uneven rotation effects through modified dither matrix patterns. The halftoning process is adjusted in advance to account for the periodic speed variations caused by gear engagement, thereby preventing interference fringes before they occur during actual printing operation.
Solution Approach 2:
The patent changes parameters by modifying the dither matrix configuration and threshold values to compensate for gear-induced rotation不均匀ity. By adjusting the halftoning parameters and dot distribution patterns, the system adapts to the periodic speed variations, maintaining uniform image density despite the mechanical imperfections of gear-driven rotation.
2Loss of information
If halftoning with dither matrix is applied to express image tones, then 256-tone input data can be converted to two-tone output, but interference fringes are generated due to interaction between dot pitch and gear uneven rotation
Solution Approach 1:
The patent applies local quality by creating spatially varying dither patterns that adapt to local conditions. Different regions of the image use customized dither matrix configurations that account for the interaction between halftoning dot pitches and gear rotation unevenness, thereby locally suppressing interference fringes while preserving tone information.
Solution Approach 2:
The patent employs asymmetry by using non-uniform, asymmetric dither matrix patterns instead of symmetric regular grids. The asymmetric dot distribution patterns help break the periodicity that causes interference with gear engagement, thereby reducing visible fringes while maintaining effective halftoning for tone representation.
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 configuration effectively restrains the generation of interference fringes, ensuring consistent image density and quality by aligning the gear pitch and line pitch within the specified ranges.
Implementation Method 1
an electrically charged photoconductor drum is irradiated with a light source such as a laser and the voltage of a corresponding portion of the photoconductor drum is changed to cause toner to adhere thereto
Implementation Method 2
a toner image formed on the photoconductor drum is transferred to a printing paper by a transfer roller applied with a voltage opposite from the photoconductor drum
Implementation Method 3
a fixing roller fixes the toner with heat and pressure
Data Source
AI summary
An image forming apparatus comprises an image data generating unit configured to convert a tone of an input value which indicates a density of a pixel by using a predetermined dither matrix and generate image data. The image forming apparatus further comprises a drive source and a gear configured to transmit a drive force from the drive source to an image carrier. The dither matrix includes a plurality of sub-matrixes arranged in a predetermined rule and a dot in each of the plurality of the sub-matrixes grows from a corresponding original point. The image forming apparatus satisfies a relation of (1) a≧0.08 mm and b/a<0.80, or (2) a<0.08 mm and b/a>1.27, where “a” is a travel distance of a printing medium per tooth of the gear in a secondary scanning direction orthogonal to the primary scanning direction, and “b” is a distance between the corresponding original points of a pair of the dots formed on the printing medium apart from each other in the secondary scanning direction on the basis of a pair of the sub-matrixes adjacent to each other in the primary scanning direction in the dither matrix.